34 arsenic ← selenium → bromine S ↑ Se ↓ Te Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	selenium, Se, 34
Chemical series	nonmetals
Group, Period, Block	16, 4, p
Appearance	gray-black, metallic luster
Standard atomic weight	78.96(3)  g·mol−1
Electron configuration	[Ar] 4s2 3d10 4p4
Electrons per shell	2, 8, 18, 6
Physical properties
Phase	solid
Density (near r.t.)	(gray) 4. Arsenic (ˈɑrsənɪk is a Chemical element that has the symbol As and Atomic number of 33 Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52 This is a typical display of the periodic table of the elements and contains the symbol and Atomic number of each element Wikipedia talkFeatured lists for an explanation of this and other inclusion tags below -->This is a list of Chemical elements, sorted by name Wikipedia talkFeatured lists for an explanation of this and other inclusion tags below -->This is a list of chemical elements by symbol, including the A table of Chemical elements ordered by Atomic number and color coded according to type of element In Chemistry a group, also known as a family, is a vertical column in the Periodic table of the Chemical elements There are 18 groups in Nonmetal is a term used in Chemistry when classifying the Chemical elements On the basis of their general physical and chemical properties every element in the In Chemistry a group, also known as a family, is a vertical column in the Periodic table of the Chemical elements There are 18 groups in In the Periodic table of the elements, a period is a horizontal row of the table A block of the Periodic table of elements is a set of adjacent groups The respective highest-energy electrons in each element in a block belong to the same Atomic See also Gold chalcogenides Periodic table A period 4 element is one of the Chemical elements in the fourth row (or period) of the periodic table of the elements. See also Electron configuration The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass To help compare different orders of magnitude, the following list describes various Mass levels between 10&minus36&thinsp kg and 1053&thinspkg In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other This article pertains to the chemical element For other uses see Argon (disambiguation. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus. In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Room temperature (also referred to as ambient temperature) is a common term to denote a certain Temperature within enclosed space at which humans are accustomed 81  g·cm−3
Density (near r.t.)	(alpha) 4. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Room temperature (also referred to as ambient temperature) is a common term to denote a certain Temperature within enclosed space at which humans are accustomed 39  g·cm−3
Density (near r.t.)	(vitreous) 4. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Room temperature (also referred to as ambient temperature) is a common term to denote a certain Temperature within enclosed space at which humans are accustomed 28  g·cm−3
Liquid density at m.p.	3. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different The melting point of a solid is the temperature range at which it changes state from solid to Liquid. 99  g·cm−3
Melting point	494 K (221 °C, 430 °F)
Boiling point	958 K (685 °C, 1265 °F)
Critical point	1766 K, 27. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The Celsius Temperature scale was previously known as the centigrade scale. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The Celsius Temperature scale was previously known as the centigrade scale. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 In Physical chemistry, Thermodynamics, Chemistry and Condensed matter physics, a critical point, also called a critical state The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic 2 MPa
Heat of fusion	(gray) 6. The standard Enthalpy of fusion (symbol \Delta{}H_{fus} also known as the heat of fusion or specific melting heat, is the amount of 69  kJ·mol−1
Heat of vaporization	95. The joule per mole (symbol J·mol-1 is an SI derived unit of energy per amount of material The enthalpy of vaporization, (symbol \Delta{}_{v}H also known as the heat of vaporization or heat of evaporation, is the Energy required 48  kJ·mol−1
Specific heat capacity	(25 °C) 25. The joule per mole (symbol J·mol-1 is an SI derived unit of energy per amount of material Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity 363  J·mol−1·K−1
Vapor pressure P(Pa) 1 10 100 1 k 10 k 100 k at T(K) 500 552 617 704 813 958
Atomic properties
Crystal structure	hexagonal
Oxidation states	6, 4, 2, 1,[1] -2 (strongly acidic oxide)
Electronegativity	2. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. In Chemistry, the oxidation state is an indicator of the degree of Oxidation of an Atom in a Chemical compound. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons 55 (Pauling scale)
Ionization energies (more)	1st:  941. The ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron These tables list the Ionization energy in kJ/mol necessary to remove one mole of Electrons from one mole of neutral gaseous Atoms (first energy respectively 0  kJ·mol−1
