内蒙古典型铅锌矿及其影响区地下水重金属污染生态环境风险评估

Assessment of the ecological risk of heavy metal pollution in groundwater of typical lead-zinc mine and influenced area in Inner Mongolia

重金属具有毒性大、易富集、难降解等特点,对生态环境构成潜在威胁。目前已建立的地下水重金属污染生态环境风险评估指标体系考虑外在影响因素相对较少,评估结果合理性有待提升。本研究对内蒙古典型铅锌矿及影响区地下水中的8种重金属含量,用单因子与模糊数学法进行重金属环境质量评价。结果显示:地下水Ni含量整体超标,而Pb、Mn、Zn、As、Se和Cd存在不同程度超标,Cu未超标,空间上地下水整体处于Ⅳ~Ⅴ类,局部为Ⅰ~Ⅱ类,其分布既受到人类活动影响,又受到土壤矿物、水动力特征等天然因素影响;潜在生态风险评价结果表明,单项潜在生态风险指数中,As、Se和Cd是轻微与很强等级间,但Cd波动较大且不稳定,Mn为中等风险,其他为轻微风险等级,多元素综合潜在生态风险为中等及以上风险,局部为轻微风险等级;通过层次分析法进行地下水重金属污染的生态环境风险评估,结果发现,研究区处于低风险与高风险等级之间,空间上由西北向东南方向递减,中等和高等风险区域占研究区31.3%,位于采矿活动区及尾矿附近。经对比发现,其结果较合理,能够真实反映实际生态环境风险情况,评估结果对当地环境污染治理提供一定参考,该评估指标体系可为相似地区生态环境评估提供支持。

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.