Exposure assessment using the clea model
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Exposure assessment using the CLEA model. Ian Martin, Principal Scientist. Over the next 30 - 40 minutes …. Origins of CLEA and its role in assessing risk Managing land contamination in England and Wales A tiered risk-based approach History and role of the CLEA model

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Exposure assessment using the CLEA model

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Exposure assessment using the clea model

Exposure assessment using the CLEA model

Ian Martin, Principal Scientist

Over the next 30 40 minutes

Over the next 30 - 40 minutes …

  • Origins of CLEA and its role in assessing risk

    • Managing land contamination in England and Wales

    • A tiered risk-based approach

    • History and role of the CLEA model

  • How does it estimate exposure

    • Predicting plant concentrations (subject of first workshop)

    • Predicting likely exposure (this workshop)

    • Gaps in understanding / future research needs

Managing land contamination

Managing land contamination

“The last hundred years have seen a massive increase in the wealth of this country and the well-being of its people. But focusing solely on economic growth risks ignoring the impact – both good and bad – on people and the environment. Had we taken account of these links in our decision making, we might have reduced or avoided costs such as contaminated land or social exclusion.”

Tony Blair

  • Land contamination may be natural or anthropogenic

  • UK policy:

    • Distinguishes between new contamination and our historical legacy

    • Takes a suitable for use approach

    • Seeks voluntary remediation as preferred method

  • Managing land contamination using the planning regime, Part 2A, and other approaches such as ‘due diligence

Is also an emotive issue

… is also an emotive issue

“…it’s as if we are at school. The person you thought was your friend turns out to be the playground bully, he hits you and then tries to say sorry…and you’re not having it”

Weston resident, Cheshire

Risk based approach

Risk-based approach

Preliminary risk assessment

Generic QRA

Detailed QRA

Tiered risk assessment from Model Procedures, CLR11 (2004)

Pollutant linkage

Contents of leaking drum enters the soil

Chemical seeps through the soil and into adjacent gardens

Family use garden and are exposed to contaminated soil

Pollutant linkage

A conceptual model represents the characteristics of the site in diagrammatic or written form that shows the possible relationships between contaminants, pathways and receptors.

Quantifying the risk

Quantifying the risk

  • Generic and detailed tiers of assessment seek to quantify the risk by judging:

    • At what level of exposure is there a risk to health?

    • At what level are people exposed, and how often, to chemicals from contaminated soils?

Clea work programme

CLEA work programme

  • Contaminated Land Exposure Assessment model and associated technical guidance

  • Framework for deriving Soil Guideline Values

  • Started in the early 1990s at Nottingham Trent University (sponsored by Department of the Environment)

  • Continued in-house by the Environment Agency from around 2000

  • Aims to provide technical guidance to assist in the quantitative assessment of risks to health from land contamination (at both generic and detailed tiers)

Solving the puzzle

Health effects

Chemical behaviour

CLEA model

Risk evaluation

Human behaviour

Solving the puzzle

Changing faces

Changing faces

  • CLEA model commissioned by DoE in 1992

  • Developed by Professor Ferguson at CRBE until 1997

  • CLEA 2002 developed by Defra, Environment Agency, and SEPA with LQM and ERM and others from 1999 - 2002. It was the first software released.

  • CLEA UK developed by Environment Agency from 2004 - 2005, learning lessons from CLEA 2002 including improved functionality and portability

  • Updated software to be published in 2008

Generic land use scenarios

Generic land-use scenarios

  • Appropriate to generic QRA

  • Based on a range of typical activities, taken as a whole, to represent a reasonable worst-case

  • Three scenarios defined in the derivation of SGV:

    • Residential

    • Allotments

    • Commercial

  • Only food chain pathway considered is the consumption of homegrown fruit and vegetables

Exposure pathways modelled

Exposure pathways modelled

Estimating exposure via produce

Estimating exposure via produce

  • Chemical concentrations in plant matter

    • Partitioning in unsaturated zone

    • Degradation and transformation processes

    • Soil-to-plant concentration factors

    • Internal plant processes

  • Exposure to homegrown produce

    • What types of fruit and vegetable do we eat?

    • How much do we eat and what proportion is homegrown?

    • How reasonable are these estimates?

What type of produce do we eat

What type of produce do we eat?

How much produce do we eat

How much produce do we eat?

  • Key information sources

    • Food Standards Agency INTAKE 2 model

    • National Diet and Nutrition Surveys 1992 – 2000

  • General population data

How much produce do we eat1

How much produce do we eat?

Proportion of homegrown produce

Proportion of homegrown produce

  • Limited data in NDNS

  • Expenditure and Food Survey collects data on purchased, takeaway, and free

Proportion of homegrown produce1

Proportion of homegrown produce

Comparison with other countries

Comparison with other countries

  • England and Wales

    • average: about 5% fruit and vegetables, 2% potatoes

    • high end: about 36% fruit and vegetables, 13% potatoes

  • The Netherlands

    • average: about 10% vegetables, 2% potatoes

    • high end: about 55% vegetables, 13% potatoes

  • Australia

    • average: about 10% fruit and vegetables

    • high end: about 35% fruit and vegetables



  • Young child (aged zero to six years)

  • Growing produce an unusual activity

  • Area required about 20 m2



  • Young child (aged zero to six years)

  • Growing produce a usual activity

  • Area required about 130 m2

Attached soil

Attached soil

  • Soil may become entrained in skin of below ground plant parts or trapped between leaves

  • Considerable uncertainty and very little quantitative information (missing link in some uptake models?)

  • FARMLAND foodchain model assumed 0.1 per cent on a dry weight basis for leafy vegetables, adopted and extended by Oatway and Mobbs (2003) to below ground crops and fruit

Food preparation and cooking

Food preparation and cooking

  • Few studies on the effect of cooking on chemical concentrations

    • Cooking changes plant structures

    • Chemicals may volatilise or degrade

    • Boiling may result in leaching

    • Peeling shown to reduce chemical concentrations / attached soil for some types of contaminants (often recommended advice)

    • Washing may also remove attached soil (often recommended advice)

  • Oatway and Mobbs (2003) assume preparation correction factors for attached soil between 0.2 – 1.0

  • Climate change / migrant populations mean that new crops are being grown in the UK and we often know very little about them and how they are prepared for eating

What about dqra

What about DQRA?

  • Site-specific advice available from Food Standards Agency

  • Consumption of homegrown pathway is not always the most important route of exposure

  • Investigations for organic chemicals likely to be challenging and costly to obtain robust data

  • Some very difficult judgements

    • foresight – could they grow fruit and vegetables here?

    • balancing benefits – five-a-day versus chemical health effects

Concluding thoughts

Concluding thoughts

  • Large uncertainties in generic approach so why bother?

    • Improves our understanding of processes and better targeting resources

    • Measurements of exposure highly variable and often challenging and costly to collect

    • Allows us to “predict” the future (you can’t always measure!)

  • Research needs

    • Understanding consumption patterns of self-sufficient gardeners

    • Impact of preparation and cooking on food concentrations

    • Guidance / tools for DQRA and assessing effectiveness of preventative advice

    • Climate change / migrant populations / global food market – impact on UK?

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