	2nd:  2045  kJ·mol−1
	3rd:  2973. The joule per mole (symbol J·mol-1 is an SI derived unit of energy per amount of material 7  kJ·mol−1
Atomic radius	115  pm
Atomic radius (calc. Atomic radius, and more generally the size of an atom, is not a precisely defined Physical quantity, nor is it constant in all circumstances A picometre ( American spelling: picometer, symbol pm) is a unit of Length in the Metric system, equal to one trillionth )	103  pm
Covalent radius	116  pm
Van der Waals radius	190 pm
Miscellaneous
Magnetic ordering	no data
Thermal conductivity	(300 K) (amorphous) 0. The covalent radius, r cov is a measure of the size of Atom which forms part of a Covalent bond. Van der Waals Volume The van der Waals volume, V, also called the atomic volume or molecular volume, is the atomic property most directly In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. 519  W·m−1·K−1
Thermal expansion	(25 °C) (amorphous) 37  µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 3350 m/s
Young's modulus	10  GPa
Shear modulus	3. When the Temperature of a substance changes the energy that is stored in the Intermolecular bonds between atoms changes Sound is a vibration that travels through an elastic medium as a Wave. In Solid mechanics, Young's modulus (E is a measure of the Stiffness of an isotropic elastic material In Materials science, shear modulus or modulus of rigidity, denoted by G, or sometimes S or μ, is defined as the ratio of Shear 7  GPa
Bulk modulus	8. 3  GPa
Poisson ratio	0. Poisson's ratio ( ν) named after Simeon Poisson, is the ratio of the relative contraction strain, or transverse strain (normal to 33
Mohs hardness	2. The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material 0
Brinell hardness	736  MPa
CAS registry number	7782-49-2
Selected isotopes
Main article: Isotopes of selenium iso NA half-life DM DE (MeV) DP 72Se syn 8. The Brinell scale characterizes the indentation Hardness of materials through the scale of penetration of an indenter loaded on a material test-piece CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to Selenium ( Se) has six naturally occurring Isotopes five of which are stable 74Se 76Se 77Se 78Se and 80Se Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides In Chemistry, natural abundance (NA refers to the abundance Isotopes of a Chemical element as naturally found on a planet Half-Life (computer-game page here It's already listed in the disambiguation page Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. The decay energy is the Energy released by a Nuclear decay. The energy difference of the Reactants is often written as Q: where Q In Nuclear physics, a decay product, also known as a daughter product, daughter isotope or daughter nuclide, is a Nuclide A synthetic radioisotope is a Radionuclide that is not found in nature no natural process or mechanism exists which produces it or it is so unstable that it decays away in 4 d ε - 72As γ 0. A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the Electron capture (sometimes called inverse beta decay) is a Decay mode for Isotopes that will occur when there are too many Protons in the Arsenic (ˈɑrsənɪk is a Chemical element that has the symbol As and Atomic number of 33 Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions 046 - 74Se 0. 87% 74Se is stable with 40 neutrons 75Se syn 119. Stable isotopes are chemical isotopes that are not Radioactive (to current knowledge This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. A synthetic radioisotope is a Radionuclide that is not found in nature no natural process or mechanism exists which produces it or it is so unstable that it decays away in 779 d ε - 75As γ 0. A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the Arsenic (ˈɑrsənɪk is a Chemical element that has the symbol As and Atomic number of 33 264, 0. 136, 0. 279 - 76Se 9. 36% 76Se is stable with 42 neutrons 77Se 7. Stable isotopes are chemical isotopes that are not Radioactive (to current knowledge This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. 63% 77Se is stable with 43 neutrons 78Se 23. Stable isotopes are chemical isotopes that are not Radioactive (to current knowledge This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. 78% 78Se is stable with 44 neutrons 79Se syn 2. Stable isotopes are chemical isotopes that are not Radioactive (to current knowledge This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. A synthetic radioisotope is a Radionuclide that is not found in nature no natural process or mechanism exists which produces it or it is so unstable that it decays away in 95×105 y β- 0. A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted 151 79Br 80Se 49. 61% 80Se is stable with 46 neutrons 82Se 8. Stable isotopes are chemical isotopes that are not Radioactive (to current knowledge This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. 73% 1. 08×1020 y β-β- 2. A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun In the process of Beta decay, unstable nuclei decay by converting a Neutron in the nucleus to a Proton and emitting an Electron and an electron 995 82Kr
References

