Heavy metals are environmental pollutants. Soil contamination with heavy metals

Soil pollution according to the size of the zones is divided into background, local, regional and global. Background pollution is close to its natural composition. Local soil pollution is considered to be near one or more sources of pollution. Regional pollution is considered when pollutants are transported up to 40 km from the source of pollution, and global pollution is when the soils of several regions are polluted.

According to the degree of contamination, soils are divided into highly polluted, moderately polluted, and slightly polluted.

In heavily contaminated soils, the amount of pollutants is several times higher than the maximum permissible concentration. They have a range of biological productivity and significant changes in physicochemical, chemical and biological characteristics, as a result of which the content of chemicals in grown crops exceeds the norm. In moderately contaminated soils, the excess of the MPC is insignificant, which does not lead to noticeable changes in its properties.

In lightly contaminated soils, the content of chemicals does not exceed the maximum permissible concentration, but exceeds the background.

Land pollution depends mainly on the class hazardous substances that enter the soil:

Class 1 - highly hazardous substances;

Class 2 - moderately hazardous substances;

Class 3 - low-hazard substances.

The hazard class of substances is established according to indicators.

Table 1 - Indicators and classes of hazardous substances

Soil contamination with radioactive substances is mainly due to atmospheric testing of atomic and nuclear weapons, which has not been stopped by individual states to this day. Falling out with radioactive fallout, 90 Sr, 137 Cs and other nuclides, entering plants, and then into food and the human body, cause radioactive contamination due to internal irradiation.

Radionuclides are chemical elements capable of spontaneous decay with the formation of new elements, as well as formed isotopes of any chemical elements. Chemical elements capable of spontaneous decay are called radioactive. The most commonly used synonym for ionizing radiation is radioactive radiation.

Radioactive radiation is a natural factor in the biosphere for all living organisms, and living organisms themselves have a certain radioactivity. Among biosphere objects, soils have the highest natural degree of radioactivity.

However, in the 20th century, humanity was faced with radioactivity that was prohibitively higher than natural, and therefore biologically anomalous. The first to suffer from excessive doses of radiation were the great scientists who discovered radioactive elements (radium, polonium), the spouses Marie Sklodowska-Curie and Pierre Curie. And then: Hiroshima and Nagasaki, tests of atomic and nuclear weapons, many disasters, including Chernobyl, etc. Vast areas were contaminated with long-lived radionuclides - 137 Cs and 90 Sr. According to current legislation, one of the criteria for classifying territories as a zone of radioactive contamination is that the density of 137 Cs contamination exceeds 37 kBq/m 2 . This excess was established at 46.5 thousand km 2 in all regions of Belarus.

Levels of territorial contamination with 90 Sr above 5.5 kBq/m2 (legally established criterion) were detected on an area of 21.1 thousand km2 in the Gomel and Mogilev regions, which accounted for 10% of the country’s territory. Contamination with isotopes 238,239+240 Pu with a density of more than 0.37 kBq/m 2 (legally established criterion) covered about 4.0 thousand km 2, or about 2% of the territory, mainly in the Gomel region (Braginsky, Narovlyansky, Khoiniki, Rechitsa , Dobrush and Loevsky districts) and Cherikovsky district of the Mogilev region.

Natural decay processes of radionuclides over the 25 years that have passed since Chernobyl disaster, made adjustments to the structure of their distribution across the regions of Belarus. During this period, pollution levels and areas decreased. From 1986 to 2010, the area of territory contaminated with 137 Cs with a density above 37 kBq/m2 (above 1 Ci/km2) decreased from 46.5 to 30.1 thousand km2 (from 23% to 14.5 %). For 90 Sr pollution with a density of 5.5 kBq/m2 (0.15 Ci/km2), this figure decreased - from 21.1 to 11.8 thousand km2 (from 10% to 5.6%) (Table 2).

pollution man-made earth radionuclide

Table 2 - Contamination of the territory of the Republic of Belarus with 137Cs as a result of the disaster at the Chernobyl nuclear power plant (as of January 1, 2012)

	Area of agricultural land, thousand hectares
Contaminated 137 Cs	including pollution density, kBq/m 2 (Ci/km 2)
37+185 (1.0+4.9)	185+370 (5.0+9.9)	370+555 (10.0+14.9)	555+1110 (15.0+29.9)	1110+1480 (30.0+39.9)
Brest
Vitebsk
Gomel
Grodno

Mogilevskaya
Republic of Belarus

The most significant objects of the biosphere, which determine the biological functions of all living things, are soils.

The radioactivity of soils is due to the content of radionuclides in them. A distinction is made between natural and artificial radioactivity.

Natural radioactivity of soils is caused by natural radioactive isotopes, which are always present in varying quantities in soils and soil-forming rocks.

Natural radionuclides are divided into 3 groups. The first group includes radioactive elements - elements all of whose isotopes are radioactive: uranium (238 U, 235 U), thorium (232 Th), radium (226 Ra) and radon (222 Rn, 220 Rn). The second group includes isotopes of “ordinary” elements that have radioactive properties: potassium (40 K), rubidium (87 Rb), calcium (48 Ca), zirconium (96 Zr), etc. The third group consists of radioactive isotopes formed in the atmosphere under action cosmic rays: tritium (3 H), beryllium (7 Be, 10 Be) and carbon (14 C).

According to the method and time of formation, radionuclides are divided into: primary - formed simultaneously with the formation of the planet (40 K, 48 Ca, 238 U); secondary decay products of primary radionuclides (total 45 - 232 Th, 235 U, 220 Rn, 222 Rn, 226 Ra, etc.); induced - formed under the influence of cosmic rays and secondary neutrons (14 C, 3 H, 24 Na). In total there are more than 300 natural radionuclides. The gross content of natural radioactive isotopes mainly depends on the soil-forming rocks. Soils formed on weathering products of acidic rocks contain more radioactive isotopes than those formed on basic and ultrabasic rocks; Heavy soils contain more of them than light soils.

Natural radioactive elements are usually distributed relatively evenly across the soil profile, but in some cases they accumulate in illuvial and gley horizons. In soils and rocks they are present mainly in a tightly bound form.

Artificial radioactivity of soils is caused by the entry into the soil of radioactive isotopes formed as a result of atomic and thermonuclear explosions, in the form of waste from the nuclear industry, or as a result of accidents at nuclear enterprises. The formation of isotopes in soils can occur due to induced radiation. The most common artificial radioactive contamination of soils is caused by the isotopes 235 U, 238 U, 239 Pu, 129 I, 131 I, 144 Ce, 140 Ba, 106 Ru, 90 Sr, 137 Cs, etc.

The environmental consequences of radioactive soil contamination are as follows. Joining in biological cycle, radionuclides enter the human body through plant and animal food and, accumulating in it, cause radioactive exposure. Radionuclides, like many other pollutants, gradually become concentrated in food chains.

From an environmental point of view, the greatest danger is 90 Sr and 137 Cs. This is due to the long half-life (28 years for 90 Sr and 33 years for 137 Cs), high radiation energy and the ability to easily be included in the biological cycle and in food chains. Strontium is close in chemical properties to calcium and is part of bone tissue, and cesium is close to potassium and is involved in many reactions of living organisms.

Artificial radionuclides are fixed mainly (up to 80-90%) in the upper layer of soil: on virgin soil - a layer of 0-10 cm, on arable land - in the arable horizon. The greatest sorption is observed in soils with a high humus content, a heavy granulometric composition, rich in montmorillonite and hydromicas, and a non-leaching type of water regime. In such soils, radionuclides are capable of migration to an insignificant extent. According to the degree of mobility in soils, radionuclides form the series 90 Sr > 106 Ru > 137 Ce > 129 J > 239 Pu. The rate of natural self-purification of soils from radioisotopes depends on the rates of their radioactive decay, vertical and horizontal migration. The half-life of a radioactive isotope is the time required for half the number of its atoms to decay.

Table 3 - Characteristics of radioactive substances

	Kerma is permanent	Gamma constant	Dose coefficient	Half life


			1.28-10 6 years

Manganese






Strontium






Promethium



		138.4 days

Plutonium				2.44 -104 years

Radioactivity in living organisms has a cumulative effect. For humans, the value of LD 50 (lethal dose, irradiation in which causes 50% of the death of biological objects) is 2.5-3.5 Gy.

A dose of 0.25 Gy is considered relatively normal for external irradiation. 0.75 Gy irradiation of the entire human body or 2.5 Gy irradiation of the thyroid gland from radioactive iodine 131 I require measures for radiation protection of the population.

The peculiarity of radioactive contamination of the soil is that the amount of radioactive impurities is extremely small, and they do not cause changes in the basic properties of the soil - pH, ratio of elements mineral nutrition, fertility level.

Therefore, first of all, it is necessary to limit (normalize) the concentrations of radioactive substances coming from the soil into crop products. Since radionuclides are mainly heavy metals, the main problems and ways of rationing, remediation and protection of soils from contamination by radionuclides and heavy metals are largely similar and can often be considered together.

Thus, the radioactivity of soils is due to the content of radionuclides in them. Natural radioactivity of soils is caused by natural radioactive isotopes, which are always present in varying quantities in soils and soil-forming rocks. Artificial radioactivity of soils is caused by the entry into the soil of radioactive isotopes formed as a result of atomic and thermonuclear explosions, in the form of waste from the nuclear industry, or as a result of accidents at nuclear enterprises.

Most often, artificial radioactive contamination of soils is caused by the isotopes 235 U, 238 U, 239 Pu, 129 I, 131 I, 144 Ce, 140 Ba, 106 Ru, 90 Sr, 137 Cs, etc. The intensity of radioactive contamination in a specific area is determined by two factors:

a) the concentration of radioactive elements and isotopes in soils;

b) the nature of the elements and isotopes themselves, which is primarily determined by the half-life.

