Consequences of soil pollution with heavy metals. Abstract of the consequences of soil pollution with heavy metals and radionuclides. Sources of environmental pollution

Heavy metals are now well ahead of such well-known pollutants as carbon dioxide and sulfur, and in the forecast they should become the most dangerous, more dangerous than nuclear waste and solid waste. Pollution with heavy metals is associated with their widespread use in industrial production coupled with weak cleaning systems, resulting in heavy metals entering the environment. 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 enter the World Ocean from it. Heavy metals are assimilated from the soil by plants, which then get into the food of more highly organized animals.

The term heavy metals, which characterizes a wide group of pollutants, was recent times significant distribution. In various scientific and applied works, the authors interpret the meaning of this concept in different ways. In this regard, the number of elements assigned to the group of heavy metals varies over a wide range. Numerous characteristics are used as membership criteria: atomic mass, density, toxicity, abundance in the natural environment, degree of involvement in natural and technogenic cycles.

In works devoted to the problems of environmental pollution natural environment and environmental monitoring, today more than 40 metals are classified as heavy metals periodic system DI. Mendeleev with atomic mass over 50 atomic units: V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, Sn, Hg, Pb, Bi, etc. At the same time, the following conditions play an important role in the categorization of heavy metals: their high toxicity for living organisms in relatively low concentrations, as well as the ability to bioaccumulate and biomagnify.

According to the classification of N. Reimers, metals with a density of more than 8 g/cm3 should be considered heavy. Thus, heavy metals include Pb, Cu, Zn, Ni, Cd, Co, Sb, Sn, Bi, Hg.

Formally, the definition of heavy metals corresponds to a large number of elements. However, according to researchers involved in practical activities related to the organization of observations of the state and pollution environment, the compounds of these elements are far from equivalent as pollutants. Therefore, in many works there is a narrowing of the scope of the group of heavy metals, in accordance with the priority criteria, due to the direction and specifics of the work. So, in the already classic works of Yu.A. Israel on the list chemical substances, to be determined in natural environments at background stations in biosphere reserves, in the heavy metals section are named Pb, Hg, Cd, As. On the other hand, according to the decision of the Task Force on Heavy Metal Emissions, which operates under the auspices of the United Nations Economic Commission for Europe and collects and analyzes information on pollutant emissions in European countries, only Zn, As, Se and Sb were classified as heavy metals.

Rationing the content of heavy metals in soil and plants is extremely difficult due to the impossibility of fully taking into account all environmental factors. So, changing only the agrochemical properties of the soil (reaction of the environment, humus content, degree of saturation with bases, granulometric composition) can reduce or increase the content of heavy metals in plants several times. There are conflicting data even on the background content of some metals. The results found and cited by researchers sometimes differ by 5-10 times.

The distribution of pollutant metals in space is very complex and depends on many factors, but in any case, it is the soil that is the main receiver and accumulator of technogenic masses of heavy metals.

The entry of heavy metals into the lithosphere as a result of technogenic dispersion occurs in a variety of ways. The most important of them is the emission during high-temperature processes (ferrous and non-ferrous metallurgy, roasting of cement raw materials, combustion of mineral fuels). In addition, the source of contamination of biocenoses can be irrigation with waters with a high content of heavy metals, the introduction of domestic sewage sludge into soils as a fertilizer, secondary pollution due to the removal of heavy metals from metallurgical enterprises by water or air flows, the influx of large amounts of heavy metals with the constant introduction of high doses of organic, mineral fertilizers and pesticides. Appendix No. 1 reflects the correspondence between sources of technogenic pollution and pollutant metals.

To characterize technogenic pollution with heavy metals, a concentration coefficient is used that is equal to the ratio of the concentration of an element in contaminated soil to its background concentration. When contaminated with several heavy metals, the degree of contamination is estimated by the value of the total concentration index (Zc) .

In Appendix No. 1, the industries that are currently operating in the territory of Komsomolsk-on-Amur are highlighted in color. The table shows that elements such as zinc, lead, cadmium require mandatory control over the MPC level, especially considering the fact that they are included in the list of major pollutants from heavy metals (Hg, Pb, Cd, As - according to Yu.A. Israel ), mainly because their technogenic accumulation in the environment goes high pace.

Based on these data, we will get acquainted in more detail with the features of these elements.

Zinc is one of the active trace elements that affect the growth and normal development of organisms. At the same time, many zinc compounds are toxic, primarily its sulfate and chloride.

MPC in Zn 2+ is 1 mg / dm 3 (limiting indicator of harmfulness - organoleptic), MPC vr Zn 2+ - 0.01 mg / dm 3 (limiting sign of harmfulness - toxicological) (Biogeochemical properties See Appendix 2).

Currently, lead occupies the first place among the causes of industrial poisoning. This is due to its widespread use in various industries (Appendix 1).

Lead is contained in emissions from metallurgy enterprises, which are now the main source of pollution, metalworking, electrical engineering, and petrochemistry. A significant source of lead is the exhaust from vehicles using leaded gasoline.

Currently, the number of cars and the intensity of their movement continues to increase, which also increases the amount of lead emissions into the environment.

The Komsomolsk-on-Amur Battery Plant during its operation was a powerful source of lead pollution in urban areas. The element, through the atmosphere, settled on the surface of the soil, accumulated and is now practically not removed from it. Today, one of the sources of pollution is also a metallurgical plant. There is a further accumulation of lead, along with previously unliquidated "reserves". With a lead content of 2-3g per 1kg of soil, the soil becomes dead.

