Arsenic contamination in soils

7/21/2019 Arsenic contamination in soils

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© Environment Agency 2002 March 2002

ISBN 1 857 05755 X

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without the prior permission of the Environment Agency.

The views expressed in this document are not necessarily those of the Environment Agency or DEFRA.

Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the

interpretation or use of the information, or reliance upon views contained herein.

Dissemination Status

Internal: Released to Regions

External: Released to Public Domain

Statement of Use

This publication sets out the derivation of the Soil Guideline Values for arsenic contamination. The report

has been written for technical professionals who are familiar with the assessment and management of the

risks posed by land contamination to human health. It is expected to be of use to all parties involved with

or interested in contamination, but in particular to those concerned with the assessment of land

contamination.

Keywords

Soil Guideline Values, arsenic, land contamination, priority contaminants, risk assessment.

Environment Agency Contact

Ian Martin, Exposure Assessment Manager, Olton Court, 10 Warwick Road, Olton, Solihull, B92 7HX




Acknowledgement

The CLEA model was developed between 1992 and 1997 by the late Professor Colin Ferguson at the

Centre for Research into the Built Environment, the Nottingham Trent University. The Environment

Agency’s National Groundwater and Contaminated Land Centre, National Centre for Risk Analysis and

Options Appraisal and Land Quality Management Ltd have prepared this report.




Contents

1 INTRODUCTION....................................................................................................................1

2 DEVELOPING SOIL GUIDELINE VALUES FOR ARSENIC .........................................3

Occurrence in soil.......................................................................................................................3

Behaviour in the soil environment..............................................................................................3

Potential for harm to human health and relevant health criteria values for soil..........................4

3 SOIL GUIDELINE VALUES FOR ARSENIC.....................................................................6

Purpose.......................................................................................................................................6

Soil Guideline Values according to land-use..............................................................................7

Further information for assessors applying these Soil Guideline Values....................................8

Comparison with other approaches ..........................................................................................10

REFERENCES....................................................................................................................................13

LIST OF TABLES

Table 1.1 Assessment of risk to human health from land contamination. Key reports from

DEFRA and the Environment Agency. .................................................................................2

Table 2.1 Index Doses derived from oral and inhalation studies............................ .............................. .5

Table 3.1 A brief description of the standard land-uses for Soil Guideline Values...............................7

Table 3.2 Soil Guideline Values for arsenic as a function of land-use ..................................................8

Table 3.3 Contribution to total exposure from soil for the relevant pathways expressed as a

percentage of the mean exposure calculated by the CLEA model.........................................9




1.1 This report is one of a series of documents issued by the Department for Environment, Food and

Rural Affairs (DEFRA), its predecessor departments, and more recently the Environment Agency.

The main purpose of the CLR series is to provide regulators, developers, landowners and other

interested parties with relevant, appropriate, authoritative and scientifically based information and

advice on the assessment of risks arising from the presence of soil contamination.

1.2 This report describes Soil Guideline Values, generic assessment criteria for assessing the risks to

human health from chronic exposure to soil contaminated with arsenic. It is essential that the

information presented here be used in conjunction with an understanding of the main reports in this

series (see Table 1.1) and in the wider context of assessing environmental risk (DETR, Environment

Agency and IEH, 2000).

1.3 This technical material can be used in support of the application of the statutory regimes addressing

land contamination, especially Part IIA of the Environmental Protection Act 1990 (the contaminated

land regime) and development control under the Town and Country Planning Acts. In particular,

they are intended to be regarded as “relevant information”, and to assist in the assessment of

“relevant and available evidence”, for the purposes of paragraphs A.31, B.39 and B.44–B.49 of the

Part IIA statutory guidance contained in DETR Circular 02/2000 (DETR, 2000).




Table 1.1 Assessment of risk to human health from land contamination. Key reports from DEFRA

and the Environment Agency.

CLR7 Assessment of Risks to Human Health from Land Contamination: An Overview of the Development of

Soil Guideline Values and Related Research (DEFRA and Environment Agency, 2002a). CLR7 serves as an

introduction to the other reports in this series. It sets out the legal framework, in particular the statutory

definition of contaminated land under Part IIA of the Environmental Protection Act (EPA) 1990; the

development and use of Soil Guideline Values; and references to related research.

