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Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria
GEXPLO-05327; No of Pages 8 Journal of Geochemical Exploration xxx (2014) xxx–xxx
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Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria Venera Tsolova Tsolova a,⁎, Mariana Blagoeva Hristova a, Jaume Bech Borras b, Núria Roca Pascual b, Martin Dimitrov Banov a a b
N. Poushkarov Institute of Soil Science, Agrotechnologies and Plant Protection, 7, Shoose Bankya, 1080 Sofia, Bulgaria Facultat de Biologia, Universitat de Barcelona, Diagonal, 643, 08028 Barcelona, Spain
a r t i c l e
i n f o
Article history: Received 11 July 2013 Received in revised form 12 February 2014 Accepted 17 February 2014 Available online xxxx Keywords: Soil extraction Technosols geochemistry Pb, Cu, Zn mobility Toxic threshold Technosols pedology
a b s t r a c t The content and availability of Pb, Cu and Zn were determined by the methods of soil extractions with aqua regia, 1 M NH4NO3 and 1 M NH4Ac. Reclaimed soils, which differ in land use, the duration of post reclamation development, geological and geographical characteristics were included in the study. In most pedons trace element total contents are irregular along depth and close to the background values in Bulgarian soils (Pb — 26 μg/g, Cu — 34 μg/g and Zn — 88 μg/g). The copper content greatly varies between the minimum of 8.5 μg/g and the maximum of 500 μg/g. The latter is defined as an intervention concentration by the Bulgarian legislation, and is accepted as a toxic threshold which affects soil functions, the environment and human health. Mobile concentrations of Pb, Cu and Zn are non-toxic assuming 8 μg/g for Cu, 4 μg/g for Pb and 43 μg/g for Zn as acceptable limits of available heavy metals in Technosols with slightly alkaline pH (7.0 - 8.0). The acidic pH (b 6.0) increases the solubility and desorption of zinc and copper, but diversely influences the bioavailability of lead. In acidic Technosols Pb and Cu mobile contents could exceed the Prüeß critical level of 1 μg/g and may provoke independent and joint toxic effects. The lithogenic origin of Cu toxicity which amounted to 47.7 μg available Cu/g soil shows the most serious risk of environmental pollution. Intensive weathering of soil surface layers does not accelerate the trace element bioavailability. Pb, Cu and Zn mobility mostly depends on pH, the content and mineralogy of fine earth fractions (b0.01 mm) and organic carbon pools in studied soils. © 2014 Elsevier B.V. All rights reserved.
Introduction Soils that have originated as a result of mining activity are called dumps, mining soils, drastically disturbed soils, reclaimed soils or anthropogenic soils. In this paper we will refer to the World Reference Base for Soil Resources (IUSS Working Group WRB, 2006) and will name them Technosols (technogenic soils), i.e., soils, which parent materials are exported or produced by human activity and would not otherwise have occurred on the surface. Technosols in Bulgaria have been studied from versatile points of view. Their morphology, mineralogy, geochemistry and pedology as well as the parent materials origin, composition and properties are elucidated (Banov, 1989; Hristova, 2013; Ivanov, 2007; Marinkina, 1999). Stability of soil structure, microbial diversity and activity are often used as indicators of the assessment of reclaimed soils quality and development (Banov, 1989; Dimitrova, 1995, 1996, 2011; Ivanov, 2007; Marinkina, 1999). One of the most important criteria for evaluating the agronomic potential of these soils is the
⁎ Corresponding author at: 7, Shoose Bankya, 1080 Sofia, Bulgaria. Tel.: +359 899424258. E-mail address: [email protected] (V.T. Tsolova).
content of potentially hazardous elements. A few studies indicate that the content and behavior of the risky elements in Technosols, especially of some radionuclides and heavy metals can create a real health danger (Banov et al., 2006; Marinkina, 1999; Misheva et al., 2007; Tsolova and Misheva, 2008). This is typical of areas with local geochemical anomalies, where toxicity may have a long lasting effect. Technosols may also be polluted during the mining and processing of mined ore materials. The combustion of coal, for example, released many chemical elements (C, S, H, K, Ca, Al, Cl, Si, Mg, Zn, Mn, Mo, Rb, Ti, Cu, Co, Cr, Br, Pb, Hg, Sb, Cd), some of which are in significant quantities. They create local anomalies in chemical composition of soils, plants and water. In fact, the vulnerability of Technosols to anthropogenic pollution could be strong. The lack of organic matter combined with low sorption and buffer capacity can lead to a greater risk of heavy metal release after weathering and to their increased mobility and bioavailability. Therefore, it is necessary to assess the risk of environment pollution and to consider the potential threat to soil resources in mine areas. This study deals with the determination of the content and the availability of Pb, Cu and Zn in reclaimed soils (Technosols), built in three mine areas in Bulgaria — Maritsa-Iztok, Chukurovo and Assarel Medet.
http://dx.doi.org/10.1016/j.gexplo.2014.02.019 0375-6742/© 2014 Elsevier B.V. All rights reserved.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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Fig. 1. Technosols located in the Maritsa-Iztok mines area.
Materials and methods
Methodology of the study
Technosols brief description
Field study follows the methodology described in the guidance for soil description (FAO, 2006). The location of the representative profiles conformed to the topography and soil catena concept in all studied spoils. Soil sampling procedure followed BSS ISO 10381-2, 4 (2005).1 The laboratory study involves:
Three sites that differ in geochemistry of parent materials, reclamation method, geographic and geologic particularities, and the duration of post-reclamation development were studied. These specific imprints on soil characteristics should provide information about the phenomena controlling heavy metal availability in Technosols. The studied soils are located in the vicinity of Maritsa-Iztok coal mines, Chukurovo coal mine and the Assarel copper mine. Iztok was the first built dump and the most developed and mature Technosols in the area of Maritsa-Iztok coal mines. It was reclaimed in 1974 by a specially developed technology which was later designated as the main method for agricultural reclamation in Bulgaria (Regulation 26/1996). This approach resulted in formation of a specific soil profile consisting of two major horizons. The surface horizon with a 40 cm depth is a transported humus horizon that consists of humus layers of natural soils occupying the territory prior to mining. The main subhorizon having a depth of 2 m is composed of suitable for reclamation yellow-green clays isolated from the stratigraphic profile of the deposit. Due to the lack of humus material, the described technology is implemented on approximately 1/2 of the dump. The rest of about 70 ha were diverted to forestry reclamation and were directly planted on the layer of clays. The main characteristics of arable soils are illustrated by representative profile 1. Representative profile 2 is situated in the forest part of the dump. The typical landscapes of the two parts of the dump are presented in Fig. 1. Technosols located close to the Chukurovo mine represent a heterogeneous mixture of Miocene geologic materials that covered the coal horizons. Soils were directly reclaimed (without humus cover or amendment) with forest species: pine (Pinus nigra J.F.A.) and birch (Betula pendula Roth.) in Zapad dump (representative profile 3) and just pine — Mlada gvardia dump (representative profile 4). Zapad dump is also among the most mature Technosols in Bulgaria, with 45 year old genesis. Mlada gvardia is a younger soil with 25 years of development. The typical landscapes of the objects are shown on Fig. 2. As a result of the activity of Assarel Medet copper plant there are few constructed dumps in the region, which are distinguished for their high copper content and strong acidity. The object of this study is the Severozapad dump, which had been built about 20 years ago. The dump is chemically reclaimed with 0.15 kg lime/m2 and covered with manure in norm of 6 kg/m2 in order to reduce the adverse impact on the environment. Biological reclamation is carried out with two plant species: birch (Betula pendula Roth) and acacia (Acacia Mill.), which form separate ecosystems (Fig. 3). Soils' characteristics are illustrated by representative profile 5.
1. Pretreatment of samples for physico-chemical analysis — BSS ISO 11464 (2012). 2. Determination of pH in H2O — by the FAO method (Dewis and Freitas, 1970). 3. Determination of effective cation exchange capacity and base saturation level using barium chloride solution — BSS ISO 11260 (2011). 4. Particle size distribution — method of Kachinsky (1958). This method differs from the method described in ISO 11277 (2009) (by sieving and sedimentation) mostly in sample pretreatment (NaOH) and sieve mesh sizes. The following sizes of major fractions are recognized by Kachinsky: Sand — this fraction involves particles with 1.00–0.05 mm equivalent spherical diameter; Silt fraction — from 0.05 to 0.001 mm equivalent diameter; and Clay b 0.001 mm. 5. Determination of total content of trace metals — method of soil extraction with aqua regia (ISO 11466, 1995) and EAAS (ISO 11047, 1998) using spectrometer Perkin-Elmer 2100. The content of heavy metals determined by soil extraction with aqua regia is conventionally called pseudototal, since there are other solvents that have more destructive effect and release larger amounts of heavy metals. Despite of this drawback, the method is standardized and widely used in the analytical practice. The content of heavy metals determined by aqua regia extraction will be used later in the meaning and for evaluation of the total content of heavy metals in studied Technosols. 6. Determination of easy soluble trace element contents. Two extraction methods were used to determine the mobility of heavy metals: □ Extraction with 1 M NH4NO3 — ISO 19730 (2008). Extraction of soil with 1 M NH4NO3-solution is used to determine readily soluble trace element contents. Like other salt solutions, 1 M NH4NO3 soil extraction method is also used to predict trace element contents in plants and the environmental risk assessment for soil contamination (Birke and Werner, 1991; Prüeß, 1992). □ 1 M NH4Ac (pH 7) — Pansu and Gautheyrou (2006). 1 M ammonium acetate (pH 7) is perhaps the most preferred reagent for exchangeable metal analysis because of the metal complexing power of the acetate ion, which prevents readsorption 1
Bulgarian State Standard.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
V.T. Tsolova et al. / Journal of Geochemical Exploration xxx (2014) xxx–xxx
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Fig. 2. Technosols located in the Chukurovo mine area.
