Toxicity and carcinogenicity of chromium compounds in humans.

Chromium is a human carcinogen primarily by inhalation exposure in occupational settings. Although lung cancer has been established as a consequence of hexavalent chromium exposure in smokers and nonsmokers, some cancers of other tissues of the gastrointestinal and central nervous systems have also been noted. Except for a few reports from China, little is known about the health risks of environmental exposures to chromium. Likewise, there has been a lack of epidemiological studies of human exposure to hexavalent Cr by drinking water or ingestion, and it has been suggested that humans can perhaps tolerate hexavalent Cr at higher levels than the current drinking water standard of 50 ppb. This review highlights the most recent data on the induction of skin tumors in mice by chronic drinking-water exposure to hexavalent chromium in combination with solar ultraviolet light. This experimental system represents an important new animal model for chromate-induced cancers by ingestion of drinking water, and it suggests by extrapolation that chromate can likely be considered a human carcinogen by ingestion as well. The potential use of this animal model for future risk assessment is discussed.