DHHS (NIOSH) Publication Number 84-117
Current Intelligence Bulletin 43
Current Intelligence Bulletins are reports issued by the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control, Atlanta, Georgia, for the purpose of disseminating new scientific information about occupational hazards. A Current Intelligence Bulletin may draw attention to a hazard previously unrecognized or may report new data suggesting that a known hazard is either more or less dangerous than was previously thought.
Current Intelligence Bulletins are prepared by the staff of the Division of Standards Development and Technology Transfer, NIOSH (Robert A. Taft Laboratories, 4676 Columbia Parkway, Cincinnati, Ohio 45226) and are distributed to representatives of organized labor, industry, public health agencies, academic institutions, and public interest groups as well as to those federal agencies, such as the Department of Labor, which have responsibilities for protecting the health of workers. It is our intention that anyone with the need to know should have ready access to the information contained in these documents; we welcome suggestions concerning their content, style, and distribution.
It is recommended that methyl chloride, methyl bromide, and methyl iodide be regarded as potential occupational carcinogens. Additionally, it is recommended that methyl chloride be considered a possible teratogen. These recommendations are based upon animal studies which have demonstrated the carcinogenic potential of these compounds and in the case of methyl chloride, teratogenic effects as well. Consequently, appropriate engineering and work practice controls should be used to reduce worker exposure The excess risk of cancer to workers or the induction of a teratogenic response in the children of workers exposed to specific airborne concentrations of these compounds has not yet been determined, but the probability of developing these adverse effects would be decreased by reducing exposure.
On the basis of this information, it is recommended that producers and users of methyl chloride, methyl bromide, and methyl iodide disseminate this information to their workers and customers and that professional and trade associations and unions inform their members of otential hazards of working with these compounds.
J. Donald Millar, M.D., D.T.P.H. (Lond.)
Assistant Surgeon General
Director, National Institutue for
Occupational Safety and Health
Centers for Disease Control
The monohalomethanes (methyl chloride, methyl bromide, and methyl iodide) are alkylating agents and thus have generated concern as to their potential for inducing mutations and cancer. All three compounds were found to be direct-acting mutagens in the Ames assay. In experimental studies in either rats or mice using various routes of administration, these three compounds have also demonstrated the ability to produce cancer. Methyl chloride produced a teratogenic effect (heart defects) in the offspring of pregnant mice exposed by inhalation at 500 and 750 ppm.
Based on these data, the National Institute for Occupational Safety and Health (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.
Physical and Chemical Properties
The three chemicals addressed in this document are commonly called the monohalogenated derivatives of methane (monohalomethanes): chloromethane, bromomethane, and iodomethane. Fluoromethane is not included since there are no data on the extent of exposure in the workplace and little to no information on toxic effects in animals or humans. These derivatives are represented by the general formula CH3X, where X represents chlorine, bromine, or iodine. Some of the physical and chemical properties of these compounds are summarized in Table 1. In this document, these compounds are referred to by their common names: methyl chloride, methyl bromide, and methyl iodide.
Table 1 Chemical and Physical Properties of th