Soil contamination with lead is at its maximum. Heavy metals are the most dangerous elements that can pollute the soil
Soil contamination with heavy metals has different sources:
1. waste from the metalworking industry;
2. industrial emissions;
3. fuel combustion products;
4. automobile exhaust gases;
5. means of chemicalization of agriculture.
Metallurgical enterprises annually emit to the surface of the earth more than 150 thousand tons of copper, 120 thousand tons of zinc, about 90 thousand tons of lead, 12 thousand tons of nickel, 1.5 thousand tons of molybdenum, about 800 tons of cobalt and about 30 tons of mercury . For 1 gram of blister copper, waste from the copper smelting industry contains 2.09 tons of dust, which contains up to 15% copper, 60% iron oxide and 4% each of arsenic, mercury, zinc and lead. Waste from mechanical engineering and chemical industries contains up to 1 thousand mg/kg of lead, up to 3 thousand mg/kg of copper, up to 10 thousand mg/kg of chromium and iron, up to 100 g/kg of phosphorus and up to 10 g/kg of manganese and nickel . In Silesia, around zinc factories, dumps containing zinc from 2 to 12% and lead from 0.5 to 3% are piled up, and in the USA ores with a zinc content of 1.8% are exploited.
More than 250 thousand tons of lead per year reach the soil surface with exhaust gases; it is a major soil pollutant of lead.
Heavy metals enter the soil together with fertilizers, which contain them as an impurity, as well as with biocides.
L. G. Bondarev (1976) calculated the possible supply of heavy metals to the surface of the soil as a result of human production activity with the complete depletion of ore reserves, in the combustion of existing coal and peat reserves and compared them with the possible reserves of metals accumulated in the humosphere to date. The resulting picture allows us to get an idea of the changes that a person is able to cause within 500-1000 years, for which the explored minerals will be sufficient.
Possible entry of metals into the biosphere upon depletion of reliable reserves of ores, coal, peat, million tons
|
Total technogenic release of metals |
Contained in the humosphere |
The ratio of man-made emissions to content in the humosphere |
|
The ratio of these quantities allows us to predict the scale of the impact of human activity on the environment, primarily on the soil cover.
The technogenic entry of metals into the soil and their fixation in humus horizons in the soil profile as a whole cannot be uniform. Its unevenness and contrast is primarily related to population density. If we consider this relationship to be proportional, then 37.3% of all metals will be dispersed in only 2% of the inhabited land mass.
The distribution of heavy metals over the soil surface is determined by many factors. It depends on the characteristics of the sources of pollution, the meteorological characteristics of the region, geochemical factors and the landscape situation as a whole.
The source of contamination generally determines the quality and quantity of the product thrown away. Moreover, the degree of its dispersion depends on the height of the emission. The zone of maximum contamination extends over a distance equal to 10-40 times the pipe height for high and hot emissions, 5-20 times the pipe height for low industrial emissions. The duration of emission particles' presence in the atmosphere depends on their mass and physicochemical properties. The heavier the particles, the faster they settle.
The unevenness of the technogenic distribution of metals is aggravated by the heterogeneity of the geochemical situation in natural landscapes. In this regard, to predict possible pollution by technogenesis products and prevent undesirable consequences of human activity, it is necessary to understand the laws of geochemistry, the laws of migration of chemical elements in various natural landscapes or geochemical settings.
Chemical elements and their compounds entering the soil undergo a number of transformations, dissipate or accumulate depending on the nature of the geochemical barriers inherent in a given territory. The concept of geochemical barriers was formulated by A.I. Perelman (1961) as areas of the hypergenesis zone in which changes in migration conditions lead to the accumulation of chemical elements. The classification of barriers is based on the types of migration of elements. On this basis, A.I. Perelman identifies four types and several classes of geochemical barriers:
1. barriers - for all elements that are biogeochemically redistributed and sorted by living organisms (oxygen, carbon, hydrogen, calcium, potassium, nitrogen, silicon, manganese, etc.);
2. physical and chemical barriers:
1) oxidizing - iron or ferromanganese (iron, manganese), manganese (manganese), sulfur (sulfur);
2) reducing – sulfide (iron, zinc, nickel, copper, cobalt, lead, arsenic, etc.), gley (vanadium, copper, silver, selenium);
3) sulfate (barium, calcium, strontium);
4) alkaline (iron, calcium, magnesium, copper, strontium, nickel, etc.);
5) acidic (silicon oxide);
6) evaporative (calcium, sodium, magnesium, sulfur, fluorine, etc.);
7) adsorption (calcium, potassium, magnesium, phosphorus, sulfur, lead, etc.);
8) thermodynamic (calcium, sulfur).
3. mechanical barriers (iron, titanium, chromium, nickel, etc.);
4. man-made barriers.
Geochemical barriers do not exist in isolation, but in combination with each other, forming complex complexes. They regulate the elemental composition of substance flows; the functioning of ecosystems largely depends on them.
Products of technogenesis, depending on their nature and the landscape situation in which they find themselves, can either be processed by natural processes and not cause significant changes in nature, or be preserved and accumulate, having a detrimental effect on all living things.
Both processes are determined by a number of factors, the analysis of which makes it possible to judge the level of biochemical stability of the landscape and predict the nature of their changes in nature under the influence of technogenesis. In autonomous landscapes, processes of self-purification from technogenic pollution develop, since the products of technogenesis are dispersed by surface and subsoil waters. In accumulative landscapes, the products of technogenesis accumulate and are preserved.
|
Industrial wastewater, kg/l |
Soil, mg/kg |
Plants, mg/kg |
Drinking water, mg/l |
Air, mg/m3 |
MPC in human blood, mg/l |
|
* At motorways, depending on traffic volume and distance to the motorway
Increasing attention to environmental protection has generated particular interest in the impact of heavy metals on soil.
From a historical point of view, interest in this problem arose with the study of soil fertility, since elements such as iron, manganese, copper, zinc, molybdenum and possibly cobalt are very important for plant life and, therefore, for animals and humans.
