ANILINE

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: 62-53-3; Chemical Formula: C₆H₅NH₂

The former OSHA 8-hour TWA permissible exposure limit for aniline was 5 ppm, with a skin notation. The ACGIH-recommended 8-hour TLV is a 2 ppm TWA, with a skin notation. The proposed PEL was 2 ppm as an 8-hour TWA, and this limit is established in the final rule. The skin notation is retained. Aniline, when first distilled, is an oily, colorless liquid that darkens on exposure to air. Occupational aniline poisoning was a relatively common occurrence in earlier years (ACGIH 1986/Ex. 1-3, p. 30). The early limits for aniline were set to guard against acute toxicity manifested as cyanosis (Henderson and Haggard 1943i, as cited in ACGIH 1986/Ex. 1-3, p. 30). Cirrhosis and chronic CNS effects were also reported (Holstein 1955/Ex. 1-913; von Oettingen 1941/Ex. 1-874). Skin absorption occurs when aniline vapor contacts the skin (Dutkiewicz 1962, as cited in ACGIH 1986/Ex. 1-3, p. 30); the dermal LD(50) in rabbits is 820 mg/kg (Dangerous Properties of Industrial Materials, 7th ed., Sax and Lewis 1989, p. 262).

Early studies suggested that less than full-shift exposures of 7 to 53 ppm of aniline vapor caused mild symptoms, while one-hour inhalation exposures to concentrations in the range of 100 to 160 ppm caused severe effects (Henderson and Haggard 1943i, as cited in ACGIH 1986/Ex. 1-3, p. 30). Later studies in several species of animals found no effects, other than a slight increase in methemoglobin in the blood of rats, after the animals had been exposed to aniline concentrations of 5 ppm for six months (Oberst, Hackley, and Comstock 1956/Ex. 1-685). An early NCI aniline hydrochloride cancer bioassay in Fischer 344 rats and B6C3F1 mice demonstrated carcinogenic effects, primarily in the spleens of rats, but multiple organ sites were also involved in rats fed 0.6 percent or 0.3 percent aniline hydrochloride for 103 weeks (NCI 1978a/Ex. 1-1118).

NIOSH (Ex. 8-47, Table N6A) testified (Tr. III-96/97) that aniline and its analogs are carcinogens; NIOSH concurred that the limit established by OSHA for aniline and its homologues is appropriate. However, NIOSH is of the opinion that OSHA should designate substances suspected of having carcinogenic potential as carcinogens. This issue is discussed in Section V of the preamble. OSHA received no other comments on aniline and its homologues.

OSHA has concluded that the former limit of 5 ppm is not sufficiently protective, since systemic effects have been observed in humans exposed to levels as low as 7 ppm and in animals at levels as low as 5 ppm. Accordingly, OSHA is establishing an 8-hour TWA of 2 ppm for aniline and retaining the skin notation, which will protect against percutaneous absorption. The Agency has determined that this limit will substantially reduce the significant risk of methemoglobinemia, which constitutes a material impairment of health, seen in exposed animals at the former level. The Agency intends to continue to monitor the evidence on the carcinogenicity of aniline in the future to determine whether other action is appropriate.