Bioavailability of soil-bound TCDD: dermal bioavailability in the rat.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), an unwanted by-product formed during the manufacture of hexachlorophene and phenoxyherbicides, has been found as an environmental contaminant in many U.S. and Western European sites. This study examines in the rat the degree of dermal absorption of TCDD bound to soil. Such information would assist regulatory agencies in evaluating the degree of exposure of humans who come in contact with TCDD-contaminated soil. Several parameters which may influence dermal absorption were studied, including TCDD dose, duration of contact, presence of crankcase oil as a co-contaminant, and environmentally contaminated vs laboratory-prepared soil. The dermal penetration of TCDD following 4 hr of contact with skin was approximately 60% of that following 24 hr of contact (P less than or equal to 0.05). Following 24 hr of contact with the skin, the degree of dermal uptake of TCDD contaminated soil was approximately 1% of the administered dose. Under the conditions of the present study, the degree of uptake does not appear to be influenced to any significant extent by the concentration of TCDD on soil, the presence of crankcase oil as co-contaminants, or by environmentally vs laboratory-contaminated soil. Although a number of parameters examined in this study did not significantly influence the degree of dermal absorption of TCDD in the rat following 24 hr of contact with the contaminated soil, the unqualified use of the 1% value to estimate human exposure would overestimate human exposure, since there is general agreement among researchers that rat skin tends to be more permeable than human skin to highly lipid-soluble compounds such as TCDD.