Selenide

Chronic oral exposure to high concentrations of selenium compounds can produce a disease called selenosis. The major signs of selenosis are hair loss, nail brittleness, and neurological abnormalities (such as numbness and other odd sensations in the extremities). Animal studies have shown that selenium may also affect sperm production and the female reproductive cycle. (L619)

Selenium readily substitutes for sulfur in biomolecules and in many biochemical reactions, especially when the concentration of selenium is high and the concentration of sulfur is low. Inactivation of the sulfhydryl enzymes necessary for oxidative reactions in cellular respiration, through effects on mitochondrial and microsomal electron transport, might contribute to acute selenium toxicity. Selenomethionine (a common organic selenium compound) also appears to randomly substitute for methionine in protein synthesis. This substitution may affect the structure and functionability of the protein, for example, by altering disulfide bridges. Inorganic forms of selenium appear to react with tissue thiols by redox catalysis, resulting in formation of reactive oxygen species and causing damage by oxidative stress. (L619)

Short-term oral exposure to high concentrations of selenium may cause nausea, vomiting, and diarrhea. Brief exposures to high levels of elemental selenium or selenium dioxide in air can result in respiratory tract irritation, bronchitis, difficulty breathing, and stomach pains. Longer-term exposure to either of these air-borne forms can cause respiratory irritation, bronchial spasms, and coughing. (L619)

Selenium may be absorbed through inhalation and ingestion, while some selenium compounds may also be absorbed dermally. Once in the body, selenium is distributed mainly to the liver and kidney. Selenium is an essential micronutrient and is a component of glutathione peroxidase, iodothyronine 5'-deiodinases, and thioredoxin reductase. Organic selenium is first metabolized into inorganic selenium. Inorganic selenium is reduced stepwise to the intermediate hydrogen selenide, which is either incorporated into selenoproteins after being transformed to selenophosphate and selenocysteinyl tRNA or excreted into the urine after being transformed into methylated metabolites of selenide. Elemental selenium is also methylated before excretion. Selenium is primarily eliminated in the urine and feces, but certain selenium compounds may also be exhaled. (L619)

Most processed selenium is used in the electronics industry, but it is also used as a nutritional supplement, in the glass industry, in the preparation of pharmaceuticals, as a nutritional feed additive for poultry and livestock, in pesticide formulations, in rubber production, as an ingredient in antidandruff shampoos, and as a constituent of fungicides. It may also be found in pigments in plastics, paints, enamels, inks, and rubber. (L619)