Arsenic Contamination of Groundwater in South and East Asian Countries - Technical Report

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March, 2005Volume II, Technical Report, No 31303

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Water and Sanitation Program-South AsiaThe World Bank55 Lodi Estate, New Delhi 110003India

Tel: (91-11) 24690488, 24690489Fax: (91-11) 24628250E-mail: [email protected]: http://www.wsp.org

The World Bank1818 H Street, N.W.Washington, D.C. 20433USA

Tel: (1-202) 4771000Fax: (1-202) 4776391E-mail: [email protected]: http://www.worldbank.org �

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Photo Credits: ©Cover: Upper Left: Suchitra Chauhan, Upper Right: Albert Tuinhof, Lower: Karin Kemper

Paper 1Page 10, 18, 20 (1&2): Guy StubbsPage 20 (3): Karin Kemper

Paper 2Page 98: Karin KemperPage 100: Guy Stubbs

Paper 3Page 166 and 208: Guy StubbsPage 168: Karin Kemper

Paper 4Page 210, 212 and 262: Karin Kemper

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1. Introduction 101

2. Arsenic: Health Effects, Recommended Values, and National Standards 102

• International and National Standards for Arsenic Intake 102• Major Limitations of Existing Epidemiological Studies 104• Major Health Effects 105• Arsenic Ingested through the Food Chain 106• Operational Responses of Countries in South and East Asia 107• Initial Responses towards Suspected Arsenic Contamination 107

– Screening and Identification of Contamination Levels in Water Sources 108– Well Switching, Painting of Tube Wells, and Awareness 113– Patient Identification 115– Treatment Management of Arsenicosis Patients 118

• Longer-Term Responses 120– Institutional Longer-Term Responses (Arsenic Country Policy) 120– Technical Longer-Term Responses Based on Surface Water 121– Technical Longer-Term Responses Based on Groundwater 123

• Dissemination of Information 128– Regional Arsenic Networks and National Databases 128– Summary Remarks 129

3. Arsenic Mitigation in the Context of the Overall Water Supply Sector 130• Background 130• Access to Improved Water Sources in Asian Countries 130• Arsenic Priority Compared to Bacteriological Water Quality Priority 130• Definition and Identification of Arsenic Contamination Hotspots 132• Remaining Issues and Recommendations 133

4. Incentives for Different Stakeholders to Address Arsenic Contamination 134• Number of People at Risk 134• Number of Arsenicosis Patients 134• Rural and Urban Areas 135• National and International Media 135• Institutional Aspects 135• Short-Term versus Long-Term Solutions 136• Reputational Risk 136

5. Conclusions 138

References 161

AnnexuresAnnex 1. Operational Responses Undertaken by South and East Asian Countries 140Annex 2. Matrices for Implementation of Operational Responses to

Arsenic Contamination 141

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Annex 3. Operational Responses to Arsenic Contamination: Questionnaire Results 148Annex 4. Government, NGOs, International Organizations Involved in

Operational Responses 155Annex 5. Health Effects of Chronic Exposure to Arsenic in Drinking Water 157

TablesTable 1. Currently Accepted National Standards of Selected Countries for

Arsenic in Drinking Water 102Table 2. Chronology of Recommended WHO Values for Arsenic in Drinking Water 103Table 3. Current Population at Risk in Asian Countries 116Table 4. Summary of Responses to Arsenic Contamination Based on Surface Water 124Table 5. Summary of Responses to Arsenic Contamination Based on Groundwater 125Table 6. Access to Improved Water Sources in Selected Asian Countries 130Table 7. Percentage of Population in Selected Asian Countries with Sanitation 131Table 8. Child Mortality Rates in Selected South and East Asian Countries 131Table 9. Conceptualized Incentive Matrix: Stakeholder Incentives for Action on

Arsenic Issues 137

BoxesBox 1. Comparison of Field Testing and Laboratory Analysis 109Box 2. Parameters to Assess the Capacity of Laboratory Analysis 110

Paper 3

Summary 167

1. Introduction 169

2. Treatment of Arsenic-Contaminated Water 170• Oxidation-Sedimentation Processes 170• Coagulation-Sedimentation-Filtration Processes 172• Sorptive Filtration 176• Membrane Techniques 182• Comparison of Arsenic Removal Technologies 182

3. Laboratory and Field Methods of Arsenic Analysis 186• Laboratory Methods 186• Field Test Kit 186

4. Alternative Water Supply Options 190• Deep Tubewell 190• Dug or Ring Well 192• Surface Water Treatment 192• Rainwater Harvesting 194• Piped Water Supply 195• Cost Comparison of Alternative Water Supply Options 196

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5. Operational Issues 198• Technology Verification and Validation 198• Sludge Disposal 199• Costs 199

6. Conclusions 202

References 203

TablesTable 1. Comparison of Main Arsenic Removal Technologies 183Table 2. Comparison of Arsenic Removal Mechanisms and Costs in Bangladesh 184Table 3. Comparison of Costs of Different Arsenic Treatment Technologies in India 185Table 4. Laboratory Analysis Methods for Arsenic 187Table 5. Comparison of Arsenic Field Test Kits 188Table 6. Advantages and Disadvantages of Rainwater Collection System 194Table 7. Costs of Alternative Technological Options in Arsenic-Affected Areas 197Table 8. Cost of Water Supply Options for Arsenic Mitigation 201

Figures

Figure 1. Double Bucket Household Arsenic Treatment Unit 173Figure 2. Stevens Institute Technology 174Figure 3. DPHE-Danida Fill and Draw Arsenic Removal Unit 174Figure 4. Tubewell-Attached Arsenic Removal Unit 175Figure 5. Correlation between Iron and Arsenic Removal in Treatment Plants 175Figure 6. Alcan Enhanced Activated Alumina Unit 178Figure 7. Granular Ferric Hydroxide-Based Arsenic Removal Unit 178Figure 8. Three Kalshi Filter for Arsenic Removal 179Figure 9. Shapla Filter for Arsenic Removal at Household Level 180Figure 10. Tetrahedron Arsenic Removal Technology 181Figure 11. Deep Tubewell with Clay Seal 191Figure 12. Pond Sand Filter for Treatment of Surface Water 193Figure 13. Plastic Sheet Catchment 194

Paper 4

Summary 211

1. The Issue 213• Aims of This Paper 213• Situational Analysis 214

2. An Ideal Approach to Evaluation of Arsenic Mitigation Measures 216• Uncertainty and the Ideal Approach 216• An Ideal Model 217• Problems with the Ideal Model 219

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Background and Introduction

i. The detrimental health effects of environmental exposure to arsenic havebecome increasingly clear in the last few years. High concentrations detected ingroundwater from a number of aquifers across the world, including in South andEast Asia, have been found responsible for health problems ranging from skindisorders to cardiovascular disease and cancer.

ii. The problem has increased greatly in recent years with the growing use oftubewells to tap groundwater for water supply and irrigation. The water deliveredby these tubewells has been found in many cases to be contaminated withhigher than recommended levels of arsenic. In the study region, countriesaffected include Bangladesh (the worst affected), India, Myanmar, Nepal, andPakistan (South Asia); and Cambodia, China (including Taiwan), Lao People’sDemocratic Republic, and Vietnam (East Asia).

iii. This study concentrates on operational responses to arsenic contamination thatmay be of practical use to actors who invest in water infrastructure in theaffected countries, including governments, donors, development banks, andnongovernmental organizations (NGOs).

Objectives and Audience of the Study

iv. The objectives of this study are (a) to take stock of current knowledge regardingthe arsenic issue; and (b) to provide options for specific and balancedoperational responses to the occurrence of arsenic in excess of permissiblelimits in groundwater in Asian countries, while taking into account the work thathas already been carried out by many different stakeholders.

v. The study provides information on (a) occurrence of arsenic in groundwater;(b) health impacts of arsenic; (c) policy responses by governments and theinternational community; (d) technological options for and costs of arsenicmitigation; and (e) economic aspects of the assessment and development ofarsenic mitigation strategies. The focus of the study is on rural rather than urbanareas, due to the particular difficulties associated with applying mitigationmeasures in scattered rural communities.

vi. The study is structured as follows:

Volume I: Policy Report. This report summarizes the main messages of VolumeII, and highlights the policy implications of arsenic mitigation.

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This Volume II comprises four specialist papers:• Paper 1. Arsenic Occurrence in Groundwater in South and East Asia: Scale,

Causes, and Mitigation• Paper 2. An Overview of Current Operational Responses to the Arsenic Issue in

South and East Asia• Paper 3. Arsenic Mitigation Technologies in South and East Asia• Paper 4. The Economics of Arsenic Mitigation

The Scale of the Arsenic Threat

vii. In South and East Asia an estimated 60 million people are at risk from highlevels of naturally-occurring arsenic in groundwater, and current data showthat at least 700,000 people in the region have thus far been affected byarsenicosis. However, although the negative health effects of arsenicingestion in general, and the specific impact of ingestion of arsenic-contaminated groundwater, have both been widely studied, there is still noclear picture of the epidemiology of arsenic in South and East Asia, anduncertainty surrounds such issues as the spatial distribution ofcontamination; the symptoms and health effects of arsenic-related diseases,and the timeframe over which they develop; and the impact of arseniccompared to other waterborne diseases whose effects may be more immediate.

viii. While arsenic is clearly an important public health threat, it needs to be notedthat morbidity and mortality due to other waterborne diseases is also a serioushealth issue. Therefore, mitigation measures to combat arsenic contamination inSouth and East Asia need to be considered within the wider context of thesupply of safe water.

ix. Due to the carcinogenic nature of arsenic, the World Health Organization(WHO) recommends a maximum permissible concentration for arsenic indrinking water of 10 µg L–1 (micrograms per liter), which has been adoptedby most industrial countries. Most developing countries still use the formerWHO-recommended concentration of 50 µg L–1 as their national standard,due to economic considerations and the lack of tools and techniques tomeasure accurately at lower concentrations. Further studies are needed toassess the relationship between levels of arsenic and health risks in order toquantify the inevitable trade-offs at different standards between suchconsiderations as health risks, the ability of people to pay for safe water,and the availability of water treatment technology.

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Distribution of Arsenic Contamination

x. The concentration of arsenic in natural waters globally, including

groundwater, is usually below the WHO guideline value of 10 µg L–1.

However, arsenic mobilization in water is favored under reducing (anaerobic)

conditions, leading to the desorption of arsenic from iron (and other metal)

oxides. In South and East Asia such conditions tend to occur in shallow

aquifers in Quaternary strata underlying the region’s large alluvial and deltaic

plains (Bengal basin, Irrawaddy delta, Mekong valley, Red River delta, Indus

plain, Yellow River plain). (Some localized groundwater arsenic problems

relate to ore mineralization and mining activity, which are not the focus of

this study.) Recent hydrogeochemical investigations have improved our

knowledge of the occurrence and distribution of arsenic in groundwater,

though much uncertainty remains regarding the source, mobilization, and

transport of the element in aquifers.

xi. One of the important findings of recent detailed aquifer surveys has been the

large degree of spatial variability in arsenic concentrations, even over distances

of a few hundred meters. Temporal variability also occurs, though insufficient

monitoring has been carried out to establish a clear picture of variations in

arsenic levels over different timescales.

Arsenic Mitigation Measures

xii. Arsenic mitigation requires a sequence of practical steps involving enquiry andassociated action. Assessing the scale of the problem (now and over time)involves field testing, laboratory testing, and monitoring; identifying appropriatemitigation strategies involves technological, economic, and socioculturalanalysis of possible responses; and implementation involves awareness raisingand direct action by governments, donors, NGOs, and other stakeholders atlocal, national, and regional levels. Sustainability in the long run remains amajor challenge.

xiii. The two main technological options for arsenic mitigation are (a) switch toalternative, arsenic-free water sources; or (b) remove arsenic from thegroundwater source. Alternatives in the first category include development ofarsenic-free aquifers, use of surface water and rainwater harvesting; alternativesin the second category involve household-level or community-level arsenicremoval technologies. For each option there will be a wide range of designspecifications and associated costs.

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xiv. Despite continuing uncertainty regarding arsenic occurrence and epidemiology,the lethal nature and now well-established effects of arsenic exposure in Southand East Asia make it necessary that informed choices and trade-off decisionsare made to address arsenic contamination of drinking water sources and thescope and extent of mitigation measures, within the context of the developmentof the water sector and the wider economy.

xv. Accordingly, a simple cost-benefit methodology has been developed thattakes into account data limitations and provides decisionmakers with anapproach for rapid assessment of the socioeconomic desirability of differentmitigation policies under various scenarios. In particular, the methodologypermits an analysis of options in order to choose between differentapproaches in dealing with (a) the risk that arsenic might be found in an areawhere a project is planned; and (b) the risk mitigation options where aproject’s goal is arsenic mitigation per se.

xvi. Demand-side perspectives are an important consideration for designing arsenicmitigation measures that meet the requirements of households andcommunities. For example, are users willing to pay for an alternative such aspiped water? Demand preferences can be assessed through contingentvaluation or willingness to pay studies and can provide important guidance todecisionmakers. There is a need to strengthen institutional capacities in thecountries to carry out such assessments.

The Political Environment of Arsenic Mitigation

xvii. Arsenic has become a highly politicized topic in the international developmentcommunity and within some affected countries due to its carcinogeniccharacteristics and due to the earlier failure to consider it as a possible naturalcontaminant in groundwater sources. This factor makes rational analysis of theissue difficult and highlights the fact that application of mitigation measuresneeds to consider the political as well as the social and economic climate. Thescattered rural communities most affected by arsenic contamination often havelimited political presence and are in particular need of support.

xviii. Governments that want to address the arsenic issue will therefore have totake a stronger lead role in their countries and on the international plane.This goes both for more strategic research and knowledge acquisitionregarding arsenic in their countries, as well as for the choice and scope ofarsenic mitigation activities.

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The Importance of an Effective Operational andStrategic Approach

xix. Significant strides have been made since arsenic was first detected in drinkingwater tubewells in Eastern India and Bangladesh in the late 1980s and early1990s. However, a range of factors — including projected population growth inthe region, continuing private investment in shallow tubewells, and the drivetowards achievement of the Millennium Development Goal related to safe watersupply — add to the urgency of adopting a more strategic approach for effectiveaction at project, national, and international levels.

xx. At project level, any interventions that consider using groundwater as a sourcemust involve an assessment of whether occurrence of arsenic would affect theoutcome of the project. Such an assessment would include consideration oftechnical factors (such as screening and possible mitigation technologies), socialand cultural factors, and economic factors (including a cost-benefit or least-costanalysis).

xxi. Some countries have taken arsenic to the national level of attention,including Bangladesh, Nepal, and Cambodia. Others, such as India,Pakistan, and China, have only started to address the issue, while in otherinternational organizations such as UNICEF and local NGOs and universitiesare the focal points for arsenic-related activities. Although thecharacteristics of arsenic contamination are unique to each affected country,study results suggest that three simple steps would help governments moreeffectively address the problem now and in the future: (a) encourage furtherresearch in potentially arsenic-affected areas in order to better determine theextent of the problem; (b) ensure that arsenic is included as a potential riskfactor in decision-making about water-related issues; and (c) developoptions for populations in known arsenic-affected areas.

xxii. At the global level, focused research on the chemistry of arsenicmobilization and the dose-response relationships for arsenic are of vitalimportance in formulating a more effective approach. If governments and theinternational community are to achieve the MDGs in water supply andsanitation then the knowledge gaps regarding arsenic need to be filled,notably by (a) further epidemiological research directly benefiting arsenic-affected countries; (b) socioeconomic research on the effects of arsenicosis,understanding behavior and designing demand-based packages for thevarious arsenic mitigation techniques; and (c) hydrogeological andhydrochemical research.

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xxiii. It also needs to be made clear that, due to the nature of arsenic itself, in the not-so-distant future there will be diminishing returns on investments in scientificarsenic research to reduce uncertainty. The important challenge will be toidentify those areas where improved research-level data collection is likely toprovide a major return. For other areas the main question will be how to managein the face of unavoidable and continuing uncertainty.

xxiv. Accordingly, the international dialogue should shift towards targeted researchpriorities that address these issues. This would also include the pursuit of theresearch agenda regarding arsenic in the food chain. Both the World Bank and anumber of development partners are contributors to the Consultative Group onInternational Agricultural Research (CGIAR) and this organization would lenditself to building up a coherent and focused research agenda on this topic inorder to provide decisionmakers with guidance regarding arsenic-contaminatedgroundwater.

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1. The detrimental health effects of environmental exposure to arsenic havebecome increasingly clear in the last few years. Drinking water constitutes one ofthe principal pathways of environmental arsenic exposure in humans and highconcentrations detected in groundwater from a number of aquifers across theworld have been found responsible for health problems ranging from skindisorders to cardiovascular disease and cancer. Food represents a furtherpotential exposure pathway to arsenic, particularly where crops are irrigated withhigh-arsenic groundwater or where food is cooked in high-arsenic water.However, the relative impact on human health is as yet unquantified and in needof further study.

2. The concentration of arsenic in natural waters globally, including groundwater, isusually low. Most have concentrations below the World Health Organization(WHO) provisional guideline value for arsenic in drinking water of 10 µg L–1.However, arsenic mobilization in water is favored under some specificgeochemical and hydrogeological conditions and concentrations can reach twoorders of magnitude higher than this in the worst cases. Most occurrences ofhigh-arsenic groundwater are undoubtedly of natural origin.

3. Major alluvial and deltaic plains and inland basins composed of youngsediments (Quaternary; thousands to tens of thousands of years old) areparticularly prone to developing groundwater arsenic problems. Many of theidentified affected aquifers are located in South and East Asia. Highconcentrations have been found in groundwater from such aquifers in theBengal basin of Bangladesh and eastern India; the Yellow River plain and someinternal basins of northern China; the lowland Terai region of Nepal; the Mekongvalley of Cambodia; the Red River delta of Vietnam; and the Irrawaddy delta ofMyanmar. Problems may also emerge in similar alluvial and deltaic environmentselsewhere in the world. Unfortunately, such flat-lying fertile plains are oftendensely populated and so poor groundwater quality can have a major impact onlarge numbers of people. The increasing incidence of arsenic-related healthproblems in these areas largely coincided with the change to using groundwaterfrom tubewells, which began in the 1970s and 1980s.

4. The detailed mechanisms by which the arsenic mobilization occurs insedimentary aquifers are still not well understood. However, the development ofreducing (anaerobic) conditions in the aquifers has been recognized as a key riskfactor for the generation of high-arsenic groundwater. Indicators of suchconditions include lack of dissolved oxygen and high dissolved iron andmanganese concentrations. High-pH, oxidizing (aerobic) groundwater conditionshave also been linked with high groundwater arsenic concentrations in some

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parts of the world, though there is as yet no evidence for this means ofoccurrence in aquifers of South and East Asia. Arid inland basins such as occurin northern China and Mongolia represent possible areas for such conditions,but few data exist for such areas. Slow groundwater movement is alsoconsidered an important risk factor since under such conditions arsenic can bedissolved from minerals in the aquifer but is not readily flushed out of thesystem. Flat-lying sedimentary basins and delta plains are typically areas of suchslow groundwater movement.

5. One of the key findings of the last few years has been that the sediments inthese high-arsenic aquifers do not contain unusually high arsenicconcentrations. Typical concentrations are of the order of 5–10 mg kg–1; valuesrather close to world averages. Nor do the sediments contain unusual arsenicminerals. It is therefore feasible that any young sedimentary aquifers coulddevelop high-arsenic groundwater, given the special geological andhydrogeological conditions outlined above. Hence, other regions in Asia andelsewhere with young sedimentary aquifers may contain groundwater with higharsenic concentrations, but have not yet been identified. Given the increasedawareness of arsenic problems and increased groundwater testing that iscurrently being undertaken in various parts of Asia, it is likely that other areaswith problems will be identified more rapidly than was previously the case. Theexistence of unrecognized problems on such a large scale as that identified inthe Bengal basin is not impossible but is considered unlikely.

6. Mineralized areas, particularly areas of mining activity, are also at increased riskof groundwater arsenic contamination, although, unlike young sedimentaryaquifers, the affected areas are typically of local extent (a few kilometers aroundthe mineralized zone). Some geothermal areas may also give rise to increasedgroundwater arsenic concentrations, though this is also a less regionallysignificant occurrence.

7. Despite the advances made in recent years in understanding where high-arsenicgroundwaters are likely to exist on a regional scale, predictability on a local scaleis still poor and probably will always be so. Short-range (well-to-well) variabilityin groundwater arsenic concentrations is often large. This means that individualwells used for drinking water need to be tested in recognized arsenic-affectedareas. Despite common associations between arsenic and a number of othertrace elements (for example iron, manganese) in groundwater, observedcorrelations in water samples are usually weak. Hence, although other elementsmay signal potential problems regionally, they are not reliable as proxy indicatorsof arsenic concentrations in individual wells.

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8. Temporal variations in groundwater arsenic concentrations are also poorlydefined. Significant seasonal and longer-term variations have been claimed tooccur in some groundwaters from affected aquifers, though the information islargely anecdotal and difficult to verify. Temporal variation has majorconsequences for mitigation efforts and is in need of further investigation.However, in the interim, major short-term changes in groundwater arsenicconcentrations are not expected in most cases. Hence, it is reasonable toassume that an initial determination is likely to be representative, provided theresult is analytically reliable.

9. In areas affected by high-arsenic groundwater, there has been muchinvestigation into finding alternative sources of safe (low-arsenic) drinking water.Many of the options focus on the use of surface water (including rainwater),water from dug wells, and water from deep aquifers.

10. Surface waters usually have low dissolved arsenic concentrations. This isbecause of the low solid:/solution ratios in surface conditions compared toaquifers, and to the oxidizing conditions that pertain in most surfaceenvironments. Under oxidizing conditions, adsorption of arsenic to sedimentsand soils occurs and mobilization in soluble form is not favored. Exceptions canoccur locally in some mining environments as a result of direct contamination orin surface waters with a major proportion of discharging high-arsenicgroundwater. However, the normally strong adsorption of arsenic to streamsediments is likely to remove the dissolved arsenic from these sources over time.Arsenic may persist in some surface waters affected by geothermal inputs orevaporation (under high-pH conditions) but high concentrations related to theseprocesses have not been identified in Asia and are not considered of majorimportance in the region. Some arsenic in surface waters may be associatedwith particulate matter rather than being truly dissolved, especially if the water isturbid. The overwhelming drawback of surface waters is their often poorbacterial quality. This also has major health implications and has been animportant factor in determining the shift towards increased use of groundwaterfrom tubewells in Asia over the last few decades. Surface waters thereforeusually require sanitary treatment before use for potable supply.

11. Dug wells have also often been found to contain groundwater with lowconcentrations of arsenic in areas where tubewell groundwaters yield highconcentrations. As with surface waters, groundwater in dug wells is typicallyrelatively oxidizing, comprising a high proportion of freshly recharged rainwaterand being open to the atmosphere. Most groundwater samples analyzed fromdug wells in Bangladesh, West Bengal, Myanmar, and Nepal have been found to

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contain arsenic concentrations less than 50 µg L–1 (the national standard formost countries in Asia). As a result of this, dug wells have been promotedin some high-arsenic areas as alternative sources of drinking water. However, theconcentrations cannot always be guaranteed to be low. Sporadic occurrencesabove 50 µg L–1 have been found in groundwater from dug wells in a number ofthe recognized high-arsenic provinces. Some may be in the particulate ratherthan dissolved fraction, but such details are rarely specified in reports from theaffected regions. Nevertheless, dissolved concentrations of up to 560 µg L–1

have been found in dug well water from Inner Mongolia (China) where anaerobicconditions have been maintained in low-lying areas of groundwater dischargethat are characterized by sluggish groundwater movement. More chemicalanalysis is required to obtain an improved database of arsenic concentrations fordug wells. As with surface waters, shallow dug wells are vulnerable tocontamination from surface pollutants and pathogenic organisms. They are alsomore prone to drying up in areas with large water table fluctuations. They aretherefore unlikely to represent a major long-term solution to the arsenic problemsidentified in most areas of South and East Asia, although they may provide asuitable interim solution (given adequate sanitary protection) in some affectedareas if their arsenic concentrations can be demonstrated to be reliably low.

12. In some arsenic-affected regions of Asia, low-arsenic groundwater has beenfound in deeper aquifers underlying the young affected sediments. Groundwaterwith low arsenic concentrations (<10 µg L–1) has been found in, for example,deep aquifers in the Bengal basin (Bangladesh, India) and the Nepal Terai. Thedepth at which these aquifers occurs varies considerably (tens to hundreds ofmeters) and so considerable confusion has arisen over the descriptions of theseaquifers. The stratigraphy of the aquifers is poorly defined in most countries.More investigation has been carried out in Bangladesh than elsewhere. Here, thedeep aquifers with low-arsenic groundwater are mineralogically distinct from theyounger overlying sediments and are relatively oxic. They are likely to be ofPleistocene age (Quaternary; greater than 10,000 years old) and are consideredto have undergone more flushing by groundwater over their geological historythan the sediments bearing high-arsenic groundwater that overlie them.

13. These older aquifers in Bangladesh, West Bengal, and Nepal represent apotential alternative source of safe (low-arsenic) drinking water for the affectedpopulations. However, considerable uncertainty exists over their long-termsustainability in the event of significant exploitation. Further hydrogeologicalresearch is required to investigate whether, and to what extent, they would besusceptible to drawdown of high-arsenic groundwater from overlying aquifers or

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saline water in coastal areas following significant aquifer development. However,research effort on these aquifers should be complementary to theimplementation of mitigation measures and not a reason for delaying them.

14. Although older, deeper Quaternary aquifers in the Bengal basin and Nepal havebeen found to contain low groundwater arsenic concentrations, this has beenfound not to be the case in some other regions. In parts of northern China, higharsenic concentrations have been found in groundwater from both shallow(young Quaternary) and deeper (older Quaternary) aquifers. Here, the inlanddeep aquifers are thought not to have been well flushed during the Quaternaryice ages because of slow groundwater flow and closed-basin conditions. Somegroundwaters in Pleistocene aquifers of Vietnam also appear to have higharsenic concentrations. Aquifer depth is therefore not an indicator ofsusceptibility to arsenic mobilization. Rather, dissolved arsenic concentrationsare determined by a combination of geochemical conditions suitable formobilizing it and hydrogeological conditions which prevent its removal. Hence,groundwater quality with respect to arsenic concentrations must be consideredon an aquifer-by-aquifer basis and good hydrogeological and geochemicalunderstanding of young sedimentary aquifers is a prerequisite to groundwaterdevelopment.

15. On a regional scale, our understanding of arsenic mobilization processes issufficiently developed to allow some kind of prediction of where arsenicproblems are likely to occur and where not. Young sedimentary aquifers inalluvial and deltaic plains and inland basins are obvious areas for prioritygroundwater testing. Randomized reconnaissance groundwater arsenic surveysof such areas are the logical first step in identifying problem areas, followed bymore detailed surveys and mitigation if problems emerge. In identified arsenicproblem areas, ideally every well used for drinking water should be tested forarsenic. Given the high toxicity of arsenic to humans, there is an argument forreconnaissance testing of groundwaters from any aquifer used for potable watersupplies regardless of aquifer type and lithology. However, groundwater testingin Asia necessarily involves prioritization, with greatest emphasis on the aquifersat greatest risk.

16. A central tenet of both understanding the nature and scale of arsenic problemsin groundwater and mitigating them is the acquisition of reliable analytical datafor arsenic. Poor data can lead to erroneous conclusions and henceinappropriate responses. However, reliable chemical analysis of arsenic in wateris not a trivial undertaking and requires continual attention to quality assurance.

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Many groundwater arsenic analyses in Asia have been carried out using field testkits and these are particularly prone to problems with poor precision andaccuracy. Great emphasis should be placed on obtaining good-quality analyticaldata during testing and monitoring programs. Such programs need to takeaccount of local laboratory arsenic analytical capability and build in capabilitydevelopment where necessary.

17. Although a number of groundwater provinces have been found with high arsenicconcentrations, it is important to keep the scale of contamination in perspective.Groundwater from most aquifers has acceptably low arsenic concentrations andin most cases is less prone to bacterial contamination. In many areas of Asia andelsewhere, groundwater represents a reliable source of safe drinking water.Indeed, in some arid areas it constitutes the only source of water. Even inBangladesh, which has suffered by far the greatest impact from groundwaterarsenic problems, national statistics based on randomly collected groundwatersamples indicate that 27% of shallow groundwaters (from tubewells <150 mdeep) have arsenic concentrations greater than the Bangladesh standard of50 µg L–1 and 46% have concentrations greater than 10 µg L–1. This means that73% and 54% respectively have concentrations below these values and aretherefore deemed to be of acceptable quality. Given that considerableinvestment has been made in groundwater in countries such as Bangladesh overthe last few decades, it would be costly and over-reactive to abandongroundwater in favor of alternatives without first carrying out testing programsand, where necessary, further hydrogeological investigations.

18. This report provides an overview of the current state of knowledge on theoccurrence, distribution, and causes of arsenic problems in water supplies inSouth and East Asia. It also characterizes likely ‘at-risk’ aquifers and the types ofindicators that may be used to identify them. Response strategies in terms ofanalytical testing and monitoring will vary widely depending on factors such asthe scale of the arsenic problem, the numbers of operating wells, the populationserved, the water use, and the scope for alternative water sources. Some ofthese issues are investigated and strategies for testing and monitoring outlined.

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Pathways of Arsenic Exposure

The dangers associated with long-term exposure to arsenic are now well known. The mostprominent health problems in affected populations are skin disorders (melanosis, keratosis,

skin cancer) but a large range of other disorders, including internal cancers (bladder, lung,kidney), cardiovascular diseases, peripheral vascular disorders, respiratory problems, anddiabetes, have also been linked to chronic high doses of ingested arsenic.

Drinking water can be one of the most important pathways of exposure to arsenic in humanpopulations and groundwater sources are thought to be responsible for the majority of theworld's chronic arsenic-related health problems. Despite this, most groundwaters have low orvery low concentrations of arsenic (well below regulatory and recommended limits) and in aglobal context they often constitute the most reliable sources of safe drinking water.Groundwater is also less vulnerable to contamination from the waterborne diseases that can bea serious problem in many surface waters. It appears to be only when certain geological andhydrogeochemical conditions arise in aquifers that arsenic problems occur on a regional andproblematic scale. This report describes those occurrences and the geochemical processescontrolling them and attempts to provide guidance on the criteria for identifying, monitoring,and dealing with these problem areas.

Although drinking water is known to be closely linked to chronic arsenic-related healthproblems, the sometimes poor relationship observed between arsenic intake from water andhealth symptoms poses the possibility that other pathways of arsenic exposure may also occur.Food is one potential source. Crops irrigated with high-arsenic groundwater are potentiallyvulnerable to arsenic take-up, particularly following long-term groundwater use and soil arsenicaccumulation. Some studies have shown higher-than-background concentrations of arsenic invegetables. Higher concentrations have typically been found in roots than in stems, leaves, oreconomic produce. However, few results have been published so far. Meharg and Rahman(2003) considered that rice irrigated with high-arsenic groundwater could represent a significantcontribution to the arsenic intake in some of the Bangladeshi population. In a study of dry ricegrain produced by groundwater irrigation, they found concentrations up to 1.8 mg kg-1

(compared, for example, with the 1 mg kg-1 Australian standard for inorganic arsenic in food).However, few samples were analyzed and the values found are higher than those in otherstudies of naturally cultivated rice carried out to date (Abedin, Cotter-Howells, and Meharg2002). The bioavailability of arsenic in rice is also uncertain and is strongly influenced by theproportions of organic and inorganic forms present. Comparatively high concentrations havebeen found in rice straw, which could affect the doses taken by grazing animals (Abedin andothers 2002). Clearly, more research needs to be carried out on arsenic uptake by crops inirrigated areas and on food for, and produced from, grazing animals. Since arsenic isphytotoxic, uptake by vegetation may be inhibited and may therefore not be the greatestconcern. However, long-term effects on crop yield, especially of rice, could become animportant issue (Abedin and Meharg, 2002).

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Arsenic-contaminated air is also a potential exposure pathway in some cases. In Guizhou

Province, southern China, severe chronic health problems have arisen from the burning of local

coal with very high arsenic concentrations (up to 35,000 mg kg-1), the exposure being both by

inhalation and consumption of chillis dried over domestic coal fires (Finkelman, Belkin, and

Zheng 1999). This pathway is much more localized than that from drinking water but, in China,

an estimated 3,000 people in several villages of Guizhou Province have arsenicosis symptoms

as a result of exposure from this source (Ding and others 2001).

Drinking Water Regulations and Guidelines

Regulatory and recommended limits for arsenic in drinking water have been reduced in recent

years following increased evidence of its toxic effects to humans. The World Health

Organization (WHO) guideline value was reduced from 50 µg L-1 to 10 µg L-1 in 1993

although the recommendation is still provisional pending further scientific evidence. Western

countries are reducing, or have reduced, their national standards in line with this change.

Despite this, national standards for arsenic in most Asian countries (except Japan and Vietnam)

remain at 50 µg L-1, in line with the pre-1993 WHO guideline value. This is largely a

consequence of analytical constraints and, in some countries, of difficulties with compliance to

a lower standard.

World Distribution of High-Arsenic Groundwaters

The concentrations of arsenic in most groundwaters are low, typically less than the WHO

guideline value of 10 µg L-1 and commonly below analytical detection limits. An investigation of

some 17,500 groundwater samples from public supply wells in the United States of America, forexample, found that 7.6% exceeded 10 µg L-1 and 1% exceeded 50 µg L-1, while 64%

contained <1 µg L-1 (Focazio and others 1999). Despite the usually low abundance in water, high

concentrations can occur in some groundwaters. Under geochemically and hydrogeologicallyfavorable conditions concentrations can reach tens to hundreds of µg L-1 and, in a few cases,

can exceed 1 mg L-1.

Most of the world's high-arsenic groundwater provinces result from natural processes involving

interactions between water and rocks. Some of the highest concentrations of arsenic are found

in sulfide and oxide minerals, especially iron sulfides and iron oxides. As a result, high arsenic

concentrations in water are often found where these minerals are in abundance. Mineralized

areas are well-documented examples. These contain ore minerals, including sulfide minerals,

typically as veins or replacements of original host rocks and result from past infiltration of

hydrothermal fluids. In mineralized areas, rates of mineral dissolution can be enhanced

significantly by mining activity and arsenic contamination can be particularly severe in water

associated with mine wastes and mine drainage. Some geothermal waters also contain high

arsenic concentrations.

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A map of the distribution of documented cases of arsenic contamination in groundwater and theenvironment is given in figure 1. Many of these cases are related to areas of mineralization andmining activity and a few are associated with geothermal sources. While these cases can besevere with often high concentrations of arsenic in waters, sediments, and soils, the scale ofcontamination is usually not of large lateral extent. This is due to the normally strong adsorptioncapacity of iron oxides, which leads to removal of arsenic and other potentially toxic traceelements from water.

Despite these associations, other areas with recognized high-arsenic groundwaters are notassociated with obvious mineralization or geothermal activity. Some of these occur in majoraquifers and may be potentially much more serious because they occupy large areas and canprovide drinking water for large populations. Unlike mining and geothermal areas, they are alsomore difficult to detect without chemical analysis of the groundwater. Several aquifers aroundthe world have now been identified with unacceptably high concentrations of arsenic. Theseinclude aquifers in parts of Argentina, Chile, Mexico, southwest United States, Hungary,Romania, Bangladesh, India, China (including Taiwan), Myanmar, Nepal, and Vietnam (figure 1).Many differences exist between these regions, but some similarities are also apparent. Themajority of the high-arsenic groundwater provinces are in young unconsolidated sediments,usually of Quaternary age, and often of Holocene (<12,000 years) age. These aquifers areusually large inland closed basins in arid or semiarid settings (for example Argentina, Mexico,southwest United States) or large alluvial and deltaic plains (for example Bengal delta, YellowRiver plain, Irrawaddy delta, Red River delta). These aquifers do not appear to containabnormally high concentrations of arsenic-bearing minerals but do have geochemical andhydrogeological conditions favorable for mobilization and retention in solution.

Figure 1. Summary of the World Distribution of Documented Problems withArsenic in Groundwater and the Environment

Source: Modified after Smedley and Kinniburgh 2002.Note: In China, arsenic has further been identified in the provinces of Jilin, Qinghai, Anhui, Beijing, and Ningxia (reported at RegionalOperational Responses to Arsenic Workshop in Nepal, 26–27 April 2004).In India, further affected states are Assam, Arunachal Pradesh, Bihar, Manipur, Meghalaya, Nagaland, Uttar Pradesh and Tripura.

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Overview

Many of the world's aquifers with recognized arsenic problems are located in Asia wherelarge alluvial and deltaic plains occur, particularly around the perimeter of the Himalayan

mountain range (figure 2). This section gives an account of the occurrence and scale ofgroundwater arsenic problems in countries where such problems have been identified. Theremay be other Quaternary aquifers with high groundwater arsenic concentrations that have notyet been identified, but since awareness of the arsenic problem has grown substantially over thelast few years, these are likely to be on a smaller scale than those already identified.

The information in this section has been compiled from published literature, as well as variousunpublished reports and websites. Many of the unpublished data are difficult to access andreports typically not peer reviewed. Data for many countries also lack spatial information,

Figure 2. Map of South and East Asia Showing the Locations of DocumentedHigh-Arsenic Groundwater Provinces

Source: Modified after Smedley 2003.

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particularly georeferenced sample points. Reporting often merely gives an indication of whetheran area is or is not affected, rather than an account of percentages of affected wells in a givenarea. In some cases, the quality of analytical data is also uncertain (box 1). These uncertaintiesmake it difficult to assess the scale of arsenic problems in many parts of South and East Asia.Nonetheless, the information available has been brought together to provide a criticalassessment of the current state of knowledge of the scale of groundwater contamination of theaquifers in Asia and to detail where apparent data gaps exist. A summary of the recognizedoccurrences, aquifers involved, and populations potentially at risk (that is, using drinking waterwith arsenic concentrations >50 µg L-1) is given in table 1. Some of these population statisticsare poorly constrained given the present state of knowledge.

Box 1. Analysis of Arsenic

Arsenic is a trace element that is present at µg L-1 concentrations in most natural waters. Samplingand analyzing such small concentrations is not a trivial task and there have been many examples inrecent years where faulty analysis has led to dubious conclusions. All surveys require a plannedand maintained quality assurance program to ensure that data produced are of good qualitythroughout the program. This includes adequate record-keeping, sample tracking, regular use ofanalytical standards, interlaboratory (round robin) checks, and duplicate analyses.

The most precise and sensitive analytical methods depend on sophisticated laboratory instrumentssuch as hydride generation-atomic absorption spectrometry (HG-AAS), inductively coupledplasma-mass spectrometry (ICP-MS), and hydride generation-atomic fluorescence spectrometry(HG-AFS). The use of HG-AAS has expanded in recent years, but many developing countries donot have such sophisticated facilities or have difficulty maintaining them, especially on the scalerequired. Costs of analysis by these techniques are typically in the range US$10–20 per sample.The HG-AAS and HG-AFS methods are at the cheaper end of this range, but the more expensiveICP methods are multielement techniques and so provide information on elements other thanarsenic. There are cheaper and more robust instruments, such as that employed by the silverdiethyldithiocarbamate (SDDC) method, but these are less sensitive, are slow, and may not beappropriate for large screening programs. Field test kits have therefore been widely used as aprimary source of data in many surveys, with laboratory methods used for checking some of theresults. Field test kits are relatively simple and inexpensive, usually costing less than US$1 persample for the materials. The early kits were insufficiently sensitive (being barely capable ofdetecting less than 100 µg L-1). However, they have improved in the last few years and the best cannow detect down to 10 µg L-1, the WHO guideline value. In practice, the reproducibility of the kitshas often proven disappointing and care has to be taken to ensure that good results are obtainedconsistently during a survey (Rahman and others 2002).

As a result of the relatively large errors involved in arsenic analysis, especially with field test kits, itis inevitable that some wells will be misclassified as "safe" when they are not, and vice versa.Procedures should be in place to assess the scale and significance of these misclassifications andto minimize their impact, for example by reanalyzing samples that are very different from thosetaken from neighboring wells. The reliability of the kits increases for concentrations well above thedrinking water standard or guideline and so they tend to be more reliable at detecting the mosttoxic waters.

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Table 1. Summary of the Distribution, Nature, and Scale of Documented Arsenic Problems(>50 µg L-1) in Aquifers in South and East Asia

Location Areal extent (km2) Population at riska Arsenic range(µg L-1)

Alluvial/deltaic/lacustrine plains

Bangladesh 150,000 35,000,000 <1-2,300

China (Inner Mongolia,Xinjiang, Shanxi) 68,000 5,600,000 40-4,400

India (West Bengal) 23,000 5,000,000 <10-3,200

Nepal 30,000 550,000 <10-200

Taiwan (China) 6,000 (?) 10,000b 10-1,800

Vietnam 1,000 10,000,000c 1-3,100

Myanmar (?) 3,000 3,400,000 -

Cambodia (?) <1,000 320,000d -

Pakistan - - -

Alluvial, Deltaic, and Lacustrine Plains

Bangladesh

Of the regions of the world with groundwater arsenic problems Bangladesh is the worst caseidentified, with some 35 million people thought to be drinking groundwater containing arsenic atconcentrations greater than 50 µg L-1 (table 1) and around 57 million drinking water withconcentrations greater than 10 µg L-1 (Gaus and others 2003). The large scale of the problemreflects the large area of affected aquifers, the high dependence of Bangladeshis ongroundwater for potable supply, and the large population in the fertile lowlands of the Bengalbasin. Today, there are an estimated 11 million tubewells in Bangladesh serving a population ofaround 133 million people (2002 estimate). The scale of arsenic contamination in Bangladeshmeans that it has received by far the greatest attention in terms of groundwater testing andmore is known about the arsenic distribution in the aquifers than in any other country in Asia(as well as most of the developed world). However, much more testing is still required.

Several surveys of arsenic in Bangladesh groundwater have been carried out over the last fewyears, both by laboratory and field methods. The Bangladesh Department of Public HealthEngineering (DPHE) and the United Nations Children's Fund (UNICEF) carried out surveys of

- Not available.a Estimated to be drinking water with arsenic >50 µg L-1. From Smedley 2003 and data sources therein.b Before mitigation.c United Nations Children's Fund (UNICEF) estimate.d Maximum.Source: World Bank Regional Operational Responses to Arsenic Workshop in Nepal, 26-27 April 2004.

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51,000 wells during 1997-1999 using arsenic field test kits. The British Geological Survey (BGS)and the DPHE conducted a survey of around 3,500 samples nationwide during 1998-1999(BGS and DPHE 2001). Over the last few years, the Bangladesh Arsenic Mitigation WaterSupply Project (BAMWSP) and a number of nongovernmental organizations (NGOs) andinternational agencies (for example the Japan International Cooperation Agency (JICA), theAsian Arsenic Network (AAN), NGO Forum, UNICEF, World Vision International, and WatsanPartnership) have carried out major screening programs of groundwaters across Bangladesh.Van Geen, Zheng, and others (2003) also analyzed samples from about 6,000 wells in easternBangladesh. To date more than 4.2 million tubewells have been tested for arsenic. However, thisis still only around 39% of the wells in the country.

High-Arsenic Shallow AquifersThe aquifers affected by arsenic are Quaternary, largely Holocene, alluvial and deltaic sedimentsassociated with the Ganges-Brahmaputra-Meghna river system. These occur as the surfacecover over a large part of Bangladesh. Groundwater from the Holocene aquifers containsarsenic at concentrations up to around 2,300 µg L-1, though concentrations span more than fourorders of magnitude (BGS and DPHE 2001). Van Geen, Zheng, and others (2003) foundconcentrations in the range <5-860 µg L-1 in groundwaters from Araihazar, east of Dhaka.

Several surveys of the groundwater have shown a highly variable distribution of arsenic, bothlaterally and with depth. This means that predictability of arsenic concentrations in individual

Figure 3. Smoothed Map of ArsenicDistribution in Groundwater fromBangladesh

Note: Samples are from tubewells <150 m deep.Source: BGS and DPHE 2001.

wells is poor and each well used for drinkingwater needs to be tested. Nonetheless, on aregional scale, trends are apparent, and theworst-affected areas with the highest averagearsenic concentrations are found in thesoutheast of the country, to the south ofDhaka (figure 3). Here, in some districts,more than 90% of shallow tubewells testedhad arsenic concentrations >50 µg L-1.Some areas with low overall arsenicconcentrations have localized hotspots withlocally high arsenic concentrations. That ofthe Chapai Nawabganj area of westernBangladesh is a notable example (figure 4 seepage 34), where the median concentration ingroundwater from Holocene sediments wasfound to be 3.9 µg L-1 but with extremes up to2,300 µg L-1 concentrated in a small area ofaround 5 x 3 km. Overall, the BGS and DPHEsurvey of shallow groundwaters found that27% exceeded 50 µg L-1 and 46% exceeded10 µg L-1.

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Figure 4. Maps of the Distribution of Arsenic in Shallow Groundwater from the ChapaiNawabganj Area, Northwest Bangladesh

Note: Samples are from tubewells <150 m deepSource: BGS and DPHE 2001.

Investigation of the depth ranges of affected tubewells suggests that concentrations are low ingroundwater from the top few meters of the aquifers close to the water table, but that theyincrease markedly over a short depth range. This is demonstrated by the profile of groundwatercompositions in a piezometer (10 cm diameter, 40 m deep) in Chapai Nawabganj, northwestBangladesh. Arsenic concentration was relatively low (17 µg L-1) at 10 m depth but increased tovalues in the range 330-400 µg L-1 over the depth interval 20-40 m (BGS and DPHE 2001)(figure 5).

The largest range and highest concentrations of arsenic are typically found at around 15-30 mdepth below surface, although the depth ranges of the peaks vary from place to place. Table 2shows the frequency distribution of arsenic concentrations with depth for all analyzed samplesfrom the BGS and DPHE (2001) survey.

Investigation of other elements of potential health concern reveals that concentrations ofmanganese are often greater than the WHO health-based guideline value of 0.5 mg L-1 andconcentrations of uranium are also sometimes high (up to 32 µg L-1). Concentrations of boronexceed WHO guidelines in some saline groundwaters from the south and east of Bangladesh.

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Figure 5. Variation in Concentration of Arsenic and Other Elements with Depth in a Purpose-Drilled Piezometer in Chapai Nawabganj, Northwest Bangladesh

Source: BGS and DPHE 2001.

Nitrate concentrations are normally low, as are most other trace elements on the WHO list ofelements considered detrimental to health. Concentrations of iron and ammonium are often highbut these are issues of acceptability on aesthetic grounds rather than health considerations.

Low-Arsenic AquifersThe BGS and DPHE (2001) map (figure 3) demonstrates the low overall arsenic concentrationsof groundwater from coarser sediments in the Tista Fan of northern Bangladesh. Lowconcentrations are also found in groundwaters from aquifers in the older (Pleistocene) upliftedplateaux of the Barind and Madhupur tracts (north-central Bangladesh). These usually haveconcentrations less than 10 µg L-1 and often significantly less. Similar results for these areashave also been obtained by other workers (for example van Geen, Zheng, and others 2003).

a Depth of intake of groundwater is difficult to determine and may be from several horizons at differing depths.Source: BGS and DPHE 2001.

Table 2. Frequency Distribution of Arsenic in Groundwater from Tubewells from QuaternaryAlluvial Aquifers in Bangladesh

Tubewell depth Number of samples (%) Total samplesrange (m)a <10 µg L-1 10-50 µg L-1 >50 µg L-1

<25 597 (53) 193 (17) 327 (30) 1,117

25-50 740 (57) 211 (16) 354 (27) 1,305

50-100 363 (55) 143 (22) 153 (23) 659

100-150 33 (26) 47 (37) 46 (37) 126

150-200 25 (78) 6 (19) 1 (3) 32

>200 286 (97) 7 (2) 2 (1) 295

Water level

Wel

l dep

th (m

)

Eh (mV) SEC (µS cm )-1 As (µg L )T-1 Fe (mg L )T

-1 SO (mg L )4-1

0 60 120 1000 1200 0 200 400 0 5 10 15 0 5 10

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

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Box 2. Shallow versus Deep Aquifers

It has been observed that groundwater from deep Quaternary aquifers in the Bengal basin(Bangladesh and West Bengal) has low or very low concentrations of arsenic, often much less than5 µg L-1. The depth at which these deep aquifers occur varies but is typically more than 100–150 mbelow surface. Deep aquifers have been tapped in southern coastal areas and northeasternBangladesh for some time but less so in other areas and their stratigraphy, lithology, and arealextent are often poorly defined. They are often said to be more oxic than the younger overlyingdeposits with a higher proportion of brown iron oxides. As older formations, they are also likely tohave been better flushed by groundwater than the overlying young sediments as a result ofincreased groundwater gradients and more active water movement during past ice ages. Assources of low-arsenic groundwater, these deep aquifers could provide drinking water for affectedpopulations in the region. More research is needed, however, to establish whether they would besecure from the effects of downward leakage of high-arsenic water (or saline water in coastalareas), given significantly increased groundwater abstraction.

In other regions of South and East Asia, groundwater from deep Quaternary aquifers does notalways have low arsenic concentrations. In Inner Mongolia, concentrations of arsenic up to310 µg L-1 have been found in groundwater from wells more than 100 m deep in an area where ashallow aquifer (less than 30 m deep) also has high groundwater arsenic concentrations. Thelithology and stratigraphy of the deep aquifer are poorly characterized. However, it is clear from thecomparisons that groundwater arsenic concentration is not a simple function of aquifer or welldepth. Rather, aquifer geology and groundwater flow history are important controlling factors.Observations show that a good understanding of the hydrogeology and geochemistry ofQuaternary alluvial, deltaic, and lacustrine aquifers is needed before significant groundwaterdevelopment should be allowed to take place.

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Groundwater from these areas is therefore expected to be normally safe from the point of viewof arsenic, although concentrations of other elements, notably iron and manganese, maybe high.

Arsenic concentrations also appear to be mostly low in groundwater from older ("deep")aquifers which occur in some areas below the Holocene deposits. The stratigraphy of the deepaquifers of Bangladesh is poorly understood at present, but where studied, the aquifers withlow-arsenic groundwater appear to be of Pleistocene age (BGS and DPHE 2001; van Geen,Zheng, and others 2003). Limited investigations indicate that they are mineralogically distinctfrom the overlying Holocene deposits. They are typically more brown in color and relativelyoxidized. The deep aquifer sediments are likely to be akin to the aquifers below the Barind andMadhupur tracts, which occur at shallower depths because of tectonic uplift.

Although these sediments are often referred to as the "deep aquifer", the definition of "deep"varies from place to place and between organizations and the subject has become ratherconfused (box 2). However, depth ranges for the low-arsenic groundwater are usually at least100-200 m. Recent data produced by the BAMWSP for groundwater samples from 60 upazilasacross Bangladesh found that out of 7,123 samples from tubewells >150 m deep, 97% hadarsenic concentrations <50 µg L-1 (percentage <10 µg L-1 unspecified; BAMWSP website). The

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BGS and DPHE (2001) national survey categorized shallow aquifers as those less than<150 m depth and deep aquifers as >150 m. Of 335 samples analyzed from >150 m depth,95% were found to have arsenic concentrations <10 µg L-1 (table 2). Most of the deepgroundwater samples analyzed in the BGS and DPHE survey were from the southerncoastal area (Barisal) and the northeast (Sylhet). In these areas, the shallow and deepaquifers appear to be separated by thick deposits of clay, which afford some hydraulicseparation between the two. By contrast, in a local study of groundwater in Faridpur areaof central Bangladesh, BGS and DPHE (2001) defined the deep aquifer as being greaterthan 100 m, based on the occurrence of sandy sediments and well depths. Here thedeeper aquifer was found not to be well separated from the shallower aquifer and a degreeof hydraulic connection between the two is therefore possible (BGS and DPHE 2001). Chemicalanalysis of samples from Faridpur revealed arsenic concentrations up to 52 µg L-1 (five samples)in groundwater from >100 m depth. Closer investigation of the wells with higher concentrationsalso showed that they were sometimes screened at multiple levels and hence took in water fromvarious horizons.

Van Geen, Zheng, and others (2003) also found consistently lower arsenic concentrationsat greater depth in the Araihazar area east of Dhaka. Here the low concentrations werefound at depths as shallow as 30 m, although the range of the low-arsenic deep aquifervaried between 30 m and 120 m. There is some question over whether the deep aquifer at30 m results from uplift of the sediments, as the study area is on the eastern edge of theMadhupur tract.

The results clearly indicate that the depth of safe aquifers varies in different parts of Bangladeshand it is not possible to define the depth at which low-arsenic water will occur, even assuming adeep aquifer exists in all areas. The variable depths are perhaps not surprising given theheterogeneity of sediments in the basin and complexities introduced by past tectonicmovements. The important criterion for determining the groundwater arsenic concentrations isthe sediment type and sediment history rather than depth.

From available data, it also appears that concentrations of manganese and uranium are lower inthe groundwater from the deeper aquifer (BGS and DPHE 2001). Concentrations of most otheranalyzed trace elements were also within acceptable ranges.

Although a number of studies have been and are being carried out on the Bangladesh deepaquifers, much remains unknown about their distribution across the country, the degree ofhydraulic separation from the shallow high-arsenic aquifers, and their viability as a long-termsource of water. Questions also remain about why higher arsenic concentrations occur in somesamples. Possibilities include drawdown from shallow levels due to hydraulic connection,drawdown via wells due to poor sealing, multiple screening of wells in both aquifers, or in situhigh-arsenic groundwater in some parts of the deep aquifer. These questions are critical to thefuture potential of the deep aquifers for water supply and need further assessment beforedevelopment of these aquifers takes place on a large scale.

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Dug WellsA number of studies have concluded that arsenic concentrations in shallow dug wells inBangladesh are usually low, even in areas where tubewells have high concentrations (box 3).Concentrations are generally <50 µg L-1, with most being <10 µg L-1 (for example Chakroborti2001). BGS and DPHE (2001) found concentrations in five dug wells from north-westBangladesh (Chapai Nawabganj) in the range <3-14 µg L1 , with a median of 7.6 µg L-1. Twosamples exceeded 10 µg L-1, albeit by a small margin. However, these were from an area withlower overall groundwater arsenic concentrations than the worst-affected parts of the country.Little difference was observed in the samples between concentrations in filtered and unfilteredaliquots and the concentrations were therefore considered to be largely dissolved.Concentrations of uranium up to 47 µg L-1, manganese up to 1.7 mg L-1 , and nitrate-N up to

Box 3. Dug Wells

Concentrations of arsenic in dug wells are often low, even in areas where those in groundwaterfrom neighboring tubewells are high. In western Bangladesh, a 30 m deep tubewell with agroundwater arsenic concentration of around 2,300 µg L-1 is located just a few meters from an 8 mdeep dug well with an arsenic concentration of less than 4 µg L-1. Groundwater in the top fewmeters below the water table is likely to be relatively aerobic because of recent inputs of rainfalland more active groundwater movement. However, it is most likely that the tendency for lowarsenic concentrations in dug wells relates in large part to their large diameter and openness toatmosphere compared to tubewells.

