|Appearance||grey metallic-looking, red, and vitreous black (not pictured) allotropes|
|Standard atomic weight Ar, std(Se)||78.971(8)|
|Selenium in the periodic table|
|Atomic number (Z)||34|
|Group||group 16 (chalcogens)|
|Electron configuration||[Ar] 3d10 4s2 4p4|
|Electrons per shell||2, 8, 18, 6|
|Phase at STP||solid|
|Melting point||494 K (221 °C, 430 °F)|
|Boiling point||958 K (685 °C, 1265 °F)|
|Density (near r.t.)||gray: 4.81 g/cm3 |
alpha: 4.39 g/cm3
vitreous: 4.28 g/cm3
|when liquid (at m.p.)||3.99 g/cm3|
|Critical point||1766 K, 27.2 MPa|
|Heat of fusion||gray: 6.69 kJ/mol|
|Heat of vaporization||95.48 kJ/mol|
|Molar heat capacity||25.363 J/(mol·K)|
|Oxidation states||−2, −1, +1, +2, +3, +4, +5, +6 (a strongly acidic oxide)|
|Electronegativity||Pauling scale: 2.55|
|Atomic radius||empirical: 120 pm|
|Covalent radius||120±4 pm|
|Van der Waals radius||190 pm|
|Spectral lines of selenium|
|Speed of sound thin rod||3350 m/s (at 20 °C)|
|Thermal expansion||amorphous: 37 µm/(m⋅K) (at 25 °C)|
|Thermal conductivity||amorphous: 0.519 W/(m⋅K)|
|Molar magnetic susceptibility||−25.0×10−6 cm3/mol (298 K)|
|Young's modulus||10 GPa|
|Shear modulus||3.7 GPa|
|Bulk modulus||8.3 GPa|
|Brinell hardness||736 MPa|
|Naming||after Selene, Greek goddess of the moon|
|Discovery and first isolation||Jöns Jakob Berzelius and Johann Gottlieb Gahn (1817)|
|Main isotopes of selenium|
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth's crust. Selenium—from Greek selḗnē (σελήνη 'Moon')—was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium (named for the Earth).
Selenium is found in metal sulfide ores, where it partially replaces the sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores, most often during production. Minerals that are pure selenide or selenate compounds are known but rare. The chief commercial uses for selenium today are glassmaking and pigments. Selenium is a semiconductor and is used in photocells. Applications in electronics, once important, have been mostly replaced with silicon semiconductor devices. Selenium is still used in a few types of DC power surge protectors and one type of fluorescent quantum dot.
Although trace amounts of selenium are necessary for cellular function in many animals, including humans, both elemental selenium and (especially) selenium salts are toxic in even small doses, causing selenosis. Selenium is listed as an ingredient in many multivitamins and other dietary supplements, as well as in infant formula, and is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants) as well as in 3 deiodinase enzymes. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts and others apparently requiring none.
Selenium forms several allotropes that interconvert with temperature changes, depending somewhat on the rate of temperature change. When prepared in chemical reactions, selenium is usually an amorphous, brick-red powder. When rapidly melted, it forms the black, vitreous form, usually sold commercially as beads. The structure of black selenium is irregular and complex and consists of polymeric rings with up to 1000 atoms per ring. Black Se is a brittle, lustrous solid that is slightly soluble in CS2. Upon heating, it softens at 50 °C and converts to gray selenium at 180 °C; the transformation temperature is reduced by presence of halogens and amines.
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 puckered Se8 rings with different arrangements, as in sulfur. 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. 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.
The most stable and dense form of selenium is gray and has a chiral hexagonal crystal lattice (space group 152 or 154 depending on the chirality) 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 Se is formed by mild heating of other allotropes, by slow cooling of molten Se, or by condensing Se vapor just below the melting point. Whereas other Se forms are insulators, gray Se is a semiconductor showing appreciable photoconductivity. Unlike the other allotropes, it is insoluble in CS2. It resists oxidation by air and is not attacked by nonoxidizing acids. With strong reducing agents, it forms polyselenides. Selenium does not exhibit the changes in viscosity that sulfur undergoes when gradually heated.
Selenium has seven naturally occurring isotopes. Five of these, 74Se, 76Se, 77Se, 78Se, 80Se, are stable, with 80Se being the most abundant (49.6% natural abundance). Also naturally occurring is the long-lived primordial radionuclide 82Se, with a half-life of 9.2×1019 years. The non-primordial radioisotope 79Se also occurs in minute quantities in uranium ores as a product of nuclear fission. Selenium also has numerous unstable synthetic isotopes ranging from 64Se to 95Se; the most stable are 75Se with a half-life of 119.78 days and 72Se with a half-life of 8.4 days. Isotopes lighter than the stable isotopes primarily undergo beta plus decay to isotopes of arsenic, and isotopes heavier than the stable isotopes undergo beta minus decay to isotopes of bromine, with some minor neutron emission branches in the heaviest known isotopes.
|79Se||Trace||Fission product||327000 yr|
|82Se||Primordial||Fission product*||~1020 yr[a]|
Selenium compounds commonly exist in the oxidation states −2, +2, +4, and +6.
- Se8 + 8 O2 → 8 SeO2
It is a polymeric solid that forms monomeric SeO2 molecules in the gas phase. It dissolves in water to form selenous acid, H2SeO3. Selenous acid can also be made directly by oxidizing elemental selenium with nitric acid:
- 3 Se + 4 HNO3 + H2O → 3 H2SeO3 + 4 NO
- 2 SeO3 → 2 SeO2 + O2 (ΔH = −54 kJ/mol)
- H2SeO3 + 2 H2S → SeS2 + 3 H2O
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 in fireworks.
- SeO2 + H2O2 → H2SeO4
Hot, concentrated selenic acid can react with gold to form gold(III) selenate.
Iodides of selenium are not well known. The only stable chloride is selenium monochloride (Se2Cl2), which might be better known as selenium(I) chloride; the corresponding bromide is also known. These species are structurally analogous to the corresponding disulfur dichloride. Selenium dichloride is an important reagent in the preparation of selenium compounds (e.g. the preparation of Se7). It is prepared by treating selenium with sulfuryl chloride (SO2Cl2). Selenium reacts with fluorine to form selenium hexafluoride:
- Se8 + 24 F2 → 8 SeF6
In comparison with its sulfur counterpart (sulfur hexafluoride), selenium hexafluoride (SeF6) is more reactive and is a toxic pulmonary irritant. Some of the selenium oxyhalides, such as selenium oxyfluoride (SeOF2) and selenium oxychloride (SeOCl2) have been used as specialty solvents.
Analogous to the behavior of other chalcogens, selenium forms hydrogen selenide, H2Se. It is a strongly odiferous, 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 include mercury selenide (HgSe), lead selenide (PbSe), zinc selenide (ZnSe), and copper indium gallium diselenide (Cu(Ga,In)Se2). These materials are semiconductors. With highly electropositive metals, such as aluminium, these selenides are prone to hydrolysis:
- Al2Se3 + 3 H2O → Al2O3 + 3 H2Se
Alkali metal selenides react with selenium to form polyselenides, Se2−
n, which exist as chains.
