Forms of finding heavy metals in the soil. Methods for determining heavy metals in soil

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 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.
• Predicting and addressing migration soluble form heavy metals.
• In some particularly severe cases, complete removal of the soil layer and its replacement with a new one is required.

The most dangerous of all these metals is lead. It has the property of accumulating to hit the human body. Mercury is not dangerous if it enters the human body once or several times, only mercury vapor is especially dangerous. I believe that industrial enterprises should use more advanced production technologies that are not so detrimental to all living things. Not one person should think, but a mass, then we will come to a good result.

PAGE_BREAK-- heavy metals, which characterizes a wide group of pollutants, has recently become widespread. 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 some cases, the definition of heavy metals includes elements that are brittle (for example, bismuth) or metalloids (for example, arsenic).

In the works devoted to the problems of environmental pollution and environmental monitoring, to date, to heavy metals include more than 40 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 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. According to the classification of N. Reimers, metals with a density of more than 8 g/cm3 should be considered heavy. Thus, heavy metals are Pb, Cu, Zn, Ni, Cd, Co, Sb, Sn, Bi, Hg.

Formally defined heavy metals corresponds a large number of elements. However, according to researchers involved in practical activities related to the organization of observations of the state and pollution of the 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 section heavy metals 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 assigned to heavy metals. According to the definition of N. Reimers, noble and rare metals stand apart from heavy metals, respectively, remain only Pb, Cu, Zn, Ni, Cd, Co, Sb, Sn, Bi, Hg. In applied work, heavy metals are most often added Pt, Ag, W, Fe, Au, Mn.

Metal ions are indispensable components of natural water bodies. Depending on the 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 organic matter; these complexes are one of the most important forms of element migration in 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.

To understand the factors that regulate the metal concentration in natural waters, their chemical reactivity, bioavailability and toxicity, it is necessary to know not only the total content, but also the proportion of free and bound metal forms.

The transition of metals in an aqueous medium to the metal complex form has three consequences:

1. There may be an increase in the total concentration of metal ions due to its transition into solution from bottom sediments;

2. The membrane permeability of complex ions can differ significantly from the permeability of hydrated ions;

3. The toxicity of the metal as a result of complexation can change greatly.

So, chelate forms Cu, Cd, Hg less toxic than free ions. To understand the factors that regulate the metal concentration in natural waters, their chemical reactivity, bioavailability and toxicity, it is necessary to know not only the total content, but also the proportion of bound and free forms.

Sources of water pollution with heavy metals are wastewater from galvanizing shops, mining, ferrous and non-ferrous metallurgy, and machine-building plants. Heavy metals are found in fertilizers and pesticides and can enter water bodies along with runoff from agricultural land.

An increase in the concentration of heavy metals in natural waters is often associated with other types of pollution, such as acidification. The precipitation of acid precipitation contributes to a decrease in the pH value and the transition of metals from a state adsorbed on mineral and organic substances to a free state.

First of all, of interest are those metals that pollute the atmosphere the most due to their use in significant volumes in production activities and, as a result of accumulation in the external environment, pose a serious danger in terms of their biological activity and toxic properties. These include lead, mercury, cadmium, zinc, bismuth, cobalt, nickel, copper, tin, antimony, vanadium, manganese, chromium, molybdenum and arsenic.
Biogeochemical properties of heavy metals

H - high, Y - moderate, H - low

Vanadium.

Vanadium is predominantly in a dispersed state and is found in iron ores, oil, asphalt, bitumen, oil shale, coal, etc. One of the main sources of vanadium pollution of natural waters is oil and its products.

It occurs in natural waters in very low concentrations: in river water 0.2 - 4.5 µg/dm3, in sea water - an average of 2 µg/dm3

In water it forms stable anionic complexes (V4O12)4- and (V10O26)6-. In the migration of vanadium, the role of its dissolved complex compounds with organic substances, especially with humic acids, is essential.

Elevated concentrations of vanadium are harmful to human health. MPCv of vanadium is 0.1 mg/dm3 (the limiting indicator of harmfulness is sanitary-toxicological), MPCvr is 0.001 mg/dm3.

The natural sources of bismuth entering natural waters are the processes of leaching of bismuth-containing minerals. The source of entry into natural waters can also be wastewater from pharmaceutical and perfume industries, some glass industry enterprises.

It is found in unpolluted surface waters in submicrogram concentrations. The highest concentration was found in groundwater and is 20 µg/dm3, in marine waters - 0.02 µg/dm3. MPCv is 0.1 mg/dm3

The main sources of iron compounds in surface waters are the processes of chemical weathering of rocks, accompanied by their mechanical destruction and dissolution. In the process of interaction with mineral and organic substances contained in natural waters, a complex complex of iron compounds is formed, which are in water in a dissolved, colloidal and suspended state. Significant amounts of iron come with underground runoff and with wastewater from enterprises of the metallurgical, metalworking, textile, paint and varnish industries and with agricultural effluents.

Phase equilibria depend on the chemical composition of water, pH, Eh, and, to some extent, temperature. In routine analysis weighted form emit particles with a size of more than 0.45 microns. It is predominantly iron-bearing minerals, iron oxide hydrate and iron compounds adsorbed on suspensions. Truly dissolved and colloidal form are usually considered together. Dissolved iron represented by compounds in ionic form, in the form of a hydroxocomplex and complexes with dissolved inorganic and organic substances of natural waters. In the ionic form, mainly Fe(II) migrates, and Fe(III) in the absence of complexing substances cannot be in a significant amount in a dissolved state.

Iron is found mainly in waters with low Eh values.

As a result of chemical and biochemical (with the participation of iron bacteria) oxidation, Fe(II) passes into Fe(III), which, upon hydrolysis, precipitates in the form of Fe(OH)3. Both Fe(II) and Fe(III) tend to form hydroxo complexes of the type +, 4+, +, 3+, - and others that coexist in solution at different concentrations depending on pH and generally determine the state of the iron-hydroxyl system. The main form of occurrence of Fe(III) in surface waters is its complex compounds with dissolved inorganic and organic compounds, mainly humic substances. At pH = 8.0, the main form is Fe(OH)3. The colloidal form of iron is the least studied; it is iron oxide hydrate Fe(OH)3 and complexes with organic substances.

The content of iron in the surface waters of the land is tenths of a milligram, near the swamps - a few milligrams. An increased content of iron is observed in swamp waters, in which it is found in the form of complexes with salts of humic acids - humates. The highest concentrations of iron (up to several tens and hundreds of milligrams per 1 dm3) are observed in groundwater with low pH values.

Being a biologically active element, iron to a certain extent affects the intensity of phytoplankton development and the qualitative composition of the microflora in the reservoir.

Iron concentrations are subject to marked seasonal fluctuations. Usually, in reservoirs with high biological productivity, during the period of summer and winter stagnation, an increase in the concentration of iron in the bottom layers of water is noticeable. The autumn-spring mixing of water masses (homothermia) is accompanied by the oxidation of Fe(II) to Fe(III) and the precipitation of the latter in the form of Fe(OH)3.

It enters natural waters during the leaching of soils, polymetallic and copper ores, as a result of the decomposition of aquatic organisms capable of accumulating it. Cadmium compounds are carried into surface water with wastewater from lead-zinc plants, ore-dressing plants, a number of chemical enterprises (sulfuric acid production), galvanic production, and also with mine waters. The decrease in the concentration of dissolved cadmium compounds occurs due to the processes of sorption, precipitation of cadmium hydroxide and carbonate and their consumption by aquatic organisms.

Dissolved forms of cadmium in natural waters are mainly mineral and organo-mineral complexes. The main suspended form of cadmium is its adsorbed compounds. A significant part of cadmium can migrate within the cells of aquatic organisms.

In river uncontaminated and slightly polluted waters, cadmium is contained in submicrogram concentrations; in polluted and waste waters, the concentration of cadmium can reach tens of micrograms per 1 dm3.

Cadmium compounds play an important role in the life of animals and humans. It is toxic in high concentrations, especially in combination with other toxic substances.

MPCv is 0.001 mg/dm3, MPCvr is 0.0005 mg/dm3 (the limiting sign of harmfulness is toxicological).

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. Dissolved forms are represented mainly by complex compounds, incl. with organic matter in natural waters. Divalent cobalt compounds are most characteristic of surface waters. In the presence of oxidizing agents, trivalent cobalt can exist in appreciable concentrations.

Cobalt is one of the biologically active elements and is always found in the body of animals and plants. Insufficient content of cobalt in plants is associated with its insufficient content in soils, which contributes to the development of anemia in animals (taiga-forest non-chernozem zone). As part of vitamin B12, cobalt has a very active effect on the intake of nitrogenous substances, an increase in the content of chlorophyll and ascorbic acid, activates biosynthesis and increases the content of protein nitrogen in plants. However, elevated concentrations of cobalt compounds are toxic.

In unpolluted and slightly polluted river waters, its content varies from tenths to thousandths of a milligram per 1 dm3, the average content in sea water is 0.5 μg/dm3. MPCv is 0.1 mg/dm3, MPCv is 0.01 mg/dm3.

Manganese

Manganese enters surface waters as a result of leaching of ferromanganese ores and other minerals containing manganese (pyrolusite, psilomelane, brownite, manganite, black ocher). Significant amounts of manganese come from the decomposition of aquatic animals and plant organisms, especially blue-green, diatoms and higher aquatic plants. Manganese compounds are discharged into reservoirs with wastewater from manganese processing plants, metallurgical plants, and enterprises chemical industry and mine waters.

A decrease in the concentration of manganese ions in natural waters occurs as a result of the oxidation of Mn(II) to MnO2 and other high-valent oxides that precipitate. The main parameters that determine the oxidation reaction are the concentration of dissolved oxygen, pH value and temperature. The concentration of dissolved manganese compounds decreases due to their utilization by algae.

The main form of migration of manganese compounds in surface waters is suspensions, the composition of which is determined in turn by the composition of rocks drained by waters, as well as colloidal hydroxides of heavy metals and sorbed manganese compounds. Of essential importance in the migration of manganese in dissolved and colloidal forms are organic substances and the processes of complex formation of manganese with inorganic and organic ligands. Mn(II) forms soluble complexes with bicarbonates and sulfates. Complexes of manganese with a chloride ion are rare. Complex compounds of Mn(II) with organic substances are usually less stable than with other transition metals. These include compounds with amines, organic acids, amino acids and humic substances. Mn(III) in high concentrations can be in a dissolved state only in the presence of strong complexing agents; Mn(YII) does not occur in natural waters.

V river waters manganese content usually ranges from 1 to 160 µg/dm3, the average content in sea waters is 2 µg/dm3, in underground waters - n.102 - n.103 µg/dm3.