They are also known as microelements because they are needed by plants in small quantities. The group of microelements also includes metals, the content of which in the soil is quite high, for example, iron, which is part of most soils and ranks fourth in the composition of the earth's crust (5%) after oxygen (46.6%), silicon (27.7 %) and aluminum (8.1%).
All trace elements can have a negative effect on plants if the concentration of their available forms exceeds certain limits. Some heavy metals, such as mercury, lead and cadmium, which appear to be of little importance to plants and animals, are hazardous to human health even at low concentrations.
Exhaust gases from vehicles, removal to the field or wastewater treatment plants, irrigation with wastewater, waste, residues and emissions from the operation of mines and industrial sites, application of phosphorus and organic fertilizers, use of pesticides, etc. led to an increase in the concentrations of heavy metals in the soil.
As long as heavy metals are firmly bound to soil constituents and are difficult to access, their negative impact on the soil and the environment will be negligible. However, if soil conditions allow heavy metals to pass into the soil solution, there is a direct danger of soil contamination, and there is a possibility of their penetration into plants, as well as into the body of humans and animals that consume these plants. In addition, heavy metals can be pollutants of plants and water bodies as a result of the use of sewage sludge. The danger of soil and plant contamination depends on: the type of plant; forms of chemical compounds in the soil; the presence of elements that counteract the influence of heavy metals and substances that form complex compounds with them; from adsorption and desorption processes; the amount of available forms of these metals in the soil and soil and climatic conditions. Consequently, the negative impact of heavy metals depends essentially on their mobility, i.e. solubility.
Heavy metals are mainly characterized by variable valency, low solubility of their hydroxides, high ability to form complex compounds and, naturally, cationic ability.
Factors that contribute to the retention of heavy metals by soil include: exchange adsorption of the surface of clays and humus, the formation of complex compounds with humus, surface adsorption and occlusion (dissolving or absorbing abilities of gases by molten or solid metals) by hydrated oxides of aluminum, iron, manganese, etc. , as well as the formation of insoluble compounds, especially during reduction.
Heavy metals in soil solution are found in both ionic and bound forms, which are in a certain equilibrium (Fig. 1).
In the figure, L r are soluble ligands, which are organic acids with low molecular weight, and L n are insoluble. The reaction of metals (M) with humic substances partially includes ion exchange.
Of course, there may be other forms of metals present in the soil that do not directly participate in this equilibrium, for example, metals from the crystal lattice of primary and secondary minerals, as well as metals from living organisms and their dead remains.
Observing changes in heavy metals in soil is impossible without knowledge of the factors that determine their mobility. The retention movement processes that determine the behavior of heavy metals in the soil are not much different from the processes that determine the behavior of other cations. Although heavy metals are sometimes found in soils in low concentrations, they form stable complexes with organic compounds and enter into specific adsorption reactions more easily than alkali and alkaline earth metals.
Migration of heavy metals in soils can occur in liquid and suspension with the help of plant roots or soil microorganisms. Migration of soluble compounds occurs along with the soil solution (diffusion) or by movement of the liquid itself. The leaching of clays and organic matter leads to the migration of all associated metals. The migration of volatile substances in gaseous form, such as dimethyl mercury, is random and this mode of movement is not particularly important. Migration in the solid phase and penetration into the crystal lattice is more of a binding mechanism than movement.
Heavy metals can be introduced or adsorbed by microorganisms, which in turn are able to participate in the migration of the corresponding metals.
Earthworms and other organisms can facilitate the migration of heavy metals through mechanical or biological means by agitating the soil or incorporating metals into their tissues.
Of all types of migration, the most important is migration in the liquid phase, because most metals enter the soil in soluble form or in the form of an aqueous suspension and virtually all interactions between heavy metals and liquid constituents of the soil occur at the boundary of the liquid and solid phases.
Heavy metals in the soil enter plants through the trophic chain and are then consumed by animals and humans. Various biological barriers participate in the cycle of heavy metals, resulting in selective bioaccumulation that protects living organisms from excess of these elements. However, the activity of biological barriers is limited, and most often heavy metals are concentrated in the soil. The resistance of soils to contamination by them varies depending on the buffer capacity.
Soils with a high adsorption capacity, respectively, and a high content of clays, as well as organic matter, can retain these elements, especially in the upper horizons. This is typical for carbonate soils and soils with a neutral reaction. In these soils, the amount of toxic compounds that can be washed into groundwater and absorbed by plants is much less than in sandy acidic soils. However, there is a great risk of increasing the concentration of elements to toxic levels, which causes an imbalance of physical, chemical and biological processes in the soil. Heavy metals retained by the organic and colloidal parts of the soil significantly limit biological activity and inhibit ytrification processes, which are important for soil fertility.
Sandy soils, which are characterized by low absorption capacity, like acidic soils, very weakly retain heavy metals, with the exception of molybdenum and selenium. Therefore, they are easily adsorbed by plants, and some of them, even in very small concentrations, have toxic effects.
The zinc content in soil ranges from 10 to 800 mg/kg, although most often it is 30-50 mg/kg. The accumulation of excess amounts of zinc negatively affects most soil processes: it causes changes in the physical and physicochemical properties of the soil, and reduces biological activity. Zinc suppresses the vital activity of microorganisms, as a result of which the processes of formation of organic matter in soils are disrupted. Excess zinc in the soil makes it difficult to ferment the decomposition of cellulose, respiration, and the action of urease.
Heavy metals, coming from the soil into plants and transmitted through food chains, have a toxic effect on plants, animals and humans.
Among the most toxic elements, first of all, mercury should be mentioned, which poses the greatest danger in the form of a highly toxic compound - methylmercury. Mercury enters the atmosphere when coal is burned and when water evaporates from polluted water bodies. It can be transported with air masses and deposited on soils in certain areas. Studies have shown that mercury is well sorbed in the upper centimeters of the humus-accumulative horizon of different types of soils of loamy mechanical composition. Its migration along the profile and leaching beyond the soil profile in such soils is insignificant. However, in soils of light mechanical composition, acidic and humus-depleted, the processes of mercury migration intensify. In such soils, the process of evaporation of organic mercury compounds, which have volatile properties, also occurs.