From an environmental point of view, the greatest danger is 90 Sr and 137 Cs. They are firmly fixed in soils, characterized by a long half-life (90 Sr - 28 years and 137 Cs - 33 years) and are easily included in the biological cycle as elements close to Ca and K. Accumulating in the body, they are constant sources of internal radiation.

In accordance with GOST, toxic chemical elements are divided into hygienic hazard classes. In terms of soils they are:

a) Class I: arsenic (As), beryllium (Be), mercury (Hg), selenium (Sn), cadmium (Cd), lead (Pb), zinc (Zn), fluorine (F);

b) Class II: chromium (Cr), cobalt (Co), boron (B), molybdenum (Mn), nickel (Ni), copper (Cu), antimony (Sb);

c) III class: barium (Ba), vanadium (V), tungsten (W), manganese (Mn), strontium (Sr).

Heavy metals already occupy the second place in terms of danger, behind pesticides and significantly ahead of such well-known pollutants as carbon dioxide and sulfur. In the future, they may become more dangerous than waste from nuclear power plants and solid waste. Heavy metal pollution is associated with their widespread use in industrial production. Due to imperfect purification systems, heavy metals end up in environment, including into the soil, polluting and poisoning it. Heavy metals are special pollutants whose monitoring is mandatory in all environments.

Soil is the main medium into which heavy metals enter, including from the atmosphere and the aquatic environment. It also serves as a source of secondary pollution of surface air and waters that flow from it into the World Ocean. From the soil, heavy metals are absorbed by plants, which then end up in food.

The term “heavy metals,” which characterizes a wide group of pollutants, has recently gained significant popularity. In various scientific and applied works, authors interpret the meaning of this concept differently. In this regard, the amount of elements classified as heavy metals varies widely. Numerous characteristics are used as membership criteria: atomic mass, density, toxicity, prevalence in the natural environment, degree of involvement in natural and man-made cycles.

In works devoted to the problems of soil pollution and environmental monitoring, today more than 40 elements are classified as heavy metals periodic table DI. Mendeleev with an atomic mass of over 40 atomic units: V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, Sn, Hg, Pb, Bi, etc. According to the classification of N. Reimers, metals with density more than 8 g/cm3. In this case, the following conditions play an important role in the categorization of heavy metals: their high toxicity to living organisms in relatively low concentrations, as well as the ability to bioaccumulate and biomagnify. Almost all metals that fall under this definition (with the exception of lead, mercury, cadmium and bismuth, the biological role of which is currently unclear) are actively involved in biological processes and are part of many enzymes.

Heavy metals enter the soil surface in various forms Oh. These are oxides and various salts of metals, both soluble and practically insoluble in water (sulfides, sulfates, arsenites, etc.). In the emissions of ore processing enterprises and non-ferrous metallurgy enterprises - the main source of environmental pollution, heavy metals - the bulk of metals (70-90%) are in the form of oxides. Once on the soil surface, they can either accumulate or dissipate, depending on the nature of the geochemical barriers inherent in the given territory. Distribution of heavy metals in various objects of the biosphere and sources of their entry into the environment (Table 4).

Table 4 - Sources of heavy metals entering the environment

	Natural pollution	Technogenic pollution

	Volcanic eruption, wind erosion.	Extraction and processing of arsenic-containing ores and minerals, pyrometallurgy and production of sulfuric acid, superphosphate; combustion of oil, peat, shale.
	Falling out with precipitation. Volcanic activity.	Ore beneficiation, sulfuric acid production, coal combustion.
		Wastewater from industries: metallurgical, engineering, textile, glass, ceramics and leather. Development of boron-containing ores.
	Widely distributed in nature, making up approximately 0.08% of the earth's crust.	Coal-fired power plants, aluminum and superphosphate fertilizer production.
	It is not found in nature in its elemental state. In the form of chromite it is part of the earth's crust.	Emissions from enterprises that mine, receive and process chromium.
	More than 100 cobalt-containing minerals are known.	Burning in progress industrial production natural and fuel materials.
	Part of many minerals.	Metallurgical process of processing and beneficiation of ores, phosphorus fertilizers, cement production, emissions from thermal power plants.
	Contains 53 minerals.	Emissions from mining industry enterprises, non-ferrous metallurgy, mechanical engineering, metalworking, chemical enterprises, transport, thermal power plants.
	The total world reserves of copper in ores are estimated at 465 million tons. It is part of the Samorodnaya minerals and is formed in the oxidation zone of sulfide deposits. Volcanic and sedimentary rocks.	Non-ferrous metallurgy enterprises, transport, fertilizers and pesticides, welding processes, galvanization, combustion of hydrocarbon fuels.
	Belong to the group of scattered elements. Widely distributed in all geospheres. Contains 64 minerals.	High temperature technological processes. Transportation losses, coal combustion. Every year, 72 kg of zinc falls on 1 km 2 of the Earth's surface with precipitation, which is 3 times more than lead and 12 times more than copper.
	Refers to rare trace elements: found as an isomorphic impurity in many minerals.	Local pollution - emissions from industrial complexes, pollution varying degrees power is thermal power plants, motors.
	A trace element, concentrated in sulfide ores. A small amount is found in native form.	The process of pyrometallurgical production of metal, as well as all processes that use mercury. Combustion of any organic fuel (oil, coal, peat, gas, wood), metallurgical production, thermal processes with non-metallic materials.
	Contained in earth's crust, is part of minerals. It enters the environment in the form of silicate soil dust, volcanic smoke, forest evaporation, sea salt aerosols and meteorite dust.	High temperature process emissions, exhaust gases, wastewater, metal mining and processing, transportation, abrasion and dispersion.

The most powerful suppliers of waste enriched with metals are enterprises for the smelting of non-ferrous metals (aluminum, alumina, copper-zinc, lead-smelting, nickel, titanium-magnesium, mercury), as well as for the processing of non-ferrous metals (radio engineering, electrical engineering, instrument-making, galvanic, etc. .). In the dust metallurgical production, ore processing plants, the concentration of Pb, Zn, Bi, Sn can be increased compared to the lithosphere by several orders of magnitude (up to 10-12), the concentration of Cd, V, Sb - tens of thousands of times, Cd, Mo, Pb, Sn, Zn, Bi, Ag - hundreds of times. Waste from non-ferrous metallurgy enterprises, paint and varnish industry plants and reinforced concrete structures is enriched with mercury. The concentrations of W, Cd, and Pb are increased in the dust of machine-building plants (Table 5).

Table 5 - Main anthropogenic sources of heavy metals

Under the influence of metal-enriched emissions, areas of landscape pollution are formed mainly at the regional and local levels. A significant amount of Pb is released into the environment with vehicle exhaust gases, which exceeds its intake with waste from metallurgical enterprises.

The world's soils are often enriched not only with heavy substances, but also with other substances of natural and anthropogenic origin. Identification of “saturation” of soils with metals and elements E.A. Novikov explained it as a consequence of the interaction between man and nature (Table 6).

The main pollutant of suburban soils in Belarus is lead. Its increased content is observed in the suburban areas of Minsk, Gomel, and Mogilev. Soil contamination with lead at the MPC level (32 mg/kg) and above was noted locally, in small areas, in the direction of the prevailing winds.

Table 6 - Combination of interaction between man and nature

As can be seen from the table, most metals, including heavy ones, are dissipated by humans. The distribution patterns of human-dispersed elements in the pedosphere represent an important and independent direction in soil research. A.P. Vinogradov, R. Mitchell, D. Swain, H. Bowen, R. Brooks, V.V Dobrovolsky. The result of their research was the identification of average concentrations of elements in the soils of individual continents, countries, regions and the world as a whole (Table 7).

In some fields of the Minsk vegetable factory, where solid household waste has been used as fertilizer for a number of years, the lead content reaches 40-57 mg/kg of soil. In the same fields, the content of mobile forms of zinc and copper in the soil is 65 and 15 mg/kg, respectively, with a maximum level for zinc of 23 mg/kg and copper of 5 mg/kg.

Along highways, the soil is heavily contaminated with lead and, to a lesser extent, cadmium. Soil contamination of roadside strips of interstate (Brest - Moscow, St. Petersburg - Odessa), republican (Minsk - Slutsk, Minsk - Logoisk) and local (Zaslavl - Dzerzhinsk, Zhabinka - B. Motykaly) roads is observed at a distance of up to 25-50 m from the road surface, depending on the terrain and the presence of forest protection belts. The maximum lead content in the soil was noted at a distance of 5-10 m from the highway. It is higher than the background value on average by 2-2.3 times, but slightly lower or close to the maximum permissible concentration. The cadmium content in the soils of Belarus is at background levels (up to 0.5 mg/kg). An excess of up to 2.5 times the background was observed locally at a distance of up to 3-5 km from large cities and reaches 1.0-1.2 mg of soil with a MPC of 3 mg/kg for Western European countries (the MPC of cadmium for soils in Belarus has not been developed). The area of soils in Belarus contaminated by various sources lead is currently approximately 100 thousand hectares, cadmium - 45 thousand hectares.

Table 7 - Combination of interaction between man and nature

Elements	Average values (US Soils, X. Shacklett, J. Bornson, 1984)	Average values (Soils of the world, A.P. Vinogradov, 1957)	Elements	Average values (US Soils, J. Borngen, 1984)	Average values (Soils of the world, A.P. Vinogradov, 1957)

Currently, agrochemical mapping is being carried out for copper content in the soils of Belarus, and it has already been established that in the republic 260.3 thousand hectares of agricultural land are contaminated with copper (Table 8).

Table 8 - Agricultural lands of Belarus contaminated with copper (thousand hectares)

The average content of mobile copper in arable soils is low and amounts to 2.1 mg/kg, and in improved hay and pasture lands - 2.4 mg/kg. In general, in the republic, 34% of arable and 36% of hay and pasture lands have a very low supply of copper (less than 1.5 mg/kg) and are in dire need of using copper-containing fertilizers. On soils with excess copper content (3.3% of agricultural land), the use of any form of fertilizer containing copper should be avoided.

