Strontium in plants. Features of radionuclide accumulation by vegetation Accumulation of radionuclides by plants of forest phytocenoses

Having entered the environment from the destroyed reactor, strontium is in a state accessible to humans. It is involved in biological chains of migration. This means that strontium accumulates in plants that humans eat. accumulates in the body of domestic animals (for example cows), which people keep in contaminated areas and, as a result, milk and meat accumulate increased amount this radionuclide. By consuming food products obtained in radiation-affected areas, a person contributes to the accumulation of strontium in the body.

Besides, strontium can enter the human body through inhalation of dust. What happens to the human body when a lot of strontium accumulates?

Where does strontium accumulate in humans?

Strontium osteotrope – that is, an element that accumulates selectively in certain tissues of living beings, including humans. This organ (tissue) is the skeleton (bones). This pattern can be explained very simply - by chemical properties strontium is similar to calcium, which is the main building element of the skeleton of all organisms. In case of calcium deficiency, and the Polesie zone is poor in this element, and in the presence of radioactive strontium, the body indiscriminately accumulates this radionuclide in the bones.

The accumulation of strontium in bones causes another important problem - the radionuclide is very slowly removed from the human body (skeleton). After two hundred days, only half of the accumulated strontium is excreted.

It is important that, accumulating in the bones, strontium irradiates important, in the language of radiobiology, critical human organs - Bone marrow. The place where human blood is formed. A high content of strontium in human bones can have a significant effect on this organ and cause corresponding diseases.

To understand how selectively strontium accumulates in bone tissue, let us point out that, for example, only one percent of strontium accumulates in muscle tissue (meat) - the rest is in the bones.

Effect of radioactive strontium

High accumulation of strontium, especially in the body of children, can lead to extremely dangerous consequences. Radioactive strontium irradiates growing bone tissue, which leads to disease and deformation of the child’s joints, and growth retardation is observed. This disease even has its own name - strontium rickets.

Most brightly Negative influence strontium on the human body is captured in a photo of a child who experienced nuclear bombing in Hiroshima.

Photo of a human being affected by incorporated strontium.

1 – photo of a child 2 years after the bombing (1947);

2 – progressive damage to the leg joint (the picture was taken 1 year after the first picture);

3 – child in 1951 (development of the disease).

As already noted, with a high accumulation of strontium in the bones, irradiation and damage to the bone marrow occurs. Chronic exposure leads to the development radiation sickness, the appearance of tumors in the blood-forming systems, and malignant tumors also occur in the bones. Causes leukemia, leads to damage to the human liver and brain.

Important preventive method The way to prevent the entry of strontium into the human body is the proper preparation of food obtained in areas contaminated with strontium-90. Cooking allows you to reduce the concentration of radionuclide several times. There is no need to neglect such simple procedures.

1.2 Accumulation of strontium radionuclide – 90 in soils and plants

Food and technical quality products - grain, tubers, oilseeds, root crops, obtained from irradiated plants, do not deteriorate significantly even when the yield is reduced to 30-40%.

The oil content in sunflower and lotus seeds depends on the dose of radiation received by the plants and the phase of their development at the start of irradiation. A similar dependence is observed in the yield of sugar in the harvest of root crops from irradiated beet plants. The content of vitamin C in tomato fruits collected from irradiated plants depends on the phase of plant development at the beginning of irradiation and the irradiation dose. For example, when a plant is irradiated during mass flowering and the beginning of fruiting with doses of 3–15 kR, the content of vitamin C in tomato fruits increased compared to the control by 3–25%. Irradiation of plants during the period of mass flowering and the beginning of fruiting with a dose of up to 10 kR inhibits the development of seeds in developing fruits, which usually become seedless.

A similar pattern was obtained in experiments with potatoes. When plants are irradiated during the period of tuberization, the yield of tubers when irradiated with doses of 7–10 kR practically does not decrease. If plants are irradiated at an earlier stage of development, the tuber yield is reduced by an average of 30–50%. In addition, the tubers are not viable due to the sterility of the eyes.

Irradiation of vegetative plants not only leads to a decrease in their productivity, but also reduces the sowing qualities of the emerging seeds. Thus, irradiation of vegetative plants not only leads to a decrease in their productivity, but also reduces the sowing qualities of the emerging seeds. Thus, when grain crops are irradiated in the most sensitive phases of development (tillering, bolling), the yield is greatly reduced, but the germination of the resulting seeds is significantly reduced, which makes it possible not to use them for sowing. If plants are irradiated at the beginning of milky ripeness (when the formation of a link occurs) even in relatively high doses, the grain yield is preserved almost completely, but such seeds cannot be used for sowing due to extremely low germination.

Thus, radioactive isotopes do not cause noticeable damage to plant organisms, but they accumulate in significant quantities in agricultural crops.

A significant part of radionuclides is found in the soil, both on the surface and in the lower layers, and their migration largely depends on the type of soil, its granulometric composition, water-physical and agrochemical properties.

The main radionuclides that determine the nature of pollution in our region are cesium - 137 and strontium - 90, which are sorted differently by the soil. The main mechanism for the fixation of strontium in the soil is ion exchange, cesium - in the 137 exchange form or by the type of ion exchange sorption on inner surface soil particles.

The absorption of strontium by soil is 90 less than that of cesium - 137, and therefore it is a more mobile radionuclide.

At the moment of release of cesium-137 into the environment, the radionuclide is initially in a highly soluble state (vapor-gas phase, fine particles, etc.)

In these cases, cesium-137 enters the soil and is easily available for absorption by plants. Subsequently, the radionuclide can be included in various reactions in the soil, and its mobility decreases, the strength of fixation increases, the radionuclide “ages”, and such “aging” represents a complex of soil crystal-chemical reactions with the possible entry of the radionuclide into the crystal structure of secondary clay minerals.

The mechanism of fixation of radioactive isotopes in the soil, their sorption has great importance, since sorption determines the migration qualities of radioisotopes, the intensity of their absorption by soils, and, consequently, their ability to penetrate into plant roots. Sorption of radioisotopes depends on many factors and one of the main ones is the mechanical and mineralogical composition of the soil; heavy soils in granulometric composition absorb radionuclides, especially cesium - 137, are fixed more strongly than light ones and with a decrease in the size of the mechanical fractions of the soil, the strength of their fixation of strontium - 90 and cesium - 137 is rising. Radionuclides are most firmly fixed by the clay fraction of the soil.

A greater retention of radioisotopes in the soil is facilitated by the presence in it of chemical elements similar in chemical properties to these isotopes. Yes, calcium chemical element, similar in its properties to strontium - 90 and the addition of lime, especially on soils with high acidity, leads to an increase in the absorption capacity of strontium - 90 and a decrease in its migration. Potassium is similar in its chemical properties to cesium - 137. Potassium, as a non-isotopic analogue of cesium, is found in the soil in macro quantities, while cesium is in ultra micro concentrations. As a result, microquantities of cesium-137 are strongly diluted in the soil solution by potassium ions, and when they are absorbed by plant root systems, there is competition for the sorption site on the root surface. Therefore, when these elements enter from the soil, antagonism of cesium and potassium ions is observed in plants.

