Distribution and ecological risks assessment of heavy metals in surface soils in the areas south of Laizhou Bay

Based on the survey data of surface soil obtained from 1 600 sampling sites in the land areas south of the Laizhou Bay, we analyzed the spatial characteristics, sources, ecological risks, and pollution status of 8 heavy metals. Results show that, in terms of concentration, the 8 elements followed an order of Cr > Zn> Ni> Pb> Cu > As> Cd> Hg. The high-value of heavy metals distribute in the mid-west, west, and southwest of the studied area, and the values are lower in the east, southeast and northeast, and the lowest in the north. The pH value of the soil reveals a rising trend from south to north. Single-factor pollution index of the 8 elements followed an order of Ni > As> Cr > Zn >Cu > Cd > Pb > Hg. The average of single-factor pollution index of the 8 elements are all lower than 0.7, indicating the clean level in China’s national standard of environmental pollution. In terms of the single-factor potential ecological risks, the 8 elements followed an order of Hg>Cd>As>Pb>Cu>Ni>Cr>Zn. Most of the studied areas are of low potential ecological risks. The areas of middle, heavy, and serious potential ecological risks are of punctate or sporadic distribution. The heavy metals in the surface soil were controlled by the geological background in the first place. Next, the heavy metals were brought in by human activities such as chemical fertilizers and agricultural chemicals from agricultural activities and from sewage of local chemical industry and mining, and automobile exhaustion and tire wear. Therefore, it is essential to intensify monitoring and early-warning of heavy metal pollution in the land areas south of Laizhou Bay, and work out case-specific control and remediation measures, to ensure the studied area free from heavy metal pollution.