ISSN 1064-2293, Eurasian Soil Science, 2009, Vol. 42, No. 4, pp. 394–404. © Pleiades Publishing, Ltd., 2009. Original Russian Text © G.A. Belogolova, O.N. Gordeeva, P.V. Koval, Q.X. Zhou, G.L. Guo, 2009, published in Pochvovedenie, 2009, No. 4, pp. 429–440.
SOIL CHEMISTRY
Regularities of the Distribution and Heavy Metal Forms in Technogenically Transformed Chernozems of the Southern Angara River Basin and Northeastern China G. A. Belogolovaa, O. N. Gordeevaa, P. V. Kovala,† Q. X. Zhoub, and G. L. Guob a
Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, P.O. Box 4019, Irkutsk, 664033 Russia E-mail:
[email protected] b Key Laboratory of Terrestrial Ecological Process, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016 China E-mail:
[email protected] Received July 4, 2007
Abstract—Specific features of heavy metals and As migration in the system soil–plant are considered on the basis of the results obtained in the analysis of different forms of toxic elements in technogenically transformed chernozems of the southern Baikal Lake basin. These results are compared to the data of analogous studies conducted in northeastern China. The regularities in the bioaccumulation of heavy metals and As were related to their forms, their concentration in the soils, and the plant species. Cadmium was found to be the most mobile element, which accumulated in the chernozems to the greatest degree; lead was the least mobile element. DOI: 10.1134/S1064229309040061 †
INTRODUCTION At the present time, in many industrial regions, soils strongly degrade owing to the disturbance of the soil cover, soil amelioration, fertilization, and chemical pollution. The main consequence of these processes is the disturbance of the humus-depending structure, the humus mineralization, and the alteration of the structure composition, rather than an increase in the content of toxic substances in the soils. As a result, the capability of toxic elements' transition to mobile forms becomes higher. The studies of technogenic transformation of chernozems are also topical from the applied standpoint, since these soils are an important basis of agriculture in many regions of the world, including Russia. The high content of organic matter affects in many ways the behavior of microelements in chernozems, including the distribution and migration of heavy metals [4, 6–8, 21]. This work presents the results of studying the forms of heavy metals and arsenic in chernozems and the behavior of toxic elements in the system soil–plants in the zone of intense technogenic pollution of the southern Baikal Lake basin as compared to the data obtained for Phaeozems of northeastern China.
the influence of industrial enterprises of the town of Svirsk and the Irkutsk–Cheremkhovo coal basin. The geological basement is composed of Jurassic terrigenous rocks (the Irkutsk depression) alternating with narrow layers of Quaternary sediments mainly developed in the Angara River basin and along its main tributaries. In the forest-steppe zone of the Irkutsk–Cheremkhovo Plain, gray forest soils, soddy-podzolic soils, and chernozems prevail (Fig. 1) [1]. Ordinary chernozems are widespread on ancient river terraces and on gentle south-facing slopes of river valleys [16, 18, 20]. The leached chernozems develop under meadow and steppe Stipa–forb vegetation. The humus content averages 8.5–6.0%. According to the humus reserves, the chernozems of the Angara River basin are referred to the most fertile soils in Irkutsk oblast [13]. In the lower part of their profiles, there are segregations of carbonates that determine their alkaline reaction. The meadow–chernozemic soils are a transitional type from chernozems to meadow soils, whose formation is related to the evolution of bog soils [25]. These soils are spread on the bottoms of dry valleys and in the lower parts of their slopes.
OBJECTS AND METHODS The study region is located in the northern part of the Irkutsk–Cheremkhovo Plain in the zone exposed to
Chernozems of the agrolandscapes in the Svirsk region on the shore of the Bratsk Reservoir (150 km to the south from Irkutsk) were studied in detail. In this territory, large sources of technogenic pollution are concentrated, including the industrial site of the former Angara metallurgic plant for the production of arsenic (used for the production of toxic compounds) and the
† Deceased.
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Ida Cheremkhovo
Svirsk
Belaya ra ga An
da
Kitoi
Ku
Irkutsk
ut Irk
1
4
2
5
3
6
l
ka
ke
0
25
50 km
i Ba
La
Fig. 1. Soils of the Irkutsk–Cheremkhovo agroindustrial region according to [1]. 1—soddy-podzolic soils; 2—soddy-calcareous soils; 3—soddy forest soils; 4—complex of soddy forest soils with chernozems, meadow, meadow–bog, and bog soils; 5—complex of leached and ordinary chernozems and meadow chernozemic soils; 6—complex of mountainous soils and foothill soils.
