Effects of inhaled methyl bromide gas on the metabolic system and kinetics of bromine ion in rats.

Wistar male rats were exposed to 2000 ppm of methyl bromide gas for one hour (single exposure experiment) or 300 ppm of the gas for 6 hours a day, 3 days a week for 4 or 8 weeks (repeated exposure experiment) to investigate the metabolism of inhaled methyl bromide. After the exposure was completed, the bromine ion concentration in serum was measured up to 60 days. The serum bromine ion concentration was determined by a headspace gas chromatography-mass spectrometry after converting bromine ion to methyl bromide by adding dimethyl sulfate in the serum samples. In the single exposure experiment, the bromine ion concentration decreased quickly within one day after the end of the exposure, and then began to decrease gradually. In the repeated exposure experiment, on the other hand, the bromine ion concentration decreased almost exponentially. A two-compartment model was applied to analyze the clearance rate of bromine ion. The biological half time of serum bromine ion was 9.1 days for the single exposure and 5.4 days for the repeated exposure. The amount of cytochrome P450 (CYP) in liver microsomes was measured after the end of exposure. CYP in liver was not significantly different after the repeated exposure but it decreased after the single exposure.