Selenium (pronounced /səˈliːniəm/) is a chemical element with the atomic number 34, represented by the chemical symbol Se. Krypton (ˈkrɪptən or /ˈkrɪptɒn/ from kryptos "hidden" is a Chemical element with the symbol Kr and Atomic number 36 Recommended values for many properties of the elements together with various references are collected on these data pages A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurs in its elemental state in nature. Nonmetal is a term used in Chemistry when classifying the Chemical elements On the basis of their general physical and chemical properties every element in the Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52 It is toxic in large amounts, but trace amounts of it are necessary for cellular function in most, if not all, animals, forming the active center of the enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants) and three known deiodinase enzymes (which convert one thyroid hormone to another). Glutathione peroxidase () is the general name of an Enzyme family with Peroxidase activity whose main biological role is to protect the organism from oxidative damage Thioredoxin Reductase (TR TrxR ( are the only known enzymes to reduce Thioredoxin (Trx Deiodinase ( is an Enzyme important in the action of Thyroid hormones. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced Selenium requirements in plants differ by species, with some plants apparently requiring none. ^[2]

Isolated selenium occurs in several different forms, the most stable of which is a dense purplish-gray semi-metal (semiconductor) form that is structurally a trigonal polymer chain. It conducts electricity better in the light than in the dark, and is used in photocells (see allotropic section below). Photosensors or photodetectors are Sensors of Light or other Electromagnetic energy Selenium also exists in many non-conductive forms: a black glass-like allotrope, as well as several red crystalline forms built of eight-membered ring molecules, like its lighter chemical cousin sulfur. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic

Selenium is found in economic quantities in sulfide ores such as pyrite, partially replacing the sulfur in the ore matrix. The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Minerals that are selenide or selenate compounds are also known, but all are rare.

Contents 1 Occurrence 2 Isotopes 3 History and global demand 4 Reference in popular culture 5 Selenium and health 5.1 Toxicity 5.2 Deficiency 5.3 Controversial health effects 6 Production and allotropic forms 7 Non-biological applications 8 Biological applications 9 Compounds 10 References 11 External links

Occurrence

Selenium occurs naturally in a number of inorganic forms, including selenide, selenate and selenite. The selenide Ion is Se2&minus A selenide is a chemical compound in which Selenium serves as an Anion with Oxidation number The selenate Ion is SeO42&minus Selenates are analogous to Sulfates and have similar chemistry Sodium selenite is a Chemical compound with the formula Na 2 Se[[Oxygen O]]3 In soils, selenium most often occurs in soluble forms like selenate (analogous to sulfate), which are leached into rivers very easily by runoff.

Selenium has a biological role, and is found in organic compounds such as dimethyl selenide, selenomethionine, selenocysteine and methylselenocysteine. Selenomethionine is an Amino acid containing Selenium. The L-isomer of selenomethionine known as Se-met and Sem is a common natural food source of Selenocysteine is an Amino acid that is present in several Enzymes (for example Glutathione peroxidases tetraiodothyronine 5' deiodinases In these compounds selenium plays an analogous role to sulfur.

Selenium is most commonly produced from selenide in many sulfide ores, such as those of copper, silver, or lead. The selenide Ion is Se2&minus A selenide is a chemical compound in which Selenium serves as an Anion with Oxidation number The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly It is obtained as a byproduct of the processing of these ores, from the anode mud of copper refineries and the mud from the lead chambers of sulfuric acid plants. An anode is an Electrode through which Electric current flows into a polarized electrical device Sulfuric (or sulphuric acid, H 2 S[[oxygen O]]4 is a strong Mineral acid. These muds can be processed by a number of means to obtain free selenium.

Natural sources of selenium include certain selenium-rich soils, and selenium that has been bioconcentrated by certain toxic plants such as locoweed. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at ftudruinsubstance is lost Locoweed is also a slang name for Cannabis, and Jimson weed. Locoweed is a term used to describe Plants from two different Anthropogenic sources of selenium include coal burning and the mining and smelting of sulfide ores. ^[3]

See also Selenide minerals.

Isotopes

Main article: isotopes of selenium

Selenium has six naturally occurring isotopes, five of which are stable: ⁷⁴Se, ⁷⁶Se, ⁷⁷Se, ⁷⁸Se, and ⁸⁰Se. Selenium ( Se) has six naturally occurring Isotopes five of which are stable 74Se 76Se 77Se 78Se and 80Se Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides The last three also occur as fission products, along with ⁷⁹Se which has a halflife of 295,000 years, and ⁸²Se which has a very long half life (~10²⁰ yr, decaying via double beta decay to ⁸²Kr) and for practical purposes can be considered to be stable. Fission products are the atomic fragments left after a large nucleus fissions. Selenium-79 is a Radioisotope of Selenium present in Spent nuclear fuel and the wastes resulting from reprocessing this fuel Half-Life (computer-game page here It's already listed in the disambiguation page Krypton (ˈkrɪptən or /ˈkrɪptɒn/ from kryptos "hidden" is a Chemical element with the symbol Kr and Atomic number 36 23 other unstable isotopes have been characterized.

