Chemical properties Strontium - characteristics of properties with a photo, its biological role in the human body, treatment with drugs based on a chemical element

Strontium(lat. Strontium), Sr, a chemical element of group II of the Mendeleev periodic system, atomic number 38, atomic mass 87.62, silver-white metal. Natural Strontium consists of a mixture of four stable isotopes: 84 Sr, 86 Sr, 87 Sr and 88 Sr; the most common is 88 Sr (82.56%).

Radioactive isotopes with mass numbers from 80 to 97 have been artificially obtained, incl. 90 Sr (T ½ = 27.7 years), formed during the fission of uranium. In 1790, the Scottish doctor A. Crawford, examining the found near locality Stronshian (in Scotland) mineral, found to contain a previously unknown "earth" which was named strontian. It later turned out to be strontium oxide SrO. In 1808, G. Davy, subjecting to electrolysis with a mercury cathode a mixture of moistened Sr(OH) 2 hydroxide with mercury oxide, obtained Strontium amalgam.

Distribution of Strontium in nature. The average content of Strontium in the earth's crust (clarke) is 3.4·10 -2% by mass; in geochemical processes, it is a satellite of calcium. About 30 Strontium minerals are known; the most important are celestine SrSO 4 and strontianite SrCO 3 . In igneous rocks, strontium is predominantly in a dispersed form and enters as an isomorphic impurity into the crystal lattice of calcium, potassium, and barium minerals. In the biosphere, Strontium accumulates in carbonate rocks and especially in the sediments of salt lakes and lagoons (celestine deposits).

Physical properties of strontium. At room temperature, the lattice of Strontium is face-centered cubic (α-Sr) with a period a = 6.0848Å; at temperatures above 248 °C, it transforms into a hexagonal modification (β-Sr) with lattice periods a = 4.32 Å and c = 7.06 Å; at 614 °C it transforms into a cubic body-centered modification (γ-Sr) with a period a = 4.85Å. Atomic radius 2.15Å, ionic radius Sr 2+ 1.20Å. The density of the α-form is 2.63 g / cm 3 (20 ° C); t pl 770 °C, t kip 1383 °C; specific heat capacity 737.4 kJ/(kg K); electrical resistivity 22.76·10 -6 ohm·cm -1 . Strontium is paramagnetic, the atomic magnetic susceptibility at room temperature is 91.2·10 -6 . Strontium is a soft ductile metal that can be easily cut with a knife.

Chemical properties. The configuration of the outer electron shell of the atom Sr 5s 2 ; in compounds it usually has an oxidation state of +2. Strontium is an alkaline earth metal Chemical properties m is similar to Ca and Ba. Strontium metal rapidly oxidizes in air, forming a yellowish surface film containing SrO oxide, SrO 2 peroxide and Sr 3 N 2 nitride. With oxygen at normal conditions forms SrO oxide (grayish-white powder), which easily transforms into carbonate SrCO 3 in air; interacts vigorously with water, forming hydroxide Sr (OH) 2 - a base stronger than Ca (OH) 2. When heated in air, it ignites easily, and powdered Strontium ignites spontaneously in air, so Strontium is stored in hermetically sealed vessels under a layer of kerosene. Rapidly decomposes water with the release of hydrogen and the formation of hydroxide. At elevated temperatures, it reacts with hydrogen (>200 °C), nitrogen (>400 °C), phosphorus, sulfur and halogens. When heated, it forms intermetallic compounds with metals, such as SrPb 3 , SrAg 4 , SrHg 8 , SrHg 12 . Of the strontium salts, the halides (except for fluoride), nitrate, acetate, and chlorate are readily soluble in water; hardly soluble carbonate, sulfate, oxalate and phosphate. Precipitation of Strontium as oxalate and sulfate is used for its analytical determination. Many Strontium salts form crystalline hydrates containing from 1 to 6 molecules of water of crystallization. SrS sulfide is gradually hydrolyzed by water; Sr 3 N 2 nitride (black crystals) is easily decomposed by water releasing NH 3 and Sr(OH) 2 . Strontium dissolves well in liquid ammonia, giving dark blue solutions.