“Sibelement” plant. These enterprises are the main sources of arsenic and heavy metal pollution in this region. The dumps of the waste of the metallurgic plant are composed of products of sintering sulfide ores represented by iron oxides and hydroxides (60–65%), aluminosilicates (19–20%), mica, quartz, feldspar, gypsum, and iron sulfates. According to different data, in the dumps, the contents of arsenic, lead, and zinc range from 0.3 to 14.2, 0.4 to1.4, and 0.12 to 0.23%, respectively; the concentration of cadmium reaches 7.6 mg/kg [19]. On the surface of the dumps, a zone of oxidation develops; its plume is observed in the soils at a distance of 20–50 m from the dump edge. The area of As pollution is elongated towards the basin of the Bratsk Reservoir. Wastes of As production occur on the surface of the first and second terraces of the Angara River. The terraces are composed of alluvium underlain by calcareous rocks of the Lower Cambrian. Leached chernozems are widespread over these territories. Compact loams characterized by their low water permeability occur at a depth of 2.0–7.5 m; they function as a geochemical barrier on the pathway of toxic elements migration to the deeper layers and the Bratsk Reservoir. Chernozems (Phaeozems according to the soil classification of FAO/UNESCO [14]) are among the main types of cultivated soils in China and the major agricultural resource in northeastern China. In addition, this EURASIAN SOIL SCIENCE
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area is one of the highly industrialized regions in this country. In this work, the results of studying the soils exposed to the influence of enterprises of chemical, cement, and other fields of industry in the outskirts of the city of Kharbin (Kheilunzyan province) are discussed. The climate of the region is moderately monsoon continental. A detailed characterization of this territory is given in [26]. The spatial investigation of chernozems on the Irkutsk–Cheremkhovo Plain was carried out near the towns of Cheremkhovo and Svirsk. Soil samples were taken from the upper humus horizon at a depth of 5–25 cm using the method of envelopes (5 × 5 m) outside the towns mentioned. The area of the sampling plot depended on the nonuniformity of the soil cover. A more detailed study of the technogenically transformed soils was conducted in Svirsk, where soil samples were taken near dumps of the former metallurgic plant that produced arsenic. Soil samples and those of ripe vegetables (potatoes, cabbage) were also collected outside this town in adjacent private kitchen gardens. The upper parts of cabbages and whole potato tubers after their washing were used for the analysis. The vegetables were comminuted and air dried. The forms of As, Pb, Cd, Cu, and Zn compounds were determined in the soils of the kitchen gardens and
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technogenic grounds using the methodology applied for studying the soils in the vicinity of the city of Kharbin. For the analysis, the method of sequential extraction [29] was used. The following fractions were extracted: (1) the easily exchangeable ions, (2) the carbonates and compounds soluble in weak acids, (3) the amorphous Fe–Mn hydroxides and elements adsorbed on them, (4) the organic substances, and (5) the insoluble residue. The soil samples were not ground in order to preserve their initial structure. For the extraction of the easily exchangeable ions, 2 g of soil were treated with 16 ml of 1 M MgCl2 at pH 7. This suspension was mixed for an hour using a rockershaker. Then, the contents of the flasks were centrifuged at 2000 rpm for an hour. After centrifuging, in the case of the presence of floating particles, the solution was filtered (blue ribbon) into pure chemical glasses (100 ml) without displacement of the soil to the filter. The wash waters (about 20 ml) were poured into the remaining residue. The residue with the wash waters was again centrifuged for 30 min at 2000 rpm. The mixture was again filtered into the same chemical glasses. The volume of the solution was measured and poured into Teflon glasses; it was evaporated to the state of wet salts. When evaporating, a 30% ç2é2 solution was added by drops to the colored extracts. 5 ml of HCl (1 : 1) were poured into the salts, and then distilled water was added to obtain the whole volume of 50 ml. This solution was analyzed. Such a procedure was performed after the isolation of each fraction. The carbonate fraction was extracted from the soil that remained after the preceding extraction. 16 ml of 1 M CH3COONa (pH 5) were poured into the residue, and the mixture was shaken for 5 h (10-min intervals every hour). The suspension obtained was centrifuged at 3000 rpm for 15 min. As some particles floated on the surface, the solution was filtered. The centrifugation and filtration with wash water (≈20 ml of distilled water) were repeated. The first and second portions of the liquid were combined, and the volume was measured. The liquid was poured into Teflon glasses for evaporation at 70°ë and further preparation for the analysis. For the extraction of the Fe–Mn hydroxides fraction, the residue that remained after the second extraction was treated with 40 ml of 0.04 M NH4OH · HCl in 25% ëç3ëééç and evaporated on a water bath at 96°ë for 6 h with periodic mixing. After cooling down to room temperature, the suspension was centrifuged at 3000 rpm for 15 min. The solution was evaporated in teflon glasses at 70°ë. After the evaporation, the salts were dissolved in 5 ml of HCl (1 : 1); distilled water was added to obtain a volume of 50 ml. The organic fraction was extracted from the remaining residue after the extraction of the third fraction using 6 ml of 0.02 M HNO3 and 10 ml of 30% ç2é2 at pH 2. The mixture was evaporated on a water bath at 85°ë for 2 h with periodic mixing. After the evaporation and cooling, 10 ml of 3.2 M CH3COONH4 in 20%
