Contaminants: Selenium

Selenium is a naturally occurring substance that is toxic at high concentrations but is also a nutritionally essential element. Hydrogen selenide is the most acutely toxic selenium compound. Acute (short-term) exposure to elemental selenium, hydrogen selenide, and selenium dioxide by inhalation results primarily in respiratory effects, such as irritation of the mucous membranes, pulmonary edema, severe bronchitis, and bronchial pneumonia. Epidemiological studies of humans chronically (long-term) exposed to high levels of selenium in food and water have reported discoloration of the skin, pathological deformation and loss of nails, loss of hair, excessive tooth decay and discoloration, lack of mental alertness, and listlessness.

Epidemiological studies have reported an inverse association between selenium levels in the blood and cancer occurrence and animal studies have reported that selenium supplementation, as sodium selenate, sodium selenite, and organic forms of selenium, results in a reduced incidence of several tumor types. The only selenium compound that has been shown to be carcinogenic in animals is selenium sulfide, which resulted in an increase in liver tumors from oral exposure. EPA has classified elemental selenium as a Group D, not classifiable as to human carcinogenicity, and selenium sulfide as a Group B2, probable human carcinogen.

Human Exposure

Food is the primary source of exposure to selenium, with an estimated selenium intake for the U.S. population ranging from 0.071 to 0.152 milligrams per day (mg/d).⁽¹⁾
Humans are usually exposed to very low levels of selenium in air, with an average selenium concentration estimated to be below 10 nanograms per cubic meter (ng/m3).⁽¹⁾
Drinking water usually contains selenium at very low levels (usually less than 0.01 milligrams per liter [mg/L]). However, occasionally, 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.⁽¹⁾
Occupational exposure to selenium in the air may occur in the metal industries, selenium-recovery processes, painting, and special trades.⁽¹⁾

Assessing Personal Exposure

Selenium can be measured in the blood, urine, and fingernails or toenails of exposed individuals.⁽¹⁾
Get more Information from the ATSDR Web site.

Health Effects

Acute Effects

Acute exposure of humans via inhalation to selenium compounds (selenium dioxide, hydrogen selenide) results primarily in respiratory effects. Acute inhalation exposure to elemental selenium dust results in irritation of the mucous membranes in the nose and throat, producing coughing, nosebleeds, dyspnea, bronchial spasms, bronchitis, and chemical pneumonia.⁽¹⁾
Gastrointestinal effects including vomiting and nausea; cardiovascular effects; neurological effects such as headaches and malaise; and irritation of the eyes were reported in humans acutely exposed to selenium compounds via inhalation.⁽¹⁾
Acute human exposure to selenium compounds via the oral route has resulted in pulmonary edema and lesions of the lung; cardiovascular effects such as tachycardia; gastrointestinal effects including nausea, vomiting, diarrhea, and abdominal pain; effects on the liver; and neurological effects such as aches, irritability, chills, and tremors.^(1,2)
"Blind staggers" disease is a disease in livestock that results from acute consumption of plants high in selenium. It is characterized by impaired vision, aimless wandering behavior, reduced consumption of food and water, and paralysis.^(1,2,4)
Acute animal tests in rats, mice, and guinea pigs, have shown hydrogen selenide to have extreme toxicity from inhalation exposure, sodium selenite to have extreme toxicity from oral exposure, and elemental selenium to have low toxicity from oral exposure.^(1,3)

More Information

References

Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Selenium (Update). Public Health Service, Department of Health and Human Services, Atlanta, GA. 1996.
U.S. Environmental Protection Agency. Final Draft for the Drinking Water Criteria Document for Selenium. Criteria and Standards Division. Office of Drinking Water, Washington, D.C. 1986.
U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.
U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Selenium and Compounds. National Center for Environmental Assessment, Office of Research and Development, Washington, D.C. 1999.

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