What is selenium?

  • (noun): A toxic nonmetallic element related to sulfur and tellurium; occurs in several allotropic forms; a stable gray metallike allotrope conducts electricity better in the light than in the dark and is used in photocells; occurs in sulfide ores (as pyrite).
    Synonyms: Se, atomic number 34


Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between those of its periodic table column-adjacent chalcogen elements sulfur and tellurium. It rarely occurs in its elemental state in nature, or as pure ore compounds. Selenium (Greek σελήνη selene meaning "Moon") was discovered in 1817 by Jöns Jakob Berzelius, who noted the similarity of the new element to the previously-known tellurium (named for the Earth).

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Some articles on selenium:

Selenium Sulfide
... Selenium sulfide can refer to either of the following Selenium disulfide, SeS2 Selenium hexasulfide, Se2S6 This set index page lists chemical compounds ...
Selenium - Biological Role - Controversial Health Effects
... A number of correlative epidemiological studies have implicated selenium deficiency (as measured by blood levels) in a number of serious or chronic diseases, such as cancer, diabetes ... In addition, selenium supplementation has been found to a chemopreventive for some types of cancer in some types of rodents ... blinded, controlled prospective trials in humans, selenium supplementation has not succeeded in reducing the incidence of any disease, nor has a meta-analysis of such selenium supplementation studies ...
Selenium Deficiency in Animals
... adjacent Canada, and the southeastern US), selenium deficiency in some animal species is common unless supplementation is carried out ... Selenium deficiency is responsible (either alone or together with vitamin E deficiency) for many of the cases of WMD ("white muscle disease"), evidenced at slaughter or during necropsy ... In general, absorption of dietary selenium is lower in ruminants than in non-ruminants, and is lower from forages than from grain ...
Lehigh Permanente Quarry - Pollution - Selenium Discharges Into Permanente Creek
... Selenium pollution in the creek downstream from the quarry ranged from 13 to 81 micrograms/liter (μg/L) ... A North Quarry water sample in January 2010 had a dissolved selenium concentration of 82 μg/L, indicating that the quarry is the source of the ... Selenium is bioaccumulated in the aquatic food web ...
Selenium Rectifier - Properties
... A selenium rectifier is about the same size as copper oxide rectifiers, but much larger than a silicon or germanium diode ... Selenium rectifiers have a long but not indefinite service life of 60,000 to 100,000 hours depending on rating and cooling ... Selenium rectifiers have an operating temperature limit of 130 C, and are not suitable for high-frequency circuits ...