Selenium is a chemical element with symbol Se and atomic
number 34. It is a nonmetal 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.
Ancient Greek σελήνη (selḗnē) "Moon") was
discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity
of the new element to the previously discovered tellurium (named for
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
Selenium is still used in a few types of DC
power surge protectors and one type of fluorescent quantum dot.
Selenium salts are toxic in large amounts, but trace amounts are
necessary for cellular function in many organisms, including all
Selenium is an ingredient in many multivitamins and other
dietary supplements, including infant formula. It is a component of
the antioxidant enzymes glutathione peroxidase and thioredoxin
reductase (which indirectly reduce certain oxidized molecules in
animals and some plants). It is also found in three deiodinase
enzymes, which convert one thyroid hormone to another. Selenium
requirements in plants differ by species, with some plants requiring
relatively large amounts and others apparently requiring none.
1.1 Physical properties
1.2 Optical properties
2 Chemical compounds
2.4 Other compounds
2.5 Organoselenium compounds
6.2 Glass production
6.4 Lithium–selenium batteries
6.5 Solar cells
6.7 Other uses
7 Biological role
7.1 Evolution in biology
7.2 Nutritional sources of selenium
7.3 Indicator plant species
7.4 Detection in biological fluids
7.7 Controversial health effects
8 See also
10 External links
Structure of hexagonal (gray) selenium
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 relatively low, monoclinic crystal symmetries and
contain nearly identical puckered Se8 rings with different
arrangements, as in sulfur. The packing is most dense in the α form.
In the Se8 rings, the Se-Se distance is 233.5 pm and Se-Se-Se angle is
105.7°. Other selenium allotropes may contain Se6 or Se7 rings.
The most stable and dense form of selenium is gray and has a hexagonal
crystal lattice consisting of helical polymeric chains, where the
Se-Se distance is 237.3 pm and Se-Se-Se angle is 130.1°. 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
Selenium does not exhibit the changes in viscosity that
sulfur undergoes when gradually heated.
Owing to its use as a photoconductor in flat-panel x-ray detectors
(see below), the optical properties of amorphous selenium (α-Se) thin
films have been the subject of intense research.
Main article: Isotopes of selenium
Selenium has seven natural isotopes, including 79Se, which occurs in
minute quantities in uranium ores, as well as 23 other synthetic
Selenium isotopes of greatest stability
See also: Category:
Selenium compounds and organoselenium chemistry
Selenium compounds commonly exist in the oxidation states −2, +2,
+4, and +6.
Selenium forms two oxides: selenium dioxide (SeO2) and selenium
Selenium dioxide is formed by the reaction of
elemental selenium with oxygen:
Se8 + 8 O2 → 8 SeO2
Structure of the polymer SeO2: The (pyramidal) Se atoms are yellow.
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
3 Se + 4 HNO3 + H2O → 3 H2SeO3 + 4 NO
Unlike sulfur, which forms a stable trioxide, selenium trioxide is
thermodynamically unstable and decomposes to the dioxide above
2 SeO3 → 2 SeO2 + O2 (ΔH = −54 kJ/mol)
Selenium trioxide is produced in the laboratory by the reaction of
anhydrous potassium selenate (K2SeO4) and sulfur trioxide (SO3).
Salts of selenous acid are called selenites. These include silver
selenite (Ag2SeO3) and sodium selenite (Na2SeO3).
Hydrogen sulfide reacts with aqueous selenous acid to produce selenium
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.
Selenium trioxide may be synthesized by dehydrating selenic acid,
H2SeO4, which is itself produced by the oxidation of selenium dioxide
with hydrogen peroxide:
SeO2 + H2O2 → H2SeO4
Hot, concentrated selenic acid can react with gold to form gold(III)
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
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 + 6 H2O → Al2O3 + 6 H2Se
Alkali metal selenides react with selenium to form polyselenides,
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
Selenium reacts with cyanides to yield selenocyanates:
8 KCN + Se8 → 8 KSeCN
Main article: Organoselenium chemistry
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
Selenium (Greek σελήνη selene meaning "Moon") was discovered in
Jöns Jakob Berzelius
Jöns Jakob 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.
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
Selenium came to medical notice later because of its toxicity to human
beings working in industries.
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 selenium in sandstone, from a uranium mine near Grants, New
See also: Category:
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
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 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
Certain solids 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.
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
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
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
During the electro winning 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 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.
Lithium–selenium (Li–Se) battery is one of the most promising
system for energy storage in the family of lithium batteries.
Li–Se battery is an alternative to
Lithium–sulfur battery with an
advantage of high electrical conductivity.
Copper indium gallium selenide is a material used in solar cells.
Amorphous selenium (α-Se) thin films have found application as
photoconductors in flat panel x-ray detectors. These detectors
utilize the amorphous selenium to capture and convert incident x-ray
photons directly into electric charge. Based on this application,
significant research has been undertaken in recent years to quantify
the optical properties of such thin films.
Small amounts of organoselenium compounds are used to modify the
vulcanization catalysts for the production of rubber.
The demand for selenium by the electronics industry is declining,
despite a number of continuing applications. 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 is dominating the market now.
Cadmium selenide was an
important component in quantum dots. Sheets of amorphous selenium
X-ray images to patterns of charge in xeroradiography and in
X-ray cameras. Ionized selenium (Se+24) is
one of the active mediums used in
Selenium is a catalyst in some chemical reactions, but it is not
widely used because of issues with toxicity. In
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.
Selenium in biology
Fire diamond for elemental selenium
Although it is toxic in large doses, selenium is an essential
micronutrient for animals. 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). 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).