The concentration of manganese in surface waters is subject to seasonal fluctuations.

The factors determining changes in manganese concentrations are the ratio between surface and underground runoff, the intensity of its consumption during photosynthesis, the decomposition of phytoplankton, microorganisms and higher aquatic vegetation, as well as the processes of its deposition on the bottom of water bodies.

The role of manganese in the life of higher plants and algae in water bodies is very large. Manganese contributes to the utilization of CO2 by plants, which increases the intensity of photosynthesis, participates in the processes of nitrate reduction and nitrogen assimilation by plants. Manganese promotes the transition of active Fe(II) to Fe(III), which protects the cell from poisoning, accelerates the growth of organisms, etc. The important ecological and physiological role of manganese necessitates the study and distribution of manganese in natural waters.

For water bodies for sanitary use, MPCv (according to the manganese ion) is set equal to 0.1 mg/dm3.

Below are maps of the distribution of average concentrations of metals: manganese, copper, nickel and lead, built according to observational data for 1989 - 1993. in 123 cities. The use of later data is considered inappropriate, since due to the reduction in production, the concentrations of suspended solids and, accordingly, metals have significantly decreased.

Impact on health. Many metals are a constituent of dust and have a significant impact on health.

Manganese enters the atmosphere from emissions from ferrous metallurgy enterprises (60% of all manganese emissions), mechanical engineering and metalworking (23%), non-ferrous metallurgy (9%), numerous small sources, for example, from welding.

High concentrations of manganese lead to the appearance of neurotoxic effects, progressive damage to the central nervous system, pneumonia.
The highest concentrations of manganese (0.57 - 0.66 µg/m3) are observed in large centers of metallurgy: in Lipetsk and Cherepovets, as well as in Magadan. Most of the cities with high concentrations of Mn (0.23 - 0.69 µg/m3) are concentrated on the Kola Peninsula: Zapolyarny, Kandalaksha, Monchegorsk, Olenegorsk (see map).

For 1991 - 1994 manganese emissions from industrial sources decreased by 62%, average concentrations - by 48%.

Copper is one of the most important trace elements. The physiological activity of copper is associated mainly with its inclusion in the composition of the active centers of redox enzymes. Insufficient copper content in soils adversely affects the synthesis of proteins, fats and vitamins and contributes to the infertility of plant organisms. Copper is involved in the process of photosynthesis and affects the absorption of nitrogen by plants. At the same time, excessive concentrations of copper have an adverse effect on plant and animal organisms.

Cu(II) compounds are the most common in natural waters. Of the Cu(I) compounds, Cu2O, Cu2S, and CuCl, which are sparingly soluble in water, are the most common. In the presence of ligands in an aqueous medium, along with the equilibrium of hydroxide dissociation, it is necessary to take into account the formation of various complex forms that are in equilibrium with metal aqua ions.

The main source of copper entering natural waters is wastewater from chemical and metallurgical industries, mine waters, and aldehyde reagents used to kill algae. Copper can form as a result of corrosion of copper pipes and other structures used in water systems. In groundwater, the copper content is due to the interaction of water with rocks containing it (chalcopyrite, chalcocite, covellite, bornite, malachite, azurite, chrysacolla, brotantine).

The maximum permissible concentration of copper in the water of reservoirs for sanitary and household water use is 0.1 mg/dm3 (the limiting sign of harmfulness is general sanitary), in the water of fishery reservoirs it is 0.001 mg/dm3.

Town

Norilsk

Monchegorsk

Krasnouralsk

Kolchugino

Zapolyarny

Emissions М (thousand tons/year) of copper oxide and average annual concentrations q (µg/m3) of copper.

Copper enters the air with emissions from metallurgical industries. In particulate matter emissions, it is contained mainly in the form of compounds, mainly copper oxide.

Non-ferrous metallurgy enterprises account for 98.7% of all anthropogenic emissions of this metal, of which 71% are carried out by enterprises of the Norilsk Nickel concern located in Zapolyarny and Nikel, Monchegorsk and Norilsk, and about 25% of copper emissions are carried out in Revda, Krasnouralsk , Kolchugino and others.

High concentrations of copper lead to intoxication, anemia and hepatitis.

As can be seen from the map, the highest concentrations of copper are noted in the cities of Lipetsk and Rudnaya Pristan. Copper concentrations are also increased in cities Kola Peninsula, in Zapolyarny, Monchegorsk, Nikel, Olenegorsk, and also in Norilsk.

Emissions of copper from industrial sources decreased by 34%, average concentrations - by 42%.

Molybdenum

Molybdenum compounds enter surface waters as a result of their leaching from exogenous minerals containing molybdenum. Molybdenum also enters water bodies with wastewater from processing plants and non-ferrous metallurgy enterprises. The decrease in the concentrations of molybdenum compounds occurs as a result of the precipitation of sparingly soluble compounds, the processes of adsorption by mineral suspensions and consumption by plant aquatic organisms.

Molybdenum in surface waters is mainly in the form MoO42-. It is highly probable that it exists in the form of organomineral complexes. The possibility of some accumulation in the colloidal state follows from the fact that the products of molybdenite oxidation are loose finely dispersed substances.

In river waters, molybdenum is found in concentrations from 2.1 to 10.6 µg/dm3. Sea water contains an average of 10 µg/dm3 of molybdenum.

In small quantities, molybdenum is necessary for the normal development of plant and animal organisms. Molybdenum is part of the xanthine oxidase enzyme. With a deficiency of molybdenum, the enzyme is formed in insufficient quantities, which causes negative reactions in the body. In high concentrations, molybdenum is harmful. With an excess of molybdenum, metabolism is disturbed.

The maximum permissible concentration of molybdenum in water bodies for sanitary use is 0.25 mg/dm3.

Arsenic enters natural waters from mineral springs, areas of arsenic mineralization (arsenic pyrites, realgar, orpiment), as well as from zones of oxidation of rocks of polymetallic, copper-cobalt and tungsten types. A certain amount of arsenic comes from soils, as well as from the decomposition of plant and animal organisms. Consumption of arsenic by aquatic organisms is one of the reasons for the decrease in its concentration in water, which is most clearly manifested during the period of intensive development of plankton.

Significant amounts of arsenic enter water bodies with wastewater from processing plants, waste from the production of dyes, tanneries and pesticide factories, as well as from agricultural lands where pesticides are used.

In natural waters, arsenic compounds are in a dissolved and suspended state, the ratio between which is determined by the chemical composition of water and pH values. In dissolved form, arsenic occurs in tri- and pentavalent forms, mainly as anions.

In unpolluted river waters, arsenic is usually found in microgram concentrations. V mineral waters its concentration can reach several milligrams per 1 dm3, in sea waters it contains on average 3 µg/dm3, in underground waters it occurs in concentrations of n.105 µg/dm3. Arsenic compounds in high concentrations are toxic to the body of animals and humans: they inhibit oxidative processes, inhibit the supply of oxygen to organs and tissues.

MPCv for arsenic is 0.05 mg/dm3 (the limiting indicator of harmfulness is sanitary-toxicological) and MPCv is 0.05 mg/dm3.

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 can decrease as a result of the precipitation of compounds such as cyanides, sulfides, carbonates or hydroxides (with increasing pH values), due to its consumption by aquatic organisms and adsorption processes.

In surface waters, nickel compounds are in dissolved, suspended, and colloidal states, the quantitative ratio between which depends on the water composition, temperature, and pH values. Sorbents of nickel compounds can be iron hydroxide, organic substances, highly dispersed calcium carbonate, clays. Dissolved forms are mainly complex ions, most often with amino acids, humic and fulvic acids, and also in the form of a strong cyanide complex. Nickel compounds are the most common in natural waters, in which it is in the +2 oxidation state. Ni3+ compounds are usually formed in an alkaline medium.

Nickel compounds play an important role in hematopoietic processes, being catalysts. Its increased content has a specific effect on cardiovascular system. Nickel is one of the carcinogenic elements. It can cause respiratory diseases. It is believed that free nickel ions (Ni2+) are about 2 times more toxic than its complex compounds.

In unpolluted and slightly polluted river waters, the nickel concentration usually ranges from 0.8 to 10 µg/dm3; in polluted it is several tens of micrograms per 1 dm3. The average concentration of nickel in sea water is 2 µg/dm3, in groundwater - n.103 µg/dm3. In underground waters washing nickel-containing rocks, nickel concentration sometimes increases up to 20 mg/dm3.

Nickel enters the atmosphere from non-ferrous metallurgy enterprises, which account for 97% of all nickel emissions, of which 89% come from enterprises of the Norilsk Nickel concern located in Zapolyarny and Nikel, Monchegorsk and Norilsk.

Increased nickel content in environment leads to the appearance endemic diseases, bronchial cancer. Nickel compounds belong to the 1st group of carcinogens.
The map shows several points with high average concentrations of nickel in the locations of the Norilsk Nickel concern: Apatity, Kandalaksha, Monchegorsk, Olenegorsk.

Nickel emissions from industrial enterprises decreased by 28%, average concentrations - by 35%.

Emissions М (thousand tons/year) and average annual concentrations q (µg/m3) of nickel.

It enters natural waters as a result of leaching of tin-containing minerals (cassiterite, stannin), as well as with wastewater from various industries (fabric dyeing, synthesis of organic dyes, production of alloys with the addition of tin, etc.).

The toxic effect of tin is small.

Tin is found in unpolluted surface waters in submicrogram concentrations. In groundwater, its concentration reaches a few micrograms per 1 dm3. MPCv is 2 mg/dm3.

Mercury compounds can enter surface waters as a result of leaching of rocks in the area of ​​mercury deposits (cinnabar, metacinnabarite, livingstone), in the process of decomposition of aquatic organisms that accumulate mercury. Significant amounts enter water bodies with wastewater from enterprises producing dyes, pesticides, pharmaceuticals, some explosives. Coal-fired thermal power plants emit significant amounts of mercury compounds into the atmosphere, which, as a result of wet and dry fallout, enter water bodies.

The decrease in the concentration of dissolved mercury compounds occurs as a result of their extraction by many marine and freshwater organisms, which have the ability to accumulate it in concentrations many times higher than its content in water, as well as adsorption processes by suspended solids and bottom sediments.

In surface waters, mercury compounds are in dissolved and suspended state. The ratio between them depends on the chemical composition of water and pH values. Suspended mercury is sorbed mercury compounds. Dissolved forms are undissociated molecules, complex organic and mineral compounds. In the water of water bodies, mercury can be in the form of methylmercury compounds.