Tetraselenium tetranitride, Se4N4, is an explosive orange compound analogous to tetrasulfur tetranitride (S4N4). It can be synthesized by the reaction of selenium tetrachloride (SeCl4) with [((CH
- 8 KCN + Se8 → 8 KSeCN
Selenium, especially in the II oxidation state, forms stable bonds to carbon, which are structurally analogous to the corresponding organosulfur compounds. Especially common are selenides (R2Se, analogues of thioethers), diselenides (R2Se2, analogues of disulfides), and selenols (RSeH, analogues of thiols). Representatives of selenides, diselenides, and selenols include respectively selenomethionine, diphenyldiselenide, and benzeneselenol. The sulfoxide in sulfur chemistry is represented in selenium chemistry by the selenoxides (formula RSe(O)R), which are intermediates in organic synthesis, as illustrated by the selenoxide elimination reaction. Consistent with trends indicated by the double bond rule, selenoketones, R(C=Se)R, and selenaldehydes, R(C=Se)H, are rarely observed.
Selenium (Greek σελήνη selene meaning "Moon") was discovered in 1817 by Jöns Jacob Berzelius and Johan Gottlieb Gahn. Both chemists owned a chemistry plant near Gripsholm, Sweden, producing sulfuric acid by the lead chamber process. The pyrite from the Falun Mine created a red precipitate in the lead chambers which was presumed to be an arsenic compound, so the pyrite's use to make acid was discontinued. Berzelius and Gahn wanted to use the pyrite and they also observed that the red precipitate gave off a smell like horseradish when burned. This smell was not typical of arsenic, but a similar odor was known from tellurium compounds. Hence, Berzelius's first letter to Alexander Marcet stated that this was a tellurium compound. However, the lack of tellurium compounds in the Falun 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 to sulfur and tellurium. Because of its similarity to tellurium, named for the Earth, Berzelius named the new element after the Moon.
In 1873, Willoughby Smith found that the electrical resistance of grey selenium was dependent on the ambient light. This led to its use as a cell for sensing light. The first commercial products using selenium were developed by Werner Siemens in the mid-1870s. The selenium cell was used in the photophone developed by Alexander 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 of light meters and similar devices. Selenium's semiconductor properties found numerous other applications in electronics. The development of selenium rectifiers began during the early 1930s, and these replaced copper oxide rectifiers because they were more efficient. These lasted in commercial applications until the 1970s, following which they were replaced with less expensive and even more efficient silicon 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 in microorganisms by biochemist, Jane Pinsent. It was discovered to be essential for mammalian life in 1957. In the 1970s, it was shown to be present in two independent sets of enzymes. This was followed by the discovery of selenocysteine in proteins. During the 1980s, selenocysteine was shown to be encoded by the codon UGA. The recoding mechanism was worked out first in bacteria and then in mammals (see SECIS element).
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. Isolation of selenium is often complicated by the presence of other compounds and elements.
Selenium occurs naturally in a number of inorganic forms, including selenide, selenate, and selenite, but these minerals are rare. The common mineral selenite is not a selenium mineral, and contains no selenite ion, but is rather a type of gypsum (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.
In living systems, selenium is found in the amino acids selenomethionine, selenocysteine, and methylselenocysteine. In these compounds, selenium plays a role analogous to that of sulfur. Another naturally occurring organoselenium compound is dimethyl selenide.
Certain soils are selenium-rich, and selenium can be bioconcentrated 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. Ocean water contains significant amounts of selenium.
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.
Anthropogenic sources of selenium include coal burning, and the mining and smelting of sulfide ores.
Selenium is most commonly produced from selenide in many sulfide ores, such as those of copper, nickel, or lead. Electrolytic metal refining is particularly productive of selenium as a byproduct, obtained from the anode mud of copper refineries. Another source was the mud from the lead chambers of sulfuric 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 of refining copper or producing sulfuric acid. Since its invention, solvent extraction and electrowinning (SX/EW) production of copper produces an increasing share of the worldwide copper supply. This changes the availability of selenium because only a comparably small part of the selenium in the ore is leached with the copper.
Industrial production of selenium usually involves the extraction of selenium dioxide from residues obtained during the purification of copper. Common production from the residue then begins by oxidation with sodium carbonate to produce selenium dioxide, which is mixed with water and acidified to form selenous acid (oxidation step). Selenous acid is bubbled with sulfur dioxide (reduction step) to give elemental selenium.
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.
Researchers found that application of selenium fertilizer to lettuce crops decreased the accumulation of lead and cadmium. Peaches and pears given a foliar selenium spray contained higher levels of selenium and also stayed firm and ripe longer when in storage. In low doses, selenium has shown a beneficial effect on plant resistance to various environmental stress factors including drought, UV-B, soil salinity, and cold or hot temperatures. However, it can damage plants at higher doses.
During the electrowinning of manganese, the addition of selenium dioxide decreases the power necessary to operate the electrolysis 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.
The largest commercial use of Se, accounting for about 50% of consumption, is for the production of glass. Se 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.
Selenium is used with bismuth in brasses to replace more toxic lead. The regulation of lead in drinking water applications such as in the US with the Safe Drinking Water Act of 1974, made a reduction of lead in brass necessary. The new brass is marketed under the name EnviroBrass. Like lead and sulfur, selenium improves the machinability of steel at concentrations around 0.15%. Selenium produces the same machinability improvement in copper alloys.
The lithium–selenium (Li–Se) battery is one of the most promising systems for energy storage in the family of lithium batteries. The Li–Se battery is an alternative to the lithium–sulfur battery, with an advantage of high electrical conductivity.
Amorphous selenium (α-Se) thin films have found application as photoconductors in flat panel x-ray detectors. These detectors use amorphous selenium to capture and convert incident x-ray photons directly into electric charge.
Selenium rectifiers were first used in 1933. Their use continued into the 1990s.
The demand for selenium by the electronics industry is declining. Its photovoltaic and photoconductive properties are still useful in photocopying, photocells, light meters and solar 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. Though once widely used, selenium rectifiers have mostly been replaced (or are being replaced) by silicon-based devices. The most notable exception is in power DC surge protection, where the superior energy capabilities of selenium suppressors make them more desirable than metal-oxide varistors.
Zinc selenide was the first material for blue LEDs, but gallium nitride dominates that market. Cadmium selenide was an important component in quantum dots. Sheets of amorphous selenium convert X-ray images to patterns of charge in xeroradiography and in solid-state, flat-panel X-ray cameras. Ionized selenium (Se+24) is one of the active mediums used in X-ray lasers.
Selenium is a catalyst in some chemical reactions, but it is not widely used because of issues with toxicity. In X-ray crystallography, incorporation of one or more selenium atoms in place of sulfur helps with multiple-wavelength anomalous dispersion and single wavelength anomalous dispersion phasing.
Selenium is used in the toning 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.
75Se is used as a gamma source in industrial radiography.