Getting Strontium. The main raw materials for the production of strontium compounds are concentrates from the enrichment of celestine and strontianite. Strontium metal is obtained by reducing strontium oxide with aluminum at 1100-1150 °C:

4SrO+ 2Al = 3Sr+ SrO Al 2 O 3 .

The process is carried out in electrovacuum apparatuses [at 1 N/m 2 (10 -2 mm Hg)] of periodic action. Vapors of strontium condense on the cooled surface of a condenser inserted into the apparatus; at the end of the reduction, the apparatus is filled with argon and the condensate is melted, which flows into the mold. Strontium is also obtained by electrolysis of a melt containing 85% SrCl 2 and 15% KCl, however, in this process, the current efficiency is low, and the metal is contaminated with salts, nitride, and oxide. In industry, electrolysis with a liquid cathode produces strontium alloys, for example, with tin.

Application of Strontium. Strontium serves to deoxidize copper and bronze. 90 Sr is a source of β-radiation in atomic electric batteries. Strontium is used to make phosphors and solar cells, as well as highly pyrophoric alloys. Strontium oxide is a component of some optical glasses and oxide cathodes of vacuum tubes. Strontium compounds give flames an intense cherry red color, which is why some of them are used in pyrotechnics. Strontianite is introduced into the slag to clean high-grade steels from sulfur and phosphorus; Strontium carbonate is used in non-evaporative getters and is also added to weather-resistant glazes and enamels for coating porcelain, steels, and heat-resistant alloys. Chromate SrCrO 4 is a very stable pigment for the manufacture of artistic paints, SrTiO 3 titanate is used as a ferroelectric, it is part of piezoceramics. Strontium salts of fatty acids ("strontium soaps") are used to make special greases.

Salts and compounds of Strontium have low toxicity; when working with them, one should be guided by the safety regulations with salts of alkali and alkaline earth metals.

Strontium in the body. Strontium is an integral part of microorganisms, plants and animals. In marine radiolarians (acantaria), the skeleton consists of strontium sulfate - celestine. Seaweed contains 26-140 mg of Strontium per 100 g of dry matter, terrestrial plants - 2.6, marine animals - 2-50, terrestrial animals - 1.4, bacteria - 0.27-30. Accumulation of Strontium by various organisms depends not only on their species, features, but also on the ratio of Strontium with other elements, mainly Ca and P, in the environment, as well as on the adaptation of organisms to a specific geochemical environment.

Animals receive Strontium with water and food. Strontium is absorbed by the thin, and excreted mainly by the large intestine. A number of substances (algae polysaccharides, cation exchange resins) prevent the absorption of Strontium. The main depot of Strontium in the body is bone tissue, the ashes of which contain about 0.02% Strontium (in other tissues - about 0.0005%). An excess of strontium salts in the diet of rats causes "strontium" rickets. In animals living on soils with a significant amount of celestine, there is an increased content of Strontium in the body, which leads to brittle bones, rickets and other diseases. In biogeochemical provinces rich in Strontium (a number of regions of Central and East Asia, Northern Europe and others), the so-called Urov disease is possible.

Strontium-90. Among the artificial isotopes of Strontium, its long-lived radionuclide 90 Sr is one of the important components of radioactive contamination of the biosphere. Once in the environment, 90 Sr is characterized by the ability to be included (mainly together with Ca) in the metabolic processes of plants, animals, and humans. Therefore, when assessing the pollution of the biosphere with 90 Sr, it is customary to calculate the ratio of 90 Sr/Ca in strontium units (1 s.u. = 1 micron μcurie 90 Sr per 1 g Ca). When 90 Sr and Ca move along biological and food chains, Strontium discrimination occurs, for the quantitative expression of which the “discrimination coefficient” is found, the ratio of 90 Sr / Ca in the next link of the biological or food chain to the same value in the previous link. In the final link of the food chain, the concentration of 90 Sr, as a rule, is much lower than in the initial one.

