Its name comes from the village of Strontian in Scotland, where the mineral containing strontium was discovered. In 1790, strontium was identified as an individual element by A. Crawford and W. Cruikshank. G. Davy first isolated metallic strontium in 1808.
Receipt:
Strontium accounts for 0.008% of the total number of atoms in the earth's crust. In addition to silicate rocks, strontium occurs in the form of its sparingly soluble carbonic and sulphate salts: SrCO 3 - strontianite, SrSO 4 - celestine.
In the free state, it can be obtained by heating the oxide with aluminum metal in high vacuum:
3SrO+2Al=Al 2 O 3 +3Sr
Physical properties:
Like calcium, strontium is a malleable golden yellow metal and is much softer than calcium. Volatile compounds of strontium color the flame carmine red.
Chemical properties:
In air, strontium is covered with a film containing, along with oxide, peroxide and strontium nitride. Due to rapid oxidation, the metal is stored in mineral oil or sealed in ampoules.
Reacts when heated with hydrogen and nitrogen, halogens. Easily displaces hydrogen not only from dilute acids, but also from water. Soluble in liquid ammonia. It is divalent in its compounds.
The most important connections:
Strontium oxide is a white refractory substance that vigorously attaches water to form a white hydroxide. Along with the oxide, white strontium(II) peroxide is known
Strontium hydroxide, Sr(OH) 2- strong base, highly soluble in water. When interacting with acids, the oxide and hydroxide easily form salts, usually colorless.
Strontium nitrate, Sr(NO 3) 2 is allocated in the form of crystalline hydrates, which are very easily soluble in water. Nitrates are similar in composition to chlorates, bromates, and iodates.
The solubility of salts in water decreases in the series: Ca - Sr - Ba and Cl - Br - I.
Strontium sulfide is a white solid. Strontium polysulfides SrS n are known.
Application:
Strontium is a getter in electrovacuum devices, a modifier of alloys, cast irons and steels. Radioactive isotopes 89 Sr and 90 Sr are used as sources b-radiation.
Strontium nitrate is used in pyrotechnics for the manufacture of compositions that, when burned, give a brightly colored red flame (fireworks and flares).
Many strontium compounds are used as components of ceramics, phosphors, and optical materials.
Strontium is able to accumulate in the human body, replacing calcium, which leads to increased bone fragility. But if this is not natural strontium, but 90 Sr formed as a result of nuclear explosions, then the consequences are much more severe: bone marrow damage, leukemia, radiation sickness.
Elmik Galina
See also:
S.I. Venetsky. About the rare and scattered. Metal stories.
STRONTIUM (Strontium, Sr) - a chemical element of the periodic system of D. I. Mendeleev, a subgroup of alkaline earth metals. In the human body, S. competes with calcium (see) for inclusion in the crystal lattice of bone oxyapatite (see). 90 Sr, one of the most long-lived radioactive fission products of uranium (see), accumulating in the atmosphere and biosphere during nuclear weapons tests (see), poses a great danger to mankind. S.'s radioactive isotopes are used in medicine for radiation therapy (see), as a radioactive label in diagnostic radiopharmaceuticals (see) in medical biol. research, as well as in atomic electric batteries. S. compounds are used in flaw detectors, in sensitive instruments, and in devices for combating static electricity. In addition, S. is used in radio electronics, pyrotechnics, in the metallurgical and chemical industries, and in the manufacture of ceramic products. S.'s connections are not poisonous. When working with metallic S., one should be guided by the rules for handling alkali metals (see) and alkaline earth metals (see).
S. was discovered as part of a mineral later named SrC03 strontianite in 1787 near the Scottish city of Strontiana.
The serial number of strontium is 38, the atomic weight (mass) is 87.62. The content of S. in the earth's crust averages 4-10 2 wt. %, in sea water - 0.013% (13 mg / l). The minerals strontianite and celestite SrSO 4 are of industrial importance.
The human body contains approx. 0.32 g of strontium, mainly in bone tissue, in the blood, the concentration of S. is normally 0.035 mg / l, in the urine - 0.039 mg / l.
S. is a soft silvery-white metal, t°pl 770°, t°kip 1383°.
According to chem. S.'s properties are similar to calcium and barium (see), in connections strontium valence 4-2, is chemically active, is oxidized under normal conditions by water with formation of Sr(OH) 2, and also by oxygen and other oxidizers.
S. enters the human body hl. arr. with plant foods, as well as with milk. It is absorbed in the small intestine and quickly exchanges with S. contained in the bones. S.'s removal from an organism is strengthened by complexes, amino acids, polyphosphates. The increased content of calcium and fluorine (see) in water interferes with S.'s cumulation in bones. With an increase in the concentration of calcium in the diet by 5 times, S.'s accumulation in the body is halved. Excessive S.'s intake with food and water due to its increased content in the soil of some geochemical. provinces (for example, in some districts of Eastern Siberia) causes an endemic disease - ur disease (see Kashin - Beck disease).
In bones, blood and other biol. S.'s substrates define hl. arr. spectral methods (see Spectroscopy).
radioactive strontium
Natural S. consists of four stable isotopes with mass numbers 84, 86, 87, and 88, of which the latter is the most common (82.56%). Eighteen radioactive isotopes of sulfur are known (with mass numbers 78–83, 85, 89–99) and four isomers of isotopes with mass numbers 79, 83, 85, and 87 (see Isomerism).
In medicine, 90Sr is used for radiation therapy in ophthalmology and dermatology, as well as in radiobiological experiments as a source of β-radiation. 85Sr is obtained either by irradiating a strontium target enriched in the 84Sr isotope with neutrons in a nuclear reactor by the reaction 84Sr (11.7) 85Sr, or produced at a cyclotron by irradiating natural rubidium targets with protons or deuterons, for example, by the reaction 85Rb (p, n) 85Sr. The radionuclide 85Sr decays with electron capture, emitting gamma radiation with an energy E gamma equal to 0.513 MeV (99.28%) and 0.868 MeV (< 0,1%).
87mSr can also be obtained by irradiating a strontium target in a reactor by the reaction 86Sr (n, gamma) 87mSr, but the yield of the desired isotope is low, in addition, 85Sr and 89Sr isotopes are formed simultaneously with 87mSr. Therefore, usually 87niSr is obtained using an isotope generator (see Radioactive Isotope Generators) based on the parent isotope of yttrium-87 - 87Y (T1 / 2 = 3.3 days). 87mSr decays with an isomeric transition, emitting gamma radiation with an Egamma energy of 0.388 MeV, and partly with electron capture (0.6%).
89Sr is contained in fission products together with 90Sr; therefore, 89Sr is obtained by irradiating natural sulfur in a reactor. In this case, an 85Sr impurity is also inevitably formed. The 89Sr isotope decays with the emission of P-radiation with an energy of 1.463 MeV (approx. 100%). The spectrum also contains a very weak line of gamma radiation with an energy E gamma equal to 0.95 MeV (0.01%).
90Sr is obtained by isolation from a mixture of uranium fission products (see). This isotope decays with the emission of beta radiation with an energy of E beta equal to 0.546 Meu (100%), without accompanying gamma radiation. The decay of 90Sr leads to the formation of a daughter radionuclide 90Y, which decays (T1 / 2 = 64 hours) with the emission of p-radiation, consisting of two components with Ep equal to 2.27 MeV (99%) and 0.513 MeV (0 .02%). The decay of 90Y also emits very weak gamma radiation with an energy of 1.75 MeV (0.02%).
Radioactive isotopes 89Sr and 90Sr, which are present in the waste of the nuclear industry and are formed during nuclear weapons testing, can enter the human body with food, water, and air when the environment is polluted. Quantification of S.'s migration in the biosphere is usually carried out in comparison with calcium. In most cases, when 90Sr moves from the previous link in the chain to the next, the concentration of 90Sr decreases per 1 g of calcium (the so-called discrimination coefficient), in adults in the body-diet link, this coefficient is 0.25.