Despite the tendency for low arsenic concentrations in dug well waters, not all are found to bebelow acceptable limits. Several dug wells from the Bengal basin have been found withconcentrations greater than the WHO guideline value of 10 µg L-1. Worse, in parts of Inner Mongoliawhere tubewell water has high concentrations, groundwater from dug wells has been found withconcentrations up to 560 µg L-1. The concentration of arsenic in dug wells is probably largelycontrolled by the redox conditions in the wells; where anaerobic conditions can be maintained,arsenic concentrations may be unacceptably high. Concentrations may also be high where locallyinfluenced by mining wastes. The concentrations of arsenic in dug wells can therefore not alwaysbe guaranteed to be low, and testing for arsenic needs to be carried out to assess their safety forpotable purposes.

Additional problems from dug wells occur because of their shallow depths. They can be atincreased risk from contamination by surface pollutants, including pathogenic bacteria, and willgenerally require disinfection before use. Enclosure of the well and adding a handpump may alsobe necessary. Restricted yields and seasonal drying up of wells are additional problems affectingtheir usefulness in some areas.

In many parts of South and East Asia, dug wells have been superseded over time by handpumpedtubewells as a means of obtaining improved yields and sanitary protection. Nonetheless, they arestill used by significant numbers of people, and in some areas they provide an alternative to high-arsenic tubewell water. In Bangladesh around 1.3 million people are estimated to be dependent ondug wells for drinking water (Ahmed and Ahmed 2002), though not all of these draw water from theunconsolidated sediments of the Bengal basin.

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28 mg L-1 were found in the dug wells from the region, all of which exceed current WHO health-based guideline values. Bacterial counts in dug wells are also often high.

Bengal Delta and Associated Aquifers, India

Problems with arsenic in groundwater in West Bengal were first recognized in the late 1980sand the health effects are now reasonably well documented. Today, it is estimated that morethan 5 million people in the state are drinking water with arsenic concentrations greater than50 µg L-1 (table 1). More recently, problems have also been found in Arunachal Pradesh, Assam,Bihar, Nagaland, Manipur, Meghalaya, Tripura, and Uttar Pradesh. The state of Mizoram alsohas important Quaternary sedimentary aquifers that are potentially at risk from highgroundwater arsenic concentrations. Recent findings of health problems in the village of SemriaOjha Patti in Bihar prompted a survey of groundwater arsenic concentrations. Of 206 tubewellstested, 57% exceeded 50 µg L-1 and 20% exceeded 300 µg L-1. Concentrations were up to1,650 µg L-1 (Chakraborti and others 2003). Associated health problems are also severe, withskin lesions reported to be prevalent in 13% of adults and 6.3% of children and neurologicalproblems in 63% of adults. As the water samples were collected from villages with identifiedhealth problems, the concentrations represent worst cases and the statistics are unlikely to berepresentative of the arsenic concentrations in the state as a whole.

More than 100,000 groundwater arsenic analyses have apparently been determined for WestBengal. Despite this, there still appears to be a lack of detailed maps of arsenic to assess thespatial distribution. Worst-affected districts have been identified but the distributions on a largerscale (within districts) are not clear and it is thought that no point source maps of groundwaterarsenic concentrations have been produced. The scale of the problem in other states withsimilar geology (Tripura, Bihar, Uttar Pradesh, Meghalaya, Mizoram) is also not known.

The affected aquifers of the region are mainly Holocene alluvial and deltaic sediments similar tothose of large parts of Bangladesh. In West Bengal, they form the western margins of theBengal basin. High arsenic concentrations have been identified in groundwaters from sometubewells in up to eight districts of West Bengal, the five worst affected being Malda,Murshidabad, Nadia, 24 North Parganas, and 24 South Parganas (figure 6 see page 40). Thesecover around 23,000 km2 to the east of the Bhagirathi-Hoogli river system. Arsenicconcentrations have been found in the range <10-3,200 µg L-1 (table 1; CGWB 1999). At thetime of writing, no data on arsenic concentrations in groundwater from Chinsurah District areavailable. Groundwaters from the laterite upland in the western part of West Bengal, as well asthe Barind and Ilambazar formations, the valley margin fan west of the Bhagirathi River, and thelower delta plain and delta front have low groundwater arsenic concentrations (PHED 1991).

The Quaternary sediment sequence increases in thickness southwards (CGWB 1999).Sedimentation patterns vary significantly laterally, but sands generally predominate to a depthof 150–200 m in Nadia and Murshidabad, while the proportion of clay increases southwards into24 North and South Parganas, as does the thickness of surface clay (Ray 1997).

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Figure 6. Map of West Bengal Showing Districts Affected by High Groundwater ArsenicConcentrations

Note: Numbers refer to number of blocks with arsenic concentrations >50 µg L–1 relative tototal number of blocks. Darker shading shows worst-affected areas (data as of 1999).

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The Quaternary sediments have a similar configuration to those of Bangladesh but the aquifershave been categorized slightly differently. A shallow "first aquifer" has been described at12–15 m depth, with an intermediate "second aquifer" at 35–46 m, and a deep "third aquifer" ataround 70–90 m depth (PHED 1991). High arsenic concentrations occur in groundwater fromthe intermediate second aquifer. Shallowest groundwaters (first aquifer) appear to have lowconcentrations, presumably because many (though not necessarily all) of the sourcesabstracting from this depth are open dug wells and are likely to contain groundwater that isoxidized through exposure to the atmosphere. Groundwaters from the deep aquifer also havelow arsenic concentrations, except where only a thin clay layer separates it from the overlyingaquifer, allowing some hydraulic connection between them. CGWB (1999) noted that the depthsof arsenic-rich groundwaters vary in the different districts but where high-arsenic groundwatersexist, they are generally in the depth range of 10–80 m. As with Bangladesh, therefore, thegroundwater arsenic concentration ranges appear to show a bell-shaped curve with depth.

As with Bangladesh, the distribution of arsenic concentrations in the groundwaters is known tobe highly variable. Some particularly high concentrations (>200 µg L-1) have been found ingroundwaters from 24 South Parganas, along the international border of 24 North Parganas,and in eastern Murshidabad (Acharyya 1997; CSME 1997).

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Terai Region, Nepal

Groundwater is abundant in the Quaternary alluvial sediments of the lowland Terai region ofsouthern Nepal and is an important resource for domestic and agricultural use. The region isestimated to have around 800,000 tubewells, which supply groundwater for some 11 millionpeople (World Bank Regional Operational Responses to Arsenic Workshop, Nepal, 26–27 April2004). About 15% of these wells were supplied by government agencies or NGOs, the restbeing private wells. Many have been installed within the last decade. Groundwater is alsoused for irrigation; these wells generally abstract from deeper levels than those used fordrinking water.

Both shallow and deep aquifers occur throughout most of the Terai region, although thethickness of sediments deposited is significantly less than found in Bangladesh. The shallowaquifer appears to be mostly unconfined and well developed, although it is thin or absent insome areas (Upadhyay 1993). The deep aquifer (precise depth uncertain) is artesian. Quaternaryalluvium also infills several intermontane basins in Nepal, most notably that of the Kathmanduvalley of central Nepal (ca. 500 km2), where sediment thickness reaches in excess of 300 m(Khadka 1993). Recent heavy abstraction of groundwater in the Kathmandu valley has resultedin falling groundwater levels (Tuinhof and Nanni 2003).

A number of surveys of groundwater quality in the Terai region have revealed the presence ofarsenic at high concentrations in some shallow tubewells (<50 m depth), though most of thoseanalyzed appear to have <10 µg L-1. Arsenic-related health problems have been detected insome of the affected areas. Water analyses have mostly been determined (using HG-AAS) byfour private laboratories in Nepal, with additional analyses from four government laboratories(Tuinhof and Nanni 2003).

The most recent water quality statistics were compiled by the National Arsenic SteeringCommittee (NASC), set up in 2001 to oversee and coordinate national arsenic testing andmitigation (Neku and Tandukar 2003; Tuinhof and Nanni 2003; Shrestha and others 2004).As of September 2003, some 25,000 water analyses of arsenic had been carried out andresults indicate that 69% of groundwaters sampled had arsenic concentrations less than10 µg L-1, while 31% exceeded 10 µg L-1, and 8% exceeded 50 µg L-1 (Tuinhof and Nanni 2003;Shrestha and others 2004). Worst affected were the districts of Rautahat, Bara, Parsa,Kapilbastu, Nawalparasi, Rupandehi, Banke, Kanchanpur, and Kailali of central and westernTerai. The highest concentration observed (Rupandehi District) was 2,600 µg L-1 (Shrestha andothers 2004).

Results from earlier surveys (table 3) show similar overall statistics to the more recentsummary. The Nepal Department of Water Supply and Sewerage (DWSS) carried out asurvey of some 4,000 tubewells from the 20 Terai districts, mostly analyzed by field testkits but with laboratory replication of some analyses. Results from the survey indicatedthat 3.3% of the samples had arsenic concentrations of >50 µg L-1 (Chitrakar and Neku2001). The highest observed concentration was 343 µg L-1 (Parsa District). From testing in

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Sources: Chitrakar and Neku 2001; Tandukar 2001; Neku and Tandukar 2003.

Table 3. Frequency Distribution of Arsenic Concentrations in Analyzed Groundwater Samplesfrom Nepal

Agency Number of samples (%) Total samples

<10 µg L-1 10-50 µg L-1 >50 µg L-1

DWSS 3,479 (89.3) 289 (7.3) 128 (3.3) 3,896

NRCS 2,206 (79) 507 (18) 77 (3) 2,790

Finnida 55 (71) 14 (18) 9 (12) 78

Tandukar 54 (61) 27 (30) 8 (9) 89

NASC (2003) 17,300 (69) 6,000 (23) 2,000 (8) 25,000

17 of the 20 Terai districts, the Nepal Red Cross Society (NRCS) also found 3% ofgroundwater sources sampled having concentrations above 50 µg L-1, the highestobserved concentration being 205 µg L-1. The spatial distribution of the worst-affectedareas was found to be similar to that reported by Chitrakar and Neku (2001). A Finnidasurvey found 12% of analyzed samples exceeding 50 µg L-1, while a survey by Tandukarfound 9% of samples exceeding this value (table 3). The highest arsenic concentrationsobserved by Tandukar (2001) were around 120 µg L-1, most of the high-arsenic samplesbeing from the River Bagmati area. The high arsenic concentrations occur in anaerobicgroundwaters and are often associated with high concentrations of dissolved iron (Tandukar2001). The percentage of samples exceeding 50 µg L-1 is generally small and much lower thanthe percentage observed in, for example, Bangladesh, but the statistics nonetheless indicate aclear requirement for further testing and remedial action. To date, there has been no substantialmitigation program in the region (Tuinhof and Nanni 2003).

Surveys appear to indicate that deeper tubewells in the Terai region have lower arsenicconcentrations. As with Bangladesh, variation in arsenic concentration with depth appearsto show a general bell-shaped curve. The largest variation and highest maximumconcentrations occur in tubewells with depths in the 10–30 m range. Concentrations aregenerally <50 µg L-1 at depths greater than around 50 m (Shrestha and others 2004).Recent analysis of groundwater from 522 irrigation wells with depths of >40–50 m werealso found to have low concentrations (Tuinhof and Nanni 2003). This suggests that thedeep aquifer offers some possibilities as an alternative source of low-arsenic water supply.However, as with Bangladesh, the susceptibility of groundwater from the deep aquifer todrawdown of high-arsenic water from overlying sediments is a matter for concern andfurther hydrogeological investigation.

At the time of writing, around 13% of wells thought to exist in the Terai region have been testedfor arsenic. Data so far available from the Kathmandu valley have revealed no arsenic problemsthere, although the extent of testing in the valley is not clear.

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Irrawaddy Delta, Myanmar

As elsewhere in Asia, traditional sources of water for domestic supply in Myanmar were dugwells, ponds, springs, and rivers. However, in the Quaternary aquifer of the Irrawaddy delta,many of these have been superseded since 1990 by the development of shallow tubewells. It isestimated that more than 400,000 wells exist in Myanmar as a whole, more than 70% of whichare privately owned. Little testing for arsenic in groundwater has been carried out in tubewellsfrom the alluvial aquifer, though a few reconnaissance surveys have been undertaken andarsenic has been found in excess of 50 µg L-1 in some. Save The Children reported from analysisof 1,912 shallow tubewells in four townships in Ayeyarwaddy Division (southern delta area) that22% of samples exceeded 50 µg L-1. The United Nations Development Programme (UNDP) andthe United Nations Centre for Human Settlements (UNCHS) detected arsenic at concentrationsgreater than 50 µg L-1 in 4% of samples (125 samples) from Nyaungshwe in Shan State insouthern Myanmar (UNDP-UNCHS 2001). The Water Resources Utilization Department (WRUD)carried out a survey of groundwater in Sittway township in the western coastal area, and inHinthada and Kyaungkone townships close to the south coast of Myanmar (WRUD 2001). InSittway township, salinity problems occur in some groundwaters and surface waters and mosttubewells are less than 15 m deep as a result. Merck field test kits were used for the analysis ofarsenic. In Hinthada and Kyaunkone townships well depths are typically around 30–50 m,although some deeper tubewells (55–70 m) were also sampled. In the southern townships of thedelta area, high iron concentrations were noted. The distribution of arsenic concentrationsdetermined by 2001 is given in table 4. Exceedances above 50 µg L-1 in shallow tubewells fromSittway, Hinthada, and Kyaunkone townships were around 10-13%. One sample from the depthinterval 56-70 m also exceeded 50 µg L-1. As with a number of other affected aquifers, dug wellsfrom the WRUD survey generally had arsenic concentrations of <10 µg L-1 (WRUD 2001).

Table 4. Frequency Distribution of Arsenic Concentrations in Groundwaters from the AlluvialAquifer of Myanmar

Township Well type Number of samples (%) Total samples

<10 µg L-1 10–50 µg L-1 >50 µg L-1

Sittway STW 17 (29.3) 35 (60.3) 6 (10.3) 58

DW 22 (96) 1 (4) 0 (0) 23

Hinthada STW 56 (68.3) 15 (18.3) 11 (13.3) 82

DW 6 (75) 1 (12.5) 1 (12.5) 8

Kyaungkone STW 48 (80) 5 (8) 7 (12) 60

DW 21 (95) 1 (5) 0 (0) 22

DTW 1 (33.3) 1 (33.3) 1 (33.3) 3

Key:STW shallow tubewellDW dug wellDTW deep tubewell (55–70 m)Source: WRUD 2001.

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More recent results from WRUD surveys have shown 15% of groundwater samples exceeding50 µg L-1 (8,937 analyses by April 2002). In these, dug wells were found to exceed 50 µg L-1 in8% of samples. As the analyses from the various surveys were carried out using Merck field testkits, the accuracy of the results is uncertain but likely to be limited. As with many other areas,the arsenic concentrations of the groundwaters of Myanmar have not been mapped in detailand investigations are in the reconnaissance stages. However, the divisions of Ayeyarwaddyand Bago (delta area), and the states of Mon and Shan, appear to be the worst affected.

Quaternary Aquifers, Taiwan, China

Health problems experienced in Taiwan have been the subject of much research since their initialdiscovery in the early 1960s and have formed the basis of many epidemiological risk assessmentsover the last 30 years. Taiwan is the classic area for the identification of blackfoot disease (forexample Tseng and others 1968; Chen and others 1985) and other peripheral vasculardisorders, but many other arsenic-related diseases have also been described from the area.

Despite being under considerable international scrutiny from an epidemiological perspectiveover the last 40 years or so, there appears to have been little effort to understand thedistribution or causes of arsenic problems in the aquifers of Taiwan. As a result, very littleinformation is available for the region. High-arsenic groundwaters have been recognized intwo areas: the southwest coastal area (Kuo 1968; Tseng and others 1968) and the northeastcoast (Hsu, Froines, and Chen 1997). Kuo (1968) observed arsenic concentrations ingroundwater samples from southwest Taiwan ranging between 10 µg L-1 and 1,800 µg L-1

(mean 500 µg L-1, n = 126), with half the samples analyzed having concentrations of400–700 µg L-1. An investigation by the Taiwan Provincial Institute of Environmental Sanitationfound that 119 townships in the affected area had arsenic concentrations in groundwater of>50 µg L-1, with 58 townships having >350 µg L-1 (Lo, Hsen, and Lin 1977). In northeasternTaiwan Hsu, Froines, and Chen (1997) reported an average arsenic concentration of 135 µg L-1

for 377 groundwater samples.

In the southwest, the high arsenic concentrations are found in deep (100-280 m) artesian wellwaters. The sediments from which these are abstracted are poorly documented, but appear toinclude deposits of black shale (Tseng and others 1968). The groundwaters are likely to bestrongly reducing as the arsenic is found to be present largely as arsenic(III) (Chen and others1994) and some of the groundwaters contain methane as well as humic substances (Tseng andothers 1968). Groundwaters abstracted in northeastern Taiwan are also reported to be artesianbut more typically shallow, with a depth range of 16–40 m (Hsu, Froines, and Chen 1997). Asfound in several other countries, groundwater from shallow dug wells have low arsenicconcentrations (Guo, Chen, and Greene 1994). This is probably a reflection of relatively oxidizingconditions in the shallow parts of the aquifer immediately around the open wells.

The arsenic problems of Taiwan are largely historical, as alternative treated surface watersupplies have been provided for the affected communities.

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Alluvial Plains, Northern China

The presence of endemic arsenicosis has been recognized in China since the 1980s and todaythe scale of the problem is known to be large. Arsenic problems related to drinking water havebeen identified in Quaternary aquifers in Xinjiang Province and more recently in parts of InnerMongolia and Shanxi Province (figure 7). Concentrations of arsenic up to 4,400 µg L-1 have beenfound in groundwater from these affected areas. These areas represent large internal drainagebasins in arid and semiarid settings. Groundwater conditions in the arsenic-affected areasappear to be strongly reducing. High-arsenic drinking water has also been identified in parts ofLiaoning, Jilin, and Ningxia Provinces in northeast and north-central China (Sun, pers. comm.,2001), although the distribution and extent of these occurrences, the geological associations,and the health consequences are not yet documented or defined. The population exposed todrinking water with concentrations in excess of 50 µg L-1 (the Chinese standard) has beenestimated as around 5.6 million (table 1), and the number of diagnosed arsenicosis patientscurrently around 20,000 (Sun and others 2001). Mitigation measures are being implemented insome areas in China, including where possible the provision of piped low-arsenic surface waterand in some cases the use of small-scale reverse osmosis plants. However, so far the mitigationefforts have covered relatively little of the area affected.

Xinjiang ProvinceThe first cases of arsenic-related health problems due to drinking water were recognized inXinjiang Province of northwest China (figure 7). The region is arid with an average annual

Figure 7. Map of China Showing the Distribution of Recognized High-Arsenic (>50 µg L-1)Groundwaters and the Locations of Quaternary Sediments

Source: Modified after Smedley and others 2003.

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precipitation of less than 185 mm. The basin is composed of a 10 km thick sequence ofsediments, including a substantial upper portion of Quaternary alluvial deposits. Artesiangroundwater has been used for drinking in the region since the 1960s (Wang and Huang1994). Wang (1984) found arsenic concentrations up to 1,200 µg L-1 in groundwaters fromthe province. Wang and Huang (1994) found concentrations of between 40 µg L-1 and 750µg L-1 in deep artesian groundwater from the Dzungaria basin on the north side of theTianshan Mountains (up to 3,800 m altitude). The region stretches some 250 km from AibiLake in the west to Mamas River in the east. Artesian groundwater from deep boreholes(70–400 m) was found to have increasing arsenic concentrations with increasing boreholedepth. Highest concentrations were also found in tubewells from the lower section of thealluvial plain. Many of these are believed to abstract groundwater from Quaternary alluvialsediments but whether some of the deeper artesian wells abstract from older formations isnot known. Shallow (nonartesian) groundwaters from wells in the depth range 2–30 m hadobserved arsenic concentrations between <10 µg L-1 and 68 µg L-1 (average 18 µg L-1). Thatin the saline Aibi Lake was reported as 175 µg L-1, while local rivers had concentrationsbetween 10 µg L-1 and 30 µg L-1.

Wang and others (1997) reported arsenic concentrations up to 880 µg L-1 from tubewells from theKuitan area of Xinjiang. A 1982 survey of 619 wells showed 102 with concentrations of arsenic>50 µg L-1. High fluoride concentrations were also noted in the groundwaters (up to 21.5 mg L-1).

Shanxi ProvinceInvestigations during the mid 1990s showed that arsenic in groundwater from wells in theDatong and Jinzhong basins in Shanxi Province exceeded 50 µg L-1 in 837 (35%) of 2,373randomly selected samples (Sun and others 2001). Concentrations in Shanyin County, theworst-affected of the regions in Shanxi Province, reached up to 4,400 µg L-1 (Sun andothers 2001).

Yellow River Plain, Inner MongoliaIn Inner Mongolia, concentrations of arsenic in excess of 50 µg L-1 have been identified ingroundwaters from aquifers in the Hetao plain, Ba Men region, and in the Tumet plain, whichincludes the Huhhot basin (Luo and others 1997; Ma and others 1999). These areas are alsoarid, with a mean annual precipitation of around 400 mm. The affected areas border the YellowRiver plain and include the towns of Boutou and Togto. In the region as a whole, around300,000 residents are believed to be drinking water containing >50 µg L-1 (Ma and others 1999).Arsenic-related health problems from the use of groundwater for drinking were first recognizedin the region in 1990 (Luo and others 1997). The most common manifestations of disease areskin lesions (melanosis, keratosis) but an increased prevalence of cancer has also been noted.Ma and others (1999) reported that 543 villages in Ba Men region and 81 villages in Tumet hadtubewells with arsenic concentrations >50 µg L-1. Around 1,500 cases of arsenic disease hadbeen identified in the area by the mid 1990s.

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The Hetao plain comprises a thick sequence of young unconsolidated sediments. In a study ofgroundwater from the Wuyuan and Alashan areas, Guo and others (2001) found that,respectively, 96% and 69% of samples analyzed had arsenic concentrations greater than50 µg L-1. Concentrations were generally much higher in groundwater from tubewells (depthrange 15–30 m) than from open dug wells (3-5 m depth) and the highest concentration recordedwas 1,350 µg L-1.

The area of Ba Men with high-arsenic groundwater appears to be around 300 x 20 km in extentand the sediments are Quaternary lacustrine deposits. Wells were mostly installed in the late1970s and well depths are typically 10–35 m. Arsenic concentrations have been found in therange 50-1,800 µg L-1 (Ma and others 1999) and around 30% of wells sampled had arsenicconcentrations >50 µg L-1. The groundwaters are reducing with arsenic being dominantlypresent as arsenic(III). Some contain high fluoride concentrations (average 1.8 mg L-1) (Ma andothers 1999).

The Huhhot basin (area around 80 x 60 km) lies to the east of the Ba Men area (figure 8). Thebasin is surrounded on three sides by high mountains of the Da Qing and Man Han ranges andis itself infilled with a thick sequence (up to 1,500 m) of poorly consolidated sediments, largelyof Quaternary age (Smedley and others 2003).

Source: Smedley and others 2003.

Figure 8. Regional Distribution of Arsenic inGroundwaters from the Shallow and DeepAquifers of the Huhhot Basin

Groundwater has been used for severaldecades for domestic supply and agriculture.Traditional sources of water were shallow dugwells that were typically 10 m or less deepand tapped the shallowest groundwater.These have now generally been abandoned infavor of tubewells that abstract at shallowlevels (typically <30 m) by handpumps or insome cases by motorized pumps.Groundwater is also present within adistinct, deeper aquifer (typically >100 mdepth). Tubewells tapping this deeperaquifer are often artesian in the central partsof the basin.

Arsenic concentrations in the Huhhot basingroundwaters range between <1 and 1,480 µgL-1 in the shallow aquifer (£100 m) andbetween <1 and 308 µg L-1 in the deep aquifer(>100 m). Of a total of 73 samples,summarized by Smedley and others (2003),25% of shallow sources and 57% of deepsources have arsenic concentrations inexcess of 50 µg L-1 (table 5 see page 48). The

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Source: Smedley and others 2003.

Table 5. Frequency Distribution of Arsenic Concentrations in Groundwater from the HuhhotBasin, Inner Mongolia

Well depth Number of samples (%) Total samples

<10 µg L-1 10–50 µg L-1 >50 µg L-1

<100 m 35 (59) 9 (15) 15 (25) 59

>100 m 6 (43) 0 (0) 8 (57) 14

- Not available.

Table 6. Summary Arsenic Data for Groundwater from Dug Wells in the High-ArsenicGroundwater Region of the Huhhot Basin

Sample Water level Well depth DOC Arsenicm m mg L-1 µg L-1

HB2 1.5 3.5 9.3 560

HB18 2.0 6 - 49

HB58 4.0 8 2.5 <1

HB4 2.0 9 11.4 200

regional distributions of arsenic in the groundwaters from the shallow and deep aquifers areshown in figure 8. Concentrations in the aerobic groundwaters from the basin margins areuniversally low. High concentrations are generally restricted to the low-lying part of the basinwhere groundwaters are strongly reducing (table 6) (Smedley and others 2001, 2003). The redoxcharacteristics of the Huhhot basin groundwaters have many similarities with those ofBangladesh and it is logical to conclude that the main geochemical processes controllingarsenic mobilization are similar in the two areas.

Of a limited number of samples of dug well water investigated, some are observed to havearsenic concentrations in excess of 50 µg L-1 (Smedley and others 2003). The affectedwells are from the part of the aquifer with high concentrations in tubewell waters. Thisobservation contrasts with the situation observed in other reducing groundwaterenvironments such as Taiwan (Guo, Chen, and Greene 1994) and the Bengal basin(Smedley and others 2003). The dug well waters of the Huhhot basin appear to bereducing, with high concentrations of dissolved organic carbon (DOC, up to 11.4 mg L-1).This, together with the fact that low-lying parts of the basin are zones of groundwaterdischarge, rates of groundwater recharge are low, and groundwater movement is sluggish,are likely reasons for the reducing conditions and stabilization of arsenic in solution(Smedley and others 2003).

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Red River Plain, Vietnam

Arsenic problems have emerged only recently in the aquifers of the Red River plain of northernVietnam. Recent suggestions are that arsenic-related health problems are beginning to beidentified among the exposed populations of Vietnam, although this is as yet unsubstantiated.The total area of the plain is around 17,000 km2. Groundwater is abstracted fromunconsolidated Quaternary alluvial sediments which comprise up to 150 m thickness of sand,silts, clay, and some conglomerates. A superficial aquifer of Holocene sediments is around10–40 m thick in the centre of the plain but thins to just 1–3 m on the margins (Tong 2002).Underlying Pleistocene sediments form the main aquifer of the region and are around 100 mthick in the centre and southeast of the plain (Berg and others 2001; Tong 2002).

Private tubewells have generally been installed over the last decade and these abstract watervia handpumps from shallow levels in the aquifer (<45 m depth). Public supply tubewells in thecity of Hanoi abstract from the deeper Pleistocene aquifer (wells around 30–70 m deep). Thelower aquifer is heavily pumped and has resulted in a seasonal drawdown of around 30 maround the centre of Hanoi (Trafford and others 1996). Water level drawdown of up to 1 m peryear has been observed in some wells in Hanoi (Tong 2002). Drawdown of the shallow aquiferhas also occurred but a significant head difference exists between the two aquifers, suggestingthat the two are not hydraulically connected (Tong 2002). This appears not to be the casenortheast of Hanoi, between the Red River and its tributary the Duong River, where poorlypermeable intervening layers between the Holocene and Pleistocene aquifers are thin or absent(Nguyen and Nguyen 2002). Whether hydraulic separation between the aquifers occurs morewidely in the plain is not known.

Groundwater is fresh in the upper parts of the plain but becomes more saline as a result ofseawater intrusion in the lower reaches. Recent overpumping of the aquifers in the urban areashas also been linked to increasing saline intrusion (Tong 2002). Many of the groundwaters of theregion have high iron and manganese concentrations and some also contain high ammoniumconcentrations (Trafford and others 1996).

Arsenic concentrations in the range 1-3,050 µg L-1 (average 159 µg L-1) were reported byBerg and others (2001) for groundwater from the Hanoi area and surrounding rural areas. Ina surveyed area of some 1,000 km2 around Hanoi, they found that the arsenicconcentrations were spatially variable, but generally higher to the south of the city on thesouthern margins of the Red River. Concentrations were found to be high in groundwatersfrom both the shallow and deeper aquifers, but the extremely high values were found in theshallow groundwater from private tubewells. Groundwater from deeper tubewells hadarsenic concentrations up to 440 µg L-1. Subsequent studies by Tong (2002) confirmed thehigh concentrations south of the city but also found some high concentrations to the westand east of the city. Concentrations were generally lower north of the Red River. Tongreported that from a survey carried out by the Geological Survey of Vietnam together withUNICEF in 1999, 153 samples out of 1,228 (12.5%) in seven provinces had arsenicconcentrations greater than 50 µg L-1. An earlier report (Tong 2001) indicated that arsenic

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concentrations are often high in groundwaters from both the Holocene and the underlyingPleistocene aquifers (table 7).

The causes of the spatial variations are not fully clear, but factors may include differencesin sediment thickness, composition, and age, and hydraulic connection between layers. Inparticular, sediments to the north of Hanoi with typically low groundwater arsenicconcentrations are predominantly of Pleistocene age and are relatively thin (Berg andothers 2001). One uncertainty in the distribution of the arsenic concentrations in thegroundwaters of the region is the impact that anthropogenic activity may have had onthe mobilization of arsenic. Since some high concentrations have been found close tothe city of Hanoi, it is possible that urban wastewater recharge to the aquifer may havehad some impact on the arsenic distributions. This remains speculation and requiresfurther investigation.

Berg and others (2001) and Tong (2002) have suggested that significant seasonal variationsexist in arsenic concentrations in given wells in relation to strong water level fluctuations. Bergand others (2001) found some very large temporal variations, with often higher concentrations inwells sampled in September (rainy season) than when sampled in December (dry season) orMay (early rainy season). By contrast, Tong (2002) reported that more samples tended toexceed the national standard of 50 µg L-1 in the dry season than the rainy season. As the data inthe case of Berg and others (2001) were not reported in relation to other parameters (forexample rainfall, water level), and in the case of Tong (2002) were presented just as ranges andpercentage exceedances, the variations are difficult to interpret and to verify. Subsequentmonitoring by the Swiss Federal Institute for Environmental Science and Technology (EAWAG)and others (with more stringent sampling and analytical procedures) has revealed much lesstemporal variation, the greatest being found in wells close to the river bank (M. Berg, pers.comm., 2004). Results have not yet been documented.

Maps have been produced showing the distribution of arsenic in groundwater in the Hanoi area(Berg and others 2001; Tong 2002) but so far mapping of the groundwater quality in the plain asa whole has not been carried out.

Table 7. Summary Arsenic Data for Groundwater from Tubewells in the Red River Plain,Vietnam, Divided into Those from the Holocene and Pleistocene Aquifers

Number of samples (%) Total samples

<10 µg L-1 10–50 µg L-1 >50 µg L-1

Tong (2001) Holocene 117 (45) 62 (24) 81 (31) 260

Tong (2001) Pleistocene 84 (40) 70 (33) 56 (27) 210

Tong (2002) undivided 740 (60.2) 335 (27.3) 153 (12.5) 1,228

Sources: Tong 2001, 2002.

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Mekong Valley: Cambodia, Laos, Thailand, and Vietnam

The Mekong River system is another large delta with potential for development of groundwaterarsenic problems. So far few investigations have been carried out in the valley as a whole. Mostinvestigation to date appears to have been carried out in Cambodia. The Mekong has asubstantial proportion of its length within Cambodia and tubewells provide a significant sourceof potable supply in the country. Water testing for arsenic is ongoing and little information hasso far been properly documented. A reconnaissance screening of around 100 tubewells from 13provinces carried out by Partners for Development in 1999 included analysis of arsenic, fluoride,some trace metals, and some pesticides. Approximately 9% of the samples analyzed hadarsenic concentrations >10 µg L-1, with observed concentrations in the range 10-500 µg L-1.Exceedances above 10 µg L-1 were found in 5 out of the 13 provinces investigated. The highestconcentrations observed were from Kandal Province, close to Phnom Penh. Several districts inthis province have a high percentage of wells with water containing arsenic in excess of theWHO guideline value (Feldman and Rosenboom 2000). Since this initial screening, field testingusing portable kits has identified groundwater sources with concentrations above 10 µg L-1 intwo additional provinces. High iron and manganese concentrations and anaerobic conditionsare common features of the groundwaters throughout the lowland areas of Cambodia.

More recently, UNICEF has been carrying out groundwater arsenic screening in the Mekongaquifers. A map of perceived "arsenic risk" in groundwater has been produced based ongeology (figure 9). Areas of greatest perceived risk are those with Holocene sediments formingthe main aquifer. Groundwater arsenic data produced by UNICEF and JICA for the region so far(June 2003) are summarized in table 8 (see page 52). Around 19% of samples from theHolocene aquifer were found to contain arsenic at concentrations >50 µg L-1. UNICEF and other

Note: Areas of perceived “increased risk” are those with aquifers of Holocene age; areas of perceived “low risk” are Pleistocene aquifers;areas of “very low risk” are crystalline basement rocks. Geological units are provisional and accuracy of national boundaries is not guaranteed.Sources: UNICEF, Cambodia; D. Fredericks, pers. comm. 2003.

Figure 9. Geological Map of Cambodia Showing Distribution of Potentially High-Arsenic Aquifers

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Table 8. Summary Arsenic Data for Groundwater from Tubewells in the Mekong Valley of Cambodia


<10 µg L-1 10–50 µg L-1 >50 µg L-1

Holocene aquifer 301 (50) 185 (31) 113 (19) 599

Pleistocene aquifer 1,184 (95) 59 (5) 3 (0.2) 1,246

Crystalline rocks 708 (96) 24 (3) 2 (0.3) 734

Sources: Data from UNICEF and JICA; D. Fredericks, pers. comm., 2003.

organizations continue to support and carry out field testing using portable kits withsupplementary laboratory analysis in Cambodia. A plan to blanket-test wells in 1,500 villagesthat abstract groundwater from Holocene sediments is currently being drawn up for thesouthern part of the country.

One noteworthy feature of the Cambodian Mekong results is that some of the highest arsenicconcentrations have been found in urban areas, around Phnom Penh. Whether this reflects animpact of urbanization (increased groundwater pumping or increased inputs of pollutants suchas organic carbon to the aquifers) is not known and is in need of further investigation.

As the Mekong valley also covers parts of Laos, Thailand, and Vietnam, arsenic problems arealso possible in the alluvial and deltaic parts of these countries. However, few data are so faravailable from these regions to assess the scale of the problem there. Doan (n.d.) providedsome arsenic data measured by spectrometry for groundwater samples from the Holocene,Pleistocene, and Pliocene aquifers of the Mekong delta area of Vietnam. Concentrations werefound to be mostly low, with only one sample exceeding 50 µg L-1. Concentrations were in therange <1–5 µg L-1 for groundwaters from Holocene deposits (9 samples, depth range 4–19 m),<1–32 µg L-1 for those from Middle and Upper Pleistocene deposits (39 samples, depthrange 5–120 m), <1–7 µg L-1 for groundwater from Lower Pleistocene deposits (12 samples,depth range 113–191 m), and <1–57 µg L-1 for groundwater from Pliocene deposits (39 samples,depth range 85–330 m). Highest concentrations in this Pliocene aquifer were in the Ben Tre areaof the central Mekong delta. The Pleistocene and Pliocene sediments are the most exploitedaquifers in the region. The Holocene sediments appear to be largely low-yielding aquitards andare not heavily used. Doan (n.d.) reported that UNICEF carried out some qualitative arsenictesting of Mekong groundwaters in Vietnam but did not detect arsenic.

UNICEF have also carried out some preliminary testing of groundwater from wells in theAttapeu, Savannakhet, Champassak, Saravan, Sekong, Khammuane, and Bolikamxay areas ofLao PDR. Results from 200 samples reported by Fengthong, Dethoudom, and Keosavanh(2002) suggested that some samples had arsenic concentrations greater than 10 µg L-1 but onlyone exceeded 50 µg L-1. The highest concentration observed in the region was 112 µg L-1

(Attapeu Province). To date, UNICEF, in collaboration with the government and the AdventistDevelopment and Relief Agency, have tested some 680 samples from drinking water sourcesand found 1% of sources having arsenic concentrations >50 µg L-1 (table 9, unpublished data).

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Table 9. Summary Arsenic Data for Groundwater from Tubewells in the Mekong Valley of Lao PDR


<10 µg L-1 10–50 µg L-1 >50 µg L-1

Holocene aquifer 531 (78) 143 (21) 6 (1) 680

Source: Data from UNICEF, 2004.

Indus Plain, Pakistan

Quaternary sediments, mainly of alluvial and deltaic origin, occur over large parts of theIndus plain of Pakistan (predominantly in Punjab and Sindh Provinces) and reach severalhundred meters thickness in some parts (WAPDA-EUAD 1989). Aquifers in these sedimentsare potentially susceptible to high groundwater arsenic concentrations. The Indussediments have some similarities with the arsenic-affected aquifers of Bangladesh andWest Bengal, being Quaternary alluvial-deltaic sediments derived from Himalayan sourcerocks. However, the region differs in having a more arid climate, greater prevalence of olderQuaternary (Pleistocene) deposits, and dominance of unconfined and aerobic aquiferconditions, with greater apparent connectivity between the river systems and the aquifers.Aerobic conditions are demonstrated by the presence of nitrate (Mahmood and others 1998;Tasneem 1999) and dissolved oxygen (Cook 1987) in many Indus groundwaters. Hence, theaquifers appear to have different redox characteristics from those of the lower parts of theBengal basin. Under the more aerobic conditions (and near-neutral pH), arsenic mobilization ingroundwater should be less favorable.

To date, only a limited amount of groundwater testing for arsenic has been carried out inPakistan. However, the Provincial Government of Punjab together with UNICEF began atesting program in northern Punjab in 2000. Districts to be tested were selected on the basis ofgeology and available water quality information. These included areas affected by coal miningand geothermal springs (Jhelum and Chakwal Districts), areas draining crystalline rock (Attockand Rawalpindi), areas with high-iron groundwaters (Sargodha), and one district from the mainIndus alluvial aquifer (Gujarat). A total of 364 samples were analyzed. The majority (90%) ofsamples had arsenic concentrations less than 10 µg L-1, although 6 samples (2%) hadconcentrations above 50 µg L-1 (table 10 see page 54) (Iqbal 2001). Further well testing forarsenic is ongoing. No confirmed cases of arsenic-related disease have been found inPakistan, although epidemiological investigations are also being undertaken in some areas.From the available data, the scale of arsenic contamination of Indus groundwaters appears tobe relatively small, although further results are needed to verify the region affected.Quaternary aeolian sand deposits occur to the east of the Indus plain (Thar and Cholistandesert areas) as well as over large parts of the Baluchistan basin of western Pakistan. Testing ofabstraction tubewells in these areas is also required. Under the arid conditions in Pakistan, highfluoride concentrations and high salinity appear to be more widespread water-related problemsthan arsenic.

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Table 10. Frequency Distribution of Arsenic Concentrations in Groundwater Samples fromNorthern Punjab

District Number of samples (%) Total samples

<10 µg L-1 10–50 µg L-1 >50 µg L-1

Gujarat 33 (87) 3 (8) 2 (5) 38

Jhelum 32 (86) 4 (11) 1 (3) 37

Chakwal 63 (88) 9 (12) 0 (0) 72

Sargodha 49 (83) 7 (12) 3 (5) 59

Attock 68 (92) 6 (8) 0 (0) 74

Rawalpindi 81 (96) 3 (4) 0 (0) 84

Total 326 (90) 30 (8) 6 (2) 364

Source: Iqbal 2001.

Mining and Mineralized Areas

Ron Phibun, Thailand

Health problems related to arsenic have been well documented in Thailand, in this case relatedto mineralization and mining activity rather than alluvial and deltaic aquifers. In terms ofdocumented health problems from drinking water, Ron Phibun District in Nakhon Si ThammaratProvince in peninsular Thailand represents the worst-known case of arsenic poisoning related tomining activity (figure 1). Health problems were first recognized in the area in 1987 and over1,000 people have been diagnosed with arsenic-related skin disorders, particularly in and closeto Ron Phibun town (Williams 1997). At the time of first recognition of the problems, some15,000 people are thought to have been drinking water with >50 µg L-1 arsenic (Fordyce andothers 1995). The affected area lies within the Southeast Asian tin belt. Primary tin-tungsten-arsenic mineralization and alluvial placer tin deposits have been mined in the district for over100 years, although mining activities have now ceased. Legacies of the mine operations includearsenopyrite-rich waste piles, waste from ore-dressing plants and disseminated waste fromsmall-scale panning by villagers. Remediation measures include transportation of waste to locallandfill. Waste piles from former bedrock mining are found to contain up to 30% arsenic(Williams and others 1996). Alluvial soils also contain high concentrations of arsenic, up to 0.5%(Fordyce and others 1995).

High arsenic concentrations found in both surface and shallow groundwaters from the areaaround the mining activity are thought to be caused by oxidation of arsenopyrite, made worseby the former mining activities and subsequent mobilization during the postmining rise ingroundwater levels (Williams 1997).

Surface waters draining the bedrock and alluvial mining areas are commonly acidic (pH <6) withSO4 as the dominant anion (up to 142 mg L-1) and with high concentrations of some trace

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metals, including aluminum (up to 10,500 µg L-1), cadmium (up to 250 µg L-1), and zinc (up to4,200 µg L-1) (Williams and others 1996). Strong positive correlations are observed between SO4

and cadmium, aluminium, beryllium, zinc, and copper. Also, SO4 correlates negatively with pH(Fordyce and others 1995). These associations suggest strongly that arsenic and the associatedtrace metals are derived by oxidation of sulfide minerals. Concentrations of the trace metalsdiminish downstream of the mining area. Highest arsenic concentrations (up to 580 µg L-1) werefound some 2–7 km downstream of the bedrock mining area (Williams and others 1996).

Shallow groundwaters (<15 m) are from alluvial and colluvial deposits and deeper groundwaters(>15 m) are from an older carbonate aquifer. The shallow aquifer shows the greatestcontamination with arsenic, with concentrations up to 5,100 µg L-1 (figure 10). In the shallowaquifer, 39% of samples collected randomly had arsenic concentrations >50 µg L-1, while in thedeeper aquifer, 15% exceeded 50 µg L-1 (table 11 see page 56) (Williams and others 1996).

The high-arsenic groundwaters of the Ron Phibun area clearly differ from many other high-arsenic groundwater provinces in Asia. In the shallow aquifer, conditions are more oxidizing thanthose prevalent in, for instance, the worst-affected areas of Bangladesh and West Bengal. Thedifferences reflect the distinct geochemical reactions that are controlling the groundwaterarsenic concentrations (section 3.3). In the groundwaters from the deeper aquifer of Ron Phibunconditions appear more similar to those from other high-arsenic aquifers in Asia and the

Figure 10. Simplified Geology of the Ron Phibun Area, Thailand, Showing the Distribution ofArsenic in Analyzed Groundwaters

Note: The distributions are (a) arsenic in groundwater from shallow tubewells (<15 m depth); (b) arsenic in groundwater from deepertubewells (>15 m). Numbers refer to samples given in Williams and others 1996.Source: Williams and others 1996.

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Table 11. Frequency Distribution of Arsenic Concentrations in Water from Phibun Area

Aquifer Number of samples (%) Total samples

<10 µg L-1 10–50 µg L-1 >50 µg L-1

Surface water 1 (4) 2 (8) 20 (83) 24

Groundwater from 7 (30) 7 (30) 9 (39) 23shallow aquifer(<15 m)

Groundwater from 9 (69) 2 (15) 2 (15) 13deeper aquifer(>15 m)

Source: Williams and others 1996.

maintenance of arsenic in solution appears to be more of a function of the presence ofreducing conditions, although leakage of high-arsenic water from the overlying shallow aquiferis also a possibility.

Rajnandgaon District, Madhya Pradesh, India

Water-related arsenic problems first became recognized in Rajnandgaon District, MadhyaPradesh, in 1999. Concentrations in groundwater samples from the worst-affected village,Kondikasa, in Chowki block, have been found to range between <10 µg L-1 and 880 µg L-1

(Chakraborti and others 1999). Out of 146 samples analyzed, 8% were found to contain morethan 50 µg L-1 arsenic (table 12). Three of these exceeding samples were from dug wells, onecontaining a concentration of 520 µg L-1. Most were from tubewells, which were usually lessthan 50 m deep (range 10–75 m). Arsenic-related skin disorders have been recognized in anumber of the villagers. Gold-mining activity has taken place in the local area, though the extentof mining and of mineralization is not documented. To date, no maps have been produced ofChowki block to indicate the distribution and scale of the problem.

Source: Chakraborti and others 1999.

Table 12. Frequency Distribution of Arsenic Concentrations in Groundwater from ChowkiBlock, Madhya Pradesh, India

Blocks Number of samples (%) Total samples

<10 µg L-1 10–50 µg L-1 >50 µg L-1

Chowki 109 (75) 25 (17) 12 (8) 146

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Other Areas

Although many areas of mining and mineralization exist in South and East Asia, few have beendocumented and the distribution of groundwater arsenic concentrations related to them isunknown. High concentrations were noted in some surface waters and groundwaters close tothe Bau mining area of Sarawak, Malaysia (Breward and Williams 1994), although there is noevidence that affected waters are used for drinking water. Arsenic is a well-known risk in sulfidemineralized areas and hence the locations of such problems can be reasonably well predicted.Despite many mining-related problems, modern mining practices are designed to minimizeenvironmental impacts. Environmental protection measures include criteria for siting andmanagement of waste piles, control of effluents, and treatment of acid mine drainage.

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Overview

There has been a considerable increase in the amount of research carried out on arsenic ingroundwater and the environment over the last few years and understanding of the

processes involved has improved as a result of studies carried out in Asia and elsewhere.However, many aspects of the mechanisms of release are still poorly understood. Our ability topredict the variations with time is limited, yet temporal variations in arsenic concentration are acentral issue to mitigation. Below are outlined what we know of the principal causes of arsenicmobilization in water and the environment and the information that is available concerningspatial and temporal variability in the arsenic-affected aquifers of Asia.

The highest concentrations of arsenic tend to occur in sulfide minerals and metal oxides,especially iron oxides. It therefore follows that where these occur in abundance, arsenicproblems can result if the release from the minerals is favored. Under most circumstances, themobilization of arsenic in surface waters and groundwaters is low because of retention in thesemineral sinks. However, the toxicity of arsenic is such that it only takes a very small proportionof the solid-phase arsenic to be released to produce a groundwater arsenic problem. There area number of drivers that can result in the release of arsenic from minerals and the build-up ofdetrimental concentrations in water. These are outlined in broad terms below.

Arsenic Sources

Arsenic occurs naturally in all minerals and rocks, although its distribution within them varieswidely. Arsenic occurs as a major constituent in more than 200 minerals, including elementalarsenic, arsenides, sulfides, oxides, arsenates, and arsenites. Most are ore minerals or theiralteration products. However, these minerals are relatively rare in the natural environment. Thegreatest concentrations of them occur in mineral veins. The most abundant arsenic ore mineralis arsenopyrite (FeAsS). This is often present in ore deposits, but is much less abundant thanarsenian pyrite (Fe(S,As)2), which is probably the most important source of arsenic in ore zones.Other arsenic sulfides found in mineralized areas are realgar (AsS) and orpiment (As2S3).

Though not a major component, arsenic is also present in varying concentrations in commonrock-forming minerals. As the chemistry of arsenic follows closely that of sulfur, the other, moreabundant, sulfide minerals also tend to have high concentrations of arsenic. The most abundantof these is pyrite (FeS2). Concentrations of arsenic in pyrite, chalcopyrite, galena, and marcasitecan be very variable but in some cases can exceed 10 weight percentage (table 13). Besidesbeing an important component of ore bodies, pyrite is also formed in low-temperaturesedimentary environments under reducing conditions. It is present in the sediments of manyrivers, lakes, and oceans, as well as in a number of aquifers. Pyrite is not stable in aerobicsystems and oxidizes to iron oxides with the release of sulfate, acidity, arsenic, and other traceelements. The presence of pyrite as a minor constituent in sulfide-rich coals is ultimatelyresponsible for the production of acid rain and acid mine drainage, and for the presence ofarsenic problems around coal mines and areas of intensive coal burning.

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Table 13. Typical Arsenic Concentrations in Rock-Forming Minerals

Mineral Arsenic concentration range (mg kg-1)

Sulfide minerals

Pyrite 100–77,000

Pyrrhotite 5–100

Marcasite 20–126,000

Galena 5–10,000

Sphalerite 5–17,000

Chalcopyrite 10–5,000

Oxide minerals

Hematite up to 160

Fe oxide (undifferentiated) up to 2,000

Fe(III) oxyhydroxide up to 76,000

Magnetite 2.7–41

Ilmenite <1

Silicate minerals

Quartz 0.4–1.3

Feldspar <0.1–2.1

Biotite 1.4

Amphibole 1.1–2.3

Olivine 0.08–0.17

Pyroxene 0.05–0.8

Carbonate minerals

Calcite 1–8

Dolomite <3

Siderite <3

Sulfate minerals

Gypsum/anhydrite <1–6

Barite <1–12

Jarosite 34–1,000

Other minerals

Apatite <1–1,000

Halite <3–30

Fluorite <2

Source: Smedley and Kinniburgh 2002 and references therein.

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High concentrations of arsenic are also found in many oxide minerals and hydrous metal oxides,

either as part of the mineral structure or adsorbed to surfaces. Concentrations in iron oxides

can also reach weight percentage values (table 13), particularly where they form as the

oxidation products of primary iron sulfides. Adsorption of arsenate to hydrous iron oxides is

known to be particularly strong. Adsorption to hydrous aluminum and manganese oxides may

also be important if these oxides are present in quantity (for example Peterson and Carpenter

1983; Brannon and Patrick 1987). Arsenic may also be adsorbed to the edges of clays and on

the surface of calcite. However, the loadings involved are much smaller on a weight basis than

for the iron oxides. Adsorption reactions are responsible for the low concentrations of arsenic

found in most natural waters.

Arsenic is also present in many other rock-forming minerals, albeit at comparatively low

concentrations. Most common silicate minerals contain around 1 mg kg-1 or less. Carbonate

minerals usually contain less than 10 mg kg-1 arsenic (table 13).

Rocks, sediments, and soils contain variable concentrations of arsenic but, not surprisingly, the

highest concentrations tend to be found in materials with abundant sulfide and oxide minerals.

Fine-grained sediments such as shales, mudstones, and their unconsolidated equivalents tend

to contain the highest concentrations of arsenic. A summary of typical concentration ranges in

common rocks, sediments, and soils is given in table 14.

Arsenic is also introduced to the environment through a number of human activities. Apart from

mining activity and the combustion of fossil fuels, which involve redistribution of naturally

occurring arsenic, concentrations in the environment can increase through the manufacture and

use of arsenical compounds such as pesticides, herbicides, crop desiccants, and additives in

livestock feed, particularly for poultry. The use of arsenical pesticides and herbicides has

decreased significantly in the last few decades, but their use for wood preservation and feed

additives is still common. The use of chromated copper arsonate (CCA) as a wood preservative

may be banned in Europe in the coming years. The environmental impact of using arsenical

compounds can be major and long lasting, although the effects of most are relatively localized.

Most environmental arsenic problems recognized today are the result of mobilization under

natural conditions.

Processes Involved in Mobilization

Oxidation of Sulfide Minerals

Many mining areas with an abundance of sulfide minerals demonstrate the environmental

effects of sulfide mineral oxidation. Acid mine drainage is one notable consequence. Oxidation

of pyrite by atmospheric oxygen can be described by the reaction:

FeS2 + 15/4O2 + 7/2H2O ® Fe(OH)3 + 2SO4-2 + 4H+

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The overall oxidation reaction leads to the generation of iron oxide (Fe(OH)3) and dissolvedsulfate (SO4) as well as the production of acid (H+). The oxidation can also lead to the release oftrace metals and arsenic into solution. Even larger quantities of arsenic can be released fromarsenic sulfide minerals such as arsenopyrite (FeAsS). However, the strong adsorption capacityof iron oxides (especially the freshly formed, poorly crystalline oxides), together with thetendency for acidic conditions, normally mean that dissolved arsenic concentrations diminish atsome distance downstream. Although a significant source of arsenic exists locally to producean aqueous arsenic problem in such areas, the local geochemical conditions are usuallyunsuitable to maintain it.

The effects of sulfide mineral oxidation have also been seen in mineralized aquifers as a resultof lowering the water table and introducing atmospheric oxygen to the aquifer. Probably thebest example to demonstrate this is the mineralized sedimentary aquifers of Wisconsin, UnitedStates. Here, historical abstraction of groundwater has led to aquifer dewatering and theaccumulation of concentrations of arsenic up to 12,000 µg L-1 in the groundwater at the levels of

Table 14. Typical Arsenic Concentration Ranges in Rocks, Sediments, and Soils

Classification Rock/sediment type Arsenic range (mg kg-1)

Igneous rocks Ultrabasic rocks 0.03–16

Basic rocks 1.5–110

Intermediate 0.09–13

Acidic rocks 0.2–15

Metamorphic rocks Quartzite 2.2–7.6

Hornfels 0.7–11

Phyllite/slate 0.5–140

Schist/gneiss <0.1–19

Amphibolite/greenstone 0.4–45

Sedimentary rocks Shale/mudstone 3–490

Sandstone 0.6–120

Limestone 0.1–20

Phosphorite 0.4–190

Iron formations and iron-rich sediment 1–2,900

Evaporite deposits 0.1–10

Coal 0.3–35,000

Bituminous shale 100–900

Unconsolidated Sediments 0.5–50

sediments and soils Soils 0.1–55

Soils near sulfide deposits 2–8,000

Source: Smedley and Kinniburgh 2002 and references therein.

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the mineralized veins (Schreiber, Simo, and Freiberg 2000). Oxidation of sulfide minerals hasbeen advocated strongly by many workers in West Bengal (for example Das and others 1994) asthe cause of groundwater arsenic problems in the Bengal basin. It is well known that authigenicsulfide minerals can form under strongly reducing conditions in sediments in aquifers, lakes,and marine settings. Generation of groundwater arsenic problems if these are allowed to oxidizeis a reasonable hypothesis. However, the evidence for this mode of occurrence in the aquifersof the Bengal basin is lacking. It is possible that such oxidation processes could be involved insome parts of the aquifers, particularly at the shallowest levels, for instance the depthspenetrated by dug wells. However, it is not considered to be the main cause of the groundwaterarsenic problems in the Bengal basin or other sedimentary aquifers in Asia where the majorarsenic problems exist. Indeed, groundwater in most dug wells from the Bengal basin has lowarsenic concentrations.