or precipitation of released metal ions (Podlesakova et al., 2002). This method is suitable for determination of readily soluble and plant available trace element contents (Gryschko et al., 2005) although it produces very low results of Cu available content (Symeonides and McRae, 1977). Generally, these procedures indicate the content of metals associated with soil components by liable binds especially their water soluble compounds and complexes with organic matter, exchangeable content of metals nonspecifically and specifically adsorbed by soil components as well as the metals co-precipitated by adsorption or occlusion (absorbed metals). Thereby we should agree with Gryschko et al. (2005) and admit that the processes influencing the mobility of trace elements are too complex to expect that just one soil extraction method
can always guarantee a correct prognosis of toxicological significant element contents. The extraction duration needed to establish the equilibrium between the processes of adsorption and desorption of elements was empirically confirmed for Technosols. Soil:solvent ratios were modified in order to increase the measurement sensibility — the extraction ratio when using 1 M NH4NO3 is 20:50 g:ml and 10:200 g:ml soil:1 M NH4Ac. 7. Assessment of pollution. A few legal criteria are used for assessing soil pollution with heavy metals: □ Limit values representing maximum permissible and intervention concentrations of heavy metals determined by the Bulgarian legislation (Table 1). Maximum permissible concentration is the
Fig. 3. Technosols located in the Assarel Medet mine area.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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Table 1 Maximum permissible and intervention concentrations of heavy metals and metalloids in soils (determined in aqua regia as total concentrations, in μg/g) — Regulation 3 (2008). Elements
pH (H2O)
Cu
b6.0 6.0–7.4 N7.4 b6.0 6.0–7.4 N7.4 b6.0 6.0–7.4 N7.4
Pb
Zn
Maximum permissible concentrations
Intervention concentrations
Arable lands
Permanent grasslands
80 150 300 60 100 120 200 300 400
80 140 200 90 130 150 220 390 450
500
500
900
content of harmful substance in the soil, in μg/g, the exceeding of which, under certain conditions, leads to disturbance of soil functions and to danger for the environment and human health. Intervention concentration is the pollutant content in soil which leads to disruption of soil functions and to danger for the environment and human health. 8. Statistical analysis. Statistical data analysis was performed using Statgraphics Centurion XVI which implements many commonly used statistical procedures. Data from extractions were additionally assessed by the F criterion, which is appropriate for comparison of the dependent quantities by their average means (Lidansky, 1988). In this approach the differences between dependent members of the compared samples (extracts) form a new variation row with new average means (d). The value of the F is calculated by the formula: F = (Σd)2 / Σ(d2), (I). Differences are considered statistically reliable when F ≥ Fcritical at df = n, where df is the degrees of freedom, n — number of samples, and P — confidential level. Results and discussion Trace metal geochemistry of Technosols at Maritsa-Iztok mines area Technosols located in the region of Maritsa-Iztok coal mines have different solums due to the applied reclamation technology and land
use. Humus reclaimed soils have a distinct humus horizon wherein the nutrients are concentrated (Table 2). In non humus reclaimed soils the organic matter content is higher, as a result of the of black clays presence. Black clays are abundantly mixed with fine coal dust and bear an increasing of clay fraction content and decreasing of pH (Tables 2, 3). The high clay content (mostly shrink-swelling) lends vertic properties and promotes long-lasting water saturation of soils. Black clays also provoke almost 100% increase of the total element contents (Table 3, profile 2), but do not create a risk of pollution. Pedogenic clay accumulation in subhorizon (Cccg1 25–70) goes with a detectable accumulation of (pseudo)total copper. The contents of the other elements in profile depth are not attached to the clay fraction. The contents of Pb, Cu and Zn in profile 1 are closer to the background values of trace elements in Bulgarian soils than those in profile 2 (Table 4). As we mentioned above, these soils are made of non-toxic, environmentally friendly and agriculturally suitable geological materials. Total element content increases toward Pb b Cu b Zn and forms the opposite trend compared to mobile concentrations. NH4NO3-extraction of soils with pH N 7 (profile 1 — humus reclaimed soils and profile 3 — soils near Chukurovo mine with humus layer development) produces very low element contents which lay below the level of detection. Bucher and Schenk (2000), and Köster and Merkel (1982) also announced that neutral salt (NH4NO3 and CaCl2) extraction could provide undetectable amounts of Cu and Pb. Since Cu and Pb mobility depends on pH, it is important to consider the soil pH in their determination. For this reason, mobile content of heavy metals in soils with pH N 7.0 was determined by extraction with NH4Ac. The extraction method with NH4NO3 was applied for profiles where pH b 7.0. The mobile concentrations of lead, copper and zinc in humus reclaimed soils vary in non-toxic and safe interval from the environmental viewpoint (Table 3). Few acceptable limits of available heavy metals (extracted with NH4Ac) have been taken into consideration to estimate the obtained values: 8 mg/kg for Cu and 43 mg/kg for Zn assumed by Davidescu et al. (1998) and Chapman (1971) threshold for NH4OAc-extractable Pb who predicted that as little as 4.0 ppm can prove toxic to some plants. In these soils the content of bioavailable Cu and Zn gradually increases in depth, while Pb prevails in areas affected by a noticeable presence of Fe minerals (30–70 cm). Aualiitia and Pickering (1987)
Table 2 Main physico-chemical characteristics of Technosols at Maritsa-Iztok mines area. Profile view
Horizon, depth (cm)
Sand (%)
Silt (%)
Technosols reclaimed with humus layer — profile 1 Аpk (0–30) 17.6 ± 7.2 36.9 Ccc1 (30–50) 36.5 ± 6.9 26.3 Сcc2 (50–70) 31.8 ± 6.7 28.5 Сcc3 (70–100) 29.8 ± 2.4 30.7
Clay (%)
Org. C (%)
Carbonates (%)
Sorption capacity (cmol(+)/kg)
± ± ± ±
13 16 4.5 7.3
45.5 37.2 39.8 39.5
± ± ± ±
13 3.8 0.4 1.7
2.04 ± 0.1 0.75 0.34 0.23
0.39 2.07 1.34 2.77
± ± ± ±
0.5 0.4 0.1 0.6
43.9 33.1 27.9 28.0
Technosols reclaimed without humus layer — profile 2 АCk (0–25) 7.84 ± 8.6 21.5 ± Cccg1 (25–70) 8.09 ± 7.6 11.3 ± Cccg2 (70–100) 16.8 ± 7.4 17.5 ± Сccg3 (N100) 6.05 ± 3.5 26.6 ±
5.4 3.3 6.7 4.9
70.7 ± 80.6 ± 65.7 ± 67.4 ±
10 6.5 0.3 6.6
2.54 1.46 1.28 0.97
0.49 0.38 0.67 0.41
± ± ± ±
0.2 0.3 0.3 0.2
40.3 37.9 38.8 32.6
± ± ± ±
0.4 0.7 0.3 0.2
Legend: Sand fraction includes particles with 1.00–0.05 mm equivalent spherical diameter; Silt fraction — from 0.05 to 0.001 mm equivalent diameter and Clay b 0.001 mm.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
V.T. Tsolova et al. / Journal of Geochemical Exploration xxx (2014) xxx–xxx
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Table 3 Total and exchangeable contents of Pb, Cu and Zn in Technosols at Maritsa-Iztok mines area. Horizons, depth (cm)
pH
Pb Total
Cu
Zn
Extractable
%
Total
Technosols reclaimed with humus layer — profile 1 Аpk (0–30) 7.25 24.8 ± 3.18 Ccc1 (30–50) 7.75 25.8 ± 5.01 Сcc2 (50–70) 7.25 26.3 ± 2.02 Сcc3 (70–100) 7.30 28.0 ± 6.54 Average 7.4 26.2
2.35 2.95 3.10 2.50 2.73
9.5 11.4 11.8 8.9 10.4
30.7 25.5 31.8 30.0 29.5
± ± ± ±
Technosols reclaimed without humus layer — profile 2 АCk (0–25) 6.10 34.2 ± 3.18 Cccg1 (25–70) 5.95 32.8 ± 4.80 Cccg2 (70–100) 5.80 37.3 ± 2.36 Сccg3 (N100) 6.00 37.7 ± 1.76 Average 6.0 35.5
0.88 1.15 0.98 0.73 0.94
2.6 3.5 2.6 1.9 2.7
65.5 70.3 63.2 55.2 63.6
± ± ± ±
Extractable
%
Total
3.21 0.50 3.06 0.00
0.25 0.35 0.45 0.50 0.39
0.8 1.4 1.4 1.7 1.3
57.8 44.0 43.3 37.2 45.6
± ± ± ±
3.61 10.6 4.65 4.19
0.15 0.53 0.40 1.03 0.53
0.2 0.8 0.6 1.9 0.9
79.2 ± 69.8 ± 70.0 ± 72.2 ± 72.8
Extractable
%
6.05 7.40 8.28 14.8
0.20 0.30 0.40 0.60 0.38
0.4 0.7 0.9 1.6 0.9
4.07 8.31 12.3 14.9
0.85 2.48 4.43 2.28 2.51
1.1 3.5 6.3 3.2 3.5
Legend: % designates the relative amount of exchangeable content of the elements, in percent.
