Exposure and Risk Assessment with Respect to Contaminated Soil: Significance of Biomarkers and Bioavailability

The evaluation of health risk from chemical exposure is evolving in concept and practice. The ability to sensitively detect levels of chemicals in the environment has served as the traditional foundation for determining exposure levels and consequent health risks. More recently, however, other parameters have been constructed to probe the pathway between environmental levels of a chemical and the biological effects of subsequent exposure. Among these, two that are discussed in this paper are bioavailability and biomarker determinations. Chemicals in the environment often are associated with a medium such as airborne particulate, water, or soil. The interaction between the chemical and its medium is dependent on the physicochemical properties of the system. In some cases, such as 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) in soil, the chemical becomes partially and irreversibly bound to the medium. Animalingestion studies of TCDD-contaminated soil suggest that some of the TCDD remains bound to the soil and does not cross the gastrointestinal barrier during digestion, and therefore only a fraction of the TCDD enters the blood and becomes bioavailable. The characterization of bioavailability provides for more accurate exposure assessment. Biomarker information potentially can validate exposure assessment information from bioavailability studies, elucidate specific biological effects from chemical exposure, and investigate genetic susceptibility issues that may increase the likelihood that an individual or population will experience increased health risks. Benzene-induced chromosome damage is discussed as an example of a significant biomarker that has demonstrated the potential for providing information useful for accurately prediction health risk.