1. Exposure assessment using the CLEA model
Ian Martin, Principal Scientist

2. 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
The talk is planned to last 30 – 40 minutes with up to 20 minutes for questions and further discussion.
The talk is split into two parts.
First, the intention is to explain the context with a brief introduction about land contamination in the UK, the origins of the CLEA work programme, and the role that the approach plays in assessing risks from soil contamination.
Second, the intention is to explain how the model estimates exposure from the consumption of produce for two scenarios. Allotments and residential gardens. The emphasis will be on predicting homegrown consumption and other factors since the concentration of chemicals in plant tissues was described at the first workshop in Reading.
Although this presentation will include new explanatory material on how to estimate exposures (as described in technical guidance being prepared by the Environment Agency), it will not cover the wider aspects of work taking place following the release of the Way Forward document.

3. 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 may be contaminated for a number of different reasons from natural contamination, industrial and waste management practices, and diffuse pollution.
We have estimated the number of sites affected to be in the order of to but only a fraction of these will require remediation.
UK policy clearly distinguishes between new contamination and our historical legacy. Through the use of legislation including Pollution Prevention and Control (PPC) and Waste Management Licensing, the Government identifies the prevention of new contamination as being of critical importance. However, we must also deal with the legacy of our rich industrial heritage on a crowded island.
The risks posed by soil contamination will vary greatly according to the use of the land and any assessment and/or remediation should take this into account.
The Government aims to maintain and improve the quality of land progressively through voluntary remediation for example, by redevelopment.
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

4. … 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

5. Risk-based approach
Preliminary risk assessment
Generic QRA
Detailed QRA
Tiered risk assessment from Model Procedures, CLR11 (2004)

6. 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.
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

7. 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?

8. 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)

9. Solving the puzzle Health effects CLEA model Human behaviour
Chemical behaviour
CLEA model
Risk evaluation
Human behaviour

10. 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 It was the first software released.
CLEA UK developed by Environment Agency from , learning lessons from CLEA 2002 including improved functionality and portability
Updated software to be published in 2008

11. 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

12. Exposure pathways modelled

13. 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?

14. 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
The original CLEA model considered only vegetables and divided them into leafy vegetables (Brussels sprouts, cabbage, lettuce) and root vegetables (carrots, onions and shallots, and potatoes). The difference was related to whether or not the edible fraction was above or below ground, and was based on only work such as that by Baes et al. (1984).
Proposed approach is based on the six groups outlined within the Food Standards Agency’s PRISM model.
Broad categories are considered important to highlight the generic nature of the assessment. Previously, the CLEA software had focused on six vegetables only and in some cases these were the only produce looked for in relation to this pathway.

15. 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
Based on population data. We do not really understand how the diets of allotment holders and self-sufficient gardeners might differ from those of the general population. Presumably diet would have an increased fruit and vegetable content, although this would be strongly seasonal, and may be supplemented by shop purchased items in the winter months.
Consumption data is estimated at the 90th percentile, in line with the FSA’s approach to generic risk assessment. The amounts of fruit and vegetables reported in the NDNS surveys also tend to be “as consumed” using standard recipe information to translate meals into original ingredients. As a result, the data is not exactly fresh weight, as it does not account for some water loss during cooking.
Age Group
Consumption 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

16. How much produce do we eat?
Infant data (between six and twelve months old) is not based on the NDNS survey information but on much older survey work (Mills and Tyler 1992).
Infant data quite different from other age categories.
Most important produce categories are green and tuber vegetables, and tree fruit.
Again, this relates to population data and not the sub-group of the population that grows its own produce.

17. Proportion of homegrown produce
Limited data in NDNS
Expenditure and Food Survey collects data on purchased, takeaway, and free
There is limited data for directly estimating the amount of homegrown produce consumed in the UK. It is a question included now in the NDNS survey but there is insufficient evidence to provide a robust estimate for generic exposure assessment.
EFS (new name for National Food Survey) included households in 2004 / 05. Free category includes homegrown plus “buy one get one free” and other sources such as free fruit at school.
Majority of the UK population grows little or no homegrown produce and the mean data from EFS 2004 / 05 reflects this. In the National Food Survey 2000, approximately 85 per cent of the households samples did not record any non-purchased items for a selection of vegetables including cabbages, leafy salads, carrots, onions, leeks, shallots, and potatoes.
NFS 2000 suggests that approximately 15 per cent of the sample accounted for all the selected non-purchased items and that this group is more likely to represent the active gardener or allotment holder. This is consistent with the estimates of garden use by MAFF over the period 1992 – 1996 where between 20 and 25 percent of gardens surveyed were found to be growing fruit and/or vegetables.
Produce category
Amount 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
Shrub
31.3
3.2
34.5
0.09
Tree
277.1
10.8
0.04

18. 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
Shrub
0.09
0.60
Tree
0.04
0.27
High end values estimated from the average homegrown fraction by dividing by 0.15, therefore transforming the data to the 15 per cent of the population that recorded consumption of homegrown produce in the National Food Survey 2000 for the six vegetable types considered in the original CLR10 report.