See also Selenium-79 for more information on recent changes in the halflife of this fission product important for the dose calculations performed in the frame of the geological disposal of long-lived radioactive waste. Selenium-79 is a Radioisotope of Selenium present in Spent nuclear fuel and the wastes resulting from reprocessing this fuel Radioactive wastes are Waste types containing radioactive Chemical elements that do not have a practical purpose

History and global demand

Selenium (Greek σελήνη selene meaning "Moon") was discovered in 1817 by Jöns Jakob Berzelius who found the element associated with tellurium (named for the Earth). Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Friherre Jöns Jacob Berzelius (20 August 1779 &ndash 7 August 1848 was a Swedish chemist Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52

Growth in selenium consumption was historically driven by steady development of new uses, including applications in rubber compounding, steel alloying, and selenium rectifiers. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Selenium Rectifiers were invented in 1933 They were used to replace Vacuum tube rectifiers and in high current battery charger applications where By 1970, selenium in rectifiers had largely been replaced by silicon, but its use as a photoconductor in plain paper copiers had become its leading application. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 During the 1980s, the photoconductor application declined (although it was still a large end-use) as more and more copiers using organic photoconductors were produced. Presently, the largest use of selenium world-wide is in glass manufacturing, followed by uses in chemicals and pigments. Electronic use, despite a number of continued applications, continues to decline. ^[4]

In 1996, continuing research showed a positive correlation between selenium supplementation and cancer prevention in humans, but widespread direct application of this important finding would not add significantly to demand owing to the small doses required. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled In the late 1990s, the use of selenium (usually with bismuth) as an additive to plumbing brasses to meet no-lead environmental standards, became important. Bismuth (ˈbɪzməθ is a Chemical element that has the symbol Bi and Atomic number 83 Plumbing, from the Latin plumbum for Lead, is the skilled trade of working with pipes, tubing and Plumbing fixtures for Brass is any Alloy of Copper and Zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties At present, total world selenium production continues to increase modestly.

Reference in popular culture

In the plot of the hit movie Evolution staring David Duchovny It is discovered that selenium, an ingredient in some dandruff shampoos, is as poisonous to invading alien life-forms as arsenic is to humans. Evolution is a 2001 comedy sci-fi movie directed by Ivan Reitman. David William Duchovny (born August 7, 1960) is a two-time Golden Globe Award -winning American television and film Actor, best known

Selenium and health

Although it is toxic in large doses, selenium is an essential micronutrient for animals. Dietary minerals are the Chemical elements required by living Organisms other than the four elements Carbon, Hydrogen, Nitrogen, and In plants, it occurs as a bystander mineral, 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). Forage is plant material (mainly plant leaves and stems eaten by grazing Livestock. Locoweed is also a slang name for Cannabis, and Jimson weed. Locoweed is a term used to describe Plants from two different ^[5] It is a component of the unusual amino acids selenocysteine and selenomethionine. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Selenocysteine is an Amino acid that is present in several Enzymes (for example Glutathione peroxidases tetraiodothyronine 5' deiodinases Selenomethionine is an Amino acid containing Selenium. The L-isomer of selenomethionine known as Se-met and Sem is a common natural food source of In humans, selenium is a trace element nutrient which 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). Dietary minerals are the Chemical elements required by living Organisms other than the four elements Carbon, Hydrogen, Nitrogen, and Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state An antioxidant is a Molecule capable of slowing or preventing the oxidation of other molecules Glutathione peroxidase () is the general name of an Enzyme family with Peroxidase activity whose main biological role is to protect the organism from oxidative damage Thioredoxin Reductase (TR TrxR ( are the only known enzymes to reduce Thioredoxin (Trx

Glutathione peroxidase (GSH-Px) catalyzes certain reactions which remove reactive oxygen species such as peroxide:

2 GSH+ H₂O₂---------GSH-Px → GSSG + 2 H₂O

Selenium also plays a role in the functioning of the thyroid gland by participating as a cofactor for the three known thyroid hormone deiodinases. Glutathione peroxidase () is the general name of an Enzyme family with Peroxidase activity whose main biological role is to protect the organism from oxidative damage The thyroid is one of the largest Endocrine glands in the body A cofactor is a non-protein Chemical compound that is bound (either tightly or loosely to an Enzyme and is required for Catalysis. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced Deiodinase ( is an Enzyme important in the action of Thyroid hormones. ^[6]

