Selenium is a chemical element with the symbol Se and atomic number 34. It is nonmetal with intermediate properties between the elements above and below in the periodic table, sulfur and tellurium, and also have similarities with arsenic. This is rare in its elemental state or as a pure ore compound in the Earth's crust. Selenium (from Ancient Greek <> span lang = "el" title = "Greek text"> ?????? (cell? N?) "Moon") was discovered in 1817 by JÃÆ'¶ns Jacob Berzelius, who noted the similarity of new elements to the eggs that were found previously (named for Earth).
Selenium is found in metal sulfide ores, in which most of it replaces sulfur. Commercially, selenium is produced as a by-product in the purification of this ore, most often during production. Pure mineral selenide or selenat compounds are known but rarely. The main commercial use for selenium today is the manufacture of glass and pigments. Selenium is a semiconductor and is used in photocells. Applications in electronics, as well as important, have largely been replaced with silicon semiconductor devices. Selenium is still used in several types of DC power surge protectors and one type of fluorescent quantum dot.
Selenium salts are toxic in large quantities, but trace amounts are required for cell function in many organisms, including all animals. Selenium is an ingredient in many multivitamins and other dietary supplements, including infant formulas. It is a component of the antioxidant enzyme glutathione peroxidase and thioredoxin reductase (which indirectly reduces certain oxidized molecules in animals and some plants). It is also found in three deiodinase enzymes, which convert one thyroid hormone to another. The requirements of selenium on plants differ by species, with some plants requiring relatively large quantities and others apparently not needing them.
Video Selenium
Characteristics
Physical properties
Selenium forms several alotropes that change with temperature changes, depending on the rate of temperature change. When prepared in a chemical reaction, selenium is usually a red brick amorphous powder. When it melts rapidly, it forms a vitreous, black form, usually sold commercially as beads. The black selenium structure is irregular and complex and consists of polymer rings with up to 1000 atoms per ring. Black Se is a dense, brittle shine that is slightly soluble in CS 2 . After heating, it softens at 50 ° C and converts to gray selenium at 180 ° C; the transformation temperature is reduced by the presence of halogens and amines.
Red?,?, And? the form is produced from a solution of black selenium by varying the rate of solvent evaporation (usually CS 2 ). They all have relatively low monoclinic crystal symmetry and contain a Se 8 ring that is almost identical to different settings, such as sulfur. The most solid packaging in? form. On the Se se ring <8>, the Se-Se distance is 233.5 μm and the Se-Se-Se angle is 105.7 Â °. Other selenium allotropes may contain Se 6 or Se 7 rings.
The most stable and dense form of selenium is gray and has a hexagonal crystal lattice composed of a helical polymer chain, where the Se-Se spacing is 237.3 μm and the Se-Se-Se angle is 130.1 Â °. The minimum distance between the chains is 343.6 pm. Se grays are formed by other allotrope light heating, by slow cooling of liquid Se, or by condensing the steam just below the melting point. While the other Se form is an insulator, Se ash is a semiconductor that shows significant photoconductivity. Unlike other allotropes, it does not dissolve in CS 2 . It is oxidized by air resistance and is not attacked by nonoxidizing acids. With a strong reducing agent, it forms polyselenides. Selenium does not show changes in sulfur viscosity when heated gradually.
Optical properties
Due to its use as a photoconductor in a flat-panel x-ray detector (see below), the optical properties of the amorphous selenium thin film (? -Se) have been the subject of intense research.
Isotope
Selenium has seven natural isotopes, including 79 Se, which occurs in minute amounts in uranium ore, as well as 23 other synthetic isotopes.
Maps Selenium
Chemical compounds
Selenium compounds are generally present in oxidation states -2, 2, 4, and 6.