Over the almost 30-year period of research into the state of ecosystems contaminated with heavy metals, much evidence has been obtained of the intensity of local soil contamination with metals.

A zone of severe pollution has formed within 3-5 km from the Cherepovets Ferrous Metallurgy Plant (Vologda region). In the vicinity of the Sredneuralsk Metallurgical Plant, pollution by aerosol fallout covered an area of more than 100 thousand hectares, with 2-2.5 thousand hectares completely devoid of vegetation cover. In landscapes exposed to emissions from the Chemkent lead plant, the greatest effect is observed in the industrial zone, where the concentration of lead in the soil is 2-3 orders of magnitude higher than the background one.

There is contamination not only with Pb, but also with Mn, the supply of which is secondary and can be caused by transfer from degraded soil. Soil degradation is observed in contaminated soils in the vicinity of the Electrozinc plant in the foothills North Caucasus. Severe pollution occurs in a 3-5 km zone from the plant. Aerosol emissions from the Ust-Kamenogorsk lead-zinc plant (Northern Kazakhstan) are enriched in metals: until recently, annual emissions of Pb amounted to 730 tons of lead, Zn 370 tons of zinc, 73,000 tons of sulfuric acid and sulfuric anhydride. Aerosol emissions and Wastewater led to the creation of a zone of severe pollution with an excess of the main groups of pollutants, orders of magnitude higher than the background levels of metal content. Soil contamination with metals is often accompanied by soil acidification.

When soils are subject to aerosol pollution, the most important factor, affecting the condition of soils, is the distance from the source of pollution. For example, the maximum contamination of plants and soils with lead coming from vehicle exhaust gases is most often observed in a 100-200-meter zone from the highway.

Impact of aerosol emissions industrial enterprises, enriched with metals, appears most often within a radius of 15-20 km, less often - within 30 km from the source of pollution.

Technological factors such as the height of the emission of aerosols from plant pipes are important. The zone of maximum soil contamination is formed within a distance equal to 10-40 times the height of high and hot industrial emissions and 5-20 times the height of low cold emissions.

Meteorological conditions have a significant influence. In accordance with the direction of the prevailing winds, the area of the predominant part of contaminated soils is formed. The higher the wind speed, the less soil in the immediate vicinity of the enterprise is polluted, and the more intense the transfer of pollutants. The highest concentrations of pollutants in the atmosphere are expected for low cold emissions at a wind speed of 1-2 m/s, for high hot emissions - at a wind speed of 4-7 m/s. Temperature inversions have an effect: under inversion conditions, turbulent exchange is weakened, which impairs the dispersion of emission aerosols and leads to pollution in the impact zone. Air humidity has an effect: at high humidity, the dispersion of pollutants decreases, since during condensation they can pass from a gaseous form into the less migratory liquid phase of aerosols, then they are removed from the atmosphere during the process of deposition. It should be taken into account that the residence time of polluting aerosol particles in a suspended state and, accordingly, the range and speed of their transfer also depend on the physicochemical properties of aerosols: larger particles settle faster than finely dispersed ones.

In the zone affected by emissions from industrial enterprises, primarily non-ferrous metallurgy enterprises, which are the most powerful supplier of heavy metals, the state of the landscape as a whole is changing. For example, the immediate surroundings of a lead-zinc plant in Primorye have turned into a man-made desert. They are completely devoid of vegetation, the soil cover is destroyed, and the surface of the slopes is severely eroded. At a distance of more than 250 m, a sparse forest of Mongolian oak has been preserved without admixture of other species; the grass cover is completely absent. In the upper horizons of the brown forest soils common here, the content of metals exceeded the background levels and clarke by tens and hundreds of times.

Judging by the content of metals in the composition of the 1N extract. HNO 3 from these contaminated soils; the main part of the metals in them is in a mobile, loosely bound state. This is a general pattern for contaminated soils. In this case, this led to an increase in the migration ability of metals and an increase in the concentration of metals in lysimetric waters by orders of magnitude. The emissions from this non-ferrous metallurgy enterprise, along with the enrichment of metals, had an increased content of sulfur oxides, which contributed to the acidification of sediments and soil acidification, their pH decreased by one.

In contrast, in fluoride-contaminated soils, soil pH levels increased, which contributed to increased mobility. organic matter: the oxidation of water extracts from soils contaminated with fluorides has increased several times.

Metals entering the soil are distributed between the solid and liquid phases of the soil. Organic and mineral components of soil solids retain metals through different mechanisms with varying strengths. These circumstances have important environmental significance. The ability of contaminated soils to influence the composition and properties of water, plants, air, and the ability of heavy metals to migrate depends on how much metals are absorbed by soils and how firmly they are retained. The buffering capacity of soils in relation to pollutants and their ability to perform barrier functions in the landscape depend on these same factors.

Quantitative indicators of the absorption capacity of soils for various chemical substances are most often determined in model experiments, bringing the studied soils into interaction with various doses of controlled substances. Possible different variants setting up these experiments in field or laboratory conditions.

Laboratory experiments are carried out under static or dynamic conditions, bringing the soil under study into interaction with solutions containing variable concentrations of metals. Based on the experimental results, metal sorption isotherms are constructed. standard method, analyzing absorption patterns using Langmuir or Freundich equations.

The accumulated experience in studying the absorption of various metal ions by soils with different properties indicates the presence of a number of general patterns. The amount of metals absorbed by the soil and the strength of their retention are a function of the concentration of metals in solutions interacting with the soil, as well as the properties of the soil and the properties of the metal; the experimental conditions also influence. At low loads, the soil is able to absorb pollutants completely due to ion exchange processes and specific sorption. This ability is manifested more strongly the more dispersed the soil is and the higher its content of organic matter. The reaction of soils is no less important: an increase in pH increases the absorption of heavy metals by soils.

Increasing the load leads to a decrease in absorption. The applied metal is not completely absorbed by the soil, but there is a linear relationship between the concentration of the metal in the solution interacting with the soil and the amount of absorbed metal. A subsequent increase in load leads to a further decrease in the amount of metal absorbed by the soil due to the limited number of positions in the exchange-sorption complex capable of exchange and non-exchange absorption of metal ions. The previously observed linear relationship between the concentration of metals in solution and their amount absorbed by solid phases is violated. At the next stage, the ability of the solid phases of the soil to absorb new doses of metal ions is almost completely exhausted; an increase in the concentration of the metal in the solution interacting with the soil practically ceases to affect the absorption of the metal. The ability of soils to absorb heavy metal ions in a wide range of their concentrations in a solution interacting with the soil indicates the polyfunctionality of such a heterogeneous natural body what the soil is, about the variety of mechanisms that ensure its ability to retain metals and protect the environment adjacent to the soil from pollution. But it is obvious that this ability of the soil is not unlimited.

Experimental data make it possible to determine the maximum absorption capacity of soils for metals. As a rule, the amount of absorbed metal ions is significantly less than the cation exchange capacity of soils. For example, the maximum sorption of Cd, Zn, Pb by soddy-podzolic soils of Belarus ranges from 16-43% of the CEC depending on the pH level, humus content and type of metal (Golovaty, 2002). The absorption capacity of loamy soils is higher than that of sandy loam soils, and that of high humus soils is higher than that of low humus soils. The type of metal also influences. The maximum amount of elements absorbed specifically by the soil falls in the series Pb, Cu, Zn, Cd.

Experimentally, it is possible to determine not only the amount of metals absorbed by soils, but also the strength of their retention by soil components. The strength of fixation of heavy metals in soils is determined based on their ability to be extracted from contaminated soils using various reagents. Since the mid-1960s. Many schemes have been proposed for the extraction fractionation of metal compounds from soils and bottom sediments. They are united by a common ideology. All fractionation schemes involve first separating metal compounds retained by the soil into those loosely and firmly bound to the soil matrix. They also suggest, among the tightly bound compounds of heavy metals, to distinguish their compounds presumably associated with the main carriers of heavy metals: silicate minerals, oxides and hydroxides of Fe and Mn, and organic substances. Among loosely bound metal compounds, it is proposed to identify groups of metal compounds retained by soil components due to various mechanisms (exchangeable, specifically sorbed, bound in complexes) (Kuznetsov, Shimko, 1990; Minkina et al. 2008).

The schemes used for the fractionation of metal compounds in contaminated soils with recommended extractants differ. All extractants are proposed on the basis of their ability to transfer the expected group of metal compounds into solution, however, they cannot provide strict selectivity for the extraction of these groups of heavy metal compounds. Nevertheless, the accumulated data on the fractional composition of metal compounds in contaminated soils allows us to identify a number of general patterns.

It has been established for different situations that when soils are contaminated, the ratio of strongly and weakly bound metal compounds changes. One example is the indicators of the state of Cu, Pb, Zn in contaminated ordinary chernozem of the Lower Don.

All soil components showed the ability to retain heavy metals both firmly and weakly. Heavy metal ions are firmly fixed by clay minerals, oxides and hydroxides of Fe and Mn, and organic substances (Minkina et al., 2008). It is important that with an increase in the total content of metals in contaminated soils by 3-4 times, the ratio of metal compounds in them changed towards an increase in the proportion of loosely bound forms. In turn, a similar change in the ratio of their constituent compounds occurred in their composition: the proportion of less mobile ones (specifically sorbed) decreased due to an increase in the proportion of exchangeable forms of metals and those forming complexes with organic substances.

Along with an increase in the total content of heavy metals in contaminated soils, there is an increase in the relative content of more mobile metal compounds. This indicates a weakening of the buffering capacity of soils towards metals and their ability to protect adjacent environments from pollution.

