OSHA's former limit for trichloroethylene, adopted from the American National Standards Institute, was 100 ppm TWA, 200 ppm as a ceiling limit not to be exceeded for more than five minutes every two hours, and 300 ppm as a peak limit. The proposed PEL for trichloroethylene was 25 ppm as an 8-hour TWA, and NIOSH (Ex. 8-47, Table N1) supported the proposed limit, which is consistent with the NIOSH REL. The ACGIH has a 50-ppm TLV-TWA and a 200-ppm TLV-STEL for trichloroethylene. Based on its review of the record evidence, OSHA has determined that a 50-ppm TWA PEL and 200-ppm STEL are appropriate limits for trichloroethylene; the final rule establishes these limits. Trichloroethylene is a colorless, nonflammable, noncorrosive liquid with the sweet odor characteristic of some chlorinated hydrocarbons.
The ACGIH (1986/Ex. 1-3) cited several studies establishing that trichloroethylene primarily affects the central nervous system and liver; some of these studies have indicated that chronic exposure to less than 100 ppm trichloroethylene is associated with a variety of nervous disturbances. Haas (1960, as cited in ACGIH 1986/Ex. 1-3, p. 595) and Grandjean, Muchinger, Turrian et al. (1955/Ex. 1-324) reported nervous symptoms among workers exposed for five years or more to trichloroethylene concentrations ranging from 1 to 335 ppm; the frequency of complaints increased when average exposures exceeded 40 ppm. Bardodej and Vyskocil (1956/Ex. 1-461) also reported symptoms of trichloroethylene poisoning, including tremors, giddiness, anxiety, and alcohol intolerance, among workers exposed above 40 ppm. In contrast, controlled laboratory experiments with human subjects exposed for up to several days to 100 or 200 ppm have generally reported no behavioral or subjective responses. The ACGIH concluded that, although the symptoms reported by workers are subjective and commonly found among individuals having no chemical exposure, the consistency of the reports "suggests the possibility of some subjective complaints as concentrations exceed about 50 ppm" (ACGIH 1986/Ex. 1-3, p. 596). Therefore, the ACGIH recommended a TLV-TWA of 50 ppm and a TLV-STEL of 200 ppm for trichloroethylene to minimize symptoms of headache, fatigue, and irritability.
The ACGIH (1986/Ex. 1-3) also reviewed some of the carcinogenicity data on trichloroethylene. In an NCI bioassay (1976b/Ex. 1-168), mice given trichloroethylene by gavage developed hepatocellular carcinomas, but rats did not. The species difference in response was attributed to a difference in the way trichloroethylene is metabolized between the mouse and rat (Stott, Quast, and Watanabe 1982/Ex. 1-833). An inhalation study in mice, rats, and Syrian hamsters (Henschler, Romen, Reichert et al. 1980/Ex. 1-330) found only an increase in the occurrence of malignant lymphomas in mice, which the authors attributed to the strain of mouse used (NMRI). The ACGIH also cited a number of epidemiologic investigations having cohorts as large as 7,688 workers, in which no correlation between cancer mortality and exposure to trichloroethylene was found (Novotna, David, and Malek 1971, as cited in ACGIH 1986/Ex. 1-3, p. 595; Axelson, Andersson, Hogstedt et al. 1978/Ex. 1-713; Tola, Vilhunen, Jarvinen, and Korkala 1980/Ex. 1-391).
After reviewing all of the available health data, NIOSH (1978m/Ex. 1-1121) concluded that the results of the NCI (1976b/ Ex. 1-168) gavage study indicate trichloroethylene (TCE) to be a potential human carcinogen, although NIOSH noted that TCE was "not considered to be a potent carcinogen." NIOSH also stated that a 100-ppm limit would not protect against the neuropathic symptoms, such as headache and fatigue, caused by exposure to trichloroethylene. In support of this conclusion, NIOSH (1978m/Ex. 1-1121) cited three health hazard evaluations conducted in facilities using trichloroethylene as a degreasing agent. In all three facilities, employees consistently experienced symptoms of dizziness, fatigue, nausea, headache, sensory irritation, and difficulty in breathing. Personal TWA exposures to trichloroethylene ranged from 37 to 112 ppm in one plant, 10 to 100 ppm in the second plant, and 10 to 95 ppm in the third plant. NIOSH (1978m/Ex. 1-1121) concluded that these reports documented the presence of adverse effects caused by acute exposure to trichloroethylene at levels of one-fourth to one-half the 100-ppm OSHA limit, at 25 to 50 ppm.
