Selenium: benefits and harm to the body, norm, sources, side effects. Selenium - characteristics of the substance with photos; determination of its daily norm for the human body; excess and deficiency; list of sources

Black metallic selenium crystals formed on a burning coal dump. Image width is 1.8 mm. Germany, North Rhine-Westphalia, Aachen, Alsdorf, Anna mine

A brittle, shiny, black non-metal (stable allotropic form, unstable form - cinnabar-red). Refers to chalcogens. It is part of the active centers of some proteins in the form of the amino acid selenocysteine. The human body contains 10-14 mg of selenium, most of it is concentrated in the liver, kidneys, spleen, heart, testicles and spermatic cords in men. Selenium is part of muscle tissue proteins and myocardial proteins.

See also:

STRUCTURE

There are two modifications of selenium:
1. Crystalline (monoclinic selenium a- and b-forms, hexagonal selenium g-forms).
2. Amorphous (powdery, colloidal and glassy forms of selenium).
The amorphous red modification of selenium is one of the unstable modifications of the element. Powdered and colloidal forms of selenium are obtained by reducing the substance from a solution of selenous acid H 2 SeO 3.
Black glassy selenium can be obtained by heating an element of any modification to a temperature of 220 degrees Celsius with rapid cooling. Hexagonal selenium is gray in color. This modification, the most thermodynamically stable, can also be obtained by heating to the melting point with further cooling to a temperature of 180-210 degrees Celsius. It is necessary to maintain this temperature regime for some time.

PROPERTIES

The melting point of the substance is 217 (α-Se) and 170–180 degrees Celsius (β-Se), and it boils at a temperature of 685 0.

Oxidation states that selenium exhibits in reactions: (-2), (+2), (+4), (+6), it is resistant to air, oxygen, water, hydrochloric acid and dilute sulfuric acid.

It can be dissolved in high concentration nitric acid, “regia vodka”, and dissolves for a longer time in an alkaline environment with oxidation. Is diamagnetic.

RESERVES AND PRODUCTION

Since selenium is mixed with sulfur, the element is extracted from ferrous sulfate. You don’t even need to do anything special for this. The 34th metal accumulates in dust cleaning chambers of sulfuric acid plants. Selenium is also taken from copper electrolysis plants. It leaves behind anode sludge. It is from this that the 34th element is isolated. It is enough to treat the sludge with solutions of sodium hydroxide and sulfur dioxide. The resulting selenium must be purified. For this purpose, the distillation method is used. Afterwards, the metal is dried.

ORIGIN

Excellent glossy crystals from burning coal dumps. Image width is 1.8 mm. Germany, North Rhine-Westphalia, Aachen, Alsdorf, Anna mine

The selenium content in the earth's crust is about 500 mg/t. The main features of the geochemistry of selenium in the earth's crust are determined by the proximity of its ionic radius to the ionic radius of sulfur. Selenium forms 37 minerals, among which first of all should be noted ashavalite FeSe, clausthalite PbSe, timannite HgSe, guanajuatite Bi 2 (Se, S) 3, hastite CoSe 2, platinite PbBi 2 (S, Se) 3, associated with various sulfides , and sometimes also with cassiterite. Native selenium is occasionally found. Sulfide deposits are of major industrial importance for selenium. The selenium content in sulfides ranges from 7 to 110 g/t. Selenium concentration in sea ​​water 4·10 -4 mg/l.

APPLICATION

One of the most important areas Its technology, production and consumption are the semiconductor properties of both selenium itself and its numerous compounds (selenides), their alloys with other elements in which selenium began to play a key role. IN modern technology Selenides of many elements are used in semiconductors, for example, tin, lead, bismuth, antimony, and lanthanide selenides. The photoelectric and thermoelectric properties of both selenium itself and selenides are especially important.
The stable isotope selenium-74 made it possible to create a plasma laser with colossal amplification in the ultraviolet region (about a billion times). The radioactive isotope selenium-75 is used as a powerful source of gamma radiation for flaw detection.
Potassium selenide together with vanadium pentoxide is used in the thermochemical production of hydrogen and oxygen from water (selenium cycle). The semiconducting properties of pure selenium were widely used in the mid-20th century to make rectifiers, especially in military equipment for the following reasons: unlike germanium, silicon, selenium is insensitive to radiation, and, in addition, the selenium rectifier diode has unique property self-healing in the event of a breakdown: the breakdown site evaporates and does not lead to a short circuit, the permissible diode current is slightly reduced, but the product remains functional. The disadvantages of selenium rectifiers include their significant dimensions.
Selenium is used as a powerful anticancer agent, as well as for the prevention of a wide range of diseases. According to studies, taking 200 mcg of selenium per day reduces the risk of rectal and colon cancer by 58%, prostate tumors by 63%, lung cancer by 46%, and reduces overall mortality from cancer by 39%.
Small concentrations of selenium suppress histamine and due to this have an antidystrophic effect and antiallergic effect. Selenium also stimulates tissue proliferation, improves the function of the gonads, heart, thyroid gland, and immune system.
In combination with iodine, selenium is used to treat iodine deficiency diseases and thyroid pathologies.
Selenium salts help restore low blood pressure during shock and collapse

Selenium - Se

CLASSIFICATION

Hey's CIM Ref1.53

Strunz (8th edition)	1/B.03-30
Nickel-Strunz (10th edition)	1.CC.10
Dana (7th edition)	1.3.3.1
Dana (8th edition)	1.3.4.1

Just like sulfur, it can be burned in air. Burns with a blue flame, turning into SeO 2 dioxide. Only SeO 2 is not a gas, but crystalline substance, highly soluble in water.

