An Evaluation of Potential Interactions of Zinc and Cadmium at a Former Zinc Smelter Site. C. G. Evans, R. A. Schoof and L. Keill, PTI Environmental Services, 15375 S. E. 30th Place, Suite 250, Bellevue, WA 98007; and Washington Department of Ecology, Olympia, WA.
Extensive literature is available regarding the protective (or antagonistic) effects of zinc on cadmium toxicity. Simultaneous administration of zinc with cadmium has been found to protect against several aspects of cadmium toxicity, including proteinuria, the critical effect used as the basis for the cadmium oral reference doses (RfDs). The potential for interactions between cadmium and zinc is of particular significance at sites where increased environmental concentrations of zinc are found in conjunction with increased concentrations of cadmium. However, these potential interactions must be evaluated in comparison with interactions that might have occurred in studies used to derive the cadmium RfD. Estimates of cadmium and zinc intake from a former zinc smelter site were compared with doses and ratios of the metals used in studies on toxicological interactions among cadmium and zinc, and with exposures of the populations from which the cadmium oral RfDs are derived. Animal studies provide strong evidence that potential antagonistic interactions between zinc and cadmium at the site may protect against the toxic effects of cadmium. However, available data from studies on various human populations supporting the derivation of the cadmium RfDs appear insufficient to determine the extent to which antagonism of cadmium toxicity by zinc may have occurred in these populations. Consequently, it was concluded that although zinc exposures at the site may be protective of potential cadmium toxicity, there are currently insufficient data to support any quantitative change in the assessment of cadmium toxicity at the site.