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ZIRCONIUM COMPOUNDS
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: 7440-67-7; Chemical Formula: Zr
The former OSHA limit for zirconium compounds was an 8-hour TWA of 5 mg/m3, measured as zirconium. The ACGIH has established a TLV-TWA of 5 mg/m3, supplemented by a 10 mg/m3 STEL, (as Zr). The proposal retained the 8-hour TWA but added a STEL of 10 mg/m3; these limits are promulgated by the final rule. Zirconium compounds may be either bluish-black powders or grayish-white lustrous metals.
The toxic effects of inhalation exposures to zirconium compounds include the formation of granulomas, both in the lungs and on the skin. Sax (Dangerous Properties of Industrial Materials, 6th ed., 1984) reports cases of pulmonary granulomas in workers exposed to zirconium aerosols. In laboratory animals, oral toxicity is low (NIOSH 1972b, as cited in ACGIH 1986/Ex. 1-3, p. 647), and inhalation studies conducted for one year at levels of 3.5 mg zirconium/m3 dust and mist resulted in limited toxicity (Stokinger 1981c/Ex. 1-1134).
NIOSH (Ex. 8-47) recommended that zirconium tetrachloride should not be included among the compounds for which the proposed zirconium PEL is applied. NIOSH cites an animal study by Spiegl et al. (1956, as cited in ACGIH 1986/Ex. 1-3, p. 647), in which a 60-day exposure to zirconium tetrachloride at a concentration of 6 mg/m3 (six hours/day, five days/week) resulted in increased mortality in rats and guinea pigs and a decrease “of borderline significance” in blood hemoglobin and red blood cell levels in dogs. Given that the observed effect level for mortality of 6 mg/m3 is close to the proposed 5 mg/m3 limit, NIOSH (Ex. 8-47) stated that a separate PEL should be considered for zirconium tetrachloride.
At this time, OSHA is establishing the PELs as proposed for all zirconium compounds, including zirconium tetrachloride. There are no reports, other than the one cited by NIOSH, that indicate that exposure to zirconium compounds causes severe toxicity at levels near the proposed 5 mg/m3 TWA PEL; in addition, the toxic reaction of dogs exposed to 6 mg/m3 was of borderline significance.
OSHA concludes that the 5 mg/m3 TWA and 10 mg/m3 STEL limits for the zirconium compounds, measured as zirconium, will protect workers from the significant risk of pulmonary effects potentially associated with the short-term exposures permitted by the 8-hour TWA alone. The Agency has determined that these effects constitute material health impairments.