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METHYL BROMIDE

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 74-83-9; Chemical Formula: CH3Br

OSHA's former PEL for methyl bromide was a 20-ppm ceiling with a skin notation, while the ACGIH limit is 5 ppm as an 8-hour TWA, with a skin notation. NIOSH recommends that the REL for this substance be set at the lowest feasible level. The Agency proposed, and the final rule establishes, a permissible exposure limit of 5 ppm (8-hour TWA), with a skin notation, for methyl bromide. Methyl bromide is a colorless, nonflammable gas with no taste and no odor at low temperatures. At levels above 5 ppm, it has a sweetish odor.

Acute poisoning from methyl bromide is characterized by lung irritation, pulmonary edema, convulsions, and coma. Chronic exposure to low concentrations of methyl bromide generally produces central nervous system effects, including muscle weakness and pain, incoordination, inability to focus one's eyes, and behavioral changes (ACGIH 1986/Ex. 1-3, p. 376; Craft 1983/Ex. 1-196). The onset of neurological signs and symptoms may be delayed for from several hours to a few days after exposure.

Methyl bromide is a gas and is predominantly an inhalation hazard, although there are suggestions that it can also be absorbed through the skin (Patty's Industrial Hygiene and Toxicology, 3rd rev. ed., Vol. 2B, p. 3443, Clayton and Clayton 1981). A report by Hine (1969/Ex. 1-70) notes that methyl bromide has been responsible for more deaths among occupationally exposed workers in California than have the organophosphates. It is hypothesized that methyl bromide has a greater potential for toxicity than do other organic bromides because its greater lipophilicity provides increased access to the brain.

Various studies demonstrate methyl bromide's toxicity in humans. Ingram (1951/Ex. 1-175) reported ill effects (symptoms not specified) after exposure to methyl bromide at concentrations of 100 ppm. Similar exposure concentrations were also reported by Hine (1969/Ex. 1-70) in a case study of two date packers in California. Johnson, Setzer, Lewis, and Anger (1977/Ex. 1-87) indicated that 34 packers became sick when exposed to an average methyl bromide concentration of 50 ppm, although concentrations in the packing room may have been as high as 100 to 150 ppm during the purging of a fumigation chamber.

Watrous (1942/Ex. 1-275) described nausea, vomiting, and headache in 90 workers who were exposed for two weeks to concentrations "generally below" 35 ppm. These symptoms emphasized the need to create a TLV to protect workers from the nausea, vomiting, and headaches (which together constitute material impairments of health) associated with lower levels of exposure. This need is strengthened by the fact that, since these symptoms are usually delayed in onset, workers may not have sufficient warning of this substance's potential neurotoxicity.

The AFL-CIO (Ex. 194, p. A-12) supports the inclusion of methyl bromide in this rulemaking, but notes that it is a potential occupational carcinogen. NIOSH takes the same position and believes that methyl bromide should be addressed in a full Section 6(b) rulemaking (Ex. 8-47, Table N6B; Tr. pp. 3-97, 3-98). OSHA shares the concerns of these commenters and intends to monitor the scientific evidence on methyl bromide's toxicity in the future. The Workers Institute for Safety and Health (WISH) (Ex. 116) is of the opinion that a ceiling limit is more appropriate than an 8-hour TWA for methyl bromide. OSHA finds, however, that the 5-ppm TWA will provide protection against the levels shown to produce poisoning in humans (generally in the 50- to 150-ppm range).

The presence of neurologic symptoms at levels below 35 ppm indicates that the former ceiling limit of 20 ppm is not adequate to protect workers from the effects of methyl bromide poisoning. OSHA is establishing a PEL of 5 ppm TWA, with a skin notation, to protect workers more adequately against these incapacitating symptoms. The Agency concludes that these limits will reduce this significant risk substantially.

 
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  • Page last reviewed: September 28, 2011
  • Page last updated: September 28, 2011
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