Page 12: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Selenium

Part II. Science and Technical Considerations (continued)

11.0 Rationale

Selenium is an essential nutrient that is naturally occurring and found mostly in the Earth's crust. The main sources of selenium in the environment include coal-fired power plants and mining and refining of metals. Selenium is used in a wide range of industries to produce glass and electronic materials and to replace lead in plumbing. Canadians are mainly exposed to selenium through the consumption of food and nutritional supplements. Other organizations, such as the Institute of Medicine, have established daily recommended intakes for selenium, but selenium deficiency is not considered to be a concern in Canada. Exposure data do not indicate significant levels of selenium in Canadian drinking water supplies.

The International Agency for Research on Cancer has determined that selenium is not classifiable as to its carcinogenicity to humans. A protective effect against cancer has even been suggested. Selenium toxicity or selenosis can occur at exposure levels much higher than the recommended daily intake. The maximum acceptable concentration (MAC) for selenium in drinking water is based on chronic selenosis symptoms, such as hair loss, nail anomalies or loss, skin anomalies and garlic odour of the breath. These symptoms have been observed in adults, and there is no evidence of an increased sensitivity to selenium toxicity in any other subgroup of the population.

A MAC of 0.05 mg/L (50 µg/L) is established for total selenium in drinking water. This MAC is achievable by available treatment technology and measurable by available analytical methods. As part of its ongoing guideline review process, Health Canada will continue to monitor new research in this area and recommend any change to the guideline that it deems necessary.

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