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
Link database: US EPA: Aquatic Life Criteria for Silver
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-279 Sea lettuce
Material database: National Institute of Standards and Technology (NIST) - SRM 1632b - Trace Elements in Coal (Bituminous)
Material database: National Research Council of Canada (NRC - CNRC) - SELM-1 Selenium enriched yeast certified reference material
Toenail clippings reveal arsenic exposure | EVISA's News
EFSA publishes reference value for manganese | EVISA's News
Material database: National Institute of Standards and Technology (NIST) - SRM 1598a - Inorganic Constituents in Animal Serum
Material database: Institute of Nuclear Chemistry and Technology (INCT/ICHTJ) - CTA-OTL-1 ORIENTAL TOBACCO LEAVES
Directory of scientists: Kevin Kubachka
Material database: The Food and Environment Research Agency (FAPAS) - Test Material T1094 (Dairy Ration)
High Accumulation of Selenium in Wheat Grains | EVISA's News
Material database: JRC - Joint Research Centre - BCR-279 Sea lettuce
Material database: American Elements - Selenium 77 Metal Isotope
Link database: Speciation, bioavailability and antigenotoxicity of Selenium species present in Selenium enriched natural products.
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-063R Skim milk powder (natural)
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals/Cyan - Loam 5
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Fresh Water Sediment 3
Material database: JRC - Joint Research Centre - ERM-DB001: Trace Elements in Human Hair
Determination of arsenic species in water by means of capillary electrophoresis coupled to electrospray mass spectrometry | EVISA's News