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: National Institute of Standards and Technology (NIST) - SRM 2974
Material database: National Institute of Standards and Technology (NIST) - SRM 1546a - Meat Homogenate
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sewage Amended Soil
Instrument database: Analytik Jena GmbH - novAA 800 - Atomic Absorption Spectrometer
Selenium species are partly converted during their enzymatic extraction from biological samples with protease XIV | EVISA's News
Does Selenium Prevent Cancer? It May Depend on Which Form People Take | EVISA's News
Material database: National Research Council of Canada (NRC - CNRC) - SELM-1 Selenium enriched yeast certified reference material
Selenomethionine shows promising results as a protective agent against Esophageal Cancer | EVISA's News
Directory of scientists: Kevin A. Francesconi
Material database: National Metrology Institute of Japan (NMIJ) - NMIJ CRM 7302-a: Trace Elements in Marine Sediment
Material database: Sigma-Aldrich - Matrix CRM - Water Pollution: Trace Metals 1-WP
New certified reference materials for the quality control of arsenic speciation in food products and biota | EVISA's News
Material database: National Institute of Standards and Technology (NIST) - SRM 1974b - Organics in Mussel Tissue (Mytilus edulis)
Material database: IAEA - MEL International Atomic Energy Agency - IAEA-407 Trace elements and methylmercury in fish tissue
High Accumulation of Selenium in Wheat Grains | EVISA's News
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: TCLP Metals - Loam 1
Selenium May Play a More Important Role in Microbes Than Previously Thought | EVISA's News
X ISTERH 2013: International Society of Trace Element Research in Humans | EVISA's Agenda of Events
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9982 Serum calibrator lyophilised for trace elements: LOT 538
Link database: Selenium in Food