HNO3 were added. After the centrifugation, the extract (if needed) was filtrated and evaporated to wet salts. The salts were dissolved in 5 ml of HCl (1 : 1), and distilled water was added to obtain a volume of 50 ml. The difficultly soluble residue was obtained after the treatment of the residue that remained after the extraction of the fourth fraction with 18 ml of çNO3 (65%) and 6 ml of HClO4 (40%) at a temperature of 180°ë. The solution obtained was dried up and dissolved in 5% HNO3 to get a volume of 25 ml. The contents of As, Pb, Cd, Zn, and Cu in the extracted fractions and in the soils were determined using the method of atomic absorption (spectrometer— Perkin-Elmer-503). Standard samples SSK-1 (calcareous sierozem) and SDPS-2 (technogenic soil) were used as the control ones. The plant samples were also analyzed in the analytic department of the Vinogradov Institute of Geochemistry of the Siberian Branch of the Russian Academy of Sciences using inductively coupled plasma mass spectrometry (ICP-MS, VG–Plasma– Guad-2, analysts A.G. Arsent’eva and O.A. Sklyarova). The studies in northeastern China were conducted on an agrolandscape located in an area of 10 km2 in the technogenically polluted zone 5 km from Kharbin. The Phaeozem samples were taken from depths of 0–20 and 20–40 cm. The air-dried soil samples were sieved through a 2 mm-meshed plastic sieve and ground in agate glasses. The consecutive extraction was performed according to the methodology described above. The heavy metal contents in the Phaeozems were determined using the atomic absorption method in an analytical laboratory of the Institute of Applied Ecology of the Chinese Academy of Sciences in Shenyang [26]. The results obtained for the 0- to 20-cm horizon of the Phaeozems were used for the comparative analysis. RESULTS The data on the contents of the analyzed elements in the soils of the agroindustrial zone (the Angara River basin) are given in Table 1. The Zn and Cu concentrations in the chernozems of different types in the studied region were a bit higher than the usual ones, but the Cd and Pb contents were greater by several times. The term usual for the soils means a range of heavy metal concentrations among which the lowest value is the concentration nontoxic for plants and the highest one is toxic for them [11]. The determination of this range for the chemical elements is based on the recommendation of German authors [27, 28] who proposed using it for the control of agricultural soils. In the alluvial–meadow soils, a relative heavy metal accumulation was observed in accordance with the location of these soils in the river valleys—the final points of the chemical elements' migration. The concentrations of Cd, Pb, and Zn in the polluted soils of China were much higher than those in the cherEURASIAN SOIL SCIENCE
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Table 1. The total content of heavy metals and arsenic in the upper horizons of the chernozems (the Irkutsk–Cheremkhovo region) and Phaeozems (northeastern China) (above the line—average, under the line—maximum–minimum), mg/kg Soils Chernozems (n = 8) Meadow–chernozemic (n = 6) Meadow (n = 12) Alluvial–meadow (n = 10) Garden soils of the town of Svirsk (n = 11) Phaeozems of northeastern China (n = 15) Normal content* APC** in cultivated soils
Pb
Cd
Zn
Cu
As
14.7 --------------17–11 14.5 --------------16–13 12.7 --------------16–10 11 --------------14–10 45.3 -----------------130–14 57.5 -----------------------67.9–48.6 0.1–20 ---------------32
0.21 -----------------------0.26–0.18 0.18 -----------------------0.21–0.15 0.24 -----------------------0.38–0.17 0.28 -----------------------0.48–0.16 0.37 -----------------------0.78–0.16 1.93 -----------------------2.29–0.68 0.1–1.0 -----------------2.0
79 --------------92–72 70 --------------72–67 76 --------------89–61 83 -----------------122–30 100.5 ---------------------225–42.5 145.2 -----------------------------214.3–103.2 3–50 -----------220
50.6 -----------------------67.8–38.1 39.1 -----------------------41.1–37.2 32.4 -----------------------37.3–27.0 33.6 -----------------------49.5–20.4 31.9 -----------------------50.4–14.7 19.8 -----------------------25.4–18.3 1–20 -----------132
16 --------------------22.5–6.5 15.6 --------------------21.7–5.8 14.9 --------------------18.0–5.6 No data 41.8 ------------------170–5.4 No data 0.1–20 ---------------20
Notes:
n is the number of samples. * According to [9, 10]. ** APC is the approximate permissible concentration [15].
nozems of the technogenic zone of Svirsk. The Cd content in the Chinese Phaeozems was 5–10 times higher than its concentration in the soils of the outskirts of Svirsk. Table 2 presents the contents of heavy metals and arsenic in different fractions and their total concentration in the soils of Svirsk. The total contents of As and heavy metals decreased with increasing distance from the main pollution source. In the soils of vegetable gardens of the town of Svirsk (plot 2), the As, Pb, Cd, and Zn concentrations exceeded by 1.5–4.0 times their contents in the virgin chernozem of plot 4 outside Svirsk (5 km from the main pollution source). The composition of each fraction extracted (%) was calculated with reference to the total composition of the soils. The representativeness of the experiment performed may be assessed according to the total content of the elements and the sum of their concentrations in the fractions extracted. The fine precision for most of the elements studied was observed within the analytic error; only in some cases did the total Zn and Cd contents in the soils differ from the sum of their concentrations in the fractions. This fact shows that, in the course of the soil formation, complex Cd and Zn compounds are formed; they appear to be represent by difficultly soluble mineral compounds that are not completely determined using traditional analytic methods. On plot 1, in the young soil developed on the technogenic ground near the industrial site of the former plant for the production of arsenic with a high content of pollutants, their weak migration was observed. As seen from Table 2 and Fig. 2A, most of the elements were in the insoluble residue and bound with the least EURASIAN SOIL SCIENCE
