Heavy metals (HMs) in soils of different land-use types in Zhengzhou, China: Occurrence, source and ecological risk

To understand the impact of urbanization process on heavy metals (HMs) (distribution, sources and risks) in soil in different land-use types, we collected soil samples from 38 sites in Zhengzhou, China, and divided them into industrial, residential and agricultural areas. Various indices, including single factor pollution index (Pi), Nemerow pollution index (PN) and geo-accumulation index (Igeo) were used to analyze the pollution levels of HMs. The results showed that the average concentrations of Pb, Cd, Cu, Zn, Cr and Mn were 30.26 mg/kg, 0.31 mg/kg, 18.26 mg/kg, 85.85 mg/kg, 76.76 mg/kg and 211.13 mg/kg, respectively. Additionally, Pb, Zn and Cr were the main pollutants and showed serious pollution levels in three land-use types. Remarkably the pollution level of Pb was particularly prominent in industrial areas due to individual sampling points. Then, the principal component analysis (PCA) showed that Pb and Mn came from traffic and natural sources (34.14%), Cd and Zn from metal smelting (28.11%), Cr and Cu from the use of pesticides and fertilizers (17.57%). Furthermore, geographic information system (GIS) and potential ecological risk index (Eri) were employed to analyze the risk of HMs. Among them, the Eri value of Cd in the industrial area was shown to be 55.5, which reached moderate pollution. Moreover, Cd has the highest contribution to risk index (RI) among all soil types. The order of RI was industrial area > residential area > agricultural area, which would contribute to the future regional planning of Zhengzhou.