Mercury compounds are highly toxic, they affect the human nervous system, cause changes in the mucous membrane, motor function and secretions gastrointestinal tract, changes in the blood, etc. Bacterial methylation processes are aimed at the formation of methylmercury compounds, which are many times more toxic than mineral salts of mercury. Methylmercury compounds accumulate in fish and can enter the human body.

MPCv of mercury is 0.0005 mg/dm3 (the limiting sign of harmfulness is sanitary-toxicological), MPCv is 0.0001 mg/dm3.

Natural sources of lead in surface waters 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. Significant factors in lowering the concentration of lead in water are its adsorption by suspended solids and sedimentation with them into bottom sediments. Among other metals, lead is extracted and accumulated by hydrobionts.

Lead is found in natural waters in a dissolved and suspended (sorbed) state. In dissolved form, it occurs in the form of mineral and organomineral complexes, as well as simple ions, in insoluble form - mainly in the form of sulfides, sulfates and carbonates.

In river waters, the lead concentration ranges from tenths to units of micrograms per 1 dm3. Even in the water of water bodies adjacent to areas of polymetallic ores, its concentration rarely reaches tens of milligrams per 1 dm3. Only in chloride thermal waters the concentration of lead sometimes reaches several milligrams per 1 dm3.

The limiting indicator of harmfulness of lead is sanitary-toxicological. MPCv of lead is 0.03 mg/dm3, MPCv is 0.1 mg/dm3.

Lead is contained in emissions from metallurgy, metalworking, electrical engineering, petrochemistry and motor transport enterprises.

The impact of lead on health occurs through the inhalation of air containing lead, and the intake of lead with food, water, and dust particles. Lead accumulates in the body, in bones and surface tissues. Lead affects the kidneys, liver, nervous system and blood-forming organs. The elderly and children are especially sensitive to even low doses of lead.

Emissions M (thousand tons/year) and average annual concentrations q (µg/m3) of lead.

In seven years, lead emissions from industrial sources have decreased by 60% due to production cuts and the closure of many enterprises. The sharp decline in industrial emissions is not accompanied by a decrease in vehicle emissions. Average lead concentrations decreased by only 41%. The difference in abatement rates and lead concentrations can be explained by the underestimation of vehicle emissions in previous years; Currently, the number of cars and the intensity of their movement has increased.

Tetraethyl lead

It enters natural waters due to the use as an antiknock agent in the motor fuel of water vehicles, as well as with surface runoff from urban areas.

This substance is characterized by high toxicity, has cumulative properties.

The sources of silver entering surface waters are groundwater and wastewater from mines, processing plants, and photographic enterprises. The increased content of silver is associated with the use of bactericidal and algicidal preparations.

In wastewater, silver can be present in dissolved and suspended form, for the most part in the form of halide salts.

In unpolluted surface waters, silver is found in submicrogram concentrations. In groundwater, the concentration of silver varies from a few to tens of micrograms per 1 dm3, in sea water, on average, 0.3 μg/dm3.

Silver ions are capable of destroying bacteria and sterilize water even in small concentrations (the lower limit of the bactericidal action of silver ions is 2.10-11 mol/dm3). The role of silver in the body of animals and humans has not been studied enough.

MPCv of silver is 0.05 mg/dm3.

Antimony enters surface waters through the leaching of antimony minerals (stibnite, senarmontite, valentinite, servingite, stibiocanite) and with wastewater from rubber, glass, dyeing, and match enterprises.

In natural waters, antimony compounds are in a dissolved and suspended state. Under the redox conditions characteristic of surface waters, both trivalent and pentavalent antimony can exist.

In unpolluted surface waters, antimony is found in submicrogram concentrations, in sea water its concentration reaches 0.5 µg/dm3, in groundwater - 10 µg/dm3. MPCv of antimony is 0.05 mg/dm3 (the limiting indicator of harmfulness is sanitary-toxicological), MPCv is 0.01 mg/dm3.

Tri- and hexavalent chromium compounds enter surface waters as a result of leaching from rocks (chromite, crocoite, uvarovite, etc.). Some quantities come from the decomposition of organisms and plants, from soils. Significant quantities can enter water bodies with wastewater from electroplating shops, dyeing shops of textile enterprises, tanneries and chemical industries. A decrease in the concentration of chromium ions can be observed as a result of their consumption by aquatic organisms and adsorption processes.

In surface waters, chromium compounds are in dissolved and suspended states, the ratio between which depends on the composition of the water, temperature, and pH of the solution. Suspended chromium compounds are mainly sorbed chromium compounds. Sorbents can be clays, iron hydroxide, highly dispersed settling calcium carbonate, plant and animal residues. In dissolved form, chromium can be in the form of chromates and bichromates. Under aerobic conditions, Cr(VI) transforms into Cr(III), whose salts in neutral and alkaline media are hydrolyzed with the release of hydroxide.

In unpolluted and slightly polluted river waters, the chromium content ranges from several tenths of a microgram per liter to several micrograms per liter, in polluted water bodies it reaches several tens and hundreds of micrograms per liter. The average concentration in sea waters is 0.05 µg/dm3, in groundwater - usually within n.10 - n.102 µg/dm3.

Cr(VI) and Cr(III) compounds in increased quantities have carcinogenic properties. Cr(VI) compounds are more dangerous.

It enters natural waters as a result of natural processes of destruction and dissolution of rocks and minerals (sphalerite, zincite, goslarite, smithsonite, calamine), as well as with wastewater from ore processing plants and electroplating shops, production of parchment paper, mineral paints, viscose fiber and others

In water, it exists mainly in ionic form or in the form of its mineral and organic complexes. Sometimes it occurs in insoluble forms: in the form of hydroxide, carbonate, sulfide, etc.

In river waters, the concentration of zinc usually ranges from 3 to 120 µg/dm3, in marine waters - from 1.5 to 10 µg/dm3. The content in ore and especially in mine waters with low pH values ​​can be significant.

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

MPCv Zn2+ is 1 mg/dm3 (limiting indicator of harmfulness - organoleptic), MPCvr Zn2+ - 0.01 mg/dm3 (limiting sign of harmfulness - toxicological).

Heavy metals are already in second place in terms of danger, yielding to pesticides and well ahead of such well-known pollutants as carbon dioxide and sulfur, but in the forecast they should become the most dangerous, more dangerous than nuclear power plant waste and solid waste. Pollution with heavy metals is associated with their widespread use in industrial production, coupled with weak cleaning systems, as a result of which heavy metals enter the environment, including the soil, polluting and poisoning it.

Heavy metals are among the priority pollutants, monitoring of which is mandatory in all environments. In various scientific and applied works, the authors interpret the meaning of the concept of "heavy metals" in different ways. In some cases, the definition of heavy metals includes elements that are brittle (for example, bismuth) or metalloids (for example, arsenic).

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.
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--PAGE_BREAK-- 3.3. lead intoxication
Currently, lead occupies the first place among the causes of industrial poisoning. This is due to its wide application in various industries. Lead ore workers are exposed to lead in lead smelters, in the production of batteries, in soldering, in printing houses, in the manufacture of crystal glass or ceramic products, leaded gasoline, lead paints, etc. Lead pollution of atmospheric air, soil and water in the vicinity of such industries, as well as near major highways, creates a threat of lead poisoning of the population living in these areas, and, above all, children, who are more sensitive to the effects of heavy metals.
It should be noted with regret that in Russia there is no state policy on the legal, regulatory and economic regulation of the impact of lead on the environment and public health, on reducing emissions (discharges, wastes) of lead and its compounds into the environment, and on the complete cessation of the production of lead-containing gasoline.

Due to the extremely unsatisfactory educational work to explain to the population the degree of danger of heavy metal exposure to the human body, in Russia the number of contingents with occupational contact with lead is not decreasing, but is gradually increasing. Cases of chronic lead intoxication have been recorded in 14 industries in Russia. The leading industries are the electrical industry (production of batteries), instrumentation, printing and non-ferrous metallurgy, in which intoxication is caused by an excess of the maximum permissible concentration (MAC) of lead in the air of the working area by 20 or more times.

A significant source of lead is automotive exhaust, as half of Russia still uses leaded gasoline. However, metallurgical plants, in particular copper smelters, remain the main source of environmental pollution. And there are leaders here. On the territory of the Sverdlovsk region there are 3 largest sources of lead emissions in the country: in the cities of Krasnouralsk, Kirovograd and Revda.

The chimneys of the Krasnouralsk copper smelter, built back in the years of Stalinist industrialization and using equipment from 1932, annually spewing 150-170 tons of lead into the city of 34,000, covering everything with lead dust.

The concentration of lead in the soil of Krasnouralsk varies from 42.9 to 790.8 mg/kg with the maximum allowable concentration MPC = 130 microns/kg. Water samples in the water supply of the neighboring village. Oktyabrsky, fed by an underground water source, recorded an excess of MPC up to two times.

Lead pollution has an impact on human health. Lead exposure disrupts the female and male reproductive systems. For women of pregnant and childbearing age, elevated levels of lead in the blood pose a particular danger, since lead disrupts menstrual function, 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.

Lead poisoning is extremely dangerous for young children - it affects the development of the brain and nervous system. Testing of 165 Krasnouralsk children from 4 years of age revealed a significant mental retardation in 75.7%, and 6.8% of the children examined were found to have mental retardation, including mental retardation.

Preschool children are most susceptible to the harmful effects of lead because their nervous systems are still in the developmental stage. Even at low doses, lead poisoning causes a decrease in intellectual development, attention and concentration, a lag in reading, leads to the development of aggressiveness, hyperactivity and other behavioral problems in the child. These developmental abnormalities can be long-term and irreversible. Low birth weight, stunting, and hearing loss are also the result of lead poisoning. High doses of intoxication lead to mental retardation, coma, convulsions and death.

A 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 recent 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. In dozens of cities, there is an excess of lead concentrations in the air and soil above the values ​​corresponding to the MPC.

The highest level of air pollution with lead, exceeding the MPC, was observed in the cities of Komsomolsk-on-Amur, Tobolsk, Tyumen, Karabash, Vladimir, Vladivostok.

The maximum loads of lead deposition leading to the degradation of terrestrial ecosystems are observed in the Moscow, Vladimir, Nizhny Novgorod, Ryazan, Tula, Rostov and Leningrad regions.

Stationary sources are responsible for the discharge of more than 50 tons of lead in the form of various compounds into water bodies. At the same time, 7 battery factories dump 35 tons of lead annually through the sewer system. An analysis of the distribution of lead discharges into water bodies on the territory of Russia shows that Leningrad, Yaroslavl, Perm, Samara, Penza and Oryol regions are leaders in this type of load.

