selenium

Selenium is a chemical element with atomic number 34, with the chemical symbol Se. Selenium occurs only rarely in the free state in nature. It is a nonmetal that is chemically related to sulfur and tellurium. It is toxic in large amounts, but trace amounts of it, forming the active center of certain enzymes such as glutathione peroxidase(GSH-Px), are necessary for the function of all cells in (probably) all animals. Selenium requirements in plants differ by species, with some plants apparently requiring none.

Isolated selenium occurs in several different forms, but the most stable of these is a dense purplish-gray semimetal (semiconductor) form that is structurally a trigonal polymer chain. It conducts electricity better in the light than in the dark, and is used in photocells (see allotropic section below). Selenium also exists in many nonconductive forms: a black glass-like substance, as well as several red crystalline forms built of eight-membered ring molecules, like its lighter cousin sulfur.

Selenium is found in economic quantities partially replacing sulfur in sulfide ores such as pyrite. Minerals that are selenide or selenate compounds are also known, but all are rare.



The term "selenium" was found in the following pages:

European Commission consults on chemicals legislation outside REACH | EVISA's News
Instrument database: Aurora Instruments Ltd. - LUMINA 3300 Atomic Fluorescence Spectrometer
Material database: The Food and Environment Research Agency (FAPAS) - Test Material T07123 (Infant Formula, Cereal)
Link database: USGS: Statistics and Information: Thallium
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9982 Serum calibrator lyophilised for trace elements
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Clay 1
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-032 - Trace elements in Moroccan phosphate rock
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Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 3
EU approves new selenium compound for use as a nutritional supplement in animals | EVISA's News
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Directory of scientists: Martine Potin-Gautier
Link database: Yeast as a cell factory for organoselenium compounds
Certified reference materials for selenium speciation | EVISA's News
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Material database: IRMM - Institute for Reference Materials and Measurements - ERM-BB422 - Fish muscle
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Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: TCLP Metals - Ash 1
Determination of arsenic species in water by means of capillary electrophoresis coupled to electrospray mass spectrometry | EVISA's News