Water Quality Standards

Chromium is widely distributed in the earth's crust. It can exist in valences of +2 to +6. Total chromium concentrations in drinking-water are usually less than 2 : g/litre, although concentrations as high as 120 : g/litre have been reported. In general, food appears to be the major source of intake.

The absorption of chromium after oral exposure is relatively low and depends on the oxidation state. Chromium(VI) is more readily absorbed from the gastrointestinal tract than chromium(III) and is able to penetrate cellular membranes. 

There are no adequate toxicity studies available to provide a basis for a NOAEL. In a long-term carcinogenicity study in rats given chromium(III) by the oral route, no increase in tumour incidence was observed. In rats, chromium(VI) is a carcinogen via the inhalation route, although the limited data available do not show evidence for carcinogenicity via the oral route. In epidemiological studies, an association has been found between exposure to chromium(VI) by the inhalation route and lung cancer. IARC has classified chromium(VI) in Group 1 (human carcinogen) and chromium(III) in Group 3.

Chromium(VI) compounds are active in a wide range of in vitro and in vivo genotoxicity tests, whereas chromium(III) compounds are not. The mutagenic activity of chromium(VI) can be decreased or abolished by reducing agents, such as human gastric juice.

In principle, it was considered that different guideline values for chromium(III) and chromium(VI) should be derived. However, current analytical methods favour a guideline value for total chromium. 

Because of the carcinogenicity of chromium(VI) by the inhalation route and its genotoxicity, the current guideline value of 0.05 mg/litre has been questioned, but the available toxicological data do not support the derivation of a new value. As a practical measure, 0.05 mg/litre, which is considered to be unlikely to give rise to significant risks to health, has been retained as the provisional guideline value until additional information becomes available and chromium can be re-evaluated.