White paper, published by Russian specialists, reports that lead pollution covers the entire country and is one of the many environmental disasters in the former Soviet Union that have come to light in last years. Most of the territory of Russia is experiencing a load from lead fallout that exceeds the critical value for the normal functioning of the ecosystem. Already in the 1990s, in dozens of cities, the excess of lead concentrations in the air and soil was higher than the values corresponding to the MPC. To date, despite the improvement of technical equipment, the situation has not changed much (Appendix 3).

Lead pollution has an impact on human health. The intake of the chemical into the body occurs by inhalation of air containing lead, and the intake of lead with food, water, and dust particles. The chemical accumulates in the body, in the bones and surface tissues. Affects the kidneys, liver, nervous system and organs of blood formation. Lead exposure disrupts the female and male reproductive systems. For women of pregnant and childbearing age elevated levels lead in the blood is of particular danger, since under its action menstrual function is disturbed, more often there are premature births, miscarriages and fetal death due to the penetration of lead through the placental barrier. Newborns have a high mortality rate. Low birth weight, stunting and hearing loss are also the result of lead poisoning.

For young children, lead poisoning is extremely dangerous, as it negatively affects the development of the brain and nervous system. Even at low doses, lead poisoning in children preschool age causes a decrease intellectual development, attention and ability to concentrate, lagging behind in reading, leads to the development of aggressiveness, hyperactivity and other problems in the child's behavior. These developmental abnormalities can be long-term and irreversible. High doses of intoxication lead to mental retardation, coma, convulsions and death.

The limiting indicator of harmfulness is sanitary-toxicological. MPC for lead is 0.03 mg/dm 3 , MPC for BP is 0.1 mg/dm 3 .

Anthropogenic sources of cadmium in the environment can be divided into two groups:

§ local emissions associated with industrial complexes that produce (these include a number of chemical enterprises, especially for the production of sulfuric acid) or use cadmium.
§ Sources of different power diffusely scattered over the Earth, ranging from thermal power plants and motors to mineral fertilizers and tobacco smoke.

Two properties of cadmium determine its importance to the environment:

1. Relatively high vapor pressure, which makes it easy to evaporate, for example, during melting or combustion of coals;
2. High solubility in water, especially at low acidic pH values (especially at pH5).

Cadmium entering the soil is mainly present in it in a mobile form, which has a negative environmental significance. The mobile form causes a relatively high migratory ability of the element in the landscape and leads to increased pollution of the flow of substances from the soil to the plants.

Soil contamination with Cd persists for a long time even after this metal ceases to be supplied again. Up to 70% of cadmium entering the soil binds to soil chemical complexes available for absorption by plants. Soil microflora also participates in the processes of formation of cadmium-organic compounds. Depending on the chemical composition, physical properties soil and forms of incoming cadmium, its transformation in the soil is completed within a few days. As a result, cadmium accumulates in ionic form in acidic waters or as insoluble hydroxide and carbonate. It can be in the soil and in the form of complex compounds. In areas of high content of cadmium in the soil, a 20-30-fold increase in its concentration in the ground parts of plants is established in comparison with plants of uncontaminated territories. The visible symptoms caused by increased cadmium levels in plants are leaf chlorosis, red-brown coloration of their edges and veins, as well as stunting and damage to the root system.

Cadmium is highly toxic. The high phytotoxicity of cadmium is explained by its proximity to chemical properties to zinc. Therefore, cadmium can replace zinc in many biochemical processes, disrupting the work of a large number of enzymes. Phytotoxicity of cadmium is manifested in the inhibitory effect on photosynthesis, disruption of transpiration and fixation. carbon dioxide, as well as in changes in the permeability of cell membranes.

specific biological significance cadmium as a trace element has not been established. Cadmium enters the human body in two ways: at work and with food. Food chains of cadmium intake are formed in areas of increased soil and water pollution with cadmium. Cadmium reduces the activity of digestive enzymes (trypsin and, to a lesser extent, pepsin), changes their activity, and activates enzymes. Cadmium affects carbohydrate metabolism, causing hyperglycemia, inhibiting the synthesis of glycogen in the liver.

MPC in is 0.001 mg/dm 3 , MPC in vr is 0.0005 mg/dm 3 (the limiting sign of harmfulness is toxicological).

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

According to the degree of pollution, the soils are divided into highly polluted, medium polluted, slightly polluted.

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

In lightly polluted soils, the content of chemicals does not exceed the MPC, but exceeds the background.

Land pollution depends mainly on the class of 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 by indicators.

Table 1 - Indicators and classes of hazardous substances

Index	Norms of concentration

Toxicity, LD 50			more than 1000
Persistence in soil, months
MAC in soil, mg/kg			more than 0.5
Persistence in plants, months
Impact on the nutritional value of agricultural products		Moderate

Soil contamination with radioactive substances is mainly due to testing in the atmosphere of atomic and nuclear weapons, which has not been terminated by individual states even today. 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 exposure.

Radionuclides - chemical elements, capable of spontaneous decay with the formation of new elements, as well as the 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 - natural factor in the biosphere for all living organisms, and living organisms themselves have a certain radioactivity. Soils have the highest natural degree of radioactivity among biospheric objects.

However, in the 20th century, humanity was faced with radioactivity beyond the limits of natural, and therefore biologically abnormal. The first victims of excessive doses of radiation were the great scientists who discovered radioactive elements (radium, polonium) spouses Maria Sklodowska-Curie and Pierre Curie. And then: Hiroshima and Nagasaki, testing of atomic and nuclear weapons, many disasters, including Chernobyl, etc. Huge areas were contaminated with long-lived radionuclides - 137 Cs and 90 Sr. According to the current legislation, one of the criteria for classifying territories as a zone of radioactive contamination is the excess density of contamination with 137 Cs of 37 kBq/m 2 . Such an excess was set at 46.5 thousand km 2 in all regions of Belarus.

