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: 67-72-1; Chemical Formula: CCl3CCl3

OSHA’s current PEL for hexachloroethane is a 1-ppm TWA, with a skin notation, which was adopted from the 1968 ACGIH TLV. The NIOSH REL for this substance is the lowest feasible level, based on hexachloroethane’s potential carcinogenicity. Hexachloroethane is a nonflammable white solid.

The basis for the 1-ppm TLV was to prevent the “serious injury potential to several organ systems” shown by animal studies (ACGIH 1986/Ex. 1-3, p. 301). Subsequently, the ACGIH revised its TLV upward to 10 ppm based, in part, on a study by Weeks, Angerhofer, Bishop et al. (1979/Ex. 1-400) that reported no adverse effects among several animal species exposed daily to 15- or 48-ppm concentrations of hexachloroethane. The ACGIH also cited an NCI study (NCI 1978b/Ex. 1-949), in which “extremely heavy dosages…administered continuously for a long period of time” resulted in the development of hepatocellular tumors in mice but not in rats. The 10-ppm TLV was further supported by a personal communication of a TLV Committee member who reported that no ill effects occurred among workers “who handled the material with few precautions” during World War II (ACGIH 1986/Ex. 1-3, p. 301). No exposure data were supplied to support this personal communication.

In 1978, NIOSH reviewed the results of an NCI (1978b/Ex. 1-949) bioassay in which hexachloroethane was administered by gavage to mice and rats. Both male and female mice exhibited an excess incidence of hepatocellular carcinoma, but rats did not. NCI concluded that early mortality may have obscured detection of a carcinogenic effect in rats (NCI 1978b/ Ex. 1-949). Toxic kidney damage was also found in mice and rats treated with hexachloroethane. Based on this evidence, NIOSH (Chloroethanes: Review of Toxicity, Current Intelligence Bulletin 27, NIOSH 1978r) has recommended that exposure to hexachloroethane be maintained at the lowest detectable level.

Several participants (Exs. 3-678, 116, 144, and 194; Tr. pp. 9-149, 9-218) commented on hexachloroethane. The New Jersey Department of Health (Ex. 144) discussed the use of EPA’s IRIS system to determine limits (OSHA’s discussion of this approach is presented in Section VI.A of this preamble). The Workers Institute of Safety and Health (WISH)(Ex. 116; Tr. p. 9-218) and the AFL-CIO (Ex. 194) stated that the ACGIH’s increase in the limit for hexachloroethane reflects an inappropriate use of safety factors; WISH was also of the opinion that OSHA should have performed a quantitative risk assessment for hexachloroethane. In response to WISH, OSHA notes: (1) that the Agency is not following the ACGIH’s move to a higher limit for hexachloroethane; and (2) that OSHA performed risk assessments only for those substances classified in the carcinogen section of this preamble.

Lawrence Hecker, Corporate Director of Industrial Hygiene and Toxicology for Abbott Laboratories (Ex. 3-678; Tr. p. 9-1149) stated that the skin notation should not be retained for hexachloroethane because this material is not systemically toxic via dermal absorption. However, in accordance with the Agency’s policy on skin notations (see Section VI.C.18 of this preamble), OSHA is retaining a skin notation for hexachloroethane in the final rule.

OSHA concludes that the evidence relied on by the ACGIH is not adequate to support raising the PEL at this time. The human evidence cited by the ACGIH is anecdotal and lacks the exposure data necessary to permit OSHA to assess whether significant risk is absent (and likely to remain so) at the 10-ppm exposure level. In addition, OSHA is concerned, as is NIOSH (Ex. 8-47, Table N6A), about the development of tumors in hexachloroethane-exposed mice demonstrated in the NCI (1978b/Ex. 1-949) study. OSHA therefore retains its PEL of 1 ppm TWA, with a skin notation, and concludes that increasing the PEL for hexachloroethane would increase the significant risk of cancer potentially associated with exposure to this substance.

Page last reviewed: September 28, 2011