Obtaining selenous acid (SeO 2 + H 2 O → H 2 SeO 3) is no more difficult than sulfurous acid. And by acting on it with a strong oxidizing agent (for example, HClO 3), they obtain selenic acid H 2 SeO 4, almost as strong as sulfuric acid.

Ask any chemist: “What color selenium? - he will probably answer that it is gray. But elementary experience can refute this statement, which is correct in principle.

Let's pass sulfur dioxide through a bottle of selenic acid (it is, if you remember, a good reducing agent), and a beautiful reaction will begin. First the solution will turn yellow, then orange, then blood red. If the initial solution was weak, then this color can persist for a long time - colloidal amorphous selenium is obtained. If the acid concentration was high enough, then almost immediately after the start of the reaction a fine powder will begin to precipitate. Its color ranges from bright red to deep burgundy, similar to that of black gladioli. This is elemental selenium, amorphous powdered elemental selenium.

It can be transformed into a glassy state by heating to 220°C and then sharply cooling. Even if the color of the powder was bright red, glassy selenium will be almost black in color, the red tint is noticeable only in the light.

You can do another experiment. Stir the same red powder (a little!) in a flask with carbon disulfide. Don’t count on rapid dissolution - the solubility of amorphous selenium in CS 2 is 0.016% at zero and slightly more (0.1%) at 50°C. Attach a reflux condenser to the flask and boil the contents for about 2 hours. Then slowly evaporate the resulting light orange liquid with a greenish tint in a glass covered with several layers of filter paper, and you will get another type of selenium - crystalline monoclinic selenium.

The wedge crystals are small, red or orange-red in color. They melt at 170°C, but if heated slowly, then at 110-120°C the crystals will change: alpha-monoclinic selenium will turn into beta-monoclinic - dark red wide short prisms. That's what selenium is like. The same selenium that is usually gray.

Gray selenium (sometimes called metallic) has crystals in a hexagonal system. Its unit cell can be represented as a slightly deformed cube. With a regular cubic structure, the six neighbors of each atom are the same distance away from it, but selenium is built a little differently. All its atoms seem to be strung on spiral chains, and the distances between neighboring atoms in one chain are approximately one and a half times less than the distance between the chains. Therefore, the elementary cubes are distorted.

The density of gray selenium is 4.79 g/cm3, the melting point is 217°C, and the boiling point is 684.8-688°C. Previously, it was believed that gray selenium exists in two modifications - SeA and SeB, the latter being a better conductor of heat and electric current; subsequent experiments refuted this point of view.

When starting experiments, you need to remember that selenium and all its compounds are poisonous. You can experiment with selenium only under traction, observing all safety regulations. The “many faces” of selenium are best explained from the perspective of the relatively young science of inorganic polymers.

Selenium polymerology

This science is still so young that many basic ideas have not been formed clearly enough in it. There is not even a generally accepted classification of inorganic polymers. The famous Soviet chemist, full member of the USSR Academy of Sciences V.V. Korshak proposed dividing all inorganic polymers primarily into homochain and heterochain. The molecules of the former are composed of atoms of one type, and of the latter - of atoms of two or more elements.

Elemental selenium (any modification!) is a homochain inorganic polymer. Naturally, the thermodynamically stable gray selenium is the best studied. It is a polymer with helical macromolecules arranged in parallel. In chains, atoms are linked covalently, and chain molecules are united by molecular forces and partially by metallic bonds.

Even molten or dissolved selenium does not “split” into individual atoms. When selenium melts, a liquid is formed, again consisting of chains and closed rings. There are eight-membered Se 8 rings,

There are also more numerous “associations”. The same is true in solution. Attempts to determine the molecular weight of selenium dissolved in carbon disulfide gave a figure of 631.68. This means that here, too, selenium exists in the form of molecules consisting of eight atoms. Apparently, this statement is also true for other solutions.

Gaseous selenium exists in the form of isolated atoms only at temperatures above 1500°C, and at lower temperatures selenium pairs consist of two-, six- and eight-membered “communities”. Up to 900°C, molecules of the composition Se6 predominate, after 1000°C - Se 2.

As for red amorphous selenium, it is also a polymer with a chain structure, but with a poorly ordered structure. In the temperature range of 70-90°C it acquires rubber-like properties, turning into a highly elastic state. Monoclinic selenium appears to be more ordered than amorphous red, but inferior to crystalline gray.

All this is clarified in last decades, and it is possible that as the science of inorganic polymers develops, many quantities and figures will still be refined. This applies not only to selenium, but also to sulfur, tellurium, phosphorus - to all elements that exist in the form of homochain polymers.

The story of selenium as told by its discoverer

The history of the discovery of element No. 34 is uneventful. This discovery did not cause any disputes or clashes, and no wonder: Selenium was discovered in 1817 by the most authoritative chemist of his time, Jens Jakob Berzelius. Berzelius's own account of how this discovery occurred has been preserved.