In addition, the effect of radionuclide migration depends on meteorological conditions (amount of precipitation).

It has been established that strontium-90 that falls on the soil surface is washed out by rain into the lowest layers. It should be noted that the migration of radionuclides in soils proceeds slowly and their main part is located in the 0–5 cm layer.

The accumulation (removal) of radionuclides by agricultural plants largely depends on the properties of the soil and the biological characteristics of the plants. On acidic soils radionuclides enter plants in much larger quantities than from slightly acidic soils. A decrease in soil acidity, as a rule, helps to reduce the size of the transfer of radionuclides into plants. Thus, depending on the properties of the soil, the content of strontium - 90 and cesium - 137 in plants can vary on average by 10 - 15 times.

And interspecific differences in agricultural crops in the accumulation of these radionuclides are observed in leguminous crops. For example, strontium - 90 and cesium - 137, are absorbed 2-6 times more intensively by leguminous crops than by cereals.

The entry of strontium-90 and cesium-137 into grass in meadows and pastures is determined by the nature of distribution in the soil profile.

In the contaminated zone, the meadows of the Ryazan region are polluted on an area of 73,491 hectares, including with a pollution density of 1.5 Ci/km 2 - 67,886 (36% of the total area), with a pollution density of 5.15 Ci/km 2 - 5,605 ha ( 3%).

In virgin areas and natural meadows, cesium is found in a layer of 0-5 cm; over the past years after the accident, no significant vertical migration has been noted along the soil profile. On plowed lands, cesium-137 is found in the arable layer.

Floodplain vegetation accumulates cesium-137 to a greater extent than upland vegetation. So, when the floodplain was polluted at 2.4 Ci/km 2 , Ki/kg of dry mass was found in the grass, and on the upland, when the pollution was 3.8 Ci/km 2 , the grass contained Ki/kg.

The accumulation of radionuclides by herbaceous plants depends on the structural features of the turf. In a cereal meadow with thick, dense turf, the content of cesium-137 in the phytomass is 3–4 times higher than in a forb meadow with loose, thin turf.

Crops with low potassium content accumulate less cesium. Cereal grasses accumulate less cesium compared to legumes. Plants are relatively resistant to radioactive effects, but they can accumulate such amounts of radionuclides that they become unsuitable for human consumption and livestock feed.

The intake of cesium-137 into plants depends on the type of soil. According to the degree of reduction in the accumulation of cesium in the plant crop, soils can be arranged in the following sequence: sod-podzolic sandy loam, sod-podzolic loamy soil, gray forest soil, chernozem, etc. The accumulation of radionuclides in crops depends not only on the type of soil, but also on the biological characteristics of the plants.

It is noted that calcium-loving plants usually absorb more strontium - 90 - than calcium-poor plants. Legumes accumulate the most strontium - 90%, root and tuber crops less, and cereals even less.

The accumulation of radionuclides in a plant depends on the content of nutrients in the soil. It has been established that mineral fertilizer applied in doses of N 90, P 90 increases the concentration of cesium - 137 in vegetable crops by 3 - 4 times, and similar applications of potassium reduce its content by 2 - 3 times. The content of calcium-containing substances has a positive effect on reducing the intake of strontium-90 in the crop of leguminous crops. For example, adding lime to leached chernozem in doses equivalent to hydrolytic acidity reduces the supply of strontium-90 to grain crops by 1.5 - 3.5 times.

The greatest effect on reducing the intake of strontium-90 in plant yields is achieved by adding complete mineral fertilizer against the background of dolomite. The efficiency of accumulation of radionuclides in plant crops is influenced by organic fertilizers and meteorological conditions, as well as the time they remain in the soil. It has been established that the accumulation of strontium - 90, cesium - 137, five years after they enter the soil, decreases by 3-4 times.

Thus, the migration of radionuclides largely depends on the type of soil, its mechanical composition, water-physical and agrochemical properties. So, many factors influence the sorption of radioisotopes, and one of the main ones is the mechanical and mineralogical composition of the soil. Absorbed radionuclides, especially cesium-137, are more strongly fixed in soils that are heavy in mechanical composition than in soils that are light. In addition, the effect of radionuclide migration depends on meteorological conditions (amount of precipitation).

The accumulation (removal) of radionuclides by agricultural plants largely depends on the properties of the soil and the biological ability of the plants.

Radioactive substances released into the atmosphere ultimately become concentrated in the soil. A few years after the radioactive fallout on earth's surface The entry of radionuclides into plants from the soil becomes the main route of their entry into human food and animal feed. In emergency situations, as shown by the accident at Chernobyl nuclear power plant, already in the second year after the fallout, the main route of radioactive substances entering the food chain is the entry of radionuclides from the soil into plants.

Radioactive substances entering the soil can be partially washed out of it and enter into groundwater. However, the soil retains radioactive substances that enter it quite firmly. The absorption of radionuclides causes a very long (for decades) presence in the soil cover and continuous entry into agricultural products. Soil, as the main component of agrocenosis, has a decisive influence on the intensity of the inclusion of radioactive substances in feed and food chains.

The absorption of radionuclides by soils prevents their movement along the soil profile, penetration into groundwater and ultimately determines their accumulation in the upper soil horizons.

The mechanism of absorption of radionuclides by plant roots is similar to the absorption of basic nutrients– macro and microelements. A certain similarity is observed in the absorption and movement of strontium - 90 and cesium - 137 by plants and their chemical analogues - calcium and potassium, therefore the content of these radionuclides in biological objects is sometimes expressed in relation to their chemical analogues, in the so-called strontium and cesium units.

Radionuclides Ru-106, Ce-144, Co-60 are concentrated mainly in the root system and move in small quantities to the above-ground organs of plants. In contrast, strontium-90 and cesium-137 accumulate in relatively large quantities in the above-ground parts of plants.

Radionuclides entering the underground part of plants are mainly concentrated in straw (leaves and stems), less in soft ones (ears, panicles without grain. Some exceptions to this pattern are cesium, the relative content of which in seeds can reach 10% and higher than the total amount in the aerial part. Cesium moves intensively throughout the plant and accumulates in relatively large quantities in young organs, which obviously causes its increased concentration in the grain.

In general, the accumulation of radionuclides and their content per unit mass of dry matter during plant growth is observed in the same pattern as for biologically important elements: with the age of plants in their above-ground organs, the absolute amount of radionuclides increases and the content per unit mass of dry matter decreases. As the yield increases, as a rule, the content of radionuclides per unit mass decreases.

From acidic soils, radionuclides enter plants in much larger quantities than from slightly acidic, neutral and slightly alkaline soils. In acidic soils, the mobility of strontium - 90 and cesium - 137 increases and the strength of their plants decreases. The addition of calcium and potassium or sodium carbonates to acidic soddy-podzolic soil in quantities equivalent to hydrolytic acidity reduces the accumulation of long-lived radionuclides of strontium and cesium in the crop.

