Selenium is achemical element; it hassymbolSe andatomic number 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 pureore compounds inEarth's crust. Selenium (fromσελήνη'moon') was discovered in 1817 byJöns Jacob Berzelius, who noted the similarity of the new element to the previously discoveredtellurium (named for the Earth).
Althoughtrace amounts of selenium are necessary forcellular function in many animals, including humans, both elemental selenium and (especially) seleniumsalts are toxic in even small doses, causingselenosis.[11] Symptoms include (in decreasing order of frequency): diarrhea, fatigue, hair loss, joint pain, nail brittleness or discoloration, nausea, headache, tingling, vomiting, and fever.[12]
Selenium is listed as an ingredient in many multivitamins and other dietary supplements, as well as ininfant formula, and is a component of the antioxidant enzymesglutathione peroxidase andthioredoxin reductase (which indirectly reduce certainoxidized molecules in animals and some plants) as well as in threedeiodinase enzymes. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts and others apparently not requiring any.[13]
Selenium forms severalallotropes that interconvert withtemperature changes, depending somewhat on the rate of temperature change. When prepared in chemical reactions, selenium is usually anamorphous, brick-red powder. When rapidly melted, it forms the black, vitreous form, usually sold commercially as beads.[14] The structure of black selenium is irregular and complex and consists ofpolymeric rings with up to 1000 atoms per ring. Black selenium is a brittle, lustrous solid that is slightly soluble inCS2. Upon heating, it softens at 50 °C and converts to gray selenium at 180 °C; the transformation temperature is reduced by presence ofhalogens andamines.[15]
The red α, β, and γ forms are produced from solutions of black selenium by varying the evaporation rate of the solvent (usually CS2). They all have a relatively low,monoclinic crystal symmetry (space group 14) and contain nearly identical puckeredcyclooctaselenium (Se8) rings as insulfur.[16] The eight atoms of a ring are not equivalent (i.e. they are not mapped one onto another by any symmetry operation), and in fact in the γ-monoclinic form, half the rings are in one configuration (and its mirror image) and half in another.[17][18] The packing is most dense in the α form. In the Se8 rings, the Se–Se distance varies depending on where the pair of atoms is in the ring, but the average is 233.5 pm, and the Se–Se–Se angle is on average 105.7°. Other selenium allotropes may contain Se6 or Se7 rings.[15]
The most stable and dense form of selenium is gray and has achiralhexagonal crystal lattice (space group 152 or 154 depending on the chirality)[19] consisting of helical polymeric chains, where the Se–Se distance is 237.3 pm and Se–Se–Se angle is 103.1°. The minimum distance between chains is 343.6 pm. Gray selenium is formed by mild heating of other allotropes, by slow cooling of molten selenium, or by condensing selenium vapor just below the melting point. Whereas other selenium forms areinsulators, gray selenium is asemiconductor showing appreciablephotoconductivity. Unlike the other allotropes, it is insoluble in CS2.[15] It resists oxidation by air and is not attacked by nonoxidizingacids. With strong reducing agents, it forms polyselenides. Selenium does not exhibit the changes in viscosity that sulfur undergoes when gradually heated.[14][20]
Selenium has seven naturally occurringisotopes. Five of these,74Se,76Se,77Se,78Se,80Se, are stable, with80Se being the most abundant (49.6% natural abundance). Also naturally occurring is the long-livedprimordial radionuclide82Se, with ahalf-life of 8.76×1019 years.[10] The non-primordial radioisotope79Se also occurs in minute quantities inuranium ores as a product ofnuclear fission. Selenium also has numerous unstablesynthetic isotopes ranging from64Se to95Se; the most stable are75Se with a half-life of 119.78 days and72Se with a half-life of 8.4 days.[21] Isotopes lighter than the stable isotopes primarily undergobeta plus decay toisotopes of arsenic, and isotopes heavier than the stable isotopes undergobeta minus decay toisotopes of bromine, with some minorneutron emission branches in the heaviest known isotopes.
