Chronic toxicity studies. II. Hexavalent and trivalent chromium administered in drinking water to rats.

Acute toxicity of chromium by topical exposure or inhalation resulting in ulcerlike lesions has been recognized as an industrial hazard for many years. 1 Prolonged exposure to chromate mists has been suggested as contributing to the high incidence of lung cancer in certain industries.2•3 Acute poisoning by ingestion is.. well documented.4·5 Animal studies haYe also been made to determine symptoms of acute toxicity.6 However, few investigations have been made on chronic toxicity of ingested chromium. The longest previous study involved periods of two to three months in which 134 parts per million (ppm) or more was shown to produce toxic symptoms in rats. 7 Extensive industrial use of chromium and disposal of chromium wastes ha \·e resulted in contamination of many water supplies in the united States. In one sun·ey, the chromium content of 24 municipal water supplies ranged from 0.001-0.04 ppm, and well waters have been reported to contain up to 25 ppm of chrumium.9 At present the maximum allowable chromate