Speciation of heavy metals in water and sediments of an urban lake system

摘要

The speciation pattern of heavy metals namely chromium, nickel, copper and lead in water and sediments of an urban lake system of high ecological significance was studied. The total available metal (dissolved) in water follows the sequence Ni>Cr>Pb>Cu. However, a different pattern Pb>Cu>Ni>Cr is observed for total available metal (metal in non-residual phases) in sediments. Significant spatial variations are observed in different geochemical forms of the metals as indicated by two-way ANOVA. This is attributed to localized anthropogenic activities. The anthropogenic parameters of water not only show statistically significant correlations among themselves but also positively correlate with the particulate forms of Cr, Cu and Pb. The total available forms of copper and lead correlate with the organic content of the sediments. Principal component analysis (PCA) separates the metals into three groups: Ⅰ (Cr); Ⅱ (Ni); Ⅲ (Cu and Pb). The polluted sites were identified using hierarchical cluster analysis. Risk assessment code (RAC) analysis indicates low to medium risk due to Cr at most of the sites. However, Ni, Cu and Pb pose medium to high risk. But Pb at a few sites presents very high risk (RAC > 50%).