The country needs Urgent measures to reduce lead pollution, but so far Russia's economic crisis overshadows environmental problems. In a prolonged industrial depression, Russia lacks the means to clean up past pollution, but if the economy starts to recover and factories return to work, pollution could only get worse.
10 most polluted cities of the former USSR

(Metals are listed in descending order of priority level for a given city)

4. Soil hygiene. Waste disposal.
The soil in cities and other settlements and their environs has long been different from the natural, biologically valuable soil, which plays an important role in maintaining the ecological balance. The soil in cities is subject to the same harmful effects as the urban air and hydrosphere, so its significant degradation occurs everywhere. Soil hygiene is not given sufficient attention, although its importance as one of the main components of the biosphere (air, water, soil) and a biological environmental factor is even more significant than water, since the amount of the latter (primarily the quality of groundwater) is determined by the state of the soil, and it is impossible to separate these factors from each other. The soil has the ability of biological self-purification: in the soil there is a splitting of the waste that has fallen into it and their mineralization; in the end, the soil compensates for the lost minerals at their expense.

If, as a result of soil overload, any of the components of its mineralizing capacity is lost, this will inevitably lead to a violation of the self-purification mechanism and to complete degradation of the soil. On the other hand, the creation optimal conditions for self-purification of the soil contributes to the preservation of ecological balance and conditions for the existence of all living organisms, including humans.

Therefore, the problem of neutralizing waste that has a harmful biological effect is not limited to the issue of their export; it is a more complex hygienic problem, since the soil is the link between water, air and man.
4.1.
The role of soil in metabolism

The biological relationship between soil and man is carried out mainly through metabolism. The soil is like a supplier minerals necessary for the metabolic cycle, for the growth of plants consumed by humans and herbivores, eaten in turn by humans and carnivores. Thus, the soil provides food for many representatives of the plant and animal world.

Consequently, the deterioration of soil quality, the decrease in its biological value, its ability to self-cleanse causes a biological chain reaction, which, in the event of prolonged harmful effects, can lead to a variety of health disorders among the population. Moreover, in case of slowing down of mineralization processes, nitrates, nitrogen, phosphorus, potassium, etc., formed during the decomposition of substances, can get into groundwater used for drinking purposes and cause serious illnesses(for example, nitrates can cause methemoglobinemia, primarily in infants).

Consumption of water from soil poor in iodine can cause endemic goiter, etc.
4.2.
Ecological relationship between soil and water and liquid waste (wastewater)

A person extracts from the soil the water necessary to maintain metabolic processes and life itself. The quality of water depends on the condition of the soil; it always reflects the biological state of a given soil.

This applies in particular to groundwater, the biological value of which is essentially determined by the properties of soils and soil, the ability of the latter to self-purify, its filtration capacity, the composition of its macroflora, microfauna, etc.

The direct influence of the soil on surface water is already less significant, it is associated mainly with precipitation. For example, after heavy rains, various pollutants are washed out of the soil into open water bodies (rivers, lakes), including artificial fertilizers (nitrogen, phosphate), pesticides, herbicides; in areas of karst, fractured deposits, pollutants can penetrate through cracks into deep The groundwater.

Inadequate wastewater treatment can also cause harmful biological effects on the soil and eventually lead to soil degradation. Therefore, soil protection in settlements is one of the main requirements for environmental protection in general.
4.3.
Soil load limits for solid waste (household and street waste, industrial waste, dry sludge from sewage sedimentation, radioactive substances, etc.)

The problem is exacerbated by the fact that, as a result of the generation of more and more solid waste in cities, the soil in their vicinity is subjected to increasing pressure. Soil properties and composition are deteriorating at an ever faster rate.

Of the 64.3 million tons of paper produced in the USA, 49.1 million tons end up in waste (out of this amount, 26 million tons are supplied by the household, and 23.1 million tons by the trading network).

In connection with the foregoing, the removal and final disposal of solid waste is a very significant, more difficult to implement hygienic problem in the context of increasing urbanization.

Final disposal of solid waste in contaminated soil is possible. However, due to the constantly deteriorating self-cleaning capacity of urban soil, the final disposal of waste buried in the ground is impossible.

A person could successfully use the biochemical processes occurring in the soil, its neutralizing and disinfecting ability to neutralize solid waste, but urban soil, as a result of centuries of human habitation and activity in cities, has long become unsuitable for this purpose.

The mechanisms of self-purification, mineralization occurring in the soil, the role of the bacteria and enzymes involved in them, as well as the intermediate and final products of the decomposition of substances are well known. Currently, research is aimed at identifying the factors that ensure the biological balance of the natural soil, as well as clarifying the question of how much solid waste (and what composition) can lead to a violation of the biological balance of the soil.
The amount of household waste (garbage) per inhabitant of some large cities of the world

It should be noted that the hygienic condition of the soil in cities as a result of its overload is rapidly deteriorating, although the ability of the soil to self-purify is the main hygienic requirement for maintaining biological balance. The soil in the cities is no longer able to cope with its task without the help of man. The only way out of this situation is the complete neutralization and destruction of waste in accordance with hygienic requirements.

Therefore, the construction of public utilities should be aimed at preserving the natural ability of the soil to self-purify, and if this ability has already become unsatisfactory, then it must be restored artificially.

The most unfavorable is the toxic effect of industrial waste, both liquid and solid. An increasing amount of such waste is getting into the soil, which it is not able to cope with. So, for example, soil contamination with arsenic was found in the vicinity of superphosphate production plants (within a radius of 3 km). As is known, some pesticides, such as organochlorine compounds that have entered the soil, do not decompose for a long time.

The situation is similar with some synthetic packaging materials (polyvinyl chloride, polyethylene, etc.).

Some toxic compounds sooner or later enter groundwater, as a result of which not only the biological balance of the soil is disturbed, but the quality of groundwater also deteriorates to such an extent that it can no longer be used as drinking water.
Percentage of the amount of basic synthetic materials contained in household waste (garbage)

*
Together with waste of other plastics that harden under the action of heat.
The problem of waste has increased today also because part of the waste, mainly human and animal feces, is used to fertilize agricultural land [feces contain a significant amount of nitrogen-0.4-0.5%, phosphorus (P203)-0.2-0 .6%, potassium (K? 0) -0.5-1.5%, carbon-5-15%]. This problem of the city has spread to the city's neighborhoods.
4.4.
The role of soil in the spread of various diseases

Soil plays a role in the spread of infectious diseases. This was reported back in the last century by Petterkoffer (1882) and Fodor (1875), who highlighted mainly the role of soil in the spread of intestinal diseases: cholera, typhoid fever, dysentery, etc. They also drew attention to the fact that some bacteria and viruses remain viable and virulent in the soil for months. Subsequently, a number of authors confirmed their observations, especially in relation to urban soil. For example, the causative agent of cholera remains viable and pathogenic in groundwater from 20 to 200 days, the causative agent of typhoid fever in feces - from 30 to 100 days, the causative agent of paratyphoid - from 30 to 60 days. (In terms of the spread of infectious diseases, urban soil is much more dangerous than field soil fertilized with manure.)

To determine the degree of soil contamination, a number of authors use the determination of the bacterial number (E. coli), as in determining the quality of water. Other authors consider it expedient to determine, in addition, the number of thermophilic bacteria involved in the process of mineralization.

The spread of infectious diseases through the soil is greatly facilitated by watering the land with sewage. At the same time, the mineralization properties of the soil also deteriorate. Therefore, watering with wastewater should be carried out under constant strict sanitary supervision and only outside the urban area.

4.5.
Harmful effect of the main types of pollutants (solid and liquid waste) leading to soil degradation

4.5.1.
Neutralization of liquid waste in the soil

In a number settlements without sewerage, some waste, including manure, is neutralized in the soil.

As you know, this is the easiest way to neutralize. However, it is admissible only if we are dealing with a biologically valuable soil that has retained the ability to self-purify, which is not typical for urban soils. If the soil no longer possesses these qualities, then in order to protect it from further degradation, there is a need for complex technical facilities for the neutralization of liquid waste.

In a number of places, waste is neutralized in compost pits. Technically, this solution is a difficult task. In addition, liquids are able to penetrate the soil over fairly long distances. The task is further complicated by the fact that urban wastewater contains an increasing amount of toxic industrial waste that worsens the mineralization properties of the soil to an even greater extent than human and animal feces. Therefore, it is permissible to drain into compost pits only wastewater that has previously undergone sedimentation. Otherwise, the filtration capacity of the soil is disturbed, then the soil loses its other protective properties, the pores gradually become blocked, etc.

The use of human feces to irrigate agricultural fields is the second way to neutralize liquid waste. This method presents a double hygienic danger: firstly, it can lead to soil overload; secondly, this waste can become a serious source of infection. Therefore, feces must first be disinfected and subjected to appropriate treatment, and only then used as a fertilizer. There are two opposing points of view here. According to hygienic requirements, faeces are subject to almost complete destruction, and from the point of view of the national economy, they represent a valuable fertilizer. Fresh faeces cannot be used for watering gardens and fields without first disinfecting them. If you still have to use fresh feces, then they require such a degree of neutralization that they are almost of no value as a fertilizer.

Feces can be used as fertilizer only in specially designated areas - with constant sanitary and hygienic control, especially for the state of groundwater, the number of flies, etc.

The requirements for the disposal and disposal of animal faeces in the soil do not differ in principle from those for the disposal of human faeces.

Until recently, manure has been a significant source of valuable nutrients for agriculture to improve soil fertility. However, in recent years, manure has lost its importance partly due to the mechanization of agriculture, partly due to the increasing use of artificial fertilizers.

In the absence of appropriate treatment and disposal, manure is also dangerous, as well as untreated human feces. Therefore, before being taken to the fields, manure is allowed to mature so that during this time (at a temperature of 60-70 ° C) the necessary biothermal processes can occur in it. After that, the manure is considered "mature" and freed from most of the pathogens contained in it (bacteria, worm eggs, etc.).

It must be remembered that manure stores can provide ideal breeding grounds for flies that promote the spread of various intestinal infections. It should be noted that flies for reproduction most readily choose pig manure, then horse, sheep and, last but not least, cow manure. Before exporting manure to the fields, it must be treated with insecticidal agents.
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CONTENTS

Introduction

1. Soil cover and its use

2. Soil erosion (water and wind) and methods of dealing with it

3. Industrial soil pollution

3.1 Acid rain

3.2 Heavy metals

3.3 Lead poisoning

4. Soil hygiene. Waste disposal

4.1 The role of soil in metabolism

4.2 Ecological relationship between soil and water and liquid waste (wastewater)

4.3 Soil load limits for solid waste (household and street waste, industrial waste, dry sludge after sewage sedimentation, radioactive substances)

4.4 The role of soil in the spread of various diseases

4.5 Harmful effects of the main types of pollutants (solid and liquid waste) leading to soil degradation

4.5.1 Decontamination of liquid waste in soil

4.5.2.1 Decontamination of solid waste in soil

4.5.2.2 Waste collection and disposal

4.5.3 Final removal and disposal

4.6 Disposal of radioactive waste

Conclusion

List of sources used

Introduction.