There is a close inverse relationship between the accumulation of strontium-90 in plants and the content of exchangeable calcium in the soil (the supply of strontium decreases with an increase in the content of exchangeable calcium in the soil).

Consequently, the dependence of the supply of strontium-90 and cesium-137 from soil to plants is quite complex, and it cannot always be determined by any one of the properties; in different soils it is necessary to take into account a complex of indicators.

The migration paths of radionuclides into the human body are different. A significant proportion of them enters the human body through the food chain: soil – plants – farm animals – livestock products – humans. In principle, radionuclides can enter the animal body through the respiratory system, gastrointestinal tract and skin surface. If during

large radioactive fallout cattle is on pasture, then the intake of radionuclides can be (in relative units): through the digestive canal 1000, respiratory organs 1, skin 0.0001. Consequently, in conditions of radioactive fallout, the main attention should be paid to the maximum possible reduction in the entry of radionuclides into the body of farm animals through the gastrointestinal tract.

Since radionuclides entering the body of animals and humans can accumulate and, having an adverse effect on human health and gene pool, it is necessary to take measures to reduce the entry of radionuclides into agricultural plants and reduce the accumulation of radioactive substances in the bodies of farm animals.

graduate work

1 Literature review

1.1 Properties of the radionuclide Strontium-90

Strontium 90 Sr is a silvery calcium-like metal coated with an oxide shell and reacts poorly, being included in the metabolism of the ecosystem as complex Ca - Fe - Al - Sr - complexes are formed. The natural content of the stable isotope in soil, bone tissue, and environment reaches 3.7 x 10 -2%, in sea water, muscle tissue 7.6 x 10 -4%. Biological functions not identified; non-toxic, can replace calcium. Radioactive isotope in natural environment absent .

Stromnium is an element of the main subgroup of the second group, fifth period periodic table chemical elements of D.I. Mendeleev, with atomic number 38. Denoted by the symbol Sr (lat. Strontium). The simple substance strontium (CAS number: 7440-24-6) is a soft, malleable and ductile alkaline earth metal of silver-white color. It has high chemical activity; in air it quickly reacts with moisture and oxygen, becoming covered with a yellow oxide film.

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 its name to the new element. The presence of a new metal oxide in this mineral was discovered almost 30 years later by William Cruickshank and Ader Crawford. Highlighted in pure form Sir Humphry Davy in 1808.

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 84 Sr (0.56%), 86 Sr (9.86%), 87 Sr (7.02%), 88 Sr (82.56%).

There are 3 ways to obtain strontium metal:

Thermal decomposition of some compounds

Electrolysis

Reduction of oxide or chloride

The main industrial method for producing strontium metal is the thermal reduction of its oxide with aluminum. Next, the resulting strontium is purified by sublimation.

The electrolytic production of strontium by electrolysis of a melted mixture of SrCl 2 and NaCl did not obtain widespread due to low current efficiency and contamination of strontium with impurities.

The thermal decomposition of strontium hydride or nitride produces finely dispersed strontium, which is prone to easy ignition.

Strontium is a soft, silvery-white metal, malleable and ductile, and can be easily cut with a knife.

Polymorphic - three of its modifications are known. Up to 215 o C, the cubic face-centered modification (b-Sr) is stable, between 215 and 605 o C - hexagonal (b-Sr), above 605 o C - cubic body-centered modification (g-Sr).

Melting point - 768 o C, Boiling point - 1390 o C.

Strontium in its compounds always exhibits a valence of +2. The properties of strontium are 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 equal to? 2.89 V. It reacts vigorously with water, forming hydroxide: Sr + 2H 2 O = Sr(OH) 2 + H 2 ^.

Interacts with acids, displaces heavy metals from their salts. It reacts weakly with concentrated acids (H 2 SO 4, HNO 3).

Strontium metal quickly 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.

Reacts vigorously 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 reacts with CO 2 to form carbide:

5Sr + 2CO 2 = SrC 2 + 4SrO (1)

Easily soluble strontium salts with the anions Cl - , I - , NO 3 - . Salts with anions F -, SO 4 2-, CO 3 2-, PO 4 3- are slightly soluble.

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

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

Strontium with a purity of 99.99-99.999% is used for the reduction of uranium.

Hard magnetic strontium ferrites are widely used as materials for the production of permanent magnets.

In pyrotechnics, strontium carbonate, nitrate, and perchlorate are used to color the flame carmine red. The magnesium-strontium alloy has strong 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 current sources in the form of strontium titanite (density 4.8 g/cm³, and 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 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 from 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 fluorionic batteries with enormous energy intensity and energy density.

Strontium alloys with tin and lead are used for casting battery current leads. Strontium-cadmium alloys for anodes of galvanic cells.

Radiation characteristics are given in Table 1.

Table 1 - Radiation characteristics of strontium 90

In cases where the isotope enters the environment, the intake of strontium into the body depends on the degree and nature of the inclusion of the metabolite in soil organic structures, food and ranges from 5 to 30%, with greater penetration into the child’s body. Regardless of the route of entry, the emitter accumulates in the skeleton (in soft tissues contains no more than 1%). It is excreted from the body extremely poorly, which leads to constant accumulation of the dose due to chronic intake of strontium into the body. Unlike natural β-active analogues (uranium, thorium, etc.), strontium is an effective β-emitter, which changes the spectrum of radiation exposure, including on the gonads, endocrine glands, red bone marrow and brain. Accumulated doses (background) fluctuate within the range (up to 0.2 x 10 -6 µCi/g in bones at doses of the order of 4.5 x 10 -2 mSv/year).

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 should not be confused. The strontium isotope 90 Sr is radioactive with a half-life of 28.9 years. 90 Sr undergoes decay, turning into radioactive 90 Y (half-life 64 hours). Complete decay of strontium-90 released into the environment will occur only after several hundred years. 90 Sr is formed when nuclear explosions and emissions from nuclear power plants.

In terms of chemical reactions, radioactive and non-radioactive isotopes of strontium are practically the same. Natural strontium -- component 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 influences the amount of strontium deposition in the skeleton.

The behavior of strontium in the body is influenced by species, gender, age, as well as pregnancy and other factors. For example, males have higher levels of deposits in their skeletons than females. Strontium is an analogue of calcium. Strontium accumulates at a high rate in the body of children up to the age of four, when bone tissue is actively being formed. Strontium metabolism changes in certain diseases of the digestive system and cardiovascular system. Routes of entry:

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, radishes, radishes, onions, cabbage, barley, rye, wheat)

Intratracheal delivery

Through the skin (cutaneous)

Inhalation (through air)

From plants or through animals, strontium-90 can directly pass into the human body.

People whose work involves 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, manufacturing magnetic materials, radioactive - production of nuclear electric batteries. atomic-hydrogen energy, radioisotope thermoelectric generators, etc.).

