ACETONITRILE

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: 75-05-8; Chemical Formula: CH₃CN

Acetonitrile is most widely used in industry as a specialty solvent and chemical intermediate. OSHA’s former occupational exposure limit for acetonitrile was a 40-ppm 8-hour TWA. The ACGIH has a 40-ppm TLV-TWA with a 60-ppm TLV-STEL, in addition to a skin notation. OSHA proposed to reduce the former 8-hour TWA PEL to 20 ppm with a skin notation; this was the NIOSH REL, and NIOSH concurred with the proposed limit (Ex. 8-47, Table N1). However, after a thorough evaluation of the record evidence, OSHA has concluded that the ACGIH limits for this substance will provide appropriate protection against acetonitrile’s systemic toxicity. Accordingly, the final rule establishes an 8-hour TWA of 40 ppm and a STEL of 60 ppm, without a skin notation, for acetonitrile.

In animal studies, acetonitrile has been found to be embryotoxic and teratogenic in rodents exposed to levels sufficiently high to cause maternal toxicity (Berteau, Levinskas, and Rodwell 1982/Ex. 1-179; Willhite 1983/ Ex. 1-43). A 13-week inhalation study conducted by the National Toxicology Program (Hazleton Laboratories, Inc. 1983, as cited in ACGIH 1986/Ex. 1-3, p. 8) found pathological changes in the liver and some blood changes in mice and rats exposed to concentrations of 400 ppm acetonitrile.

The human evidence describing the toxic effects associated with exposure to acetonitrile consists of a report by Pozzani, Carpenter, Palm et al. (1959/Ex. 1-106), who exposed human subjects to acetonitrile vapor, and a case report by Amdur (1959/Ex. 1-143), who described a poisoning incident involving acetonitrile. None of three subjects exposed to 40 ppm for four hours reported any adverse responses during the exposure period, but one subject experienced tightness of the chest a few hours after termination of exposure, as well as a cooling sensation in the lungs the following day. None of the subjects had elevated blood cyanide levels; one subject showed a slightly elevated urinary thiocyanate level. Pozzani et al. (1959/Ex. 1-106) also exposed two subjects to 80 ppm and 160 ppm of acetonitrile for four hours. When exposed to 80 ppm, subjects reported no adverse response; however, at 160 ppm, one subject experienced slight flushing of the face and chest tightness a few hours after exposure (Pozzani, Carpenter, Palm et al. 1959/Ex. 1-106).

In addition to the Pozzani et al. (1959/Ex. 1-106) study, NIOSH (1978g/Ex. 1-262) cites a report by Amdur (1959/Ex. 1-143), who investigated an incident in which 16 painters became ill (with one death) after using an acetonitrile-containing material in a confined space. Amdur (1959/Ex. 1-143) reported no further incidents after adequate ventilation was installed and acetonitrile levels were maintained at about 17 ppm. NIOSH concluded that exposure to 40 ppm may have produced minimal effects and that no observable effects were produced at 17 ppm (NIOSH 1978g/Ex. 1-262, p. 97). Therefore, NIOSH recommended that exposure not exceed 20 ppm as a 10-hour TWA. Other than the comment by NIOSH (Ex. 8-47), no comments were received on this substance.

OSHA has carefully re-evaluated the evidence of acetonitrile’s toxicity to determine the appropriate permissible exposure limits to establish in the final rule. The Agency concludes that the evidence in humans suggests that no adverse effects are experienced at long-term exposures of 40 ppm and that a short-term limit of 60 ppm will provide protection against the facial flushing and chest tightness experienced by workers exposed for several hours to levels above these concentrations. In addition, in accordance with the policy on skin notations enunciated in Section VI.C.18, OSHA is not including a skin notation for acetonitrile in the final rule (the dermal LD(50) in rabbits is 1250 mg/kg).

In the final rule, OSHA is therefore retaining its existing 8-hour TWA for acetonitrile and adding a STEL of 60 ppm to protect against this substance’s systemic effects. The Agency concludes that these limits will prevent the significant risk of acute illness (and, in one case, death) observed in workers exposed to excessive short-term exposures of acetonitrile; the Agency finds that these health effects clearly constitute material impairments of health. In the proposal, OSHA specifically requested information on the feasibility of achieving the proposed limit; no comments were received, and OSHA accordingly assumes that the final rule’s limits, which are higher than the limit proposed, are feasible.