1.Arsenic Contamination Of GroundwaterSeminar Report 2012-13 Department of Civil EngineeringIndian Institute of TechnologyBanaras Hindu UniversityUnder the guidance of: Submitted by:Prof. Devendra Mohan Mayank Saxena 09103EN008 B.Tech, Part-IV

2. ABSTRACTNatural groundwater arsenic-contamination and the sufferings of people as a result, has become acrucial water quality problem in many parts of the world, particularly in Bengal delta, Bangladesh andWest Bengal (India). It has recently been recognized that As-contaminated groundwater used forirrigation may pose an equally serious health hazard to people eating food from the crops irrigated andthat As accumulating in irrigated soils poses a serious threat to sustainable agriculture in affected areas.This report reviews the nature of those threats, taking into account the natural and anthropogenicsources of arsenic pollution, areas affected and health impact of arsenic contamination of groundwater. 3. ACKNOWLEDGEMENTApart from ones own effort, the success of any work largely depends on the encouragement andguidance of the others. I would like to take this opportunity to express my gratitude to the peopleinstrumental in the successful completion of this reportMy special thanks to Prof. Devendra Mohan ( Department of civil engineering,IIT-BHU) for mentoringmy report. I show my greatest appreciation to him for his tremendous support and help. I feel motivatedand encouraged after working under his guidance and without whom this project would not have beenmaterialized.I would also like to acknowledge and extend my heartiest gratitude to my classmates Mr. AyushAgarwal, Mr. Bhuvanesh Shukla and Mr. Deepak Kumar who gave important suggestions andtremendous support which was very vital for success of my report. 4. 1. INTRODUCTIONArsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in many minerals,usually in conjunction with sulfur and metals, and also as a pure elemental crystal. Arsenic is a metalloid.It can exist in various allotropes, although only the gray form has important use in industry. Arsenic isnotoriously poisonous to multicellular life, although a few species of bacteria are able to use arseniccompounds as respiratory metabolites. Various physical and chemical properties of arsenic are asfollows-1.1 PHYSICAL PROPERTIES OF ARSENICArsenic occurs in three most common allotropes which are metallic grey, yellow and black arsenic, withgray being the most common. Gray arsenic adopts a double-layered structure consisting of manyinterlocked ruffled six-membered rings. Nearest and next-nearest neighbors form a distorted octahedralcomplex, with the three atoms in the same double-layer being slightly closer than the three atoms in thenext.[8] This relatively close packing leads to a high density of 5.73 g/cm3. Gray arsenic is a semimetal,but becomes a semiconductor with a bandgap of 1.21.4 eV if amorphized. Yellow arsenic is soft andwaxy, and have four atoms arranged in a tetrahedral structure in which each atom is bound to each ofthe other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile,least dense and most toxic. Solid yellow arsenic is produced by rapid cooling of arsenic vapor, As4. It israpidly transformed into the gray arsenic by light. The yellow form has a density of 1.97 g/cm3. Phase solid Density 5.727g/cm3 Liquid density at 5.22g/cm3 m.p Sublimation Point 881K Triple point1090K, 3628 kPa Heat of Fusion24.44kJ/mole Heat of Vaporization34.76kJ/mole Sublimation Point 881KPhysical Properties of Arsenic 5. 