The influence of non-radioactive strontium appears extremely rarely and only under the influence of other factors (calcium and vitamin D deficiency, malnutrition, imbalances in the ratio of microelements such as barium, molybdenum, selenium, etc.). Then it can cause “strontium rickets” and “urological disease” in children - damage and deformation of joints, growth retardation and other disorders. On the contrary, radioactive strontium almost always has a negative effect on the human body:

It is deposited in the skeleton (bones), affecting bone tissue and bone marrow, which leads to the development of radiation sickness, tumors of hematopoietic tissue and bones.

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

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 bones. Long-term radiation exposure to 90 Sr and 90 Y affects bone tissue and bone marrow, which leads to the development of radiation sickness, tumors of hematopoietic tissue and bones.

Once in the soil, strontium-90, together with soluble calcium compounds, enters plants, from which it can enter the human body directly or through animals. This creates a chain of transmission of radioactive strontium: soil - plants - animals - humans. Penetrating into the human body, strontium accumulates mainly in the bones and thus exposes the body to long-term internal radioactive effects. The result of this exposure, as shown by research conducted by scientists in experiments on animals (dogs, rats, etc.), is a serious illness of the body. Damage to the hematopoietic organs and the development of tumors in the bones come to the fore. Under normal conditions, the “supplier” of radioactive strontium is experimental explosions of nuclear and thermal nuclear weapons. Research by American scientists has established that even a small amount of radiation exposure is certainly harmful to a healthy person. If we take into account that even with extremely small doses of this effect, sudden changes in those cells of the body on which the reproduction of offspring depends, it is quite clear that nuclear explosions pose a mortal danger to those not yet born! Strontium received its name from the mineral strontianite (carbon dioxide salt of strontium), found in 1787 in Scotland near the village of Strontian. The English researcher A. Crawford, studying strontianite, suggested the presence of a new, as yet unknown “earth” in it. The individual peculiarity of strontianite was also established by Klaproth. The English chemist T. Hope in 1792 proved the presence of a new metal in strontianite, isolated in free form in 1808 by G. Davy.

However, regardless of Western scientists, Russian chemist T.E. Lovitz in 1792, examining the mineral barite, came to the conclusion that, in addition to barium oxide, it also contained “strontian earth” as an impurity. Extremely cautious in his conclusions, Lovitz did not dare to publish them until the completion of the secondary verification of the experiments, which required the accumulation of a large amount of “strontian earth”. Therefore, Lovitz’s research “On strontian earth in heavy spar,” although published after Klaproth’s research, was actually carried out before him. They indicate the discovery of strontium in a new mineral - strontium sulfate, now called celestine. From this mineral, the simplest marine organisms - radiolarians, acantharia - build the spines of their skeleton. From the needles of dying invertebrates, clusters of celestine itself were formed

1.2 Accumulation of strontium-90 radionuclide in soils and plants

The food and technical quality of products - grain, tubers, oilseeds, root crops - obtained from irradiated plants does not deteriorate significantly even when the yield is reduced to 30-40%.

The oil content in sunflower and lotus seeds depends on the dose of radiation received by the plants and the phase of their development at the start of irradiation. A similar dependence is observed in the yield of sugar in the harvest of root crops from irradiated beet plants. The content of vitamin C in tomato fruits collected from irradiated plants depends on the phase of plant development at the beginning of irradiation and the irradiation dose. For example, when a plant was irradiated during mass flowering and the beginning of fruiting with doses of 3 - 15 kR, the content of vitamin C in tomato fruits increased by 3 - 25% compared to the control. Irradiation of plants during the period of mass flowering and the beginning of fruiting with a dose of up to 10 kR inhibits the development of seeds in developing fruits, which usually become seedless.

A similar pattern was obtained in experiments with potatoes. When plants are irradiated during the period of tuber formation, the yield of tubers when irradiated with doses of 7 - 10 kR practically does not decrease. If plants are irradiated at an earlier stage of development, the tuber yield is reduced by an average of 30 - 50%. In addition, the tubers are not viable due to the sterility of the eyes.

Thus, radioactive isotopes do not cause noticeable damage to plant organisms, but they accumulate in significant quantities in agricultural crops.

The main radionuclides that determine the nature of pollution in our region are cesium - 137 and strontium - 90, which are sorted differently by the soil. The main mechanism for fixing strontium in the soil is ion exchange, cesium - in the 137 exchange form or by the type of ion exchange sorption on the inner surface of soil particles.

The absorption of strontium by soil is 90 less than that of cesium - 137, and therefore it is a more mobile radionuclide.

At the moment of release of cesium-137 into the environment, the radionuclide is initially in a highly soluble state (vapor-gas phase, fine particles, etc.)

The mechanism of fixation of radioactive isotopes in the soil, their sorption is of great importance, since sorption determines the migration qualities of radioisotopes, the intensity of their absorption by soils, and, consequently, their ability to penetrate into plant roots. Sorption of radioisotopes depends on many factors and one of the main ones is the mechanical and mineralogical composition of the soil; heavy soils in granulometric composition absorb radionuclides, especially cesium - 137, are fixed more strongly than light ones and with a decrease in the size of the mechanical fractions of the soil, the strength of their fixation of strontium - 90 and cesium - 137 is rising. Radionuclides are most firmly fixed by the clay fraction of the soil.

A greater retention of radioisotopes in the soil is facilitated by the presence in it of chemical elements similar in chemical properties to these isotopes. Thus, calcium is a chemical element similar in its properties to strontium-90 and the addition of lime, especially on soils with high acidity, leads to an increase in the absorption capacity of strontium-90 and a decrease in its migration. Potassium is similar in its chemical properties to cesium - 137. Potassium, as a non-isotopic analogue of cesium, is found in the soil in macro quantities, while cesium is in ultra micro concentrations. As a result, microquantities of cesium-137 are strongly diluted in the soil solution by potassium ions, and when they are absorbed by plant root systems, competition for the sorption site on the root surface is observed. Therefore, when these elements enter from the soil, antagonism of cesium and potassium ions is observed in plants.

In addition, the effect of radionuclide migration depends on meteorological conditions (amount of precipitation).

The accumulation (removal) of radionuclides by agricultural plants largely depends on the properties of the soil and the biological characteristics of the plants. On acidic soils, radionuclides enter plants in much larger quantities than from slightly acidic soils. A decrease in soil acidity, as a rule, helps to reduce the size of the transfer of radionuclides into plants. Thus, depending on the properties of the soil, the content of strontium - 90 and cesium - 137 in plants can vary on average by 10 - 15 times.

And interspecific differences in agricultural crops in the accumulation of these radionuclides are observed in leguminous crops. For example, strontium - 90 and cesium - 137, are absorbed 2 - 6 times more intensively by leguminous crops than by cereals.

The entry of strontium-90 and cesium-137 into grass in meadows and pastures is determined by the nature of distribution in the soil profile.

The accumulation of radionuclides by herbaceous plants depends on the structural features of the turf. In a cereal meadow with thick, dense turf, the content of cesium-137 in the phytomass is 3-4 times higher than in a forb meadow with loose, thin turf.

