tltonl手表后面sapphlre crystal waterreslstant 10atm automatlc 77是什么意思_百度知道
tltonl手表后面sapphlre crystal waterreslstant 10atm automatlc 77是什么意思
sapphlre crystal 蓝宝石玻璃waterreslstant 10atm 手表防水10个大气压automatlc 全自动机械77 应该是辨别编号
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求翻译：TL-12007G 3ATM WATER RESLSTANT ALL STAINLESS是什么意思？
TL-12007G 3ATM WATER RESLSTANT ALL STAINLESS
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TL- 12007G 3ATM水RESLSTANT全不锈钢
所有不锈TL-12007G 3ATM的水RESLSTANT
TL-12007G 3ATM水RESLSTANT所有不锈
TL-12007 G 3ATM 水 RESLSTANT 全不锈钢
铊-12007G 3ATM 水 RESLSTANT 所有 STAINLESS
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请输入您需要翻译的文本！From Wikipedia, the free encyclopedia
This article is about the chemical element.
For the software testing framework, see .
← selenium →
  , sometimes considered a
  (Ar)
[] 3d10 4s2 4p4
2, 8, 18, 6
Physical properties
494  (221 °C, 430 °F)
958 K (685 °C, ;°F)
near 
gray: 4.81 g/cm3
alpha: 4.39 g/cm3
vitreous: 4.28 g/cm3
when liquid, at m.p.
3.99 g/cm3
;K, 27.2 MPa
gray: 6.69 
95.48 kJ/mol
25.363 J/(mol·K)
P (Pa)
100 k
at T (K)
Atomic properties
6, 5, 4, 3, 2, 1, -1, -2 (a strongly
Pauling scale: 2.55
1st: 941.0 kJ/mol
2nd: ;kJ/mol
3rd: 0;kJ/mol
empirical: 120 
120±4 pm
190 pm
Miscellanea
thin rod
;m/s (at 20 °C)
amorphous: 37 um/(m·K) (at 25 °C)
amorphous: 0.519 W/(m·K)
10 GPa
3.7 GPa
8.3 GPa
736 MPa
after , Greek goddess of the moon
and first isolation
Most stable
8.4 d
119.779 d
0.264, 0.136,
77Se is stable with 43 neutrons
78Se is stable with 44 neutrons
3.27×105 y
1.08×1020 y
Decay modes in parentheses are predicted, but have not yet been observed
Selenium is a
with symbol Se and  34. It is a
with properties that are intermediate between those of its
column-adjacent
and . It rarely occurs in its elemental state in nature, or as pure ore compounds. Selenium ( σελ?νη
meaning "Moon") was discovered in 1817 by , who noted the similarity of the new element to the previously known
(named for the Earth).
Selenium is found in
, 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 are rare. The chief commercial uses for selenium today are in
and in . Selenium is a
and is used in . Uses in , once important, have been mostly supplanted by
semiconductor devices. Selenium continues to be used in a few types of DC power
and one type of
Selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms, including all animals. Selenium is an ingredient in many multivitamins and other dietary supplements, including . It is a component of the antioxidant enzymes
(which indirectly reduce certain
molecules in animals and some plants). It is also found in three
enzymes, which convert one
to another. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts, and others apparently requiring none.
Structure of hexagonal (gray) selenium
Selenium exists in several
that interconvert upon heating and cooling carried out at different temperatures and rates. As prepared in chemical reactions, selenium is usually an , brick-red powder. When rapidly melted, it forms the black, vitreous form, which is usually sold industrially 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 . 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 .
The red α, β, and γ forms are produced from solutions of black selenium by varying evaporation rates of the solvent (usually CS2). They all have relatively low,
crystal symmetries and contain nearly identical puckered Se8 rings arranged in different fashions, as in . 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 . Unlike the other allotropes, it is insoluble in CS2. It resists oxidation by air and is not attacked by nonoxidizing . With strong reducing agents, it forms polyselenides. Selenium does not exhibit the unusual changes in viscosity that sulfur undergoes when gradually heated.
