Heavy metals are the most dangerous elements that can pollute the soil. Heavy metals in soil

heavy metal plant soil

The content of HMs in soils depends, as established by many researchers, on the composition of the original rocks, a significant diversity of which is associated with the complex geological history of the development of territories (Kovda, 1973). The chemical composition of soil-forming rocks, represented by the weathering products of rocks, is predetermined by the chemical composition of the original rocks and depends on the conditions of hypergene transformation.

In recent decades, anthropogenic activity of mankind has been intensively involved in the processes of HM migration in the natural environment. quantities chemical elements, entering the environment as a result of technogenesis, in some cases significantly exceed the level of their natural intake. For example, the global release of Pb from natural sources per year is 12 thousand tons. and anthropogenic emissions of 332 thousand tons. (Nriagu, 1989). Involved in natural migration cycles, anthropogenic flows lead to the rapid spread of pollutants in the natural components of the urban landscape, where their interaction with humans is inevitable. The volumes of pollutants containing HM increase annually and cause damage to the natural environment, undermine the existing ecological balance and adversely affect human health.

The main sources of anthropogenic HM release into the environment are thermal power plants, metallurgical enterprises, quarries and mines for the extraction of polymetallic ores, transport, chemicals protection of agricultural crops from diseases and pests, burning of oil and various wastes, production of glass, fertilizers, cement, etc. The most powerful HM haloes arise around ferrous and especially non-ferrous metallurgy enterprises as a result of atmospheric emissions (Kovalsky, 1974; Dobrovolsky, 1983; Israel, 1984; Geochemistry…, 1986; Saet, 1987; Panin, 2000; Kabala and Singh, 2001). The action of pollutants extends to tens of kilometers from the source of elements entering the atmosphere. Thus, metals in an amount of 10 to 30% of the total emissions into the atmosphere spread over a distance of 10 km or more from an industrial enterprise. At the same time, combined pollution of plants is observed, which consists of the direct settling of aerosols and dust on the surface of leaves and the root assimilation of HMs accumulated in the soil over a long period of pollution from the atmosphere (Ilyin, Syso, 2001).

The dimensions below can be judged from. anthropogenic activities humanity: the contribution of technogenic lead is 94-97% (the rest is natural sources), cadmium - 84-89%, copper - 56-87%, nickel - 66-75%, mercury - 58%, etc. At the same time, 26-44% of the world anthropogenic flow of these elements falls on Europe, and the share of the European territory of the former USSR is 28-42% of all emissions in Europe (Vronsky, 1996). The level of technogenic fallout of HMs from the atmosphere in different regions of the world is not the same and depends on the presence of developed deposits, the degree of development of the mining and processing and industrial industries, transport, urbanization of territories, etc.

The study of the share participation of various industries in the global flow of HM emissions shows: 73% of copper and 55% of cadmium are associated with emissions from copper and nickel production enterprises; 54% of mercury emissions come from coal combustion; 46% of nickel - for the combustion of petroleum products; 86% of lead enters the atmosphere from vehicles (Vronsky, 1996). Agriculture also supplies a certain amount of HM to the environment, where pesticides and mineral fertilizers are used, in particular, superphosphates contain significant amounts of chromium, cadmium, cobalt, copper, nickel, vanadium, zinc, etc.

Elements emitted into the atmosphere through the pipes of chemical, heavy and nuclear industries have a noticeable effect on the environment. The share of thermal and other power plants in atmospheric pollution is 27%, ferrous metallurgy enterprises - 24.3%, enterprises for the extraction and manufacture of building materials - 8.1% (Alekseev, 1987; Ilyin, 1991). HMs (with the exception of mercury) are mainly introduced into the atmosphere as aerosols. The set of metals and their content in aerosols are determined by the specialization of industrial and energy activities. When coal, oil, and shale are burned, the elements contained in these fuels enter the atmosphere along with smoke. So, coal contains cerium, chromium, lead, mercury, silver, tin, titanium, as well as uranium, radium and other metals.

The most significant environmental pollution is caused by powerful thermal stations (Maistrenko et al., 1996). Every year, only when burning coal, 8700 times more mercury is released into the atmosphere than can be included in the natural biogeochemical cycle, 60 times more uranium, 40 times more cadmium, 10 times more yttrium and zirconium, and 3-4 times more tin. 90% of cadmium, mercury, tin, titanium and zinc polluting the atmosphere gets into it when coal is burned. This largely affects the Republic of Buryatia, where energy companies using coal are the largest air pollutants. Among them (according to their contribution to total emissions), Gusinoozerskaya GRES (30%) and CHPP-1 of Ulan-Ude (10%) stand out.

Significant pollution of atmospheric air and soil occurs due to transport. Most HMs contained in dust and gas emissions from industrial enterprises are, as a rule, more soluble than natural compounds (Bol'shakov et al., 1993). Large industrialized cities stand out among the most active sources of HMs. Metals accumulate relatively quickly in the soils of cities and are extremely slowly removed from them: the half-life of zinc is up to 500 years, cadmium is up to 1100 years, copper is up to 1500 years, lead is up to several thousand years (Maistrenko et al., 1996). In many cities of the world, high rates of HM pollution have led to the disruption of the main agroecological functions of soils (Orlov et al., 1991; Kasimov et al., 1995). Cultivation of agricultural plants used for food near these territories is potentially dangerous, since crops accumulate excessive amounts of HMs that can lead to various diseases in humans and animals.

According to a number of authors (Ilyin and Stepanova, 1979; Zyrin, 1985; Gorbatov and Zyrin, 1987, etc.), it is more correct to assess the degree of soil contamination with HMs by the content of their most bioavailable mobile forms. However, maximum allowable concentrations (MPCs) of mobile forms of most HMs have not yet been developed. Therefore, the literature data on the level of their content, leading to adverse environmental consequences, can serve as a criterion for comparison.

Below is a brief description of the properties of metals, concerning the features of their behavior in soils.

Lead (Pb). Atomic mass 207.2. The primary element is a toxicant. All soluble lead compounds are poisonous. Under natural conditions, it exists mainly in the form of PbS. Clark Pb's earth's crust 16.0 mg/kg (Vinogradov, 1957). Compared to other HMs, it is the least mobile, and the degree of element mobility is greatly reduced when soils are limed. Mobile Pb is present in the form of complexes with organic matter (60 - 80% mobile Pb). At high pH values, lead is chemically fixed in the soil in the form of hydroxide, phosphate, carbonate, and Pb-organic complexes (Zinc and cadmium…, 1992; Heavy…, 1997).

The natural content of lead in soils is inherited from parent rocks and is closely related to their mineralogical and chemical composition (Beus et al., 1976; Kabata-Pendias, Pendias, 1989). The average concentration of this element in the soils of the world reaches, according to various estimates, from 10 (Saet et al., 1990) to 35 mg/kg (Bowen, 1979). The MPC of lead for soils in Russia corresponds to 30 mg/kg (Instructive…, 1990), in Germany - 100 mg/kg (Kloke, 1980).

The high concentration of lead in soils can be associated with both natural geochemical anomalies and anthropogenic impact. With technogenic pollution, the highest concentration of the element, as a rule, is found in the upper soil layer. In some industrial areas, it reaches 1000 mg/kg (Dobrovolsky, 1983), and in the surface layer of soils around non-ferrous metallurgy enterprises in Western Europe - 545 mg/kg (Rautse, Kyrstya, 1986).

The content of lead in soils in Russia varies significantly depending on the type of soil, the proximity of industrial enterprises and natural geochemical anomalies. In the soils of residential areas, especially those associated with the use and production of lead-containing products, the content of this element is often tens or more times higher than the MPC (Table 1.4). By preliminary estimates up to 28% of the country's territory has a Pb content in the soil, on average, below the background level, and 11% can be classified as a risk zone. At the same time, in Russian Federation the problem of soil pollution with lead is mainly a problem of residential areas (Snakin et al., 1998).