Levels of 90 Sr contamination above 5.5 kBq/m 2 (legislated criterion) were detected on an area of 21.1 thousand km 2 in the Gomel and Mogilev regions, which was 10% of the country's territory. Contamination with 238.239+240 Pu isotopes with a density of more than 0.37 kBq/m 2 (a 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.

The natural decay processes of radionuclides over the 25 years that have passed since the Chernobyl disaster have made adjustments to the structure of their distribution in the regions of Belarus. During this period, the levels and areas of pollution have decreased. From 1986 to 2010, the area of the 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 / m 2 (0.15 Ci / km 2), this indicator decreased - from 21.1 to 11.8 thousand km 2 (from 10% to 5.6%) (Table 2).

pollution technogenic 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 ha
Contaminated with 137 Cs	including pollution density, kBq/m2 (Ci/km2)
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 biological functions all living things are the soil.

The radioactivity of soils is due to the content of radionuclides in them. There are natural and artificial radioactivity.

The natural radioactivity of soils is caused by natural radioactive isotopes, which are always present in varying amounts 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 with 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 the action of 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 action of cosmic rays and secondary neutrons (14 C, 3 H, 24 Na). There are more than 300 natural radionuclides in total. The gross content of natural radioactive isotopes mainly depends on parent rocks. Soils formed on the weathering products of acidic rocks contain more radioactive isotopes 24 than those formed on basic and ultrabasic rocks; heavy soils contain more of them than light ones.

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

The 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. Most often, artificial radioactive contamination of soils is caused by 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 contamination of soils are as follows. Being included in the biological cycle, radionuclides enter the human body through plant and animal food and, accumulating in it, cause radioactive exposure. Radionuclides, like many other pollutants, are gradually concentrated in food chains.

From an ecological point of view, 90 Sr and 137 Cs pose the greatest danger. This is due to a 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, in the food chain. In terms of chemical properties, strontium is close to calcium and is part of bone tissue, while cesium is close to potassium and is included in many reactions of living organisms.

Artificial radionuclides are fixed mainly (up to 80-90%) in the upper soil layer: on virgin soil - a layer of 0-10 cm, on arable land - in the arable horizon. Soils with the highest sorption high content humus, heavy granulometric composition, rich in montmorillonite and hydromicas, with a non-leaching type of water regime. In such soils, radionuclides are only slightly capable of migrating. 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 it takes for half the number of its atoms to decay.

Table 3 - Characteristics of radioactive substances

	Kerma constant	Gamma constant	Dose exposure factor	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, exposure to which causes 50% death of biological objects) is 2.5-3.5 Gy.

A dose of 0.25 Gy is considered conditionally normal for external exposure. 0.75 Gy whole body exposure or 2.5 Gy thyroid exposure from radioactive iodine 131 I require measures for radiation protection of the population.

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

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, sanitation and protection of soils from contamination by radionuclides and heavy metals are more similar and can often be considered together.

Thus, the radioactivity of soils is due to the content of radionuclides in them. The natural radioactivity of soils is caused by naturally occurring radioactive isotopes, which are always present in varying amounts in soils and soil-forming rocks. The 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 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 particular area is determined by two factors:

a) concentration 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 ecological point of view, 90 Sr and 137 Cs pose the greatest danger. They are firmly fixed in soils, are 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. Soils are:

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

b) II class: 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 now occupy the second place in terms of danger, yielding to pesticides and significantly ahead of such well-known pollutants as carbon dioxide and sulfur. In the future, they may become more dangerous than nuclear power plant waste and solid waste. Pollution with heavy metals is associated with their widespread use in industrial production. Due to imperfect cleaning systems, heavy metals enter the environment, including the soil, polluting and poisoning it. Heavy metals are special pollutants, monitoring of which is obligatory 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 enter the World Ocean from it. From the soil, heavy metals are absorbed by plants, which then fall into food.

The term "heavy metals", which characterizes a wide group of pollutants, has recently become widely used. In various scientific and applied works, the authors interpret the meaning of this concept in different ways. In this regard, the number of elements assigned to the group of heavy metals varies over a wide range. Numerous characteristics are used as membership criteria: atomic mass, density, toxicity, abundance in the natural environment, degree of involvement in natural and technogenic cycles.

In works devoted to the problems of soil pollution and environmental monitoring, today more than 40 elements of D.I. Mendeleev with an atomic mass of more than 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, heavy metals should be considered with with a density of more than 8 g / cm 3. At the same time, 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 their ability to bioaccumulate and biomagnify. Almost all metals falling under this definition (with the exception of lead, mercury, cadmium and bismuth, biological role which is currently not clear), are actively involved in biological processes, are part of many enzymes.