It is noted that calcium-loving plants usually absorb more strontium - 90 - than calcium-poor plants. Legumes accumulate the most strontium - 90%, root crops and tubers less, and cereals even less.

The accumulation of radionuclides in a plant depends on the content of nutrients in the soil. It has been established that mineral fertilizer applied in doses of N 90, P 90 increases the concentration of cesium-137 in vegetable crops by 3-4 times, and similar applications of potassium reduce its content by 2-3 times. The content of calcium-containing substances has a positive effect on reducing the intake of strontium-90 in the crop of leguminous crops. For example, adding lime to leached chernozem in doses equivalent to hydrolytic acidity reduces the supply of strontium-90 to grain crops by 1.5 - 3.5 times.

The greatest effect on reducing the intake of strontium-90 in plant yields is achieved by applying complete mineral fertilizer against the background of dolomite. The efficiency of accumulation of radionuclides in plant crops is influenced by organic fertilizers and meteorological conditions, as well as the time they remain in the soil. It has been established that the accumulation of strontium - 90, cesium - 137, five years after they enter the soil, decreases by 3-4 times.

The accumulation (removal) of radionuclides by agricultural plants largely depends on the properties of the soil and the biological ability of the plants.

Radioactive substances released into the atmosphere ultimately become concentrated in the soil. Several years after radioactive fallout on the earth's surface, the entry of radionuclides into plants from the soil becomes the main route of their entry into human food and animal feed. In emergency situations, as the accident at the Chernobyl nuclear power plant showed, already in the second year after fallout, the main route for radioactive substances to enter food chains is the entry of radionuclides from the soil into plants.

Radioactive substances entering the soil can be partially washed out of it and enter groundwater. However, the soil retains radioactive substances that enter it quite firmly. The absorption of radionuclides causes a very long (for decades) presence in the soil cover and continuous entry into agricultural products. Soil, as the main component of agrocenosis, has a decisive influence on the intensity of the inclusion of radioactive substances in feed and food chains.

The absorption of radionuclides by soils prevents their movement along the soil profile, penetration into groundwater and ultimately determines their accumulation in the upper soil horizons.

The mechanism of absorption of radionuclides by plant roots is similar to the absorption of basic nutrients - macro and microelements. A certain similarity is observed in the absorption and movement of strontium - 90 and cesium - 137 by plants and their chemical analogues - calcium and potassium, therefore the content of these radionuclides in biological objects is sometimes expressed in relation to their chemical analogues, in the so-called strontium and cesium units.

Radionuclides entering the underground part of plants are mainly concentrated in straw (leaves and stems), less - in soft ones (ears, panicles without grain. Some exceptions to this pattern are cesium, the relative content of which in seeds can reach 10% and higher than the total amount in the aerial part. Cesium moves intensively throughout the plant and accumulates in relatively large quantities in young organs, which obviously causes its increased concentration in the grain.

The migration paths of radionuclides into the human body are different. A significant proportion of them enters the human body through the food chain: soil - plants - farm animals - livestock products - humans. In principle, radionuclides can enter the animal body through the respiratory system, gastrointestinal tract and skin surface. If during

radioactive fallout of cattle is on pasture, then the intake of radionuclides can be (in relative units): through the digestive canal 1000, respiratory organs 1, skin 0.0001. Consequently, in conditions of radioactive fallout, the main attention should be paid to the maximum possible reduction in the entry of radionuclides into the body of farm animals through the gastrointestinal tract.

1.3 Features of strontium-90 migration into the environment

The radionuclide 90 Sr is characterized by greater mobility in soils compared to 137 Cs. The absorption of 90 Sr in soils is mainly due to ion exchange. Most of it lingers in the upper horizons. The speed of its migration along the soil profile depends on the physicochemical and mineralogical characteristics of the soil.

If there is a humus horizon in the soil profile located under a layer of litter or turf, 90 Sr is concentrated in this horizon. In soils such as soddy-podzolic sandy, humus-peaty-gley loamy on sand, chernozemic-meadow podzolized, leached chernozem, there is a slight increase in the radionuclide content in the upper part of the illuvial horizon.

In saline soils, a second maximum appears, which is associated with lower solubility of strontium sulfate and its mobility. In the upper horizon it is retained in the salt crust. Concentration in the humus horizon is explained by the high humus content, large cation absorption capacity and the formation of low-mobile compounds with soil organic matter.

In model experiments when adding 90 Sr to different soils placed in vegetation vessels, it was found that the rate of its migration under experimental conditions increases with an increase in the content of exchangeable calcium. An increase in the migration ability of 90 Sr in the soil profile with an increase in calcium content was also observed in field conditions. The migration of strontium-90 also increases with increasing acidity and organic matter content.

Forest vegetation plays an important role in the migration of 90Sr. During periods of intense radioactive fallout, trees act as a screen on which radioactive aerosols are deposited. Radionuclides retained by the surface of leaves and needles enter the soil surface with fallen leaves and needles. The characteristics of the forest litter have a significant impact on the content and distribution of strontium-90. In deciduous litters, the 90 Sr content gradually decreases from the top layer to the bottom; in coniferous litters, a significant accumulation of the radionuclide occurs in the lower humified part of the litter.

Table 2 - Formation of strontium 90

When 235 U and 239 Pu are fissioned by thermal neutrons in a reactor, 90 Sr is formed with yields of 5.77 and 2.25%. Significant amounts of 90 Sr (7.4 10 17 Bq) were released into the atmosphere during nuclear weapons testing in 1945-1980. .

When released, most of the radionuclides enter the stratosphere (the layer of the atmosphere lying at an altitude of 10-50 km) and remain there for many months, slowly descending and dispersing over the entire surface globe. The half-life of 89 Sr is 50.5 days, and when it enters the stratosphere during nuclear explosions, it mainly decays there, not presenting such a great radiation hazard to earthlings as 90 Sr and 137 Cs, which, when they fall out, pollute the surface of the Earth for many years.

On the other hand, in case of accidents at nuclear reactors, such as at the Chernobyl nuclear power plant, when the accumulated equilibrium activity of 89 Sr is 10 times higher than the activity of 90 Sr, which, due to its long half-life, does not have time to accumulate during 2-3 years of reactor operation, the situation is changing. Immediately after the Chernobyl accident, the activity of the released short-lived radionuclides 89 Sr was many times higher than 90 Sr or 137 Cs.

After nuclear weapons testing, radioactive fallout consists mainly of water-soluble and ion-exchangeable forms of 90 Sr, while after the Chernobyl accident, 90 Sr was often deposited in the forms of stable compounds.

During the operation of a nuclear power plant, 90 Sr, like 137 Cs, released into the environment ultimately accumulates either in the upper layers of soil in terrestrial systems or in bottom sediments of natural water reservoirs. In this case, strontium migrates over very short distances, for example, 1 cm over several years.