Cadmium (Cd). Atomic mass 112.4. Cadmium is similar in chemical properties to zinc, but differs from it in greater mobility in acidic environments and better availability for plants. In the soil solution, the metal is present in the form of Cd2+ and forms complex ions and organic chelates. The main factor, which determines the content of the element in soils in the absence of anthropogenic influence, - parent rocks (Vinogradov, 1962; Mineev et al., 1981; Dobrovolsky, 1983; Ilyin, 1991; Zinc and cadmium ..., 1992; Cadmium: ecological ..., 1994). Clark of cadmium in the lithosphere 0.13 mg/kg (Kabata-Pendias, Pendias, 1989). In soil-forming rocks, the average metal content is: in clays and clay shales - 0.15 mg / kg, loess and loess-like loams - 0.08, sands and sandy loams - 0.03 mg / kg (Zinc and cadmium ..., 1992). In the Quaternary deposits of Western Siberia, the concentration of cadmium varies within 0.01-0.08 mg/kg.

The mobility of cadmium in soil depends on the environment and redox potential (Heavy…, 1997).

The average content of cadmium in the soils of the world is 0.5 mg/kg (Saet et al., 1990). Its concentration in the soil cover of the European part of Russia is 0.14 mg / kg - in soddy-podzolic soil, 0.24 mg / kg - in chernozem (Zinc and cadmium ..., 1992), 0.07 mg / kg - in the main types soils of Western Siberia (Ilyin, 1991). The approximate allowable content (AEC) of cadmium for sandy and sandy loamy soils in Russia is 0.5 mg/kg, in Germany the MPC of cadmium is 3 mg/kg (Kloke, 1980).

Soil pollution with cadmium is considered one of the most dangerous environmental phenomena, since it accumulates in plants above the norm even with slight soil contamination (Kadmii …, 1994; Ovcharenko, 1998). The highest concentrations of cadmium in the upper soil layer are observed in mining areas - up to 469 mg/kg (Kabata-Pendias, Pendias, 1989), around zinc smelters they reach 1700 mg/kg (Rautse, Kyrstya, 1986).

Zinc (Zn). Atomic mass 65.4. Its clarke in the earth's crust is 83 mg/kg. Zinc is concentrated in clay deposits and shales in amounts from 80 to 120 mg/kg (Kabata-Pendias, Pendias, 1989), in deluvial, loess-like and carbonate loamy deposits of the Urals, in loams of Western Siberia - from 60 to 80 mg/kg.

Important factors influencing the mobility of Zn in soils are the content of clay minerals and the pH value. With an increase in pH, the element passes into organic complexes and is bound by the soil. Zinc ions also lose their mobility, getting into the interpacket spaces of the montmorillonite crystal lattice. With organic matter, Zn forms stable forms; therefore, in most cases, it accumulates in soil horizons with a high content of humus and in peat.

The reasons for the increased content of zinc in soils can be both natural geochemical anomalies and technogenic pollution. The main anthropogenic sources of its receipt are, first of all, non-ferrous metallurgy enterprises. Soil contamination with this metal in some areas has led to its extremely high accumulation in the upper soil layer - up to 66400 mg/kg. In garden soils, up to 250 or more mg/kg of zinc accumulates (Kabata-Pendias, Pendias, 1989). AEC for zinc for sandy and sandy loamy soils is 55 mg/kg; German scientists recommend MAC equal to 100 mg/kg (Kloke, 1980).

Copper (Cu). Atomic mass 63.5. Clark in the earth's crust 47 mg/kg (Vinogradov, 1962). Chemically, copper is an inactive metal. The fundamental factor influencing the value of Cu content is its concentration in soil-forming rocks (Goryunova et al., 2001). Of the igneous rocks, the largest amount of the element is accumulated by the main rocks - basalts (100-140 mg/kg) and andesites (20-30 mg/kg). Covering and loess-like loams (20-40 mg/kg) are less rich in copper. Its lowest content is noted in sandstones, limestones and granites (5-15 mg/kg) (Kovalsky, Andriyanova, 1970; Kabata-Pendias, Pendias, 1989). The concentration of metal in clays of the European part of the territory of the former USSR reaches 25 mg/kg (Malgin, 1978; Kovda, 1989), in loess-like loams - 18 mg/kg (Kovda, 1989). Sandy and sandy soil-forming rocks of the Altai Mountains accumulate an average of 31 mg/kg of copper (Malgin, 1978), and 19 mg/kg of copper in the south of Western Siberia (Ilyin, 1973).

In soils, copper is a weakly migratory element, although the content of the mobile form is quite high. The amount of mobile copper depends on many factors: the chemical and mineralogical composition of the parent rock, the pH of the soil solution, the content of organic matter, etc. (Vinogradov, 1957; Peive, 1961; Kovalsky and Andriyanova, 1970; Alekseev, 1987, etc.). The largest amount of copper in the soil is associated with oxides of iron, manganese, iron and aluminum hydroxides, and, especially, with vermiculite montmorillonite. Humic and fulvic acids are able to form stable complexes with copper. At pH 7-8, the solubility of copper is the lowest.

The average content of copper in the soils of the world is 30 mg/kg (Bowen, 1979). Near industrial sources of pollution, in some cases, soil contamination with copper up to 3500 mg/kg can be observed (Kabata-Pendias, Pendias, 1989). The average content of metal in the soils of the central and southern regions of the former USSR is 4.5–10.0 mg/kg, in the south of Western Siberia - 30.6 mg/kg (Ilyin, 1973), in Siberia and the Far East - 27.8 mg/kg (Makeev, 1973). MPC for copper in Russia is 55 mg/kg (Instructive ..., 1990), APC for sandy and sandy loamy soils - 33 mg/kg (Control ..., 1998), in Germany - 100 mg/kg (Kloke, 1980).

Nickel (Ni). Atomic mass 58.7. In continental sediments, it is present mainly as sulfides and arsenites, and is also associated with carbonates, phosphates, and silicates. The clarke of an element in the earth's crust is 58 mg/kg (Vinogradov, 1957). Ultrabasic (1400-2000 mg/kg) and basic (200-1000 mg/kg) rocks accumulate the greatest amount of metal, while sedimentary and acidic rocks contain it in much lower concentrations - 5-90 and 5-15 mg/kg, respectively (Reuce , Kyrstya, 1986; Kabata-Pendias and Pendias, 1989). Of great importance in the accumulation of nickel by soil-forming rocks is their granulometric composition. On the example of soil-forming rocks of Western Siberia, it can be seen that in lighter rocks its content is the lowest, in heavy rocks it is the highest: in sands - 17, sandy loams and light loams - 22, medium loams - 36, heavy loams and clays - 46 (Ilyin, 2002) .

The content of nickel in soils largely depends on the availability of this element in soil-forming rocks (Kabata-Pendias, Pendias, 1989). The highest concentrations of nickel, as a rule, are observed in clayey and loamy soils, in soils formed on basic and volcanic rocks and rich in organic matter. The distribution of Ni in the soil profile is determined by the content of organic matter, amorphous oxides, and the amount of clay fraction.