and Elzinga and Sparks (2002) established that Pb may be retained by hydrated Al and Fe oxides or amorphous silica emerging from the edges of weathered silicate minerals. Such retention is specific in nature and favored by low pH. Pb is also known to form various compounds with apatite and, in calcareous soils, with carbonate minerals (Cao et al., 2004). In profile 2 the mobile contents (1 M NH4NO3-extractable) seem to not trend to any soil components presumably due to initial pedogenesis and ped's heterogeneous organization. However, the mobile Pb predominates in the upper part of the soils (25–70 cm); zinc — between 70 and 100 cm and Cu — below 100 cm. In order to assess the risk for contamination of forest ecosystems we used the Prüeß critical levels. Prüeß (1992) fixed 1 mg/kg for Pb and Cu and 30 μg/g for Zn (based on 1 М NH4NO3 extract) as critical values for soil phytotoxicity. Thus, lead may cause toxic effect on all forest species because it prevails in 25–70 cm depth while Cu occurs at the deeper horizons and might have the more limited effect. However, the high clay content additionally limits the mobility of the studied elements. It should be noticed that the reagent is more efficient and extracted more zinc compared to profile 1 bearing in mind the little differences between total contents. Gryschko et al. (2005) reveal that chemical mechanisms involved when metals are extracted with 1 M NH4NO3 are a slight decrease in pH of the extraction solution and an increase in ionic strength. Most of the colloids and parts of the soluble metal– organic complexes are precipitated due to the high ionic strength. High ionic strength also decreases the activity of metal–OH+ species and the electrostatic potential of the particle surfaces, which in turn, increases desorption of heavy metal cations from negatively charged soil surfaces. Generally, the effects of high ionic strength on desorption of trace elements and on precipitation of colloids and soluble metal organic complexes and the formation of soluble metal ammine complexes have to be considered. The formation of amine complexes has been described as a heavy metal mobilizing mechanism in ammonium based extraction solutions (Lebourg et al., 1996; Pueyo et al., 2004). The trend of Pb, Cu and Zn lower availability in surface horizons (better pronounced in profile 2) might be associated with biological migration (uptake). Simple variation analysis shows the main sources of mobile zinc, copper and lead in slightly alkaline soils (profile 1, Fig. 4). Lead and copper mobile contents do not directly depend on their total concentrations (R2 b 0.20) and reveal the complexity of exchange processes in soil matrix. Lead exchangeable content basically depended on the content of dust earth fraction (sizes from 0.005 to 0.001 mm, R2 =0.99) and organic carbon (R2 = 0.70), which is also associated with dust fraction. Still, the mineral phase is not the collector of the pseudo total lead — the organic matter is his main accumulation pool and source (Fig. 4). Copper is associated with the fine mineral phase (size particles b 0.01 mm, R2 = 0.83), and the content of its exchangeable
forms depends mainly on the content of the organic matter (R2 = 0.90) and colloid exchange capacity (Fig. 4). The correlations between total and mobile concentrations of elements are better pronounced in profile 2 (R2Cu,Pb = − 0.70; R2Zn = −0.81). The criterion F also shows a high confidential level of the differences (≥F0,01) and close correlation between pairs of values. In this profile, a cross-correlation between the total concentrations of copper and mobile lead appears (R2 = 0.91). This allows us to assume that the exchangeable lead might be sorbed (adsorbed or absorbed) by the native copper, which occurs in abundance in Bulgaria (Kovachev, 1994) or is released from metal sulphides which are also found in the stratigraphic profile of the deposit. Perhaps the dust fraction consists of these minerals because it totally correlated with mobile lead (R2 = 0.999). Calculated relative contents indicate that about 10% of lead, 1% of copper and 0.9% of zinc are easily exchangeable and could pass in the soil solution. Trace metal geochemistry of Technosols at Chukurovo mine area The main difference between Technosols located in Chukurovo mine area is pH which allows us to study metal mobility in various geochemical environments. Particle size distribution along with profile depth could also reveal the behavior and fate of the studied metals in Technosols. Young soils (profile 4) are rich in pyrite and abounded with coal admixtures which reflect on pH and organic carbon content (Table 5). Both soils have very low sorption capacity prompted by domination of kaolinite and micas (illite) and negligible content of smectite minerals (Tsolova, 2005). In geochemical aspect, the genetically older soils (profile 3) represent a zone with higher trace element diffusion wherein the minimum values of 8.5 μg/g for Cu, 15.7 μg/g for Pb and 39.8 μg/g for Zn are established (Table 6). The zones of maximum accumulation of clay and silt fractions in both forest soils are zones of maximum accumulation of the studied elements. Slightly alkaline soils (considering the pH average value) copy the trend established in slightly alkaline soils located in Maritsa-Iztok mines area — higher amounts of mobile lead than those of zinc and copper. Zinc concentrations in both soils flow within the safe interval, although the acidic environment enhances its exchangeable content (profile 4). Considering the acid pH and Prüeß (1992) precautionary Table 4 Background concentrations of heavy metals and metalloids in soils (determined as a total concentrations in aqua regia, μg/g) — Regulation 3 (2008). As
Cd
Cu
Cr
Ni
Pb
Zn
Hg
Co
10
0.4
34
65
46
26
88
0.03
20
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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Fig. 4. Statistically significant relationships in profile 1.
Table 5 Main physico-chemical characteristics of Technosols at Chukurovo mine area. Profile view
Silt (%)
Clay (%)
Org. C (%)
Carbonates (%)
Sorption capacity (cmol(+)/ kg)
Technosols “Zapad” — profile 3 АС (0–5) 49.3 С (5–22) 50.8 Сgк1 (22–52) 30.2 Сgк2 (52–74) 42.7 Сg1 (74–100) 44.8 Сg2 (N100) 57.4
41.4 37.0 47.9 42.6 43.6 35.4
9.40 12.4 22.0 14.8 11.8 7.35
1.69 0.62 0.69 0.64 0.49 –
0.00 0.00 0.62 ± 0.4 0.62 ± 0.4 0.00 0.00
12.9 10.0 16.0 11.5 11.5 10.3
Technosols “Mlada gvardia” — profile 4 С1 (0–35) 34.7 С2 (35–60) 16.0 Сg (60–90) 20.8
55.4 64.1 60.3
10.0 ± 1.3 20.0 ± 0.3 19.0 ± 0.1
0.00 0.00 0.00
13.0 18.2 17.0
Horizons, depth (cm)
Sand (%)
values, the harmful biological effect of lead could be expected in these soils. Trace elements formed several statistically significant correlations in genetically older soils with versatile pH (profile 3). Pb total and mobile contents are closely bound up with fine fraction (b0.01 mm) and cation exchange. The negative correlations between Pb mobile content, fine earth fraction (b 0.01 mm) and cation exchange (R2 = − 0.85; R2= − 0.62) confirmed the specific adsorption of Pb. The mobile Cu is not associated with any soil component and Zn mobility is determined by the organic carbon content (R2 = 0.90). Due to the initial process of humus accumulation and transformation, and the presence of less active clays, soils fixed about 3 μg/g lead, 0.3 μg/g copper and 0.7 μg/g zinc.
± ± ± ± ± ±
1.1 6.0 8.7 1.1 3.0 0.8
± ± ± ± ±
0.5 0.4 0.0 0.0 0.2
2.28 ± 0.2 4.57 ± 0.2 5.21 ± 0.9
The lower pH in profile 4 increases the solubility and desorption of zinc, but slightly influences the bioavailability of lead and copper. Pb mobile content could exceed the critical level of 1 μg/g and may provoke soil toxicity. The intensive weathering of soil surface does not increase the elements' soluble content, except for Zn in profile 3. Obviously, the surface accumulation of non silicate and inorganic amorphous compounds of Fe, Al and Mn2 established in these soils (Marinkina and Djokova, 2002) is irrelevant to Pb and Cu fixation. It is reasonable to suggest
2
Methods of Merha and Jackson (1960) and Tamm (1936) were used.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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Table 6 Total and exchangeable contents of Pb, Cu and Zn in soils at Chukurovo mine area. Horizons, depth (cm)
pH
Pb
Cu
Total
Zn
Extractable
%
Total 11.4 ± 13.6 ± 14.6 ± 11.9 ± 9.13 ± 8.50 ± 11.5
Technosols “Zapad” — profile 3 АС (0–5) 6.25 С (5–22) 6.45 Сgк1 (22–52) 7.55 Сgк2 (52–74) 7.70 Сg1 (74–100) 7.50 Сg2 (N100) 7.55 Average 7.17
19.8 ± 17.3 ± 27.0 ± 21.5 ± 16.5 ± 15.7 ± 19.6
2.5 0.3 4.6 4.5 1.4 0.8
2.45 2.55 1.95 1.90 2.85 3.05 2.46
12.4 14.7 7.2 8.8 17.3 19.4 13.3
Technosols “Mlada gvardia” — profile 4 С1 (0–35) 4.50 С2 (35–60) 4.40 Сg (60–90) 4.40 Average 4.4
22.2 ± 2.4 33.8 ± 0.3 31.6 ± 1.3 29.2
2.03 2.05 1.58 1.89
9.1 6.1 5.0 6.7
Extractable
%
Total
0.2 2.6 0.5 0.2 1.2 0.7
0.30 0.25 0.25 0.20 0.35 0.25 0.27
0.6 0.5 0.5 0.5 0.8 0.6 0.58
47.1 ± 46.8 ± 54.9 ± 41.7 ± 44.0 ± 39.8 ± 45.7
0.6 0.2 4.0 2.0 1.0 2.2
1.40 0.65 0.55 0.45 0.60 0.70 0.73
13.4 ± 0.9 18.3 ± 0.4 17.5 ± 0.7 16.4
0.23 0.15 0.15 0.18
1.7 0.8 0.9 1.1
59.7 ± 4.2 66.4 ± 3.0 65.6 ± 2.0 63.9
6.23 9.15 8.28 7.89
that these compounds may facilitate Zn transport across Technosols, composed of Miocene sediments.
