STYRENE

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: 100-42-5; Chemical Formula: C₆H₅CHCH₂

OSHA’s former exposure limits for styrene (listed in 29 CFR 1910.1000, Table Z-2) were 100 ppm as an 8-hour TWA, 200 ppm as a STEL, not to be exceeded for more than 5 minutes in any 3-hour period, and 600 ppm as a ceiling limit. OSHA proposed revising these limits to 50 ppm as an 8-hour TWA and 100 ppm as a 15-minute STEL, based on both the ACGIH TLVs and the NIOSH RELs, which are identical. NIOSH (Ex. 150, Comments on Styrene) concurs that these limits are appropriate for styrene, and they are established in the final rule. Styrene monomer is a colorless, oily liquid with an aromatic odor.

In the proposal, styrene was located in the cancer category; in the final rule, it has been moved into the narcotics section, for the reasons discussed below. According to the generic methodology used by OSHA to group the 428 substances included in this rulemaking, substances were grouped according to the guidelines given by the ACGIH for assigning an appropriate exposure limit for a particular substance. In other words, if the ACGIH noted that a particular TLV was designed to protect against irritant effects, that substance was classified by OSHA in the sensory irritant category. This classification scheme was chosen by OSHA because it facilitated the rulemaking process (made unusually complex by the broad scope of the issues addressed) and made the discussion of hundreds of substances easier. However, as is often the case with classification schemes, this methodology oversimplifies the issues, particularly in those situations where a substance has more than one serious health effect.

Styrene is a case in point. This widely used substance is an irritant, a narcotic, and a neuropathic agent; some studies also show that animals exposed to styrene vapor develop tumors. The ACGIH Documentation (1986/Ex.1-3) for styrene states:

• [A] time-weighted average TLV of 50 ppm, one-tenth the lowest concentration possibly causing lymphoid or hematopoietic tumors in female rats, and a STEL of 100 ppm are suggested as reasonable limits [for styrene] (emphasis added) (ACGIH 1986/Ex. 1-3, p. 539).

Because the ACGIH limit had been set with reference to tumorigenicity (notwithstanding the lack of an A1 or A2 cancer designation), styrene fell into the category of carcinogens for the purposes of the proposal (53 FR 21202).

Many commenters objected to the proposal’s classification of styrene as a carcinogen (Exs. 3-741, 3-742, 3-1059, L3-1312B, 8-12, 8-32, 8-48, 8-54, 34, 36, 103, 155, and 187; Tr. 8/3/88, pp. 5-9 to 5-127; Tr. pp. 11-265, 11-266). For example, the Styrene Information and Research Council (SIRC) stated:

• Regarding the long-term animal studies on styrene…there have been nine…seven of which were via the oral route and two via inhalation….All of these studies showed either no evidence of cancer or gave inconclusive results due to study limitations, e.g., faulty study design, high background tumor incidence and/or high morbidity in test and control groups of animals (Ex. 3-742, p. 10).

Other commenters echoed the view of the SIRC. For example, a paper prepared by the Epidemiology Department of the Dow Chemical Company and reported on in Dow’s prehearing submission (Ex. 3-741, p. 55) concludes: “[O]verall these data do not support a causal link between lymphatic and hematopoietic cancer and styrene.” Dr. Gregory Bond (Ex. 103 and testimony) also criticized the epidemiology studies relied on by OSHA in the proposal, as did the Chemical Manufacturers Association (Ex. 8-54). J. Roger Crawford, Director of Environmental Control for the Outboard Marine Corporation, a manufacturer of outboard and inboard engines, lawn care equipment, and marine products, commented that OSHA’s conclusion in the proposal about the carcinogenicity of styrene “is clearly outside the mainstream of most scientific opinion” (Ex. 8-12, p. 3).

In posthearing testimony on behalf of the SIRC, Dr. Robert G. Tardiff, Director of Versar, Incorporated’s Risk Focus Division, described the comments of EPA’s Science Advisory Board (SAB) on a draft EPA Water Criteria Document on Styrene. Dr. Tardiff reported that the SAB had advised EPA to consider styrene a “possible human carcinogen (Category C) at best” (Ex. 34, p. 4). Dr. Tardiff further commented that the Category C classification “would generally lead EPA to regulate the compound based on protection against non-cancer pathology” (Ex. 34, pp. 4-5).