Compound calkon
Selenium forms two oxides: selenium dioxide (SeO 2 ) and selenium trioxide (SeO 3 ). Selenium dioxide is formed by the selenium reaction of the element with oxygen:
This is the polymer solid that forms the monomer mol mOse SeO 2 in the gas phase. It dissolves in water to form selenous acid, H 2 SeO 3 . Selenous acid can also be made directly by oxidizing the element of selenium with nitric acid:
- 3 Se 4 HNO 3 H - sub <2> <- sub> 2 SeO 3 4 NO
Unlike sulfur, which forms stable trioxide, thermodynamically selenium trioxide is unstable and decomposes to dioxide above 185 ° C:
- 2 SeO 3 -> 2 SeO 2 O 2 (? H = -54 kJ/mol) >
Selenium trioxide is produced in the laboratory by the reaction of potassium selenate anhydride (K 2 SeO 4 ) and sulfur trioxide (SO 3 ).
Selenous acid salts are called selenites. These include silver selenite (Ag 2 SeO 3 ) and sodium selenite (Na 2 SeO 3 ).
Hydrogen sulfide reacts with an aqueous selenous acid to produce selenium disulfide:
- H 2 SeO 3 2 H 2 S -> SeS 2 3 H 2 O
Selenium disulfide consists of 8 membered rings. It has an approximate composition of SeS 2 , with individual rings varying in composition, such as Se 4 S 4 and Se 2 S 6 . Selenium disulfide has been used in shampoos as antidandruff agents, inhibitors in polymer chemistry, glass dyes, and reducing agents in fireworks.
Selenium trioxide can be synthesized by dehydration of selenic acid, H 2 SeO 4 , which itself is produced by the oxidation of selenium dioxide with hydrogen peroxide: 2 O 2 -> H 2 /sub>
Hot, concentrated selenat acid can react with gold to form gold (III) selenat.
Halogen compounds
The selenium Iodide is not well known. The only stable chloride is selenium monochloride (Se 2 Cl 2 ), which may be better known as selenium (I) chloride; Suitable bromides are also known. The species is structurally analogous to the appropriate disulfur dichloride. Selenium dichloride is an important reagent in the preparation of selenium compounds (eg preparation Se 7 ). This is prepared by treating selenium with sulfuryl chloride (SO 2 Cl 2 ). Selenium reacts with fluorine to form selenium hexafluoride:
- Se 8 24 F 2 -> 8 SeF 6
Compared with its sulfur (sulfur hexafluoride) counterpart, selenium hexafluoride (SeF 6 ) is more reactive and is a toxic lung irritant. Some selenium oxyhalides, such as selenium oxyfluoride (SeOF 2 ) and selenium oxychloride (SeOCl 2 ) have been used as special solvents.
Selenides
Similar to other chalcogens behavior, selenium forms hydrogen selenide, H 2 Se. This is a very dangerous gas, toxic, and colorless. It is more acidic than H 2 S. In the solution it is ionized to HSe - . Dianion selenide Se 2 - forms various compounds, including 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) Se 2 ). These materials are semiconductors. With highly electropositive metals, such as aluminum, this selenoid is susceptible to hydrolysis:
- Al 2 Se 3 3 H 2 O -> Al 2 O 3 3 H 2 Se
Seleniide alkali metals react with selenium to form polyselenides, Se 2 - n , existing as a chain.
Other compounds
Tetraselenium tetranitride, Se 4 N 4 , adalah senyawa oranye eksplosif yang analog dengan tetrasit tetranitrida (S 4 N 4 ). Ini dapat disintesis oleh reaksi selenium tetrachloride (SeCl 4 ) dengan [((CH
3 )
3 Si)
2 N ]
2 Se .
Selenium reacts with cyanide to produce selenocyanate:
- 8 KCN Se 8 -> 8 KSeCN
Organoselenium compounds
Selenium, especially in the oxidation state II, forms a stable bond to carbon, which is structurally analogous to the corresponding organosulfur compound. Particularly common are selenides (R 2 Se, analogues of thioethers), diselenides (R 2 Se 2 , analogs of disulphide), and selenol (RSeH, analog thiols). Representatives of selenides, diselenides, and selenols include respectively selenomethionine, diphenyldiselenide, and benzeneselenol. Sulfides in sulfur chemistry are represented in selenium chemistry by selenoxides (RSe (O) R), which is an intermediate in organic synthesis, as illustrated by selenoxide elimination reactions. Consistent with the trends indicated by the double bond rule, selenocetones, R (C = Se) R, and selenaldehydes, R (C = Se) H, are rarely observed.
