Dermal Exposure to Soil: A Comparison of Parameters Used in Superfund Risk Assessments with Available Experimental Measurements. J. E. Johnson and J. C. Kissel, Department of Environmental Health, University of Washington, SC-34, Seattle, WA 98195
Estimates of dermal exposures to contaminated soils are highly uncertain, and site cleanup costs may be very sensitive to cleanup targets derived from those estimates. If remediation goals are driven by dermal pathway risk estimates, the appropriateness of cleanup expenditures are especially subject to question. To determine the extent to which this is a real problem, screening of over 200 Superfund risk assessments from the period 1989-1992 was conducted. About one in six of the risk assessments examined projects lifetime excess cancer risks attributable to dermal contact with soil to be greater than the nominal regulatory threshold of 1 x 10-4. At about half of these sites, the dermal/soil pathway is projected to contribute the largest carcinogenic risk associated with surface soil contamination and may therefore drive cleanup of that medium (although some other pathway, such as groundwater ingestion, presents the greatest projected risk). Ten sites have been identified at which the dermal/soil pathway is projected to present a larger carcinogenic risk than any other pathway. Assumptions leading to these risk projections are of interest. Key parameters defining soil exposure include soil loading, skin area exposed to soil, and frequency and duration of exposure. Distributions of assumed values will be presented for three targets: residential adult, residential child, and occupational adult, and compared with experimental values where available. Analysis will also be presented of the relative contribution of assumed exposure parameters to projected dermal risks.