1.2. CHEMICAL PROPERTIESArsenic is a member of Va group of periodic table. It occur in nature in four oxidation states -3,0,+3,+5with -3 being most toxic and +5 being least toxic. In groundwater, Arsenic is found in only two oxidationstates i.e +3 and +5. Various chemical properties of Arsenic are summarize in the following table Symbol As Atomic number33 Element category Metalloid Group,period,block Va,4,p Atomic weight74.92160 Electronegativity2.18(pauling scale) Atomic radius119 pm Van der Waals radius 185 pm CHEMICAL PROPERTIES OF ARSENIC1.3 ARSENIC CONTAMINATION OF GROUNDWATERArsenic contamination of groundwater is a natural occurring high concentration of arsenic in deeperlevels of groundwater. As per WHO, maximum permissible limit of arsenic in groundwater is 10 g/liter.Arsenic contamination poses a serious health hazard to about 150 million people worldwide(Ravenscroft et al. 2009). Around 110 million of those people live in ten countries in South and South-east Asia: Bangladesh, Cambodia, China, India, Laos, Myanmar, Nepal, Pakistan, Taiwan and Vietnam(Brammer and Ravenscroft, 2009). Recently it has also been found that As-contaminated groundwaterused for irrigation may pose an equally serious health hazard to people eating food from the cropsirrigated and that As accumulating in irrigated soils poses a serious threat to sustainable agriculture inaffected areas. Arsenic is found in nature in soils and rocks, natural waters and organisms. It is mobilizedthrough a combination of natural processes such as weathering reactions, biological activity and volcanicemissions as well as through a range of anthropogenic activities. Most environmental As problems arethe result of mobilization under natural conditions. However, man has had an important additional 6. impact through mining activity, combustion of fossil fuels, the use of arsenical pesticides, herbicides andcrop desiccants.2. DISTRIBUTION OF ARSENIC2.1 CONTINENT-WISE DISTRIBUTION2.1.1 ASIAMain areas affected from arsenic contamination of groundwater in Asia are Xinjiang, Liaoning, Jilin,inner Mongolia, Ningxia, Shanxi, Jhelum basin (Pakistan), Bangladesh, Nepal, Guizhou (China), Taiwan,Hanoi (Vietnam), Myanmar, West Bengal (India), Uttar Pradesh (India) , Cambodia, Ronphibun(Thailand), Gujarat (India) (Chakraborti et al,2002).DISTRIBUTION OF ARSENIC IN ASIA1) Xinjiang; (2) Jilin; (3) Liaoning; (4) inner Mongolia; (5) Ningxia; (6) Shanxi, all foregoing in China; (7) Jhelum, Pakistan; (8)Pakistan; (9) Bangladesh; (10) Nepal; (11) Guizhou, China; (12) Taiwan; (13) Hanoi, Vietnam; (14) Myanmar; (15) Lao PDR;(16) WB, India; (17) Cambodia; (18) Ronphibun, Thailand. 7. 2.1.2 EUROPEIn Europe, problem of arsenic contamination of groundwater is less as compared to Asia. MajorEuropean countries affected from this problem are Hungary, Romania and South-west Finland. InHungary concentration of arsenic in groundwater is 1-174 g.L-1, in Romania, concentration is about 1-176 g.L-1 (Sharma and Sohn, 2009).2.1.3 AUSTRALIAAustralia is a country rich in minerals that constitute a significant source of arsenic contamination to theenvironment, in addition to anthropogenic sources, such as mining activities and pesticide usage. In1991, survey data revealed elevated levels of arsenic in surface water and groundwater of Victoria(Mukherjee et al, 2006).2.1.5 NORTH AMERICASome locations in the United States, such as Fallon, Nevada, have long been known to havegroundwater with relatively high arsenic concentrations (in excess of 0.08 mg/L). Even some surfacewaters, such as the Verde River in Arizona, sometimes exceed 0.01 mg/L arsenic, especially during low-flow periods when the river flow is dominated by groundwater discharge.( Taqueer and Quereshi, 1995).Other Affected areas in North America are Hermosillo, Yaqui river watershed, Valle del Guadiana,Morales in San Luis Potosi city, Puebla state, Taxco, Pol Chucabkatun, Luna-Sen, Salamanca, Acambaro,Zacatecas, Santa Ma. De la Paz, Puebla state (Bundschuh et al, 2012).2.1.4 SOUTH AMERICAAreas of South America affected from arsenic contamination are Chile, Brazil, Argentina, Peru, Ecuador,Tambo river and Papallacta lake area, Tumbaco, Locumba Valley, Quebrada de Camarones, TatioGeothermal springs, upper Pilcomayo river basin, Garayalde ( Uruguay), Santa Barbara dist. , Rimac riverbasin, Geothermal water from EL Carchi, Imbabura, Pichincha, Cotopaxi, Puno, Lluta and Azata valleys,Morococha mining region (Bundschuh et al, 2012). 