History
Selenium (Greek ?????????????????????????????????????????????????????????????????????????????????????????????????? ???????????????????????????) Selenium (Greek ??????????????????? Both chemists have a chemical plant near Gripsholm, Sweden, which produces sulfuric acid through the process of lead space.Pyrite from the mine of Falun creates red sludge in the main room which is considered as arsenic compound, so the use of pyrite to make the acid is stopped Berzelius and Gahn want to use pyrite and they also observe that the red sediment emits a smell like radish when burned. this is not typical of arsenic, but the same odor is known from the tellurium compound.Therefore, the first letter of Berzelius to Alexander Marcet states that this is a tellurium compound.However, the lack of an egg compound in the mineral miner Falun ultimately caused Berzelius to re-analyze the red sediment, and in 1818 he wrote a second letter to Marcet describing un sur newly discovered similar to sulfur and tellurium. Because of its resemblance to tellurium, named for Earth, Berzelius names the new element after the Moon.
In 1873, Willoughby Smith discovered that the electrical resistance of gray selenium depends on ambient light. This causes its use as a cell to sense light. The first commercial product using selenium was developed by Werner Siemens in the mid-1870s. Selenium cells are used in a 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 is used in the design of light meters and similar devices. The properties of semiconductor Selenium find many other applications in electronics. The development of selenium rectifiers began in the early 1930s, and this replaced the copper oxide rectifiers because they were more efficient. This went on in commercial applications until the 1970s, after which it was replaced with cheaper and even more efficient silicon rectifiers.
Selenium came to medical notice later due to his toxicity to humans working in the industry. Selenium is also recognized as an important animal poison, which is seen in animals that have eaten high selenium crops. In 1954, the first clue of selenium-specific biologic function was found in microorganisms by chemist Jane Pinsent. It was found to be essential to the life of mammals in 1957. In the 1970s, it was shown to be present in two independent sets of enzymes. This is followed by the discovery of selenocysteine ​​â € <â €
Genesis
Native (ie, elements) selenium is a rare mineral, which usually does not form a good crystal, but, when it does, they are a steep rhombohedra or small acicular crystal. Selenium isolation 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. Common minerals are not selenium minerals, and contain no selenite ions, but rather a kind of gypsum (calcium sulfate hydrate) called selenium for months before the discovery of selenium. Selenium is most often found as an impurity, replacing a small fraction of sulfur in sulphide ores from many metals.
In living systems, selenium is found in amino acids selenomethionine, selenocysteine, and methylselenocysteine. In this compound, selenium plays an analogous role with sulfur. Other naturally occurring organoselenium compounds are dimethyl selenide.
Certain solids are selenium-rich, and selenium can be biodegradable by some plants. Within the soil, selenium most commonly occurs in soluble forms such as selenate (analogous to sulfate), which is easily washed into rivers by runoff. Sea water contains a lot of selenium.
The sources of anthropogenic selenium include coal combustion, and the mining and smelting of sulphide ores.
Production
Selenium is most often produced from selenide in many sulphide ores, such as those of copper, nickel, or tin. The purification of electrolytic metal is particularly productive of selenium as a by-product, obtained from the anode mud from a copper refinery. Another source is the mud from the main chambers of the sulfuric acid factories, a process that is no longer used. Selenium can be purified from this mud by a number of methods. However, most of the elemental selenium comes as a by-product of copper refining or producing sulfuric acid. Since its discovery, the production of solvent extraction and electrowinning (SX/EW) from copper has resulted in an increased share of copper supply worldwide. This alters the availability of selenium because only a small percentage of selenium is ore is washed with copper.