The level of nickel concentration in the upper soil layer also depends on the degree of their technogenic pollution. In areas with a developed metalworking industry, very high accumulation of nickel occurs in soils: in Canada, its gross content reaches 206–26,000 mg/kg, and in Great Britain, the content of mobile forms reaches 506–600 mg/kg. In the soils of Great Britain, Holland, Germany, treated with sewage sludge, nickel accumulates up to 84-101 mg/kg (Kabata-Pendias, Pendias, 1989). In Russia (according to a survey of 40-60% of agricultural soils), 2.8% of the soil cover is contaminated with this element. The proportion of soils contaminated with Ni among other HMs (Pb, Cd, Zn, Cr, Co, As, etc.) is actually the most significant and is second only to soils contaminated with copper (3.8%) (Aristarkhov, Kharitonova, 2002). According to land monitoring data of the State Station of the Agrochemical Service "Buryatskaya" for 1993-1997. on the territory of the Republic of Buryatia, an excess of the MAC of nickel was registered by 1.4% of the land of the surveyed area of agricultural land, among which the soils of Zakamensky (20% of the land are polluted - 46 thousand hectares) and Khorinsky districts (11% of the land are polluted - 8 thousand hectares) are distinguished.

Chrome (Cr). Atomic mass 52. In natural compounds, chromium has a valence of +3 and +6. Most of Cr3+ is present in chromite FeCr2O4 or other minerals of the spinel series, where it replaces Fe and Al, to which it is very close in its geochemical properties and ionic radius.

Clark of chromium in the earth's crust - 83 mg / kg. Its highest concentrations among igneous rocks are typical for ultrabasic and basic (1600-3400 and 170-200 mg/kg, respectively), lower - for medium rocks (15-50 mg/kg) and the lowest - for acidic (4-25 mg/kg). kg). Among sedimentary rocks, the maximum content of the element was found in clay sediments and shales (60-120 mg/kg), the minimum content was found in sandstones and limestones (5-40 mg/kg) (Kabata-Pendias, Pendias, 1989). The content of metal in soil-forming rocks of different regions is very diverse. In the European part of the former USSR, its content in the most common soil-forming rocks such as loess, loess-like carbonate and mantle loams averages 75-95 mg/kg (Yakushevskaya, 1973). The soil-forming rocks of Western Siberia contain an average of 58 mg/kg of Cr, and its amount is closely related to the granulometric composition of the rocks: sandy and sandy loamy rocks - 16 mg/kg, and medium loamy and clayey rocks - about 60 mg/kg (Ilyin, Syso, 2001) .

In soils, most of the chromium is present in the form of Cr3+. In an acidic environment, the Cr3+ ion is inert; at pH 5.5, it precipitates almost completely. The Cr6+ ion is extremely unstable and is easily mobilized in both acidic and alkaline soils. The adsorption of chromium by clays depends on the pH of the medium: with an increase in pH, the adsorption of Cr6+ decreases, while that of Cr3+ increases. Soil organic matter stimulates the reduction of Cr6+ to Cr3+.

The natural content of chromium in soils depends mainly on its concentration in soil-forming rocks (Kabata-Pendias, Pendias, 1989; Krasnokutskaya et al., 1990), and the distribution along the soil profile depends on the features of soil formation, in particular, on the granulometric composition of genetic horizons. The average content of chromium in soils is 70 mg/kg (Bowen, 1979). The highest content of the element is observed in soils formed on basic and volcanic rocks rich in this metal. The average content of Cr in the soils of the USA is 54 mg/kg, China - 150 mg/kg (Kabata-Pendias, Pendias, 1989), Ukraine - 400 mg/kg (Bespamyatnov, Krotov, 1985). In Russia, its high concentrations in soils under natural conditions are due to the enrichment of soil-forming rocks. Kursk chernozems contain 83 mg/kg of chromium, soddy-podzolic soils of the Moscow region - 100 mg/kg. The soils of the Urals, formed on serpentinites, contain up to 10,000 mg/kg of metal, and 86–115 mg/kg in Western Siberia (Yakushevskaya, 1973; Krasnokutskaya et al., 1990; Ilyin and Syso, 2001).

The contribution of anthropogenic sources to the supply of chromium is very significant. Chromium metal is mainly used for chromium plating as a component of alloy steels. Soil pollution with Cr has been noted due to emissions from cement plants, iron-chromium slag dumps, oil refineries, ferrous and non-ferrous metallurgy enterprises, the use of industrial wastewater sludge in agriculture, especially tanneries, and mineral fertilizers. The highest concentrations of chromium in technogenically polluted soils reach 400 or more mg/kg (Kabata-Pendias, Pendias, 1989), which is especially characteristic of large cities (Table 1.4). In Buryatia, according to land monitoring data conducted by the Buryatskaya State Agrochemical Service Station for 1993-1997, 22 thousand hectares are contaminated with chromium. Excesses of MPC by 1.6-1.8 times were noted in Dzhida (6.2 thousand ha), Zakamensky (17.0 thousand ha) and Tunkinsky (14.0 thousand ha) districts.

Rationing of the content of heavy metals

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

Many scales have been proposed

environmental regulation of heavy metals. In some cases, the maximum allowable concentration is taken to be the highest metal content observed in ordinary anthropogenic soils, in others- content, which is the limiting phytotoxicity. In most cases, MPCs have been proposed for heavy metals that exceed the upper limit by several times.

To characterize technogenic pollution

heavy metals use a concentration factor equal to the ratio of the concentration of the element in contaminated soil to its background concentration. When contaminated with several heavy metals, the degree of contamination is estimated by the value of the total concentration index (Zc). The scale of soil contamination with heavy metals proposed by IMGRE is shown in Table 1.

Table 1. Scheme for assessing soils for agricultural use by the degree of contamination with chemicals (Goskomgidromet of the USSR, No. 02-10 51-233 dated 10.12.90)

Soil category according to the degree of pollution	Zc	Pollution relative to MPC	Possible use of soils	Necessary activities
Permissible	<16,0	Exceeds the background, but not above the MPC	Use for any culture	Reducing the level of exposure to sources of soil pollution. Decreased availability of toxicants for plants.
Moderately dangerous	16,1- 32,0	Exceeds the MPC at the limiting general sanitary and migratory water hazard indicator, but below the MPC by the translocation indicator	Use for any crops subject to quality control of crop products	Activities similar to category 1. If there are substances with a limiting migration water indicator, the content of these substances in surface and ground waters is monitored.
Highly dangerous	32,1- 128	Exceeds MPC with limiting translocation indicator of harmfulness	Use for industrial crops without obtaining food and feed from them. Eliminate Chemical Concentrator Plants	Activities similar to the category 1. Mandatory control over the content of toxicants in plants used as food and feed. Limiting the use of green mass for livestock feed, especially concentrator plants.
extremely dangerous	> 128	Exceeds MPC in all respects	Exclude from agricultural use	Reducing the level of pollution and binding of toxicants in the atmosphere, soil and water.

Officially approved MPCs

Table 2 shows officially approved MPCs and permissible levels of their content in terms of harmfulness. In accordance with the scheme adopted by medical hygienists, the regulation of heavy metals in soils is divided into translocation (transition of an element into plants), migratory water (transition into water), and general sanitary (influence on the self-cleaning capacity of soils and soil microbiocenosis).

Table 2. Maximum Permissible Concentrations (MACs) of Chemical Substances in Soils and Permissible Levels of Their Content in Terms of Harmfulness (as of 01/01/1991. Goskompriroda USSR, No. 02-2333 dated 12/10/90).

Name of substances	MPC, mg/kg of soil, taking into account the background	Harm indicators
Name of substances	MPC, mg/kg of soil, taking into account the background	Translocation	Water	general sanitary

Water soluble forms
Fluorine	10,0	10,0	10,0	10,0
Movable forms
Copper	3,0	3,5	72,0	3,0
Nickel	4,0	6,7	14,0	4,0
Zinc	23,0	23,0	200,0	37,0
Cobalt	5,0	25,0	>1000	5,0
Fluorine	2,8	2,8	-	-
Chromium	6,0	-	-	6,0
Gross content
Antimony	4,5	4,5	4,5	50,0
Manganese	1500,0	3500,0	1500,0	1500,0
Vanadium	150,0	170,0	350,0	150,0
Lead **	30,0	35,0	260,0	30,0
Arsenic **	2,0	2,0	15,0	10,0
Mercury	2,1	2,1	33,3	5,0
Lead+mercury	20+1	20+1	30+2	30+2
Copper*	55	-	-	-
Nickel*	85	-	-	-
Zinc*	100	-	-	-

* - gross content - approximate.
** - contradiction; for arsenic, the average background content is 6 mg/kg; the background content of lead usually also exceeds the MPC norms.

