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:

EFSA publishes reference value for manganese | EVISA's News
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-185R - Bovine Liver
Material database: JRC - Joint Research Centre - BCR-397 - Trace elements in human hair
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-638
Link database: Selenium speciation and bioavailability
Link database: USGS: Trace-Elements and Radon in Groundwater Across the United States, 1992-2003
Directory of scientists: Przemyslaw Niedzielski
Material database: National Research Council of Canada (NRC - CNRC) - HISS-1 Marine Sediment Reference Materials for Trace Metals and other Constituents
Workshop des DFG-Graduiertenkollegs 826 über Elementspeziation: Methodenentwicklungen und ihre Anwendungen in den Umwelt- und Lebenswissenschaften | EVISA's Agenda of Events
Material database: National Institute of Standards and Technology (NIST) - SRM 1947 - Lake Michigan Fish Tissue
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-176R - Fly ash
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8881 Blood Serum Control lyophilised, trace elements level II: LOT 544
Material database: National Institute of Standards and Technology (NIST) - SRM 1570a - Trace Elements in Spinach Leaves
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Sand 2
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Clay 2
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sediment 1
Material database: JRC - Joint Research Centre - BCR-288 - Lead with added impurities
Material database: Institute of Nuclear Chemistry and Technology (INCT/ICHTJ) - CTA-OTL-1 ORIENTAL TOBACCO LEAVES
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8841 Whole blood, lyophilized, trace elements level II: LOT 445
Material database: National Institute for Environmental Studies (NIES) - NIES CRM 18: Human Urine