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:

Company database: PS Analytical
Material database: LGC Ltd. - ERM-DA120a - Human serum
Link database: Selenium and Vitamin E Cancer Prevention Trial
Improving the Determination of Toxic Metal Species in Drugs | EVISA's News
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Clay 2
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-288 - Lead
Instrument database: Analytik Jena AG - HydrEA
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 6
Brain Benefits of Aerobic Exercise Lost to Mercury Exposure | EVISA's News
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 2
Link database: EFSA: L-selenomethionine as a source of selenium added for nutritional purposes to food supplements
Link database: Hazardous Substances Data Bank: Hydrogenselenide
New selenium metabolites found in human serum | EVISA's News
New reference materials for the characterisation of selenium-enriched food products | EVISA's News
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8848 Urine Control lyophilised / trace elements level II
Experts in Speciation Analysis came together in Münster, September 4-7, 2007: Part 3 | EVISA's News
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-288 - Lead with added impurities
Material database: ISC Science - IES-Se77 77Se-enriched standard solution
Link database: Metal Speciation Toxicokinetics Database: Selenium
Material database: National Institute of Standards and Technology (NIST) - SRM 1548a - Typical Diet