“I investigated, in collaboration with Gottlieb Hahn, the method used for the production of sulfuric acid in Gripsholm. We found a precipitate in the sulfuric acid, partly red and partly light brown. This sediment, tested with a blowpipe, emitted a faint rare odor and formed a lead bead. According to Klaproth, such an odor is an indication of the presence of tellurium. Gan noted that at the Falun mine, where the sulfur necessary for the production of acid is collected, a similar odor is also felt, indicating the presence of tellurium. Curiosity, aroused by the hope of discovering a new rare metal in this brown sediment, led me to investigate the sediment. Having decided to separate tellurium, I was unable, however, to discover any tellurium in the sediment. Then I collected everything that was formed during the production of sulfuric acid by burning Falun sulfur over several months, and subjected the resulting large quantities of sediment to a thorough study. I found that the mass (that is, the sediment) contained a hitherto unknown metal, very similar in its properties to tellurium. In accordance with this analogy, I named the new body selenium (Selenium) from the Greek (moon), since tellurium is named after Tellus - our planet.

Just as the Moon is a satellite of the Earth, so selenium is a satellite of tellurium.

First uses of selenium

“Of all the uses of selenium, the oldest and by far the most extensive is the glass and ceramics industry.”

These words are taken from the "Handbook of Rare Metals", published in 1965. The first half of this statement is indisputable, the second is doubtful. What does “most extensive” mean? It is unlikely that these words can be attributed to the scale of selenium consumption by a particular industry. For many years now, the main consumer of selenium has been semiconductor technology. Nevertheless, the role of selenium in glassmaking is still quite large. Selenium, like manganese, is added to the glass mass to decolorize the glass and eliminate the greenish tint caused by the admixture of iron compounds. The compound of selenium with cadmium is the main dye in the production of ruby ​​glass; The same substance gives red color to ceramics and enamels.

Selenium is used in relatively small quantities in the rubber industry - as a filler, and in the steel industry - to produce alloys with a fine-grained structure. But these applications of element No. 34 are not the main ones; they did not cause a sharp increase in demand for selenium in the early 50s. Compare the price of selenium in 1930 and 1956: 3.3 dollars per kilogram and 33, respectively. Most rare elements have become cheaper during this time, but selenium has become 10 times more expensive! The reason is that it was in the 50s that the semiconducting properties of selenium began to be widely used.

Rectifier, photocell, solar battery

Ordinary gray selenium has semiconducting properties; it is a p-type semiconductor, i.e., conductivity in it is created mainly not by electrons, but by “holes”. And what is very important, the semiconducting properties of selenium are clearly manifested not only in ideal single crystals, but also in polycrystalline structures.

But, as you know, with the help of only one type of semiconductor (no matter what), the electric current cannot be amplified or rectified. Alternating current turns into direct current at the boundary of p- and n-type semiconductors, when the so-called pn junction occurs. Therefore, cadmium sulfide, an n-type semiconductor, often works together with selenium in a selenium rectifier. This is how selenium rectifiers are made.

A thin, 0.5-0.75 mm layer of selenium is applied to a nickel-plated iron plate. After heat treatment, a “barrier layer” of cadmium sulfide is also applied on top. Now this “sandwich” can pass electrons in almost only one direction: from the iron plate to the “barrier” and through the “barrier” to the balancing electrode. Usually these “sandwiches” are made in the form of disks, from which the rectifier itself is assembled. Selenium rectifiers are capable of converting current into thousands of amperes.

Another practically very important property of semiconductor selenium is its ability to sharply increase electrical conductivity under the influence of light. The action of selenium photocells and many other devices is based on this property.

It should be borne in mind that the operating principles of selenium and cesium solar cells are different. Cesium, when exposed to photons of light, releases additional electrons. This is the phenomenon of external photoelectric effect. In selenium, under the influence of light, the number of holes increases, and its own electrical conductivity increases. This is an internal photoelectric effect.

The effect of light on the electrical properties of selenium is twofold. The first is a decrease in its resistance to light. Second, no less important, is the photovoltaic effect, i.e. the direct conversion of light energy into electricity in a selenium device. To cause the photovoltaic effect, it is necessary that the photon energy be greater than a certain threshold, minimum value for a given photocell.

The simplest device that uses exactly this effect is an exposure meter, which we use when taking photographs to determine the aperture and shutter speed. The device reacts to the illumination of the subject being photographed, and everything else has already been done (recalculated) for us by those who designed the exposure meter. Selenium exposure meters are very widespread - they are used by both amateurs and professionals.

More complex devices of the same type are solar panels that operate on Earth and in space. Their operating principle is the same as that of an exposure meter. Only in one case, the resulting current only deflects a thin arrow, and in the other it powers a whole complex of on-board equipment of an artificial Earth satellite.

A copy is made by a selenium drum

In 1938, the American engineer Carlson patented the “selenium photography” method, which is now called xerography, or electrography. This is perhaps the most quick way obtaining high-quality black and white copies from any original - be it a drawing, engraving or reprint of a magazine article. It is important that this method can produce (and produce quickly) tens and hundreds of copies, and if the original is pale, the copies can be made much more contrasting. And you don’t need special paper - a xerographic copy can be made even on a paper napkin.

Electrographic machines are now produced in many countries, the principle of their operation is the same everywhere. Their action is based on the already mentioned internal photoeffect inherent in selenium. The main part of the electrographic machine is a metal drum, very smooth, processed to the highest 14th class of purity and coated with a layer of selenium deposited in a vacuum.

This machine works like this. The original from which a copy is to be made is inserted into the receiving window. Movable rollers transfer it under the bright light of fluorescent lamps, and a system consisting of mirrors and a photographic lens transmits the image to a selenium drum. It is already prepared for reception: a corotron is installed next to the drum - a device that creates a strong electric field. Once within the corotron's range of action, part of the selenium drum is charged with static electricity of a certain sign. But then an image was projected onto selenium, and the areas illuminated by the light reflected were immediately discharged - the electrical conductivity increased and the charges went away. But not from everywhere. In those places that remained in the shadows thanks to dark lines and signs, the charge remained. During the “development” process, this charge will attract particles of finely dispersed dye, also already prepared.