Plants can receive 90 Sr directly from direct contamination of the leaves or from the soil through the roots (in this case, the type of soil, its moisture content, pH, content of Ca and organic matter, etc., have a great influence). Relatively more 90 Sr is accumulated by leguminous plants, root and tuber crops, less by cereals, including cereals, and flax. Significantly less 90 Sr is accumulated in seeds and fruits than in other organs (for example, 90 Sr is 10 times more in wheat leaves and stems than in grain). In animals (comes mainly with plant foods) and humans (comes mainly with cow's milk and fish), 90 Sr accumulates mainly in the bones. The amount of 90 Sr deposition in the body of animals and humans depends on the age of the individual, the amount of incoming radionuclide, the rate of growth of new bone tissue, and others. 90 Sr poses a great danger to children, in whose body it enters with milk and accumulates in rapidly growing bone tissue.

The biological effect of 90 Sr is associated with the nature of its distribution in the body (accumulation in the skeleton) and depends on the dose of β-irradiation created by it and its daughter radioisotope 90 Y. With prolonged intake of 90 Sr into the body, even in relatively small amounts, as a result of continuous irradiation bone tissue, leukemia and bone cancer can develop. Significant changes in bone tissue are observed when the content of 90 Sr in the diet is about 1 microcurie per 1 g of Ca. Conclusion in 1963 in Moscow of the Test Ban Treaty nuclear weapons in the atmosphere, space and under water led to an almost complete release of the atmosphere from 90 Sr and a decrease in its mobile forms in the soil.

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 does not occur in its pure form in nature. 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 about strontium deficiency in the human body in the specialized literature. Experiments conducted on animals show that a lack of strontium 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 this disease there is a development of dystrophic changes in bones and joints, especially during a 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 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, through 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.

Atomic number - 38

Atomic mass - 87.62

Density, kg/m³ - 2600

Melting point, ° С - 768

Heat capacity, kJ / (kg ° С) - 0.737

Electronegativity - 1.0

Covalent radius, Å - 1.91

1st ionization potential, ev - 5.69

The history of the discovery of strontium

In 1764, a mineral was found in a lead mine near the Scottish village of Strontian, which they called strontianite. For a long time it was considered a variety of fluorite CaF 2 or witherite BaCO 3, but in 1790 the English mineralogists Crawford and Cruikshank analyzed this mineral and found that it contained a new "earth", and in the current language, oxide.

Independently of them, the same mineral was studied by another English chemist, Hope. Having come to the same results, he announced that there is a new element in strontianite - the metal strontium.

Apparently, the discovery was already “in the air”, because almost simultaneously the prominent German chemist Klaproth announced the discovery of a new “earth”.

In the same years, the well-known Russian chemist, Academician Toviy Egorovich Lovits, also came across traces of "strontium earth". He had long been interested in the mineral known as heavy spar. In this mineral (its composition is BaSO 4), Karl Scheele discovered in 1774 the oxide of the new element barium. We do not know why Lovitz was not indifferent to heavy spar; it is only known that the scientist, who discovered the adsorption properties of coal and did much more in the field of general and organic chemistry, collected samples of this mineral. But Lovitz was not just a collector, he soon began to systematically study heavy spar and in 1792 came to the conclusion that this mineral contained an unknown impurity. He managed to extract quite a lot from his collection - more than 100 g of new "earth" and continued to explore its properties. The results of the study were published in 1795.

So, almost simultaneously, several researchers in different countries came close to the discovery of strontium. But in its elementary form it was singled out only in 1808.

The outstanding scientist of his time, Humphry Davy, already understood that the element of strontium earth must, apparently, be an alkaline earth metal, and he obtained it by electrolysis, i.e. in the same way as calcium, magnesium, barium. More specifically, the world's first metallic strontium was obtained by electrolysis of its moistened hydroxide. The strontium released at the cathode instantly combined with mercury, forming an amalgam. Decomposing the amalgam by heating, Davy isolated the pure metal.

The presence of strontium in nature

Strontium is found in sea water (0.1 mg/l), in soils (0.035 wt %). By mass, in geochemical processes, it is a satellite of calcium. In igneous rocks, strontium is predominantly in a dispersed form and enters as an isomorphic impurity into the crystal lattice of calcium, potassium, and barium minerals. In the biosphere, Strontium accumulates in carbonate rocks and especially in the sediments of salt lakes and lagoons.

