Percutaneous Absorption of 4-Cyanophenol from Freshly Contaminated Soil in Vitro:  Effects of Soil Loading and Contamination Concentration

Despite the skin's excellent barrier function, dermal exposure to soil contaminated with toxic chemicals can represent a significant health hazard (e.g., via multiple work related contacts in the farming and waste disposal industries). The development of environmental standards or limits for chemical levels in soil has been impeded because quantification of percutaneous uptake from this medium has not been well-defined. The objective of the research described here, therefore, was to better characterize the rate and extent of dermal penetration as a function of soil loading and degree of soil contamination. The absorption of a model compound (4-cyanophenol, CP) across hairless mouse skin in vitro has been determined at four different soil loadings (5, 11, 38 and 148 mg cm-2) and at six levels of soil contamination (concentrations ranging from 0.19 to 38 mg/g soil). Following 8 h of exposure, the amount of CP absorbed was independent of soil loading when CP concentration was constant, implying that the quantity of soil present was always sufficient to provide at least a single layer of tightly packed particles. At the lowest loadings, however, with increasing times of exposure, the CP transport rate fell off due to depletion of chemical from the soil. At constant soil loading (38 mg cm-2), CP flux (Jss) across the skin was linearly proportional to the level of contamination ( ) over the range 0.19 to 23.5 mg of CP per gram of soil: Jss (μg cm-2 h-1) = (1.1 × 10-5 g cm-2 h-1) × (μg/g soil). At the highest CP contamination concentration, however, the transport rate was about an order of magnitude higher than expected, possibly due to the presence of pure CP crystals. In conclusion, these results provide new quantifications of the characteristics of dermal uptake from chemically contaminated soils and important information with which to develop and verify predictive models of dermal absorption.