When mercury was added to sandy, clay and peat soils at the rate of 200 and 100 kg/ha, the crop on sandy soil was completely destroyed, regardless of the level of liming. On peat soil, the yield has decreased. On clay soil, a decrease in yield occurred only with a low dose of lime.
Lead also has the ability to be transmitted through food chains, accumulating in the tissues of plants, animals and humans. A dose of lead equal to 100 mg/kg dry weight of feed is considered lethal for animals.
Lead dust settles on the soil surface, is adsorbed by organic substances, moves along the profile with soil solutions, but is carried outside the soil profile in small quantities.
Due to migration processes under acidic conditions, technogenic lead anomalies are formed in soils over a length of 100 m. Lead from soils enters plants and accumulates in them. In wheat and barley grain its amount is 5-8 times higher than the background content, in tops and potatoes - more than 20 times, in tubers - more than 26 times.
Cadmium, like vanadium and zinc, accumulates in the humus layer of soils. The nature of its distribution in the soil profile and landscape apparently has much in common with other metals, in particular with the nature of the distribution of lead.
However, cadmium is less firmly fixed in the soil profile than lead. Maximum adsorption of cadmium is characteristic of neutral and alkaline soils with a high humus content and high absorption capacity. Its content in podzolic soils can range from hundredths to 1 mg/kg, in chernozems - up to 15-30, and in red soils - up to 60 mg/kg.
Many soil invertebrates concentrate cadmium in their bodies. Cadmium is absorbed by earthworms, woodlice and snails 10-15 times more actively than lead and zinc. Cadmium is toxic to agricultural plants, and even if high concentrations of cadmium do not have a noticeable effect on the yield of agricultural crops, its toxicity affects the quality of products, since the cadmium content in plants increases.
Arsenic enters the soil with the products of coal combustion, with waste from the metallurgical industry, and from fertilizer production plants. Arsenic is retained most firmly in soils containing active forms of iron, aluminum, and calcium. The toxicity of arsenic in soils is known to everyone. Soil contamination with arsenic causes, for example, the death of earthworms. The background content of arsenic in soils is hundredths of a milligram per kilogram of soil.
Fluorine and its compounds are widely used in nuclear, oil, chemical and other industries. It enters the soil with emissions from metallurgical enterprises, in particular aluminum smelters, and also as an admixture when applying superphosphate and some other insecticides.
By polluting the soil, fluorine causes a decrease in yield not only due to its direct toxic effect, but also by changing the ratio of nutrients in the soil. The greatest adsorption of fluorine occurs in soils with a well-developed soil absorption complex. Soluble fluoride compounds move along the soil profile with the downward flow of soil solutions and can enter groundwater. Soil contamination with fluoride compounds destroys the soil structure and reduces soil permeability.
Zinc and copper are less toxic than the above-mentioned heavy metals, but their excessive amounts in waste from the metallurgical industry pollute the soil and inhibit the growth of microorganisms, reduce the enzymatic activity of soils, and reduce plant yields.
It should be noted that the toxicity of heavy metals increases when they act together on living organisms in the soil. The combined effect of zinc and cadmium has a several times stronger inhibitory effect on microorganisms than with the same concentration of each element separately.
Since heavy metals are usually found in various combinations both in fuel combustion products and in emissions from the metallurgical industry, their effect on the nature surrounding sources of pollution is stronger than expected based on the concentration of individual elements.
Near enterprises, the natural phytocenoses of enterprises become more uniform in species composition, since many species cannot withstand increased concentrations of heavy metals in the soil. The number of species can be reduced to 2-3, and sometimes to the formation of monocenoses.
In forest phytocenoses, lichens and mosses are the first to respond to pollution. The tree layer is the most stable. However, prolonged or high-intensity exposure causes dry-resistant phenomena in it.
Soil is the surface of the earth that has properties that characterize both living and inanimate nature.
The soil is an indicator of the general. Pollution enters the soil with precipitation and surface waste. They are also introduced into the soil layer by soil rocks and groundwater.
The group of heavy metals includes everything with a density exceeding that of iron. The paradox of these elements is that in certain quantities they are necessary to ensure the normal functioning of plants and organisms.
But their excess can lead to serious illnesses and even death. The food cycle causes harmful compounds to enter the human body and often cause great harm to health.
Sources of heavy metal pollution are: There is a method by which the permissible metal content is calculated. In this case, the total value of several metals Zc is taken into account.
- acceptable;
- moderately dangerous;
- highly dangerous;
- extremely dangerous.
Soil conservation is very important. Constant control and monitoring does not allow growing agricultural products and grazing livestock on contaminated lands.
Heavy metals polluting soil
There are three hazard classes of heavy metals. The World Health Organization considers the most dangerous contaminations to be lead, mercury and cadmium. But high concentrations of other elements are no less harmful.
Mercury
Soil contamination with mercury occurs through the ingress of pesticides, various household waste, such as fluorescent lamps, and elements of damaged measuring instruments.
According to official data, the annual emission of mercury is more than five thousand tons. Mercury can enter the human body from contaminated soil.
If this happens regularly, severe dysfunction of many organs can occur, including the nervous system.
If not treated properly, death can occur.
Lead
Lead is very dangerous for humans and all living organisms.
It is extremely toxic. When one ton of lead is mined, twenty-five kilograms enter the environment. Large amounts of lead enter the soil through exhaust gases. 
The area of soil contamination along the routes is over two hundred meters around. Once in the soil, lead is absorbed by plants that are eaten by humans and animals, including livestock, the meat of which is also present in our menu. Excess lead affects the central nervous system, brain, liver and kidneys. It is dangerous due to its carcinogenic and mutagenic effects.
Cadmium
Soil contamination with cadmium is a huge danger to the human body. When ingested, it causes skeletal deformation, stunted growth in children, and severe back pain.
