An element with the atomic symbol Se, atomic number 34, and atomic weight 78.96. It is an essential micronutrient for mammals and other animals but is toxic in large amounts. Selenium protects intracellular structures against oxidative damage. It is an essential component of GLUTATHIONE PEROXIDASE. Essential dietary component Although it is toxic in large doses, selenium is an essential micronutrient for animals.


Selenium is a nonmetal element with the atomic number 34 and the chemical symbol Se. Isolated selenium occurs in several different forms, the most stable of which is a dense purplish-gray semiconductor form. Selenium rarely occurs in its elemental state in nature and is usually found in sulfide ores such as pyrite, partially replacing the sulfur in the ore matrix. It may also be found in silver, copper, lead, and nickel minerals. Selenium is mainly used in the electronics industry, in glassmaking, and in chemicals and pigments. Though selenium salts are toxic in large amounts, trace amounts of the element are necessary for cellular function in most animals, forming the active center of the enzymes glutathione peroxidase, thioredoxin reductase, and three known deiodinase enzymes. (L620)

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