A certain part of the soils, both in Russia and around the world, every year goes out of agricultural circulation due to various reasons, which are discussed in detail in the UIR. Thousands or more hectares of land are affected by erosion, acid rain, mismanagement and toxic waste. To avoid this, you need to get acquainted with the most productive and inexpensive land reclamation measures (see the definition of land reclamation in the main part of the work), which increase the fertility of the soil cover, and above all with the negative impact on the ground, and how to avoid it.

These studies provide insight into the harmful effects on soil and have been conducted on a number of books, articles and scientific journals dedicated to soil problems and environmental protection.

The very problem of soil pollution and degradation has always been relevant. Now we can add to what has been said that in our time, anthropogenic influence greatly affects nature and is only growing, and the soil is one of the main sources of food and clothing for us, not to mention the fact that we walk on it and will always be in close contact with her.

1. Soil cover and its use.

The soil cover is the most important natural formation. Its significance for the life of society is determined by the fact that the soil is the main source of food, providing 97-98% of the food resources of the world's population. At the same time, the soil cover is a place of human activity, which hosts industrial and agricultural production.

Highlighting the special role of food in the life of society, even V. I. Lenin pointed out: “The real foundations of the economy are the food fund.”

The most important property of the soil cover is its fertility, which is understood as the totality of soil properties that ensure the harvest of agricultural crops. The natural fertility of the soil is regulated by the supply of nutrients in the soil and its water, air and thermal regimes. The role of the soil cover in the productivity of terrestrial ecological systems is great, since the soil nourishes land plants with water and many compounds and is essential component photosynthetic activity of plants. Soil fertility also depends on the amount of solar energy accumulated in it. Living organisms, plants and animals inhabiting the Earth fix solar energy in the form of phyto- or zoomass. The productivity of terrestrial ecological systems depends on thermal and water balance the earth's surface, which determines the variety of forms of matter and substance exchange within the geographic envelope of the planet.

Analyzing the importance of land for social production, K. Marx singled out two concepts: land-matter and land-capital. The first of these is to be understood land that arose in the process of its evolutionary development in addition to the will and consciousness of people and is the place of human settlement and the source of his food. From the moment when the land in the process of development of human society becomes a means of production, it acts in a new quality - capital, without which the labor process is unthinkable, “...because it gives the worker ... a place on which he stands ... , and its process-scope...”. It is for this reason that the earth is a universal factor in any human activity.

The role and place of land is not the same in various spheres of material production, primarily in industry and agriculture. In the manufacturing industry, in construction, in transport, the land is the place where labor processes take place, regardless of the natural fertility of the soil. In a different capacity is the land in agriculture. Under the influence of human labor, natural fertility is transformed from potential into economic. The specificity of the use of land resources in agriculture leads to the fact that they act in two different qualities, as an object of labor and as a means of production. K. Marx noted: “Only by a new investment of capital in plots of land ... people increased the land-capital without any increase in the matter of the earth, i.e., the space of the earth.”

The land in agriculture acts as a productive force due to its natural fertility, which does not remain constant. With the rational use of land, such fertility can be increased by improving its water, air and thermal regime through reclamation measures and increasing the content of nutrients in the soil. On the contrary, with the irrational use of land resources, their fertility decreases, as a result of which there is a decrease in crop yields. In some places, the cultivation of crops becomes completely impossible, especially on saline and eroded soils.

With a low level of development of the productive forces of society, the expansion of food production occurs due to the involvement of new lands in agriculture, which corresponds to the extensive development of agriculture. Two conditions contribute to this: the availability of free land and the possibility of farming at an affordable average level of capital costs per unit area. This use of land resources and agriculture is typical of many developing countries in the modern world.

In the era of scientific and technological revolution, there was a sharp demarcation of the system of farming in industrialized and developing countries. The former are characterized by the intensification of agriculture using the achievements of the scientific and technological revolution, in which agriculture develops not by increasing the area of ​​cultivated land, but by increasing the amount of capital invested in land. The well-known limited land resources for most industrialized capitalist countries, the increase in demand for agricultural products throughout the world due to high population growth, more high culture agriculture contributed to the transfer of agriculture in these countries back in the 50s to the path of intensive development. The acceleration of the process of intensification of agriculture in the industrialized capitalist countries is connected not only with the achievements of the scientific and technological revolution, but mainly with the profitability of investing capital in agriculture, which concentrated agricultural production in the hands of large landowners and ruined small farmers.

Agriculture developed in other ways in developing countries. Among the acute natural resource problems of these countries, the following can be distinguished: low agricultural culture, which caused degradation of soils (increased erosion, salinization, reduced fertility) and natural vegetation (for example, tropical forests), depletion water resources, desertification of lands, especially clearly manifested on the African continent. All these factors associated with the socio-economic problems of developing countries have led to chronic food shortages in these countries. Thus, at the beginning of the 1980s, in terms of the provision of grain (222 kg) and meat (14 kg) per person, the developing countries were several times inferior to the industrially developed capitalist countries, respectively. The solution of the food problem in developing countries is unthinkable without major socio-economic transformations.

In our country, the basis of land relations is the nationwide (nationwide) ownership of land, which arose as a result of the nationalization of all land. Agrarian relations are built on the basis of plans according to which agriculture should develop in the future, with financial and credit assistance from the state and the supply of the necessary amount of machinery and fertilizers. Payment of agricultural workers according to the quantity and quality of labor stimulates a constant increase in their standard of living.

The use of the land fund as a whole is carried out on the basis of long-term state plans. An example of such plans was the development of virgin and fallow lands in the east of the country (mid-1950s), thanks to which it became possible in a short time to introduce more than 41 million hectares of new areas into arable land. Another example is a set of measures related to the implementation of the Food Program, which provides for the acceleration of the development of agricultural production through an increase in the culture of agriculture, a wide implementation of land reclamation measures, as well as the implementation of a broad program of socio-economic reconstruction of agricultural areas.

The land resources of the world as a whole provide food for more people than is currently available and will be in the near future. However, due to population growth, especially in developing countries, the amount of arable land per capita is declining.

Recently, due to the rapid development of industry, there has been a significant increase in the level of heavy metals in the environment. The term "heavy metals" is applied to metals either with a density exceeding 5 g/cm 3 or with an atomic number greater than 20. Although, there is another point of view, according to which more than 40 chemical elements with atomic masses greater than 50 at. units Among the chemical elements, heavy metals are the most toxic and second only to pesticides in terms of their level of danger. At the same time, the following chemical elements are toxic: Co, Ni, Cu, Zn, Sn, As, Se, Te, Rb, Ag, Cd, Au, Hg, Pb, Sb, Bi, Pt.

Phytotoxicity of heavy metals depends on their chemical properties: valency, ionic radius and ability to complex formation. In most cases, according to the degree of toxicity, the elements are arranged in the sequence: Cu> Ni> Cd> Zn> Pb> Hg> Fe> Mo> Mn. However, this series may change somewhat due to the unequal precipitation of elements by the soil and the transfer to a state inaccessible to plants, growing conditions, and the physiological and genetic characteristics of the plants themselves. The transformation and migration of heavy metals occurs under the direct and indirect influence of the complex formation reaction. When assessing environmental pollution, it is necessary to take into account the properties of the soil and, first of all, the granulometric composition, humus content and buffering. Buffering capacity is understood as the ability of soils to maintain the concentration of metals in the soil solution at a constant level.

In soils, heavy metals are present in two phases - solid and in soil solution. The form of existence of metals is determined by the reaction of the environment, the chemical and material composition of the soil solution and, first of all, the content of organic substances. Elements - complexants that pollute the soil are concentrated mainly in its upper 10 cm layer. However, when low-buffer soil is acidified, a significant proportion of metals from the exchange-absorbed state passes into the soil solution. Cadmium, copper, nickel, cobalt have a strong migration ability in an acidic environment. A decrease in pH by 1.8-2 units leads to an increase in the mobility of zinc by 3.8-5.4, cadmium - by 4-8, copper - by 2-3 times.

Table 1 MPC (MAC) standards, background concentrations of chemical elements in soils (mg/kg)

Thus, when entering the soil, heavy metals quickly interact with organic ligands to form complex compounds. So, at low concentrations in the soil (20-30 mg/kg), approximately 30% of lead is in the form of complexes with organic substances. The share of lead complex compounds increases with its concentration up to 400 mg/g, and then decreases. Metals are also sorbed (exchange or non-exchange) by precipitation of iron and manganese hydroxides, clay minerals, and soil organic matter. Metals available to plants and capable of leaching are found in the soil solution in the form of free ions, complexes, and chelates.

The uptake of HMs by the soil to a greater extent depends on the reaction of the environment and on which anions prevail in the soil solution. In an acidic environment, copper, lead and zinc are more sorbed, and in an alkaline environment, cadmium and cobalt are intensively absorbed. Copper preferentially binds to organic ligands and iron hydroxides.

Table 2 Mobility of trace elements in various soils depending on the pH of the soil solution

Soil-climatic factors often determine the direction and rate of migration and transformation of HMs in the soil. Thus, the conditions of the soil and water regimes of the forest-steppe zone contribute to the intensive vertical migration of HM along the soil profile, including the possible transfer of metals with water flow along cracks, root courses, etc.

Nickel (Ni) is an element of group VIII of the periodic system with an atomic mass of 58.71. Nickel, along with Mn, Fe, Co and Cu, belongs to the so-called transition metals, the compounds of which are highly biologically active. Due to the structural features electron orbitals the above metals, including nickel, have a well-pronounced ability to complex formation. Nickel is able to form stable complexes with, for example, cysteine ​​and citrate, as well as with many organic and inorganic ligands. The geochemical composition of parent rocks largely determines the nickel content in soils. The greatest amount of nickel is contained in soils formed from basic and ultrabasic rocks. According to some authors, the limits of excess and toxic levels of nickel for most species vary from 10 to 100 mg/kg. The bulk of nickel is immovably fixed in the soil, and very weak migration in the colloidal state and in the composition of mechanical suspensions does not affect their distribution along the vertical profile and is quite uniform.

Lead (Pb). The chemistry of lead in soil is determined by a delicate balance of oppositely directed processes: sorption-desorption, dissolution-transition to a solid state. Lead released into the soil with emissions is included in the cycle of physical, chemical and physico-chemical transformations. At first, the processes of mechanical displacement dominate (lead particles move along the surface and in the soil along cracks) and convective diffusion. Then, as solid-phase lead compounds dissolve, more complex physicochemical processes (in particular, ion diffusion processes) come into play, accompanied by the transformation of lead compounds that come with dust.