Officially approved UEC

DECs developed in 1995 for the gross content of 6 heavy metals and arsenic make it possible to obtain more complete description about soil pollution with heavy metals, since they take into account the level of reaction of the environment and the granulometric composition of the soil.

Table 3 Approximately Permissible Concentrations (APC) of heavy metals and arsenic in soils with different physical and chemical properties (gross content, mg/kg) (Supplement No. 1 to the list of MPC and APC No. 6229-91).

Element	Soil group	JDC with background	Aggregate state of affairs in soils	Hazard classes	Peculiarities actions on the body
Nickel	Sandy and sandy	20	Solid: in the form of salts, in adsorbed form, in the composition of minerals	2	It is low toxic for warm-blooded animals and humans. Has a mutogenic effect
	<5,5	40
	Close to neutral, (loamy and clayey), pHKCl >5.5	80
Copper	Sandy and sandy	33		2	Increases cell permeability, inhibits glutathione reductase, disrupts metabolism by interacting with -SH, -NH2 and COOH- groups
	Acid (loamy and clayey), pH KCl<5,5	66
	Close to neutral, (loamy and clayey), pH KCl>5.5	132
Zinc	Sandy and sandy	55	Solid: in the form of salts, organo-mineral compounds, in adsorbed form, in the composition of minerals	1	Deficiency or excess cause deviations in development. Poisoning due to violation of the technology of introducing zinc-containing pesticides
	Acid (loamy and clayey), pH KCl<5,5	110
	Close to neutral, (loamy and clayey), pH KCl>5.5	220
Arsenic	Sandy and sandy	2	Solid: in the form of salts, organo-mineral compounds, in adsorbed form, in the composition of minerals	1	Poisonous in-in, inhibiting various enzymes, a negative effect on metabolism. Possible carcinogenic effect
	Acid (loamy and clayey), pH KCl<5,5	5
	Close to neutral, (loamy and clayey), pH KCl>5.5	10
Cadmium	Sandy and sandy	0,5	Solid: in the form of salts, organo-mineral compounds, in adsorbed form, in the composition of minerals	1	Highly toxic in-in, blocks the sulfhydryl groups of enzymes, disrupts the exchange of iron and calcium, disrupts DNA synthesis.
	Acid (loamy and clayey), pH KCl<5,5	1,0
	Close to neutral, (loamy and clayey), pH KCl>5.5	2,0
Lead	Sandy and sandy	32	Solid: in the form of salts, organo-mineral compounds, in adsorbed form, in the composition of minerals	1	Miscellaneous negative effect. Blocks -SH groups of proteins, inhibits enzymes, causes poisoning, damage to the nervous system.
	Acid (loamy and clayey), pH KCl<5,5	65
	Close to neutral, (loamy and clayey), pH KCl>5.5	130

It follows from the materials that the requirements for gross forms of heavy metals are mainly presented. Among the mobile only copper, nickel, zinc, chromium and cobalt. Therefore, at present, the developed standards no longer meet all the requirements.

is a capacity factor that primarily reflects the potential danger of contamination of plant products, infiltration and surface waters. It characterizes the general contamination of the soil, but does not reflect the degree of availability of elements for the plant. To characterize the state of soil nutrition of plants, only their mobile forms are used.

Definition of movable forms

They are determined using various extractants. The total amount of the mobile form of the metal - using an acid extract (for example, 1N HCL). The most mobile part of the mobile reserves of heavy metals in the soil passes into the ammonium acetate buffer. The concentration of metals in the water extract shows the degree of mobility of elements in the soil, being the most dangerous and "aggressive" fraction.

Regulations for movable molds

Several indicative normative scales have been proposed. Below is an example of one of the scales for the maximum allowable mobile forms of heavy metals.

Table 4. Maximum allowable content of the mobile form of heavy metals in soil, mg/kg extractant 1n. HCl (H. Chuldzhiyan et al., 1988).

Element	Content	Element	Content	Element	Content
hg	0,1	Sb	15	Pb	60
CD	1,0	As	15	Zn	60
co	12	Ni	36	V	80
Cr	15	Cu	50	Mn	600

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FAQ?	into the soil	in gel	result	those data	prices

Introduction

The state of the natural environment is the most important factor determining the life of a person and society. High concentrations of many chemical elements and compounds, caused by technogenic processes, are currently found in all natural environments: atmosphere, water, soil, and plants.

Soil - special natural formation, which has a number of properties inherent in animate and inanimate nature; consists of genetically related horizons (form a soil profile) resulting from the transformation of the surface layers of the lithosphere under the combined influence of water, air and organisms; characterized by fertility. The soil plays an important role in the cycle of heavy metals, they are heterogeneous mixtures of various organic and organo-mineral constituents of clay minerals, oxides of iron (Fe), aluminum (Al) and manganese (Mn) and other solid particles, as well as various soluble compounds. Due to the diversity of soil types, their redox conditions and reactivity, the mechanisms and ways of binding heavy metals in soils are diverse. Heavy metals, in soils contained in various forms: in the crystal lattice of minerals in the form of an isomorphic admixture, in salt and oxide form, as part of various organic substances, in an ion-exchange state and in a soluble form in soil solution. It should be noted that heavy metals, coming from the soil into plants and then into the organisms of animals and humans, have the ability to gradually accumulate. The most toxic mercury, cadmium, lead, arsenic, poisoning them causes severe consequences. Less toxic: zinc and copper, however, their contamination of soils inhibits microbiological activity and reduces biological productivity.

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

When determining heavy metals in soils and soil components, atomic absorption analysis of soils and various extracts is used (for example, extraction of Zn, Cu, Pb, Fe, Ni, which extracts 70–90% of the gross content of heavy metals from contaminated soil samples). The method has a number of advantages: good sensitivity, selectivity, fairly good reproducibility of results, ease of analysis. It makes it possible to determine up to 70 elements, provides a detection limit of many elements at the level of 0.1--0.01 μg/ml, which in many cases makes it possible to analyze soils and plants without preliminary concentration of elements.

The purpose of this work is to determine the content of acid-soluble forms of metals (lead, copper, zinc, nickel, iron) in soil samples of the Tula region by atomic absorption spectroscopy.

To achieve this goal, it was necessary to solve the following tasks:

1. To study the principle of operation of the atomic absorption spectrometer with electrothermal atomization "MGA-915M".

2. Determine the concentration of each heavy metal in soil samples.

3. Assess the degree of contamination of the selected objects.

1. Literature review

absorption spectroscopy lead copper

1.1 Soil pollution

A pollutant can be any physical agent, chemical substance or species that enters or occurs in the environment in quantities outside its usual concentration, limits, limits of natural fluctuations or average natural background at the time in question.

The main indicator characterizing the impact of pollutants on the environment is the maximum permissible concentration (MAC). From the point of view of ecology, the maximum permissible concentrations of a particular substance are the upper limits of limiting environmental factors (in particular, chemical compounds), at which their content does not go beyond the permissible boundaries of the human ecological niche.

In accordance with the degree of resistance against pollutants, soils are distinguished:

1. very resistant;

2. resistant;

3. medium resistant;

4. unstable;

5. very unstable.

