Spatial Distribution and Pollution Assessment of Potentially Toxic Elements in Urban Forest Soil of Nanjing, China

Our study aimed to assess the pollution levels and ecological risk of potentially toxic elements (PTEs): Pb, Cd, Cu, Cr, Zn, Ni, and As in the urban forest soil of Nanjing, China. A total of 180 topsoil (0 similar to 20cm) samples were collected with the aid of GPS according to 1 x 1 km grid cells in six different function zones: road green belt (RGB), urban square (US), urban garden (UG), institution greenland (IG), residential greenland (RG), and urban rural forest (URF). The concentrations of seven PTEs in study areas were higher than their background values (BVs), and three anthropogenic origins were identified: industrial origin, traffic origin, and agricultural origin by principle analysis (PCA), coupled cluster analysis (CA), and kriging interpolation. The potential ecological risk index (PERI) in the Nanjing urban forest soils was 305.62, in a state of significant pollution, which was mainly due to high contents of Pb, Cd, As, and Zn by correlation analysis. There were three distribution patterns for seven PTEs and PERI: Pb, Cd, As, and PERI presented similar island pattern which took traffic and commercial center as a hot spot (TCIP), while Cr and Ni presented an island pattern that took chemical plants as hotspot (CPIP), and Cu and Zn presented a scattered point pattern (SPP).