In soils contaminated with metals, the most important microbiological and Chemical properties. The state of microbiocenosis is worsening. On contaminated soils, more resistant species are selected, and less resistant species of microorganisms are eliminated. In this case, new types of microorganisms may appear that are usually absent on uncontaminated soils. The consequence of these processes is a decrease in the biochemical activity of soils. It has been established that in soils contaminated with metals, nitrifying activity decreases, as a result of which fungal mycelium actively develops and the number of saprophytic bacteria decreases. In contaminated soils, the mineralization of organic nitrogen decreases. The influence of metal pollution on the enzymatic activity of soils was revealed: a decrease in urease and dehydrogenase, phosphatase, and ammonifying activity in them.

Metal pollution affects soil fauna and microfauna. When forest cover is damaged, the number of insects (ticks, wingless insects) in the forest floor decreases, while the number of spiders and centipedes may remain stable. Soil invertebrates also suffer, and earthworms often die.

Are getting worse physical properties soil Soils lose their inherent structure, their overall porosity decreases, and water permeability decreases.

The chemical properties of soils change under the influence of pollution. These changes are assessed using two groups of indicators: biochemical and pedochemical (Glazovskaya, 1976). These indicators are also called direct and indirect, specific and nonspecific.

Biochemical indicators reflect the effect of pollutants on living organisms, their direct specific effect. It is caused by the influence of chemicals on biochemical processes in plants, microorganisms, vertebrate and invertebrate inhabitants of the soil. The result of pollution is a decrease in biomass, plant yield and its quality, and possibly death. Soil microorganisms are suppressed, their numbers, diversity, and biological activity decrease. Biochemical indicators of the state of contaminated soils are indicators of the total content of pollutants in them (in this case, heavy metals), indicators of the content of mobile metal compounds, which are directly related to the toxic effect of metals on living organisms.

The pedochemical (indirect, nonspecific) effect of pollutants (in this case, metals) is due to their influence on soil chemical conditions, which, in turn, affect the living conditions in soils of living organisms and their condition. Acid-base, redox conditions, humus status of soils, and ion-exchange properties of soils are of utmost importance. For example, gaseous emissions containing oxides of sulfur and nitrogen, entering the soil in the form of nitric and sulfuric acids, cause a decrease in soil pH by 1-2 units. Hydrolytically acidic fertilizers help lower soil pH to a lesser extent. Soil acidification, in turn, leads to an increase in the mobility of various chemical elements in soils, for example, manganese and aluminum. Acidification of the soil solution contributes to a change in the ratio of various forms of chemical elements in favor of an increase in the proportion of more toxic compounds (for example, free forms of aluminum). A decrease in the mobility of phosphorus in the soil was noted with an excess amount of zinc in it. A decrease in the mobility of nitrogen compounds is the result of a violation of their biochemical activity when soils are polluted.

Changes in acid-base conditions and enzymatic activity are accompanied by a deterioration in the humus state of contaminated soils; a decrease in humus content and a change in its fractional composition are noted. The result is a change in the ion exchange properties of soils. For example, it was noted that in chernozems contaminated by emissions from a copper plant, the content of exchangeable forms of calcium and magnesium decreased, and the degree of soil saturation with bases changed.

The conventionality of such a division of the effects of pollutants on soils is obvious. Chlorides, sulfates, and nitrates have not only a pedochemical effect on soils. They can negatively affect living organisms directly, disrupting the course of biochemical processes in them. For example, sulfates that enter the soil in quantities of 300 kg/ha or more can accumulate in plants in quantities exceeding their permissible level. Soil contamination with sodium fluorides leads to damage to plants both under the influence of their toxic effects and under the influence of the highly alkaline reaction they cause.

Using the example of mercury, let us consider the relationship between natural and man-made metal compounds in various parts of the biogeocenosis, their joint impact on living organisms, including human health.

Mercury is one of the most dangerous metals that pollutes the environment. The global level of annual mercury production is about 10 thousand tons. There are three main groups of industries with high emissions of mercury and its compounds into the environment:

1. Non-ferrous metallurgy enterprises producing metallic mercury from mercury ores and concentrates, as well as by recycling various mercury-containing products;

2. Enterprises in the chemical and electrical industries where mercury is used as one of the elements of the production cycle (for example, during amalgamation, which is associated with the production of mercury and non-ferrous metals);

3. Enterprises mining and processing ores of various metals (in addition to mercury), including through heat treatment of ore raw materials; enterprises producing cement, flux for metallurgy; production processes involving the combustion of hydrocarbon fuels (oil, gas, coal). In general, these are those industries where mercury is an associated component, sometimes even in noticeable quantities.

Enterprises of ferrous metallurgy and the chemical and pharmaceutical industry, production of thermal and electrical energy, production of chlorine and caustic soda, instrument making, extraction of precious metals from ores (for example, gold mining enterprises), etc. also contribute to mercury pollution. In agricultural production, the use of protective equipment control of plants from pests and diseases leads to the spread of mercury-containing compounds.

About half of the mercury produced is lost during mining, processing and use. Mercury-containing compounds enter the environment from gas emissions, wastewater, solid liquid, paste waste. The most significant losses occur during the pyrometallurgical method of its production. Mercury is lost through cinders, waste gases, dust and ventilation emissions. The mercury content in hydrocarbon gases can reach 1-3 mg/m 3, in oil 2-10 -3%. The atmosphere contains a high proportion of volatile forms of free mercury and methylmercury, Hg 0 and (CH 3) 2 Hg.

Having a long lifetime (from several months to three years), these compounds can be transported over long distances. Only a small part of elemental mercury is sorbed on fine dust particles and reaches the earth's surface during the process of dry deposition. About 10-20% of mercury becomes water-soluble compounds and falls out with precipitation, then is absorbed by soil components and bottom sediments.

From the earth's surface, due to evaporation, part of the mercury partially re-enters the atmosphere, replenishing the supply of its volatile compounds.

The peculiarities of the cycle of mercury and its compounds in nature are determined by such properties of mercury as its volatility, stability in the external environment, solubility in precipitation, ability to be sorption by soils and suspended surface water, ability to undergo biotic and abiotic transformations (Kuzubova et al., 2000) . Technogenic releases of mercury disrupt the natural cycle of the metal and pose a threat to the ecosystem.

Among mercury compounds, the most toxic are organic derivatives of mercury, primarily methylmercury and dimethylmercury. Attention to mercury in the environment began in the 1950s. Then the general alarm was caused by the mass poisoning of people living on the shores of Minamata Bay (Japan), whose main occupation was fishing, which was the main product of their diet. When it became known that the cause of the poisoning was pollution of the bay waters with industrial wastewater with high mercury content, mercury pollution of the ecosystem attracted the attention of researchers in many countries.

The mercury content in natural waters is low; the average concentration in the waters of the hypergenesis zone is 0.1 ∙ 10 -4 mg/l, in the ocean - 3 ∙ 10 -5 mg/l. Mercury in waters is present in monovalent and divalent states; under reducing conditions it is in the form of uncharged particles. It is distinguished by its ability to form complexes with various ligands. In waters, hydroxo-, chloride, citric acid, fulvate and other complexes dominate among mercury compounds. Methyl derivatives of mercury are the most toxic.

The formation of methylmercury occurs mainly in water columns and sediments of fresh and marine waters. The supplier of methyl groups for its formation are various organic substances present in natural waters and their destruction products. The formation of methylmercury is ensured by interrelated biochemical and photochemical processes. The progress of the process depends on temperature, redox and acid-base conditions, on the composition of microorganisms and their biological activity. Interval optimal conditions for the formation of methylmercury is quite wide: pH 6-8, temperature 20-70 °C. An increase in the intensity of solar radiation helps to activate the process. The process of mercury methylation is reversible; it is associated with demethylation processes.

The formation of the most toxic mercury compounds is observed in the waters of new artificial reservoirs. They are flooded with masses of organic material, supplying large quantities of water-soluble organic substances, which are included in the processes of microbial methylation. One of the products of these processes is methylated forms of mercury. The end result is an accumulation of methylmercury in the fish. These patterns are clearly evident in young reservoirs of the USA, Finland, and Canada. It has been established that the maximum accumulation of mercury in fish in reservoirs occurs 5-10 years after flooding, and a return to natural levels of their content may occur no earlier than 15-20 years after flooding.

Methyl mercury derivatives are actively absorbed by living organisms. Mercury is characterized by a very high accumulation coefficient. The cumulative properties of mercury are manifested in an increase in its content in the series: phytoplankton-macrophytoplankton-planktivorous fish-predatory fish-mammals. This distinguishes mercury from many other metals. The half-life of mercury from the body is estimated at months and years.

The combination of the high efficiency of assimilation of methylated mercury compounds by living organisms and the low rate of their elimination from organisms leads to the fact that it is in this form that mercury enters the food chain and accumulates maximally in the body of animals.

The greatest toxicity of methylmercury compared to its other compounds is due to a number of its properties: good solubility in lipids, facilitating free penetration into the cell, where it easily interacts with proteins. The biological consequences of these processes are mutagenic, embryotoxic, genotoxic and other dangerous changes in organisms. It is generally accepted that for humans, fish and fish products are the predominant sources of methylmercury. Its toxic effect on the human body manifests itself mainly in damage to the nervous system, areas of the cerebral cortex responsible for sensory, visual and auditory functions.

In Russia in the 1980s, extensive comprehensive research state of mercury in biogeocenosis. This was the area of the Katun River basin, where the construction of the Katun hydroelectric power station was planned. The spread of rocks enriched with mercury in the region caused alarm; mercury mines operated within the deposit. A warning also sounded from the results of studies carried out by that time in different countries, indicating the formation of methylated mercury derivatives in the waters of reservoirs, even in the absence of the spread of ore bodies in the region.

