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:

Decreased risk of colorectal cancer linked with higher selenium status | EVISA's News
Link database: Australian Government: National Pollutant Inventory: Selenium & compounds
Material database: IAEA - MEL International Atomic Energy Agency - IAEA-470 Oyster tissue
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8881 Blood Serum Control lyophilised, trace elements level II: LOT 347
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9943 Whole blood calibrator lyophilised for trace elements
New selenium-containing proteins identified in selenium-rich yeast | EVISA's News
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8881 Blood Serum Control lyophilised, trace elements level II
Link database: National Research Council: Selenium in Nutrition
Material database: National Research Council of Canada (NRC - CNRC) - HISS-1 Marine Sediment Reference Materials for Trace Metals and other Constituents
Material database: National Institute of Standards and Technology (NIST) - SRM 1849a - Infant/Adult Nutritional Formula
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: TCLP Metals - Sandy Loam 6
High Accumulation of Selenium in Wheat Grains | EVISA's News
Material database: American Elements - Selenium 76 Metal Isotope
Material database: National Institute of Standards and Technology (NIST) - SRM 1649a - Urban Dust
Link database: ePlantScience.com: Plant Nutrition » Other Beneficial Elements » Selenium
Link database: USGS: Statistics and Information: Selenium
Material database: National Institute of Standards and Technology (NIST) - SRM 2976 - Mussel Tissue (Trace Elements & Methylmercury) Freeze-dried
Material database: NIES - National Institute for Environmental Studies - CRM 18: Human Urine
Link database: Human Metabolome Database: Tellurium
Selenium species are partly converted during their enzymatic extraction from biological samples with protease XIV | EVISA's News