On the soil surface, heavy metals enter into various forms. These are oxides and various salts of metals, both soluble and practically insoluble in water (sulfides, sulfates, arsenites, etc.). In the composition of emissions from ore processing enterprises and non-ferrous metallurgy enterprises - the main source of environmental pollution - heavy metals - the bulk of metals (70-90%) is in the form of oxides. Getting on the soil surface, they can either accumulate or disperse, 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 in the environment

	natural pollution	Man-made pollution

	Volcanic eruption, wind erosion.	Extraction and processing of arsenic-containing ores and minerals, pyrometallurgy and production of sulfuric acid, superphosphate; burning, oil, peat, shale.
	Fallout with precipitation. Volcanic activity.	Ore dressing, sulfuric acid production, coal combustion.
		Wastewater from industries: metallurgical, machine-building, textile, glass, ceramic and leather. Development of boron-containing ores.
	It is widely distributed in nature, making up approximately 0.08% of the earth's crust.	Coal-fired power plants, production of aluminum and superphosphate fertilizers.
	It does not occur in nature in its elemental state. In the form of chromite, it is part of the earth's crust.	Emissions from enterprises where chromium is mined, received and processed.
	More than 100 cobalt-containing minerals are known.	Combustion in the process of industrial production of natural and fuel materials.
	Included in many minerals.	Metallurgical process of processing and enrichment of ores, phosphate fertilizers, cement production, emissions from thermal power plants.
	It is part of 53 minerals.	Emissions from enterprises of the mining industry, non-ferrous metallurgy, machine-building, metalworking, chemical enterprises, transport, thermal power plants.
	The total world reserves of copper in ores are estimated at 465 million tons. It is included in the composition of minerals Native is formed in the zone of oxidation 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. Widespread in all geospheres. It is part of 64 minerals.	High-temperature technological processes. Losses during transportation, burning coal. Annually, with atmospheric precipitation, 72 kg of zinc falls on 1 km 2 of the Earth's surface, which is 3 times more than lead and 12 times more than copper.
	It belongs to rare trace elements: it is found as an isomorphic impurity in many minerals.	Local pollution - emissions industrial complexes, pollution of varying degrees of power is thermal power plants, motors.
	Dispersed element, concentrated in sulfide ores. A small amount occurs natively.	The process of pyrometallurgical production of metal, as well as all processes in which mercury is used. Combustion of any organic fuel (oil, coal, peat, gas, wood) metallurgical production, thermal processes with non-metallic materials.
	Contained in earth's crust, is found in minerals. It enters the environment in the form of silicate soil dust, volcanic smoke, forest vapors, marine salt aerosols and meteorite dust.	Emissions from products from high temperature processes, exhaust gases, wastewater, metal mining and processing, transportation, attrition and dispersion.

The most powerful suppliers of metal-enriched wastes are non-ferrous metal smelting enterprises (aluminum, alumina, copper-zinc, lead-smelting, nickel, titanium-magnesium, mercury), as well as non-ferrous metal processing (radio engineering, electrical engineering, instrument-making, electroplating, etc. .). In the dust of metallurgical industries, 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. Wastes from non-ferrous metallurgy enterprises, paint and varnish factories and reinforced concrete structures are enriched with mercury. The concentration of W, Cd, Pb is increased in the dust of machine-building plants (Table 5).

Table 5 - Main technogenic 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 car exhaust gases, which exceeds its intake with waste from metallurgical enterprises.

The soils of the world are often enriched not only with heavy, 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).

Lead is the main pollutant element in the suburban soils of Belarus. Its increased content is observed in the suburban areas of Minsk, Gomel, 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 a person. The patterns of distribution of human-dispersed elements in the pedosphere are 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 the average values of the concentrations of elements in the soils of individual continents of countries, regions and the whole world (Table 7).

In some fields of the Minsk Vegetable Factory, where municipal solid 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, while the limiting level for zinc is 23 mg/kg and copper is 5 mg/kg.

Along the highways, the soil is heavily polluted with lead and, to a lesser extent, with cadmium. Roadside soil pollution highways interstate (Brest - Moscow, St. Petersburg - Odessa), republican (Minsk - Slutsk, Minsk - Logoysk) and local (Zaslavl - Dzerzhinsk, Zhabinka - B. Motykaly) values are observed at a distance of up to 25-50 m from the roadway, depending from the terrain and the presence of forest protection belts. The maximum content of lead in the soil was noted at a distance of 5-10 m from the highway. It is higher than the background value by an average of 2-2.3 times, but somewhat lower or close to the MPC. The content of cadmium in the soils of Belarus is at the background level (up to 0.5 mg/kg). Exceeding the background up to 2.5 times was noted locally at a distance of up to 3-5 km from large cities and reaches 1.0-1.2 mg of soil at a MPC of 3 mg/kg for countries Western Europe(MAC of cadmium for the soils of Belarus has not been developed). The area of soils in Belarus contaminated from various sources with lead is currently approximately 100 thousand hectares, with cadmium - 45 thousand hectares.

Table 7 - Combination of interaction between man and nature

Elements	Average values (US soils, X. Shacklett, J. Borngsn, 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 the content of copper in the soils of Belarus, and it has already been established that 260.3 thousand hectares of agricultural land in the republic are contaminated with copper (Table 8).

Table 8 - Agricultural land in Belarus contaminated with copper (thousand ha)

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

Soil is the surface of the earth, which has properties that characterize both living and inanimate nature.

The soil is an indicator of the total. Pollution enters the soil with atmospheric precipitation, surface waste. They are also introduced into the soil layer by soil rocks and groundwater.

The group of heavy metals includes all with a density exceeding the density of iron. The paradox of these elements is that they are necessary in certain quantities to ensure the normal functioning of plants and organisms.

But their excess can lead to serious illness and even death. The food cycle causes harmful compounds to enter the human body and often cause great harm to health.

Sources of heavy metal pollution are. There is a method by which the allowable metal content is calculated. This takes into account the total value of several metals Zc.

admissible;
moderately dangerous;
high-dangerous;
extremely dangerous.

Soil protection is very important. Constant control and monitoring does not allow growing agricultural products and grazing livestock on contaminated lands.