Main article:
Selenium has six naturally occurring , five of which are stable: 74Se, 76Se, 77Se, 78Se, and 80Se. The last three also occur as , along with , which has a
of 327,000 years. The final naturally occurring isotope, 82Se, has a very long half-life (~1020 yr, decaying via double beta decay to ), which, for practical purposes, can be considered to be stable. Twenty-three other unstable isotopes have been characterized.
for more information on recent changes in the measured half-life of this long-lived fission product, important for the dose calculations performed in the frame of the geological disposal of long-lived .
Selenium compounds commonly exist in the
-2, +2, +4, and +6.
Selenium forms two :
(SeO2) and
(SeO3). 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.
solid that forms monomeric SeO2 molecules in the gas phase. It dissolves in water to form , 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 , selenium trioxide is thermodynamically unstable and decomposes to the dioxide above 185 °C:
2 SeO3 → 2 SeO2 + O2 (ΔH = -54 kJ/mol)
Selenium trioxide is produced in the laboratory by the reaction of
(K2SeO4) and sulfur trioxide (SO3).
of selenous acid are called selenites. These include
(Ag2SeO3) and
(Na2SeO3).
reacts with aqueous selenous acid to produce :
H2SeO3 + 2 H2S → SeS2 + 3 H2O
Selenium disulfide consists of 8-membered rings of a nearly statistical distribution of sulfur and selenium atoms. 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 anti agent, an inhibitor in polymer chemistry, a glass dye, and a reducing agent in .
Selenium trioxide may be synthesized by dehydrating , H2SeO4, which is itself produced by the oxidation of selenium dioxide with :
SeO2 + H2O2 → H2SeO4
Hot, concentrated selenic acid is capable of dissolving gold, forming gold(III) selenate.
of selenium are not well known. The only stable
(Se2Cl2), which might be better known as selenium(I) the corresponding
is also known. These species are structurally analogous to the corresponding . 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
(SO2Cl2). Selenium reacts with
Se8 + 24 F2 → 8 SeF6
In comparison with its sulfur counterpart (),
(SeF6) is more reactive and is a toxic
irritant. Some of the selenium oxyhalides, such as
(SeOF2) and
(SeOCl2) have been used as specialty solvents.
Analogous to the behavior of other chalcogens, selenium forms a dihydride H2Se. It is a strongly , 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
(ZnSe), and
(Cu(Ga,In)Se2). These materials are . With highly electropositive metals, such as , these selenides are prone to hydrolysis:
Al2Se3 + 6 H2O → Al2O3 + 6 H2Se
Alkali metal selenides react with selenium to form polyselenides, Se2-
n, which exist as chains.
Tetraselenium tetranitride, Se4N4, is an explosive orange compound analogous to
(S4N4). It can be synthesized by the reaction of
(SeCl4) with [((CH
Selenium reacts with
to yield selenocyanates:
8 KCN + Se8 → 8 KSeCN
Main article:
Selenium, especially in the II oxidation state, forms stable bonds to , which are structurally analogous to the corresponding . Especially common are selenides (R2Se, analogues of ), diselenides (R2Se2, analogues of ), and
(RSeH, analogues of ). Representatives of selenides, diselenides, and selenols include respectively , , and . The
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
reaction. Consistent with trends indicated by the , selenoketones, R(C=Se)R, and selenaldehydes, R(C=Se)H, are rarely observed.
Selenium ( σελ?νη
meaning "Moon") was discovered in 1817 by
and . Both chemists owned a chemistry plant near , Sweden, producing
by the . The pyrite from the
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
when burned. This smell was not typical of arsenic, but a similar odor was known from
compounds. Hence, Berzelius's first letter to
stated that this was a tellurium compound. However, the lack of tellurium compounds in the
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
and tellurium. Because of its similarity to tellurium, named for the Earth, Berzelius named the new element after the .
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
in the mid-1870s. The selenium cell was used in the
developed by
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
and similar devices. Selenium's semiconductor properties found numerous other applications in electronics. The development of
began during the early 1930s, and these replaced
rectifiers because of their superior efficiencies. These lasted in commercial applications until the 1970s, following which they were replaced with less expensive and even more efficient .
