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.

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, prevalence in the natural environment, the degree of involvement in natural and technogenic cycles.

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.

The most powerful suppliers of metal-enriched wastes are non-ferrous metal smelting enterprises (aluminum, alumina, copper-zinc, lead-smelting, nickel, titanium-magnesium, mercury, etc.), as well as non-ferrous metal processing (radio engineering, electrical engineering, instrument-making, galvanic, 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. Waste from non-ferrous metallurgy enterprises, paint and varnish industry plants and reinforced concrete structures enriched with mercury. in the dust machine-building plants increased concentrations of W, Cd, Pb (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 polluted 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 pollution source, climatic conditions(strength and direction of winds), terrain, technological factors (the state of waste, the way waste enters the environment, the height of the pipes of enterprises).

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

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

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.

FEDERAL AGENCY FOR EDUCATION STATE EDUCATIONAL INSTITUTION

HIGHER PROFESSIONAL EDUCATION "VORONEZH STATE UNIVERSITY"

SOIL POLLUTION WITH HEAVY METALS. METHODS FOR CONTROL AND REGULATION OF CONTAMINATED SOILS

Educational and methodical manual for universities

Compiled by: Kh.A. Dzhuvelikyan, D.I. Shcheglov, N.S. Gorbunova

Publishing and Printing Center of Voronezh State University

Approved by the Scientific and Methodological Council of the Faculty of Biology and Soil on July 4, 2009, Protocol No. 10

Reviewer Dr. of Biol. sciences, prof. L.A. Yablonsky

The teaching aid was prepared at the Department of Soil Science and Land Management of the Faculty of Biology and Soil of Voronezh State University.

For specialty 020701 - Soil science

GENERAL INFORMATION ABOUT POLLUTION

Pollutants- these are substances of anthropogenic origin entering the environment in quantities exceeding the natural level of their intake. Soil pollution- a type of anthropogenic degradation, in which the content of chemicals in soils subject to anthropogenic impact exceeds the natural regional background level. Exceeding the content of certain chemicals in the human environment (compared to natural levels) due to their intake from anthropogenic sources is an environmental hazard.

Human use of chemicals in economic activities and their involvement in the cycle of anthropogenic transformations into environment is constantly growing. A characteristic of the intensity of extraction and use chemical elements is technophilicity - the ratio of the annual extraction or production of an element in tons to its clarke in the lithosphere (A.I. Perelman, 1999). High technophilicity is typical for the elements most actively used by man, especially for those whose natural level in the lithosphere is low. high levels technophilicity is typical for such metals as Bi, Hg, Sb, Pb, Cu, Se, Ag, As, Mo, Sn, Cr, Zn, the need for which is great for various types of industries. With a low content of these elements in rocks (10–2–10–6%), their extraction is significant. This leads to the extraction of colossal amounts of ores containing these elements from the bowels of the earth, and to their subsequent global dispersion in the environment.

In addition to technophility, other quantitative characteristics of technogenesis have been proposed. Thus, the ratio of the technophilicity of an element to its biophilicity (biophilicity - clarkes of the concentration of chemical elements in living matter) M.A. Glazovskaya named destructive activity of the elements of technogenesis. The destructive activity of the elements of technogenesis characterizes the degree of danger of the elements for living organisms. Another quantitative characteristic of the anthropogenic involvement of chemical elements in their global cycles on the planet is mobilization factor or technogenic enrichment factor, which is calculated as the ratio of the technogenic flux of a chemical element to its natural flux. The level of the technogenic enrichment factor, as well as the technophilicity of elements, is not only an indicator of their mobilization from the lithosphere to terrestrial natural environments, but also a reflection of the level of emissions of chemical elements with industrial waste into the environment.