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mobile organic and Fe–Mn fractions. The content and share of the most mobile element forms was low. The weak mobility of these chemical elements in the soils on the technogenic ground was also partly related to their presence also in the mineral form. In the garden soils of plot 2 located at a distance of 500 m from the main technogenic zone, the total heavy metal content remained rather high (Table 2, Fig. 2B). In the soils of this zone, the percentage of mobile forms of the elements increased considerably as compared to that in the technogenic grounds. In these soils, the contents of As and Pb in the ion-exchangeable form (the most available for plants) increased by an order of magnitude; those of Cd and Zn by 2 times and 2 orders of magnitude, respectively, versus the technogenic grounds. As a result, As, Cd, Pb, and Zn accumulated in the vegetables on this plot [3]. In some cases, their contents considerably exceeded the “normal” concentrations for plants. According to Kabata-Pendias et al. [12], “normal” for plants are considered concentrations calculated on the basis of the chemical composition of the world organic matter (per dry mass). Very sensitive plant species and plant species capable of maintaining their vital activity under an excess of some element in the environment were excluded from the analysis. At a distance of 1 km from the industrial site, in the kitchen garden soils of plot 3, the total concentrations of the elements studied, except for Zn, decreased markedly, as well as their contents in the most mobile fraction (fraction 1). On plot 4 (the suburbs of Svirsk), in the virgin soils, minimal concentrations of these elements were found. Consequently, the contents of their
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Table 2. The distribution of heavy metal and arsenic compounds in soils of the town of Svirsk (above the line—mg/kg, below the line—%) Sample, fraction 1exch 2carb 3Fe + Mn 4org 5res Σ fractions Total content 1exch 2carb 3Fe + Mn 4org 5res Σ fractions Total content 1exch 2carb 3Fe + Mn 4org 5res Σ fractions Total content 1exch 2carb 3Fe + Mn 4org 5res Σ fractions Total content
As
Pb
Cu
Zn
Cd
Plot 1—technogenic ground nearby the industrial site 2.57/0.27 0.76/0.10 0.27/0.06 b.d.l./0 6.48/0.68 0.65/0.08 1.05/0.22 0.175/0.05 83.7/8.81 54.1/6.95 9.54/2.03 62.1/16.17 165.2/17.4 63.22/8.13 60.48/12.90 26.74/6.96 780.0/82.1 762.0/97.94 318.0/67.80 176.0/45.83 1037.9/109.26 880.7/113.2 389.3/83.01 265.02/69.014 950.0/100 778.0/100 469.0/100 384.0/100 Plot 2—kitchen garden soils, 500 m from the industrial site 15.68/9.22 6.67/6.54 b.d.l. 6.867/7.31 8.34/4.91 0.66/0.65 0.53/1.06 b.d.l. 5.2/3.05 9.08/8.90 0.4/0.8 15.2/16.17 11.05/6.50 34.13/33.46 3.74/7.48 2.6/2.77 127.0/74.71 32.0/31.37 45.2/90.4 77.5/82.45 167.3/98.39 82.54/80.92 49.87/99.74 102.17/108.7 170.0/100 102.0/100 50.0/100 94.0/100 Plot 3—kitchen garden soils, 1000 m from the industrial site 2.94/7.95 0.53/0.75 b.d.l. b.d.l. 1.12/3.03 0.32/0.45 0.32/0.7 0.48/0.17 4.72/12.76 11.67/16.44 0.21/0.46 64.78/22.73 2.08/5.62 20.21/28.46 6.72/14.61 22.4/7.86 32.0/86.49 29.0/40.85 35.0/76.10 86.0/30.18 42.86/115.8 61.73/86.95 42.25/91.86 173.66/60.93 37.0/100 71.0/100 46.0/100 285.0/100 Plot 4—virgin soil, 5000 m from the industrial site 0.07/0.35 0.86/3.58 b.d.l. 0.61/0.72 0.02/0.10 0.29/1.21 1.68/4.94 b.d.l. 0.19/0.95 1.25/5.21 b.d.l. 8.36/9.84 0.29/1.45 4.42/18.42 0.78/2.29 0.91/1.07 18.0/90.0 17.0/70.83 35.0/102.94 92.0/108.24 18.57/92.9 23.82/99.25 37.46/110.2 101.88/119.86 20.0/100 24.0/100 34.0/100 85.0/100
0.13/9.22 b.d.l. 1.23/87.23 0.07/4.96 0.63/44.68 2.05/146.1 1.41/100 0.05/18.52 b.d.l. 0.116/42.96 b.d.l. 0.077/28.52 0.19/90 0.27/100 0.13/22.41 0.144/24.83 0.21/36.21 b.d.l. 0.14/24.14 0.62/107.6 0.58/100 0.0245/12.89 b.d.l. 0.0247/13.0 b.d.l. 0.071/37.37 0.12/63.3 0.19/100
Note: Fractions: 1exch—easily exchangeable ions, Meexch; 2carb—carbonates, Mecarb; 3Fe + Mn—Fe and Mn hydroxides; 4org—organic compounds, Meorg; 5res—insoluble residue, Meres. b.d.l.—content below the detection limit (the limit of the Cu, Zn, and Cd detection is 0.001 mg/kg).
mobile forms, except for the Cd content, decreased; the share of the Cd mobile form remained high. According to the relative share of the elements studied (%), in the extracted fractions, the elements formed the following sequences: Cures (90.4) > Cuorg (7.5) > Cucarb (1.1) > CuFe + Mn (0.8) > Cuexch (below the detection limit); the total content in the soils is 50 mg/kg; Znres (82.4) > ZnFe + Mn (16.2) > Znexch (7.3) > Znorg (2.8) > Zncarb (below the detection limit); the total content is 94 mg/kg;
Asres (74.7) > Asexch (9.2) > Asorg (6.5) > Ascarb (4.9) > AsFe + Mn (3.1); the total content is 170 mg/kg; Pborg (33.5) > Pbres (31.4) > PbFe + Mn (8.9) > Pbexch (6.5) > Pbcarb (0.6); the total content is 102 mg/kg; CdFe + Mn (43.0) > Cdres (28.5) > Cdexch (18.5) > Cdcarb and Cdorg (below the detection limit); the total content is 0.27 mg/kg. The sequences of these elements in the typical Phaeozems of the Kharbin technogenic zone [26] are the following (Fig. 2D): Cures > Cuorg > Cuexch > CuFe + Mn > Cucarb; EURASIAN SOIL SCIENCE
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Ä
B
C
D
399
80 60 40 20 0 100 80 60 40 20 0 As
Pb
Cu
Zn
As
Cd
1
2
Pb 3
Cu 4
Zn
Cd
5
Fig. 2. The contents of the elements in fractions (% of the total contents) of the soils of Svirsk (A, B, C) and nearby Kharbin (D). A—plot 1, soils on technogenic ground near the industrial site; B—plot 2, kitchen garden soils, 500 m from the industrial site; C—plot 3, kitcen garden soils, 1000 m from the industrial site; D—Phaeozem of the technogenic agrolandscape nearby Kharbin. Fractions: 1—easily exchangeable ions, 2—carbonates, 3—Fe and Mn hydroxides, 4—organic substances, 5—insoluble residue (the plot numbers are given in Table 2).