Heavy metals polluting the soil

There are three hazard classes of heavy metals. The World Health Organization considers lead, mercury and cadmium to be the most dangerous. But no less harmful is the high concentration of other elements.

Mercury

Pollution of soil with mercury occurs when pesticides, various household wastes, such as fluorescent lamps, elements of damaged measuring instruments.

According to official data, the annual release of mercury is more than five thousand tons. Mercury can enter the human body from contaminated soil.

If this happens regularly, severe disorders of the work of many organs can occur, including the nervous system.

With improper treatment, a fatal outcome is possible.

Lead

Lead is very dangerous for humans and all living organisms.

It is extremely toxic. When one ton of lead is mined, twenty-five kilograms are released into the environment. A large amount of lead enters the soil with the release of exhaust gases.

The soil pollution zone along the routes is over two hundred meters around. Once in the soil, lead is absorbed by plants that are eaten by humans and animals, including livestock, whose meat is also on our menu. Excess lead affects the central nervous system, brain, liver and kidneys. It is dangerous for its carcinogenic and mutagenic effects.

Cadmium

Soil contamination with cadmium is a huge danger to the human body. When ingested, it causes skeletal deformities, stunted growth in children, and severe back pain.

Copper and zinc

A high concentration of these elements in the soil causes growth to slow down and the fruiting of plants to deteriorate, which ultimately leads to a sharp decrease in yield. In humans, changes occur in the brain, liver and pancreas.

Molybdenum

Excess molybdenum causes gout and damage to the nervous system.

The danger of heavy metals lies in the fact that they are poorly excreted from the body, accumulate in it. They can form very toxic compounds, easily pass from one environment to another, do not decompose. At the same time, they cause severe diseases, often leading to irreversible consequences.

Antimony

Present in some ores.

It is part of the alloys used in various industrial fields.

Its excess causes severe eating disorders.

Arsenic

The main source of soil contamination with arsenic are substances used to control pests of agricultural plants, such as herbicides, insecticides. Arsenic is a cumulative poison that causes chronic. Its compounds provoke diseases of the nervous system, brain, and skin.

Manganese

In the soil and plants, a high content of this element is observed.

If an additional amount of manganese enters the soil, a dangerous excess of it is quickly created. This affects the human body in the form of destruction of the nervous system.

An excess of other heavy elements is no less dangerous.

From the foregoing, we can conclude that the accumulation of heavy metals in the soil entails severe consequences for human health and the environment as a whole.

The main methods of combating soil pollution with heavy metals

Methods for dealing with soil contamination with heavy metals can be physical, chemical and biological. Among them are the following methods:

An increase in soil acidity increases the possibility. Therefore, the introduction of organic matter and clay, liming help to some extent in the fight against pollution.
Sowing, mowing and removing some plants, such as clover, from the soil surface significantly reduces the concentration of heavy metals in the soil. Besides this way is completely environmentally friendly.
Underground water detoxification, its pumping and cleaning.
Prediction and elimination of migration of soluble form of heavy metals.
In some particularly severe cases, complete removal of the soil layer and its replacement with a new one is required.

Heavy metals (HMs) include about 40 metals with atomic masses over 50 and density over 5 g/cm 3 , although light beryllium is also included among HMs. Both features are rather conditional and the lists of HMs do not match for them.

According to toxicity and distribution in the environment, a priority group of HMs can be distinguished: Pb, Hg, Cd, As, Bi, Sn, V, Sb. Somewhat less important are: Cr, Cu, Zn, Mn, Ni, Co, Mo.

All HMs are poisonous to some extent, although some of them (Fe, Cu, Co, Zn, Mn) are part of biomolecules and vitamins.

Heavy metals of anthropogenic origin enter the soil from the air in the form of solid or liquid precipitation. Forest tracts with their developed contact surface especially intensively retain heavy metals.

In general, the risk of heavy metal pollution from the air exists equally for all soils. Heavy metals adversely affect soil processes, soil fertility and the quality of agricultural products. Restoring the biological productivity of soils contaminated with heavy metals is one of the most difficult problems in the protection of biocenoses.

An important feature metals is pollution resistant. The element itself cannot collapse, passing from one compound to another or moving between the liquid and solid phases. Redox transitions of metals with variable valence are possible.

HM concentrations dangerous for plants depend on the genetic type of the soil. The main indicators affecting the accumulation of HMs in soils are acid-base properties and humus content.

It is almost impossible to take into account all the diversity of soil-geochemical conditions when establishing the MPC of heavy metals. Currently, for a number of heavy metals, AECs have been established for their content in soils, which are used as MPCs (Appendix 3).

When the allowable values of HM content in soils are exceeded, these elements accumulate in plants in amounts exceeding their MPC in feed and food products.

In polluted soils, the penetration depth of HMs usually does not exceed 20 cm, however, in case of severe contamination, HMs can penetrate to a depth of up to 1.5 m. Among all heavy metals, zinc and mercury have the highest migration ability and are distributed evenly in the soil layer at a depth of 0...20 cm, while lead accumulates only in the surface layer (0...2.5 cm). An intermediate position between these metals is occupied by cadmium.

At lead the tendency to accumulation in the soil is clearly expressed; its ions are inactive even at low pH values. For different types of soils, the rate of lead leaching varies from 4 g to 30 g/ha per year. At the same time, the amount of lead introduced in different areas can be 40...530 g/ha per year. Lead entering the soil during chemical contamination forms hydroxide relatively easily in a neutral or alkaline environment. If the soil contains soluble phosphates, then lead hydroxide turns into sparingly soluble phosphates.