8. DISTRIBUTION OF ARSENIC IN SOUTH AMERICA(76) Loa riverbasin/Atacamadesert, (77) Tatiogeothermal springs,(78) Coquimbo,Valle del Elqui,(79) Maipu river basin;Bolivia: (80) El Alto(LaPaz), (81) Oruro,(82) Poop basin, (83) North ofPotos dept., (84) Upper Pilcomayoriver basin; (85) Lipz and south ofPotos dep.; Argentina:(86) NWArgentine Andean highland, e.g.San Antonio de Los Cobres andmany other localities, (87) Chaco plain,(88) Pampa plain, (89)Copahue,(90) Garayalde and Camarones(Chubut prov.); Uruguay: (91) San Josdept.; Brazil: Minas Gerais st.: (92)Nova Lima dist., (93) SantaBrbaradist., (94) Ouro Preto/Mariana dist. (63) El diamantegold mine; Caldas dep.; Ecuador: (64) Tamboriver and Papallacta lake area(Quijos county,Napo prov.), (65) Guayllabamba, (66)Tumbaco, (67) Geothermal waters from ElCarchi, Imbabura, Pichincha, Cotopaxi,andTungurahua prov.; Peru: (68)Morococha miningregion/La Oroya smelting complex (Yauli prov,Junin dep.), (69) Rmac river basin,(70)Huaytar prov. (Huancavlica dep.), (71) Puno(Puno dep.), (72) Locumba valley (Tacna dep.;Ilo city water supply), (74) Arica area(Llutaand Azapavalleys, (75) Quebradade Camarones (73)Tacna area (SamaQuebrada de la Yarada) 9. 2.1.6 AFRICAAreas affected from arsenic contamination in Africa are Obuasi and Bolgatunga regions of Ghana(Smedley, 1996). Other areas are Yatenga, Ankobra basin, Offin basin, Ekondo Titi, Okavango Delta(Ravenscroft, 2007)DISTRIBUTION OF ARSENIC IN AFRICA 10. 2.2 DISTRIBUTION OF ARSENIC IN INDIAN SUB-CONTINENT2.2.1 PAKISTANAreas affected from arsenic contamination in Pakistan include Manchar Lake Jamshoro (Sindh), someparts of Ravi basin, Sialkot, Kasur city, Muzaffargarh, Multan, Karachi (Azizullah et al, 2011). LocationConc. Of Reference -1 As(in ug.L ) Various spots of Karachi Well water of Multan Muzzafargarh Manchar Lake2.2.2 SRI LANKAAreas affected from arsenic contamination in SriLanka are Rajarata, Anuradhapura and some parts ofColombo (Jayasumana et al, 2007).2.2.3 NEPALMajor areas affected from arsenic contamination in Nepal are Nawalparasi, Bara, Parsa, Rautahat,Rupandehi, Kapilvastu, Rautahat, and Kailali with concentration between 50-2621 g/l (Pokhrel et al,2007).2.2.4 BANGLADESHMajor areas affected from arsenic contamination are Sylhet, Brahmanbaria, Mymensingh, Narayanganj,Sherpur, Bogra, Netrokona, Kishoreganj, Meherpur, Thakurgaon, Moulavibazar, Comilla, Madaripur,Chittagong, Rangamati, Khulna, Thakurgaon, Panchagarh, Sirajganj, Rangpur. 11. DISTRIBUTION OF ARSENIC IN BANGLADESH (adapted from Chakraborti et al, 2007) 12. 2.2.5 INDIA2.2.5.1 WEST BENGAL Malda, Murshidabad, Nadia, North Parganas, Parganas, Bardhaman, Howrah, Hoogly and Kolkata haveconcentration more than 300 g/l. Kooch Bihar, Jalpaiguri, Darjeeling, North Dinajpur and SouthDinajpur have concentration about 50g/l (Chakraborti et al, 2007).DISTRIBUTION OF ARSENIC IN WEST BENGAL (adapted from Chakraborti et al, 2001) 13. 2.2.5.2 UTTAR PRADESHMain areas affected from arsenic contamination in Uttar Pradesh are Varanasi, Gazipur and ballia. Thearea and population of the 3affected districts are 11450 km2 (4.8 % of the total area of UP) and8.7million, approximately 5.3 % of the total population of UP (Chakraborti et al).2.2.5.3 BIHARMain areas affected from arsenic contamination in Bihar are Chakani village (Brahampur) and Baraharablock in Buxar district. There is also a probability of arsenic contamination in districts close to arseniccontaminated Tarai region of Nepal.2.2.5.4 OTHERSOthers areas contaminated from arsenic in India are Sahibganj district of Jharkhand, Imphal East, ImphalWest, Thoubal and Bishnupur (Manipur) (Chakraborti et al), Rajnandgaon and Kanker District(Chattisgarh) (Shukla et al, 2009).3. SOURCES OF ARSENIC3.1 ARSENIC MOBILIZATION MECHANISMFour mechanisms have been proposed for the mobilization of arsenic into ground water Reductive