Abstract: Heavy metals have the characteristics of high toxicity, easy accumulation, and refractory degradation, which pose a potential threat to the ecological environment. The established ecological environment risk assessment index system of heavy metals in groundwater considers relatively limited external factors, and the rationality of the assessment results needs to be improved. In this study, based on the contents and spatial distributions of eight heavy metals in groundwater in typical lead-zinc mines and surrounding areas in Inner Mongolia, single factor and fuzzy mathematics were used to evaluate the environmental quality of heavy metals. The results showed that the Ni content in groundwater generally exceeded the standard, while Pb, Mn, Zn, As, Se and Cd exceeded the standard to varying degrees, and Cu did not exceed the standard. Spatially, the groundwater was generally at grades IV-V, and locally at grades I-II. The distribution of heavy metals was affected by human activities, as well as by natural factors such as soil minerals and hydrodynamic characteristics. The results of the potential ecological risk assessment showed that the single potential ecological risk index for As, Se, and Cd was between mild and strong levels, while fluctuated greatly for Cd, moderate for Mn, and mild for the rest. The comprehensive potential ecological risk of multiple elements was moderate or severe, with slight risk locally. The ecological environment risk assessment of heavy metal pollution in groundwater was carried out by the analytic hierarchy process, and the results showed that the ecoenvironmental risks in the study area was between low and high levels, decreasing spatially from northwest to southeast, and the areas with medium or high risk levels accounting for 31.3% of the study area, which was located near the mining activity area and tailings. Our results were reasonable and comprehensive, reflecting the actual eco-environment risk. The evaluation results can provide reference for local environmental pollution control, while the evaluation index system can provide support for ecological environment assessment in similar areas.

Key words: groundwater, heavy metal pollution, risk assessment, lead-zinc mine.