Dermal absorption of benzo[a]pyrene from soil: Assessment of flux and application to risk assessment of contaminated sites

Abstract

Soil cleanup standards and assessment of human health risks at contaminated sites are based in part on predicted human exposure to soil contaminants, including from direct skin contact. Available investigations of dermal absorption from soil are relatively sparse and have been conducted with a variety of different methods, many of which fail to account for important physical and chemical drivers of skin permeation. To improve understanding of the soil-dermal exposure pathway, in vitro assessments of radiolabeled benzo[a]pyrene (BaP) absorption through human epidermis were conducted. Experiments employed four test soils, which were artificially weathered and applied to epidermis at multiple BaP concentrations and exposure durations. Experiments were also conducted with unweathered soils and BaP deposited onto skin from acetone. For weathered soils, absorption was independent of soil type, the mass in the receptor fluid was proportional to exposure duration but independent of concentration, and the mass recovered in the skin after washing was proportional to concentration and independent of exposure time. Results from the weathered and unweathered soils were essentially similar. The findings are consistent with concentrations that exceeded the BaP sorption capacity of all soils tested, and with BaP mass in the wash skin dominated by particles that were not removed by washing. Flux into and through skin from soils were lower by an order of magnitude from acetone-deposited BaP. Potential barriers and opportunities for improving guidance for the assessment of dermal exposure from contaminated soils were also examined, as the current method is relatively simplistic and based on an experimentally-determined parameter that is susceptible to distortion by common methodological pitfalls. A practical recommendation is described that is easily implemented, empirically and theoretically supported, and represents a more health protective approach until further methodological improvements are feasible.