dissolution Alkali desorption Geothermal action Sulphide oxidation3.1.1 REDUCTIVE DISSOLUTIONIron (III) oxyhydroxides are of particular environmental relevance because they often occur as finegrained particles and exhibit high reactive surfaces. The Fe(II)/Fe(III) redox couple is an importantelectron-transfer mediator for many biological and chemical species. As a consequence, the stability ofFe(III) oxyhydroxides in soils exerts a major control on mobility of both organic and inorganic pollutantssuch as arsenic. Iron-reducing bacteria which are present in waterlogged soils and aquifers couplethe oxidation of organic matter with the reduction of various Fe(III) oxyhydroxides for their metabolism.A direct consequence of Fe(III) reduction is the associated trace metal release into soil solution (Fakih etal,2009). 14. 3.1.2 ALKALI DESORPTIONLaboratory studies show that arsenic adsorbed to iron, manganese and aluminum oxides and clayminerals may be desorbed at pH >8.0, leaving the carrier phase as a solid. The best-documentedexample comes from the southwest USA (Baxfield and Plummer, 2003), and others come fromOklahoma, Spain, China and from volcanic deposits in Argentina (Nicolli et al, 1989).3.1.3 SULPHIDE OXIDATIONArsenic sulfide minerals such as orpiment and realgar are of significant economic interest in manymining operations because of their role as reliable indicators of gold mineralization .These minerals arealso of great environmental interest because the oxidative dissolution of these minerals can potentiallyincrease the concentrations of As in natural water ( Lengke and Tempel, 2004). The proposed overallreactions of arsenic sulfide oxidation are written as:As2S3 + 7O2 + 6H2O 2HAsO42- + 3SO42- + 10H+AsS + 2.75O2 + 2.5H2O HAsO42- +SO42- + 4H+3.1.4 GEOTHERMAL ACTIONMixing of geothermal solutions and fresh ground water can lead to high arsenic concentrations in somelocations (Smedley and Kinniburgh, 2002).3.2 MAJOR AREAS CONTAMINATED FROM ARSENIC AND ARSENICMOBILIZATION MECHANISM INVOLVEDContaminated Areas Mechanism involvedReferencesWest BengalReductive dissolution Harvey et al,2004Bangladesh Reductive dissolution and inHarvey et al,2004; some parts geochemicalAnawar et al 2001South-West USA Alkali desorption Baxfield and Plummer, 2003Perth (Australia)Sulphide OxidationAppleyard et al,2006 15. Mid-West USAReductive Dissolution Kelly et al,2005Spain Alkali Desorption Ravenscroft 2007Argentina Alkali Desorption Nicolli et al,1989Danube (Europe) Reductive dissolution Kelly et al, 2005China Alkali desorption Ravenscroft 2007Chile (South America) Geothermal activity Smith et al,1998Tibet plateau Geothermal activity Ravenscroft 2007Ghana (Africa)Sulphide oxidationSmedley 19953.3 ANTHROPOLOGICAL ACTIVITIES LEADING TO ARSENICCONTAMINATION OF GROUNDWATERMany compounds of arsenic are used in various field which have a potential to spread arseniccontamination. Some of the major compounds are:3.3.1 CHROMATED COPPER ARSENATEChromated copper arsenate (CCA) has been long used for treating wood in order to increase its lifetimein outdoor applications. It had been observed that the chemical and structural forms of either Cr or As inthe exposed wood are the same as in freshly treated material (Nico et al,2004). The leaching of dislodgeabled residues of CCA-preserved wood with simulated biological fluids (sweat or gastric juice) indicatedthe main presence of free As(V) anionic species. Another source of As comes from CCA-impregnatingplants, whose soils may contain high pools of potential contamination.3.3.2 4-HYDROXY-3-NITROBENZENE ARSONIC ACID (ROXARSONE)The common use of antibiotic additive Roxarsone is in poultry farm to increase the chicken weight.However As is largely excreted and consequently poultry litter can contain high As levels (Villaescusaand Bollinger,2007): up to 40 mg/kg (dry weight). Moreover such As from poultry litter is easily watersoluble with 7090% extraction rate (Garbarino et al.2003; Rutherford et al. 2003), and transformed toAs(V) due to both photo degradation and mineralization in the presence of nitrate and organic matter(Bednar et al. 2003). 