The carcinogenicity of chromium

The carcinogenicity of chromium compounds is reviewed with specific attention to the gaps in knowledge for risk estimation and research needs. The most important problems at present are whether trivalent chromium compounds cause cancer, and whether there is a difference in cancer causing effects between the soluble and the slightly soluble hexavalent compounds in the practical exposure situation. Dose estimates for risk estimation based on epidemiological investigations are also lacking. Present evidence indicates that the trivalent chromium compounds do not cause cancer although high concentrations in some in vitro systems have shown genetic toxicity. Hexavalent chromium compounds cause cancer in humans, in experimental animals and exert genetic toxicity in bacteria and in mammalian cells in vitro. Epidemiological evidence and animal experiments indicate that the slightly soluble hexavalent salts are the most potent carcinogens, but proper identification and characterization of exposure patterns in epidemiological work are lacking. Workers also tend to have mixed exposures. Soluble and slightly soluble salts are equally potent genotoxic agents in vitro. Further work for establishing dose estimates for risk evaluation in epidemiological work is important. In vitro systems should be applied for further identification of the mechanism of the carcinogenic effects, and animal experiments are urgent for comparison of the carcinogenic potency of the different hexavalent salts. Hexavalent chromium salts must be regarded as established carcinogens, and proper action should be taken in all industries with regard to such exposure. At present the carcinogenic risk to the general population caused by chromium compounds seems to be negligible, chromium in cigarettes, however, is an uncertainty in this respect. The amount of chromium and the type of chromium compounds inhaled from cigarettes is not known.