CLR8 Priority Contaminants for the Assessment of Land (DEFRA and Environment Agency, 2002b). This

identifies priority contaminants (or families of contaminants), selected on the basis that they are likely to be

present on many current or former sites affected by industrial or waste management activity in the United

Kingdom in sufficient concentrations to cause harm; and that they pose a risk, to either human health,

buildings, water resources or ecosystems. It also indicates which contaminants are likely to be associated

with particular industries.

CLR9 Contaminants in Soil: Collation of Toxicological Data and Intake Values for Humans (DEFRA and

Environment Agency, 2002c). This report sets out the approach to the selection of tolerable daily intakes and

Index Doses for contaminants to support the derivation of Soil Guideline Values.

CLR10 The Contaminated Land Exposure Assessment Model (CLEA): Technical Basis and Algorithms

(DEFRA and Environment Agency, 2002d). This report describes the conceptual exposure models for each

standard land-use that are used to derive the Soil Guideline Values. It sets out the technical basis for

modelling exposure and provides a comprehensive reference to all default parameters and algorithms used.

TOX 1 (DEFRA and Environment Agency, 2002e). This report details the derivation of the oral and

inhalation Index Doses for arsenic.

This document:

SGV 1 Soil Guideline Values for Arsenic Contamination. This report presents the Soil Guideline Values for

arsenic and sets out their derivation.




Occurrence in soil

2.1 Arsenic occurs naturally in many soils as the weathered product of mineralisation (Mitchell and

Barr, 1995). More than 200 arsenic-containing minerals have been identified, the most common of

which is arsenopyrite, a mineral often associated with sulphide mineralisation (O’Neill, 1995). A

mean arsenic concentration of 10 mg kg-1

for 2691 uncontaminated soils has been reported (Berrow

and Reaves, 1984). In the south-west of England, Culbard and Johnson (1984) have reported mean

soil concentrations of 424 mg kg–1

in mineralised areas and between 29 and 51 mg kg–1

in the top

0.05 m of reportedly non-mineralised areas. A survey of stream sediments in England and Wales

showed elevated concentrations of arsenic (between 15 and 433 mg kg–1

) over much of Cornwall

and west Devon, the Northampton ironstones and the Lake District (Environment Agency, in

preparation).

1

2.2 One of the principal sources of arsenic pollution has been the mining and processing of mineral ore

and gangue, predominantly as a by-product of the extraction of copper, lead, tin and silver (Mitchell

and Barr, 1995; Kavanagh et al., 1997). Atmospheric deposition from copper smelting and the

burning of fossil fuels is also an important input to the soil. Arsenical compounds have also been

used in the glass and ceramics, electronics, textile and tanning industries. In addition, contamination

has arisen from the widespread use of agrochemicals such as pesticides and wood preservatives in

agriculture (Sanock et al., 1995; O’Neill, 1995). Urban surveys of soils in Wolverhampton and

Stoke reported arsenic concentrations in the range 2–167 mg kg–1

(Environment Agency, in

preparation).

Behaviour in the soil environment

2.3 Arsenic is found in Group VA of the Periodic Table along with nitrogen and phosphorus. Arsenic

is often described as a metalloid element, but for the purposes of describing its chemical behaviour

in soil it can be thought of as a non-metal, forming covalent compounds or being found in complex

anionic species (O’Neill, 1995).

2.4 Natural sources of arsenic in soil are mainly oxysalts and sulphur-containing minerals (O’Neill,

1995). Under “normal” oxidising conditions, the most common dissolved arsenic species is the

arsenate oxyanion, in which arsenic exists in the +5 oxidation state, As(V). Under more reducing

conditions, such as that found under conditions of waterlogging, the more stable arsenical species

is the arsenite oxyanion, in which arsenic exists in the +3 oxidation state, As(III). Haswell et al.

(1985), in a study in the south-west of England, observed that over 90% of dissolved arsenic in

aerobic soils occurred as arsenate, but that this level dropped to between 15 and 40% under

waterlogged conditions (where arsenite became the predominant dissolved species).

1 Although direct correlation between the concentration of contaminants in soils and stream sediments has not

been undertaken, the National Contamination Review of Great Britain (Appleton, 1995) concluded that elevated

stream concentrations were likely to reflect higher regional soil concentrations of contaminants.