16. 3.3.3 MONOSODIUM METHANEARSONATE (MSMA)It a common arsenical herbicide used in golf course green treatment, led to a systematic monitoring ofrelated soils and the water percolating through these soils .Presumably due to microbial activity in thesoil, MSMA was found to be transformed to As(V),As(III), MMA and DMA; after 14 weeks, almost20% ofinorganic As originating from MSMA can percolate below the rhizosphere (Villaescusa andBollinger,2008). Other anthropological causes of arsenic contamination are not yet verified but it is hypothesizedthat excessive use of groundwater create an environment which favors arsenic mobilizationthrough soil. Improper disposal of mining wastes also causes the groundwater contamination in mining areas.4. IMPACTS OF ARSENIC CONTAMINATIONBefore discussing about the impacts of arsenic contamination let us first discuss about the toxicity oftwo arsenic species: As(III) and As(IV) present in groundwater.4.1 TOXICITY OF ARSENICIt is commonly accepted that inorganic As(III) compounds are approximately 6080 times more toxic tohumans than As(V) ones (Villaescusa and Bollinger,2008). The acute toxicity of arsenic is related to itschemical form and oxidation state. Toxicity of any chemical species is measured in LD50 (LD50 withrespect to any biological species is the amount required to kill 50% of a given test species.). Toxicity levelof some arsenic compounds are shown in the table.CHEMICAL SPECIES (sex) LD50 (mg/kg)REFERNCESArsenite Mouse (male)8 Bencko et al,1978Arsenite Hamster (male)8 Petrick et al,2001Arsenate Mouse (male)22Bencko et al,1978ArsenobetaineMouse (male)>4260 Kaise et al, 1985 17. Arsenic trioxideMouse (male) 26-48Harrison et al, 1958MMA Hamster (male) 2Petrick et al,2001DMA Mouse (male) 648Kaise et al, 1985TMAOMouse (male) 5500 Kaise et al, 19854.1.1 MECHANISM OF PENTAVALENT ARSENIC TOXICITYArsenate can replace phosphate in many biochemical reactions because they have similar structure andproperties (Hughes, 2001). For example: Arsenate reacts in vitro with glucose and gluconate to formglucose-6-arsenate and 6-arsenogluconate, respectively. These compounds resemble glucose-6-phosphate and 6-phosphogluconate, respectively. Arsenate can also replace phosphate in the sodium pump and the anion exchange transportsystem of the human red blood cell (Hughes, 2001). Arsenate uncouples in vitro formation ofadenosine-5-triphosphate (ATP) by a mechanismtermed arsenolysis. Depletion of ATP by arsenate has been observed in cellular systems. ATPlevels are reduced in human erythrocytes (Winski and Carter,1998) after in vitro exposure toarsenate.4.1.2 MECHANISM OF TRIVALENT ARSENIC TOXICITYSpecific functional groups within enzymes, receptors or coenzymes, such as thiols or vicinal sulfhydryls,have a major role in the activity of these molecules. Trivalent arsenic readily react in vitro with thesethiol-containing molecules (Hughes,2001). The binding of trivalent arsenic to critical thiol groups mayinhibit important biochemical events which could lead to toxicity. Pyruvate dehydrogenase (PDH) is amulti-subunit complex that requires lipoic acid (a dithiol) for enzymatic activity so arsenite inhibits PDHby binding to the lipoic acid which ultimately leads to the decreased production of ATP (Hughes,2001). 18. 