19. 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
Australia – National Environment Protection Council (1999). A reasonably large proportion of households engage in home food production, with 34.8% of households producing one or more vegetable types, 36.1% producing one or more types of fruit, 6.6% producing eggs, and 1.3% producing poultry meat. For those households producing food, exposure to contaminants via this pathway may be quite significant. For generic risk assessment, the default assumptions might be that 35% of fruit and vegetables, 25% of poultry meat and 200% of egg consumption are derived from home-grown sources. For the standard residential scenarios, the assumption is that less than 10% of fruit and vegetables are homegrown.
The Netherlands – RIVM (2001). RIVM compared data for the whole population with that found in kitchen gardens by those that do grow their own produce. The categories considered are broadly similar to those examined in the revised CLEA report. Taking into account that about 18 per cent of the Dutch population eats around 55 per cent of vegetables and 13 per cent of potatoes from their own gardens, and 88 per cent do not eat from their own gardens, the average is around 10 per cent for vegetables and 2 per cent for potatoes. The Dutch concluded that 10 per cent represented a maximal value for 82 per cent of the population. They noted that 3 per cent of population grew up to 50 per cent of their own produce and a further 15 per cent grew lesser proportions between the two. 10 per cent is the default Dutch figure although allotment gardens were excluded because of the importance of this pathway.

20. Annual household consumption
Residential
Young child (aged zero to six years)
Growing produce an unusual activity
Area required about 20 m2
Most people grow no fruit and vegetables in their gardens. Therefore it is an unusual activity.
Required garden area was much requested by practitioners during review of CLR10. The table assumes that the household consists of two adults and two children and they consume produce at the daily rate (adjusted for the homegrown fraction) for 365 days per year. Estimated yields are based primarily on growing space considerations and typical yields recommended by the Royal Horticultural Society. This assumes a single cropping and that fruit trees are of the dwarf / bush variety.
Typical yields are indicative of each category and that actual area required is based on calculations for specific fruit and vegetables. The lowest yields around 1 kg fw m-2 were reported for soft fruits including strawberries and raspberries. The highest yields were for potatoes, spinach, lettuce, rhubarb, cucumbers, and some root vegetables such as beetroot, radish, and parsnip.
MAFF (1999) in a report on pesticide use estimated that 85 per cent of residential gardens occupied an area greater than 100 m2 and that 34 per cent were greater than 450 m2. The default scenario assumes a garden area of 100 m2 and therefore assumes that 20% is given over to fruit and vegetable production.
Produce category
Annual 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

21. Annual household consumption
Allotments
Young child (aged zero to six years)
Growing produce a usual activity
Area required about 130 m2
Whether or not children use allotments divided the contaminated land community during the debate around the way forward.
An important assumption in this generic land use scenario is the presence of children at the allotment site on a regular but infrequent basis. The risk assessor should consider whether this aspect of the conceptual model is correct for the site being investigated, for example by talking with allotment holders or carrying out a site survey. An alternative option is to consider only the adult gardener; however, care should be taken where exposure is primarily via the consumption of homegrown produce, since the gardener’s family would likely have similar intakes and child exposure may be high even if they rarely visit the site.
For example, consider the case study given by Atkins at CONSOIL The local authority initially concluded that children rarely used the site. Atkins observed that children did visit the site on a regular but infrequent basis with peak frequency in the 7 – 10 year old age range. Other major organisations such as the Greater London Authority and Birmingham City Council have observed an increase in applicants amongst women with young children. In 1998, the House of Commons select committee observed that allotments should be made more child friendly with unused plots converted to play areas.
An important uncertainty in our understanding of allotment holders is whether their diet differs significantly from the general population. Do they consume a higher proportion of fruit and vegetables than everyone else? We don’t know. Because growing produce is a usual activity then we adopt the high end assumptions about the homegrown fraction.
Typical yields are indicative of each category and that actual area required is based on calculations for specific fruit and vegetables.
According to a survey of English allotments in 1997, about half of the individual plots are about 10 rod or about 300 m2 in size. Therefore the assumed area covered by fruit and vegetables is about one-third of the total plot area.
Produce category
Annual 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

22. 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

23. 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

24. 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
Although this talk is primarily about the CLEA model it would be remiss not to say anything about DQRA.

25. 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?
Research needs are for understanding exposure patterns and exclude those that look at plant uptake (which was the subject of Workshop 1)