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Section 1. Biology
Isagaliev Murodjon Tuychiboyevich, Senior scientific researcher The research institute of Soil science and Agrochemistry, E-mail: murodjon-isa@mail.ru
Biogeochemistry of mercury in mountain-brown soils
Abstract: Our studies have found that in the mountain-brown soils content, maximum permissible concentration, Clark concentration and dispersion, radial migration, coefficient ofbiological absorption of mercury higher in favor of the mine below. The genetic horizons of virgin and conditionally-irrigated soils above the mercury mine contained within 0.42-1.15 mg/kg.
Keywords: mercury, virgin and conditionally-irrigated mountain brown soils, biogeochemical indicators, maximum permissible concentration, migration, accumulation.
Aristotle 350 BC, called mercury as liquid silver, hydrargyrum, "silver water" occurs in Pliny, Central Asian nations designated mercury as "simab" that indicates in forsi as silver water. Simab mined at Almaden in Europe, Huankovelike in Peru, as in Russia. Old development places of mercury found in Central Asia, are mining deposits of Chauvai, Haydarkon and others. Around which formed special halos, stretches for several kilometers beyond the fields.
Chauvai deposits located in the south of Fergana at a distance of 50-60 km in mountain systems of Alai, where to the north borders with the mountains of Saribel at the altitude of 1200 meters. Here begins river Chauvai that downstream at a distance of 10 km flows into the river Isfayramsay. Isfayramsay river flows through a series of villages, towns and the city of Fergana, is further used completely in order to irrigation and watering. The importance of the study and evaluation of the content and the biogeochemistry of mercury in the soil, air, water, plants and in other facilities of the region due to the fact that the Ferghana region borders with the industrial object, i. e. a mercury-antimony deposit, this neighborhood brings both advantages and disadvantages.
We according to the method of landscape-geochemical research studied the migration of mercury in eluvial dedicated to the well-drained elevated landscape elements.
Here, the water table is deep and are not involved in soil formation processes. The migration of elements, including mercury goes on principle removal of substances mainly by water flowing downward. Here active biological capture elements of natural and agricultural plants that hold chemicals, including mercury, in the biogeochemical cycles in elementary geochemical landscapes opposes to the removal.
We studied the mountain-brown carbonate soils that formed on the northern slopes of solar exposition in eluvial-xeromorphic moisture conditions under sparse grassland and trees and shrubs, on powerful fine earth and skeleton eluvials, deluvials.
We have collected and compiled averages samples of soils and plants according to morphogenetic method from two key areas where laid on 4 soil sample profiles. The first group of soil sample profiles laid on the virgin site, and the second on conditionally irrigated key areas. The two key areas were taken at the same distance from the mine Chauvai to the south and the north for 500 m, i. e. up and down from the mine. The depth of the soil sample profiles and the power of genetic horizons for the purpose of easy comparison, taking into account the depth of the tillage horizon adopted as the same, such as 0-7, 8-15, 15-60, 60-100, 100-120 cm. In virgin soils (soil sample profile. 1, 2) the content of humus in the sod horizon (0-7 cm), in average is 4.2%, under the sod (8-15 cm) is 3.3%.
The nitrogen content varies at 0,28-0,45%. The content of total phosphorus in these horizons ranges at 0.20-0.22%, mobile at
40-60 mg/kg. The content of total and mobile forms of potassium, respectively, varies between 2.2-2.5%; 250-320 mg/kg.
Effervescence with 10% hydrochloric acid is observed on the surface. That is, in the sod and under the sod horizons carbonate content varies between 4-7%. Throughout the profile of its content is at 4-21%. The soil reaction is neutral and slightly alkaline pH of the aqueous extract varies in the range of 6.5-7.5. Total of absorbed cations in the studied soils (Ca++, Mg++, K+, Na+) is 1214 mg/eq to 100 g of soil.
In the conditionally-irrigated soils (soil sample profile 1a, 2a) the humus content in the tillage horizon is 2.3%, which is less than in virgin soils. They can be classified as low-humus soils. But it should be noted that the humus content throughout the profile remains almost stable and fluctuates in the range of 0.9-2.3%. The content of total nitrogen, which depends on the amount of humus, is quite high. In the content of total and mobile forms of phosphorus, potassium, significant differences between the studied virgin, conditionally-irrigated soils is not observed. Small differences in the upper horizons are existing they are associated with a slight decrease of humus in conditionally-irrigated soils.
The average mercury content in the studied vegetation cover, at above the mine is 1.64 mg/kg, at lower the mine is 3.51 mg/kg. Changes of the content of mercury in uncontaminated soil profiles is inherited mainly from the parent rock. However, Hg easily volatile metal, so in accumulation of mercury it is difficult to rule out the role of additional sources such as a mercury-antimony deposit, thermal activity of lithosphere and others.
The accumulation of mercury in the soil and its horizons associated with the organic matter of the soil, i. e., with humus, for this reason, its concentration in the upper humus layers of conditionally-irrigated and natural soils is higher. In the genetic horizons ofvirgin soils above the mine the content of mercury (M) is 0.42-1.0 mg/kg, whereas in conditionally-irrigated soil is 0.51-1.15 mg/kg, its maximum content accounts for 0-15, 15-60 cm horizons, i. e., horizons with more humus.
It is necessary to emphasize the role of mercury-antimony deposits, which relatively seriously pollute soil and vegetative cover underlying zone. In this case the mercury content, as in virgin and in conditionally irrigated soils and plants is quite high, so in the profile of virgin soils it contains 5.8-7.2 mg/kg, and in conditionally irrigated soils 3.7-7.8 mg/kg.