Like soluble compounds of other alkaline earth elements, soluble compounds of S. are well absorbed from went. - kish. a path (10-60%), absorption of poorly soluble connections S. (eg, SrTi03) makes less than 1%. The degree of absorption of S.'s radionuclides in the intestine depends on age. With an increase in the calcium content in the diet, S.'s accumulation in the body decreases. Milk promotes increase in S.'s absorption and calcium in intestines. It is believed that this is due to the presence of lactose and lysine in milk.
When inhaled, soluble S. compounds are quickly eliminated from the lungs, while poorly soluble SrTi03 is exchanged in the lungs extremely slowly. Penetration of radionuclide S. through the intact skin makes apprx. one%. Through damaged skin (cut wound, burns, etc.)? as well as from subcutaneous tissue and muscle tissue, S. is absorbed almost completely.
S. is an osteotropic element. Regardless of the route and rhythm of entry into the body, soluble 90Sr compounds selectively accumulate in the bones. Less than 1% of 90Sr is retained in soft tissues.
With intravenous administration, S. is very quickly eliminated from the bloodstream. Soon after administration, the concentration of S. in the bones becomes 100 times or more higher than in soft tissues. Nek-ry differences in accumulation 90Sr in separate bodies and fabrics are noted. A relatively higher concentration of 90Sr in experimental animals is found in the kidneys, salivary and thyroid glands, and the lowest - in the skin, bone marrow and adrenal glands. The concentration of 90Sr in the renal cortex is always higher than in the medulla. S. initially lingers on the bone surfaces (periosteum, endosteum), and then is distributed relatively evenly throughout the entire volume of the bone. Nevertheless, the distribution of 90Sr in different parts of the same bone and in different bones turns out to be uneven. During the first time after administration, the concentration of 90Sr in the epiphysis and metaphysis of the bone of experimental animals is approximately 2 times higher than in the diaphysis. From the epiphysis and metaphysis, 90Sr is excreted faster than from the diaphysis: in 2 months. the concentration of 90Sr in the epiphysis and metaphysis of the bone decreases by 4 times, and in the diaphysis almost does not change. Initially 90Sr concentrates in those sites in which there is an active formation of a bone. Abundant blood and lymph circulation in the epimetaphyseal areas of the bone contributes to a more intense deposition of 90Sr in them compared to the diaphysis of the tubular bone. The amount of 90Sr deposition in the bones of animals is not constant. A sharp decrease in 90Sr fixation in bones with age was found in all animal species. Deposition of 90Sr in the skeleton significantly depends on gender, pregnancy, lactation, and the state of the neuroendocrine system. A higher deposition of 90Sr in the skeleton was noted in male rats. In the skeleton of pregnant females, 90Sr accumulates less (up to 25%) than in control animals. Lactation has a significant effect on the accumulation of 90Sr in the skeleton of females. With the introduction of 90Sr 24 hours after birth, 90Sr is retained in the skeleton of rats 1.5-2 times less than in non-lactating females.
The penetration of 90Sr into the tissues of the embryo and fetus depends on the stage of their development, the state of the placenta, and the duration of circulation of the isotope in the mother's blood. Penetration of 90Sr into the fetus is the greater, the longer the gestational age at the time of administration of the radionuclide.
To reduce the damaging effect of strontium radionuclides, it is necessary to limit their accumulation in the body. For this purpose, when the skin is contaminated, it is necessary to quickly decontaminate its open areas (with the preparation "Protection-7", washing powders "Era" or "Astra", NEDE paste). In case of oral intake of strontium radionuclides, antidotes should be used to bind or absorb the radionuclide. Such antidotes include activated barium sulfate (adso-bar), polysurmin, alginic acid preparations, etc. For example, the drug adsobar, when taken immediately after radionuclides enter the stomach, reduces their absorption by 10-30 times. Adsorbents and antidotes should be prescribed immediately after detection of damage by strontium radionuclides, since delay in this case leads to a sharp decrease in their positive effect. At the same time, it is recommended to prescribe emetics (apomorphine) or produce abundant gastric lavage, use saline laxatives, cleansing enemas. In case of damage by dust-like preparations, abundant washing of the nose and oral cavity, expectorants (thermopsis with soda), ammonium chloride, injections of calcium preparations, diuretics are necessary. In later periods after the lesion, to reduce the deposition of S.'s radionuclides in the bones, it is recommended to use the so-called. stable strontium (S. lactate or S. gluconate). Large doses of oral calcium or intravenous MofyT replace stable strontium preparations if these are not available. In connection with the good reabsorption of strontium radionuclides in the renal tubules, the use of diuretics is also indicated.
A certain decrease in the accumulation of S.'s radionuclides in the body can be achieved by creating a competitive relationship between them and a stable isotope of S. or calcium, as well as by creating a deficiency of these elements in cases where S.'s radionuclide has already been fixed in the skeleton. However, effective means of decorporation of radioactive strontium from the body have not yet been found.
The minimum significant activity that does not require registration or obtaining permission from the State Sanitary Inspection for 85mSr, 85Sr, 89Sr and 90Sr is 3.5*10 -8 , 10 -10 , 2.8*10 -11 and 1.2*10, respectively -12 curies/l.
Bibliography: Borisov V.P. and others. Emergency care for acute radiation exposure, M., 1976; Buldakov L. A. and Moskalev Yu. I. Problems of distribution and experimental estimation of admissible levels of Cs137, Sr90 and Ru106, M., 1968, bibliogr.; Voinar A. I. The biological role of trace elements in the body of animals and humans, p. 46, M., 1960; Ilyin JI. A. and Ivannikov A. T. Radioactive substances and wounds, M., 1979; To and with and in fi-on B. S. and T about r ben to about V. P. Life of a bone tissue, M., 1979; JI e in and V. I N. Obtaining radioactive preparations, M., 1972; Metabolism of strontium, ed. J. M. A. Lenihena and others, trans. from English, M., 1971; Poluektov N. S. and others. Analytical chemistry of strontium, M., 1978; P em and G. Course of inorganic chemistry, trans. from German, vol. 1, M., 1972; Protection of the patient in radionuclide investigations, Oxford, 1969, bibliogr.; Table of isotopes, ed. by C. M. Lederer a. V. S. Shirley, N. Y. a. o., 1978.
A. V. Babkov, Yu. I. Moskalev (rad.).
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Introduction
5. Sampling approaches
Offers
Introduction
A very dangerous type of impact on the biosphere is radioactive radiation. This type of environmental pollution appeared only at the beginning of the 20th century, since the discovery of the phenomenon of radioactivity and attempts to use radioactive elements in science and technology. Known types of radioactive transformations are accompanied by various radiations. These are a-rays, consisting of helium nuclei, b-rays, which are a stream of fast electrons, and y-rays, which have a high penetrating power. Fragments of nuclear fission of uranium, plutonium, cesium, barium, strontium, iodine and other radioactive elements have a strong biological effect.
The combination of properties of strontium-90 leads it, along with cesium-137 and radioactive isotopes of iodine, to the category of the most dangerous and terrible radioactive pollutants. Stable isotopes of strontium are of little danger in themselves, but radioactive isotopes of strontium pose a great danger to all living things. The radioactive isotope of strontium strontium-90 is considered to be one of the most terrible and dangerous anthropogenic radioactive pollutants. This is due, first of all, to the fact that it has a very short half-life - 29 years, which causes a very high level of its activity and powerful radiation, and on the other hand, its ability to be efficiently metabolized and included in the life of the body. Strontium is an almost complete chemical analogue of calcium, therefore, when it enters the body, it is deposited in all calcium-containing tissues and fluids - in bones and teeth, providing effective radiation damage to body tissues from the inside.
