Sequential extraction of Zn in deposol

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1 ORIGINAL SCIENTIFIC PAPER Sequential extraction of Zn in deposol Ivana Trajkovic 1, Vlado Licina 1, Zoran Atanackovic 1 1 Belgrade University, Faculty of Agriculture, Nemanjina 6, Belgrade, Serbia, (ivana.trajkovic@agrif.bg.ac.rs) Abstract The aim of the study is prediction of environmental risk of heavy metal by using sequenstial extraction. The soil samples were collected at two different locations, two coal mining areas in Serbia which are potential contaminant spots. Tessier's sheme was applayed for soil fractionation. Fractions were rearranged into five fractions defined as two acid soluble, reducible, oxidisable and residual. Highest concentration of Zn was found in fifth fraction (residual fraction) at both locations, but samples from Kolubara had higher concentration. Lowest concentration of Zn was found in water-soluble and exchangeable adsorbed fraction which is environmentaly dangerous. Key words: zinc, sequential extraction, deposol, environment Introduction The mobility of metals in the environment depends strongly on their chemical forms or type of the binding of the element. The determination of total concentrations in soils does not give sufficient information about the mobility of metals. In many instances, biological toxicity of the elements is related more closely to the concentrations of particular physicochemical forms (Merian, 1991). Speciation studies of trace elements in various phases in the environment are widely used in investigating the effects of a particular element in the ecosystem. Metal cations in soils may be present in several different physico-chemical forms, i.e. as simple or complex ions, as easily exchangeable ions, as organically bound, as occluded by or coprecipitated with metal oxides or carbonates or phosphates and secondary minerals, or as ions in crystal lattices of primary minerals (Lake, 1984.). In order to assess the chemical forms of heavy metals in soils, extraction procedures have been applied, both as single and sequential schemes. The use of sequential extraction furnishes detailed information about origin, mode of occurrence, mobilization and transport of trace metals. Many of the sequential extraction schemes employed are based on the five-stage procedure of Tessier et al. (Zemberiova, 2006.) The fate of trace elements added to soils is controlled by adsorption and subsequent redistribution among the solid phase, e.g. by diffusion into soil minerals and complexation by organic matter (Brümmer, 1986; McBride, 1989). Such processes may reduce metal mobility, causing accumulation of trace metals added to soils. Conversely, remobilization of trace metals previously fixed by soil constituents, e.g. by changing ph or redox conditions, is affected by metal fractionation (Karczewska, 1999) Therefore, determining trace metal fractionation in soils is essential in predicting the fate of trace metals as affected by soil genesis or anthropogenic impacts, i.e. for long-term risk assessment (Hirner, 1992). Moreover, methods for metal fractionation are required for the assessment of remedial needs at contaminated sites and may be used to check on the success of remedial actions, e.g. metal immobilization or removal from soil. Various sequential extraction procedures have been proposed and modified for diverse soil conditions. A method proposed by Teissier et al.(1979) initially for sediments, has been applied to soils (Clevenger, 1990; Chlopecka, 1993). Total metal content of soils is useful for many geochemical applications but often the th Croatian & 8 th International Symposium on Agriculture Dubrovnik Croatia