It has been established that lead migrates both vertically and horizontally, with the second process prevailing over the first. Over 3 years of observations on a forb meadow, lead dust applied locally to the soil surface moved in a horizontal direction by 25–35 cm, while its penetration depth into the soil thickness was 10–15 cm. Biological factors play an important role in lead migration: plant roots absorb ions metals; during the growing season, they move in the thickness of the soil; When plants die and decompose, lead is released into the surrounding soil mass.

It is known that the soil has the ability to bind (sorb) technogenic lead that has entered it. Sorption is believed to include several processes: complete exchange with the cations of the absorbing complex of soils (nonspecific adsorption) and a series of complexation reactions of lead with donors of soil components (specific adsorption). In the soil, lead is associated mainly with organic matter, as well as with clay minerals, manganese oxides, iron and aluminum hydroxides. By binding lead, humus prevents its migration to adjacent environments and limits its entry into plants. Of the clay minerals, illites are characterized by a tendency to lead sorption. An increase in soil pH during liming leads to an even greater binding of lead by the soil due to the formation of sparingly soluble compounds (hydroxides, carbonates, etc.).

Lead, which is present in the soil in mobile forms, is fixed with time by soil components and becomes inaccessible to plants. According to domestic researchers, lead is most strongly fixed in chernozem and peat-silt soils.

Cadmium (Cd) A feature of cadmium that distinguishes it from other HMs is that it is present in the soil solution mainly in the form of cations (Cd 2+), although in soil with a neutral reaction of the environment it can form sparingly soluble complexes with sulfates, phosphates or hydroxides.

According to available data, the concentration of cadmium in soil solutions of background soils ranges from 0.2 to 6 µg/l. In the foci of soil pollution, it increases to 300-400 µg/l.

It is known that cadmium in soils is very mobile; is able to pass in large quantities from the solid phase to the liquid and vice versa (which makes it difficult to predict its entry into the plant). The mechanisms that regulate the concentration of cadmium in the soil solution are determined by the processes of sorption (by sorption we mean adsorption, precipitation, and complex formation). Cadmium is absorbed by the soil in smaller amounts than other HMs. To characterize the mobility of heavy metals in soil, the ratio of the concentrations of metals in the solid phase to that in the equilibrium solution is used. High values ​​of this ratio indicate that HMs are retained in the solid phase due to the sorption reaction, low values ​​- due to the fact that the metals are in solution, from where they can migrate to other media or enter into various reactions (geochemical or biological). It is known that the leading process in the binding of cadmium is adsorption by clays. Recent studies have also shown a large role in this process of hydroxyl groups, iron oxides and organic matter. At a low level of pollution and a neutral reaction of the medium, cadmium is adsorbed mainly by iron oxides. And in an acidic environment (pH = 5), organic matter begins to act as a powerful adsorbent. At a lower pH (pH=4), the adsorption functions pass almost exclusively to the organic matter. Mineral components in these processes cease to play any role.

It is known that cadmium is not only sorbed by the soil surface, but also fixed due to precipitation, coagulation, and interpacket absorption by clay minerals. It diffuses into soil particles through micropores and in other ways.

Cadmium is fixed in soils in different ways different type. So far, little is known about the competitive relationships of cadmium with other metals in the processes of sorption in the soil-absorbing complex. According to expert research Technical University Copenhagen (Denmark), in the presence of nickel, cobalt and zinc, the absorption of cadmium by the soil was suppressed. Other studies have shown that the processes of sorption of cadmium by soil decay in the presence of chloride ions. Saturation of the soil with Ca 2+ ions led to an increase in the sorption capacity of cadmium. Many bonds of cadmium with soil components turn out to be fragile; under certain conditions (for example, an acid reaction of the environment), it is released and goes back into solution.

The role of microorganisms in the process of cadmium dissolution and its transition to a mobile state is revealed. As a result of their vital activity, either water-soluble metal complexes are formed, or physical and chemical conditions are created that favor the transition of cadmium from the solid phase to the liquid.

The processes that occur with cadmium in the soil (sorption-desorption, transition into solution, etc.) are interconnected and interdependent, the flow of this metal into plants depends on their direction, intensity and depth. It is known that the value of sorption of cadmium by soil depends on the value of pH: the higher the pH of the soil, the more it absorbs cadmium. Thus, according to available data, in the pH range from 4 to 7.7, with an increase in pH per unit, the sorption capacity of soils with respect to cadmium increased approximately threefold.

Zinc (Zn). Zinc deficiency can manifest itself both on acidic, strongly podzolized light soils, and on carbonate, zinc-poor, and highly humus soils. The manifestation of zinc deficiency is enhanced by the use of high doses of phosphate fertilizers and strong plowing of the subsoil to the arable horizon.

The highest total zinc content in tundra (53-76 mg/kg) and chernozem (24-90 mg/kg) soils, the lowest - in sod-podzolic soils (20-67 mg/kg). Zinc deficiency is most often manifested in neutral and slightly alkaline calcareous soils. In acidic soils, zinc is more mobile and available to plants.

Zinc is present in the soil in the ionic form, where it is adsorbed by the cation exchange mechanism in an acidic or as a result of chemisorption in an alkaline medium. The Zn 2+ ion is the most mobile. The mobility of zinc in the soil is mainly influenced by the pH value and the content of clay minerals. At pH<6 подвижность Zn 2+ возрастает, что приводит к его выщелачиванию. Попадая в межпакетные пространства кристаллической решетки монтмориллонита, ионы цинка теряют свою подвижность. Кроме того, цинк образует устойчивые формы с органическим веществом почвы, поэтому он накапливается в основном в горизонтах почв с высоким содержанием гумуса и в торфе.

According to A.P. Vinogradov (1952), all chemical elements, to one degree or another, participate in the life of plants, and if many of them are considered physiologically significant, it is only because there is no evidence for this yet. Entering the plant in a small amount and becoming an integral part or activators of enzymes in them, the microelement performs service functions in metabolic processes. When unusually high concentrations of elements enter the environment, they become toxic to plants. The penetration of heavy metals into plant tissues in excess amounts leads to a disruption in the normal functioning of their organs, and this disruption is the stronger, the greater the excess of toxicants. As a result, productivity drops. The toxic effect of HM manifests itself from the early stages of plant development, but to varying degrees on different soils and for different crops.

The absorption of chemical elements by plants is an active process. Passive diffusion is only 2-3% of the total mass of digested mineral components. When the content of metals in the soil is at the background level, active absorption of ions occurs, and if we take into account the low mobility of these elements in soils, then their absorption should be preceded by the mobilization of strongly bound metals. When the content of HMs in the root layer is in amounts significantly exceeding the limiting concentrations at which the metal can be fixed at the expense of the internal resources of the soil, such amounts of metals enter the roots that the membranes can no longer retain. As a result, the supply of ions or compounds of elements ceases to be regulated by cellular mechanisms. HMs accumulate more intensively on acidic soils than on soils with a neutral or close to neutral reaction of the environment. The measure of the actual participation of HM ions in chemical reactions is their activity. The toxic effect of high concentrations of HMs on plants can manifest itself in disruption of the supply and distribution of other chemical elements. The character of HM interaction with other elements varies depending on their concentrations. Migration and entry into the plant is carried out in the form of complex compounds.

In the initial period of environmental pollution with heavy metals, due to the buffer properties of the soil, leading to the inactivation of toxicants, plants will practically not experience adverse effects. However, the protective functions of the soil are not unlimited. As the level of heavy metal pollution increases, their inactivation becomes incomplete and the ion flux attacks the roots. Part of the ions the plant is able to transfer to a less active state even before they penetrate into the root system of plants. This is, for example, chelation with the help of root secretions or adsorption on the outer surface of the roots with the formation of complex compounds. In addition, as shown by vegetation experiments with obviously toxic doses of zinc, nickel, cadmium, cobalt, copper, and lead, the roots are located in soil layers not contaminated with HMs, and in these variants there are no symptoms of phototoxicity.

Despite the protective functions of the root system, HMs enter the root under conditions of pollution. In this case, protection mechanisms come into play, due to which the specific distribution of HMs among plant organs occurs, which makes it possible to secure their growth and development as completely as possible. At the same time, the content, for example, of HMs in root and seed tissues under conditions of a highly polluted environment can differ by 500–600 times, which indicates the great protective capabilities of this underground plant organ.

An excess of chemical elements causes toxicosis in plants. As the HM concentration increases, plant growth is initially delayed, then leaf chlorosis sets in, which is replaced by necrosis, and, finally, the root system is damaged. The toxic effect of HM can manifest itself directly and indirectly. The direct effect of excess HM in plant cells is due to complex formation reactions, which result in blocking of enzymes or precipitation of proteins. The deactivation of enzymatic systems occurs as a result of the replacement of the enzyme metal with a metal contaminant. At a critical content of the toxicant, the catalytic ability of the enzyme is significantly reduced or completely blocked.

AP Vinogradov (1952) singled out plants that are capable of concentrating elements. He pointed out two types of plants - concentrators:

1) plants concentrating elements on a mass scale;

2) plants with selective (species) concentration.

Plants of the first type are enriched with chemical elements if the latter are contained in the soil in an increased amount. The concentration in this case is caused by an environmental factor.

Plants of the second type are characterized by a constantly high amount of one or another chemical element, regardless of its content in the environment. It is due to a genetically fixed need.

Considering the mechanism of absorption of heavy metals from the soil into plants, we can speak of barrier (non-concentrating) and barrier-free (concentrating) types of element accumulation. Barrier accumulation is characteristic of most higher plants and is not characteristic of bryophytes and lichens. So, in the work of M. A. Toikka and L. N. Potekhina (1980), sphagnum (2.66 mg/kg) was named as a plant-concentrator of cobalt; copper (10.0 mg/kg) - birch, stone fruit, lily of the valley; manganese (1100 mg / kg) - blueberries. Lepp et al. (1987) found high concentrations of cadmium in the sporophores of the fungus Amanita muscaria growing in birch forests. In the sporophores of the fungus, the content of cadmium was 29.9 mg/kg of dry weight, and in the soil on which they grew, it was 0.4 mg/kg. There is an opinion that plants that are cobalt concentrators are also highly tolerant to nickel and are able to accumulate it in large quantities. These include, in particular, plants of the families Boraginaceae, Brassicaceae, Myrtaceae, Fabaceae, Caryophyllaceae. Nickel concentrators and superconcentrators are also found among medicinal plants. The superconcentrators include the melon tree, belladonna belladonna, yellow mache, motherwort heart, meat red passion flower and lanceolate thermopsis. The type of accumulation of chemical elements that are in high concentrations in the nutrient medium depends on the phases of plant vegetation. Barrier-free accumulation is typical for the seedling phase, when plants do not have differentiation of above-ground parts into various organs, and in the final phases of vegetation - after maturation, as well as during winter dormancy, when barrier-free accumulation can be accompanied by the release of excess amounts of chemical elements in the solid phase (Kovalevsky, 1991).