1. General characteristics of strontium
Strontium is an element of the main subgroup of the second group, the fifth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 38. It is designated by the symbol Sr (lat. Strontium). The simple substance strontium is a soft, malleable and ductile alkaline earth metal of a silvery-white color. It has a high chemical activity, in air it quickly reacts with moisture and oxygen, becoming covered with a yellow oxide film. Strontium got its name from the mineral strontianite, found in 1787 in a lead mine near Strontian (Scotland). In 1790, the English chemist Crawford Ader (1748-1795) showed that strontianite contained a new, as yet unknown "earth". This feature of strontianite was also established by the German chemist Martin Heinrich Klaproth (Klaproth Martin Heinrich) (1743-1817). The English chemist T. Hope (Hope T.) in 1791 proved that strontianite contains a new element. He clearly distinguished the compounds of barium, strontium and calcium, using, among other methods, the characteristic color of the flame: yellow-green for barium, bright red for strontium, and orange-red for calcium.
Independently of Western scientists, the St. Petersburg academician Tobiash (Toviy Egorovich) Lovitz (1757-1804) in 1792, investigating the mineral barite, came to the conclusion that, in addition to barium oxide, "strontium earth" was also present in it as an impurity. He managed to extract more than 100 g of new "earth" from heavy spar and studied its properties. In free form, strontium was first isolated by the English chemist and physicist Humphry Davy in 1808. Strontium metal was obtained by electrolysis of its moistened hydroxide. The strontium released at the cathode combined with mercury, forming an amalgam. Decomposing the amalgam by heating, Davy isolated the pure metal.
Strontium is a soft silvery-white metal, malleable and malleable, and can be easily cut with a knife. Polymorphine - three of its modifications are known. Up to 215 ° C, the cubic face-centered modification (b-Sr) is stable, between 215 and 605 ° C - hexagonal (v-Sr), above 605 ° C - cubic body-centered modification (g-Sr). Melting point - 768 o C, Boiling point - 1390 o C.
Strontium in its compounds always exhibits a +2 valence. By properties, strontium is close to calcium and barium, occupying an intermediate position between them. In the electrochemical series of voltages, strontium is among the most active metals (its normal electrode potential is ? 2.89 V. It reacts vigorously with water, forming hydroxide:
Sr + 2H 2 O \u003d Sr (OH) 2 + H 2 ^
Interacts with acids, displaces heavy metals from their salts. With concentrated acids (H 2 SO 4 , HNO 3) reacts weakly.
Strontium metal rapidly oxidizes in air, forming a yellowish film, in which, in addition to SrO oxide, SrO 2 peroxide and Sr 3 N 2 nitride are always present. When heated in air, it ignites; powdered strontium in air is prone to self-ignition.
Vigorously reacts with non-metals - sulfur, phosphorus, halogens. Interacts with hydrogen (above 200 o C), nitrogen (above 400 o C). Practically does not react with alkalis.
At high temperatures, it reacts with CO2 to form carbide:
5Sr + 2CO 2 = SrC 2 + 4SrO
Easily soluble salts of strontium with anions Cl?, I?, NO 3?. Salts with anions F?, SO42?, CO32?, PO43? sparingly soluble (Poluektov, 1978).
strontium radioactive contamination
2. Main sources of strontium in natural environments and living organisms
Strontium is an integral part of microorganisms, plants and animals. In marine radiolarians, the skeleton consists of strontium sulfate - celestine. Seaweeds contain 26-140 mg of strontium per 100 g of dry matter, land plants - about 2.6, marine animals - 2-50, land animals - about 1.4, bacteria - 0.27-30. Accumulation of strontium by various organisms depends not only on their species, characteristics, but also on the ratio of the content of strontium and other elements, mainly calcium and phosphorus, in the environment.
Animals receive strontium with water and food. Some substances, such as algae polysaccharides, interfere with the absorption of strontium. Strontium accumulates in bone tissue, the ashes of which contain about 0.02% strontium (in other tissues - about 0.0005%).
As a result of nuclear tests and accidents at nuclear power plants, a large amount of radioactive strontium-90 entered the environment, the half-life of which is 29.12 years. Until the testing of atomic and hydrogen weapons in three environments was not banned, the number of victims of radioactive strontium grew from year to year.
Within a year after the completion of atmospheric nuclear explosions, as a result of the self-purification of the atmosphere, most of the radioactive products, including strontium-90, fell out of the atmosphere onto the earth's surface. Pollution of the natural environment due to the removal of radioactive products of nuclear explosions from the stratosphere, which were carried out at the planet's test sites in 1954-1980, now plays a secondary role, the contribution of this process to atmospheric air pollution with 90Sr is two orders of magnitude less than from wind-driven dust lifting from soil contaminated during nuclear tests and as a result of radiation accidents.
Strontium-90, along with cesium-137, are the main polluting radionuclides in Russia. The radiation situation is significantly affected by the presence of contaminated zones that appeared as a result of accidents at the Chernobyl nuclear power plant in 1986 and at the Mayak plant in the Chelyabinsk region in 1957 ("Kyshtym accident"), as well as in the vicinity of some nuclear fuel cycle enterprises.
Now the average concentration of 90Sr in the air outside the territories contaminated as a result of the Chernobyl and Kyshtym accidents has reached the levels observed before the accident at the Chernobyl nuclear power plant. The hydrological systems associated with the areas contaminated during these accidents are significantly affected by the washout of strontium-90 from the soil surface.
Getting into the soil, strontium, together with soluble calcium compounds, enters the plants. More than others accumulate 90Sr legumes, roots and tubers, less - cereals, including cereals, and flax. Significantly less 90Sr accumulates in seeds and fruits than in other organs (for example, 90Sr is 10 times more in leaves and stems of wheat than in grain).
From plants, strontium-90 can pass directly or through animals into the human body. In men, strontium-90 accumulates to a greater extent than in women. In the first months of a child's life, the deposition of strontium-90 is an order of magnitude higher than in an adult, it enters the body with milk and accumulates in rapidly growing bone tissue.
In terms of physical abundance in the earth's crust, strontium occupies 23rd place - its mass fraction is 0.014% (in the lithosphere - 0.045%). The mole fraction of metal in the earth's crust is 0.0029%. Strontium is found in sea water (8 mg / l). In nature, strontium occurs as a mixture of 4 stable isotopes 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.02%), 88Sr (82, 56%) (Orlov, 2002).
3. Hygienic parameters for the use of strontium
Strontium is poorly absorbed in the intestinal tract, and most of the metal that enters the body is excreted from it. Strontium remaining in the body replaces calcium and accumulates in small amounts in the bones. With a significant accumulation of strontium, there is a possibility of suppressing the process of calcification of growing bones and stopping growth. Non-radioactive strontium poses a risk to human health, and its amount in products is subject to FAO/WHO control (Kaplin, 2006).
Radionuclides entering the biosphere cause numerous environmental consequences. As a result of surface runoff, radionuclides can accumulate in depressions, hollows and other accumulative relief elements. Nuclides enter plants and migrate vigorously through food chains. Soil microorganisms accumulate radioactive elements, which is well detected by autoradiography. Based on this principle, methods for identifying microbial populations are being developed for diagnosing geochemical provinces with a high content of radionuclides.
The study of the behavior of radionuclides is of particular importance in connection with their entry into the chain "soil - plant - animal - man". Species differences in the content of nuclides in plants are due to the nature of the distribution of root systems.
In terms of the scale of radionuclides influx into the phytomass, plant communities are arranged in the following order: feather grass steppe > bluegrass-oatmeal meadow > forb-grass meadow. The maximum accumulation of radionuclides is observed in plants of the cereal family, followed by forbs, and legumes accumulate the least amount of nuclides.
Strontium-90 is easily adsorbed by soil due to cation exchange or fixed by soil organic matter to form insoluble compounds. Irrigation and intensive tillage can accelerate the process of its washing down the profile. The removal of strontium-90 by surface waters is also possible, followed by accumulation in depressions (depressions) of the relief.
