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: CODA-CERVA: Selenium
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sand 1
Material database: National Institute of Standards and Technology (NIST) - SRM 1946 - Lake Superior Fish Tissue
Instrument database: Aurora Instruments Ltd. - LUMINA 3300 Atomic Fluorescence Spectrometer
Material database: JRC - Joint Research Centre - ERM-CE101 TROUT MUSCLE (trace elements)
Link database: Encyclopedia of Earth: Selenium
Link database: National Research Council: Selenium in Nutrition
Material database: National Institute of Standards and Technology (NIST) - SRM 1577c - Bovine Liver
Material database: National Institute of Standards and Technology (NIST) - SRM 1566 b - Oyster Tissue
Material database: National Research Council of Canada (NRC - CNRC) - LUTS-1: non defatted lobster hepatopancreas
Link database: USGS: Trace-Elements and Radon in Groundwater Across the United States, 1992-2003
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sewage Sludge 4
Material database: National Institute of Standards and Technology (NIST) - SRM 1643d - Trace Elements in Water
Link database: Hazardous Substances Data Bank: Selenium methionine
Special issue on "Advances in speciation techniques and methodology" available | EVISA's News
Material database: National Institute for Environmental Studies (NIES) - NIES CRM 27: Typical Japanese Diet
Instrument database: PS Analytical - 10.825 HPLC-AFS System for Speciation Analysis of Sb, As and Se
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 9
Application of Mass Spectrometry to Speciation Analysis in the Life Sciences | EVISA's Agenda of Events
Material database: National Analysis Center for Iron & Steel (NACIS) - NCS ZC73012 - Trace Elements in Cabbage (NIM-GBW10014)