Human health exposure from contaminated land: A DEFRA report
James Lymer (Wardell-Armstrong LLP)
ECG Bulletin July 2014
ECG Bulletin July 2014
A new classification system aids the assessment of risk to human health from exposure to contaminated land in the UK. This article explains the methodology.
In April 2012, DEFRA (Department for the Environment, Food and Rural Affairs) introduced a new, four-category system for classifying land under Part 2A of the Environmental Protection Act for cases of a significant possibility of significant harm to human health. Land is determined as contaminated under Part 2A if it falls within Categories 1 or 2; Category 4 includes land where the level of risk posed is acceptably low. To support the assessment and classification of land within these categories, DEFRA commissioned a research project to develop a methodology for deriving Category 4 screening levels (C4SLs) and recommend values for six substances. The project was awarded to a research team led by CL:AIRE (Contaminated Land: Applications in Real Environments).
Following publication of the CL:AIRE report in December 2013 (1), DEFRA issued a policy companion document in March 2014, outlining a methodology for deriving C4SLs and providing recommended C4SL values for six substances: arsenic, benzene, benzo(a)pyrene, cadmium, chromium(VI), and lead. These values were derived for four generic land uses: residential, commercial, allotments, and public open space.
Category 4 Screening levels describe a level of risk that, although above minimal, is strongly precautionary. Soil guideline values (SGVs) and other generic assessment criteria (GAC) are derived at a risk that is considered to be minimal. Therefore, C4SLs describe a higher level of risk than do SGVs and GAC. C4SLs are intended not only for use in the Part 2A system but also as generic screening criteria for land development planning within a generic quantitative risk assessment (GQRA).
Methodology
The methodology for deriving C4SLs is based on the Environment Agency, Contaminated Land Exposure Assessment (CLEA) model used to derive the SGVs (2, 3).
A more pragmatic approach was adopted in selecting parameters for the CLEA model to derive C4SLs compared to the derivation of SGVs. The approach included modification of the toxicology and/or the exposure parameters used in the model. To address uncertainty in the parameters used, a sensitivity analysis was also undertaken as part of the C4SL derivation. For the SGV derivation process, the toxicology input (health criteria values) is an estimated contaminant concentration that would pose a tolerable or minimal risk to human health. For the C4SL derivation process, the toxicology input (low level of toxicological concern or LLTC values) is the estimated concentration of a contaminant that would pose a low risk to human health.
An example of a C4SL
Inorganic arsenic compounds are considered carcinogenic both via inhalation and ingestion, and it is classed as a non-threshold contaminant. The CLEA model is used to estimate the average daily exposure from arsenic in soil, which is equivalent to its toxicity value. This is reported as a soil concentration that represents a low risk to long term human health, known as a C4SL. Recommended arsenic C4SLs are: residential (with home-grown produce), 37 mg/kg; residential (without home-grown produce), 40 mg/kg; allotments, 49 mg/kg; commercial, 640 mg/kg; public open space 1, 79 mg/kg; public open space 2, 168 mg/kg. Further details on the derivation and application of these values are presented in the main SP1010 report and companion document, and in the CLEA framework reports.
References
1. DEFRA, SP1010 – Development of Category 4 Screening Levels for assessment of land affected by contamination, published on 20 December 2013.
2. Environment Agency, CLEA Reports: see https://www.gov.uk/government/collections/land-contamination-technical-guidance
3. Previous ECG Bulletin articles on contaminated land may be found in the July 2008 issue (pp 18-20) and the January 2010 issue (p 36).
The author is Chair of the ECG.
In April 2012, DEFRA (Department for the Environment, Food and Rural Affairs) introduced a new, four-category system for classifying land under Part 2A of the Environmental Protection Act for cases of a significant possibility of significant harm to human health. Land is determined as contaminated under Part 2A if it falls within Categories 1 or 2; Category 4 includes land where the level of risk posed is acceptably low. To support the assessment and classification of land within these categories, DEFRA commissioned a research project to develop a methodology for deriving Category 4 screening levels (C4SLs) and recommend values for six substances. The project was awarded to a research team led by CL:AIRE (Contaminated Land: Applications in Real Environments).
Following publication of the CL:AIRE report in December 2013 (1), DEFRA issued a policy companion document in March 2014, outlining a methodology for deriving C4SLs and providing recommended C4SL values for six substances: arsenic, benzene, benzo(a)pyrene, cadmium, chromium(VI), and lead. These values were derived for four generic land uses: residential, commercial, allotments, and public open space.
Category 4 Screening levels describe a level of risk that, although above minimal, is strongly precautionary. Soil guideline values (SGVs) and other generic assessment criteria (GAC) are derived at a risk that is considered to be minimal. Therefore, C4SLs describe a higher level of risk than do SGVs and GAC. C4SLs are intended not only for use in the Part 2A system but also as generic screening criteria for land development planning within a generic quantitative risk assessment (GQRA).
Methodology
The methodology for deriving C4SLs is based on the Environment Agency, Contaminated Land Exposure Assessment (CLEA) model used to derive the SGVs (2, 3).
A more pragmatic approach was adopted in selecting parameters for the CLEA model to derive C4SLs compared to the derivation of SGVs. The approach included modification of the toxicology and/or the exposure parameters used in the model. To address uncertainty in the parameters used, a sensitivity analysis was also undertaken as part of the C4SL derivation. For the SGV derivation process, the toxicology input (health criteria values) is an estimated contaminant concentration that would pose a tolerable or minimal risk to human health. For the C4SL derivation process, the toxicology input (low level of toxicological concern or LLTC values) is the estimated concentration of a contaminant that would pose a low risk to human health.
An example of a C4SL
Inorganic arsenic compounds are considered carcinogenic both via inhalation and ingestion, and it is classed as a non-threshold contaminant. The CLEA model is used to estimate the average daily exposure from arsenic in soil, which is equivalent to its toxicity value. This is reported as a soil concentration that represents a low risk to long term human health, known as a C4SL. Recommended arsenic C4SLs are: residential (with home-grown produce), 37 mg/kg; residential (without home-grown produce), 40 mg/kg; allotments, 49 mg/kg; commercial, 640 mg/kg; public open space 1, 79 mg/kg; public open space 2, 168 mg/kg. Further details on the derivation and application of these values are presented in the main SP1010 report and companion document, and in the CLEA framework reports.
References
1. DEFRA, SP1010 – Development of Category 4 Screening Levels for assessment of land affected by contamination, published on 20 December 2013.
2. Environment Agency, CLEA Reports: see https://www.gov.uk/government/collections/land-contamination-technical-guidance
3. Previous ECG Bulletin articles on contaminated land may be found in the July 2008 issue (pp 18-20) and the January 2010 issue (p 36).
The author is Chair of the ECG.
