Sequential Extraction of some Heavy Metals in Tropical Agricultural Soils from Ogun state, Nigeria

T. M. Osobamiro, G. O. Adewuyi, O. M. Ajibade

Abstract


Speciation of metals in soil samples is an integral factor in appraising their potential environmental impacts. Sequential extraction method was used to determine speciation of heavy metals in tropical Agricultural soils.  Soil samples were randomly collected from arable and oil plantation farms in Ago-Iwoye farm settlement in Ogun state, Nigeria. The heavy metals in the soil samples were sequentially extracted by Tessier and Silveira methods and their concentrations were determined using atomic absorption spectrophotometer. Physicochemical parameters of the soils were also assessed. Results showed that levels of heavy metals extracted in Fe and Mn oxide fractions(mg/kg) with Tessier method were; Mn (<14.4), Fe(<387), Pb(<2.37), Zn(<52.4) and Ni(<6.96) while for Silveira; Mn (<27.7), Fe(<1091), Pb (10.9), Zn(<85.7) and Ni (<9.36). Some of the physicochemical obtained properties were; pH (<6.23), organic carbon (<22.4 g/kg), CEC (<6.28 cmol/kg) and Total Fe (<1812 mg/kg). These revealed that higher concentrations of metals were extracted in the three steps (Fe and Mn oxide fractions) extraction method of Silveira compared to single step extraction of Tessier. Physicochemical and mineralogical composition revealed that the soil was rich in Fe and carbonate minerals and these play vital role in metal speciation. Conclusively, this study has shown that Silveira sequential extraction method was more appropriate for the sequential extraction of heavy metals in the study soil as a typical tropical soil and has also provided more knowledge and use of appropriate sequential extraction of metals in soil management and pollution prevention.

Key words: Sequential extraction, tropical soil, toxic metals, Fe-oxide mineral, soil properties, Mineralogical composition


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Chemical Society of Nigeria