However, EPA’s Guidelines for Carcinogen Risk Assessment (51 FR 33992) interpret the meaning of a Category C designation somewhat differently than does Dr. Tardiff. In a letter dated March 9, 1988 from the SAB to EPA’s Administrator, Lee M. Thomas (Attachment to Ex. 124), the SAB makes clear that factors other than category are important to consider for regulatory purposes:

• From a scientific point of view, it seems inappropriate for EPA and other agencies to regulate substances that are classified as B2 [probable human carcinogens] and not to consider regulation of compounds classified as C…. A substance classified as C (limited evidence in animals) for which human exposure is high may represent a much greater potential threat to human health [than substances with classifications of B2, B1, or A where exposures are lower]. EPA and other agencies…may, therefore, wish to take steps to reduce high exposures to substances in the C category whenever there appears to be a potentially significant threat to human health (in the sense [where risk estimates are]…above the threshold where regulation may be judged appropriate) (Attachment to Ex. 124).

Several animal and human studies have suggested that styrene may be a carcinogen. A nested case-control study conducted by McMichael, Spirta, Gamble, and Tousey (1976/Ex. 1-206) found significantly increased risks of lymphatic and hematopoietic cancer, lymphatic leukemia, and stomach cancer among workers exposed to both styrene and butadiene. A retrospective cohort mortality study by Meinhardt, Lemen, Crandall, and Young (1982/Ex. 1-199), also among workers exposed concurrently to styrene and butadiene, reported an excess risk of leukemia and aleukemia. In a study sponsored by the Chemical Manufacturers Association (Dow 1978, as cited in EPA 1987/Ex. 1-836), male and female Sprague-Dawley rats were exposed to styrene vapor at concentrations of 600 to 1200 ppm, six hours per day, five days per week, for 18 or 20 months. The higher exposure level was reduced to 1000 ppm after the first two months of exposure because of excessively reduced weight in the male rats. A statistically significant increased incidence of mammary tumors was reported in low-dose female rats (7 of 87) compared with controls (1 of 85); no increase in mammary tumors was reported among high-dose female rats. The authors questioned the significance of this response, since historical control animals from the same laboratory showed a higher background incidence of mammary tumors than did the controls used in this study.

In a 1979 NCI study (NCI 1979b/Ex. 1-948), male and female B6C3F1 mice and Fischer 344 rats were treated by gavage five days per week for 78 weeks (low-dose rat groups were treated for 103 weeks). The study was terminated at 91 weeks for mice and at 104 to 105 weeks for rats. Dose-related increases in alveolar/bronchiolar adenomas and carcinomas were observed only in the low-dose (150 mg/kg) and high-dose (300 mg/kg) male mice; the incidence of tumors for vehicle controls, low-dose, and high-dose male mice was 0/20, 6/44, and 9/43, respectively. Although the historical incidence of tumors among untreated controls was 12 percent (32/271), the historical incidence of vehicle controls was 0/40.

However, the human studies cannot be used to definitely demonstrate styrene’s carcinogencity because there were confounding exposures in these cohorts to butadiene, a substance identified by the NTP as carcinogenic. The animal studies also have limitations, such as high background rates of cancer in the controls and non-treatment-related mortality in some of the test animals.

Thus, at this time, OSHA believes that the current evidence on styrene’s carcinogenicity does not support its classification in the final rule as a carcinogen. OSHA has reviewed additional evidence and has determined that the most appropriate basis for classifying styrene in this rulemaking is the substance’s demonstrated narcotic effects. In its criteria document (1983a), NIOSH agrees that styrene is primarily a narcotic and central-nervous-system toxin:

• The principal health effects due to styrene exposure involve the central nervous system. These effects include subjective complaints of headache, fatigue, dizziness, confusion, drowsiness, malaise, difficulty in concentrating, and a feeling of intoxication….There have also been reports of liver injury, peripheral nervous system dysfunction, abnormal pulmonary function, chromosomal changes, reproductive effects, and carcinogenicity related to styrene expo-sures. Although data concerning these latter adverse effects are not well defined at this time, they do provide cause for concern (NIOSH 1983a, p. 150).

Accordingly, OSHA has placed the health-effects discussion for styrene in the preamble section labeled “Narcotic Effects” in this final rule.

OSHA proposed to reduce its former exposure limits for styrene to 50 ppm as an 8-hour TWA and 100 ppm as a 15-minute STEL. The Agency finds clear evidence, based on styrene’s narcotic effects, to support these limits. Richard Olsen, representing the Dow Chemical Company, agrees, and stated at the hearing that 50 ppm is likely to be the most “appropriate” limit for styrene (Tr. 3, pp. 250, 251). There is a considerable body of health-effects information in humans for styrene in the toxicological literature. Subjects exposed at 800 ppm for four hours experienced eye and throat irritation and also reported listlessness, drowsiness, and impaired balance (NIOSH 1983a, p. 150). At a concentration of 376 ppm, five human volunteers experienced eye and respiratory tract irritation within 20 minutes and demonstrated decrements in motor function (NIOSH 1983a, p. 150). Three subjects exposed to 100 ppm of styrene for 90 minutes had slower reaction times; on repeated exposure, sleepiness, fatigue, headache, difficulty in concentration, malaise, nasal irritation, and nausea occurred in another group of subjects (NIOSH 1983a, p. 150).