Trace metals geochemistry of Technosols at Assarel Medet mine area Soils located in the area of Assarel Medet copper mine are gravel soils, poor of colloids and organic matter (Table 7). Signs of water erosion impact indicate that surface runoff could play a significant role for redistribution of soil particles in the environment. Geochemistry of Assarel's soils is remarkable for high copper content. The obtained copper values in the root layer of studied soils are about 2 times higher compared to the maximum permissible content in grasslands (Tables 1, 8). In deeper layer, the copper total content coincides with the intervention concentration (500 μg/g) which is assumed as very risky for environment and human health. Soil reclamation leads to the formation of a sublayer with new geochemical distribution of the elements. It displays as lead and copper dispersion and zinc concentration. It could be said that the reclamation masks the lithogenic characteristics of parent materials and enhances a mosaic nature of spatial (3D) distribution of trace elements (Table 8). The implemented chemical reclamation reduces the mobility of copper about 100 times and abates its phytotoxic content to the safe level. It
Extractable
% 3.0 1.4 1.0 1.1 1.4 1.8 1.59
10.4 13.8 12.6 12.3
also immobilizes the solubility of Zn and strongly reduces its availability to another level (b0.4 μg/g) which may cause Zn deficiency. Acid environment reduces the mobile lead content (average about 6 times), in contrast to mobile zinc content, which increases about 30 times. The maximum mobile concentration of Cu 47.7 μg/g established in non reclaimed layer of Assarel's soils does critically exceed the Prüeß threshold of 1 μg/g and shows the most serious risk of environmental pollution. Due to the limited number of samples no explicit conclusions could be made at present. Conclusion Technosols located in coal regions are geochemical zones with low content of Pb, Cu and Zn. In most of these pedons the elements' total contents are irregular along depth and close to the background values in Bulgarian soils. Technosols in Assarel copper mine area featured high total copper content. It coincides with the intervention concentration of 500 μg/g, which is assumed to seriously damage soil functions, the environment and human health. • Mobile concentrations of lead, copper and zinc are non-toxic assuming 8 mg/kg for Cu, 4 mg/kg for Pb and 43 mg/kg for Zn as acceptable limits of available heavy metals in Technosols with slightly alkaline pH.
Table 7 Main physico-chemical characteristics of Technosols in Assarel Medet mine area (profile 5). Profile view
Horizons, depth (cm)
Sand (%)
Silt (%)
Clay (%)
Org. C (%)
Carbonates (%)
Sorption capacity (cmol(+)/kg)
АС (0–5) 1С (5–25) 2С (25–70)
89.9 82.0 83.7
8.40 15.0 13.3
1.73 3.00 3.00
0.88 ± 0.1 0.24 ± 0.1 0.42 ± 0.0
0.00 0.00 0.00
14.6 10.5 21.5
Table 8 Total and mobile contents of Pb, Cu and Zn in soils at Assarel Medet mine area. Horizons, depth (cm)
pH
Technosols “Assarel Medet” — profile 5 АС (0–5) 6.30 1С (5–25) 6.00 2С (25–70) 3.40 Average 5.23
Pb
Cu
Zn
Total
Extractable
%
Total
Extractable
%
Total
Extractable
%
30.6 22.0 27.5 26.7
0.60 0.55 0.10 0.42
1.96 2.50 0.36 1.6
480 417 500 466
0.40 0.95 47.7 16.4
0.08 0.23 9.54 3.3
75.3 102 77.8 84.9
0.20 0.40 6.60 2.40
0.27 0.39 8.48 3.1
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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• The soil acidic pH increases the solubility and desorption of zinc and copper, but diversely influences the bioavailability of lead. Pb and Cu mobile contents could exceed the critical level of 1 μg/g and may provoke independent and joint toxic effects in acidic Technosols. The lithogenic origin of Cu toxicity that amounted to 47.7 μg available Cu/g shows the most serious risk of environmental pollution. • Intensive weathering of soil surface layers does not accelerate the trace element bioavailability. Pb, Cu and Zn mobility mostly depends on the pH, content and mineralogy of fine earth fractions (b0.01 mm) and organic carbon pools in the studied soils. References Aualiitia, T.U., Pickering, W.F., 1987. The specific sorption of trace amounts of Cu, Pb and Cd by inorganic particulates. Water Air and Soil Pollution 35, 171–185. Banov, M., 1989. Study of Some Soil-genetic Changes in Lands Reclaimed Without Humus Cover from the Region of Maritsa-Iztok Mines. Ph.D Thesis N. Poushkarov Institute of Soil Science, Sofia (188 pp.). Banov, M., Tsolova, V., Misheva, L., 2006. Properties and reclamation of lands disturbed by geotechnologic uranium mining. Ecol. Ind. 8 (1–2), 60–63. Birke, C., Werner, W., 1991. Eignung chemischer Bodenextraktions-verfahren zur Prognose der Schwermetallgehalte in Pflanzen. Forschungszentrum Jülich GmbH, Berichte aus der ökologischen. Forschung Band, 6 224–288. BSS EN ISO 11260, 2011. Soil Quality — Determination of Effective Cation Exchange Capacity and Base Saturation Level Using Barium Chloride Solution. BSS ISO 10381-2, 2005. Soil Quality — Sampling — Part 2: Guidance on Sampling Techniques. BSS ISO 10381-4, 2005. Soil Quality — Sampling — Part 4: Guidance on the Procedure for Investigation of Natural, Near-natural and Cultivated Sites. BSS ISO 11464, 2012. Soil Quality — Pretreatment of Samples for Physico-chemical Analysis. Bucher, Annette S., Schenk, Manfred K., 2000. Characterization of phytoavailable copper in compost–peat substrates and determination of a toxicity level. J. Am. Soc. Hortic. Sci. 125 (6), 765–770. Cao, X., Ma, L.Q., Rhue, D.R., Appel, C.S., 2004. Mechanisms of lead, copper and zinc retention by phosphate rock. Environ. Pollut. 131, 435–444. Chapman, H.D., 1971. Proceedings of the International Symposium on Soil Fertility Evaluation. New Delhi, vol. 1, pp. 927–947. Davidescu, D., Davidescu, V., Lacatuşu, R., 1998. Microelements in Agriculture. Publishing House of Romanian Academy, Bucharest (Published in Romanian, 278 pp.). Dewis, J., Freitas, F., 1970. Physical and Chemical Methods of Soil and Water Analysis. Soils Bulletin, 10. FAO, Rome (275 pp.). Dimitrova, A., 1995. Microbiological activity of substrata meant for reclamation of lands disturbed by mine industry. Soil Sci. Agrochem. Ecol. (2), 60–61. Dimitrova, A., 1996. Two levels of bioassay for study of soil productivity. Proceeding of the International Conference of Land Degradation, 10-14.06, 1996, Adana, Turkey (4:250). Dimitrova, A., 2011. Biotechnoloical methods and manners for increasing the effectiveness of non humus reclamation. Proceedings of International Conference “100 years Soil Science in Bulgaria”, Part 2, pp. 861–865. Elzinga, E.J., Sparks, D.L., 2002. X-ray absorption spectroscopy study of the effects of pH and ionic strength on Pb(II) sorption to amorphous silica. Environ. Sci. Technol. 36, 4352–4357. FAO, 2006. Guidelines for Soil Description, Fourth edition. (Rome, 97 pp.). Gryschko, Rainer, Kuhnle, Rainer, Terytze, Konstantin, Breuer, Jörn, Stahr, Karl, 2005. Soil extraction of readily soluble heavy metals and As with 1 M NH4NO3-solution — evaluation of DIN 19730. J. Soils Sediments 5 (2), 101–106. http://dx.doi.org/10.1065/ jss2004.10.119. Hristova, M., 2013. Content and Availability of Microelements–Metals in Technogenic Soils. Ph.D Thesis N. Poushkarov Institute of Soil Science, Sofia 140 pp.
