Dermal absorption of dihalomethane vapors.

The dermal absorption of dibromomethane (DBM) and bromochloromethane (BCM) vapors was studied in rats placed in a specially designed chamber incorporating individual respiratory protection to avoid pulmonary uptake. Exposures (DBM: 500 to 10,000 ppm; BCM: 2500 to 40,000 ppm) lasted 4 hr during which time five blood samples were drawn from jugular cannulae for analysis of the parent dihalomethane by gas chromatography. Estimates of the amounts of chemicals stored in tissues and exhaled were based on concentrations in the blood and tissue partition coefficients, tissue volumes, and ventilation rate. Total metabolism was estimated from the amount of bromide released during the 4-hr exposure. The total amount of vapor absorbed through the skin was calculated from the estimates of the amount of parent chemical in blood and tissues, and the amounts exhaled and metabolized. The dermal flux for each concentration (DBM: 0.004 to 0.078 mg/cm2/hr; BCM: 0.011 to 0.164 mg/cm2/hr) was calculated by dividing the amount absorbed by exposed surface area and duration of exposure. Flux was divided by exposure concentration to calculate a permeability constant. With each dihalomethane the permeability constants (DBM: congruent to 1.12 cm/hr; BCM: congruent to 0.79 cm/hr) were essentially independent of exposure concentration. This study shows that a whole-body dermal vapor exposure in rodents is technically possible, and quantitation of penetration can be accomplished using calculations based on achieved blood concentrations and some measure of metabolism.