2 speciation (bioavailability) of these metals is more of an interest agriculturally in terms of what is biologically extractable (Cottenie and Verloo, 1980). The procedure adapted by Tessier et al. (Tessier et al,1979) is generally accepted as the most commonly used protocol followed closely by the BCR (Ryan et al., 2008,Shan and Chen, 1993) but is still plagued by limitations discussed below. The theory behind SEP is that the most mobile metals are removed in the first fraction and continue in order of decreasing of mobility. All SEPs facilitate fractionation. Tessier et al. named these fractions exchangeable, carbonate bound, Fe and Mn oxide bound, organic matter bound, and residual. These are also often referred to in the literature as exchangeable, weakly absorbed, hydrous-oxide bound, organic bound, and lattice material components, respectively (Maiz et al., 2000). Typically metals of anthropogenic inputs tend to reside in the first four fractions and metals found in the residual fraction are of natural occurrence in the parent rock (Ratuzny et al., 2009.) Material and methods Soil samples were taken from two coal mine area in Serbia, Kostolac and Kolubara. Three depth were sampled (0-30cm, 30-60cm and 60-90cm). Tessier (1979) analytical procedure were used. Steps of procedure were given bellow. 1. Water-soluble and exchangeable adsorbed ml of 0.1 M CaCl 2 (ph 7.0) were added to 10g air-dried soil (<0.25mm). After shaking over head for 20 min at 20ºC, samples were filtrated; 2. Specifically adsorbed and carbonate bound ml of 1 M NaOAc (ph 5.0) were added to 10g air dried (<0.25mm). After shaking over head for 5h at 20ºC, samples were filtrated; 3. Metals bound to Mn and Fe oxides - in plastic centrifuge vials were weighed 2.5g sample. After repeated extraction of the first two fractions, they were rinsed of excess extraction solution with deionized water. After this it was added 50ml of 0.04 M NH 2 OH- HCl in 25% HOAc, (adjusted to ph 3.0). The vials were placed in a water bath and kept 6 h at 95 C, and shaked periodically. After that, the vials were make up to volume of 50 ml of deionized water and shaked over head for 10 min, solution was separated by centrifugation(10min at 3000 min -1 ) and filtred in polyethtlene bottles.for extraction remainig solution, 20 ml of deionized water (5 min shaking over head and centrifugation (10min at 3000 min -1 ) ; 4. Metals bound to organic matter: 7.5 ml of 0.02 M HNO 3 and 12.5 ml of 30% H 2 O 2,(adjusted to ph 2.0) were added and vials were placed in a water bath at 85 C for 2 hours, periodically shaked. After cooling, 7.5 ml of 30% H 2 O 2 ( ph 2.0) were added and the vials were returned to 85 C for next 3 hours, occasionally shaked. After cooling, it was added 12.5 ml of 3.2 M NH4OAc in 20% HNO3, to prevent readsorption of metals. The final volume of 50 ml adjusted by adding deionized water. The vials were shaked over head for 30min, and solution were separated by centrifugation (10 min at 3000 min -1 ) and filtred in polyethylene bottles.the remaining solution was extracted with 20 ml of deionized water (5min shaking over head and centrifugation 10 min at 3000 min -1 ); 5. Residual fraction The remaining soil was digested by aqua regia according Blum.et al. (1989). Initial samples were also digested by aqua regia. Results obtained by sequential extraction are particularly susceptible to irreproducibility since errors can easily be propagated between steps. Sources of recovery error in sequential extraction schemes include losses during the inter-stage washing process, sample heterogeneity and summing errors when the trace metal values are near the analytical detection limit. An important consideration in the reliability of a sequential extraction data is the percent recovery relative to a single digestion using a mixture of strong mineral acids, i.e. gross total. 48. hrvatski i 8. međunarodni simpozij agronoma Dubrovnik Hrvatska 107

3 Statistical procedure Statistical data were done in sigma plot. The recovery rate (definded by the sum of five fractions compared to a single digestion by aqua regia) was evaluated by matched pairs signed rank test. Corelations were done by Pearson product moment. Results and discusion The recovery rates defined as the sum of five fractions compared to a single digestion by aqua regia were satisfactory. The difference in the median values between the two groups is not great enough to exclude the possibility that the difference is due to random sampling variability, there is not a statistically significant difference (P = 0.589). Total content of Zn are shown in Table 1, colone AG, the relative distribution of this metal among operationally definded fractions is depicted in Figure 1. Figure 1 Content of Zn in difernt fractions in deposols In all samples the highest concentration of Zn was in the fifth fraction (residual fraction). Samples from Kolubara (30-60 cm) had highest concentration in residual fraction (up to mg/kg). In this residual fraction, the metals have the strongest association with the crystalline structures of the minerals and therefore are the most difficult to separate. Highest concentration of Zn found in Kostolac was at 0-30 cm depth, also in residual fraction (24.30 mg/kg). Metals bound to Fe and Mn oxides theoretically represent the contents of each metal bound to iron and manganese oxides that would be released if the solid matrix were subjected to more reducing conditions. However, the levels extracted in this stage would be influenced by the efficiency and selectivity of the reagents used in previous stages. Therefore, the results may be too high if the carbonates have not been completely dissolved or too low if part of the iron and manganese hydroxides have already been extracted. These oxides are well known sinks in the surface environment for heavy metal sand are thermodynamically unstable under the anoxic circumstances. Organic bond fractions shows the amount of metal bound to organic matter and sulphurs, which would be released into the environment if conditions became oxidative. Lowest concentration of Zn was found in first two fractions (water-soluble and exchangeable adsorbed and specifically adsorbed and carbonate bound) special in first fraction (Figure 1). This fraction is envisaged to remove predominantly water-soluble, exchangeable and carbonate bound metals. It shows the amount of each element that would be released into the environment if conditions became more acidic. It is the fraction with most labile union to the solid matrix th Croatian & 8 th International Symposium on Agriculture Dubrovnik Croatia

