Comprehensive assessment and source apportionment of heavy metals in Shanghai agricultural soils with different fertility levels

For the purpose of pollution assessment and source apportionment of heavy metals in agricultural soils with different fertility levels, an intensive sampling (1848 samples) was conducted in Shanghai city. Various indices, including the pollution index (PI), Nemerow integrated pollution index (NIPI), geoaccumulation index (GI) and potential ecological risk index (RI), were employed to assess the pollution status caused by heavy metals. In view of the spatial heterogeneity of heavy metal concentrations, in this work a synthesis of principal component analysis (PCA) with spatial lag modeling (SLM) is proposed to explore quantitatively the sources of heavy metals and the contributions of each component. The results showed that the mean heavy metal concentrations followed a decreasing order: Cr (72.02 +/- 8.90 mg/kg) > Pb (25.57 +/- 7.38 mg/kg) > As (6.98 +/- 1.97 mg/kg) > Cd (0.19 +/- 0.10 mg/kg) > Hg (0.12 +/- 0.08 mg/kg). Although the mean heavy metal concentrations did not exceed the corresponding national standards, the percentages of sampling locations exhibiting higher concentrations relative to the background values were found to be equal to 43.29% for Pb, 32.63% for Cd, 27.54% for Hg, 11.26% for Cr, and 10.93% for As, which indicate significant local accumulation of heavy metal pollutants within the study area. Industrial activities, natural sources and agricultural activities are the main pollution sources that account for 27.92%, 27.48% and 20.64% of the total pollution, respectively. Industrial activities with high Pb and Hg loadings have a large contribution to good fertility soils (39.38%). It was found that agricultural activity is the main contributor of Cd pollution, having a large contribution (33.46%) to low fertility soils. Cr and As pollution comes mainly from natural sources, with relatively equal contribution to soils with various fertility levels. The present study improves understanding of the pollution status of heavy metals in Shanghai agricultural soils, and also serves as reference for pollution source apportionment in other regions.