THE CONCEPT OF MAN-MADE ANOMALIES

Geochemical anomaly- a section of the earth's crust (or surface of the earth), characterized by significantly increased concentrations of any chemical elements or their compounds compared to background values ​​and regularly located relative to accumulations of minerals. The identification of technogenic anomalies is one of the most important ecological and geochemical tasks in assessing the state of the environment. Anomalies are formed in the components of the landscape as a result of the intake of various substances from technogenic sources and represent a certain volume within which the values ​​of anomalous concentrations of elements are greater than the background values. According to the prevalence of A.I. Perelman and N.S. Kasimov (1999) identifies the following man-made anomalies:

1) global - covering the entire globe (for example, increased

2) regional - formed in certain parts of the continents, natural zones and regions as a result of the use of pesticides, mineral fertilizers, acidification of precipitation with emissions of sulfur compounds, etc.;

3) local - formed in the atmosphere, soils, waters, plants around local man-made sources: factories, mines, etc.

According to the formation environment, man-made anomalies are divided into:

1) on lithochemical (in soils, rocks);

2) hydrogeochemical (in waters);

3) atmogeochemical (in the atmosphere, snow);

4) biochemical (in organisms).

According to the duration of the source of pollution, they are divided into:

– for short-term (accidental releases, etc.);

– medium-term (with the cessation of impact, for example, the cessation of the development of mineral deposits);

– long-term stationary (anomalies of factories, cities, agricultural landscapes, for example, KMA, Norilsk Nickel).

When assessing technogenic anomalies, background areas are chosen far from technogenic sources of pollutants, as a rule, more than 30–50 km away. One of the anomalous criteria is the coefficient of technogenic concentration or anomaly Kc, which is the ratio of the element content in the considered anomalous object to its background content in the landscape components.

To assess the impact of the amount of pollutants entering the body, hygienic pollution standards are also used - pre-

specific allowable concentrations. This is the maximum content. harmful substance in a natural object or product (water, air, soil, food) that does not affect human health or other organisms.

Pollutants are divided into classes according to hazard (GOST

17.4.1.0283): Class I (highly hazardous) - As, Cd, Hg, Se, Pb, F, benzo(a)pyrene, Zn; Class II (moderately hazardous) - B, Co, Ni, Mo, Cu, Sb, Cr; Class III (low hazardous) - Ba, V, W, Mn, Sr, acetophenone.

SOIL POLLUTION WITH HEAVY METALS

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, 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.

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, prevalence in the natural environment, the degree of involvement in natural and technogenic cycles.

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 (1990),

heavy metals should be considered 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 falling under this definition

iron (with the exception of lead, mercury, cadmium and bismuth, whose biological role is currently unclear), actively participate in biological processes, and are part of many enzymes.

The most powerful suppliers of metal-enriched wastes are non-ferrous metal smelting enterprises (aluminum, alumina, copper-zinc, lead-smelting, nickel, titanium-magnesium, mercury, etc.), as well as non-ferrous metal processing (radio engineering, electrical engineering, instrument-making, galvanic, 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 concentrations of W, Cd, and Pb are increased in dust from machine-building plants (Table 1).

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 polluted 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 (Gaponyuk, 1985).

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

HM dissipation depends on the height of the source of emissions into the atmosphere. According to M.E. Berlyand (1975), 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

Soil contamination zones around point pollution sources

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.

MIGRATION OF HEAVY METALS IN THE SOIL PROFILE

The accumulation of the main part of pollutants is observed mainly in the humus-accumulative soil horizon, where they are bound by aluminosilicates, non-silicate minerals, organic substances due to various interaction reactions. The composition and amount of elements retained in the soil depend on the content and composition of humus, acid-base and redox conditions, sorption capacity, and the intensity of biological absorption. Some of the heavy metals are firmly held by these components and not only do not participate in migration along the soil profile, but also do not pose a danger.

for living organisms. The negative environmental consequences of soil pollution are associated with mobile metal compounds.

AT within the soil profile, the technogenic flow of substances meets a number of soil-geochemical barriers. These include carbonate, gypsum, illuvial horizons (illuvial-ferruginous-humus). Some of the highly toxic elements can transform into compounds that are difficult for plants to access, while other elements that are mobile in a given soil geochemical environment can migrate in the soil layer, representing a potential hazard to biota. The mobility of elements largely depends on the acid-base and redox conditions in soils. In neutral soils, Zn, V, As, Se compounds are mobile, which can be leached during seasonal wetting of soils.

