Dermal absorption of organic chemical vapors in rats and humans.

Quantitation of chemical vapor penetration through skin is necessary for assessment of health hazards involved in some occupational environments. Information on penetration of vapors through human skin is minimal because human exposures are not sanctioned. We have investigated the whole-body dermal penetration of styrene, xylene, toluene, perchloroethylene, benzene, halothane, hexane, and isoflurane in rats and compared the permeability constants with available human studies on vapor penetration. Rats with closely clipped fur were exposed to organic chemical vapors (3000 to 60,000 ppm) while breathing fresh air through a latex mask. Blood concentrations taken during the 4-hr exposures were determined by sampling through indwelling jugular cannulas. A physiologically based pharmacokinetic model was used to predict permeability constants consistent with the experimental blood concentrations. Permeability constants (cm/hr) were estimated by a least-square optimization and ranged from 1.75 cm/hr for styrene to 0.03 cm/hr for isoflurane. Rat permeability constants were uniformly two to four times greater when compared to the human constants which were calculated from the literature. These results indicate that organic vapor permeability constants in rats are a conservative estimate of organic vapor permeability constants in humans and that the consistent differences in permeability constants between these two species may be due to physiological differences in the skin.