Penetration of Chlorophenols through Human Skin Penta and tetrachlorophenol are widely used wood preservatives which have received increasing regulatory attention form EPA and OSHA. While primary concerns have focused on dioxin contaminant levels there has been considerable controversy over the risks associated with perdermal penetration: both in the workplace and the environment. Based on very limited acute dose rate experiments, the EPA has estimated dermal penetration of 50% for pentachlorophenol inorganic solutions (typically diesel oil) and 1% for aqueous sodium pentachlorophenate solutions. No estimates are available for tetrachlorophenol.