The sensitivity or resistance of soils to pollutants should be determined in accordance with:

2) its quality;

3) biological activity;

4) depth of the humus horizon;

6) clay minerals;

7) the depth of the soil profile.

Soils are polluted with various chemicals, pesticides, waste Agriculture, industrial production and household enterprises. Chemical compounds entering the soil accumulate and lead to a gradual change in the chemical and physical properties of the soil, reduce the number of living organisms, and worsen its fertility.

Soil pollution and disruption of the normal circulation of substances occurs as a result of the underdosed use of mineral fertilizers and pesticides. In a number of branches of agriculture, pesticides are used in large quantities for plant protection and weed control. Their annual application, often several times a season, leads to their accumulation in the soil and its poisoning.

Together with manure and faeces, pathogenic bacteria, helminth eggs and other harmful organisms often enter the soil, which enter the human body through food.

The soil is polluted with oil products when refueling cars in the fields and in forests, at logging sites, etc. .

Incoming heavy metals into the soil during the operation of vehicles, as well as abrasion of road surfaces, enter: iron, nickel, zinc, lead and other elements.

surrounding industrial enterprises different profiles, soils, contain toxic elements in quantities exceeding the permissible norms by tens and hundreds of times

The highest, surface horizon of the lithosphere undergoes the greatest transformation. Land occupies 29.2% of the surface the globe and includes lands of various categories, of which the most important is fertile soil. In case of improper exploitation, soils are irretrievably destroyed as a result of erosion, salinization, pollution by industrial and other wastes.

Under the influence of human activities, accelerated erosion occurs, when soils are destroyed 100-1000 times faster than under natural conditions. As a result of such erosion, 2 billion hectares of fertile land, or 27% of agricultural land, have been lost over the past century.

Chemical compounds entering the soil accumulate and lead to a gradual change in the chemical and physical properties of the soil, reduce the number of living organisms, and worsen its fertility.

Soil pollution is associated with air and water pollution. Various solid and liquid wastes of industrial production, agriculture and municipal enterprises get into the soil. The main soil pollutants are metals and their compounds.

The intensive development of industry, energy, transport, as well as the intensification of agricultural production contribute to an increase in the anthropogenic load on agricultural ecosystems and, above all, on the soil cover. As a result, soils are contaminated with heavy metals. Heavy metals, which enter the biosphere mainly as a result of industrial and transport emissions, are one of its most dangerous pollutants. Therefore, the study of their behavior in soils and the protective capabilities of soils is an important environmental problem.

Heavy metals accumulate in the soil and contribute to a gradual change in its chemical composition disruption of plant and living organisms. From the soil, heavy metals can enter the body of people and animals and cause undesirable consequences. In the human body, heavy metals are involved in vital biochemical processes. Exceeding the permissible concentrations leads to serious diseases.

Thus, soil pollution with heavy metals has the following sources:

1. Automobile exhaust gas waste

2. Products of fuel combustion

3. Industrial emissions

4. Metal industry

5. Means of chemicalization of agriculture.

1.2 Heavy metals in soil

Currently, in Russia, both officially approved and non-official standards are used to assess soil pollution with heavy metals. Their main purpose is to prevent the entry of excessive amounts of anthropogenically accumulated in the soil heavy metals into the human body and thereby avoid their negative impact. The soil, unlike homogeneous water and air environments, is a complex heterogeneous system that changes the behavior of toxicants depending on its properties. Difficulties in a reasonable assessment of the soil-ecological state is one of the reasons different levels soil phytotoxicity.

Soils play an important role in the cycle of heavy metals and other trace elements. They are heterogeneous mixtures of various organic and organo-mineral constituents of clay minerals, oxides of iron, aluminum and manganese and other solid particles, as well as various soluble compounds. Due to the diversity of soil types, their redox conditions and reactivity, the mechanisms and ways of binding heavy metals in soils are diverse. The absorption of microelements by soils during technogenic pollution is influenced by the mechanical composition, reaction, content of humus and carbonates, absorption capacity and conditions of the water regime. Trace elements, including heavy metals, are contained in soils in various forms: in the crystal lattice of minerals in the form of an isomorphic admixture, in salt and oxide form, as part of various organic substances, in an ion-exchange state and in a soluble form in soil solution. The behavior of microelements in soils is influenced by redox conditions, the reaction of the environment, the concentration of carbon dioxide and the presence of organic matter. Changes in the redox state of soils significantly affect the behavior of microelements with variable valence. Thus, during oxidation, manganese passes into insoluble forms, while chromium and vanadium, on the contrary, acquire mobility and migrate. With an acidic soil reaction, the mobility of copper, manganese, zinc, cobalt increases and the mobility of Molybdenum decreases. Boron, fluorine and iodine are mobile in acidic and alkaline environments.

The mobility of chemical elements in the soil changes as a result of a shift in the equilibrium between the compounds of the element in the solid and liquid phases. Pollutants entering the soil can pass into a firmly fixed state, which is difficult for plants to access. Higher resistance of soils to pollution is determined by those properties of soils that contribute to the strong fixation of pollutants. An increase in the concentration of CO2 in the soil solution leads to an increase in the mobility of manganese, nickel, and barium as a result of the transition of carbonates of these elements to bicarbonates. Humic and organic substances of a non-specific nature (formic, citric, oxalic and other acids) can bind microelements, forming both soluble and hardly soluble compounds for plants.

Water-soluble metal compounds quickly migrate along the soil profile. The effect of organic substances on the migration of metals in the soil is twofold. In the process of mineralization of organic substances in the soil, low-molecular water-soluble mineral compounds are formed, migrating to the lower part of the profile. Heavy metals form low-molecular complexes with these substances. With a deeper transformation of organic substances, the formation of high-molecular humic acids occurs, and their effect on the migration of metals is different. Fulvic acids combine with metals to form chelate compounds that are soluble in a wide pH range and migrate down the soil profile. Metals form complexes with humic acids, which are characterized by inertness, insoluble in an acidic environment, which contributes to the accumulation of heavy metals in the organogenic horizon. Metal complexes with fulvic acids and humic acids are most stable at pH from 3 to 7.

An example of the transformation of zinc and cadmium in soils is their transition to the liquid phase due to dissolution processes (Alekseenko et al., 1992). Cadmium has high toxicity and relatively high mobility in the soil and availability for plants. Since technogenic compounds of these metals are thermodynamically unstable under soil conditions, their transition to the liquid phase of soils is irreversible. Further transformation of zinc and cadmium in soils is associated with reversible processes occurring between the soil solution and the soil absorbing complex, stable precipitation of poorly soluble salts of zinc and cadmium, higher plants and microorganisms.

1.3 Sources of heavy metals entering objects environment

Heavy metals include more than forty chemical elements of D.I. Mendeleev, the mass of atoms of which is more than fifty atomic units.

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

Sources of heavy metals are divided into natural (weathering of rocks and minerals, erosion processes, volcanic activity) and man-made (mining and processing of minerals, fuel combustion, traffic, agricultural activities). Part of man-made emissions entering the environment in the form of fine aerosols is transported over considerable distances and causes global pollution. The other part enters drainless water bodies, where heavy metals accumulate and become a source of secondary pollution, i.e. the formation of hazardous contaminants in the course of physical and chemical processes occurring directly in the environment (for example, the formation of poisonous phosgene gas from non-toxic substances).

Heavy metals accumulate in the soil, especially in the upper humus horizons, and are slowly removed by leaching, consumption by plants, erosion and deflation - soil blowing. The period of half-removal or removal of half of the initial concentration is a long time: for zinc - from 70 to 510 years, for cadmium - from 13 to 110 years, for copper - from 310 to 1500 years and for lead - from 740 to 5900 years.