Dietary selenium comes from nuts, cereals, meat, fish, and eggs. Brazil nuts are the richest ordinary dietary source (though this is soil-dependent, since the Brazil nut does not require high levels of the element for its own needs). The Brazil nut ( Bertholletia excelsa) is a South American Tree in the family Lecythidaceae, and also the name of the tree's commercially High levels are found in meats such as kidney, crab and lobster, in that order. The kidneys are complicated organs that have numerous biological roles Crabs are decapod Crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (βραχύ / brachy Clawed lobsters compose a family ( Nephropidae, sometimes also Homaridae) of large marine Crustaceans Lobsters are economically important as ^[7][8]

Toxicity

Although selenium is an essential trace element, it is toxic if taken in excess. Dietary minerals are the Chemical elements required by living Organisms other than the four elements Carbon, Hydrogen, Nitrogen, and Exceeding the Tolerable Upper Intake Level of 400 micrograms per day can lead to selenosis. The Dietary Reference Intake (or DRI is a system of Nutrition recommendations from the Institute of Medicine (IOM of the US National Academy of Sciences ^[9] Symptoms of selenosis include a garlic odour on the breath, gastrointestinal disorders, hair loss, sloughing of nails, fatigue, irritability and neurological damage. Extreme cases of selenosis can result in cirrhosis of the liver, pulmonary edema and death. Cirrhosis is a consequence of chronic Liver Disease characterized by replacement of liver tissue by fibrous Scar tissue as well as regenerative Pulmonary Edema (American English or oedema (British English is swelling and/or fluid accumulation in the Lungs It leads to impaired gas exchange and may cause ^[10]

Elemental selenium and most metallic selenides have relatively low toxicities because of their low bioavailability. The selenide Ion is Se2&minus A selenide is a chemical compound in which Selenium serves as an Anion with Oxidation number In Pharmacology, bioavailability is used to describe the fraction of an administered Dose of unchanged drug that reaches the Systemic circulation, one of By contrast, selenate and selenite are very toxic, and have modes of action similar to that of arsenic. The selenate Ion is SeO42&minus Selenates are analogous to Sulfates and have similar chemistry Selenous acid (also known as selenious acid) is the Chemical compound with the formula H2SeO3 perhaps more descriptively written Hydrogen selenide is an extremely toxic, corrosive gas. Hydrogen selenide is H2Se the simplest Hydride of Selenium. H2Se is a colorless flammable gas under standard conditions ^[11] 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. Selenomethionine is an Amino acid containing Selenium. The L-isomer of selenomethionine known as Se-met and Sem is a common natural food source of Selenocysteine is an Amino acid that is present in several Enzymes (for example Glutathione peroxidases tetraiodothyronine 5' deiodinases In Pharmacology, bioavailability is used to describe the fraction of an administered Dose of unchanged drug that reaches the Systemic circulation, one of Nano-size selenium has equal efficacy, but much lower toxicity. Nanotechnology, sometimes shortened to nanotech, refers to a field of Applied science whose theme is the control of matter on an Atomic and Molecular ^{[12][13][14][15][16][17][18]}

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. High selenium levels produced in this fashion have been found to have caused certain congenital disorders in wetland birds. ^[19]

Deficiency

Selenium deficiency is relatively rare in healthy well-nourished individuals. It can occur in patients with severely compromised intestinal function, or those undergoing total parenteral nutrition. In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists Total Parenteral nutrition (TPN is the practice of feeding a person Intravenously bypassing the usual process of Eating and Digestion. Alternatively, people dependent on food grown from selenium-deficient soil are also at risk. In the USA, the Dietary Reference Intake for adults is 55 µg/day. The Dietary Reference Intake (or DRI is a system of Nutrition recommendations from the Institute of Medicine (IOM of the US National Academy of Sciences In the UK it is 75 µg/day for adult males and 60 µg/day for adult females. 55 µg/day recommendation is based on full expression of plasma glutathione peroxidase. Glutathione peroxidase () is the general name of an Enzyme family with Peroxidase activity whose main biological role is to protect the organism from oxidative damage Selenoprotein P^[20] is a better indicator of selenium nutritional status, and full expression of it would require more than 66 µg/day. ^[21]