Conducted in the late 1980s. Studies of unplowed areas in Kyshtym, contaminated in 1957 with 90 Sr and other radionuclides from a waste explosion, showed that 90 Sr during this period of time reached a depth of 15 cm, which means that its migration rate was 0.5 cm/g. From the soil through root system 90 Sr is carried into plants and is included in grains, beans, carrots and other products. This removal is determined by the transfer coefficient (TC), which depends on the type of soil and pH of the environment.

In order to reduce the removal of 90 Sr from the soil to plants, soil plowing and fertilizer application are used.

The most effective is deep plowing, which leads to the burying of activity below the layer in which the plant roots are located. In areas of the Southern Urals contaminated with 90 Sr after the accident in Kyshtym, good results when plowing to a depth of 50 cm. From the data in the table it follows that an effective measure, along with the application of N, P and K fertilizers, is liming the soil.

Table 3 - Some characteristic values of the CP of 90 Sr from soil to plant (Bq kg-1 dry crop/Bq kg-1 dry soil) (Explanation: CP is given for the top layer 20 cm deep, and values for grasses are given for the top layer soil depth 10 cm)

Table 4 - Effect of agricultural countermeasures on the uptake of 90 Sr by meadow plants in the vicinity of Gomel (Belarus)

Radioactive strontium enters the human body through the gastrointestinal tract, lungs and skin. Soluble strontium compounds are well absorbed from the gastrointestinal tract, the resorption value is 0.1-0.6, and resorption is less than 0.01 for poorly soluble compounds. Strontium is quickly absorbed from the lungs. 5 minutes after intratracheal administration in an amount of 1.48 · 10 4 Bq/g, 33.3% of the administered amount remains in the lungs, after 24 hours - 0.39%. When strontium isotopes are applied to the skin in an amount of 2.4 · 10 5 Bq/cm 2, activity is detected immediately after contamination of the skin surface.

During strontium resorption from the gastrointestinal tract important have diet, chemical compound of radionuclide and physiological factors (age, lactation and pregnancy, state of mineral metabolism, nervous and endocrine systems). The amount of radionuclide absorption from the gastrointestinal tract decreases with increasing age, with increasing calcium and phosphorus content in the diet, and with the administration of high doses of thyroxine. Taking sodium alginate 20 minutes before the administration of strontium reduces its content in the blood by 8-10 times, and lactose, lysine and arginine, on the contrary, double the amount of strontium absorption from the gastrointestinal tract.

Regardless of the route and frequency of soluble compounds of radioactive strontium entering the body, it selectively accumulates in the skeleton, and less than 1% is retained in soft tissues. After intravenous administration of radioactive strontium into the human body, after 100 days, 20% of the injected amount will remain in it, while in monkeys it is 47%, and in rabbits it is 7.5%. The proportion of strontium deposits in the skeleton depends on the route of its entry. With intratracheal entry, 76% is deposited, inhalation - 31.6%, intra-abdominal - 81.2% and cutaneous - only 7? .

In experiments on animals, it was established that when radioactive strontium was administered intramuscularly or orally to females at different stages of pregnancy, most of it (50-70) was deposited in the fetuses in last days pregnancy. Distribution of radioactive strontium in different parts the same bone and in different bones unevenly. Strontium is deposited in areas of bones that have the largest growth zone, where enhanced bone formation occurs.

Taking into account the function of retention and excretion of 90 Sr through the kidneys, Abramov and Golutvina calculated the dose from these radionuclides on the bone surface with single and chronic administration of radionuclides in an amount of 37 kBq/day. The table shows that with a single administration of strontium radionuclides, the total dose from 89 Sr after several half-lives of this nuclide practically does not increase, and the dose from 90 Sr, due to the sum of small decay constants and biological removal, continuously increases.

Table 5 - Estimated dose on the bone surface during single and chronic administration of radionuclides 89 Sr and 90 Sr into the body in an amount of 37 kBq/day.

Time after administration, days.	Dose from 89 Sr, mSv	Dose from 90 Sr, mSv
Single administration





Chronic administration

An age-related model for the deposition of strontium and other alkaline earth elements in human bones across the entire age range, starting from birth, has been proposed. It has been shown that the expected equivalent doses to the bone marrow upon intake of 90 Sr in the first months after birth are an order of magnitude higher than those upon entry into the body of an adult.

Strontium is excreted from the body of humans and animals through both feces and urine. When taken orally, most of the strontium is excreted in the feces. Over 8 days, the total excretion of 89 Sr is 77.9%, of which 5% is in the urine.

Several half-lives of 90 Sr from the body have been established. A short half-life (2.5-8.5 days) characterizes the removal of strontium from soft tissues, a long period (90-154 days) - mainly from bones. With long-term oral or parenteral administration of 90 Sr to the body, the half-life from the skeleton increases significantly, and the initial short half-life is absent or very short. In humans and animals, after a single oral intake of strontium radionuclides in milk during lactation, from 0.04 to 4% per 1 liter of milk from the administered radionuclide is released; with chronic intake of 90 Sr into the body with milk, 0.05-6.3% per 1 liter is released in relation to the daily norm.

The administration of acutely effective amounts of 90 Sr causes the development of typical acute radiation pathology. There are pronounced changes in the peripheral blood: leukopenia, lymphopenia, neutropenia, reticulopenia. Changes in red blood, acceleration of the erythrocyte sedimentation reaction, slowing of blood clotting and an increase in plasma volume are observed.

In dogs that received 0.74 kBq/kg of 90 Sr daily in food for 3-3.5 years, disturbances in carbohydrate metabolism, changes in the secretory and excretory functions of the liver and kidneys were revealed. Smaller amounts of 90 Sr (0.675 kBq/kg) did not lead to significant functional changes in their body, however, over 9-13 years, 80% of the dogs from the experimental group died, and 11% from the control group.

Long-term administration of 90 Sr to dogs with food (0.74-0.074 kBq/kg) and accumulation of the total absorbed dose in the skeleton up to 3.6-9.0 Gy leads to an increase in the occurrence of benign and malignant tumors of soft tissues (in 3-5 times more often than control animals). Chronic administration of 90 Sr to these animals (0.74 kBq/kg per day for 3 years), creating a tissue dose rate in the skeleton of up to 1.5 Gy/g, can cause the development of leukemia and osteosarcoma. With chronic administration of 10 times smaller quantities of this radionuclide (absorbed dose in the skeleton up to 0.5 Gy/g), disturbances in the development of the offspring and a decrease in their viability are observed.

The radioactivity of 90 Sr is determined by its daughter 90 Y, which precipitates in the form of oxalates. 90 Y is isolated from food products by extraction with methylphosphonic acid monoisooctyl ester. 90 Y is extracted from bone tissue ash with tributyl phosphate. Activity is measured using a low-background setup. Determination of 89 Sr in food products, vegetation and bone tissue is based on the precipitation of strontium with fuming nitric acid followed by measurement of activity. When radioactive strontium isotopes come into contact with open areas skin decontamination is carried out with a 5% solution of pentacin, a 5% solution of Na 2 (EDTA) or a 2% solution of hydrochloric acid, as well as detergent powders. If strontium radionuclides enter the gastrointestinal tract, take orally the drug "Adsorbar" or barium sulfate (25 g with 200 ml of water), sodium or calcium alginate (15 g with 200 ml of water) or the drug "Polysurmin" (4 g with 200 ml of water). Emetics are used and extensive gastric lavage is performed. After cleansing the stomach, adsorbents with saline laxatives are reintroduced. In case of damage from dust products, the nasopharynx and oral cavity are washed abundantly, expectorants and diuretics are used.