2.5 Whether As(V) or As(III) predominates in soil is a function not only of soil redox potential but also

of pH and microbial activity (Moore et al., 1988). A further complicating factor is the presence of

clay minerals, iron and aluminium oxides, and organic matter, which influence the solubility of

arsenic, inhibiting its leaching and slowing its rate of oxidation and reduction (O’Neill, 1995).

2.6 The quantity of soluble or potentially soluble arsenic in a soil varies widely with pH, redox potential

and the presence of other components such as iron and manganese oxides, clay minerals and organic

matter content. Both arsenate and arsenite are strongly adsorbed onto iron and aluminium oxides,

clay mineral surfaces and soil organic matter. Under acidic conditions, the dissolution of iron oxides

has been observed to increase the concentration of arsenic in solution (Masscheleyn et al., 1991).

2.7 The level of arsenic in edible plants is generally reported to be low. It has been proposed by Bril and

Postma (1992) that the plant uptake of arsenic from soil can be modelled against pH, but this has

been discounted by other researchers (Merry et al., 1986; Livesey and Huang, 1981). There is a

paucity of available data on the uptake of arsenic by garden vegetables under typical soil conditions,

and therefore soil-to-plant concentration factors (CF) are based on simple interpretations of available

data. In the derivation of this set of Soil Guideline Values, a CF of 0.009 µg g–1

DW plant over µg

g–1

DW soil for arsenic has been assumed for both root and leafy vegetables (RIVM, 2001).

2.8 It is not clear to what extent organic arsenic compounds, and inorganic volatile compounds such as

arsine, are formed and released from soils. Microbial activity can cause methylation, demethylation

and hydride formation in the presence of sulphur-bearing substrates, if the redox potential is low

enough (Moore et al., 1988). A number of studies have suggested that volatile arsines are produced

from lawns and moist soils, and that arsine and methylarsines are produced from soils treated with

arsenate, arsenite, monomethylarsonate or dimethylarsinate (O’Neill, 1995). However, in most

circumstances, the rates of formation and the likely concentrations of volatile compounds present

are likely to be too small for concern. Volatile arsenic compounds are therefore not considered in

the derivation of the Soil Guideline Values.

Potential for harm to human health and relevant health criteria values for soil

2.9 The principles behind the selection of health criteria values and the definition of concepts and terms

used are outlined in CLR9 (DEFRA and Environment Agency, 2002c). Information on the toxicity

of arsenic and reasons behind the selection of the most appropriate health criteria values for the

derivation of this set of Soil Guideline Values are described in Contaminants in Soil: Collation of

Toxicological Data and Intake Values for Humans. Arsenic (DEFRA and Environment Agency,

2002e). Reference to these documents is necessary to understand the information presented below.

2.10 Skin lesions are the most sensitive indicator of systemic toxicity resulting from chronic oral exposure

to arsenic, whilst lung cancer has been associated with inhaled arsenic. Index Doses have been

derived for both the oral and inhalation routes (see Table 2.1) because inorganic arsenic compounds

are carcinogenic by both routes in humans, and are genotoxic. It is prudent to assume that there is

no threshold for these effects.

2.11 The oral Index Dose is derived from the WHO recommended provisional drinking-water guideline

value of 10 µg L–1

, which is based on drinking-water studies in which the incidence of skin effects




was observed to be related to arsenic intake. By assuming that 2 L day–1

of water is consumed by

a 70 kg adult, this would correspond to approximately 0.3 µg kg–1

bw day–1

. This value is in general

agreement with those derived by other organisations, even though the logic behind the derivation

differs.

2.12 The basis for the inhalation Index Dose is WHO’s estimate that an arsenic concentration of 6.6 ng

m–3

is associated with a lifetime additional lung cancer risk of 10-5

. Assuming that a 70 kg adult

inhales 20 m3 per day, this atmospheric concentration translates to an inhalation Index Dose of 1.9

ng kg–1

bw day–1

, rounded up to 2 ng kg–1

bw day–1

. The WHO risk estimate was based on a number

of studies that examined elevated occurrences of lung cancer in smelter workers exposed to arsenic

emissions.

2.13 The Index Dose represents an intake that poses a minimal risk level from possible exposure to a

particular substance from a source, with the additional requirement that exposure needs to be

reduced to as low a level as reasonably practicable (DEFRA and Environment Agency, 2002c).