Selenium deficiency can lead to Keshan disease, which is potentially fatal. Keshan disease is a congestive Cardiomyopathy caused by dietary deficiency in the mineral Selenium. Selenium deficiency also contributes (along with iodine deficiency) to Kashin-Beck disease. ^[22] The primary symptom of Keshan disease is myocardial necrosis, leading to weakening of the heart. Myocardium is the muscular tissue of the Heart. Relationship to other layers The other tissues of the heart are the Endocardium Necrosis (in Greek Νεκρός = "dead" is the name given to unnatural Death of cells and living tissue. Kashin-Beck disease results in atrophy, degeneration and necrosis of cartilage tissue. Atrophy is the partial or complete Wasting away of a part of the Body. Necrosis (in Greek Νεκρός = "dead" is the name given to unnatural Death of cells and living tissue. Cartilage is a type of dense Connective tissue. It is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix ^[23] Keshan disease also makes the body more susceptible to illness caused by other nutritional, biochemical, or infectious diseases. These diseases are most common in certain parts of China where the soil is extremely deficient in selenium. Studies in Jiangsu Province of China have indicated a reduction in the prevalence of these diseases by taking selenium supplements. ( Postal map spelling: Kiangsu) is a province of the People's Republic of China, located along the east coast of the country

Selenium is also necessary for the conversion of the thyroid hormone thyroxine (T4) into its more active counterpart, triiodothyronine, and as such a deficiency can cause symptoms of hypothyroidism, including extreme fatigue, mental slowing, goitre, cretinism and recurrent miscarriage. Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid Hypothyroidism is the disease state in humans and animals caused by insufficient production of Thyroid hormone by the Thyroid gland. A goitre ( BrE) or goiter ( AmE) ( Latin struma) also called a bronchocele, is a swelling in the neck (just below the This article is about the medical term For the Marxist political concept see Parliamentary cretinism. Habitual abortion, recurrent miscarriage or recurrent pregnancy loss (RPL is the occurrence of repeated (three or more consecutive pregnancies that ^[10]

Controversial health effects

Cancer

Several studies have suggested a link between cancer and selenium deficiency. ^{[24][25][26][27][28][29][30]} A study conducted on the effect of selenium supplementation on the recurrence of skin cancers did not demonstrate a reduced rate of recurrence of skin cancers, but did show a significantly reduced occurrence of total cancers. ^[31] Dietary selenium prevents chemically induced carcinogenesis in many rodent studies. ^[32] In these studies, organic seleno-compounds are more potent and less toxic than selenium salts (e. g. , selenocyanates, selenomethionine, selenium-rich Brazil nuts, or selenium-enriched garlic or broccoli). Selenium may help prevent cancer by acting as an antioxidant or by enhancing immune activity. An antioxidant is a Molecule capable of slowing or preventing the oxidation of other molecules Not all studies agree on the cancer-fighting effects of selenium. One study of naturally occurring levels of selenium in over 60,000 participants did not show a significant correlation between those levels and cancer. ^[33] The SU. VI. MAX study^[34] concluded that low-dose supplementation (with 120 mg of ascorbic acid, 30 mg of vitamin E, 6 mg of beta carotene, 100 µg of selenium, and 20 mg of zinc) resulted in a 31% reduction in the incidence of cancer and a 37% reduction in all cause mortality in males, but did not get a significant result for females. ^[35] The SELECT study^[36] is currently investigating the effect of selenium and vitamin E supplementation on incidence of prostate cancer. See also Tocopherol, Tocotrienol Vitamin E is the collective name for a set of 8 related Tocopherols and Tocotrienols which are fat-soluble However, selenium has been proven to help chemotherapy treatment by enhancing the efficacy of the treatment, reducing the toxicity of chemotherapeutic drugs, and preventing the body's resistance to the drugs. ^[37] One study^[38] of cancer cells in vitro showed that chemotherapeutic drugs, such as Taxol and Adriamycin, were more toxic to strains of cancer cells grown in culture when selenium was added.

HIV/AIDS

Some research has indicated a geographical link between regions of selenium deficient soils and peak incidences of HIV/AIDS infection. Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome For example, much of sub-Saharan Africa is low in selenium. Sub-Saharan Africa is a geographical term used to describe the area of the African continent which lies south of the Sahara, or those African countries However, Senegal is not, and also has a significantly lower level of AIDS infection than the rest of the continent. Senegal (le Sénégal officially the Republic of Senegal, is a country south of the Sénégal River in western Africa. AIDS appears to involve a slow and progressive decline in levels of selenium in the body. Whether this decline in selenium levels is a direct result of the replication of HIV^[39] or related more generally to the overall malabsorption of nutrients by AIDS patients remains debated.