In the humus part of the soil, the primary transformation of the compounds that got into it occurs.

Heavy metals have a high capacity for a variety of chemical, physicochemical and biological reactions. Many of them have a variable valency and are involved in redox processes. Heavy metals and their compounds, like other chemical compounds, are able to move and redistribute in living environments, i.e. migrate . The migration of heavy metal compounds occurs largely in the form of an organo-mineral component. Some of the organic compounds with which metals bind are represented by products of microbiological activity. Mercury is characterized by the ability to accumulate in the links of the "food chain" (this was discussed earlier). Soil microorganisms can produce mercury-resistant populations that convert metallic mercury into substances toxic to higher organisms. Some algae, fungi and bacteria are able to accumulate mercury in their cells. Mercury, lead, cadmium are included in the general list of the most important environmental pollutants, agreed by the countries that are members of the UN. Let us dwell on these substances and add iron and nickel to them.

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

Initially, mercury enters the ocean in the form of Hg2+, then it interacts with organic substances and, with the help of anaerobic organisms, passes into toxic substances methylmercury (CH3 Hg) + and dimethylmercury (CH3 -Hg-CH3),

Mercury is present not only in the hydrosphere, but also in the atmosphere, as it has a relatively high vapor pressure. The natural content of mercury is ~0.003-0.009 µg/m3.

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

The world production of mercury is currently over 10,000 tons per year, most of this amount is used in the production of chlorine. Mercury enters the air as a result of burning fossil fuels. Analysis of the ice of the Greenland Ice Dome showed that, starting from 800 AD. until the 1950s, the mercury content remained constant, but since the 50s. of our century, the amount of mercury has doubled.

Mercury and its compounds are life threatening. Methylmercury is especially dangerous for animals and humans, as it quickly passes from the blood into the brain tissue, destroying the cerebellum and the cerebral cortex. The clinical symptoms of such a lesion are numbness, loss of orientation in space, loss of vision. Symptoms of mercury poisoning do not appear immediately. Another unpleasant consequence of methylmercury poisoning is the penetration of mercury into the placenta and its accumulation in the fetus, and the mother does not experience pain. Methylmercury is teratogenic in humans. Mercury belongs to the 1st hazard class.

Metallic mercury is dangerous if swallowed and inhaled. At the same time, a person has a metallic taste in the mouth, nausea, vomiting, abdominal cramps, teeth turn black and begin to crumble. Spilled mercury breaks into droplets and, if this happens, the mercury must be carefully collected. Inorganic mercury compounds are practically non-volatile, so the danger is the ingress of mercury into the body through the mouth and skin. Mercury salts corrode the skin and mucous membranes of the body. The ingress of mercury salts into the body causes inflammation of the pharynx, difficulty swallowing, numbness, vomiting, and abdominal pain. In an adult human, if about 350 mg of mercury is ingested, death can occur.

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

The content of lead in igneous rocks makes it possible to attribute it to the category of rare metals. It is concentrated in sulfide rocks that are found in many places in the world. Lead is easily isolated by smelting from the ore. In its natural state, it is found mainly in the form of galena (PbS). Lead contained in the earth's crust can be washed out under the influence of atmospheric processes, gradually passing into the oceans. Pb2+ ions are rather unstable, and the content of lead in ionic form is only 10 -8%. However, it accumulates in ocean sediments as sulfites or sulfates. In fresh water, the lead content is much higher and can reach 2 x 10 -6%, and in soil it is approximately the same amount as in the earth's crust (1.5 x 10 -3%) due to the instability of this element in the geochemical cycle.

Lead ores contain 2-20% lead. The concentrate obtained by the flotation method contains 60-80% Pb. It is heated to remove sulfur and lead is smelted. Such primary processes are large scale. If waste is used to produce lead, the smelting processes are called secondary. The annual world consumption of lead is more than 3 million tons, of which 40% is used for the production of batteries, 20% for the production of lead alkyl - gasoline additives, 12% is used in construction, 28% for other purposes.

About 180 thousand tons of lead migrate annually in the world as a result of the impact of atmospheric processes. During the extraction and processing of lead ores, more than 20% of lead is lost. Even at these stages, the release of lead into the environment is equal to its amount entering the environment as a result of exposure to atmospheric processes on igneous rocks.

The most serious source of environmental pollution with lead is the exhaust of automobile engines. The antiknock tetramethyl - or tetraethylswinep - has been added to most gasolines since 1923 at about 80 mg/l.

Gasoline can contain 380 mg of lead, and the total content of tetraethyl lead reaches 1 g/l. During the combustion of gasoline, about 75% of the lead contained in it is released in the form of an aerosol and dispersed in the air, further redistributing at different distances from the roadway. When driving, from 25 to 75% of this lead, depending on driving conditions, is released into the atmosphere. Its main mass is deposited on the ground, but a noticeable part of it remains in the air.

Lead dust not only covers roadsides and soils in and around industrial cities, it is also found in the ice of North Greenland, and in 1756 the lead content in the ice was 20 µg/t, in 1860 it was already 50 µg/t, and in 1965 - 210 µg/t. Active sources of lead pollution are coal-fired power plants and household stoves. Sources of lead contamination in the home can be glazed earthenware; lead contained in coloring pigments.

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

Organic lead compounds are considered even more toxic than inorganic ones. The main source from which lead enters the human body is food, along with this, inhaled air plays an important role, and in children, lead-containing dust and paints they swallow. Inhaled dust is approximately 30-35% retained in the lungs, a significant proportion of it is absorbed by the blood stream. Absorption in the gastrointestinal tract is generally 5-10%, in children - 50%. Deficiency of calcium and vitamin D enhances the absorption of lead. Acute lead poisoning is rare. Their symptoms are salivation, vomiting, intestinal colic, acute kidney failure, brain damage. In severe cases, death occurs within a few days. Early symptoms of lead poisoning include irritability, depression, and irritability. In case of poisoning organic compounds lead, its elevated content is found in the blood.

Due to global environmental pollution with lead, it has become a ubiquitous component of any food and feed. Plant foods generally contain more lead than animal products.

cadmium and zinc.

Cadmium, zinc and copper are the most important metals in the study of pollution problems, as they are widely distributed in the world and have toxic properties. Cadmium and zinc (as well as: lead and mercury) are found mainly in sulfide sediments. As a result of atmospheric processes, these elements easily enter the oceans. Soils contain approximately 4.5x10 -4%. Vegetation contains varying amounts of both elements, but the zinc content in plant ash is relatively high - 0.14; since this element plays an essential role in plant nutrition. About 1 million kg of cadmium enters the atmosphere annually as a result of the activities of cadmium smelting plants, which is about 45% of the total pollution by this element. 52% of pollution comes from the combustion or processing of products containing cadmium. Cadmium has a relatively high volatility, so it easily diffuses into the atmosphere. The sources of air pollution with zinc are the same as with cadmium.

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

Fertilizers are a potential source of cadmium contamination. At the same time, cadmium is introduced into plants that are used by humans for food, and at the end of the chain they pass into the human body. Zinc is the least toxic of all the heavy metals listed above. However, all elements become toxic if found in excess; zinc is no exception. The physiological effect of zinc is its action as an enzyme activator. In large quantities, it causes vomiting, this dose is approximately 150 mg for an adult.

Cadmium is much more toxic than zinc. He and his compounds belong to the I class of danger. It penetrates the human body over a long period. Breathing air for 8 hours at a cadmium concentration of 5 mg/m3 can cause death. In chronic cadmium poisoning, protein appears in the urine, and blood pressure rises.

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

One effective way to prevent cadmium and zinc from being released as pollution is to control the content of these metals in emissions from smelters and other industries.

Antimony, Arsenic, Cobalt.