ISO 11047, 1998. Soil Quality - Determination of Cd, Cr, Co, Cu, Pb, Mn, Ni and Zn in Aqua Regia Extracts of Soils — Flame and Electrothermal Atomic Absorption Spectrometric Methods. ISO 11277, 2009. Soil Quality — Determination of Particle Size Distribution in Mineral Soil Material — Method by Sieving and Sedimentation. ISO 11466, 1995. Soil Quality - Extraction of Trace Elements Soluble in Aqua Regia. ISO 19730, 2008. Soil Quality — Extraction of Trace Elements from Soil Using Ammonium Nitrate Solution. IUSS Working Group WRB, 2006. World Reference Base for Soil Resources 2006, World Soil Resources Reports No. 1032nd edition. FAO, Rome92-5-105511-4. Ivanov, P., 2007. Soil formation processes in reclaimed lands from restored landscapes, destroyed by industry in different ways of using . Ph.D.Thesis National Center of Agricultural Science, N. Poushkarov Institute of Soil Science, Sofia, p. 156. Kachinsky, A., 1958. Mechanical and Micro-aggregates Composition of Soil, Methods for its Determination. Russian Academy of Sciences, Moscow (191 pp.). Köster, W., Merkel, D., 1982. Beziehungen zwischen den Gehalten an Zn, Cd, Pb und Cu in Böden und Pflanzen bei Anwendung unterschiedlicher Bodenuntersuchungsmethoden. Landwirtschaftl. Forschung, Kongreßband, 39 245–254. Kovachev, V., 1994. Copper deposits in Bulgaria and the possibilities for their use in ancient times. Proceedings “Problems of the Earliest Metallurgy”, 4. University of Mining and Geology, Sofia, pp. 90–119. Lebourg, A., Sterckeman, T., Ciesielski, H., Proix, N., 1996. Intérêt de differents reactifs d'extraction chimique pour l'evaluation de la biodisponibilite des metaux en trace du sol. Agronomie 16, 201–215. Lidansky, T., 1988. Statistical Methods in Biology and Agriculture. Zemizdat, Sofia (375 pp.). Marinkina (Tsolova), V., 1999. Studying and Possibilities for Reclamation of Sulphide Containing Materials Disclosed in the Open Cast Mining. Ph.D. Thesis Agricultural Academy, N. Poushkarov Institute of Soil Science and Agroecology, Sofia (231 pp.). Marinkina, V., Djokova, M., 2002. Extractable compounds of iron, aluminiun and manganese in reclaimed lands from “Chukurovo” mine district. Soil Sci. Agrochem. Ecol. XXXVII (1–3), 213–215. Merha, O.P., Jackson, M.L., 1960. Iron oxide removal from soils and clays by a dithionite– citrate system buffered with sodium bicarbonate. Clays Clay Miner. 5, 317–327. Misheva, L., Tsolova, V., Banov, M., Poynarova, M., Hadjiyanakiev, Y., Zlatev, A., Kojuharova, S., Zelyazkova, S., Vasileva, Z., 2007. Possibilities for Utilization of Lands and Territories Polluted with Radionuclides and Heavy Metals. National Center of Agricultural Science, N. Poushkarov Institute of Soil Science, Sofia (39 pp.). Pansu, Marc, Gautheyrou, Jacques, 2006. Handbook of Soil Analysis, Mineralogical, Organic and Inorganic Methods. Springer-Verlag Berlin Heidelberg, The Netherlands978-3540-31210-9. Podlesakova, E., Nemecek, J., Vacha, R., 2002. Critical Values of Trace Elements in Soils from the Viewpoint of the Transfer Pathway Soil–Plant. ROSTINNA VYROVA, 48 (2002(5):193-2002). Prüeß, A., 1992. Vorsorgewrte und Prufwerte fur mobile und mibilisierbare potentiell okotoxische Spurenelenente in Boden. Verlag Ulrivh E, Graner Wendlingen. Pueyo, M., López-Sánchez, J.F., Rauret, G., 2004. Assessment of CaCl2, NaNO3 and NH4NO3 extraction procedures for the study of Cd, Cu, Pb, and Zn extractability in contaminated soils. Anal. Chim. Acta. 504, 217–226. Regulation 26 about reclamation of disturbed areas, improvement of low-productive lands, excavation and utilization of humus layer. State J. 89 (Bg). Regulation 3 about the rates of levels of pollutants in soil. State Journal 36/1979, Amended. State Journal. 71 of August 12, 2008. (Bg). Symeonides, A., McRae, S., 1977. The assessment of plant available cadmium in soils. J. Environ. Qual. 6 (2), 120–122. Tamm, O., 1936. Eine method zur Bestimmung der Anorganischen Komponenten der Gelcomplexen in Boden. Meld zur Statlus Skogs, vol. 19 386–404. Tsolova, V., 2005. Clayey minerals in reclaimed lands at the “Chukurovo” mine region. Soil Sci. Agrochem. Ecol. XL (3), 25–30. Tsolova, V., Misheva, L., 2008. Phytoavailability of heavy metals in contaminated cinnamon soils (chromic luvisol). Ecol. Saf. (ISSN: 1313-2563) 2 (part 2), 353–360.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria Venera Tsolova Tsolova a,⁎, Mariana Blagoeva Hristova a, Jaume Bech Borras b, Núria Roca Pascual b, Martin Dimitrov Banov a a b
N. Poushkarov Institute of Soil Science, Agrotechnologies and Plant Protection, 7, Shoose Bankya, 1080 Sofia, Bulgaria Facultat de Biologia, Universitat de Barcelona, Diagonal, 643, 08028 Barcelona, Spain
a r t i c l e
i n f o
Article history: Received 11 July 2013 Received in revised form 12 February 2014 Accepted 17 February 2014 Available online xxxx Keywords: Soil extraction Technosols geochemistry Pb, Cu, Zn mobility Toxic threshold Technosols pedology
a b s t r a c t The content and availability of Pb, Cu and Zn were determined by the methods of soil extractions with aqua regia, 1 M NH4NO3 and 1 M NH4Ac. Reclaimed soils, which differ in land use, the duration of post reclamation development, geological and geographical characteristics were included in the study. In most pedons trace element total contents are irregular along depth and close to the background values in Bulgarian soils (Pb — 26 μg/g, Cu — 34 μg/g and Zn — 88 μg/g). The copper content greatly varies between the minimum of 8.5 μg/g and the maximum of 500 μg/g. The latter is defined as an intervention concentration by the Bulgarian legislation, and is accepted as a toxic threshold which affects soil functions, the environment and human health. Mobile concentrations of Pb, Cu and Zn are non-toxic assuming 8 μg/g for Cu, 4 μg/g for Pb and 43 μg/g for Zn as acceptable limits of available heavy metals in Technosols with slightly alkaline pH (7.0 - 8.0). The acidic pH (b 6.0) increases the solubility and desorption of zinc and copper, but diversely influences the bioavailability of lead. In acidic Technosols Pb and Cu mobile contents could exceed the Prüeß critical level of 1 μg/g and may provoke independent and joint toxic effects. The lithogenic origin of Cu toxicity which amounted to 47.7 μg available Cu/g soil shows the most serious risk of environmental pollution. Intensive weathering of soil surface layers does not accelerate the trace element bioavailability. Pb, Cu and Zn mobility mostly depends on pH, the content and mineralogy of fine earth fractions (b0.01 mm) and organic carbon pools in studied soils. © 2014 Elsevier B.V. All rights reserved.
Introduction Soils that have originated as a result of mining activity are called dumps, mining soils, drastically disturbed soils, reclaimed soils or anthropogenic soils. In this paper we will refer to the World Reference Base for Soil Resources (IUSS Working Group WRB, 2006) and will name them Technosols (technogenic soils), i.e., soils, which parent materials are exported or produced by human activity and would not otherwise have occurred on the surface. Technosols in Bulgaria have been studied from versatile points of view. Their morphology, mineralogy, geochemistry and pedology as well as the parent materials origin, composition and properties are elucidated (Banov, 1989; Hristova, 2013; Ivanov, 2007; Marinkina, 1999). Stability of soil structure, microbial diversity and activity are often used as indicators of the assessment of reclaimed soils quality and development (Banov, 1989; Dimitrova, 1995, 1996, 2011; Ivanov, 2007; Marinkina, 1999). One of the most important criteria for evaluating the agronomic potential of these soils is the
⁎ Corresponding author at: 7, Shoose Bankya, 1080 Sofia, Bulgaria. Tel.: +359 899424258. E-mail address: [email protected] (V.T. Tsolova).
content of potentially hazardous elements. A few studies indicate that the content and behavior of the risky elements in Technosols, especially of some radionuclides and heavy metals can create a real health danger (Banov et al., 2006; Marinkina, 1999; Misheva et al., 2007; Tsolova and Misheva, 2008). This is typical of areas with local geochemical anomalies, where toxicity may have a long lasting effect. Technosols may also be polluted during the mining and processing of mined ore materials. The combustion of coal, for example, released many chemical elements (C, S, H, K, Ca, Al, Cl, Si, Mg, Zn, Mn, Mo, Rb, Ti, Cu, Co, Cr, Br, Pb, Hg, Sb, Cd), some of which are in significant quantities. They create local anomalies in chemical composition of soils, plants and water. In fact, the vulnerability of Technosols to anthropogenic pollution could be strong. The lack of organic matter combined with low sorption and buffer capacity can lead to a greater risk of heavy metal release after weathering and to their increased mobility and bioavailability. Therefore, it is necessary to assess the risk of environment pollution and to consider the potential threat to soil resources in mine areas. This study deals with the determination of the content and the availability of Pb, Cu and Zn in reclaimed soils (Technosols), built in three mine areas in Bulgaria — Maritsa-Iztok, Chukurovo and Assarel Medet.
http://dx.doi.org/10.1016/j.gexplo.2014.02.019 0375-6742/© 2014 Elsevier B.V. All rights reserved.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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Fig. 1. Technosols located in the Maritsa-Iztok mines area.
Materials and methods
Methodology of the study
Technosols brief description
Field study follows the methodology described in the guidance for soil description (FAO, 2006). The location of the representative profiles conformed to the topography and soil catena concept in all studied spoils. Soil sampling procedure followed BSS ISO 10381-2, 4 (2005).1 The laboratory study involves:
Three sites that differ in geochemistry of parent materials, reclamation method, geographic and geologic particularities, and the duration of post-reclamation development were studied. These specific imprints on soil characteristics should provide information about the phenomena controlling heavy metal availability in Technosols. The studied soils are located in the vicinity of Maritsa-Iztok coal mines, Chukurovo coal mine and the Assarel copper mine. Iztok was the first built dump and the most developed and mature Technosols in the area of Maritsa-Iztok coal mines. It was reclaimed in 1974 by a specially developed technology which was later designated as the main method for agricultural reclamation in Bulgaria (Regulation 26/1996). This approach resulted in formation of a specific soil profile consisting of two major horizons. The surface horizon with a 40 cm depth is a transported humus horizon that consists of humus layers of natural soils occupying the territory prior to mining. The main subhorizon having a depth of 2 m is composed of suitable for reclamation yellow-green clays isolated from the stratigraphic profile of the deposit. Due to the lack of humus material, the described technology is implemented on approximately 1/2 of the dump. The rest of about 70 ha were diverted to forestry reclamation and were directly planted on the layer of clays. The main characteristics of arable soils are illustrated by representative profile 1. Representative profile 2 is situated in the forest part of the dump. The typical landscapes of the two parts of the dump are presented in Fig. 1. Technosols located close to the Chukurovo mine represent a heterogeneous mixture of Miocene geologic materials that covered the coal horizons. Soils were directly reclaimed (without humus cover or amendment) with forest species: pine (Pinus nigra J.F.A.) and birch (Betula pendula Roth.) in Zapad dump (representative profile 3) and just pine — Mlada gvardia dump (representative profile 4). Zapad dump is also among the most mature Technosols in Bulgaria, with 45 year old genesis. Mlada gvardia is a younger soil with 25 years of development. The typical landscapes of the objects are shown on Fig. 2. As a result of the activity of Assarel Medet copper plant there are few constructed dumps in the region, which are distinguished for their high copper content and strong acidity. The object of this study is the Severozapad dump, which had been built about 20 years ago. The dump is chemically reclaimed with 0.15 kg lime/m2 and covered with manure in norm of 6 kg/m2 in order to reduce the adverse impact on the environment. Biological reclamation is carried out with two plant species: birch (Betula pendula Roth) and acacia (Acacia Mill.), which form separate ecosystems (Fig. 3). Soils' characteristics are illustrated by representative profile 5.