Release from Iron Oxides

Release under Reducing ConditionsOne of the main conclusions from recent research studies has been that desorption ordissolution of arsenic from iron oxides is an important or even dominant control on the regionaldistributions of arsenic in water. The onset of reducing conditions in aquifers can lead to aseries of changes in the water and sediment chemistry as well as in the structure of the ironoxides. Many of these changes are poorly understood on a molecular scale. Some criticalreactions in the change to reducing conditions and to subsequent arsenic release are likely tobe the reduction of arsenic from its oxidized (As(V)) form to its reduced (As(III)) form. Undermany conditions, As(III) is less strongly adsorbed to iron oxides than As(V) and reduction shouldtherefore involve a net release from adsorption sites. Dissolution of the iron oxides themselvesunder reducing conditions is another potentially important process. Additional influences suchas competition from other anionic solutes (for example phosphate) for adsorption sites may alsobe important. It is notable, for example, that reducing aquifers such as those of Bangladesh,West Bengal, and China have relatively high concentrations of dissolved phosphate. These aresometimes in excess of 1 mg L-1 and almost always in excess of the concentrations ofdissolved arsenic.

The onset of reducing conditions in aquifers may result from rapid burial, particularly evident inareas of rapidly accumulating sediment (for example deltas). Burial of organic matter along withthe sediments facilitates microbial activity, which plays an important role in the generation of thereducing conditions (BGS and DPHE 2001; McArthur and others 2001). The role of microbes inthe reduction and mobilization process has been increasingly recognised in recent years(Oremland and others 2002; Islam and others 2004). The rates of the arsenic release reactionsunder such conditions are likely to be dependent on a number of factors, including rates ofsedimentation, diffusion of gases, and microbial reactions, but they are likely to be relativelyrapid on a geological timescale. The onset of reducing conditions and release from iron oxidesis believed to be the main process controlling the high arsenic concentrations in thesedimentary aquifers of Asia.

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The nature of the organic matter involved in the generation of reducing conditions in arsenic-affected aquifers has been disputed in recent years. Some have cited disseminated fine-grainedsolid and dissolved organic matter as the key redox driver (for example BGS and DPHE 2001),others cite occurrences of peat (McArthur and others 2001), while some have suggested thatrecent anthropogenic organic carbon is responsible (Harvey and others 2002). Whatever theorigin, the importance of organic matter in controlling the redox conditions in reducing aquiferssuch as those of the Bengal basin is widely acknowledged.

In the groundwaters from the shallow aquifer of Bangladesh, the highest and most variableconcentrations of arsenic occur in strongly reducing groundwaters below the redox boundary(zone over which the groundwater changes from oxidizing to reducing conditions, usually just afew meters below the piezometric surface) (figure 11). Dug wells typically penetrate theshallowest levels of aquifers where conditions are relatively oxidized. Tubewells usually

Figure 11. Schematic Diagram of the Aquifers in Southern Bangladesh Showing theDistribution of Arsenic and the Configuration of Wells

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penetrate to deeper levels than dug wells in order to obtain better groundwater yields (althoughdepths are usually the minimum required to achieve this). Entry of air to the open large-diameterwells also helps to maintain their relatively oxidized status in most circumstances (except instagnant groundwater conditions with excess organic matter). Under most conditions, therefore,groundwater in dug wells is likely to have relatively low arsenic concentrations as a combinedfunction of shallow depth and the nature of the well construction.

Release at High pHUnder aerobic and acidic to neutral conditions characteristic of many natural environments,adsorption of arsenic (as As(V)) to iron oxides is normally strong and aqueous concentrationsare therefore usually low. However, the sorption is less strong at high pH. Increases in pH(especially above pH 8.5 or so) will therefore result in desorption of arsenic from oxide surfacesand a resultant increase in dissolved concentrations. Such processes are considered to havebeen responsible for the release of arsenic in oxidizing Quaternary sedimentary aquifers in, forexample, the arid inland basins of Argentina (Smedley and others 2002) and southwestUnited States (Robertson 1989). Similar conditions have not been found to date in Asiansedimentary aquifers but the process may take place in some areas (for example arid regions ofChina or Pakistan).

Release from Other Metal Oxides

Although more research has been done on arsenic and its association with iron oxides,aluminum and manganese oxides can also adsorb arsenic and may be additional sources orsinks for arsenic if present in quantity in any given aquifer. They are likely to be less significantthan iron oxides in controlling arsenic concentrations in groundwater, but cannot be ignored,and have been cited as potential sources of arsenic in some aquifers, including those inBangladesh and Argentina.

Groundwater Flow and Transport

Geochemical conditions suitable for arsenic release are important in generating groundwaterarsenic problems but the problems will only remain if the arsenic is not flushed away by movinggroundwater over time. Another feature of many of the high-arsenic groundwater provinces ofAsia is slow groundwater movement. A combination of young sediments (often <10,000 yearsold) and slow rates of aquifer flushing (for example low rates of recharge, poor sedimentpermeability, low hydraulic gradients) mean that arsenic accumulated through geochemicalprocesses has not been flushed from the aquifer during its evolutionary history. This argumenthas been used in part to explain why the deep (Pleistocene) aquifers of Bangladesh and othernear-coastal aquifers have low arsenic concentrations. During pre-Holocene times, it is knownthat glacial conditions were associated with long-term low relative sea level (up to 120 m belowthose of the present day; figure 12). This would have resulted in greater head gradients in thepast and more active groundwater movement (box 4 see page 66). It has been suggested thatthe deep aquifer had a longer history of flushing during the pre-Holocene past and that solutearsenic accumulated in the past has been flushed from the aquifer over time (BGS and DPHE

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Figure 12. Sea Level Changes during the Last 140,000 Years

Source: After Pirazzoli 1996.

2001). Interestingly, such steep head gradients would not have affected inland basins such asthose of northern China and so deep aquifers in such areas would not have been subject tosuch active groundwater flow during past ice ages.

It is also likely that sediments of the older deeper aquifers are mineralogically and texturallydistinct from the younger Holocene deposits, a factor that may have a bearing on thegroundwater arsenic concentrations. Certainly in Bangladesh, evidence suggests that thedeeper Pleistocene sediments are dominantly more brown in color than the Holocene depositsand therefore appear to be more oxidized. More work on the sediment chemistry of the deepaquifers of the Bengal basin is required to investigate this further.

Impact of Human Activities

A relevant question that has not been fully answered by the various studies of arsenicoccurrence in South and East Asia is the extent to which human activities have contributed tothe arsenic problems in different situations. It is clear that in sulfide mining areas such activitiesas excavating ore minerals, redistributing waste piles, and pumping mine effluent haveexacerbated the problem. However, in sedimentary aquifers, the relationships are much lessclear cut. Scientists working in West Bengal in the 1990s were of the opinion that the arsenicproblem was of recent origin and related to the dewatering and oxidation of sedimentaryaquifers containing pyrite (or arsenopyrite) through overabstraction of groundwater for irrigationof rice crops. Convincing evidence for this has never been produced, and subsequent studies inthe Bengal basin have related the occurrence of arsenic to the presence of natural stronglyreducing conditions coupled with slow groundwater movement. From this conclusion, it followsthat the arsenic phenomenon is not recent but originated from the time of sediment burial and

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Box 4. Frequently Asked Questions

Why are arsenic concentrations often high in the shallow aquifers of Bangladesh butusually low in the deep aquifer?

This question is difficult to answer for certain because little information currently exists on thegeology and hydrogeology of the deep aquifer. Limited data available so far suggest that the older(deeper) sediments are lithologically different. They are often brown in contrast to the overlyingsediments, which are variable but commonly grey. The color changes suggest changes in redoxconditions, the deeper sediments being relatively oxic. Differences in hydrogeological history arealso likely to be significant. Older sediments at depth have undergone longer periods ofgroundwater flushing. During the last glacial maximum around 12,000 years ago relative sea levelwould have been much lower than its present level, resulting in steeper groundwater gradients andmore active groundwater flow. Young (Holocene) sediments overlying these deposits have beendeposited in postglacial times, have not had such a long history of flushing, and have not beensubject to such large relative sea level fluctuations. They also contain freshly formed mineralswhich may be highly prone to reaction under reducing aquifer conditions.

Why are concentrations in groundwater from deep aquifers in other areas notalways low?

In contrast to Bangladesh, deep aquifer sediments of unknown but probable Pleistocene age inInner Mongolia (China) contain groundwater with sometimes high arsenic concentrations. In these,the sediment lithology is poorly defined as few geological studies have been carried out. It is likelythat these have not been well flushed since deposition as the area is an internal drainage basin thatwould not have been so greatly influenced by past sea level fluctuations. The deep aquifers ofInner Mongolia are thought to be occupied by very slow-moving groundwater.

Are the arsenic concentrations in wells going to improve or deteriorate with time?

At present, there are insufficient data to define the nature of variability in individual wells over periodsof days to weeks to years and more monitoring data are needed to define the temporal trends. Mixingof waters with different compositions will necessarily involve changes in arsenic concentration but onwhat scale and over what period are uncertain. Such changes will involve decreases as well asincreases. Variations are likely to be greater at shallow depths than at deeper levels becausegroundwater flow is more active near the water table and inputs greater. In the first instance, it isreasonable to assume that an initial arsenic concentration (provided it is analytically reliable) will berepresentative for a given well and that it will not change significantly in the short term.

the onset of reduction. The arsenic in Bangladesh groundwaters may therefore have beenpresent for hundreds to thousands of years (BGS and DPHE 2001).

That is not to say that no impact can be expected from human activities. The impacts ofpumping on groundwater flow mean that some changes to the aquifer systems are likely in themedium to long term. Quantifying those impacts is difficult. There are various dimensions to thepotential human influences, including the impacts of pumping-induced flow on transport of

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arsenic both within and between aquifers, impact of pollutants such as organic carbon andphosphate on aquifer redox and sorption/desorption reactions, and impact of seasonalwaterlogging of soils for rice production on subsurface redox conditions.

It is interesting that arsenic problems in the Red River delta of Vietnam are close to southernHanoi and those of Cambodia close to Phnomh Penh. Whether this reflects a bias in regionaltesting or real highs in urban areas compared to rural areas is still open to question. Disposal ofurban wastewater including sewage along open drains has been documented for Hanoi forexample (Trafford and others 1996). Harvey and others (2002) concluded that groundwaterarsenic problems in part of Bangladesh were related to the introduction of organic carbon to theaquifer from surface pollutants. However, the evidence presented for this was unconvincing andthe conclusion has sparked much subsequent debate. The impacts on groundwater quality ofthe human influences described above have received insufficient attention in past studies andrequire further investigation in order to ensure that groundwater resources will be sustainableand protected.

At-Risk Aquifers

The previous sections indicate that many uncertainties exist over the spatial distribution ofarsenic problems in groundwaters of Asia and elsewhere. However, sufficient information isavailable on the recognized high-arsenic groundwater provinces to allow them to be broadlycategorized in terms of geology, hydrogeology, and the processes likely to be controllingarsenic mobilization. A number of risk factors for the development of high-arsenic groundwaterswere identified and summarized by Smedley and Kinniburgh (2002). These are highlighted infigure 13. While no single factor is likely to be sufficient to identify likely at-risk aquifers,combinations of factors can be of value in pinpointing areas deserving increased priority forgroundwater chemical analysis.

In arsenic-affected aquifers of Asia, some notable parallels in geology and hydrogeology areidentifiable. Apart from areas related to bedrock mineralization and mining activity (Ron Phibun,Thailand; Madhya Pradesh, India), and localized areas of geothermal activity, the documentedcases included in chapter 2 are from young (Quaternary) sedimentary aquifers of alluvial,deltaic, or lacustrine origin. Sediments rich in iron oxides may be particularly susceptible. Insuch aquifers, the presence of reducing conditions appears to be a key factor in determining ona regional scale where high groundwater arsenic concentrations will occur. Groundwaters with,for example, high concentrations of iron, manganese, and ammonium will therefore be morelikely to have high concentrations of arsenic than those with low concentrations. Where data forthese are available they can act as warning signs of potential arsenic problems, although, asnoted above, they cannot be taken as direct indicators of arsenic concentrations. Ancillaryinformation such as low or no dissolved oxygen, low concentrations of sulfate, and highconcentrations of dissolved organic carbon can also be of use in defining reducing aquifers(figure 13).

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Slow groundwater movement is also a common feature of the identified high-arsenicgroundwater provinces of Asia and elsewhere. Aquifers with limited recharge or low hydraulicgradients are likely to have slow groundwater flow.

Aquifer size and sedimentation rate may also be relevant criteria in determining groundwaterquality. The Bengal basin is one of the largest and most rapidly accreting sediment basins in theworld and the rapid burial of organic matter along with sediments (restriction of air access) mayaccelerate the onset of reducing conditions.

Arsenic problems have also been found in oxidizing conditions in some arid and semiarid inland(closed) basins. As noted above, these groundwaters are typically characterized by high pH (>8)

Note: Not all indicators of low flushing rates necessarily apply to all environments.Source: Smedley and Kinniburgh 2002.

High-arsenic groundwater province

Mixing/dilution

Mineral dissolutione.g. pyrite oxidation

Oxidizing or mildly reducing

Increased temperatureIncreased salinity (Na, Cl)

High B, Li, F, Si02

High pH >7

High Fe, SO4

Possibly low pHPresence of other tracemetals (Cu, Ni, Pb, Zn,

Al, Co, Cd)

Env

ironm

ent

Pro

cess

Ind

icat

ors

Geothermally influenced groundwater Low-temperature groundwater

Nonmining areas Sulfide mining and mineralized areas

Low rate of flushing:a

Young aquifer (Quaternary)Low hydraulic gradient (deltas, closed basin)

Slow groundwater flowPoor drainage

Arid/semiarid environmentOld groundwaters

High chemical spatial variabilityLarge volume of young sediments:

Large deltas and inland basin

Low Eh (<50 mV)No dissolved oxygen

High Fe, Mn, NH4

Low SO4 (<5 mg L-1)High alkalinity (>500 mg L-1)

Possibly high DOC (>10 mg L-1)

Reducing:Reductive desorption and

dissolution(Fe oxides) Confined aquifers

Oxidizing:Desorption (Fe oxides)

Evaporation

High pH (>8)High alkalinity (>500 mg L-1)

Possibly high F, U, B, Se, MoIncreased salinity

High Eh, DOC

E.g. Bangladesh; China (Inner Mongolia); Taiwan;West Bengal in India; Nepal

Possibly: Cambodia; some parts of northernChina; Lao PDR; Vietnam

E.g. PakistanPossibly: Some parts of northern China

Figure 13. Classification of Groundwater Environments Susceptible to Arsenic Problemsfrom Natural Sources

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and are accompanied by high salinity. High concentrations of trace elements such as fluoride,molybdenum, and boron are also characteristic. While none of the oxidizing, high-pH

groundwater provinces recognized so far is from Asia, this is not to say that such conditions will

not occur. Major deposits of Quaternary sediments (including loess) cover large parts ofnorthern China, for example. Quaternary aeolian deposits of Pakistan, including the Baluchistan

basin, also contain high-pH groundwater. It is believed that the groundwaters in these areas

have not been tested for arsenic.

One of the key findings of the last few years has been that the affected sedimentary aquifers ofAsia (for example Bangladesh, China) do not have anomalously high concentrations of arsenic

in the sediments. This is important because it implies that potentially any young sediments

could develop groundwater arsenic problems, given a combination of geochemical conditionsconducive to the release of arsenic (reducing conditions or oxidizing, high-pH conditions) and

hydrogeological conditions that prevent it from being flushed from the aquifer. Other alluvial and

deltaic plains, such as the lower reaches of the Yellow River plain and Yangtze River of Chinaand the Chao Phraya River of Thailand, deserve further investigation.

Variability in Arsenic Concentrations

Spatial Variability

A high degree of spatial variability in arsenic concentrations both areally and with depth hasbeen noted in many of the recognized problem aquifers. Such variability is a naturalconsequence of sediment heterogeneity and poor mixing brought about by sluggishgroundwater movement. Notable vertical variations in sediment texture, composition, and grainsize have been observed from sediments in Bangladesh on a scale of centimeters. This canhave large impacts on groundwater movement between layers, on water-rock interactions, andon local redox conditions. Small differences in depth of closely spaced wells can result in thetapping of different horizons (figure 11). Lack of homogenization of groundwaters and poorhydraulic connection between layers can maintain chemical differences on local scales.Besides, it should be borne in mind that in terms of thresholds of acceptability the differencebetween concentrations of 10 µg L-1 and 50 µg L-1 is critical, yet geochemically the differencesare very small.

Many high-arsenic groundwaters appear to be associated with occurrence of finer-grained andiron oxide-rich deposits, such as accumulate preferentially in low-lying distal parts of deltas orin low-flow zones of river flood plains. The occurrence of local arsenic hotspots observed in,for instance, Bangladesh aquifers may be explained by the localized occurrence offine-grained sediments in inside meanders and oxbow lakes. Together with locally slowgroundwater movement in these areas, this may be responsible for the build-up (and lack offlushing) of arsenic.

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Temporal Variability

High-Arsenic AquifersThe timescales over which temporal variations in arsenic concentrations may exist range fromhours (diurnal changes) through seasons to years or decades. The potential causes of suchchanges are also variable: changes in groundwater pumping rate over the course of a day;seasonal variations in recharge, irrigation abstraction, and head gradients; long-term changes inpumping regimes and climate. During the seasonal or annual cycle of a major abstractionsource such as an irrigation well or municipal supply well, the chemical composition ofabstracted groundwater may be affected by the variable contribution from different depths,which changes with time. Initial discharge tends to be dominated by flow from the shallowesthorizons with deeper flow becoming more important with time as the cone of groundwaterdepression deepens. This influence is likely to be less important for small handpumpedtubewells which individually involve much smaller abstractions. Changes in chemicalcompositions over longer timescales may result from long-term changes in groundwater level.To date, there has been very little investigation of the temporal variations in groundwaterchemistry in high-arsenic aquifers from Asia and much more needs to be done to assesswhether variations are significant in a practical sense.

In Bangladesh, BGS and DPHE (2001) did not find evidence of significant temporal variationduring fortnightly monitoring of groundwater from specially drilled piezometers over the courseof a year. An example of this monitoring is given for Faridpur in central Bangladesh in figure 14.Little variation was found either at shallow (tens of meters) or deep (150 m) levels. Continuedmonitoring of these piezometers after the completion of the BGS and DPHE project could haverevealed useful information on the temporal variations over longer timescales, but unfortunatelythis was not carried out. As with the BGS and DPHE (2001) results, Tareq and others (2003) didnot find significant seasonal variation in groundwater arsenic concentrations in 10 shallowtubewells from Bangladesh. Variations in arsenic concentration monitored premonsoon,syn-monsoon and postmonsoon were in the range 10-16% and largely within analytical error.

Few time series data are documented for the groundwaters of West Bengal and, as withBangladesh, there remains uncertainty over whether significant temporal variations in arsenicconcentration occur. They may occur in some places and not others. CGWB (1999) concludedfrom West Bengal groundwaters that groundwater arsenic concentrations vary seasonally, withminima during the postmonsoon period, considered to be due to dilution of groundwater bymonsoon recharge. However, the conclusion is apparently based on small sample sets(4–6 samples at any given location) collected over a short time interval (less than one year).Chatterjee and others (1995) noted a variation of around 30% in time series data frommonitoring of groundwaters over the period of a year in their study of parts of 24 ParganasNorth and South, but detected no significant seasonal changes in the variation.

Deep (Older) AquifersIt has often been said in relation to the deep aquifers of the Bengal basin that some wells that

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Figure 14. Monitoring Data for Groundwater from Selected Wells and Specially DrilledPiezometers in Faridpur Area, Central Bangladesh

Source: BGS and DPHE 2001.

were once arsenic free have become contaminated with time (for example Mandal and others1996). However, documentation and data in support of this conclusion are difficult to find. Sincethe long-term trends in groundwater arsenic concentrations are a critical issue for thesustainability of the deep aquifers, the data that indicate such variations need to bedocumented properly and be open to peer review. If temporal trends are apparent ingroundwater from deep aquifers, there are a number of reasons why this may be the case.These include inadequate sealing of tubewells, multiple screening of tubewells at differentdepths to improve yields, as well as natural hydraulic connectivity between aquifers (as statedabove). They also may represent analytical problems. A statistical approach is needed ininterpreting time series data.

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Dug WellsFew time series data exist for dug wells in arsenic-affected areas. Arsenic concentrations in dugwells may be susceptible to temporal change as the groundwaters abstracted from them arefrom the shallowest levels and therefore subject to the largest changes in recharge inputs,pollutant inputs, and redox conditions. They may also vary if particulate contents vary with timeand water samples taken from them are not filtered. Despite these possibilities, groundwater inthree dug wells from northwest Bangladesh monitored by BGS and DPHE (2001) over thecourse of a year showed little statistically significant variation. Concentrations were low andin the range 0.5–2 µg L-1, with only two individual measurements from the wells exceeding10 µg L-1. More data are clearly needed to determine whether significant temporal changesoccur in other areas, particularly where local groundwater arsenic concentrations are high. Therelative contributions of particulate and dissolved fractions should also be investigated bymeasurement of other parameters (notably iron) as well as arsenic.

Arsenic in Surface WaterLittle information is available on the arsenic concentrations of surface waters in regions withhigh groundwater arsenic concentrations. Even less is available on temporal variations. Thegreater likelihood of high suspended loads in surface waters means that the concentrations arepotentially more variable than in most groundwaters as the arsenic associated with particles canbe significant. Concentrations in particles are likely to be in the range 5–10 mg kg-1, in line withthe concentrations of average sediments, but may be higher in iron-rich particles. There is alsopotential that river waters will vary seasonally as a result of the variations in the proportion ofbaseflow compared to runoff. This has not been studied in detail. However, most of theevidence points to surface waters generally having low arsenic concentrations, even wheregroundwater arsenic concentrations are high.

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Overview

The previous sections highlight the extreme variability in arsenic concentrations both withinand between aquifers and have shown some of the issues associated with identifying safe

sources of water and determining suitable alternatives. One of the key developments of the pastfew years has been the realization that the mode of occurrence of arsenic in water can varysubstantially. The mechanisms of arsenic occurrence in water in mining and mineralized areascan be very different from those in young sedimentary aquifers and their distribution and scalecan also differ considerably. Some of the options for water supply are detailed further in thissection, along with the risks associated with them and potential strategies for dealing with thoserisks. The choice of water supply in any given area must depend on many technical and socialfactors that need to be assessed locally. The options, risks, and potential mitigation strategiesare summarized in table 15, at the end of this chapter.

Mining and Mineralized Areas

In areas with rich deposits of sulfide minerals, both surface waters and groundwaters arepotentially vulnerable to high arsenic concentrations. Other toxic trace elements may also bepresent in excessive concentrations (for example copper, lead, zinc, cobalt, cadmium, nickel). Inthese areas, surface waters, groundwaters, and soils are all potentially affected by high arsenicconcentrations. However, the scale of contamination is likely to be localized, on the scale of afew kilometers around the site of mineralization. Mitigation of the problem therefore centers onidentifying contaminated water sources and finding alternative supplies locally. Bothidentification of at-risk sources and mitigation should be less of a problem than in arsenic-affected sedimentary aquifers. Environmental problems are usually exacerbated by miningactivity and are therefore largely predictable.

Sedimentary Aquifers

Shallow Groundwater

Shallow TubewellsOf the sedimentary aquifers in South and East Asia with recognized arsenic problems, themajority are composed of young sediments at shallow depths of less than 50-100 m or so. InBangladesh the highest concentrations and largest range of concentrations are found in theshallow aquifers, which are dominantly of Holocene (<12,000 years) age. The extreme variabilityindicates that on a local scale, the scale relevant to mitigation, no reliable method can be usedto predict their concentrations accurately and no substitute therefore exists for testing each wellfor arsenic if it is to be used for drinking water. This is not to say that on a regional scale somesort of prioritization would not be possible given some knowledge of the distribution ofsediment textures, hydrogeology, and water chemistry. Bangladesh groundwaters tend to have

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highest arsenic concentrations in the low-lying parts of the delta. This is also evident in otheraquifers of Asia (for example Huhhot basin, China) (Smedley and others 2003). However, ourunderstanding of the distribution of arsenic in groundwater at present does not allow predictionof such trends with confidence, even on a regional scale, and hence major testing programs insuch susceptible aquifers are needed regardless of local geological variations.

The distributions of arsenic in different districts of Bangladesh vary widely (BGS and PDHE2001). The worst-affected districts identified from the BGS and DPHE (2001) study were(percentage of samples with arsenic concentrations greater than 50 µg L-1 in parentheses):Chandpur (90%), Munshiganj (83%), Gopalganj (79%), Madaripur (69%), Noakhali (69%),Satkira (67%), Comilla (65%), Faridpur (65%), Shariatpur (65%), Meherpur (60%), Bagerhat(60%), and Lakshmipur (56%). In the worst-affected areas it would probably be appropriateto abandon use of the shallow aquifer in the long term in favor of alternative sources ofdrinking water.

On the other hand, on a national scale, the BGS and DPHE (2001) survey showed that fortubewells <150 m deep, 27% exceeded 50 µg L-1 and 46% exceeded 10 µg L-1. This means that73% and 54% of wells had concentrations below these limits respectively. Also, 24% ofsamples analyzed had concentrations below the analytical detection limit, usually 0.25 µg L-1 or0.5 µg L-1. The districts of Thakurgaon, Barguna, Jaipurhat, Lalmonirhat, Natore, Nilphamari,Panchagarh, and Patuakhali all had no samples with arsenic >50 µg L-1 in the survey. Thismeans that large-scale abandonment of tubewells in many parts of Bangladesh is unnecessary.The same holds for most other sedimentary aquifers of Asia where arsenic problems have beenencountered. Major investments have been made in shallow tubewells across Asia and in manyplaces these still constitute a reliable source of safe drinking water. There is also the potentialfor segregation of wells for different uses. High-arsenic wells could be used, for example, forwashing and other domestic purposes, provided the wells are labeled adequately.

In many areas with high-arsenic groundwater domestic-scale treatment is being carried out inorder to remove or reduce the arsenic in drinking water supplies. These usually involve eitheraeration and sedimentation, coagulation and filtration, adsorption, ion exchange, or membranefiltration (Edwards 1994; Hering and others 1996; Ahmed 2003). While many of these techniqueshave been adapted for domestic use in affected areas and the technologies have improvedsignificantly in recent years, issues remain over their sustainability and the disposal of high-arsenic waste products. They can provide a useful short-term solution in affected areas but areunlikely to form the basis of long-term mitigation strategies.

It should be borne in mind that the shallow high-arsenic groundwaters of the Bengal basin andother areas of South and East Asia also often have problems with a number of other traceelements that can be detrimental to health (for example high manganese, uranium, boronconcentrations) or can cause problems with acceptability (high salinity, iron, ammoniumconcentrations). In arid areas (for example northern China) the shallow aquifers can also haveproblems with high fluoride concentrations. These other elements rarely correlate well with

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arsenic and so shallow groundwaters of good quality in respect of arsenic concentrations maynot necessarily be of good quality in other respects. Defining acceptability criteria for potablewater supplies should therefore involve consideration of other potentially detrimentalconstituents and not just arsenic.

Dug WellsIt has been traditionally accepted that shallow groundwater from open dug wells usually has low

concentrations of arsenic. Evidence from Bangladesh (BGS and DPHE 2001), West Bengal(Chakraborti 2001), Myanmar (WRUD 2001), and Taiwan (Guo, Chen, and Greene 1994)

indicates that many dug wells contain water complying with the WHO guideline value of

10 µg L-1 and most comply with the national standard of 50 µg L-1.

Despite this tendency, a rather different situation is apparent for groundwater from dug wells inInner Mongolia. As shown in earlier section, dug wells in the Huhhot basin were found to

contain groundwater with arsenic concentrations up to 560 µg L-1 in the area where tubewell

arsenic concentrations were also high (Smedley and others 2003). Some recent studies inBangladesh and Myanmar also appear to be finding higher arsenic concentrations in dug wells

than previously appreciated, although supporting evidence has not yet been published to verify

this. Some of the higher concentrations observed may be due to particulate rather than dissolvedarsenic and concentrations may therefore vary depending on the turbidity of the groundwaters.

Particulate matter could presumably be removed by some simple filtration or settling.

The findings suggest that in any given aquifer, concentrations of arsenic in dug wells cannot be

assumed to have acceptably low arsenic concentrations without a testing program to confirm

the concentration ranges. Care should also be taken in analyzing for arsenic that the relativecontributions of dissolved and particulate arsenic are determined.

Since traditional large-diameter dug wells are normally open to the atmosphere and tap theshallowest levels of the aquifer, they are also potentially vulnerable to contamination from

bacteria and other surface pollutants. Well siting and construction are therefore important

criteria for well protection. Locating wells at some distance from latrines and other contaminantsources is important, as is installation of adequate sanitary seals. Installation of handpumps

removes potential contamination from introduced buckets and disinfection of water can give

protection against waterborne diseases. Periodic cleaning of the well can help to reducesuspended material.

One of the major constraints on the use of dug wells is likely to be well yields. This is

especially the case in areas with relatively large water level fluctuations, where dug wells can dry

up in the dry season. Poor water quality is linked to this to some extent, as particle settlingbecomes more difficult when wells dry up. Poor well yields may be the ultimate limit of the

sustainability of dug wells in some areas. They are also not suitable in areas with thick layers of

superficial clay.

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Evidence from the BGS and DPHE (2001) study of Bangladesh suggests that dug wells alsocontain potentially detrimental concentrations of uranium (up to 47 µg L-1). Dug wells had thehighest concentrations of uranium identified in groundwaters from Bangladesh. Fewepidemiological data exist to set a safe limit for uranium in drinking water, but new WHOguidelines include a provisional value for uranium of 9 µg L-1. Concentrations of nitrate alsoexceeded the WHO guideline value in some wells, presumably as a result of surface pollution.

Hence, for the reasons outlined above, dug wells may offer a suitable short-term solution toarsenic problems in some affected areas of Asia. However, they are unlikely to form a majorcomponent of long-term mitigation strategies for most areas.

Groundwater from Deep (Older) Aquifers

Although analyses of groundwater from deep aquifers in the Bengal basin are still relativelylimited, there appears sufficient information available to indicate that deep (older) aquifers in theregion have much lower arsenic concentrations than many of the shallow aquifers above. TheBGS and DPHE (2001) results suggested this for areas of south and east Bangladesh. CGWB(1999) found comparatively low concentrations in the deep aquifers of West Bengal. Van Geen,Ahmed, and others (2003) found similar results east of Dhaka. Data for other elements are alsosparse, but where available they suggest that concentrations of manganese, uranium, and mostother trace elements are also low in these deep aquifers. The older sediments therefore offerpotentially good prospects as alternative sources of safe water for the Bengal basin. Van Geen,Ahmed, and others (2003) reported successes with take-up of groundwater supplied by sixnewly installed "deep" (60–140 m, but pre-Holocene) community wells in a badly affected partof Bangladesh. In the short time since the wells have been installed they are said to haveproved popular with the local communities and women have been willing to walk up tohundreds of meters for their drinking water. The authors reported that such wells could providedrinking water for up to 500 people living within 150 m of the well in densely populated villages.Whether willingness to walk for supplies of drinking water would be a widespread phenomenonin arsenic-affected areas is untested and deserves further investigation.

Considerable uncertainties remain over the deep aquifers, particularly with respect to (a) theirlateral extent; (b) their depth ranges (as demonstrated by the van Geen, Ahmed, and others2003 example); and (c) the variation in their hydraulic separation from the shallow aquifers. Inmany places these will not have been assessed if adequate supplies of water have beenavailable at shallower depths.

An important risk with development of such deep (low-arsenic) aquifers is from potentialdrawdown of high-arsenic groundwater from shallower levels and contamination in the longterm (decades or longer). This can occur if intervening layers of clay are thin or absent, or ifseals on wells penetrating the deep aquifer are inadequate. Flow modeling of the Bangladeshaquifers (BGS and DPHE 2001) suggested that flow down to deep levels (100 m or more) islikely to be slow even under active pumping conditions. Modeling of aquifers in the Faridpur

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area of central Bangladesh suggested that rates of groundwater movement to a well screenedat 110–135 m depth from the water table at a lateral distance of 500 m would be of the order of200 years. The rate was found to be highly dependent on local lithology.

Detailed hydrogeological investigations are therefore an essential prerequisite to thedevelopment of such aquifers on a regional scale. The quality of well construction also needs tobe high. Subsequent groundwater quality monitoring for arsenic and a number of associatedparameters also needs to be carried out. The greatest threat is from abstraction of largevolumes of water for irrigation. Regulation of water abstraction should therefore be an integralpart of water management policy to protect the deep aquifers. Introduction of abstractionlicensing would be a logical step in policy development. Recording of well log information in asystematic way for newly drilled deep tubewells would also improve the knowledge base onthe aquifers.

It is clear from investigations in other regions of South and East Asia that deep aquifers are notalways low-arsenic aquifers. The Huhhot basin of Inner Mongolia is a case in point. Here,groundwater from (probably) Pleistocene aquifers at 100-400 m depth contains arsenicconcentrations in the range <1–308 µg L-1. The variations reiterate the fact that aquifer depth isnot an indicator of groundwater arsenic status. They also stress the need for detailedhydrogeological investigations in young sedimentary aquifers to identify sources and modeltheir responses to groundwater development before any development takes place.

Surface Water

RainwaterOf all the sources of drinking water available for communities, rainwater is the least likely to faceproblems with arsenic contamination. Concentrations of dissolved solids will usually also bevery low (perhaps too low). Rainwater harvesting offers a potential source of drinking water forindividual households in areas where other sources are unsuitable. The method requires asuitable roof for collection and storage tank with adequate sealing to protect it from bacterialand algal contamination. It has been estimated that about half of households in Bangladeshhave roofs suitable for collection of rainwater (for example galvanized iron, tiled surfaces) butthat many of the poorer families would not be suitably equipped (Ahmed and Ahmed 2002).Rainwater harvesting can provide a seasonal supply of water for drinking but its period of usewill be more limited in arid areas. Even so, provision of rainwater can still be beneficial even ifavailable for only a few months of the year.

Rivers, PondsSurface water usually has very low arsenic concentrations (typically <5 µg L-1). Exceptionsinclude waters affected by mining activity and some geothermal areas. These are generallyeasily identified. As noted above, mining-contaminated waters are also usually localized towithin a few kilometers of the mining activity (Smedley and Kinniburgh 2002), although thoseaffected by geothermal inputs can be more widespread.

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Surface waters in the arsenic-affected regions of South and East Asia usually have lowconcentrations. Indeed, this is why there are many proponents of treated surface water as anoption for safe water supply in Bangladesh and elsewhere. BGS and DPHE (2001) foundconcentrations of <2 µg L-1 in five river samples from the affected areas of Bangladesh. A sixthsample, from the Mahananda River flowing through the Chapai Nawabganj arsenic hotspot areaof western Bangladesh, had a concentration of 29 µg L-1 (in March 1999) although repeatsampling (in December 1999) gave a value of 2.7 µg L-1, an order of magnitude lower. Whetherthis difference represents real seasonal changes is difficult to assess on the basis of suchlimited data. It does highlight the possibility that dry season groundwater discharge to the riversystems could raise the surface water arsenic concentrations, especially in the worst-affectedareas. Small rivers may be more affected than large rivers with greater volumes of water.However, oxidation of the reduced arsenic and consequent adsorption will lower the dissolvedconcentration being discharged to a large extent. The extent will depend upon, for example, theinitial concentration and the river baseflow index (proportion of groundwater present).

A worse problem associated with the use of surface water is the potential risk from bacterialand other waterborne diseases arising from pollution. This problem means that surface waterwill probably always require adequate treatment to remove such hazards before use. At thevillage level this has been achieved through the use of pond sand filters. At a municipal levelwater treatment works can be installed for treatment of larger volumes. It is likely that anyarsenic present in the initial waters will be removed by both of these treatment systems toconcentrations below the drinking water thresholds. Other potential problems with the quality ofsurface water sources include inputs of nitrate and possibly organic compounds (pesticides,solvents) in some areas as a result of pollution. Concentrations of these will vary depending onlocal conditions and are difficult to remove by low-technology treatment methods.

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Table 15. Risks Associated with the Use of Drinking Water from Various Sources at VariousScales and Potential Mitigation Strategies

Source Risk for supply Mitigation strategy

Household scale Village scale Urban scale

Shallow tubewells High arsenic Water testing; Water testing; Alternative(Holocene concentration alternative source alternative source source/municipalaquirfers) if concentration if concentration treatment plant if

high high concentrationhigh

High concentrations Water testing; Water testing; Water testing;of other inorganic treatment difficult treatment difficult treatment plantconstituents(e.g. Mn, U, NH

4, B)

Deep tubewells Drawdown of n.a. Carry out prior site Carry out prior site(older sedimentary high-arsenic water investigations; investigations;aquifers) from shallow aquifers restrict use to restrict use to

drinking water; drinking water;regulate regulateabstraction abstraction

Dug wells Poor yields if wells Occasional use; Relocate/deepen n.a.dry up seasonally alternative source; wells

walk to other wells

Bacterial and other Disinfection, Well protection: n.a.waterborne diseases, filtration sanitary seals,high particulate loads handpump

installation, waterdisinfection,periodic cleaning.Relocate wellsaway from pollutionsources

Other inorganic Difficult Water treatment n.a.water quality difficult. Relocateproblems (e.g. nitrate, wells away fromuranium, manganese) pollution sources

(nitrate)

Arsenic may exceed Water testing Water testing n.a.prescribed limits necessary. necessary.

Treatment difficult Treatment difficult

Surface water Potential bacterial Small-scale water Small-scale water Urban waterproblems, high treatment (e.g. pond treatment (pond treatment plantsparticulate loads sand filters) sand filters)

Other pollutants (e.g. Difficult Difficult Urban waternitrate, pesticides) treatment plants

Rainwater Seasonal, difficult in Partial supply n.a. n.a.arid areasBacterial Storage protection, n.a. n.a.contamination disinfection

n.a. Not applicable.

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Overview

Although our ability to predict arsenic concentrations in groundwater from a given area oraquifer is still rather limited, knowledge of its occurrence and distribution has improved

greatly over the last few years. We therefore probably know enough about where highconcentrations tend to occur to make reasonable estimates of likely at-risk aquifers on aregional scale. Young sediments in alluvial and deltaic plains and inland basins as well as areasof mining activity and mineralization are obvious target areas for further evaluation. Theguidelines for improving understanding of the arsenic problem and how to go about dealing withit are broadly the same in any region at increased risk from arsenic contamination. First, thescale of the problem needs to be assessed. Second, where problems exist, it is necessary tofind out whether or not the situation is becoming worse with time. Third, where problems exist,it is necessary to identify the potential strategies or alternatives that are most appropriate forsupplying safe (low-arsenic) water.

Central to these issues is arsenic testing. In any testing program it is important to distinguishbetween reconnaissance testing: that necessary for establishing the scale of a groundwaterarsenic problem; and blanket testing: that required for compliance and health protection.Blanket testing involves the analysis of a sample of water from every well used for drinkingwater. For reconnaissance testing the numbers of samples need not be large; they shouldhowever be collected on a randomized basis. Monitoring is the repeat sampling of a given watersource in order to assess temporal changes over a given timescale (as distinct from repeattesting to cross-check analytical results).

The quality of analytical results is also paramount; analysis of arsenic in water is by no means atrivial task, yet reliable analytical data are key to understanding the nature and scale ofgroundwater arsenic problems as well as dealing with them. Instigation of any new arsenictesting or monitoring program requires consideration of the analytical capability of the locallaboratories. In some cases, development of laboratory capability (for example qualityassurance procedures, training, equipment upgrades, increased throughput) may be requiredand should be built into the testing program.

Appropriate mitigation responses for arsenic-affected regions will necessarily vary accordingto local geological and hydrogeological conditions, climate, population affected, andinfrastructural factors. Surface water may or may not be available as an alternative. Othergroundwater aquifers at different depths or in different locations may be available for use andneed additional assessment. Decisions about what action to take in respect of the arsenic-affected aquifer depend on factors such as percentage of wells of unacceptable quality andrange in concentrations (degree by which such standards such as 50 µg L-1 or 10 µg L-1 areexceeded). Below are outlined strategies for assessing the scale and distribution of arsenicproblems in South and East Asian aquifers and for providing the necessary information as abasis for mitigation.

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Aquifer Development and Well Testing

Aquifers of Low Potential Risk

It follows from earlier section that our ability to define with accuracy where low-arsenic aquifersare likely to be is limited. Broadly, they are likely to include carbonate rocks, crystallinebasement rocks, and other old (pre-Quaternary) sediments that have not been affected bymineralization or geothermal inputs. However, given the potential health risks associated witharsenic in drinking water, there is an argument for some randomized reconnaissance-scaletesting of existing wells for arsenic in areas with little or no information, regardless of theirperceived risk status (based on our current understanding). Provided the testing is random,survey results will provide information on the concentration ranges of arsenic to be expected ina given aquifer or region. Testing for arsenic alone may be sufficient in this case but otherconstituents of health concern could be included, depending on available budgets (for exampleiron, manganese, fluoride, nitrate; electrical conductance would also be useful).

Newly drilled boreholes should also include analysis of arsenic, at least on a subset of samples.Identification of significant numbers of samples with unacceptably high arsenic concentrations(say >10 µg L-1) should trigger a program for more extensive chemical analysis and geochemicalinvestigation. This should involve analysis of a wider suite of analytes aimed at identifying thecauses as well as the scale of the arsenic problem. Until a more detailed understanding of thearsenic concentrations in groundwaters of different aquifers in the developing world (andelsewhere) is available, including arsenic as a chemical analyte is a logical cautious approach.Although correlations between arsenic and other elements (such as iron) have often been notedin groundwaters, the correlations are usually insufficiently good to rely on proxy analytes.

Potentially High-Arsenic Aquifers

As with any other area, aquifers at greater potential risk from high arsenic concentrations requirethe scale of any groundwater arsenic problem to be defined and the likelihood of future changesassessed. In undeveloped areas where little previous information is available and newgroundwater supply projects are planned, merely testing for arsenic will determine the scale ofthe problem but will not define the processes involved. These need to be established tounderstand the aquifer better and ensure that groundwater use will be sustainable and thatsubsequent investment is appropriate. There is therefore a need for a detailed hydrogeologicaland geochemical investigation before any project implementation. This may involve collation ofall available hydrogeological data (for example well depths, water levels, aquifer physicalcharacteristics, pumping rates, groundwater yields), collection of new water samples for moredetailed chemical analysis (a more comprehensive range of analytes), and assessment of sedimentchemistry and mineralogy (table 16 see page 82). Such studies can be time consuming and mayhave large cost implications. In some countries local institutions may be equipped to carry outthese investigations. In others, expertise from external organizations may be required. The size ofthe prior investigation work should be commensurate with the size of the intended water supplyprogram, amounting to say 5-10% of the projected implementation cost.

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In areas where groundwater is already in use but water quality data are limited or absent,reconnaissance testing is necessary in the first instance to define the scale of anyarsenic problem.

Defining the concentration ranges and spatial distributions of arsenic in groundwater is bestachieved by some sort of randomized groundwater survey (most importantly, not based onprevious knowledge of groundwater arsenic concentrations). The scale of groundwater testingshould be commensurate with the numbers of people dependent on the water supply andpotentially affected by it. In Bangladesh the density of wells sampled in the BGS and DPHE(2001) national survey was 1 per 37 km2. The number of samples tested represented onlyaround 0.05% of the tubewells believed to be present in Bangladesh. The survey provedinadequate to pick out many of the localized arsenic hotspots that occur in some areas but didserve to identify the worst-affected parts of the country and the depth ranges of the tubewellswith the worst problems. It therefore highlighted priority areas for mitigation. These were seen tobe the southeastern part of Bangladesh. Subsequent surveys by various organizations mayhave refined the data distributions, but do not appear to have changed the overall conclusionsconcerning the worst-affected areas and hence the priority areas for mitigation.

The BGS and DPHE (2001) survey statistics indicated that 27% of shallow tubewells inBangladesh had arsenic concentrations >50 µg L-1. This figure compares well with an earlierestimate of exceedances above 50 µg L-1 for the whole country (26%) based on data from BGS,DPHE, and other organizations (DPHE-BGS-MML 1999). Of course, these data just providesummary statistics and define regional distributions and do not define concentrations in

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Table 16. Arsenic Testing Strategies in Potential High-Arsenic Groundwater Provinces

Area Existing drinking water wells New drinking water wells

Untested areas Randomized reconnaissance Initial hydrogeological andgroundwater arsenic survey. Scale of geochemical site/regionalsurvey dependent on number of wells, investigation. Test drilling;areal extent of aquifer, number of analysis of groundwater for arsenicpeople served. Stratified random during drilling and on completion.approach (stratification based ongeology, well depth). Blanket arsenictesting of wells used for public supply,schools, hospitals.

Established Blanket testing for arsenic. Decision to drill new wells basedgroundwater on previous results. Alternativesarsenic problem necessary in badly affectedareas aquifers. In marginal cases,

selection of well location, depth,etc., based on previousinformation. Analysis for arsenicon completion.

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individual wells. This latter is needed for compliance testing. The BGS and DPHE (2001) surveyshowed the high degree of spatial variability in groundwater arsenic concentrations and, as withmany other surveys, demonstrated the need for testing of individual wells used for drinking water.

Wells used for irrigation should also be tested ultimately as these represent a potential, thoughless direct and as yet unquantified, threat to health. They are, however, of a lower priority.

Survey samples need to be georeferenced (latitude and longitude data or other national grid)and notes made of aquifer type, well depth, well age, well owner, well number if available, andlocation. Other aquifers present in the region (for example the deep (Pleistocene) aquifer inBangladesh) should also be tested on a randomized basis to assess their potential asalternatives. The data need to be analyzed to assess whether statistically significantvariations exist in variables such as well depth, well age, and sediment type. The datashould be incorporated into a database for ready storage and manipulation. The data shouldalso be mapped.

In areas where some initial surveys have been carried out and where arsenic problems havebeen recognized, spatial patterns may be discernible. If these are significant, they shouldhighlight where mitigation needs to be targeted and where not. Past experience shows thatmany arsenic-affected aquifers have highly variable groundwater arsenic concentrations on alocal scale. In this case and where concentrations are high, blanket testing of wells will mostprobably be required. This is best achieved by laboratory analysis using reliable local facilitiesequipped for rapid throughput of samples. Where these are absent, facilities should be set upand equipped for analysis of arsenic and a range of other diagnostic elements. Where setting upof laboratories is not possible or where the scale of testing is very large and facilities inadequateto cope with the scale of testing required (for example Bangladesh), field test kits can be analternative. The technology for these has improved in the last few years and while older kitswere barely able to determine concentrations of arsenic at less than 100 µg L-1, the sensitivity ofnewer designs is better. Wherever possible, capability to test reliably at 10 µg L-1 should beaimed for. Wherever possible, a subset of samples analyzed by field test kits (say 10%) shouldbe cross-checked by a reliable laboratory analysis. A premium should be placed on reliability ofanalytical results and quality assurance should be a critical and ongoing undertaking with anygroundwater testing or monitoring program (box 1 see page 31).

Past hydrogeochemical investigations of high-arsenic aquifers have shown correlations withother elements (for example iron, manganese) but these are rarely sufficiently significant to beuseful in a practical sense. Results indicate that there are no suitable reliable proxy indicatorsfor arsenic concentration in groundwater.

Deep Aquifers below High-Arsenic Aquifers

As the deep (Pleistocene) aquifers of Bangladesh, West Bengal, and Nepal are identified asbeing potentially suitable sources for drinking water supply and also being vulnerable tocontamination from above, it is important that future development of such sources on a major

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scale is preceded by detailed hydrogeological and hydrochemical investigations. These shouldinclude sedimentological studies to assess physical aquifer dimensions; pumping tests andgroundwater flow modeling to determine flow mechanisms and assess the likelihood ofdrawdown from shallow levels; and testing of a wide range of chemical parameters to determinecontrolling processes and assess other elements of potential health concern.

During development of such deep aquifers, it is of importance to collate and document as muchhydrogeological information as possible. In the case of Bangladesh, for instance, collection ofinformation such as sediment texture (sand, silt, clay) and sediment color would be helpful andwould demand little extra cost. Texture gives information on water storage capacity andsediment history. In the Bengal basin, experience has shown that reddish-colored sediments atdepth are most likely to contain groundwater with low concentrations of arsenic and iron. Colorgives information on redox conditions and stratigraphy and can help date the aquifers. Theredox conditions and aquifer age have both proven critical to the quality of water with respect tomany other elements of health concern as well as arsenic. Databasing of such information isalso important.

Collection of such information on these potentially valuable aquifers is of great importance, butshould not serve to delay mitigation efforts in areas with recognized arsenic problems.

Monitoring

Monitoring can be a major and expensive task. Production of good analytical data is paramountand, as stated above, analysis of arsenic is difficult (box 1 see page 31). Analytical problemsshould therefore be expected and variations viewed with skepticism until found to bestatistically significant. As a first approximation, it is reasonable to assume that temporalchanges will not be major in the short term and that an initial analysis is likely to berepresentative for a given groundwater source (unless, as stated above, the analysis is suspect).Hence, single analyses can give an indication of fitness for drinking water in the absence of timeseries information. In general, larger fluctuations in chemical composition can be expected atshallower levels where groundwater throughputs are higher and compositions more stronglyinfluenced by changing groundwater head gradients. Chemical compositions in deeper aquiferscan be expected to be more stable and changes are likely to be dampened and over longertimescales, unless affected directly by flow (leakage) from other neighboring aquifers.

Shallow Sedimentary Aquifers with Recognized Arsenic Problems

On the scale of arsenic problems recognized in countries such as Bangladesh, even initialtesting for arsenic is a major logistical and analytical undertaking. Compliance monitoring oftubewells and dug wells defined to be initially "safe" is an even more demanding, and in manycases impossible, task. The scale of monitoring possible in any given region will depend on thenumbers of operating drinking water wells and the resources (funds, analytical capabilities)available. Monitoring should be of secondary priority to initial testing but is a necessary

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undertaking given the current uncertainty in temporal variations in arsenic concentrations.Monitoring is required not only for raw groundwater from shallow tubewells but also for waterfrom dug wells (especially those with concentrations >50 µg L-1, which should be retested toverify the concentration) and for treated water that has been through an arsenic removal plant.Recent investigations have shown that not all treated groundwaters have acceptably lowconcentrations of arsenic (Mahmud and Nuruzzaman, 2003).

The concentration ranges chosen for monitoring wells vary according to the reason formonitoring. For compliance monitoring, priority would be appropriate for wells withconcentrations of the order to 10-50 µg L-1 and wells used for major public supply. For researchpurposes, monitoring of groundwater sources with concentrations outside this range (both lowand high) would be of value.

The frequency of monitoring also depends on the objective of the monitoring exercise.Assessment of short-term (diurnal) changes requires frequent monitoring over periods of hours.Observation of seasonal changes requires weekly or fortnightly monitoring. Longer-termchanges require monitoring annually or biannually.

Deep (Older) Aquifers in Arsenic-Prone Areas

The deep aquifers of the Bengal basin represent a special case in that they appear to be largelyfree of arsenic and are a potentially important alternative source of drinking water, yet theirvulnerability to contamination from the high-arsenic shallower aquifer is in large part untested.An important component of a groundwater protection policy for the deep aquifers of the Bengalbasin (and other aquifers vulnerable to such leakage from contaminated aquifers) is the regularmonitoring of groundwater quality in order to detect any deterioration in the medium or longterm and to take mitigating action if necessary. Annual or biannual monitoring of such tubewellsused for public water supply would be appropriate. Arsenic would be the most importantanalyte but a range of other parameters (water level, electrical conductance, iron, manganese)would also be useful. Monitoring for these selected parameters should be conducted for severalyears (five and preferably longer). That is not to say that the tubewells should not be used until asuitable run of time series data have been collected. A subset of samples should also be testedfor all health-related parameters. Such monitoring can be a large task, but the number of deepwells installed is likely to be much smaller than shallow handpumped tubewells.

Further Research Needed to Assess Temporal Variations

Sufficient uncertainty remains over the temporal variations in arsenic concentrations ingroundwaters in affected aquifers that research programs need to be undertaken in specificareas to obtain further monitoring data. On a research scale, this is a relatively easy program toset up and could have been instigated in many of the affected areas shortly after their discovery.Accumulated data from the regular monitoring of selected wells over periods of months or a fewyears would have helped to identify the periodicity, scale, and causes of any observed temporalvariations and resolve many of the uncertainties that persist.

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Ideally, a program involving monthly monitoring of selected tubewells in affected areas(monitoring for arsenic as well as water level, electrical conductance, iron, manganese) shouldbe undertaken in some areas in order to identify seasonal trends. Such monitoring should beover the course of several years (two minimum). Monitoring of groundwater quality at differentdepths in recognized high-arsenic aquifers is also required. Such programs have been started inBangladesh and elsewhere but more monitoring is needed to collect a larger body of time seriesdata. Studies of diurnal variations in heavily used tubewells are also required to establish waterquality variations over the course of days.

Little information is so far available on the temporal variation in arsenic concentration in dugwells. Specific monitoring programs in a few shallow wells, sampled approximately monthly, canbe carried out to establish temporal variations, especially in relation to water level changes.

Seasonal monitoring of surface waters in areas with badly affected aquifers would help toestablish whether temporal variations exist and whether they are sufficiently significant to causeconsistent exceedances above national standards and the WHO guideline value. Monthlysampling of filtered (0.45 µm pore size or less) river water over the period of a year wouldprovide information on whether variations are significant in an operational sense. It is stressedthat analysis of unfiltered water is likely to produce highly variable results depending on theturbidity of the water since arsenic analysis usually involves acidification, and at any given timethe result will include suspended as well as dissolved arsenic.

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High arsenic concentrations recognized in many parts of Asia and elsewhere are dominantlyfound in groundwater, and many of the health consequences encountered have emerged

in relatively recent years as a result of the increased use of groundwater from tubewells fordrinking and irrigation. In terms of numbers of groundwater sources affected and populations atrisk problems are greatest in Bangladesh, but major problems have also been identified in India(West Bengal, and more recently Assam, Arunachal Pradesh, Bihar, Manipur, Meghalaya,Nagaland, Uttar Pradesh and Tripura), northern China, Vietnam, Taiwan, Thailand, Cambodia,Myanmar, and Nepal. Occasional high-arsenic groundwaters have also been found in Pakistan,although the occurrences there appear to be less widespread. High-arsenic groundwaters inaffected areas tend to be found in alluvial or deltaic aquifers or in inland basins. Hence, much ofthe distribution is linked to the occurrence of young (Quaternary) sediments in the region's largealluvial and deltaic plains (Bengal basin, Irrawaddy delta, Mekong valley, Red River delta, Indusplain, Yellow River plain). Although groundwater arsenic problems have been detected in somemiddle sections of the Indus and Mekong valleys, such problems have apparently not emergedin the lower reaches (deltaic areas). Whether this represents lack of testing or whether arsenicproblems do not occur there is as yet uncertain. However, the young Quaternary aquifers mostsusceptible to developing groundwater arsenic problems appear to be less used in these areasas a result of poor well yields or high groundwater salinity. Other Quaternary sedimentaryaquifers in Asia have not been investigated and so their arsenic status is unknown. Somelocalized groundwater arsenic problems relate to ore mineralization and mining activity (forexample peninsular Thailand; Madhya Pradesh, India).

