Oxidation of inactive trivalent chromium to the mutagenic hexavalent form

Soluble trivalent chromium compounds (chromium potassium sulfate, chromium nitrate, chromium chloride, neochromium and chromium alum) were inactive for Salmonella typhimurium TA100, even at milligram amounts per plate. No effect could be detected either in the absence or in the presence of rat-liver, lung or muscle microsomal fractions, of rat-muscle mitochondria (with or without ATP), of oxidized glutathione (GSSG), or of human serum, plasma or erythrocyte lysates. Conversely, addition of a strongly oxidizing agent (potassium permanganate) resulted in toxic effects in plates incorporating more than 40--80 microgram of compounds and elicited a dose-effect mutagenic response at 10--40 microgram per plate. These effects could be ascribed to oxidation of chromium from the trivalent to the active hexavalent state. Insoluble chromite, as tested in the spot test, was spontaneously mutagenic, owing to contamination of the industrial product with hexavalent chromium. The results obtained may be useful to interpret the findings of carcinogenicity tests and to predict health hazards linked to chromium.