Mixing in a vessel with glass beads, the dye particles, like the drum, acquired charges of static electricity. But their charges are of the opposite sign; Typically the drum receives positive charges and the dye receives negative charges. The paper on which the image is to be transferred also receives a positive charge, but stronger than that on the drum.

When it is pressed tightly against the drum (of course, this is not done manually; you cannot touch the drum at all), the stronger charge will attract the dye particles, and the electrical forces will hold the dye on the paper. Of course, one cannot expect that these forces will operate forever, or at least for a long time. Therefore, the last stage of obtaining electrographic copies is heat treatment, which occurs right there in the machine.

The dye used can melt and be absorbed by the paper. After heat treatment, it is securely fixed to the sheet (it is difficult to erase with an eraser). The whole process takes no more than 1.5 minutes. While the heat treatment was going on, the selenium drum managed to rotate around its axis and special brushes removed the remnants of the old dye from it. The surface of the drum is ready to receive a new image.

Global trends are such that people are increasingly thinking about the state of their body and health in general. Research is being conducted and theories of the influence of certain chemical compounds on organs and systems. Selenium was no exception, since the benefits of this chemical element for living organisms are invaluable.

What is selenium?

Selenium is one of the chemical elements presented in the periodic table of D.I. Mendeleev. Refers to non-metals. Its atomic number is 34. Selenium minerals can be black, red or gray in color.

Natural selenium is found in the earth's crust. It got its name from Greek word"Selena" (Moon). Found in mineral waters and sea water. Its properties are similar to sulfur, but its chemical activity is less.

Biological role of a substance in living nature

Selenium is one of the elements necessary for life, as it is part of proteins. In proteins it is represented by the amino acid selenocysteine. Selenium deficiency (especially in children) is fatal.

In the human body, this element performs several functions:

• immunomodulatory;
• anticancer;
• promotes the formation of certain hormones;
• is an antioxidant.

Interesting fact

Selenium is also present in the nuclei of living cells. It promotes the metabolism of nucleic acids. Nucleic acids (DNA and RNA) are found in all living organisms and are responsible for the transmission of hereditary information.

Benefits of selenium

For the human body, this element plays an invaluable role. But you should be careful with it, since its deficiency (as well as its excess) can lead to the death of a living organism. The recommended daily dose of the substance for normal human life is 70-100 mcg.

Why is this microelement so necessary for any body?

1. It has anti-radiation and anti-toxic effects.
2. Reduces the likelihood of mutation risk.
3. Strengthens myocardial muscle fibers and prevents the development of diseases of the cardiovascular system.
4. Normalizes metabolic processes.
5. Promotes the formation of thyroid hormones (triiodotyranine) and the absorption of iodine.
6. Removes salts heavy metals from fabrics (lead, mercury, cadmium).
7. Promotes the synthesis of pancreatic hormones. Enhances insulin production. Therapy with selenium-containing drugs is used for type II diabetes mellitus. This treatment gives good results and with pancreatitis.
8. Normalizes the functioning of the gastrointestinal tract (improves mucus secretion and enzyme production).
9. Stimulates the production of interferon, which allows the immune system to successfully fight influenza viruses.
10. Accelerates the synthesis of vitamin E, enhancing its effect as an antioxidant.
11. Reduces the severity of some common diseases (psoriasis, bronchial asthma, dermatosis). For this purpose, selenium is used in combination with vitamins E and C.
12. Helps improve joint mobility. Used for arthritis, arthrosis, rheumatism. In traumatology it is used for fractures, as it promotes the growth of bone tissue.
13. The nervous system responds quite well to selenium intake: memory and neuron activity improve. Sometimes the trace element is used in the fight against multiple sclerosis.
14. Selenium improves mineral metabolism, promotes harmonious functioning of the kidneys and urinary system. Used in the treatment of pyelonephritis.
15. The protective effect of the non-metal allows the restoration of liver cells. Used in hepatoprotective drugs for cirrhosis.
16. Protects humans from the toxic effects of waste products of mold fungi.

Note

Selenium is also extremely important for men's health: the microelement helps enhance reproductive function, significantly increasing the activity of male germ cells.

This element increases the activity of the immune system, which is extremely important in childhood. Selenium deficiency can lead to endemic cretinism and mental retardation. And in combination with the Coxsackie virus, which lately spreads across to the globe, microelement deficiency can provoke Keshan disease. This pathology leads to degeneration of myocardial tissue with further necrosis. Without qualified help, it causes death.

Anti-cancer properties of the element

Unfortunately, malignant neoplasms are increasingly affecting people in all corners of the planet. Cancer treatment is expensive and does not always lead to positive results. Taking certain substances helps reduce the risk of developing cancer. One of these substances is selenium.

This trace element helps reduce the risk of tumor development by almost 40%. It seems incredible, but a sufficient amount of selenium-rich foods in your diet will help prevent cancer. And selenium therapy during oncology can almost halve the mortality rate of patients.

Many developed countries have long adopted programs for the “selenization” of the population. The main objectives of such programs are aimed at preventing pathologies among residents. Research in recent years shows that the benefits of selenium in the process of such programs are obvious: the risk of developing oncology is significantly reduced, as well as pathologies of the cardiovascular and immune systems.