Hyperaccumulating plants have been found in the families Brassicaceae, Euphorbiaceae, Asteraceae, Lamiaceae, and Scrophulariaceae (Baker 1995). The best known and studied among them is Brassica juncea (Indian mustard) - a plant that develops a large biomass and is capable of accumulating Pb, Cr (VI), Cd, Cu, Ni, Zn, 90Sr, B and Se (Nanda Kumar et al. 1995 ; Salt et al. 1995; Raskin et al. 1994). Of the various plant species tested, B. juncea had the most pronounced ability to transport lead to the aerial parts, while accumulating more than 1.8% of this element in the aerial organs (in terms of dry weight). With the exception of sunflower (Helianthus annuus) and tobacco (Nicotiana tabacum), other plant species outside the Brassicaceae family had a bioavailability coefficient of less than 1.

According to the classification of plants according to the response to the presence of heavy metals in the growing medium, used by many foreign authors, plants have three main strategies for growing on soils contaminated with metals:

Metal excluders.

Such plants retain a constant low concentration of the metal despite wide variation in its concentration in the soil, retaining mainly the metal in the roots. Exclusion plants are capable of altering membrane permeability and the metal-binding capacity of cell walls or releasing large amounts of chelating agents.

Metal indicators.

These include plant species that actively accumulate metal in the aboveground parts and generally reflect the level of metal content in the soil. They are tolerant to the current level of metal concentration due to the formation of extracellular metal-binding compounds (chelators), or change the nature of the metal compartmentation by storing it in metal-insensitive areas. Plant species accumulating metals. Plants belonging to this group can accumulate the metal in aboveground biomass at concentrations much higher than those in the soil. Baker and Brooks defined metal hyperaccumulators as plants containing more than 0.1%, i.e. more than 1000 mg/g copper, cadmium, chromium, lead, nickel, cobalt or 1% (more than 10,000 mg/g) zinc and manganese in dry weight. For rare metals, this value is more than 0.01% on a dry weight basis. Researchers identify hyperaccumulative species by collecting plants from areas where soils contain metals in concentrations above background levels, such as in contaminated areas or ore body outcrops. The phenomenon of hyperaccumulation raises many questions for researchers. For example, what is the significance of the accumulation of metal in highly toxic concentrations for plants. The final answer to this question has not yet been received, but there are several main hypotheses. It is believed that such plants have an enhanced ion uptake system (the “unintentional” uptake hypothesis) to perform certain physiological functions that have not yet been investigated. It is also believed that hyperaccumulation is one of the types of plant tolerance to a high content of metals in the growing environment.

The presence of elevated concentrations of metals in the soil leads to their accumulation in wild flora and agricultural crops, which is accompanied by contamination of food chains. High concentrations of metals make the soil unsuitable for plant growth, and therefore biodiversity is disturbed. Soils contaminated with heavy metals can be remediated by chemical, physical and biological means. In general, they can be classified into two categories.

The ex-situ method requires the removal of contaminated soil for on-site or off-site cultivation, and the return of the treated soil to its original location. The sequence of ex situ methods used to clean up contaminated soils includes excavation, detoxification, and/or decomposition of the contaminant by physical or chemical means, resulting in the contaminant being stabilized, settled, immobilized, incinerated, or decomposed.

The in-situ method involves cleaning contaminated soil without excavating it. Reed et al. defined in-situ remediation technologies as degradation or transformation of the contaminant, immobilization to reduce bioavailability, and separation of the contaminant from the soil. The in-situ method is preferred over the ex-situ method due to its low cost and its gentle effect on the ecosystem. The traditional ex situ method involves removing heavy metal contaminated soil and burying it, which is not an optimal choice because burying the contaminated soil off site simply moves the contamination problem elsewhere; however, there is a certain risk associated with the transport of contaminated soil. Dilution of heavy metals to an acceptable level by adding clean soil to contaminated soil and mixing them, covering the soil with an inert material can be an alternative to cleaning the soil within the contaminated site.

Immobilization of an inorganic contaminant can be used as a remediation method for soils contaminated with heavy metals. It can be achieved by complexation of contaminants, or by increasing the pH of the soil by liming. Raising the pH reduces the solubility of heavy metals such as Cd, Cu, Ni and Zn in the soil. Although the risk of being taken up by plants is reduced, the concentration of metals in the soil remains unchanged. Most of these traditional road cleanup technologies are causing further damage to an already damaged environment. Bioremediation technologies, called "phytoremediation", involve the use of green plants and their associated microbiota for in-situ treatment of contaminated soils and groundwater. The idea of ​​using metal accumulating plants to remove heavy metals and other compounds was first proposed in 1983. The term "phytoremediation" consists of the Greek prefix phyto- (plant) attached to the Latin root remedium (recovery).

Rhizome filtration involves the use of plants (both terrestrial and aquatic) to adsorb, concentrate and deposit contaminants in roots from polluted water sources with low contaminant concentrations. This method can partially treat industrial effluents, surface runoff from agricultural land and facilities, or acidic drainage from mines and mines. Rhizome filtration can be applied to lead, cadmium, copper, nickel, zinc and chromium, which are mainly retained by the roots. The advantages of rhizofiltration include its ability to be used both "in-situ" and "ex-situ" and use plant species that are not hyperaccumulators. The ability of sunflower, Indian mustard, tobacco, rye, spinach, and corn to remove lead from wastewater has been studied, with sunflower showing the highest cleaning efficiency.

Phytostabilization is used primarily for the treatment of soils, sediments and sewage sludge and depends on the ability of plant roots to limit the mobility and bioavailability of contaminants in the soil. Phytostabilization is carried out by means of sorption, precipitation and complexation of metals. Plants reduce the amount of water seeping through contaminated soil, which prevents erosion processes, the penetration of dissolved contaminants into surface and ground water and their spread to uncontaminated areas. The advantage of phytostabilization is that this method does not require the removal of contaminated plant biomass. However, its main disadvantage is the preservation of the contaminant in the soil, and therefore the use of this purification method should be accompanied by constant monitoring of the content and bioavailability of contaminants.

Phytoextraction is the most appropriate way to remove heavy metal salts from soils without destroying soil structure and fertility. Some authors call this method phytoaccumulation. Since the plant absorbs, concentrates and precipitates toxic metals and radionuclides from contaminated soils in biomass, it is the best way to clean up areas with diffuse surface contamination and relatively low concentrations of contaminants. There are two main phytoextraction strategies:

Phytoextraction in the presence of chelates, or induced phytoextraction, in which the addition of artificial chelates increases the mobility and absorption of the metal contaminant;

Sequential phytoextraction, in which the removal of metal depends on the natural ability of plants to purify; at the same time, only the number of seeding (planting) of plants is under control. The discovery of hyperaccumulative species further contributed to the development of this technology. In order to make this technology realistically feasible, plants must extract large concentrations of heavy metals from their roots, move them to aboveground biomass, and produce large amounts of plant biomass. In this case, factors such as growth rate, element selectivity, disease resistance, and harvesting method are important. However, slow growth, superficially spreading root systems, and low biomass productivity limit the use of hyperaccumulative species to clean up areas contaminated with heavy metals.

Phytoevaporation involves the use of plants to remove contaminants from the soil, transform them into a volatile form, and transpiration into the atmosphere. Phytoevaporation is used primarily to remove mercury by converting the mercury ion into the less toxic elemental mercury. The disadvantage is that mercury released into the atmosphere is likely to be recycled through deposition and then re-introduced into the ecosystem. American researchers have found that some plants growing on a substrate rich in selenium produce volatile selenium in the form of dimethyl selenide and dimethyl diselenide. There are reports that phytoevaporation has been successfully applied to tritium, a radioactive isotope of hydrogen), which decayed to stable helium with a half-life of about 12 years. Phytodegradation. In organic matter phytoremediation, plant metabolism is involved in the recovery of the contaminant through transformation, decomposition, stabilization, or evaporation of pollutants from soil and groundwater. Phytodegradation is the decomposition of organic substances absorbed by a plant into simpler molecules that are incorporated into plant tissues.

Plants contain enzymes that can break down and convert gun waste, chlorinated solvents such as trichlorethylene and other herbicides. Enzymes are usually dehalogenases, oxygenases and reductases. Rhizodegradation is the decomposition of organic compounds in the soil through microbial activity in the root zone (rhizosphere) and is a much slower process than phytodegradation. The above methods of phytoremediation can be used in a complex way. Thus, it can be seen from the review of the literature that phytoremediation is currently a rapidly developing area of ​​research. Over the past ten years, researchers from many countries of the world have received experimental confirmation, including in the field, of the prospects of this method for cleaning polluted media from organic, inorganic contaminants and radionuclides.

This environmentally friendly and inexpensive way to clean up contaminated areas is a real alternative to traditional methods of restoring disturbed and polluted lands. In Russia, the commercial application of phytoremediation for soils contaminated with heavy metals and various organic compounds, such as petroleum products, is in its infancy. Large-scale studies are needed to search for fast-growing plants with a pronounced ability to accumulate contaminants from among cultivated and wild-growing species characteristic of a particular region, experimental confirmation of their high phytoremediation potential, and study of ways to increase it. A separate important area of ​​research is the study of the issue of utilization of contaminated plant biomass in order to prevent re-contamination of various components of the ecosystem and the entry of contaminants into food chains.

The chemical composition of the soils of different territories is heterogeneous and the distribution of chemical elements contained in the soils across the territory is uneven. Thus, for example, being predominantly in a dispersed state, heavy metals are capable of forming local bonds, where their concentrations are many hundreds and thousands of times higher than Clarke levels.

A number of chemical elements are necessary for the normal functioning of the body. Their deficiency, excess or imbalance can cause diseases called microelementoses 1 , or biogeochemical endemias, which can be both natural and man-made. In their distribution, an important role belongs to water, as well as food products, in which chemical elements enter from the soil through food chains.

It has been experimentally established that the percentage of HM in plants is affected by the percentage of HM in soil, atmosphere, and water (in the case of algae). It was also noticed that on soils with the same content of heavy metals, the same crop gives a different yield, although the climatic conditions also coincided. Then the dependence of productivity on soil acidity was discovered.