The glutathione peroxidase family of enzymes (GSH-Px) catalyze certain
reactions that remove reactive oxygen species such as hydrogen
peroxide and organic hydroperoxides:
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 alien. A reduction of 21% on TPO
antibodies is reported with the dietary intake of 0.2 mg of
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.
Evolution in biology
Main article: Evolution of dietary antioxidants
From about three billion years ago, prokaryotic selenoprotein families
drive the evolution of selenocysteine, an amino acid.
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 urchin, fish, and chicken.
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
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
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
Nutritional sources of selenium
Dietary selenium comes from nuts, cereals and mushrooms. Brazil nuts
are the richest dietary source (though this is soil-dependent, since
Brazil nut does not require high levels of the element for its own
Recommended Dietary Allowance (RDA) 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.
In June 2015 the U.S.
Food and Drug Administration
Food and Drug Administration (FDA) published its
final rule establishing the requirement of minimum and maximum levels
of selenium in infant formula.
The selenium content in the human body is believed to be in the
13–20 milligram 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
(including some locoweeds), prince's plume (Stanleya sp.), woody
Xylorhiza sp.), and false goldenweed (
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 elimination
in the urine. Cancer patients receiving daily oral doses of
selenothionine may achieve very high plasma and urine selenium
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
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 ten to fifteen times higher than normal
in the blood samples, and 15 to 20 times higher than normal in the
Selenium was later confirmed to be the toxic
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.
Relationship between survival of juvenile salmon and concentration of
selenium in their tissues after 90 days (Chinook salmon) or 45
days (Atlantic salmon) exposure to dietary selenium. The 10%
lethality level (LC10=1.84 µg/g) was derived by applying the biphasic
model of Brain and Cousens to only the Chinook salmon data. The
Chinook salmon data comprise two series of dietary treatments,
combined here because the effects on survival are indistinguishable.
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.
Occupational Safety and Health Administration
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
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
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
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
Controversial health effects
Selenium in biology
A number of correlative epidemiological studies have implicated
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 a chemopreventive for some types of cancer in
some types of rodents. One study of 118 exocrine pancreatic cancer
(EPC) patients and 399 hospital controls in eastern Spain found high
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^ Rayman, Margaret P. (2000). "The importance of selenium to human
health". The Lancet. 356 (9225): 233–41.
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^ Amaral, A.F.S.; Porta, M.; Silverman, D.T.; et al. (2012).
"Pancreatic cancer risk and levels of trace elements". Gut. 61:
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Find more aboutSeleniumat's sister projects
Definitions from Wiktionary
Media from Wikimedia Commons
Textbooks from Wikibooks
Learning resources from Wikiversity
Data from Wikidata
The Periodic Table of Videos
The Periodic Table of Videos (University of Nottingham)
National Institutes of Health page on Selenium
ATSDR – Toxicological Profile: Selenium
CDC - NIOSH Pocket Guide to Chemical Hazards
Peter van der Krogt elements site
Periodic table (Large cells)
Alkaline earth metal
Prostanoid signaling modulators
Agonists: Prostaglandin D2
Prostaglandin E1 (alprostadil)
Prostaglandin E2 (dinoprostone)
Prostaglandin E1 (alprostadil)
Prostaglandin E2 (dinoprostone)
Prostaglandin E1 (alprostadil)
Prostaglandin E2 (dinoprostone)
Prostaglandin E1 (alprostadil)
Prostaglandin E2 (dinoprostone)
Agonists: 16,16-Dimethyl Prostaglandin E2
Prostaglandin F2α (dinoprost)
Prostaglandin F2α (dinoprost)
Prostacyclin (prostaglandin I2, epoprostenol)
Prostaglandin E1 (alprostadil)
Agonists: Carbocyclic thromboxane A2
Pinane thromboxane A2
Salicylic acids: Aloxiprin
Aspirin (acetylsalicylic acid)
Mesalazine (5-aminosalicylic acid)
Salicylate (salicylic acid)
Triflusal; Acetic acids: Aceclofenac
Zomepirac; Propionic acids: Alminoprofen
Bucloxic acid (blucloxate)
Tiaprofenic acid (tiaprofenate)
Vedaprofen; Anthranilic acids (fenamic acids): Etofenamic acid
Floctafenic acid (floctafenate)
Flufenamic acid (flufenamate)
Meclofenamic acid (meclofenamate)
Mefenamic acid (mefenamate)
Morniflumic acid (morniflumate)
Niflumic acid (niflumate)
Talinflumic acid (talinflumate)
Tolfenamic acid (tolfenamate); Pyrazolones: Azapropazone
Phenylbutazone; Enolic acids (oxicams): Ampiroxicam
Tenoxicam; 4-Aminoquinolines: Antrafenine
Glafenine; Quinazolines: Fluproquazone
Proquazone; Aminonicotinic acids: Clonixeril
Flunixin; Sulfonanilides: Flosulide
Nimesulide; Aminophenols (anilines): Acetanilide
Propacetamol; Selective COX-2 inhibitors (coxibs): Apricoxib
Valdecoxib; Others/unsorted: Anitrazafen
Menatetrenone (vitamin K2)
Selenium (selenium tetrachloride, sodium selenite, selenium disulfide)
Precursors: Linoleic acid
γ-Linolenic acid (gamolenic acid)
Leukotriene signaling modulators
Nuclear receptor modulators
Thyroid hormone receptor modulators
Sobetirome (GC-1, GRX-431)
Tetraiodothyroacetic acid (Tetrac)
Inhibitors: Cyanogenic glycosides
Perchlorates (e.g., potassium perchlorate)
Pertechnetates (e.g., sodium pertechnetate)
Ipodate sodium (sodium iopodate)
See also: Receptor/signaling modulators
Nuclear receptor modulators
BNF: cb121383271 (data)