Exposure assessment using the CLEA modelIan 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

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

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

“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

… 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

Preliminary risk assessment

Generic QRA

Detailed QRA

Tiered risk assessment from Model Procedures, CLR11 (2004)

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

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

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 programmeContaminated Land Exposure Assessment model and associated technical guidanceFramework for deriving Soil Guideline ValuesStarted in the early 1990s at Nottingham Trent University (sponsored by Department of the Environment)Continued in-house by the Environment Agency from around 2000Aims 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

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 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

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?Produce group Included crops

Green vegetables

Beans (broad, French, green and runner beans), Brussels sprouts, cabbage (red, white, greens and kale), cauliflower, lettuce, spinach, peas (garden and mange tout), stem vegetables (broccoli, celery, asparagus), okra, globe artichokes, Chinese leaves, endives, chicory, chard, dandelion, watercress and fresh herbs (basil, coriander, tarragon, sage, parsley and mint).

Root vegetables

Beetroot, carrot, cassava, garlic, ginger, Jerusalem artichoke, leeks, onions, parsnips, radish, rhubarb, salsify, swede, sweet potato, turnips and yam.

Tuber vegetables

Potatoes

Herbaceous fruit

Aubergine, courgettes, cucumber, marrow, pumpkin, strawberries, tomatoes

Shrub fruit Bilberries, blackberries, cranberries, gooseberries, loganberries, mulberries, physalis, raspberries, blackcurrants, redcurrants, and white currants

Tree fruit Apples, apricots, cherries, peaches, pears and plums

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

Age GroupConsumption rate (g fw kg-1 bw day-1)

Green Root Tuber Herb. Shrub Tree Total

Infant 7.12 10.69 16.03 1.83 2.23 3.82 41.72

Toddler 6.85 3.3 5.46 3.96 0.54 11.96 32.07

Young person 3.74 1.77 3.38 1.85 0.16 4.26 15.16

Adult 2.94 1.4 1.79 1.61 0.22 2.97 10.93

How much produce do we eat?

Green Root Tuber Herb. Shrub Tree

InfantToddler

Young personAdult

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

Percentage Total

Produce categories

Infant

Toddler

Young person

Adult

Proportion of homegrown produce Limited data in NDNS Expenditure and Food Survey collects data on

purchased, takeaway, and free

Produce categoryAmount bought into the household (g person-1 week-1)

Non-purchased fraction

Purchased Free Total

Green 223.4 12.6 235.9 0.05

Root 271.4 16.6 288.0 0.06

Tuber 557.9 11.7 569.5 0.02

Herb. 211.8 14.5 226.3 0.06

Shrub 31.3 3.2 34.5 0.09

Tree 277.1 10.8 288.0 0.04

Proportion of homegrown produce

Produce category

Homegrown fraction 

(average) (high end)

Green 0.05 0.33

Root 0.06 0.40

Tuber 0.02 0.13

Herbaceous 0.06 0.40

Shrub 0.09 0.60

Tree 0.04 0.27

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

Residential Young child (aged zero to six years) Growing produce an unusual activity Area required about 20 m2

Produce categoryAnnual household consumption Typical yields Area required

kg fw kg fw m-2 m2

Green 16.8 2.8 7.7

Root 5.7 4.7 1.7

Tuber 3.0 4.4 0.7

Herb. 8.2 5.1 4.0

Shrub 1.5 0.8 1.9

Tree 7.8 1.8 3.9

       

    Total area 19.9

Allotments Young child (aged zero to six years) Growing produce a usual activity Area required about 130 m2

Produce categoryAnnual household consumption Typical yields Area required

kg fw kg fw m-2 m2

Green 111.8 2.8 51.5

Root 38.3 4.7 11.3

Tuber 20.2 4.4 4.6

Herb. 54.5 5.1 26.9

Shrub 10.3 0.8 12.9

Tree 52.2 1.8 25.7

       

    Total area 132.9

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 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? 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 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?