Selenium industrial production usually involves the extraction of selenium dioxide from residues obtained during copper refining. The general production of the residue then begins with oxidation with sodium carbonate to produce selenium dioxide, which is mixed with water and acidified to form selenous acid (oxidation step). Selenous acid is melted with sulfur dioxide (reduction step) to give the element selenium.
Approximately 2,000 tons of selenium are produced in 2011 worldwide, mostly in Germany (650 t), Japan (630 t), Belgium (200 t), and Russia (140 t), and total reserves estimated at 93,000 tonnes. This data excludes two major manufacturers, the United States and China. The previous sharp increase was observed in 2004 from 4-5 to $ 27/lb. Prices were relatively stable during 2004-2010 of approximately US $ 30 per pound (in 100-pound lots) but increased to $ 65/lb in 2011. Consumption in 2010 is 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 tons/year.
Apps
Electrolysis of manganese
During electro winning from manganese, the addition of selenium dioxide reduces the power required to operate the electrolysis cell. China is the largest consumer of selenium dioxide for this purpose. For every ton of manganese, an average of 2 kg of selenium oxide is used.
Glass production
The largest commercial use of Se, accounting for about 50% of consumption, is for glass production. Compound se gives a red color to the glass. This color cancels the green or yellow color that appears from the typical iron droppings for most glass. For this purpose, various salts of selenit and selenat are added. For other applications, red color may be desirable, generated by a mixture of CdSe and CdS.
Alloy
Selenium is used with bismuth in brass to replace more toxic tin. The tin regulations in drinking water applications under the Safe Drinking Water Act of 1974 made the reduction of lead in brass required. New brass is marketed under the name EnviroBrass. Like lead and sulfur, selenium improves steel machinability at a concentration of about 0.15%. Selenium produces the same increase in machinability in copper alloys.
Lithium-selenium battery
Lithium-selenium (Li-Se) batteries are one of the most promising systems for energy storage in a family of lithium batteries. Li-Se batteries are an alternative to Lithium-sulfur batteries with high electrical conductivity advantages.
Solar cell
Copper indium gallium selenide is the material used in solar cells.
Photoconductors
The amorphous selenium (-Se) thin membrane has found application as a photoconductor on a flat-panel x-ray detector. These detectors utilize amorphous selenium to capture and convert x-ray incident incidents directly into electrical charges. Based on this application, significant research has been done in recent years to measure the optical properties of these thin films.
Other uses
Small amounts of organoselenium compounds are used to modify vulcanization catalysts for rubber production.
Selenium demand by the electronics industry is declining, although some applications continue. Its photovoltaic and photoconductive properties are still useful in photocopying, photocell, light meters, and solar cells. Its use as a photoconductor in ordinary paper copiers was once a prominent application, but in the 1980s, photoconductor applications declined (though still in large end use) as more and more photocopiers switched to organic photoconductors. Although once widely used, selenium rectifiers have largely been replaced (or replaced) by silicon-based devices. The most important exception is in DC power surge protection, where superior energy capability of selenium suppressors makes them more desirable than metal oxide varistors.
Zinc selenide is the first material for blue LEDs, but gallium nitride dominates the market now. Cadmium selenide is an important component in quantum dots. The sheets of amorphous selenium convert the X-ray image into a charge pattern in xeroradiography and a flat-panel X-ray camera. The ionized selenium (Se 24) is one of the active medium used in X-ray lasers.
Selenium is a catalyst in several chemical reactions, but is not widely used because of problems with toxicity. In X-ray crystallography, the incorporation of one or more selenium atoms in the sulfur site helps with multi-wavelength anomaly dispersion and single wavelength anomaly dispersion phases.
Selenium is used in toning photo prints, and is sold as a toner by many photographers. Selenium intensified and extended the color range of black-and-white photographic photographs and enhanced fingerprint immortality.