Significant soil contamination with lead can be found along major highways, near non-ferrous metallurgy enterprises, near waste incinerators, where there is no flue gas treatment. The ongoing gradual replacement of motor fuels containing tetraethyl lead with lead-free fuels has shown positive results: the influx of lead into the soil has sharply decreased and in the future this source of pollution will be largely eliminated.

The risk of lead with soil particles entering the child's body is one of the determining factors in assessing the risk of soil contamination. settlements. Background concentrations of lead in soils different type fluctuate within 10…70 mg/kg. According to American researchers, the content of lead in urban soils should not exceed 100 mg / kg - while protecting the child's body from excessive intake of lead through hands and contaminated toys. In real conditions, the content of lead in the soil significantly exceeds this level. In most cities, the content of lead in the soil varies within 30...150 mg/kg, with an average value of about 100 mg/kg. The highest lead content - from 100 to 1000 mg/kg - is found in the soil of cities where metallurgical and battery enterprises are located (Alchevsk, Zaporozhye, Dneprodzerzhinsk, Dnepropetrovsk, Donetsk, Mariupol, Krivoy Rog).

Plants are more tolerant of lead than humans and animals, so lead levels in plant foods and forage need to be carefully monitored.

In animals on pastures, the first signs of lead poisoning are observed at a daily dose of about 50 mg/kg of dry hay (on heavily lead-contaminated soils, the resulting hay may contain lead 6.5 g/kg of dry hay!). For humans, when eating lettuce, the MPC is 7.5 mg of lead per 1 kg of leaves.

Unlike lead cadmium enters the soil in much smaller quantities: about 3…35 g/ha per year. Cadmium is introduced into the soil from the air (about 3 g/ha per year) or with phosphorus-containing fertilizers (35...260 g/t). In some cases, cadmium processing plants may be the source of contamination. In acidic soils with a pH value<6 ионы кадмия весьма подвижны и накопления металла не наблюдается. При значениях рН>6 cadmium is deposited together with the hydroxides of iron, manganese and aluminum, while the loss of protons by OH groups occurs. Such a process becomes reversible with a decrease in pH, and cadmium, as well as other HMs, can diffuse irreversibly slowly into crystal lattice oxides and clays.

Cadmium compounds with humic acids are much less stable than similar lead compounds. Accordingly, the accumulation of cadmium in humus proceeds to a much lesser extent than the accumulation of lead.

Cadmium sulfide, which is formed from sulfates under favorable reduction conditions, can be mentioned as a specific cadmium compound in the soil. Cadmium carbonate is formed only at pH values >8, thus, the prerequisites for its implementation are extremely low.

Recently, much attention has been paid to the fact that an increased concentration of cadmium is found in biological sludge, which is introduced into the soil to improve it. About 90% of the cadmium present in sewage, passes into biological sludge: 30% during the initial sedimentation and 60 ... 70% during its further processing.

It is almost impossible to remove cadmium from sludge. However, more careful control of the content of cadmium in wastewater makes it possible to reduce its content in the sludge to values below 10 mg/kg of dry matter. Therefore, the practice of using sewage sludge as a fertilizer varies greatly from country to country.

The main parameters that determine the content of cadmium in soil solutions or its sorption by soil minerals and organic components are the pH and type of soil, as well as the presence of other elements, such as calcium.

In soil solutions, the concentration of cadmium can be 0.1 ... 1 µg / l. In the upper soil layers, up to 25 cm deep, depending on the concentration and type of soil, the element can be retained for 25...50 years, and in some cases even 200...800 years.

Plants assimilate from the mineral substances of the soil not only elements vital for them, but also those whose physiological effect is either unknown or indifferent to the plant. The content of cadmium in a plant is completely determined by its physical and morphological properties- its genotype.

The transfer coefficient of heavy metals from soil to plants is given below:

Pb 0.01…0.1 Ni 0.1…1.0 Zn 1…10

Cr 0.01…0.1 Cu 0.1…1.0 Cd 1…10

Cadmium is prone to active bioconcentration, which leads in a fairly short time to its accumulation in excess bioavailable concentrations. Therefore, cadmium, in comparison with other HMs, is the most powerful soil toxicant (Cd > Ni > Cu > Zn).

Between certain types plants show significant differences. If spinach (300 ppb), head lettuce (42 ppb), parsley (31 ppb), as well as celery, watercress, beets and chives can be attributed to plants "enriched" with cadmium, then Legumes, tomatoes, stone fruits and pome fruits contain relatively little cadmium (10...20 ppb). All concentrations are relative to the weight of the fresh plant (or fruit). Of the grain crops, wheat grain is more heavily contaminated with cadmium than rye grain (50 and 25 ppb), but 80...90% of the cadmium received from the roots remains in the roots and straw.

The uptake of cadmium by plants from the soil (soil/plant transfer) depends not only on the type of plant, but also on the content of cadmium in the soil. With a high concentration of cadmium in the soil (more than 40 mg/kg), its uptake by roots takes the first place; at a lower content, the greatest absorption occurs from the air through young shoots. Growth duration also affects cadmium enrichment: the shorter the growing season, the lower the transfer from soil to plant. This is the reason why the accumulation of cadmium in plants from fertilizers is less than its dilution due to the acceleration of plant growth caused by the action of the same fertilizers.

If a high concentration of cadmium is reached in plants, this can lead to disturbances in the normal growth of plants. The yield of beans and carrots, for example, is reduced by 50% if the cadmium content of the substrate is 250 ppm. In carrots, the leaves wilt at a cadmium concentration of 50 mg/kg of substrate. In beans, at this concentration, rusty (sharply defined) spots appear on the leaves. In oats, chlorosis (reduced chlorophyll content) can be observed at the ends of the leaves.

