Bioavailability of heavy metals in the soil of Doustbaglu region (Meshginshahr) and determining toxic species by sequential extraction and Visual Minteq software

Document Type : Original Article


1 Department of Earth Sciences, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran

2 Department of Analytical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Tabriz, Iran


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.


Forghani, G., Moore, F., Lee, S. and Qishlagi, A., 2009. Geochemistry and speciation of metals in sediments of the Maharlu Salin Lake, Shiraz, SW Iran. Environmental Earth Science. 173-184.
James, B.R. and Bartlett, R.J., 1988. Mobility and bioavailability of chromium in soil, In: Nriagu, J.O., Nieborer, E. (Eds), Chromium in natural and human Environments. Wiley Inter Science, New Yourk. 413 p.
Jochum, K.P., Hofmann, A. W. and Seufert, H.M., 1993. Tin in mantle-derived rocks: constraints on Earth evolution. Geochimica et Cosmochimica Acta. 57, 3585-3595.
Kabata-Pendias, A. and Mukherjee, A.B., 2007. Trace elements from soil to human. Pulway, Springer Science. 576 p.
Kabata-Pendias, A. and Pendias, H., 2001. Trace Elements in Soils and Plants”. Third Edition, CRC press.
Mizerna, K., 2018. Determination of forms of heavy metals in bottom ash from households using sequential extraction. E3S web of conferences 44, 00116., EKO-DOK 2018.
Mohammadi, M., Siahcheshm, K. and Sorouraddin, S.M., 2020. Environmental Ecotoxicology of Heavy Metals Contaminants of the Dostbaglou Alteration Area, Ardabil Province. Journal of Environmental Sciences, Shahid Beheshti University. 18 (4), 41-52.
Panichayapichet, P., Nitisorvut, S., Simachaya, W. and Wangkiat, A., 2008. Source Identification and Speciation of Metals in the Topsoil of the Khli Ti Watershed, Thailand. Water, Air, soil Pollut. 194(1), 259-273.
Savic-Gajic, I., Savic, I. M. and Gajic, D., 2016. The role and health risk of heavy metals in human organism. In: Castillo, R. (Eds.), Heavy Metals and Health. Nova Science Publishers.
Solomon, A., Rasheed, K. and Olanipekun, E., 2016. Spatial distribution and speciation of heavy metal in sediment of river Ilaje, Nigeria. International Research Journal of Pure and Applied Chemistry. 10(2), 1-10.
Tepavitcharova, S., Tosorov, T., Dassenkis, M. and Paraskevopoulon, V., 2010. Chemical speciation in waters influenced by Lead-Zinc Metallurgical industry. Environ. Monit. Assess. 169, 27-36.
Tessier, A., Compbell, P.G.C. and Blesson, M., 1979.  Sequential extraction procedure for speciation of particulate trace metal. Analysis Chemistry. 844-851.
WHO, 2011. Guidelines for Drinking-Water Quality. World Health Organization. 4, 315-318.
Williams, P.L., James, R.C. and Roberts, S.M., 2003. Principle of toxicology environmental and industrial applications. 325-344.