Strontium is an integral part of microorganisms, plants and animals. In marine radiolarians (acantaria), the skeleton consists of strontium sulfate - celestine. Seaweed contains 26-140 mg of Strontium per 100 g of dry matter, terrestrial plants - 2.6, marine animals - 2-50, terrestrial animals - 1.4, bacteria - 0.27-30. Accumulation of Strontium by various organisms depends not only on their species, features, but also on the ratio of Strontium with other elements, mainly Ca and P, in the environment, as well as on the adaptation of organisms to a specific geochemical environment.

In nature, strontium occurs as a mixture of 4 stable isotopes 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.02%), 88Sr (82.56%). Radioactive isotopes with mass numbers from 80 to 97 have been artificially obtained, incl. 90 Sr (T ½ = 27.7 years), formed during the fission of uranium.

Obtaining strontium

There are 3 ways to obtain metallic strontium:

thermal decomposition of some compounds
electrolysis of a melt containing 85% SrCl 2 and 15% KCl, however, in this process, the current efficiency is low, and the metal is contaminated with salts, nitride and oxide. In industry, electrolysis with a liquid cathode produces strontium alloys, for example, with tin.
oxide or chloride reduction

The main raw materials for the production of strontium compounds are concentrates from the enrichment of celestine and strontianite. Strontium metal is obtained by reducing strontium oxide with aluminum at 1100-1150 °C:

4SrO+ 2Al = 3Sr+ SrO Al 2 O 3 .

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.

Physical properties of strontium

At room temperature, the lattice of Strontium is face-centered cubic (α-Sr) with a period a = 6.0848Å; at temperatures above 248 °C, it transforms into a hexagonal modification (β-Sr) with lattice periods a = 4.32 Å and c = 7.06 Å; at 614 °C it transforms into a cubic body-centered modification (γ-Sr) with a period a = 4.85Å. Atomic radius 2.15Å, ionic radius Sr 2+ 1.20Å. The density of the α-form is 2.63 g / cm 3 (20 ° C); t pl 770 °C, t kip 1383 °C; specific heat capacity 737.4 kJ/(kg K); electrical resistivity 22.76·10 -6 ohm·cm -1 . Strontium is paramagnetic, the atomic magnetic susceptibility at room temperature is 91.2·10 -6 . Strontium is a soft ductile metal that can be easily cut with a knife.

Polymorphene - 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 of strontium

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

Reacts with acids 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 of strontium

The main areas of application of strontium and its chemical compounds are the radio-electronic industry, pyrotechnics, metallurgy, and the food industry.

Strontium is used for alloying copper and some of its alloys, for introducing into battery lead alloys, for desulfurizing cast iron, copper and steels.

Strontium with a purity of 99.99-99.999% is used to reduce uranium.

Magnetically hard strontium ferrites are widely used as materials for the production of permanent magnets.

Long before the discovery of strontium, its undeciphered compounds were used in pyrotechnics to produce red lights. Until the mid-40s of the 20th century, strontium was, first of all, the metal of fireworks, fun and salutes. The magnesium-strontium alloy has the strongest pyrophoric properties and is used in pyrotechnics for incendiary and signal compositions.

Radioactive 90 Sr (half-life 28.9 years) is used in the production of radioisotope power sources in the form of strontium titanate (density 4.8 g/cm³, energy release about 0.54 W/cm³).

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.

Strontium oxide is used as a component of superconducting ceramics.

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.

The metal is used in glazes and enamels for coating dishes. Strontium glazes are not only harmless, but also affordable (strontium carbonate SrCO 3 is 3.5 times cheaper than red lead). All positive traits lead glazes are also characteristic of them. Moreover, products coated with such glazes acquire additional hardness, heat resistance, and chemical resistance.

Strontium is an active metal. This prevents its wide application in technology. But, on the other hand, the high chemical activity of strontium makes it possible to use it in certain areas of the national economy. In particular, it is used in the smelting of copper and bronze - strontium binds sulfur, phosphorus, carbon and increases the fluidity of the slag. Thus, strontium contributes to the purification of the metal from numerous impurities. In addition, the addition of strontium increases the hardness of copper, almost without reducing its electrical conductivity. Strontium is introduced into electric vacuum tubes to absorb the remaining oxygen and nitrogen, to make the vacuum deeper.

The effect of strontium on the human body

Salts and compounds of strontium have low toxicity; when working with them, one should be guided by the safety regulations with salts of alkali and alkaline earth metals.