In high concentrations, selenium acts as an environmental contaminant. Sources of pollution include waste materials from certain mining, agricultural, petrochemical, and industrial manufacturing operations. In Belews 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 a Duke Energy coal-fired power plant. At the Kesterson National Wildlife Refuge in California, thousands of fish and waterbirds were poisoned by selenium in agricultural irrigation drainage.
Substantial physiological changes may occur in fish with high tissue concentrations of selenium. Fish affected by selenium may experience swelling of the gill lamellae, which impedes oxygen diffusion across the gills and blood flow within the gills. Respiratory capacity is further reduced due to selenium binding to hemoglobin. 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.
Selenium is bioaccumulated in aquatic habitats, which results in higher concentrations in organisms than the surrounding water. Organoselenium compounds can be concentrated over 200,000 times by zooplankton when water concentrations are in the 0.5 to 0.8 μg Se/L range. Inorganic selenium bioaccumulates more readily in phytoplankton 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 and aquatic 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 ug Se/L. Many benthic invertebrates can tolerate selenium concentrations up to 300 μg/L of Se in their diet.
Selenium pollution is impacting oceans across the world and is mainly caused by anthropogenic factors such as farming runoff and industrial processes. Fish are a major source of protein for humans. In fact, 16.7% of the worlds animal protein intake came from fish in 2010. With fish as a source of protein for humans, it is important to be aware of the selenium pollution for its potential effect on humans.
The high bioaccumulation of selenium in aquatic environments causes large 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 season could have an impact on the harmful effects of selenium on fish. To help reduce the amount of selenium entering the oceans, policies can be put into place such as using microbes or enzymes that target and break down metalloids like selenium.
|NFPA 704 (fire diamond)|
Although it is toxic in large doses, selenium is an essential micronutrient for animals. In plants, it occurs as a bystander mineral[clarification needed], sometimes in toxic proportions in forage (some plants may accumulate selenium as a defense against being eaten by animals, but other plants, such as locoweed, require selenium, and their growth indicates the presence of selenium in soil). See more on plant nutrition below.[clarification needed]
Selenium is a component of the unusual amino acids selenocysteine and selenomethionine. In humans, selenium is a trace element nutrient that functions as cofactor for reduction of antioxidant enzymes, such as glutathione peroxidases and certain forms of thioredoxin reductase found in animals and some plants (this enzyme occurs in all living organisms, but not all forms of it in plants require selenium).
- 2 GSH + H2O2----GSH-Px → GSSG + 2 H2O
The thyroid gland and every cell that uses thyroid hormone use selenium, which is a cofactor for the three of the four known types of thyroid hormone deiodinases, which activate and then deactivate various thyroid hormones and their metabolites; the iodothyronine deiodinases are the subfamily of deiodinase enzymes that use selenium as the otherwise rare amino acid selenocysteine. (Only the deiodinase iodotyrosine deiodinase, which works on the last breakdown products of thyroid hormone, does not use selenium.)
Selenium may inhibit Hashimoto's disease, in which the body's own thyroid cells are attacked as foreign. A reduction of 21% on TPO antibodies is reported with the dietary intake of 0.2 mg of selenium.
Increased dietary selenium reduces the effects of mercury toxicity, although it is effective only at low to modest doses of mercury. Evidence suggests that the molecular mechanisms of mercury toxicity includes the irreversible inhibition of selenoenzymes that are required to prevent and reverse oxidative damage in brain and endocrine tissues. An antioxidant, selenoneine, which is derived from selenium and has been found to be present in the blood of bluefin tuna, is the subject of scientific research regarding its possible roles in inflammatory and chronic diseases, methylmercury detoxification, and oxidative damages. It seems as though when mercury levels in a marine fish rise, so do the selenium levels. To the knowledge of researchers, there are no reports of mercury levels exceeding that of selenium levels in ocean fish.
Evolution in biology
From about three billion years ago, prokaryotic selenoprotein families drive the evolution of selenocysteine, an amino acid. Selenium is incorporated into several prokaryotic selenoprotein families in bacteria, archaea, and eukaryotes as selenocysteine, where selenoprotein peroxiredoxins protect bacterial and eukaryotic cells against oxidative damage. Selenoprotein families of GSH-Px and the deiodinases of eukaryotic cells seem to have a bacterial phylogenetic origin. The selenocysteine-containing form occurs in species as diverse as green algae, diatoms, sea urchins, fish, and chickens. Selenium enzymes are involved in the small reducing molecules glutathione and thioredoxin. One family of selenium-bearing molecules (the glutathione peroxidases) destroys peroxide and repairs damaged peroxidized cell membranes, using glutathione. Another selenium-bearing enzyme in some plants and in animals (thioredoxin reductase) generates reduced thioredoxin, a dithiol that serves as an electron source for peroxidases and also the important reducing enzyme ribonucleotide reductase that makes DNA precursors from RNA precursors.
Trace elements involved in GSH-Px and superoxide dismutase enzymes activities, i.e. selenium, vanadium, magnesium, copper, and zinc, may have been lacking in some terrestrial mineral-deficient areas. Marine organisms retained and sometimes expanded their selenoproteomes, whereas the selenoproteomes of some terrestrial organisms were reduced or completely lost. These findings suggest that, with the exception of vertebrates, aquatic life supports selenium use, whereas terrestrial habitats lead to reduced use of this trace element. Marine fishes and vertebrate thyroid glands have the highest concentration of selenium and iodine. From about 500 million years ago, freshwater and terrestrial plants slowly optimized the production of "new" endogenous antioxidants such as ascorbic acid (vitamin C), polyphenols (including flavonoids), tocopherols, etc. A few of these appeared more recently, in the last 50–200 million years, in fruits and flowers of angiosperm plants. In fact, the angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the late Jurassic period.
The deiodinase isoenzymes constitute another family of eukaryotic selenoproteins with identified enzyme function. Deiodinases are able to extract electrons from iodides, and iodides from iodothyronines. They are, thus, involved in thyroid-hormone regulation, participating in the protection of thyrocytes from damage by H2O2 produced for thyroid-hormone biosynthesis. About 200 million years ago, new selenoproteins were developed as mammalian GSH-Px enzymes.
Nutritional sources of selenium
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).
The US Recommended 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.
The selenium content in the human body is believed to be in the 13–20 mg range.
Indicator plant species
Certain species of 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 are Astragalus species (including some locoweeds), prince's plume (Stanleya sp.), woody asters (Xylorhiza sp.), and false goldenweed (Oonopsis sp.)
Detection in biological fluids
Selenium may be measured in blood, plasma, serum, or urine to monitor excessive environmental or occupational exposure, to confirm a diagnosis of poisoning in hospitalized victims, or investigate a suspected case of fatal overdose. 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 elimination in the urine. Cancer patients receiving daily oral doses of selenothionine may achieve very high plasma and urine selenium concentrations.
Although selenium is an essential trace element, it is toxic if taken in excess. Exceeding the Tolerable Upper Intake Level of 400 micrograms per day can lead to selenosis. This 400 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. 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 avoid creating an imbalance of nutrients in the diet and to accord with data from other countries. In China, people who ingested corn grown in extremely selenium-rich stony coal (carbonaceous shale) 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.
