Previously, OSHA had no exposure limits for insoluble tungsten and its compounds. The ACGIH has established 5 mg/m3 as an 8-hour TWA and 10 mg/m3 as a short-term exposure limit for these substances. NIOSH recommends a limit of 5 mg/m3 as a 10-hour TWA. The proposed PEL for this group of substances was 5 mg/m3 as an 8-hour TWA and 10 mg/m3 as a 15-minute STEL. NIOSH (Ex. 8-47) concurred with OSHA's proposed limits. The final rule promulgates a 5 mg/m3 8-hour TWA and a 10 mg/m3 5-minute STEL, measured as tungsten. Tungsten is a gray, hard metal.
Rats fed a diet containing 0.5 percent insoluble tungsten compounds died, and another group of rats fed 0.1 percent of these compounds suffered noticeable weight loss (Kinard and Van de Erve 1941/Ex. 1-492). Studies in rats fed tungsten at 2, 5, or 10 percent of their diet showed that females in all dose groups had a 15-percent reduction in weight gain (Kinard and Van de Erve 1943/Ex. 1-493). The intraperitoneal LD(50) for tungsten metal powder in rats was 5 g/kg body weight; survivors showed minor liver and spleen changes at necropsy (Fredrick and Bradley 1946, as cited in ACGIH 1986/Ex. 1-3, p. 614). Studies of the tissues of guinea pigs intratracheally injected with tungsten metal and tungsten carbide revealed moderate interstitial cellular proliferation and no changes, respectively. However, Soviet studies involving similar intratracheal injections showed proliferation of the intra-alveolar septa (Kaplun and Mezentseva 1960, as cited in ACGIH 1986/Ex. 1-3, p. 614). The NIOSH criteria document for tungsten (1977h, as cited in ACGIH 1986/Ex. 1-3, p. 614) reports that Russian investigators found a 9- to 11-percent incidence of pulmonary fibrosis in workers exposed to tungsten (Kaplun and Mezentseva 1959/Ex. 1-961; and Mezentseva 1967, as cited in ACGIH 1986/Ex. 1-3, p. 614). NIOSH (1977h) recommended that the standard for tungsten and its insoluble compounds be set at 5 mg/m3 to protect against pulmonary effects.
Stokinger (in Patty's Industrial Hygiene and Toxicology, 3rd rev. ed., Vol. 2A, Clayton and Clayton 1981) reported on several epidemiological studies of workers in the "hard metal industry," in which tungsten carbide is machined. These studies describe a condition known as hard metal disease, which may be accompanied by pulmonary fibrosis. The disease is characterized by a moderate incidence of cough, dyspnea, and wheezing, a high incidence of minor radiological abnormalities with a few instances of marked abnormalities, and development of hypersensitivity asthma in some workers (which may be due to exposure to the cobalt that is used as a binding agent). The disease is progressive and potentially lethal. Stokinger (in Patty's Industrial Hygiene and Toxicology, 3rd rev. ed., Vol. 2A, Clayton and Clayton 1981, p. 1992) reported that, unlike other lung diseases produced by inorganic dust, there is no correlation between onset of symptoms, length of exposure, and the development of interstitial fibrosis. Analysis of the lung of one worker who had clinical signs and radiological changes showed the presence of large amounts of tungsten with much smaller amounts of other metals.
Mr. H.K. Thompson, Corporate Industrial Hygiene Manager for Caterpillar, Inc. (Ex. 3-349), questioned the need for a STEL for tungsten. OSHA believes that, given the potential seriousness of hard metal disease and the uncertainties regarding the relationship between exposure and response, a short-term limit for tungsten will provide additional assurance that the 8-hour TWA PEL is not exceeded. Therefore, in accordance with OSHA's policy for establishing STELs in this rulemaking (see Section IV.C.17), OSHA finds that a STEL for tungsten is necessary.
In the final rule, OSHA is establishing an 8-hour TWA of 5 mg/m3 and a STEL of 10 mg/m3 for tungsten and its insoluble compounds, measured as tungsten. The Agency concludes that these limits will substantially reduce the significant risk of pulmonary fibrosis and other lung effects, which constitute material impairments of health that are associated with exposure to this metal and its insoluble compounds at levels above the new PELs.