The influence of natural and man-made mercury flows in the area of the proposed construction of the Katunskaya HPP resulted in increased concentrations of mercury in soils. The localization of mercury contamination was also noted in the bottom sediments of the upper part of the Katun River. Several forecasts of the environmental situation in the area of the proposed construction of a hydroelectric power station and the creation of a reservoir were compiled, but due to the ongoing restructuring in the country, work in this direction was suspended.

One of the strongest and most common chemical pollution is heavy metal pollution. Heavy metals include more than 40 chemical elements of the periodic table D.I. Mendeleev, the mass of atoms of which is over 50 atomic units.

This group of elements is actively involved in biological processes, being part of many enzymes. The group of “heavy metals” largely coincides with the concept of “microelements”. Hence lead, zinc, cadmium, mercury, molybdenum, chromium, manganese, nickel, tin, cobalt, titanium, copper, vanadium are heavy metals.

Sources of heavy metals are divided into natural (weathering of rocks and minerals, erosion processes, volcanic activity) and man-made (mining and processing of minerals, fuel combustion, traffic, activities Agriculture). Some of the man-made emissions entering the natural environment in the form of fine aerosols are transported over significant distances and cause global pollution.

The other part enters drainless reservoirs, where heavy metals accumulate and become a source of secondary pollution, i.e. the formation of dangerous pollutants during physical and chemical processes occurring directly in the environment (for example, the formation of poisonous phosgene gas from non-toxic substances). Heavy metals accumulate in the soil, especially in the upper humus horizons, and are slowly removed by leaching, consumption by plants, erosion and deflation - blowing out of soils.

The period of half-removal or removal of half of the initial concentration is a long time: for zinc - from 70 to 510 years, for cadmium - from 13 to 110 years, for copper - from 310 to 1500 years and for lead - from 740 to 5900 years. In the humus part of the soil, the primary transformation of the compounds found in it occurs.

Heavy metals have a high ability for a variety of chemical, physicochemical and biological reactions. Many of them have variable valency and participate in redox processes. Heavy metals and their compounds, like other chemical compounds, are capable of moving and being redistributed in living environments, i.e. migrate.

The migration of heavy metal compounds occurs largely in the form of an organomineral component. Some of the organic compounds with which metals bind are represented by products of microbiological activity. Mercury is characterized by its ability to accumulate in parts of the “food chain” (this was discussed earlier). Soil microorganisms can produce mercury-resistant populations that convert metallic mercury into substances that are toxic to higher organisms. Some algae, fungi and bacteria can accumulate mercury in their cells.

Mercury, lead, cadmium are included in the general list of the most important environmental pollutants, agreed upon by the countries that are members of the UN. Let's take a closer look at these substances.

Heavy metals- a group of chemical elements with the properties of metals (including semimetals) and significant atomic weight or density. There are about forty different definitions of the term heavy metals, and it is impossible to point to one of them as the most accepted. Accordingly, the list of heavy metals according to different definitions will include different elements. The criterion used may be atomic weight over 50, in which case all metals starting with vanadium are included in the list, regardless of density. Another frequently used criterion is a density approximately equal to or greater than the density of iron (8 g/cm3), then such elements as lead, mercury, copper, cadmium, cobalt are included in the list, and, for example, lighter tin falls out of the list. There are classifications based on other values of threshold density or atomic weight. Some classifications make exceptions for noble and rare metals, without classifying them as heavy; some exclude non-ferrous metals (iron, manganese).

Term heavy metals is most often considered not from a chemical, but from a medical and environmental point of view and, thus, when included in this category, not only the chemical and physical properties of the element are taken into account, but also its biological activity and toxicity, as well as the volume of use in economic activities.

In addition to lead, mercury has been studied most fully compared to other microelements.

Mercury is extremely poorly distributed in the earth's crust (-0.1 x 10-4%), but is convenient for extraction, as it is concentrated in sulfide residues, for example, in the form of cinnabar (HgS). In this form, mercury is relatively harmless, but atmospheric processes, volcanic and human activity led to the accumulation of about 50 million tons of this metal in the world's oceans. The natural removal of mercury into the ocean as a result of erosion is 5000 tons/year, and another 5000 tons/year of mercury is carried out as a result of human activity.

Initially, mercury enters the ocean in the form of Hg2+, then it interacts with organic substances and, with the help of anaerobic organisms, turns into toxic substances methylmercury (CH3Hg)+ and dimethylmercury (CH3-Hg-CH3). Mercury is present not only in the hydrosphere, but also in the atmosphere , since it has a relatively high vapor pressure. The natural content of mercury is ~0.003-0.009 μg/m3.

Mercury is characterized by a short residence time in water and quickly passes into sediments in the form of compounds with organic substances found in them. Because mercury is adsorbed by sediment, it can slowly be released and dissolved in water, resulting in a source of chronic pollution that acts long time after the original source of contamination has disappeared.

Global mercury production is currently over 10,000 tons per year, most of which is used in the production of chlorine. Mercury enters the air from the burning of fossil fuels. Analysis of the ice from the Greenland Ice Dome has shown that since 800 AD. until the 1950s, the mercury content remained constant, but since the 50s. this century, the amount of mercury has doubled. Figure 1 shows the paths of cyclic migration of mercury. Mercury and its compounds are dangerous to life. Methylmercury is especially dangerous for animals and humans, as it quickly passes from the blood into the brain tissue, destroying the cerebellum and cerebral cortex. Clinical symptoms of such a lesion are numbness, loss of orientation in space, loss of vision. Symptoms of mercury poisoning do not appear immediately. To others unpleasant consequence Methylmercury poisoning is the penetration of mercury into the placenta and its accumulation in the fetus, and the mother does not experience pain. Methylmercury has a teratogenic effect in humans. Mercury belongs to hazard class I.

Mercury metal is dangerous if it is swallowed or its vapors are inhaled. In this case, a person develops a metallic taste in the mouth, nausea, vomiting, abdominal cramps, teeth turn black and begin to crumble. Spilled mercury scatters into droplets and, if this happens, the mercury must be carefully collected.

Inorganic mercury compounds are practically non-volatile, so the danger is when mercury enters the body through the mouth and skin. Mercury salts corrode the skin and mucous membranes of the body. The ingestion of mercury salts into the body causes inflammation of the pharynx, difficulty swallowing, numbness, vomiting, and abdominal pain.

In an adult, ingestion of about 350 mg of mercury can cause death.

Mercury pollution can be reduced by banning the production and use of certain products. There is no doubt that mercury pollution will always be a pressing problem. But with the introduction of strict control over industrial waste containing mercury, as well as food products you can reduce the risk of mercury poisoning.

Every year, about 180 thousand tons of lead migrate around the world as a result of atmospheric processes. During the mining and processing of lead ores, more than 20% of lead is lost. Even at these stages, the release of lead into the environment is equal to the amount that enters the environment as a result of the impact of atmospheric processes on igneous rocks.

The most serious source of lead pollution in the habitat of organisms is exhaust from automobile engines. The antiknock agent tetramethyl - or tetraethyl swinep - has been added to most gasolines since 1923 in an amount of about 80 mg/l. When a car is driven, from 25 to 75% of this lead is released into the atmosphere, depending on driving conditions. The bulk of it settles on the ground, but a noticeable part of it remains in the air.

Lead dust not only covers the sides of highways and the soil in and around industrial cities, it is also found in the ice of Northern Greenland, and in 1756 the lead content in ice was 20 µg/t, in 1860 it was already 50 µg/t, and in 1965 - 210 µg/t.

Active sources of lead pollution include power plants and household coal-fired furnaces.

Sources of lead contamination in the home may include glazed pottery; lead contained in coloring pigments.

Lead is not vital necessary element. It is toxic and belongs to hazard class I. Its inorganic compounds disrupt metabolism and are enzyme inhibitors (like most heavy metals). One of the most insidious consequences of the action of inorganic lead compounds is considered to be its ability to replace calcium in the bones and be a constant source of poisoning for a long time. The biological half-life of lead in bones is about 10 years. The amount of lead accumulated in the bones increases with age, and at 30-40 years of age in persons whose occupation is not associated with lead contamination, it is 80-200 mg.

Organic lead compounds are considered even more toxic than inorganic lead compounds.

Cadmium, zinc and copper are the most important metals when studying pollution problems, as they are widespread in the world and have toxic properties. Cadmium and zinc (as well as lead and mercury) are found mainly in sulfide sediments. As a result of atmospheric processes, these elements easily enter the oceans.

About 1 million kg of cadmium enters the atmosphere annually as a result of the activities of its smelting plants, which accounts for about 45% of the total pollution with this element. 52% of contaminants come from burning or recycling products containing cadmium. Cadmium has relatively high volatility, so it easily penetrates into the atmosphere. The sources of air pollution with zinc are the same as those with cadmium.

Cadmium enters natural waters as a result of its use in galvanic processes and equipment. The most serious sources of zinc pollution in water are zinc smelters and electroplating plants.

Fertilizers are a potential source of cadmium contamination. In this case, cadmium is introduced into plants consumed by humans as food, and at the end of the chain passes into the human body. Cadmium and zinc easily enter seawater and the ocean through the surface and groundwater networks.

Cadmium and zinc accumulate in certain animal organs (especially the liver and kidneys).

Zinc is the least toxic of all the above heavy metals. However, all elements become toxic if found in excess; zinc is no exception. The physiological effect of zinc is its action as an enzyme activator. In large quantities it causes vomiting, this dose is approximately 150 mg for an adult.

Cadmium is much more toxic than zinc. It and its compounds belong to hazard class I. It penetrates the human body over a long period. Inhalation of air for 8 hours at a cadmium concentration of 5 mg/m3 can lead to death.

With chronic cadmium poisoning, protein appears in the urine and blood pressure rises.

When studying the presence of cadmium in food products, it was revealed that the excretions human body rarely contain as much cadmium as was absorbed. There is currently no consensus on the acceptable safe content of cadmium in food.