As a rule, in agricultural crops, the maximum accumulation of strontium-90 is observed in the roots, less - in the leaves and insignificant amounts - in the fruits and grains. Through the trophic chains, strontium-90 is easily transmitted to animals and humans, tends to accumulate in bones and causes great harm to health.
The maximum permissible concentration (MAC) of strontium-90 in the air of working premises is 0.185 (Bq/l), in the water of open reservoirs 18.5 (Bq/l). Permissible levels of 90Sr in food products in accordance with the requirements of SanPiN 2.3.2.1078-01 are in grains, cheeses, fish, cereals, flour, sugar, salt 100-140 (Bq / kg), meat, vegetables, fruits, butter, bread , pasta - 50-80 (Bq/kg), vegetable oil 50-80 (Bq/l), milk - 25, drinking water - 8 (Bq/l) (Orlov, 2002).
4. Toxicological characteristics of strontium
Salts and compounds of strontium are low-toxic substances, however, with an excess of strontium, bone tissue, liver and brain are affected. Being close to calcium in chemical properties, strontium sharply differs from it in its biological action. Excessive content of this element in soils, waters and foodstuffs causes "Urov disease" in humans and animals (named after the Urov River in Eastern Transbaikalia) - joint damage and deformity, growth retardation and other disorders.
The radioactive isotopes of strontium are especially dangerous. Radioactive strontium is concentrated in the skeleton and thus exposes the body to long-term radioactive effects. The biological effect of 90Sr is related to the nature of its distribution in the body and depends on the dose of b-irradiation created by it and its daughter radioisotope 90Y. With prolonged intake of 90Sr into the body, even in relatively small amounts, as a result of continuous irradiation of bone tissue, leukemia and bone cancer can develop. The complete decay of strontium-90, which has entered the environment, will occur only after a few hundred years.
There is little information about the toxicity of Sr to plants, and plants vary greatly in tolerance to this element. According to Shaklett et al., the toxic level of Sr for plants is 30 mg/kg ash (Kaplin, 2006; Kabata-Pendias, 1989).
5. Sampling approaches
Sampling is the first and quite simple, but at the same time a responsible stage of the analysis. There are several requirements for sampling:
1. Sampling must be aseptic and carried out using a sterile sampler into a sterile container, which must be hermetically sealed for transport of the sample to the laboratory.
2. The sample must be representative, i.e. have a sufficient volume, the value of which is determined by the requirements for the content of a particular microorganism, and be produced in a place that ensures the adequacy of the sample to the entire volume of the analyzed object.
3. The sample taken must be processed immediately, if immediate processing is not possible, stored in a refrigerator.
To obtain reproducible results, the experiment requires close attention to all details. One of the sources of error in determining Sr is the heterogeneity of the sample and the unrepresentativeness of the surface. If the grinding of a solid sample (powders of ores, rocks, enrichment products, raw mixtures, salts, etc.) reaches 100 mesh or less, then such samples can be considered quite homogeneous due to the high penetrating power of hard radiation. To reduce the effects of absorption and excitation, distorting the calibration graphs, the analyzed sample is diluted with a substance transparent to X-rays (polystyrene, boric acid, starch, aluminum hydroxide, water, etc.). The degree of dilution is determined experimentally. A powder sample with an evenly distributed diluent and an internal standard is briquetted or dissolved. The thickness of the briquette (tablet) should be large enough (about 1-2 mm) so that the radiation intensity of the sample does not depend on the size of the sample. Prepared briquettes (tablets) are suitable for multiple measurements. The test substance can be placed in powder form directly into the cuvettes of the instrument. The sample powder can be placed in a Plexiglas holder and pressed under a polymer film or applied to an adhesive film (Orlov, 2002; Poluektov, 1978).
6. Analytical methods for the determination of strontium in samples
When determining Sr in natural and industrial objects, spectral methods have found the greatest application - emission spectrographic and flame photometric. Recently, the atomic absorption method has been widely used. The photometric method, which requires preliminary separation of strontium from other elements, is used relatively rarely. For the same reason, and also due to the duration of the analysis, gravimetric and titrimetric methods are almost never used at present.
1. Gravimetric methods
Gravimetric methods are used to determine strontium in most cases after its separation from other alkaline earth elements.
2. Titrimetric methods
The titrimetric determination of strontium can be made after it has been separated from all or most of the interfering elements. The complexometric method has found the greatest distribution.
3. Spectrophotometric methods of determination
These methods can be divided into direct and indirect. Direct methods are based on the formation of colored compounds by the action of reagents on strontium ions. In indirect methods, strontium is precipitated in the form of a sparingly soluble compound with a colored reagent present in excess, the precipitate is separated, and the concentration of strontium in the sample is determined by the amount of unbound reagent.
Examples of direct determination methods:
Determination of strontium with nitroortanil C (nitrochromazo) or ortanil C. Interfering with the determination of barium, lead (2), giving a color reaction with the reagent; zirconium, titanium, thallium and some other elements lead to a sharp underestimation of the results. Sensitivity? 0.05 mcg/mL.
Determination of strontium with dimethylsulfanazo III and dimethylsulfanazo
Elements III-VI of their groups should be removed. The amount of ammonium salts and alkali metals should be no more than 10 mg. Sulfates and phosphates interfere if they are more than 0.03 mmol. Many metals interfere with the determination, including Ca and Mg, if their content in the sample? 0.3 µmol, and Cu(II) ?0.25 µmol. There are also many other restrictions.
Determination of strontium with carboxynitrase
The reaction of strontium with carboxynitrase is one of the most sensitive. Using this reaction, 0.08-0.6 μg / ml is determined.
Indirect methods for the determination of strontium
Due to their low selectivity, indirect methods are not currently used, therefore, only the following will be mentioned: 8-Oxyquinoline method; method using picrolonic acid; determination of strontium using chromate.
4. Electrochemical methods
Polarographic method
Barium ions interfere with the determination of strontium (but this can be eliminated by selecting a suitable background, which is (C2H5) 4NBr in absolute ethanol). In the presence of approximately equal concentrations of Mg and Ca, the determination of Sr is impossible. It is necessary to first separate Ba, Ca, Na, K if their concentrations significantly exceed the concentration of Sr.
Differential polarographic method
It makes it possible to determine small amounts of strontium in the presence of large amounts of Na and K. Sensitivity - 0.0001 mol Sr / mol salt.
Inversion polarography
Allows you to determine strontium in very low concentrations (10-5 - 10-9 M), if it is first concentrated in a drop of mercury by electrolysis, and then subjected to anodic dissolution. The oscilloscope technique is used. The average error is 3-5%.
Conductometric method
The determinations are carried out after the preliminary separation of the group of elements Li, K, Na, Ca and Ba, which are included in the soluble salts of building materials.
5. Spectral methods
Spectrographic (spark and arc) method
The most intense Sr lines lie in the visible region of the spectrum: 4607.33; 4077.71 and 4215.52 A, the latter 2 being in the area of cyan bands. Therefore, when used for analysis of an arc with carbon electrodes, these lines are less suitable. The 4607.33 A line is characterized by strong self-absorption; therefore, it is recommended to use it when determining only low concentrations of Sr (below 0.1%). At its high contents, the Sr lines 4811.88 and 4832.08 ?, as well as 3464.46 A are used. background. Buffer mixtures are used to stabilize the arc burning temperature, eliminate the influence of Ca, Mg, Na, and achieve a higher accuracy in determining Sr. To eliminate the bands of cyanide, the determination of Sr is carried out in argon or the samples are converted into fluorine compounds. The sensitivity of determination of Sr in the arc is 5*10-5 - 1*10-4%, the relative error of determination is ±4-15%. ). The sensitivity of determining Sr in a spark is (1-5) * 10-4%. Determination error ±4-6%. In order to increase the accuracy and absolute sensitivity of the analysis, as well as to eliminate the influence of interfering lines of foreign elements, it is proposed to use an interferometer crossed with a spectrograph.
