Selenium

Selenium is a <a href="/facts/Chemical_element/0jducgWD">chemical element</a>; it has <a href="/facts/Symbol_(chemistry)/2Fe1VAL0">symbol</a> Se and <a href="/facts/Atomic_number/bgAr581S">atomic number</a> 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elemental state or as pure <a href="/facts/Ore/kgc9DssX">ore</a> compounds in <a href="/facts/Earth%2527s_crust/VSy2u31r">Earth's crust</a>. Selenium (σελήνη 'moon') was discovered in 1817 by <a href="/facts/J%25C3%25B6ns_Jacob_Berzelius/HakSv3sP">Jöns Jacob Berzelius</a>, who noted the similarity of the new element to the previously discovered <a href="/facts/Tellurium/v7QvfIvS">tellurium</a> (named for the Earth).
Selenium is found in metal sulfide ores, where it substitutes for sulfur. Commercially, selenium is produced as a <a href="/facts/Byproduct/qDosnqoD">byproduct</a> in the refining of these ores. Minerals that are pure <a href="/facts/Selenide/vA9Ls4xH">selenide</a> or <a href="/facts/Selenate/drzesLxu">selenate</a> compounds are rare. The chief commercial uses for selenium today are <a href="/facts/Glassmaking/aErFHSUC">glassmaking</a> and <a href="/facts/Pigment/I3clCYkF">pigments</a>. Selenium is a <a href="/facts/Semiconductor/zFf3mGTE">semiconductor</a> and is used in <a href="/facts/Photocell/7cSkXS6s">photocells</a>. Applications in <a href="/facts/Electronics/E4JhgISq">electronics</a>, once important, have been mostly replaced with <a href="/facts/Silicon/cgWx0hdr">silicon</a> semiconductor devices. Selenium is still used in a few types of <a href="/facts/Direct_current/r9MNUx84">DC power</a> <a href="/facts/Surge_protector/o3LqlVNv">surge protectors</a> and one type of <a href="/facts/Fluorescence/qsJVT2qP">fluorescent</a> <a href="/facts/Quantum_dot/K5Ytv8Yw">quantum dot</a>.
Although <a href="/facts/Essential_trace_element/ACv8EG7f">trace</a> amounts of selenium are necessary for <a href="/facts/Cell_(biology)/bLM9UQvy">cellular function</a> in many animals, including humans, both elemental selenium and (especially) selenium <a href="/facts/Salt_(chemistry)/lsSKwGpn">salts</a> are toxic in even small doses, causing selenosis. Symptoms include (in decreasing order of frequency): diarrhea, fatigue, hair loss, joint pain, nail brittleness or discoloration, nausea, headache, tingling, vomiting, and fever.
Selenium is listed as an ingredient in many multivitamins and other dietary supplements, as well as in <a href="/facts/Infant_formula/lrbUhzXV">infant formula</a>, and is a component of the antioxidant enzymes <a href="/facts/Glutathione_peroxidase/Y7AQpAub">glutathione peroxidase</a> and <a href="/facts/Thioredoxin_reductase/WD4BSDxj">thioredoxin reductase</a> (which indirectly reduce certain <a href="/facts/Redox/Pyd5RVcj">oxidized</a> molecules in animals and some plants) as well as in three <a href="/facts/Deiodinase/HzyLgjXr">deiodinase</a> enzymes. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts and others apparently not requiring any.

Selenium open-in-new

Selenium