One of the key hydrogeochemical advances of the last few years has been in the betterunderstanding of the diverse mechanisms of arsenic mobilization in groundwater, as well itsderivation from different mineral sources. The most important mineral sources in aquifers aremetal oxides (especially iron oxides) and sulfide minerals (especially pyrite, FeS2). Release ofarsenic from sediments to groundwater can be initiated as a result of the development ofreducing (anaerobic) conditions, leading to the desorption of arsenic from iron oxides andbreakdown of the oxides themselves. Such reducing conditions are commonly found infine-grained deltaic, alluvial, and lacustrine sediments.

Release of arsenic can also occur in groundwaters with high pH (>8) in oxidizing (aerobic)conditions. These tend to occur in arid and semiarid settings with pH increases resulting fromextensive mineral reaction and evaporation. High-arsenic groundwaters with this type ofassociation have not been reported in Quaternary aquifers in South and East Asia but are foundin some arid inland basins in the Americas (western United States, Mexico, Argentina).Analogous conditions could occur in some arid parts of the region, such as northern China orwestern Pakistan, but there is as yet no evidence for this.

Mobilization of arsenic in mineralized and mining areas is linked to the oxidation of sulfideminerals. Here, occurrences can affect both surface waters and groundwaters but the affectedareas are typically localized (a few kilometers around the mineralized zone) as a result of thenormally strong capacity of soils and aerobic sediments to adsorb arsenic.

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Despite this improved understanding of the occurrences and distribution of arsenic ingroundwater, there remains much uncertainty regarding the nature of the source, mobilization,and transport of the element in aquifers. It is only in the last few years that detailedhydrogeochemical investigations have been carried out in affected regions. Earlier responses towater-related arsenic problems typically involved engineering solutions or finding alternativewater sources, with little emphasis on research. It is worthy of note that, despite the majorepidemiological investigations that have been carried out in Taiwan since the discovery ofarsenic-related problems there in the 1960s, there has been little hydrogeochemical researchcarried out in the region. Even today, the aquifers of Taiwan are poorly documented and thearsenic occurrence little understood.

One of the important findings of recent detailed aquifer surveys has been the large degree ofspatial variability in arsenic concentrations, even over distances of a few hundred meters. Thismeans that predictability of arsenic concentrations on a local scale is poor (and probably willalways be so). Hence, blanket testing of individual wells in affected areas is necessary. This canbe a major task in countries like Bangladesh where the scale of contamination is large. There isalso uncertainty in the temporal variability of arsenic concentrations in groundwater as very littlegroundwater monitoring has been carried out. Some studies have noted unexpectedly largetemporal variations over various timescales but the supporting data are often sparse andinaccessible and so these reports cannot be relied upon. More controlled monitoring of affectedgroundwaters is required to determine the variability in the short term (daily), the medium term(seasonally), and the long term (years, decades).

The emerging arsenic problems have revealed the dangers of groundwater development withoutconsideration of water quality in tandem with water quantity. Understanding of the risk factorsinvolved in development of high-arsenic groundwaters has allowed targeting those aquifersperceived to be most susceptible to developing groundwater arsenic problems in recent years(for example Quaternary sediments in Cambodia, Myanmar, Nepal). However, the toxicity ofarsenic is such that it should also be given greater attention in other aquifers used for drinkingwater supply. There is an argument for routine testing for arsenic in all new wells provided inmajor groundwater development projects, regardless of aquifer type. Randomizedreconnaissance-scale sampling for arsenic is also recommended for existing public supply wellsin all aquifer types where no arsenic data currently exist in order to obtain basic statistics on thedistribution of arsenic concentrations. Groundwater development in previously unexploited butpotentially vulnerable young sedimentary aquifers needs to be preceded by detailedhydrogeological and hydrochemical investigations to ensure that groundwater will be ofsufficiently high and sustainable quality. The scale of investigations should be commensuratewith the scale of proposed development.

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Adsorption. Adherence of a chemical or compound to a solid surface.

Alluvial. Deposited by rivers.

Aquifer. Water-bearing rock formation.

Desorption. Release of a chemical or compound from a solid surface (opposite of adsorption).

Distal. Remote from the origin (for example sediments in lower reaches of a delta).

Geothermal. Pertaining to the internal heat of the earth. Geothermal zones are areas of highheat flow, where hot water or steam issue at the earth's surface. They are found close totectonic plate boundaries or associated with volcanic systems within plates. Heat sources forgeothermal systems may be from magmatism, metamorphism, or tectonic movements.

Pyrite. Iron sulfide (FeS2), also known as fool's gold. Occurs commonly in zones of oremineralization and in sediments in reducing conditions.

Quaternary. Period of geological time extending from about 2 million years ago to the presentday. Divided into the earliest period, the Pleistocene, and the subsequent Holocene (the last13,000 years). Strata of Quaternary age are very young on a geological timescale.

Mineralization. The presence of ore or non-ore minerals in host rocks, concentrated as veins, oras replacements of existing minerals or disseminated occurrences; typically gives rise to rockswith high concentrations of some of the rarer elements.

Redox reactions. Coupled chemical oxidation and reduction reactions involving the exchangeof electrons. Many elements have changeable redox states; in groundwater the most importantredox reactions involve the oxidation or reduction of iron and manganese, introduction orconsumption of nitrogen compounds (including nitrate), introduction or consumption of oxygen(including dissolved oxygen), and consumption of organic carbon.

Reducing conditions. Anaerobic conditions, formed where nearly all of the oxygen has beenconsumed by reactions such as oxidation of organic matter or of sulfide; reducing conditionscommonly occur in confined aquifers.

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Upadhyay, S. K. 1993. "Use of Groundwater Resources to Alleviate Poverty in Nepal: PolicyIssues." In: F. Kahnert and G. Levine, eds., Groundwater Irrigation and the Rural Poor: Optionsfor Development in the Gangetic Basin. World Bank, Washington, D.C.

van Geen, A., K. M. Ahmed, A. A. Seddique, and M. Shamsudduha. 2003. "CommunityWells to Mitigate the Arsenic Crisis in Bangladesh." Bulletin of the World Health Organization81:632–638.

van Geen, A., Y. Zheng, R. Versteeg, M. Stute, A. Horneman, R. Dhar, M. Steckler, A. Gelman,C. Small, H. Ahsan, J. H. Graziano, I. Hussain, and K. M. Ahmed. 2003. "Spatial Variability ofArsenic in 6000 Tube Wells in a 25 km2 Area of Bangladesh." Water Resources Research39:1140.

Wang, G. 1984. "Arsenic Poisoning from Drinking Water in Xinjiang." Chinese Journal ofPreventative Medicine 18:105–107.

Wang, G. Q., Y. Z. Huang, B. Y. Xiao, X. C. Qian, H. Yao, Y. Hu, Y. L. Gu, C. Zhang, and K. T. Liu.1997. "Toxicity from Water Containing Arsenic and Fluoride in Xinjiang." Fluoride 30:81–84.

Wang, L. and J. Huang. 1994. "Chronic Arsenism from Drinking Water in Some Areas ofXinjiang, China." In: J. O. Nriagu, ed., Arsenic in the Environment, Part II: Human Health andEcosystem Effects 159–172. New York: John Wiley.

WAPDA-EUAD (Water and Power Development Authority, Environment and Urban AffairsDivision). 1989. Booklet on Hydrogeological Map of Pakistan, 1:2,000,00 Scale. Lahore:Government of Pakistan, WAPDA-EUAD.

Williams, M. 1997. Mining-Related Arsenic Hazards: Thailand Case Study. Technical ReportWC/97/49. British Geological Survey.

Williams, M., F. Fordyce, A. Paijitprapapon, and P. Charoenchaisri. 1996. "ArsenicContamination in Surface Drainage and Groundwater in Part of the Southeast Asian Tin Belt,Nakhon Si Thammarat Province, Southern Thailand." Environmental Geology 27:16–33.

WRUD. 2001. Preliminary Study on Arsenic Contamination in Selected Areas of Myanmar.Report of the Water Resources Utilization Department, Ministry of Agriculture and Irrigation,Myanmar.

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1. This paper focuses on the operational responses to natural groundwatercontamination in affected countries of South and East Asia. The paper first outlinesthe health effects of arsenic ingested through water and the different recommendedpermissible values of maximum concentration of arsenic in drinking water, andpresents a critical analysis of the current status of epidemiological knowledge.

2. This is followed by a comprehensive presentation of the operational responsesimplemented to mitigate arsenic contamination in the study countries, and anassessment of such operational responses in the overall context of the watersupply sector. Finally, an attempt is made to highlight the political economy ofarsenic mitigation and to assess the options for addressing arsenic from thisperspective.

3. The paper also extracts the major lessons learned when implementing short-termand long-term mitigation measures in South and East Asian countries. These aredivided into technical, financial and economic, social and cultural, and institutionalissues, and are summarized in overview matrices in annex 2.

4. The outcome of the paper is a tool that aims to help decisionmakers in government,multilateral and bilateral institutions, nongovernmental organizations, academics,and water practitioners in general address arsenic contamination of groundwater. Bybringing together information from a variety of sources, including published andunpublished literature, results of a specially administered survey, and outcomes ofa regional workshop held in Kathmandu in 2004, the paper collates, synthesizes,and makes accessible the vast range of arsenic-related information currentlyavailable in order to inform and facilitate concrete operational responses to thearsenic issue.

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Natural arsenic contamination of groundwater affects a number of countries worldwide, andspecifically in South and East Asia. This paper first reviews the operational responses to

natural arsenic contamination of groundwater in Asian countries that have hitherto beendeveloped and carried out; second, it analyzes the success and failure of these responses; andthird, it presents practical guidance for stakeholders, at either the country or project level, tobetter address the arsenic issue. This is critical since governments, the World Bank, and otherdevelopment partners implement water projects in this region and are responsible for providingsafe drinking water. Stakeholders need to be aware of this contamination, have tools to identify it,and have practical information to provide a proactive response or, where the contamination hasbeen identified at a later stage, a reactive response.

The countries in South and East Asia so far identified as affected by natural arseniccontamination of groundwater are Bangladesh, Cambodia, China (including Taiwan), India, LaoPeople's Democratic Republic (PDR), Myanmar, Nepal, Pakistan, and Vietnam.

This paper deals with natural arsenic contamination rather than contamination of mining andgeothermal origins, and with rural rather than urban areas. The focus on natural contamination,which is due to the release of arsenic from sediment to water, stems from the fact that thiscontamination is still unpredictable, and is thus far more difficult to address than contaminationof mining and geothermal origin. Similarly, contamination in rural areas presents a greaterchallenge than that faced in more compact urban areas.

The operational responses to deal with arsenic that have been implemented to date includescreening of tubewells, identification and treatment of those affected by contamination, sharing ofarsenic-safe wells, awareness raising, and development of alternative water provision through,for instance, dug wells, pond sand filters, rainwater harvesting, arsenic removal plants, andtapping deep groundwater.

The paper is structured in four chapters. Chapter 1 presents the health effects and therecommended maximum permissible values of arsenic in water. A critical analysis is providedregarding the lack of epidemiological studies on the health effects of arsenic and the currentuncertainty regarding safe levels of arsenic in drinking water.

Chapter 2 presents the operational responses implemented in South and East Asian countries. Anassessment is made of the lessons learned and the remaining issues on which no conclusions canyet been drawn.

Chapter 3 discusses arsenic mitigation in the overall context of water supply, including ananalysis of the priority accorded to arsenic contamination.

Chapter 4 analyzes incentives for stakeholders to be active (or inactive) in implementingoperational responses to arsenic contamination. These incentives influence the political economyand are drawn from the lessons learned and other issues analyzed in chapter 2. Due to the largenumber of countries affected, and recognizing that the political economy varies from country tocountry, this paper does not address political economy in depth for each individual country butrather discusses incentives generally.

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Arsenic is a substance that is carcinogenic – capable of causing cancer. Organic arseniccompounds are less toxic than inorganic compounds, the latter being more commonly found

in natural arsenic water contamination. The recommended standards for the maximumacceptable dose of arsenic are based on health risks, but the lack of epidemiological data on lowdoses of exposure makes the health risks difficult to assess with certainty.

This chapter presents international and national standards for arsenic intake in drinking andirrigation water; the major assumptions regarding the interpretation of epidemiological data usedto assess the recommended maximum permissible values and standards; the major healtheffects of arsenic; the status of the debate on arsenic intake from the food chain; and the effectsof trace elements on reducing or increasing arsenic toxicity.

International and National Standards for Arsenic Intake

Regarding arsenic concentration in irrigation water, neither international agencies nor individualcountries propose any recommended maximum permissible values. For drinking water, however,due to the carcinogenic nature of the substance, the World Health Organization (WHO) has issueda provisional guideline recommending a maximum permissible arsenic concentration of 10 µg L-1

(micrograms per liter). WHO guidelines are meant to be used as a basis for setting nationalstandards to ensure the safety of public water supplies and the guideline values recommendedare not mandatory limits. Such limits are meant to be set by national authorities, considering localenvironmental, social, economic, and cultural conditions.

Most developed countries have adopted the provisional guideline value as a national standard forarsenic in drinking water. On the other hand, most developing countries still use the formerWHO-recommended concentration of 50 µg L-1 as their national standard. Table 1 uses a sampleof countries to illustrate the range of values adopted (7 µg L-1 to 50 µg L-1).

103102 Table 1. Currently Accepted National Standards of Selected Countries for Arsenic in Drinking Water

Country/region Standard: µg L-1 Country Standard: µg L-1

Australia (1997) 7 Bangladesh (1997) 50

European Union (1998) 10 Cambodia 50

Japan (1993) 10 China 50

USA (2002) 10 India 50

Vietnam 10 Lao PDR (1999) 50

Canada 25 Myanmar 50

Nepal 50

Pakistan 50

Source: Ahmed 2003.

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The fact that some countries have adopted the recommended maximum permissible value of 10µg L-1 while others still use a value of 50 µg L-1 is related to the chronology of recommendedmaximum permissible values proposed by the WHO (table 2). In 1993 the WHO recommendedlowering the maximum permissible value from 50 µg L-1 to 10 µg L-1 as a precautionary measurebecause of the carcinogenic effects of arsenic, especially regarding internal cancers. So far mostdeveloped countries have adopted this new recommended value as a national standard (table 1).

Most developing countries, however, have not lowered their national standards because they feelthey could not afford the associated economic costs, including treatment and monitoring costs.For further discussion of this issue see Paper 4.

The United States Environmental Protection Agency (EPA) conducted an economic study withconcentrations of 3, 5, 10, and 20 µg L-1 and found that, given the conditions prevailing in theUnited States of America, the recommended maximum permissible value of 10 µg L-1 representedthe best trade-off among health risks, the ability of people to pay for safe water, and theavailability of water treatment technology. The standard of 10 µg L-1 will be further lowered astreatment technology becomes more affordable. The WHO-recommended maximum permissiblevalue for carcinogenic substances is usually related to acceptable health risk, defined as thatoccurring when the excess lifetime risk for cancer equals 10-5 (that is, 1 person in 100,000).However, in the case of arsenic, the EPA estimates that this risk would mean a standard as lowas 0.17 µg L-1 (Ahmed 2003), which is considered far too expensive even for industrial countriesto achieve.

The health risks used in the EPA estimate were based on data from an epidemiological studyconducted in Taiwan. Since the study only considered the risk of skin cancer and lacked data oninternal cancers, and because of several conservative assumptions in the EPA model, the healthrisks may have been underestimated. On the other hand, the actual rate of skin cancer may beoverestimated because of possible simultaneous exposure to other carcinogenic compounds(Ahmed 2003).

Even though the exact health effects of an arsenic concentration of 50 µg L-1 have not beenquantified, many correlations between internal cancer and low concentration of arsenic have been

Table 2. Chronology of Recommended WHO Values for Arsenic in Drinking Water

1958 First WHO International Drinking Water Standard: 200 µg L-1

1963 WHO recommend lowering guide value to 50 µg L-1

1974, 1984 Affirmation of 50 µg L-1 as guide value

1984 WHO Guidelines replace International Drinking Water Standard, providing abasis for national standards by individual countries

1993 WHO provisional guideline recommends lowering guide value to 10 µg L-1

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found. Therefore it is important that localized epidemiological studies are carried out in a strategicmanner, to more clearly inform decisionmakers.

Major Limitations of Existing Epidemiological Studies

Humans are exposed to different forms of arsenic from the atmosphere, food, and water. Animportant distinction needs to be made between inorganic and organic arsenic, inorganic arsenicbeing the carcinogenic form, though organic arsenic also has adverse health effects. Inorganicarsenic is the only form that occurs in water, and is therefore the focus of this study.1 The studyof kinetics and metabolisms of arsenicals in humans is complex due to the following issues(ATSDR 2002):

• Physicochemical properties and bioavailability vary with form of arsenic.• There are many routes of exposure (inhalation, ingestion, and dermal).• The intake of arsenic can be either acute or chronic.• Length of exposure can be short, medium, or long term.• The differing susceptibility to arsenic between humans and animals makes the quantitative

dose response data from animals unreliable for determining levels of significant humanexposure.

This paper focuses on the human health effects of chronic exposure to arsenic by ingestion. Thisfocus has been chosen as the main source of arsenic poisoning is through contaminatedgroundwater, and the secondary source is through the food chain.

In the literature, the health effects of arsenic have been estimated from data from various regions(for example Australia, Argentina, Chile, Taiwan). Nevertheless, clear linkages between a givenconcentration of arsenic in drinking water and its health effects are difficult because of thefollowing issues:

• In most cases of ingestion, the chemical forms of arsenic are unknown.• Most studies do not consider the volume of drinking water consumed.• Most studies do not report the temporal variations of the concentration of arsenic in the

source over a long period.• There is a lack of data about the relative importance of arsenic intake from sources other than

drinking water, in particular from the food chain.

Because of these issues, it is difficult to assess the exact health effects for a particularconcentration of arsenic in groundwater. The available epidemiological studies present the healtheffects based on the exposure dose of arsenic, which is defined as the quantity of arsenic that isingested per kg of weight per day and can be calculated according to equation 1.

1 See Paper 1 regarding organic and inorganic arsenic and the oxidation state of inorganic arsenic.

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Equation 1. Health Effects of Arsenic Exposure Dose

ED = C * DI BW

Where:ED = exposure dose (mg kg-1 day-1)C = exposure concentration (mg L-1)DI = daily intake of water (L day-1)BW = body weight (kg)

When estimating exposure dose one of the usual assumptions is that daily water intake is 2 liters(Ahmed 2003; ATSDR 2002; WHO 2001b). However, based on the literature reviewed, daily intakein rural areas tends to be higher, and varies from 3 to 5 liters (Ahmed 2003; Masud 2000).Importantly, health risk estimations increase as daily intake increases.

It appears that improved nutrition increases tolerance to arsenic contamination. For example, insome arsenic-affected villages of West Bengal in India, families with access to nutritious foodshow almost no arsenical skin lesions compared with undernourished families, despite the factthat both are consuming the same arsenic-contaminated water. Hence the poor, who are morelikely to be malnourished, tend to be most affected by arsenic contamination.

In summary, existing epidemiological studies are still often based on simplifying assumptionsthat introduce a number of uncertainties when quantifying the relationship between theconcentration of arsenic and health effects.

Major Health Effects

This section focuses on the major health effects of arsenic, which include skin lesions, blackfootdisease, diabetes, hypertension, skin cancers, and internal cancers. In annex 5 a detailed matrixof the health effects is provided with (when available) the exposure dose and the concentration ofarsenic based on equation 1 with sensitivity analysis of the daily water intake (2, 3, and 5 liters).

Arsenic has various health effects ranging from arsenicosis to skin cancers and internal cancers.However, so far there is still no widely accepted definition of what constitutes arsenicosis, theterm used for the pattern of skin changes that occurs after chronic ingestion of arsenic. Theseskin changes are usually the first symptoms to appear in the presence of high concentrations ofarsenic in drinking water. However, two epidemiological studies of chronic ingestion suggest thatthese lesions could appear for concentrations lower than 100 µg L-1. Another primary noncancerhealth effect is blackfoot disease, which was first observed in Taiwan. This peripheral vasculardisease leads, eventually, to a dry gangrene and the spontaneous amputation of affectedextremities (Kaufmann and others 2001).

The cancer effects of chronic exposure to arsenic through drinking water include skin cancersand internal cancers (lung, bladder, and kidney). In 1988 the EPA estimated that in the United

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States chronic ingestion of 50 µg L-1 results in a skin cancer rate of 1 in 400; in 1992, the EPAestimated that the internal cancer mortality risk is about 1.3 in 100 at 50 µg L-1. In 1999 the UnitedStates National Research Council (NRC) estimated the overall cancer mortality risk to be about1 in 100 at 50 µg L-1 (NRC 1999; Smith and others 2002).

Internal cancers are of primary concern since they account for most fatalities resulting fromchronic ingestion of arsenic through drinking water. Skin cancers are not usually fatal if they areidentified at an early stage, and their external symptoms make diagnosis more likely than withinternal cancers.

Arsenic Ingested through the Food Chain

The proportion of inorganic arsenic ingested through food may be significant, even when the arsenic

concentration of drinking water is higher than 50 µg L-1. For example, a recent study conducted in

Mexico (Del Razo and others 2002), where the concentration of arsenic in drinking water was as

high as 400 µg L-1, found that even so 30% of inorganic arsenic intake came from food.

The quantities of organic and inorganic arsenic in food should always be quantified, since the

form of arsenic affects its bioavailability and thus its toxicity to humans. Unlike water, where

arsenic is always inorganic, food can contain either organic or inorganic arsenic. Different studies

have found different proportions of organic and inorganic arsenic in food. For example, an EPA

study found the percentages of inorganic arsenic in rice, vegetables, and fruit to be 35%, 5%,

and 10% respectively (EPA 1988); a study conducted in West Bengal found the percentages of

inorganic arsenic in rice and vegetables to be 95% and 5% respectively (Roychowdhury,

Tokunaga, and Ando 2003); and another Bengali study found the percentage of inorganic arsenic

in rice to be 43.8% (Roychowdhury and others 2002). This wide range of values shows that the

total amount of arsenic (both organic and inorganic) in a food sample cannot be taken as an

accurate indication of the toxicity of the sample.

In soil irrigated with water having significant arsenic concentrations, higher concentrations of

arsenic were found in the peel or skin of the crops, while lower arsenic concentration were found

in the edible part of the raw crops. A study by Das and others (2004) found the arsenic content of

some vegetables to be greater than the recommended limit of 1 mg kg-1 set in the UnitedKingdom and Australia. Another concern regarding the use of contaminated water for irrigation isthe effect of arsenic on the yield, though this has as yet received little study. There is no currentprecise definition of what concentration of arsenic in irrigation water would have a quantifiableimpact on agriculture yield or on human health.

The amount of arsenic in food seems to be related to both the amount of arsenic in the waterused for cooking and the cooking process used. For example, a study (Roychowdhury and others2002) showed that the concentration of arsenic in cooked rice was higher than that in raw rice andabsorbed water combined, suggesting a chelating effect by rice grains. Due to water evaporation

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during the cooking process, the quantity of water used is important and this also affects theamount of arsenic in food. In addition, another study (Devesa and others 2001) reported notransformation of arsenic at temperatures up to 120°C. Thus, the boiling process used to cook thefood probably does not alter the chemical form of arsenic nor the amount of inorganic arsenic inthe food at the end of the cooking process (Del Razo and others 2002).

There is no standard maximum level of arsenic in food in South and East Asian countries. In the

United Kingdom and Australia the maximum food hygiene standard for the arsenic level in food is

1 mg of arsenic per kg (Warren and others 2003).

Studies related to the interaction of arsenic with other elements are limited. So far, most studies

have focused on fluoride, selenium, and zinc. The main findings are that (a) fluoride neither

increases nor decreases arsenic toxicity; (b) selenium and arsenic might reduce each other's

effects in the body; and (c) a deficit of zinc might increase the toxicity of arsenic. Thus it seems

that other elements may play a role in the effective toxicity of arsenic in drinking water.

So far, the intake of arsenic from food seems to depend more on the amount of arsenic in the

cooking water than in the water used for watering crops. However, research is still needed to fully

confirm that cooking water is more detrimental than irrigation water in the accumulation of arsenic

in the food chain.

Operational Responses of Countries in South and East Asia

The operational responses implemented thus far in South and East Asian countries are difficult to

compare because most of the information available is for South Asia, particularly Bangladesh,

Nepal, and West Bengal in India. Information related to East Asian countries is much more

difficult to find in international literature. Therefore, in order to collect more information on

operational responses in South and East Asian countries, the study team sent a questionnaire to

major stakeholders. The summary of the questionnaire responses is provided in annex 3. In

addition, in the context of the study, the World Bank/WSP Regional Operational Responses to

Arsenic Workshop was held in Nepal, 26–27 April 2004. The preliminary results of the study wereshared with 50 participants representing 7 out of the 11 countries facing arsenic contamination,as well as international organizations, donors, and researchers. The major information and datacollected are included in this report.

A summary of operational responses implemented in South and East Asian countries ispresented in annex 1.

Initial Responses towards Suspected Arsenic Contamination

Initial responses towards suspected arsenic contamination include well screening andidentification of water contamination in tubewells, switching from contaminated to arsenic-safe

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wells, painting of tubewells, awareness raising, and identification and treatment of arsenicosispatients. These responses are presented in more detail below. Each section outlines the stepsthat can be taken and, where available, the lessons learned from these mitigation measures.Most of the lessons learned are from Bangladesh, Nepal, and West Bengal (India), since theseare the cases for which most information is available.

Screening and Identification of Contamination Levels in Water Sources

BackgroundRegardless of the scale of arsenic contamination in water, there are two methods ofmeasurement: the field test kit, and laboratory chemical analysis.2 The field test measures aremore qualitative than quantitative. The choice of method for analysis depends on several criteria,including the precision of measurement required.

Choice of Screening MethodologyThere are two kinds of field test: those that provide a Yes or No answer and those that provide arange of concentration.3 The Yes/No field test does not provide useful information for furtheranalysis or for the implementation of mitigation measures. The field test that does provide arange of concentration is only appropriate in certain circumstances. Box 1 outlines parametersthat help to determine which test is appropriate, assuming that the laboratory test is efficient andsubject to quality assurance.

Quality assurance is necessary to ensure reliability of analysis within a particular laboratory, andconsistency of measurement between laboratories. Box 2 (see page 110) provides parameters toassess the capacity of a laboratory to perform analyses in order to facilitate quality assuranceimplementation and, ultimately, to provide accurate and usable data.

West Bengal in India is the only location where the screening of arsenic is conducted exclusivelyusing laboratory spectrometer analysis, thereby reducing the risk of a well being misclassified ascontaminated and thereby lost as a source of water.

Other Asian countries employ a mix of field testing and laboratory testing, or field testing only.With field tests there is a higher risk of well misclassification; this risk can be reduced through,for example, retesting contaminated wells or using multiple testing. For example, in Pakistan 10%of field tests are cross-checked using laboratory analysis; while in West Bengal 3% of thesamples analyzed with spectrometer are cross-checked with referenced laboratories using theatomic absorption spectrometer (AAS) (reported at Regional Workshop, Nepal, April 2004).

The only country that is planning large-scale monitoring of screened tubewells is Bangladesh, asstipulated in its National Arsenic Policy approved in March 2004. The National Arsenic Policy

2 A detailed description of field tests and laboratory analysis techniques is provided in Paper 3.3 The Yes/No field test kits do not provide any information on the range of concentration. The only information provided is whether theconcentration is higher or lower than the national standard of most Asian countries(50 µg L-1).

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Box 1. Comparison of Field Testing and Laboratory Analysis

Whether to use a field test kit or laboratory analysis is not always a clear-cut decision and must takeinto account a range of trade-offs related to the cost of the analysis, accuracy of the analysis, timeconstraints, logistical requirements, and training.

Cost of analysis. In Bangladesh, for example, the reported cost of laboratory chemical analysis isapproximately US$8.60 per analysis, while the price of a field test is approximately $0.50. However,in West Bengal, the price of laboratory analysis is approximately $1.60. Thus the difference in costbetween the field test kit and laboratory analysis varies in significance from country to country.

Capacity of laboratories (samples/month). Given that there are approximately 11 million tubewells inBangladesh, there are insufficient laboratories to analyze all samples. Regional laboratories inBangladesh have a capacity of about 300 samples per month, so additional screening has to bedone using the field test kit.

Time needed to process the analysis. The field test provides an immediate answer and, dependingon the brand, waiting time varies from 5 to 30 minutes (Kinniburgh and Kosmus 2002). The timerequired to conduct the chemical analysis will depend on the availability of laboratories near thesampling point and the time needed for actual analysis. This can take months, in contrast to theimmediate feedback to well owners provided by the field test kit.

Logistics. It is essential that samples are labeled properly and that the information on whether thewell is safe or unsafe is communicated to the communities in a short time and in a reliable manner.

Training. Field test kits are easy to use, so related training is far easier to conduct than that neededto ensure good-quality laboratory analysis. However, the number of people to be trained is higherfor field test kits than for laboratory analysis.

Opportunity for decentralization. The field test kit has considerable potential for decentralizationand community involvement in the identification of safe or contaminated wells. This communityinvolvement might be lost if only laboratory analysis is used.

makes provision for monitoring of 2% of the safe (green) tubewells every six months. However,there is no specification as to whether field or laboratory testing is to be used, or regarding theprocedures to ensure the reliability of water quality analyses.

Another issue to take into account in interpreting test results is seasonal variability. In Cambodia,for example, the major risk aquifer is connected to a river and arsenic levels recorded intubewells vary seasonally, with lower levels resulting from a wet-season influx of low-arsenicriver water into the aquifer (reported at Regional Workshop, Nepal, April 2004).

Choice of Scale of ScreeningThe screening of water sources can be conducted on a large scale (national, state level) oron a more localized scale (project level). In Bangladesh, West Bengal, and Nepal screeninghas so far been conducted on a large scale. In other countries where arsenic has beenidentified, for example Cambodia, Lao PDR, Myanmar, and Pakistan, screening has been

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Box 2. Parameters to Assess the Capacity of Laboratory Analysis

The main argument for the use of laboratory analysis rather than a field test kit is the reliability of theresults. However, if a given country has weak capacity for conducting chemical analysis, the valueadded from laboratory analysis could be negated. Therefore it is important to assess the capacity oflaboratory analysis, taking into account the following:

• The current availability of the equipment to conduct analyses.• The current status of the suppliers of this equipment.• The regular availability of equipment and materials, for example distilled water.• Whether the financing of equipment and supplies is from a central institution or is done at the

laboratory level. This could affect the length of time it takes for supplies to reach thelaboratories; in the worst case supply shortages could interrupt work.

• The current training program for laboratory staff, which should take into account availableposts in laboratories and staff turnover.

• Sampling and conservation of samples should follow accepted, standard procedures.• The procedures to ensure quality checks and laboratory certification have to be assessed. This

process of certification does not need to be nationwide; it could be carried out among smallerunits such as departments. An internal track record of these processes and all analysesperformed should be kept at each laboratory. When there is a procedure of certification the levelof transparency must be assessed.

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conducted on a small scale in some parts of the countries. So what are the criteria that helpassess whether the screening should be conducted on a national or local level?

When contamination is identified hydrogeologists and geochemists can, from the first results ofscreening, make certain assumptions about the potential scale of contamination based on thesize and level of use of the aquifer. This will enable them to give advice on the scale of furtherscreening (national, subnational, local) and on the design of the screening grid used to checkthese assumptions.

In Bangladesh the decision to adopt blanket screening was based on the heterogeneity of theaquifers, which meant that a base sample screening would not accurately represent the level ofarsenic contamination of tubewells used for drinking water. In Pakistan the screening is dividedinto three steps: (a) a sample base screening based on a grid of 10 km x 10 km; (b) furtherscreening using a smaller grid of 2.5 km x 2.5 km; and (c) a blanket screening of the hotspot(reported at Regional Workshop, Nepal, April 2004).

When an aquifer is discovered to be contaminated it is important to identify other vulnerableaquifers in the same area. Vulnerable aquifers are those that are naturally connected to thecontaminated aquifer, or are not separated and protected from contamination by animpermeable layer. Similarly, when an aquifer is separated from the contaminated aquifer by animpermeable layer it is not naturally vulnerable unless a connection is created, for examplethrough poor well construction.

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It is difficult to predict contamination rates when there is water flow from a contaminated to asafe aquifer. The first step is to assess the exact impact of the dilution effect, which affects therate at which arsenic concentration will increase and therefore reach the maximum permissiblelevel. It is difficult, however, to determine to what extent arsenic will react with the environment; itmay be adsorbed, or it may interfere in biological processes. As a result of these interactionsincrease in arsenic concentration may be delayed, although there is currently insufficientknowledge and data to correctly model these interactions and to accurately predict this delay.Therefore only the dilution effect is usually taken into account in such models, even though thismay result in an underestimation of the period of delay.

Among the factors deciding the scale of the screening is the level of priority accorded bygovernment to the issue of arsenic contamination. The incentives that lead stakeholders,including government, to be active or inactive are addressed in chapter 4. When an agency findsarsenic contamination during the course of a project it is important to define who is responsiblefor screening beyond the scope of the agency's own project and for implementing themitigation measures.

Institutional Arrangements for Arsenic Screening in Different CountriesIf the government decides to conduct a large-scale screening an institutional model needs to bechosen. So far in most countries two approaches have been applied. The first is to treat thescreening as a public good and the second is to consider the screening the responsibility of thetubewell owners. The first model is by far the most common. In this case government, usuallyassisted by nongovernmental organizations (NGOs) and international agencies, conducts thescreening. For example, in Bangladesh and Nepal the government is taking the lead, while inCambodia, Vietnam, Lao PDR, and China the United Nations Children's Fund (UNICEF) is themain international agency leading the screening. The second model, where screening is demandbased, has been applied in India, specifically in West Bengal. UNICEF and the state authoritiesof West Bengal screen all public tubewells, but private tubewell testing is the responsibility of theowner. Information on the availability of laboratories is provided and widely disseminated. So far,there is not enough information to determine whether one model is more efficient or effective thanthe other.

Remaining Issues and Lessons LearnedTechnical issues:• Regarding the choice between the field test kit and laboratory analysis, one option proposed

in the literature is to use the field test kit for large-scale screening and cross-check usinglaboratory analysis when the capacity assessment is satisfactory.

• The best way to reduce the risk of misclassification, for both the field test kit and thelaboratory, is to provide adequate training to ensure precise measurements, and to maximize,when possible, the number of repetitive analyses.

• Although there is a high degree of heterogeneity in arsenic concentration within a given area,correlation among neighboring wells can help identify some misclassification.

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• It is important to consider the scale of screening (large scale, project scale) in relation toother factors.

• Test for possible interference of field test kit results by other constituents of the water, whichmay account for some of the false positives and negatives.4

• The frequency of the screening is significant where there is high seasonal variability ofarsenic in tubewells, as in Cambodia.

• Screening should be conducted because arsenic is flavorless and odorless; the only way toidentify it is to test for it. In addition, if the measurement is wrong there is no simple way tobecome aware of the mistake.

Social and cultural issues:• The use of the field test kit tends to create curiosity and thus constitutes a tool for

awareness raising.

Economic issues:• The monitoring of screened wells is still an issue in many countries. After the initial screening,

should the priority be to screen all tubewells or only the safe ones? The rationale of retestinga contaminated well is to identify any misclassification, knowing that in some hotspots asafe tubewell could be the only source of arsenic-safe and bacteriologically safe water.Costs, however, are a significant factor, and the benefits of rescreening schemes need tobe assessed.

• For longer-term decision-making, universal sampling has certain benefits compared tosample-based screening. However, it is worth noting that one of the lessons learned inBangladesh is that if a well is not tested in a contaminated area and if people do not haveconvenient alternative solutions, they will use this well assuming that if it has not been testedthen it should be safe.

Institutional issues:• The choice of screening model (the public-good approach or demand-based screening).• The dissemination of data, both for screening conducted by government agencies and by

NGOs, is critical to ensure the transparency of information.

Summary RemarksThe following guidelines are applicable when deciding on the method of testing (field test orlaboratory analysis):

• If the field test kit is the method of screening then 3% to 10% of the samples should becross-checked with laboratory analysis.

• The capacity of laboratory analysis should be assessed to ensure that quality assurance

is implemented.

4 False positives have an actual concentration lower than 50 µg L-1, but are falsely labeled unsafe as the field test shows a concentrationhigher than 50 µg L-1. False negatives have an actual concentration higher than 50 µg L-1, but are falsely labeled safe as the field testshows a concentration lower than 50 µg L-1.

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• If using large-scale screening, the first screening could use a large grid with a few samples,but with adequate regional distribution to enable hydrogeologists and geochemists to identifycontaminated and vulnerable aquifers. These results would provide a first approximation ofwhere the hotspots are situated and which zones should be prioritized to conduct a moreprecise screening and to implement mitigation measures.

• Although not operationalized in the sample of countries that are the subject of this study, amonitoring plan is of utmost importance.

Well Switching, Painting of Tube Wells, and Awareness

BackgroundWhen screening is conducted and arsenic-contaminated wells (those with levels above theaccepted standard) are identified, the first step to mitigate the local population's exposure mightbe sharing of safe tubewells. Therefore, awareness campaigns need to make clear how torecognize safe tubewells. So far arsenic screening accompanied by the physical marking of safeor contaminated tubewells takes place in Bangladesh, Cambodia, Nepal, Pakistan, and WestBengal in India. A tubewell is considered unsafe if its concentration of arsenic is higher than thenational standard.

So far, all the countries that have marked tubewells have done so in different ways. InBangladesh, Cambodia, and Pakistan, the spouts of the contaminated tubewells are painted inred if the concentration of arsenic is higher than 50 µg L-1 (the national standard) and in green ifthe concentration of arsenic is lower than 50 µg L-1. In Nepal, a cross (X) is painted on thetubewell if the concentration is higher than 50 µg L-1 and a check (v) is painted if the concentrationof arsenic is lower than 50 µg L-1. In West Bengal, it was decided that confusion could best beavoided by marking only the safe tubewells; those with a concentration of arsenic lower than50 µg L-1 (the national standard) are painted in blue.

Widening Awareness of Water QualityThere is a need to make sure that communities use only safe tubewells. Many countries haveincreasingly developed groundwater supplies because of the poor bacteriological quality ofsurface water, a common problem in the surveyed countries. The use of groundwater reduces therisk of waterborne disease, but has brought with it the need to explain clearly that the cleanwater from some tubewells contains poison that can neither be seen nor tasted.

In order to avoid confusion among communities, people should be informed that clear and cleanwater might be contaminated with arsenic. In Bangladesh and in West Bengal in India UNICEFhas developed a well-researched information package. Other materials have also beendeveloped by the Bangladesh Arsenic Mitigation Water Supply Project (BAMWSP) and NGOs. Allmaterials are used widely. In Nepal the National Arsenic Steering Committee (NASC) hasdeveloped a standard information package to help clarify the sometimes contradictory messagesrelated to bacteriological and arsenic contamination of water. However, there is still further needfor the development of awareness campaigns on poor water quality.

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Participants at the Regional Arsenic Workshop emphasized the need to ensure that awarenesscampaigns use community-specific communication methods. In Cambodia, for example,awareness campaigns use puppets, a popular form of entertainment in the country.

Remaining Issues and Lessons Learned

Social and cultural issues:

• It has been widely disseminated that dug wells are less arsenic-contaminated than

tubewells; therefore some people think that the problem is associated with the technology

being used. As a result, there is a possibility that some people may conclude that the

problem is not in the groundwater quality per se but that it is associated with their tubewell

and the way to fix it would be to purchase another handpump.

• Since most wells are privately owned, neighbors may be reluctant to share. In addition, most

tubewells are situated in the courtyard of houses so there is a privacy issue. Sharing of

arsenic-safe wells as a solution can therefore not be taken for granted.

• If the density of users at each well increases, some people are afraid that their tubewells will

become arsenic contaminated as well.

• The complaints related to sharing safe tubewells include excessive wear on equipment; new

users do not clean up after themselves; and people come at late hours. In some hotspots

there are simply not enough safe tubewells to meet demand for drinking water.

• When people say they have no other water source, they may actually mean that they have no

other tolerable source. Sharing is perceived as a reduction in the quality of life.

• Women, who traditionally collect water, might not be allowed in some places to leave their

immediate household unaccompanied.

• In Bangladesh the choice of red to indicate arsenic contamination seems, in some cases, to

be confused with iron precipitation, which leaves an orange-red color.

• Awareness campaigns must explain clearly that arsenic is not a germ that can be killed by

boiling water.

• In some places people are having difficulty distinguishing arsenic-related skin discoloration

from other skin diseases or infections.

• Color and sign interpretation of marked tubewells is a new concept for some people.

• Repetition is important, because experience shows that memory and motivation fade

in time.

• In many countries the identification of arsenic implies an increase of collection distance and

time due to the change in water source; therefore women's work load increases substantially.

This also needs to be factored into the provision of arsenic-safe water.

• Awareness campaigns should be carried out regularly and not only at the time of screening.

• For years groundwater has been presented as the "safe" source of water; thus the arsenic-

related message contradicts conventional wisdom about safe water. However, the awareness

campaign related to poor surface water quality should not stop because of the more recent

problem of arsenic contamination.

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Technical issues:• Tubewells should be retested and repainted regularly, since painting can be altered during

the rainy season.

Summary RemarksWhen arsenic is identified, ensure that safe tubewells are marked and that the choice of color ormarks is understandable to communities. Whether unsafe tubewells should be marked or not isstill an open question; the consensus seems to be that in the case of blanket screening thepreferable approach is to mark the unsafe tubewells, while in the case of sample base screeningit may be preferable not to mark unsafe tubewells.5

Awareness campaigns should address arsenic contamination, but also maintain awareness aboutpoor surface water quality. There is a need to address both quality problems and not substituteawareness of the health risks due to arsenic for awareness of the risks related to poor surfacewater quality. In addition, the awareness campaign should use community-specificcommunication methods in order to reach the maximum of people in the community.

Patient Identification

BackgroundPatient identification, also called case finding, may be passive or active. Passive patientidentification is simply allowing individuals to present themselves for treatment, while activepatient identification involves going out to the field to examine individuals for signs of arsenic-related disease.

In Bangladesh and Nepal patient identification is often carried out during tubewell screening.Although arsenic can cause a variety of health conditions, most patient identification has beenbased on skin lesion-related symptoms.

In West Bengal patient identification is mainly passive, although the Joint Plan of Action, betweenthe state and UNICEF, has initiated an epidemiology survey. The first step is the training ofdoctors and NGOs to properly identify patients and to suggest appropriate mitigation measures;active identification has also been suggested.

Training of Testers in Patient IdentificationWhen patient identification is carried out alongside tubewell testing, the testers must be providedwith sufficient training to distinguish between skin lesions related to arsenic ingestion and otherskin lesions, bearing in mind that (a) there is still no universally agreed case definition ofarsenicosis disease; and (b) the actual extent to which exposed persons will develop skinlesions and other arsenic-related conditions is difficult to predict. Therefore the capacity buildingof testers and health workers is critical to ensure reliable patient identification.

5 Blanket screening means that 100% of the tubewells in a given region are tested. Sample base screening means that a selection oftubewells is screened and from that data conclusions are drawn as to the levels of contamination in the other tubewells.

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Identification Based on Skin Lesions and on Laboratory AnalysisSome people are subclinically affected by arsenic even though they do not show skin lesions.For example, in contaminated areas in Bangladesh, some studies have shown that children andadults without skin lesions at present may have high concentration of arsenic in their hair, nail,and urine samples. Therefore, patient identification based solely on the presence of skin lesionsmay underestimate actual numbers affected by arsenic.

However, identification of arsenic-affected patients using laboratory analysis of nail, blood, andhair samples is very expensive and requires strong laboratory capacity, and implementation on alarge scale is not generally feasible.

Current Estimate and Projections of Number of Arsenicosis PatientsThe current estimates of the number of patients with arsenicosis in South and East Asiancountries is summarized in table 3. A review of studies conducted in parts of the world other thanAsia projects that, if the at-risk population continues to drink arsenic-contaminated water,between 16% and 21% of the population will be affected (WHO 2001a). This projection is basedon the assumption that the estimation of the population at risk is accurate, the clinical case

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Table 3. Current Population at Risk in Asian Countries

Region/country Present estimation Number of arsenicosis Year of firstof number at risk in patients identified discoverymillions (% of total so far

population)

East AsiaCambodia Max. 0.3 (2.7%) - 2000

China 3 (0.2%) 522,566 1980s

Lao PDR - - -

Myanmar 5 (10%) - 1999

Taiwan 0.2 - 1960s

Vietnam 11 (13.7%) - 1998

South AsiaBangladesh 35 (28%) 10,000 (partial results) 1993

India (West Bengal) 5 (6.25%) 200,000 1978

Nepal 0.3 (3.4%) 8,600 1999

Pakistan - 242 cases per 2000100,000 peoplebased on the resultsof 10 districts

- Not available.Sources: Bhattacharya 2002; Ng, Wang, and Shraim 2003; Kinniburgh and Kosmus 2002; WHO 2001a; Smith, Lingas, and Rahman 2000;Berg and others 2001; information reported at Regional Workshop, Nepal, April 2004.

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recognition is accurate, and survey results of other regions can be generalized. However, the16–21% estimate has no reliable statistical confidence intervals. For example, in Bangladesh astudy conducted by the Massachusetts Institute of Technology estimated the arsenic healthburden through a model of dose-response function (Yu, Harvey, and Harvey 2003). The studypredicted that long-term exposure will result in approximately 1.2 million cases ofhyperpigmentation, 600,000 cases of keratosis, 125,000 cases of skin cancer, and 3,000 fatalitiesper year from internal cancer. Another estimate of the arsenic-related health burden inBangladesh concluded that the total risk of cancer would be equal to 375,000 affected people(Ahmed 2003). So far, these two figures are the only quantification of the potential arsenic-relatedhealth burden. They depend heavily on epidemiological assumptions and demonstrate how the lackof reliable epidemiological information adds uncertainties to the projected number of people at risk.

Lessons Learned and Remaining IssuesSocial issues:• Gender sensitivity: In Bangladesh, for example, each team engaged in tubewell screening

and patient identification surveys includes at least two females.• Actively include information that arsenicosis is not contagious to ensure that the community

will not stigmatize arsenicosis patients due to misinformation.

Economic issues:• Patient identification and medical referrals, along with public education, should be integrated

into all tubewell testing efforts. This seems to be the most cost-effective way to activelyidentify arsenicosis sufferers.

• Identification of arsenic-affected patients is generally based on the skin effects, which arenot necessarily the first symptoms. However, identification based on laboratory analyses istoo expensive to be implemented at large scale.

• Arsenic can cause a variety of health conditions, thus there is still the issue of identificationof those patients who do not develop skin lesions. The cost of the epidemiological surveyrequired to identify all such patients would be prohibitive. However, such studies could beconducted on a small scale in order to allow estimates of the scope of the arsenic problem ina country or region within a country.

• The most efficient way to conduct a nationwide survey is in conjunction with an existingpopulation program.

Technical issues:• There is a need to ensure proper training of tubewell testers and health workers so that they

can distinguish between the skin lesions resulting from arsenic exposure and other skinlesions.

• Standardized criteria for diagnosing and grading skin lesions must be developed andcarefully followed. The WHO is leading an effort to develop such criteria. When finalized theyshould be widely used by government institutions and by all organizations engaged in casefinding, treatment, and surveillance.

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Summary RemarksThere is a clear need to improve information about the epidemiology in arsenic-affectedpopulations. This needs to happen in a strategic manner, and can be achieved by combiningpatient identification with well screening. At the same time, targeted epidemiological studiesneed to be carried out in order to supply data to assist arsenic mitigation activities inAsian countries.

Treatment Management of Arsenicosis Patients

BackgroundAlthough a number of clinical treatments have been advocated, there is no universal medicaltreatment for chronic arsenicosis. The only measure that will prevent future damage is to supplythe patient with drinking water that is free from arsenic and, if it is administered at an early stage,it seems to remedy past damage caused by arsenic. The first priority should be to removepeople from the source of exposure and then follow up with symptomatic management. To date,there are no well-designed studies to show whether cessation of exposure leads to improvementin skin keratoses. However, anecdotal interviews of patients suggest that mild to moderatekeratosis improves with cessation of exposure.

Chelation, which is often presented as a treatment of arsenicosis, has been proven effectivemainly in cases of acute poisoning. The principle of chelation therapy is to provide thepatient with a chemical to which arsenic binds strongly, and which is then excreted in urine.The provision of such treatment could remove large stores of arsenic (from acute exposure)from the body in a matter of hours. However, although chelation might have a positive resultin some patients with chronic poisoning, so far there is no complete study that assesses itseffectiveness for chronic exposure. In addition, it is difficult to ascertain to what extentimprovement in skin lesions after chelation therapy is attributable to the therapy, and towhat extent it is attributable to cessation of exposure. Therefore, patient improvement afterchelation therapy does not provide sufficient evidence of its effectiveness (Kaufmann andothers 2001; NRC 1999).

Evidence from Taiwan suggests that some nutritional factors may reduce cancer risks associatedwith arsenic. It has been proposed that providing vitamins and improving diet may be of benefitto patients. In particular, vitamin A is known to be beneficial in the differentiation of varioustissues, particularly the skin. If the doses given are not excessive, there are other nutritionalbenefits to be gained. Thus, it is recommended that all patients with skin lesions be givenmultivitamin tablets and that research projects be undertaken to establish whether or not they areeffective for patients with arsenicosis (NRC 1999).

Arsenic is a probable contributor to causation of diabetes mellitus and hypertension. For thisreason, urinary or blood glucose and blood pressure should be tested in all patients witharsenicosis and appropriate treatment and monitoring should be started if necessary (Kaufmannand others 2001).

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In Bangladesh people identified with skin lesions are given vitamins and ointment. In WestBengal (India), under the Joint Plan of Action, a network of clinics will be set up at the district,

subdivision, and block level. At the same time, in both countries, studies are being conducted to

provide a better estimation of the arsenic impact on human health.

Remaining Issues and Lessons LearnedSocial issues:

• The fact that arsenicosis is not treatable with folk remedies should be emphasized inawareness campaigns (Some of the scarce literature on social issues regarding arsenic

suggests that some people may spend a considerable portion of their income trying to find a

homemade cure).• The fact that the only way to prevent arsenic contamination is not to drink contaminated

water should be emphasized in awareness programs.

• Ensure that treatment protocols are easy to follow.• Ensure that people are informed about the fact that arsenicosis is not contagious.

Technical issues:

• Awareness campaigns should stress that chelation cannot be viewed as a successful

treatment while exposure to arsenic-contaminated water continues.

• Advanced keratoses are extremely debilitating and complications such as superimposed

fungal infections may cause serious problems. Providing moisturizing lotions and treatment

for infections may be beneficial and should be part of routine care in advanced cases.

• Arsenic has adverse health effects other than skin lesions, such as diabetes, and these

diseases have to be treated as well.

• In remote rural areas clinics, equipment, and expertise are generally unavailable, so training

of health workers should be conducted to help patients in the absence of effective treatment.

However, in some countries health and population sector programs might not have the

capacity to conduct the required nationwide training for all clinical workers within a short

period of time.

Institutional issues:• Health and water supply institutions need to work together since the major treatment for

arsenic is an alternative safe water source.

• Doctor absenteeism might be another important factor in some countries. For example, a

recent study conducted in Bangladesh estimated doctor absenteeism to be around 75% in

rural areas (Chaudhury and Hammer 2003). This is a critical issue, especially if health workers

do not have adequate training to help patients affected by arsenic contamination.

Summary RemarksThe preferable approach is to ensure that identified patients have follow-up treatment in the local

health institution. The capacity building of health workers in remote rural areas is critical and

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health and water sector professionals need to work together to make sure that people haveaccess to information and to medicines.

Longer-Term Responses

Longer-term responses are institutional and technical. The institutional aspects are mainly relatedto the country's arsenic policy and strategies. Technical longer-term responses can be dividedinto two types based on the source of water: surface water and groundwater. Surface waterresponses include pond sand filters, rainwater harvesting, and piped water supply. Groundwaterresponses include dug wells, deep tubewells, piped water supply, and arsenic removaltreatment plants.

Institutional Longer-Term Responses (Arsenic Country Policy)

BackgroundA country can respond to arsenic contamination by establishing an arsenic policy and/or strategy.The objective is to provide overall direction and guidance for dealing with arsenic and to setpriorities for operational responses in the short, medium, and long terms.

So far, Bangladesh is the only country to have adopted a national arsenic policy (March 2004) andto have developed a detailed plan of action. The policy seeks to identify the nature and extent ofthe problem through screening and patient identification and to provide guidelines for mitigationof arsenic contamination through (a) public awareness; (b) provision of arsenic-safe water supplywith a preference for surface water over groundwater, and the promotion of piped water supplywhen feasible; (c) diagnosis and management of patients; and (d) capacity building at all levels(from government to local communities). The arsenic policy also recommends mapping of thecountry's deep aquifer to ensure that deep wells will be built in regions where deep groundwateris separated from the shallow aquifers by a substantial impervious layer.

In Nepal the National Arsenic Steering Committee (NASC) is chiefly responsible for arsenicstrategy. It has formulated national guidelines, which detail the steps to be taken to addressarsenic contamination of groundwater and stipulate how safe and unsafe tubewells are to bemarked. The NASC has also produced a standard set of information, education, andcommunication materials for awareness promotion within the community.

In Cambodia a recently established arsenic committee is working closely with UNICEF and anumber of NGOs. The committee organizes screening of tubewells and provides differentstakeholders with field test kits. In Pakistan, UNICEF is also working closely with the provinces inthe screening of tubewells and other water sources.

In India, in 1999, UNICEF entered into a strategic alliance with the government of West Bengalthrough a Joint Plan of Action, which incorporates the following: (a) a community-based watermonitoring system; (b) alternative technologies for supply of arsenic-free water (including arsenic

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removal at the household level and piped water supply); (c) health surveillance, patientidentification, and early treatment programs; (d) awareness campaigns; (e) research on arsenichealth effects in women and children; (f) networking and information sharing among stakeholders;and (g) monitoring mechanisms at all levels. The Joint Plan of Action effectively constitutes astrategy to deal with arsenic contamination in the short and long term.