Compared to plants, many types of fungi accumulate large amounts of cadmium. Mushrooms with a high content of cadmium include some varieties of champignons, in particular sheep champignon, while meadow and cultivated champignons contain relatively little cadmium. In the study of various parts of mushrooms, it was found that the plates in them contain more cadmium than the cap itself, and the least cadmium in the stem of the mushroom. As experiments on growing champignons show, a two-threefold increase in the content of cadmium in mushrooms is found if its concentration in the substrate increases by 10 times.

Earthworms have the ability to rapidly accumulate cadmium from the soil, as a result of which they are suitable for bioindication of cadmium residues in the soil.

Ion mobility copper even higher than the mobility of cadmium ions. This creates more favorable conditions for the absorption of copper by plants. Due to its high mobility, copper is more easily washed out of the soil than lead. The solubility of copper compounds in soil increases markedly at pH values< 5. Хотя медь в следовых концентрациях считается необходимой для жизнедеятельности, у растений токсические эффекты проявляются при содержании 20 мг на кг сухого вещества.

The algaecidal action of copper is known. Copper has a toxic effect on microorganisms, while a concentration of about 0.1 mg / l is sufficient. The mobility of copper ions in the humus layer is lower than in the underlying mineral layer.

Relatively mobile elements in the soil include zinc. Zinc is one of the most common metals in technology and everyday life, so its annual application to the soil is quite large: it is 100 ... 2700 g per hectare. The soil near the enterprises processing zinc-containing ores is especially polluted.

The solubility of zinc in soil begins to increase at pH values<6. При более высоких значениях рН и в присутствии фосфатов усвояемость цинка растениями значительно понижается. Для сохранения цинка в почве важнейшую роль играют процессы адсорбции и десорбции, определяемые значением рН, в глинах и различных оксидах. В лесных гумусовых почвах цинк не накапливается; например, он быстро вымывается благодаря постоянному естественному поддержанию кислой среды.

For plants, a toxic effect is created at a content of about 200 mg of zinc per kg of dry material. The human body is sufficiently resistant to zinc and the risk of poisoning when using agricultural products containing zinc is low. However, soil contamination with zinc is a serious environmental problem, as it affects many plant species. At pH values>6, zinc accumulates in the soil in large quantities due to interaction with clays.

Various connections gland play a significant role in soil processes due to the ability of the element to change the degree of oxidation with the formation of compounds different solubility, oxidation, mobility. Iron in very high degree involved in anthropogenic activity, it is characterized by such a high technophilicity that they often talk about the modern "ferruginization" of the biosphere. More than 10 billion tons of iron are currently involved in the technosphere, 60% of which is dispersed in space.

Aeration of restored soil horizons, various dumps, waste heaps leads to oxidation reactions; while the iron sulfides present in such materials are converted to iron sulfates with the simultaneous formation of sulfuric acid:

4FeS 2 + 6H 2 O + 15O 2 \u003d 4FeSO 4 (OH) + 4H 2 SO 4

In such media, the pH values can decrease to 2.5...3.0. Sulphuric acid destroys carbonates with the formation of gypsum, magnesium and sodium sulfates. Periodic change in the redox conditions of the environment leads to soil decarbonization, further development stable acidic environment with a pH of 4 ... 2.5, and iron compounds and manganese accumulate in the surface horizons.

Hydroxides and oxides of iron and manganese during the formation of precipitates easily capture and bind nickel, cobalt, copper, chromium, vanadium, arsenic.

Main sources of soil pollution nickel - enterprises of metallurgy, mechanical engineering, chemical industry, combustion of coal and fuel oil at thermal power plants and boiler houses. Anthropogenic nickel pollution is observed at a distance of up to 80...100 km or more from the emission source.

The mobility of nickel in soil depends on the concentration of organic matter (humic acids), pH, and the potential of the medium. Nickel migration is complex. On the one hand, nickel comes from the soil in the form of a soil solution to plants and surface water, on the other hand, its amount in the soil is replenished due to the destruction of soil minerals, the death of plants and microorganisms, and also due to its introduction into the soil with precipitation and dust, with mineral fertilizers.

The main source of soil pollution chromium - combustion of fuel and waste from galvanic production, as well as slag dumps in the production of ferrochromium, chromium steels; some phosphate fertilizers contain chromium up to 10 2 ... 10 4 mg/kg.

Since Cr +3 in acidic environment inert (precipitating almost completely at pH 5.5), its compounds in the soil are very stable. On the contrary, Cr +6 is highly unstable and easily mobilized in acidic and alkaline soils. A decrease in the mobility of chromium in soils can lead to its deficiency in plants. Chromium is part of chlorophyll, which gives plant leaves green color, and ensures the assimilation of carbon dioxide from the air by plants.

It has been established that liming, as well as the use of organic substances and phosphorus compounds, significantly reduces the toxicity of chromates in contaminated soils. When soils are contaminated with hexavalent chromium, acidification and then the use of reducing agents (eg, sulfur) are used to reduce it to Cr +3 , after which liming is carried out to precipitate Cr +3 compounds.

The high concentration of chromium in the soil of cities (9...85 mg/kg) is associated with its high content in rain and surface waters.

