Abstract Percutaneous Absorbtion of Pentachlorophenol from Soil. Wester, R. C., Maibach, H. I., Sedik, L., Melendres, J., Wade, M., and DiZio, S. (1993). Fundam. Appl. Toxicol. 20, 68-71. Pentachlorophenol (PCP) is one of the most heavily used pesticides. About 80% of PCP is used for wood preservation, whereas the remainder is used as an herbicide, fungicide, and disinfectant. PCP is a probable human carcinogen, based on animal studies. Illness and death have been reported where PCP is in direct contact with skin. PCP is the most ubiquitous compound found when the general population is screened for pesticide residue. PCP is found in soil as well as other environmental sources. Our objective was to determine the skin bioavailability of PCP from soil and from the control vehicle acetone. In vivo in the Rhesus monkey, percutaneous absorption of PCP was 24.4 ± 6.4% of applied dose from soil and 29.2 ± 5.8% of applied dose from acetone vehicle for a 24-hr exposure period. This amount of absorption makes PCP one of the more extensively absorbed compounds to date. Additionally, the 14 C half-life was 4.5 days following both intravenous and skin administration of [ 14C]PCP. These data suggest high bioavailability and an extended biological interaction period with the long half-life. In vitro percutaneous absorption with human cadaver skin and human plasma receptor fluid underestimated the in vivo absorption. Receptor fluid accumulation was 0.6 ± 0.09% and 1.5 ± 0.2% for two skill sources for PCP in acetone vehicle and 0.01 ± 0.00% and 0.00 ± 0.08% for two skin sources with soil vehicle. Skin content after skill surface wash ranged from 2.6 to 3.7% for acetone vehicle and 0.07-0.11% for soil vehicle. Overall accountability for in vitro dose ranged from 81 to 96%.