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: 7440-25-7; Chemical Formulas: Tantalum metal (Ta); Tantalum oxide (Ta2O5)
OSHA's former PEL for tantalum is 5 mg/m3. The Agency proposed to retain this limit and to supplement it with a 15-minute STEL of 10 mg/m3, and NIOSH (Ex. 8-47, Table N1) concurred with this proposal. The final rule retains an 8-hour TWA for tantalum metal dust and oxide but does not adopt the proposed STEL for these substances (see Section XI.C.17 for a discussion of OSHA's rationale in regard to STELs). The ACGIH has a 5-mg/m3 TWA but has recently deleted its former 15-minute STEL of 10 mg/m3. Tantalum dust is a black powder and tantalum oxide is a white, microcrystalline powder.
Animal studies by Miller, Davis, Goldman, and Wyatts (1953/Ex. 1-40) have not implicated tantalum as a cause of pnuemoconiosis, although an exposure to 100 mg tantalum oxide produced "soft white circumscribed pigmented dust lesions" in the lungs of these animals (ACGIH 1986/Ex. 1-3, p. 554). Additionally, this particular study demonstrated transient bronchitis, interstitial pneumonitis, and hyperemia at the 100-mg exposure level. Tantalum oxide has been used as a dressing for burns (Olsen 1944/Ex. 1-651), and the use of tantalum gauze in surgical repair produced no long-term adverse effects (Dales and Kyle 1958/Ex. 1-587). No adverse health effects have been associated with industrial exposures to tantalum or its compounds (Cochran, Doull, Mazur, and DuBois 1950/Ex. 1-586). A single oral dose of 6500 mg/kg oxide was virtually nontoxic to rats (ACGIH 1986/Ex. 1-3, p. 554).
OSHA concludes that the existing 5-mg/m3 TWA for these compounds should be retained to protect workers from the respiratory effects of exposure, which constitute material health impairments. The final rule retains the Agency's former PEL of 5 mg/m3 for tantalum (metal dust and oxide).
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