The accumulation or leaching of toxic elements that have entered the soil largely depends on the content of humus, which binds and retains a number of toxic metals, but primarily copper, zinc, manganese, strontium, selenium, cobalt, nickel (in humus, the amount of these elements hundreds to thousands of times more than in the mineral component of soils).

natural processes ( solar radiation, climate, weathering, migration, decomposition, leaching) contribute to self-purification of soils, the main characteristic of which is its duration. Duration of self-cleaning- this is the time during which there is a decrease by 96% of the mass fraction of a pollutant from the initial value or to its background value. For self-purification of soils, as well as their restoration, a lot of time is required, which depends on the nature of pollution and natural conditions. The process of self-purification of soils lasts from several days to several years, and the process of restoration of disturbed lands takes hundreds of years.

The ability of soils to self-cleanse from heavy metals is low. Of the pretty rich organic matter forest soils of the temperate zone with surface runoff removes only about 5% of lead from the atmosphere and about 30% of zinc and copper. The rest of the precipitated HMs are almost completely retained in the surface soil layer, since migration down the soil profile is extremely slow: at a rate of 0.1–0.4 cm/year. Therefore, the half-life of lead, depending on the type of soil, can be from 150 to 400 years, and for zinc and cadmium - 100-200 years.

Agricultural soils are somewhat faster cleared of excess amounts of some HMs due to more intensive migration due to surface and subsoil runoff, and also due to the fact that a significant part of microelements through root system turns into green biomass and is carried away with the crop.

It should be noted that soil contamination with some toxic substances significantly inhibits the process of self-purification of soils from bacteria of the Escherichia coli group. Thus, at the content of 3,4-benzpyrene 100 μg/kg of soil, the number of these bacteria in the soil is 2.5 times higher than in the control, and at a concentration of more than 100 μg/kg and up to 100 mg/kg, they are much more numerous.

Soil studies in the area of metallurgical centers, carried out by the Institute of Soil Science and Agrochemistry, indicate that within a radius of 10 km, the lead content is 10 times higher than the background value. The greatest excess was noted in the cities of Dnepropetrovsk, Zaporozhye and Mariupol. The content of cadmium 10…100 times higher than the background level was noted around Donetsk, Zaporozhye, Kharkov, Lysichansk; chrome - around Donetsk, Zaporozhye, Krivoy Rog, Nikopol; iron, nickel - around Krivoy Rog; manganese - in the Nikopol region. In general, according to the same institute, about 20% of Ukraine's territory is contaminated with heavy metals.

When assessing the degree of pollution with heavy metals, data on MPC and their background content in the soils of the main natural and climatic zones of Ukraine are used. If an elevated content of several metals is established in the soil, the pollution is assessed by the metal, the content of which exceeds the standard to the greatest extent.

Heavy metals (HMs) are already ranked second in terms of danger, behind pesticides and well ahead of such well-known pollutants as carbon dioxide and sulfur. In the future, they may become more dangerous than nuclear power plant waste and solid waste. HM contamination is associated with their widespread use in industrial production. Due to imperfect purification systems, HMs enter the environment, including the soil, polluting and poisoning it. HMs are special pollutants, the monitoring of which is obligatory in all environments.

Soil is the main medium into which HMs enter, including from the atmosphere and the aquatic environment. It also serves as a source of secondary pollution of surface air and waters that enter the World Ocean from it.

HMs are absorbed from the soil by plants, which then get into food.

In works devoted to the problems of environmental pollution and environmental monitoring, today more than 40 elements of D.I. Mendeleev with an atomic mass of more than 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, heavy metals should be considered with with a density of more than 8 g/cm3. At the same time, 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 their 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 not clear at the moment), are actively involved in biological processes, are part of many enzymes.

In the dust of metallurgical industries, 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. Wastes from non-ferrous metallurgy enterprises, paint and varnish factories and reinforced concrete structures are enriched with mercury. The concentrations of W, Cd, and Pb are increased in dust from machine-building plants (Table 1).

Table 1. Main technogenic sources of heavy metals

Under the influence of metal-enriched emissions, areas of landscape pollution are formed mainly at the regional and local levels. The influence of energy enterprises on environmental pollution is not due to the concentration of metals in waste, but to their huge amount. The mass of waste, for example, in industrial centers, exceeds their total amount coming from all other sources of pollution. A significant amount of Pb is released into the environment with car exhaust gases, which exceeds its intake with waste from metallurgical enterprises.

Arable soils are contaminated with elements such as Hg, As, Pb, Cu, Sn, Bi, which enter the soil as part of pesticides, biocides, plant growth stimulants, structure formers. Non-traditional fertilizers made from various waste products often contain a wide range of contaminants at high concentrations. Of the traditional mineral fertilizers, phosphate fertilizers contain impurities of Mn, Zn, Ni, Cr, Pb, Cu, Cd.

The distribution in the landscape of metals released into the atmosphere from technogenic sources is determined by the distance from the source of pollution, climatic conditions (strength and direction of winds), terrain, and technological factors (the state of waste, the way waste enters the environment, the height of pipes of enterprises).

HM dissipation depends on the height of the source of emissions into the atmosphere. According to M.E. Berland, with high chimneys, a significant concentration of emissions is created in the surface layer of the atmosphere at a distance of 10-40 chimney heights. Six zones are distinguished around such pollution sources (Table 2). The area of influence of individual industrial enterprises on the adjacent territory can reach 1000 km2.

Table 2. Zones of soil contamination around point sources of pollution

	Distance from pollution source in km	Excess of HM content in relation to the background
Security zone of the enterprise

Soil pollution zones and their size are closely related to the vectors of the prevailing winds. The relief, vegetation, urban buildings can change the direction and speed of movement of the surface layer of air. Similarly to the zones of soil pollution, zones of vegetation cover pollution can also be distinguished.