Trivalent chromium (Cr[III]) is the most common natural state of chromium and is essential in man and animals for efficient lipid, glucose, and protein metabolism. Chromium(III) is considered non-toxic; however, if present in raw water, it is oxidized to hexavalent chromium (Cr[(VI]) during chlorination. Chromium(VI) is not considered an essential nutrient, and known harmful effects of chromium in man are attributed primarily to this form.
Knowledge of the toxic effects of hexavalent chromium is derived almost entirely from occupational exposures, with the main effects being observed on the skin and respiratory tract. At the present maximum acceptable concentration in drinking water (0.05 mg/L), hexavalent chromium has not had any known harmful effects on the health of man or animals. Data available are insufficient to determine whether higher concentrations would be equally safe.
The maximum acceptable concentration for chromium in drinking water is therefore 0.05 mg/L. Available survey data indicate that concentrations of total chromium in drinking water are low, averaging 0.0023 mg/L. Although chromium salts impart odour and taste to water, the concentration at which this occurs, 1.5 mg/L, is considerably higher than the maximum acceptable concentration.