It is apolymeric solid that forms monomeric SeO2 molecules in the gas phase. It dissolves in water to formselenous acid, H2SeO3. Selenous acid can also be made directly by oxidizing elemental selenium withnitric acid:[24]
3 Se + 4 HNO3 + H2O → 3 H2SeO3 + 4 NO
Unlike sulfur, which forms a stabletrioxide, selenium trioxide is thermodynamically unstable and decomposes to the dioxide above 185 °C:[14][24]
2 SeO3 → 2 SeO2 + O2 (ΔH = −54 kJ/mol)
Selenium trioxide is produced in the laboratory by the reaction ofanhydrouspotassium selenate (K2SeO4) and sulfur trioxide (SO3).[25]
Selenium disulfide consists of 8-membered rings. It has an approximate composition of SeS2, with individual rings varying in composition, such as Se4S4 and Se2S6. Selenium disulfide has been used in shampoo as an antidandruff agent, an inhibitor in polymer chemistry, a glass dye, and a reducing agent infireworks.[24]
Selenium trioxide may be synthesized by dehydratingselenic acid, H2SeO4, which is itself produced by the oxidation of selenium dioxide withhydrogen peroxide:[26]
SeO2 + H2O2 → H2SeO4
Hot, concentrated selenic acid reacts with gold to form gold(III) selenate.[27]
The only stablechlorides areselenium tetrachloride (SeCl4) andselenium monochloride (Se2Cl2), which might be better known as selenium(I) chloride and is structurally analogous todisulfur dichloride. Metastable solutions ofselenium dichloride can be prepared fromsulfuryl chloride and selenium (reaction of the elements generates thetetrachloride instead), and constitute an important reagent in the preparation of selenium compounds (e.g. Se7). The correspondingbromides are all known, and recapitulate the same stability and structure as the chlorides.[29]
Analogous to the behavior of other chalcogens, selenium formshydrogen selenide, H2Se. It is a stronglyodiferous, toxic, and colorless gas. It is more acidic than H2S. In solution it ionizes to HSe−. The selenide dianion Se2− forms a variety of compounds, including the minerals from which selenium is obtained commercially. Illustrative selenides includemercury selenide (HgSe),lead selenide (PbSe),zinc selenide (ZnSe), andcopper indium gallium diselenide (Cu(Ga,In)Se2). These materials aresemiconductors. With highly electropositive metals, such asaluminium, these selenides are prone to hydrolysis, which may be described by this idealized equation:[14]
Al2Se3 + 6 H2O → 2 Al(OH)3 + 3 H2Se
Alkali metal selenides react with selenium to form polyselenides,Se2− n, which exist as chains and rings.
Selenium, especially in the II oxidation state, forms a variety of organic derivatives. They are structurally analogous to the correspondingorganosulfur compounds. Especially common are selenides (R2Se, analogues ofthioethers), diselenides (R2Se2, analogues ofdisulfides), andselenols (RSeH, analogues ofthiols). Representatives of selenides, diselenides, and selenols include respectivelyselenomethionine,diphenyldiselenide, andbenzeneselenol. Thesulfoxide in sulfur chemistry is represented in selenium chemistry by the selenoxides (formula RSe(O)R), which are intermediates in organic synthesis, as illustrated by theselenoxide elimination reaction. Consistent with trends indicated by thedouble bond rule, selenoketones, R(C=Se)R, and selenaldehydes, R(C=Se)H, are rarely observed.[37]
Selenium is named after theSelene, the Greek Goddess of theMoon
Selenium (Greek σελήνηselene meaning "Moon") was discovered in 1817 byJöns Jacob Berzelius andJohan Gottlieb Gahn.[38] Both chemists owned a chemistry plant nearGripsholm, Sweden, producingsulfuric acid by thelead chamber process.Pyrite samples from theFalun Mine produced a red solid precipitate in the lead chambers, which was presumed to be an arsenic compound, so the use of pyrite to make acid was discontinued. Berzelius and Gahn, who wanted to use the pyrite, observed that the red precipitate gave off an odor likehorseradish when burned. This smell was not typical of arsenic, but a similar odor was known fromtellurium compounds. Hence, Berzelius's first letter toAlexander Marcet stated that this was a tellurium compound. However, the lack of tellurium compounds in theFalun Mine minerals eventually led Berzelius to reanalyze the red precipitate, and in 1818 he wrote a second letter to Marcet describing a newly found element similar tosulfur and tellurium. Because of its similarity to tellurium, named for the Earth, Berzelius named the new element after theMoon.[39][40]