1. Pretreatment of samples for physico-chemical analysis — BSS ISO 11464 (2012). 2. Determination of pH in H2O — by the FAO method (Dewis and Freitas, 1970). 3. Determination of effective cation exchange capacity and base saturation level using barium chloride solution — BSS ISO 11260 (2011). 4. Particle size distribution — method of Kachinsky (1958). This method differs from the method described in ISO 11277 (2009) (by sieving and sedimentation) mostly in sample pretreatment (NaOH) and sieve mesh sizes. The following sizes of major fractions are recognized by Kachinsky: Sand — this fraction involves particles with 1.00–0.05 mm equivalent spherical diameter; Silt fraction — from 0.05 to 0.001 mm equivalent diameter; and Clay b 0.001 mm. 5. Determination of total content of trace metals — method of soil extraction with aqua regia (ISO 11466, 1995) and EAAS (ISO 11047, 1998) using spectrometer Perkin-Elmer 2100. The content of heavy metals determined by soil extraction with aqua regia is conventionally called pseudototal, since there are other solvents that have more destructive effect and release larger amounts of heavy metals. Despite of this drawback, the method is standardized and widely used in the analytical practice. The content of heavy metals determined by aqua regia extraction will be used later in the meaning and for evaluation of the total content of heavy metals in studied Technosols. 6. Determination of easy soluble trace element contents. Two extraction methods were used to determine the mobility of heavy metals: □ Extraction with 1 M NH4NO3 — ISO 19730 (2008). Extraction of soil with 1 M NH4NO3-solution is used to determine readily soluble trace element contents. Like other salt solutions, 1 M NH4NO3 soil extraction method is also used to predict trace element contents in plants and the environmental risk assessment for soil contamination (Birke and Werner, 1991; Prüeß, 1992). □ 1 M NH4Ac (pH 7) — Pansu and Gautheyrou (2006). 1 M ammonium acetate (pH 7) is perhaps the most preferred reagent for exchangeable metal analysis because of the metal complexing power of the acetate ion, which prevents readsorption 1
Bulgarian State Standard.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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3
Fig. 2. Technosols located in the Chukurovo mine area.
or precipitation of released metal ions (Podlesakova et al., 2002). This method is suitable for determination of readily soluble and plant available trace element contents (Gryschko et al., 2005) although it produces very low results of Cu available content (Symeonides and McRae, 1977). Generally, these procedures indicate the content of metals associated with soil components by liable binds especially their water soluble compounds and complexes with organic matter, exchangeable content of metals nonspecifically and specifically adsorbed by soil components as well as the metals co-precipitated by adsorption or occlusion (absorbed metals). Thereby we should agree with Gryschko et al. (2005) and admit that the processes influencing the mobility of trace elements are too complex to expect that just one soil extraction method
can always guarantee a correct prognosis of toxicological significant element contents. The extraction duration needed to establish the equilibrium between the processes of adsorption and desorption of elements was empirically confirmed for Technosols. Soil:solvent ratios were modified in order to increase the measurement sensibility — the extraction ratio when using 1 M NH4NO3 is 20:50 g:ml and 10:200 g:ml soil:1 M NH4Ac. 7. Assessment of pollution. A few legal criteria are used for assessing soil pollution with heavy metals: □ Limit values representing maximum permissible and intervention concentrations of heavy metals determined by the Bulgarian legislation (Table 1). Maximum permissible concentration is the
Fig. 3. Technosols located in the Assarel Medet mine area.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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Table 1 Maximum permissible and intervention concentrations of heavy metals and metalloids in soils (determined in aqua regia as total concentrations, in μg/g) — Regulation 3 (2008). Elements
pH (H2O)
Cu
b6.0 6.0–7.4 N7.4 b6.0 6.0–7.4 N7.4 b6.0 6.0–7.4 N7.4
Pb
Zn
Maximum permissible concentrations
Intervention concentrations
Arable lands
Permanent grasslands
80 150 300 60 100 120 200 300 400
80 140 200 90 130 150 220 390 450
500
500
900
content of harmful substance in the soil, in μg/g, the exceeding of which, under certain conditions, leads to disturbance of soil functions and to danger for the environment and human health. Intervention concentration is the pollutant content in soil which leads to disruption of soil functions and to danger for the environment and human health. 8. Statistical analysis. Statistical data analysis was performed using Statgraphics Centurion XVI which implements many commonly used statistical procedures. Data from extractions were additionally assessed by the F criterion, which is appropriate for comparison of the dependent quantities by their average means (Lidansky, 1988). In this approach the differences between dependent members of the compared samples (extracts) form a new variation row with new average means (d). The value of the F is calculated by the formula: F = (Σd)2 / Σ(d2), (I). Differences are considered statistically reliable when F ≥ Fcritical at df = n, where df is the degrees of freedom, n — number of samples, and P — confidential level. Results and discussion Trace metal geochemistry of Technosols at Maritsa-Iztok mines area Technosols located in the region of Maritsa-Iztok coal mines have different solums due to the applied reclamation technology and land
use. Humus reclaimed soils have a distinct humus horizon wherein the nutrients are concentrated (Table 2). In non humus reclaimed soils the organic matter content is higher, as a result of the of black clays presence. Black clays are abundantly mixed with fine coal dust and bear an increasing of clay fraction content and decreasing of pH (Tables 2, 3). The high clay content (mostly shrink-swelling) lends vertic properties and promotes long-lasting water saturation of soils. Black clays also provoke almost 100% increase of the total element contents (Table 3, profile 2), but do not create a risk of pollution. Pedogenic clay accumulation in subhorizon (Cccg1 25–70) goes with a detectable accumulation of (pseudo)total copper. The contents of the other elements in profile depth are not attached to the clay fraction. The contents of Pb, Cu and Zn in profile 1 are closer to the background values of trace elements in Bulgarian soils than those in profile 2 (Table 4). As we mentioned above, these soils are made of non-toxic, environmentally friendly and agriculturally suitable geological materials. Total element content increases toward Pb b Cu b Zn and forms the opposite trend compared to mobile concentrations. NH4NO3-extraction of soils with pH N 7 (profile 1 — humus reclaimed soils and profile 3 — soils near Chukurovo mine with humus layer development) produces very low element contents which lay below the level of detection. Bucher and Schenk (2000), and Köster and Merkel (1982) also announced that neutral salt (NH4NO3 and CaCl2) extraction could provide undetectable amounts of Cu and Pb. Since Cu and Pb mobility depends on pH, it is important to consider the soil pH in their determination. For this reason, mobile content of heavy metals in soils with pH N 7.0 was determined by extraction with NH4Ac. The extraction method with NH4NO3 was applied for profiles where pH b 7.0. The mobile concentrations of lead, copper and zinc in humus reclaimed soils vary in non-toxic and safe interval from the environmental viewpoint (Table 3). Few acceptable limits of available heavy metals (extracted with NH4Ac) have been taken into consideration to estimate the obtained values: 8 mg/kg for Cu and 43 mg/kg for Zn assumed by Davidescu et al. (1998) and Chapman (1971) threshold for NH4OAc-extractable Pb who predicted that as little as 4.0 ppm can prove toxic to some plants. In these soils the content of bioavailable Cu and Zn gradually increases in depth, while Pb prevails in areas affected by a noticeable presence of Fe minerals (30–70 cm). Aualiitia and Pickering (1987)
Table 2 Main physico-chemical characteristics of Technosols at Maritsa-Iztok mines area. Profile view
Horizon, depth (cm)
Sand (%)
Silt (%)
Technosols reclaimed with humus layer — profile 1 Аpk (0–30) 17.6 ± 7.2 36.9 Ccc1 (30–50) 36.5 ± 6.9 26.3 Сcc2 (50–70) 31.8 ± 6.7 28.5 Сcc3 (70–100) 29.8 ± 2.4 30.7
Clay (%)
Org. C (%)
Carbonates (%)
Sorption capacity (cmol(+)/kg)
± ± ± ±
13 16 4.5 7.3
45.5 37.2 39.8 39.5
± ± ± ±
13 3.8 0.4 1.7
2.04 ± 0.1 0.75 0.34 0.23
0.39 2.07 1.34 2.77
± ± ± ±
0.5 0.4 0.1 0.6
43.9 33.1 27.9 28.0
Technosols reclaimed without humus layer — profile 2 АCk (0–25) 7.84 ± 8.6 21.5 ± Cccg1 (25–70) 8.09 ± 7.6 11.3 ± Cccg2 (70–100) 16.8 ± 7.4 17.5 ± Сccg3 (N100) 6.05 ± 3.5 26.6 ±
5.4 3.3 6.7 4.9
70.7 ± 80.6 ± 65.7 ± 67.4 ±
10 6.5 0.3 6.6
2.54 1.46 1.28 0.97
0.49 0.38 0.67 0.41
± ± ± ±
0.2 0.3 0.3 0.2
40.3 37.9 38.8 32.6
± ± ± ±
0.4 0.7 0.3 0.2
Legend: Sand fraction includes particles with 1.00–0.05 mm equivalent spherical diameter; Silt fraction — from 0.05 to 0.001 mm equivalent diameter and Clay b 0.001 mm.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
V.T. Tsolova et al. / Journal of Geochemical Exploration xxx (2014) xxx–xxx
5
Table 3 Total and exchangeable contents of Pb, Cu and Zn in Technosols at Maritsa-Iztok mines area. Horizons, depth (cm)
pH
Pb Total
Cu
Zn
Extractable
%
Total
Technosols reclaimed with humus layer — profile 1 Аpk (0–30) 7.25 24.8 ± 3.18 Ccc1 (30–50) 7.75 25.8 ± 5.01 Сcc2 (50–70) 7.25 26.3 ± 2.02 Сcc3 (70–100) 7.30 28.0 ± 6.54 Average 7.4 26.2
2.35 2.95 3.10 2.50 2.73
9.5 11.4 11.8 8.9 10.4
30.7 25.5 31.8 30.0 29.5
± ± ± ±
Technosols reclaimed without humus layer — profile 2 АCk (0–25) 6.10 34.2 ± 3.18 Cccg1 (25–70) 5.95 32.8 ± 4.80 Cccg2 (70–100) 5.80 37.3 ± 2.36 Сccg3 (N100) 6.00 37.7 ± 1.76 Average 6.0 35.5
0.88 1.15 0.98 0.73 0.94
2.6 3.5 2.6 1.9 2.7
65.5 70.3 63.2 55.2 63.6
± ± ± ±
Extractable
%
Total
3.21 0.50 3.06 0.00
0.25 0.35 0.45 0.50 0.39
0.8 1.4 1.4 1.7 1.3
57.8 44.0 43.3 37.2 45.6
± ± ± ±
3.61 10.6 4.65 4.19
0.15 0.53 0.40 1.03 0.53
0.2 0.8 0.6 1.9 0.9
79.2 ± 69.8 ± 70.0 ± 72.2 ± 72.8
Extractable
%
6.05 7.40 8.28 14.8
0.20 0.30 0.40 0.60 0.38
0.4 0.7 0.9 1.6 0.9
4.07 8.31 12.3 14.9
0.85 2.48 4.43 2.28 2.51
1.1 3.5 6.3 3.2 3.5
Legend: % designates the relative amount of exchangeable content of the elements, in percent.