Therefore, background exposure to inorganic arsenic is not considered and the Index Dose itself is

the health criteria value used to derive Soil Guideline Values.

2.14 There is some consensus that organic arsenicals are much less toxic and carcinogenic than inorganic

arsenic, but there are not sufficient data from which to derive guidelines for oral or inhalation

exposure. The health criteria values derived here are applicable only to inorganic forms of arsenic.

Table 2.1 Index Doses derived from oral and inhalation studies

Oral Index Dose

( µg kg–1 bw day–1)

Inhalation Index Dose

( µg kg–1 bw day–1)

0.3 0.002




Purpose

3.1 Soil Guideline Values are a screening tool for use in the assessment of land affected by

contamination. They can be used to assess the risks posed to human health from exposure to soil

contamination in relation to land-use. They represent “intervention values”: indicators to an assessor

that soil concentrations above this level might present an unacceptable risk to the health of site-users

and that further investigation and/or remediation is required. Further information on applying Soil

Guideline Values in the regulatory context, including Part IIA of EPA 1990, can be found in CLR7

Assessment of Risks to Human Health from Land Contamination: An Overview of the Development

of Soil Guideline Values and Related Research (DEFRA and Environment Agency, 2002a).

3.2 Soil Guideline Values have been developed on the basis of many critical assumptions about possible

exposure to soil contamination and the development of conceptual exposure models to describe

different land-uses. The standard land-uses considered are described briefly in Table 3.1. It is

important that an assessor understands these conceptual models and is aware of their assumptions

and limitations before applying Soil Guideline Values to an area of land. See CLR10 The

Contaminated Land Exposure Assessment (CLEA) Model: Technical Basis and Algorithms for a

detailed description of the CLEA model on which these Soil Guideline Values are based (DEFRA

and Environment Agency, 2002d).

3.3 If used correctly, an exceedance of a Soil Guideline Value can indicate a potentially significant risk

to human health. However, this does not necessarily imply that there is an actual risk to health, andthe assessor should take into account site-specific circumstances. Furthermore, if incorrectly applied

to a site where the critical pathway or chemical form of the contaminant is not one that has currently

been evaluated, a potentially significant risk might be present even though a Soil Guideline Value

is not exceeded. So it is important that a risk assessor uses Soil Guideline Values as a component

of an overall risk assessment and management strategy for a site in accordance with good practice

(DEFRA and Environment Agency, in preparation; DETR, Environment Agency and IEH, 2000)

and, in particular, an appropriate sampling and testing strategy (DEFRA and Environment Agency,

2002a).




Table 3.1 A brief description of the standard land-uses for Soil Guideline Values

Further information on the underlying conceptual exposure models for each land-use can be found in

DEFRA and Environment Agency (2002d).

Residential

People live in a wide variety of dwellings including, for example, detached, semi-detached and terraced

property up to two storeys high. This land-use takes into account several different house designs, including

buildings based on suspended floors and ground-bearing slabs. It assumes that residents have private gardens

and/or access to community open space close to the home. Exposure has been estimated with and without a

contribution from eating homegrown vegetables, which represents the key difference in potential exposure to

contamination between those living in a house with a garden and those living in a house where no private

garden area is available.

Allotments

Provision of open space, commonly made by the local authority, for local people to grow fruit and vegetables

for their own consumption. Typically, each plot is about a one-fortieth of a hectare, with several plots to a

site. Although some allotment holders may choose to keep animals, including rabbits, hens and ducks,

potential exposure to contaminated meat and eggs has not been considered.

Commercial/industrial

There are many different kinds of workplace and work-related activities. This land-use assumes that work

takes place in a permanent single-storey building, factory, or warehouse where employees spend most time

indoors involved in office-based or relatively light physical work. This land-use is not designed to consider

those sites involving 100% hard cover (such as car parks) where the risks to the site-user are from ingestion or

skin contact because of the implausibility of such exposures arising while the constructed surface remains

intact. Further guidance on the limitations in applying this land-use to different industries can be found in

DEFRA and Environment Agency (2002d).