Znres > Znorg > Zncarb > ZnFe + Mn > Znexch (below the detection limit); Pbres > PbFe + Mn > Pborg > Pbcarb > Pbexch; CdFe + Mn > Cdexch > Cdcarb > Cdorg > Cdres. In all the cases, a trend of Cd accumulation by iron and manganese hydroxides and in the ion-exchangeable fractions (in relation to the other elements) was revealed. Lead and copper were bound with organic matter more firmly, especially in the polluted soils of the town of Svirsk; zinc was mainly bound with the insoluble residue. The most bioavailable ion-exchangeable fraction is of special interest. According to the percentage of the elements in this fraction (Meexch) of the polluted kitchen garden soils of Svirsk (plot 2), the following sequence demonstrating the mobility of the pollutants was obtained (%): Cdexch (18.5) > Asexch (9.2) > Znexch (7.3) > Pbexch (6.5) > Cuexch (below the detection limit). In the Phaeozems of Kharbin, the sequence of these elements was as follows: Cd > Cu > Pb > Zn. In both cases, the maximal mobility was found for Cd in the polluted soils and in the weakly polluted virgin ones (plot 4) as well. In Svirsk and at 8 points outside this town, the contents of heavy metals and As were determined simultaneously in the soils and vegetables. The results of these studies are given in Table 3. Point 1 in Table 3 corresponds to plot 2 in Table 2. The rest of the points were EURASIAN SOIL SCIENCE
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located at different distances from the main pollution source (industrial dumps). Points 7 and 8 were located in a relatively pure zone outside the town of Svirsk. The vegetables grown on the contaminated soils had elevated contents of pollutants. In the impact zone (point 1), the As, Cd, and Pb contents in the vegetables were an order of magnitude higher than in the vegetables grown in the relatively pure region (points 7–8) outside Svirsk (Table 3). The interrelations between the contents of As, Cd, and Pb in the vegetables and soils are considered from the approximation of the relationships described by the graphs of the 2-order polynomial trend (Fig. 3). A more distinct correlation was revealed only for potatoes and the soil. The As content in the cabbage well correlated with its accumulation in the soil; a relation between the concentrations of Pb and Cd in the cabbage and soil was absent. The Pb content in the potatoes had a complicated but regular dependence on its concentration in the soil. The Pb content increased in the potatoes grown on the soil with the low concentrations of this element and organic carbon (Corg). On the strongly polluted soils (points 1–4), the Pb content in potatoes was rather low, although the Corg concentration in the soil was rather high (4.0–14.5%). However, in the less lead-polluted soils (points 7–8), an elevated Pb content in the potatoes was detected at the Corg content of 1.9–3.0%. This fact attests that the soil organic matter can accumulate Pb and the latter becomes less available for
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Table 3. The concentrations of heavy metals and arsenic (mg/kg) in vegetables (per dry matter) and soils of Svirsk related to the distance of dumps from the former plant for As production Object Cabbage Potatos Soil Cabbage Potatos Soil Cabbage Potatos Soil Cabbage Potatos Soil Cabbage Potatos Soil Cabbage Potatos Soil Cabbage Potatos Soil Cabbage Potatos Soil “Normal” content in plant
As
Pb
Cd
Point 1, 500 m, Corg 6.4% 6.5 (0.04) 4.6 (0.045) 0.25 (0.86) 1.7 (0.01) 0.07 (0.0007) 0.02 (0.07) 170 102 0.29 Point 2, 1000 m, Corg 14.5% 0.12 (0.05) 0.02 (0.0001) 0.03 (0.09) 0.11 (0.004) 0.01 (0.0001) 0.01 (0.03) 26.3 127 0.33 Point 3, 1500 m, Corg 4.0% 0.83 (0.025) 1.5 (0.03) 0.05 (0.13) 0.48 (0.014) 0.16 (0.003) 0.02 (0.05) 33 51 0.37 Point 4, 1500 m, Corg 5.9% 0.35 (0.006) 0.01 (0.0001) 0.02 (0.05) 0.42 (0.007) 0.08 (0.001) 0.03 (0.08) 60.7 67 0.4 Point 5, 2000 m, Corg 5.5% 0.14 (0.008) 0.01 (0.0003) 0.05 (0.06) 0.28 (0.016) 0.19 (0.006) 0.04 (0.05) 17 32 0.78 Point 6, 2000 m, Corg 4.7% – – 0.02 (0.05) 0.1 (0.006) 0.29 (0.006) 0.03 (0.08) 16.4 48 0.40 Point 7, outside the town, Corg 1.9% 0.05 (0.009) 0.15 (0.01) 0.012 (0.11) 0.01 (0.002) 0.6 (0.04) 0.01 (0.09) 5.8 15 0.11 Point 8, outside the town, Corg 3.0% 0.05 (0.009) 0.15 (0.01) 0.013 (0.13) 0.01 (0.002) 0.28 (0.02) 0.01 (0.1) 5.4 15 0.10 0.02–0.2
0.5–3.0
0.03–0.05
Cu 2.7 (0.05) 4.2 (0.08) 50
Zn 21.2 (0.22) 13.3 (0.14) 94
3.2 (0.1) 2.5 (0.08) 30.3
26.7 (0.24) 9.8 (0.09) 113.4
4.2 (0.08) 1.6 (0.03) 50.4
26.9 (0.26) 9.6 (0.09) 105.2
2.0 (0.04) 1.5 (0.03) 48
20.3 (0.09) 7.6 (0.034) 225
3.0 (0.1) 2.8 (0.09) 31.4
38.6 (0.27) 18.3 (0.13) 143
– 15 (0.05) 27.9
– 13.9 (0.13) 106.9
1.2 (0.05) 1.9 (0.09) 22
2.4 (0.03) 4.1 (0.05) 76
1.5 (0.03) 1.6 (0.04) 45
3.0 (0.03) 3.6 (0.03) 104
2.9–4.0
10–25
Note: In the parentheses are the coefficients of biological absorption (Cb). The “normal” contents in plants are given according to [12]. The contents higher than the “normal” ones are in bold. Corg—the content of organic substance in the soils.