In 1873,Willoughby Smith found that theelectrical conductivity of grey selenium was affected by light.[41][42] This led to its use as a cell for sensing light. The first commercial products using selenium were developed byWerner Siemens in the mid-1870s. The selenium cell was used in thephotophone developed byAlexander Graham Bell in 1879. Selenium transmits an electric current proportional to the amount of light falling on its surface. This phenomenon was used in the design oflight meters and similar devices. Selenium's semiconductor properties found numerous other applications in electronics.[43][44][45] The development ofselenium rectifiers began during the early 1930s, and these replacedcopper oxide rectifiers because they were more efficient.[46][47][48] These lasted in commercial applications until the 1970s, following which they were replaced with less expensive and even more efficientsilicon rectifiers.
Selenium came to medical notice later because of its toxicity to industrial workers. Selenium was also recognized as an important veterinary toxin, which is seen in animals that have eaten high-selenium plants. In 1954, the first hints of specific biological functions of selenium were discovered inmicroorganisms by biochemist,Jane Pinsent.[49][50] It was discovered to be essential for mammalian life in 1957.[51][52] In the 1970s, it was shown to be present in two independent sets ofenzymes. This was followed by the discovery ofselenocysteine in proteins. During the 1980s, selenocysteine was shown to be encoded by thecodon UGA. The recoding mechanism was worked out first inbacteria and then inmammals (seeSECIS element).[53]
Native selenium in sandstone, from a uranium mine nearGrants, New Mexico
Native (i.e., elemental) selenium is a rare mineral, which does not usually form good crystals, but, when it does, they are steep rhombohedra or tiny acicular (hair-like) crystals.[54] Isolation of selenium is often complicated by the presence of other compounds and elements.
Selenium occurs naturally in a number of inorganic forms, includingselenide,selenate, andselenite, but these minerals are rare. The common mineralselenite is not a selenium mineral, and contains noselenite ion, but is rather a type ofgypsum (calcium sulfate hydrate) named like selenium for the moon well before the discovery of selenium. Selenium is most commonly found as an impurity, replacing a small part of the sulfur in sulfide ores of many metals.[55][56]
Certain soils are selenium-rich, and selenium can bebioconcentrated by some plants. In soils, selenium most often occurs in soluble forms such as selenate (analogous to sulfate), which are leached into rivers very easily by runoff.[55][56] Ocean water contains significant amounts of selenium.[59][60]
Typical background concentrations of selenium do not exceed 1 ng/m3 in the atmosphere; 1 mg/kg in soil and vegetation and 0.5 μg/L in freshwater and seawater.[61]
Anthropogenic sources of selenium include coal burning, and the mining and smelting of sulfide ores.[62]
Selenium is most commonly produced fromselenide in manysulfideores, such as those ofcopper,nickel, orlead. Electrolytic metal refining is particularly productive of selenium as a byproduct, obtained from theanode mud of copper refineries. Another source was the mud from thelead chambers ofsulfuric acid plants, a process that is no longer used. Selenium can be refined from these muds by a number of methods. However, most elemental selenium comes as a byproduct ofrefining copper or producingsulfuric acid.[63][64] Since its invention,solvent extraction and electrowinning (SX/EW) production of copper produces an increasing share of the worldwide copper supply.[65] This changes the availability of selenium because only a comparably small part of the selenium in the ore is leached with the copper.[66]
Industrial production of selenium usually involves the extraction ofselenium dioxide from residues obtained during the purification of copper. Common production from the residue then begins by oxidation withsodium carbonate to produce selenium dioxide, which is mixed with water andacidified to formselenous acid (oxidation step). Selenous acid is bubbled withsulfur dioxide (reduction step) to give elemental selenium.[67][68]
