Soil Pollution with Heavy Metals in the Industrial Cities of Mongolia
Natalia E. Kosheleva1, Nikolay S. Kasimov2, Dechingungaa Dorjgotov2, Sergey N. Bazha3, Petr D. Gunin3,
Dmitry L. Golovanov1, Sandag Enkh-Amgalan2 and Ochirbat Batkhishig2
1Faculty of Geography, Moscow State University, Moscow, Russia,
2Institute of Geography, Mongolian Academy of Sciences, Ulaanbaatar
3Institute for Ecology and Evolution, Russian Academy of Sciences, Moscow, Russia,
The technogenic anomalies in heavy metal patterns in the soils of Ulaanbaatar, Darkhan, and Erdenet cities are characterized both qualitatively and quantitatively. These data permitted to evaluate the background geochemical situation in the study area, and the technogenic specialization of the cities. The geochemical properties of urban soils were shown to display a spatial variability associated with certain functional zones. The ecological status of polluted urban soils was assessed basing on regulatory heavy metal values accepted in Mongolia.
Keyword: Heavy metals,urban soils,functional zones,technogenic anomalies,pollution,Mongolia
For the recent ten years, the industrial development of Mongolia and growth of the urban population appear to be a basic reason of growing ecological problems on the territory of the large cities. The aggravation of technogenic pressure on the environment was accompanied by air and water pollution, accumulation of pollutants in soil cover, which cause deterioration of life conditions of the urban population. Social-economical and medicoecological parameters of the environment in Ulaanbaatar determined at the beginning of 1990s have been changed considerably. Thus, goal of this work is to establish qualitative and quantitative characteristics of man-induced geochemical anomalies of the heavy metals (HM), which are dominant pollutants in the soils of three large industrial centers of Mongolia – Ulaanbaatar, Erdenet and Darkhan. Cities are situated in the intermountain valleys and depressions of Khentei mountainous region within the basin of Selenge river. Ulaanbaatar is the capital city with various industries; Erdenet is the big centre of mining, concentration and primary processing of the copper and molybdenum ore, and in Darkhan ferrous metallurgy, dressing of leather, production of chemical compounds and building constructions were concentrated. The research included: | characterization of geochemical composition of background soils in the study region, including geochemical anomaly of natural ore deposit in Erdenet city; | evaluation of man-induced geochemical transformation of soils in urban environment as a whole and in different functional zones; | assessment of ecological status of polluted urban soils on the basis of the regulatory HM values accepted in Mongolia. To address these problems the environmentalgeochemical conception was used. It is based on the analysis of concentrations of chemical elements and their compounds in depositing media of urban landscapes (in soils, snow and vegetation cover), which rather exactly refl ect process of air pollution and their impact on the environment (Glazovskaya, 1988; Saet et al., 1990; Kasimov, 1995).
Material and Methods
This work was based on the materials of Joint Russian-Mongolian Complex Biological Expedition. Soil sampling was carried out in December 2007 on the territory of Ulaanbaatar (99 samples), Darkhan (46 samples) and Erdenet (50 samples) cities. The mixed soil samples have been taken according to the method of “envelope” from topsoil (0-10 sm) with intervals of 500-800 m. Coal samples were collected from three brown coal deposits nearby Ulaanbaatar city – Nalaikh, Baganuur, Chuluut; the ashes of thermal power station TPS-3 were received from the committee for air control at the Ministry of Nature, Environment and Tourism of Mongolia. Bulk content of Cu, Zn, Pb, Ni, Co, Cr, V, W, Sn, Ga, Ge, Ti, Mn, Y,Zr, Sn, Ba in soil samples was determined using semiquantitative spectral method at spectrograph DPHS-465C in the laboratory of Alexandrov Geology-geochemical expedition of Institute of Mineralogy, Geochemistry and Cristalchemistry of Rare Elements (Russia). The Hg concentration was determined using methods of nonplasmic atomic absorption at instrument PA-915. Basic physico-chemical properties of soils were studied with routine methods (Orlov, 1985). To evaluate accuracy of semi-quantitative spectral method, part of the soil samples, as well as samples of brown coals and ashes of TPS were analyzed using mass-spectral and atomic-emissive methods with inductively-coupled plasma (ICPMS) in Research Institute of Mineral Resources with instruments Elan-6100 and Optima-4300 DV (“Perkin Elmer”, USA). Both methods gave similar results for studied heavy metals. Analytical data received was grouped in relation to functional zones and processed statistically using STATISTICA 7 package (Mathsoft, 2004). The stable associations of elements in soils were discovered with method of cluster analysis (algorithm Complete Linkage), the similarity in metal patterns was characterized with correlation coeffi cients. Concentration (CC) or dispersion (CD) coeffi cients of metals in background soils were calculated compared to their global clarkes defi ned by A. P. Vinogradov (1962), as they occupy intermediate position between Greenwood & Ernsho’s (2008) and Bowen’s estimations (Bowen, 1979). Coeffi cients of concentration (Cc) or dispersion (Cd) of heavy metals in urban soils were calculated in relation to background soils. Technogenic-geochemical specialization of urban soils was determined by formula, which included metals with Kc > 1, values of Kc were pointed out in low cases. The ecological-geochemical assessment of urban soils was received on the basis of bulk pollution coeffi cients Zc:
Regional soil-geochemical background and its transformation in the large industrial centers. To assess technogenic-geochemical transformation of the urban soils chemical composition of background dark-chestnut soils and soils of recreation landscapes was determined and their geochemical spectra were built (Fig. 1a). Background content of the most of metals in the three cities is similar, it is near the world clarkes for Zn, Mn, V, Ti, Cr, Zr, Hg, Ba, and lower for Ge, Co, Y, Ni (CD=1.7-8.4).