Signs and 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 exhibit cirrhosis of the liver, pulmonary edema, or death. Elemental selenium and most metallic selenides have relatively low toxicities because of low bioavailability. By contrast, selenates and selenites have an oxidant mode of action similar to that of arsenic trioxide and are very toxic. The chronic toxic dose of selenite for humans is about 2400 to 3000 micrograms of selenium per day. Hydrogen selenide is an extremely toxic, corrosive gas. Selenium also occurs in organic compounds, such as dimethyl selenide, selenomethionine, selenocysteine and methylselenocysteine, all of which have high bioavailability and are toxic in large doses.
On 19 April 2009, 21 polo ponies died shortly before a match in the United States Polo Open. Three days later, a pharmacy released a statement explaining that the horses had received an incorrect dose of one of the ingredients used in a vitamin/mineral supplement compound that had been incorrectly prepared by a compounding pharmacy. Analysis of blood levels of inorganic compounds in the supplement indicated the selenium concentrations were 10 to 15 times higher than normal in the blood samples, and 15 to 20 times higher than normal in the liver samples. Selenium was later confirmed to be the toxic factor.
Selenium poisoning of water systems may result whenever new agricultural runoff courses through normally dry, undeveloped lands. This process leaches natural soluble selenium compounds (such as selenates) into the water, which may then be concentrated in new "wetlands" as the water evaporates. Selenium pollution of waterways also occurs when selenium is leached from coal flue ash, mining and metal smelting, crude oil processing, and landfill. The resultant high selenium levels in waterways were found to cause congenital disorders in oviparous species, including wetland birds and fish. Elevated dietary methylmercury levels can amplify the harm of selenium toxicity in oviparous species.
In fish and other wildlife, selenium is necessary for life, but toxic in high doses. For salmon, the optimal concentration of selenium is about 1 microgram selenium per gram of whole body weight. Much below that level, young salmon die from deficiency; much above, they die from toxic excess.
The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for selenium in the workplace at 0.2 mg/m3 over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a Recommended exposure limit (REL) of 0.2 mg/m3 over an 8-hour workday. At levels of 1 mg/m3, selenium is immediately dangerous to life and health.
Selenium deficiency can occur in patients with severely compromised intestinal function, those undergoing total parenteral nutrition, and in those of advanced age (over 90). Also, people dependent on food grown from selenium-deficient soil are at risk. Although New Zealand soil has low levels of selenium, adverse health effects have not been detected in the residents.
Selenium deficiency, defined by low (<60% of normal) selenoenzyme activity levels in brain and endocrine tissues, occurs only when a low selenium level is linked with an additional stress, such as high exposures to mercury or increased oxidant stress from vitamin E deficiency.
Selenium interacts with other nutrients, such as iodine and vitamin E. The effect of selenium deficiency on health remains uncertain, particularly in relation to Kashin-Beck disease. Also, selenium interacts with other minerals, such as zinc and copper. High doses of Se supplements in pregnant animals might disturb the Zn:Cu ratio and lead to Zn reduction; in such treatment cases, Zn levels should be monitored. Further studies are needed to confirm these interactions.
In the regions (e.g. various regions within North America) where low selenium soil levels lead to low concentrations in the plants, some animal species may be deficient unless selenium is supplemented with diet or injection. Ruminants are particularly susceptible. In general, absorption of dietary selenium is lower in ruminants than other animals, and is lower from forages than from grain. Ruminants grazing certain forages, e.g., some white clover varieties containing cyanogenic glycosides, may have higher selenium requirements, presumably because cyanide is released from the aglycone by glucosidase activity in the rumen and glutathione peroxidases is deactivated by the cyanide acting on the glutathione moiety. Neonate ruminants at risk of white muscle disease may be administered both selenium and vitamin E by injection; some of the WMD myopathies respond only to selenium, some only to vitamin E, and some to either.
Accumulating evidence suggests a chemo-preventive role of selenium in cancer risk and incidence. At nutritional levels, defined as the amount sufficient to saturate selenoproteins, selenium functions as an anti-oxidant and plays a possible chemo-preventive role against cancer through scavenging ROS; thereby, preventing damage to the DNA and the occurrence of mutations. The effects of selenium status on cancer have been studied in several clinical trials and epidemiologic studies in humans, suggesting beneficial effects of higher selenium status in preventing the recurrence of lung cancer and patients with different cancer types. Furthermore, the nutritional prevention of cancer trial demonstrated that selenium-enriched yeast reduced the incidence and mortality of colorectal, prostate and lung cancers. Recently, a human intervention study involving more than 300 lung cancer patients showed that selenium seral level over 69 μg L−1 is significantly associated with improved overall survival.
- For all practical purposes, 82Se is stable.
- "Standard Atomic Weights: Selenium". CIAAW. 2013.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- Magnetic susceptibility of the elements and inorganic compounds, in Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
- Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
- Ruyle, George. "Poisonous Plants on Arizona Rangelands" (PDF). The University of Arizona. Archived from the original (PDF) on 15 July 2004. Retrieved 5 January 2009.
- House, James E. (2008). Inorganic chemistry. Academic Press. p. 524. ISBN 978-0-12-356786-4.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 751–752. ISBN 978-0-08-037941-8.
- 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.
- "β –Se (Al ) Structure: A_mP32_14_8e". Encyclopedia of Crystallographic Prototypes.
- "β –Se (Al ) Structure: A_mP32_14_16e". Encyclopedia of Crystallographic Prototypes.
- "β –Se (Al ) Structure: A_hP3_152_a". Encyclopedia of Crystallographic Prototypes.
- on YouTube
- Jafar, Mousa M. Abdul-Gader; Saleh, Mahmoud H.; Ahmad, Mais Jamil A.; Bulos, Basim N.; Al-Daraghmeh, Tariq M. (1 April 2016). "Retrieval of optical constants of undoped amorphous selenium films from an analysis of their normal-incidence transmittance spectra using numeric PUMA method". Journal of Materials Science: Materials in Electronics. 27 (4): 3281–3291. doi:10.1007/s10854-015-4156-z. ISSN 0957-4522. S2CID 138011595.
- Saleh, Mahmoud H.; Ershaidat, Nidal M.; Ahmad, Mais Jamil A.; Bulos, Basim N.; Jafar, Mousa M. Abdul-Gader (1 June 2017). "Evaluation of spectral dispersion of optical constants of a-Se films from their normal-incidence transmittance spectra using Swanepoel algebraic envelope approach". Optical Review. 24 (3): 260–277. Bibcode:2017OptRv..24..260S. doi:10.1007/s10043-017-0311-5. ISSN 1340-6000. S2CID 125766615.
- Minkov, D.A.; Gavrilov, G.M.; Angelov, G.V.; Moreno, J.M.D.; Vazquez, C.G.; Ruano, S.M.F.; Marquez, E. (2018). "Optimisation of the envelope method for characterisation of optical thin film on substrate specimens from their normal incidence transmittance spectrum". Thin Solid Films. 645: 370–378. Bibcode:2018TSF...645..370M. doi:10.1016/j.tsf.2017.11.003.
- Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
- "The half-life of 79Se". Physikalisch-Technische Bundesanstalt. 23 September 2010. Retrieved 29 May 2012.
- Jörg, Gerhard; Bühnemann, Rolf; Hollas, Simon; et al. (2010). "Preparation of radiochemically pure 79Se and highly precise determination of its half-life". Applied Radiation and Isotopes. 68 (12): 2339–2351. doi:10.1016/j.apradiso.2010.05.006. PMID 20627600.
- Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. San Diego: Academic Press. p. 583. ISBN 978-0-12-352651-9.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 780. ISBN 978-0-08-037941-8.
- Seppelt, K.; Desmarteau, Darryl D. (1980). Selenoyl difluoride. Inorganic Syntheses. 20. pp. 36–38. doi:10.1002/9780470132517.ch9. ISBN 978-0-471-07715-2. The report describes the synthesis of selenic acid.
- Lenher, V. (April 1902). "Action of selenic acid on gold". Journal of the American Chemical Society. 24 (4): 354–355. doi:10.1021/ja02018a005.
- Xu, Zhengtao (2007). Devillanova, Francesco A. (ed.). Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium. Royal Society of Chemistry. p. 460. ISBN 978-0-85404-366-8.
- 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. ISBN 978-0-471-26883-3.
- Woollins, Derek; Kelly, Paul F. (1993). "The Reactivity of Se4N4 in Liquid Ammonia". Polyhedron. 12 (10): 1129–1133. doi:10.1016/S0277-5387(00)88201-7.
- 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
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.
- Erker, G.; Hock, R.; Krüger, C.; Werner, S.; Klärner, F.G.; Artschwager-Perl, U. (1990). "Synthesis and Cycloadditions of Monomeric Selenobenzophenone". Angewandte Chemie International Edition in English. 29 (9): 1067–1068. doi:10.1002/anie.199010671.
- 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".)
- Weeks, Mary Elvira (1932). "The discovery of the elements. VI. Tellurium and selenium". Journal of Chemical Education. 9 (3): 474. Bibcode:1932JChEd...9..474W. doi:10.1021/ed009p474.
- Trofast, Jan (2011). "Berzelius' Discovery of Selenium". Chemistry International. 33 (5): 16–19. PDF
- Smith, Willoughby (1873). "The action of light on selenium". Journal of the Society of Telegraph Engineers. 2 (4): 31–33. doi:10.1049/jste-1.1873.0023.
- Smith, Willoughby (20 February 1873). "Effect of light on selenium during the passage of an electric current". Nature. 7 (173): 303. Bibcode:1873Natur...7R.303.. doi:10.1038/007303e0.
- Bonnier Corporation (1876). "Action of light on selenium". Popular Science. 10 (1): 116.
- Levinshtein, M.E.; Simin, G.S. (1 December 1992). Earliest semiconductor device. Getting to Know Semiconductors. pp. 77–79. ISBN 978-981-02-3516-1.
- Winston, Brian (29 May 1998). Media Technology and Society: A History: From the Telegraph to the Internet. p. 89. ISBN 978-0-415-14229-8.
- Morris, Peter Robin (1990). A History of the World Semiconductor Industry. p. 18. ISBN 978-0-86341-227-1.
- Bergmann, Ludwig (1931). "Über eine neue Selen-Sperrschicht-Photozelle". Physikalische Zeitschrift. 32: 286–288.
- Waitkins, G.R.; Bearse, A.E.; Shutt, R. (1942). "Industrial Utilization of Selenium and Tellurium". Industrial & Engineering Chemistry. 34 (8): 899–910. doi:10.1021/ie50392a002.
- Pinsent, Jane (1954). "The need for selenite and molybdate in the formation of formic dehydrogenase by members of the Coli-aerogenes group of bacteria". Biochem. J. 57 (1): 10–16. doi:10.1042/bj0570010. PMC 1269698. PMID 13159942.
- Stadtman, Thressa C. (2002). "Some Functions of the Essential Trace Element, Selenium". Trace Elements in Man and Animals 10. Trace Elements in Man and Animals. 10. pp. 831–836. doi:10.1007/0-306-47466-2_267. ISBN 978-0-306-46378-5.
- Schwarz, Klaus; Foltz, Calvin M. (1957). "Selenium as an Integral Part of Factor 3 Against Dietary Necrotic Liver Degeneration". Journal of the American Chemical Society. 79 (12): 3292–3293. doi:10.1021/ja01569a087.
- Oldfield, James E. (2006). "Selenium: A historical perspective". Selenium. Selenium. pp. 1–6. doi:10.1007/0-387-33827-6_1. ISBN 978-0-387-33826-2.
- Hatfield, D. L.; Gladyshev, V.N. (2002). "How Selenium Has Altered Our Understanding of the Genetic Code". Molecular and Cellular Biology. 22 (11): 3565–3576. doi:10.1128/MCB.22.11.3565-3576.2002. PMC 133838. PMID 11997494.
- "Native Selenium". Webminerals. Retrieved 6 June 2009.
- Kabata-Pendias, A. (1998). "Geochemistry of selenium". Journal of Environmental Pathology, Toxicology and Oncology. 17 (3–4): 173–177. PMID 9726787.
- Fordyce, Fiona (2007). "Selenium Geochemistry and Health" (PDF). AMBIO: A Journal of the Human Environment. 36 (1): 94–97. doi:10.1579/0044-7447(2007)36[94:SGAH]2.0.CO;2. PMID 17408199.
- Wessjohann, Ludger A.; Schneider, Alex; Abbas, Muhammad; Brandt, Wolfgang (2007). "Selenium in chemistry and biochemistry in comparison to sulfur". Biological Chemistry. 388 (10): 997–1006. doi:10.1515/BC.2007.138. PMID 17937613. S2CID 34918691.
- Birringer, Marc; Pilawa, Sandra; Flohé, Leopold (2002). "Trends in selenium biochemistry". Natural Product Reports. 19 (6): 693–718. doi:10.1039/B205802M. PMID 12521265.
- Amouroux, David; Liss, Peter S.; Tessier, Emmanuel; et al. (2001). "Role of oceans as biogenic sources of selenium". Earth and Planetary Science Letters. 189 (3–4): 277–283. Bibcode:2001E&PSL.189..277A. doi:10.1016/S0012-821X(01)00370-3.
- Haug, Anna; Graham, Robin D.; Christophersen, Olav A.; Lyons, Graham H. (2007). "How to use the world's scarce selenium resources efficiently to increase the selenium concentration in food". Microbial Ecology in Health and Disease. 19 (4): 209–228. doi:10.1080/08910600701698986. PMC 2556185. PMID 18833333.
- Rieuwerts, John (2015). The Elements of Environmental Pollution. London and New York: Earthscan Routledge. p. 262. ISBN 978-0-415-85919-6. OCLC 886492996.CS1 maint: date and year (link)
- "Public Health Statement: Selenium" (PDF). Agency for Toxic Substances and Disease Registry. Retrieved 5 January 2009.