The accumulation of mobile compounds of elements that are especially dangerous for organisms depends on the water and air regimes of soils: their smallest accumulation is observed in permeable soils of the leaching regime, it increases in soils with a non-leaching regime and is maximum in soils with an effusion regime. With evaporative concentration and alkaline reaction, Se, As, V can be accumulated in the soil in an easily accessible form, and under conditions of a reducing environment, Hg in the form of methylated compounds.

However, it should be borne in mind that under the conditions of the leaching regime, the potential mobility of metals is realized, and they can be taken out of the soil profile, being sources of secondary pollution. groundwater.

AT in acidic soils with a predominance of oxidizing conditions (podzolic soils, well drained), heavy metals such as Cd and Hg form easily mobile forms. On the contrary, Pb, As, Se form low-mobility compounds that can accumulate in humus and illuvial horizons and negatively affect the state of soil biota. If S is present in the composition of the pollutants, a secondary hydrogen sulfide environment is created under reducing conditions, and many metals form insoluble or slightly soluble sulfides.

AT In waterlogged soils, Mo, V, As, and Se are present in inactive forms. A significant part of the elements in acidic waterlogged soils is present in relatively mobile and dangerous forms for living matter; such are the compounds of Pb, Cr, Ni, Co, Cu, Zn, Cd and Hg. In slightly acidic and neutral soils with good aeration, hardly soluble Pb compounds are formed, especially during liming. In neutral soils, Zn, V, As, Se compounds are mobile, while Cd and Hg can be retained in the humus and illuvial horizons. As alkalinity increases, the risk of soil contamination with these elements increases.

THE CONCEPT OF SOIL ENVIRONMENTAL MONITORING

Soil environmental monitoring – system of regular non-limiting

limited in space and time control of soils, which provides information about their condition in order to assess the past, present and forecast changes in the future. Soil monitoring aims to identify anthropogenic changes in soils that may ultimately harm human health. The special role of soil monitoring is due to the fact that all changes in the composition and properties of soils affect the fulfillment of their ecological functions by soils, and, consequently, the state of the biosphere.

Of great importance is the fact that in the soil, in contrast to the air of the atmosphere and surface waters, the environmental consequences of anthropogenic impact usually manifest themselves later, but they are more stable and last longer. There is a need to assess the long-term consequences of this impact, for example, the possibility of mobilization of pollutants in soils, as a result of which soil can turn from a “depot” of pollutants into their secondary source.

Types of soil environmental monitoring

The identification of types of soil environmental monitoring is based on differences in the combination of informative soil indicators corresponding to the tasks of each of them. On the basis of differences in the mechanisms and scales of manifestation of soil degradation, two groups of types of monito-

ring: the first group - global monitoring, the second - local and regional.

Global Soil Monitoring – component global monitoring of the biosphere. It is carried out to assess the impact on the state of soils of the environmental consequences of long-range atmospheric transport of pollutants in connection with the danger of planetary pollution of the biosphere and the global processes accompanying it. The results of global or biospheric monitoring characterize global changes the state of living organisms on the planet under the influence of human activity.

The purpose of local and regional monitoring is to identify the impact of soil degradation on ecosystems at the local and regional levels and directly on human living conditions in the field of nature management.

Local monitoring also called sanitary-hygienic or impact. It is aimed at controlling the level of content in the environment of those pollutants that are emitted by a specific

One of the strongest and most widespread chemical pollution is heavy metal pollution. Heavy metals include more than 40 chemical elements of D.I. Mendeleev, the mass of atoms of which is more than 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 "trace elements". 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 rocks and minerals, erosion processes, volcanic activity) and technogenic (mining and processing of minerals, fuel combustion, traffic, agricultural activities). Part of technogenic emissions coming into natural environment in the form of fine aerosols, is transported over considerable distances and causes global pollution.

The other part enters drainless water bodies, where heavy metals accumulate and become a source of secondary pollution, i.e. the formation of hazardous contaminants in the course of 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 - soil blowing.

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 that got into it occurs.