Harm to the human body

Despite positive qualities Selenium, this microelement can cause enormous harm to the body. Doctors strongly recommend using it in doses so as not to cause excess.

Negative impact chemical substance on the skin is as follows.

• When non-metal salts come into contact with the epidermis, a strong reaction occurs. A feeling of numbness and dermatitis are a small part of the consequences. The element can cause severe chemical burns.
• If the substance gets on the mucous membranes (eyes, mouth), irritation, pain, and hyperemia occurs. Causes conjunctivitis.

All selenium compounds are toxic. Hydrogen selenide is especially dangerous in this regard. Gray, or metallic, selenium is the least dangerous, but even 1 gram of the substance ingested can cause poisoning. Symptoms: abdominal pain, nausea, vomiting, diarrhea. After some time, the symptoms go away.

The female body and selenium

For women, a sufficient amount of micronutrients in the diet plays an important role. It provides many vital processes:

1. normalizes metabolism, which allows women to look slim;
2. delays the onset of menopause;
3. improves reproductive function, which allows you to easily get pregnant;
4. improves the condition of skin, hair and nails;
5. prevents the development of inflammatory processes in the female genital organs.

Thanks to a sufficient amount of this microelement, the risk of developing uterine and mammary gland cancer is reduced. If oncology has begun, then chemical element allows you to successfully cure the tumor. Taking selenium reduces the risk of having to remove the uterus, which allows you to preserve reproductive function.

During pregnancy, the microelement is also very important. It helps to cope with many difficulties of bearing a child:

1. prevents toxic effects on the fetus;
2. reduces the risk of developing fetal mutations;
3. improves the condition of toxicosis;
4. allows the female body to quickly recover in the postpartum period.

It is very important to consume enough selenium while breastfeeding. It ensures good health of the mother and good health of the child. But you should not choose vitamin complexes with a high selenium content - give preference to natural sources of this substance.

Symptoms of selenium deficiency and excess

How does a substance deficiency manifest itself? Its deficiency can be understood by the following symptoms:

• weakness and aches throughout the body;
• constant drowsiness;
• deterioration of skin and hair condition;
• vision problems arise (temporary myopia);
• there is a constant feeling of aching in the muscles;
• Rashes may appear on various areas of the skin.
• memory deteriorates;
• body weight may increase;
• immunity decreases, colds often occur.

But the following symptoms indicate an overabundance of the substance:

• abdominal pain, nausea, vomiting;
• bowel movements may become more frequent;
• alopecia (hair loss) develops;
• the breath smells like garlic (therefore, sometimes excess selenium can be confused with arsenic poisoning);
• dizziness and headache appear;
• eyes hurt and turn red.

Available Sources of Selenium

To understand how much of a substance is contained in certain products, just look comparison table. It contains plant products that are record holders for selenium content.

Product name	Microelement content in mcg per 100 g of raw product
Bertholetia (Brazil nut) grains	1500
Dates	400
Oyster mushroom (mushrooms)	130
Coconut pulp	70-100
Sunflower seeds	50
Corn	30
Broccoli	2,5

The following table lists animal products rich in selenium.

The pharmaceutical industry presents vitamin complexes enriched with selenium and preparations with a high content of this substance. Such medications should not be taken without medical prescription: they have a fairly large number of side effects and contraindications. Children, pregnant and nursing mothers especially should not experiment with such complexes.

To get the required amount of microelement, you should not stuff yourself with chemicals. It is enough to review your diet and enrich it with the necessary products. And resort to pharmaceutical products only as a last resort. Take care of your health!

You've probably often read about microelements that are useful and necessary for the body. One of these substances is the chemical element Se (selenium). It was discovered as an independent element only two centuries ago, and its necessity for the body was proven much later.

Selenium Facts

Here are a few interesting facts from difficult and unusual story getting to know selenium and its role in the human body:

• It was discovered as an independent element in 1817 by J. Ya. Berzelius.
• Industrial use begins in the mid-19th century.
• The first solar cells were made using selenium.
• From 1900 to 1950, the use of selenium was extremely limited due to its proven toxicity.
• 1954 marked the release of the first scientific article about the positive biological properties of selenium.
• Since the 1950s, the effects of selenium on the human and animal body have been studied.
• The selenium content in the body is 10-15 milligrams.
• The daily human need is 70-100 micrograms.
• Selenium is part of a whole group of enzymes.
• Both deficiency and excess of selenium negatively affect the body.

Despite being contained in the body in very small quantities, selenium is important for all human cells, tissues and organs, as it performs many important functions. This is due to its inclusion in a number of enzymes, as well as its presence in the nucleus of each cell. In order to understand what happens with an excess or deficiency of selenium, it is necessary to first describe its physiological effects.