Flame emission photometry
Due to its simplicity and reliability, the flame photometric method for the determination of strontium is widely used, especially in the analysis of rocks and minerals, natural and waste water, biological and other materials. It is suitable for the determination of both small and large contents of the element with a sufficiently high accuracy (1-2 rel.%) and sensitivity, and in most cases the determination of strontium can be performed without separation from other elements. The highest sensitivity is achieved when using equipment with automatic spectrum recording and high-temperature flames. The highest sensitivity is achieved with RF plasma 0.00002 µg Sr/mL.
With the pulse method of evaporation, the absolute limit of detection of Sr is 1*10-13-2*10-12 g (acetylene-nitrous oxide mixture flame). With sufficiently large amounts of the sample (~10 mg), the relative limit of the determined strontium content is reduced to 1*10-7%, while when the sample solution is introduced into the flame with the help of an atomizer, it is equal to 3*10-5%.
Atomic absorption spectrophotometry
Sr is determined by measuring the absorption of light by its atoms. The most commonly used line is strontium 460.7 nm, with a lower sensitivity, strontium can be determined from lines 242.8; 256.9; 293.2; 689.3 nm. When using high-temperature flames, strontium can also be determined from the 407.8 ion line (ion-absorption spectroscopy). There are two types of interference in this analysis method. The first type of interference is associated with the formation of non-volatile compounds and manifests itself in the flame of a mixture of acetylene with air. The influence of Al, Ti, Zr cations, and other PO4 and SiO3 anions is most often noted. Another type of interference is due to the ionization of strontium atoms, for example, due to the influence of Ca and Ba, an increase in atomic absorption from the presence of Na and K, etc. Detection sensitivity of strontium 1 *10-4-4*10-12 g.
6. Activation method
The method of determining the activity of 87mSr has found the greatest distribution. In most cases, the determination is made by measuring the activity after radiochemical separation of Sr, which is carried out using precipitation, extraction and ion exchange methods.
The use of a high-resolution r-spectrometer makes it possible to increase the accuracy of the method and reduce the number of separation operations, since it is possible to determine Sr in the presence of a number of foreign elements. The detection sensitivity of strontium is about 6*10-5 g/g.
7. Mass spectrometric method
Mass spectroscopy is used to determine the isotopic composition of strontium, the knowledge of which is necessary when calculating the geological age of samples using the rubidium-strontium method and when determining trace amounts of strontium in various objects using the isotope dilution method. The limiting absolute sensitivity of the determination of Sr by the vacuum spark mass spectral method is 9*10-11.
8. X-ray fluorescence method
The X-ray fluorescent method for the determination of strontium has recently found increasing use. Its advantage is the ability to perform analysis without destroying the sample and the speed of execution (the analysis lasts 2–5 minutes). The method eliminates the influence of the base, its reproducibility is ± 2--5%. The sensitivity of the method (1-1SG4 -- 1-10~3% Sr) is sufficient for most purposes.
The XRF method is based on the collection and subsequent analysis of the spectrum obtained by exposing the material under study to X-rays. When irradiated, the atom goes into an excited state, accompanied by ionization of a certain level. An atom stays in an excited state for an extremely short time, about one 10-7 seconds, after which it returns to a quiet position (ground state). In this case, electrons from the outer shells either fill the formed vacancies, and the excess energy is emitted in the form of a photon, or the energy is transferred to another electron from the outer shells (Auger electron). In this case, each atom emits a photoelectron with an energy of a strictly defined value. Then, respectively, the structure of matter is judged by the energy and the number of quanta (Orlov, 2002; Poluektov, 1978).
7. Selecting the type of indicator. Population characteristics used to assess the state of the population under the influence of strontium
Bioindication (bioindication) is the detection and determination of environmentally significant natural and anthropogenic loads based on the reactions of living organisms to them directly in their habitat. Living objects (or systems) are cells, organisms, populations, communities. They can be used to evaluate both abiotic factors (temperature, humidity, acidity, salinity, content of pollutants, etc.) and biotic factors (well-being of organisms, their populations and communities).
There are several different forms of bioindication. If two identical reactions are caused by different anthropogenic factors, then this will be a non-specific bioindication. If certain changes can be associated with the influence of any one factor, then this type of bioindication is called specific.
The use of biological methods for assessing the environment implies the identification of animal or plant species that are sensitive to one or another type of impact. Organisms or communities of organisms whose vital functions are so closely correlated with certain environmental factors that they can be used to evaluate them are called bioindicators.
Types of bioindicators:
1. Sensitive. Quickly reacts with a significant deviation of indicators from the norm. For example, deviations in the behavior of animals, in the physiological reactions of cells, can be detected almost immediately after the onset of the disrupting factor.
2. Accumulative. Accumulates effects without manifesting disturbances. For example, a forest at the initial stages of its pollution or trampling will be the same in terms of its main characteristics (species composition, diversity, abundance, etc.). Only after some time will rare species begin to disappear, dominating forms change, the total number of organisms changes, etc. Thus, the forest community as a bioindicator will not immediately detect environmental disturbance.
An ideal biological indicator must meet a number of requirements:
Be characteristic of given conditions, have a high abundance in a given ecotope;
Live in this place for a number of years, which makes it possible to trace the dynamics of pollution;
Be in conditions convenient for sampling;
Be characterized by a positive correlation between the concentration of pollutants in the indicator organism and the object of study;
Possess high tolerance to a wide range of toxic substances;
The response of a bioindicator to a certain physical or chemical effect should be clearly expressed, that is, specific, easy to register visually or with the help of instruments;
The bioindicator should be used in the natural conditions of its existence;
The bioindicator should have a short period of ontogenesis in order to be able to trace the influence of the factor on subsequent generations.
In order to bioindicate radioactive contamination of soils, sedentary soil inhabitants with a long period of development (earthworms, centipedes, beetle larvae) are most convenient.
Of great importance in indicating even relatively low levels of soil contamination with radionuclides is the study of changes in characteristic morphological characters in soil arthropod species. Such disorders are more often caused by gene mutations caused by radiation exposure. In the uncontaminated parts of the range, these characters change insignificantly in these species. The most noticeable deviations under polluted conditions include changes in the distribution of bristles on the body of springtails, benthic, two-tailed, bristletails, centipedes.
A good indicator of water pollution by radionuclides are lake-pond molluscs and daphnia crustaceans, which can be recommended as test objects for this type of pollution. The reaction of mollusks to an increased content of radionuclides in the reservoir was expressed in a change in the color of the body and shell, morphometric parameters, inhibition of generative and plastic metabolism, and a violation of the reaction of embryos to the climatic conditions of the season. In daphnia in polluted reservoirs, the death of some individuals in the population, an increase in fertility and body size were observed.
In aquatic ecosystems, aquatic plants are also a reliable bioindicator of the radiation situation. In particular, Canadian elodea or water plague, which develops well in fresh and brackish waters, intensively accumulates radionuclides 90Sr, 137Cs, which are not detected by standard radiation monitoring of waters. This type can be widely used in settling tanks for wastewater treatment from radionuclides.
In terrestrial ecosystems, good indicators that accumulate radionuclides, in particular 90Sr, include sphagnum mosses, pine and spruce needles, stinging nettle, coltsfoot, common wormwood, pink clover, creeping clover, timothy meadow, bedstraw, mouse pea, chickweed hard-leaved, May lily of the valley, river gravilate, cocksfoot, couch grass, etc. As these plants accumulate radionuclides, the content of manganese in their ashes decreases by 3-10 times (Turovtsev, 2004).
8. Toxicological methods for assessing the impact of the present dose of strontium on biota components
Biotesting is one of the research methods in biological monitoring, which is used to determine the degree of damaging effect of chemicals that are potentially hazardous to living organisms in controlled experimental laboratory or field conditions by recording changes in biologically significant indicators (test functions) of the test objects under study, with subsequent assessment of their condition in accordance with the selected criterion of toxicity.