Selenium came to medical notice later because of its toxicity to
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 . Its essentiality for mammalian life was discovered in 1957. In the 1970s, it was shown to be present in two independent sets of . This was followed by the discovery of
in proteins. During the 1980s, selenocysteine was shown to be encoded by the . The recoding mechanism was worked out first in
and then in
Native selenium in sandstone, from a uranium mine near
See also: .
Native (i.e., elemental) selenium is a rare mineral, which does not usually form good crystals, but, when it does, they are steep rhombohedra or tiny acicular (hair-like) crystals. Isolation of selenium is often complicated by the presence of other compounds and elements.
Selenium occurs naturally in a number of inorganic forms, including -, -, and -containing minerals, but these minerals are rare. The common mineral
is not a selenium mineral, and contains no , but is rather a type of
(calcium sulfate hydrate) named like selenium for the moon well before the discovery of selenium. Selenium is most commonly found quite impurely, replacing a small part of the sulfur in sulfide ores of many metals.
In living systems, selenium is found in the amino acids , , and . In these compounds, selenium plays a role analogous to that of sulfur. Another naturally occurring
is dimethyl selenide.
Certain solids are selenium-rich, and selenium can be
by certain 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
, such as those of , , or . Electrolytic metal refining is particularly conducive to producing selenium as a byproduct, and it is obtained from the
mud of copper refineries. Another source was the mud from the
plants but this method to produce sulfuric acid is no longer used. These muds can be processed by a number of means to obtain selenium. However, most elemental selenium comes as a byproduct of
copper or producing . Since the invention of
(SX/EW) for the production of copper this method takes an increasing share of the worldwide copper production. This changes the availability of selenium because only a comparably small part of the selenium in the ore is leached together with the copper.
Industrial production of selenium usually involves the extraction of
from residues obtained during the purification of copper. Common production from the residue then begins by oxidation with
to produce selenium dioxide. The selenium dioxide is then mixed with water and the solution is
( step). Selenous acid is bubbled with
( step) to give elemental selenium.
About 2,000 tonnes of selenium were produced in 2011 worldwide, mostly in Germany (650 t), Japan (630 t), Belgium (200 t), and Russia (140 t), and the total reserves were estimated at 93,000 tonnes. These data however exclude two major producers, the United States and China. The price was relatively stable during
at about US$30 per pound (per 100-pound lot) but increased to $65 /lb in 2011. A previous sharp increase was observed in 2004 from 4–5 to $27/lb. The consumption in 2010 was divided as follows: metallurgy – 30%, glass manufacturing – 30%, agriculture – 10%, chemicals and pigments – 10%, and electronics – 10%. China is the dominant consumer of selenium at 1,500–2,000 tonnes/year.
During the
of manganese an addition of selenium dioxide decreases the power necessary to operate the . China is the largest consumer of selenium dioxide for this purpose. For every tonne of manganese, an average of 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 that are typical for most glass. For this purpose various selenite and selenate salts are added. For other applications, the red color may be desirable, in which case mixtures of CdSe and CdS are added.
Selenium is used with
to replace more toxic . The regulation of lead in drinking water applications with the
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%. The same improvement is also observed in copper alloys, so selenium is also used in machinable copper alloys.
is a material used in the production of solar cells.
Small amounts of organoselenium compounds are used to modify the
catalysts used in the production of rubber.
The demand for selenium by the electronics industry is declining, despite a number of continuing applications. Because of its
properties, selenium is used in , ,
and . 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 the use of organic photoconductors. It was once widely used in . 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 , where the superior energy capabilities of selenium suppressors make them more desirable than .
was the first material for blue , but gallium nitride is dominating the market now.
has played an important part in the fabrication of . Sheets of amorphous selenium convert
images to patterns of charge in
and in solid-state, flat-panel X-ray cameras.
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
Selenium is used in the , and it is sold as a toner by numerous photographic manufacturers. Its use 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.