4.2 WHY IS ARSENIC BAD FOR HEALTH?Arsenic dissolved in water is acutely toxic and can lead to a number of health problems. Long-termexposure to arsenic in drinking-water causes increased risks of cancer in the skin, lungs, bladder andkidney. It also leads to other skin-related problems such hyperkeratosis and changes in pigmentation.Consumption of arsenic also leads to disturbance of the cardiovascular and nervous system functionsand eventually leads to death. Increased risks of lung and bladder cancer and of arsenic-associated skinlesions have been reported for consuming drinking-water with arsenic concentrations equal to orgreater than 50 parts per billion (or microgram per liter). (WHO Environmental Health Criteria).Arsenicosis, or arsenic toxicity, develops after two to five years of exposure to arsenic contaminateddrinking water, depending on the amount of water consumption and arsenic concentration in water.Initially, the skin begins to darken (called diffuse melanosis). This happens first in the palms. Diffusemelanosis leads to spotted melanosis, when darkened spots begin to appear on the chest, back andlimbs, although the latter is what is usual among people, and so is taken to be an early symptom. At alater stage, leucomelanosis sets in: the body begins to show black and white spots.Keratosis is the middle stage of arsenicosis. The skin, in portions, becomes hard and fibrous; it is as if thebody has broken out into hard boils, or ulcers. Diffuse or nodular keratosis on the palm of the hand orsole of the foot is a sign of moderately severe toxicity. Rough dry skin, often with palpable nodules onhands, feet and legs means severe toxicity. This can lead to the formation of gangrene, and cancer.Arsenic poisoning brings with it other complications: liver and spleen enlargement and cirrhosis of theliver; myocardial degeneration and cardiac failure; peripheral neuropathy affecting primary sensoryfunctions; diabetes mellitus and goiter. Another unfortunate and complicating fact about arsenicpoisoning, is that it generally takes from seven to 10 years sometimes longer, for the disease to berecognized. When it finally is, it may be too late to treat.SYSTEMEFFECTSkinSkin LesionsCardiovascularBlackfoot diseaseNervous Peripheral neuropathy, EncephalopathyEndocrine DiabetesRenal Proximal tubule degeneration, papillaryand cortical necrosisHematological Bone marrow depression ADAPTED FROM HUGHES,2002 19. PEOPLE SUFFERNING FROM ARSENIC POISONING 20. DRINKINGWATER/FOOD NATURALMINING/ DEPOSITS/SOILSCOALBURNING HUMAN EXPOSURE TO ARSENIC UPTAKEEXCRETIONCELLULAR METABOLISM/TOXICITY ACCUMULATION CARCINOGEN NON-CARCINOGEN CHROMOSOMAL ABNORMALITIES CARDIOVASCULAR OXIDATIVE STRESSAND NON- CARDIOVASCULAR AFFECTS ABERRATIONS IN GENE EXPRESSION MODIFICATION OF CELL PROLIFERATION HUMAN EXPOSURE TO EXPOSURE AND VARIOUS MODE OF ARSENIC TOXICITY ( adapted from Roy and Saha) 21. CONCLUSIONThis review, based on a large number of accessible sources of information on As contamination ingroundwater suggests that arsenic contamination is highest in South and South-East Asia and lowest inAfrica. Most of the sources of arsenic contamination are natural whereas anthropological activities workas a catalyst in the mobilization of arsenic. Various mechanisms for mobilization of arsenic through soilare proposed which depends mainly upon the hydro-geochemical properties of the area. Inorganicarsenic is a carcinogen for human (not yet proved for animals) and it also causes various cardiovascularand vascular diseases to human. About 137 million people in more than 70 countries are probablyaffected by arsenic poisoning of drinking water, so it is very important to take measures to reduce thearsenic concentration in groundwater on a large scale. Reverse Osmosis filter system should be installedin households to avoid arsenic poisoning. 22. REFERENCES Hugh Brammer, Peter Ravenscroft, 2008. Arsenic in groundwater: A threat tosustainable agriculture in South and South-east Asia. Dipankar Chakraborti , Mohammad Mahmudur Rahman , Bhaskar Das ,Matthew Murrill, Sankar Dey , Subhas Chandra Mukherjee , Ratan Kumar Dhar ,Bhajan Kumar Biswas ,Uttam Kumar Chowdhury , Shibtosh Roy , Shahariar Sorif ,Mohammad Selim ,Mahmuder Rahman , Quazi Quamruzzaman,2010. Status of groundwater arseniccontamination in Bangladesh: A 14-year study report H.M. Anawar, J. Akaib, K.M.G. Mostofa, S. Safiullah, S.M. Tareq, 2001. Arsenic poisoningin groundwater:Health risk and