Water Quality Standards

Cadmium metal is used in the steel industry and in plastics. Cadmium compounds are widely used in batteries. Cadmium is released to the environment in wastewater, and diffuse pollution is caused by contamination from fertilizers and local air pollution. Contamination in drinking-water may also be caused by impurities in the zinc of galvanized pipes and solders and some metal fittings, although levels in drinking-water are usually less than 1 µg/litre. Food is the main source of daily exposure to cadmium. The daily oral intake is 10-35 µg. Smoking is a significant additional source of cadmium exposure.

Absorption of cadmium compounds is dependent on the solubility of the compounds. Cadmium accumulates primarily in the kidneys and has a long biological half-life in humans of 10-35 years.

There is evidence that cadmium is carcinogenic by the inhalation route, and IARC has classified cadmium and cadmium compounds in Group 2A. However, there is no evidence of carcinogenicity by the oral route, and no clear evidence for the genotoxicity of cadmium.

The kidney is the main target organ for cadmium toxicity. The critical cadmium concentration in the renal cortex that would produce a 10% prevalence of low-molecular-weight proteinuria in the general population is about 200 mg/kg, and would be reached after a daily dietary intake of about 175 µg per person for 50 years.

Assuming an absorption rate for dietary cadmium of 5% and a daily excretion rate of 0.005% of body burden, JECFA concluded that, if levels of cadmium in the renal cortex are not to exceed 50 mg/kg, the total intake of cadmium should not exceed 1 µg/kg of body weight per day. The provisional tolerable weekly intake (PTWI) was therefore set at 7 µg/kg of body weight. It is recognized that the margin between the PTWI and the actual weekly intake of cadmium by the general population is small, less than 10-fold, and that this margin may be even smaller in smokers. A guideline value for cadmium of 0.003 mg/litre is established based on an allocation of 10% of the PTWI to drinking-water.