Low selenium levels in AIDS patients have been directly correlated with decreased immune cell count and increased disease progression and risk of death. ^[40] Selenium normally acts as an antioxidant, so low levels of it may increase oxidative stress on the immune system leading to more rapid decline of the immune system. An antioxidant is a Molecule capable of slowing or preventing the oxidation of other molecules Others have argued that HIV encodes for the human selenoenzyme glutathione peroxidase, which depletes the victim's selenium levels. Glutathione peroxidase () is the general name of an Enzyme family with Peroxidase activity whose main biological role is to protect the organism from oxidative damage Depleted selenium levels in turn lead to a decline in CD4 helper T-cells, further weakening the immune system. T helper cells (also known as effector T cells or Th cells) are a sub-group of Lymphocytes (a type of White blood cell or ^[41]

Regardless of the cause of depleted selenium levels in AIDS patients, studies have shown that selenium deficiency does strongly correlate with the progression of the disease and the risk of death. ^[42][43][44]

Tuberculosis

Some research has suggested that selenium supplementation, along with other nutrients, can help prevent the recurrence of tuberculosis. ^[45]

Diabetes

A well-controlled study showed that selenium intake is positively correlated with the risk of developing type II diabetes. Because high serum selenium levels are positively associated with the prevalence of diabetes, and because selenium deficiency is rare, supplementation is not recommended in well-nourished populations such as the U. S. ^[46]

Production and allotropic forms

Selenium is a common byproduct of copper refining, or the production of sulfuric acid. ^[47][48][49] Isolation of selenium is often complicated by the presence of other compounds and elements. Commonly, production begins by oxidation with sodium carbonate to produce sodium selenite. The sodium selenite is then acidified with sulfuric acid producing selenous acid. The selenous acid is finally bubbled with sulfur dioxide producing elemental red amorphous selenium.

Selenium produced in chemical reactions invariably appears as the amorphous red form-- an insoluble brick red powder. When this form is rapidly melted, it forms the black, vitreous form which is usually sold industrially as beads. The most thermodynamically stable and dense form of selenium is the electrically conductive gray (trigonal) form, which is composed of long helical chains of selenium atoms. The conductivity of this form is notably light sensitive. Selenium also exists in three different deep red crystalline monoclinic forms, which are composed of Se₈ molecules, similar to many allotropes of sulfur. ^[50]

Non-biological applications

Chemistry

Selenium is a catalyst in many chemical reactions and is widely used in various industrial and laboratory syntheses, especially Organoselenium chemistry. Organoselenium compounds are Chemical compounds containing Carbon to Selenium Chemical bonds Organoselenium chemistry is the corresponding It is also widely used in structure determination of proteins and nucleic acids by X-ray crystallography (incorporation of one or more Se atoms helps with MAD phasing. Multi-wavelength anomalous dispersion (sometimes Multi-wavelength anomalous diffraction; abbreviated MAD) is a technique used in X-ray crystallography that )

Manufacturing and materials use

The largest use of selenium world-wide is in glass and ceramic manufacturing, where it is used to give a red color to glasses, enamels and glazes as well as to remove color from glass by counteracting the green tint imparted by ferrous impurities. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many The word ceramic is derived from the Greek word κεραμικός ( keramikos) In a discussion of Material science, enamel (or vitreous enamel or porcelain enamel in U Glaze is a layer or coating of a Vitreous substance which has been fired to fuse to a ceramic object to color decorate strengthen or waterproof it

Selenium is used with bismuth in brasses to replace more toxic lead. Bismuth (ˈbɪzməθ is a Chemical element that has the symbol Bi and Atomic number 83 Brass is any Alloy of Copper and Zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly It is also used to improve abrasion resistance in vulcanized rubbers. Vulcanization (or Vulcanisation refers to a specific curing process of Rubber involving high heat and the addition of Sulfur or other equivalent curatives

Electronics

Because of its photovoltaic and photoconductive properties, selenium is used in photocopying, photocells, light meters and solar cells. Photovoltaics ( PV) is the field of technology and research related to the application of Solar cells for Energy by converting Sunlight directly Photoconductivity is an optical and electrical phenomenon in which a material becomes more conductive due to the absorption of electro-magnetic radiation A photocopier (or copier is a machine that makes Paper copies of documents and other visual images quickly and cheaply Photosensors or photodetectors are Sensors of Light or other Electromagnetic energy A light meter is a device used to measure the amount of Light. A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect. It was once widely used in rectifiers. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. These uses have mostly been replaced by silicon-based devices, or are in the process of being replaced. 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. A surge protector is an appliance designed to protect electrical devices from Voltage spikes A surge protector attempts to regulate the Voltage supplied A varistor is an electronic component with a significant non- ohmic current - Voltage characteristic

Sheets of amorphous selenium convert x-ray images to patterns of charge in xeroradiography and in solid-state flat panel x-ray cameras. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Xeroradiography is a type of X-ray in which a picture of the body is Recorded on paper rather than on Film.