In the vicinity of Ulaanbaatar, only a high level of W (CC=1.5) was found, and in Darkhan it is inherent in Pb, Sn, Mo, Ag and W (CC=1.9-1.5). The region of copper-molybdenum ore deposit in Erdenet is characterized by high content of Mo, Cu, Ag (CC=8.2-2.8). The urban soils are accumulating HMs incoming from technogenic sources (Fig. 1b). In Ulaanbaatar city, multi-elemental geochemical anomaly of Ag3,0Pb2,4Sn2,1Hg1,9Ge1,7Zn1,7W1,5 with relatively low concentration factors has been formed. Its appearance is associated with various industries functioning in the city for a long period and gushing out various pollutants. The soil pollution in Darkhan with Cr5,0Hg3,1W3,0 indicates its industrial specialization, which is defi ned by tanning industry, gold mining and heat-and-power engineering using brown coal. Soils of Erdenet accumulate Mo2,2Cu1,8Sn1,5Ge1,5. The source of these elements appeared to be the dump sludge of mining and processing enterprises enriched of Cu and Mo, as well as products of brown coals combustion with high content of Sn and Ge, which spread by wind. Spatial geochemical heterogeneity of the urban soils. The geochemical heterogeneity of soils in the cities is caused by functional structure of their territories. It includes traffi c zone, ger zone, many-storeyed residential blocks, industrial and recreation zones. For each zone, average concentrations of HMs and parameters of their variability were calculated, associations of elements were determined and geochemical spectra were plotted (Table 1). In Ulaanbaatar, the highest level of pollutant accumulation in soils has been observed near highways and within many-storeyed residential blocks in the central old part of the city, where Pb, Hg, Ag, Zn, Mo, Cu have enhanced concentrations (Cc=3-1.5). In industrial zone, Cc was lower at 0.5 because of large area where industrial emissions incoming from pipes disperse in the atmosphere at considerable height. The weak pollution was found on ger areas situated in suburbs of the city. Despite the fact that these quarters are relatively young Pb and Ge have been accumulated there. The main source of these elements is ash, which forms during incomplete combustion of brown coal used to heat gers.
Geochemical heterogeneity within the zones is rather high (Fig. 2). It is displayed in increased variability of concentrations of chemical elements and formation of local amonalies with extremely high content of some elements. Comparison of microelement composition of brown coals and ashes of TPS allowed discovering prior pollutants of urban landscapes in Ulaanbaatar, connected with heat-andpower engineering activities (Table 2). The brown coal of Ulaanbaatar, as a most part of sulphureous coals, is enriched with calcophilous elements (Se, Sb, Bi, Pb), as well as W, Be, Mo – elements, which defi ne geochemical specialization of coal-bearing basin. In comparison with coals of the world (Yudovich, Ketris, 2005) coals of Ulaanbaatar have high content of Cu and Pb, and ashes were enriched with W, as well as natural radionuclides, Th and U. The ratio of microelement content in ashes of TPS versus their content in coal showed elements, which transfer to gas phase – Se, Sb, Hg, Te, Bi and possibly, Pb. They do not accumulate in solid phase, spread for a long distance and infl uence negatively to population health. The most stable associations of elements, which were found almost in all the functional zones of the city, are: Cu–Zn–Pb; Ni–Co–Ga; Cr–V; Mn–Ti; Ba–Zr. The fi rst association combines elements from technogenic sources, fi rst of all from vehicles. The second and the third associations include the elements, accumulated in fi ne dust fractions and their concerted variation was associated with heterogeneity of soil texture. The fourth and the fi fth associations refl ect geochemical features of soil-forming rocks on the territory of city.
