Selenium
(endorsed 1996)
Guideline
Based on health considerations, the concentration of selenium in drinking water should not exceed 0.01 mg/L.
General description
Selenium and selenium salts are widespread in the environment. Selenium is released from natural and human-made sources, with the main source being the burning of coal. Selenium is also a by-product of the processing of sulfide ores, chiefly in the copper refining industry.
The major use of selenium is in the manufacture of electronic components. It is used in several other industries, and selenium compounds are used in some insecticides, in hair shampoos as an anti-dandruff agent, and as a nutritional feed additive for poultry and livestock.
Selenium concentrations in source waters are generally very low and depend on local geochemistry, pH and the presence of iron salts. Concentrations in drinking water supplies overseas are generally below 0.01 mg/L but groundwater concentrations as high as 6 mg/L have been reported in the United States.
Food is the major source of intake for Australians. Cereal and grain products contribute most to intake, while fish and liver contain the highest selenium concentrations. Average daily intakes for Australian adults are between 0.06 mg and 0.13 mg.
Typical values in Australian drinking water
In major Australian reticulated supplies, selenium concentrations are less than 0.005 mg/L. Selenium concentrations in groundwater are not a problem in Australia, as they are in some overseas supplies.
Treatment of drinking water
Selenium concentrations in drinking water can be reduced by coagulation with ferric chloride and by lime softening. Coagulation with alum is much less effective. Activated alumina absorption is the most effective means of treatment, but only at low pH.
Measurement
The selenium concentration in drinking water can be determined by hydride generation followed by atomic absorption spectroscopy (APHA Method 3500-Se Part C 1992). The limit of determination is 0.001 mg/L.
Health considerations
Selenium is an essential element for many species, including humans. Signs of selenium deficiency in humans are not well established but may include a chronic disorder of the heart muscle, other heart diseases and cancer. The Australian recommended dietary intake to maintain health is approximately 0.001 mg/kg body weight per day.
Most water-soluble selenium compounds are effectively absorbed by the gastrointestinal tract. Selenium is then distributed to most organs, with highest concentrations found in the kidney, liver and spleen.
The toxicity of selenium varies considerably among the different selenium compounds. Selenite and selenate are much more toxic than selenium sulfide.
An extensive review and summary of the human and animal toxicity data for selenium is available (IPCS 1987).
There have been a number of reports of ill effects attributed to short- and long-term exposure to selenium; most of these have resulted from occupational exposure or accidental poisoning; acute or chronic nutritional toxicity is comparatively rare. Intakes above about 1 mg/day over prolonged periods may produce nail deformities characteristic of selenosis. Other features of excess selenium intake include nonspecific symptoms such as gastrointestinal disturbances, dermatitis, dizziness, lassitude and a garlic odour to the breath.
A 2-year study on 140 people with an average selenium intake of 0.24 mg/day reported no effect associated with the level of selenium intake.
Domestic animals developed a symptom known as ‘blind staggers’ when fed plants that had accumulated selenium. The animals had impaired vision, depressed appetite and a tendency to wander in circles. This led to paralysis and death from respiratory failure.
Except for selenium sulfide, experiments with laboratory animals indicate that selenium compounds are not carcinogenic, with some selenium compounds displaying an anticarcinogenic effect. Results for selenium sulfide indicate that it causes liver and skin tumours in mice.
Tests for mutagenic activity using bacteria have reported both positive and negative results. Studies indicate that selenite can cause chromosome damage to mammalian cells.
The International Agency for Research on Cancer has concluded that selenium is not classifiable as to its carcinogenicity in humans (Group 3, inadequate evidence in humans and in animals) (IARC 1987).
Derivation of guideline
The guideline value for selenium in drinking water was derived as follows:
where:
0.24 mg per day is the acceptable daily intake (Longnecker et al. 1991).
0.1 is the proportion of daily intake attributable to the consumption of water.
2 L/day is the average amount of water consumed by an adult.
References
APHA Method 3500-Se Part C (1992). Selenium: Continuous hydride generation/Atomic Absorption Spectrometric method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.
IARC (International Agency for Research on Cancer) (1987). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Overall Evaluations of Carcinogenicity. An updating of IARC monographs volumes 1 to 42. World Health Organization, IARC, Supplement 7.
IPCS (International Programme on Chemical Safety) (1987). Selenium. Environmental Health Criteria, 58. World Health Organization, IPCS.
Longnecker MP, Taylor PR, Levander OA, Howe M, Veillon C, McAdam PA, Patterson KY, Holden JM, Stampfer MJ, Morris JS, Willet WC (1991). Selenium in diet, blood, and toenails in relation to human health in a seleniferous area. American Journal of Clinical Nutrition, 53:1288–94.
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