geochemical sources in Bangladesh Virender K. Sharma, Mary Sohn, 2009. Aquatic arsenic: Toxicity, speciation,transformations, and remediation Dipankar Chakraborti , Mohammad M. Rahman , Kunal Paul ,Uttam K. Chowdhury ,Mrinal K. Sengupta , Dilip Lodh ,Chitta R. Chanda , Kshitish C. Saha , Subhash C.Mukherjee,2001. Arsenic calamity in the Indian subcontinent: What lessons have beenlearned? P.L. Smedley, D.G. Kinniburgh,2001. A review of the source, behaviour and distributionof arsenic in natural waters Dericks Praise Shukla , C.S. Dubey , Ningthoujam P. Singh , M. Tajbakhsh , M.Chaudhry,2010. Sources and controls of Arsenic contamination in groundwater ofRajnandgaon and Kanker District, Chattisgarh, Central India Jochen Bundschuh , Marta I. Litter, Faruque Parvez , Gabriela Romn-Ross , Hugo B.Nicolli ,Jiin-Shuh Jean, Chen-Wuing Liu , Dina Lpez , Mara A. Armienta , Luiz R.G.Guilherme, Alina Gomez Cuevas , Lorena Cornejo , Luis Cumbal , Regla Toujaguez,2011.One century of arsenic exposure in Latin America: A review of history and occurrencefrom 14 countries D. Pokhrel, B.S. Bhandari, T. Viraraghavan, 2008. Arsenic contamination of groundwaterin the Terai region of Nepal: An overview of health concerns and treatment options Pradosh Roy and Anupama Saha. Metabolism and toxicity of arsenic: A humancarcinogen 23. Dipankar Chakraborti, Bhaskar Das, Bishwajit Nayak, Arup Pal, MohammadMahmadur.Rahman, Mrinal Kumar Sengupta, Md. Amir Hossain, Sad Ahamed,Manabendranath Sahu,Kshitish Chandra Saha, Subhash Chandra Mukherjee,Shyamapada Pati, Rathindra Nath Dutta, Quazi Quamruzzaman. Groundwater ArsenicContamination in Ganga-Meghna-Brahmaputra Plain, its Health Effects and an Approachfor Mitigation. Amitava Mukherjee, Mrinal Kumar Sengupta, M. Amir Hossain, Sad Ahamed, BhaskarDas, Bishwajit Nayak, Dilip Lodh, Mohammad Mahmudur Rahman, and DipankarChakraborti,2006. Arsenic Contamination in Groundwater: A Global Perspective withEmphasis on the Asian Scenario. Isabel Villaescusa, Jean-Claude Bollinger, 2008. Arsenic in drinking water: sources,occurrence and health effects (a review) Kwadwo Ansong Asante, Tetsuro Agusa , Annamalai Subramanian, Osmund D. Ansa-Asare , Charles A. Biney , Shinsuke Tanabe,2006. Contamination status of arsenic andother trace elements in drinking water and residents from Tarkwa, a historic miningtownship in Ghana. Pauline L. Smedley, 1996. Arsenic in rural groundwater in Ghana Azizullah Azizullah , Muhammad Nasir Khan Khattak , Peter Richter , Donat-PeterHder,2010. Water pollution in Pakistan and its impact on public health A review R.T. Nickson, J.M. McArthur , B. Shrestha , T.O. Kyaw-Myint , D. Lowry, 2004. Arsenic andother drinking water quality issues, Muzaffargarh District, Pakistan Peter Ravenscroft, 2007. Predicting the global extent of arsenic pollution ofgroundwater and its potential impact on human health Michael F. Hughes, Arsenic toxicity and potential mechanisms of action Vivek Singh Chauhan, R.T. Nickson, Divya Chauhan, L. Iyengar, NaliniSankararamakrishnan, 2009. Ground water geochemistry of Ballia district, UttarPradesh, India and mechanism of arsenic release Suiling Wang, Catherine N. Mulligan, 2005. Occurrence of arsenic contamination inCanada: Sources, behavior and distribution Mohamad Fakih, Mlanie Davranche, Aline Dia, Bernd Nowack, Guillaume Morin,Patrice Petitjean, Xavier Chtellier, Grard Gruau, 2008. Environmental impact of As(V)Fe oxyhydroxide reductive dissolution: An experimental insight 24. MAGGY F. LENGKE1, REGINA N. TEMPEL, 2004. Geochemical modeling of arsenic sulfideoxidation kinetics in a mining environment Bethany OShea, Jerzy Jankowski, Jesmond Sammut, 2006. The source of naturallyoccurring arsenic in a coastal sand aquifer of eastern Australia http://en.wikipedia.org/wiki/Arsenic_contamination_of_groundwater http://en.wikipedia.org/wiki/Arsenic http://en.wikipedia.org/wiki/Arsenic_poisoning http://water.epa.gov/lawsregs/rulesregs/sdwa/arsenic/index.cfm