Copper and zinc
A high concentration of these elements in the soil causes plant growth to slow down and fruiting to deteriorate, which ultimately leads to a sharp decrease in yield. A person experiences changes in the brain, liver and pancreas.
Molybdenum
Excess molybdenum causes gout and damage to the nervous system.
The danger of heavy metals is that they are poorly excreted from the body and accumulate in it. They can form very toxic compounds, easily pass from one environment to another, and do not decompose. At the same time, they cause severe diseases, often leading to irreversible consequences.Antimony
Present in some ores.
It is part of 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, for example, herbicides and insecticides. Arsenic is an accumulating poison that causes chronic. Its compounds provoke diseases of the nervous system, brain, and skin.
Manganese
A high content of this element is observed in soil and plants. 
When additional manganese enters the soil, it quickly creates a dangerous excess. This affects the human body in the form of destruction of the nervous system.
An overabundance of other heavy elements is no less dangerous.
From the above, we can conclude that the accumulation of heavy metals in the soil entails serious consequences for human health and the environment as a whole.
Basic methods of combating soil contamination with heavy metals
Methods for combating 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 addition of organic matter and clay and liming help to some extent in the fight against pollution.
- Seeding, mowing and removing certain plants, such as clover, from the soil surface significantly reduces the concentration of heavy metals in the soil. In addition, this method is completely environmentally friendly.
- Detoxification of groundwater, its pumping and purification.
- Prediction and elimination of migration of the soluble form of heavy metals.
- In some particularly severe cases, it is necessary to completely remove the soil layer and replace it with a new one.
The most dangerous of all the metals listed is lead. It has the ability to accumulate and attack the human body. Mercury is not dangerous if it enters the human body once or several times; only mercury vapor is particularly dangerous. I believe that industrial enterprises should use more advanced production technologies that are not so destructive to all living things. Not just one person, but the masses should think, then we will come to a good result.
FEDERAL AGENCY FOR EDUCATION STATE EDUCATIONAL INSTITUTION
HIGHER PROFESSIONAL EDUCATION "VORONEZH STATE UNIVERSITY"
SOIL POLLUTION WITH HEAVY METALS. METHODS OF CONTROL AND REGULATION OF CONTAMINATED SOILS
Educational and methodological manual for universities
Compiled by: H.A. Juvelikyan, D.I. Shcheglov, N.S. Gorbunova
Publishing and Printing Center of Voronezh State University
Approved by the scientific and methodological council of the Faculty of Biology and Soil Science on July 4, 2009, protocol No. 10
Reviewer Dr. Biol. sciences, prof. L.A. Yablonskikh
The educational and methodological manual was prepared at the Department of Soil Science and Land Resources Management, Faculty of Biology and Soil Science, Voronezh State University.
For specialty 020701 – Soil science
General information about pollution................................................................... ............................... | |
The concept of man-made anomalies................................................................. ....................... | |
Soil contamination with heavy metals.................................................................... ............... | |
Migration of heavy metals in the soil profile.................................................... | |
The concept of soil environmental monitoring............................................................ | |
Indicators of soil condition determined during their monitoring.................................... | |
Environmental standardization of the quality of contaminated soils.................................... | |
General requirements for the classification of soils susceptible to contamination...... | |
Literature................................................. ........................................................ ........ |
GENERAL INFORMATION ABOUT POLLUTION
Pollutants
– these are substances of anthropogenic origin that enter the environment in quantities exceeding the natural level of their intake. Soil pollution– a type of anthropogenic degradation in which the content of chemicals in soils subject to anthropogenic impact exceeds the natural regional background level. Exceeding the content of certain chemicals in the human environment (compared to natural levels) due to their arrival from anthropogenic sources poses an environmental hazard.Human use of chemicals in economic activities and their involvement in the cycle of anthropogenic transformations in the environment is constantly growing. A characteristic of the intensity of extraction and use of chemical elements is technophilicity - the ratio of the annual extraction or production of an element in tons to its clarke in the lithosphere (A.I. Perelman, 1999). High technophilicity is characteristic of elements most actively used by humans, especially those whose natural level in the lithosphere is low. High levels of technophile are characteristic of such metals as Bi, Hg, Sb, Pb, Cu, Se, Ag, As, Mo, Sn, Cr, Zn, the demand for which is great in various types of production. When the content of these elements in rocks is low (10–2–10–6%), their extraction is significant. This leads to the extraction from the depths of the earth of colossal quantities of ores containing these elements, and to their subsequent global dispersion in the environment.
In addition to technophile, other quantitative characteristics of technogenesis have been proposed. Thus, the ratio of the technophilicity of an element to its biophilicity (biophilicity is the clarke concentration of chemical elements in living matter) M.A. Glazovskaya named destructive activity of technogenesis elements. The destructive activity of technogenesis elements characterizes the degree of danger of the elements for living organisms. Another quantitative characteristic of the anthropogenic involvement of chemical elements in their global cycles on the planet is mobilization factor or technogenic enrichment factor, which is calculated as the ratio of the technogenic flow of a chemical element to its natural flow. The level of the technogenic enrichment factor, as well as the technophilicity of elements, is not only an indicator of their mobilization from the lithosphere into terrestrial natural environments, but also a reflection of the level of emissions of chemical elements with industrial waste into the environment.
THE CONCEPT OF TECHNOGENIC ANOMALIES
Geochemical anomaly- a section of the earth's crust (or surface of the earth), characterized by significantly increased concentrations of any chemical elements or their compounds compared to background values and naturally located relative to accumulations of minerals. Identification of man-made anomalies is one of the most important ecological and geochemical tasks in assessing the state of the environment. Anomalies are formed in landscape components as a result of the supply of various substances from technogenic sources and represent a certain volume within which the values of anomalous concentrations of elements are greater than background values. According to the prevalence of A.I. Perelman and N.S. Kasimov (1999) distinguishes the following man-made anomalies:
1) global – covering the entire globe (for example, increased
2) regional - formed in certain parts of continents, natural zones and regions as a result of the use of pesticides, mineral fertilizers, acidification of atmospheric precipitation with emissions of sulfur compounds, etc.;
3) local - formed in the atmosphere, soils, waters, plants around local technogenic sources: factories, mines, etc.