Summary RemarksIt is important for relevant institutions to have short-term and long-term strategies for dealing witharsenic contamination. As is apparent in South Asia, no single strategy is applicable to allcountries or localities. In Bangladesh and Nepal the government, in collaboration with a variety ofstakeholders, is the focus of strategy, while in West Bengal the choice has been made toelaborate a plan in conjunction with an international agency, in this case UNICEF. Theseexperiences show that (a) there is now a body of information — as evidenced in this paper —that permits the design of such policies and strategies, despite continuing uncertainty aboutmany features of arsenic contamination; (b) more information is still needed to enable governmentsand other stakeholders to be more specific in defining proposed actions; and (c) policies andstrategies need to be flexible enough to incorporate any further information that will becomeavailable over time. The final challenge is to ensure that such policies or strategies are enforced.

Technical Longer-Term Responses Based on Surface Water

BackgroundLonger-term responses based on surface water include pond sand filters, rainwater harvesting,and piped water supply. Technical details for each of these operational responses are providedin Paper 3. This section focuses on the lessons learned and their implementation.

The pond sand filter technique is based on a filtration process by which water is purified bypassing it through a porous medium. Slow sand filtration uses a bed of fine sand through whichthe water slowly percolates downward.

In Bangladesh pond sand filter technology has been used for arsenic mitigation but the level ofacceptance has been low, due in part to doubts about the bacteriological quality of water. Onepond sand filter can supply the daily drinking and cooking water requirements for 40 to 60families. In the literature, Myanmar is the only other country in the study region using ponds as amitigation option for arsenic contamination.

Rainwater is used in many parts of the world to meet demand for fresh water. The principle is tocollect rainwater, either via a sheet material rooftop or a plastic sheet, and then divert it to astorage container. In the study region there have been reports of use of this technique fromBangladesh, Cambodia, and Taiwan.

Piped water supply can use surface water after simple water treatment. Generally, treatment isneeded to reduce turbidity and includes chlorination to protect against bacteriologicalcontamination of surface water. Bangladesh and India are employing the piped water option as a

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major component of their mitigation strategies, and Cambodia is also using this technique.Bangladesh is now embarking on a large pilot operation to implement piped village water supply.In India, in particular in West Bengal, this response has also been recommended on a larger scalefor multiple villages. In general, the level of acceptance for the piped water supply option is highbecause of its convenience.

Remaining Issues and Lessons LearnedPond sand filters – social and cultural issues:• The community should pledge involvement in operation and maintenance of the pond

sand filter.• Increasingly, in Bangladesh, ponds have become important sources of income because of

fish culture, so farmers are reluctant to give up their ponds for pond sand filter construction.• Some users have complained about the taste of water from this source.• Pond sand water is generally contaminated with pathogens. The bacteriological quality of

water fluctuates between a little over the WHO/Bangladesh standard to hundreds of timeshigher than that.

Pond sand filters – economic issues:• The initial capital cost of construction is high – about US$430-690, depending on the size of

the pond sand filter.

Pond sand filters – technical issues:• The selected pond should not be used for fish culture, watering and washing livestock, or

other domestic purposes, and should be protected from such activities.• The selected pond should be perennial.• The quality of water varies seasonally and is improved with the addition of bleaching

powder solution.

Rainwater harvesting – social issues:• Some users complain about the taste of the water.• It has been reported from Bangladesh that the return to rainwater harvesting may be viewed

as a step backwards to several decades ago when it was quite widely used.• In Cambodia rainwater harvesting has been practiced for a long time and is reported to be

well accepted.

Rainwater harvesting – economic issues:• In Bangladesh the cost of a rainwater harvesting system is an issue.• In addition, this solution does not cover the dry season, when another mitigation measure

must be used, adding to the cost.

Rainwater harvesting – technical issues:• Rainwater harvesting is a useful alternative to other sources, but in areas with a prolonged

dry season it can only be a partial solution.

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• Water quality is a concern: the first rain may flush impurities, including animal feces, offthe roof. Not storing the first rain and cleaning the roof reduces the risk of inadequatewater quality.

Piped water supply – social issues:

• This option functions best in larger villages where density is high enough to ensure viability.

• It is important to ensure that all people are connected, in particular the poorest segment ofthe population.

• Appropriate institutional arrangements for operation and maintenance of the system shouldbe in place.

Piped water supply – economic issues:• Affordability by different income groups within the community needs to be considered.• Operation and maintenance needs to be covered by the price of the service.

Piped water supply – technical issues:• A high level of skill is necessary for design and construction, and capacity building among

local artisans is an important consideration.• A high level of skill is also needed for operation and maintenance.• Permits monitoring of one single source for water quality rather than multiple sources in

one village.

Summary RemarksThis section has examined some of the advantages and disadvantages of the operationalresponses using surface water. Taking into account such factors, certain solutions may presentthemselves as the best trade-off between the range of options that may be applicable in a givensituation. However, care must be taken to devise solutions that address fully the goal ofproviding drinkable water, rather than addressing only the problems related to arseniccontamination. Table 4 (see page 124) summarizes the options.

Technical Longer-Term Responses Based on Groundwater

BackgroundThe longer-term responses based on groundwater include dug wells, deep tubewells, pipedwater supply, and arsenic removal filters or plants. The technical details of each of theseoperational responses are provided in Paper 3. This section focuses on lessons learned fromtheir implementation.

Dug wells are excavated below the water table until the incoming water exceeds the digger'sbailing rate. They are typically lined with stones, bricks, tiles, or other material to preventcollapse, and are covered with a cap of wood, stone, or concrete to prevent contamination fromthe surface. This option has been used in Bangladesh and Nepal. The UNICEF Plan of Actionproposes dug wells as a mitigation option in Myanmar.

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One major concern related to dug wells is that recent investigations show that some dug wellsare also contaminated with arsenic (APSU 2004). Indeed, some dug wells in Bangladesh, China,Myanmar, and Nepal have been found to have arsenic contamination.

The deep aquifers in Bangladesh, West Bengal in India, and Nepal have been found free ofarsenic thus far. However, in other places, including China, deep groundwater has been found tobe even more contaminated with arsenic than shallow groundwater. This means thatmeasurement of the contamination level must be conducted before any exploitation of deepgroundwater. In the case of Bangladesh, the assumption is that the pre-Holocene aquifer hasbeen flushed and therefore all mobile arsenic has been leached from this aquifer, while in Chinathis process might not have taken place. A more detailed explanation is presented in Paper 1.

In Pakistan the preliminary findings of UNICEF screening showed no arsenic in the deepgroundwater, though the number of samples was limited (reported at Regional Workshop, Nepal,April 2004). In Cambodia the main issue related to use of the deep groundwater is the poor yield ofdeep tubewells, which adds significantly to the unit cost of the investment. In Cambodia the generalacceptance of rainwater harvesting makes it a viable alternative to use of deep groundwater.

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Table 4. Summary of Responses to Arsenic Contamination Based on Surface Water

Operational Advantages Disadvantagesresponses

Pond sand filter Technically easy to Poor bacteriological water qualityimplement Low service level

Complaints about the taste of waterSelected pond sand filter should be used onlyfor drinking water

Rainwater harvesting Technically easy to Poor bacteriological water quality when notimplement adequately maintained

Low service level

In some regions, cannot provide water for theentire year

Complaints about the taste of the water

Can only be a partial solution in areas withprolonged dry season

Piped water supply Adequate water quality High level of skill necessary for designwhen treatment is carried and constructionout correctly

Issues of operation and maintenance andSustainable source of management must be consideredsupply

Other issues include affordability and systemcoverage

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In Bangladesh and Nepal mapping of groundwater is being conducted to identify at which deptharsenic-safe groundwater is located and to identify where the shallow groundwater (Holoceneplain) is separated from the deep groundwater (Pleistocene terrace) by a clay layer. Theexistence of this clay protects deep groundwater from potential contamination by shallowgroundwater. So far, there is still no wide consensus on whether groundwater mapping should beconducted through geophysical investigations or on a case-by-case basis when drilling wells. InIndia the Central Groundwater Board has conducted research on the deep aquifer in West Bengal.Bangladesh, Nepal, and West Bengal already use deep groundwater as a mitigation option forarsenic contamination. UNICEF proposes use of deep groundwater in its Plan of Action for Myanmar.

In Bangladesh, as in several other countries, the debate centers on the following issues: whetherdeep groundwater should be used or not; the risk of arsenic-contaminated water leaking from theshallow to the deep aquifer; and what assurances there are that the deep aquifer sediments willnot also release arsenic into the water at some future point. One important way to handle allthese uncertainties is to strengthen groundwater management, which includes a monitoringprocess, regulation of deep groundwater exploitation, and a process of collecting and storingdata that would be helpful for further research on potential chemical contamination.

A detailed explanation of the different arsenic removal technologies is provided in Paper 3.Arsenic removal plants can be located at the household level or community level. At thehousehold level, the arsenic removal unit could be located in the house or attached to thetubewell. This mitigation measure has been implemented in Bangladesh, Nepal, Vietnam, andWest Bengal in India. UNICEF also proposes its implementation in Myanmar. However, concernhas been expressed in Cambodia that the unit may be difficult to maintain at the household level(reported at Regional Workshop, Nepal, April 2004). A pilot is currently being developed inBangladesh to investigate this concern.

Community arsenic removal plants can be useful for small villages and have been implementedin Bangladesh, India, Vietnam, and Taiwan. In general, the main issue on the technical side ishow to ensure the effectiveness of arsenic removal technologies in the field, and, on theinstitutional side, how to ensure large-scale implementation and sustainability.

Lessons Learned and Remaining IssuesDug wells – social and cultural issues:• In a number of areas issues of taste and odor, and the possibility of bacteriological

contamination, are hindering acceptance of dug well water for drinking.• Use of handpump technology can aid acceptance of the dug well but there have been

complaints about the smell associated with chlorination.

Dug wells – technical issues:

• Bacteriological contamination levels of dug well water are often unacceptable.

• Monitoring of arsenic contamination is needed, especially during the dry season.

• Use of dug well handpumps enables bacteriological quality to be improved and maintained

at an acceptable level by regular chlorination.

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• Proper lining and a well-designed apron are crucial for prevention of surface water contamination.

• The community should ensure that dug wells are kept in sanitary condition.

• Yield is reduced when the water table drops in the dry season or if abstraction is greater

than recharge.

Deep tubewells – social and cultural issues:

• Due to the cost of installation, deep tubewells are usually shared by several (or many)

households. This may mean that people have to walk long distances to collect safe water.

• The shortage of deep wells means that people have to wait a long time to get water.

Deep tubewells – economic issues:

• Initial capital cost is high, around US$700-800.

Deep tubewells – technical issues:

• Since there is no clear understanding so far of the processes by which arsenic is released

into water, there is still discussion as to whether deep groundwater will remain arsenic safe

after medium-term or long-term exploitation.6

• There is also the need to ensure that the correct technique for drilling deep tubewells is usedand that it taps the deep groundwater (not the shallow).

Deep tubewells – institutional issues:• Groundwater management must be implemented to ensure that deep tubewells are used only

for drinking and cooking purposes.

Piped water supply:• Issues are the same as those for piped water supply using surface water except that

treatment for bacteriological contamination is usually not necessary; however, arsenicremoval treatment may be necessary.

Arsenic removal filters at the household level – social and cultural issues:• The process is time consuming, and the smell and taste are not always good.• Water becomes warm after standing for the recommended time, and cold water is preferred for

drinking.• Too many water storage containers are required.• People are not in the habit of filtering their water.• The unit is not always easy to operate and maintain.• The advantage is that it allows rural households to continue using their handpumps.• There may be difficulties in obtaining the necessary chemicals.

Arsenic removal filters at the household level – economic issues:• The technology is expensive, and operation and maintenance costs may be high.

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6 This is in the case of countries where deep groundwater is not contaminated, such as Bangladesh and Nepal.

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Arsenic removal filters at the household level – technical issues:

• The concentration of remaining arsenic in some cases remains higher than the standard.

• When using alum treatment, the health risk of alum remaining in water is a concern.

• Monitoring is more difficult to conduct at the household level.

Arsenic removal filters at the community level – social and cultural issues:

• There is a need to organize responsibility for maintenance to ensure the sustainability of the

water treatment unit.

Arsenic removal filters at the community level – technical issues:

• Monitoring is easier to conduct at the community level than at the household level.

Arsenic removal filters at the community level – institutional issues:

• There needs to be a routine for checking that water is arsenic safe.

• If the source is surface water there should also be a process for checking its bacteriological

quality.

• Effective supply chains need to be developed for large-scale and sustainable solutions.

Local government should be involved in ensuring effective supply chains.

Table 5. Summary of Responses to Arsenic Contamination Based on Groundwater

Operational Advantages Disadvantagesresponses

Dug wells Technically easy to Poor bacteriological water qualityimplementcontamination Some dug wells might also have arsenic

Possible low level of acceptanceLow service level

Switch to safe Can provide potentially Difficult to predict whether the alternativeaquifer good water quality, but aquifer will become contaminated

needs to be monitoredPotential low level of service

Arsenic removal Good chance of Proven and sustainable option not yettechnology sustainability at the generally available at household level

community levelDifficult to monitor at household level Peopledo not always like the taste of the water

Operation and maintenance may becomplicated

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Summary RemarksTable 5 summarizes the advantages and disadvantages of each of the described operationalresponses, enabling an assessment of the trade-off most applicable to a given situation.However, some operational responses, while addressing the problems related to arseniccontamination, may give rise to water quality problems, and therefore do not address fully thetarget of providing drinkable water. Such partial solutions should be avoided whenever possible.

Dissemination of Information

Regional Arsenic Networks and National Databases

The development of a database provides stakeholders with access to information. Institutionally,

it is useful to ensure that data are stored following a specific process and are checked and

cleaned. Dissemination, accessibility, and transparency of data are critical for an issue as

sensitive as water contamination. Scientifically, a database provides a baseline that can aid

identification of a long-term trend. For example, the lack of a historical baseline in Bangladesh

means that it cannot be ascertained whether arsenic has always been present in the groundwater

or appeared only after exploitation of the aquifer.

In Bangladesh the National Arsenic Mitigation Information Center (NAMIC), a component of the

BAMWSP, is responsible for collecting data related to arsenic. NAMIC collects its own data under

the auspices of the BAMWSP and additional data from other stakeholders according to an agreed

format. Some of the data are provided online (www.bamwsp.org). In addition, NGO-Forum

provides a list of the major governmental agencies, international agencies, and NGOs that work in

arsenic contamination (www.naisu.info).

In Nepal, with the support of the United States Geological Survey, the Environmental and Public

Health Organization has prepared a national database for arsenic, which currently contains

18,000 arsenic level readings. Pakistan and Cambodia (annex 3) also have databases to

centralize all the information from arsenic screening. In the three countries the contribution to the

database is on a voluntary basis; however, in Cambodia, the Ministry of Rural Development and

UNICEF make receipt of testing kits dependent upon contribution to the database. In India the

Central Groundwater Board also has a web page with some arsenic-related data

(www.cgwaindia.com/arsenic.htm).

Regional information can be exchanged through the Asian Arsenic Network (AAN)

(www.asia-arsenic.net/index-e.htm).

The Global Positioning System (GPS) can be used to locate tubewells on a database, though

differentiating individual wells may be difficult where the density of tubewells is greater than the

resolution of the GPS, as may occur in Cambodia and Bangladesh (reported at Regional

Workshop, Nepal, April 2004). Whatever method is used to differentiate wells in such

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circumstances should be practical enough to be used by all stakeholders, allowing levels of

arsenic in individual wells to be monitored over time.

Summary Remarks

Once established, a database should be sustainable. In some cases a database is developedwithin a project and the collection of data is dependent on project financing. The institutionalprocess to ensure the sustainability of data is usually not given priority at this time. However,during such projects the technical process of data collection, including where to measure and atwhat frequency, should be developed in parallel with the institutional process to make sure thatcost recovery of the data collection takes place after project closure. This raises the issue ofwhether or not access to data should be free of charge; and, in the event of a charge, whetherusage would be sufficient to ensure cost recovery.

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Background

Most South and East Asian countries where groundwater arsenic contamination has beenidentified have inadequate surface water quality, mainly due to microbial contamination. In

these countries solutions to water supply problems may require a trade-off between the long-term health effects of a contaminant such as arsenic and the short-term health effects ofmicrobial contamination.

Access to Improved Water Sources in Asian Countries

Until recently, most sectoral programs concentrated on the lack of access to improved watersupply. Table 6 shows the increase in access to improved water sources in South and East Asiancountries during the 1990s. However, other problems, such as inadequate sanitation, are stillpresent in the region (table 7) and, despite improvements, child mortality remains high (table 8).

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Table 6. Access to Improved Water Sources in Selected Asian Countries

Population with access to improved water source (%)

1990 2000

Country Urban Rural Total Urban Rural Totalpopulation population

Bangladesh 99 93 94 99 97 97

Cambodia - - - 54 26 30

China - - 71 - - 75

India 88 61 68 95 79 84

Lao PDR - - - 61 29 37

Nepal 93 64 67 94 87 88

Pakistan 96 77 83 95 87 90

Vietnam 86 48 55 95 72 77

- Not available.Sources: World Bank 2003a: www.wsp.org/07_eastasia.asp; www.wsp.org/07_southasia.asp.

Arsenic Priority Compared to Bacteriological Water Quality Priority

Available data indicate that the rate of mortality due to waterborne diseases is greater than thatresulting from arsenic contamination. Based on information in the literature, the best estimate ofmortality due to diarrhea in Bangladesh is 120,000–200,000 people per year, of which possiblyhalf can be attributed to drinking of pathogen-contaminated water (Alaerts and Khouri 2004).Similarly, the best estimates put mortality due to arsenicosis at 20,000–40,000 people per year.

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Table 7. Percentage of Population in Selected Asian Countries with Sanitation

Population with access to sanitation (%)

1990 2000

Country Urban Rural Total Urban Rural Totalpopulation population

Bangladesh 81 31 41 71 41 48

Cambodia - - - 56 10 17

China - - 29 - - 38

India 44 6 16 61 15 28

Lao PDR - - - 67 19 30

Nepal - - 20 - - 28

Pakistan 52 23 36 82 38 62

Vietnam - - 29 - - 47

- Not available.Sources: World Bank 2003a: www.wsp.org/07_eastasia.asp; www.wsp.org/07_southasia.asp.

Table 8. Child Mortality Rates in Selected South and East Asian Countries

Infant mortality rate (per 1,000) Under-five mortality rate (per 1,000)

Country 1980 2001 1980 2001

Bangladesh 129 51 205 77

Cambodia 110 97 190 138

China 42 31 64 39

India 113 67 173 93

Lao PDR 135 87 200 100

Nepal 133 66 195 91

Pakistan 105 84 157 109

Thailand 45 24 58 28

Vietnam 50 30 70 38

However, it is not known whether arsenic morbidity is higher than waterborne disease morbidity.Thus, there are insufficient data to resolve the issue of how to prioritize between short-termcontamination of surface water and long-term contamination by arsenic.

As regards contamination with arsenic, certain criteria can help assess the level of prioritythat should be given to the problem: (a) the concentration of arsenic in drinking and cooking

Source: World Bank 2003a.

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water; (b) the spatial distribution of the contaminated tubewells; and (c) the proximity ofother water sources that are safe.

There is a positive correlation between the concentration of arsenic and its health effects. Ifthe only available sources have high arsenic concentrations (more than a few hundred µg L-1)and most of the tubewells are contaminated, there is practically no access to safe water. Inthis case the morbidity of arsenic is very high, and the shift to surface water might beconsidered, providing adequate chlorination is carried out or that people are advised to boilwater for drinking purposes. If the average concentration of arsenic is less than 100 µg L-1, thereis a longer timeframe for planning action. Solutions such as either providing surface water safefrom arsenic and bacteria, or piped water either from surface water or another aquifer, can beproperly planned to ensure that people get access to safe water. Another scenario could be thatsome tubewells have high concentrations of arsenic but the percentage of contaminated wells islow, which means that people will still have access to safe water within a reasonable walkingdistance. This kind of case-by-case or village-by-village analysis can provide insight intosuitable steps to be taken.

The financial sustainability of any water supply technology is necessary to ensure long-termsustainability of the supply, and must include operation and maintenance of the system, be itwells, pond sand filters, or piped water supply. Such recurrent costs and responsibilities forincurring them will vary according to such factors as whether the water supply is private (forexample individually installed household wells) or operated by the community.

In the shift to arsenic-safe options governments will have to involve communities in cost sharing,both for capital costs and for long-term operation and maintenance. With water supply provisionstill free in a number of countries, this relatively new concept may not be widely accepted bygovernment or by users. Indeed, moving from surface water to groundwater allowed people tohave clean clear water almost free of charge in terms of operation and maintenance costs. Nowthat some tubewells can no longer be used, alternative safe sources of water may have highoperation and maintenance costs. Users would have to pay for water on a regular basis andreceive a quality of service equal to or less than that available with tubewells. Therefore, asapplicable in a given country, willingness to pay studies will be crucial in deciding whatmitigation options are not only technologically appropriate but also socially accepted in the longrun. Such studies have been carried out by the Water and Sanitation Program in, for example,Bangladesh (WSP 2003) and have played an important role in informing policy decisionsregarding the introduction of piped water supply.

Definition and Identification of Arsenic Contamination Hotspots

Color coding of tubewells has been used to signify which wells are arsenic safe and which arenot (see section above). There is no record in the literature of more than two colors being used to

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identify degrees of contamination; for example, one color could indicate an arsenic concentrationless than 10 µg L-1, another could indicate the range 10–50 µg L-1, another the range50–200 µg L-1, and another a concentration higher that 200 µg L-1. Such levels of precision wouldbe possible in countries where laboratory testing was the norm, but not in countries that rely onfield test kits. Also, use of additional colors would add complexity to any awareness campaign.However, an advantage would be that users could tell which of the contaminated tubewells wereless harmful and which more harmful. A long-term advantage could be that if the nationalstandard in some countries was lowered to, for example, the present recommendedmaximum permissible value of the WHO (10 µg L-1) tubewells would not have to berescreened and reclassified, and sufficient data would be available to enable costing of themeasures associated with adjustment of the national standard.

The problem of prioritizing mitigation measures for arsenic contamination is illustrated byBangladesh, where emergency villages are defined as those with more than 80% of tubewellscontaminated. However, this does not always provide a full enough picture on which to baseoperational responses; for example, 80% of tubewells contaminated with, say, 60 µg L-1 may beless harmful than 70% of wells contaminated at an arsenic level of 200 µg L-1. Therefore, whendefinition of hotspots is based only on the percentage of tubewells with a concentration ofarsenic higher than WHO guidelines or national standards, there is insufficient information todevelop a plan of action.

Remaining Issues and Recommendations

Institutional setting of water quality monitoring is a concern. Which institution should beresponsible for the first screening and the monitoring? Should the operator or an independentorganization such as an NGO or the community conduct them? What about sustainability andtransparency and access to the related data?

Since some countries such as Bangladesh, Nepal, and India also have the option of usingdeep groundwater, the legal aspects of groundwater management will have to be taken intoaccount. Especially where exploitation of deep groundwater is concerned, should permitsbe introduced to ensure that the deep groundwater will be used exclusively for drinking andcooking purposes or is it assumed that, because of the cost, people will not use the deepgroundwater for irrigation purposes? Hence, for long-term planning, there is a need todevelop and strengthen the legal framework for groundwater management.

Although arsenic contamination is covered far more in the international media thanwaterborne diseases, this should not imply that the bacteriological quality problem faced bySouth and East Asian countries should be put aside. The decision regarding the setting ofpriorities has to be taken based on criteria such as the level of contamination of arsenic,and the access to safe water based on bacteriological and chemical parameters.

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The major stakeholders in natural arsenic contamination are water users, government, NGOs,donors, and international agencies. The incentives for each stakeholder to be active in

addressing the issue are different. While a government would be expected to be more influencedby public pressure, for example in the run-up to elections, an international agency might be moreconcerned with the reputational risk associated with its choices. The incentives for an NGO maystem less from public pressure or reputational risk (although this could also be possible) thanfrom the wish to influence decisions in a given sector. When no other stakeholder is addressingthe issue, there is an incentive for the users themselves to act to remedy the situation. Incentivesdiscussed here are the number of people at risk, number of arsenicosis patients, rural and urbanareas affected, national and international media coverage, cross-sector responses needed, waterservice pricing, short-term versus long-term solutions, reputational risk, and transparency of themitigation measures.

Number of People at Risk

The number of people at risk from arsenic contamination does not seem in itself to be anincentive for stakeholders to become active. Those at risk are those drinking contaminated water;only a certain proportion will develop the clinical symptoms of arsenic poisoning. Ahmed (2003)estimated the percentage of the total population at risk to be about 25% in Bangladesh, 6% inWest Bengal (India), and 2.4% in Nepal. Fewer data are available for East Asian countries than forSouth Asian countries, perhaps due to lack of identification of the problem, though in Vietnam thepercentage of the population at risk has been estimated at 13%, or 11 million people (Berg andothers 2001). Lack of information, however, prevents an accurate current assessment of arseniccontamination in East Asian countries.

Number of Arsenicosis Patients

The number of actual arsenicosis patients might be considered more of an incentive forstakeholders to become active. For example, while the estimate of the percentage of populationat risk in Vietnam is double that of West Bengal, the number of (identified) arsenicosis patients isreported to be nil in Vietnam compared to around 200,000 in West Bengal (WSP 2003). There is noindication from the literature that Vietnam is in the process of providing mitigation measures on alarge scale for the at-risk population. It is important to note that the use of groundwater inVietnam is quite recent (less than 10 years). Since the latency of arsenic-related diseases isbetween 10 and 15 years, Vietnam could register a large number of arsenicosis sufferers in a fewyears – which would increase the incentive to address the issue, but unfortunately at already avery advanced stage. Hence, the first identification of arsenicosis patients is a greater incentivefor government, donors, NGOs, and international agencies to act than the population-at-riskmeasurement. This is not surprising, given the many other issues that developing countries haveto contend with, but investments in patient screening and epidemiology now could prevent costlyemergency mitigation interventions later.

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Rural and Urban Areas

Except in the cases of Vietnam and Cambodia, arsenic-contaminated groundwater has mainlybeen detected in rural areas. In urban areas it is easier to deal with the arsenic problem whenthere is a point source water supply. For example, in Hanoi water treatment plants use aerationand sand filtration for iron and manganese removal from the pumped groundwater, which alsoeliminates some arsenic from the raw groundwater, although in some cases this is not enough toreduce it to levels below the national standard. In such circumstances, established facilities canbe upgraded to address the arsenic problem. On the other hand, in rural areas, the problem is farmore complicated because water sources are dispersed and difficult to improve on anemergency basis. Provision of mitigation measures by government and donors may take a longtime, though NGOs might be more flexible and better suited to act quickly at this decentralizedlevel. Even so, the scale of the problem is significant.

Importantly, rural populations often have less political clout than urban populations, which are typicallymore informed and politicized. Rural populations also suffer from the organizational problems thattends to afflict large groups with many free riders, weakening their voice as a group. This may in turnweaken the incentive for politicians to address arsenic contamination in rural areas.

National and International Media

National media coverage can be an incentive for stakeholder activity since there isreputational risk associated with providing unsafe water. However, this type of mediacoverage may act as a disincentive to action; if it is alarmist or factually inaccurate thencertain stakeholders may prefer to avoid possible controversy.

International media coverage might also create an incentive by raising global awareness,encouraging international agencies to orient their projects to take into account arsenic issues, andgovernments to commit more money to this purpose. However, care must be taken that this shiftwill not cause governments to reallocate resources from other equally important but lesspublicized problems.

For the media themselves, there is an incentive to cover such controversial issues as arseniccontamination because they increase circulation. However, the short-term coverage is often incontrast to the long-term, chronic nature of the problem.

Institutional Aspects

Arsenic is a cross-sectoral issue in that it involves water supply, water resources management,health, and (rural) development institutions. This can create difficulties if the institutions do notcoordinate with one another. Transparency in the choice of mitigation measures can be anincentive encouraging stakeholders to be active and to work together.

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The pricing of water supply services provides users with an incentive to hold providersaccountable for water quality. This is not always an incentive for government to implementcharges for water supply services since they then become accountable. Tubewells in rural areasprovide clean water that is almost free in terms of operation and maintenance costs. However,most of the solutions to address arsenic contamination will be less convenient and somemitigation measures will involve a charge for water supply service, which can be a difficult reformto introduce in some countries.

Short-Term versus Long-Term Solutions

Government, international agencies, and NGOs might feel greater incentive to implement short-term solutions rather than long-term solutions that are less immediately rewarding. Thedevelopment of arsenic policies and strategies can be a means of increasing the likelihood thatlong-term solutions will be implemented as well.

Reputational Risk

Reputational risk can act as an incentive to make government and international agencies active.However, as in Bangladesh, the controversy surrounding arsenic contamination may discouragecertain stakeholders from risking their reputations by becoming involved in the issue. This hasdelayed decision-making on such mitigation measures as the use of arsenic-free deepgroundwater, which could provide safe water in the short and medium term.

Table 9 provides a conceptual summary of the political economy of arsenic contamination ofgroundwater. It provides an indication why — up to now — mainly donors and internationalagencies and some country governments have been responding to arsenic contamination.Clearly, as more arsenic-affected areas are being identified and as the number of arsenicosispatients is going to rise, it can be expected that stakeholders will become more active. It is,however, important that in the meantime a more rational basis for dealing with arseniccontamination is created in order to avoid delayed — or exaggerated — responses.An important aspect in this regard is investment in epidemiological studies and economicanalyses, as outlined in Paper 4.

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Low incentive Medium incentive Great incentive

Table 9. Conceptualized Incentive Matrix: Stakeholder Incentives for Action on Arsenic Issues

Incentive factors Government Donors/international NGOsagencies

Number of people at risk

Number of arsenicosis patients

Rural areas

Urban areas

National media coverage

International media coverage

Water pricing and accountability

Transparency in choice ofmitigation measures

Availability of short-term solutions

Availability of long-term solutions

Perception of reputational risk

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In certain areas, natural arsenic contamination of groundwater has made effective access tosafe drinking water difficult to achieve. If the concentration in water of a chemical parameter,

such as arsenic, is higher than the maximum permissible national drinking water standards, the

water is considered contaminated and no longer potable. In Bangladesh, for example, arseniccontamination has reduced the amount of safe drinking water by about 20% in the last decade.

Two main issues generate substantial uncertainties in accurately predicting the impact of specific

short-term or long-term mitigation measures. The first is the lack of understanding of how arsenic

is released from sediment to water, and the second is the lack of epidemiological data on thehealth impact of low concentrations of arsenic in drinking water. Indeed, since the arsenic release

process is not fully understood, it becomes difficult to be certain that a given mitigation measure

will always provide arsenic-safe water. Also, since the epidemiology of arsenic is not fullyunderstood, estimation of the real health outcome for lower arsenic concentrations provided by a

given mitigation measure is difficult. For example, regarding the exploitation of the deep

(Pleistocene) aquifer, so far no arsenic has been found in deep tubewell water in Nepal, WestBengal, or Bangladesh. However, due to these uncertainties, whether deep groundwater will

remain arsenic safe in the long term, and what the real health outcome of using deep groundwater

compared to other mitigation measures will be, are difficult to determine.

Practically speaking, mitigation measures should be implemented as soon as arsenic has been

identified. While the success of implementation depends mainly on socioeconomic factorssuch as people's acceptance of an option and its capital cost, scientific understanding of

arsenic has value added on the quantification of impacts, but not on the implementation of

mitigation measures per se. Therefore, instead of delaying implementation until arseniccontamination is fully understood, both implementation and scientific investigation should be

conducted in parallel.

At the policy level (that is, action the government needs to take), when arsenic contamination is

identified in groundwater there is a need to assess:

• The scale of contamination: As the first screening results become available hydrogeologists

and geochemists should recommend whether the screening needs to be implemented at theproject level or if national screening needs to be conducted.

• The emergency level based on the population at risk, the number of arsenicosis patients, the

time of exposure, and the concentration of arsenic in water.

Based on the contamination scale and the emergency level, government should implement a

regional emergency plan of action with short-term and long-term components to mitigate arseniccontamination. Potential emergency and short-term responses include dug wells, pond sand

filters, rainwater harvesting, arsenic removal filters at the household level, and use of a safe

aquifer. Potential long-term operational responses are arsenic removal plants at the communitylevel, piped water supply, and use of a safe aquifer.

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At the implementation level (that is, action that needs to be taken at the project level), whenarsenic is identified, there is a need to conduct the following actions:

• Ensure that the appropriate government institution is informed about the contamination.

• Ensure that the data are available and properly stored for further scientific research on thecontamination, and are also available to different stakeholders that either use the water orimplement water projects in or beyond the project area.

• Ensure that in the project area the government requires the operator to check arsenic on aregular basis and makes the results available to stakeholders.

Whether the project should be continued is a decision for both the institution or internationalagency and the government. There is a need to ensure that arsenic mitigation occurs in anintegrated manner with ongoing projects.

One of the questions for donors and international agencies is whether a water project wherearsenic is identified should be pursued or not. Knowing that arsenic has long-term health effectsand that poor surface water quality has short-term effects, the question is how to address bothissues in a balanced way. If the project is to continue, government should provide assurancesthat appropriate measures will be taken to mitigate the arsenic contamination.

Finally, arsenic contamination has changed people's minds about the generally accepted rule that"groundwater equals safe drinking water". Although such water may be bacteriologically saferecent events have cast increasing doubts on its chemical safety. There are still other sources ofwater contamination in South and East Asian countries that need to be addressed, such asfluoride, manganese, sodium, iron, and uranium, in addition to bacteriological contamination. Adevelopment agency's target should be to ensure that all the mechanisms for water qualitymonitoring are set and implemented now, either for surface water or groundwater, to reduce therisk of providing unsafe drinking water.

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sist

ency

of a

rsen

icve

rsus

lab

orat

ory

anal

ysis

is c

hose

n, e

nsur

e ca

pac

ity is

suf

ficie

nt a

nd a

conc

entr

atio

n d

ata

anal

ysis

)q

ualit

y as

sura

nce

mec

hani

sm is

imp

lem

ente

d

Tech

nica

l cap

acity

Ad

equa

te tr

aini

ng m

ust b

e p

rovi

ded

and

refr

eshe

r cou

rses

Trai

n p

eop

le fo

r a

first

scr

eeni

ng, b

ut e

nsur

efo

r m

easu

ring

shou

ld b

e re

qui

red

, oth

erw

ise

tech

nica

l ass

ista

nce

need

s to

that

the

y w

ill b

e av

aila

ble

for

mon

itorin

gar

seni

cb

e m

ade

avai

lab

le a

fter

the

clos

ure

of th

e p

roje

ctco

ncen

trat

ions

Pro

vid

e tr

aini

ng-f

or-t

rain

er c

ours

es t

o en

sure

cap

acity

isre

tain

ed a

nd s

usta

ined

Ass

essi

ng e

xten

tD

eter

min

atio

n of

whe

ther

to s

cree

n a

larg

e or

loca

l are

aIn

form

atio

n on

the

ext

ent

of a

rsen

icof

ars

enic

shou

ld b

e le

ft t

o a

hyd

roge

olog

ist.

Con

duc

t a

first

scr

eeni

ngco

ntam

inat

ion

is c

ritic

al in

the

dev

elop

men

tco

ntam

inat

ion

inus

ing

a la

rge

grid

to

acq

uire

crit

ical

info

rmat

ion

on t

heof

a p

ragm

atic

act

ion

pla

n an

d a

nth

e sh

orte

st t

ime

loca

tion

of t

he h

otsp

ots

whe

re p

reci

se s

cree

ning

sho

uld

asse

ssm

ent o

f ap

pro

pria

te o

per

atio

nal

pos

sib

leb

e co

nduc

ted

resp

onse

sS

amp

ling

stra

tegy

— w

heth

er to

scr

een

all

tub

ewel

ls o

r jus

t a s

mal

l per

cent

age

— m

ust b

e d

ecid

ed b

yth

e re

spon

sib

le a

genc

y

Ens

urin

g th

atE

nsur

e th

e co

mm

unity

is p

rop

erly

tra

ined

in t

he o

per

atio

nIm

pro

ve w

ater

qua

lity

by

pre

vent

ing

aal

tern

ativ

e w

ater

and

mai

nten

ance

of d

iffer

ent o

per

atio

nal r

esp

onse

s (d

ugp

ollu

tant

shi

ft t

o th

e w

ater

qua

lity

pro

ble

m,

sour

ces

pre

sent

wel

l, p

ond

san

d fi

lter,

rain

wat

er h

arve

stin

g, w

ater

trea

tmen

t,sa

y fr

om a

rsen

ic to

bac

teria

or t

o so

me

safe

leve

ls o

fp

iped

saf

e w

ater

)ot

her c

hem

ical

bac

teria

and

oth

erE

nsur

e al

tern

ativ

e p

otab

le w

ater

sou

rces

are

als

o re

gula

rlych

emic

al p

aram

eter

sm

onito

red

for

con

tam

inan

ts

Ens

urin

g th

atE

ach

miti

gatio

n m

easu

re m

ust i

nclu

de

clea

r sp

ecifi

catio

nsIn

crea

sed

sus

tain

abili

ty o

f m

itiga

tion

miti

gatio

n m

easu

res

of t

he m

inim

um q

ualit

y re

qui

red

mea

sure

s th

roug

h en

hanc

ed q

ualit

y of

spec

ify a

ndE

nsur

e a

func

tiona

l pro

cess

is in

pla

ce to

ver

ify c

ontr

acto

rseq

uip

men

t use

dde

linea

te a

ccep

tabl

ear

e fo

llow

ing

the

miti

gatio

n re

qui

rem

ents

mat

eria

ls a

nd q

ualit

yst

and

ard

s to

be

used

Con

td. o

n ne

xt p

age

�� (��&��,��-��

143142

Issu

es

Recom

mendati

ons

Exp

ecte

d o

utc

om

es

Pro

vid

ing

pat

ient

sP

rovi

de

arse

nico

sis

pat

ient

s w

ith v

itam

ins,

moi

stur

izin

gR

ever

se a

rsen

ic e

ffect

or,

at le

ast,

red

uce

with

ad

equa

telo

tions

, an

d t

reat

men

t fo

r in

fect

ions

peo

ple

's s

uffe

ring

and

the

mor

bid

ity r

ate

trea

tmen

tM

axim

ize

pat

ient

con

tact

with

a p

reve

ntiv

e he

alth

ap

pro

ach

from

ars

enic

-rel

ated

dis

ease

sb

y p

lann

ing

trea

tmen

t for

oth

er d

isea

ses,

suc

h as

dia

bet

es

Mar

king

tub

ewel

lsR

etes

t tub

ewel

ls o

nce

or tw

ice

a ye

arM

ake

sure

that

peo

ple

hav

e ea

sy a

cces

s to

regu

larly

tub

ewel

l saf

ety

info

rmat

ion

listin

g w

hich

tub

ewel

ls a

re s

afe

or u

nsaf

e

Cro

ss-c

heck

ing

For e

xam

ple

, NA

MIC

dat

a in

Ban

glad

esh

have

bee

n cr

oss-

Pre

serv

es re

liab

ility

of c

olle

cted

dat

a in

aco

llect

ed d

ata

chec

ked

with

dat

a co

llect

ed b

y C

olum

bia

Uni

vers

ityco

st-e

ffec

tive

way

amon

g d

iffer

ent

stak

ehol

der

s

Ens

urin

g th

at–

Avo

ids

a w

ater

sho

rtag

e th

at fo

rces

peo

ple

alte

rnat

ive

wat

erto

drin

k co

ntam

inat

ed w

ater

sour

ces

have

the

cap

acity

to m

eet

dem

and

"��+��,&�&��*��,��-��.��!��(��

�� *��$�� !��(��*��

Tab

le 2

. Fin

anci

al a

nd E

cono

mic

Issu

es

Issu

es

Recom

mendati

ons

Exp

ecte

d o

utc

om

es

Cho

osin

g a

Ass

ess

bot

h ex

pec

ted

ben

efits

and

cos

ts o

f miti

gatio

nC

reat

e b

asis

for

ratio

nal d

ecis

ion-

mak

ing

onm

itiga

tion

optio

no

ptio

nsm

itiga

tion

optio

ns a

nd p

rogr

ams

bas

ed o

n th

eb

enef

its a

nd c

osts

Ass

essi

ng p

ricin

gC

ond

uct

a w

illin

gnes

s to

pay

stu

dy

to d

eter

min

e th

e ra

nge

Ens

ures

cos

t rec

over

y of

op

erat

ion

and

affo

rdab

ility

for

of w

ater

fees

peo

ple

can

aff

ord

mai

nten

ance

cos

ts w

ith m

inim

al b

urd

en o

nth

e p

oor

the

poo

r se

gmen

t of

the

pop

ulat

ion

Dec

idin

g w

hich

–If

a p

rogr

essi

ve fi

nanc

ial m

echa

nism

for

stak

ehol

der

(s)

scre

enin

g an

d m

onito

ring

is n

ot id

entif

ied

shou

ld p

ay f

or t

hefr

om t

he b

egin

ning

, whe

n d

onor

s le

ave

the

scre

enin

g an

d th

eco

llect

ion

of d

ata

is li

kely

to

stop

mon

itorin

g of

tub

ewel

ls, p

atie

ntid

entif

icat

ion,

and

awar

enes

sca

mpa

igns

Red

ucin

g th

e co

sts

Tub

ewel

l tes

ting

shou

ld b

e d

one

in c

once

rt w

ith p

atie

ntA

llow

s fo

r co

st-e

ffec

tive

pat

ient

asso

ciat

ed w

ithid

entif

icat

ion

iden

tific

atio

nsc

reen

ing

and

pat

ient

id

entif

icat

ion

Find

ing

mec

hani

sms

Cre

ate

a p

ublic

-priv

ate

fund

to c

omp

ensa

te th

ose

mos

tS

usta

inab

ility

of

thes

e em

erge

ncy

or s

hort

-to

com

pen

sate

imp

acte

d b

y ec

onom

ic lo

ss, f

or e

xam

ple

peo

ple

who

can

not

term

sol

utio

nsp

eop

le th

at m

ay lo

seus

e th

eir

pon

d fo

r fis

hing

pur

pos

es, p

eop

le w

ho e

xper

ienc

ein

com

e b

ecau

se o

fa

lack

of p

rivac

y b

ecau

se th

ey s

hare

saf

e tu

bew

ells

miti

gatio

n m

easu

res

�� (��&��,��-��

145144

Tab

le 3

. So

cial

and

Cul

tura

l Iss

ues

Issu

es

Recom

mendati

ons

Exp

ecte

d o

utc

om

es

Dis

sem

inat

ion

ofC

reat

e a

web

site

whe

re d

ata

mig

ht e

ither

be

avai

lab

le fr

ee o

fTr

ansp

aren

cy o

f the

info

rmat

ion

rela

ted

to

data

char

ge o

r with

cle

ar s

tep

s on

how

the

dat

a ca

n b

e p

urch

ased

.th

e ex

tent

of a

rsen

ic c

onta

min

atio

nP

rovi

de,

at

min

imum

, th

e fo

llow

ing

info

rmat

ion:

(a) g

eogr

aphi

cal d

istr

ibut

ion

of a

ffec

ted

are

as;

(b) l

ocat

ion

of a

rsen

ic-c

onta

min

ated

tub

ewel

ls; a

nd(c

) nu

mb

er o

f aff

ecte

d p

erso

ns o

r id

entif

ied

pat

ient

s

Par

adig

m s

hift

ing

Mak

e it

clea

r th

roug

h p

ublic

ann

ounc

emen

ts th

at w

hile

Incr

easi

ng p

eop

le's

will

ingn

ess

to h

ave

thei

raw

ay fr

om "

clea

rsu

rfac

e w

ater

is u

nsaf

e, s

ome

clea

r gro

und

wat

er c

an a

lso

be

wat

er m

onito

red

wat

er e

qua

ls s

afe

cont

amin

ated

. Ind

eed

for m

any

year

s p

eop

le in

Asi

anw

ater

"co

untr

ies

have

imm

edia

tely

ass

ocia

ted

cle

ar g

roun

dw

ater

Incr

easi

ng p

ublic

aw

aren

ess

that

wat

erw

ith p

otab

le d

rinki

ng w

ater

and

turb

id s

urfa

ce w

ater

as

cont

amin

ants

are

not

alw

ays

visi

ble

unsa

fe t

o d

rink

Co

ord

inat

ion

Ther

e w

ill a

lway

s b

e so

me

unce

rtai

ntie

s an

d th

eref

ore

man

yA

void

s co

nfus

ing

peo

ple

on

the

orig

in a

ndb

etw

een

scie

ntis

tsp

ossi

ble

ans

wer

s. H

owev

er: (

a) s

cien

tific

com

mun

ity a

ndp

oten

tial e

xten

t of

the

ars

enic

con

tam

inat

ion

and

don

ors

tosc

ient

ists

mus

t agr

ee o

n on

e (s

imp

le) s

tory

to te

ll th

e p

ublic

;p

rob

lem

ensu

re i

nfor

mat

ion

(b) q

ualif

y st

atem

ents

by

clea

rly e

xpla

inin

g w

hat f

acts

are

dis

sem

inat

ed to

the

know

n w

ith c

erta

inty

and

wha

t in

form

atio

n is

stil

l deb

atab

le.

pub

lic is

con

sist

ent

Pub

licly

sta

te a

ssum

ptio

n m

ade,

if a

pp

licab

le

Co

ord

inat

ing

Avo

id t

estin

g al

way

s th

e sa

me

villa

ges

and

fam

ilies

with

in t

heIn

crea

ses

the

cove

rage

of p

eop

le w

ho h

ave

oper

atio

nal a

ctio

nsaf

fect

ed a

rea

by

diff

eren

t sta

keho

lder

s, b

ut in

stea

d tr

y to

acce

ss to

saf

e w

ater

amon

g st

akeh

old

ers

cove

r the

larg

est g

eogr

aphi

cal a

reas

Find

ing

ince

ntiv

es t

oLi

mit

the

num

ber

of p

eop

le w

ho h

ave

to s

hare

the

sam

eS

pre

ads

the

soci

al b

urd

en a

nd a

void

s ta

xing

incr

ease

peo

ple

'stu

bew

ell.

Wor

k w

ith th

e co

mm

unity

to c

reat

e a

feas

ible

the

good

will

of t

he (s

ame)

few

peo

ple

who

will

ingn

ess

with

inco

mm

unity

pla

n th

at m

aps

out

whi

ch f

amily

sho

uld

go

tow

illin

gly

offe

red

the

ir he

lpco

mm

uniti

es t

oth

e ot

her

shar

e sa

fe w

ells

Mak

ing

sure

tha

t fo

rA

void

cre

atin

g ge

nder

-rel

ated

issu

es a

t the

tim

e of

Ad

dre

sses

sen

sitiv

e ge

nder

issu

esp

atie

nt i

den

tific

atio

nex

amin

atio

n b

y in

clud

ing

a m

ale

and

fem

ale

exam

iner

inA

void

s un

der

estim

atin

g th

e nu

mb

er o

f

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Issu

es

Recom

mendati

ons

Exp

ecte

d o

utc

om

es

ther

e ar

e w

omen

on

each

team

(cas

e st

udy:

Ban

glad

esh)

fem

ale

arse

nico

sis

pat

ient

sea

ch te

am

Cre

atin

g le

gib

leC

reat

e a

des

ign

or c

olor

-cod

ed m

ark

cultu

rally

sen

sitiv

eE

nhan

ces

effe

ctiv

enes

s of

the

awar

enes

san

d u

nder

stoo

dto

peo

ple

in th

e ru

ral a

rea

cam

pai

gn b

y ea

sily

reac

hing

a w

ide

aud

ienc

em

arks

on

tub

ewel

ls lo

cate

dP

lace

des

ign

or m

ark

in a

n ea

sily

reco

gniz

ed a

nd v

isib

lein

rur

allo

catio

n ne

ar t

he t

ubew

ell

com

mun

ities

Ens

urin

g he

alth

Pro

mot

ing

the

use

of v

itam

ins

is n

ot s

uffic

ient

as

aD

rives

mes

sage

hom

e to

peo

ple

: ad

vanc

ed-

wor

kers

and

pre

vent

ive

or tr

eatm

ent m

easu

re a

t ear

ly s

tage

s of

stag

e ar

seni

cosi

s is

not

trea

tab

led

octo

rs ta

ke th

ear

seni

cosi

s co

ntra

ctio

n; t

he o

nly

optio

n th

at e

xist

stim

e to

exp

lain

is t

o st

op d

rinki

ng a

rsen

ic-c

onta

min

ated

wat

er. S

tres

s th

atp

reve

ntiv

eth

ere

is n

o cu

re fo

r ad

vanc

ed-s

tage

ars

enic

osis

mea

sure

s

Mai

ntai

ning

pub

licE

nsur

e co

ntin

ued

pro

duc

tion

of m

essa

ges

to t

he p

ublic

tha

tA

void

s a

sim

ple

pro

ble

m s

hift

of t

he r

isk

awar

enes

s ab

out

exp

lain

sur

face

wat

er is

uns

afe

and

con

tam

inat

edfr

om a

rsen

ic to

bac

teria

arse

nic

and

oth

erw

ater

-rel

ated

dis

ease

s as

soci

ated

with

poo

rm

icro

bio

logi

cal

qua

lity

of s

urfa

cew

ater

and

wat

erso

urce

s, s

uch

asd

ug w

ell,

pon

ds,

etc

.

�� (��&��,��-��

147146

Tab

le 4

. Ins

titut

iona

l Iss

ues

Issu

es

Recom

mendati

ons

Exp

ecte

d o

utc

om

es

Ens

urin

g p

oor

Pro

vid

e a

sub

sid

y to

ens

ure

that

poo

r co

mm

uniti

es c

anA

pp

lies

a fa

ir p

rice

for w

ater

to e

ach

peo

ple

will

be

affo

rd c

ost o

f ser

vice

sse

gmen

t of

the

pop

ulat

ion

equa

lly s

erve

din

the

pro

visi

on o

fm

itiga

tion

mea

sure

s

Co

ord

inat

ing

Pro

pos

e p

roje

cts

whe

re in

stitu

tions

of b

oth

sect

ors

are

the

Imp

rove

s in

stitu

tiona

l eff

icie

ncy

by

avoi

din

gac

tiviti

es b

etw

een

imp

lem

entin

g ag

enci

esw

aste

ful s

pen

din

g on

sim

ilar

actio

n ite

ms

wat

er a

nd h

ealth

Dev

elop

wor

ksho

ps

covi

ng to

pic

s re

leva

nt to

bot

h se

ctor

sse

ctor

s, a

nd th

eir

Cre

ates

foru

m to

ad

dre

ss p

oten

tial

corr

esp

ond

ing

Cre

ate

a tr

ansp

aren

t in

form

atio

n d

isse

min

atio

n sy

stem

inte

rinst

itutio

nal

conf

licts

of

inte

rest

inst

itutio

nsb

etw

een

the

sect

ors

and

inst

itutio

ns fo

r ge

nera

lan

noun

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149148

Annex 3. Operational Responses to Arsenic Contamination: Questionnaire Results

Country Four countries responded to the survey:Bangladesh, Cambodia, Nepal, and Pakistan

State/Province (if applicable)

Country national standard for arsenic 50 µg L-1 for all respondent countries(µg L-1 or ppb)

Answer provided by: BRAC, AusAID, FAO, UNICEF, Partners for(Name/institution/address/email) Development, Irrigation Ministry of Nepal

The questionnaire was in two parts. The first part focused on general issues regarding theoperational responses towards arsenic contamination, and the second focused onimplementation aspects of these operational responses. The tables below indicate the questionsin the left column, and summarize country responses in the right column.

Part 1. General Issues Survey

Water resources availability and use in the country

Questions Results

How much groundwater and surface water In Bangladesh, Nepal, and Pakistan groundwater isrespectively is used countrywide for drinking used first and foremost for irrigation (by a largewater supply, irrigation and industry? margin), then for drinking water supply, and finally

for industrial purposes.

What is the percentage of groundwater and Not enough answers to provide any regionwidesurface water used in the rural and in the urban conclusion.areas respectively for drinking water, industryand irrigation?

a) When and by what institution/person was the Except for Bangladesh, where the first screeningfirst discovery of arsenic in groundwater made? was conducted in 1993, the first screenings inb) What are the areas, so far, identified and what Cambodia, Nepal, and Pakistan were conductedpercentage of the country consists of these between 1999 and 2000.contaminated areas? Distribution of contaminated areas within the four

countries was as follows: in Bangladesh,contamination occurred in the deltaic areas; inCambodia, in the areas close to the Mekong River;in Nepal, in the southern Terai plain; in Pakistan, inthe provinces of Punjab and Sind.

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Is there a specific national policy, law (or Bangladesh is ahead of the other countries withprotocols) regarding arsenic? If not, why not? respect to its national arsenic policy.If yes, which institution is responsible toimplement these? (Please provide a summary/copy of the policy/law/protocol/decree.)

Is there a groundwater law in the country? So far there is no groundwater law in the fourWhen was it instituted? If not, is one under countries. However, Nepal is in the process ofdevelopment (law already initiated, law under reviewing a draft groundwater law, and in Pakistandevelopment, or no law)? UNICEF and the Ministry of Environment are

planning to initiate one during 2004.

Is there a surface water or general water law Cambodia, Pakistan, and Nepal each have a surfacein the country? When was it instituted? If not, water law. In Nepal the surface water law wasis it under development (law already initiated, instituted in 1992.law under development, or no law)?

Is there a national database on arsenic All four countries have a database.contamination? If not, why?

Is contribution to the database enforced by It is voluntary in Bangladesh, Nepal, and Pakistan,law or is it voluntary? and mandatory in Cambodia as the contribution to

the database is a condition for receiving a testing kitfrom UNICEF and MRD.

Mitigation measures

When was the first regionwide screening All four countries mark tubewells in the screeningconducted? And when was the first nationwide process. In Bangladesh, Cambodia, and Pakistan thescreening conducted? marking is based on colors, specifically green andWas a systematic marking of the contaminated/ red. In Nepal, markings take the form of either asafe tubewells/other sources done? How was cross or a check (√).the marking done?If no screening conducted either regionwide ornationwide, why?

Which arsenic-related activities are being Patient care has not been implemented so far inundertaken in your country? Nepal or Pakistan.

To your knowledge, which governmental UNICEF is involved in the four countries, ininstitution/NGO/development partner is particular in Cambodia and Pakistan. In Bangladeshcarrying out these activities? the number of stakeholders is much higher than in

other countries. The major NGOs in Cambodia areRDI and PDF.

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Mitigation measures

Are the different actors coordinating these Regarding the coordinating agencies: there was noactivities? If yes, by whom and how is it done? consensus in Bangladesh; in Cambodia, UNICEF isIs the coordination effective? Why? If not, seen as taking this role; and in Nepal the Nationalwhy not? Steering Committee for Arsenic is the coordinating

agency. Pakistan has not yet begun a nationwidecoordination effort.