About 2,000 tonnes of selenium were produced in 2011 worldwide, mostly in Germany (650 t), Japan (630 t), Belgium (200 t), and Russia (140 t), and the total reserves were estimated at 93,000 tonnes. These data exclude two major producers: the United States and China. A previous sharp increase was observed in 2004 from $4–$5 to $27/lb. The price was relatively stable during 2004–2010 at about US$30 per pound (in 100 pound lots) but increased to $65/lb in 2011. The consumption in 2010 was divided as follows: metallurgy – 30%, glass manufacturing – 30%, agriculture – 10%, chemicals and pigments – 10%, and electronics – 10%. China is the dominant consumer of selenium at 1,500–2,000 tonnes/year.[69]
During theelectrowinning of manganese, the addition ofselenium dioxide decreases the power necessary to operate theelectrolysis cells. China is the largest consumer of selenium dioxide for this purpose. For every tonne of manganese, an average 2 kg selenium oxide is used.[69][70]
The largest commercial use of selenium, accounting for about 50% of consumption, is for the production of glass. Selenium compounds confer a red color to glass. This color cancels out the green or yellow tints that arise from iron impurities typical for most glass. For this purpose, various selenite and selenate salts are added. For other applications, a red color may be desired, produced by mixtures of CdSe and CdS.[71]
Selenium is used withbismuth inbrasses to replace more toxiclead. The regulation of lead in drinking water applications such as in the US with theSafe Drinking Water Act of 1974, made a reduction of lead in brass necessary. The new brass is marketed under the name EnviroBrass.[72] Like lead and sulfur, selenium improves the machinability of steel at concentrations around 0.15%.[73][74] Selenium produces the same machinability improvement in copper alloys.[75]
Selenium was used as the photoabsorbing layer in the first solid-state solar cell, which was demonstrated by the English physicistWilliam Grylls Adams and his student Richard Evans Day in 1876.[77] Only a few years later,Charles Fritts fabricated the first thin-film solar cell, also using selenium as the photoabsorber. However, with the emergence of silicon solar cells in the 1950s, research on selenium thin-film solar cells declined. As a result, the record efficiency of 5.0% demonstrated by Tokio Nakada and Akio Kunioka in 1985 remained unchanged for more than 30 years.[78] In 2017, researchers fromIBM achieved a new record efficiency of 6.5% by redesigning the device structure.[79] Following this achievement, selenium has gained renewed interest as a wide bandgap photoabsorber with the potential of being integrated intandem with lower bandgap photoabsorbers.[80] In 2024, the first selenium-based tandem solar cell was demonstrated, showcasing a selenium top cell monolithically integrated with a silicon bottom cell.[81] However, a significant deficit in theopen-circuit voltage is currently the main limiting factor to further improve the efficiency, necessitating defect-engineering strategies for selenium thin-films to enhance thecarrier lifetime.[82][83] Recent theoretical studies using first-principles defect calculations have shown that selenium exhibits intrinsic point defect tolerance, suggesting that interfaces and extended defects are the primary factors limiting device performance.[84] As of now, the only defect-engineering strategy that has been investigated for selenium thin-film solar cells involvescrystallizing selenium using a laser.[85]
Amorphous selenium (α-Se) thin films have found application as photoconductors inflat-panel X-ray detectors. These detectors use amorphous selenium to capture and convert incident X-ray photons directly into electric charge. Selenium has been chosen for this application among other semiconductors owing to a combination of its favorable technological and physical properties:[86][87]
Amorphous selenium has a low melting point, high vapor pressure, and uniform structure. These three properties allow quick and easy deposition of large-area uniform films with a thickness up to 1 mm at a rate of 1–5 μm/min. Their uniformity and lack of grain boundaries, which are intrinsic to polycrystalline materials, improve the X-ray image quality. Meanwhile the large area is essential for scanning the human body or luggage items.