According to the environment of formation, man-made anomalies are divided:
1) to lithochemical (in soils, rocks);
2) hydrogeochemical (in waters);
3) atmospheric geochemical (in the atmosphere, snow);
4) biochemical (in organisms).
According to the duration of the pollution source, they are divided:
– for short-term (emergency emissions, etc.);
– medium-term (with cessation of impact, for example, cessation of development of mineral deposits);
– long-term stationary (anomalies of factories, cities, agricultural landscapes, for example KMA, Norilsk Nickel).
When assessing man-made anomalies, background areas are selected far from man-made sources of pollutants, usually more than 30–50 km. One of the criteria for anomaly is the coefficient of technogenic concentration or anomaly Kc, which is the ratio of the content of an element in the anomalous object under consideration to its background content in the landscape components.
To assess the impact of the amount of pollutants entering the body, hygienic pollution standards are also used - pre-
separately permissible concentrations. This is the maximum content of a harmful substance in a natural object or product (water, air, soil, food), which does not affect the health of humans or other organisms.
Pollutants are divided into classes according to their hazard (GOST
17.4.1.0283): Class I (highly hazardous) – As, Cd, Hg, Se, Pb, F, benzo(a)pyrene, Zn; Class II (moderately hazardous) – B, Co, Ni, Mo, Cu, Sb, Cr; Class III (low hazardous) – Ba, V, W, Mn, Sr, acetophenone.
SOIL POLLUTION WITH HEAVY METALS
Heavy metals (HMs) already occupy the second place in terms of danger, behind pesticides and significantly ahead of such well-known pollutants as carbon dioxide and sulfur. In the future, they may become more dangerous than waste from nuclear power plants and solid waste. Pollution with heavy metals is associated with their widespread use in industrial production. Due to imperfect purification systems, heavy metals enter the environment, including the soil, polluting and poisoning it. HMs are specific pollutants, monitoring of which is mandatory in all environments.
Soil is the main environment into which heavy metals enter, including from the atmosphere and the aquatic environment. It also serves as a source of secondary pollution of surface air and waters that flow from it into the World Ocean. From the soil, HMs are absorbed by plants, which then end up in food.
The term “heavy metals,” which characterizes a wide group of pollutants, has recently gained significant popularity. In various scientific and applied works, authors interpret the meaning of this concept differently. In this regard, the amount of elements classified as heavy metals varies widely. Numerous characteristics are used as membership criteria: atomic mass, density, toxicity, prevalence in the natural environment, degree of involvement in natural and man-made cycles.
In works devoted to the problems of environmental pollution and environmental monitoring, today more than 40 elements of the periodic table of D.I. are classified as heavy metals. Mendeleev with an atomic mass of over 40 atomic units: V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, Sn, Hg, Pb, Bi, etc. According to the classification of N. Reimers (1990),
Metals with a density of more than 8 g/cm3 should be considered heavy. In this case, the following conditions play an important role in the categorization of heavy metals: their high toxicity to living organisms in relatively low concentrations, as well as the ability to bioaccumulate and biomagnify. Almost all metals falling under this definition
nie (with the exception of lead, mercury, cadmium and bismuth, the biological role of which is currently unclear), actively participate in biological processes and are part of many enzymes.
The most powerful suppliers of waste enriched with metals are enterprises for the smelting of non-ferrous metals (aluminum, alumina, copper-zinc, lead-smelting, nickel, titanium-magnesium, mercury, etc.), as well as for the processing of non-ferrous metals (radio engineering, electrical engineering, instrument making, galvanic, etc.).
In the dust of metallurgical industries and ore processing plants, the concentration of Pb, Zn, Bi, Sn can be increased by several orders of magnitude (up to 10–12) compared to the lithosphere, the concentration of Cd, V, Sb - tens of thousands of times, Cd, Mo, Pb, Sn, Zn, Bi, Ag - hundreds of times. Waste from non-ferrous metallurgy enterprises, paint and varnish industry plants and reinforced concrete structures is enriched with mercury. The concentrations of W, Cd, and Pb are increased in the dust of machine-building plants (Table 1).
Under the influence of metal-enriched emissions, areas of landscape pollution are formed mainly at the regional and local levels. The impact of energy enterprises on environmental pollution is not due to the concentration of metals in waste, but to their huge quantity. The mass of waste, for example, in industrial centers, exceeds the total amount coming from all other sources of pollution. A significant amount of Pb is released into the environment with vehicle exhaust gases, which exceeds its intake with waste from metallurgical enterprises.
Arable soils are polluted by such elements as Hg, As, Pb, Cu, Sn, Bi, which enter the soil as part of pesticides, biocides, plant growth stimulants, and structure formers. Non-traditional fertilizers, made from various wastes, often contain a wide range of pollutants in high concentrations. Among traditional mineral fertilizers, phosphorus fertilizers contain impurities Mn, Zn, Ni, Cr, Pb, Cu, Cd (Gaponyuk, 1985).
The distribution of metals released into the atmosphere from technogenic sources in the landscape is determined by the distance from the source of pollution, climatic conditions (strength and direction of winds), terrain, technological factors (state of waste, method of waste entering the environment, height of enterprise pipes).
The dispersion of heavy metals depends on the height of the source of emissions into the atmosphere. According to calculations by M.E. Berland (1975), with high chimneys, a significant concentration of emissions is created in the surface layer of the atmosphere at a distance of 10–40 chimney heights. There are 6 zones around such pollution sources (Table 2). The area of influence of individual industrial enterprises on the adjacent territory can reach 1000 km2.
table 2
Soil contamination zones around point sources of pollution
Distance from | Excess content |
|||
source for | TM ratios in relation to |
|||
dirt in km | to the background |
|||
Security zone of the enterprise | ||||
Soil contamination zones and their size are closely related to the vectors of prevailing winds. Relief, vegetation, and urban buildings can change the direction and speed of movement of the surface layer of air. Similar to the zones of soil contamination, zones of vegetation contamination can also be identified.