and Elzinga and Sparks (2002) established that Pb may be retained by hydrated Al and Fe oxides or amorphous silica emerging from the edges of weathered silicate minerals. Such retention is specific in nature and favored by low pH. Pb is also known to form various compounds with apatite and, in calcareous soils, with carbonate minerals (Cao et al., 2004). In profile 2 the mobile contents (1 M NH4NO3-extractable) seem to not trend to any soil components presumably due to initial pedogenesis and ped's heterogeneous organization. However, the mobile Pb predominates in the upper part of the soils (25–70 cm); zinc — between 70 and 100 cm and Cu — below 100 cm. In order to assess the risk for contamination of forest ecosystems we used the Prüeß critical levels. Prüeß (1992) fixed 1 mg/kg for Pb and Cu and 30 μg/g for Zn (based on 1 М NH4NO3 extract) as critical values for soil phytotoxicity. Thus, lead may cause toxic effect on all forest species because it prevails in 25–70 cm depth while Cu occurs at the deeper horizons and might have the more limited effect. However, the high clay content additionally limits the mobility of the studied elements. It should be noticed that the reagent is more efficient and extracted more zinc compared to profile 1 bearing in mind the little differences between total contents. Gryschko et al. (2005) reveal that chemical mechanisms involved when metals are extracted with 1 M NH4NO3 are a slight decrease in pH of the extraction solution and an increase in ionic strength. Most of the colloids and parts of the soluble metal– organic complexes are precipitated due to the high ionic strength. High ionic strength also decreases the activity of metal–OH+ species and the electrostatic potential of the particle surfaces, which in turn, increases desorption of heavy metal cations from negatively charged soil surfaces. Generally, the effects of high ionic strength on desorption of trace elements and on precipitation of colloids and soluble metal organic complexes and the formation of soluble metal ammine complexes have to be considered. The formation of amine complexes has been described as a heavy metal mobilizing mechanism in ammonium based extraction solutions (Lebourg et al., 1996; Pueyo et al., 2004). The trend of Pb, Cu and Zn lower availability in surface horizons (better pronounced in profile 2) might be associated with biological migration (uptake). Simple variation analysis shows the main sources of mobile zinc, copper and lead in slightly alkaline soils (profile 1, Fig. 4). Lead and copper mobile contents do not directly depend on their total concentrations (R2 b 0.20) and reveal the complexity of exchange processes in soil matrix. Lead exchangeable content basically depended on the content of dust earth fraction (sizes from 0.005 to 0.001 mm, R2 =0.99) and organic carbon (R2 = 0.70), which is also associated with dust fraction. Still, the mineral phase is not the collector of the pseudo total lead — the organic matter is his main accumulation pool and source (Fig. 4). Copper is associated with the fine mineral phase (size particles b 0.01 mm, R2 = 0.83), and the content of its exchangeable
forms depends mainly on the content of the organic matter (R2 = 0.90) and colloid exchange capacity (Fig. 4). The correlations between total and mobile concentrations of elements are better pronounced in profile 2 (R2Cu,Pb = − 0.70; R2Zn = −0.81). The criterion F also shows a high confidential level of the differences (≥F0,01) and close correlation between pairs of values. In this profile, a cross-correlation between the total concentrations of copper and mobile lead appears (R2 = 0.91). This allows us to assume that the exchangeable lead might be sorbed (adsorbed or absorbed) by the native copper, which occurs in abundance in Bulgaria (Kovachev, 1994) or is released from metal sulphides which are also found in the stratigraphic profile of the deposit. Perhaps the dust fraction consists of these minerals because it totally correlated with mobile lead (R2 = 0.999). Calculated relative contents indicate that about 10% of lead, 1% of copper and 0.9% of zinc are easily exchangeable and could pass in the soil solution. Trace metal geochemistry of Technosols at Chukurovo mine area The main difference between Technosols located in Chukurovo mine area is pH which allows us to study metal mobility in various geochemical environments. Particle size distribution along with profile depth could also reveal the behavior and fate of the studied metals in Technosols. Young soils (profile 4) are rich in pyrite and abounded with coal admixtures which reflect on pH and organic carbon content (Table 5). Both soils have very low sorption capacity prompted by domination of kaolinite and micas (illite) and negligible content of smectite minerals (Tsolova, 2005). In geochemical aspect, the genetically older soils (profile 3) represent a zone with higher trace element diffusion wherein the minimum values of 8.5 μg/g for Cu, 15.7 μg/g for Pb and 39.8 μg/g for Zn are established (Table 6). The zones of maximum accumulation of clay and silt fractions in both forest soils are zones of maximum accumulation of the studied elements. Slightly alkaline soils (considering the pH average value) copy the trend established in slightly alkaline soils located in Maritsa-Iztok mines area — higher amounts of mobile lead than those of zinc and copper. Zinc concentrations in both soils flow within the safe interval, although the acidic environment enhances its exchangeable content (profile 4). Considering the acid pH and Prüeß (1992) precautionary Table 4 Background concentrations of heavy metals and metalloids in soils (determined as a total concentrations in aqua regia, μg/g) — Regulation 3 (2008). As
Cd
Cu
Cr
Ni
Pb
Zn
Hg
Co
10
0.4
34
65
46
26
88
0.03
20
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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V.T. Tsolova et al. / Journal of Geochemical Exploration xxx (2014) xxx–xxx
Fig. 4. Statistically significant relationships in profile 1.
Table 5 Main physico-chemical characteristics of Technosols at Chukurovo mine area. Profile view
Silt (%)
Clay (%)
Org. C (%)
Carbonates (%)
Sorption capacity (cmol(+)/ kg)
Technosols “Zapad” — profile 3 АС (0–5) 49.3 С (5–22) 50.8 Сgк1 (22–52) 30.2 Сgк2 (52–74) 42.7 Сg1 (74–100) 44.8 Сg2 (N100) 57.4
41.4 37.0 47.9 42.6 43.6 35.4
9.40 12.4 22.0 14.8 11.8 7.35
1.69 0.62 0.69 0.64 0.49 –
0.00 0.00 0.62 ± 0.4 0.62 ± 0.4 0.00 0.00
12.9 10.0 16.0 11.5 11.5 10.3
Technosols “Mlada gvardia” — profile 4 С1 (0–35) 34.7 С2 (35–60) 16.0 Сg (60–90) 20.8
55.4 64.1 60.3
10.0 ± 1.3 20.0 ± 0.3 19.0 ± 0.1
0.00 0.00 0.00
13.0 18.2 17.0
Horizons, depth (cm)
Sand (%)
values, the harmful biological effect of lead could be expected in these soils. Trace elements formed several statistically significant correlations in genetically older soils with versatile pH (profile 3). Pb total and mobile contents are closely bound up with fine fraction (b0.01 mm) and cation exchange. The negative correlations between Pb mobile content, fine earth fraction (b 0.01 mm) and cation exchange (R2 = − 0.85; R2= − 0.62) confirmed the specific adsorption of Pb. The mobile Cu is not associated with any soil component and Zn mobility is determined by the organic carbon content (R2 = 0.90). Due to the initial process of humus accumulation and transformation, and the presence of less active clays, soils fixed about 3 μg/g lead, 0.3 μg/g copper and 0.7 μg/g zinc.
± ± ± ± ± ±
1.1 6.0 8.7 1.1 3.0 0.8
± ± ± ± ±
0.5 0.4 0.0 0.0 0.2
2.28 ± 0.2 4.57 ± 0.2 5.21 ± 0.9
The lower pH in profile 4 increases the solubility and desorption of zinc, but slightly influences the bioavailability of lead and copper. Pb mobile content could exceed the critical level of 1 μg/g and may provoke soil toxicity. The intensive weathering of soil surface does not increase the elements' soluble content, except for Zn in profile 3. Obviously, the surface accumulation of non silicate and inorganic amorphous compounds of Fe, Al and Mn2 established in these soils (Marinkina and Djokova, 2002) is irrelevant to Pb and Cu fixation. It is reasonable to suggest
2
Methods of Merha and Jackson (1960) and Tamm (1936) were used.