In accordance with NRB-99, the permissible concentration of 90 Sr in the air of working premises is approximately 24 times lower than 89 Sr, which indicates its exceptional radiation hazard. For the population, the permissible concentration of 90 Sr in the atmospheric air is regulated (NRB-99) by a value equal to 2.7 Bq/m 3, which is beyond the sensitivity of most methods for isolating and measuring the radioactivity of this radionuclide.

Table 6 - GWP, e, DOA in the air of working premises depending on chemical compounds and nuclear physical properties of radionuclides 89 Sr and 90 Sr, MSUA and MZA of these isotopes in the workplace

Table 7 - DOA in air, e, GWP with air, water and food of radionuclides 89 Sr and 90 Sr and hydrocarbons when supplied with water for the population

Research has established that 80-90% of radionuclides are concentrated in the active zone where the bulk of the roots of agricultural crops are located. On lands uncultivated after the Chernobyl disaster, almost all radionuclides are located in the upper part (up to 10-15 cm) of humus horizons, and on arable soils radionuclides are distributed relatively evenly throughout the entire depth of the cultivated layer. Calculations show that in the near future, self-purification of the root layer of contaminated soils due to the vertical migration of radionuclides will be insignificant.

At the same time, processes of local secondary contamination of agricultural soils due to horizontal migration of radionuclides due to wind and water erosion are observed. The content of cesium-137 in the arable horizon of various relief elements of slope lands as a result of water erosion on crops of annual crops over nine years was redistributed up to 1.5-3.0 times.

The increase in the density of soil contamination with cesium-137 in the accumulation zone (lower parts of slopes and depressions) compared to the washout zone averaged from 13% with annual soil washout of less than 5 t/ha to 75% with washout of 12-20 t/ha. On permanent crops of perennial grasses, no solid runoff was observed, and no significant differences in the density of soil contamination among slope elements were established. As a result of wind erosion of drained peat-bog and sandy soils used for sowing annual crops, local differences in the density of contamination of the arable horizon with radiocesium reached 1.5-2.0 times. This emphasizes the need to protect soils from water and wind erosion, which also reduces the loss of the humus layer and reduces the likelihood of product contamination in local areas of land.

Thus, radioactive isotopes do not cause noticeable damage to plant organisms, but they accumulate in significant quantities in agricultural crops.

The main radionuclides that determine the nature of pollution in our region are cesium - 137 and strontium - 90, which are sorted differently by the soil. The main mechanism for the fixation of strontium in the soil is ion exchange, cesium - in the exchange form or by the type of ion exchange sorption on the inner surface of soil particles.

The absorption of strontium by soil is 90 less than that of cesium - 137, and therefore it is a more mobile radionuclide.

At the moment of release of cesium-137 into the environment, the radionuclide is initially in a highly soluble state (vapor-gas phase, fine particles, etc.)

A greater retention of radioisotopes in the soil is facilitated by the presence in it of chemical elements similar in chemical properties to these isotopes. Thus, calcium is a chemical element similar in its properties to strontium-90 and the addition of lime, especially on soils with high acidity, leads to an increase in the absorption capacity of strontium-90 and a decrease in its migration. Potassium is similar in its chemical properties to cesium - 137. Potassium, as a non-isotopic analogue of cesium, is found in the soil in macro quantities, while cesium is in ultra micro concentrations. As a result, microquantities of cesium-137 are strongly diluted in the soil solution by potassium ions, and when they are absorbed by plant root systems, there is competition for the sorption site on the root surface. Therefore, when these elements enter from the soil, antagonism of cesium and potassium ions is observed in plants.

In addition, the effect of radionuclide migration depends on meteorological conditions (amount of precipitation).

The accumulation (removal) of radionuclides by agricultural plants largely depends on the properties of the soil and the biological characteristics of the plants. On acidic soils, radionuclides enter plants in much larger quantities than from slightly acidic soils. A decrease in soil acidity, as a rule, helps to reduce the size of the transfer of radionuclides into plants. Thus, depending on the properties of the soil, the content of strontium - 90 and cesium - 137 in plants can vary on average by 10 - 15 times.

The entry of strontium-90 and cesium-137 into grass in meadows and pastures is determined by the nature of distribution in the soil profile.

Floodplain vegetation accumulates cesium-137 to a greater extent than upland vegetation. So, when the floodplain was polluted, 2.4 Ci/km 2 was found in the grass

Ki/kg of dry mass, and on the dry land with pollution of 3.8 Ci/km 2 the grass contained Ki/kg.

It is noted that calcium-loving plants usually absorb more strontium - 90 - than calcium-poor plants. Legumes accumulate the most strontium - 90%, root and tuber crops less, and cereals even less.

The accumulation (removal) of radionuclides by agricultural plants largely depends on the properties of the soil and the biological ability of the plants.

Radioactive strontium can enter plants in two ways: aerial, through the aboveground organs of plants, and root.

The proportion of radionuclides deposited on the surface of plants during aerial entry per unit area, out of the total amount that fell on this area, is called primary retention. Not only different types of plants, but also different organs and parts of plants have different abilities to retain radionuclides fallen from the atmosphere. Filed by B.N. Annenkova and E.V. Yudintseva (1991), the primary retention of an aqueous solution of 90 8 g by spring wheat was: for leaves - 41%, for stems - 18, for chaff - 11 and for grain - 0.5%. Such a high retention capacity is due to the fact that radionuclides in precipitation are in very low concentrations (ultramicroconcentrations) and under such conditions are quickly and completely sorbed on most surfaces, including the leaf surface. However, this is only possible in the case of precipitation of water-soluble forms of radionuclides and does not apply to contamination with solid dust particles, such as fuel. The time it takes for half of the retained radionuclides to be removed by rain and wind is s herbaceous plants for temperate climate zones it is approximately 1-5 weeks.

908g is not only sorbed on the surface of plants, but can also partially penetrate into the tissues of above-ground organs. However, despite the fact that strontium is an analogue of calcium, necessary for plant metabolism, these processes occur slowly, and their intensity is much lower than with aerial intake of 137 C5.
908g is characterized by high mobility in the soil-plant system. At the same pollution density, the intake of 90 8g from soils into plants is on average 3-5 times higher than 137 Cs, although when these radionuclides enter plants from aqueous solutions, 137 Cs turns out to be more mobile. The main reason These differences are the nature of the interaction of radionuclides with soil - 137 Cs is to a greater extent sorbed in the soil non-exchangeably, while 90 8g is found in the soil mainly in exchangeable forms.