Selenium is less toxic than many compound semiconductors that contain arsenic or heavy metals such as mercury or lead.
The mobility in applied electric field is sufficiently high both for electrons and holes, so that in a typical 0.2 mm thick device, c. 98% of electrons and holes produced by X-rays are collected at the electrodes without being trapped by various defects. Consequently, device sensitivity is high, and its behavior is easy to describe by simple transport equations.
Selenium rectifiers were first used in 1933. They have mostly been replaced by silicon-based devices. One notable exception is in power DCsurge protection, where the superior energy capabilities of selenium suppressors make them more desirable thanmetal-oxide varistors.[citation needed]
The demand for selenium by the electronics industry is declining.[69] Itsphotovoltaic andphotoconductive properties are still useful inphotocopying,[88][89][90][91]photocells,light meters andsolar cells. Its use as a photoconductor in plain-paper copiers once was a leading application, but in the 1980s, the photoconductor application declined (although it was still a large end-use) as more and more copiers switched to organic photoconductors.[citation needed]
Zinc selenide was the first material for blueLEDs, butgallium nitride dominates that market.[92]Cadmium selenide can be used to makequantum dots.[93] Sheets of amorphous selenium convertX-ray images to patterns of charge inxeroradiography and in solid-state, flat-panel X-ray cameras.[94] Ionized selenium (Se+24, where 24 of the outer D, S and P orbitals are stripped away due to high input energies[clarification needed]) is one of the active mediums used in X-ray lasers.[95]75Se is used as a gamma source in industrial radiography.[96]
Selenium catalyzes some chemical reactions, but it is not widely used because of issues with toxicity.[97] InX-ray crystallography, incorporation of one or more selenium atoms in place of sulfur helps with multiple-wavelength anomalous dispersion andsingle wavelength anomalous dispersion phasing.[98]
Selenium is used in thetoning of photographic prints, and it is sold as a toner by numerous photographic manufacturers. Selenium intensifies and extends the tonal range of black-and-white photographic images and improves the permanence of prints.[99][100][101] Small amounts of organoselenium compounds have been used to modify the catalysts used for thevulcanization for the production of rubber.[66] Selenium is used in some anti-dandruff shampoos in the form ofselenium disulfide such as Selsun and Vichy Dereos[102] brands.
Selenium pollution might impact some aquatic systems and may be caused by anthropogenic factors such as farming runoff and industrial processes.[103] People who eat more fish are generally healthier than those who eat less,[104] which suggests no major human health concern from selenium pollution, although selenium has a potential effect on humans.[105]
Selenium poisoning of water systems may result whenever newagricultural run-off courses through dry lands. This process leaches natural soluble selenium compounds (such as selenates) into the water, which may then be concentrated in wetlands as the water evaporates. Selenium pollution of waterways also occurs when selenium is leached from coal flue ash, mining andmetal smelting, crude oil processing, and landfill.[106] High selenium levels in waterways were found to cause congenital disorders in oviparous species, including wetland birds[107] and fish.[108] Elevated dietarymethylmercury levels can amplify the harm of selenium toxicity in oviparous species.[109][110]
Selenium isbioaccumulated in aquatic habitats, which results in higher concentrations in organisms than the surrounding water. Organoselenium compounds can be concentrated over 200,000 times byzooplankton when water concentrations are in the 0.5 to 0.8 μg Se/L range. Inorganic selenium bioaccumulates more readily inphytoplankton than zooplankton. Phytoplankton can concentrate inorganic selenium by a factor of 3000. Further concentration through bioaccumulation occurs along the food chain, as predators consume selenium-rich prey. It is recommended that a water concentration of 2 μg Se/L be considered highly hazardous to sensitive fish andaquatic birds. Selenium poisoning can be passed from parents to offspring through the egg, and selenium poisoning may persist for many generations. Reproduction of mallard ducks is impaired at dietary concentrations of 7 μg Se/L. Manybenthic invertebrates can tolerate selenium concentrations up to 300 μg/L of selenium in their diet.[111]