Heavy metals have a high capacity for a variety of chemical, physicochemical and biological reactions. Many of them have a variable valency and are involved in redox processes. Heavy metals and their compounds, like other chemical compounds, are able to move and redistribute in living environments, i.e. migrate.

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

Mercury, lead, cadmium are included in the general list of the most important environmental pollutants, agreed 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 a significant atomic weight or density. About forty different definitions of the term heavy metals are known, and it is impossible to point to one of them as the most accepted. Accordingly, the list of heavy metals under different definitions will include different elements. The criterion used may be an atomic weight over 50, in which case all metals starting with vanadium, regardless of density, are included in the list. Another frequently used criterion is a density approximately equal to or greater than the density of iron (8 g/cm3), then elements such as lead, mercury, copper, cadmium, cobalt fall into the list, and, for example, lighter tin drops 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, not classifying them as heavy, some exclude non-ferrous metals (iron, manganese).

Term heavy metals 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 chemical and physical properties element, but also its biological activity and toxicity, as well as the amount of use in economic activity.

In addition to lead, mercury has been studied most fully in comparison with other microelements.

Mercury is extremely rare in earth's crust(-0.1 x 10-4%), however, it 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 activities have led to the fact that about 50 million tons of this metal have accumulated in the world's oceans. The natural removal of mercury to the ocean as a result of erosion is 5000 tons/year, another 5000 tons/year of mercury is removed as a result of human activities.

Initially, mercury enters the ocean in the form of Hg2 +, then it interacts with organic substances and, with the help of anaerobic organisms, passes into toxic substances methylmercury (CH3Hg) + and dimethylmercury (CH3-Hg-CH3), Mercury is present not only in the hydrosphere, but also in the atmosphere because 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 in them. Because mercury is adsorbed to sediment, it can be slowly released and dissolved in water, resulting in a chronic source of pollution that persists long after the original source of pollution has disappeared.

The world production of mercury is currently over 10,000 tons per year, most of of this amount is used in the production of chlorine. Mercury enters the air as a result of burning fossil fuels. Analysis of the ice of the Greenland Ice Dome showed that, starting from 800 AD. until the 1950s, the mercury content remained constant, but since the 50s. of our century, the amount of mercury has doubled. Figure 1 shows the ways of cyclic migration of mercury. Mercury and its compounds are life threatening. Methylmercury is especially dangerous for animals and humans, as it quickly passes from the blood into the brain tissue, destroying the cerebellum and the cerebral cortex. The clinical symptoms of such a lesion are numbness, loss of orientation in space, loss of vision. Symptoms of mercury poisoning do not appear immediately. Other an 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 is teratogenic in humans. Mercury belongs to the 1st hazard class.

Metallic mercury is dangerous if swallowed and inhaled. At the same time, a person has a metallic taste in the mouth, nausea, vomiting, abdominal cramps, teeth turn black and begin to crumble. Spilled mercury breaks into droplets and, if this happens, the mercury must be carefully collected.

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

In adults, ingestion of about 350 mg of mercury can lead to death.

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

About 180 thousand tons of lead migrate annually in the world as a result of the impact of atmospheric processes. During the extraction 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 its amount entering the environment as a result of exposure to atmospheric processes on igneous rocks.

The most serious source of environmental pollution with lead is the exhaust of automobile engines. The antiknock tetramethyl - or tetraethylswinep - has been added to most gasolines since 1923 at about 80 mg/l. When driving, from 25 to 75% of this lead, depending on driving conditions, is released into the atmosphere. Its main mass is deposited on the ground, but a noticeable part of it remains in the air.

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

Active sources of lead pollution are coal-fired power plants and household stoves.

Sources of lead contamination in the home can be glazed earthenware; lead contained in coloring pigments.

Lead is not a vital 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 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 the age of 30-40 in persons not associated with lead pollution by occupation, it is 80-200 mg.

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

Cadmium, zinc and copper are the most important metals in the study of pollution problems, as they are widely distributed 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 plants for its smelting, which is about 45% general pollution this element. 52% of pollution comes from the combustion or processing of products containing cadmium. Cadmium has a relatively high volatility, so it easily diffuses into the atmosphere. The sources of air pollution with zinc are the same as with cadmium.

