INTERACTION OF ZINC AND CADMIUM AND TOXICITY SULFIDE ACTIVATORS
INTERACTION OF ZINC AND CADMIUM
ZINC IS AN ESSENTIAL nutrient and is toxic only at very high doses. Therefore, the subcommittee focused its review of the potential toxicity of ZnCdS on its most toxic component, cadmium, and examined the effect of zinc only in regard to its potential interactions with cadmium.
There are only two studies in the literature that investigated the toxic interaction of zinc and cadmium by the inhalation route. In rats exposed to cadmium chloride by inhalation, simultaneous exposure to zinc oxide prevents fatalities (Oldiges and Glaser, 1986) and lung cancer (Oldiges et al., 1989). The subcommittee believes that the results of these studies are not relevant to zinc cadmium sulfide exposures for two reasons. First, ZnCdS is a sintered compound. The sintered compound reportedly does not contain free zinc sulfide or cadmium sulfide, because the sintering process is highly efficient. Second, in the unlikely event that ZnCdS breaks down into its components, the exposure would be to such small amounts of the components, a biological response is unlikely.
TOXICITY OF COPPER AND SILVER
Copper or silver was added to ZnCdS as an activator at concentrations of less than 100 parts per million (ppm).
Copper is an essential nutrient that is incorporated into numerous enzymes; the National Research Council's recommended dietary allowance (RDA) for copper is 2-3 mg/d (NRC 1980). Because the ZnCdS formulation contained copper at less than 100 ppm (Sheila Fabiano, USR Optronix, personal commun., 1995), doses of copper much lower than the RDA would have been associated with exposure to ZnCdS. Therefore, the subcommittee concluded that copper toxicity from the Army's tests should not be a concern.
Silver is only toxic at high levels. The Occupational Safety and Health Administration permissible exposure level (PEL) for silver is 0.01 mg/m3 (OSHA 1989). Because the ZnCdS formulation contained silver at less than 100 ppm (Sheila Fabiano, USR Optronix, personal commun., 1995), the subcommittee concluded that doses of silver associated with exposure to ZnCdS would have been too low to warrant concern.
NRC (National Research Council). 1980. Recommended Dietary Allowances. 9th Rev. Ed. Washington, D.C.: National Academy Press. 185 pp.
Oldiges, H., and U. Glaser. 1986. The inhalative toxicity of different cadmium compounds in rats. Trace Elem. Med. 3:72-75.
Oldiges, H., D. Hochrainer, and U. Glaser. 1989. Long-term inhalation study with Wistar rats and four cadmium compounds. Toxicol. Environ. Chem. 19:217-222.
OSHA (Occupational Safety and Health Administration). 1989. Air Contaminants. Final Rule 29 CFR. Fed. Regist. 54(12):2332-2983.