One of the effective ways to prevent the entry of cadmium and zinc in the form of pollution is to introduce controls on the content of these metals in emissions from smelters and other industrial enterprises.

In addition to the metals discussed earlier (mercury, lead, cadmium, zinc), there are other toxic elements whose entry into the habitat of organisms as a result of human activities is of serious concern.

Antimony is present along with arsenic in ores containing metal sulfides. World antimony production is about 70 tons per year. Antimony is a component of alloys, is used in the production of matches, and in its pure form is used in semiconductors.

The toxic effect of antimony is similar to arsenic. Large amounts of antimony cause vomiting; with chronic antimony poisoning, digestive tract upset occurs, accompanied by vomiting and a decrease in temperature. Arsenic occurs naturally in the form of sulfates. Its content in lead-zinc concentrates is about 1%. Due to its volatility, it easily enters the atmosphere.

The strongest sources of pollution with this metal are herbicides (chemicals to control weeds), fungicides (substances to control fungal diseases plants) and insecticides (substances used to control harmful insects).

According to its toxic properties, arsenic is an accumulating poison. Based on the degree of toxicity, a distinction should be made between elemental arsenic and its compounds. Elemental arsenic is relatively little toxic, but has teratogenic properties. The harmful effects on hereditary material (mutagenicity) are disputed.

Arsenic compounds are slowly absorbed through the skin and quickly absorbed through the lungs and gastrointestinal tract. Lethal dose for humans - 0.15-0.3 g. Chronic poisoning causes nervous diseases, weakness, numbness of the limbs, itching, darkening of the skin, bone marrow atrophy, liver changes. Arsenic compounds are carcinogenic to humans. Arsenic and its compounds belong to hazard class II.

Cobalt is not widely used. For example, it is used in the steel industry and in the production of polymers. When ingested in large quantities, cobalt negatively affects the hemoglobin content in human blood and can cause blood diseases. Cobalt is believed to cause Graves' disease. This element is dangerous to the life of organisms due to its extremely high reactivity and belongs to hazard class I.

Copper is found in sulfide sediments along with lead, cadamium and zinc. It is present in small quantities in zinc concentrates and can be transported over long distances in air and water. Abnormal copper content is found in plants with air and water. Abnormal copper levels are found in plants and soils more than 8 km from the smelter. Copper salts belong to hazard class II. The toxic properties of copper have been studied much less than the same properties of other elements. The absorption of large amounts of copper by humans leads to Wilson's disease, with excess copper deposited in the brain tissue, skin, liver, and pancreas.

The natural content of manganese in plants, animals and soils is very high. The main areas of manganese production are the production of alloy steels, alloys, electric batteries and other chemical current sources. The presence of manganese in the air in excess of the norm (the average daily MPC of manganese in the atmosphere - the air of populated areas - is 0.01 mg/m3) has a harmful effect on the human body, which is expressed in the progressive destruction of the central nervous system. Manganese belongs to hazard class II.

Metal ions are essential components of natural bodies of water. Depending on environmental conditions (pH, redox potential, presence of ligands), they exist in different oxidation states and are part of a variety of inorganic and organometallic compounds, which can be truly dissolved, colloidal dispersed, or part of mineral and organic suspensions. Truly dissolved forms of metals, in turn, are very diverse, which is associated with the processes of hydrolysis, hydrolytic polymerization (formation of polynuclear hydroxo complexes) and complexation with various ligands. Accordingly, both the catalytic properties of metals and their availability for aquatic microorganisms depend on the forms of their existence in the aquatic ecosystem. Many metals form fairly strong complexes with organic matter; These complexes are one of the most important forms of migration of elements in natural waters. Most organic complexes are formed via the chelate cycle and are stable. Complexes formed by soil acids with salts of iron, aluminum, titanium, uranium, vanadium, copper, molybdenum and other heavy metals are relatively well soluble in neutral, slightly acidic and slightly alkaline environments. Therefore, organometallic complexes are capable of migrating in natural waters over very long distances. This is especially important for low-mineralized and primarily surface waters, in which the formation of other complexes is impossible.

Heavy metals and their salts are widespread industrial pollutants. They enter reservoirs from natural sources (rocks, surface layers of soil and groundwater), with wastewater from many industrial enterprises and atmospheric precipitation, which are polluted by smoke emissions.

Heavy metals as microelements are constantly found in natural reservoirs and organs of aquatic organisms (see table). Depending on geochemical conditions, wide fluctuations in their level are observed.

Natural sources of lead entering surface waters are the dissolution processes of endogenous (galena) and exogenous (anglesite, cerussite, etc.) minerals. Significant increase in lead content in the environment (including in surface waters) is associated with the combustion of coal, the use of tetraethyl lead as an anti-knock agent in motor fuel, and the removal of ore processing plants, some metallurgical plants, chemical plants, mines, etc. into water bodies with wastewater.

The presence of nickel in natural waters is due to the composition of the rocks through which the water passes: it is found in places where sulfide copper-nickel ores and iron-nickel ores are deposited. It enters water from soils and from plant and animal organisms during their decay. Increased nickel content compared to other types of algae was found in blue-green algae. Nickel compounds also enter water bodies with wastewater from nickel plating shops, synthetic rubber plants, and nickel concentration factories. Huge nickel emissions accompany the burning of fossil fuels. Its concentration may decrease as a result of the precipitation of compounds such as cyanides, sulfides, carbonates or hydroxides (with increasing pH values), due to its consumption by aquatic organisms and adsorption processes. In surface waters, nickel compounds are in dissolved, suspended and colloidal states, the quantitative ratio between which depends on the composition of the water, temperature and pH values. Sorbents for nickel compounds can be iron hydroxide, organic substances, highly dispersed calcium carbonate, and clays.

Cobalt compounds enter natural waters as a result of leaching processes from copper pyrite and other ores, from soils during the decomposition of organisms and plants, as well as with wastewater from metallurgical, metalworking and chemical plants. Some amounts of cobalt come from soils as a result of decomposition of plant and animal organisms. Cobalt compounds in natural waters are in a dissolved and suspended state, the quantitative relationship between which is determined by the chemical composition of the water, temperature and pH values.

Currently, there are two main groups of analytical methods for the determination of heavy metals: electrochemical and spectrometric methods. Recently, with the development of microelectronics, electrochemical methods have received new development, whereas previously they were gradually replaced by spectrometric methods. Among spectrometric methods for the determination of heavy metals, the first place is occupied by atomic absorption spectrometry with different atomization of samples: flame atomic absorption spectrometry (FAAS) and atomic absorption spectrometry with electrothermal atomization in a graphite cell (GF AAS). The main methods for determining several elements simultaneously are inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). With the exception of ICP-MS, other spectrometric methods have too high detection limits for the determination of heavy metals in water.

Determination of the content of heavy metals in a sample is carried out by transferring the sample into solution - through chemical dissolution in a suitable solvent (water, aqueous solutions of acids, less often alkalis) or fusion with a suitable flux from alkalis, oxides, salts, followed by leaching with water. After this, the compound of the desired metal is converted into a precipitate by adding a solution of the appropriate reagent - salt or alkali, the precipitate is separated, dried or calcined to a constant weight, and the content of heavy metals is determined by weighing on an analytical balance and recalculating the initial content in the sample. When used professionally, the method gives the most exact values content of heavy metals, but requires a lot of time.

To determine the content of heavy metals by electrochemical methods, the sample must also be transferred into an aqueous solution. After this, the content of heavy metals is determined by various electrochemical methods - polarographic (voltammetric), potentiometric, coulometric, conductometric and others, as well as a combination of some of them. listed methods with titration. The basis for determining the content of heavy metals using these methods is the analysis of current-voltage characteristics, the potentials of ion-selective electrodes, the integral charge necessary for the deposition of the desired metal on the electrode of the electrochemical cell (cathode), the electrical conductivity of the solution, etc., as well as electrochemical control of neutralization reactions and others in solutions. Using these methods, it is possible to determine heavy metals up to 10-9 mol/l.

The duration of residence of polluting components in the soil is much higher than in other parts of the biosphere, which leads to changes in the composition and properties of the soil as a dynamic system and ultimately causes an imbalance in ecological processes.

Under normal natural conditions, all processes occurring in soils are in balance. Changes in the composition and properties of the soil can be caused by natural phenomena, but most often humans are to blame for disturbing the equilibrium state of the soil:

atmospheric transport of pollutants in the form of aerosols and dust (heavy metals, fluorine, arsenic, oxides of sulfur, nitrogen, etc.)
agricultural pollution (fertilizers, pesticides)
unearthly pollution - dumps of large-scale production and emissions from fuel and energy complexes
pollution by oil and petroleum products
plant litter. Toxic elements in any state are absorbed by the leaves or deposited on the leaf surface. Then, when the leaves fall, these compounds enter the soil.

The determination of heavy metals is primarily carried out in soils located in areas of environmental disaster, on agricultural lands adjacent to soil pollutants with heavy metals, and in fields intended for growing environmentally friendly products.

In soil samples, “mobile” forms of heavy metals or their total content are determined. As a rule, if it is necessary to control technogenic contamination of soils with heavy metals, it is customary to determine their gross content. However, the gross content cannot always characterize the degree of danger of soil pollution, since the soil is capable of binding metal compounds, converting them into compounds inaccessible to plants. It is more correct to talk about the role of “mobile” and “accessible” forms for plants. It is advisable to determine the content of mobile forms of metals in the case of high total amounts in the soil, as well as when it is necessary to characterize the migration of metal pollutants from the soil to plants.

If soils are contaminated with heavy metals and radionuclides, it is almost impossible to clean them. So far the only way is known: to sow such soils fast growing crops, giving greater phytomass. Such crops that extract heavy metals must be destroyed after ripening. It takes decades to restore contaminated soils.

