Kamal Siahcheshm; Mahnaz Mohammadi; Saied Mohammad Sorouraddin
Abstract
Introduction: Oxidation of sulfide mineralized zones during the weathering processes is intensified by biological and chemical reactions and the resulting Acid Mine Drainage (AMD) causes the release and mobility of toxic and heavy metals from the parent rock and their concentration in soil or water. ...
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Introduction: Oxidation of sulfide mineralized zones during the weathering processes is intensified by biological and chemical reactions and the resulting Acid Mine Drainage (AMD) causes the release and mobility of toxic and heavy metals from the parent rock and their concentration in soil or water. In this study, soil samples taken from the surroundings of the village of Doustbaglu (northwest of Meshginshahr), which is considered a typical mineralization and alteration area, were studied and chemical species, toxicity, and origin of heavy elements were determined.Material and methods: In this study, total concentration and bioavailability of heavy elements i.e. As, Cd, Cu, Cr, Pb, Sb, Ni, and Zn in five surface soil samples were evaluated by Tessier sequential extraction method in five phases (exchangeable, connected to carbonate, bound to iron and manganese oxides, bound to organic matter, and residual phase) and using the Visual Minteq thermodynamic software.Results and discussion: The results of the sequential extraction method showed that the highest concentration of the total concentration of all studied heavy elements was retained in the residual fraction (stabilized in the mineral structure). This indicates the geogenic origin of these elements and can be considered the result of erosion and weathering of rocks in the region. Compared to other elements, Sb had a higher concentration in potentially available fractions (e.g. exchangeable, carbonate-bound, bound to Fe-and Mn-oxides, and/or organic matter) and can be readily available to plants and toxic. The software output delineates that the predominant species in the examined samples were lead as Pb (SO4)22-, Pb2+ and PbSO4(aq); copper as CuSO4 (aq) and Cu2+; nickel as NiSO4 (aq), Ni2+ and NiSO4; antimony as Sb(OH)3, Sb(OH)2+ and Sb(OH)61-; zinc as Zn(SO4)22-, ZnSO4(aq) and Zn2+; arsenic as H3AsO3 and H2AsO4-; cadmium as Cd(SO4)22-, and Cd2+. The predominant species of chromium were CrSO4+, CrOHSO4(aq), and HCrO4-. In general, the free water-soluble species of these elements were more mobile than other species; instead, the concentration of these species was very low relatively, and most of these elements were more present in the form of complexes with low mobility.Conclusion: Based on sequential extraction results, all studied elements showed high ecological risk potential and significant pollution in the sediment of waterways and surface soil horizons of the Doustbaglu area. Analysis of the findings of Visual Minteq software indicates that the most active types of elements and related concentrations, among all possible types, include: Cd2+(1.49%), CrOHSO4(aq)(25.20%), Cu2+(10/38%), Pb2+(1/37%), ZnSO4(aq) (18.83%), respectively. Since more mobile species have low concentrations and on the other hand, according to the results of sequential extraction, most of the studied elements are present in the remaining phase, so the bioavailability and toxicity of these elements are estimated to be negligible. In general, it can be concluded that only a small percentage of elements are present in bioavailable fractions, and this can alleviate concerns about the possibility of element release by changing environmental conditions and thus accessibility to plants.
Mahnaz Mohammadi; Kamal Siahcheshm; Saeed Mohammad Sorouraddin
Abstract
Introduction: Oxidation of sulfide-mineralized zones during weathering, intensifies by the biological and chemical reactions and the released acidic mine drainage (AMD) mobilizes toxic and heavy elements from the parent rock and concentrates them in soil or water environment. The village of Doustbaglu ...
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Introduction: Oxidation of sulfide-mineralized zones during weathering, intensifies by the biological and chemical reactions and the released acidic mine drainage (AMD) mobilizes toxic and heavy elements from the parent rock and concentrates them in soil or water environment. The village of Doustbaglu is located in a mountainous area to the northwest of Meshgin-shahr city, has numerous farmlands overlooking the extensive alteration zones. Field studies indicate the fact that unfortunately, especially skin diseases, liver and cancer are prevalent in the area. The importance of knowledge of heavy metal enrichment in soil resources and the high potential of Doustbaglu area for the production of agricultural and horticultural crops and its direct relationship with human health reveals the necessity of conducting this study to evaluate heavy metal contamination and identify possible sources. Material and methods: In this study, total concentration and bioavailability of heavy metals including: As, Cd, Cu, Cr, Pb, Sb, Ni and Zn in 70 surface soil samples were evaluated by ICP-MS analysis. Calculation of contamination rates of soil samples using different environmental indices including modified contamination index, soil heavy metals ecological risk index, pollution load index and Nemerow’s index indicates high contamination occurrence of these elements. Results and discussion: The results of mCd index show high degree of contamination of Cu, Cr, Cd, Pb, Sb, Ni, Zn and As in most samples. High values of the ecological risk index (up to 2076/9), indicate the level of serious contamination risk of some samples. The PLI index in 10 samples showed PLI valuesConclusion: Based on the results of geo-environmental indices, all eight studied elements showed highecological risk potential and significant contamination occurrence in stream sediments and surface horizons ofthe Doustbaglu district.
