Contaminated Soils (I): In Vitro Dermal Absorption of Benzo[a]Pyrene in Human Skin

Abstract

Dermal absorption of the lipophile and potential carcinogen benzo[a]pyrene (BaP) in soils from contaminated sites was simulated in vitro using human skin exposed to ¹⁴C-BaP-spiked soil. This study is the first in a series of tests at Health Canada with several soil contaminants spanning a wide range of lipophilicity conducted with viable human skin. Breast skin was obtained fresh from a local hospital and dermatomed to a thickness of 0.4–0.5 mm. Teflon Bronaugh diffusion cells were perfused with HEPES buffered Hanks saline (pH 7.4) with 4% bovine serum albumin (BSA) and fractions were collected at 6-h intervals for up to 24 h exposure either to ¹⁴C-BaP applied in acetone or spiked in a commercial gardening soil. As skin depot ¹⁴C levels were still high at 24 h, the study was repeated for up to 42 h to examine skin depot bioavailability. Skin was washed with soapy water at 24 h in both the 24- and 42-h studies. Exposure to ¹⁴C-BaP both with and without soil was conducted in triplicate with skin specimens from at least 4 patients. In the 24-h exposure tests including the skin depot there was 15 and 56% absorption with and without soil, respectively. The lower total percent absorption from the spiked soil applied to skin resulted from lower depot absorption of 8% with and 45% without soil. Data for 42-h studies were similar and revealed no significant decrease in skin depot levels. Including the 42-h depots there was 16 and 50% absorption with and without soil, respectively, with respective depots of 7 and 39%. As there was no significant difference between the 24- and 42-h depots both with and without soil, the data suggest the depot for BaP was not bioavailable for at least the additional 18-h post soap wash exposure. The bioavailability of BaP is discussed in relation to previous in vitro and in vivo studies in perspective with dermal exposure to contaminated soils.

We thank Dr. Michael Bell and the staff of the Ottawa Hospital for human skin surgical waste tissue. This project was approved by the Ottawa Hospital Research Ethics Board. We are indebted to the Bureau of Risk and Impact Assessment of Health Canada for internal funding of our project. We thank Stephen Lee for his dedicated effort preparing our research library database. Finally we are exceedingly grateful to Dr. Jamie Nakai and Hart MacPherson for reviewing the article before publication.