Element fractionation in soil from urban-industrialized areas using sequential extraction

Abstract

The application of solid-liquid extraction is proposed to assess extractable fractions of components in soil. The application of a several step scheme could give a lot of information about mobility of metals associated with specific solid phases, especially after separation of top and bottom layers of studied soil. In this study, it was aimed to take into solution metal fractions of major (Ca, Mg, Mn, Fe) and trace elements (Cr, Co, Cu, Zn, As, Cd, Pb) from soil collected in urban areas. The fractions were defined by using chemical extraction operationally. The extraction behavior of studied elements in a six-step sequential extraction procedure is discussed with respect to the properties of the reagents used. Here, metal fractionation of four soil samples (Parabraun Erde), top (0-10 cm) and bottom (10-30 cm) layers, collected from German anthropogenically influenced areas are presented. Methods. The following reagents were used in the six-step extraction scheme: 0.01 mol L-1 ammonium acetate, 0.1 mol L-1 acetic acid, 0.05 mol L-1 hydroxylamine hydrochloride (pH 2, 0.1 mol L-1 ascorbic acid in oxalate buffer, hydrogen peroxide, and hot cone, nitric acid. In extracts, the studied elements were determined by ICP-MS and ICP-OES. The extractability of most of the major and trace elements is similar for all steps for both layers of soils. The results obtained for Ca, Mg, Mn and Fe indicate that the soils contain rather moderately soluble carbonate and Mn oxides which are present in the soil in an ‘aged’ form. The trace elements studied (Cr, Co, Ni, Cu, Zn, As, Cd and Pb) from manganese and iron oxides and organic matter are mainly leached. The studies indicate that the mobile fraction of elements is mainly bound to easily reducible Mn oxides, moderately reducible Mn and Fe oxides and organic matter. It has been found that the concentration and proportion of different metal fractions are similar for surface and mineral layers of these soils collected in areas with anthropogenic influence. The results of this study show that soils collected in anthropogenically influenced areas contain more trace elements and the elements are more mobile. The statistical estimation of results obtained after digestion without complete dissolution of soil matrix demonstrates that the digestion procedure is suitable for quantification of total content of studied soils using ICP methods.