Defining Health Based Soil Cleanup Objectives: How to Select a Cancer Risk Level ? Pascal Empereur-Bissonnet, MD, telephone 33 1 47 64 72 62, fax 33 1 47 64 73 15, e-mail pascal.empereur@edfgdf.fr, William Dab, MD-PhD, Vincent Nedellec, MS, and Jacques Lambrozo, MD, EDF-GDF, Service des Etudes Médicales, 22-30 avenue de Wagram 75008, Paris

The recent development of risk assessment procedures gives decision-makers access to quantified estimates of the health risks to present or future users of sites polluted by toxic substances. This change leads to set cleanup objectives, which are concentrations of pollutants in soil, explicitly based on human health. Basically, the ideal is to protect the population from all hazards. For systemic effects, which occur only above a certain dose, this objective is easily reached by cleaning soil so that human exposure never exceeds the adverse effect threshold. On the other hand, no safety limit of dose is assumed for genotoxic carcinogenic effects; under this hypothesis, zero cancer risk exists only for zero human exposure. In practice, so radical elimination of contact with pollutants is nearly always impossible, for technical and financial reasons. The health based objective must therefore be reviewed: a tolerable level of cancer risk has to be defined and then translated into the concentrations of chemicals that can remain in the soil after remediation. There is not, however, any universal threshold level of risk that is societally acceptable. Defining this limit is essentially a socio-economical and ethical question that deserves a wider discussion, at the highest political level.

While we wait for this to come to pass, three approaches might be proposed:

1. The interpretation of the legal concept of "de minimis" permits the selection of a risk level that is below legislative or regulatory concern;
2. Target values are defined as a function of the local or regional background concentrations of natural and anthropogenic pollutants in soil or other media;
3. Cancer risk level is chosen after a comparison of environmental risks and current risk management practices for general and occupational exposures.

Advantages and drawbacks of each approach will be discussed in the paper. We conclude that the comparative framework seems the most interesting because it gives a global and quantified view of interactions between humans and the environment. Such a comparison provides a rational basis for negotiations between risk managers, public authorities and all concerned citizens and prepares the foundation for the indispensable public debate about the acceptability of health risk.

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