Selenium & compounds: Health effects
Description
The severity of health effects will depend on how much selenium a person has been exposed to, for how long, the nature of the selenium compound(s), and current state of health. Trace amounts of selenium are essential for humans and most diets usually provide enough selenium to meet the daily requirement. Diets lacking selenium have resulted in heart problems and muscle pain. Diets with too much selenium can be harmful at levels 5 to 10 times higher than the daily requirement. Accidentally swallowing a large quantity of selenium supplement pills could be life-threatening without immediate medical treatment. Eating too much selenium over long periods of time can result in excessive tooth decay, discolouration of the skin and teeth, brittle hair, deformed nails, fatigue, irritability, depression and pallor. Feeling and control in the arms and legs may also be lost. People exposed to very high levels of selenium in the workplace have reported headaches, dizziness, fatigue, irritation (eye, nose, throat and bronchial tubes), collection of fluid in the lungs, and severe bronchitis. The exact levels at which these effects occur are not known. Upon contact with skin, selenium compounds have caused rashes, swelling, and pain. It may also protect against the toxicity of heavy metals such as cadmium, mercury and silver.
More details about two selenium compounds follow.
Selenium sulfide is very different from the selenium compounds found in foods and in the environment. Selenium sulfide has not caused cancer in animals when it is placed on the skin, and the use of anti-dandruff shampoos containing selenium sulfide is considered safe. When ingested it is reasonably anticipated to be a carcinogen.
Selenium hydride is the most acutely toxic selenium compound, resembling arsenic in its physiological reactions. Acute (short term) exposure to selenium hydride by inhalation results primarily in respiratory effects, such as irritation of the mucous membranes, collection of fluid in the lungs, severe bronchitis, and bronchial pneumonia.
Entering the body
Selenium can be inhaled or ingested.
Exposure
Food is the primary source of exposure to selenium. Humans are usually breathing very low levels of selenium in air. Drinking water usually contains selenium at very low levels. Higher levels of selenium may be found in drinking water, usually in areas where high levels of selenium in soil contribute to the selenium content of the water. Occupational exposure to selenium in the air may occur in the metal industries, selenium recovery processes, painting, and special trades. Higher selenium levels may be encountered when living in the vicinity of these industries.
Health guidelines
Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 1996):
Maximum of 0.01 mg/L (i.e. 0.00001 g/L)
Worksafe Australia has set the exposure standard for selenium compounds (excluding selenium hydride) to 0.2 milligram/m3 (TWA, as selenium). The exposure standard for selenium hydride and selenium hexafluoride is 0.05 ppm or 0.16 milligram/m3 (TWA, as selenium). Selenium and selenium compounds are classified as toxic by inhalation and if swallowed.
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