How many tubewells/other water supply The only country for which the number of tubewellssources are there in the country? is reported is Bangladesh, with about 10 millionHow many tubewells/other sources are there tubewells. The number of tubewells is not reportedin the arsenic-affected areas? in Cambodia, Nepal, or Pakistan.How many tubewells/other sources havebeen screened?Will all the tubewells/other sources be screenedin the long term? If not, why not?

What is the tone of the national media coverage The tone of the national coverage of arsenicregarding arsenic contamination? contamination has been reported as: alarmist in

Bangladesh and Nepal; fact based in Pakistan; andnonexistent in Cambodia.

How would you rate, on a scale from 1 to 3, The arsenic problem is rated as very important inthe arsenic problem compared with other Bangladesh and Pakistan; and of mediumproblems faced by your country? importance in Cambodia and Nepal.

Which institution/NGO/international UNICEF is seen as the main driver in addressingorganization is the main driver in addressing arsenic issues in both Cambodia and Pakistan; inthe arsenic issue? How did this institution come Nepal it is the Department of Water Supply andto take the lead? Sewerage; and in Bangladesh several agencies have

been reported as being the main drivers: DPHE,DANIDA, UNICEF, and the World Bank.

When exploring a new source of water, are there Bangladesh and Cambodia have a standardstandard protocols about the chemical protocol for drinking water supply.parameters to check water quality for drinking None of the four countries seems to have awater supply, or irrigation? standard protocol for irrigation.

Is arsenic one of the parameters of these Although arsenic is a parameter of the protocol inprotocols? Bangladesh and Cambodia and should be a factorIf yes, is arsenic occurrence a factor in the in the decision as to whether to use the waterdecision about the choice of using the water source, it does not seem to be implemented.source? And if it is detected, what are theactions conducted regarding thiscontamination?

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Part 2. Specific Implementation of Mitigation Measures

Implementation aspects of mitigation measures

Is there any monitoring for the screened In all four countries limited or no monitoring istubewells/other water supply sources? reported.If yes what frequency and how is it done?If not, why?

What method is used for the screening? Field test kits are used for screening in all four(e.g. field test kit, laboratory or both). Is cross- countries. Cross-checking with laboratories ischecking of field test and laboratory analysis reported in all countries.applied? If yes, how is it done?

What are the main problems encountered in the Ensuring the effectiveness of the field test.process of screening, both on the technical and Limited capacity of government staff.on the institutional side? The transport of samples from the field to laboratory.

Describe the present awareness campaign TV, radio, and distribution of printed material are the(TV, radio, newspaper, etc.) What are the lessons media used for the awareness campaign.learned on the best way to communicate Lessons learned:information about arsenic? Use community-specific communication methods,

e.g. karaoke (when applicable), video.Verbal communication with the community is one ofthe most effective means of communication.Mitigation should accompany awareness campaignsas providing an alarmist message without providinga solution is counterproductive.

What mitigation measures are already applied Screening is the mitigation measure that has beenand tested (e.g. dug well/surface water/rainwater conducted in the four countries. So far, all theharvesting/water treatment/deep groundwater/ mitigation options have been tested in Bangladesh.others)? In Cambodia dug wells, rainwater harvesting,

community water treatment, and ceramic filters forsurface water treatment have been implemented. InNepal water treatment at the household level hasbeen tested on an experimental basis. In Pakistandug wells are used and household-level treatment isbeing promoted.

How are mitigation measures (dug well/surface In Bangladesh and Cambodia all the implementedwater/rainwater harvesting/water treatment/ mitigation options are selected at the communitydeep groundwater/others) selected level. In Nepal screening is selected by the central(e.g. feasibility study, community decision, agency and donors, while household watercentral agency)? treatment is only selected by donors. In Pakistan the

implementation of mitigation options is based onfeasibility studies.

What are the major problems encountered in It is difficult to operate the pond sand filter.implementation of the mitigation measures and It is difficult to make people change behavior andwhat has functioned well? switch from tubewells to other water sources.

The capital cost of the initial infrastructure foralternative water supply is a problem.

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153152

Health aspects of the mitigation measures

a) Which agencies are responsible for patient In Bangladesh many agencies are responsible foridentification? arsenic identification, namely: Dhaka Community

b) Do they coordinate their work? Hospital, upazila health complex at upazila level,c) If yes how is it done? If the coordination is and the Ministry of Health and Family Welfare. In

not effective what are the reasons? Cambodia and Nepal it is the Ministry of Health. Ind) Is the screening based on skin lesions or are Pakistan patient identification has not started yet.

there measurements (arsenic in hair, nail, In Bangladesh the reported information is thatand blood)? there is no coordination among the agencies, while

in Cambodia it seems to be coordinated.In Cambodia the coordination is through the ArsenicInterministerial Subcommittee and via UNICEF/WHO assistance.The screening is mainly based on skin lesions inBangladesh, Cambodia, and Nepal. In Pakistanmeasurement is also based on arsenic in the nail.

How is medical management of arsenicosis In Bangladesh it is organized mainly throughpatients organized? government hospitals, DCH, and UNICEF. InWhat is the procedure for monitoring patients? addition, through the financial assistance of

BAMWSP, DCH trained doctors in the identificationand management of arsenicosis patients. None ofthe countries reported any procedure for monitoringpatients.

What is the current estimate of the number of For Bangladesh the range is from 13,000 to morepatients with arsenicosis? What is the current than 19,000 arsenicosis patients. In Pakistan, thereestimate of the population at risk? are approximately 140 arsenicosis cases per

100,000 people in Punjab. It is reported that nopatients have been identified as yet in Cambodia.

Research aspects of arsenic contamination

Is there any research done in your country/state/ There seems to be a lot of research in bothprovince on the origin of the arsenic in the Bangladesh and Cambodia involving both localsediment, its release to the groundwater, and and foreign research institutions. Small-scalethe migration with the groundwater flow? research in Nepal has been reported with

involvement of the USGS. No research has beenreported in Pakistan.

If yes, what institutions are involved: localuniversities, local research institutes,government agencies, foreign universities,foreign research institutes, NGOs, etc.?

Is there any outcome of research on arsenic While Bangladesh is the only country where researchaccumulation in the food chain? on arsenic accumulation has been reported, no

conclusions as yet are available.

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Research aspects of arsenic contamination

Is there national quality control of laboratories? Nepal is the only country where there is nationalIf yes, how is it conducted (frequency, control of laboratories.methodology, responsible institution, etc.)? In Nepal, the Department of

Meteorology and Standards accredits the privatelaboratories; however, this is not mandatory and isdone on a voluntary basis.

Economic aspects of the mitigation measures

What is the cost of each mitigation measure? Bangladesh is the only country where most of theHow many people were served? costs are available. These costs are summarized in

the table at the end of this annex.In the case of Pakistan the following lump sum wasprovided: (Pitcher + awareness raising + testing &marking)/HH = Rs 1,500.

In general, in your opinion, what are the main lessons learned on the operational responsesthat have been conducted?

Social

It is possible to train female village volunteers to test the tubewells for arsenic.

Local women with limited educational background can also be trained on preliminary identification ofarsenicosis patients, awareness education, alternative water supply, and monitoring of these options.Community needs to be mobilized in arsenic mitigation.

There is no unique solution because of technical limitations and cultural acceptance of mitigation options.

Communication of arsenic issues to private individuals installing tubewells is a challenge.

Technical

Local mason can be trained in the construction and manufacture of different mitigation options.

Monitoring of safe water options for arsenic and bacteria (when applied, e.g. for surface water) as well asfor other potential contaminants.

Since there is so far no treatment for arsenicosis, there is a need to provide arsenic patients with safewater for drinking and cooking purposes.

Much research is needed to find out effective treatment regimens for patients in different stagesof arsenicosis.

Many treatment units, either home based or community based, produce sludge that contains a highconcentration of arsenic. A countrywide proper management system for this sludge should be set up sothat rural people can manage this sludge in a convenient way.

Economic

Need low-cost solutions.

Need for fee collection to cover ongoing maintenance issues.

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155154

Institutional

Set a priority to implement mitigation options in the most-affected villages.

There should be more coordination among different governmental and nongovernmental agenciesworking in the country.

The longer-term solutions must be based on a long-term vision. This may include the provision of pipedwater supply to its population and the optimum use of its surface water. The potential role that the localgovernments can play in this longer vision must be fully explored; towards this, experimentation andpilot projects should not wait.

Standardized field testing and data management are needed.

Government needs to be in the driver's seat in screening and implementing mitigation options.

Bangladesh: Costs of Mitigation Measures (Response to Questionnaire Item 32)

Cost per unit (taka) Number of people served

Screening with field test Tk 30 (total cost Tk 3,000) 100 households

Screening with laboratory Tk 500 by AASanalysis Tk 300 by spectrometer

Awareness campaign Tk 1,500 per village meeting 100 households

Dug well New: Tk 40,000–50,000 40–50 households(Renovation: Tk 10,000average)Tk 35,000–40,000 20–30 families comprising 5 members

Pond sand filter Tk 50,000–60,000 50–70 householdsTk 30,000–40,000 20–30 families comprising 5 members

Rainwater harvesting Tk 10,000–12,000 (3,200 liters) 1 householdTk 8,000 (3,200 liters) 1 family comprising 5 members

Deep groundwater Tk 40,000 average 50–60 householdsTk 35,000–40,000 20–30 families comprising 5 members

Household treatment Depends on the watertreatment

Community treatment Depends on the watertreatment

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ysis

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day

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167166

1. This paper presents the technologies for treatment of arsenic-contaminated water,arsenic detection and measurement technologies, and alternative safe wateroptions. After a brief introduction (chapter 1), chapter 2 examines the principles ofarsenic removal from drinking water and explores the major technologies associatedwith each. Chapter 3 describes the laboratory and field methods of arsenicdetection and measurement. Chapter 4 presents alternative options for arsenic-safewater supplies. Chapter 5 analyzes some operational issues related to themitigation options presented in the paper.

2. The objective of the paper is to provide technical staff in governments,development organizations, nongovernmental organizations and other interestedstakeholders with up-to-date information on the technical aspects of arsenicmitigation in order to familiarize them with the most commonly used mitigationmethods. For treatment of arsenic-contaminated water, there are four basicprocesses: (a) oxidation-sedimentation; (b) coagulation-sedimentation-filtration;(c) sorptive filtration; and (d) membrane techniques. For alternative water supplyoptions, there are four main options: (a) use of an alternative safe aquifer, accessedby a deep tubewell or dug well; (b) use of surface water employing, for example, apond sand filter or multistage filters; (c) use of rainwater; and (d) piped water supplybased on either ground or surface water.

3. The paper is designed as a tool to inform the decision-making process whendeciding which arsenic mitigation option is best suited to a particular project. It laysout the advantages and disadvantages of each mitigation method, and the relatedoperational issues.

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Arsenic is present in the environment and humans all over the world are exposed to small amounts, mostly through food, water, and air. But the presence of high levels of arsenic in

groundwater, the main source of drinking water in many countries around the world, has drawnthe attention of the scientific community. Groundwater, free from pathogenic microorganisms andavailable in adequate quantity via tubewells sunk in shallow aquifers in the flood plains, provideslow-cost drinking water to scattered rural populations. Unfortunately, millions are exposed to highlevels of inorganic arsenic through drinking this water. It has become a major public healthproblem in many countries in South and East Asia and a great burden on water supplyauthorities. Treatment of arsenic contamination of water, in contrast to that of many otherimpurities, is difficult, particularly for rural households supplied with scattered handpumptubewells. In developing countries like Bangladesh and India the high prevalence ofcontamination, the isolation and poverty of the rural population, and the high cost and complexityof arsenic removal systems have imposed a programmatic and policy challenge on anunprecedented scale.

Source substitution is often considered more feasible than arsenic removal. The use of alternativesources requires a major technological shift in water supply. Treatment of arsenic-contaminatedwater for the removal of arsenic to an acceptable level is one of the options for safe watersupply. Since the detection of arsenic in groundwater, a lot of effort has been mobilized fortreatment of arsenic-contaminated water to make it safe for drinking. During the last few yearsmany arsenic detection and test methods and small-scale arsenic removal technologies havebeen developed, field-tested, and used under different programs in developing countries. Thisshort review of these technologies is intended as an update of the technological developments inarsenic testing, arsenic removal, and alternative water supplies. It is hoped that the review willbe of assistance to those involved in arsenic mitigation in South and East Asian countries.

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Arsenic in groundwater is present mainly in nonionic trivalent (As(III)) and ionic pentavalent(As(V)) inorganic forms in different proportions depending on the environmental conditions of

the aquifer. The solubility of arsenic in water is usually controlled by redox conditions, pH,biological activity, and adsorption reactions. The reducing condition at low Eh value convertsarsenic into a more mobile As(III) form, whereas at high Eh value As(V) is the major arsenicspecies. As(III) is more toxic than As(V) and difficult to remove from water by most techniques.

There are several methods available for removal of arsenic from water in large conventionaltreatment plants. The most commonly used processes of arsenic removal from water have beendescribed by Cheng and others (1994), Hering and others (1996), Hering and others (1997),Kartinen and Martin (1995), Shen (1973), and Joshi and Chaudhuri (1996). A detailed review ofarsenic removal technologies has been presented by Sorg and Logsdon (1978). Jekel (1994) hasdocumented several advances in arsenic removal technologies. In view of the lowering of thestandard of the United States Environmental Protection Agency (EPA) for the maximumpermissible levels of arsenic in drinking water, a review of arsenic removal technologies wascarried out to consider the economic factors involved in implementing more stringent drinkingwater standards for arsenic (Chen and others 1999). Many of the arsenic removal technologieshave been discussed in details in the AWWA (American Water Works Association) reference book(Pontius 1990). A review of low-cost well water treatment technologies for arsenic removal, with alist of companies and organizations involved in arsenic removal technologies, has been compiledby Murcott (2000). Comprehensive reviews of arsenic removal processes have been documentedby Ahmed, Ali, and Adeel (2001), Johnston, Heijnen, and Wurzel (2000), and Ahmed (2003). TheAWWA conducted a comprehensive study on arsenic treatability options and evaluation ofresiduals management issues (AWWA 1999).

The basic principles of arsenic removal from water are based on conventional techniques ofoxidation, coprecipitation and adsorption on coagulated flocs, adsorption onto sorptive media,ion exchange, and membrane filtration. Oxidation of As(III) to As(V) is needed for effective removalof arsenic from groundwater by most treatment methods. The most common arsenic removaltechnologies can be grouped into the following four categories:

• Oxidation and sedimentation• Coagulation and filtration• Sorptive filtration• Membrane filtration

The principal mechanisms and technologies for arsenic removal using the above technologicaloptions are described in detail in the following sections.

Oxidation-Sedimentation Processes

Most treatment methods are effective in removing arsenic in pentavalent form and hence includean oxidation step as pretreatment to convert arsenite to arsenate. Arsenite can be oxidized by

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oxygen, ozone, free chlorine, hypochlorite, permanganate, hydrogen peroxide, and Fulton’sreagent, but atmospheric oxygen, hypochloride, and permanganate are commonly used foroxidation in developing countries. The oxidation processes convert predominantly nonchargedarsenite to charged arsenate, which can be easily removed from water.

Atmospheric oxygen is the most readily available oxidizing agent and many treatment pressesprefer oxidation by air. But air oxidation of arsenic is a very slow process and it can take weeksfor oxidation to occur (Pierce and Moore 1982). Air oxidation of arsenite can be catalyzed bybacteria, strong acidic or alkali solutions, copper, powdered activated carbon, and hightemperature (Edwards 1994). Chemicals such as chlorine and permanganate can rapidly oxidizearsenite to arsenate under a wide range of conditions. Hypochloride is readily available in ruralareas but the potency (available chlorine) of the hypochloride decreases when it is poorly stored.Potassium permanganate is also readily available in developing countries. It is more stable thanbleaching powder and has a long shelf life. Ozone and hydrogen peroxide are very effectiveoxidants but their use in developing countries is limited. Filtration of water through a bedcontaining solid manganese oxides can rapidly oxidize arsenic without releasing excessivemanganese into the filtered water.

In situ oxidation of arsenic and iron in the aquifer has been tried in Bangladesh under the ArsenicMitigation Pilot Project of the Department of Public Health Engineering (DPHE) and the DanishAgency for International Development (Danida). The aerated tubewell water is stored in feed watertanks and released back into the aquifers through the tubewell by opening a valve in a pipeconnecting the water tank to the tubewell pipe under the pump head. The dissolved oxygen inwater oxidizes arsenite to less-mobile arsenate and the ferrous iron in the aquifer to ferric iron,resulting in a reduction of the arsenic content in tubewell water. Experimental results show thatarsenic in the tubewell water following in situ oxidation is reduced to about half due tounderground precipitation and adsorption on ferric iron. The method is chemical free and simpleand is likely to be accepted by the people but the method is unable to reduce arsenic content toan acceptable level when arsenic content in groundwater is high.

Chlorine and potassium permanganate are used for oxidation of As(III) to As(V) in many treatmentprocesses in Bangladesh and India. SORAS (solar oxidation and removal of arsenic) is a simplemethod of solar oxidation of arsenic in transparent bottles to reduce arsenic content of drinkingwater (Wegelin and others 2000). Ultraviolet radiation can catalyze the process of oxidation ofarsenite in the presence of other oxidants such as oxygen (Young 1996). Experiments inBangladesh show that the process on average can reduce the arsenic content of water to aboutone-third of the original concentration.

As a process, passive sedimentation has received considerable attention because of ruralpeople’s habit of drinking stored water from pitchers. Oxidation of water during collection andsubsequent storage in houses may cause a reduction in arsenic concentration in stored water.Experiments conducted in Bangladesh showed zero to high reductions in arsenic from drinkingwater by passive sedimentation. Arsenic reduction by plain sedimentation appears to be

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dependent on water quality and in particular the presence of alkalinity and precipitating iron inwater. Passive sedimentation, in most cases, failed to reduce arsenic to the desired level of50 µg L-1 in a rapid assessment of technologies conducted in Bangladesh (BAMWSP-DFID-WaterAid 2001).

Coagulation-Sedimentation-Filtration Processes

In the process of coagulation and flocculation, arsenic is removed from solution through threemechanisms:

• Precipitation: The formation of insoluble compounds• Coprecipitation: The incorporation of soluble arsenic species into a growing metal

hydroxide phase• Adsorption: The electrostatic binding of soluble arsenic to external surfaces of the insoluble

metal hydroxide (Edwards 1994)

Precipitation, coprecipitation, and adsorption by coagulation with metal salts and lime followed

by filtration is a well-documented method of arsenic removal from water. This method can

effectively remove arsenic and many other suspended and dissolved solids from water, including

iron, manganese, phosphate, fluoride, and microorganisms, reducing turbidity, color, and odor

and resulting in a significant improvement in water quality. Thus removal of arsenic from water

using this method is associated with other ancillary health and aesthetic benefits.

Water treatment with coagulants such as aluminium alum (Al2(SO4)3.18H2O), ferric chloride (FeCl3),

and ferric sulfate (Fe2(SO4)3.7H2O) is effective in removing arsenic from water. Oxidation of As(III) to

As(V) is required as a pretreatment for efficient removal. It has been suggested that preformed

hydroxides of iron and aluminium remove arsenic through adsorption, while in situ formation

leads to coprecipitation as well (Edwards 1994). In alum coagulation the removal is most effective

in the pH range 7.2–7.5, and in iron coagulation efficient removal is achieved in a wider pH range,

usually between 6.0 and 8.5 (Ahmed and Rahaman 2000). The effects of cations and anions are

very important in arsenic removal by coagulation. Anions compete with arsenic for sorptive sitesand lower the removal rates. Manning and Goldberg (1996) indicated the theoretical affinity atneutral pH for anion sorption on metal oxides as:

PO4 > SeO3 > AsO4 > AsO3 >> SiO4 > SO2 > F > B(OH)3

The presence of more than one anion can have a synergistic effect on arsenic removal. Addition

of either silicate or phosphate has some effects on arsenic removal but presence of both can

reduce arsenate removal by 39% and arsenite removal by 69% (Meng, Bang, and Korfiatis 2000).

Based on arsenic removal studies in Bangladesh, Meng and Korfiatis (2001) concluded that

elevated levels of phosphate and silicate in Bangladesh well water dramatically decreased

adsorption of arsenic by ferric hydroxides.

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The technologies developed based on the coagulation-sedimentation-filtration process include:

• Bucket treatment unit• Stevens Institute technology• Fill and draw treatment unit• Tubewell-attached arsenic treatment unit• Iron-arsenic treatment unit

The bucket treatment unit, developed by the DPHE-Danida Project and improved by the

Bangladesh University of Engineering and Technology (BUET), is based on coagulation,

coprecipitation, and adsorption processes. It consists of two buckets, each with a capacity of

20 liters, placed one above the other. Chemicals are mixed manually with arsenic-contaminated

water in the upper red bucket by vigorous stirring with a wooden stick and then flocculated by

gentle stirring for about 90 seconds. The mixed water is allowed to settle and then flow into the

lower green bucket and water is collected through a sand filter installed in the lower bucket. The

modified bucket treatment unit shown in figure 1 has been found to be very effective in removing

iron, manganese, phosphate, and silica along with arsenic.

The Stevens Institute technology also uses two buckets, one to mix chemicals (iron coagulant

and hypochloride) supplied in packets and the other to separate flocs using the processes of

sedimentation and filtration (figure 2 see page 174). The second bucket has an inner bucket with

slits on the sides to help sedimentation and keep the filter sand bed in place. The chemicals

form visible large flocs when mixed (by stirring with a stick). Clean water is collected through a

plastic pipe fitted with an outlet covered with a cloth filter to prevent the entry of sand. Theefficiency of the system has been described by Meng and Korfitis (2001).

Figure 1. Double Bucket Household Arsenic Treatment Unit (Ali and Others, 2001)

Topbucket

Bottombucket

PVC slottedscreen

Sand filter

Cloth screen

Flexibleplastic pipe

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The fill and draw system is a community-level treatment unit designed and installed under theDPHE-Danida Project. It has a 600 liter capacity (effective) tank with a slightly tapered bottom forcollection and withdrawal of settled sludge (figure 3). The tank is fitted with a manually operatedmixer with flat blade impellers. The tank is filled with arsenic-contaminated water and therequired quantity of oxidant and coagulant are added to the water. The water is then mixed for30 seconds by rotating the mixing device at the rate of 60 revolutions per minute (rpm) and leftovernight for sedimentation. The settled water is then drawn through a pipe fitted at a level a fewinches above the bottom of the tank and passed through a sand bed, and is finally collectedthrough a tap for drinking. The mixing and flocculation processes in this unit are better controlledto effect higher removal of arsenic. The experimental units installed by the DPHE-Danida projectare serving clusters of families and educational institutions.

The tubewell-attached arsenic removal unit was designed and installed by the All India Instituteof Hygiene and Public Health (AIIH&PH) (figure 4). The principles of arsenic removal by alum

Figure 2. Stevens Institute Technology (Drawn by Ahmed, 2003)

Mixing stick

ChemicalsTransfer of chemicalmixed water

Main bucket

Interior bucket

Slits

Outlet withcloth filter

Plastic pipe todeliver treatedwater

Filtersand

Figure 3. DPHE-Danida Fill and Draw Arsenic Removal Unit (Drawn by Ahmed, 2003)

Handle

Filtration unit

Treated water

Gear System

Cover

Impeller

Tank

Sludgewithdrawalpipe

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coagulation, sedimentation, and filtration have been employed in this compact unit for watertreatment at the village level in West Bengal, India. The arsenic removal plant, attached to ahandpump-operated tubewell, has been found effective in removing 90% of the arsenic fromtubewell water. The treatment process involves the addition of sodium hypochloride (Cl2) andaluminium alum in diluted form, mixing, flocculation, sedimentation, and upflow filtration in acompact unit.

Figure 4. Tubewell-Attached Arsenic Removal Unit designed by All India Institute of Hygieneand Public Health (Ahmed and Rahman, 2000)

A - Mixing; B - Flocculation; C - Sedimentation; D - Filtration (upflow)

C

AB

D

Iron-arsenic removal plants use naturally occurring iron, which precipitates on oxidation andremoves arsenic by adsorption. Several models of iron-arsenic removal plants have beendesigned and installed in Bangladesh. A study suggests that As(III) is oxidized to As(V) in theplants, facilitating arsenic removal (Dahi and Liang, 1998). The iron-arsenic removal relationshipwith good correlation in some operating iron-arsenic removal plants has been plotted in figure 5.Results shows that most iron removal plants can lower arsenic content of tubewell water to halfto one-fifth of the original concentration. The main problem is to keep the community systemoperational through regular washing of the filter bed.

20

100

30 40 50 60 70 80 90 100

90

80

70

60

50

40

30

20

y = 0.8718x + 0.4547

R2 = 0.6911

Ars

enic

Rem

ova

l , %

Iron Removal, %

Figure 5. Correlation between Iron and Arsenic Removal in Treatment Plants (Dhai and Liang, 1998)

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Some medium-scale iron-arsenic removal plants with capacities of 2,000–3,000 m3 day-1 havebeen constructed for water supplies in district towns in Bangladesh. The main treatmentprocesses involve aeration, sedimentation, and rapid sand filtration with provision for addition ofchemicals if required. The units operating on natural iron content of water have efficienciesvarying between 40% and 80%. These plants are working well except that the water requirementfor washing the filter beds is very high. Operations of small and medium-sized iron-arsenicremoval plants in Bangladesh suggest that arsenic removal by coprecipitation and adsorption onnatural iron flocs has good potential for arsenic content up to about 100 µg L-1.

Water treatment by the addition of quick lime (CaO) or hydrated lime (Ca(OH)2) also removesarsenic. Lime treatment is a process similar to coagulation with metal salts. The precipitatedcalcium hydroxide (Ca(OH)2) acts as a sorbing flocculent for arsenic. Excess lime will not dissolvebut remains as a thickener and coagulant aid that has to be removed along with precipitatesthrough sedimentation and filtration processes. It has generally been observed that arsenicremoval by lime is relatively low, usually between 40% and 70%. The highest removal isachieved at pH 10.6 to 11.4. McNeill and Edward (1997) studied arsenic removal by softeningand found that the main mechanism of arsenic removal was sorption of arsenic onto magnesiumhydroxide solids that form during softening. Trace levels of phosphate were found to slightlyreduce arsenic removal below pH 12 while arsenic removal efficiency at lower pH can beincreased by the addition of a small amount of iron. The disadvantage of arsenic removal by limeis that it requires large lime doses, in the order of 800–1,200 mg L-1, and consequently a largevolume of sludge is produced. Water treated by lime would require secondary treatment in orderto adjust pH to an acceptable level. Lime softening may be used as a pretreatment to befollowed by alum or iron coagulation.

Sorptive Filtration

Several sorptive media have been reported to remove arsenic from water. These are activatedalumina, activated carbon, iron- and manganese-coated sand, kaolinite clay, hydrated ferricoxide, activated bauxite, titanium oxide, cerium oxide, silicium oxide, and many natural andsynthetic media. The efficiency of sorptive media depends on the use of an oxidizing agent as anaid to sorption of arsenic. Saturation of media by different contaminants and components ofwater takes place at different stages of the operation, depending on the specific sorption affinityof the medium to the given component. Saturation means that the sorptive sites of the mediumhave been exhausted and the medium is no longer able to remove the impurities. The mostcommonly used media for arsenic removal in small treatment plants include:

• Activated alumina• Granulated ferric oxide and hydroxide• Metallic iron• Iron-coated sand or brick dust• Cerium oxide• Ion exchange media

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Arsenic removal by activated alumina is controlled by the pH and arsenic content of water.Arsenic removal is optimum in the narrow pH range from 5.5 to 6.0 when the surface is positivelycharged. The efficiency drops as the point of zero charge is approached and at pH 8.2, where thesurface is negatively charged, the removal capacities are only 2–5% of the capacity at optimalpH (Clifford 1999). The number of bed volumes that can be treated at optimum pH beforebreakthrough is dependent on the influent arsenic concentration. The bed volume can beestimated using the following equation, where As is the initial arsenic concentration in water inmicrograms per liter (Ghurye, Clifford, and Tripp 1999):

Bed volume = 210,000 (As)-0.57

The actual bed volume is much lower due to the presence of other competing ions in naturalwater. Arsenic removal capacities of activated alumina have been reported to vary from 1 mg g-1

to 4 mg g-1 (Fox 1989; Gupta and Chen 1978). Clifford (1999) reported the selectivity of activatedalumina as:

OH-1>H2AsO4-1>Si(OH)3O

-1>HSeO3-1>F>SO4

-2>CrO4-2>>HCO3

-1>Cl-1>NO3-1>Br-1>I-1

Regeneration of saturated alumina is carried out by exposing the medium to 4% caustic soda(NaOH), either in batch or by flow through the column resulting in high-arsenic-contaminatedcaustic waste water. The residual caustic soda is then washed out and the medium is neutralizedwith a 2% solution of sulfuric acid rinse. During the process about 5–10% of the alumina is lostand the capacity of the regenerated medium is reduced by 30–40%. The activated aluminaneeds replacement after 3–4 regenerations. As with the coagulation process, prechlorinationimproves the column capacity dramatically. The activated alumina-based sorptive media used inBangladesh and India include:

• BUET activated alumina• Alcan enhanced activated alumina• Apyron arsenic treatment unit• Oxide (India) Pvt. Ltd.• RPM Marketing Pvt. Ltd.

Arsenic is removed by sorptive filtration through activated alumina. Some units use pretreatment(for example oxidation, sand filtration) to increase efficiency. The Alcan enhanced activatedalumina arrangement is shown attached to a tubewell in figure 6 (see page 178). The unit issimple and robust in design. No chemicals are added during treatment and the process whollyrelies on the active surface of the media for adsorption of arsenic from water. Other ions presentin natural water, such as iron and phosphate, may compete for active sites on alumina andreduce the arsenic removal capacity of the unit. Iron present in shallow tubewell water atelevated levels will eventually accumulate in an activated alumina bed and interfere with flow ofwater through the bed. The unit can produce more than 3,600 liters of arsenic-safe drinking waterper day for 100 families. Apyron Technologies Inc. (United States of America) has developed an

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Figure 6. Alcan Enhanced Activated Alumina Unit (Drawn by Ahmed, 2003)

arsenic treatment unit in which its Aqua-Bind™ medium is used for arsenic removal fromgroundwater. Aqua-Bind contains activated alumina and manganese oxides that can selectivelyremove As(III) and As(V). The BUET activated alumina units have oxidation and prefiltrationprovisions prior to filtration through activated alumina.

Granular ferric hydroxide (AdsorpAs®) is a highly effective adsorbent used for the adsorptiveremoval of arsenate, arsenite, and phosphate from natural water. It has an adsorptioncapacity of 45g kg-1 for arsenic and 16 g kg-1 for phosphorus on a dry weight basis (Pal2001). M/S Pal Trockner (P) Ltd, India, and Sidko Limited, Bangladesh, have installed severalgranular ferric hydroxide-based arsenic removal units in India and Bangladesh. Theproponents of the unit claim that AdsorpAs® has very high arsenic removal capacity, andproduces relatively small amounts of residual spent media. The typical residual mass ofspent AdsorpAs® is in the range of 5–25 g/m3 of treated water. The typical arrangement ofthe Sidko/Pal Trockner unit (figure 7) requires aeration for oxidation of water and prefiltrationfor removal of iron flocs before filtration through active media. Chemicon and Associates hasdeveloped and marketed an arsenic removal plant based on adsorption technology in whichcrystalline ferric oxide is used as an adsorbent. The unit has a prefiltration unit containingmanganese oxide for oxidation of As(III) to As(V) and retention of iron precipitates.

Figure 7. Granular Ferric Hydroxide-Based Arsenic Removal Unit (Pal, 2001)

Inlet(water from tubewell)

Tubewell

Oulet(treated water)

Adsorption bedGravel filter bed

Treatedwater outflowContaminated

water inflow

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The Sono 3-Kolshi filter shown in figure 8 uses zero valent iron filings (cast-iron turnings), sand,brick chips, and wood coke to remove arsenic and other trace metals from groundwater inBangladesh (Munir and others 2001; Khan and others, 2000). The filtration system consists ofthree kalshi (burned clay pitchers), widely used in Bangladesh for storage of drinking and cookingwater. The top kalshi contains 3 kg cast-iron turnings from a local machine shop or iron worksand 2 kg sand on top of the iron turnings. The middle kalshi contains 2 kg sand, 1 kg charcoal,and 2 kg brick chips. Brick chips are also placed around the holes to prevent leakage of finermaterials. Tubewell water is poured in the top kalshi and filtered water is collected from thebottom kalshi.

Figure 8. Three Kalshi Filter for Arsenic Removal (Drawn by Ahmed, 2003 based on Khan andOthers, 2000)

Nikolaidis and Lackovic (1998) showed that 97% of arsenic can be removed by adsorption on amixture of zero valent iron filings and sand through formation of coprecipitates, mixedprecipitates, and adsorption onto the ferric hydroxide solids. Thousands of units using thistechnology were distributed in arsenic-affected areas but the feedback from the users was notvery encouraging. If groundwater contains excess iron the one-time use unit quickly becomesclogged. Field observations indicated that the iron filings bond together into solid mass over time,making cleaning and replacement of materials difficult. The unit has been renamed Sono 45-25arsenic removal technology and the materials of the upper two units have been put into twobuckets to overcome some of the problems mentioned above.

The BUET iron-coated sand filter was constructed and tested on an experimental basis andfound to be very effective in removing arsenic from groundwater. The unit needs pretreatment forthe removal of excess iron to avoid clogging of the active filter bed. Iron-coated sand is preparedfollowing a procedure similar to that adopted by Joshi and Chaudhuri (1996). The Shapla arsenicfilter (figure 9 see page 180), a household-level arsenic removal unit, has been developed and is

Raw water

Filter medium 1:sand, iron fillings &brick chips

Filter medium 2:sand, charcoal &brick chips

Filtered water

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being promoted by International Development Enterprises (IDE) , Bangladesh. The adsorptionmedium is iron-coated brick chips manufactured by treating brick chips with a ferrous sulfatesolution. It works on the same principle as iron-coated sand. The water collected fromcontaminated tubewells is allowed to pass through the filter medium, which is placed in anearthen container with a drainage system underneath.

The READ-F arsenic filter is promoted by Shin Nihon Salt Co. Ltd., Japan, and Brota ServicesInternational, Bangladesh, for arsenic removal in Bangladesh. READ-F displays high selectivityfor arsenic ions under a broad range of conditions and effectively adsorbs both arsenite andarsenate. Oxidation of arsenite to arsenate is not needed for arsenic removal, nor is adjustmentof pH required before or after treatment. The READ-F is ethylene-vinyl alcohol copolymer-bornehydrous cerium oxide in which hydrous cerium oxide (CeO2.nH2O) is the adsorbent. Laboratorytests at the BUET and field testing of the materials at several sites under the supervision of theBAMWSP showed that the adsorbent is highly efficient in removing arsenic from groundwater(Shin Nihon Salt Co. Ltd. 2000). One household treatment unit and one community treatment unitbased on the READ-F adsorbent are being promoted in Bangladesh. The units need iron removalby sand filtration to avoid clogging of the resin bed by iron flocs. In the household unit both thesand and resin beds have been arranged in one container while in the community unit sand andresin beds are placed in separate containers. READ-F can be regenerated by adding sodiumhydroxide and then sodium hypochloride and finally washing with water. The regenerated READ-Fneeds neutralization by hydrochloric acid and washing with water for reuse.

The SAFI filter is a household-level candle filter developed and used in Bangladesh. The candleis made of composite porous materials such as kaolinite and iron oxide on which hydrated ferricoxide is deposited by sequential chemical and heat treatment. The filter works on the principle ofadsorption filtration on the chemically treated active porous composite materials of the candle.

The ion exchange process is similar to that of activated alumina; however, the medium is asynthetic resin of relatively well defined ion exchange capacity. The synthetic resin is based on across-linked polymer skeleton called the matrix. The charged functional groups are attached to

Figure 9. Shapla Filter for Arsenic Removal at Household Level by IDE (Ahmed, 2003)

Flexible waterdelivery pipe

Lid

Iron-coated crushedbrick particles

Cloth filter onperforated plate

Support Treatedwaterin abucket

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the matrix through covalent bonding and fall into strongly acidic, weakly acidic, strongly basic,and weakly basic groups (Clifford 1999). The resins are normally used for removal of specificundesirable cations or anions from water. The strongly basic resins can be pretreated with anionssuch as Cl-1 and used for the removal of a wide range of negatively charged species, includingarsenate. Clifford (1999) reports the relative affinities of some anions for strong-base anionresins as:

CrO4-2>>SeO4

-2>>SO4-2>>HSO4

-1>NO3-1>Br-1>HAsO4

-2>SeO3-2>HSO3

-3>NO2-1>Cl-1

The arsenic removal capacity is dependent on sulfate and nitrate contents of raw water, assulfate and nitrate are exchanged before arsenic. The ion exchange process is less dependent onthe pH of water. Arsenite, being uncharged, is not removed by ion exchange. Hence, preoxidationof As(III) to As(V) is required for removal of arsenite using the ion exchange process. The excessoxidant often needs to be removed before the ion exchange in order to avoid damage of thesensitive resins. Development of ion-specific resin for exclusive removal of arsenic can make theprocess very attractive.

Tetrahedron (United States) promoted ion exchange-based arsenic removal technology inBangladesh (figure 10). About 150 units were installed at various locations in Bangladesh underthe supervision of the BAMWSP. The technology proved its arsenic removal efficiency even athigh flow rates. It consists of a stabilizer and an ion exchanger (resin column) with facilities forchlorination using chlorine tablets. Tubewell water is pumped or poured into the stabilizer througha sieve containing the chlorine tablet. The water mixed with chlorine is stored in the stabilizer andsubsequently flows through the resin column when the tap is opened for collection of water.Chlorine from the tablet dissolved in the water kills bacteria and oxidizes arsenic and iron.

Water System International (WSI) India has developed and patented an ion exchangeprocess for arsenic removal from tubewell water. The so-called bucket of resin unit isencased in a rectangular container placed adjacent to the tubewell. There are three cylinders

Figure 10. Tetrahedron Arsenic Removal Technology (Drawn by Ahmed, 2003)

Chlorine source

Sievestabilizer

Stone chips

Stand

Resin column(ion exchanger)

Column head tap

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inside the container. Water in the first cylinder is mixed with an oxidizing agent to oxidizeAs(III) to As(V) while As(V) is removed in the second cylinder, which is filled with WSI-patented processed resin. The treated water is then allowed to flow through a bed ofactivated alumina to further reduce residual arsenic from water. Ion Exchange (India) Ltd. hasalso developed and marketed an arsenic removal community-level plant based on ionexchange resin.

Membrane Techniques

Synthetic membranes can remove many contaminants from water including bacteria, viruses,salts, and various metal ions. They are of two main types: low-pressure membranes, used inmicrofiltration and ultrafiltration; and high-pressure membranes, used in nonofiltration and reverseosmosis. The latter have pore sizes appropriate to the removal of arsenic.

In recent years, new-generation membranes for nonofiltration and reverse osmosis havebeen developed that operate at lower pressure and are less expensive. Arsenic removal bymembrane filtration is independent of pH and the presence of other solutes but is adverselyaffected by the presence of colloidal matters. Iron and manganese can also lead to scalingand membrane fouling. Once fouled by impurities in water, the membrane cannot bebackwashed. Water containing high levels of suspended solids requires pretreatment forarsenic removal using membrane techniques. Most membranes, however, cannot withstandoxidizing agents. EPA (2002) reported that nonofiltration was capable of over 90% removal ofarsenic, while reverse osmosis provided removal efficiencies of greater that 95% when atideal pressure. Water rejection (about 20–25% of the influent) may be an issue in water-scarce regions (EPA 2002). A few reverse osmosis and nonofiltration units have beensuccessfully used in Bangladesh on an experimental basis.

Comparison of Arsenic Removal Technologies

Remarkable technological developments in arsenic removal from rural water supply based onconventional arsenic removal processes have taken place during the last five years. The relativeadvantages and disadvantages of different arsenic removal processes are compared in table 1.

Competition between arsenic removal technologies is based on a number of factors. Costappears to be a major determinant in the selection of treatment option by users. The availablecosts of some of the arsenic removal technologies have been summarized in table 2. The costsof similar technologies in India are also compared in table 3.

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Table 1. Comparison of Main Arsenic Removal Technologies

Technology Advantages Disadvantages

Oxidation and • Relatively simple, low cost, but • Processes remove only some ofsedimentation: air slow process (air) the arsenicoxidation, chemical • Relatively simple and rapid • Used as pretreatment foroxidation process (chemical) other processes

• Oxidizes other impurities andkills microbes

Coagulation and filtration: • Relatively low capital cost • Not ideal for anion-rich wateralum coagulation, iron • Relatively simple in operation treatment (e.g. containingcoagulation • Common chemicals available phosphates)

• Produces toxic sludge• Low removal of As(III)• Preoxidation is required• Efficiencies may be inadequate

to meet strict standards

Sorption techniques: • Relatively well known and • Not ideal for anion-rich wateractivated alumina, iron- commercially available treatment (e.g. containingcoated sand, ion exchange • Well-defined technique phosphates)resin, other sorbents • Many possibilities and scope • Produces arsenic-rich liquid and

for development solid wastes• Replacement/regeneration is

required• High-tech operation and

maintenance• Relatively high cost

Membrane techniques: • Well-defined and high removal • High capital and running costsnanofiltration, reverse efficiency • High-tech operation andosmosis • No toxic solid wastes produced maintenance

• Capable of removal of other • Arsenic-rich rejected water iscontaminants produced

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Table 2. Comparison of Arsenic Removal Mechanisms and Costs in Bangladesh

Type of unit Removal Type Capital cost/ Operation andmechanism unit(US$) maintenance costs/

family/year (US$)

Sono 45-25 Adsorption by oxidized Household 13 0.5–1.5iron chips and sand

Shapla filter Adsorption of iron- Household 4 11coated brick chips

SAFI filter Adsorption Household 40 6

Bucket Oxidation and Household 6–8 25treatment unit coagulation-

sedimentation-filtration

Fill and draw Oxidation and Community 250 15coagulation- (15 households)sedimentation-filtration

Arsenic Aeration, sedimentation, Urban water 240,000 1–1.5removal unit rapid filtration supply(6,000for urban water households)supply

Sidko Adsorption by granular Community 4,250 10Fe(OH)3 (75 households)

Apyron Adsorption by Al-Mn Community Taka 0.01/L/100ppb arsenicoxides (Aqua-BindTM) (65 households) concentration in water

Iron-arsenic Aeration, sedimentation, Community 200 1removal plant rapid filtration (10 households)

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Table 3. Comparison of Costs of Different Arsenic Treatment Technologies in India

Technology Treatment process Type Capacity Cost (US$)(manufacturer)

AMAL (Oxide Adsorption by activated Household 7,000–8,000 L 50India Catalyst alumina Community 1,500,000 L/cycle 1,250; 400/chargePvt. Ltd., WB)

RPM Marketing Activated alumina + Community 200,000/cycle 1,200; 500/chargePvt. Ltd. AAFS-50 (patented)

All India Institute Oxidation followed Household 30 L/d 5of Hygiene & by coprecipitation- Community 12,000 L/d 1,000Public Health filtration

Public Health Adsorption on red Community 600–1,000 L/h 1,000Engineering hematite, sand, andDepartment, India activated alumina

Pal Trockner Ltd., Adsorption by ferric Household 20 L/d 8India hydroxide Community 900,000 L/cycle 2,000; 625/charge

Chemicon & Adsorption by ferric Community 2,000,000 L/cycle 4,500; 400/chargeAssociates oxide

Ion Exchange Adsorption by ion Community 30,000 L/cycle 2,000(India) Ltd. exchange resin

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Analysis of groundwater for arsenic has become a routine procedure in the assessment of thequality of water for the development of groundwater-based water supply. The need for

stringent water quality standards and guidelines has given rise to demand for analysis of arsenicat trace levels. Laboratory analytical methods are relatively more accurate than field testing butinvolve considerable measurement skills and costs. The extent and nature of contamination inmany countries demands large-scale measurements of arsenic for screening as well asmonitoring and surveillance of water points. Developing countries with limited laboratory capacityhave adopted low-cost semiquantitative arsenic measurement by field test kits to accomplishthe huge task of screening and monitoring. This section provides a short overview of laboratoryand field methods of analysis of arsenic in water.

Laboratory Methods

A variety of analytical methods for laboratory determination of arsenic has been described in hasliterature but many of them essentially employ similar principles. The most common methodsprescribed for use after proper validation by international and national standard methods includeatomic absorption spectrometry (AAS), inductively coupled plasma (ICP), anodic strippingvoltammetry (ASV), and silver diethyldithiocarbamate (SDDC) spectrometric method. AAS is asensitive single-element technique with known and controllable interference. Both hydridegeneration (HG) and graphite furnace (GF) AAS methods are widely used for analysis of arsenic inwater. ICP atomic emission spectrometry (AES) and mass spectrometry (MS) are multielementtechniques, also with known and controllable interference. ASV is a useful technique for analysisof dissolved arsenic and arsenic speciation but needs special precautions for accuracy. TheSDDC spectrometric method has been widely used for its simplicity and low cost but suffersfrom interference and reproducibility. A summary of laboratory analytical techniques, withimportant features, is presented in table 4 (Rasmussen and Anderson 2002; Khaliquzzaman andKhan 2003).

Field Test Kit

Laboratory methods of arsenic measurement are costly and the number of laboratories witharsenic measurement capabilities is too few in the developing countries to meet present needs.Field test kits have been developed for detection and measurement of arsenic by differentinstitutions and agencies in Bangladesh and in other countries. The detection and semiquantativemeasurement of arsenic by all field test kits is based on the Gutzeit procedure, which involvesthe conversion of all arsenic in water into As(III) by reduction, and then formation of arsine gas byfurther reduction using nascent hydrogen in an acid solution in a Gutzeit generator. The techniqueis also known as the mercuric bromide stain method (APHA-AWWA-WEA 1985). Presentlyavailable arsenic test kits have been developed adopting various modifications of the method.The arsine, thus liberated, produces a yellow to brown stain on a vertical paper strip impregnated

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a Abbreviations used:ASV anodic stripping voltammetryGF-AAS graphite furnace-atomic absorption spectrometryHG-AAS hydride generation-atomic absorption spectrometryICP-AES inductively coupled plasma-atomic emission spectrometryICP-MS inductively coupled plasma-mass spectrometrySDDC silver diethyldithiocarbamateb Abbreviations used/references:ASTM American Society for Testing and Materials (ASTM 1998)CD Committee DraftEPA Environmental Protection Agency, United StatesISO International Organization for Standardization (ISO 1982, 1996, 2000)SM Standard Method

Table 4. Laboratory Analysis Methods for Arsenic

Techniquesa Method Sample size System cost Comments Methodsb

detection (ml) (thousands US$)limit (mg L-1)

HG-AAS 0.05–2 50 20–100 Single element ISO 11969 (1990)SM 3114BC (1998)EPA 1632 (1996)ASTM 2972-93B(1998)

GF-AAS 1–5 1–2 30–100 Single element ISO/CD 15586(2000)SM 3113B(1998)EPA 200.9 (1994)ASTM 2972-93C(1998)

ICP-AES 35–50 10–20 60–200 Multielement SM 3120B(1998)EPA 200.7 (1994)

ICP-MS 0.02–1 10–20 150–400 Multielement SM 3125B (1998)EPA 200.8 (1994)

ASV 0.1–2 25–50 5–20 Only free EPA 7063 (1996)dissolvedarsenic

SDDC 1–10 100 2–10 Single element ISO 6595 (1982)SM 3500 (1998)

with mercuric bromide. The amount of arsenic present in the water is directly related to theintensity of the color. The color developed on mercuric bromide-soaked paper is compared eitherwith a standard color chart or measured by a photometer to determine the arsenic concentrationof the water sample. In some field test kits the generated arsine is passed through a columncontaining a roll of cotton moistened with lead acetate solution to absorb hydrogen sulfide gas, ifany is present in the gas stream. The important features of some arsenic field test kits aresummarized in table 5 (see page 188).

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189188A number of researchers and organizations have evaluated the performance of arsenic field testkits. The National Environmental Engineering Research Institute, Nagpur, India, evaluated theAsian Arsenic Network (AAN) kit (0.02–0.70 mg L-1), the National Institute of Preventive and SocialMedicine (NIPSOM) kit, the Merck kit (0.10–3.0 mg L-1), the Aqua kit, and the AIIH&PH kit (NEERI-WHO 1998). The Shriram Institute for Industrial Research, India, studied the performance of fivedifferent arsenic field test kits used in India (SIIR 1998). NGO Forum for Drinking Water Supplyand Sanitation, Bangladesh, in collaboration with the School of Environmental Studies, JadavpurUniversity, Calcutta, West Bengal, India, evaluated the NIPSOM kit, the General PharmaceuticalLtd. (GPL) kit, the Merck kit (0.025–3.0 mg L-1), and the Arsenator (NGO Forum-JU 1999). InBangladesh the performance of some arsenic test kits was evaluated as a requirement for theprocurement of field test kits by the Bangladesh Arsenic Mitigation Water Supply Project(BAMWSP 2001).

Table 5. Comparison of Arsenic Field Test Kits

Kit type Manufacturer Range (µg L-1) Cost (US$) Comments

E-Mark kit M/S E-Mark, Germany 100–3,000 (old) 50–100 Colors match with ranges5–500 (new) of arsenic concentration.

HACH kit HACH Company, USA 10–500 (50 ml One-time use for 100–sample) 300 tests350–4,000(9.6 ml sample)

Econo QuickTM Industrial Test Systems 10–1,000Inc., USA

AIIH&PH kit All India Institute of Yes/No type 40–60 Produces color ifHygiene and Public at 50 µg L-1 concentration exceedsHealth (AIIH&PH) 50 µg L-1. One-time use

Aqua kit Aqua Consortium (India) Yes/No typeat 50 µg L-1

AAN-Hironaka Dr. Hironaka, Fukuoka 20–700 Not on sale Colors match with rangekit City Inst. For Hygiene & of arsenic concentration.

Environment, Japan One-time use for 100tests

NIPSOM kit NIPSOM, with technical 10–700 40–80assistance from AAN-Hironaka

GPL kit General Pharmaceuticals 10–2,500 Ltd., Dhaka

BUET kit BUET, Dhaka 10–700 Not on sale

Digital Wagtech International <10–500 1,250 Quantitative valuesArsenator obtained

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Recently, several arsenic field test kits were tested for their efficacy under the EPA’sEnvironmental Technology Verification Program. The performances of the field test kits wereevaluated for accuracy, precision, linearity, method detection limit, matrix interference effects,operator bias, and rate of false positives or false negatives. The EPA issued verification reportsand verification statements for these arsenic field test kits (Abbgy and others 2002; EPA 2003)

The accuracy of arsenic measurement using the mercuric bromide stain method depends onmany factors. The first consideration is the method’s ability to eliminate the effects of interferingsubstances such as sulfide. The second consideration is the generation of arsine gas, which canbe achieved in several ways. Most kits use zinc, which may contain arsenic as an impurity andinterfere with the process. The advantage of using the chemicals in tablet form can be availed inthe case of arsine generation using sodium tetrahydroborate (NaBH4) and aminosulfonic acid. Anexcess amount of the reducing agent is required in this case to produce sufficient hydrogen gasto strip the arsine gas out of the solution and transfer it to mercuric bromide paper. The passingof arsine gas through mercuric bromide paper gives more reliable results at low concentrationsthan passing it over the surface of a small strip of mercuric bromide paper inserted into thereactor. The third consideration is that quantification of the arsenic concentration by visualcomparison is subjective and varies from person to person. The faint yellow color is notdiscernible to the average human eye. Again, for better results, the color comparison shouldbe made as soon as possible as the light-sensitive stain changes color rapidly. The resultsobtained by arsenic field test kits are, therefore, very much dependent on the type andquality of chemicals, preparation, the preservation and age of the chemicals, the quality ofwater, the quality of equipment, the operator’s skill, and the procedure of measurement (Jaliland Ahmed 2003).

The costs of equipment for arsenic measurement are shown in tables 4 and 5. The equipmentcosts of most laboratory methods are very high. Operation and maintenance costs are also veryhigh. Further, the service facilities of laboratory equipment manufacturers are not always availablein developing countries. Semiquantitative measurement using arsenic field test kits can be doneat low cost, making them affordable in developing countries, though the level of accuracy is lowerthan with laboratory tests.

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The shallow tubewell technology in alluvial aquifers of recent origin in the South Asia Region,which provided drinking water at low cost, has been found to be contaminated with arsenic

in many places. This unexpected calamity has exposed millions of people in contaminated areasto unsafe water. The risk has been magnified by the existence of very high levels of arsenic intubewell water in areas where the percentage of contaminated tubewells is also very high. In theabsence of an alternative source, people in such hotspots often have an unfortunate choicebetween continuing to drink arsenic-contaminated water or using unprotected surface waterand exposing themselves to the risk of waterborne diseases. Arsenic toxicity has no knowneffective treatment, but drinking arsenic-free water can greatly reduce the symptoms. Apartfrom treatment of arsenic-contaminated water, potential alternative water sources forarsenic-safe water supplies include:

• Deep tubewell• Dug or ring well• Rainwater harvesting• Treatment of surface water• Piped water supply

Deep Tubewell

Aquifers are water-containing rocks that have been laid down during different geological timeperiods. Deeper aquifers are often separated from those above by relatively impermeable stratathat keep them free of the arsenic contamination of shallower aquifers1. A study in Bangladesh bythe British Geological Survey (BGS) and the DPHE has shown that of tubewells with a depthgreater than 150 m, only about 1% have levels of arsenic above 50 µg L-1, and 5% have arseniclevels above 10 µg L-1 (BGS-DPHE 2001). As such, deep aquifers separated from shallowcontaminated aquifers by impermeable layers can be a dependable source of arsenic-safe water.

The presence of a relatively impermeable layer separating a deep uncontaminated aquifer from ashallow contaminated aquifer is a prerequisite for installation of a deep tubewell for arsenic-safewater. The annular spaces of the boreholes of the deep tubewells must be sealed, at least at thelevel of the impermeable strata, to avoid percolation of arsenic-contaminated water (figure 11). Itis very difficult to seal a small-bore tubewell but technological refinement using clay as a sealantis ongoing. A protocol for the installation of deep tubewells for arsenic mitigation has beendeveloped in Bangladesh (Government of Bangladesh 2004).

In the coastal area of Bangladesh proven arsenic-safe deep aquifers protected by overlyingthick clay layers are available for the development of safe water supplies. In other areas,arsenic-safe aquifers separated from arsenic-contaminated shallow aquifers are availablebut extensive and very costly hydrogeological investigations are required to delineate those

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1 In some areas, e.g. China, the deeper aquifers may be arsenic-affected. See paper 1.