Soil Guideline Values according to land-use

3.4 The Soil Guideline Values for arsenic contamination are summarised in Table 3.2. For residential

and allotment land-uses the Soil Guideline Values are set to be protective of young children because

in general they are more likely to have higher exposures to soil contaminants. For the

commercial/industrial land-use, an adult is assumed to be the critical receptor, with exposure

considered over the working lifetime.

3.5 The Soil Guideline Values have been estimated using the CLEA model where certain parameters,

such as body weight, are treated probabilistically by Monte Carlo sampling. The Soil Guideline

Value is the concentration at which predicted exposure equals the relevant health criteria value for

each standard land-use. Because the final exposure is itself a distribution of values, a point in this

distribution is chosen for comparison with the relevant health criteria value. In deriving the Soil

Guideline Values in this report, the Monte Carlo components in CLEA are sampled 5000 times and

the 95th percentile of the predicted exposure compared with the health criteria value. See CLR10

for a detailed discussion (DEFRA and Environment Agency, 2002d). The final Soil Guideline

Values reported in Table 3.2 have been rounded to the nearest one or two significant figures.

3.6 The Soil Guideline Values for arsenic are based on inorganic forms only for two reasons:




• The Index Doses for arsenic are based only on consideration of inorganic compounds (DEFRA

and Environment Agency, 2002e).

• There are differences in the fate and transport of organic and inorganic compounds of arsenic,

which means that human exposure should be considered separately.

Table 3.2 Soil Guideline Values for arsenic as a function of land-use

Standard land-use

Soil Guideline Value

(mg kg–1

dry weight soil)

Residential with plant uptake 20

Residential without plant uptake 20

Allotments 20

Commercial/industrial 500

Notes

1. Based on total inorganic arsenic concentration in the soil.

2. Not applicable to arsenic present primarily in an organic form or where there is a

likelihood of arsine gas being generated.

3. Based on intake of arsenic only and compared with oral Index Dose value.

4. Based on sandy soil as defined in CLR10 (DEFRA and Environment Agency,

2002d).

3.7 The Soil Guideline Values for arsenic are based on considering oral exposure and compared with

the oral Index Dose described in paragraph 2.11. Dermal and inhalation routes have been excluded

from this comparison because for many types of arsenic contamination and in the context of the

standard land-uses the contribution of these pathways to overall exposure will be much less than

1%. To check that this assumption was valid, inhalation exposures at the Soil Guideline Value level

for each land-use were evaluated to ensure that these were always less than the inhalation Index

Dose (see paragraph 2.12).

3.8 The Soil Guideline Values are based on the sandy soil described in CLR10 and may vary according

to the other soil types outlined in that report. The availability of arsenic to plants depends on a

number of factors (see paragraphs 2.6 and 2.7) although there is insufficient information to provide

a robust correlation with specific soil parameters (such as pH, redox potential, iron and manganese

oxide content) that are broadly applicable to generating Soil Guideline Values. Therefore the Soil

Guideline Values reported here do not vary according to pH.

Further information for assessors applying these Soil Guideline Values

3.9 In applying the Soil Guideline Values in this report to a contaminated site, assessors will find the

advice presented in the following paragraphs useful. It is good practice for risk assessors to

accompany their risk assessment with an appropriate risk evaluation, including a clear statement of

whether or not representative soil concentrations from the site exceed any generic or site-specific

assessment criteria (DEFRA and Environment Agency, in preparation; DETR, Environment Agency




and IEH, 2000). In using Soil Guideline Values it is essential that the assessor reviews the wider

context as discussed in CLR7 (DEFRA and Environment Agency, 2002a).

3.10 The assessor is referred to TOX 1 (DEFRA and Environment Agency, 2002e) for a detailed

explanation of the derivation of the health criteria values used in this report, and the attendant

uncertainties. This is important, especially when considering the significance of any exceedance of

a Soil Guideline Value.

Table 3.3 Contribution to total exposure from soil for the relevant pathways expressed as a

percentage of the mean exposure calculated by the CLEA model

Contribution to exposure from soil according to land-use (%)Exposure pathway Residential with plant

uptake and allotments

Residential without

plant uptake

Commercial

/industrial

Ingestion of soil and indoor dust 71 100 100

Consumption of homegrownvegetables

22 – –

Ingestion of soil attached to

vegetables7 – –

Notes

1. Soil Guideline Values derived by comparing only oral exposure routes with oral Index Dose.

2. “–“ indicates that this pathway is not included in the conceptual model for the standard land-use.