- "Public Health Statement: Selenium – Production, Import/Export, Use, and Disposal" (PDF). Agency for Toxic Substances and Disease Registry. Retrieved 5 January 2009.
- "Chemistry: Periodic Table: selenium: key information". webelements. Retrieved 2009-01-06.
- Bartos, P.J. (2002). "SX-EW copper and the technology cycle". Resources Policy. 28 (3–4): 85–94. doi:10.1016/S0301-4207(03)00025-4.
- Naumov, A. V. (2010). "Selenium and tellurium: State of the markets, the crisis, and its consequences". Metallurgist. 54 (3–4): 197–200. doi:10.1007/s11015-010-9280-7. S2CID 137066827.
- Hoffmann, James E. (1989). "Recovering selenium and tellurium from copper refinery slimes". JOM. 41 (7): 33–38. Bibcode:1989JOM....41g..33H. doi:10.1007/BF03220269. S2CID 138253358.
- Hyvärinen, Olli; Lindroos, Leo; Yllö, Erkki (1989). "Recovering selenium from copper refinery slimes". JOM. 41 (7): 42–43. Bibcode:1989JOM....41g..42H. doi:10.1007/BF03220271. S2CID 138555797.
- "Selenium and Tellurium: Statistics and Information". United States Geological Survey. Retrieved 2012-05-30.
- Feng, Renwei; Wei, Chaoyang; Tu, Shuxin (2013). "The roles of selenium in protecting plants against abiotic stresses". Environmental and Experimental Botany. 87: 58–68. doi:10.1016/j.envexpbot.2012.09.002.
- Sun, Yan; Tian, Xike; He, Binbin; et al. (2011). "Studies of the reduction mechanism of selenium dioxide and its impact on the microstructure of manganese electrodeposit". Electrochimica Acta. 56 (24): 8305–8310. doi:10.1016/j.electacta.2011.06.111.
- Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a23_525.
- Davis, Joseph R. (2001). Copper and Copper Alloys. ASM Int. p. 91. ISBN 978-0-87170-726-0.
- Isakov, Edmund (2008-10-31). Cutting Data for Turning of Steel. p. 67. ISBN 978-0-8311-3314-6.
- Gol'Dshtein, Ya. E.; Mushtakova, T. L.; Komissarova, T. A. (1979). "Effect of selenium on the structure and properties of structural steel". Metal Science and Heat Treatment. 21 (10): 741–746. Bibcode:1979MSHT...21..741G. doi:10.1007/BF00708374. S2CID 135853965.
- Davis, Joseph R. (2001). Copper and Copper Alloys. ASM International. p. 278. ISBN 978-0-87170-726-0.
- Eftekhari, Ali (2017). "The rise of lithium–selenium batteries". Sustainable Energy & Fuels. 1: 14–29. doi:10.1039/C6SE00094K.
- Deutsche Gesellschaft für Sonnenenergie (2008). "Copper indium diselenide (CIS) cell". Planning and Installing Photovoltaic Systems: A Guide for Installers, Architects and Engineers. Earthscan. pp. 43–44. ISBN 978-1-84407-442-6.
- Wee Chong Tan (July 2006). Optical Properties of Amorphous Selenium Films (PDF) (Master of Science thesis). University of Saskatchewan. Archived from the original (PDF) on 2015-11-29. Retrieved 2017-11-16.
- Direct vs. Indirect Conversion Archived January 2, 2010, at the Wayback Machine
- Springett, B. E. (1988). "Application of Selenium-Tellurium Photoconductors to the Xerographic Copying and Printing Processes". Phosphorus and Sulfur and the Related Elements. 38 (3–4): 341–350. doi:10.1080/03086648808079729.
- Williams, Rob (2006). Computer Systems Architecture: A Networking Approach. Prentice Hall. pp. 547–548. ISBN 978-0-321-34079-5.
- Diels, Jean-Claude; Arissian, Ladan (2011). "The Laser Printer". Lasers. Wiley-VCH. pp. 81–83. ISBN 978-3-527-64005-8.
- Meller, Gregor & Grasser, Tibor (2009). Organic Electronics. Springer. pp. 3–5. ISBN 978-3-642-04537-0.
- Normile, Dennis (2000). "The birth of the Blues". Popular Science. p. 57.
- Kasap, Safa; Frey, Joel B.; Belev, George; et al. (2009). "Amorphous selenium and its alloys from early xeroradiography to high resolution X-ray image detectors and ultrasensitive imaging tubes". Physica Status Solidi B. 246 (8): 1794–1805. Bibcode:2009PSSBR.246.1794K. doi:10.1002/pssb.200982007.
- Svelto, Orazio (1998). Principles of LASERs fourth ed. Plenum. p. 457. ISBN 978-0-306-45748-7.
- Hai-Fu, F.; Woolfson, M. M.; Jia-Xing, Y. (1993). "New Techniques of Applying Multi-Wavelength Anomalous Scattering Data". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 442 (1914): 13–32. Bibcode:1993RSPSA.442...13H. doi:10.1098/rspa.1993.0087. S2CID 122722520.
- MacLean, Marion E. (1937). "A project for general chemistry students: Color toning of photographic prints". Journal of Chemical Education. 14 (1): 31. Bibcode:1937JChEd..14...31M. doi:10.1021/ed014p31.
- Penichon, Sylvie (1999). "Differences in Image Tonality Produced by Different Toning Protocols for Matte Collodion Photographs". Journal of the American Institute for Conservation. 38 (2): 124–143. doi:10.2307/3180042. JSTOR 3180042.
- McKenzie, Joy (2003). Exploring Basic Black & White Photography. Delmar. p. 176. ISBN 978-1-4018-1556-1.
- Hayward, Peter; Currie, Dean. "Radiography of Welds Using Selenium 75, Ir 192 and X-rays" (PDF).
- Lemly, Dennis (1998). Selenium Assessment in Aquatic Ecosystems: A guide for hazard evaluation and water quality criteria. Springer. ISBN 0-387-95346-9.
- Lemly, A. Dennis (2004-09-01). "Aquatic selenium pollution is a global environmental safety issue". Ecotoxicology and Environmental Safety. 59 (1): 44–56. doi:10.1016/S0147-6513(03)00095-2. ISSN 0147-6513. PMID 15261722.
- Gribble, Matthew; Karimi, Roxanne; Feingold, Beth; Nyland, Jennifer; O'Hara, Todd; Gladyshev, Michail; Chen, Celia (10/8/2015). "Mercury, selenium and fish oils in marine food webs and implications for human health". Journal of the Marine Biological Association of the United Kingdom. 1 (96): 43–59. doi:10.1017/S0025315415001356. PMC 4720108. PMID 26834292 – via Cambridge. Check date values in:
- Hamilton, Steven J. (2004-06-29). "Review of selenium toxicity in the aquatic food chain". Science of the Total Environment. 326 (1): 1–31. Bibcode:2004ScTEn.326....1H. doi:10.1016/j.scitotenv.2004.01.019. ISSN 0048-9697. PMID 15142762.