MIGRATION OF HEAVY METALS IN THE SOIL PROFILE
The accumulation of the main part of pollutants is observed mainly in the humus-accumulative soil horizon, where they are bound by aluminosilicates, non-silicate minerals, and organic substances due to various interaction reactions. The composition and quantity of elements retained in the soil depend on the content and composition of humus, acid-base and redox conditions, sorption capacity, and the intensity of biological absorption. Some heavy metals are firmly retained by these components and not only do not participate in migration along the soil profile, but also do not pose a danger
for living organisms. The negative environmental consequences of soil pollution are associated with mobile metal compounds.
IN within the soil profile, the technogenic flow of substances encounters a number of soil-geochemical barriers. These include carbonate, gypsum, and illuvial horizons (illuvial-iron-humus). Some highly toxic elements can transform into compounds that are difficult for plants to access; other elements, mobile in a given soil-geochemical environment, can migrate in the soil column, representing a potential danger to biota. The mobility of elements largely depends on the acid-base and redox conditions in soils. In neutral soils, Zn, V, As, and Se compounds are mobile and can be leached during seasonal soil wetting.
The accumulation of mobile compounds of elements that are especially dangerous for organisms depends on the water and air regimes of soils: the lowest accumulation is observed in permeable soils of the leaching regime, it increases in soils with a non-leaching regime and is maximum in soils with an exudate regime. At evaporative concentration and alkaline reaction, Se, As, V can accumulate in the soil in an easily accessible form, and under reducing environment conditions, Hg can accumulate in the form of methylated compounds.
However, it should be borne in mind that under leaching conditions the potential mobility of metals is realized, and they can be carried beyond the soil profile, becoming sources of secondary pollution of groundwater.
IN In acidic soils with a predominance of oxidizing conditions (podzolic soils, well-drained), heavy metals such as Cd and Hg form easily mobile forms. On the contrary, Pb, As, and Se form low-mobile compounds that can accumulate in humus and illuvial horizons and negatively affect the state of soil biota. If S is present in the pollutants, under reducing conditions a secondary hydrogen sulfide environment is created and many metals form insoluble or slightly soluble sulfides.
IN In marshy soils, Mo, V, As, and Se are present in sedentary forms. A significant part of the elements in acidic swampy soils is present in forms that are relatively mobile and dangerous for living matter; these are the compounds Pb, Cr, Ni, Co, Cu, Zn, Cd and Hg. In slightly acidic and neutral soils with good aeration, sparingly soluble Pb compounds are formed, especially during liming. In neutral soils, the compounds Zn, V, As, Se are mobile, and Cd and Hg can be retained in the humus and illuvial horizons. As alkalinity increases, the risk of soil contamination by the listed elements increases.
CONCEPT OF SOIL ECOLOGICAL MONITORING
Soil environmental monitoring – system of regular un- limit
limited in space and time control of soils, which provides information about their condition in order to assess the past, present and predict changes in the future. Soil monitoring aims to identify anthropogenic changes in soils that may ultimately harm human health. The special role of soil monitoring is due to the fact that all changes in the composition and properties of soils are reflected in the performance of soils’ ecological functions, and, consequently, on the state of the biosphere.
It is of great importance that in soil, unlike atmospheric air and surface water, the environmental consequences of anthropogenic impact usually appear later, but they are more stable and last longer. There is a need to evaluate the long-term consequences of this impact, for example, the possibility of mobilizing pollutants in soils, as a result of which the soil can turn from a “depot” of pollutants into their secondary source.
Types of soil environmental monitoring
The identification of types of soil environmental monitoring is based on differences in the combination of informative soil indicators corresponding to the tasks of each of them. Based on the differences in the mechanisms and scales of soil degradation, two groups of types of monitoring are distinguished:
ring: first group – global monitoring, the second – local and regional.
Global soil monitoring is an integral part of global monitoring of the biosphere. It is carried out to assess the impact on the state of soils of the environmental consequences of long-distance atmospheric transport of pollutants in connection with the danger of planetary pollution of the biosphere and accompanying processes at the global level. The results of global or biosphere monitoring characterize global changes in the state of living organisms on the planet under the influence of human activity.
The purpose of local and regional monitoring is to identify the impact of soil degradation on ecosystems at the local and regional levels and directly on human living conditions in the sphere of environmental management.
Local monitoring also called sanitary-hygienic or impact. It is aimed at controlling the level of pollutants in the environment that are emitted by a particular enterprise.
Soil contamination with heavy metals has different sources:
1. waste from the metalworking industry;
2. industrial emissions;
3. fuel combustion products;
4. automobile exhaust gases;
5. means of chemicalization of agriculture.
Metallurgical enterprises annually emit to the surface of the earth more than 150 thousand tons of copper, 120 thousand tons of zinc, about 90 thousand tons of lead, 12 thousand tons of nickel, 1.5 thousand tons of molybdenum, about 800 tons of cobalt and about 30 tons of mercury . For 1 gram of blister copper, waste from the copper smelting industry contains 2.09 tons of dust, which contains up to 15% copper, 60% iron oxide and 4% each of arsenic, mercury, zinc and lead. Waste from mechanical engineering and chemical industries contains up to 1 g/kg of lead, up to 3 g/kg of copper, up to 10 g/kg of chromium and iron, up to 100 g/kg of phosphorus and up to 10 g/kg of manganese and nickel. In Silesia, around zinc factories, dumps containing zinc from 2 to 12% and lead from 0.5 to 3% are piled up, and in the USA ores with a zinc content of 1.8% are exploited.
More than 250 thousand tons of lead per year reach the soil surface with exhaust gases; it is a major soil pollutant of lead. Heavy metals enter the soil along with fertilizers, which contain them as impurities.
