An assessment of spatial distribution and source identification of five toxic heavy metals in Nanjing, China

Abstract

Spatial distributions and concentrations of heavy metals in vegetable plots in Nanjing were analyzed for assessment of environmental contamination status and source identification by GIS. Compared with background reference values, the average concentrations of all tested elements (Cu, Zn, Cd, As and Pb) except Cu exceeded the secondary evaluation standard of soil environmental quality. Coefficients of variation, arranged from large to small, were Cd > As > Zn > Pb > Cu. Semi-variance functions showed that the five elements were closely spatially correlated within the sampling range. The spatial distributions of Cu and Zn, As and Pb were similar to some extent. Multivariate statistical analysis showed that heavy metal contents were positively correlated with soil nutrients. The organic matter content was highly significantly positively correlated with the content of Zn and Cd and significantly positively correlated with As. CEC was highly significantly positively correlated with Cu and significantly positively correlated with Pb. However, pH and heavy metal concentrations were not significantly correlated. Principal components analysis indicated that Pb and Zn had a natural crustal source; Cu was mainly derived from discharged metallurgical waste; Cd and As came from agricultural pollution. Moreover, correlation analysis indicated that the Cd and As may have the same source.