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:

Material database: ISC Science - IES-Se77 77Se-enriched standard solution
Link database: US EPA: SOP for the determination of As and Se in soils, sediments ans solids by GFAAS
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sediment 1
Link database: ChEBI: L-selenohomocysteine
Experts in Bioimaging came together in Münster, May 24-25, 2018 | EVISA's News
Material database: National Institute of Standards and Technology (NIST) - SRM 1598a - Inorganic Constituents in Animal Serum
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9988 Urine calibrator lyophilised for trace elements: LOT 122
Material database: National Analysis Center for Iron & Steel (NACIS) - NCS ZC73012 - Trace Elements in Cabbage (NIM-GBW10014)
Material database: IAEA - MEL International Atomic Energy Agency - IAEA-436 Trace Elements and Methylmercury in Tuna Fish Tissue Homogenate
Material database: National Institute of Standards and Technology (NIST) - SRM 2976
Material database: The Food and Environment Research Agency (FAPAS) - Test Material T07138 (Milk Powder)
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 3
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Sand 3
Link database: Selenium and its Relationship to Cancer
Atomic Fluorescence Spectrometry as a Detection System for Speciation Analysis | EVISA's News
Link database: US EPA: Aquatic Life Criteria for Silver
Material database: National Institute of Standards and Technology (NIST) - SRM 1567a - Wheat Flour
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9988 Urine calibrator lyophilised for trace elements: LOT 432
Link database: The Globe and Mail:
Material database: National Institute for Environmental Studies (NIES) - NIES CRM 27: Typical Japanese Diet