In the soils of Darkhan the most wide spectrum of pollutants, W15Cr8,8Hg2,6Ge1,9Mo1,9Zr1,5 was determined in the industrial zone. The soils of ger quarters are characterized by the following formula of technogenic-geochemical specialization: W9,1Zn1,8Mo1,7Hg1,5. In the soils of many-storey residential blocks signifi cant accumulation of W8,6Hg2,7Ge1,5Zn1,5 was revealed. The main features of soil geochemical transformation in Darkhan were displayed in composition of element associations. The most stable are: Cu– Zn–Pb; Mo–W–Ge; Sn–Ga; Zr–Y–Ba; Ni–V; Co–Ti. First three, for fair, are of man-caused origin; moreover, the contamination spreads over large area. The most dangerous/hazardous metals – Cr, Ag, Hg – do not form stable association because of point character of contamination. In the soils of Erdenet the most contrasting man-made anomaly is in the quarters of gers, where Sn2,6Ge2,4Zn1,7Cu1,6Mo1,5 are accumulated. In the soils of the industrial zone Cu1,8Mo1,5 are accumulated, in many-storeyed residential blocks – Ge2,2Zn2,0. For traffi c zone, pollution was not determined, possibly, because of its transient geochemical position on the slope of river valley. The soil-geochemical heterogeneity of Erdenet is characterized by specifi c association of elements in each functional zone. Among them the most stable are Cu–Ag–Mo; Mn–Ba–Ti–Y–Zr, refl ecting composition of soil-forming rocks, and Pb–Zn, showing man-caused contamination. Environmental-geochemical assessment of urban soil pollution. The values of bulk soil pollution coeffi cient Zc for Ulaanbaatar and Erdenet appear to be low in all functional zones. In the fi rst city, Zc varies from 2.5 (ger blocks) to 8.7 (many-storeyed blocks), while in the second one – from 1.3 (highways) to 5.1 (ger blocks) due to high background content of some HMs. The highest Zc values are usual for soils of Darkhan – in residential and traffi c zones it varies within 11-14, in industrial zone it achieves 26.7, what corresponds to average level of contamination. To assess the ecological status of soils in Ulaanbaatar, Darkhan and Erdenet, the concentrations of HM in upper soil horizons were obtained and then compared with regulatory HM values accepted in Mongolia (Dotjgotov et al., 2008), which defi ned according to granulometric composition of soils (Table 1). Results of comparative estimations indicated that in Ulaanbaatar excess of MPC was fi xed only for Cr (MPC excess was found at 25% of the city area), Mo (19 %), Zn (15 %) and Cu (10 %). Portion of man-caused polluted soils is more considerable in two other cities: in Darkhan the most hazardous pollutants are Cr (80 %), V (60), Mo (49), Cu (27), Zn (24), Pb (13), in Erdenet – Cu (82 %), Mo (71), Cr (51), V (24) and Zn (20).
Background geochemical specialization of the region soils displays low or similar HM concentrations compared to their world clarkes. For Ulaanbaatar, exception is W (CC=1.5), in Darkhan – Pb, Sn, Mo, Ag and W (CC=1.9-1.5). A contrasting natural geochemical anomaly was found in soils of Erdenet with high content of Mo (CC=8.2), Cu (5.2), Ag (2.8). Man-caused geochemical specialization of Ulaanbaatar – Ag3,0Pb2,4Sn2,1Hg1,9Ge1,7Zn 1,7W1,5 – has been formed under infl uence of many different sources of soil pollution. Major pollutants of Darkhan soils – Cr5,0Hg3,1W3,0. – were derived from tanning-production, gold mining and heat-and-power engineering. In Erdenet the technogenic accumulation of Mo2,2Cu1,8Sn1,5Ge1,5 enhances natural ore anomaly of the fi rst two metals. Geochemical specialization of functional zones of Ulaanbaatar was shown in wide spectrum of pollutant elements, which present in soils of many-storeyed residential blocks and highways – Hg, Pb, Ag, Zn, W, Ge, Cu, Sn, Mo, Cu. In Darkhan, extremely high level of W and Cr accumulation in soils was observed of the industrial zone and that of W and Hg – in soils of residential and traffi c zones. In Erdenet, the most contrasting man-caused anomaly was determined in soils of ger blocks: Sn2,6Ge2,4Zn1,7Cu1,6Mo1,5. The soils of industrial zone accumulate Cu1,8Mo1,5, many-storeyed blocks – Ge2,2Zn2,0. In Ulaanbaatar soil bulk pollution coeffi cient Zc changes from 2.5 (ger blocks) to 8.7 (manystoreyed blocks). Maximum values of Zc were determined in soils of Darkhan – 26.7 in the industrial zone, 11-14 in residential and traffi c zones. In Erdenet Zc values are not too high – from 1.3 (highways) to 5.1 (ger quarters) – due to high background content of some HMs. Environmental-geochemical assessment of urban soils determined the excess of MPC for four metals (Cr, Mo, Zn, Cu) on 15-25 % of the area of Ulaanbaatar. Ecological situation in two other cities is more hazardous: excess of MPC for Cr, V, Mn was determined on 50-80 % of area of Darkhan and that of Cu, Mo, Cr – in Erdenet city.
The study was carried out with fi nancial support by the Joint Russian-Mongolian Complex Biological Expedition, RAS and MAS, and Ministry of Education and Science of the Russian Federation.
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