Current intelligence bulletin 43 - monohalomethanes. Methyl chloride CH3Cl, methyl bromide CH3Br, methyl iodide CH3I (with reference package).
A review of the data and a summary of findings regarding the potential human health hazards of the monohalomethanes methyl- chloride (74873), methyl-bromide (74839), and methyl-iodide (74884) were presented. Background information was presented on the three compounds, including physical and chemical properties, and production, use and potential for occupational exposure. The OSHA permissible exposure limits for occupational exposure and the American Conference of Governmental Industrial Hygienists recommended threshold limit values were listed; both standards include a skin notation for methyl-bromide and methyl-iodide, indicating the potential contribution to the overall exposure by the cutaneous route. Median lethal concentrations reported for 30 minute inhalation exposures of rats to methyl-chloride, methyl- bromide, and methyl-iodide were 72,000, 2,800 and 1,750 parts per million, respectively. These monohalomethanes had been found to be mutagenic in in-vitro test systems, and carcinogenic in rats and mice. In addition, methyl-bromide was found to be teratogenic in mice, and to induce degeneration and atrophy of the seminiferous tubules in male rats. Reported health effects in humans on exposure to these compounds included headache, nausea, vomiting, drowsiness, dizziness, giddiness, diarrhea, confusion, ataxia, slurred speech, paralysis, convulsions, delirium, coma, and death. In severe poisoning, the primary target organs were the lungs, liver, kidney, and brain. Based on this information, NIOSH recommends that methyl- chloride, methyl-bromide, and methyl-iodide be considered as potential occupational carcinogens and that methyl-chloride be considered a potential occupational teratogen. General guidelines for minimizing worker exposure to the monohalomethanes were presented in an appendix. These included exposure monitoring, product substitution, contaminant controls, worker isolation, personal protective equipment, and medical surveillance.