Main article:
Although it is toxic in large doses, selenium is an essential
for animals. In plants, it occurs as a bystander mineral, sometimes in toxic proportions in
(some plants may accumulate selenium as a defense against being eaten by animals, but other plants such as
require selenium, and their growth indicates the presence of selenium in soil). See more on plant nutrition below.[]
Selenium is a component of the unusual
and . In humans, selenium is a
nutrient that functions as
enzymes, such as
and certain forms of
found in animals and some plants (this enzyme occurs in all living organisms, but not all forms of it in plants require selenium).
family of enzymes (GSH-Px) catalyze certain reactions that remove reactive oxygen species such as
and organic :
2 GSH + H2O2----GSH-Px → GSSG + 2 H2O
Selenium also plays a role in the functioning of the
gland and in every cell that uses thyroid hormone, by participating as a cofactor for the three of the four known types of
, which activate and then deactivate various thyroid hormones a the
are the subfamily of deiodinase enzymes that use selenium as the otherwise rare amino acid selenocysteine. (Only the deiodinase , which works on the last breakdown products of thyroid hormone, does not use selenium.)
Selenium may inhibit , in which the body's own thyroid cells are attacked as alien. A reduction of 21% on TPO antibodies was reported with the dietary intake of 0.2 mg of selenium.
Increased dietary selenium intakes reduce the effects of mercury toxicity, although this protective effect is only apparent 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.
Main article:
From about three billion years ago, prokaryotic selenoprotein families drive the evolution of selenocysteine, an amino acid. Selenium is incorporated into several prokaryotic selenoprotein families in bacteria, archaea, and eukaryotes as selenocysteine, where selenoprotein peroxiredoxins protect bacterial and eukaryotic cells against oxidative damage. Selenoprotein families of GSH-Px and the deiodinases of eukaryotic cells seem to have a bacterial
origin. The selenocysteine-containing form occurs in species as diverse as green algae, diatoms, sea urchin, fish, and chicken. Selenium enzymes are involved in use of the small reducing molecules
and . One family of selenium-containing molecules (the ) destroys peroxide and repairs damaged peroxidized cell membranes, using glutathione. Another selenium-containing enzyme in some plants and in animals () generates reduced thioredoxin, a dithiol that serves as an electron source for peroxidases and also the important reducing enzyme
that makes DNA precursors from RNA precursors.
Trace elements involved in GSH-Px and superoxide dismutase enzymes activities, i.e. selenium, , , , and , 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 , 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 Mya, freshwater and terrestrial plants slowly optimized the production of "new" endogenous antioxidants such as
(vitamin C),
(including flavonoids), , 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
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
from damage by H2O2 produced for thyroid-hormone biosynthesis. About 200 Mya, new selenoproteins were developed as mammalian GSH-Px enzymes.
Dietary selenium comes from nuts, cereals and mushrooms.
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).
Recommended Dietary Allowance ~ 55 /day. Selenium as a dietary supplement is available in many forms, including multi-vitamins/mineral supplements - typically 20 ug/day. Selenium-specific supplements may have -200 ug/day.
In June 2015 the U.S.
(FDA) published its final rule establishing the requirement of minimum and maximum levels of selenium in .
The human body's content of selenium is believed to be in the 13–20 milligram range.
Certain species of plants are considered indicators of high selenium content of the soil, since they require high levels of selenium to thrive. The main selenium indicator plants are
species (including some ), prince's plume ( sp.), woody asters ( sp.), and false goldenweed ( sp.)
The substance loosely called
(approximate formula SeS2) is the active ingredient in some anti-dandruff shampoos. The selenium compound kills the scalp fungus , which causes shedding of dry skin fragments. The ingredient is also used in body lotions to treat
due to infection by a different species of Malassezia fungus.
Selenium may be measured in blood, plasma, serum or urine to monitor excessive environmental or occupational exposure, confirm a diagnosis of poisoning in hospitalized victims or to assist in a forensic investigation in a case of fatal overdosage. Some analytical techniques are capable of distinguishing organic from inorganic forms of the element. Both organic and inorganic forms of selenium are largely converted to monosaccharide conjugates (selenosugars) in the body prior to being eliminated in the urine. Cancer patients receiving daily oral doses of selenothionine may achieve very high plasma and urine selenium concentrations.
Although selenium is an essential , it is toxic if taken in excess. Exceeding the
of 400 micrograms per day can lead to selenosis. This 400  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 not only avoid , but also to avoid creating an imbalance of nutrients in the diet and to account for data from other countries. In China, people who ingested corn grown in extremely selenium-rich stony coal (carbonaceous ) have suffered from selenium toxicity. This coal was shown to have selenium content as high as 9.1%, the highest concentration in coal ever recorded in literature.