Heavy metals that are highly toxic include lead, mercury, nickel, copper, cadmium, zinc, tin, manganese, chromium, arsenic, aluminum, and iron. These substances are widely used in production, as a result of which they accumulate in huge quantities in the environment and easily enter the human body both with food and water, and by inhaling air.

When the content of heavy metals in the body exceeds the maximum permissible concentrations, their negative impact on humans begins. In addition to direct consequences in the form of poisoning, there are also indirect ones - heavy metal ions clog the channels of the kidneys and liver, thereby reducing the ability of these organs to filter. As a result, toxins and cell waste products accumulate in the body, which leads to a general deterioration in human health.

The whole danger of exposure to heavy metals lies in the fact that they remain in the human body forever. They can only be removed by consuming proteins contained in milk and porcini mushrooms, as well as pectin, which can be found in marmalade and fruit and berry jelly. It is very important that all products are obtained in environmentally friendly areas and do not contain harmful substances.

Due to anthropogenic activities, a huge amount of various chemical elements and their compounds enter the environment - up to 5 tons of organic and mineral waste per person annually. From half to two-thirds of these inputs remain in slag and ash, forming local anomalies in the chemical composition of soils and waters.

Enterprises, buildings, urban economy, industrial, household and fecal waste from populated areas and industrial areas not only alienate the soil, but also disrupt the normal biogeochemistry and biology of soil-ecological systems for tens of kilometers around. To some extent, every city or industrial center is the cause of the emergence of large biogeochemical anomalies that are dangerous to humans.

The source of heavy metals is mainly industrial emissions. At the same time, forest ecosystems suffer significantly more than agricultural soils and crops. Particularly toxic are lead, cadmium, mercury, arsenic and chromium.

Heavy metals, as a rule, accumulate in the soil layer, especially in the upper humus horizons. The half-life of heavy metals removal from soil (leaching, erosion, consumption by plants, deflation) is depending on the soil type for:

zinc - 70-510 years;
cadmium - 13-POLET;
copper - 310-1500 years;
lead - 740-5900 years.

The complex and sometimes irreversible consequences of the influence of heavy metals can be understood and foreseen only on the basis of a landscape-biogeochemical approach to the problem of toxicants in the biosphere. The following indicators especially affect pollution levels and the toxic-ecological situation:

bioproductivity of soils and humus content in them;
acid-base character of soils and waters;
redox conditions;
concentration of soil solutions;
soil absorption capacity;
granulometric composition of soils;
type of water regime.

The role of these factors has not yet been sufficiently studied, although it is the soil cover that is the final recipient of most technogenic chemicals involved in the biosphere. Soils are the main accumulator, sorbent and destroyer of toxicants.

A significant portion of metals enters soils from anthropogenic activities. Dispersion begins from the moment of extraction of ore, gas, oil, coal and other minerals. The chain of dispersion of elements can be traced from the producing mine, quarry, then losses occur during the transportation of raw materials to the processing plant; at the factory itself, dispersion continues along the processing line of processing, then in the process of metallurgical processing, metal production and up to dumps, industrial and domestic landfills.

A wide range of elements come with emissions from industrial enterprises in significant quantities, and pollutants are not always associated with the main products of enterprises, but can be part of impurities. Thus, near a lead smelter, priority pollutants, in addition to lead and zinc, may include cadmium, copper, mercury, arsenic, and selenium, and near aluminum smelting enterprises, fluorine, arsenic, and beryllium. A significant part of emissions from enterprises enters the global cycle - up to 50% of lead, zinc, copper and up to 90% of mercury.

The annual production of some metals exceeds their natural migration, especially significantly for lead and iron. It is obvious that the pressure of technogenic metal flows on the environment, including soil, is increasing.

The proximity of the source of pollution affects atmospheric pollution soil Thus, two large enterprises in the Sverdlovsk region - the Ural Aluminum Smelter and the Krasnoyarsk Thermal Power Plant - turned out to be sources of technogenic pollution atmospheric air with pronounced boundaries of the fallout of technogenic metals with precipitation.

The danger of soil contamination with technogenic metals from air aerosols exists for any type of soil and in any place in the city, with the only difference being that soils located closer to the source of technogenesis (metallurgical plant, thermal power plant, gas station or mobile transport) will be more polluted.

Often the intensive action of enterprises extends over a small area, which leads to an increase in the content of heavy metals, arsenic compounds, fluorine, sulfur oxides, sulfuric acid, sometimes hydrochloric acid, cyanides in concentrations often exceeding the maximum permissible concentration (Table 4.1). Grass cover and forest plantations are dying, soil cover is being destroyed, and erosion processes are developing. Up to 30-40% of heavy metals from the soil can enter groundwater.

However, soil also serves as a powerful geochemical barrier to the flow of pollutants, but only to a certain limit. Calculations show that chernozems are capable of firmly fixing up to 40-60 t/ha of lead only in the arable layer 0-20 cm thick, podzolic soils - 2-6 t/ha, and soil horizons as a whole - up to 100 t/ha, but at the same time an acute toxicological situation arises in the soil itself.

Still alone A feature of soil is the ability to actively transform compounds entering it. Mineral and organic components take part in these reactions, and biological transformation is possible. At the same time, the most common processes are the transition of water-soluble compounds of heavy metals into sparingly soluble ones (oxides, hydroxides, salts with low production Table 4.1. List of sources of pollution and chemical elements, the accumulation of which is possible in the soil in the zone of influence of these sources (Guidelines MU 2.1.7.730-99 “Hygienic assessment of soil quality in populated areas”)

Sources pollution	Type of production	Concentration factor K s
Sources pollution	Type of production
Non-ferrous metallurgy	Production of non-ferrous metals from ores and concentrates	Pb, Zn, Cu, Ag	Sn, As, Cd, Sb, Hg, Se, Bi
	Recycling of non-ferrous metals	Pb, Zn, Sn, Cu
	Production of hard and refractory non-ferrous metals
	Titanium production	Ag, Zn, Pb, V, Cu	Ti, Mn, Mo, Sn, V
Ferrous metallurgy	Production of alloy steels	Co, Mo, Bi, W, Zn
Ferrous metallurgy	Iron ore production
Mechanical engineering and metalworking industry	Enterprises with heat treatment of metals (without foundries)		Ni, Cr, Hg, Sn, Cu
	Production of lead batteries
	Production of devices for the electronic and electrical industry
Chemical industry	Superphosphate production		Rare earths, Cu, Cr, As, It
Chemical industry	Plastics production
Industry building materials	Cement production
Printing industry	Type foundries, printing houses
Municipal solid waste		Pb, Cd, Sn, Cu, Ag, Sb, Zn
Sewage sludge		Pb, Cd, V, Ni, Sn, Cr, Cu, Zn

by reducing the solubility of PR) as part of the soil absorption complex (SAC): organic matter forms complex compounds with heavy metal ions. The interaction of metal ions with soil components occurs according to the type of reactions of sorption, precipitation-dissolution, complex formation, and the formation of simple salts. The speed and direction of transformation processes depend on the pH of the environment, the content of fine particles, and the amount of humus.

For environmental consequences soil contamination with heavy metals, the concentrations and forms of presence of heavy metals in the soil solution become significant. The mobility of heavy metals is closely related to the composition of the liquid phase: low solubility of heavy metal oxides and hydroxides is usually observed in soils with a neutral or alkaline reaction. On the contrary, the mobility of heavy metals is highest when the soil solution reacts strongly, so the toxic effect of heavy metals in strongly acidic taiga-forest landscapes can be very significant compared to neutral or alkaline soils. The toxicity of elements to plants and living organisms is directly related to their mobility in soils. In addition to acidity, toxicity is influenced by soil properties that determine the strength of fixation of incoming pollutants; the joint presence of various ions has a significant effect.

The greatest danger to higher organisms, including humans, is the consequences of microbial transformation of inorganic compounds of heavy metals into complex compounds. The consequences of metal pollution can also be disruption of soil trophic chains in biogeocenoses. It is also possible to change entire complexes, communities of microorganisms and soil animals. Heavy metals inhibit important microbiological processes in the soil - the transformation of carbon compounds - the so-called “respiration” of the soil, as well as nitrogen fixation.

FEDERAL AGENCY OF MARINE AND RIVER TRANSPORT
FEDERAL BUDGET EDUCATIONAL INSTITUTION
HIGHER PROFESSIONAL EDUCATION
MARINE STATE UNIVERSITY
named after Admiral G.I. Nevelsky

Department of Environmental Protection

ABSTRACT
in the discipline "Physico-chemical processes"

Consequences of soil contamination with heavy metals and radionuclides.

Checked by the teacher:
Firsova L.Yu.
Completed by student gr. ___
Khodanova S.V.

Vladivostok 2012
CONTENT

Introduction
1 Heavy metals in soils

2 Radionuclides in soils. Nuclear pollution
Conclusion
List of sources used

INTRODUCTION

Soil is not just an inert medium on the surface of which human activity takes place, but a dynamic, developing system that includes many organic and inorganic components, which have a network of cavities and pores, and these, in turn, contain gases and liquids. The spatial distribution of these components determines the main types of soils on the globe.
In addition, soils contain a huge number of living organisms, they are called biota: from bacteria and fungi to worms and rodents. Soil is formed on parent rocks under the combined influence of climate, vegetation, soil organisms and time. Therefore, changes in any of these factors can lead to changes in soils. Soil formation is a long process: the formation of a 30 cm layer of soil takes from 1000 to 10,000 years. Consequently, the rates of soil formation are so low that soil can be considered a non-renewable resource.
The soil cover of the Earth is essential component biosphere of the Earth. It is the soil shell that determines many of the processes occurring in the biosphere. The most important importance of soils is the accumulation of organic matter, various chemical elements, and energy. Soil cover functions as a biological absorber, destroyer and neutralizer of various pollutants. If this link of the biosphere is destroyed, then the existing functioning of the biosphere will be irreversibly disrupted. That is why it is extremely important to study the global biochemical significance of the soil cover, its current state and changes under the influence of anthropogenic activities.

