OSHA had no former limit for exposure to tungsten and its soluble compounds. The ACGIH limit is 1 mg/m3 TWA, with a 3 mg/m3 STEL, measured as tungsten. NIOSH recommends a 1 mg/m3 10-hour TWA for tungsten and its soluble compounds. OSHA proposed an 8-hour TWA PEL of 1 mg/m3 and a 15-minute STEL of 3 mg/m3; NIOSH (Ex. 8-47, Table N1) concurred with the addition of a STEL to the 1 mg/m3 TWA limit. The final rule establishes limits of 1 mg/m3 as an 8-hour TWA and 3 mg/m3 as a 15-minute STEL, measured as tungsten. Tungsten is a grey, hard metal.
Animal studies have shown that the LD(50) for soluble sodium tungstate when injected subcutaneously in rats ranges from 140 to 160 mg/kg (Kinard and Van de Erve 1940/Ex. 1-788). Soluble tungsten's lethal effects are the result of systemic poisoning that occurs as the compound is absorbed by multiple organs; this is followed by cellular asphyxiation (International Labour Office [ILO] 1934c, as cited in ACGIH 1986/Ex. 1-3, p. 614). Karantassis (1924, as cited in ACGIH 1986/Ex. 1-3, p. 614) also observed a systemic response in guinea pigs given soluble sodium tungstate or pure soluble tungsten either orally or intravenously; the animals developed anorexia, colic, trembling, and difficulty in breathing prior to death. Rats fed a diet containing 0.5 percent tungsten as soluble sodium tungstate or tungsten oxide died from this dose. Dietary doses of 0.1 percent tungsten oxide and the sodium salt caused weight loss in rats, but no deaths (Kinard and Van de Erve 1941/Ex. 1-492). Tungsten is believed to act by antagonizing the action of molybdenum (Higgins, Richert, and Westerfield 1956/Ex. 1-487). In its criteria document for tungsten (1977h, as cited in ACGIH 1986/Ex. 1-3, p. 614), NIOSH states that information on the effects of exposure to soluble tungsten compounds in the working population is not available. The ACGIH (1986/Ex. 1-3, p. 614) recommends a lower TLV for the soluble, as compared to the insoluble, compounds of tungsten because of the former's greater systemic toxicity. No comments other than those of NIOSH (Ex. 8-47) were received on this substance.
In the final rule, OSHA is establishing an 8-hour TWA of 1 mg/m3 and a STEL of 3 mg/m3 for tungsten and its soluble compounds, measured as tungsten. The Agency concludes that these limits will protect workers against the significant risks of systemic toxicity, anorexia, colic, incoordination, trembling, and dyspnea, all of which constitute material health impairments that are associated with exposure to these compounds at levels above the new PELs.