Exposure-risk relationship for selenium

Status:

completed 01/2013

Aims:

Selenium is a vital trace element that must be absorbed regularly through the diet. Selenium deficiency is associated with a range of health disorders such as susceptibility to infection and cardiovascular diseases. The substance is therefore believed to have a protective action for human health. Studies exist which indicate that an adequate dietary intake of selenium provides protection against tumours of the gastrointestinal and respiratory tracts in humans.

In industry, exposure to selenium may occur in the manufacture of copper, pigments, plastics, electronic equipment and other products, and during the combustion of coal. The primary intake route for selenium in an occupational context is via the respiratory tract.

Certain selenium compounds, particularly selenium sulphide, have been seen to have a toxic action in tests on animals. The carcinogenic potential of selenium is however disputed, since the data are insufficient to permit valid conclusions. Evaluations made to date are based upon animal tests performed with selenium sulphide and sodium selenate. Only at higher doses have these substances been shown to exhibit carcinogenic potential, however.

The objective of the present project was to document the status quo on the health effects of selenium and its compounds. The project was to ascertain whether an exposure-risk relationship for selenium could be determined.

Activities/Methods:

Comprehensive surveys of the international literature were conducted in order to identify toxicological and epidemiological studies into the toxicity and carcinogenicity of selenium and its compounds. The study results and the findings from existing reviews were summarized and examined for their suitability as a basis for formulation of an exposure-risk relationship.

The project was co-ordinated by the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA), conducted by ENVIRON (a commercial company), and supervised by a working group composed of experts.

Results:

The epidemiological studies contain indications that organic selenium compounds have an effect of protecting against the risk of various forms of cancer, particularly among men. Evidence of an increase in the cancer risk was not found. The results of the epidemiological studies are frequently based upon the intake of selenium as a food supplement in the USA. Owing to the diverse nature of the data, the conclusions are not validated.

Many toxicological studies show evidence of an elevated risk of liver cancer when high doses of selenium sulphide are administered orally. Only studies of unsatisfactory quality are available concerning the inhalation of selenium, however. In certain concentration ranges, some toxicological studies also describe a protective effect against cancer. This effect is however not confirmed by other studies and therefore continues to be controversial.

In-vitro studies show selenium and its inorganic compounds to have certain genotoxic effects, particularly at high concentrations. The diabetes II end point was also considered in the interpretations, as it is described in numerous studies. The study results are contradictory; a causal relationship between selenium and diabetes II cannot therefore be confirmed.

Overall, although data are available concerning the risk presented by selenium for the endpoints of cancer and diabetes, the quality of the available studies is not sufficient for deduction of an exposure-risk relationship. A point of departure (POD) could not be determined for selenium.

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