plants. This phenomenon is also confirmed by the low values of the coefficient of biological absorption (Cb) of lead in the potatoes grown on plots 1 and 2. The maximal Cb was found for cadmium; a high Cb in the vegetables was determined for Zn. Typical plants, including wild ones, horseweed (Erigeron canadensis), wormwood (Artemisia annua and Artemisia sieversiana) and crops (soybeans (Glycine
max) and maize (Zea mays)) grown on the polluted Phaeozems of Kharbin were analyzed (Table 4). The Cd, Pb, Cu, and Zn contents in the plants and soils of this region were higher than in the vegetables grown in Svirsk. The heavy metals were absorbed most intensely by the wild-growing plants. In the agricultural plants (soybeans, maize, and vegetables) growing near Svirsk, the Cb was much lower. Among the elements investigated, Cd and Zn accumulated most actively. EURASIAN SOIL SCIENCE
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Potatoes
1.5 I
8
1
1.0 0.5
R2
1
= 0.98
4 3
5–8
2
4
5–8
2 0 0.6
25
50
75
100
125
150
175
7 R2
0.4
0 5
3
6
8 0.2
4
3 30
1 70
50
0.03
90
110
2 130 5
1 7
0 0.05
0.25
0.45
0.65
175
5
6
4
30
50 1
70
2 90
110
130
R2 = 0.04
0.15
R2 = 0.78
3
0.10
2
8
0 10 0.25
150
3
0.20
4 6
III 0.02
1
125
100
R2 = 0.22
2
5
0 10 0.04
75
1
4
= 0.69
4
25 2 50
3
II
0.01
Cabbage
6
R2 = 0.96
401
0.85
0.05 8 7 0 0.05 Soil
2 4 0.25
3
5
6
0.45
0.65
0.85
Fig. 3. Relationships between the contents (mg/kg) of As (I), Pb (II), and Cd (III) in potatoes and cabbage and in the soils. Regression equations: As (potatoes)—y = 1E + 0.5x2 + 0.0075x + 0.0145; As (cabbage)—y = 0.0003x2 – 0.0072x + 0.1649. Pb (potatoes)—y = 4E – 0.5x2 – 0.0092x + 0.5445; Pb (cabbage)—y = 0.0003x2 + 0.0549x – 1.0338. Cd (potatoes)—y = –0.0112x2 + 0.0565x + 0.0034; Cd (cabbage)—y = – 0.3039x2 – 0.2743x – 0.009.
Among the heavy metals, Zn is known to be one of the highly biophilous elements. The lowest Cb values were characteristic of Pb. This is a distinguishing feature of this element for all the plants. DISCUSSION The use of different methods for extraction, despite their limitations, allows distinguishing some principal features for the occurrence of elements in soils: the degree of fixation, the migration capacity, the relative biological availability, etc. [2, 17, 26, 29]. The most available form for plants, except for the water-soluble one, is that of easily exchangeable ions sorbed by the surface of different soil components. The forms of carbonates, Fe–Mn hydroxides, and the organic fraction closely follow them. The residual forms are mainly included into the crystalline lattice of minerals and are weakly available for plants. The comparison of the soils of the Angara River basin and the Kharbin area showed that the soils of the latter were strongly polluted by Cd, Pb, and Zn. The EURASIAN SOIL SCIENCE
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elevated concentrations of As, Cd, Pb, Cu, and Zn in the soils of Svirsk were determined in close vicinity to the main pollution sources (the former plant for As production and the “Sibelement” plant). At a distance of the first kilometers from the pollution sources, the contents of these elements approached that typical for the background. In both cases, the pollution was at the level close to the approximate permissible one for cultivated soils or exceeded it. The analysis of the data on the heavy metal and As extraction showed that, in the zones of technogenic pollution, the share of their mobile forms increased. Probably, this regularity is characteristic of the majority of the technogenically polluted areas [2]. Cadmium deserves special attention; its concentration in the polluted kitchen garden soils of Svirsk was 0.37 mg/kg and, in the Phaeozems of Kharbin, 0.68– 2.29 mg/kg. For comparison, the Cd content was 0.17 mg/kg in the chernozems of Novosibirsk oblast. The state soil standard calculated for chernozems of Kursk oblast is 0.1 mg/kg [11]. Cadmium is a strong genotoxic and carcinogenic poison [24].
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Table 4. The contents of heavy metals in the soils and plants (mg/kg of dry matter) in the technogenic zone near Kharbin Plants Erigeron canadensis Artemisia annua Artemisia sieversiana Glycine max Zea mays MPC** for leguminous plants Soil
Cd 2.33 ± 0.48* (1.2) 1.62 ± 0.45 (0.84) 0.93 ± 0.12 (0.48) 0.62 ± 0.13 (0.32) 0.14 ± 0.04 (0.07) 0.1 1.93
Pb 3.31 ± 0.66 (0.06) 1.56 ± 0.43 (0.03) 1.25 ± 0.20 (0.02) 0.75 ± 0.21 (0.01) 0.83 ± 0.41 (0.01) 0.5 57.5
Cu
Zn
6.89 ± 0.85 (0.35) 5.28 ± 1.09 (0.27) 3.24 ± 0.86 (0.16) 3.77 ± 0.86 (0.19) 1.82 ± 0.43 (0.09) 10 19.8
52.8 ± 10.5 (0.36) 56.4 ± 10.1 (0.39) 31.8 ± 7.1 (0.22) 51.6 ± 5.2 (0.36) 22.7 ± 5.4 (0.16) 50 145.2
Notes: In the parentheses—Cb. * Variation of the element contents determined using different methods, n = 3 [26]. ** MPC—maximum permissible concentration according to [23].