Radial migration throughout the soil profile, both in virgin and in conditionally-irrigated soils occurs. Background content of mercury in soils is difficult to estimate because of the wide influence of anthropogenic pollution from this metal and its migration ability. Despite this, the available indicators in different soils of the world show that the average concentration of Hg in the surface layer of the soil does not exceed 400 mg/kg (A. Kabata-Pendias, H. Pendias, [1,
Biogeochemistry of mercury in mountain-brown soils
180-190]). According to Haidoutic C. and others [2, 251] interval of mercury concentration in different Greece soils ranges from 33 to 98 mg/kg, and for the contaminated soils from 45 to 325 mg/kg.
Background concentrations of mercury in the soil are 0.n mg/kg according to international standards. The content of the metal that exceeds this norm, it can be regarded as contaminated from different sources.
In the contaminated soils of UK (B. E. Duvies, [3, 394]), USA (C. J. Blanton, C. E. Desforges et al., [4, 139]), Japan (S. Gotoh, S. Tokudome et al., [5, 391]), Germany (N. El-Bassan et al., [6, 309]) the mercury content is in the range 0.21-40 mg/kg.
In this migration characteristics of mercury in soils, as well as other heavy elements depends on the forms of the presence, the chemical properties of mercury and redox conditions, the waterair mode, agrochemical properties, soil reclamation condition and other factors.
The main indicators of internal factors of migration should include ionic potential of Kartledzha, according to which the ion potential ofmercury is equal to 1.78 and according to this indicator occupies an intermediate position, i. e., between I and group III elements.
No less important factors of internal migration of elements considered to be an energy constant of elements. This indicator of mercury is 15.2, this energy due to the energy of the crystal lattice, sulfur mercury, which takes place in our objects. With regard to the accumulation of Hg in plants grown on contaminated sites higher, it is associated with mercury ores.
Hg is water migrant, slightly mobile element in an oxidizing condition and practically immobile in a hydrogen sulfide environment. It is precipitated alkaline barriers. It migrates in an oxidizing condition. Unfortunately, threshold concentrations for individual groups of plants and soils are not yet developed. We know that plants are able to absorb from the environment, depending on the conditions, a number of elements. This property of plants depends on a number of factors related to the plants themselves, and the element, soil cover and others. This ability of plants characterized by the coefficient of biological absorption (Ax), which shows how many times the content of the element in the plant ash greater than in the lithosphere or the soil. According to our estimates given in the table and in a number of biological absorption of mercury elements, the element of the biological average absorption, Ax, in the plants above the mine varies in the range of 1.04-3.90.
There is an interesting fact, in spite of the fact that the plants below the mine contains almost twice higher mercury than in the plants above the mine, Ax, much lower and varies in the range of 0.45-0.94, which is associated with quite contaminated background on this the key area and the electoral capacity of plants to high concentrations of heavy elements such as Hg. The maximum permissible concentration (MPC) of mercury in soils taken 2.1 mg/kg. This figure is not definitive and it varies depending on the properties of different soils.
At the same time the MPC coefficient shows how many times more or less elements contained in the studied soils than in the whole of the soil (soil clark). Studies show that in uncontaminated soils samples 1, 1 a the MPC coefficient is in the range 0.20-0.55, is almost 4-10 times less Hg contained in these soils, compared to Clark. In the contaminated soils the MPC rate was expected at 1.78-3.55. It is clear from the above that the mercury contamination goes around the soil profile, regardless of its condition. This was facilitated by Clark concentration (CC) mercury, which is in the soils above the mine is 1.75-4.79, below the mine is 15.5832.50 that provides a basis for the allocation of a biogeochemical province of mercury concentration, especially in the area of the below mine. It must be remembered that mercury is trace element and this indicator (Cr) in the studied soils is in the range 0.03-0.57.
Local migration (Cm) factor of mercury in the soils below and above the mine, regardless of the location varies in the range of 0.95-2.38. It should be emphasized that a Cm in genetic upper horizons of soil higher than in all studied lower genetic soil layers.
From the above it follows that, according to geochemical classification of mercury migration in landscapes under the studied mountain-brown soils condition is included in the group of mobile and slightly mobile, in an oxidizing condition it accumulates in alkaline barriers. In this case the soil is performed as the barrier function to the path of mercury.
With the accumulation of mercury soil is polluted, partially loses fertility and growing plants on it absorbs it and included in the subsequent cycle, forming mercury biogeochemical province. This province in the studied conditions is azonal where their characteristics do not correspond to the general characteristics of the zone the anomaly is associated with ore occurrences and techno-genic pollution.
References:
1. Кабата-Пендиас А., Пендиас Х. Микроэлементы в почвах и растениях. - М. Мир. 1989. - С. 180-190.
2. Haidoutic C., Skarlou V., Tsoulouchu F. Mercury contents of some Greek soils. Geoderma, 35, 1985, 251.
3. Duvies B. E. Heavy metal pollution of British agricultural soils with special reference to the role oflead and copper mining, in Proc. Int. Semin. on soil Environment and Fertility Management in intensive agriculture, - Tokyo, 1977, 394.
4. Blanton C. J., Desforges C. E., Nowland L. W., Ehlman A. S. A survey of mercury distributions in the Terlingau area of Texas, in Truce Subset, in Environ. Health, vol. 9, 1975, 139.
5. Gotoh S., Tokudome S., Koga H. Mercury in soil derived, from igneous rock in northern Kyushu, Japan, Soil sci. Plant Nutr., 24, 1978, 391.
6. El-Bassan N., Poelstra P., Frissel M. J. Chrom und Quecksilber in einem seit 80 Jahren met stadtischen Abwasser berieselten Bodem, Z. Ptlanzener-naehr Bodenkd. 3. 1975, 309.