The entry of cadmium into natural waters occurs as a result of its use in galvanic processes and technology. The most serious sources of water pollution with zinc are zinc smelters and electroplating plants.

Fertilizers are a potential source of cadmium contamination. At the same time, cadmium is introduced into plants that are used by humans for food, and at the end of the chain they pass into the human body. Cadmium and zinc readily enter seawater and the ocean through a network of surface and groundwater.

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

Zinc is the least toxic of all the heavy metals listed above. 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. AT large quantities it induces vomiting, this dose is approximately 150 mg for an adult.

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

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

In the study of the presence of cadmium in food, it was found that the excretion 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 effective way to prevent the release of cadmium and zinc in the form of pollution is to control the content of these metals in the emissions of smelters and other industrial enterprises.

In addition to the metals discussed earlier (mercury, lead, cadmium, zinc), there are other toxic elements, the introduction of which into the environment of organisms as a result of human activities causes serious concern.

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

The toxic effect of antimony is similar to that of arsenic. Large amounts of antimony cause vomiting, with chronic antimony poisoning, an upset of the digestive tract 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 contamination with this metal are herbicides ( chemical substances weed control), fungicides (substances used to control fungal plant diseases) and insecticides (substances used to control harmful insects).

According to its toxic properties, arsenic belongs to the accumulating poisons. According to the degree of toxicity, elemental arsenic and its compounds should be distinguished. Elemental arsenic is relatively slightly toxic, but has teratogenic properties. Harmful effect on hereditary material (mutagenicity) is disputed.

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

Cobalt is not widely used. So, for example, it is used in the steel industry, in the production of polymers. When ingested in large quantities, cobalt adversely affects the hemoglobin content in human blood and can cause blood diseases. It is believed that cobalt causes Graves' disease. This element is dangerous for 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, cadmium, and zinc. It is present in small amounts in zinc concentrates and can be transported long distances in air and water. Abnormal copper content is found in plants with air and water. Abnormal copper content is found in plants and soils at a distance of more than 8 km from the smelter. Copper salts belong to II hazard class. Toxic properties Copper has been studied much less than the same properties of other elements. The absorption of large amounts of copper by a person leads to Wilson's disease, while excess copper is 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 alloyed steels, alloys, electric batteries and other chemical current sources. The presence of manganese in the air in excess of the norm (the average daily concentration of manganese in the atmosphere - the air of populated areas - is 0.01 mg / m3) adversely affects the human body, which is expressed in the progressive destruction of the central nervous system. Manganese belongs to II hazard class.

Metal ions are indispensable components of natural water bodies. Depending on environmental conditions (pH, redox potential, the presence of ligands), they exist in different degrees of oxidation and are part of a variety of inorganic and organometallic compounds, which can be truly dissolved, colloidal-dispersed, or be part of mineral and organic suspensions. The 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 the availability for aquatic microorganisms depend on the forms of their existence in the aquatic ecosystem. Many metals form fairly strong complexes with organics; these complexes are one of the most important forms of migration of elements into natural waters. Most organic complexes are formed by the chelate cycle and are stable. The 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 media. Therefore, organometallic complexes are capable of migrating in natural waters over very considerable distances. This is especially important for low-mineralized and, first of all, surface waters, in which the formation of other complexes is impossible.

Heavy metals and their salts are widespread industrial pollutants. They enter water bodies 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 trace elements are constantly found in natural water bodies and organs of aquatic organisms (see table). Depending on the geochemical conditions, there are wide fluctuations in their level.

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

The presence of nickel in natural waters is due to the composition of the rocks through which water passes: it is found in places of deposits of sulfide copper-nickel ores and iron-nickel ores. It enters the water from soils and from plant and animal organisms during their decay. An increased content of nickel 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 enrichment plants. 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 an increase in pH values), due to the consumption of it 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 water composition, temperature, and pH values. Sorbents of nickel compounds can be iron hydroxide, organic substances, highly dispersed calcium carbonate, clays.