- Charya, Lakshangy (2017). Mohan Naik, Milind; Kumar Dubey, Santosh (eds.). Marine Pollution and Microbial Remediation. Singapore: Springer Science+Business Media Singapore. pp. 223–237. ISBN 978-981-10-1042-2.
- Linus Pauling Institute at Oregon State University lpi.oregonstate.edu
- Pakdel, Farzad; Ghazavi, Roghayeh; Heidary, Roghayeh; Nezamabadi, Athena; Parvizi, Maryam; Haji Safar Ali Memar, Mahsa; Gharebaghi, Reza; Heidary, Fatemeh (2019). "Effect of Selenium on Thyroid Disorders: Scientometric Analysis". Iranian Journal of Public Health. 48 (3): 410–420. ISSN 2251-6085. PMC 6570790. PMID 31223567.
- "Selenium". Linus Pauling Institute at Oregon State University. Retrieved 2009-01-05.
- Mazokopakis, E. E.; Papadakis, J. A.; Papadomanolaki, M. G.; et al. (2007). "Effects of 12 months treatment with L-selenomethionine on serum anti-TPO Levels in Patients with Hashimoto's thyroiditis". Thyroid. 17 (7): 609–612. doi:10.1089/thy.2007.0040. PMID 17696828.
- Ralston, N. V.; Ralston, C. R.; Blackwell, JL III; Raymond, L. J. (2008). "Dietary and tissue selenium in relation to methylmercury toxicity" (PDF). Neurotoxicology. 29 (5): 802–811. CiteSeerX 10.1.1.549.3878. doi:10.1016/j.neuro.2008.07.007. PMID 18761370.
- Penglase, S.; Hamre, K.; Ellingsen, S. (2014). "Selenium prevents downregulation of antioxidant selenoprotein genes by methylmercury". Free Radical Biology and Medicine. 75: 95–104. doi:10.1016/j.freeradbiomed.2014.07.019. hdl:1956/8708. PMID 25064324.
- Usuki, F.; Yamashita, A.; Fujimura, M. (2011). "Post-transcriptional defects of antioxidant selenoenzymes cause oxidative stress under methylmercury exposure". The Journal of Biological Chemistry. 286 (8): 6641–6649. doi:10.1074/jbc.M110.168872. PMC 3057802. PMID 21106535.
- Ohi, G.; Seki, H.; Maeda, H.; Yagyu, H. (1975). "Protective effect of selenite against methylmercury toxicity: observations concerning time, dose and route factors in the development of selenium attenuation". Industrial Health. 13 (3): 93–99. doi:10.2486/indhealth.13.93.
- Ralston, NVC; Raymond, L. J. (2010). "Dietary selenium's protective effects against methylmercury toxicity". Toxicology. 278 (1): 112–123. doi:10.1016/j.tox.2010.06.004. PMID 20561558.
- Carvalho, CML; Chew, Hashemy SI; Hashemy, J.; et al. (2008). "Inhibition of the human thioredoxin system: A molecular mechanism of mercury toxicity". Journal of Biological Chemistry. 283 (18): 11913–11923. doi:10.1074/jbc.M710133200. PMID 18321861.
- Michiaki Yamashita, Shintaro Imamura, Md. Anwar Hossain, Ken Touhata, Takeshi Yabu, and Yumiko Yamashita, Strong antioxidant activity of the novel selenium-containing imidazole compound ″selenoneine″, The FASEB Journal, vol. 26 no. 1, supplement 969.13, April 2012
- Yamashita, Y; Yabu, T; Yamashita, M (2010). "Discovery of the strong antioxidant selenoneine in tuna and selenium redox metabolism". World J Biol Chem. 1 (5): 144–50. doi:10.4331/wjbc.v1.i5.144. PMC 3083957. PMID 21540999.
- Raymond, Laura; Ralston, Nicholas (November 2004). "Mercury: selenium interactions and health implications" (PDF). SMDJ Seychelles Medical and Dental Journal. 7: 72–77 – via Amalgam Information.
- Gladyshev, Vadim N.; Hatfield, Dolph L. (1999). "Selenocysteine-containing proteins in mammals". Journal of Biomedical Science. 6 (3): 151–160. doi:10.1007/BF02255899. PMID 10343164.
- Stadtman, T. C. (1996). "Selenocysteine". Annual Review of Biochemistry. 65: 83–100. doi:10.1146/annurev.bi.65.070196.000503. PMID 8811175.
- Lobanov, Alexey V.; Fomenko, Dmitri E.; Zhang, Yan; et al. (2007). "Evolutionary dynamics of eukaryotic selenoproteomes: large selenoproteomes may associate with aquatic life and small with terrestrial life". Genome Biology. 8 (9): R198. doi:10.1186/gb-2007-8-9-r198. PMC 2375036. PMID 17880704.
- Venturi, Sebastiano; Venturi, Mattia (2007), "Evolution of Dietary Antioxidant Defences", European EpiMarker, 11 (3), pp. 1–11
- Castellano, Sergi; Novoselov, Sergey V.; Kryukov, Gregory V.; et al. (2004). "Reconsidering the evolution of eukaryotic selenoproteins: a novel nonmammalian family with scattered phylogenetic distribution". EMBO Reports. 5 (1): 71–7. doi:10.1038/sj.embor.7400036. PMC 1298953. PMID 14710190.
- Kryukov, Gregory V.; Gladyshev, Vadim N. (2004). "The prokaryotic selenoproteome". EMBO Reports. 5 (5): 538–43. doi:10.1038/sj.embor.7400126. PMC 1299047. PMID 15105824.
- Wilting, R.; Schorling, S.; Persson, B. C.; Böck, A. (1997). "Selenoprotein synthesis in archaea: identification of an mRNA element of Methanococcus jannaschii probably directing selenocysteine insertion". Journal of Molecular Biology. 266 (4): 637–41. doi:10.1006/jmbi.1996.0812. PMID 9102456.
- Zhang, Yan; Fomenko, Dmitri E.; Gladyshev, Vadim N. (2005). "The microbial selenoproteome of the Sargasso Sea". Genome Biology. 6 (4): R37. doi:10.1186/gb-2005-6-4-r37. PMC 1088965. PMID 15833124.
- Barclay, Margaret N. I.; MacPherson, Allan; Dixon, James (1995). "Selenium content of a range of UK food". Journal of Food Composition and Analysis. 8 (4): 307–318. doi:10.1006/jfca.1995.1025.
- "Selenium Fact Sheet". ODS.OD.NIH.gov. US: The Office of Dietary Supplements, National Institutes of Health. (includes a list of selenium-rich foods)
- "FDA Issues Final Rule to Add Selenium to List of Required Nutrients for Infant Formula". www.fda.gov. Archived from the original on November 14, 2017. Retrieved September 10, 2015.
- A common reference for this is Schroeder, H. A.; Frost, D. V.; Balassa, J. J. (1970). "Essential trace metals in man: Selenium". Journal of Chronic Diseases. 23 (4): 227–43. doi:10.1016/0021-9681(70)90003-2. OSTI 6424964. PMID 4926392.
