Comparison of Soil Ingestion Rates Derived from Dose Reconstruction at Contaminated Sites with Estimates Obtained in Tracer Mass Balance Studies. J. Kissel, S. Bartell, and A. Wawrukiewicz, Department of Environmental Health, CRESP*, University of Washington, Box 357234, Seattle, WA 98195-7234
Soil ingestion is commonly assumed to be a dominant route of exposure to contaminants in soils. Risks attributed to the ingestion pathway often drive soil cleanup requirements. Regulatory protocols currently depend heavily on ingestion estimates derived from investigations employing a mass balance on selected elemental tracers found in food, soil and excreta. A review of tracer study results has been conducted. Estimated ingestion rates are inconsistent both within and across studies. Given the significance of these parameters, it is appropriate to examine cases for which both soil contamination levels and some measure of body burden are available. Cases identified to date include arsenic exposure at a former smelter site, PCB exposures in the vicinity of a landfill, pesticide exposures in farm worker families, and declining blood lead levels following remedial measures. Distributions of ingestion rates that can account for observed exposures have been computed. In the case of lead, development of a pharmacokinetic model accounting for bone storage and release was required. Preliminary results suggest that median soil ingestion rates for children are less than the 200 mg/day RAGS default. The relative availability of the biomarkers in soil is a consistently significant source of uncertainty.
*Research supported by the Department of Energy through funds to the Consortium for Risk Evaluation with Stakeholder Participation.