Scientific basis for an occupational standard for cadmium.

The U.S. Occupational Safety and Health Administration (OSHA) has proposed a revised 8-hour permissible exposure limit (PEL) for cadmium in air of either 1 or 5 micrograms/m3, based upon the prevention of lung cancer and kidney dysfunction. To evaluate the scientific basis for these alternative standards, we compare the OSHA estimates of risk, derived from mathematical modelling of selected studies, to empirical data on lung cancer and kidney dysfunction in the published literature. At least seven epidemiologic studies examine renal tubular proteinuria by cumulative cadmium exposure. Three suggest increased proteinuria at cumulative exposures below 500 micrograms/m3-year (equivalent to a PEL of 11.1 micrograms/m3 over 45 working years). One shows prevalence increasing at cumulative exposures between 100 and 299 micrograms/m3 (equivalent to a PEL between 2.2 and 6.6 micrograms/m3). Insufficient data exist to estimate a no-effect level for kidney toxicity. For lung cancer, qualitative evidence of carcinogenicity in humans is seen in four of five occupational cohorts. Quantitative estimates of risk based on epidemiologic data provide lower and more plausible estimates of lifetime risk than do estimates from a rodent bioassay. The data overall suggest that the PEL for cadmium should not exceed 5 micrograms/m3 to protect workers from kidney dysfunction and lung cancer over a working lifetime.