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 strontium almost always has a negative effect on the human body:

1. It is 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.

2. Causes leukemia and malignant tumors (cancer) of the bones, as well as damage to the liver and brain.

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.

The influence of non-radioactive strontium is extremely rare and only when exposed to other factors (calcium and vitamin D deficiency, 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 - damage and deformity of the joints, growth retardation and other disorders.

Strontium-90.

Once in the environment, 90 Sr is characterized by the ability to be included (mainly together with Ca) in the metabolic processes of plants, animals, and humans. Therefore, when assessing the pollution of the biosphere with 90 Sr, it is customary to calculate the ratio of 90 Sr/Ca in strontium units (1 s.u. = 1 micron μcurie 90 Sr per 1 g Ca). When 90 Sr and Ca move along biological and food chains, Strontium discrimination occurs, for the quantitative expression of which the “discrimination coefficient” is found, the ratio of 90 Sr / Ca in the next link of the biological or food chain to the same value in the previous link. In the final link of the food chain, the concentration of 90 Sr, as a rule, is much lower than in the initial one.

Plants can receive 90 Sr directly from direct contamination of the leaves or from the soil through the roots. Relatively more 90 Sr is accumulated by leguminous plants, root and tuber crops, less by cereals, including cereals, and flax. Significantly less 90 Sr is accumulated in seeds and fruits than in other organs (for example, 90 Sr is 10 times more in wheat leaves and stems than in grain). In animals (comes mainly with plant foods) and humans (comes mainly with cow's milk and fish), 90 Sr accumulates mainly in the bones. The amount of 90 Sr deposition in the body of animals and humans depends on the age of the individual, the amount of incoming radionuclide, the rate of growth of new bone tissue, and others. 90 Sr poses a great danger to children, in whose body it enters with milk and accumulates in rapidly growing bone tissue.

For humans, the half-life of strontium-90 is 90-154 days.

The conclusion in 1963 in Moscow of the Treaty on the Ban on Tests of Nuclear Weapons in the Atmosphere, Outer Space and Under Water led to the almost complete release of the atmosphere from 90 Sr and a decrease in its mobile forms in the soil.

After the accident at the Chernobyl nuclear power plant, the entire territory with significant contamination with strontium-90 was within a 30-kilometer zone. A large amount of strontium-90 got into water bodies, but in river water its concentration did not exceed the maximum allowable for drinking water anywhere (except for the Pripyat River in early May 1986 in its lower reaches).

During the accident at the Chernobyl nuclear power plant, relatively little of it got into the environment - the total release is estimated at 0.22 MKi. Historically, much attention has been paid to this radionuclide in radiation hygiene. There are several reasons for this. Firstly, strontium-90 accounts for a significant part of the activity in the mixture of products of a nuclear explosion: 35% of the total activity immediately after the explosion and 25% after 15-20 years, and secondly, nuclear accidents at the Mayak Production Association in the South Urals in 1957 and 1967, when a significant amount of strontium-90 was released into the environment.

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 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.

38	← Strontium→ Yttrium

Atom properties

Name, symbol, number

Strontium / Strontium (Sr), 38

Atomic mass
(molar mass)

87.62(1) a. e.m. (g/mol)

Electronic configuration

Atom radius

Chemical properties

covalent radius

Ion radius

Electronegativity

0.95 (Pauling scale)

Electrode potential

Oxidation states

Ionization energy
(first electron)

549.0 (5.69) kJ/mol (eV)

Thermodynamic properties of a simple substance

Density (at n.a.)

Melting temperature

Boiling temperature

Oud. heat of fusion

9.20 kJ/mol

Oud. heat of evaporation

144 kJ/mol

Molar heat capacity

26.79 J/(K mol)

Molar volume

33.7 cm³/mol

The crystal lattice of a simple substance

Lattice structure

cubic face-centered

Lattice parameters

Debye temperature

Other characteristics

Thermal conductivity

(300 K) (35.4) W/(m K)

In 1764, a mineral was found in a lead mine near the Scottish village of Strontian, which they called strontianite. For a long time it was considered a variety of fluorite CaF2 or witherite BaCO3, but in 1790 the English mineralogists Crawford and Cruickshank analyzed this mineral and found that it contained a new "earth", and in the current language, oxide.