3.11 As noted in paragraph 3.7 the Soil Guideline Values presented here are based only on oral exposure.The proportion of exposure attributable to each individual pathway for each standard land-use is

summarised in Table 3.3.

3.12 The dominant exposure pathway driving the risk in this set of Soil Guideline Values is the direct

ingestion of soil and soil-derived indoor dust (see Table 3.3). The uncertainties in modelling

exposure via this pathway are discussed in CLR10 (DEFRA and Environment Agency, 2002d). The

consumption of homegrown vegetables contributes up to 30% of total oral exposure in the standard

residential and allotment land-uses. In applying the Soil Guideline Values that include plant uptake,

the assessor should consider the impact of soil pH on the likelihood of exposure via this pathway.

Outside of the typical pH range of 6–8, the bioavailability of arsenic to plants should be determined

on a site-specific basis and, where appropriate, further investigation (including the sampling of fruits

and vegetables) is recommended.

3.13 Inhalation of soil-derived dusts contributes less than 1% of total exposure for each of the standard

land uses described in Table 3.1. However, in undertaking a site assessment, the assessor should

always consider the possibility that inhalation of dust may be a more important exposure pathway;

for example, where:

• the majority of the site is bare for long periods and dry/windy conditions prevail,

• activities such as vehicle movements increase dust generation,

• the contamination itself is present in a dry and/or dusty form.




In such cases, the assessor should estimate the risk posed by dust inhalation by carrying out a more

detailed site-specific assessment.

3.14 The Soil Guideline Values for arsenic for both the standard residential and allotment land-uses lie

within the range of naturally occurring soil contamination in parts of the UK (see paragraph 2.1).

A key assumption that assessors should take into account in evaluating risk is that the Soil Guideline

Values are based on intakes and it is assumed that 100% of the arsenic in soil is taken up by the

systemic circulation. Where arsenic is either strongly bound to the surface of soil particles or present

in an insoluble form, then its bioavailability to the human body may be less than 100%.2 This effect

is likely to be difficult to quantify in practice and should be considered only as part of a more

detailed site investigation and risk assessment. It is not justifiable to assume that the bioavailability

of a contaminant at concentrations within the range found in natural soils for a particular region of

the UK is likely to be less than 100% without further investigation.

3.15 Guidance on using Soil Guideline Values in the presence of one or more other contaminants is given

in CLR9 (DEFRA and Environment Agency, 2002c). In general, for non-threshold substances,

chemical mixtures are only considered where effects are mediated through the same receptor or

where substances act on the same target organ or biological system. In the case of arsenic, it is worth

noting that the critical threshold and non-threshold effects are dermatological.

3.16 The Soil Guideline Values presented here apply only to the protection of health from long-term chronic

exposure to arsenic contamination. However, as noted in DEFRA and Environment Agency (2002e),

arsenic poisoning can occur as a result of very high single exposures in the range 70–300 mg (the

calculated range for the acute lethal dose). Significant acute effects can also occur below the lethal

dose, including severe gastrointestinal damage and haemorrhaging with resultant vomiting and

diarrhoea. Although such levels of exposure are likely to occur rarely and only at arsenic soil

concentrations substantially above the Soil Guideline Value, an assessor dealing with small hotspots

of highly elevated concentrations of arsenic should always consider the potential for acute toxicity.

Comparison with other approaches

3.17 It is essential that any comparison between the Soil Guideline Values presented in this report and

other approaches, including quantitative criteria, should be informed by reference to the conceptual

models behind each set of guidelines and taking into account the context in which they are intended

to apply. There are a number of reasons why the generic assessment criteria developed in one

country may differ from those found in another.

3.18 It is not easy to transpose guidance from one jurisdiction to another and to make comparisons

between the various quantitative levels set. Such guideline values may have been developed in a

different management context, depending on legislation and policy, with different overall

objectives.3 There may be subtle but significant differences between the conceptual exposure

models that take into account the different ways that people behave between countries and

2 It is important to note that a reduction in apparent solubility of arsenic within a particular aqueous solution isnot necessarily reliable evidence of a reduction in its bioavailability to the human body.3 Such objectives might include as intervention values or as remediation standards to be applied to different

current and future uses.




differences in site conditions such as soil pH, soil type and depth to water table. The characterisation

of the critical human receptor may also be quite different, and this can have a major impact on the

guidelines derived.

