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Risk Assessment Techniques
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Basic Principles
Environmental Risk
Who wants to be Mayor of London
Sampling problems
Risk Assessment
Mr Micawber
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Basic Principles
The two basic principles in contaminated land are firstly "Caveat Emptor" (buyer beware) and secondly "The Polluter Pays".
It is the first one that causes the major problems in terms of risk assessment techniques. Often perceived risks are greater than
The basic model of environmental risk requires first that there is a hazard (BSE), and then that three key factors all being in place.
- Source (a poor Cow)
- Pathway (a Beefburger)
- Target (You)
This of course is rather simplistic, if you want to be more precise, the model is
- Source (a financially challenged Bovine)
- Pathway (a processed meal consisting of Rusks, Water, Beef)
- Target (a member of Humankind)
The basic theory is that as long as one of these key factors is missing, then there is no risk of contamination. Once the Environment Act 1995 comes into force, this risk-based approach to contaminated land will be implemented.
This will be based on the CLEA (Contaminated Land Exposure Assessment) model, which was due to be published in 1998, but hopefully it will see the light of day in 1999. The trigger concentrations for various contaminants will be derived from the CLEA model.
CLEA values are currently in preparation for Arsenic, Cadmium, Chromium, Cyanide, Inorganic Lead, Inorganic Mercury, Nickel, Phenol, Polycyclic Aromatic Hydrocarbons and Selenium.
In the US the US Environmental Protection Agency, (Region III - Pennsylvania), provides a good risk-based concentration listing at www.epa.gov/reg3hwmd/riskmenu.htm. The
ECOTOXicology (www.epa.gov/ecotox/) database is also a good source for locating single chemical toxicity data for aquatic life, terrestrial plants and wildlife. The database integrates five EPA databases, Office of Research and Development (ORD), National Health and Environmental Effects Research Laboratory (NHEERL), aquatic life (AQUIRE), terrestrial plants (PHYTOTOX), and terrestrial wildlife (TERRETOX)."
The CLEA model is of course of great practical use in other sectors of risk manangement - for example the recent selection of the 'Official' Labour party candidate to be
Mayor of London.
- Source (Ken Livingstone / Frank Dobson)
- Pathway (Trade Union Block Vote)
- Target (The mugs who will pay the bill)
'Red Ken' had no pathway, was newtered, hence posed no health hazard!
Once a potential risk has been identified it is necessary to quantify it, in the light of a site's potential end use.
However care must be taken to sample the site in a manner that will reduce the risk that the samples taken are not themselves representative of the contamination present on the site.
The problem with man-made contamination (as opposed to natural pollution) is that solid contaminants are often distributed in a random manner and are very heterogeneous. The different contaminants on the site may not have all been deposited in a similar manner, hence predicting their distribution and location can be somewhat difficult.
Perception of risk is also somewhat problematic as literally "One man's meat is another's poison" So its OK for Prince Charles to eat 'beef on the bone' but not for those of us who don't have the 'blue blood' that is obviously what is required to kill off those pesky prions!
Risk assessment is both qualitative (Arsenic is dangerous) and quantitative (EEC limits in 2003 will be 10 ppb)
Qualitative risk assessment involves the use of so-called 'target values'. This of course varies between different countries so that in the UK we use ICRCL, whilst in The Netherlands they use the Dutch List.
Quantitative risk assessment however is site-specific, in that a given site (with unique characteristics) is assessed as to the potential for hazards to migrate. A contaminant 'dose' at the receptor is calculated and then compared to toxicological data. If this 'magic-number' is exceeded then there is a risk.
To use the analogy of the Arsenic, if the limit is 10 ppb (parts per billion - to put that in context, a millimetre in a kilometre is 1 part per million), and you eat 8ppm then you are not at risk (assuming you excrete the stuff!). Conversely if you eat 12 ppb, then you may well end up like Napoleon did - dead!
The CLEA model can best be understood in the context of Charles Dickens character 'Mr Micawber' (in the novel 'David Copperfield') who states :-
-
Annual income twenty pounds, annual expenditure nineteen nineteen six, result happiness. Annual income Twenty pounds annual expenditure Twenty Pounds ought and six, result misery.
There are of course other risk assessment techniques currently in use including :-
- The Dutch risk-assessment model
- The US EPA methodology
- RBCA (known as Rebecca) based on the ASTM methodology