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Figure 11. Deep Tubewell with Clay Seal (Ahmed, 2004)

aquifers. In the meantime, installation of deep tubewells following a deep tubewell protocolwill continue through examination of water quality and soil strata in test boreholes in theprospective deep tubewell areas.

However, there are many areas where separating impermeable layers are absent and aquifers areformed by stratified layers of silt and medium sand. The deep tubewells in those areas may yieldarsenic-safe water initially but are likely to experience an increase in the arsenic content of waterover time due to mixing of contaminated and uncontaminated waters. However, recharge of deepaquifers by infiltration through coarse media and replenishment by the horizontal movement ofwater are likely to keep such aquifers arsenic free even after prolonged water abstraction.Information about the configuration of an aquifer and its recharge mechanism is critical for theinstallation of deep tubewells.

Experience in the design and installation of tubewells shows that reddish sand produces thebest-quality water in terms of dissolved iron and arsenic. The reddish color of sand is produced

by oxidation of iron on sand grains in a ferric form that will not release arsenic or iron in

groundwater. On the contrary, ferric iron-coated sand will adsorb arsenic from groundwater. This

mechanism is probably responsible for the relative freedom from arsenic of the Dhaka water

supply, in contrast to the arsenic contamination that occurs in surrounding areas. Hence,

installation of tubewells in reddish sand, if available, should be safe from arsenic contamination.

Manually operated deeptubewell

Slity Clay

Arsenic-contaminatedshallow aquifer(sandy silt)

Relatively impermeable Clayey layer

Arsenic-safer deepaquifer (fine to mediumsand)

Strainer

Sand trap

Water table

Clay seal

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Dug or Ring Well

Dug wells are the oldest method of groundwater withdrawal for water supply. The water from dug

wells has been found to be relatively free from dissolved arsenic and iron, even in locations

where tubewells are contaminated. The reasons for this are not fully known, but possible

explanations include:

• The oxidation of dug well water due to its exposure to open air and agitation during water

withdrawal can cause precipitation of dissolved arsenic and iron.

• Dug wells accumulate groundwater from the top layer of a water table, which is replenished

each year by arsenic-safe rain and percolation of surface waters through the aerated zone of

the soil. The fresh recharges also dilute contaminated groundwater.

A study in an acute arsenic problem area shows that frequent withdrawal of water initiates

ingress of arsenic-contaminated water into dug wells and reduces the subsequent in situ

oxidation that, under normal operating conditions, increases the oxygen content of water and the

reduction of arsenic. Since the upper layer of soil contains organic debris, dug well water is often

characterized by bad odor, high turbidity and color, and high ammonia content. Dug wells are

also susceptible to bacterial contamination. Percolation of contaminated surface water is the

most common cause of well water pollution. Satisfactory protection against bacteriological

contamination is possible by sealing the well top with a watertight concrete slab, lining the well,

and constructing a proper apron around the well. Water may be withdrawn through the installation

of a manually operated handpump. Completely closed dug wells have good sanitary protection

but the absence of oxygen can adversely affect the quality of the water.

Construction and operational difficulties have been encountered in silty and loose to medium-

dense sandy soils. Sand boiling interferes with the digging, and sometimes leads to collapse of

dug wells. Constructed dug wells are also gradually filled up during operation by sand boiling.

Water in the well needs chlorination for disinfection after construction. Application of lime also

improves the quality of dug well water. Disinfection of well water should be continued for open

dug wells during operation by pot chlorination, but controlling the chlorine dose in dug well water

is difficult.

Surface Water Treatment

A prospective option for the development of a surface water-based water supply system is theconstruction of community slow sand filters, commonly known as pond sand filters inBangladesh, where they were originally designed for the filtration of pond water. This is apackage-type slow sand filter unit developed to treat surface waters, usually low-saline pondwater, for domestic water supply in coastal areas. The water from the pond or river is pumped by

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a manually operated tubewell to feed the filter bed, which is raised from the ground (figure 12).The treated water is collected through a tap. Tests have found that treated water from a pondsand filter is normally bacteriologically safe or within tolerable limits. The sand in the filter bedusually needs to be cleaned and replaced every two months. The operating conditions for slowsand filters include:

• Low turbidity, not exceeding 30 nephelometric turbidity units (NTU)• Low bacterial count• No algal bloom, absence of cynobacter• Free from bad smell and color

Figure 12. Pond Sand Filter for Treatment of Surface Water (Ahmed and Others, 2002)

A protected surface water source is ideal for slow sand filtration. The problems encounteredwhen the above operating conditions are not maintained include low discharge, the need forfrequent washing, and poor effluent quality. Since these are small units, community involvementin their operation and maintenance is absolutely essential in order to keep the systemoperational. By June 2000, the DPHE had installed 3,710 pond sand filter units, a significantproportion of which remain out of operation due to poor maintenance, drying of the source, orexcessive contamination of the water source.

The package-type slow sand filter is a low-cost technology with very high efficiency in turbidityand bacterial removal. It has received preference as an alternative water supply system formedium-size settlements in arsenic-affected areas. Although pond sand filters have a very highbacterial removal efficiency they may not reduce bacterial count to acceptable levels in cases of

Surfacewater

Clearwater

Under drainagesystem Raw water from pond

Handpump for water supplyto filter

Filter sand

Coarseaggregate

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heavily contaminated surface water. In such cases, the treated water may require chlorination tomeet drinking water standards.

A combined filter consisting of roughing filters and a slow sand filter is needed when the turbidityof water exceeds 30 NTU. The roughing filters remove turbidity and color to levels acceptable forefficient operation of the slow sand filter. Small-scale conventional surface water treatment plantsinvolving coagulation-sedimentation-filtration and disinfection can be constructed to cope withvariable raw water quality for community water supplies but the cost will be relatively high.

Rainwater Harvesting

Rainwater harvesting can be an alternative source of drinking water in arsenic-contaminatedSouth Asian countries. The relative advantages and disadvantages of rainwater harvesting areshown in table 6. A rainwater-based water supply system requires a determination of the storagetank capacity and the catchment area for rainwater collection in relation to the water requirement,rainfall intensity, and distribution. The availability of rainwater is limited by the rainfall intensityand availability of a suitable catchment area. The unequal distribution of rainwater over the yearin Asian countries requires a larger storage tank for uninterrupted water supply throughout theyear. This storage tank constitutes the main cost of the system.

The catchment area for rainwater collection is usually the roof, which is connected to the storagetank by a gutter system. Rainwater can be collected from any type of roof but concrete, tiles,and metal roofs give clean water. The corrugated iron sheet roofs commonly used in Bangladeshand India perform well as catchment areas. The poorer segments of the population are in a

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Table 6. Advantages and Disadvantages of Rainwater Collection System

Advantages Disadvantages

• The quality of rainwater is comparatively good • The initial cost may prevent a family frominstalling a rainwater harvesting system

• The system is independent and therefore • Water availability is limited by the rainfallsuitable for scattered settlements intensity and available roof area

• Local materials and craftsmanship can be used • Mineral-free rainwater has a flat taste, whichin construction of rainwater system may not be liked by many

• No energy costs are incurred in running the • Mineral-free water may cause nutritionsystem deficiencies in people who are on mineral-

deficient diets

• Ease of maintenance by the owner/user • The poorer segment of the population may nothave a roof suitable for rainwater harvesting

• The system can be located very close to the • May not last through the entire dry season.consumption point

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disadvantageous position in respect to theutilization of rainwater as a source of watersupply. These people have smaller thatchedroofs or no roof at all to be used as acatchment for rainwater collection. A thatchedroof can be used as a catchment area bycovering it with polyethylene but it requiresgood skills to guide water to the storage tank.In coastal areas of Bangladesh, cloths fixed atfour corners with a pitcher underneath areused during rainfall for rainwater collection. Aplastic sheet, as shown in figure 13, has beentried as a catchment for rainwater harvestingfor people who do not have a roof suitable forrainwater collection. The use of land surface asa catchment area and underground gravel orsand-packed reservoirs as storage tanks canbe an alternative system of rainwater collectionand storage. In this case, the water has to bechanneled towards the reservoir and allowed

Figure 13. Plastic Sheet Catchment (Ahmedand others, 2002)

to pass through a sand bed before entering underground reservoirs. This process is analogous torecharge of underground aquifers by rainwater during the rainy season for utilization in the dry season.

The quality of rainwater is relatively good but it is not free of all impurities. Analysis of storedrainwater has shown some bacteriological contamination. Cleanliness of the roof and storage tankis critical to maintaining the good quality of rainwater. The first runoff from the roof should bediscarded to prevent entry of impurities from the roof. If the storage tank is clean, the bacteria orparasites carried with the flowing rainwater will tend to die off. Some devices and good practiceshave been suggested to store or divert the first foul flush away from the storage tank. In case ofdifficulties in the rejection of first flow, cleaning of the roof and gutter at the beginning of the rainyseason and their regular maintenance are very important to ensure better quality of the rainwater.The storage tank requires cleaning and disinfection when the tank is empty or at least once in ayear. Rainwater is essentially lacking in minerals, the presence of which is considered essentialin appropriate proportions. The mineral salts in natural ground and surface waters sometimesimpart a pleasing taste to water.

Piped Water Supply

Piped water supply is the ultimate goal of safe water supply to the consumer because:

• Water can be delivered to close proximity of the consumers.• Piped water is protected from external contamination.

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• Better quality control through monitoring is possible.• Institutional arrangements for operation and maintenance are feasible.• Water of required quantity can be collected with ease.

In terms of convenience in collection and use, only piped water can compete with the existingsystem of tubewells for water supply. It can be a feasible option for clustered rural settlementsand urban fringes. Water can be made available through house connection, yard connection, orstandpost, depending on the affordability of each option to the consumer. The water can beproduced, according to demand, by sinking deep tubewells into an arsenic-safe aquifer or bytreatment of surface water or even arsenic-contaminated tubewell water by community-leveltreatment plants. Rural piped water supply has received priority for arsenic mitigation inBangladesh and a large number of pilot schemes by different organizations are underimplementation. It appears that piped water supply will be a suitable option for populations livingin clustered settlements, but it will be a difficult and costly option for scattered populations.

Cost Comparison of Alternative Water Supply Options

As has been discussed in this chapter, a variety of alternative technological options is availablefor water supply in arsenic-affected areas. The cost of arsenic mitigation will depend on the typeof technology adopted. The costs of installation and operation of some major technologicaloptions available from various organizations involved in arsenic mitigation are summarized intable 7.

The quality and quantity of water, reliability, cost, and convenience of collection of water varywidely for the various options. Deep tubewells can provide water at nominal operation andmaintenance costs but they are not feasible, nor able to provide arsenic-free water, at alllocations. Dug or ring wells can provide water at moderate installation and nominal operation andmaintenance costs. It is not yet fully known whether the quality of water can be maintained atdesired levels. Bacteriological quality is likely to remain at safe levels under conditions of propersanitary protection. Piped water supply can be provided at a higher cost and with relativelyhigher operation and maintenance costs but the convenience and health benefits are muchgreater because water of adequate quantity and relatively superior quality for all domesticpurposes, including sanitation, becomes available at or near residences. Increasing the numberof households connected reduces average costs. Available data suggest that the average cost ofpiped water supply becomes lower than other options when the number of households exceeds500 (see paper 4). The relative cost of installation for a rainwater harvesting system at householdlevel with only about 50% reliability is very high. Installation of community rainwater harvestingsystems may be cheaper, but management of such systems may be difficult.

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Source: Government of Bangladesh 2002.

Table 7. Costs of Alternative Technological Options in Arsenic-Affected Areas

Alternative No. of Unit cost Operation and CommentsTechnological households (US$) maintenanceoptions per unit costs/year (US$)

Rainwater harvesting 1 200 5 Low reliability

Dug or ring well 25 800 3 Depth about 8 m

Deep tubewell 50 900 4 Depth about 300 m

Pond sand filters 50 800 10–20 Slow sand filterprocess

Surface water treatment 1,000 15,000 3,000 Conventionalprocess

Piped water supply 1,000 40,000 800 Systems are basedon arsenic-safegroundwater

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The presence of arsenic in low concentration and the need to reduce it to levels associatedwith desired health benefits have given rise to many operational difficulties. Measurement of

arsenic at low concentration is difficult, as is the monitoring of treatment system performance.Validation of the claims of proponents concerning the performance of treatment technologies andarsenic measurement devices is an important requirement. Safe disposal of toxic sludge andspent media is an environmental concern. The technologies based on patented media orprocesses and imported components may face operational difficulties due to lack of availabilityand supply of materials and components.

Operational issues are very important for small-scale water treatment facilities at the householdand community levels. It is not possible to make an institutional arrangement for operation, repair,and maintenance of small water supply systems. People’s participation and capacity building atthe local level are considered vital for keeping the system operational. There are many examplesof failure of small water supply systems in the absence of initiatives, commitment, andownership of the system. In many cases, the small system may be more costly due to scalingdown of a conventional system for water treatment.

Technology Verification and Validation

Quite a lot of development of arsenic treatment and measurement technologies has taken placeover the last five years in response to demand. Verification and validation of the claims of thesetechnologies are needed to help buyers select the right technology. The EPA has developedprotocols for validation of arsenic treatment technologies and arsenic field test kits under itsEnvironmental Technology Verification Program. The protocols have been developed incollaboration with the Environmental Technology Verification Program in Canada and BettleLaboratories, United States (EPA 2003). The WHO has developed generic protocols for adoptionin South-East Asia Region countries (WHO 2003).

A systematic evaluation of arsenic mitigation technologies is being conducted under theEnvironmental Technology Verification–Arsenic Mitigation Program by the Bangladesh Council ofScientific and Industrial Research in collaboration with the Ontario Centre for EnvironmentalTechnology Advancement, Canada. Generic and technology-specific test protocols consistentwith environmental and operative conditions in Bangladesh have been developed for thisverification program. The program has thus far completed verification of five arsenic removaltechnologies in Phase I (BCSIR 2003). An additional 14 technologies are pending for verification inPhase II of the program.

Verification of some technologies in Bangladesh shows that their performance is very muchdependent on pH, and the presence of phosphate and silica in natural groundwater. Most of thetechnologies do not meet the claims of the proponents concerning treatment capacity. Areduction in the rated capacity will further increase the cost of treatment per unit volume of water.

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Sludge Disposal

Since arsenic cannot be destroyed all arsenic treatment technologies ultimately concentratearsenic in sorption media, sludge, or liquid media. A variety of arsenic-rich solids andsemisolids, such as arsenic-saturated hydrous ferric or aluminium oxides and other filter media,are generated from arsenic removal processes. Regeneration of activated alumina and ionexchange resins results in various liquid wastes that may be acidic, caustic, saline, and tooarsenic rich for simple disposal. Hence, environmentally safe disposal of sludge, saturatedmedia, and liquid wastes rich in arsenic is a concern.

The EPA has developed a toxic characteristic leaching procedure (TCLP) test to identify wasteslikely to leach toxic chemicals into groundwater. The permissible level for TCLP leachate isgenerally 100 times higher than the maximum contaminant level in drinking water, for example5,000 µg L for leached arsenic when the acceptable level in drinking water is 50 µg L. Sludgeleaching more that 5,000 µg L of arsenic would be considered hazardous and would requiredisposal in a special hazardous waste landfill. The TCLP test was conducted on different typesof wastes collected from arsenic treatment units and materials in Bangladesh (Eriksen-Hamel andZinia 2001; Ali and others 2003). It has been observed that in almost all cases arsenic leachingwas very minor. Arsenic leaching tests were conducted at the BUET using different extractionfluids. For all extractants arsenic concentration in the column effluents was initially very high, butthen dropped sharply (Ali and others 2003). Several researchers also conducted TCLP tests onsludge resulting from arsenic removal with aluminium and ferric salts and found arsenic inleachate in the range of 9–1,500 µg L (Brewster 1992; Chen and others 1999). These arseniclevels in leachate are well below the level required for classification as hazardous wastes. Itappears that most sludge would not be considered hazardous even if the WHO guideline value of10 µg L-1 for arsenic in drinking water were considered.

Hazardous wastes are often blended into stable waste or engineering materials such as glass,brick, concrete, or cement block. There is a possibility of air pollution or water pollutiondownstream of kilns burning brick containing arsenic-contaminated sludge due to volatilization ofarsenic during burning at high temperatures. In Hungary experiments showed that some 30% ofarsenic in the coagulated sludge was lost to atmosphere in this way (Johnston, Heijnen, andWurzel 2000). Sludge or spent filter media with low arsenic content can be disposed of on land orin landfills without significant increase in the background concentration of arsenic. Wastes withhigh concentration of arsenic may need solidification or confinement before final disposal.

Costs

The cost of arsenic removal technology is an important factor for its adoption and sustainable usein rural areas. The cost of the technologies depends on many factors such as the materials usedfor fabrication of components, quantity of media or chemicals used, and quality of groundwater.

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Most of the technologies have been installed and are being operated under field testing and pilot-scale operations. Hence the costs of installation, operation, and maintenance of all the arsenicremoval systems are not known or are yet to be standardized based on modifications to suit thelocal conditions. The available costs and system capacities of some arsenic removaltechnologies are presented in tables 2 and 3. The costs of alternative water supply systems arepresented in table 7.

The unit costs of water produced by different water supply systems to meet present servicelevels have been calculated on the basis of annualized capital recovery using an annual interestrate of 12% (table 8). It has been assumed that the arsenic-safe water required per family fordrinking and cooking is 45 L/day. However, the water production capacity of most alternativewater supply systems is much higher than this and can serve additional users, or provideexisting users with more water for all household purposes. If the full water production capacitiesof these systems are utilized the cost per unit volume of water is greatly reduced.

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Table 8. Cost of Water Supply Options for Arsenic Mitigation

Technology Tech life Annualized Operation & Water output Unit cost(years) capital maintenance (m3) (US$/m3)

recovery (US$)a cost/year(US$)

Alternative water supply:

Rainwater harvesting 15 30 5 16.4 2.134

Deep tubewell 20 120 4 820 0.1514,500 0.028b

Pond sand filter 15 117 15 820 0.1612,000 0.066b

Dug or ring well 25 102 3 410 0.2561,456 0.072b

Conventional 20 2,008 3,000 16,400 0.305treatment

Piped water 20 5,872 800 16,400 0.37573,000 0.084b

Arsenic treatment (households) based on:

Coagulation-filtration 3 3 25 16.4 1.70

Iron-coated sand/ 6 0.9 11 16.4 0.73brick dust

Iron filings 5 3 1 16.4 0.24

Synthetic media 5 1.2 29 16.4 1.84

Activated alumina 4 3.2 36 16.4 2.39

Arsenic treatment (community) based on:

Coagulation-filtration 10 44 250 246 1.21

Granulated ferric 10–15 500–600 450–500 820–900 1.20hydroxide/oxide

Activated alumina 10–15 30–125 500–520 164–200 3.20

Ion exchange 10 50 35 25 3.40

Reverse osmosis 10 440 780 328 3.72

As-Fe removal (air 20 32,000 7,500 730,000 0.054oxidation-filtration)

a The capital recovery/amortization factor has been calculated using the formula:

where i = interest rate and N = number of years.

b Development of full potential of the system.

(1 + i)N

((1 + i)N -1) / i

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The problem of treatment of arsenic-contaminated water arises from the requirement for itsremoval to very low levels to meet the stringent drinking water quality standards and

guideline values for arsenic. Arsenic removal technologies have improved significantly over thelast few years but many of the technologies do not work satisfactorily for natural groundwater.Reliable, cost-effective, and sustainable treatment technologies are yet to be identified andfurther developed. All the technologies have their strengths and weaknesses and are beingrefined to accommodate rural conditions. Modifications based on pilot-scale implementation ofthe technologies are in progress with the objectives of:

• Improving efficiency of arsenic removal• Reducing capital and operation cost of the systems• Making the technology user friendly• Overcoming maintenance problems• Resolving sludge and arsenic concentrates management problems.

Because of the cost and operational complexity of arsenic removal technologies, alternativewater supply options are often given preference in arsenic mitigation. Surface water of desirablequality is not always available for low-cost water supply, while the cost of treatment of surfacewater using conventional coagulation-sedimentation-filtration and disinfection processes is veryhigh. Rainwater harvesting as a household option is also costly. Dug wells do not produce ormaintain water of desirable quality in all locations and are difficult to construct in some areas.

The technologies are site specific and there are various considerations for selection of a particulartechnology in any given locality. Some of the important considerations for the development ofsustainable water supply options for purposes of arsenic mitigation are:

• The profile of the beneficiaries and settlement pattern• Present water supply system and level of arsenic in the drinking water• Possible alternative sources of water for water supply• Relative risk and cost of development of water supply system• The level of technical and managerial capacity building needed• Affordability and willingness to pay.

A lot of effort has been spent developing the performance of arsenic field test kits. Although theaccuracy of arsenic detection and measurement by field test kits is not fully satisfactory, it is aconvenient tool for testing water in rural areas. Field test kits are being widely used and willcontinue to be used in the near future until a network of in-country laboratories is established fortesting arsenic at a reasonable cost. It is therefore essential to improve the performance of thefield test kits and implement quality assurance programs for field-based measurement withback-up support from available in-country laboratories to meet the present need.

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Abbgy, A., T. Kelly, C. Lawrie, and K. Riggs. 2002. Environmental Technology Verification Report:QuickTM Arsenic Test Kit. EPA Environmental Technology Verification Program.

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Ahmed, M. F. 2003. "Treatment of Arsenic Contaminated Water." In: M. F. Ahmed, ed., ArsenicContamination: Bangladesh Perspective 354-403. Dhaka, Bangladesh: ITN-Bangladesh.

Ahmed, M.F. 2004. " Cost of Water Supply Options for Arsenic Mitigation''. In : People-CentredApproached to Water and Environmental Sanitation, Preprint, 30th WEDC International Conference600-603. Vientiane, Lao PDR

Ahmed, M. F., M. A. Ali, and Z. Adeel, eds. 2001. Technologies for Arsenic Removal from DrinkingWater. ISBN 984-31-1305-6. Bangladesh University of Engineering & Technology and UnitedNations University. www.unu.edu/env/Arsenic/BUETWorkshop.htm.

Ahmed, M. F. and M. M. Rahaman. 2000. Water Supply and Sanitation - Low Income UrbanCommunities. International Training Network Centre, Bangladesh University of Engineering andTechnology.

Ali, M. A., A. B. M. Badruzzaman, M. A. Jalil, M.D. Hossain, M. M. Hussainuzzaman,M. Badruzzaman, O.I. Mohammad and N. Akhter.2001. "Development of Low-cost Technologiesfor Removal of Arsenic from Groundwater'' In: Ahmed, M. F., M. A. Ali, and Z. Adeel, eds.,Technologies for Arsenic Removal from Drinking Water. 99-120. Bangladesh University ofEngineering & Technology and United Nations University.

Ali, M. A., A. B. M. Badruzzaman, M. A. Jalil, M. F. Ahmed, A. Al-Masud, M. Kamruzzaman, andA. R. Rahman. 2003. "Fate of Arsenic in Wastes Generated from Arsenic Removal Units." In:M. F. Ahmed and others, eds., Fate of Arsenic in the Environment 147-160. Bangladesh Universityof Engineering and Technology and United Nations University.

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AWWA (American Water Works Association). 1999. Arsenic Treatability Options and Evaluation ofResiduals Management Options. AWWA Research Foundation.

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BAMWSP (Bangladesh Arsenic Mitigation Water Supply Project). 2001. Evaluation of Performanceof Arsenic Field Test Kits. Unpublished Report.

BAMWSP-DFID-WaterAid (Bangladesh Arsenic Mitigation Water Supply Project, United KingdomDepartment for International Development, WaterAid Bangladesh). 2001. Rapid Assessment ofHousehold Level Arsenic Removal Technologies, Phase-I and Phase-II. Final Report. W. S. AtkinsInternational Limited.

BCSIR (Bangladesh Council of Scientific and Industrial Research). 2003. Performance Evaluationand Verification of Five Arsenic Removal Technologies. Environmental Technology Verification–Arsenic Mitigation Program, Phase I.

BGS-DPHE (British Geological Survey and Bangladesh Department of Public Health Engineering).2001. Arsenic Contamination of Groundwater in Bangladesh Volume 2. D. G. Kinniburgh andP. L. Smedley, eds. British Geological Survey Report WC/00/119.

Brewster, M. D. 1992. “Removing Arsenic from Contaminated Wastewater.” Water Environment &Technology 4(11):54–57.

Chen, H. W., M. M. Frey, D. Clifford, L. S. McNeill, and M. Edwards. 1999. “Arsenic TreatmentConsiderations.” J. American Water Works Association 91(3):74–85.

Cheng, C. R., S. Liang, H. C. Wang, and M. D. Beuhler. 1994. “Enhanced Coagulation for ArsenicRemoval.” J. American Water Works Association 86(9):79–90.

Clifford, D. 1999. “Ion Exchange and Inorganic Adsorption.” In: F. Pontius, ed., Water Quality andTreatment: A Handbook of Community Water Supplies. American Water Works Association.New York: McGraw Hill.

Dahi, E. and Q. Liang. 1998. Arsenic Removal in Hand Pump Connected Iron Removal Plants inNoakhali, Bangladesh. Presented at International Conference on Arsenic Pollution of Ground Waterin Bangladesh: Causes, Effect and Remedies, Dhaka, 8–12 February 1998.

Edwards, M. 1994. “Chemistry of Arsenic Removal During Coagulation and Fe-Mn Oxidation.”J. American Water Works Association 86(9):64–78.

EPA (United States Environmental Protection Agency). 2002. Arsenic in Drinking Water TreatmentTechnologies: Removal. www.epa.gov/ogwdw000/ars/treat.html.

EPA (United States Environmental Protection Agency). 2003. Environmental Technology VerificationProgram. www.epa.govt/etv/verifications/vcenter1-21.html.

Eriksen-Hamel, N. and K. N. Zinia. 2001. “A Study of Arsenic Treatment Technologies andLeaching Characteristics of Arsenic Contaminated Sludge.” In: Ahmed, M. F., M. A. Ali, and

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Fox, K. R. 1989. “Field Experience with Point-of-Use Treatment Systems for Arsenic Removal.”J. American Water Works Association 81(2):94–101.

Ghurye, G., D. Clifford, and A. Tripp. 1999. “Combined Arsenic and Nitrate Removal by IonExchange.” J. American Water Works Association 91(10):85–96.

Government of Bangladesh. 2002. Arsenic Mitigation in Bangladesh. Ministry of LocalGovernment, Rural Development and Cooperatives, Local Government Division.

Government of Bangladesh. 2004. National Policy for Arsenic Mitigation 2004 and ImplementationPlan for Arsenic Mitigation in Bangladesh. Government of Bangladesh, Ministry of LocalGovernment, Rural Development and Cooperatives, Local Government Division.

Gupta, S. and K. Chen. 1978. “Arsenic Removal by Adsorption.” J. Water Poll. Contr. Fed.50:493–506.

Hering, J. G., P. Y. Chen, J. A. Wilkie, and M. Elimelech. 1997. “Arsenic Removal from DrinkingWater During Coagulation.” ASCE J. Environmental Engineering 123(8):800–807.

Hering, J. G., P. Y. Chen, J. A. Wilkie, M. Elimelech, and S. Liang. 1996. “Arsenic Removal byFerric Chloride.” J. American Water Works Association 88(4):155–167.

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ISO (International Organization for Standardization). 1996. Water Quality – Determination of Arsenic– Atomic Absorption Spectrometric Method (Hydride Technique). ISO 11969.

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Jalil, M. A. and M. F. Ahmed. 2003. “Arsenic Detection and Measurement by Field Kits.” In:M. F. Ahmed, ed., Arsenic Contamination: Bangladesh Perspective. Dhaka, Bangladesh:ITN-Bangladesh.

Jekel, M. R. 1994. “Removal of Arsenic in Drinking Water Treatment.” In: J. O. Nriagu, ed.,Arsenic in the Environment, Part 1: Cycling and Characterization. New York: John Wiley &Sons, Inc.

Johnston, R., H. Heijnen, and P. Wurzel. 2000. Safe Water Technology.www.who.int/water_sanitation_health/arsenic/ArsenicUNRep7.htm.

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Joshi, A. and M. Chaudhuri. 1996. “Removal of Arsenic from Groundwater by Iron-Oxide-CoatedSand.” ASCE J. Environmental Engineering 122(8):769–771.

Kartinen, E. O. and C. J. Martin. 1995. “An Overview of Arsenic Removal Processes.”J. Desalination 103:79–88.

Khaliquzzaman, M. and A. H. Khan. 2003. “Analysis of Water for Arsenic in Bangladesh.” In:M. F. Ahmed, ed., Arsenic Contamination: Bangladesh Perspective. Dhaka, Bangladesh: ITN-Bangladesh.

Khan, A. H., S. B. Rasul, A. K. M. Munir, M. Alauddin, M. Habibuddowlah, and A. Hussam. 2000.“On Two Simple Arsenic Removal Methods for Groundwater of Bangladesh.” In: M. F. Ahmed,ed., Bangladesh Environment 2000 151–173. Bangladesh Poribesh Andolon.

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Meng, X. G. and G. P. Korfiatis. 2001. “Removal of Arsenic from Bangladesh Well Water UsingHousehold Filtration System.” In: Ahmed, M. F., M. A. Ali, and Z. Adeel, eds., Technologies forArsenic Removal from Drinking Water 121–130. Bangladesh University of Engineering &Technology and United Nations University.

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Young, E. 1996. “Cleaning Up Arsenic and Old Waste.” New Scientist 14 December 1996.

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1. This paper introduces an approach that provides a quick and readily applicable method for

performing a cost-benefit analysis of different arsenic mitigation policies. In particular, our

suggested approach estimates benefits of mitigation activities as the sum of forgone

medical costs and saved output productivity achieved by reducing arsenic exposure. The

present value of these benefits is then compared with the present value of costs of various

mitigation measures in order to investigate when and which mitigation policies pass a cost-

benefit analysis (that is, produce a positive change in social welfare).

2. The paper applies this approach in order to provide some estimate of costs and benefits of

arsenic mitigation in one case study country: Bangladesh. This case study serves as an

applied example of such rapid socioeconomic evaluation and is also used as a basis for

discussing trade-offs in decisionmaking with respect to the allocation of financial resources.

Our approach is applicable to both cases: (a) the risk that arsenic might be found in an area

where a project is planned; and (b) approaches in regard to risk mitigation options where a

project aims at arsenic mitigation per se.

3. Our case study showed that for the case of Bangladesh the cost-benefit ratios for many

relevant mitigation techniques and policies are positive under varying levels of success in

terms of their effectiveness. These results indicate the imminent need for facing the arsenic

crisis in Bangladesh, but also the clarity with which our approach can answer the difficult

question on the balance of relevant costs and benefits of various mitigation options

and policies.

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Aims of This Paper

This paper reviews existing studies and data on arsenic mitigation in those countries where ithas been undertaken, and the costs of achieving such mitigation. Then these costs are

compared with relevant benefits, while taking into consideration the limited knowledge baseregarding the epidemiology of arsenic in the region. Discussion of the different limits for arsenic indrinking water in different countries and simulation of cost implications from implementing eachlimit, as well as the trade-offs between different water sources (ground or surface water, forexample) in a range of socioeconomic circumstances, is central to the paper.

All decisions imply a money value of benefits, while policies can only be accepted orrejected. If a policy costs $X, accepting and implementing it implies that benefits exceed$X. Rejecting the policy implies that benefits are less than $X. Hence, there is no escapefrom monetary valuation. This paper provides a general introduction to the way of thinkingabout costs and benefits of mitigating (natural) pollutants, including considerations oftrade-offs in decisionmaking with respect to the allocation of financial resources in abudget-constrained environment.

In particular, a methodology is suggested for analyzing options in order to choose betweendifferent approaches in dealing with (a) the risk that arsenic might be found in an area where aproject is planned; and (b) approaches to risk mitigation options where a project’s goal is arsenicmitigation per se.

The paper also provides decisionmakers and project managers with an efficient and readilyapplicable methodology for rapid assessment of the socioeconomic desirability of differentarsenic mitigation policies under various scenarios. The proper way of deciding whether toimplement a particular mitigation policy involves conducting a cost-benefit analysis (CBA), whichin turn involves (a) consideration of several different policy options to test costs and benefits ofeach; (b) a general equilibrium approach to the costs of a policy; (c) behavioral studies of wateruser responses to different levels of mitigation; and (d) behavioral studies of user responses tononavailability of contaminated water, especially substitution with other sources of water. Thetrue compliance cost of any arsenic mitigation policy is unknown but some estimated figures canbe used. However, we do not know the full behavioral reactions to different possiblemitigation policies.

An alternative, equally ideal model on which decisionmaking could be based involves(a) estimation of changes in levels of exposure; (b) exposure-response functions linking levels tohuman mortality, human morbidity, and ecosystems and species; (c) willingness to pay formeasures that avoid impacts identified in exposure-response relationships; and (d) allocation ofbenefits and costs to time periods (years). Such a procedure for estimating health benefits ismore tractable than a CBA, but remains very difficult due to the absence of (a) a behavioralmodel of the economic sectors that use arsenic-contaminated water; (b) knowledge of change inexposure; (c) knowledge of exposure-response functions; and (d) internalization assumptions foroccupational effects.

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215214

In the absence of a full study (because of missing information and prevailing uncertainties) andgiven the millions of people around the world who are currently menaced by arsenic poisoning,health policymakers need to devise policies capable of counteracting this threat based on an"nth best" approach. One method of analysis would be a cohort study, selecting control (nointervention) and intervention villages (with implementation of mitigation methods) and tracking theeffects of the disease on people’s health and livelihood, including coping mechanisms, oversome period of time. Any study method using real populations would, however, only provideresults after long periods, which limits this method’s applicability to the immediate public healthconcern. In addition, it is questionable whether long-term cohort follow-up would be achieved in acountry where tracking of individuals is limited. Finally, ethical considerations would precludesuch studies as soon as it becomes apparent that mitigation methods do work and provide relief.

Our suggested approach attempts to estimate the medical costs and forgone productivity fromspecific diseases or health end states. The paper applies this approach in order to provide someestimate of costs and benefits of arsenic mitigation in one case study country, namelyBangladesh. Of the regions of the world with groundwater arsenic problems Bangladesh is theworst case that has been identified, with some 35 million people thought to be drinkinggroundwater containing arsenic at concentrations greater than 50 µg L-1 and around 57 milliondrinking water with more than 10 µg L-1 (see, Paper 1 of this report). The large scale of theproblem reflects the large area of affected aquifers, the high dependence of Bangladeshis ongroundwater for potable supply, and the large population accumulated in the fertile lowlands ofthe Bengal Basin. Today, there are an estimated 11 million tubewells in Bangladesh serving apopulation of around 130 million people. The scale of arsenic contamination in Bangladesh meansthat it has received by far the greatest attention in terms of groundwater testing and more isknown about the arsenic distribution in the aquifers than in any other country in Asia (as well asmost of the developed world). However, much more testing is still required. Our Bangladeshicase study serves as an applied example of such a rapid socioeconomic evaluation and will alsobe used as a basis for discussing trade-offs in decisionmaking with respect to the allocation offinancial resources.

Situational Analysis

Groundwater is a significant source of drinking water in many parts of the world. Well-protectedgroundwater is safer in terms of microbiological quality than water from open dug wells andponds. However, groundwater is notoriously prone to chemical and other types of contaminationfrom natural sources or anthropogenic activities. One of these is contamination caused by highconcentration levels of arsenic in water. Arsenic is a chemical that is widely distributed in natureand principally occurs in the form of inorganic or organic compounds.

The available treatment technologies for arsenic removal provide varying results depending onthe concentration of arsenic in the water, the chemical composition of the water (includinginterfering particles), and the amount of water to be treated. Another important consideration isthe feasibility and cost of the treatment process. The most commonly used biophysical methods

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are coagulation, softening, iron and manganese oxidation, anion exchange, activated aluminamembrane processes, and electrodialysis. The frequently prohibitive cost of these technologiesin rural contexts has prompted the search for alternative sources of arsenic-free water, such asrainwater harvesting.

Reliable data on exposure and health effects are rarely available, but it is clear that there aremany countries in the world where arsenic in drinking water has been detected at concentrationsgreater than the WHO guideline value of 10 µg L-1, or the prevailing national standard. Theseinclude Argentina, Chile, Japan, Mexico, New Zealand, the Philippines, the United States ofAmerica, and some countries in South and East Asia, as described in detail in Paper 1.

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In order to show what is necessary for a proper evaluation of arsenic mitigation measures thischapter lays out an "ideal" approach – one based on a conceptually sound model, but which

as a function of its assumptions has certain limitations. This permits us to judge the gap betweenwhat should be done and what can be done in practice.

Uncertainty and the Ideal Approach

One misconception needs to be dispelled at the outset. One of the criticisms of economic(cost-benefit) approaches to policy evaluation is that they add to the uncertainty associated withevaluation. As such, it is argued, the approaches are best not adopted in the first place.There are indeed uncertainties, and often significant uncertainties, in cost-benefit appraisal.The problem is that the uncertainty is not reduced through nonadoption of cost-benefit analysis(CBA). Invariably, uncertainty is actually increased when CBA is not used. There are manyreasons for this conclusion, but two will suffice.

First, what CBA does is to compare benefits and costs in the same units (money).1 This permits adecision of whether or not to adopt the policy at all. Adoption follows if benefits exceed costsand not otherwise. Failure to monetize benefits means that the choice context is one of cost-effectiveness in which costs are in money units but effectiveness is in a different unit, forexample some notion of risk reduction (such as lives saved). However, cost-effectiveness canonly rank alternative policies; it cannot say whether anything should be done. We may, forexample, choose policy A over B because A secures more risk reduction per dollar than B.Nevertheless, both A and B could still fail cost-benefit tests, indicating that neither should beundertaken. Thus, a failure to adopt CBA increases risk because a new risk emerges, namelythat incorrect policies are adopted.

Second, the risk reduction in question will show up in various ways. On the simplest level it maymanifest itself in reduced mortality and reduced morbidity. Cost-effectiveness analysis cannotnow be conducted unless we have some idea of the relative importance of reducing one form ofrisk over another form of risk. Relative importance is measured by a set of weights, such that theratio of the weights on any two forms of risk reduction reflects the relative importance of reducingone risk compared to another. If weights are not adopted, it is not possible to make anycomparison between options, and rational decisionmaking is not possible. All decision analysisinvolves one means or another of selecting weights: by implied political preference, overt expertjudgments, or, in the case of CBA, individuals’ willingness to pay for one change compared to

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1 This simple observation also explains why one cannot logically avoid monetization. First, all policies have costs. If they did not have costs,there would be no need to consider whether or not they are “good” policies. Hence the acceptance of a policy implies that benefits mustexceed costs, which sets a lower bound on the scale of monetary benefits. If the policy is rejected, the reverse applies. Second, costs aremeasured in monetary terms and few people have difficulty in agreeing that this is the correct way to measure costs. But costs are simplynegative benefits, since all costs are properly measured by the forgone benefits of spending money on the chosen project rather than onsomething else. So, positive money costs are the same thing as negative money benefits. It follows that benefits must also be expressible inmonetary units.

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another. In short, CBA’s weights are prices. Compared to a situation in which there is noknowledge of weights at all, CBA reduces uncertainty and does not increase it. It then becomesan issue of which set of weights is preferable. One advantage of CBA weights (prices) is thatthey reflect the preferences of those exposed to risk, and are hence more democratic thanexpert weights.2

An Ideal Model

The ideal approach to measuring the social benefits and costs of arsenic mitigation would be

as follows.

First, some assessment would need to be made of the extent to which the selected mitigation

strategy will reduce human and environmental exposure to arsenic contamination. Refer to this

change as ∆X where X refers to exposure. This stage of the analysis would therefore produce the

policy effect on exposure.

Second, we need an exposure-response relationship. Two effects can be identified. The first is

the effect on human health, call this ∆H. Again, there will be many different health effects, ranging

from reduced premature mortality to changes in, for example, hospital admissions and days

away from work. Therefore, ∆H is a vector. It is helpful to divide human health effects into

reduced occupational risks (∆HO) and reduced public health risks (∆HP). This is because there

may be differences in the way the two effects are to be valued in monetary terms. The second

effect is the environmental impact on ecosystems and biodiversity. Call this ∆E. Then, the sum of

the effects is ∆HO + ∆HP + ∆E = ∆I where I is overall impact.

Third, we need economic values for each impact since it is implicit in the equation for ∆I that the

effects are expressed in the same units. We refer to these as the shadow prices because they

are the prices that would be attached to the reduced risk if there were an overt market for risk

reduction. These shadow prices reflect individuals’ willingness to pay for avoiding the ill health or

negative environmental impact associated with arsenic. Again there will be a whole set of

shadow prices covering all of the impacts. We refer to these shadow prices as P and they are

formally equivalent to the weights discussed in next section.

Fourth, we need to know when in time the changes in exposure will occur. This is because future

changes in exposure will be valued less than near-term changes in exposure. The economic

2 It could be argued that political weights are best of all since politicians are elected to make such decisions. Unfortunately, the politicalmodel underlying this view is naïve, and assumes politicians always act in the best interests of voters. Moreover, techniques such as CBAare designed as checks on political decisionmaking; this is the purpose of policy analysis.

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concept that reflects the different weights attached to time is known as a discount factor. The

process of attaching weights to time is known as discounting. The discount factor (DF) is linked

to the discount rate(s) (expressed as an interest rate; that is, in percentage terms) as shown in

equation 1:

Equation 1. Discount Factor

Where t = time (years from the present).3

Timing is important, however; not all mitigation measures can predict the exact timing ofexposure reduction. For example the regulator or policymaker, in a situation where a village’sgroundwater resources are contaminated, can decide to introduce piped arsenic-free watersupply. Exposure to arsenic will be reduced at the moment piped water supply is introduced, ifthe regulator can effectively monitor that the inhabitants of the village do not continue to use othercontaminated groundwater sources. Monitoring of abstraction activities is difficult, timeconsuming, and hence expensive, especially when areas are heavily populated. As a resultmonitoring will have to be coupled with an attempt to increase social awareness of the adverseeffects of using contaminated water (for example through an educational campaign). Aneducational campaign, however, will be costly and a medium-term measure. Overall, even formitigation measures as drastic as introducing another source of water, the timing of reductionexposure is not as evident as might be imagined.

Moreover, if a regulator is interested in restricting groundwater abstraction in order to reduce thepossible anthropogenic impacts of pumping on groundwater contamination, then the exact timingof the contribution of this measure to exposure reduction (and possibly the timing of reintroducinggroundwater as a water source) becomes even more difficult to identify. The significant impactsof pumping on groundwater flow may result in medium-term or long-term changes in the aquifersystems (see Paper 1 of this report). Not only is it difficult to quantify these impacts, both withregards to their time and space dimension, but it is also necessary to be aware of the variousdimensions of the potential human influences. These include the impacts of pumping-inducedflow on transport of arsenic both within and between aquifers, impact of pollutants such asorganic carbon and phosphate on aquifer redox and sorption or desorption, and impact ofseasonal waterlogging of soils for rice production on subsurface redox conditions.

Fifth, we need to know where the exposure changes occur. For example, if they occur in heavilypopulated areas the benefits of risk reductions will be higher. Environmental effects are evenmore location specific.

DF =1

(1 + s)t

3 Space precludes further discussion of discounting. It should be noted that it is not possible to avoid discounting. Not discounting isformally equivalent to discounting at 0%. Unfortunately, zero discounting has logical implications that make it undesirable, howeverreasonable it may at first appear (Koundouri and others 2002).

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The ideal model can now be summarized as follows. The benefits that ensue from arsenicmitigation are given by equation 2.4

Equation 2. Ideal Model of Benefits Ensuing from Arsenic Mitigation

Where:

i = the individual impactsPV(B) = the present value of benefits from arsenic mitigation and is the value that would becompared to the present value of costs.

A particular mitigation option would pass a cost-benefit test if PV(B) > PV(C) (present value ofcosts), as shown in equation 3.

Equation 3. Mitigation Option Passing a Cost-Benefit Test

Notice that the situation in equation 3 could be met overall in a country but a particular mitigationoption could fail in any one region of the country. Similarly, a mitigation policy could fail a cost-benefit test at the country level, but pass it in a given region.

Problems with the Ideal Model

Models of the kind shown in equation 3 have been used fairly extensively for such air pollutantsas sulfur and nitrogen oxides, particulate matter, and volatile organic compounds (Olsthoorn andothers 1999; Krewitt and others 1999). These models make use of long-established emission-diffusion-deposition models (such as RAINS Europe), which also contain measurable ecosystemimpacts based on notions of critical loads.5 They also have established exposure-responserelationships for human health. The policies that are simulated also have known, or reasonablyknown, time schedules over which the pollutants are reduced. Finally, they utilize economicvalues per effect based on longstanding work under the ExternE program of DGXII in theEuropean Commission.

The contrast with what is known about arsenic pollution is a stark one. In order to be able toprovide an overall policy-level model that will be able to measure the social benefits and costs of

PV (B – C) =(1 + s)t

Σi,t

∆ Ii,t (∆Xt )PV (Costs) > 0

4 Equation 2 ignores location for convenience of exposition, but it will be appreciated that benefits and costs vary by location.5 A critical load is the maximum level of deposition of airborne pollutants that produces no discernible change in the receiving ecosystem.Above this level, some form of ecological damage occurs. Note that critical loads relate solely to ecosystems and not to health effects. Acritical level would be that ambient concentration that produced no discernible change in, for example, human health, materials corrosion,or crop loss.

PV (B) =(1 + s)t

Σi,t

∆ Ii,t(∆Xt )

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arsenic mitigation one would need to know the following (and unfortunately we do not):

• The effects of mitigation activities on exposure (∆X), since this is dependent on thebehavioral reaction of producers, users, and regulators to (a) the changes in informationgenerated by arsenic mitigation efforts and relevant educational campaigns; and (b) the costsof regulation. Put another way, we have no economic model of the relevant economy –including all users – with which to simulate the effects of any policy change.

• The health and environmental exposure-response functions (∆I(∆X)) for arsenic pollution, ofwhich, in any event, there are many thousands.

• The locations at which risks will change.

• The split between occupational and public health effects.

• The time schedule of ∆X, although some assumption could be made about this.

We do have some economic values for health end states, but valuation of environmental effectswould not be possible since we have no idea of the end states of the changes in, for example,groundwater flows (both in terms of quantity and quality).

We conclude that it is not possible to approximate the ideal model in the case of arsenicmitigation. The information is simply not available. After recognizing that we have to move awayfrom the first-best world of full information and certainty, in the next section we develop a so-called nth best model, which allows approximation of the costs and benefits of arsenicmitigation, but does not claim to be an exact representation (model) of the actual situation. Thereasons for the need to have an approximate rather than an accurate model have been explainedin this section and need to be taken very seriously by any policymaker who would choose tomake use of this paper. This paper should be thought of as providing guidance on themethodological approach that one should use when contemplating the economic costs andbenefits of different arsenic mitigation policies. However, the empirical application of thesuggested methodological approach should be treated with great caution and results should beread as case study specific, derived under conditions of severe information scarcity andpervasive uncertainty, with regards both to the human and physical reactions to implementablemitigation policies.

The merit of our methodological approach compared to an approach attempting to implement thefirst-best (ideal) model, is that it explicitly accepts, identifies, and characterizes the heroicassumptions made in the evaluation process. We hope that this feature of the proposed nth bestmodel will act as a constant reminder of the pervasive uncertainties and incomplete informationthat prevail in arsenic mitigation policies.

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The Nth Best Model

Given the circumstances, we have to proceed in a far more ad hoc way.

The first thing to do is to invert equation 3 and find out just how large the benefits need to be fora particular arsenic mitigation policy to pass a cost-benefit test. We do this for health effects onlysince we cannot estimate environmental effects. This procedure gives us a benchmark. If healthbenefits exceed this level then we know that the particular policy comfortably passes a cost-benefit test. We also have a minimum estimate of benefits since environmental effects are notcalculated and these unknown benefits would need to be added.

Second, we need some crude ways in which benefits can be estimated given certainassumptions. Water intended for human consumption should be both safe and wholesome.This has been defined as water that is free from pathogenic agents, free from harmful chemicalsubstances, pleasant to taste, free from color and odor, and usable for domestic purposes(Park 1997). Without ample safe drinking water, communities cannot be healthy.

Cvjetanovic (1986) reviews the various mechanisms by which the provision of safe water supplyis transformed into health benefits. His conceptual framework shows that an investment in watersupply and sanitation results in an improvement in the quantity and/or quality of water availableto the household. This yields direct health benefits resulting from improved nutrition, personalhygiene, and the interruption of water-related disease. Moreover, the health benefits fromreducing water-related disease can in some circumstances translate into greater work capacity,which may contribute to increased production and hence to overall economic development.According to Becker (1971, 1981), the household uses time, labor, and purchased goods to createcommodities for the household. The household attempts to produce safe water for consumption,which is dependent on time and resource constraints. Safe water for household use is dependenton the time and labor used in the collection of water, the time and resources used to boil orsterilize the water, and managing water within the household. Households may not have accessto safe water supplies because the financial, labor, or time and energy costs of collection andmanagement are too high, either at a given point in time or perpetually.

The provision of a local safe water supply source is likely to considerably reduce the burden ofproducing safe water for the household. The labor cost of collecting water is borne largely bywomen and girls, who are responsible for domestic chores in most developing countries. It hasbeen found in Kenya that carrying water may account for up to 85% of total daily energy intake offemales (Dufaut 1990). While this is not currently the case everywhere in South and East Asia, ifarsenic mitigation activities imply switching wells to a safe well, which might be located at asignificant distance from the house, then it may mean that even in these countries women haveto walk long distances for water. A number of physical ailments may result from carrying heavyloads, including head, neck, and spinal problems (Dufaut 1990). Clearly there is considerable

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health benefit to be gained from decreasing women’s weight-bearing responsibilities. In addition,Krishna (1990) points to the indirect health benefits that may be gained from mothers havinggreater time to spend on childcare. The extent of benefit is related to service level (proximity topoint of use) and to reliability.

All of these health benefits should be seriously considered in a CBA of various potentialmitigation measures, especially when mitigation measures are likely to deprive women of thesehealth benefits. That is, due consideration should be paid to the incentives that various mitigationmeasures create for the people, which will to a large extent define the acceptability andeffectiveness of the measures. If a mitigation measure is too costly in terms of time and adversehealth effects then implementation will be difficult and monitoring very expensive, if it is possibleat all.

Access to safe water will also depend on nonmaterial factors, such as basic hygiene knowledge,social position, and water quality. Basic hygiene knowledge and high water quality facilitateaccess to safe water. It is said that these factors alter the efficiency of the household as a safewater producer. Social factors affecting access to water supply sources will also determine theability of the household to produce safe water. Lower-caste households may not have access tohigh-quality water supply sources due to cultural norms, which embrace principles of socialexclusion. Conversely, higher-caste households may be unwilling to share high-quality watersupply sources with lower-caste households, which instead may choose alternative sources oflower-quality water. In other social contexts, the effects on higher castes may be adverse, forexample if they are socially excluded from water sources used by lower castes.

A model for calculating these benefits is developed in chapter 4. Our model, however, takes intoaccount only some of the identified health benefits and occupational benefits. Other socialbenefits, such as those outlined in the last three paragraphs of this section, are not included inthe application of our model due to the lack of relevant information. In the case that such relevantestimates exist, our model is flexible enough to accommodate such benefits.

Is Passing a Cost-Benefit Test Sufficient?

The requirement that benefits be greater than costs is not sufficient for a policymaker to sanctioninvestment in a particular project. We can say that a cost-benefit ratio >1 is a necessarycondition for approval of a project, but is not a sufficient condition for its approval. This isbecause every government invariably faces a limited budget and cannot undertake all projectswhere social benefits exceed social costs. We therefore require a procedure to rank differentprojects. It is tempting simply to rank them using the net present value of benefits, but this isactually a mistake. This is easily demonstrated by table 1.

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This shows three projects, X, Y, and Z, with the present value (PV) of their benefits, costs, andnet benefits. Suppose the budget constraint is 100 units. Then a ranking by NPV (benefits) wouldsuggest X, Z, Y and we would undertake X only with a cost of 100. The gain to society would beNPV(X) = 100. But casual inspection shows that we could afford Y and Z, and the NPV would beNPV(Y) + NPV(Z) = 60 + 70 = 130. Clearly, ranking by NPV does not give us the right answer. Thisis given by a ranking of PV (benefits) divided by PV (costs), or the so-called benefit-cost ratio.

The above discussion points to an additional consideration: that one should try to develop a clearpicture of how arsenic mitigation interventions figure in the overall water and sanitation sector andin the broader economy of a country. For example, interventions in sanitation that woulddrastically reduce diarrhea and infant mortality rates might be another way of achievingsignificant social benefits in a developing country such as Bangladesh. Alternatively, perhapsinvesting in education and transport infrastructure or investing in other sectors of the economywould produce higher social net present value. Given the different potential social welfare-increasing projects, the policymaker should rank them according to the cost-benefit ratiosassociated with each one, as discussed above.

It should be noted, however, that the ability to perform such a ranking exercise depends on theavailability of CBAs for all potential investments, which is an expensive endeavor. Developingcountries will not have the means to accommodate such an expensive and holistic exercise;however, they should implement this exercise for policies when possible to prioritize projects.Prioritization will reflect ethical judgments within the country, or binding constraints imposed bythe national or international political and policy arena.

Another point to note, and one which was touched upon in this section of this paper, is that whenembarking on such CBA one should be aware of the long-run effects of proposed projects andmitigation measures. In the calculation of present values of costs and benefits of public sectorprojects and policies, future values are multiplied by a discount factor that is calculated from the

a. PV = present value. b. NPV = net present value.

Table 1. Ranking of Projects

Project PV PV NPV PV (benefits)/(costs)a (benefits) (benefits)b PV (costs)

X 100 200 100 2.0

Y 50 110 60 2.2

Z 50 120 70 2.4

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social discount rate (social time preference rate). However, at even a modest rate, the practice ofdiscounting reduces the value of costs or benefits for long periods of time (many years) andhence almost to zero. This disenfranchizes future generations from consideration in today’sdecisions. Recent work on discounting over the long term has now made it clear that constantrate discounting has only a limited justification, and that it is possible to make recommendationsfor better practice (Koundouri and others 2002; Pearce and others 2003). The recent literatureargues that discount rates vary with time and that, in general, they decline as the time horizonincreases.6 The effects of declining discount rates on the appraisal of relatively long-termgovernment policies, programs, and projects can be summarized as follows:

• Is small over a short (for example 30-year) period, but large over a very long period

• Can influence the choice of a policy or project

• Does not always support the option perceived as best for the environment

• Can affect financial planning, in both public and private sectors

• May result in reevaluation of hurdle cost-benefit ratios or budgets in the public sector

Finally, one should keep in mind that economic policy is about making comparisons of theeconomic situation, which requires knowledge about the desirability of the change that an actionseeks to bring about. In the real world, choices lead to gains by some and losses by others. Toavoid making value judgments in this context, a number of compensation tests have beendevised in an effort to find a basis to compare states that is founded on efficiency.7 However,attempts to devise a criterion based solely on efficiency, and without resort to ethical judgments,are simply not available and economists’ policy recommendations are controversial.