Independently of them, the same mineral was studied by another English chemist, Hope. Having come to the same results, he announced that there is a new element in strontianite - the metal strontium.

Apparently, the discovery was already “in the air”, because almost simultaneously the prominent German chemist Klaproth announced the discovery of a new “earth”.

In the same years, the well-known Russian chemist, Academician Toviy Egorovich Lovitz, also came across traces of "strontium earth". He had long been interested in the mineral known as heavy spar. In this mineral (its composition is BaSO4), Karl Scheele discovered in 1774 the oxide of the new element barium. We do not know why Lovitz was not indifferent to heavy spar; it is only known that the scientist, who discovered the adsorption properties of coal and did much more in the field of general and organic chemistry, collected samples of this mineral. But Lovitz was not just a collector, he soon began to systematically study heavy spar and in 1792 came to the conclusion that this mineral contained an unknown impurity. He managed to extract quite a lot from his collection - more than 100 g of new "earth" and continued to explore its properties. The results of the study were published in 1795.

So, almost simultaneously, several researchers in different countries came close to the discovery of strontium. But in its elementary form it was singled out only in 1808.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http:// www. all best. en/

Introduction

5. Sampling approaches

Offers

Introduction

Very dangerous view impact on the biosphere is 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 contains 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. Strontium was first isolated in free form by the English chemist and physicist Humphry Davy in 1808. Strontium metal was obtained by electrolysis of its moist 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.

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. Seaweed contains 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. The accumulation of strontium by various organisms depends not only on their type and 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 number of radioactive strontium-90, which has a half-life of 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 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, carried out at the planet's test sites in 1954-1980, now plays a secondary role, the contribution of this process to pollution atmospheric air 90Sr is two orders of magnitude less than from wind-driven dust rise from soil contaminated with nuclear testing 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 Mayak Production Association in 1986. Chelyabinsk region in 1957 ("Kyshtym accident"), as well as in the vicinity of some enterprises of the nuclear fuel cycle.

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 is also possible surface waters with subsequent 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 food products causes "Urov disease" in humans and animals (named after the Urov River in Eastern Transbaikalia) - damage and deformity of the joints, 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 curves, 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 precipitates 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 high concentrations, 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 determining Sr in the arc is 5*10-5 - 1*10-4%, relative error determination of ±4-15%. The use of a pulsed arc discharge of high current in argon can significantly increase the sensitivity of the determination of Sr (3 * 10-12 g). 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 content of strontium 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 observed. 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-ray radiation. 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 a while will they begin to disappear. rare species, there will be a change in the prevailing forms, the total number of organisms will change, 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, dioica 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. chemical substances potentially hazardous to living organisms under controlled experimental laboratory or field conditions by registering changes in biologically significant indicators (test functions) of the test objects under study, followed by an assessment of their condition in accordance with the selected toxicity criterion.

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.

A variety of 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. These can be bacteria, algae, invertebrates, and also 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 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 identify 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, cuttings of wild plants of meadow-steppe vegetation or monocultures of annual and perennial agricultural plants are used, 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 1x1 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 the method of atomic adsorption on an atomic spectrophotometer "AAS Kvant 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. natural source is the process of weathering of rocks and minerals.

Distribution, behavior and concentration of the toxicant in natural environments depends on the relief (the slope of the area in the area of the industrial zone, the compliance of the substrate for degradation, etc.), climatic conditions (the temperature regime of air and soil, the amount of precipitation per unit area, wind speed), the physicochemical, biological and nutritional status of soils (the presence and the 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 animal organisms, 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 biological features 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, conductive plant 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 sample preparation and poor reproducibility of the results, the high cost of the equipment and its operation.

Also biological methods testing are a group of highly sensitive methods of analysis and favorably differ in 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 foods 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 foodstuffs, the replacement of contaminated foodstuffs with clean ones.

When working with radioactive strontium, it is necessary to comply with sanitary rules and radioactive safety standards with the use of 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, healthy lifestyle life, sport, 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 measures of laboratory and field research. 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: Tutorial. - 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.

Hosted on Allbest.ru

...