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: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Sand 3
Link database: ChEBI: L-selenohomocysteine
A short report from the speciation workshop TraceSpec 2009 | EVISA's News
Link database: Hazardous Substances Data Bank: Selenium dimethyldithiocarbamate
Material database: IAEA - MEL International Atomic Energy Agency - IAEA-436 Trace Elements and Methylmercury in Tuna Fish Tissue Homogenate
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-288 - Lead
Material database: National Institute of Standards and Technology (NIST) - SRM 1567b - Wheat Flour
Certified Reference Materials for Chemical Speciation Analysis | EVISA's News
Directory of scientists: Zdenka Šlejkovec
Directory of scientists: Bente Gammelgaard
New selenium-containing proteins identified in selenium-rich yeast | EVISA's News
Material database: IRMM - Institute for Reference Materials and Measurements - ERM-CD281 - Rye Grass
Material database: National Metrology Institute of Japan (NMIJ) - NMIJ CRM 7402-a Trace Elements, Arsenobetaine and Methylmercury in Cod Fish Tissue
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sediment 1
Directory of scientists: Florence Pannier
New theory for the cause of Earth's mass extinctions: lack of essential selenium | EVISA's News
Material database: National Research Council of Canada (NRC - CNRC) - VITB-1: Elevated-level Multivitamin Certified Reference Material for Minerals and Vitamins
Decreased risk of colorectal cancer linked with higher selenium status | EVISA's News
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 2
Material database: IRMM - Institute for Reference Materials and Measurements - ERM-DB001: Trace Elements in Human Hair