Cobalt compounds enter natural waters as a result of their leaching 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 the decomposition of plant and animal organisms. Cobalt compounds in natural waters are in a dissolved and suspended state, the quantitative ratio between which is determined by the chemical composition of 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, while earlier they were gradually supplanted by spectrometric methods. Among the spectrometric methods for the determination of heavy metals, the first place is occupied by atomic absorption spectrometry with different atomization of samples: atomic absorption spectrometry with flame atomization (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 a detection limit for the determination of heavy metals in water.

The determination of the content of heavy metals in a sample is carried out by transferring the sample into a solution - due to chemical dissolution in a suitable solvent (water, aqueous solutions of acids, less often alkalis) or fusion with a suitable flux from among alkalis, oxides, salts, followed by leaching with water. After that, the compound of the desired metal is precipitated by adding a solution of the corresponding 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 to the initial content in the sample. With qualified application, the method gives the most exact values heavy metal content, but requires high costs time.

To determine the content of heavy metals by electrochemical methods, the sample must also be converted into water solution. After that, 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 these methods with titration. The basis for determining the content of heavy metals by these methods is the analysis of current-voltage characteristics, 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 the electrochemical control of neutralization and others in solutions. Using these methods, heavy metals up to 10-9 mol/l can be determined.

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

In natural normal conditions all processes occurring in soils are in balance. Changes in the composition and properties of the soil can be caused natural phenomena, but most often a person is guilty of violating the equilibrium state of the soil:

1. atmospheric transport of pollutants in the form of aerosols and dust (heavy metals, fluorine, arsenic, oxides of sulfur, nitrogen, etc.)
2. agricultural pollution (fertilizers, pesticides)
3. unearthly pollution - dumps of large-capacity industries and emissions from fuel and energy complexes
4. pollution by oil and oil products
5. plant debris. 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 ecological disaster zones, 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 the technogenic contamination of soils with heavy metals, it is customary to determine their gross content. However, the total content may not always characterize the degree of danger of soil pollution, since the soil is able to bind metal compounds, converting them into compounds inaccessible to plants. It would be more correct to speak about the role of "mobile" and "accessible" forms for plants. It is desirable to determine the content of mobile forms of metals in the case of their high gross amounts in the soil, and also when it is necessary to characterize the migration of pollutant metals from soil to plants.

If the soils are contaminated with heavy metals and radionuclides, then it is almost impossible to clean them. So far, the only way is known: to sow such soils with fast-growing crops that give a large phytomass. Such cultures that extract heavy metals are subject to destruction after maturation. It takes decades to restore polluted 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 huge quantities accumulate in the environment and easily enter the human body both with food and water, and by inhalation of air.

When the content of heavy metals in the body exceeds the maximum permissible concentration, their negative impact on a person 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, which reduces the ability of these organs to filter. As a result, toxins and waste products of cells 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 using 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 ecologically clean areas and do not contain harmful substances.

Heavy metals are biochemically active elements that enter the cycle of organic substances and affect mainly living organisms. Heavy metals include elements such as lead, copper, zinc, cadmium, nickel, cobalt and a number of others.

The migration of heavy metals in soils depends, first of all, on alkaline-acid and redox conditions, which determine the diversity of soil-geochemical conditions. An important role in the migration of heavy metals in the soil profile is played by geochemical barriers, which in some cases enhance, in others weaken (due to the ability to conserve) the resistance of soils to heavy metal pollution. At each of the geochemical barriers, a certain group of chemical elements with similar geochemical properties lingers.

Specifics of the main soil-forming processes and type water regime determine the nature of the distribution of heavy metals in soils: accumulation, conservation or removal. Groups of soils with the accumulation of heavy metals in different parts of the soil profile were identified: on the surface, in the upper, in the middle, with two maxima. In addition, soils in the zone were identified, which are characterized by the concentration of heavy metals due to intra-profile cryogenic conservation. A special group is formed by soils where, under the conditions of leaching and periodically leaching regimes, heavy metals are removed from the profile. The intra-profile distribution of heavy metals has great importance to assess soil pollution and predict the intensity of accumulation of pollutants in them. The characteristic of the intra-profile distribution of heavy metals is supplemented by the grouping of soils according to the intensity of their involvement in the biological cycle. In total, three gradations are distinguished: high, moderate and weak.