The physiological functions of selenium include:

• Protecting the body from biological threats. As part of special proteins united in the group of selenoproteins, this element plays an important role in regulating the body's immune system. With its help, the body provides an adequate response to the introduction of bacteria, fungi, viruses, as well as protozoan microorganisms.
• Protecting the body from chemical threats. Both during functioning and from the external environment, the body constantly contains aggressive compounds that damage and destroy cells. Their action is resisted by a special, nonspecific antioxidant-antiradical defense system, which includes a number of enzymes, biologically active substances and some other factors, including cellular ones. Selenium is integral part a significant number of compounds from this system.
• Participation in the metabolism of fats, proteins and carbohydrates. Selenium is necessary for the regulation of normal synthesis of thyroid hormones, and also promotes the complete absorption of elements such as iodine from food and water. Indirectly, through these and other biologically active compounds, selenium affects all types of metabolism in the body.
• Regulation of cell division. Selenium, like some other elements, is a necessary factor for normal cell division. The presence of selenium in cells prevents mutations and the development of tumor cells, and in existing cancer cells, it triggers mechanisms for their destruction.
• Anti-inflammatory effect. It lies in the regulation chemical reactions and the actions of biologically active molecules that are responsible for the course of the inflammatory - protective reaction. These substances are called inflammatory mediators, and selenium helps normalize their release. The role of this substance is especially important in alleviating conditions characterized by an excessive response of the body, such as bronchial asthma, arthritis, psoriasis and chronic forms of colitis.
• Detoxifying properties. Selenium has the ability to reliably bind and promote rapid removal from the body of heavy metal ions: cadmium, mercury, lead, synthetic drugs, a number of toxic compounds of biological nature - toxins of bacteria, fungi, protozoa.
• Cytoprotective effect. Thanks to selenium, the processes of aging and damage to both individual cells and the entire body are significantly inhibited. That is why the presence of this element in required quantities promotes the longest possible functioning of central cells nervous system, cardiac muscle, liver and bone marrow.
• Reproductive effect. Selenium is metabolically very closely related to substances such as ascorbic acid (Vitamin “C”) and tocopherol (Vitamin E), biotin (Vitamin H). All these substances, and first of all, selenium, are extremely necessary for the normal functioning of the human reproductive system. The effect of selenium extends both to the synthesis of sex hormones and to the process of formation of germ cells.
• Other effects. Selenium plays an important role in the metabolism of other chemical elements in the body. This applies to iron, copper, iodine, zinc and others, and this influence is mutual and interconnected.

Important:Selenium is necessary for the body, as it participates in almost all processes in the human body. By itself, it is quite toxic, so what is important is the necessary intake of it into the body - within the range of 70 - 100 mcg per day. A deficiency of selenium in the body, just like its excess, leads to pronounced negative changes.

Factors leading to excess or deficiency of selenium

The main factors contributing to selenium deficiency in the body include:

• living in regions with low selenium content in the soil;
• diseases gastrointestinal tract with a violation of the absorption process;
• practiced vegetarianism, fasting, excessive dieting;
• and alcohol consumption;
• taking certain pharmacological drugs - oral contraceptives, laxatives, statins, adsorbents.
• old age;
• excessive consumption of selenium during pregnancy, chronic intoxication, for example, with pollutants, in unfavorable environmental conditions;

A rarer condition is excess selenium intake into the body and is mainly associated with:

• dietary habits with an excess of foods rich in selenium - mainly seafood;
• unreasonable or excessive intake of selenium medications;
• accidental rapid intake of significant doses of selenium into the body;
• chronic excess intake of selenium into the body, for example, with a low level of safety precautions in some chemical industries.

With an abnormally low intake of selenium from water and food into the body over a long period of time, a number of negative phenomena are observed that can occur independently, disguise themselves as other diseases, or aggravate the picture of existing ones. For the convenience of describing such conditions, we will present them in the same sequence in which the physiological effects of this element were described.

As a result of selenium deficiency,:

• . Its protective properties are significantly weakened. Moreover, all components of the immune system are negatively affected - from leukocytes to antibodies. With prolonged and severe selenium deficiency, states of almost complete immune deficiency can occur. This is manifested by the body's susceptibility to infections of any type. Any infectious diseases are severe, with frequent complications, and are difficult to correct with medication. Recovery from selenium deficiency takes a long time and is rarely complete.
• Antioxidant protection. Selenium deficiency leads to rapid and massive damage to individual cells and rapid wear and tear of tissues and organs. The patient has various types tissue degeneration, atherosclerotic and other vascular changes. Rapid degeneration of tissues of the central nervous system, bone marrow, muscle fibers. The result of selenium deficiency is various nonspecific diseases, and also, most importantly, aggravation of the course of existing diseases, such as coronary heart disease, bronchial asthma, endocrine pathology and many, many others. This is manifested in more frequent exacerbations, maximum severity of clinical manifestations, more difficult recovery and short duration of remissions.
• Metabolism. Disturbances manifest themselves in aggravation of the course of existing endocrine disorders, as well as excess or, on the contrary, underweight, which cannot be actively corrected with the help of diets. There are often disturbances in water and salt metabolism, the metabolism of other important macro- and microelements, which cascade to even more profound negative changes in the body.
• Normal cell division. This condition is one of the risk factors for the development of tumors, both malignant and benign. If a situation arises where selenium deficiency occurs with tumors already existing in the body, this leads to a sharp increase in the growth and progression of tumors, the occurrence of relapses and the appearance of multiple metastases in malignant tumors.
• Anti-inflammatory function. Inflammatory reactions and processes associated with inflammatory mediators, such as bronchial asthma, allergic reactions of various types, are more pronounced and severe. In this case, they are much less amenable to drug correction.
• Cell protection. The protection of cells from biological toxins, organic and inorganic compounds, especially heavy metal ions, as well as toxic metabolic products of the body itself is sharply reduced, which is manifested both in a decrease in the overall resistance of the body and in the appearance of a variety of diseases.
• Reproductive function. It is one of the first to suffer, especially among men. This not only in most cases is the cause of male infertility, but also leads to a decrease in the severity of desire and sexual activity. If selenium deficiency develops in women during pregnancy and this deficiency remains uncorrected, this can lead to various pathologies of fetal development. In some cases, a catastrophic lack of selenium causes spontaneous abortions and miscarriage.