Although heavy metals are sometimes found in soils in low concentrations, they form stable complexes with organic compounds and enter into specific adsorption reactions more easily than alkali and alkaline earth metals. Near enterprises, the natural phytocenoses of enterprises become more uniform in species composition, since many species cannot withstand increasing the concentration of heavy metals in the soil. The number of species can be reduced to 2-3, and sometimes until monocenoses form. In forest phytocenoses, lichens and mosses are the first to respond to pollution. The tree layer is the most stable. However, long-term or high-intensity exposure causes dry-resistant phenomena in it. Restoration of disturbed soil cover requires a long time and large investments.
A particularly difficult task is restoring vegetation cover to overburden dumps and tailings (tailings) of workings where metal ores were mined: such tailings are usually poor in nutrients, rich in toxic metals, and have poor water retention. A serious environmental problem is wind erosion of mine dumps.
Standardization of heavy metal content in soilStandardization of the content of heavy metals in soil and plants is extremely difficult due to the impossibility of fully taking into account all environmental factors. Thus, changing only the agrochemical properties of the soil (medium reaction, humus content, degree of saturation with bases, particle size distribution) can reduce or increase the content of heavy metals in plants several times. There are conflicting data even about the background content of some metals. The results given by researchers sometimes differ by 5-10 times.
Many scales for environmental regulation of heavy metals have been proposed. In some cases, the highest content of metals observed in ordinary anthropogenic soils is taken as the maximum permissible concentration, in others - the content that is the limit for phytotoxicity. In most cases, maximum permissible concentrations have been proposed for heavy metals, which exceed the actual permissible values of metal concentrations by several times.
To characterize technogenic pollution with heavy metals, a concentration coefficient is used, equal to the ratio of the concentration of the element in contaminated soil to its background concentration.
Table 1 shows the officially approved maximum concentration limits and permissible levels of their content according to hazard indicators. In accordance with the scheme adopted by medical hygienists, the regulation of heavy metals in soils is divided into translocation (transition of the element into plants), migratory water (transition into water), and general sanitary (effect on the self-purifying ability of soils and soil microbiocenosis).
FEDERAL AGENCY OF MARINE AND RIVER TRANSPORT
FEDERAL BUDGET EDUCATIONAL INSTITUTION
HIGHER PROFESSIONAL EDUCATION
MARINE STATE UNIVERSITY
named after Admiral G.I. Nevelsky
Department of Environmental Protection
ABSTRACT
in the discipline "Physico-chemical processes"
Consequences of soil contamination with heavy metals and radionuclides.
Checked by the teacher:
Firsova L.Yu.
Completed by student gr. ___
Khodanova S.V.
Vladivostok 2012
CONTENT
Introduction
1 Heavy metals in soils
Conclusion
List of sources used
INTRODUCTION
Soil is not just an inert medium on the surface of which human activity takes place, but a dynamic, developing system that includes many organic and inorganic components, which have a network of cavities and pores, and these, in turn, contain gases and liquids. The spatial distribution of these components determines the main types of soils on the globe.
In addition, soils contain a huge number of living organisms, they are called biota: from bacteria and fungi to worms and rodents. Soil is formed on parent rocks under the combined influence of climate, vegetation, soil organisms and time. Therefore, changes in any of these factors can lead to changes in soils. Soil formation is a long process: the formation of a 30 cm layer of soil takes from 1000 to 10,000 years. Consequently, the rates of soil formation are so low that soil can be considered a non-renewable resource.
The Earth's soil cover is the most important component of the Earth's biosphere. It is the soil shell that determines many of the processes occurring in the biosphere. The most important importance of soils is the accumulation of organic matter, various chemical elements, and energy. Soil cover functions as a biological absorber, destroyer and neutralizer of various pollutants. If this link of the biosphere is destroyed, then the existing functioning of the biosphere will be irreversibly disrupted. That is why it is extremely important to study the global biochemical significance of the soil cover, its current state and changes under the influence of anthropogenic activities.
1 Heavy metals in soils
- Sources of heavy metals entering the soil
There are many trace elements among HMs that are biologically important for living organisms. They are necessary and indispensable components of biocatalysts and bioregulators of the most important physiological processes. However, the excess content of heavy metals in various objects of the biosphere has a depressing and even toxic effect on living organisms.
Sources of heavy metals entering the soil are divided into natural (weathering of rocks and minerals, erosion processes, volcanic activity) and technogenic (mining and processing of minerals, fuel combustion, influence of vehicles, agriculture, etc.) Agricultural lands, in addition to pollution through the atmosphere, HMs are also polluted specifically through the use of pesticides, mineral and organic fertilizers, liming, and the use of wastewater. Recently, scientists have been paying special attention to urban soils. The latter are experiencing a significant technogenic process, an integral part of which is HM pollution.
HMs reach the soil surface in various forms. These are oxides and various salts of metals, both soluble and practically insoluble in water (sulfides, sulfates, arsenites, etc.). In the emissions of ore processing enterprises and non-ferrous metallurgy enterprises - the main source of environmental pollution with heavy metals - the bulk of metals (70-90%) are in the form of oxides.
Once on the soil surface, HMs can either accumulate or dissipate, depending on the nature of the geochemical barriers inherent in a given area.
Most of the HMs arriving on the soil surface are fixed in the upper humus horizons. HMs are sorbed on the surface of soil particles, bind to soil organic matter, in particular in the form of elemental organic compounds, accumulate in iron hydroxides, form part of the crystal lattices of clay minerals, produce their own minerals as a result of isomorphic replacement, and are in a soluble state in soil moisture and gaseous state in the soil air, are an integral part of the soil biota.
The degree of mobility of heavy metals depends on the geochemical situation and the level of technogenic impact. The heavy particle size distribution and high content of organic matter lead to the binding of HMs in the soil. An increase in pH values increases the sorption of cation-forming metals (copper, zinc, nickel, mercury, lead, etc.) and increases the mobility of anion-forming metals (molybdenum, chromium, vanadium, etc.). Increasing oxidative conditions increases the migration ability of metals. As a result, according to their ability to bind the majority of HMs, soils form the following series: gray soil > chernozem > soddy-podzolic soil.
