Spatial distribution, source identification, and risk assessment of heavy metals in the soils from a mining region: a case study of Bayan Obo in northwestern China

Bayan Obo deposit is the largest light rare earth ore deposit in the world, which releases a lot of heavy metals to the surrounding environment during the long-term mining process. To make efficient protection plan, it is necessary to investigate the concentration, spatial distribution, contamination sources, and environmental-health risks of heavy metals surrounding the Bayan Obo deposit. A total of 46 soil samples were collected from mining areas. Mn, Cu, Zn, Pb, Cd, As, Hg and Cr concentrations in each soil sample were determined. The spatial distribution characteristics of heavy metals in soils were studied by using ArcGIS spatial interpolation analysis. Multivariate statistical analyses were applied to identify the pollution sources of heavy metals. The environmental-health risks of heavy metals were evaluated by calculating geo-accumulation index (I gₑₒ), potential ecological risk index (RI), risk assessment code (RAC), modified risk assessment code (mRAC), potential non-carcinogenic risk (HI) and carcinogenic risks (CR). The results showed that the average values of other heavy metals except Cr and As were considerably higher than the background values of Inner Mongolia and control area, which indicated the accumulation of these metals in this area, especially Cd. Cu, Zn, Mn, Cd and Pb showed similar spatial distributions, exhibiting a high level near the metal ore. Hg was mainly distributed in areas with intense industrial activities. Four origins were identified by multivariate analysis: industrial activities and fuel combustion for Hg, mining activities for Cu, traffic source for Mn and Pb, the combination of mining and traffic activities for Cd and Zn, and Cr and As was mainly controlled by natural sources. The results of the environment risk assessment showed Bayan Obo mining region was a region seriously polluted by high amount of heavy metals and low bioavailability. There is no potential carcinogenic and non-carcinogenic risk. The research results provide a scientific basis and technical support for monitoring and early warning of soil pollution in mining areas.