Pay attention!Selenium is quite a toxic substance!

Acute selenium intoxication is extremely rare and is observed when large doses of inorganic selenium are simultaneously ingested into the body, which is usually associated with accidental drug overdoses and man-made causes - accidents at selenium mining or processing facilities. IN in this case clinical manifestations directly correlate with the amount of dose entering the body.

Symptoms usually include general toxic effects. The patient has:

• abdominal pain and frequent stools; This symptom gradually fades away over several days;
• constant nausea, vomiting, which does not bring relief, but is not profuse;
• a rather sharp, pronounced garlic odor from the mouth;
• severe headache, especially when moving, muscle pain;
• Occasionally, photophobia and lacrimation may occur in bright indoor lighting;
• weakness, increased fatigue, drowsiness without proper sleep.

Carrying out general detoxification measures in intensive care units is quite enough to help the body recover from acute selenium poisoning without any special consequences.

Important!There is no specific antidote for acute selenium poisoning.

Chronic selenium intoxication is not so common, and is mainly associated with living in regions containing excess selenium in soil, water and foods. Also, chronic selenium intoxication can occur in industrially undeveloped countries among employees of selenium mining or processing enterprises, when, due to poverty, no one cares about the safety and health of workers.

The main symptoms of chronic excess selenium intake into the body are:

Pay attention! The result of all of the above is the following conclusion. Both excess and deficiency of selenium in the body leads to various pathologies or aggravates the course of existing diseases. That is why it is necessary to ensure that the body receives a strictly necessary dose of selenium.

Selenium has a remarkable feature - its deficiency can be easily corrected with nutrition. To do this, you need to add foods rich in this element to your daily diet.

Three important features should be taken into account:

• When food is thermally processed, the amount of selenium is reduced on average by about half its original level.
• Foods rich in simple carbohydrates (sugars), alcohol, and excessively fatty foods reduce the level of absorbable selenium by almost 4 times.
• The average daily requirement of the body for selenium is 70 – 100 micrograms.

Below is a list of foods containing selenium per 100 grams of raw food, in descending order:

Please note: The champion in selenium content is Bertolecia, or Brazil nut - one of its fruits can cover the body's daily need for this element. A certain disadvantage may be the exotic nature and low prevalence of the product for ordinary Russians.

Our usual products containing selenium are:

• poultry (turkey, duck, chicken) 70-55 mcg and animals (pork, lamb, beef) – 55-40 mcg, and poultry meat contains more selenium;
• seafood (fish, shrimp, squid and more exotic lobsters, octopus, crabs) – 50-35 mcg;
• chicken eggs - 32 mcg;
• grains and legumes – corn, rice, beans, lentils – 30-20 mcg;
• pistachios – 19 mcg;
• peas - 13 mcg;
• common nuts - peanuts, walnut, hazel, almonds – 7-2.5 mcg;
• vegetables and fruits - up to maximum 2 mcg.

As you can see, a varied diet, even without special correction, can meet the body's needs for selenium. Moreover, calculating the number of necessary products is very simple.

A state of selenium deficiency or excess can be established if disorders are suspected and confirmed by appropriate special biochemical tests. If the element is insufficient, correction is carried out with diet and, in the case of laboratory-proven ineffectiveness of the diet, drugs containing selenium may be prescribed.

Selenium(Selenium), Se, chemical element of group VI periodic table Mendeleev; atomic number 34, atomic mass 78, 96; predominantly non-metallic. Natural Selenium is a mixture of six stable isotopes - 74 Se (0.87%), 76 Se (9.01%), 77 Se (7.58%), 78 Se (23.52%), 80 Se (49. 82%), 82 Se (9.19%). From radioactive isotopes highest value has 75 Se with a half-life of 121 days. The element was discovered in 1817 by I. Berzelius (the name is given from the Greek selene - Moon).

Distribution of Selenium in nature. Selenium is a very rare and trace element, its content in the earth's crust (clarke) is 5·10 -6% by mass. The history of selenium in the earth's crust is closely related to the history of sulfur. Selenium has the ability to concentrate and, despite its low clarke, forms 38 independent minerals - natural selenides, selenites, selenates and others. Isomorphic impurities of Selenium in sulfides and native sulfur are characteristic.

Selenium migrates vigorously in the biosphere. Sources for the accumulation of Selenium in living organisms are igneous rocks, volcanic smoke, and volcanic thermal waters. Therefore, in areas of modern and ancient volcanism, soils and sedimentary rocks are often enriched with Selenium (on average in clays and shales - 6·10 -5%).