75 Se is used as a gamma source in industrial radiography.
The role of biology
Although toxic in large doses, selenium is an essential micronutrient for animals. In plants, these occur as observer minerals, sometimes in toxic proportions in forage (some plants can accumulate selenium as a defense against eating by animals, but other plants, such as locoweed, require selenium, and their growth indicates the presence of selenium in the soil). See more about the nutritional crops below.
Selenium is a component of the amino acid selenocysteine ​​â € Family enzymes glutathione peroxidase (GSH-Px) catalyzes certain reactions that eliminate reactive oxygen species such as hydrogen peroxide and organic hydroperoxides:
The thyroid gland and every cell that uses thyroid hormones use selenium, which is a cofactor for three of the four known types of thyroid deiodinase, which activate and then inactivate various thyroid hormones and their metabolites; the iodothyronine deiodinases is a subfamily of deiodinase enzymes that use selenium as selenocysteine ​​â € <â € Selenium can inhibit Hashimoto's disease, in which the body's own thyroid cells are attacked as aliens. A 21% reduction in TPO antibodies was reported with a 0.2 mg selenium diet intake. Increased selenium diet reduces the effects of mercury toxicity, although it is only effective at low doses of mercury. The evidence suggests that the molecular mechanisms of mercury toxicity include inhibition of the irreversible selenoenzymes necessary to prevent and reverse oxidative damage in the brain and endocrine tissues. The antioxidant, selenoneine, which is derived from selenium and has been found present in bluefin tuna, is the subject of scientific research on possible roles in inflammatory and chronic diseases, methylmercury detoxification, and oxidative damage. Evolution in biology
From about three billion years ago, the prokaryotic selenoprotein family encouraged the evolution of selenocysteine, an amino acid. Selenium is incorporated into several families of prokaryotic selenoproteins in bacteria, archaea, and eukaryotes as selenocysteine, in which perokshedoxin selenoprotein protects bacterial and eukaryotic cells against oxidative damage. The selenoprotein family of GSH-Px and eukaryotic cell deiodinase appear to have a bacterial phylogenetic origin. The forms containing selenocysteine ​​occur in diverse species such as green algae, diatoms, sea urchins, fish, and chickens. The enzyme selenium is involved in small molecules that reduce glutathione and thioredoxin. A family of selenium-bearing molecules (glutathione peroxidases) destroys peroxides and fixes damaged peroxidized cell membranes, using glutathione. Other selenium-bearing enzymes in some plants and in animals (thioredoxin reductase) result in decreased thioredoxin, dithiol that serves as a source of electrons for peroxidase as well as reduction of an important reducing enzyme ribonucleotide that precursors DNA from RNA precursors.
The trace elements involved in the activity of GSH-Px and superoxide dismutase enzymes, namely selenium, vanadium, magnesium, copper, and zinc, may be lacking in some regions that lack terrestrial minerals. Marine organisms retain and sometimes expand their selenoproteomes, while the selenoproteomes of some terrestrial organisms are reduced or completely lost. These findings suggest that, with the exception of vertebrates, aquatic life supports the use of selenium, whereas terrestrial habitats lead to reduced use of these trace elements. Marine fish and vertebrate thyroid glands have the highest concentrations of selenium and iodine. From about 500 million years ago, freshwater and terrestrial plants gradually optimized the production of new "endogenous" antioxidants such as ascorbic acid (vitamin C), polyphenols (including flavonoids), tocopherols, etc. Some of these have emerged lately, in the last 50-200 million years, in fruit and flower angiosperm plants. In fact, angiosperms (the dominant type of plants today) and most of their antioxidant pigments evolved during the final Jurassic period.
Isoenzyme deiodinase forms another family of eukaryotic selenoproteins with identified enzyme function. Deiodinases are able to extract electrons from iodides, and iodides from iodothyronines. They are, therefore, involved in the regulation of thyroid hormones, participating in the protection of thyrocytes from damage by H 2 O 2 produced for thyroid hormone biosynthesis. About 200 million years ago, new selenoproteins were developed as GSH-Px mammalian enzymes.
