秦岭某钼矿区开发对东川河流域Cd的影响

Evaluation of Cd pollution of a molybdenum ore area in Dongchuan River basin of the Qinling Mountain

为了探索矿业活动对河流水质产生的影响,以秦岭某大型钼矿区下游的东川河流域为研究对象,通过现场采样与室内测试的方法,分析了地表水、沉积物、岩矿样品中重金属Cd的含量特征。采用污染超标倍数法、地累积指数法及Hakanson潜在生态风险评价法分别对东川河流域的河水和底泥样品进行了污染现状评价和生态风险程度评价,最后讨论了Cd的来源。结果表明:东川河主沟16个河水采样点位中,有11个点位的Cd含量明显高于未受矿业活动影响的对照区各点位Cd含量值,Cd含量变异系数达到95.65%,并且从上游到下游各点位Cd含量呈偏态分布,说明东川河流域Cd受矿业活动影响显著。东川河主沟16个河水采样点中有15个Cd含量满足地表水Ⅱ类水标准,比重为93.75%,可以判断东川河整体水质较好。仅5号点位超Ⅱ类水质标准,污染超标倍数为1,为轻度污染。地累积指数分析结果表明,东川河主沟11个底泥样品均存在不同程度的污染:污染最严重的10号点位达到中度-强污染级别;污染最轻的8、9、13号点位为无污染-中度污染;大多数点位为中度污染。东川河主沟11件底泥样品重金属Cd的潜在生态危害指数平均值为120.27,表明东川河主沟底泥总体达到强生态风险程度。酸性矿山废水、原生地质背景、底泥释放、大气干湿降尘等是造成东川河流域Cd重金属污染的主要污染源。

In order to explore the impact of mining activities on river water quality,the authors chose the Dongchuan River basin,downstream of a large molybdenum ore area in the Qinling Mountains,as the research object.Through on-site sampling and indoor testing,the characteristics of heavy metal Cd in surface water,sediments,and rock samples were analyzed.The contamination status and ecological risk assessment of the river and sediment samples in the Dongchuan River basin were evaluated using the exceeding pollution standard multiple method,the geoaccumulation index method,and the Hakanson potential ecological risk assessment method,with a discussion on the source of Cd.The results show that the Cd content of the16river sampling sites in the main channel of Dongchuan River was significantly higher than that in the control sites that are not affected by mining activities,the coefficient of variation of Cd content reached95.65%and the Cd content from upstream to downstream showed a skewed distribution;the information shows that Cd in the Dongchuan River basin was significantly affected by mining activity.The Cd content of93.75%of the16river water sampling points in the main channel of Dongchuan River meets class II water standard for surface water,and it can be judged that the overall water quality of Dongchuan River is better.Only the No.5point exceeds the class II water quality standard.The multiple of exceeding pollution standard is1,suggesting light pollution.The results of geoaccumulation index analysis show that11sediment samples from the main channel of Dongchuan River had different levels of pollution:sampling point10,the most seriously polluted point,reached the moderate-strong pollution level;sampling points8,9and13,the least polluted point,were pollution-free and moderately polluted;and most sites were moderately polluted.The average value of the potential ecological risk index of heavy metal Cd in11samples of Dongchuan River’s main canal was120.27,indicating that the total sediments of the main channel of Dongchuan River reached a level of strong ecological risk.Acid mine drainage,primary geological background,sediment release,atmospheric dry and wet dust fall seem to be the major pollution sources of heavy metal Cd in the Dongchuan River basin.