Effects attributable to central nervous system depression were seen in a six-week study involving human subjects exposed to 20, 100, or 125 ppm styrene; the authors of the study reported visual-evoked-response and electroencephalogram changes in these subjects (NIOSH 1983a, p. 150). Other studies report irritation of the eyes and throat at concentrations ranging from 1 to 100 ppm (NIOSH 1983a, p. 151).

Workers in reinforced plastics (RP) facilities in many countries have also evidenced narcotic effects as a consequence of styrene exposure. Swedish, Dutch, and Czechoslovakian workers in RP plants complained of headache, fatigue, drowsiness, giddiness, and dizziness at exposure levels in the range of 4 to 195 ppm (NIOSH 1983a, p. 151).

Respiratory effects were observed in U.S. RP workers exposed to from 9 to 111 ppm styrene; symptoms included wheezing, shortness of breath, and chest tightness. Another study showed a significantly greater number of RP workers with abnormal pulmonary function when compared with workers from a nonstyrene facility (NIOSH 1983a, p. 154).

NIOSH concluded, based on its extensive review of the health-effects literature for styrene, that an 8-hour TWA exposure limit of 50 ppm was appropriate to protect against the health effects observed in workers exposed to styrene at levels of 100 ppm and below. NIOSH also recommends a STEL of 100 ppm for styrene to prevent acute eye and upper-respiratory-tract irritation (NIOSH 1983a, p. 156). The State of New Jersey’s Department of Public Health (Ex. 144) urged OSHA to derive a PEL for styrene on the basis of EPA’s IRIS data, but this approach was criticized by other commenters (Ex. 187). The use of IRIS data for limit-setting purposes is addressed in Section VI.A of the preamble. At the hearing, representatives of the International Chemical Workers Union urged OSHA to adopt a lower PEL because considerable risk remains at the 50-ppm level (Tr. 9, p. 216). However, the AFL-CIO (Ex. 194) agrees with NIOSH that the 50-ppm and 100-ppm TWA and STEL limits are appropriate.

OSHA finds that workplace exposures to styrene are associated with health effects ranging from narcosis to neuropathies and irritation, which together constitute material impairments of health. The Agency finds that an 8-hour TWA of 50 ppm and a STEL of 100 ppm are necessary to protect against these significant risks of material health impairment. The Agency also notes that large chemical companies (for example, Rohm and Haas and the Dow Chemical Company) have already established internal corporate limits of 25 or 50 ppm (8-hour TWAs) for styrene to protect their workers from the range of serious health effects associated with exposure to this substance (Ex. 25, Appendix II, pp. 1-3).

Some commenters (Ex. 155; Tr. p. 10-111) pointed to the fact that the State of Washington has not yet adopted a 50-ppm limit for styrene as evidence of this limit’s infeasibility; however, OSHA notes that Stephen Cant, for the State of Washington’s Department of Public Health, stated that his department was monitoring the health evidence for styrene and considered the State’s 100-ppm limit an “incremental improvement” (Tr. 2, pp. 105, 106).

OSHA notes that, with the exception of two operations in a single industry (i.e., the boat-building industry), these limits have been found to be achievable with engineering and work-practice controls in all styrene-using operations, including styrene manufacture and other reinforced-plastics operations. OSHA finds that general dilution ventilation, local exhaust ventilation, and process enclosure can be used effectively in tub, shower, and diving board manufacturing because the size and configuration of these items lend themselves to effective control. However, in two operations, manual layup and sprayup, in the boat-building industry, there is insufficient data in this record to indicate that compliance can generally be achieved with engineering and work-practice controls. For these boat-building operations, employers may use any combination of engineering controls, work practices, and respiratory protection to achieve these limits (see the discussion in Section VII of this preamble). For these operations, engineering controls and work practices will only be required to achieve full compliance with the final rule’s PELs in cases where the Assistant Secretary can demonstrate that engineering controls and work practices can generally achieve these limits. In the absence of such a finding, the employer must nonetheless use engineering controls and work practices to achieve compliance with the Agency’s former PELs for styrene.