Human and canine exposures to methylene chloride vapor.

Well-controlled experimental exposures to methylene chloride vapor lasting for 2 or 4 hours were performed in human beings and dogs. The exposure concentrations ranged from 100 to 1000 ppm in the dogs and from 100 to 200 ppm in man. Serial breath and blood curves from both species were directly proportional to the magnitude of exposure. The average 24-hour urinary excretions of methylene chloride for the 100- and 200-ppm exposures in man were approximately 23 µg and 82 µg, respectively. During comparable exposures the dog absorbed substantially more methylene chloride vapor than man. Prolonging the exposure from 2 to 4 hours did not result in a substantial increase in solvent absorption. These studies have demonstrated that it is possible to make accurate extrapolations to human exposures from animal experiments provided the appropriate attention is given to factors such as the exposure duration, the time of collection after the exposure, the extent of metabolic involvement, and kinetic parameters. In suc...