The purpose of biotesting is to identify the degree and nature of the toxicity of water contaminated with biologically hazardous substances on hydrobionts and to assess the possible danger of this water for aquatic and other organisms.
Various test organisms are used as objects for biotesting - experimental biological objects exposed to certain doses or concentrations of poisons that cause one or another toxic effect in them, which is recorded and evaluated in the experiment. It can be bacteria, algae, invertebrates, and vertebrates.
For guaranteed detection of the presence of a toxic agent of unknown chemical composition, a set of objects representing different community groups should be used, the state of which is assessed by parameters related to different levels of integrity.
A biotest is understood as an assessment (test) under strictly defined conditions of the action of a substance or a complex of substances on living organisms by registering changes in one or another biological (or physiological-biochemical) indicator of the object under study compared to the control. The main requirement for biotests is sensitivity and speed of response, a clear response to external influences. There are acute and chronic biotests. The former are designed to obtain express information about the toxicity of the test substance for a given test organism, the latter to reveal the long-term effect of toxicants, in particular, low and ultralow concentrations (Turovtsev, 2004).
Own experience
Topic: Determination of the ecological status of the territory for the content of strontium
Purpose: identification of unfavorable areas of the study region and differentiation of estimates of their contamination with strontium
Methodology: The method is carried out by biotesting and includes sampling of bioindicators, drying them to a constant weight, isolating the average sample, determining the total strontium content in it, comparing the obtained values with the established data, beyond which the ecological status of the territory is determined, while as bioindicators use cuttings of wild plants of meadow-steppe vegetation or monocultures of annual and perennial agricultural plants, sampling is carried out during the flowering phenophase by complete mowing of vegetation from 1 m 2 of the latter in an amount equal to 1 sample per 1000-5000 ha for the territory of a large region, and for local agrocenosis in the amount of 1 sample per 100 ha, while the isolation of strontium from the average sample is carried out with concentrated nitric acid, followed by its determination in the extract by atomic adsorption, and the comparison of the obtained values is carried out with the background content of strontium in air-dry oh mass of medium cuttings of wild vegetation. To compare the data obtained, the values of the background content of strontium in the air-dry mass of average cuts of wild vegetation are used in the range from 20 to 500 mg/kg.
Progress of work: For biotesting of the Vargashinsky district of the Kurgan region with an area of 10,000 hectares, we select 10 samples of medium cuts of wild species of meadow-steppe vegetation. To do this, we select 10 sampling sites evenly over the territory of the district during the phenophase of flowering of vegetation. We impose a frame of 1×1 m on the vegetation and fix the site depending on the density of the herbage, but in such a way that the volume of plant mass from each site is at least 1 kg. The ground part of the grass cover within the frame is completely cut off with a knife or other suitable tool. The cutting height of plants is at least 3 cm from the soil surface. Plant samples are dried to an air-dry state in an oven for 3 hours at a temperature of 105°C, then cooled in a desiccator and weighed. Repeat drying for 1 hour and subsequent weighing until a constant weight is reached (the difference in weight in two successive weighings should be no more than 0.1% of the initial sample weight). The dried sample is preliminarily crushed and an average sample weighing at least 200 g is taken by quartering. Strontium is isolated as follows. We select a weighed portion of 1 g from a dried quartered sample and grind it in an IKA All basic laboratory mill at a speed of 25,000 rpm to a particle size of 0.001-0.1 mm. From the crushed mass on an analytical balance, we take a sample of 100 mg, which is placed in a 50 ml polyethylene conical test tube (Rustech type) and filled with 1 ml of concentrated nitric acid. In this form, the analyzed sample is kept for at least 1 hour. Then the volume with distilled water is brought to 50 ml; the precipitate is filtered off, and the extract is analyzed for the content of gross strontium by atomic adsorption on an atomic spectrophotometer "AAS Quantum Z.ETA". If there are 10 analyzed samples, the measurement results are averaged.
According to the results of the study, it can be said that the main sources of strontium (mostly its oxide) are industrial wastewater from various industries, in agricultural production - phosphorus and phosphorus-containing fertilizers and ameliorants. The natural source is the process of weathering rocks and minerals.
The distribution, behavior and concentration of the toxicant in natural environments depends on the relief (slope of the terrain in the area of the industrial zone, compliance of the degradation substrate, etc.), climatic conditions (temperature regime of air and soil, the amount of precipitation per unit area, wind speed), physical the chemical, biological and nutritional status of soils (the presence and ratio of microorganisms and fungi, redox and acid-base conditions, the presence of mineral nutrition elements, etc.), as well as the ways of entry (with constant and temporary water flows, with precipitation from the atmosphere, evaporation of mineralized groundwater) and other factors.
Being an element of active bioabsorption and accumulation, as well as an analogue of calcium, strontium easily enters food chains from the soil into plants and animals, accumulating in certain organs and tissues. In plants - in mechanical tissues of vegetative organs, in animals - in bone tissue, kidneys and liver. But depending on the biological characteristics of the organism and the properties of the environment, the element is accumulated in various quantities and excreted at different rates.
Strontium inhibits the development of microorganisms, placing most of them in the resistance zone, disrupts the growth and vital activity of fungi, invertebrates and crustaceans. The strontium radionuclide causes mutations at the genetic level, which subsequently manifests itself in morphological changes.
The toxicant has a high migration ability, especially in a liquid medium (reservoirs, soil solution, plant conductive tissues, bile and circulatory system of both humans and animals). But under certain soil-ecological conditions, it precipitates and accumulates.
Strontium inhibits the entry of calcium and partly phosphorus into living organisms. At the same time, the structure of membranes and the musculoskeletal system, the composition of blood, cerebral fluid, etc.
Investigating the analytical methods for determining the toxicant in samples, we can conclude that many methods are able to compete with X-ray fluorescence analysis, and even surpass it in sensitivity, but along with this, they have some disadvantages. For example: the need for preliminary separation, the precipitation of the element being determined, the interfering influence of foreign elements, the significant influence of the matrix composition, the superposition of spectral lines, long-term sample preparation and poor reproducibility of the results, the high cost of the equipment and its operation.
Also, biological testing methods are a group of highly sensitive methods of analysis and compare favorably with their simplicity, comparative unpretentiousness to laboratory conditions, low cost and versatility.
Offers
In regions of radioactive contamination, measures to protect the population should be aimed at:
To reduce the content of radionuclides in plant and animal foodstuffs with the help of agro-reclamation and veterinary measures. In animals treated with strontium sorbents (barium sulfate, bentonite and modified preparations based on them), during the Chernobyl accident, using these measures, it was possible to achieve a 3-5-fold decrease in the deposition of radionuclides in the bone tissue of animals;
For technological processing of contaminated raw materials;
For the culinary processing of food products, the replacement of contaminated food products with clean ones.
When working with radioactive strontium, it is necessary to comply with sanitary rules and radioactive safety standards using special protective measures in accordance with the class of work.
In the prevention of the consequences of exposure, much attention should be paid to increasing the resistance of the body of the victims (rational nutrition, a healthy lifestyle, sports, etc.).
The study and regulation of the intake and accumulation of strontium in the elements of ecosystems is a complex of complex labor-intensive and energy-consuming activities of laboratory and field studies. Therefore, the best way to prevent the entry of a toxicant into landscapes and organisms is monitoring in the area of environmentally hazardous objects - sources of pollution.
List of used literature
1. Isidorov V.A., Introduction to chemical ecotoxicology: Textbook. - St. Petersburg: Himizdat, 1999. - 144 p.: ill.
2. Kaplin VG, Fundamentals of ecotoxicology: Textbook. - M.: KolosS, 2006. - 232 p.: ill.
3. Kabata-Pendias A., Pendias X. Trace elements in soils and plants: Per. from English. - M.: Mir, 1989. - 439 p.: ill.
4. Orlov D.S., Ecology and protection of the biosphere in case of chemical pollution: Textbook for chemical, chemical-technological. and biol. specialist. universities / D.S. Orlov, L.K. Sadovnikova, I.N. Lozanovskaya.- M.: Higher. school, - 2002. - 334 p.: ill.
