Trace metal pollution in topsoil surrounding the Xiangtan manganese mine area (South-Central China): source identification, spatial distribution and assessment of potential ecological risks

In this study, we identified heavy metal sources, investigated their spatial distribution in topsoil and assessed their potential ecological risk in the area surrounding a typical manganese mining area in Xiangtan, Hunan Province, China. The concentrations of Mn, Cu, Pb, Zn, Cd, Ni, Cr and Hg in the topsoil of the study area were measured. With the exception of Cr and Hg, it was found that other heavy metals exceeded the corresponding soil background values of hunan province. The spatial variation of heavy metals was visualized by GIS, and the results show that heavy metals in topsoil are mainly enriched around mines and smelters. Accompanied with spatial distribution, trend analysis, Pearson's correlation and principle component analysis, two groups of heavy metals were identified: Mn, Cu, Pb, Zn, Cd and Ni can be attributed to industrial and mining activities, whereas Cr and Hg are of natural origin. The results also revealed that the prevailing wind direction, erosion of mine tailings and rain water runoff may play significant roles in heavy metal diffusion and transfer. In addition, the environmental risk of heavy metal pollution was evaluated using geoaccumulation indexes and potential ecological risk indexes (PERI) applied to the study area. The comprehensive potential ecological risk index of heavy metals is at a high risk level in the manganese mine area. The comprehensive potential ecological risk index of heavy metals is mostly at a moderate risk level around the manganese mine area. Further, 79.01% of the potential ecological risk was from Cd in the study area.