Is the selenium drinking water standard justified?
Four cases are presented which suggest that the present U.S.E.P.A. drinking water standard for selenium of 10 micrograms/L in inappropriate. The rationale upon which this standard is based is that selenium is carcinogenic, induces dental caries formation, and is highly toxic to animals. However, a critical assessment of this literature can not support these claims. Case no. 1 demonstrates that there is insufficient evidence to classify selenium as a carcinogen. Data derived from the three respective groups of researchers claiming a carcinogenic effect induced by selenium are obscure due to 1) the inability to accurately identify malignancies, 2) the apparent opposite effects of different selenium compounds, and 3) the lack of proper controls. Case no. 2 reviews recent evidence that selenium reduces the incidence of cancer in laboratory animals and in man, an effect which can probably be attributed to the antioxidant properties of selenium compounds. Case no. 3 provides evidence which does not permit the classification of selenium as a cariogenic element. Epidemiological studies supporting such a claim are inadequate since they lack properly matched control groups. Animal data do not support this link as well. Case no. 4 is a review of studies which clearly demonstrate the essentiality of selenium, an aspect of selenium metabolism that was not considered when the 10 micrograms/L standard was promulgated. In light of the four cases presented and an assessment of selenium toxicity in man, it is concluded that the 10 micrograms/L standard can not be justified. Instead, it is suggested that 50 micrograms/L selenium should provide sufficient protection from the toxic effects of this element. This is consistent with the current state of knowledge with respect to the potential adverse health effects associated with selenium.