6 There are several strands to the arguments in favor of declining long-run interest rates. The first set of arguments derives from empiricalobservations of how people actually discount the future. There is some evidence that individuals’ time preference rates are not constantover time, but decrease with time. Individuals are observed to discount values in the near future at a higher rate than values in the distantfuture. While some evidence still supports time-constant discount rates, the balance of the empirical literature suggests that discount ratesdecline in a hyperbolic fashion with time. The second set of arguments in favor of time-varying discount rates derives from uncertaintyabout economic magnitudes. Two parameters have been selected for the main focus of this approach. The first is the discount rate itself.The argument is that uncertainty about the social weight to be attached to future costs and benefits – the discount factor – produces acertainty-equivalent discount rate, which will generally decline over time. The second uncertain parameter is the future state of theeconomy as embodied in uncertainty about future consumption levels. Under certain assumptions, this form of uncertainty also produces atime-declining discount rate. The third set of arguments for time-declining discount rates does not derive from empirical observation orfrom uncertainty. Instead, this approach – the “social choice” approach – directly addresses the concerns of many that constant-ratediscounting shifts unfair burdens of social cost onto future generations. It adopts specific assumptions (axioms) about what a reasonableand fair balance of interests would be between current and future generations, and then shows that this balance can be brought about bya time-declining discount rate. Any one, or all, of these three lines of arguments supports the hypothesis that the social time preferencerate decline with time. Moreover, there have been a number of attempts to construct models to quantify the shape of this decline and, insome cases, to test them empirically.7 An excellent discussion of compensation tests can be found in Chipman and Moore 1978.

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8 Arsenic is also associated with peripheral vascular disease, which is a condition that results in gangrene in the extremities and usuallyoccurs in conjunction with skin lesions. Other cardiovascular problems such as hypertension (Chen and others 1995) and ischemic heartdisease have also been found to be associated with arsenic (Tsuda and others 1995). Moreover, Guha Mazumder and others (1998) foundevidence of liver enlargement and restrictive lung disease. In terms of hematological effects, anemia is commonly cited (NRC 1999).Another widely suggested health effect is diabetes mellitus.

As indicated in chapter 2, the CBA undertaken in this paper will only take into account someof the health-related costs of arsenic contamination and resulting occupational hazards.

These costs will translate into benefits if avoided through the implementation of effectivemitigation measures. Hence, in order to derive the cost-benefit ratio of the different mitigationmeasures these benefits should be compared with the costs of the relevant mitigation measures.These costs and benefits are described in this chapter.

Health Effects of Arsenic in Drinking Water

The World Health Organization (WHO) recommendations on the acceptability and safety of levelsof arsenic in drinking water have dropped twentyfold from a concentration of 200 µg L-1 in 1958 to10 µg L-1 in its 1993 Drinking Water Guidelines. However, some countries are still using the formerWHO standard of 50 µg L-1. For example, the Bangladesh Standards for Testing Institution setsthe maximum permissible limit for arsenic at this former level.

Differences in standards derive partly from the fact that there is no widely accepted completedefinition of what constitutes arsenicosis. Inorganic arsenic is a classified carcinogen (IARC 1980)that also has a multitude of noncancer effects. The widespread effects of arsenic are perhapsresponsible in part for the lack of a widely accepted care definition for arsenicosis. Furthermore,some symptoms of arsenicosis (such as shortness of breath) may be observationallyindistinguishable from the health effects of other illnesses. A comprehensive review of the healtheffects of arsenic contamination of drinking water is undertaken in Paper 2 of this report. Thepurpose of this section is to highlight some of the main findings of the literature on health effects,especially with respect to predictive use of the available information. In addition, arsenicpoisoning may be acute or chronic. In the context of community drinking water supply, onlychronic exposure is relevant. Acute poisoning is therefore not discussed further.

According to the United States National Research Council report (NRC 1999, p. 89), the mostwidely noted noncancer effect of chronic arsenic consumption is skin lesions. Over time, arsenicexposure is associated with keratoses on the hands and feet. The time from exposure tomanifestation is debated in the literature, while the youngest age reported for patients withhyperpigmentation and keratosis is two years of age (Rosenberg 1974). In Bangladesh, GuhaMazumder and others (1998) suggest a minimum time gap of five years between first exposureand initial manifestations.

Cancer Health Effects8

Hutchinson (1887) identified arsenic as a carcinogen because of the high number of skin cancers

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occurring in patients treated with arsenicals. The International Agency for Research on Cancer(IARC 1980) classified inorganic arsenic compounds as skin and lung (via inhalation) carcinogens.In the period following this classification, concerns have grown over the possibility of arsenic indrinking water causing a number of other cancers.

An early study by Tseng and others (1968) found evidence of a dose-response relationshipbetween concentration of arsenic in drinking water and prevalence of skin cancer. TheInternational Program on Chemical Safety (IPCS 1981) estimated skin cancer risk from lifetimeexposure to arsenic in drinking water at 5% for 200 µg L-1, based on the findings of Tseng (1977).Based on the increased incidence of skin cancer observed in the population in Taiwan, China, theUnited States Environmental Protection Agency (EPA 1988) has used a multistage model that isboth linear and quadratic in dose to estimate the lifetime skin cancer risk associated with theingestion of arsenic in drinking water. With this model and data on males, the concentrations ofarsenic in drinking water associated with estimated excess lifetime skin cancer risks of 10-4, 10-5,and 10-6 are 1.7, 0.17, and 0.017 µg L-1 respectively. Considering other data and the fact that theconcentration of arsenic in drinking water at an estimated skin cancer risk of 10-5 is below thepractical quantification limit of 10 µg L-1, the provisional guideline value of 10 µg L-1 isrecommended (WHO 1996). The guideline value is associated with an excess lifetime risk for skincancer of 6 x 10-4 (that is, six persons in 10,000).

High levels of arsenic in drinking water are also associated with a number of internal cancers.However, it is difficult to quantitatively establish risk in many of the studies, due to problems inmeasuring exposure to arsenic. Chen and others (1985) calculated standardized mortality ratiosfor a number of cancers in 84 villages in Taiwan. Mortality for the period 1968-1986 wascompared with age and sex-adjusted expected mortality. Significantly, increased mortality wasobserved among both males and females for bladder, kidney, lung, liver, and colon cancers.However, the authors were not able to directly estimate arsenic concentrations in well water.Chen and Wang (1990) were able to use data on arsenic concentrations in 83,656 wells in 314precincts and townships collected from 1974 to 1976 in Taiwan. The authors used a multipleregression approach to control for socioeconomic confounding factors, and compared age-adjusted mortality rates with average arsenic concentrations in each township. They found asignificant relationship between arsenic concentration and mortality from cancers of the liver,nasal cavity, lung, bladder, and kidney for both sexes.

The above-mentioned studies all used an ecological design and are thus susceptible to bias fromconfounding factors. However, the bladder and lung cancer results of these studies are alsoconfirmed by cohort studies, which may be less susceptible to this form of bias. These studiesare also useful in providing data on the latency period of internal cancers. Cuzick, Sasieni, andEvans (1992) studied a cohort of patients treated with Fowler’s solution (potassium arsenite) inEngland from 1945 to 1969. The authors found evidence that the period between first exposureand death from bladder cancer varied from 10 years to over 20 years.

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To conclude, the results from studies of cancer indicate strong evidence that exposure toarsenic is related to skin, lung, and bladder cancer. It is likely that arsenic causes a number ofother cancers, but thus far epidemiological evidence has not been consistent for other sites inthe body.

Treatment of Arsenicosis Sufferers

Guha Mazumder (1996) suggested that the first stage in treating those with arsenicosis should bethe immediate cessation of consumption of arsenic-contaminated water. Once this has beenachieved, the emphasis should be on the provision of a diet high in protein and vitamins. Thechelating agents DMPS (dimercaptopropane sulphonate) and DMSA (dimercaptosuccinic acid) arerecommended as treatment drugs (Angle 1995). However, Guha Mazumder (1996) notes that thesedrugs are very expensive. Palliative care may be the only affordable treatment in rural areas ofdeveloping counties, where expensive drugs and protein-rich diets are unlikely to be available tothe vast majority of people. In the case of keratosis, application of ointment containing salicylicacid can help to soften the skin and ease the patient’s pain.

Mitigation of Arsenic in Drinking Water

This section will analyze the technologies that can be used to provide safe drinking water in ruralBangladesh, which serves as an example for most relevant mitigation options. The availableoptions for safe water can be classified by source: groundwater, surface water, and rainwater.Recent years have seen increasing acceptance of strategies for incremental improvement inenvironment and health in general and of demand-driven approaches to water supply andsanitation in particular. It is inappropriate therefore to pursue a single overall technologicalsolution but rather to inform communities and individuals of alternatives and their characteristicsin order to facilitate choice of the most appropriate options.

Groundwater

The simplest and most immediately achievable option is the sharing of tubewells that arecurrently either free from arsenic or contain very low levels. Wells containing arsenic may still beused safely for such activities as washing laundry, and a simple color coding (using, for example,"traffic light" colors) may have a significant impact on community arsenic exposure if carefullyand continuously backed up by awareness raising and education. However, in the most highlycontaminated areas not enough tubewells will contain safe levels of arsenic. Furthermore, colorcoding would have to be monitored carefully over time, as tubewells with previously safe testresults may be later found to contain increased levels of arsenic. The principal costs of such anapproach relate to the ongoing testing and labeling of wells and of continuous awareness raisingand education. These costs may be borne by the community or by an outside agency. Inpractice, the household burden of water collection is likely to increase (because a greater averagedistance will be traveled in order to collect the same volume of water).

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For some countries, such as Bangladesh and Nepal, the other alternative for groundwater supplyis the development of deep tubewells. The principal costs of such an approach relate to thecosts of developing the deep tubewells. These include the costs of training and equipping drillingteams as well as the direct costs of drilling itself, including a proportion of unsuccessful bores.These costs may be borne by the community or an outside agency. If contaminated wells remainin use for other purposes such as laundering ongoing awareness raising and education will beessential. If new wells are appropriately sited then the household burden of water collection maybe constant or even decrease. Deep tubewells have been in use for years in coastal areasbecause of high salinity in shallow aquifers. However, it is not possible to exploit this technologyin all areas because rock formations may make drilling infeasible.

The Danish Agency for International Development (Danida) has conducted research in Noakhali inBangladesh since November 1998 on the removal of arsenic using a mix of 200 µg L-1 alum and1.5 µg L-1 KMnO4 introduced into a large bucket (18 liters), of which the supernatant is drained offafter 1–1.5 hours into a bucket standing beneath it. Cost of chemicals for an average family isTk 10/US$0.2 a month. Lab tests show a reduction in arsenic levels of 1,100 µg L-1 to 16 µg L-1. Inthe field tests arsenic ranging from 120–450 µg L-1 was reduced to 20–40 µg L-1 consistently.Though well within the Bangladesh standard, the removal efficiency was considerably less thanin the laboratory. Stirring (time, mixing efficiency – paddle stick instead of cane stick) is believedto make a difference and Danida is currently verifying this in a field test. Danida has alsodesigned a two-bucket column (total investment cost for the set is Tk 300/US$6), whichcircumvents the resuspension of the settled solids. Danida reports that 50–80% of the two-bucket systems deliver water within Bangladesh standards (Danida 2000).

Coprecipitation is a well-known phenomenon and has been the subject of a small study byWaterAid in East Madaripur near Chittagong. Iron ranges from 0 to 10 µg L-1. In the first phase ofthe study it seemed that removal rates were very good. However, upon further study it was foundthat some wells showed very low removal rates. It seems that salinity has a detrimental effect onremoval. Hardness may possibly have an effect as well.

The Danida and WaterAid studies also examined the sustainability of methods at the householdlevel. Apart from initial acceptance of a suitable method, households will also have to apply thetechnique consistently and properly to continue to avail themselves of the benefits of arsenicavoidance.

The Pan American Center for Sanitary Engineering and Environmental Sciences (CEPIS)9 in Peruhas developed a technology called ALUFLOC for arsenic removal at the household level and ithas been tested in Argentina. ALUFLOC is a sachet containing chemicals that are added to abucket of arsenic-contaminated tubewell water. After about an hour the treatment process iscomplete and the water is safe for consumption. Preliminary field test results suggest thatALUFLOC is effective in reducing arsenic content to safe levels. However, it is necessary to

9 CEPIS is part of the Pan American Health Organization (PAHO), the WHO Regional Office for the Americas.

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optimize the product for treating tubewell water with a concentration of arsenic greater than1,000 µg L-1. The cost of the technology is estimated at US$0.15 per bucket treated, given theassumption of production at an industrial level. The cost of such an approach relates to theongoing need for awareness raising and education; the cost of treatment materials (includingmanufacture and distribution); and the costs of additional household expenditure on equipment(such as additional buckets) and in terms of time. It may however be deployed rapidly and costsmay be borne by the community or an outside agency, or may be subsidized.

Surface Water

Surface water (including rainwater, rivers, lakes) is typically low in arsenic and therefore apotentially attractive source of drinking water in arsenic-rich areas. However, surface waters arefrequently contaminated with human and animal fecal matter and other material and are unsafefor this reason. This risk initially led to the preference for groundwater sources in Bangladesh andother developing countries worldwide. The critical issues in arsenic-rich areas therefore concernwhether treating surface water for fecal contamination can be reliably achieved at a lower overallcost than securing groundwater from low-arsenic sources or through treatment to remove arsenicfrom groundwater.

Surface Water TreatmentTreatment of surface water can be achieved by several means. Slow sand filtration, for example, is atypical method of treatment for rural areas and small towns. The water passes slowly through a largetank filled with sand and gravel. There is some reservation about the sustainability of this method inBangladesh. The reasons for this include the need for careful maintenance and the risk ofbacteriological infection if the system is not operated properly. However, pond sand filters are stilluseful as an option in Bangladesh, especially in the coastal belt where there are few alternatives.

The key elements in the decisionmaking process leading to the selection of technology usingsurface water rather than groundwater concern the costs of capital investment in infrastructureand the cost of maintenance, including supervisory support. If wells containing arsenic remain inuse, ongoing awareness raising and education will be required. The household burden of watercollection is likely to increase (as the number of available sources is likely to decrease) unlessthe opportunity is taken to make capital investments to develop piped distribution.

RainwaterRainwater harvesting is a recognized water technology in use in many developing countries aroundthe world (WHO-IRC 1997). The United Nations Children’s Fund (UNICEF) has promoteddissemination of the technology since 1994 in Bangladesh. The rainwater is collected using either asheet material rooftop and guttering or a plastic sheet and is then diverted to a storage container.

Rainwater harvesting is capital intensive and the costs (and availability) of suitable roofing,materials for guttering, and storage tanks are important factors. Rainwater use has proven to besuccessful in Taiwan, Sri Lanka, and Thailand.

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In some circumstances there is the possibility of chemical contamination of the collected water,particularly where air pollution is a major problem and where bacteriological contamination maybe caused by bird droppings. There is also the possibility of contamination (for example intrusionof insects), particularly when the water is stored for long periods. Health inspections are neededregularly to ensure that the water is of good quality. However, these reservations might be lessproblematic as rainwater quality in many circumstances is at least as good as the piped waterdistributed in many towns in Bangladesh.

The above are only examples of technologies that might be considered as alternatives togroundwater abstraction. Other low-cost technologies that might be considered include use ofsprings and infiltration galleries.

In our empirical application we consider eight alternative technologies designed to providearsenic-free water: dug wells, roof rainwater combined with dug wells for the dry season, deeptubewells, arsenic removal in existing shallow tubewells, pond sand filters, deep productionwells (piped scheme), impoundment-engineered pond (piped scheme), and surface waterinfiltration (piped scheme).

Technology Choice

The following analysis is based on Bangladesh data and naturally it will vary in differentcountries, due mainly to the population density, the severity of the arsenic problem, and thegeographic distribution of the population. Moreover, we take into account only the rural populationof Bangladesh. The technology options considered can all be applied in Bangladesh, but some ofthem may not be applicable in other countries. For example, in some countries deep tubewellsmay not be useful because the aquifer structure is such that deep tubewells may also becontaminated (see Paper 1).

The choice between these technologies should take into account their cost-effectiveness inproviding arsenic-free and microbiologically safe drinking water. Different options may have verydifferent balances of cost between, for example, capital and recurrent costs and may impactdifferently on the household costs of water management. However, the criteria of sustainabilityand acceptance by rural users must be incorporated into the calculation of cost-effectiveness inorder to aid the decisionmaking process concerning which mitigation method(s) to implement.Table 2 indicates the mitigation options for which cost evaluation is conducted.

The aforementioned technology options are evaluated for three kinds of villages: small (100households), medium (500 households), and large (1,000 households). We further assume thateach household consists of an average 5.5 members and that the distribution of income is asfollows: 10% have high income, 20% have medium income, and 70% have low income. The levelof service provided to each household depends on the income of the household. The high-income people will be provided water by multiple taps (one for each household), the medium-income people will have a single yard tap per two or three households, while a communal

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standpost will be provided per 10 households of low income. The distribution of income as wellas the level of service is necessary for the most accurate cost estimation.

Table 3 shows the capital costs and operation and maintenance annual costs applied to a smallvillage of 100 households.10 The most expensive technology in terms of capital costs is option B(both B1 and B2), which combines rainwater harvesting with the construction of dug wells or

Table 2. Arsenic Mitigation Technology Options

Option no. Technology

A Dug wells

B1 Roof rainwater harvesting/household (60 m2) + dug well for dry season

B2 Roof rainwater harvesting/household (60 m2) + deep tubewell for dry season

C Deep tubewell

D Existing shallow tubewell with household arsenic removal

E1 Pond sand filter

E2 Pond sand filter (30 households/pond sand filter)

F Piped scheme deep production well

G Piped scheme impoundment-engineered pond

H Piped scheme surface water infiltration gallery

a. Costs are for a small village of 100 households.

Table 3. Small Village: Capital and Operation and Maintenance Costs

Technology Capital costs Operation &(US$)a maintenance costs (US$)a

A Dug wells 17,750 2,968

B1 Rainwater harvesting + dug well 33,913 3,523

B2 Rainwater harvesting + deep tubewell 35,335 2,819

C Deep tubewell 21,561 1,083

D Shallow tubewell with arsenic removal 7,966 4,237

E1 Pond sand filter 25,719 2,242

E2 Pond sand filter (30 households/unit) 3,810 332

F Deep production well, piped 19,432 3,051

G Impoundment, piped 19,432 3,390

H River abstraction, piped 17,653 3,051

10 A detailed description of the costs involved in each technology for a village of 500 households is given in annex 1.

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deep tubewells. In terms of operation and maintenance expenses option D is the mostexpensive, due to the costs of the arsenic removal techniques. The level of service provided fora small village by each of the techniques is summarized in table 4.

Type of service: a. multiple taps; b. single yard tap; c. communal standposts.

Table 4. Small Village: Technology-Specific Level of Service

Technology No. of households per unit Total for 100by income households

High Medium Low(10%)a (20%)b (70%)c

A Dug wells 1 3 10 24

B1/2 Rainwater + dug well/tubewell 1 1 1 100

C Deep tubewell 1 3 10 24

D Shallow tubewell/arsenic removal 1 1 1 100

E1 Pond sand filter 1 2 10 27

E2 Pond sand filter (30 households/unit) 30 30 30 4

F Deep production well, piped 1 2 10 27

G Impoundment, piped 1 2 10 27

H River abstraction, piped 1 2 10 27

In the same mode, for a medium village of 500 households, table 5 shows the capital costs andannual operation and maintenance costs, while table 6 shows the level of service.

a. Costs are for a medium village of 500 households.

Table 5. Medium Village: Capital and Operation and Maintenance Costs


A Dug wells 88,750 14,842






E2 Pond sand filter (30 households/unit) 16,193 1,412




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Table 6. Medium Village: Technology-Specific Level of Service

Technology No. of households per unit Total for 500by income households



B1/2 Rainwater + dug well/tubewell 1 3 10 118


D Shallow tubewell/arsenic removal 1 1 1 500






For a large village of 1,000 households, table 7 shows the capital costs and annual operation andmaintenance costs, while table 8 (see page 234) shows the level of service.

a. Costs are for a large village of 1,000 households.

Table 7. Large Village: Capital and Operation and Maintenance Costs


A Dug wells 177,500 29,684






E2 Pond sand filter (30 households/unit) 32,386 2,824




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Table 8. Large Village: Technology-Specific Level of Service

Technology No. of households per unit Total for 1,000by income households



B1/2 Rainwater + dug well/tubewell 1 3 10 1,000


D Shallow tubewell/arsenic removal 1 1 1 1,000






We further conducted a present value analysis in order to identify the technology option with thelowest cost for each kind of village. Our analysis suggests that the most efficient option for smallvillages is option C, deep tubewells, while for medium and large villages option H, riverabstraction (piped), should be employed. These options guarantee arsenic-free water. However, ifwe disregard the issue of the level of service, the most efficient technique is pond sand filters(30 households per pond sand filter). Special attention should be paid to avoidance of bacterialcontamination of the water, as percolation of contaminated surface water is the most commonroute of pollution. Disinfection of the water by pot chlorination should be continued duringoperation. As regards option F, the deep aquifers in Bangladesh have been found to be relativelyfree from arsenic contamination. The study by the British Geological Survey and the Departmentof Public Health Engineering (BGS and DPHE 2001) has shown that only about 1% of tubewellshaving a depth greater than 150 m are contaminated with arsenic at concentrations higher than50 µg L-1 and 5% of tubewells have arsenic content above 10 µg L-1 (See Paper 1 for a moredetailed analysis). The combination of deep production wells with piped water supply can ensurethe provision of good quality water to people. Details for the present value of the total costs ofthe various techniques for each of the three sizes of village are given in tables 9, 10, and 11.The numbers in bold indicate the least costly options.

The first column of tables 9, 10, and 11 refers to a discount rate of 10% for a 10-year period, thesecond column to a discount rate of 10% for a 15-year period, and the third column to a discountrate of 15% for a 20-year period. These figures can be used as the basis for a sensitivityanalysis, whose reasoning derives from: (a) 10–15% is the lending rate in Bangladesh; and(b) 10-20 years is a reasonable payout period given the financial market in Bangladesh.

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a. Total costs of serving all small villages of 100 households. Figures in bold indicate least-cost options.b. DR = discount rate.

Table 9. Small Villages: Present Value Analysis of Technology Costs

Technology Costs (millions US$)a

DRb 10% for DRb 10% for DRb 15% for10 years 15 years 20 years

A Dug wells 35,989 43,021 36,330

B1 Rainwater harvesting + dug well 55,561 63,908 55,966

B2 Rainwater harvesting + deep tubewell 52,660 59,339 52,984

C Deep tubewell 28,216 30,781 28,340

D Shallow tubewell with arsenic removal 34,002 44,041 34,489

E1 Pond sand filter 39,497 44,809 39,754

E2 Pond sand filter (30 households/unit) 5,851 6,638 5,890

F Deep production well, piped 38,178 45,406 38,528

G Impoundment, piped 40,261 48,292 40,650

H River abstraction, piped 36,399 43,626 36,749

a. Total costs of serving all medium villages of 500 households. Figures in bold indicate least-cost options.b. DR = discount rate.

Table 10. Medium Villages: Present Value Analysis of Technology Costs



A Dug wells 179,946 215,107 181,650



C Deep tubewell 141,078 153,907 141,700







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11 There are very wide differences in the levels of exposure to arsenic throughout this rural population. Using data in Maddison, Luque, andPearce 2004 we calculated an average exposure level for the entire rural population of 57 mg L-1, which forms the basis of the analysisundertaken here.

a. Total costs of serving all large villages of 1,000 households. Figures in bold indicate least-cost options.b. DR = discount rate.

Table 11. Large Villages: Present Value Analysis of Technology Costs



A Dug wells 359,893 430,213 363,300



C Deep tubewell 282,156 307,814 283,399







In order to assess the total cost of providing the Bangladesh people with arsenic-free water, weneed to make some further assumptions. These assumptions, which are listed below, areadopted solely for demonstration purposes and they do not reflect in any way the policy prioritiesof the World Bank.

• Technology is chosen according to the geographic population distribution.

• Deep tubewells are the optimal choice for small villages up to 100 households, while riverabstraction (piped) is the optimal choice for medium and large villages of 500 and1,000 households.

• 40% of the population is assumed to inhabit small villages, while the remainder of thepopulation is equally divided between medium and large villages.

• Out of the total population (129 million), roughly 29 million people live in arsenic-affectedareas. Moreover, we concern ourselves here with the rural population, which is approximately99 million.11

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• The methodology outlined can be implemented in a range of cases: for example, for onevillage, for a specific region, or for the whole region.

The rural population, approximately 99 million people, consists of around 18 million households.Given the geographic distribution of the population, we will assume for analytical purposes that7,200,000 households live in small villages (72,000 villages of 100 households), 5,400,000households live in medium villages (10,800 villages of 500 households), and 5,400,000households live in large villages (5,400 villages of 1,000 households). Tables 12, 13, and 14indicate the costs applicable to each of the three categories of village. Table 15 indicates totalcapital and operation and maintenance costs for the entire rural population. In this mode, totalcapital costs for the selected technology options range from US$0.6 to $6.4 billion, and totaloperation and maintenance costs range from $0.05 to $0.8 billion per year (table 15 see page 239).

a. Costs are for an estimated 72,000 small villages of 100 households each = 7,200,000 households.

Table 12. Small Villages: Total Costs of Mitigation Technology Options

Technology Capital costs Operation &(million US$)a maintenance costs (US$)a

A Dug wells 1,278.00 213.72

B1 Rainwater harvesting + dug well 2,441.75 253.67

B2 Rainwater harvesting + deep tubewell 2,544.15 203.00

C Deep tubewell 1,552.37 77.98

D Shallow tubewell with arsenic removal 573.56 305.08

E1 Pond sand filter 1,851.74 161.45

E2 Pond sand filter (30 households/unit) 274.33 23.92

F Deep production well, piped 1,399.12 219.66

G Impoundment, piped 1,399.12 244.07

H River abstraction, piped 1,270.98 219.66

Contd. on next page

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a. Costs are for an estimated 10,800 medium villages of 500 households each = 5,400,000 households.

Table 13. Medium Villages: Total Costs of Mitigation Technology Options


A Dug wells 958.50 160.29







F Deep production well, piped 508.61 73.22

G Impoundment, piped 521.05 82.37

H River abstraction, piped 480.97 73.22

a. Costs are for an estimated 5,400 large villages of 1,000 households each = 5,400,000 households.

Table 14. Large Villages: Total Costs of Mitigation Technology Options


A Dug wells 958.50 160.29







F Deep production well, piped 470.20 50.34

G Impoundment, piped 481.00 56.75

H River abstraction, piped 459.13 50.34

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a. Aggregate costs for all small, medium, and large villages (tables 12, 13, and 14).

Table 15. All Villages: Total Costs of Mitigation Technology Options


A Dug wells 3,195.00 534.31




D Shallow tubewell with arsenic removal 1,433.90 762.71



F Deep production well, piped 2,377.93 343.22

G Impoundment, piped 2,401.18 383.19

H River abstraction, piped 2,211.08 343.22

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Methodology for the Model

The model developed in this chapter is a CBA model described by the following equation:

We proceed by calculating the present value of costs and then estimating the relevant benefits.

Data and Estimates for the Model

Given our analysis of capital costs and operation and maintenance expenses in the previouschapter, we translate these figures into present values by using a 50-year horizon and a5%, 10%, and 15% discount rate.12 Moreover, we disaggregate these costs into costs paid byindividuals and costs paid by the government based on the assumption that 20% of capitalcosts are paid by the individuals who bear the operation and maintenance expenses as well.This disaggregation is directly related to health benefits, as health expenditure is both privateand public. As table 16 suggests, the present value of total costs is in the range US$1.6 billion to$15.4 billion for the 5% discount rate. Using the optimal choice, however, this cost drops to$0.5 billion for the government and to $1.1billion for individuals (total $1.7 billion). The respectivefigures for the 10% and 15% discount rates are $1.1 billion and $0.9 billion.

For a mitigation policy to result in a positive present value, the present value of benefits needsto exceed the present value of relevant costs, as these costs are calculated in table 16. Inwhat follows we state the technique and basic assumptions made for the calculation of therelevant benefits.

Due to data nonavailability, we take into account only two sources of arsenic mitigation benefits.The first amounts to direct medical expense savings as reduced arsenic exposure dramaticallyimproves people’s health. The second amounts to indirect benefits of improved productivity andelevated output growth. Due to the lack of estimates on other social benefits, these are notincluded in our model. Our exact technique for calculating these benefits is defined negatively;that is, we estimate the costs the government would bear if no mitigation policy were undertaken.Hence, benefits are implicitly calculated as reduced costs and their present value is equal to thediscounted cash flow of benefits for a 50-year horizon.

%��

PV (B – C) =(1 + s)t

Σi,t

∆ Ii,t (∆Xt )PV (Costs) > 0

12 In this chapter both costs and benefits are discounted at 5%, 10%, and 15%. Since health benefits should be discounted for a period ofat least 50 years as they spread over a lifetime, we do the same with the costs. The relevant discount rate for benefits spread over the longrun (more than 30 years) should be much lower than the one used on short-run projects. This is the reason the 5% discount rate is used inaddition to the 10% and 15% discount rates. In the previous chapter only 10–15% was used as the focus was only on costs, and(a) 10–15% is the lending rate in Bangladesh; and (b) 10–20 years is a reasonable payout period given the financial market in Bangladesh.

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First, output benefits are calculated as foregone output for each person that becomes affected byarsenic-related diseases. In order to project the number of people who develop fatal cancer dueto arsenic, we associate the level of arsenic in water with the risk of cancer. Specifically, theWHO (1993) set a provisional guideline value of 10 µg L-1 for arsenic in drinking water, which isassociated with a lifetime excess skin cancer of about 6 per 10,000 persons. The Bangladeshstandard of 50 µg L-1 is associated with a higher risk: 30 per 10,000 persons. Using the modeldeveloped by the United States Environmental Protection Agency and the distribution ofpopulation exposed to different levels of arsenic, the estimated total number of excess skincancer victims is 375,000 if the present arsenic contamination level is maintained. If theBangladesh standard is met, this figure drops to 55,000 and, if the WHO standard is met, itfurther drops to 15,000 (Ahmed 2003). However, skin cancer is not the only disease related toarsenic. Yu, Harvey, and Harvey (2003) estimate the number of people developinghyperpigmentation to be 1,200,000 and those developing keratosis to be 600,000. We project thenumber of people who die or become unable to work in the next 10 years to be approximately50,000 per year (increasing by that number each year). This figure is derived by dividing theestimated 2.5 million people that are expected to develop arsenic-related diseases in the next50 years, by 50 years (in order to get a per year estimate of affected people).

From a more detailed survey of the data currently available in the literature, Maddison, Luque,and Pearce (2004) estimate the annual impact on health from arsenic in Bangladesh as shown intable 17 (see page 242).

Table 16. Present Value of Costs of Arsenic Mitigation Options for Whole Population

Technology Govt Present value of Present value ofcost private cost total cost

5% 10% 15% 5% 10% 15%

A Dug wells 2,556 10,393 5,937 4,198 12,949 8,493 6,754

B1 Rainwater + dug well 4,883 12,798 7,509 5,445 17,682 12,392 10,328

B2 Rainwater + deep tubewell 5,088 10, 437 6,249 4,616 15,525 11,338 9,704

C Deep tubewell 3,105 4,335 2,709 2,075 7,440 5,814 5,179

D Shallow tubewell/ 1,147 14,211 7,849 5,367 15, 358 8,996 6,514arsenic removal

E1 Pond sand filter 3,703 8,294 4,928 3,614 11,998 8,631 7,318

E2 Pond sand filter 499 1,118 664 487 1,618 1,164 987(30 households/unit)

F Deep production well, piped 1,902 6,741 3,879 2,762 8,664 5,781 4,664

G Impoundment, piped 1,921 7,476 4,279 3,032 9,397 6,200 4,953

H River abstraction, piped 1,769 6,708 3,845 2,728 8,477 5,614 4,497

Combined option 1,994 4,178 2,497 1,841 6,172 4,491 3,835

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Estimates by Maddison, Luque, and Pearce (2004) suggest that 6,500 people die from cancerevery year (a total of 326,000 people in a period of 50 years), while a maximum13 of 2.5 millionpeople develop some kind of arsenicosis. In our model, we add to the number of fatalities fromcancer (6,500 people) an additional 1.7% of the total number of arsenic-affected people. This1.7% represents the number of people that develop nonfatal diseases and become unable towork and produce.

Annual gross domestic product (GDP) is adjusted for the loss in output due to people becomingunable to work or dying. As a starting value for GDP, we take the 2002 GDP estimated at US$239billion in purchasing power parity terms. We then assume that GDP increases by 4% each yearover the next 50 years. The output lost is then calculated as the fraction of GDP the people

13 Individuals suffering from keratosis can also suffer from cough, weakness, etc. Therefore, it is not possible to translate the sum of thepeople suffering from different symptoms, as shown in table 17, into a unique figure indicating the total number of people suffering fromarsenicosis. The figures in the table, however, can be translated into a range of possible numbers. This range will vary from 971,230(assuming that every person who develops arsenicosis will have all the symptoms) to 2,592,083 (assuming that each person has a uniquesymptom, in which case the number of people with arsenicosis is the sum of the number of symptoms).

a. Figures indicate average number of cases occurring in each year (not number of new cases).Source: Maddison, Luque, and Pearce 2004, p. 32.

Table 17. Bangladesh: Estimated Health Impact of Arsenic Contamination of Tubewells

Impact on health/ Males Females Combinedtype of illness

Cancer cases:

Fatal cancers/year 3,809 2,718 6,528

Nonfatal cancers/year 1,071 1,024 2,095

Total cancer fatalitiesaccumulated over 50 years 190,450 135,900 326,400

Arsenicosis casesa:

Keratoses 277,759 74,473 352,233

Hyperpigmentation 654,718 316,511 971,230

Cough 21,823 68,887 90,712

Chest sounds 144,831 67,025 211,858

Breathlessness 93,247 176,874 270,122

Weakness 132,927 240,176 373,104

Glucosuria 67,887 63,551 131,439

High blood pressure 94,396 88,366 182,762

Total arsenicosis cases ineach year 1,487,588 1,095,863 2,583,460

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becoming ill would have produced. These output benefits amount to present values of$88.36 billion, $22.89 billion, and $8.77 billion for constant discount rates of 5%, 10%, and15% respectively over a 50-year period.

Information from the National Institute of Preventive and Social Medicine (NIPSOM) ofBangladesh14 indicates that the medical expenditure for treating mild to moderate arsenicosis isUS$4 to $5 per month, and the treatment generally lasts from three to six months. As far asarsenicosis cancers are concerned, the medical expenditure ranges from $300 to $1,000 perpatient. Using the information above, we calculate the direct medical cost of treating mild tomoderate arsenicosis, as well as arsenicosis cancer. Referring back to table 17, 8,623 people(6,500 fatal cancers plus 2,095 nonfatal cancers) are expected to develop cancer per year, while971,230 to 2,583,460 people will develop some other arsenic-related disease. In our calculationswe use this range (971,230 to 2,583,460) as an approximation of the number of treatments of mildto moderate arsenicosis per year. Then, using the upper bound of the estimates of medical costsprovided by NIPSOM, we find that the total cost of treating arsenicosis cancer amounts toUS$8,623,00015 and the cost of treating the rest of arsenic-related diseases is a number between$29,136,900 (= 971,230 x $30) and $77,503,800 (= 2,583,460 x $30). Using the average of the costof treating noncancer arsenic-related diseases, and discounting the sum of medical expenditureon both cancer and mild to moderate arsenic-related diseases for a 50-year period at rates of5%, 10%, and 15%, we get the present value of medical costs, which amount to $1.14 billion,$0.62 billion, and $0.41 billion respectively.

Before moving to section 4.3, where we calculate the net present value of different mitigationtechnologies, it is crucial to note that the calculated health expenditures in the previousparagraph represent lower bounds of the relevant magnitudes. That is, while these are the currentactual expenditures made, they may not be really sufficient for the treatment of arsenic-relatedillnesses in Bangladesh. Thus it is likely that these are underestimates of the optimal level of therelevant health expenditure. This possibility is reinforced if one looks at the results of thecontingent valuation study conducted by the Water and Sanitation Program, South Asia inDecember 2002 (Ahmad and others 2002). For rural Bangladesh, this study estimated thewillingness to pay for arsenic-free, safe drinking water (that is, it estimated the value of avoidingarsenic-related health risks, which can approximate the value of avoiding the relevant healthexpenditure attached to these risks) to be equal to 0.2% to 0.3% of the average income of ruralhouseholds. Although economic theory dictates that in a CBA one should use optimal levels ofcosts and benefits, we decided to use the lower bounds calculated in the previous paragraph inorder to minimize the risk of exaggerating the health expenditure cost. Certainly our analysisshows that productivity losses due to illness are the primary component that drives the numbers,while the health expenditures are a secondary component to the net present value results.

14 Private communication with Dr. Akhtar.15 This is calculated as ((6,528 + 2,095) x 1,000).

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Results for the Model

Taken together both output and medical costs generate a present value that ranges from US$9.18billion to $23.51 billion to $89.50 billion as the discount rate ranges from 15% to 10% to 5%.16

The resulting net present value ranges from $8.2–1.1 billion to $22.3–11.1 billion to $71.8–87.9billion as the discount rate ranges from 15% to 10% to 5% (while the variation under the samediscount rate reflects varying costs of different technology options). The net present value arisingfrom these calculations can be as large as 11% of current Bangladesh GDP. However, inestimating the benefits of the arsenic mitigation program it is unrealistic to assume that amitigation policy will be fully (100%) effective in removing arsenic.

For this reason we further proceed in estimating the benefits under two scenarios:(a) effectiveness of mitigation technology amounts to 70% of exposure reduction; and(b) effectiveness of mitigation technology amounts to 50% of exposure reduction. Under scenario(a) the relevant net present value (discounted at 10%) amounts to approximately $9.5 (15–4)billion, which constitutes around 4% of Bangladesh GDP. Under scenario (b) the relevant netpresent value (discounted at 10%) amounts to approximately US$5 ((–0.6) – 10.6) billion, around2% of Bangladesh GDP.

Tables 18, 19, and 20 (see page 246, 247 and 248) show analytically our results on the netpresent value of various arsenic mitigation policies, with different degrees of effectiveness, anddiscounted at different interest rates. The effect of a lower discount rate on the resulting level ofnet present value, and consequently the desirability of a project is obvious from these tables.

With the exception of the option of rainwater harvesting (+ dug well) when discounted at a 10%rate, all other considered mitigation technologies are welfare increasing (that is, they pass a CBA)under all three levels of effectiveness at both 5% and 10% discount rates. However, whendiscounted at a 15% rate many of the mitigation technologies do not pass a CBA at lower than100% level of effectiveness. Moreover, rainwater harvesting (+ dug well) and rainwater harvesting(+ deep tubewell) are not welfare increasing even at 100% level of effectiveness. This resultindicates that one needs to carefully evaluate what mitigation measures are implemented andthat it is not true that any mitigation technology can be applied. Moreover, these results indicatethat at the project level, one may want to carry out a least-cost analysis.

The use of pond sand filters (30 households per unit), taking account of the level of service, turnsout to be superior to other technologies. However, even though our analysis concludes that pondsand filters are the most economically efficient option, two real-life caveats make this option lessattractive. First, pond sand filters are often very polluted. To take this into account in a CBA oneshould ideally include in the methodology a risk-weighting factor, which will indicate the increase

16 Using a different methodology, which relies on the estimation of epidemiological dose-response functions, Maddison, Luque, and Pearce(2004, p. 34) estimate the present value of benefits at US$138.7 billion, which is comparable to our total health benefit of $162.2 billion.

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of child morbidity and mortality due to water sources. The second caveat refers to the lack ofspace in Bangladesh for accommodating so many pond sand filters. In earlier years space wasnot an issue, but now there is either not enough land in any given village due to the highpopulation density, or people actually use the ponds for fish farming, a significant source ofincome in rural Bangladesh. This situation makes the shadow price involved in using the pondvery high, as it should include the price of the land where the pond will be situated. It can evenbe the case that the corresponding land has to be purchased through an actual moneytransaction, which makes the relevant price an explicit one.

Overall, no significant discrepancies among technologies are documented. The more dramaticeffect on the desirability of different mitigation technologies emerges by the changes in thechoice of discount rate of the future flow of cost and benefits. As expected, as the discount rateincreases, the net benefits of mitigation policies are reduced, to the point that, with a15% discount rate, we encounter negative net present value. This exercise highlights thesignificance of the choice of the discount rate, as well as the importance of the ability to predictthe degree of effectiveness of a proposed policy.

The approach suggested and applied above is applicable to both cases: (a) the risk that arsenicmight be found in an area where a project is planned; and (b) approaches regarding riskmitigation options where a project’s stated purpose is arsenic mitigation itself. While therelevance of our approach to case (b) has already been demonstrated in this paper, below weclarify how the methodology can be applied to case (a).

The methodology can be applied in cases in which arsenic contamination is not as widespreadas in Bangladesh and decisions have to be made about what needs to be done in advance of aproject planned in an area with a high risk of being contaminated. More specifically, in such acase the policymaker should try to collect information (through hydrogeological surveys) on theexistence and extent of contamination in the area under consideration. After acquiring thisinformation, the policymaker should apply the suggested methodology in order to perform a rapidCBA, which will help decide whether it is affordable to mitigate arsenic and then complete theproject under consideration, or whether arsenic mitigation is too expensive, possibly due toextensive contamination in the area. If the latter is true (that is, mitigation costs are significantlyhigher than benefits), then the relevant area should not be further developed through the otherplanned project, as development would attract people to the area, resulting in more people beingexposed to arsenic in the future.

At this point it is worth mentioning that in order to establish the extent of contamination it isnecessary to have a well-structured screening methodology and knowledge of the hydrogeologyof the different areas in a country. This highlights the importance of investment in a screeningprogram, as well as hydrogeological studies of high-risk areas. Both of these are necessary toolsfor acquiring knowledge about what is going on in a certain country, region, or area beforemitigation measures or development plans are implemented. Although both of these tools arequite expensive (for example, the price of arsenic laboratory analysis is US$9, not taking into

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Table 18. NPV (in Billion US$) of Arsenic Mitigation Policies, Discounted at 5%

100% successful

Technology Costs Health Output Benefits NPVb

(PV)a benefits benefits (PV)a

A Dug wells 12.9 1.1 88.4 89.5 76.6

B1 Rainwater harvest + dug well 17.7 1.1 88.4 89.5 71.8

B2 Rainwater harvest + deep tubewell 15.5 1.1 88.4 89.5 74.0

C Deep tubewell 7.4 1.1 88.4 89.5 82.1

D Shallow tubewell / arsenic removal 15.4 1.1 88.4 89.5 74.1

E1 Pond sand filter 12.0 1.1 88.4 89.5 77.5

E2 Pond sand filter (30 households/unit) 1.6 1.1 88.4 89.5 87.9

F Deep production well, piped 8.6 1.1 88.4 89.5 80.9

G Impoundment, piped 9.4 1.1 88.4 89.5 80.1

H River abstraction, piped 8.5 1.1 88.4 89.5 81.0

50% successful

Technology Costs Health Output Benefits NPV(PV) benefits benefits (PV)

A Dug wells 12.9 0.6 44.2 44.8 31.8



C Deep tubewell 7.4 0.6 44.2 44.8 37.3







70% successful


A Dug wells 12.9 0.8 61.9 62.7 49.7



C Deep tubewell 7.4 0.8 61.9 62.7 55.2







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100% successful



A Dug wells 8.5 0.6 22.9 23.5 15.0



C Deep tubewell 5.8 0.6 22.9 23.5 17.7







50% successful


A Dug wells 8.5 0.3 11.4 11.8 3.3

B1 Rainwater harvest + dug well 12.4 0.3 11.4 11.8 -0.6


C Deep tubewell 5.8 0.3 11.4 11.8 5.9







70% successful


A Dug wells 8.5 0.4 16.0 16.5 8.0



C Deep tubewell 5.8 0.4 16.0 16.5 10.6







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100% successful



A Dug wells 6.8 0.4 8.8 9.2 2.4


B2 Rainwater harvest + deep tubewell 9.7 0.4 8.8 9.2 -0.5

C Deep tubewell 5.2 0.4 8.8 9.2 4.0







50% successful


A Dug wells 6.8 0.2 4.4 4.6 -2.2



C Deep tubewell 5.2 0.2 4.4 4.6 -0.6

D Shallow tubewell / arsenic removal 6.5 0.2 4.4 4.6 -1.9

E1 Pond sand filter 7.3 0.2 4.4 4.6 -2.7


F Deep production well, piped 4.7 0.2 4.4 4.6 -0.1

G Impoundment, piped 5.0 0.2 4.4 4.6 -0.4

H River abstraction, piped 4.5 0.2 4.4 4.6 -0.1

70% successful


A Dug wells 6.8 0.3 6.1 6.4 -0.3



C Deep tubewell 5.2 0.3 6.1 6.4 1.2

D Shallow tubewell / arsenic removal 6.5 0.3 6.1 6.4 -0.1

E1 Pond sand filter 7.3 0.3 6.1 6.4 -0.9





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account transportation costs, while the price of a field kit is $0.5 per test) they are a necessaryfirst step of any decision about project implementation.

The logic behind this necessity is the following. The long-run nature of project-specificdevelopments means that initial screening costs will be discounted over a long-run horizon;hence, these costs will be relatively small in net present value terms irrespective of their absoluteinitial value. On the contrary, the effects of arsenic contamination could be detrimental to both theeconomy and health of the inhabitants of an area over a much shorter horizon. Moreover, it shouldbe kept in mind that the decision to develop a particular area is irreversible in practical terms.This characteristic of irreversibility necessitates great caution about the decision to develop ornot, hence such decisions should be taken under minimum risk conditions. The combined resultof these three effects increases the net potential benefit to society that can be achieved throughgathering information regarding the existence and extent of arsenic contamination prior to anyother project-related appraisal.

This discussion indicates that an option value underlies the development of particular projects inhigh-risk areas. Option value is a measure of people’s (society’s) risk aversion to factors thatmight affect future access to use of environmental or biological assets. More precisely, the optionvalue relevant to our discussion is the premium that society is willing to pay to avoid having toface the effects of arsenic contamination in the area where economic and social development isplanned. In our case, this premium is the money that the society (the government) will spend onscreening and hydrological studies in order to gather enough information to allow the choice of adevelopment area with a minimum risk of arsenic contamination. This allows society to reducethe risk (variance) associated with future welfare.

In conclusion, as long as society is risk averse and the development horizon is long, screeningand hydrological studies that enable such risk reductions are likely to be welfare increasing.

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This paper reviews existing studies and data on arsenic contamination, related health effects,and the costs of mitigation in those countries where it has been undertaken. Then it

introduces an approach which provides a quick and readily applicable method for performing aCBA of different arsenic mitigation policies. In particular, our suggested approach estimatesbenefits of mitigation activities as the sum of foregone medical costs and saved outputproductivity achieved through the reduction of arsenic exposure. The present value of thesebenefits is then compared with the present value of costs of various mitigation measures in orderto determine when and which mitigation policies pass a CBA (that is, produce a positive changeto social welfare).

The paper applies this approach in order to provide some estimate of costs and benefits ofarsenic mitigation in one case study country, Bangladesh. This case study serves as an appliedexample of a rapid socioeconomic evaluation and is also used as a basis for discussing trade-offs in decisionmaking with respect to the allocation of financial resources. Our approach isapplicable to the following cases: (a) where there is risk that arsenic might be found in an areawhere a project is planned; and (b) in regard to risk mitigation options where a project’s goal isarsenic mitigation per se.

With the exception of the option of rainwater harvesting (+ dug well) when discounted at a 10%rate, all other considered mitigation technologies are welfare increasing (that is, they pass a cost-benefit analysis) under all three levels of effectiveness at both 5% and 10% discount rates.However, when discounted at a 15% rate, many of the mitigation technologies do not pass a CBAat lower than 100% level of effectiveness. Moreover, rainwater harvesting (+ dug well) andrainwater harvesting (+ deep tubewell) are not welfare increasing even at 100% level ofeffectiveness. This result indicates that one needs to carefully evaluate what mitigation measuresare implemented and that it is not true that any mitigation technology can be applied. Moreover,these results indicate that, at the project level, one may want to carry out a least-cost analysis.

It is also worth mentioning that (a) in our calculation we did not take into account theenvironmental benefits of mitigation strategies (mainly due to lack of precise data); and that(b) the health expenditures only represent a lower bound. That is, the calculated net benefitsfrom arsenic mitigation are underestimates of the true benefits and should be used as a veryconservative figure of welfare increases to be derived from implementing the variousmitigation policies.

Finally, these figures indicate the imminent need for facing the arsenic crisis in Bangladesh, butalso the clarity with which our approach can answer the difficult question on the balance ofrelevant costs and benefits of various mitigation policies.

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Detailed Technology Costs

The tables below itemize the costs of each technology for a village of 500 households.

Average Village Model: 500 Households

Nos.

Homesteads (clusters) 50

Households @ 10 per homestead 500

Population @ 5.5 per household 2,750

Option A: Dug Wells

Capital costs Unit Qty Rate (US$) Amt (US$)

Excavation: depth 12.5 m m3 10 10 102

Pipe rings supply m 12.5 20 254

Pipe rings install m 12.5 8 106

Handpump supply & install no. 1 68 68

Transport sum 1 85 85

Contingencies and handover/training sum 1 34 34

Platform + other core components work sum 1 102 102

Total 750

Operation & maintenance Unit Qty Rate (US$) Amt (US$)costs annual

Chemical: disinfection kg 15 2 25

Labour days 24 2 41

Spares/parts sum 1 17 17

Water quality monitoring sum 5 8 42

Total 125

Infrastructure required Income

High Medium Low Total

Proportion 10% 20% 70% 100%

Households 50 100 350 500

Households/dug well 1 3 10 n.a.

No. of dug wells 50 33 35 118

Financial costs

Capital 88,750

Annual operation & maintenance 14,842


Income Categories


Proportion 10% 20% 70% 100%


Population 275 550 1,925 2,750

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Option B1: Roof Rainwater Harvest/Household (60 sq m) + Dug Well

Capital costs: roof catchment Unit Qty Rate (US$) Amt (US$)

Roof gutters m 36 3 107

Pipework m 7 5 36

Tank 3.2 m3 on platform/3 month storage no. 1 105 105

Handpump supply and install no. 0 n.a. n.a.



Roof rainwater harvest capital cost Total 273

Dug well capital cost sum 1 750 750

Operation & maintenance costs Unit Qty Rate (US$) Amt (US$)annual (roof catchment)

Chemical: disinfection kg 0.25 2 0

Labour days 7 2 12



Total 24

Dug well months 12 10.45 125

Infrastructure required IncomeHigh Medium Low Total

Proportion 10% 20% 70% 100%


Households/rainwater harvest 1 1 1 n.a.

No. of rainwater harvest systems 50 100 350 500

Households/dug well 3 10 20 n.a.

No. of dug wells 17 10 18 44

Financial costs

Capital 169,566



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Option B2: Roof Rainwater Harvest/Household (60 sq m) + Deep Tubewell

Capital costs: roof catchment Unit Qty Rate (US$) Amt (US$)

Roof gutters m 36 3 107

Pipework m 7 5 36

Tank 3.2 m3 on platform/3 month storage no. 1 105 105

Handpump supply and install no. 0 n.a. n.a.



Roof rainwater harvest capital cost Total 273

Deep tubewell capital cost sum 1 911 911

Operation & maintenance costs Unit Qty Rate (US$) Amt (US$)annual (roof catchment)

Chemical: disinfection kg 0.25 2 0

Labour days 7 2 12



Total 24

Deep tubewell months 12 4 46



Proportion 10% 20% 70% 100%


Households/rainwater harvest 1 1 1 n.a.

No. of rainwater harvest systems 50 100 350 500

Households/deep tubewell 3 10 20 n.a.

No. of deep tubewells 17 10 18 44

Financial costs

Capital 176,677



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255254

Option C: Hand Deep Tubewell


Sinking m 250 0.3 64

35 mm pipe supply + stainer m 250 1.7 424

Pipe install m 250 0.8 212

Handpump supply & install no. 1 127.1 127

Transport sum 1 33.9 34

Contingencies and handover sum 1 16.9 17

Platform + other core components work sum 1 33.9 34

Total 911


Chemical: disinfection kg 0 n.a. n.a.

Labour days 12 1.7 20

Spares/parts sum 1 16.9 17

Water quality monitoring sum 1 8.5 8

Total 46



Proportion 10% 20% 70% 100%


Households/deep tubewell 1 3 10 n.a.

No. of deep tubewells 50 33 35 118

Financial costs

Capital 107,804



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Option D: Existing Shallow Tubewell with Household Arsenic Removal


Arsenic removal supply & install no. 1 50.8 51


Contingencies and handover/training sum 1 25.4 25

Total 80


Chemical: disinfection kg 0 n.a. n.a.

Labour days 0 n.a. n.a.

Media/spares/parts sum 1 25.4 25

Water testing (for arsenic) sum 2 8.5 17

Total 42



Proportion 10% 20% 70% 100%


Households/arsenic removal unit 1 1 1 n.a.

No. of arsenic removal 50 100 350 500

Financial costs

Capital 39,831



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257256


Option E: Pond Sand Filter


Excavation m3 6 3.4 20

Reinforced concrete including formwork m3 4 1.7 7

Block wall m2 48 11.9 569

Handpump supply & install no. 1 67.8 68


Contingencies and handover/training sum 1 254.2 254

Total 953


Chemical: disinfection kg 15 1.7 25

Labour days 24 1.7 41

Spares/parts sum 1 16.9 17

Total 83



Proportion 10% 20% 70% 100%


Households/pond sand filter 1 2 10 n.a.

No. of pond sand filters 50 50 35 135

Financial costs

Capital 128,593


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Option G: Piped Scheme Impoundment: Engineered Pond


Impoundment sum 4,237

Intake/infiltration gallery sum 1,508

Pumping facilities sum 6,356

Masonry/concrete storage tanks sum 8,305

Trunk main/transmission main sum 847

Distribution system sum 18,271

House connections sum 8,720

Capital costs Total 48,246Operation & maintenance costs annual Total 7,627

Option H: Piped Scheme Surface Water: River Abstraction/Infiltration Gallery


Intake/infiltration gallery sum 2,034







Option F: Piped Scheme Deep Production Well (Domestic)


Production wells sum 3,627

Sinking/drilling and core samples m 300 3.2 966







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Date post:	22-Mar-2016
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Arsenic Contamination of Groundwater in South and East Asian Countries - Technical Report

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