CHARACTERISING ASSOCIATIONS BETWEEN GEOCHEMICAL LEAD FRACTIONS AND SELECTED PROPERTIES OF A SEWAGE SLUDGE-AMENDED MONTMORILLONITIC VERTISOL

Multivariate analytical techniques have been used to understand total concentration of heavy metal association with soil properties but not many of these studies have investigated the association between heavy metals concentrations in different geochemical fractions of sludge-amended soils and soil properties. This study investigated the relationship between selected properties of a montmorillonitic vertisol, and the concentrations of lead (Pb) in different geochemical fractions of the vertisol before and after sludge addition. The vertisol was amended with sludge at different ratios of sludge: soil. Lead concentrations in the exchangeable, carbonate bound, reducible, oxidizable and residual fractions of the vertisol were extracted using a five stage sequential extraction procedure. Results of concentrations from laboratory analyses were subjected to correlation and principal component analyses (PCA). Lead concentrations in the different fractions of the montmorillonitic vertisol without sludge followed the order residual fraction > oxidizable fraction > exchangeable fraction > carbonate bound fraction > reducible fraction and correlated with Fe, cation exchange capacity (CEC) Mn, and pH. In the sludge-amended vertisol correlations were observed between CEC/Pb fractions and organic matter (OM)/Pb fractions at an SAR of 5%, and CEC/Pb fractions, OM/Pb fractions, Fe/Pb fractions and Mn/Pb fractions as sludge application rate increased. No associations were observed at higher sludge application rates. Sludge affected the properties of the vertisol and consequently the concentration of Pb in the different fractions and their association with these properties. Correlation and PCA analyses can be useful in understanding effects of sludge addition on the association between heavy metals in different geochemical fractions of soils and soil properties.