Bioaccumulation of selenium in aquatic environments causes fish kills depending on the species in the affected area. There are, however, a few species that have been seen to survive these events and tolerate the increased selenium. It has also been suggested that the season could have an impact on the harmful effects of selenium on fish.[112] Substantial physiological changes may occur in fish with high tissue concentrations of selenium. Fish affected by selenium may experience swelling of thegill lamellae, which impedes oxygen diffusion across the gills and blood flow within the gills. Respiratory capacity is further reduced due to selenium binding tohemoglobin. Other problems include degeneration of liver tissue, swelling around the heart, damaged egg follicles in ovaries,cataracts, and accumulation of fluid in the body cavity and head. Selenium often causes a malformed fish fetus which may have problems feeding or respiring; distortion of the fins or spine is also common. Adult fish may appear healthy despite their inability to produce viable offspring.[citation needed]
InBelews Lake North Carolina, 19 species of fish were eliminated from the lake due to 150–200 μg Se/L wastewater discharged from 1974 to 1986 from aDuke Energy coal-fired power plant.[113] At theKesterson National Wildlife Refuge in California, thousands of fish and waterbirds were poisoned by selenium in agricultural irrigation drainage.[citation needed]
Although it is toxic in large doses, selenium is an essentialmicronutrient for animals. In plants, it occurs as a bystander mineral,[114] sometimes in toxic proportions inforage (some plants may accumulate selenium as a defense against being eaten by animals,[115] but other plants, such aslocoweed, require selenium, and their growth indicates the presence of selenium in soil).[116] The selenium content in the human body is believed to be in the range of 13–20 mg.[117]
Thethyroid gland and every cell that uses thyroid hormone also use selenium,[120] which is a cofactor for the three of the four known types ofthyroid hormone deiodinases, which activate and then deactivate variousthyroid hormones and their metabolites; theiodothyronine deiodinases are the subfamily of deiodinase enzymes that use selenium as the otherwise rare amino acid selenocysteine.
Increased dietary selenium reduces the effects of mercury toxicity,[121][122][123] although it is effective only at low to modest doses of mercury.[124] Evidence suggests that the molecular mechanisms of mercury toxicity include the irreversible inhibition of selenoenzymes that are required to prevent and reverse oxidative damage in brain and endocrine tissues.[125][126] The selenium-containing compoundselenoneine is present in the blood ofbluefin tuna.[127][128] Certain plants are considered indicators of high selenium content of the soil because they require high levels of selenium to thrive. The main selenium indicator plants areAstragalus species (including somelocoweeds), prince's plume (Stanleya sp.), woody asters (Xylorhiza sp.), and false goldenweed (Oonopsis sp.).[129]
Dietary selenium comes from meat, nuts, cereals, and mushrooms.Brazil nuts are the richest dietary source (though this is soil-dependent since the Brazil nut does not require high levels of the element for its own needs).[130][131]
The USRecommended Dietary Allowance (RDA) of selenium for teenagers and adults is 55 μg/day. Selenium as a dietary supplement is available in many forms, including multi-vitamins/mineral supplements, which typically contain 55 or 70 μg/serving. Selenium-specific supplements typically contain either 100 or 200 μg/serving.[citation needed] In June 2015, the USFood and Drug Administration (FDA) published its final rule establishing a requirement for minimum and maximum levels of selenium ininfant formula.[132]
