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).