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
Q18
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7
Table 6 Total and exchangeable contents of Pb, Cu and Zn in soils at Chukurovo mine area. Horizons, depth (cm)
pH
Pb
Cu
Total
Zn
Extractable
%
Total 11.4 ± 13.6 ± 14.6 ± 11.9 ± 9.13 ± 8.50 ± 11.5
Technosols “Zapad” — profile 3 АС (0–5) 6.25 С (5–22) 6.45 Сgк1 (22–52) 7.55 Сgк2 (52–74) 7.70 Сg1 (74–100) 7.50 Сg2 (N100) 7.55 Average 7.17
19.8 ± 17.3 ± 27.0 ± 21.5 ± 16.5 ± 15.7 ± 19.6
2.5 0.3 4.6 4.5 1.4 0.8
2.45 2.55 1.95 1.90 2.85 3.05 2.46
12.4 14.7 7.2 8.8 17.3 19.4 13.3
Technosols “Mlada gvardia” — profile 4 С1 (0–35) 4.50 С2 (35–60) 4.40 Сg (60–90) 4.40 Average 4.4
22.2 ± 2.4 33.8 ± 0.3 31.6 ± 1.3 29.2
2.03 2.05 1.58 1.89
9.1 6.1 5.0 6.7
Extractable
%
Total
0.2 2.6 0.5 0.2 1.2 0.7
0.30 0.25 0.25 0.20 0.35 0.25 0.27
0.6 0.5 0.5 0.5 0.8 0.6 0.58
47.1 ± 46.8 ± 54.9 ± 41.7 ± 44.0 ± 39.8 ± 45.7
0.6 0.2 4.0 2.0 1.0 2.2
1.40 0.65 0.55 0.45 0.60 0.70 0.73
13.4 ± 0.9 18.3 ± 0.4 17.5 ± 0.7 16.4
0.23 0.15 0.15 0.18
1.7 0.8 0.9 1.1
59.7 ± 4.2 66.4 ± 3.0 65.6 ± 2.0 63.9
6.23 9.15 8.28 7.89
that these compounds may facilitate Zn transport across Technosols, composed of Miocene sediments.
Trace metals geochemistry of Technosols at Assarel Medet mine area Soils located in the area of Assarel Medet copper mine are gravel soils, poor of colloids and organic matter (Table 7). Signs of water erosion impact indicate that surface runoff could play a significant role for redistribution of soil particles in the environment. Geochemistry of Assarel's soils is remarkable for high copper content. The obtained copper values in the root layer of studied soils are about 2 times higher compared to the maximum permissible content in grasslands (Tables 1, 8). In deeper layer, the copper total content coincides with the intervention concentration (500 μg/g) which is assumed as very risky for environment and human health. Soil reclamation leads to the formation of a sublayer with new geochemical distribution of the elements. It displays as lead and copper dispersion and zinc concentration. It could be said that the reclamation masks the lithogenic characteristics of parent materials and enhances a mosaic nature of spatial (3D) distribution of trace elements (Table 8). The implemented chemical reclamation reduces the mobility of copper about 100 times and abates its phytotoxic content to the safe level. It
Extractable
% 3.0 1.4 1.0 1.1 1.4 1.8 1.59
10.4 13.8 12.6 12.3
also immobilizes the solubility of Zn and strongly reduces its availability to another level (b0.4 μg/g) which may cause Zn deficiency. Acid environment reduces the mobile lead content (average about 6 times), in contrast to mobile zinc content, which increases about 30 times. The maximum mobile concentration of Cu 47.7 μg/g established in non reclaimed layer of Assarel's soils does critically exceed the Prüeß threshold of 1 μg/g and shows the most serious risk of environmental pollution. Due to the limited number of samples no explicit conclusions could be made at present. Conclusion Technosols located in coal regions are geochemical zones with low content of Pb, Cu and Zn. In most of these pedons the elements' total contents are irregular along depth and close to the background values in Bulgarian soils. Technosols in Assarel copper mine area featured high total copper content. It coincides with the intervention concentration of 500 μg/g, which is assumed to seriously damage soil functions, the environment and human health. • Mobile concentrations of lead, copper and zinc are non-toxic assuming 8 mg/kg for Cu, 4 mg/kg for Pb and 43 mg/kg for Zn as acceptable limits of available heavy metals in Technosols with slightly alkaline pH.
Table 7 Main physico-chemical characteristics of Technosols in Assarel Medet mine area (profile 5). Profile view
Horizons, depth (cm)
Sand (%)
Silt (%)
Clay (%)
Org. C (%)
Carbonates (%)
Sorption capacity (cmol(+)/kg)
АС (0–5) 1С (5–25) 2С (25–70)
89.9 82.0 83.7
8.40 15.0 13.3
1.73 3.00 3.00
0.88 ± 0.1 0.24 ± 0.1 0.42 ± 0.0
0.00 0.00 0.00
14.6 10.5 21.5
Table 8 Total and mobile contents of Pb, Cu and Zn in soils at Assarel Medet mine area. Horizons, depth (cm)
pH
Technosols “Assarel Medet” — profile 5 АС (0–5) 6.30 1С (5–25) 6.00 2С (25–70) 3.40 Average 5.23
Pb
Cu
Zn
Total
Extractable
%
Total
Extractable
%
Total
Extractable
%
30.6 22.0 27.5 26.7
0.60 0.55 0.10 0.42
1.96 2.50 0.36 1.6
480 417 500 466
0.40 0.95 47.7 16.4
0.08 0.23 9.54 3.3
75.3 102 77.8 84.9
0.20 0.40 6.60 2.40
0.27 0.39 8.48 3.1
Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019
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• The soil acidic pH increases the solubility and desorption of zinc and copper, but diversely influences the bioavailability of lead. Pb and Cu mobile contents could exceed the critical level of 1 μg/g and may provoke independent and joint toxic effects in acidic Technosols. The lithogenic origin of Cu toxicity that amounted to 47.7 μg available Cu/g shows the most serious risk of environmental pollution. • Intensive weathering of soil surface layers does not accelerate the trace element bioavailability. Pb, Cu and Zn mobility mostly depends on the pH, content and mineralogy of fine earth fractions (b0.01 mm) and organic carbon pools in the studied soils. References Aualiitia, T.U., Pickering, W.F., 1987. The specific sorption of trace amounts of Cu, Pb and Cd by inorganic particulates. Water Air and Soil Pollution 35, 171–185. Banov, M., 1989. Study of Some Soil-genetic Changes in Lands Reclaimed Without Humus Cover from the Region of Maritsa-Iztok Mines. Ph.D Thesis N. Poushkarov Institute of Soil Science, Sofia (188 pp.). Banov, M., Tsolova, V., Misheva, L., 2006. Properties and reclamation of lands disturbed by geotechnologic uranium mining. Ecol. Ind. 8 (1–2), 60–63. Birke, C., Werner, W., 1991. Eignung chemischer Bodenextraktions-verfahren zur Prognose der Schwermetallgehalte in Pflanzen. Forschungszentrum Jülich GmbH, Berichte aus der ökologischen. Forschung Band, 6 224–288. BSS EN ISO 11260, 2011. Soil Quality — Determination of Effective Cation Exchange Capacity and Base Saturation Level Using Barium Chloride Solution. BSS ISO 10381-2, 2005. Soil Quality — Sampling — Part 2: Guidance on Sampling Techniques. BSS ISO 10381-4, 2005. Soil Quality — Sampling — Part 4: Guidance on the Procedure for Investigation of Natural, Near-natural and Cultivated Sites. BSS ISO 11464, 2012. Soil Quality — Pretreatment of Samples for Physico-chemical Analysis. Bucher, Annette S., Schenk, Manfred K., 2000. Characterization of phytoavailable copper in compost–peat substrates and determination of a toxicity level. J. Am. Soc. Hortic. Sci. 125 (6), 765–770. Cao, X., Ma, L.Q., Rhue, D.R., Appel, C.S., 2004. Mechanisms of lead, copper and zinc retention by phosphate rock. Environ. Pollut. 131, 435–444. Chapman, H.D., 1971. Proceedings of the International Symposium on Soil Fertility Evaluation. New Delhi, vol. 1, pp. 927–947. Davidescu, D., Davidescu, V., Lacatuşu, R., 1998. Microelements in Agriculture. Publishing House of Romanian Academy, Bucharest (Published in Romanian, 278 pp.). Dewis, J., Freitas, F., 1970. Physical and Chemical Methods of Soil and Water Analysis. Soils Bulletin, 10. FAO, Rome (275 pp.). Dimitrova, A., 1995. Microbiological activity of substrata meant for reclamation of lands disturbed by mine industry. Soil Sci. Agrochem. Ecol. (2), 60–61. Dimitrova, A., 1996. Two levels of bioassay for study of soil productivity. Proceeding of the International Conference of Land Degradation, 10-14.06, 1996, Adana, Turkey (4:250). Dimitrova, A., 2011. Biotechnoloical methods and manners for increasing the effectiveness of non humus reclamation. Proceedings of International Conference “100 years Soil Science in Bulgaria”, Part 2, pp. 861–865. Elzinga, E.J., Sparks, D.L., 2002. X-ray absorption spectroscopy study of the effects of pH and ionic strength on Pb(II) sorption to amorphous silica. Environ. Sci. Technol. 36, 4352–4357. FAO, 2006. Guidelines for Soil Description, Fourth edition. (Rome, 97 pp.). Gryschko, Rainer, Kuhnle, Rainer, Terytze, Konstantin, Breuer, Jörn, Stahr, Karl, 2005. Soil extraction of readily soluble heavy metals and As with 1 M NH4NO3-solution — evaluation of DIN 19730. J. Soils Sediments 5 (2), 101–106. http://dx.doi.org/10.1065/ jss2004.10.119. Hristova, M., 2013. Content and Availability of Microelements–Metals in Technogenic Soils. Ph.D Thesis N. Poushkarov Institute of Soil Science, Sofia 140 pp.
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Please cite this article as: Tsolova, V.T., et al., Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria, J. Geochem. Explor. (2014), http://dx.doi.org/10.1016/j.gexplo.2014.02.019