In the polluted chernozems and Phaeozems, as compared to the unpolluted soils, the content and share of mobile forms of cadmium and its availability drastically increased. This fact is of principal importance. In the polluted soils under study, the content of the easily exchangeable Cd fraction was 30–50%; together with the carbonate and hydroxide fractions, it can exceed 80%. Upon acidification of soils, the availability of Cd for plants should increase. Since pollution by heavy metals, especially by Cd, is characteristic of many industrial regions of Russia and the world [5, 11], the specific features of the Cd distribution in the soils found in this research deserve detailed investigation. The high mobility and availability of Cd in the biosphere are determined to a greater degree by its capacity to enter chelate compounds, which can accelerate its accumulation in plants [5, 26]. The most known cases of Cd intoxication are related to the consumption of rice grown in fields irrigated by waste of ore mining enterprises (the “itai-itai” disease in Japan). In the polluted soils, Zn, Cu, and Pb, unlike cadmium, were detected predominantly in the difficultly soluble compounds. An evident predominance of As (the priority pollutant) in the residual fraction was found in the soils of Svirsk. In the case with Pb, the residual fraction competed with the organic and hydroxide ones. According to the data of Varshal et al. [4], in the polluted soils, the main amounts of technogenic lead may be accumulated by humus acids. Evidently, the lower mobility, the availability of lead for plants, and its further migration may be determined by this fact. From 40 to 90% of the total copper and zinc contents were in the insoluble residue. Their concentrations in the different fractions are very diverse in the
polluted soils of different regions. Nevertheless, the proportion between the Cu contents in the different fractions of the polluted soils nearby Svirsk was similar to that revealed for chernozems of Kursk oblast: the Cu concentration was higher in the organic fraction than in the Fe–Mn hydroxide fraction [22]. Particularly, in the chernozems of Kursk oblast with a total Cu content of 30 mg/kg, the contribution of the different fractions (%) corresponds to the following sequence: Cures (92) > Cuorg (7) > CuFe + Mn (0.3). In the other fractions (the exchangeable and carbonate), the Cu concentration was lower than the detection limit. The sequences for the Zn content in the polluted soils of Svirsk (total content 94 mg/kg) and the chernozems of Kursk oblast (76 mg/kg) were similar. This fact shows that this trend in the heavy metal distribution by the fractions is characteristic of chernozemic soils. The data obtained confirm that the plant species differ in their ability to accumulate heavy metals and arsenic. In addition, their accumulation is also related to the degree of soil pollution (the total element content) and, especially, to the form of elements in the soil. The As concentration in the vegetables grown in the kitchen garden soils of Svirsk was proportional to its content in these soils. The Cd accumulation in the vegetables was directly related to the high share of its easily exchangeable form and the other close-reserve forms in the polluted soil. The high level of bioaccumulation was peculiar to zinc; the share of its mobile forms was considerable in all the tested soils of Svirsk. This element often accumulates in amounts exceeding its normal content in plants. High coefficients of biological Zn accumulation were also characteristic of the Phaeozems. As mentioned above, Zn is one of the most important elements for plants [11, 12]. EURASIAN SOIL SCIENCE
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Lead, despite the considerable share of its mobile forms in the soil (20%), was weakly consumed by the plants in both study objects. The Pb accumulation in the plants depended little on its concentration in the chernozemic soils; it appeared to be related to the organic matter content in the soils to a greater extent. The Cu content, mainly being in the bound form in the soils, did not reach a high level in the vegetables. The coefficients of the biological accumulation drastically differed among the soils with different pollution rates and in the different plant species. The vegetables grown on the less polluted soils of Svirsk can absorb considerable amounts of heavy metals. Even taking into account the species specificity, it is worth noting that the drastic decrease in the biological absorption of the elements in the regions of intense pollution and the considerable differences between the plant species attest that some plant species have different barrier properties. This circumstance may be useful for the selection of crops for polluted soils. Particularly, in northeastern China, maize, which is distinguished by the lowest Cb among the plants studied, can be a such crop. Wild plants with the capability to accumulate heavy metals may be used for phytoremediation of the soils. CONCLUSIONS The investigations conducted in the Lake Baikal basin and northeastern China have confirmed the prospects of using different methods of extraction for the assessment of the fixation, mobility, and bioavailability of toxicants in the soils. In both studied regions, the contents of As, Cd, Pb, Zn, and Cu were close to the approximate permissible concentrations for cultivated soils or exceeded them. In the zones of technogenic pollution, the contents of mobile forms of heavy metals and As increases resulting in their higher migration and bioavailability. This regularity appears to be of common character. Cadmium, one of the strongest genotoxic and carcinogenic poisons, was highly mobile and available. Probably, this property is related to the ability of cadmium to enter the composition of very mobile chelate compounds, which provides the transfer and accumulation of this element in plants. Copper, zinc, and arsenic were present in the soils studied, as a rule, in bound forms. Lead is mainly contained in the insoluble residue, in the hydroxide and organic fractions. This circumstance determines its lower mobility and bioavailability as compared to cadmium. The biological accumulation of heavy metals and arsenic depends on the specific features of the plant species and the forms of the element present in the soil. In the strongly polluted regions, among the crops studied, the highest values of Cb were revealed for soybeans and cabbage and the lowest ones for maize. The EURASIAN SOIL SCIENCE