Although selenium is an essentialtrace element, it is toxic if taken in excess. Exceeding theTolerable Upper Intake Level of 400 micrograms per day can lead to selenosis.[133] This 400 microgram (μg) Tolerable Upper Intake Level is based primarily on a 1986 study of five Chinese patients who exhibited overt signs of selenosis and a follow-up study on the same five people in 1992.[134] The 1992 study actually found the maximum safe dietary Se intake to be approximately 800 micrograms per day (15 micrograms per kilogram body weight), but suggested 400 micrograms per day to not only avoidtoxicity, but also to avoid creating an imbalance of nutrients in the diet and to account for data from other countries.[135] In China, people who ingested corn grown in extremely selenium-rich stony coal (carbonaceousshale) have suffered from selenium toxicity. This coal was shown to have selenium content as high as 9.1%, the highest concentration in coal ever recorded in literature.[136]
Symptoms of selenosis include a garlic odor on the breath, gastrointestinal disorders, hair loss, sloughing of nails, fatigue, irritability, and neurological damage. Extreme cases of selenosis can result incirrhosis of the liver,pulmonary edema, and death.[137] Elemental selenium and most metallicselenides have relatively low toxicities because of their lowbioavailability. By contrast,selenates andselenites are very toxic, having an oxidant mode of action similar to that of arsenic trioxide. The chronic toxic dose of selenite for humans is about 2400 to 3000 micrograms of selenium per day for a long time.[138]Hydrogen selenide is an extremely toxic, corrosive gas.[139] Selenium also occurs in organic compounds, such as dimethyl selenide,selenomethionine,selenocysteine andmethylselenocysteine, all of which have highbioavailability and are toxic in large doses.
Selenium may be measured in blood, plasma, serum or urine to monitor excessive environmental or occupational exposure, confirm a diagnosis of poisoning in hospitalized victims or to assist in a forensic investigation in a case of fatal overdosage. Some analytical techniques are capable of distinguishing organic from inorganic forms of the element. Both organic and inorganic forms of selenium are largely converted to monosaccharide conjugates (selenosugars) in the body prior to being eliminated in the urine. Cancer patients receiving daily oral doses of selenothionine may achieve very high plasma and urine selenium concentrations.[141]
Selenium deficiency can occur in patients with severely compromisedintestinal function, those undergoingtotal parenteral nutrition, and[142] in those of advanced age (over 90). Also, people dependent on food grown from selenium-deficient soil are at risk. AlthoughNew Zealand has low levels of selenium in its soil, adverse health effects have not been detected.[143]
Selenium deficiency as defined by low (<60% of normal) selenoenzyme activity levels in brain and endocrine tissues only occurs when a low selenium status is linked with an additional stress, such as high exposures to mercury[144] or as a result of increased oxidant stress due to vitamin E deficiency.[145]
Selenium interacts with other nutrients, such asiodide andvitamin E. The interaction is observed in theetiology of many deficiency diseases in animals, and pure selenium deficiency is rare. The effect of selenium deficiency on health remains uncertain, particularly in relation toKashin-Beck disease.[146]
The effects of selenium intake on cancer have been studied in severalclinical trials andepidemiologic studies in humans. Selenium may have achemo-preventive role incancer risk as ananti-oxidant, and it might trigger the immune response. At low levels, it is used in the body to create anti-oxidantselenoproteins, at higher doses than normal it causes cell death.[147]
Selenium (in close interrelation withiodine) plays a role in thyroid health. Selenium is a cofactor for the three thyroid hormonedeiodinases, helping activate and then deactivate various thyroid hormones and their metabolites. Isolated selenium deficiency is now being investigated for its role in the induction of autoimmune reactions in the thyroid gland inHashimoto's disease.[148] In a case of combined iodine and selenium deficiency was shown to play a thyroid-protecting role.[149]
^Se(−1) has been observed in diselenides(Se2−2, such asdisodium diselenide (Na2Se2); seeHolleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (2008).Lehrbuch der Anorganischen Chemie (in German) (102 ed.). Walter de Gruyter. p. 829.ISBN9783110206845. andH. Föppl; E. Busmann; F.-K. Frorath (1962). "Die Kristallstrukturen von α-Na2S2 und K2S2, β-Na2S2 und Na2Se2".Zeitschrift für anorganische und allgemeine Chemie (in German).314 (1):12–20.doi:10.1002/zaac.19623140104.