Photography

Selenium is used in the toning of photographic prints, and it is sold as a toner by numerous photographic manufacturers including Kodak and Fotospeed. In Photography, toning is a photographic process carried out on silver-based ( Black-and-white) photographic prints to change their colour Eastman Kodak Company ( is an American multinational Public company which produces imaging and photographic materials and equipment Its use intensifies and extends the tonal range of black and white photographic images as well as improving the permanence of prints.

Nondestructive testing

Selenium is a highly effective Gamma source used in Industrial radiography. Nondestructive testing ( NDT) also called nondestructive examination ( NDE) and nondestructive inspection ( NDI) is testing that does Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Industrial Radiography is the use of ionising Electromagnetic radiation to view objects in a way that can't be seen otherwise

Biological applications

Medical use

The substance loosely called selenium sulfide, SeS₂, actually selenium disulfide or selenium (IV) sulfide, is the active ingredient in some dandruff shampoos. Selenium(IV sulfide (also selenium(IV sulphide; see spelling) selenium disulfide loose name: selenium sulfide. ^[51] The effect of the active ingredient is to kill the scalp fungus Malassezia which causes shedding of dry skin fragments. Malassezia (formerly known as Pityrosporum) is a genus of related Fungi, classified as Yeasts naturally found on the skin surfaces of many The ingredient is also used in body lotions to treat Tinea versicolor due to infection by a different species of Malassezia fungus. Tinea versicolor or Pityriasis versicolor is a common skin Infection caused by the Yeast Malassezia furfur (formerly ^[52]

Nutrition

Selenium is used widely in vitamin preparations and other dietary supplements, in small doses (typically 50 to 200 micrograms per day for adult humans). A vitamin is an Organic compound required as a Nutrient in tiny amounts by an Organism. Some livestock feeds are fortified with selenium as well. In Agriculture, fodder or animal feed is any Foodstuff that is used specifically to feed Domesticated Livestock, such as

Compounds

• Copper indium gallium selenide Cu(Ga,In)Se₂
• Mercury selenide (HgSe)
• Hydrogen selenide (H₂Se)
• Lead Selenide (PbSe)
• Selenium dioxide (SeO₂)
• Selenic acid (H₂SeO₄)
• Selenous acid (H₂SeO₃)
• Selenium sulfides: Se₄S₄, SeS₂, Se₂S₆
• Sodium selenite (Na₂SeO₃)
• Zinc selenide (ZnSe)

Selenium also occurs in the III oxidation state, but only in the Se₄¹²⁺ cation; Se(III) compounds are not otherwise known. Copper indium gallium selenide ( CIGS) is a new Semiconductor material composed of Copper, Indium, Gallium, and Selenium Mercury selenide (HgSe is a chemical compound of mercury and Selenium. Hydrogen selenide is H2Se the simplest Hydride of Selenium. H2Se is a colorless flammable gas under standard conditions Lead selenide () or lead(II selenide, a Selenide of Lead, is a Semiconductor material. Selenium dioxide is the Chemical compound with the formula SeO2 Selenic acid is the Chemical compound with the formula H2 SeO sub>4 Selenous acid (also known as selenious acid) is the Chemical compound with the formula H2SeO3 perhaps more descriptively written Selenium(IV sulfide (also selenium(IV sulphide; see spelling) selenium disulfide loose name: selenium sulfide. Sodium selenite is a Chemical compound with the formula Na 2 Se[[Oxygen O]]3 Zinc selenide ( Zn[[Selenium Se]] is a light yellow binary solid compound ^[53]

See also Selenium compounds and organoselenium chemistry. Organoselenium compounds are Chemical compounds containing Carbon to Selenium Chemical bonds Organoselenium chemistry is the corresponding

References

External links

• Los Alamos National Labs Chemistry Division - Selenium
• WebElements.com - Selenium
• National Institutes of Health page on Selenium
• ATSDR - Toxicological Profile: Selenium
• Peter van der Krogt elements site

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