5. Poluektov N.S., Mishchenko V.T., Analytical chemistry of strontium: Textbook. - M.: Nauka, 1978.- 223 p.
6. V.D. Turovtsev V.D., Krasnov V.S., Bioindication: Textbook. - Tver: Tver. state. un-t, 2004. - 260 p.
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|
Strontium |
|
|---|---|
| atomic number | |
| Appearance of a simple substance |
malleable, silvery-white metal |
| Atom properties | |
| Atomic mass (molar mass) |
87.62 a. e.m. (g/mol) |
| Atom radius | |
| Ionization energy (first electron) |
549.0 (5.69) kJ/mol (eV) |
| Electronic configuration | |
| Chemical properties | |
| covalent radius | |
| Ion radius | |
| Electronegativity (according to Pauling) |
|
| Electrode potential | |
| Oxidation states | |
| Thermodynamic properties of a simple substance | |
| Density | |
| Molar heat capacity |
26.79 J/(K mol) |
| Thermal conductivity |
(35.4) W/(m K) |
| Melting temperature | |
| Melting heat |
9.20 kJ/mol |
| Boiling temperature | |
| Heat of evaporation |
144 kJ/mol |
| Molar volume |
33.7 cm³/mol |
| The crystal lattice of a simple substance | |
| Lattice structure |
cubic face-centered |
| Lattice parameters | |
| c/a ratio | — |
| Debye temperature | |
| Sr | 38 |
| 87,62 | |
| 5s 2 | |
| Strontium | |
Strontium- an element of the main subgroup of the second group, the fifth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 38. It is denoted by the symbol Sr (lat. Strontium). The simple substance strontium (CAS number: 7440-24-6) is a soft, malleable and ductile silver-white alkaline earth metal. It has a high chemical activity, in air it quickly reacts with moisture and oxygen, becoming covered with a yellow oxide film.
History and origin of the name
The new element was discovered in the mineral strontianite, found in 1764 in a lead mine near the Scottish village of Stronshian, which later gave the name to the new element. The presence of a new metal oxide in this mineral was established almost 30 years later by William Cruikshank and Ader Crawford. Isolated in its purest form by Sir Humphry Davy in 1808.
Presence in nature
Strontium is found in sea water (0.1 mg/l), in soils (0.035 wt %).
In nature, strontium occurs as a mixture of 4 stable isotopes 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.02%), 88Sr (82.56%).
Obtaining Strontium
Three ways to obtain metallic strontium:
- thermal decomposition of some compounds
– electrolysis
- reduction of oxide or chloride
The main industrial method for obtaining metallic strontium is the thermal reduction of its oxide with aluminum. Further, the resulting strontium is purified by sublimation.
The electrolytic production of strontium by electrolysis of a melt of a mixture of SrCl 2 and NaCl has not become widespread due to the low current efficiency and contamination of strontium with impurities.
During thermal decomposition of strontium hydride or nitride, finely dispersed strontium is formed, which is prone to easy ignition.
Physical properties
Strontium is a soft, silvery-white metal, malleable and malleable, and can be easily cut with a knife.
Polymorphine - three of its modifications are known. Up to 215 o C, the cubic face-centered modification (α-Sr) is stable, between 215 and 605 o C - hexagonal (β-Sr), above 605 o C - cubic body-centered modification (γ-Sr).
Melting point - 768 o C, Boiling point - 1390 o C.
Chemical properties
Strontium in its compounds always exhibits a +2 valence. By properties, strontium is close to calcium and barium, occupying an intermediate position between them.
In the electrochemical series of voltages, strontium is among the most active metals (its normal electrode potential is −2.89 V. It reacts vigorously with water, forming hydroxide:
Sr + 2H 2 O \u003d Sr (OH) 2 + H 2
Interacts with acids, displaces heavy metals from their salts. With concentrated acids (H 2 SO 4 , HNO 3) reacts weakly.
Strontium metal rapidly oxidizes in air, forming a yellowish film, in which, in addition to SrO oxide, SrO 2 peroxide and Sr 3 N 2 nitride are always present. When heated in air, it ignites; powdered strontium in air is prone to self-ignition.
Vigorously reacts with non-metals - sulfur, phosphorus, halogens. Interacts with hydrogen (above 200 o C), nitrogen (above 400 o C). Practically does not react with alkalis.
At high temperatures, it reacts with CO 2, forming a carbide:
5Sr + 2CO 2 = SrC 2 + 4SrO
Easily soluble salts of strontium with anions Cl - , I - , NO 3 - . Salts with anions F -, SO 4 2-, CO 3 2-, PO 4 3- are sparingly soluble.
Application
The main areas of application of strontium and its chemical compounds are the radio-electronic industry, pyrotechnics, metallurgy, and the food industry.
Metallurgy
Strontium is used for alloying copper and some of its alloys, for introducing into battery lead alloys, for desulfurizing cast iron, copper and steels.
Metalthermy
Strontium with a purity of 99.99-99.999% is used to reduce uranium.
Magnetic materials
Magnetically hard strontium ferrites are widely used materials for the production of permanent magnets.
Pyrotechnics
In pyrotechnics, strontium carbonate, nitrate, perchlorate are used to color the flame in a brick red color. The magnesium-strontium alloy has the strongest pyrophoric properties and is used in pyrotechnics for incendiary and signal compositions.
isotopes
Radioactive 90 Sr (half-life 28.9 years) is used in the production of radioisotope current sources in the form of strontium titanate (density 4.8 g/cm³, energy release about 0.54 W/cm³).
Nuclear energy
Strontium uranate plays an important role in the production of hydrogen (strontium-uranate cycle, Los Alamos, USA) by the thermochemical method (atomic hydrogen energy), and in particular, methods are being developed for the direct fission of uranium nuclei in the composition of strontium uranate to produce heat during the decomposition of water into hydrogen and oxygen.
High temperature superconductivity
Strontium oxide is used as a component of superconducting ceramics.
Chemical current sources
Strontium fluoride is used as a component of solid-state fluorine batteries with enormous energy capacity and energy density.
Alloys of strontium with tin and lead are used for casting battery down conductors. Strontium-cadmium alloys for anodes of galvanic cells.
Biological role
Impact on the human body
One should not confuse the effect on the human body of natural (non-radioactive, low-toxic, and moreover, widely used for the treatment of osteoporosis) and radioactive isotopes of strontium. The strontium isotope 90 Sr is radioactive with a half-life of 28.9 years. 90 Sr undergoes β-decay, turning into radioactive 90 Y (half-life 64 hours). The complete decay of strontium-90 that has entered the environment will occur only after several hundred years. 90 Sr is formed during nuclear explosions and emissions from nuclear power plants. Radioactive and non-radioactive isotopes of strontium practically do not differ in chemical reactions. Natural strontium is an integral part of microorganisms, plants and animals. Regardless of the route and rhythm of entry into the body, soluble strontium compounds accumulate in the skeleton. Less than 1% is retained in soft tissues. The route of entry affects the amount of strontium deposition in the skeleton. The behavior of strontium in the body is influenced by the type, gender, age, as well as pregnancy, and other factors. For example, in the skeleton of men, deposits are higher than in the skeleton of women. Strontium is an analogue of calcium. Strontium accumulates at a high rate in the body of children up to the age of four, when there is an active formation of bone tissue. The exchange of strontium changes in some diseases of the digestive system and the cardiovascular system. Entry routes:
- water (the maximum permissible concentration of strontium in water in the Russian Federation is 8 mg / l, and in the USA - 4 mg / l)
- food (tomatoes, beets, dill, parsley, radish, radish, onion, cabbage, barley, rye, wheat)
- intratracheal intake
- through the skin (cutaneous)
- inhalation (through the air)
- from plants or through animals, strontium-90 can directly pass into the human body.