1 Heavy metals in soils

Heavy metals (HM) include more than 40 chemical elements of the periodic table D.I. Mendeleev, the mass of atoms of which is over 50 atomic mass units (a.m.u.). These are Pb, Zn, Cd, Hg, Cu, Mo, Mn, Ni, Sn, Co, etc. The existing concept of “heavy metals” is not strict, because HMs often include non-metal elements, for example As, Se, and sometimes even F, Be and other elements whose atomic mass is less than 50 amu.
There are many trace elements among HMs that are biologically important for living organisms. They are necessary and indispensable components of biocatalysts and bioregulators of the most important physiological processes. However, the excess content of heavy metals in various objects of the biosphere has a depressing and even toxic effect on living organisms.
Sources of heavy metals entering the soil are divided into natural (weathering of rocks and minerals, erosion processes, volcanic activity) and technogenic (mining and processing of minerals, fuel combustion, influence of vehicles, agriculture, etc.) Agricultural lands, in addition to pollution through the atmosphere, HMs are also polluted specifically through the use of pesticides, mineral and organic fertilizers, liming, and the use of wastewater. Last time, Special attention scientists are focusing on urban soils. The latter are experiencing a significant technogenic process, an integral part of which is HM pollution.
HMs reach the soil surface in various forms. These are oxides and various salts of metals, both soluble and practically insoluble in water (sulfides, sulfates, arsenites, etc.). In the emissions of ore processing enterprises and non-ferrous metallurgy enterprises - the main source of environmental pollution with heavy metals - the bulk of metals (70-90%) are in the form of oxides.
Once on the soil surface, HMs can either accumulate or dissipate, depending on the nature of the geochemical barriers inherent in a given area.
Most of the HMs arriving on the soil surface are fixed in the upper humus horizons. HMs are sorbed on the surface of soil particles, bind to soil organic matter, in particular in the form of elemental organic compounds, accumulate in iron hydroxides, form part of the crystal lattices of clay minerals, produce their own minerals as a result of isomorphic replacement, and are in a soluble state in soil moisture and gaseous state in the soil air, are an integral part of the soil biota.
The degree of mobility of heavy metals depends on the geochemical situation and the level of technogenic impact. The heavy particle size distribution and high content of organic matter lead to the binding of HMs in the soil. An increase in pH values increases the sorption of cation-forming metals (copper, zinc, nickel, mercury, lead, etc.) and increases the mobility of anion-forming metals (molybdenum, chromium, vanadium, etc.). Increasing oxidative conditions increases the migration ability of metals. As a result, according to their ability to bind the majority of HMs, soils form the following series: gray soil > chernozem > soddy-podzolic soil.

Soil contamination with heavy metals has two negative aspects. Firstly, moving through food chains from soil to plants, and from there into the body of animals and humans, heavy metals cause serious diseases in them. An increase in morbidity among the population and a reduction in life expectancy, as well as a decrease in the quantity and quality of crops of agricultural plants and livestock products.
Secondly, accumulating in large quantities in the soil, HMs are capable of changing many of its properties. First of all, changes affect the biological properties of the soil: the total number of microorganisms decreases, their species composition (diversity) narrows, the structure of microbial communities changes, the intensity of basic microbiological processes and the activity of soil enzymes decreases, etc. Severe contamination with heavy metals leads to changes in more conservative soil characteristics, such as humus status, structure, pH, etc. The result of this is partial, and in some cases, complete loss of soil fertility.

In nature, there are areas with insufficient or excessive content of HMs in soils. The abnormal content of heavy metals in soils is due to two groups of reasons: biogeochemical characteristics of ecosystems and the influence of technogenic flows of matter. In the first case, areas where the concentration of chemical elements is higher or lower than the optimal level for living organisms are called natural geochemical anomalies or biogeochemical provinces. Here, the anomalous content of elements is due to natural causes - the characteristics of soil-forming rocks, the soil-forming process, and the presence of ore anomalies. In the second case, the territories are called man-made geochemical anomalies. Depending on the scale, they are divided into global, regional and local.
Soil, unlike other components of the natural environment, not only geochemically accumulates pollution components, but also acts as a natural buffer that controls the transfer of chemical elements and compounds into the atmosphere, hydrosphere and living matter.
Various plants, animals and humans require a certain composition of soil and water for their life. In places of geochemical anomalies, aggravated transmission of deviations from the norm in mineral composition occurs throughout the food chain. As a result of disturbances in mineral nutrition, changes in the species composition of phyto-, zoo- and microbial communities, diseases of wild plant forms, a decrease in the quantity and quality of crops of agricultural plants and livestock products, an increase in morbidity among the population and a decrease in life expectancy are observed.
The toxic effect of HMs on biological systems is primarily due to the fact that they easily bind to sulfhydryl groups of proteins (including enzymes), suppressing their synthesis and, thereby, disrupting metabolism in the body.
Living organisms have developed various mechanisms of resistance to HMs: from the reduction of HM ions into less toxic compounds to the activation of ion transport systems that effectively and specifically remove toxic ions from the cell into the external environment.
The most significant consequence of the impact of heavy metals on living organisms, which manifests itself at the biogeocenotic and biosphere levels of organization of living matter, is the blocking of the oxidation processes of organic matter. This leads to a decrease in the rate of its mineralization and accumulation in ecosystems. At the same time, an increase in the concentration of organic matter causes it to bind HM, which temporarily relieves the load on the ecosystem. A decrease in the rate of decomposition of organic matter due to a decrease in the number of organisms, their biomass and the intensity of vital activity is considered a passive response of ecosystems to HM pollution. Active resistance of organisms to anthropogenic loads manifests itself only during the lifetime accumulation of metals in bodies and skeletons. The most resistant species are responsible for this process.
The resistance of living organisms, primarily plants, to elevated concentrations of heavy metals and their ability to accumulate high concentrations of metals can pose a great danger to human health, since they allow the penetration of pollutants into food chains.

The issue of regulating the content of heavy metals in soil is very complicated. Its solution should be based on the recognition of the multifunctionality of the soil. In the process of rationing, soil can be considered from various positions: as a natural body, as a habitat and substrate for plants, animals and microorganisms, as an object and means of agricultural and industrial production, as a natural reservoir containing pathogenic microorganisms. Standardization of HM content in soil must be carried out on the basis of soil-ecological principles, which deny the possibility of finding uniform values for all soils.
There are two main approaches to the issue of remediation of soils contaminated with heavy metals. The first is aimed at clearing the soil of HM. Purification can be carried out by leaching, by extracting HM from the soil with the help of plants, by removing the top contaminated layer of soil, etc. The second approach is based on fixing HMs in the soil, converting them into forms that are insoluble in water and inaccessible to living organisms. To achieve this, it is proposed to add organic matter, phosphorus mineral fertilizers, ion exchange resins, natural zeolites, brown coal, liming the soil, etc. to the soil. However, any method of fixing HMs in the soil has its own validity period. Sooner or later, part of the HM will again begin to enter the soil solution, and from there into living organisms.

Soils contain almost all chemical elements known in nature, including radionuclides.
Radionuclides are chemical elements capable of spontaneous decay with the formation of new elements, as well as formed isotopes of any chemical elements. The consequence of nuclear decay is ionizing radiation in the form of a flow of alpha particles (flow of helium nuclei, protons) and beta particles (flow of electrons), neutrons, gamma radiation and X-rays. This phenomenon is called radioactivity. Chemical elements capable of spontaneous decay are called radioactive. The most commonly used synonym for ionizing radiation is radioactive radiation.
Ionizing radiation is a flow of charged or neutral particles and electromagnetic quanta, the interaction of which with a medium leads to ionization and excitation of its atoms and molecules. Ionizing radiation has an electromagnetic (gamma and x-ray radiation) and corpuscular (alpha radiation, beta radiation, neutron radiation) nature.
Gamma radiation is electromagnetic radiation caused by gamma rays (discrete beams or quanta called photons) if, after alpha or beta decay, the nucleus remains in an excited state. Gamma rays in air can travel considerable distances. A high-energy photon of gamma rays can pass through the human body. Intense gamma radiation can damage not only the skin, but also internal organs. Dense and heavy materials, iron, and lead protect against this radiation. Gamma radiation can be created artificially in accelerators of infected particles (microtron), for example, bremsstrahlung gamma radiation from fast accelerator electrons when they hit a target.
X-ray radiation is similar to gamma radiation. Cosmic X-rays are absorbed by the atmosphere. X-rays are produced artificially and fall in the lower part of the energy spectrum of electromagnetic radiation.
Radioactive radiation is a natural factor in the biosphere for all living organisms, and living organisms themselves have a certain radioactivity. Among biosphere objects, soils have the highest natural degree of radioactivity. Under these conditions, nature prospered for many millions of years, except in exceptional cases due to geochemical anomalies associated with the deposit of radioactive rocks, for example, uranium ores.
However, in the 20th century, humanity was faced with radioactivity that was prohibitively higher than natural, and therefore biologically abnormal. The first to suffer from excessive doses of radiation were the great scientists who discovered radioactive elements (radium, polonium), the spouses Marie Sklodowska-Curie and Pierre Curie. And then: Hiroshima and Nagasaki, tests of atomic and nuclear weapons, many disasters, including Chernobyl, etc.
The most significant objects of the biosphere, determining the biological functions of all living things, are soils.
The radioactivity of soils is due to the content of radionuclides in them. A distinction is made between natural and artificial radioactivity.
Natural radioactivity of soils is caused by natural radioactive isotopes, which are always present in varying quantities in soils and soil-forming rocks. Natural radionuclides are divided into 3 groups.
The first group includes radioactive elements - elements all of whose isotopes are radioactive: uranium (238
etc.................

Heavy metals are environmental pollutants. Soil contamination with heavy metals

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