In vitro Studies

The effect of soil loading on the dermal uptake of soil-borne contaminants was examined using an in vitro evaporation/penetration apparatus and abdominal skin from human cadavers. Dermal uptake of two 14C-labeled pesticides, lindane, and 2,4-dichlorophenoxyacetic acid (2,4-D), was assessed at nominal soil loadings of 1, 5, and 10 mg/cm². Sub-150-micrometer fractions of two soils with differing organic carbon contents were employed. Mean 24-h dermal absorption values ranged from 0.45 to 2.35% for lindane and from 0.18 to 1.64% for 2,4-D, depending upon soil load and type. Mean mass fluxes ranged from 8.8 to 32 pg/cm²/h for lindane and from 1.9 to 6.4 pg/cm²/h for 2,4-D. Results were aggregated as ratios of flux or percent absorption at 1 and 10 mg/cm² to corresponding values obtained at 5 mg/cm². Fluxes at 5 and 10 mg/cm² did not differ significantly, but flux at 1 mg/cm² was about one-half the value observed at the higher loadings. The most plausible explanation for this decrease in mass flux is incomplete (submonolayer) coverage of the skin. Evidence in the form of electron micrographs is presented in support of this conclusion. Relative percent absorption increased significantly with decreases in soil load from 10 to 5 and from 5 to 1 mg/cm². This effect was inversely proportional to loading reduction in the former case, but was less than proportional due to the impact of contact area reduction (and, in the case of lindane, volatilization losses) in the latter. Percent dermal absorption data obtained in the laboratory require adjustment for differences in loading and coverage before application to assessment of exposure to contaminants in soil. Description of dermal absorption from soil in a manner comparable to that used to describe absorption from a liquid or vapor (i.e., using a driving force and a mass transfer coefficient) would reduce confusion on this point and is recommended.

Taylor & Francis, 1996, used with permission. If you are interested in more information about the Journal of Toxicology & Environmental Health, please visit the Taylor & Francis Publishers web site.

Apparatus: this picture displays the diffusion cell apparatus in the experiments.

Skin (no soil): this picture displays an electron micrograph of a bare skin sample (i.e., the skin has not been exposed to any soil). This picture and three following provide perspective on soil loadings that constitute a monolayer.

Skin (1 mg/cm²): this picture displays an electron micrograph of a skin sample that is loaded with soil at 1 mg/cm².

Skin (5 mg/cm²): this picture displays an electron micrograph of a skin sample that is loaded with soil at 5 mg/cm².

Skin (10 mg/cm²): this picture displays an electron micrograph of a skin sample that is loaded with soil at 10 mg/cm².