Physical properties of Selenium. Configuration of the outer electron shell of the Se atom 4s 2 4p 4 ; two p-electrons have paired spins, and the other two have unpaired spins, so Selenium atoms are able to form Se 2 molecules or chains of Se n atoms. Chains of Selenium atoms can be closed into ring molecules Se 8 . The diversity of the molecular structure determines the existence of Selenium in various allotropic modifications: amorphous (powdery, colloidal, glassy) and crystalline (monoclinic α- and β-forms and hexagonal γ-forms). Amorphous (red) powdered and colloidal Selenium (density 4.25 g/cm 3 at 25 ° C) is obtained by reduction from a solution of selenous acid H 2 SeO 3, rapid cooling of Selenium vapor and other methods. Glassy (black) Selenium (density 4.28 g/cm 3 at 25 °C) is obtained by heating any modification of Selenium above 220 °C, followed by rapid cooling. Vitreous Selenium has a glassy luster and is fragile. Thermodynamically, hexagonal (gray) Selenium is the most stable. It is obtained from other forms of Selenium by heating until melting with slow cooling to 180-210 ° C and holding at this temperature. Its lattice is built from parallel spiral chains of atoms. The atoms within the chains are bonded covalently. Lattice constants a = 4.36 Å, c = 4.95 Å, atomic radius 1.6 Å, ionic radii Se 2- 1.98 Å and Se 4+ 0.69 Å, density 4.807 g/cm 3 at 20 °C, t pl 217 °C, boiling point 685 °C. Selena vapors are yellowish in color. In pairs, four polymer forms Se 8 = Se 6 = Se 4 = Se 2 are in equilibrium. Above 900 °C Se 2 dominates. The specific heat capacity of hexagonal Selenium is 0.19-0.32 kJ/(kg K), at -198 - + 25 °C and 0.34 kJ/(kg K) at 217 °C; thermal conductivity coefficient 2.344 W/(m K), temperature coefficient of linear expansion at 20 °C: hexagonal monocrystalline Selenium along the c-axis 17.88·10 -6, perpendicular to the c-axis 74.09·10 -6, polycrystalline 49, 27·10 -6; isothermal compressibility β 0 = 11.3·10 -3 kbar -1 ; coefficient of electrical resistance in the dark at 20 °C 10 2 -10 12 ohm cm. All modifications of Selenium have photoelectric properties. Hexagonal Selenium up to the melting point is an impurity semiconductor with hole conductivity. Selenium is diamagnetic (its vapors are paramagnetic).

Chemical properties of Selenium. Selenium is stable in air; oxygen, water, salt and dilute sulfuric acid they have no effect on it, are highly soluble in concentrated nitric acid and aqua regia, and dissolve in alkalis with oxidation. Selenium in compounds has oxidation states -2, + 2, + 4, +6. Ionization energy Se 0 → Se 1+ → Se 2+ → Se 3+, respectively, 0.75; 21.5; 32 ev.

With oxygen, Selenium forms a series of oxides: SeO, Se 2 O 3, SeO 2, SeO 3. The last two are anhydrides of selenic H 2 SeO 3 and selenic H 2 SeO 4 acids (salts - selenites and selenates). SeO 2 is the most stable. With halogens, Selenium gives compounds SeF 6, SeF 4, SeCl 4, SeBr 4, Se 2 Cl 2 and others. Sulfur and tellurium form a continuous series of solid solutions with Selenium. With nitrogen, Selenium gives Se 4 N 4, with carbon -CSe 2. Compounds with phosphorus P 2 Se 3, P 4 Se 3, P 2 Se 5 are known. Hydrogen interacts with Selenium at t>=200 °C, forming H 2 Se; a solution of H 2 Se in water is called hydroselenic acid. When interacting with metals, Selenium forms selenides. Numerous complex compounds of Selenium have been obtained. All selenium compounds are poisonous.

Getting Selenium. Selenium is obtained from waste from sulfuric acid, pulp and paper production and anode sludge from electrolytic refining of copper. Selenium is present in sludge along with sulfur, tellurium, heavy and noble metals. To extract Selenium, the sludge is filtered and subjected to either oxidative roasting (about 700 °C) or heating with concentrated sulfuric acid. The resulting volatile SeO 2 is captured in scrubbers and electrostatic precipitators. Technical selenium is precipitated from solutions with sulfur dioxide. Sintering of sludge with soda is also used, followed by leaching of sodium selenate with water and separating selenium from the solution. To obtain high purity Selenium used as semiconductor material, rough Selenium is refined by vacuum distillation, recrystallization and others.

Application of Selenium. Due to its low cost and reliability, Selenium is used in converter technology in rectifying semiconductor diodes, as well as for photoelectric devices (hexagonal), electrophotographic copying devices (amorphous Selenium), the synthesis of various selenides, as phosphors in television, optical and signal devices, thermistors, etc. n. Selenium is widely used for decolorizing green glass and producing ruby ​​glasses; in metallurgy - to give cast steel a fine-grained structure, improve the mechanical properties of stainless steels; in the chemical industry - as a catalyst; Selenium is also used in the pharmaceutical industry and other industries.

Selenium in the body. Most living creatures contain from 0.01 to 1 mg/kg Selenium in their tissues. It is concentrated by some microorganisms, fungi, marine organisms and plants. Legumes (for example, astragalus, neptunia, acacia), cruciferous, madder, and asteraceae are known to accumulate Selenium up to 1000 mg/kg (on a dry weight basis); Selenium is an essential element for some plants. Various organoselenium compounds, mainly selenium analogues of sulfur-containing amino acids - selencysthionine, selenhomocysteine, methylselenomethionine, were found in concentration plants. An important role in the biogenic migration of selenium is played by microorganisms that reduce selenites to metallic selenium and oxidize selenides. There are biogeochemical provinces of Selene.

The requirement of humans and animals for Selenium does not exceed 50-100 mcg/kg of diet. It has antioxidant properties, increases the perception of light by the retina, and affects many enzymatic reactions. When Selenium content in the diet is more than 2 mg/kg, acute and chronic forms of poisoning occur in animals. High concentrations of Selenium inhibit redox enzymes, disrupt the synthesis of methionine and the growth of supporting tissues, and cause anemia. The lack of Selenium in feed is associated with the appearance of so-called white muscle disease of animals, necrotizing liver degeneration, and exudative diathesis; Sodium selenite is used to prevent these diseases.