Antimony is present together with arsenic in ores containing metal sulfides. World production of antimony is about 70 tons per year. Antimony is a component of alloys, it is used in the manufacture of matches, in its pure form it is used in semiconductors. The toxic effect of antimony is similar to arsenic. Large amounts of antimony cause vomiting, with chronic antimony poisoning, an upset of the digestive tract occurs, accompanied by vomiting and a decrease in temperature. Arsenic occurs naturally in the form of sulfates. Its content in lead-zinc concentrates is about 1%. Due to its volatility, it easily enters the atmosphere.

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

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

Arsenic compounds are slowly absorbed through the skin, rapidly absorbed through the lungs and gastrointestinal tract. The lethal dose for humans is 0.15-0.3 g.

Chronic poisoning causes nervous diseases, weakness, numbness of the extremities, itching, darkening of the skin, bone marrow atrophy, liver changes. Arsenic compounds are carcinogenic to humans. Arsenic and its compounds belong to II hazard class.

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

Copper and Manganese.

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

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

Currently, in Russia, both officially approved and non-official standards are used to assess soil pollution with heavy metals. Their main purpose is to prevent the entry of anthropogenically accumulated HMs in the human body in an excessive amount and thereby avoid their negative impact. The soil, unlike homogeneous water and air media, is a complex heterogeneous system that changes the behavior of toxicants depending on its properties. the difficulties of a reasonable assessment of the soil-ecological state is one of the reasons for the different levels of soil phytotoxicity established by different researchers.

Technogenic sources of iron in the environment. In the areas of metallurgical plants, solid emissions contain from 22,000 to 31,000 mg/kg of iron.

As a result, iron accumulates in garden crops.

A lot of iron enters wastewater and sludge from the industries of metallurgical, chemical, machine-building, metalworking, petrochemical, chemical-pharmaceutical, paint and varnish, textile industries. The content of iron in the composition of the raw sludge falling in the primary settling tanks of a large industrial city can reach 1428 mg/kg. Smoke, industrial dust can contain large amounts of iron in the form of aerosols of iron, its oxides, ores. Dust of iron or its oxides is formed when sharpening metal tools, cleaning parts from rust, rolling iron sheets, electric welding and other production processes containing iron or its compounds.

Iron can accumulate in soils, water bodies, air, and living organisms. The main iron minerals are subjected in nature to photochemical destruction, complex formation, microbiological leaching, as a result of which iron from sparingly soluble minerals passes into water bodies.

Iron-containing minerals are oxidized by bacteria such as Th. Ferrooxidans. The oxidation of sulfides can be described in a general way using the example of pyrite by the following microbiological and chemical processes. As can be seen, in this case, one more component, sulfuric acid, polluting surface waters, is formed. The scale of its microbiological education can be judged by this example. Pyrite is a common impurity component of coal deposits, and its leaching leads to acidification of mine waters. According to one estimate, in 1932. about 3 million tons of pSO4 entered the US Ohio River with mine waters. Microbiological leaching of iron is carried out not only due to oxidation, but also during the reduction of oxidized ores. Microorganisms belonging to different groups take part in it.

In particular, the reduction of Fe3 to Fe2 is carried out by representatives of the genera Bacillus and Pseudomonas, as well as some fungi.

The processes mentioned here, which are widespread in nature, also occur in the dumps of mining enterprises, metallurgical plants that produce a large number of waste slag, cinder, etc. With rain, flood and groundwater, metals released from solid matrices are transferred to rivers and reservoirs. Iron is found in natural waters in different states and forms in a truly dissolved form, it is part of bottom sediments and heterogeneous systems of suspensions and colloids. Bottom sediments of rivers and reservoirs act as a storage of iron. The high content of iron is due to the geochemical features of the formation of soil horizons. Its increased content in the soil cover may be due to the use of waters with a natural high content of iron for irrigation.

Hazard class - no division into hazard classes is provided.

The limiting indicator of harmfulness - harmfulness is not defined.

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 peculiarities of the structure of 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 main mass 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.

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 from sewage nickel-plating shops, synthetic rubber plants, nickel concentrators. Huge nickel emissions accompany the burning of fossil fuels.

Its concentration can decrease as a result of precipitation of compounds such as sulfides, cyanides, carbonates or hydroxides (with an increase in 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 the 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.

Metallurgical enterprises annually emit 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 to the surface of the earth . 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. Wastes from engineering and chemical industries contain 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, dumps with zinc content from 2 to 12% and lead from 0.5 to 3% are piled up around zinc plants.

With exhaust gases, more than 250 thousand tons of lead per year enters the soil surface; it is the main soil pollutant with lead.

1.4 Methods for the determination of heavy metals

To date, there are two groups of basic analytical methods that determine the presence of heavy metals in the soil:

1. Electrochemical

Electrochemical methods are classified according to the nature of the analytical signal. Thus, during the analysis, it is possible to measure the potential of one of the electrodes (potentiometry), the resistance of the cell, or the electrical conductivity of the solution (conductometry). In many cases, an external voltage is applied to the electrodes, after which the strength of the current passing through the solution is measured (voltammetric methods, in particular polarography). At the same time, redox reactions occur on the surface of the electrodes, that is, the solution is electrolyzed. If we carry out the electrolysis to the end and measure the amount of electricity used to oxidize (or reduce) the substance being determined, we can calculate the mass of this substance. This method is called coulometry. Sometimes the content of the analyte is calculated by the weight gain of the electrode, i.e., by the mass of the electrolysis product released on it (electrogravimetry).

Electrochemical methods are quite selective (except for conductometry), therefore, with their help, some elements are quantitatively determined in the presence of others, they are separately determined different forms one element, divide complex mixtures and identify their components, and also concentrate some microimpurities. Electrochemical methods are widely used to control the composition of natural and waste waters, soils and food products, process solutions and biological fluids. Appropriate techniques do not require complex equipment, they do not use high temperatures and pressures. Different electrochemical methods differ in sensitivity, accuracy, rapidity and other indicators, and therefore complement each other well.

Consider the methods of the electrochemical group:

Voltammetry:

Voltammetric methods are methods of analysis based on recording and studying the dependence of the current flowing through an electrolytic cell on an external applied voltage. A graphic representation of this dependence is called a voltammogram. Analysis of the voltammogram provides information on the qualitative and quantitative composition of the analyte.

To register voltammograms, an electrolytic cell is needed, consisting of an indicator electrode and a reference electrode. The reference electrode is usually a saturated calomel electrode or a layer of mercury at the bottom of the cell. A dripping mercury electrode, microdisk platinum or graphite electrodes are used as an indicator.

Depending on the type of indicator electrode, voltammetric methods are usually divided into polarography and voltammetry proper. If a mercury dripping electrode is used as an indicator electrode, then the obtained dependences of the current on the voltage are called polarograms and, accordingly, the analysis method is called polarography. The method was created by the outstanding Czech electrochemist and Nobel Prize winner Jar. Geyrovsky (1922). When working with any other indicator electrode, including stationary mercury, one deals with voltammetry.

Potentiometry:

Potentiometric analysis is the measurement of the performance of those substances that are in the ionic state. In other words, under the objects of study are solutions, almost always aqueous, although the analysis of solids is also carried out if there is the presence of soluble elements. Some particles may require an electrode with a sensing membrane of a certain shape, which will help analyze viscous substances or gels.

Potentiometric analysis is carried out in several ways. The first is direct potentiometry. Most often, this method is carried out to measure the pH level and it depends on the type of measuring electrode itself. This method is the easiest. The second method is potentiometric titration, which is carried out in a variety of ways. Its essence lies in the fact that in order to calculate the indicators, a number of chemical reactions are carried out under the control of an ion-selective electrode. This method differs from the previous one in greater labor costs, but also in a more accurate result. And the third method - the method of additions - is related to the above. It is carried out in a variety of options, which allow you to make an analysis of low concentrations.

