Comparative Research of the Successive Extraction Schemes for the Forms of Pb, Zn, Cu and Cd in Industrially Polluted Region

V. ANGELOVA1, G. BEKJAROV2 and K. IVANOV1
1 Agricultural University, Dept. of Chemistry, BG-4000 Plovdiv, Bulgaria
2 Gardening and Canning Institute, BG-4000 Plovdiv, Bulgaria

Abstract

ANGELOVA, V., G. BEKJAROV and K. IVANOV, 2002. Comparative research of the successive extraction schemes for the forms of Pb, Zn, Cu and Cd in industrially polluted region. Bulg. J. Agric. Sci., 8: 569–575

The objective of the present work was to evaluate and compare 3 from the most commonly used schemes for defining the forms of the metals in soil. For the purposes of the research we used soil from a heavily polluted region in proximity to the Non-Ferrous-Metal Works near Plovdiv, containing extreme quantities of Pb, Zn, Cu and Cd. In performing the analyses we followed the proposed by Xian (1987), Tessier et al. (1979) and Shuman (1985) successive extraction procedures. The schemes of Xian (1987) and Tessier et al. (1979) include partitionation of the metals into 5 operately defined fractions: exchangeable, bound to organic substance, bound to oxides, bound to carbonates and residue. The scheme of Shuman allows defining the metals connected with the phases with a high capacity of retaining and absorbing the metals and namely the amorphous Mn oxides, amorphous Fe oxides and crystalline Fe oxides. The scheme of Shuman (1985) includes besides the above described forms also defining the metals contained in sand, silt and clay.
The quantitative measurements were performed on a 3030 B “Perkin-Elmer” atomic – absorption spectrometer.
Pb, Zn and Cu were strongly associated with the soil components and should be considered less available to plants. In terms of Cd, in contrast to the other heavy metals, a significant part of it is found in the exchangeable fraction and should be considered mobile and potentially bioavailable. Using the sequential extraction procedures as a measure of availability, mobility and bioavailability of these four metals in this polluted alluvial calcaric soil were Cd> Pb> Cu>Zn.
It was found a very good coincidence in the results for distribution and forms of Pb, Zn, Cu and Cd, obtained by the schemes of Xian and Tessier. The main differences from the scheme of Shuman are explained by the fact, that in these scheme are not determined the metals in the carbonate fraction. It's concluded that the best results can be obtained by the combination of the investigated sequential extraction procedures.

Key words: sequential extraction procedure, heavy metals, polluted soils