Source of selenium nutrition
Selenium diets come from nuts, cereals and mushrooms. Brazil nuts are the richest source of food (though this depends on soil, since Brazil nuts do not require a high level of ingredients for their own needs).
Recommended Dietary Nutrition US (RDA) for adolescents and adults is 55 Ã,Âμg/day. Selenium as a dietary supplement is available in various forms, including multi-vitamin/mineral supplements, which typically contain 55 or 70 Âμg/servings. Selenium-specific supplements usually contain 100 or 200Ã,Âμg/portion.
In June 2015, the US Food and Drug Administration (FDA) published its final rule establishing minimum and maximum levels of selenium in formula milk.
The content of selenium in the human body is believed to be in the range of 13-20 milligrams.
Plant type indicator
Certain plant species are considered as indicators of high selenium content from the soil because they require high selenium levels to thrive. The main selenium indicator plants are the species of Astragalus (including some locoweeds), plume prince ( Stanleya sp.), Daisies ( Xylorhiza sp.), and fake goldenweed ( Oonopsis sp.)
Detection in biological fluid
Selenium can be measured in blood, plasma, serum, or urine to monitor excessive environmental or occupational exposure, to confirm the diagnosis of poisoning in hospitalized victims, or to investigate suspected cases of fatal overdose. Some analytical techniques are able to differentiate organic from inorganic elements. Both organic and inorganic forms of selenium are largely converted into monosaccharide conjugates (selenosugars) in the body before urinary elimination. Cancer patients who receive daily oral doses of selenothionine can achieve high plasma selenium and urine concentrations.
Toxicity
Although selenium is an essential element, it is toxic if consumed in excess. Exceeding the Intake Tolerable Level 400 micrograms per day may cause selenosis. This 400Ã,Âμg Tolerable Upper Intake Level is based primarily on a 1986 study of five Chinese patients showing signs of selenosis and follow-up studies in the same five people in 1992. The 1992 study actually found the maximum safe dietary intake to be consumed. about 800 micrograms per day (15 micrograms per kilogram of body weight), but it is recommended 400 micrograms per day to avoid creating nutritional imbalances in food and to adjust to data from other countries. In China, people who digest corn grown in highly-selenium-rich rocky coal (carbon shale) have suffered from selenium toxicity. The coal is proven to have a 9.1% selenium content, the highest concentration in coal ever recorded.
Signs and symptoms of selenosis include odor of garlic on the breath, gastrointestinal disorders, hair loss, nail decay, fatigue, irritability, and nerve damage. Extreme cases of selenosis may indicate cirrhosis of the liver, pulmonary edema, or death. The most selenium and selenoid metal elements have relatively low toxicity due to low bioavailability. In contrast, selenates and selenites have an oxidant action similar to arsenic trioxide and are highly toxic. The chronic toxic dose of selenite to humans is about 2,400 to 3,000 micrograms of selenium per day. Hydrogen selenide is a highly toxic corrosive gas. Selenium also occurs in organic compounds, such as dimethyl selenide, selenometionin, selenocysteine, and methylselenocysteine, all of which have high bioavailability and are toxic in large doses.
On April 19, 2009, 21 polo horses died shortly before the game in the United States Polo Open. Three days later, a pharmacy released a statement explaining that the horses had received the wrong doses of one of the ingredients used in supplements of vitamin/mineral supplements that had been wrongly prepared by the compounding pharmacies. Analysis of blood levels of inorganic compounds in supplements showed selenium concentrations ten to fifteen times higher than normal in blood samples, and 15 to 20 times higher than normal in liver samples. Selenium is then confirmed to be a toxic factor.