- Soil contamination with heavy metals
Secondly, accumulating in large quantities in the soil, HMs are capable of changing many of its properties. First of all, changes affect the biological properties of the soil: the total number of microorganisms decreases, their species composition (diversity) narrows, the structure of microbial communities changes, the intensity of basic microbiological processes and the activity of soil enzymes decreases, etc. Severe contamination with heavy metals leads to changes in more conservative soil characteristics, such as humus status, structure, pH, etc. The result of this is partial, and in some cases, complete loss of soil fertility.
- Natural and man-made anomalies
Soil, unlike other components of the natural environment, not only geochemically accumulates pollution components, but also acts as a natural buffer that controls the transfer of chemical elements and compounds into the atmosphere, hydrosphere and living matter.
Various plants, animals and humans require a certain composition of soil and water for their life. In places of geochemical anomalies, aggravated transmission of deviations from the norm in mineral composition occurs throughout the food chain. As a result of disturbances in mineral nutrition, changes in the species composition of phyto-, zoo- and microbial communities, diseases of wild plant forms, a decrease in the quantity and quality of crops of agricultural plants and livestock products, an increase in morbidity among the population and a decrease in life expectancy are observed.
The toxic effect of HMs on biological systems is primarily due to the fact that they easily bind to sulfhydryl groups of proteins (including enzymes), suppressing their synthesis and, thereby, disrupting metabolism in the body.
Living organisms have developed various mechanisms of resistance to HMs: from the reduction of HM ions into less toxic compounds to the activation of ion transport systems that effectively and specifically remove toxic ions from the cell into the external environment.
The most significant consequence of the impact of heavy metals on living organisms, which manifests itself at the biogeocenotic and biosphere levels of organization of living matter, is the blocking of the oxidation processes of organic matter. This leads to a decrease in the rate of its mineralization and accumulation in ecosystems. At the same time, an increase in the concentration of organic matter causes it to bind HM, which temporarily relieves the load on the ecosystem. A decrease in the rate of decomposition of organic matter due to a decrease in the number of organisms, their biomass and the intensity of vital activity is considered a passive response of ecosystems to HM pollution. Active resistance of organisms to anthropogenic loads manifests itself only during the lifetime accumulation of metals in bodies and skeletons. The most resistant species are responsible for this process.
The resistance of living organisms, primarily plants, to elevated concentrations of heavy metals and their ability to accumulate high concentrations of metals can pose a great danger to human health, since they allow the penetration of pollutants into food chains.
- Standardization of heavy metal content in soil and soil cleansing
There are two main approaches to the issue of remediation of soils contaminated with heavy metals. The first is aimed at clearing the soil of HM. Purification can be carried out by leaching, by extracting HM from the soil with the help of plants, by removing the top contaminated layer of soil, etc. The second approach is based on fixing HMs in the soil, converting them into forms that are insoluble in water and inaccessible to living organisms. To achieve this, it is proposed to add organic matter, phosphorus mineral fertilizers, ion exchange resins, natural zeolites, brown coal, liming the soil, etc. to the soil. However, any method of fixing HMs in the soil has its own validity period. Sooner or later, part of the HM will again begin to enter the soil solution, and from there into living organisms.
- Radionuclides in soils. Nuclear pollution
Soils contain almost all chemical elements known in nature, including radionuclides.
Radionuclides are chemical elements capable of spontaneous decay with the formation of new elements, as well as formed isotopes of any chemical elements. The consequence of nuclear decay is ionizing radiation in the form of a flow of alpha particles (flow of helium nuclei, protons) and beta particles (flow of electrons), neutrons, gamma radiation and X-rays. This phenomenon is called radioactivity. Chemical elements capable of spontaneous decay are called radioactive. The most commonly used synonym for ionizing radiation is radioactive radiation.
Ionizing radiation is a flow of charged or neutral particles and electromagnetic quanta, the interaction of which with a medium leads to ionization and excitation of its atoms and molecules. Ionizing radiation has an electromagnetic (gamma and x-ray radiation) and corpuscular (alpha radiation, beta radiation, neutron radiation) nature.
Gamma radiation is electromagnetic radiation caused by gamma rays (discrete beams or quanta called photons) if, after alpha or beta decay, the nucleus remains in an excited state. Gamma rays in air can travel considerable distances. A high-energy photon of gamma rays can pass through the human body. Intense gamma radiation can damage not only the skin, but also internal organs. Dense and heavy materials, iron, and lead protect against this radiation. Gamma radiation can be created artificially in accelerators of infected particles (microtron), for example, bremsstrahlung gamma radiation from fast accelerator electrons when they hit a target.
X-ray radiation is similar to gamma radiation. Cosmic X-rays are absorbed by the atmosphere. X-rays are produced artificially and fall in the lower part of the energy spectrum of electromagnetic radiation.
Radioactive radiation is a natural factor in the biosphere for all living organisms, and living organisms themselves have a certain radioactivity. Among biosphere objects, soils have the highest natural degree of radioactivity. Under these conditions, nature prospered for many millions of years, except in exceptional cases due to geochemical anomalies associated with the deposit of radioactive rocks, for example, uranium ores.
However, in the 20th century, humanity was faced with radioactivity that was prohibitively higher than natural, and therefore biologically abnormal. The first to suffer from excessive doses of radiation were the great scientists who discovered radioactive elements (radium, polonium), the spouses Marie Sklodowska-Curie and Pierre Curie. And then: Hiroshima and Nagasaki, tests of atomic and nuclear weapons, many disasters, including Chernobyl, etc.
The most significant objects of the biosphere, determining the biological functions of all living things, are soils.
The radioactivity of soils is due to the content of radionuclides in them. A distinction is made between natural and artificial radioactivity.
Natural radioactivity of soils is caused by natural radioactive isotopes, which are always present in varying quantities in soils and soil-forming rocks. Natural radionuclides are divided into 3 groups.
The first group includes radioactive elements - elements all of whose isotopes are radioactive: uranium (238
etc.................