The geochemical environment of the migration of heavy metals in the soils of river floodplains is peculiar, where, with increased watering, the mobility of chemical elements and compounds increases significantly. The specificity of geochemical processes here is due, first of all, to the pronounced seasonality of the change in redox conditions. This is due to the peculiarities of the hydrological regime of rivers: the duration of spring floods, the presence or absence of autumn floods, and the nature of the low-water period. The duration of flood water flooding of floodplain terraces determines the predominance of either oxidative (short-term floodplain flooding) or redox (long-term flooding) conditions.

Arable soils are subjected to the greatest technogenic impacts of an areal nature. The main source of pollution, with which up to 50% of the total amount of heavy metals enters arable soils, is phosphate fertilizers. To determine the degree of potential contamination of arable soils, a coupled analysis of soil properties and pollutant properties was carried out: the content, composition of humus and particle size distribution of soils, as well as alkaline-acid conditions were taken into account. Data on the concentration of heavy metals in phosphorites of deposits of different genesis made it possible to calculate their average content, taking into account the approximate doses of fertilizers applied to arable soils in different regions. The assessment of soil properties is correlated with the values ​​of agrogenic load. The cumulative integral assessment formed the basis for identifying the degree of potential soil contamination with heavy metals.

The most dangerous in terms of the degree of contamination with heavy metals are multi-humus, clay-loam soils with an alkaline reaction of the environment: dark gray forest soils, and dark chestnut soils with a high accumulative capacity. The Moscow and Bryansk regions are also characterized by an increased risk of soil pollution with heavy metals. The situation with soddy-podzolic soils does not contribute to the accumulation of heavy metals here, but in these areas the technogenic load is high and the soils do not have time to "self-purify".

Ecological and toxicological assessment of soils for the content of heavy metals showed that 1.7% of agricultural land is contaminated with substances of hazard class I (highly hazardous) and 3.8% - hazard class II (moderately hazardous). Soil contamination with heavy metals and arsenic content above the established norms was detected in the Republic of Buryatia, the Republic of Dagestan, the Republic of Mordovia, the Republic of Tyva, in the Krasnoyarsk and Primorsky Territories, in Ivanovo, Irkutsk, Kemerovo, Kostroma, Murmansk, Novgorod, Orenburg, Sakhalin, Chita regions.

Local contamination of soils with heavy metals is associated primarily with large cities and. The assessment of the risk of soil contamination by heavy metal complexes was carried out according to the total indicator Zc.

Soil contamination with heavy metals

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 danger 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 of metals is the stability of pollution. 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, 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 danger of lead with soil particles entering the child's body is one of the determining factors in assessing the risk of soil pollution in settlements. Background concentrations of lead in soils of different types range from 10 to 70 mg/kg. According to American researchers, the content of lead in urban soils should not exceed 100 mg / kg - this ensures the protection of 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 lead content in the soil varies between 30…150 mg/kg at average 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, with the loss of protons by OH groups. 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 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 can reduce its content in the sludge to values ​​below 10 mg/kg of dry matter. Therefore, the practice of using silt treatment facilities as a fertilizer is very different in different countries.

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 such physiological action which are 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).

Significant differences are observed between individual plant species. 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 a large number of cadmium. with mushrooms high content cadmium include some varieties of champignons, in particular sheep champignon, while meadow and cultivated champignons contain relatively little cadmium. When examining 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 uptake 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 of different solubility, oxidation, mobility. Iron is involved in anthropogenic activity to a very high degree; it is characterized by such a high technophilicity that it is often said that 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. Sulfuric 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 waters, 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 is inert in an acidic environment (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 soil self-purification, 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. From fairly rich in organic matter forest soils of the temperate zone with surface runoff, only about 5% of the lead coming from the atmosphere and about 30% of zinc and copper are removed. 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 passes through the root system into green biomass and is carried away with the harvest.

It should be noted that soil pollution by 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 research in the area metallurgical centers, conducted 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.