- people whose work is related to strontium (in medicine, radioactive strontium is used as applicators in the treatment of skin and eye diseases. The main areas of application of natural strontium are the radio-electronic industry, pyrotechnics, metallurgy, metallothermy, food industry, production of magnetic materials, radioactive - pr - in atomic electric batteries, atomic hydrogen energy, radioisotope thermoelectric generators, etc.)
The influence of non-radioactive strontium is extremely rare and only under the influence of other factors (deficiency of calcium and vitamin D, malnutrition, violations of the ratio of trace elements such as barium, molybdenum, selenium, etc.). Then it can cause “strontium rickets” and “uro disease” in children - joint damage and deformity, growth retardation and other disorders. On the contrary, radioactive strontium almost always negatively affects the human body:
- deposited in the skeleton (bones), affects the bone tissue and bone marrow, which leads to the development of radiation sickness, tumors of the hematopoietic tissue and bones.
- causes leukemia and malignant tumors (cancer) of the bones, as well as damage to the liver and brain
isotopes
Strontium-90
The strontium isotope 90 Sr is radioactive with a half-life of 28.79 years. 90 Sr undergoes β-decay, turning into radioactive yttrium 90 Y (half-life 64 hours). 90 Sr is formed during nuclear explosions and emissions from nuclear power plants.
Strontium is an analogue of calcium and is able to be firmly deposited in the bones. Long-term exposure to 90 Sr and 90 Y affects the bone tissue and bone marrow, which leads to the development of radiation sickness, tumors of the hematopoietic tissue and bones.
Strontium in the human body: role, sources, deficiency and excess
Strontium (Sr) is a chemical element that occupies D.I. Mendeleev 38th place. In its simplest form, under normal conditions, it is an alkaline earth silver-white metal, very ductile, soft and malleable (easily cut with a knife). In air, it is very quickly oxidized by oxygen and moisture, becoming covered with yellow oxide. Chemically very active.
Strontium was discovered in 1787 by two chemists W. Cruikshank and A. Crawford, and was first isolated in pure form by H. Davy in 1808. It got its name from the Scottish village of Stronshian, where in 1764 a previously unknown mineral was discovered, also named strontium after the village.
Due to its high chemical activity, strontium is not found in nature in its pure form. In nature, it is quite common, it is part of about 40 minerals, of which the most common are celestine (strontium sulfate) and strontianite (strontium carbonate). It is from these minerals that strontium is mined on an industrial scale. The largest deposits of strontium ores are found in the USA (Arizona and California), Russia and some other countries.
Strontium and its compounds are widely used in the radio-electronic industry, metallurgy, food industry and pyrotechnics.
Strontium very often accompanies calcium in minerals and is a fairly common chemical element. Its mass fraction in the earth's crust is about 0.014%, its concentration in sea water is about 8 mg/l.
The role of strontium in the human body
Very often, when they talk about the effect of strontium on the human body, they have a negative connotation. This is a very common misconception due to the fact that its radioactive isotope 90 Sr is indeed extremely hazardous to health. It is formed during nuclear reactions in reactors and during nuclear explosions, and when it enters the human body, it is deposited in the bone marrow and very often leads to very tragic consequences, since it literally blocks blood formation. But ordinary, non-radioactive, strontium in reasonable doses is not only not dangerous, but simply necessary for the human body. Strontium is even used in the treatment of osteoporosis.
In general, strontium is found in almost all living organisms, both in plants and in animals. It is an analogue of calcium and can easily replace it in bone tissue without any particular health effects. By the way, it is this chemical property of strontium that makes its mentioned radioactive isotope extremely dangerous. Almost all (99%) of strontium is deposited in bone tissue, and less than 1% of strontium is retained in other tissues of the body. The concentration of strontium in the blood is about 0.02 µg/ml, in the lymph nodes 0.30 µg/g, lungs 0.2 µg/g, ovaries 0.14 µg/g, kidneys and liver 0.10 µg/g.
In young children (under the age of 4 years), strontium accumulates in the body, since bone tissue is actively formed during this period. The body of an adult contains about 300-400 mg of strontium, which is quite a lot compared to other trace elements.
Strontium prevents the development of osteoporosis and dental caries.
A synergist and at the same time an antagonist of strontium is calcium, which is very close to it in its chemical properties.
Sources of strontium in the human body
The exact daily human need for strontium has not been established; according to some of the available information, it is up to 3-4 mg. It is estimated that on average a person consumes 0.8-3.0 mg of strontium per day with food.
Strontium supplied with food is absorbed only by 5-10%. Its absorption occurs mainly in the duodenum and ileum. Strontium is excreted mainly through the kidneys, to a much lesser extent with bile. Only unabsorbed strontium is found in feces.
Improves the absorption of strontium vitamin D, lactose, amino acids arginine and lysine. In turn, a plant-based diet high in fiber, as well as sodium and barium sulfates, reduce the absorption of strontium in the digestive tract.
Foods containing strontium:
- legumes (beans, peas, beans, soybeans);
- cereals (buckwheat, oats, millet, soft and durum wheat, wild rice, rye);
- plants that form tubers, as well as root crops (potatoes, beets, turnips, carrots, ginger);
- fruits (apricot, quince, pineapple, grapes, pear, kiwi);
- greens (celery, dill, arugula);
- nuts (peanuts, Brazil nuts, cashews, macadamia, pistachios, hazelnuts);
- meat products, especially bones and cartilage.
Lack of strontium in the human body
There is no information on strontium deficiency in the human body in the specialized literature. Animal experiments show that strontium deficiency leads to developmental delay, growth inhibition, tooth decay (caries), and calcification of bones and teeth.
Excess strontium in the human body
With an excess of strontium, a disease can develop, which is popularly called "Urov's disease", and in medical language - "strontium rickets" or Kashin-Beck's disease. This disease was first identified among the population that lived in the basin of the river. Ural and Eastern Siberia. Resident of the city of Nerchensk I.M. Yurensky in 1849 in the journal "Proceedings of the Free Economic Society" wrote an article "On the ugliness of the inhabitants of the banks of the Urova in Eastern Siberia."
For a long time, doctors could not explain the nature of this endemic disease. Later studies explained the nature of this phenomenon. It turned out that this disease occurs due to the fact that strontium ions, when they enter the body in excess, displace a significant proportion of calcium from the bones, which leads to a deficiency of the latter. As a result, the whole organism suffers, but the most typical manifestation of this disease is the development of dystrophic changes in bones and joints, especially during the period of intensive growth (in children). In addition, the phosphorus-calcium ratio in the blood is disturbed, intestinal dysbacteriosis, pulmonary fibrosis develop.
To remove excess strontium from the body, dietary fiber, magnesium and calcium compounds, sodium and barium sulfates are used.
However, the radioactive strontium-90 mentioned above is of particular danger. Accumulating in the bones, it not only affects the bone marrow, preventing the body from performing the hematopoietic function, but also causes radiation sickness, affects the brain and liver, and increases the risk of developing cancer, especially blood cancer, by a thousand times.
The situation is aggravated by the fact that strontium-90 has a medium-long half-life (28.9 years) - just the average duration of the generation of people. Therefore, in the case of radioactive contamination of the area, it is not necessary to wait for its rapid decontamination, but at the same time, its radioactivity is very high. Other radioactive elements decay either very quickly, for example, many isotopes of iodine have a half-life of hours and days, or very slowly, so they have low radiation activity. Neither one nor the other can be said about strontium-90.
But that's not all. The fact is that strontium-90, when it enters the soil, displaces calcium and is subsequently absorbed by plants, animals and, along the food chain, reaches a person with all the ensuing consequences. Especially "rich" in strontium are root crops and green parts of plants. As a result, agricultural land contaminated with radioactive strontium can be taken out of circulation for hundreds of years.
