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 Analysis Center for Iron & Steel (NACIS) - NCS ZC73012 - Trace Elements in Cabbage (NIM-GBW10014)
Directory of scientists: Bernhard Michalke
Link database: US FDA: Selenium Regulations
Link database: Hazardous Substances Data Bank: Seleno-(DL) cysteine
Arsenic species in rice: Origin, uptake and geographical variation | EVISA's News
Use of certified reference materials (CRMs) for speciation analysis | EVISA's News
Instrument database: PS Analytical - 10.055 Millennium Excalibur
Material database: National Institute of Standards and Technology (NIST) - SRM 1974b - Organics in Mussel Tissue (Mytilus edulis)
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 8
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8883 Control blood plasma, lyophilised, trace elements level I: LOT 1286
Material database: National Research Council of Canada (NRC - CNRC) - TORT-3: Lobster Hepatopancreas Reference Material for Trace Metals
Link database: Human Metabolome Database: Tellurium
Directory of scientists: Marie Vahter
Decreased risk of colorectal cancer linked with higher selenium status | EVISA's News
Preservation of arsenic speciation in natural water samples for up to three months | EVISA's News
Link database: Selenium in Food
Material database: The Food and Environment Research Agency (FAPAS) - Test Material T07123 (Infant Formula, Cereal)
Material database: National Institute of Standards and Technology (NIST) - SRM 363 - Chrom-Vanadium Steel (Modified)
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: TCLP Metals - Loamy Sand 3
Material database: National Analysis Center for Iron & Steel (NACIS) - NCS ZC73013 - Trace Elements in Spinach