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:

Link database: Selenium and its Relationship to Cancer
Natural wetlands contribute significantly to elemental cycling by volatilization | EVISA's News
Material database: SUPELCO by Sigma-Aldrich - Se-(Methyl)selenocysteine Hydrochloride
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Sand 10
Instrument database: PS Analytical - 10.055 Millennium Excalibur
ICP-OES sensitivity for silicon depends on silicon-species | EVISA's News
Material database: Canadian Certified Reference Materials Project (CCRMP) - CH-4 Gold Ore Certified Reference Material
Material database: Food Analysis Performance Assessment Scheme (FAPAS) - Test Material T07123 (Infant Formula, Cereal)
Material database: National Institute of Standards and Technology (NIST) - SRM 1849a - Infant/Adult Nutritional Formula
Material database: National Institute of Standards and Technology (NIST) - SRM 1646a - Estuarine Sediment
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: TCLP Metals - Loamy Sand 3
Material database: National Metrology Institute of Japan (NMIJ) - NMIJ CRM 7303-a: Trace Elements in Lake Sediment
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-638
Material database: IAEA - MEL International Atomic Energy Agency - IAEA-436 Trace Elements and Methylmercury in Tuna Fish Tissue Homogenate
Material database: LGC Ltd. - LGC7330 - Selenomethionine enriched with 76Se
Mercury and Autism: Is there a Link ? | EVISA's News
Link database: USGS: Trace-Elements and Radon in Groundwater Across the United States, 1992-2003
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-032 - Trace elements in Moroccan phosphate rock
Link database: US FDA: Selenium Regulations
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-279 - Sea lettuce