4 and, therefore, the most dangerous to the environment. This phase is susceptible to changes in ph. Similar results were obtained bz Anju and Banerjee (2010). Initial samples was also digested by aqua regia and this results was compared with sumary of all five fractions. Recovery percent was given in Table 1. Table 1. Summary of five definded fraction, total content according to aqua regia and recovery percent of them for Zn in deposols sum I-V AR recovery mg/kg % Kostolac 0-30cm Kostolac 30-60cm Kostolac 60-90cm Kolubara 0-30cm Kolubara 30-60cm Kolubara 60-90cm Conclusion According to Tessier's sheme, highest concentration of Zn in two different locality of deposol in Serbia, were found in residual fraction. Concentration of Zn in acid soluble fraction wich is potentially environmental dangerous is very low. Despite high total concentration of Zn in deposol, specialy in Kolubara, sequential extraction shown that it is not threat for environment. Literature Anju M., Banerjee D.K. (2010). Comparison of twosequential extraction procedures for heavy metal partitioning in mine tailings. Chemosphere. Volume (78-11): Blum W.E.H., Spiegel H. and Wenzel W.W. (1989). Bodenzustandsinventur. Konzeption, Durchführung und Bewertung. Bundesministerium für Landund Forstwirtschaft, Wien. Brümmer G.W.(1986). Heavy metal species, mobility and availability in soils. In The importance of the chemical "speciation" in environmental processes, Chlopecka, A. (1993). Forms of trace metals from inorganic sources in soils amounts found in spring barley. Water, Air, and Soil Pollution, Volume(69): Clevenger, T.E. (1990). Use of sequential extraction to evaluate the heavy metals in mining wastes. Water, Air, and Soil Pollution. Volume (50): Cottenie, A. and Verloo, M. (1984). Analytical diagnosis of soil pollution with heavy metals, Fresenius Journal of Analytical Chemistry. Volume( 317): Hirner, A.V. (1992). Trace element speciation in soils and sediments using sequential chemical extraction methods. Intern. J. Environ. Anal. Chem. Volume (46): Karczewska A.,Wenzel W.W, Mavrodieva R. (1999). Effect of metal sources and indigenous soil ph on metal fractions in soil, Environmental Geochemistry and Health Lake,D.L., Kirk, P.W.W., Lester, J.N. (1984). J. Environ. Qual. Volume (13): 175. Maiz, I., Arambarri, I., Garcia, R. and Mill an, E. (2000). Evaluation of heavy metal availability in polluted soils by two sequential extraction procedures using factor analysis. Environmental Pollution, Volume (110, no. 1): 3 9. McBride, N.M., (1989) Reactions controlling heavy metal solubility in soils. Advances in Soil Science, Volume (10): Merian, E. (1991). Metals and their Compounds in the Environment: Occurrence, Analysis and Biological Relevance, VCH, Weinheim, hrvatski i 8. međunarodni simpozij agronoma Dubrovnik Hrvatska 109

5 Ratuzny, T., Gong, Z. and Wilke, B.M. (2009). Total concentrations and speciation of heavy metals in soils of the Shenyang Zhangshi Irrigation Area, China,Environmental Monitoring and Assessment. Volume( 156, no. 1 4): Ryan, P.C. Hillier, S. and Wall, A. J. (2008). Stepwise effects of the BCR sequential chemical extraction procedure on dissolution and metal release from common ferromagnesian clay minerals: a combined solution chemistry and X-ray powder diffraction study. Science of the Total Environment. Volume (407): Shan, X.Q. and Chen, B. (1993). Evaluation of sequential extraction for speciation of trace metals in model soil containing natural minerals and humic acid. Analytical Chemistry. Volume( 65, no. 6): Teissier, A., Campbell, P.G.C. and Bisson, M. (1979). Sequential extraction procedure for the specification of particulate trace metals. Analytical Chemistry. Volume(51): Zemberyova, M., Bartekova, J., Hagarova, I. (2006). The utilization of modified BCR three-step sequential extraction procedure for the fractionation of Cd, Cr, Cu, Ni, Pb and Zn in soil reference materials of different origins. Talanta. Volume (70): th Croatian & 8 th International Symposium on Agriculture Dubrovnik Croatia