Root intake of 90 8g depends on the properties of soils and biological characteristics of plants and varies within very wide limits: accumulation coefficients (Kn) can vary by 30-400 times. On different types of soils, Kn 90 8g varies for the same crop from 5 to 15 times. In general, the greater the absorption capacity of soils, the higher the content of organic matter, the heavier the mechanical composition of the soil and the mineral part is well represented by clay minerals with high absorption capacity, the lower the coefficients of transfer of 90 8g from soil to plants. The maximum accumulation coefficients are observed on peat soils and mineral soils of light mechanical composition - sandy and sandy loam, and the minimum - on fertile heavy loamy and clayey soils (gray forest and chernozems). Increased transfer of radionuclide into crop yields is facilitated by soil waterlogging.

Among many soil properties, acidity and exchangeable calcium content have the main influence on the supply of 90 8g to plants. With increasing acidity, the intensity of radionuclides entering plants increases by 1.5-3.5 times. With an increase in the content of exchangeable calcium, the accumulation of 90 8g in plants, on the contrary, decreases.

On carbonate soils, non-exchangeable fixation of 90 8g occurs, and this leads to a decrease in its accumulation in plants by 1.1-3 times. For example, in carbonate chernozem, compared to leached soil, the content of water-soluble 90 8 g is 1.5-3 times lower and the amount of non-exchangeable 90 8 g is 4-6% higher.

The rate of transfer of 90 8g in the “soil-plant” link and further along trophic chains depends on the content of the accompanying carriers: isotopic (stable strontium) and non-isotopic (stable calcium). In this case, the role of calcium for radionuclide transport is more important than strontium, since the amount of the former is significantly greater than the latter. For example, the concentration of stable strontium in the soil is on average 2-3 10 _3%, and calcium - about 1.4%.

To assess the movement of radioactive strontium in biological objects, the ratio of the content of 90 8g to Ca is used, which is usually expressed in strontium units(s.e.).

1 s.e. = 37 mBq 90 8g/g Ca.

The ratio of strontium units in plants to strontium units in soil is called discrimination coefficient(CD):

KD = s.e. in plant/s.e. in the soil.

Discrimination of strontium and calcium in relation to each other does not occur when the number of atoms is 90 8g and calcium passes from the soil to the plants in the same ratio. However, quite often, when moving 90 8g from one unit to another, a decrease in its content relative to calcium is observed. In this case, they talk about discrimination of strontium in relation to calcium. In the most

more typical soils in the middle zone of the European part of the Russian Federation, the discrimination coefficient ranges from 0.4 to 0.9 for vegetative organs of plants and from 0.3 to 0.5 for grain (Table 5.15; Korneev, 1972; Russell, 1971).

Table 5.15

Average Discrimination Coefficient (CD)

The ratio of 90 8g to calcium in grain is always less than in straw, and in beet and carrot leaves it is less than in root vegetables. On soils rich in exchangeable calcium, the discrimination coefficient is usually higher than on soils low in calcium, which is due to the competition of these elements when entering plants. This is important to consider when growing fodder crops, since the feed should not only contain a low content of radioactive strontium, but also high content calcium, which prevents the entry of 90 Bg into the body of animals.

The accumulation of 90 Bg in plants is influenced by their biological features. Depending on the type of plant, the accumulation of 90 8g in biomass can differ from 2 to 30 times, and depending on the variety - from 1.5 to 7 times.

The minimum accumulation of 90 8 g occurs in grain and potato tubers, the maximum in legumes and leguminous crops. If we compare the accumulation coefficients of 90 Bg in cereals and legumes, then in legumes they will be significantly higher (Table 5.16).

Table 5.16

Transfer coefficients of 90 Bg to various agricultural crops on soddy-podzolic sandy loam soils (Bq/kg)/(kBq/m2)

90 8g accumulates mainly in the vegetative organs of plants. There is always much less of it in grains, seeds and fruits than in other organs. Moreover, strontium predominantly accumulates not in the roots, but in aboveground parts plants.

In descending order of 90 Bg concentration, field crops are distributed as follows:

cereals, legumes and pulses: spring rape > lupine > peas > vetch > barley > spring wheat > oats > winter wheat> winter rye;
green mass: legumes, perennial grasses > cereal-grain legume grass mixtures > clover > lupine > perennial legume-cereal mixtures > peas > perennial cereal grasses > vetch >

> spring rape > pea-oat mixture > vetch-oat mixture >

> corn;

Natural cenoses: forbs > sedges > grass-forbs > forbs-cereals > cereals > meadow bluegrass > hedgehog grass.

The concentration of radioactive strontium in crops depends on the calcium content of plants. From the table 5.17 (Marakushkin, 1977, cited from: Priester, 1991) it is clear that the higher the calcium content in the culture, the more 90 8g accumulates in them.

Table 5.17

(field experiment with constant level of soil contamination)

The distribution of the plant root system also affects the accumulation of 90 8g. For example, such dense bush grasses as fescue and bluegrass accumulate 90 8g, 1.5-3.0 times more than rhizomatous grasses - creeping wheatgrass and awnless brome. This is due to the fact that in densely bushy cereals the tillering node is located on the soil surface and the young roots that form end up in the uppermost contaminated soil layer. In rhizomatous cereals, the tillering node and, accordingly, new roots are formed at a depth of 5-20 cm, where the content of 908g in natural ecosystems is much lower. Crops with a shallow distribution of the root system are always more contaminated with radionuclide.

Grasses from natural meadows have higher concentrations of 90 8 g in biomass than sown grasses, which is explained by the greater mobility of the radionuclide in the upper turf soil horizon, where it is in a form more accessible to plants than in mineral soil horizons.

in forest ecosystems. In case of aerial pollution of forest ecosystems, 90 8g remains firmly fixed in the outer integument for a long time woody plants. It is characterized by low mobility and, when foliar contamination occurs, practically does not move through the tissues and pathways of plants.

However, the accumulation of 90 8g through the roots, in contrast to assimilation through the leaves, is much more pronounced in both woody and herbaceous vegetation. Over time, this leads to a noticeable accumulation of radiostrontium in all parts of plants, including wood. U coniferous species In trees, the accumulation of radionuclides due to root entry is noticeably weaker than in deciduous trees. The most significant amount of 90 8g is absorbed by aspen, mountain ash, brittle buckthorn, willows, and common hazel. A higher accumulation of 90 8g compared to |37 Cs is also typical for spruce, oak, maple, birch, and linden.

The ratio of 90 8g: 137 C5 in wood changes significantly over time, from 0.2-0.7 during aerial pollution to 6-7 with a predominance of root input. This is due to the fact that |37 Cs, in contrast to 90 8g, moves more easily through plant organs after reaching the surface of leaves than through roots, since it is firmly sorbed by the soil. 90 8g is found in the soil at more accessible form. Thus, it is noted that 5-7 years after the contamination of the forests of the Chernobyl zone, the content of 90 Bg in wood increased by 5-15 times compared to the first year (Klekovkin, 2004). Root absorption of 90 8g is enhanced on hydromorphic soils.