Predicting vehicle effects on the dermal absorption of halogenated methanes using physiologically based modeling

Occupational and environmental settings present opportunities for humans to come into contact with a variety of chemicals via the dermal route. The chemicals contacting the skin are likely to be diluted with a vehicle or present as a component of a mixture. In order to support risk assessment activities, we evaluated the vehicle effects on dermal penetration of two halogenated hydrocarbons, dibromomethane (DBM) and bromochloromethane (BCM). In vivo exposures to 15 combinations of of these in water, mineral oil, and corn oil vehicles were conducted, and blood was sampled for dibromomethane and bromochloromethane during the exposure at 0.5, 1, 2, 4, 8, 12, and 24 h. A physiologically based pharmacokinetic (PBPK) model was used to estimate the total amounts of dibromomethane or bromochloromethane that were absorbed during the exposure, and the dermal permeability coefficients were determined. While the permeability coefficients for dibromomethane and bromochloromethane were approximately 73- and 40-fold higher, respectively, in the water vehicle than in the corn oil, the permeability coefficient, when normalized for the skin:vehicle matrix partition coefficient, varied by less than a factor of 2. The permeability in an aqueous vehicle was then successfully used to predict the permeability coefficient for dibromomethane in a nonpolar vehicle, peanut oil.