Abstract:
The effects of soil loading and organic carbon (OC) content on the uptake of contaminants in soil were examined using an in vitro evaporation/penetration apparatus with cadaveric human skin. Dermal uptake from soil of two 14C-labeled pesticides, lindane, and 2,4-dichlorophenoxyacetic acid (2,4-D), was assessed for the sub-150 um fraction of two soils with differing OC contents at soil loadings of 1, 5 and 10 mg/cm2. Dermal uptake values ranged from 0.45 to 2.35 percent for lindance and 0.18 to 1.59 percent for 2,4-D depending upon soil load and type. Although the percent dermal uptake of the compounds increased with decreasing soil load, the proportionality of this effect did not extend to the more environmentally plausible 1 mg/cm2. Mass fluxes ranged from 26.7 to 8.8 pg/cm2/hr for lindane and 6.9 to 1.9 pg/cm2/hr for 2,4-D, decreasing significantly at the lowest soil loading for both compounds in either soil. It is likely that this decrease in mass flux is due to incomplete (sub-monolayer) coverage on the skin. Therefore, neither direct application of percent dermal uptake values obtained at high loadings nor adjustment based on an assumption of constant mass flux is likely to provide an accurate estimate of dermal absorption at realistic soil landings. In the experiments reported here, OC content had little effect on the distribution of linmdane and a small but significant effect with 2,4-D. This effect was not proportional to the 6.5-fold difference in OC content between the soils.