Selenium poisoning water systems can occur every time a new agricultural runoff program passes through normally dry and undeveloped land. This process dissolves natural selenium compounds (such as selens) into the water, which can then be concentrated in the new "wetlands" as water evaporates. Pollution of selenium in waterways also occurs when selenium is spared from coal ash waste, metal mining and smelting, crude oil processing, and landfill. The high selenium levels produced in the aqueduct are found to cause congenital disruption in oviparous species, including wetland birds and fish. Increased dietary methylmercury levels can reinforce the danger of selenium toxicity in species that live outside of the sidelines.
In fish and other wildlife, selenium is required for life, but is toxic in high doses. For salmon, the optimal selenium concentration is about 1 microgram of selenium per gram of overall body weight. Far below that level, young salmon die from lack; far above, they die because of the excess poison.
Occupational Safety and Health Administration (OSHA) has set a legal limit (Exposure limits allowed) for selenium at work at 0.2 m/m 3 for 8 hours of work. The National Institute for Occupational Safety and Health (NIOSH) has set a Recommended Recommended (REL) limit of 0.2 m/m 3 for 8 hours. At a level of 1 mg/m 3 , selenium is immediately harmful to life and health.
Disadvantages
Selenium deficiency can occur in patients with highly impaired bowel function, those who underwent total parenteral nutrition, and in elderly (more than 90). Also, people who depend on foods that grow from soils with selenium deficiency are at risk. Although New Zealand soils have low levels of selenium, adverse health effects have not been detected in the population.
Selenium deficiency, defined by low (& lt; 60% of normal) levels of selenoenzyme activity in the brain and endocrine tissue, occurs only when low selenium levels are associated with additional stress, such as high exposure to mercury or increased oxidant stress of vitamin E. deficiency.
Selenium interacts with other nutrients, such as iodine and vitamin E. The effect of selenium deficiency on health remains unclear, especially in relation to Kashin-Beck's disease. Also, selenium interacts with other minerals, such as zinc and copper. Supplements High doses in pregnant animals may interfere with the ratio of Zn: Cu and cause Zn reduction; in the case of such treatment, Zn levels should be monitored. More research is needed to confirm this interaction.
In areas (eg different regions of North America) where low selenium soil levels cause low concentrations in plants, some animal species may be deficient unless selenium is added with diet or injection. Ruminants are very vulnerable. In general, the absorption of dietary selenium is lower in ruminant animals than other animals, and lower than forage than from whole grains. Some gum rosinants, for example, some white clover varieties containing cyanogenic glycosides, may have higher selenium requirements, possibly because cyanide is released from aglycons by glucosidase activity in the rumen and glutathione peroxidase is disabled by cyanide acting on the glutathione side. Ruminant neonates at risk for white muscle disease may be given selenium and vitamin E by injection; some WMD myopathies respond only to selenium, some just for vitamin E, and some others.
Controversial health effects
A number of correlative epidemiological studies have involved selenium deficiency (measured by blood levels) in a number of serious or chronic diseases, such as cancer, diabetes, HIV/AIDS, and tuberculosis. In addition, selenium supplementation has been found to be chemopreventive for some cancers in some rodents. One study of 118 pancreatic exocrine cancer patients (EPC) and 399 hospital controls in eastern Spain found high selenium concentrations inversely proportional to EPC risk. In a randomized, blind, controlled, prospective trial in humans, selenium supplementation has not been successful in reducing the incidence of any disease, or lacks a meta-analysis of selenium supplementation studies that detect overall mortality decline. However, selenium supplementation may be beneficial in cancer patients receiving radiotherapy.
See also
- ACES (nutritional supplements)
- Abundance of elements in the Earth's crust
- Yeast selenium
- Selene
References
External links
- Selenium on Video Periodic Table (University of Nottingham)
- The National Institutes of Health page on Selenium
- Assay
- ATSDRÃ, - Toxicology Profile: Selenium
- CDC - NIOSH A Pocket Guide for Chemical Hazards
- Site of Peter van der Krogt's element
Source of the article : Wikipedia
0 Comments