Soil contamination with cadmium, mercury, lead, arsenic, copper, zinc and manganese seems to be the most studied. Consider soil contamination with these metals separately for each. 2

Cadmium (Cd)

The content of cadmium in the earth's crust is approximately 0.15 mg/kg. Cadmium is concentrated in volcanic (from 0.001 to 1.8 mg/kg), metamorphic (from 0.04 to 1.0 mg/kg) and sedimentary rocks (from 0.1 to 11.0 mg/kg). Soils formed on the basis of such source materials contain 0.1‑0.3; 0.1 - 1.0 and 3.0 - 11.0 mg/kg of cadmium, respectively.

In acidic soils, cadmium is present in the form of Cd 2+ , CdCl + , CdSO 4 , and in calcareous soils - in the form of Cd 2+ , CdCl + , CdSO 4 , CdHCO 3 + .

The uptake of cadmium by plants drops significantly when acidic soils are limed. In this case, an increase in pH reduces the solubility of cadmium in soil moisture, as well as the bioavailability of soil cadmium. Thus, the content of cadmium in beet leaves on calcareous soils was less than the content of cadmium in the same plants on unlimed soils. A similar effect was shown for rice and wheat -->.

The negative effect of an increase in pH on cadmium availability is associated with a decrease not only in the solubility of cadmium in the soil solution phase, but also in root activity, which affects absorption.

Cadmium is rather inactive in soils, and if a cadmium-containing material is added to its surface, most of it remains intact.

Methods for removing contaminants from soil include either removing the contaminated layer itself, removing cadmium from the layer, or covering the contaminated layer. Cadmium can be converted into complex insoluble compounds with available chelating agents (eg, ethylenediaminetetraacetic acid). .

Due to the relatively rapid uptake of cadmium from the soil by plants and the low toxic action At the usual concentrations, cadmium can accumulate in plants and enter the food chain faster than lead and zinc. Therefore, cadmium poses the greatest danger to human health when waste is introduced into the soil.

The procedure for minimizing the amount of cadmium that can enter the human food chain from contaminated soils is plant soil, not used for food or those crops that absorb small amounts of cadmium.

In general, crops on acidic soils absorb more cadmium than those on neutral or alkaline soils. Therefore, liming acidic soils is an effective means of reducing the amount of absorbed cadmium.

Mercury (Hg)

Mercury is found in nature in the form of metal vapor Hg 0 formed during its evaporation from the earth's crust; in the form of inorganic salts of Hg (I) and Hg (II), and in the form of an organic compound of methylmercury CH 3 Hg +, monomethyl- and dimethyl derivatives of CH 3 Hg + and (CH 3) 2 Hg.

Mercury accumulates in the upper horizon (0-40 cm) of the soil and migrates weakly into its deeper layers. Mercury compounds are highly stable soil substances. Plants growing on mercury-contaminated soil absorb a significant amount of the element and accumulate it in dangerous concentrations, or do not grow.

Lead (Pb)

According to the data of experiments carried out under sand culture conditions with the introduction of soil threshold concentrations of Hg (25 mg/kg) and Pb (25 mg/kg) and exceeding the threshold by 2–20 times, oat plants grow and develop normally up to a certain level of pollution. As the concentration of metals increases (for Pb starting from a dose of 100 mg/kg), the appearance plants. At extreme doses of metals, plants die within three weeks from the start of the experiments. The content of metals in biomass components is distributed in descending order as follows: roots - above-ground part - grain.

The total intake of lead into the atmosphere (and, consequently, partially into the soil) from vehicles in Russia in 1996 was estimated at about 4.0 thousand tons, including 2.16 thousand tons contributed by freight transport. The maximum lead load was in the Moscow and Samara regions, followed by the Kaluga, Nizhny Novgorod, Vladimir regions and other subjects of the Russian Federation located in the central part of the European territory of Russia and North Caucasus. The largest absolute lead emissions were observed in the Ural (685 t), Volga (651 t) and West Siberian (568 t) regions. And the most adverse impact of lead emissions was noted in Tatarstan, Krasnodar and Stavropol Territories, Rostov, Moscow, Leningrad, Nizhny Novgorod, Volgograd, Voronezh, Saratov and Samara regions (newspaper “ Green World”, special issue No. 28, 1997).

Arsenic (As)

Arsenic is found in the environment in a variety of chemically stable forms. Its two main oxidation states are As(III) and As(V). In nature, pentavalent arsenic is common in the form of various inorganic compounds, although trivalent arsenic is easily found in water, especially under anaerobic conditions.

Copper(cu)

Natural copper minerals in soils include sulfates, phosphates, oxides, and hydroxides. Copper sulfides can form in poorly drained or flooded soils where reducing conditions are realized. Copper minerals are usually too soluble to remain in freely drained agricultural soils. In polluted metal soils, however, the chemical environment can be controlled by non-equilibrium processes leading to the accumulation of metastable solid phases. It is assumed that covellite (CuS) or chalcopyrite (CuFeS 2) can also be found in restored, copper-contaminated soils.

Traces of copper may be present as separate sulfide inclusions in silicates and may isomorphically replace cations in phyllosilicates. Charge-unbalanced clay minerals nonspecifically absorb copper, while oxides and hydroxides of iron and manganese show a very high specific affinity for copper. High molecular weight organic compounds are capable of being solid absorbents for copper, while low molecular weight organic substances tend to form soluble complexes.

The complexity of soil composition limits the possibility of quantitative separation of copper compounds into specific chemical forms. points to -->Presence large mass copper conglomerates is found both in organic substances and in oxides of Fe and Mn. The introduction of copper-containing waste or inorganic copper salts increases the concentration of copper compounds in the soil, capable of being extracted with relatively mild reagents; thus, copper can be found in the soil in the form of labile chemical forms. But the easily soluble and replaceable element - copper - forms a small number of forms capable of absorption by plants, usually less than 5% of the total copper content in the soil.

Copper toxicity increases with increasing soil pH and low soil cation exchange capacity. Copper enrichment due to extraction occurs only in the surface layers of the soil, and crops with a deep root system do not suffer from this.

The environment and plant nutrition can affect the phytotoxicity of copper. For example, copper toxicity to rice in flatlands was clearly noted when the plants were watered with cold rather than warm water. The fact is that microbiological activity is suppressed in cold soil and creates those reducing conditions in the soil that would contribute to the precipitation of copper from solution.

Phytotoxicity for copper occurs initially from an excess of available copper in the soil and is enhanced by soil acidity. Since copper is relatively inactive in the soil, almost all of the copper that enters the soil remains in the upper layers. The introduction of organic substances into copper-contaminated soils can reduce toxicity due to the adsorption of soluble metal by the organic substrate (in this case, Cu 2+ ions are converted into complex compounds less accessible to the plant) or by increasing the mobility of Cu 2+ ions and washing them out of the soil in the form of soluble organocopper complexes.

Zinc (Zn)

Zinc can be found in the soil in the form of oxosulfates, carbonates, phosphates, silicates, oxides and hydroxides. These inorganic compounds metastable in well-drained agricultural land. Apparently, sphalerite ZnS is the thermodynamically predominant form in both reduced and oxidized soils. Some association of zinc with phosphorus and chlorine is evident in reduced sediments contaminated with heavy metals. Therefore, relatively soluble zinc salts should be found in metal-rich soils.

Zinc is isomorphically replaced by other cations in silicate minerals and can be occluded or co-precipitated with manganese and iron hydroxides. Phyllosilicates, carbonates, hydrated metal oxides, and organic compounds absorb zinc well, using both specific and non-specific binding sites.

The solubility of zinc increases in acidic soils, as well as in complex formation with low molecular weight organic ligands. Reducing conditions can reduce the solubility of zinc due to the formation of insoluble ZnS.

Zinc phytotoxicity usually manifests itself when plant roots come into contact with an excess zinc solution in the soil. The transport of zinc through the soil occurs through exchange and diffusion, the latter process being dominant in soils with low zinc content. Metabolic transport is more significant in high-zinc soils, in which the concentrations of soluble zinc are relatively stable.

The mobility of zinc in soils is increased in the presence of chelating agents (natural or synthetic). The increase in the concentration of soluble zinc caused by the formation of soluble chelates compensates for the decrease in mobility due to the increase in molecular size. Zinc concentrations in plant tissues, total uptake, and symptoms of toxicity are positively correlated with the concentration of zinc in the root-washing solution.

The free Zn 2+ ion is predominantly absorbed by the root system of plants; therefore, the formation of soluble chelates contributes to the solubility of this metal in soils, and this reaction compensates for the reduced availability of zinc in the chelated form.

The initial form of metal contamination affects the potential for zinc toxicity: the availability of zinc to a plant in fertilized soils with an equivalent total content of this metal decreases in the series ZnSO 4 >sludge>garbage compost.

Most experiments on soil contamination with Zn-containing sludge did not show a drop in yield or their obvious phytotoxicity; however, their long-term application at a high rate can damage plants. Simple application of zinc in the form of ZnSO 4 causes a decrease in crop growth in acidic soils, while long-term application of zinc in almost neutral soils goes unnoticed.

Toxicity levels in agricultural soils zinc reaches are usually due to surface zinc; it usually does not penetrate deeper than 15-30 cm. The deep roots of certain crops can avoid contact with excess zinc due to their location in uncontaminated subsoil.

Liming soils contaminated with zinc reduces the concentration of the latter in field crops. Additives of NaOH or Ca(OH) 2 reduce the toxicity of zinc in vegetables grown on high-zinc peat soils, although in these soils the uptake of zinc by plants is very limited. Iron deficiency caused by zinc can be eliminated by applying iron chelates or FeSO 4 to the soil or directly to the leaves. Physical removal or disposal of the zinc-contaminated top layer altogether may avoid the toxic effects of the metal on plants.

Manganese

In the soil, manganese is found in three oxidation states: +2, +3, +4. For the most part, this metal is associated with primary minerals or with secondary metal oxides. In the soil, the total amount of manganese fluctuates at the level of 500 - 900 mg/kg.

The solubility of Mn 4+ is extremely low; trivalent manganese is very unstable in soils. Most of the manganese in soils is present as Mn 2+ , while in well aerated soils, most of it in the solid phase is present as an oxide, in which the metal is in oxidation state IV; in poorly aerated soils, manganese is slowly reduced by the microbial environment and passes into the soil solution, thus becoming highly mobile.

The solubility of Mn 2+ increases significantly at low pH values, but the absorption of manganese by plants decreases.

Manganese toxicity often occurs where total manganese levels are medium to high, soil pH is fairly low, and soil oxygen availability is also low (i.e. reducing conditions are present). To eliminate the effect of these conditions, soil pH should be increased by liming, efforts should be made to improve soil drainage, reduce water inflow, i.e. generally improve the structure of the soil.