3.19 The Interdepartmental Committee for the Redevelopment of Contaminated Land (ICRCL) published

trigger concentrations for arsenic (ICRCL, 1987). The threshold concentration for arsenic for

domestic gardens and allotments is 10 mg kg–1

and that for “parks, playing fields and open space”

is 40 mg kg–1

. No action values were published. There is little information available about the

conceptual model implicit in these values and therefore further direct comparison with the new Soil

Guideline Values is difficult.

3.20 A comparison of the Soil Guideline Values with generic assessment criteria in other countries shows

that there is a considerable range of values. A large component of this variation appears to come

from uncertainty surrounding the toxicological database and differences in policy on exposure and

averaging periods.

3.21 The current Dutch integrated Intervention Value (IV) for arsenic and all land-uses is 55 mg kg–1

(RIVM, 1994). This is based on the ecotoxicity IV since the human IV is 678 mg kg–1

. Pathways

included in the human IV include direct ingestion of soil, consumption of crops and inhalation of

soil-derived dust. Arsenic is considered to be a threshold contaminant and exposure is averaged over

a lifetime. Adjusting for the default soil type used in CLEA (15% clay and 2% soil organic matter)

the human health IV would reduce to approximately 350 mg kg-1

, still significantly higher than the

Soil Guideline Values in this report. The Dutch health criterion value4 and their application of

lifetime averaging and exposure periods are the most significant factors in explaining the difference.

3.22 While the UK aims to be protective of sensitive groups within the UK population, the current IV

are based on the average Dutch person. If the Soil Guideline Value for the residential setting,

including plant uptake, were derived using the Dutch health criterion value, lifetime exposure and

averaging, and with the inclusion of background exposure, it would be approximately 430 mg kg-1

.

3.23 It is likely that the Dutch IV will soon be changing (RIVM, 2001). The new guidelines are termed

“serious risk concentration” (SRC) and the proposed integrated SRC for arsenic is 85 mg kg–1

.

Again, this is based on considerations of ecotoxicity since the proposed human health SRC is 576

mg kg–1

, still significantly higher than the Soil Guideline Values in this report. However, the Dutch

still use a higher health criterion value5 and apply lifetime exposure, which are significant factors

in demonstrating this difference. Taking into account the proposed Dutch TDI and lifetime

averaging, the SGV produced by the CLEA model would rise to 200 mg kg–1

.

3.24 The USEPA has two Soil Screening Levels (SSL) for arsenic, one for ingestion and one for

inhalation. The ingestion SSL is 0.4 mg kg–1

(USEPA, 1996). The only pathway assumed is direct

soil ingestion. The SSLs were developed to “help standardise and accelerate the evaluation and

cleanup of contaminated soils at sites on the National Priorities List (NPL) with anticipated future

residential land use scenarios”. The US EPA assumes that arsenic is a carcinogen, that exposure is

4 The Dutch apply a TDI of 2.1 µg kg–1 bw day–1 for the derivation of the human health IV for arsenic.5 The Dutch propose to apply a TDI value of 1 µg kg–1 bw day–1 for the derivation of the human health SRC for

arsenic.




for 30 years over an averaging period of 70 years, and that the acceptable risk of contracting cancer

is one in a million.




Appleton JD (1995) Review of ‘Natural’ Contamination in Great Britain. Report no. PECD 7/1/734,

Department of the Environment.

Berrow ML and Reaves GA (1984) Background levels of trace elements in soils. In Proc. Int. Symp.

Environmental Contamination, London 333–340.

Bril J and Postma L (1992) A management model to assess the extent of movement of chemicals through

soils. In Proc. Eur. Conf. Chemical Time Bombs: Delayed Effects of Chemicals in Soils and Sediments,

eds ter Meulen GRB et al., Hoofddorp, The Netherlands. ISBN 9071111628.

Culbard EB and Johnson LR (1984) An assessment of arsenic in house dust and garden soils from SW

England and their implications for human health. In Proc. Int. Symp. Environmental Contamination,

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Arsenic contamination in soils

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