DOI: 10.5593/sgem2010.09.16.S1.766


Sunday 1 August 2010 by Libadmin2010

10th International Multidisciplinary Scientific GeoConference - SGEM2010, www.sgem.org, SGEM2010 Conference Proceedings/ ISBN 10: 954-91818-1-2, June 20-26, 2010, Vol. 2, 165-172 pp


Lead (Pb) mobility in soils and hence its availability for plant uptake may be influenced
by several soil properties, some of which are modified by sludge application. It is
therefore imperative to understand how these modified properties affect Pb
concentrations in different geochemical fractions of sludge-amended soils. Vertisols are
common in arid- and semi-arid areas and are used extensively for agriculture. This study
aimed at determining the relationship between selected soil properties (pH, organic
matter (OM) content, cation exchange capacity (CEC), weight percent (wt %) clay,
concentrations of Fe and Al) in a montmorillonitic vertisol, and the concentrations of Pb
in differen geochemical fractions of the vertisol before and after sludge addition. The
vertisol was amended with sludge at volume/volume percent (v/v %) ratios of 5:95,
10:90, and 20:80 sludge:vertisol. Lead concentrations in the exchangeable (S1),
carbonate (S2), reducible (S3), oxidizable (S4) and residual (S5) fractions of the vertisol
were extracted using a five stage sequential extraction procedure. Results were
subjected to multivariate analyses which included regression analyses, Bonferroni
adjusted two-step cluster analyses, and principal component analyses. Lead
concentrations in the different fractions followed the order S4> S1 > S5 > S2 > S3.
Lead concentration increased with sludge application rate (SAR) in all samples. Two
clusters were identified through cluster analyses. In the vertisol with no sludge, CEC
and pH appeared to be the most significant factors affecting segregation of Pb into the
different fractions (P< 0.05) with pH explaining 80%, 84.6% and 77.4% of the
variations observed in Pb concentration in the S1, S3 and S4 fractions respectively. At
SAR of 5%, 10% and 20%, OM content becomes significant in determining partitioning
of Pb into the different fractions with Fe becoming more important at higher sludge
application rates. Findings of the study indicate that in the application of sludge to soils,
the pH, OM and Fe content of the soils should be taken into consideration as they may
influence the bioavailability and eventually bioaccumulation of Pb in plants.

Keywords: Multivariate analyses, Sequential extraction; Sludge application rate, Pb mobility; Vertisol

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