MONOMETHYLANILINE

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: 100-61-8; Chemical Formula: C₆H₅NHCH₃

OSHA’s former PEL for monomethylaniline (N-methyl aniline) was 2 ppm, measured as an 8-hour TWA; this limit was accompanied by a skin notation, indicating that this chemical can readily penetrate the skin. The ACGIH has a limit of 0.5 ppm TWA for monomethylaniline, also with a skin notation. OSHA proposed to reduce the 8-hour TWA PEL to 0.5 ppm and to retain the skin notation; NIOSH (Ex. 8-47, Table N1) concurs, and these limits are established by the final rule. Monomethylaniline is a colorless liquid that turns reddish-brown after standing.

Treon, Deichmann, Sigmon, and associates (1949/Ex. 1-676) found that monomethylaniline applied to the skin of laboratory animals resulted in systemic poisoning, and that the oral LD(50) in rabbits was 280 mg/kg. A later study by Treon and associates (1950/Ex. 1-533) showed that guinea pigs, rabbits, and rats died from 130 or fewer seven-hour exposures to 7.6 ppm monomethylaniline. In the same study, a monkey survived the same number and length of exposures at 2.4 ppm, and a dog survived 50 exposures at 86 ppm. Exposed animals later developed blood changes, including methemoglobinemia and Heinz bodies (Treon, Sigmon, Wright et al. 1950/Ex. 1-533). NIOSH was the only commenter to the record on monomethylaniline.

In the final rule, OSHA is establishing a 0.5-ppm TWA limit, with a skin notation, for this substance. The Agency concludes that these limits will protect workers from the significant risk of metabolic and blood effects, such as methemoglobinemia, potentially associated with exposure to monomethylaniline. The skin notation will protect workers from the risk of systemic poisoning posed by the skin absorption of this substance. OSHA finds that the methemoglobinemia and skin irritation associated with exposure to monomethylaniline exposure constitute material health impairments.