- Zane Davis, T. (2008-03-27). "Selenium in Plants" (PDF). p. 8. Retrieved 2008-12-05.
- Baselt, R. (2008). Disposition of Toxic Drugs and Chemicals in Man (8th ed.). Foster City, CA: Biomedical Publications. pp. 1416–1420. ISBN 978-0-9626523-5-6.
- Razaghi, Ali; Poorebrahim, Mansour; Sarhan, Dhifaf; Björnstedt, Mikael (2021-09-01). "Selenium stimulates the antitumour immunity: Insights to future research". European Journal of Cancer. 155: 256–267. doi:10.1016/j.ejca.2021.07.013. ISSN 0959-8049. PMID 34392068.
- "Dietary Supplement Fact Sheet: Selenium". National Institutes of Health; Office of Dietary Supplements. Retrieved 2009-01-05.
- Panel on Dietary Antioxidants and Related Compounds, Subcommittees on Upper Reference Levels of Nutrients and Interpretation and Uses of DRIs, 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. doi:10.17226/9810. ISBN 978-0-309-06949-6. PMID 25077263.CS1 maint: multiple names: authors list (link)
- Yang, G.; Zhou, R. (1994). "Further Observations on the Human Maximum Safe Dietary Selenium Intake in a Seleniferous Area of China". Journal of Trace Elements and Electrolytes in Health and Disease. 8 (3–4): 159–165. PMID 7599506.
- Yang, Guang-Qi; Xia, Yi-Ming (1995). "Studies on Human Dietary Requirements and Safe Range of Dietary Intakes of Selenium in China and Their Application in the Prevention of Related Endemic Diseases". Biomedical and Environmental Sciences. 8 (3): 187–201. PMID 8561918.
- "Public Health Statement: Health Effects" (PDF). Agency for Toxic Substances and Disease Registry. Retrieved 2009-01-05.
- Wilber, C. G. (1980). "Toxicology of selenium". Clinical Toxicology. 17 (2): 171–230. doi:10.3109/15563658008985076. PMID 6998645.
- Olson, O. E. (1986). "Selenium Toxicity in Animals with Emphasis on Man". International Journal of Toxicology. 5: 45–70. doi:10.3109/10915818609140736. S2CID 74619246.
- "Polo pony selenium levels up to 20 times higher than normal". 2009-05-06. Retrieved 2009-05-05.
- Lemly, D. (2004). "Aquatic selenium pollution is a global environmental safety issue". Ecotoxicology and Environmental Safety. 59 (1): 44–56. doi:10.1016/S0147-6513(03)00095-2. PMID 15261722.
- Ohlendorf, H. M. (2003). Ecotoxicology of selenium. Handbook of ecotoxicology. Boca Raton: Lewis Publishers. pp. 466–491. ISBN 978-1-56670-546-2.
- Lemly, A. D. (1997). "A teratogenic deformity index for evaluating impacts of selenium on fish populations". Ecotoxicology and Environmental Safety. 37 (3): 259–266. doi:10.1006/eesa.1997.1554. PMID 9378093.
- Penglase, S.; Hamre, K.; Ellingsen, S. (2014). "Selenium and mercury have a synergistic negative effect on fish reproduction". Aquatic Toxicology. 149: 16–24. doi:10.1016/j.aquatox.2014.01.020. PMID 24555955.
- Heinz, G. H.; Hoffman, D. J. (1998). "Methylmercury chloride and selenomethionine interactions on health and reproduction in mallards". Environmental Toxicology and Chemistry. 17 (2): 139–145. doi:10.1002/etc.5620170202.
- Hamilton, Steven J.; Buhl, Kevin J.; Faerber, Neil L.; et al. (1990). "Toxicity of organic selenium in the diet to chinook salmon". Environ. Toxicol. Chem. 9 (3): 347–358. doi:10.1002/etc.5620090310.
- Poston, H. A.; Combs Jr., G. F.; Leibovitz, L. (1976). "Vitamin E and selenium interrelations in the diet of Atlantic salmon (Salmo salar): gross, histological and biochemical signs". Journal of Nutrition. 106 (7): 892–904. doi:10.1093/jn/106.7.892. PMID 932827.
- Brain, P.; Cousens, R. (1989). "An equation to describe dose responses where there is stimulation of growth at low doses". Weed Research. 29 (2): 93–96. doi:10.1111/j.1365-3180.1989.tb00845.x.
- "CDC - NIOSH Pocket Guide to Chemical Hazards - Selenium". www.cdc.gov. Retrieved 2015-11-21.
- Ravaglia, G.; Forti, P.; Maioli, F.; et al. (2000). "Effect of micronutrient status on natural killer cell immune function in healthy free-living subjects aged ≥90 y". American Journal of Clinical Nutrition. 71 (2): 590–598. doi:10.1093/ajcn/71.2.590. PMID 10648276.
- MedSafe Editorial Team. "Selenium". Prescriber Update Articles. New Zealand Medicines and Medical Devices Safety Authority. Retrieved 2009-07-13.
- Ralston, N. V. C.; Raymond, L. J. (2010). "Dietary selenium's protective effects against methylmercury toxicity". Toxicology. 278 (1): 112–123. doi:10.1016/j.tox.2010.06.004. PMID 20561558.
- Mann, Jim; Truswell, A. Stewart (2002). Essentials of Human Nutrition (2nd ed.). Oxford University Press. ISBN 978-0-19-262756-8.
- Moreno-Reyes, R.; Mathieu, F.; Boelaert, M.; et al. (2003). "Selenium and iodine supplementation of rural Tibetan children affected by Kashin-Beck osteoarthropathy". American Journal of Clinical Nutrition. 78 (1): 137–144. doi:10.1093/ajcn/78.1.137. PMID 12816783.
- Kachuee, R.; Moeini, M.; Suori, M. (2013). "The effect of dietary organic and inorganic selenium supplementation on serum Se, Cu, Fe and Zn status during the late pregnancy in Merghoz goats and their kids". Small Ruminant Research. 110 (1): 20–27. doi:10.1016/j.smallrumres.2012.08.010.
- National Research Council, Subcommittee on Sheep Nutrition (1985). Nutrient requirements of sheep. 6th ed., National Academy Press, Washington, ISBN 0309035961.
- National Research Council, Committee on Nutrient Requirements of Small Ruminants (2007). Nutrient requirements of small ruminants. National Academies Press, Washington, ISBN 0-309-10213-8.
- Coop, I. E.; Blakely, R. L. (1949). "The metabolism and toxicity of cyanides and cyanogenic glycosides in sheep". N. Z. J. Sci. Technol. 30: 277–291.
- Kraus, R. J.; Prohaska, J. R.; Ganther, H. E. (1980). "Oxidized forms of ovine erythrocyte glutathione peroxidase. Cyanide inhibition of 4-glutathione:4-selenoenzyme". Biochim. Biophys. Acta. 615 (1): 19–26. doi:10.1016/0005-2744(80)90004-2. PMID 7426660.
- Kahn, C. M. (ed.) (2005). Merck veterinary manual. 9th ed. Merck & Co., Inc., Whitehouse Station, ISBN 0911910506.