Coulometry:

Coulometry is an electrochemical method of analysis based on measuring the amount of electricity required for the electrochemical transformation of an analyte. There are two types of analysis in coulometry:

direct coulometry;

coulometric titration.

Conductometry:

Conductometric methods of analysis are based on measuring the electrical conductivity of the studied solutions. There are several methods of conductometric analysis:

direct conductometry - a method that allows you to directly determine the concentration of the electrolyte by measuring the electrical conductivity of a solution with a known qualitative composition;

· conductometric titration - an analysis method based on determining the content of a substance by a break in the titration curve. The curve is built by measuring the specific electrical conductivity of the analyzed solution, which changes as a result of chemical reactions during the titration process;

· chronoconductometric titration - based on the determination of the content of the substance by the time spent titration, automatically recorded on the chart tape recorder of the titration curve.

Thus, it is possible to find and calculate the content of heavy metals with a low detection limit in a soil sample.

2. Extraction-photometric methods

These methods are used very widely in analytical chemistry, and the determination of the analyzed component in the extract can be carried out both photometrically and by another method: polarographic, spectral.

At the same time, there are some groups of extraction methods in which the photometric finish is the most effective, providing the necessary speed and accuracy of determination. These methods are called extraction-photometric. A very common is the method by which a certain microelement is converted into a water-soluble colored compound, it is extracted, and the extract is photomodeled. This technique eliminates the interfering influence of foreign components and increases the sensitivity of the determination, since during extraction, microimpurities are concentrated. For example, the determination of iron impurities in cobalt or nickel salts is carried out by extraction of its thiocainate complexes with amyl alcohol.

Spectrophotometry

The spectrophotometric method of analysis is based on the spectral-selective absorption of a monochromatic flux of light energy as it passes through the test solution. The method makes it possible to determine the concentrations of individual components of mixtures of colored substances that have an absorption maximum at different wavelengths; it is more sensitive and accurate than the photoelectrocolorimetric method. It is known that the photocolorimetric method of analysis is applicable only to the analysis of colored solutions, colorless solutions in the visible region of the spectrum have an insignificant absorption coefficient. However, many colorless and slightly colored compounds (especially organic ones) have characteristic absorption bands in the ultraviolet and infrared regions of the spectrum, which is used for their quantitative determination. The spectrophotometric method of analysis is applicable for measuring light absorption in various regions of the visible spectrum, in the ultraviolet and infrared regions of the spectrum, which greatly expands the analytical capabilities of the method.

The spectrophotometric method in the ultraviolet region of the spectrum makes it possible to individually determine two- and three-component mixtures of substances. The quantitative determination of the components of a mixture is based on the fact that the optical density of any mixture is equal to the sum of the optical densities of the individual components.

Atomic - absorption spectroscopy.

The method of atomic absorption spectroscopy is currently the most convenient for determining the content of metals in environmental objects, food products, soils, various alloys. The method is also used in geology to analyze the composition of rocks, metallurgy to determine the composition of steels.

The method of atomic absorption spectroscopy is recommended by most of the state standards for the determination of mobile zinc in soil, natural and water, as well as in a variety of non-ferrous alloys.

The method is based on the absorption of electromagnetic radiation by free atoms in a stationary (unexcited) state. At a wavelength corresponding to the transition of an atom from the ground to an excited electronic state, the population of the ground level decreases. The analytical signal depends on the number of unexcited particles in the analyzed sample (i.e., on the concentration of the element being determined), therefore, by measuring the amount of absorbed electromagnetic radiation, it is possible to determine the concentration of the element being determined in the initial sample.

The method is based on the absorption of ultraviolet or visible radiation by gas atoms. To pass the sample into a gaseous atomic state, it is injected into the flame. A lamp with a hollow cathode made of the metal to be determined is used as a radiation source. The wavelength interval of the spectral line emitted by the light source and the absorption line of the same element in the flame is very narrow, so the interfering absorption of other elements hardly affects the results of the analysis. The method of atomic absorption spectral analysis is characterized by high absolute and relative sensitivity. The method allows to determine with great accuracy in solutions about eighty elements in low concentrations, therefore it is widely used in biology, medicine (for the analysis of organic liquids), in geology, soil science (for the determination of trace elements in soils) and other fields of science, as well as in metallurgy. for research and control of technological processes.

Through a layer of atomic vapor samples obtained with the help of an atomizer pass radiation in the range of 190-850 nm. As a result of the absorption of light quanta, atoms pass into excited energy states. These transitions in atomic spectra correspond to the so-called. resonant lines characteristic of a given element. According to the Bouguer-Lambert-Beer law, the measure of element concentration is the optical density A = lg(I0/I), where I0 and I are the intensity of radiation from the source, respectively, before and after passing through the absorbing layer.

Figure 1.1 Schematic diagram of an atomic absorption spectrometer: 1-hollow cathode lamp or electrodeless lamp; 2-graphite cell; 3-monochromator; 4-detector

In terms of accuracy and sensitivity, this method surpasses many others; therefore, it is used in the certification of reference alloys and geological rocks (by transferring into solution).

The essential difference between atomic absorption and flame emission spectrometry is that the latter method measures the radiation emitted by excited atoms in a flame, while atomic absorption is based on the measurement of radiation absorbed by neutral, unexcited atoms in a flame, of which there are many in a flame. times more than excited. This explains the high sensitivity of the method in determining elements that have a high excitation energy, i.e., are difficult to excite.

The light source in AAS is a hollow cathode lamp that emits light having a very narrow wavelength range, on the order of 0.001 nm. The absorption line of the element being determined is somewhat wider than the emitted band, which makes it possible to measure the absorption line at its maximum. The device contains the necessary set of lamps, each lamp is designed to determine only one of any element.

The “cuvette” in AAS is the flame itself. Since Baer's law is observed in AAS, the sensitivity of the method depends on the length of the absorbing flame layer, which must be constant and sufficiently large.

A flame is used, for which acetylene, propane or hydrogen is used as a fuel, and air, oxygen or nitrogen oxide is used as an oxidizing agent (1). The selected gas mixture determines the temperature of the flame. Air-acetylene and air-propane flames have low temperature(2200-2400 °C). Such a flame is used to determine elements whose compounds readily decompose at these temperatures. An air-propane flame is used when there are difficulties in obtaining acetylene; such a replacement complicates the work, since commercial propane contains impurities that pollute the flame. When determining elements that form difficult-to-dissociate compounds, a high-temperature flame is used (3000-3200 °C, created by a mixture of nitric oxide (1) - acetylene. Such a flame is necessary when determining aluminum, beryllium, silicon, vanadium and molybdenum. To determine arsenic and selenium converted into their hydrides, a reducing flame is required, which is formed by burning hydrogen in an argon-air mixture. Mercury is determined (flameless method "because it can exist in a vapor state and at room temperature.

1. Rudnaya Pristan (Primor. Territory)	lead, zinc, copper, manganese + vanadium, manganese.
2. Belovo (Kemerovo region)	zinc, lead, copper, nickel.
3. Revda (Sverdlovsk region)	copper, zinc, lead.
4. Magnitogorsk	nickel, zinc, lead.
5. Deep (Belarus)	copper, lead, zinc.
6. Ust-Kamenogorsk (Kazakhstan)	zinc, copper, nickel.
7. Dalnegorsk (Primorsky Territory)	lead, zinc.
8. Monchegorsk (Murmansk region)	nickel.
9. Alaverdi (Armenia)	copper, nickel, lead.
10. Konstantinovka (Ukraine)	lead, mercury.

Heavy metals are the most dangerous elements that can pollute the soil. Heavy metals in soil

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