Selenium

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).

Selenium is found impurely in metal sulfide ores, where it partially replaces the sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores, most often during copper production. Minerals that are pure selenide or selenate compounds are known, but are rare. The chief commercial uses for selenium today are in glassmaking and in pigments. Selenium is a semiconductor and is used in photocells. Uses in electronics, once important, have been mostly supplanted by silicon semiconductor devices. Selenium continues to be used in a few types of DC power surge protectors and one type of fluorescent quantum dot.

Selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms, including all animals. Selenium is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants). It is also found in three deiodinase enzymes, which convert one thyroid hormone to another. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts, and others apparently requiring none.

Read more about Selenium:  Chemical Compounds, History, Occurrence, Production, Biological Role

Other articles related to "selenium":

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 ...
Selenium Deficiency in Animals
... much of the northeastern and northwestern US and adjacent Canada, and the southeastern US), selenium deficiency in some animal species is common unless supplementation ... 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 ... In general, absorption of dietary selenium is lower in ruminants than in non-ruminants, and is lower from forages than from grain ...
Selenium Sulfide
... Selenium sulfide can refer to either of the following Selenium disulfide, SeS2 Selenium hexasulfide, Se2S6 This set index page lists chemical compounds articles associated with the same name ...
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 pollution ... Selenium is bioaccumulated in the aquatic food web ...
Selenium - Biological Role - Controversial Health Effects
... epidemiological studies have implicated selenium deficiency (as measured by blood levels) in a number of serious or chronic diseases, such as cancer, diabetes, HIV/AIDS, and tuberculosis ... In addition, selenium supplementation has been found to a chemopreventive for some types of cancer in some types of rodents ... However, in randomized, blinded, controlled prospective trials in humans, selenium supplementation has not succeeded in reducing the incidence of any disease, nor has a meta-analysis ...