^A Se(0) atom has been identified using DFT in [ReOSe(2-pySe)3]; seeCargnelutti, Roberta; Lang, Ernesto S.; Piquini, Paulo; Abram, Ulrich (2014). "Synthesis and structure of [ReOSe(2-Se-py)3]: A rhenium(V) complex with selenium(0) as a ligand".Inorganic Chemistry Communications.45:48–50.doi:10.1016/j.inoche.2014.04.003.ISSN1387-7003.
^Se(III) has been observed in Se2NBr3; seeLau, Carsten; Neumüller, Bernhard; Vyboishchikov, Sergei F.; Frenking, Gernot; Dehnicke, Kurt; Hiller, Wolfgang; Herker, Martin (1996). "Se2NBr3, Se2NCl5, Se2NCl−6: New Nitride Halides of Selenium(III) and Selenium(IV)".Chemistry: A European Journal.2 (11):1393–1396.doi:10.1002/chem.19960021108.
^Arblaster, John W. (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^Olav Foss and Vitalijus Janickis (1980). "Crystal structure of γ-monoclinic selenium".Journal of the Chemical Society, Dalton Transactions (4):624–627.doi:10.1039/DT9800000624.
^"The half-life of79Se". Physikalisch-Technische Bundesanstalt. 23 September 2010. Archived fromthe original on 27 September 2011. Retrieved29 May 2012.
^Seppelt, K.; Desmarteau, Darryl D. (1980). "Selenonyl Difluoride".Inorganic Syntheses. Vol. 20. pp. 36–38.doi:10.1002/9780470132517.ch9.ISBN978-0-471-07715-2. The report describes the synthesis of selenic acid.
^Proctor, Nick H.; Hathaway, Gloria J. (2004). Hughes, James P. (ed.).Proctor and Hughes' chemical hazards of the workplace (5th ed.). Wiley-IEEE. p. 625.ISBN978-0-471-26883-3.
^Xu, Zhengtao (2007). Devillanova, Francesco A. (ed.).Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium. Royal Society of Chemistry. p. 460.ISBN978-0-85404-366-8.
^Kelly, P.F.; Slawin, A.M.Z.; Soriano-Rama, A. (1997). "Use of Se4N4 and Se(NSO)2 in the preparation of palladium adducts of diselenium dinitride, Se2N2; crystal structure of[PPh 4] 2[Pd 2Br 6(Se 2N 2)]".Dalton Transactions (4):559–562.doi:10.1039/a606311j.
^Siivari, Jari; Chivers, Tristram; Laitinen, Risto S. (1993). "A simple, efficient synthesis of tetraselenium tetranitride".Inorganic Chemistry.32 (8):1519–1520.doi:10.1021/ic00060a031.
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^Berzelius, J.J. (1818)."Lettre de M. Berzelius à M. Berthollet sur deux métaux nouveaux" [Letter from Mr. Berzelius to Mr. Berthollet on two new metals].Annales de Chimie et de Physique. 2nd series (in French).7:199–206. From p. 203:"Cependant, pour rappeler les rapports de cette dernière avec le tellure, je l'ai nommée sélénium." (However, in order to recall the relationships of this latter [substance (viz, selenium)] to tellurium, I have named it "selenium".)
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^Eftekhari, Ali (2017). "The rise of lithium–selenium batteries".Sustainable Energy & Fuels.1:14–29.doi:10.1039/C6SE00094K.
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^a report of the Panel on Dietary Antioxidants and Related Compounds, Subcommittees on Upper Reference Leves of Nutrients and of Interpretation and Use of Dietary Reference Intakes, and the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine. (August 15, 2000).Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Institute of Medicine. pp. 314–315.ISBN978-0-309-06949-6.{{cite book}}: CS1 maint: multiple names: authors list (link)
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