NIOSH recommended a 25-ppm TWA limit for trichloroethylene based on the health hazard reports described above as well as on a NIOSH evaluation of several NIOSH industrial hygiene reports showing that degreasing operations, including those using open-top tanks, are able to achieve 25 ppm uniformly by the use of engineering controls. NIOSH reasoned that these open-tank operations would be among the most difficult of all TCE-using operations to control. Since publication of the NIOSH (1978m/Ex. 1-1121) report, several recent bioassays on trichloroethylene have been published and are currently being reviewed by EPA. Fukuda, Takemoto, and Tsuruta (1983/Ex. 1-1109) exposed female rats and mice to 50, 150, or 450 ppm trichloroethylene for 103 weeks and reported an increased incidence of lung tumors among mice only. Maltoni, Lefemine, and Cotti (1986/Ex. 1-1160) exposed rats and mice to 100, 300, or 600 ppm trichloroethylene and reported a significant increase of renal adenocarcinomas and Leydig cell tumors in rats, as well as a significant increase in hepatomas and lung tumors in mice. In 1986, the NTP reported an increase in the incidence of kidney tumors in rats given trichloroethylene by gavage; however, the NTP considered the tumor response to be weak (3 of 49 animals) and reported that the results were only statistically significant after corrections for high mortality were made.
Based on the information discussed above, OSHA proposed to revise the PEL for trichloroethylene to 25 ppm as an 8-hour TWA. The proposed limit was supported by NIOSH (Ex. 8-47) and by the AFL-CIO (Ex. 194), which consider trichloroethylene a potential carcinogen. However, the Dow Chemical Company objected to this proposed limit on the grounds that:
Dow also pointed out that neither the ACGIH nor IARC has classified trichloroethylene as a potential carcinogen and that EPA's Science Advisory Board concluded that the weight of evidence for TCE's carcinogenicity "lies on a continuum between their categories B2 [probable human carcinogen] and C [possible human carcinogen]" (Ex. 3-741, p. 62). Dow concluded:
The Halogenated Solvents Industry Alliance (Ex. 8-89, pp. 3-18) expressed an opinion similar to that of Dow Chemical. In its posthearing submission, Dow submitted the written findings of the EPA's Science Advisory Board (SAB) on trichloroethylene (letter dated March 9, 1988 to Lee M. Thomas, Administrator of EPA, Ex. 106D). In this letter, the SAB concluded that "[t]richloroethylene has the potential to cause cancer in humans, but its potency is low."
The Science Advisory Board also stated:
OSHA believes that the evidence described above supports OSHA's preliminary conclusion in the NPRM (53 FR 21013) that the former 100-ppm TWA PEL for trichloroethylene is insufficiently protective against CNS effects and, further, that exposure to trichloroethylene may present a possible carcinogenic hazard. However, OSHA concludes that the evidence for adverse CNS effects below concentrations of 50 ppm is equivocal; exposures exceeding 50 ppm were found in each of the facilities studied by NIOSH in which symptoms of CNS disturbances were reported. Furthermore, OSHA finds that it is premature to establish a PEL for trichloroethylene based on evidence of its carcinogenicity, given the uncertainties in the evidence. Therefore, OSHA concludes that it is appropriate at this time to establish a TWA PEL of 50 ppm and a STEL of 200 ppm to reduce the signficant risk of adverse CNS effects that are associated with exposure to trichloroethylene at the former OSHA limits. The Agency considers the adverse effects resulting from exposure to trichloroethylene to be material impairments of health. Accordingly, the Agency is establishing a 50 ppm TWA PEL and 200 ppm STEL for trichloroethylene in the final rule.