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different plant species had different barrier properties with respect to the heavy metals. Evidently, the barrier properties for toxicants in different crops and wild plants deserve special investigation and are of great importance for the selection of agricultural plants for cultivating on polluted soils. ACKNOWLEDGMENTS This work was supported by the Russian–Chinese Project of the Russian Foundation for Basic Research (GFEN no. 05-05-39013). REFERENCES 1. Atlas. Irkutsk Oblast: Ecological Conditions (Ross. Akad. Nauk, Moscow, 2004) [in Russian]. 2. G. A. Belogolova, A. G. Arsent’eva, and V. R. Mamitko, “Occurrence Forms of Elements in the Zones of Technogenic Contamination,” Dokl. Akad. Nauk 337 (5), 650– 654 (1994). 3. G. A. Belogolova, P. V. Koval’, Yu. N. Udodov, et al., “Heavy Metals in the Trophic Chain of Humans in the Angara Industrial Zone,” in Food Quality and Safety (Irkutsk, 2004), pp. 8–14 [in Russian]. 4. G. M. Varshal, A. A. Nesterov, S. D. Khushvakhtova, I. Ya. Koshcheeva, V. N. Danilova, and Yu. V. Kholin, “Lead(II) Complexation with Humus Acids and the Effect of These Processes on Lead Mobility in Waters and Soils,” in Applied Geochemistry, Vol. 2: Ecological Geochemistry, Ed. by E. K. Burenkova (IMGRE, Moscow, 2001), pp. 459–473 [in Russian]. 5. S. N. Volkov, “Technogenic Biogeochemistry of Cadmium in the Environments as a Phenomenon of the Current Development of the Biosphere (A Review),” in Geochemistry of Natural and Technogenically Modified Biogeosystems (Nauchnyi Mir, Moscow, 2006), pp. 179– 202 [in Russian]. 6. S. N. Volkov and V. V. Ivanov, “New Information on the Ecological Geochemistry of Metals and Changes in Their Properties in Technogenesis,” in Applied Geochemistry, Vol. 2: Ecological Geochemistry, Ed. by E. K. Burenkova (IMGRE, Moscow, 2001), pp. 433–458 [in Russian]. 7. V. V. Dobrovol’skii, “Migration Forms and Migration of Heavy Metals in the Biosphere,” in Geochemistry of Natural and Technogenically Modified Biogeosystems (Nauchnyi Mir, Moscow, 2006), pp. 35–54 [in Russian]. 8. V. V. Dobrovol’skii, “Role of Soil Organic Matter in the Migration of Heavy Metals,” Priroda, No. 7, 35–39 (2004). 9. V. V. Ivanov, Ecological Geochemistry of Elements: Reference Book (Nedra, Moscow, 1994), Vol. 4 [in Russian]. 10. V. V. Ivanov, Ecological Geochemistry of Elements: Reference Book (Nedra, Moscow, 1994), Vol. 5 [in Russian]. 11. V. B. Il’in and A. I. Syso, Trace Elements and Heavy Metals in Soils and Plants of Novosibirsk Oblast (Ross. Akad. Nauk, Novosibirsk, 2001) [in Russian]. 12. A. Kabata-Pendias and H. Pendias, Trace Elements in Soils and Plants (CRC, Boca Raton, 1989).
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13. L. L. Kalep, “Agroindustrial Characterization of Agricultural Lands in the Irkutsk Oblast,” in Soils of Irkutsk Oblast, Their Use, and Reclamation (Irkutsk, 1979), pp. 49–69 [in Russian]. 14. L. O. Karpachevskii, Ecological Soil Science (GEOS, Moscow, 2005) [in Russian]. 15. Control of Chemical and Biological Parameters of the Environment, Ed. by L. K. Isaev (St. Petersburg, 1998) [in Russian]. 16. M. A. Korzun and V. A. Kuz’min, “Soils of Irkutsk Oblast,” in Soils of Irkutsk Oblast, Their Use, and Reclamation (Irkutsk, 1979), pp. 17–35 [in Russian]. 17. V. A. Kuznetsov and G. A. Shimko, Sequential Extraction Method in Geochemical Studies (Nauka i Tekhnika, Minsk, 1990) [in Russian]. 18. V. A. Kuz’min, Soils of Cisbaikalia and Northern Transbaikalia (Nauka, Novosibirsk, 1988) [in Russian]. 19. I. S. Lomonosov, V. N. Makarov, A. P. Khaustov, et al., Ecogeochemistry of Cities in the Eastern Siberia (Ross. Akad. Nauk, Yakutsk, 1993) [in Russian]. 20. O. G. Lopatovskaya and V. N. Mikhailichenko, Soil Ecological-Reclamation Complexes of the Cheremkhovo Angara Region (Ross. Akad. Nauk, Novosibirsk, 2002) [in Russian]. 21. D. S. Orlov, Soil Chemistry (Mosk. Gos. Univ., Moscow, 1992) [in Russian].
22. T. V. Pampura, “Comparative Analysis of Adsorption Isotherms and Sorbed Cu and Zn Forms in Chernozem,” in Heavy Metals in the Environment (Pushchino, 1997), pp. 266–281 [in Russian]. 23. V. M. Pozdnyakovskii, Sanitary Principles of Nutrition and Food Inspection (Novosibirsk, 1996) [in Russian]. 24. V. G. Rebrov and O. A. Gromova, Vitamins and Trace Elements (Alev-V, Moscow, 2003) [in Russian]. 25. Sh. D. Khismatullin, “Problems in the Rational Use of Saline Soils in Irkutsk Oblast,” in Soils of Irkutsk Oblast, Their Use, and Reclamation (Irkutsk, 1979), pp. 76–87 [in Russian]. 26. G. L. Guo, Q. X. Zhou, P. V. Koval, and G. A. Belogolova, “Speciation Distribution of Cd, Pb, Cu, and Zn in Contaminated Phaeozem in North-East China Using Single and Sequential Extraction Procedures,” Aust. J. Soil Res. 44, 135–142 (2006). 27. Th. Eikmann and A. Kloke, “Nutzungs und Schutzgutbezogene Orientierungswerte fur (Schad) Stoff in Böden,” VDLUFA-Mitteilungen, No. 1, 19–26 (1991). 28. A. Klok, “Richtwerte-80: Orientierungsdaten fur tolerierbare Gesamtgehalte einger Elemente in Kulturböden,” VDLUFA-Mitteilungen, Nos. 1–3, 9–11 (1980). 29. A. Tessier, P. G. C. Cambell, and M. Bission, “Sequential Extraction Procedure for the Speciation of Particulate Trace Metals,” Anal. Chem., No. 51, 844–851 (1979).
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