Signs and symptoms of selenosis include a garlic odor on the breath, gastrointestinal disorders, hair loss,
of nails, fatigue, irritability, and neurological damage. Extreme cases of selenosis can result in
of the liver, , and death. Elemental selenium and most metallic
have relatively low toxicities because of their low . By contrast,
are very toxic, having an oxidant mode of action similar to that of arsenic trioxide. The chronic toxic dose of selenite for humans is about 2400 to 3000 micrograms of selenium per day for a long time.
is an extremely toxic, corrosive gas. Selenium also occurs in organic compounds, such as dimethyl selenide, ,
and , all of which have high
and are toxic in large doses.
On 19 April 2009, 21
ponies died shortly before a match in the United States Polo Open. Three days later, a pharmacy released a statement explaining that the horses had received an incorrect dose of one of the ingredients used in a vitamin/mineral supplement compound that had been incorrectly compounded by a . Analysis of blood levels of
in the supplement indicated the selenium concentrations were ten to fifteen times higher than normal in the horses' , and 15 to 20 times higher than normal in their liver samples. It was later confirmed that selenium was the ingredient in question.
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 to waterways also occurs from leaching of selenium from coal flue ash, mining and metal smelting, crude oil processing and landfill. The resulting high selenium levels in waterways have been found to have caused certain congenital disorders in oviparous species such as wetland birds, and fish. Elevated dietary methylmercury levels can enhance the negative effects 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 ug/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, low levels of selenium cause deficiency while high levels cause toxicity. For example, in salmon, the optimal concentration of selenium in the fish tissue (whole body) is about 1 microgram selenium per gram of tissue (dry weight). At levels much below that concentration, young salmon die from much above that level they die from toxic excess.
(OSHA) has set the legal limit () for selenium exposure in the workplace as 0.2 mg/m3 over an 8-hour workday. The
(NIOSH) has set a
(REL) of 0.2 mg/m3 over an 8-hour workday. At levels of 1 mg/m3, selenium is .
Main article:
Selenium deficiency is rare in healthy, well-nourished individuals. It can occur in patients with severely compromised
function, those undergoing , and in those of advanced age (over 90). Also, people dependent on food grown from selenium-deficient soil are at risk. Although New Zealand has low levels of selenium in its soil, adverse health effects have not been detected.
Selenium deficiency as defined by low (&60% of normal) selenoenzyme activity levels in brain and endocrine tissues occurs only when a low selenium status is linked with an additional stress, such as high exposures to mercury or as a result of increased oxidant stress due to vitamin E deficiency.
There are interactions between selenium and other nutrients, such as
and . The effect of selenium deficiency on health remains uncertain, particularly in relation to . Also, there are interactions between selenium and other minerals, such as
and . It seems that a high dose of Se supplements to pregnant animals might disturb the Zn:Cu ratio which, in turn, leads to Zn reduction. It can be concluded that the Zn status should be monitored when high doses of Se are supplemented to pregnant animals. Further studies need to be done with higher levels of Se supplement to confirm these interactions.
In some regions (e.g. various regions within North America) where low available selenium levels in soil lead to low concentrations in dry matter of plants, Se deficiency in some animal species may occur unless dietary (or injected) selenium supplementation is done. Ruminants are particularly susceptible. In general, absorption of dietary selenium is lower in ruminants than in non-ruminants, 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 of cyanide from the aglycone released by glucosidase activity in the rumen and inactivation of glutathione peroxidases due to absorbed cyanide's effect on the glutathione . Neonate ruminants at risk of WMD (white muscle disease) may be administered both selenium and vitamin E some of the WMD
respond only to selenium, some only to vitamin E, and some to either.
Main article:
A number of correlative epidemiological studies have implicated selenium deficiency (as measured by blood levels) in a number of serious or chronic diseases, such as cancer, , , and . In addition, selenium supplementation has been found to be a chemopreventive for some types of cancer in some types of rodents. However, in
in humans, selenium supplementation has not succeeded in reducing the incidence of any disease, nor has a
of such selenium supplementation studies detected a decrease in overall mortality.
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