京蒙沙源区水库大气重金属干、湿沉降水环境污染机理及源解析研究

Inner Mongolia is an important source area of sandstorm of northwest in China. The sand dust not only affects the environmental air quality, but also has a serious impact on the water environment of the sand source area. Previous studies mainly concentrated in upstream of the sewage to the waters of lake and reservoir pollution contribution, ignoring the dust particles as an important carrier of pollutants in the atmospheric dry and wet deposition forms into the water on the water environment pollution contribution and due to the occurrence of adsorption and desorption of lead to water environment change difference. Research object of this project is big river estuary reservoir located in the Hunshandake sand source area, using Cu, Zn, Pb, Cd, Cr, Hg, as a total of 7 kinds of heavy metals as target pollutants, analysis of response relationship between grain size characteristics and heavy metal content of the dry sedimentation of the atmosphere, revealing adsorption and desorption mechanisms of the atmospheric deposition of heavy metals in water environmental media, to estimate pollution load and contribution rate of the atmospheric dry and wet deposition heavy metals, using NKCMB2.0 model and the factorization method to track the main source causing heavy metal pollution of sand source area, and using the environmental health risk assessment model recommended by the United States Environmental Protection Agency to carry out health risk assessment, to make clear water heavy metal pollution and health risk level, identify the safe function of drinking water and provide basic information and guidance for the treatment of heavy metal pollution in the sediment source area in the late period of the reservoir.

内蒙古是中国西北华北重要的沙尘暴源区。风沙降尘不仅影响环境空气质量，而且对沙源区水环境也产生严重影响。以往的研究主要集中于上游排污对湖库水域的污染贡献，忽略了沙尘颗粒物作为污染物的重要载体以大气干、湿沉降形式进入水体对水环境的污染贡献及因发生吸附-解吸作用导致水环境发生变异问题。本项目以位于浑善达克沙地内的大河口水库为研究对象，以Cu、Zn、Pb、Cd、Cr、Hg、As共7种重金属为目标污染物，剖析大气干沉降颗粒的粒度特征与重金属含量的响应关系，揭示大气沉降重金属在水环境介质中的吸附-解吸机理，估算大气干、湿沉降重金属入库污染负荷，应用NKCMB2.0受体模型结合因子分析法追踪引起沙源区水库重金属污染的主要源向，最终应用美国环境保护署推荐的环境健康风险评价模型进行健康风险评价，明确水源地重金属污染健康风险等级，识别出水库的饮水安全功能并为后期沙源区水库重金属污染治理提供基础信息和指导作用。

大气重金属污染物通过大气介质的大尺度输入使沙区水域水环境防治工作受到巨大挑战。本项目开展了沙源区水库大气重金属干、湿沉降特征分析，揭示干沉降颗粒吸附-解吸机理，解析大气重金属沉降污染来源，评估重金属污染健康风险等级。主要成果为：.分析大沉降物的粒度特征和化学特征。降尘颗粒平均粒径11.04φ~78.21φ，中值为48.59φ，变化幅度较大，最小的是采样点JC6，最大的是采样点JC2。偏度范围0.06~0.65，中值为0.31，降尘颗粒大小较为均匀。300~500目和小于500目的细颗粒质量分布较大，集中在春季多风沙季节，占总降尘质量27.15%。.揭示大气重金属干、湿沉降时空分异规律。重金属干沉降量呈现出的冬、春季明显高于夏、秋季的季节性差异特征。干沉降量较高的监测点集中在JC3、JC4和JC7。水库附近的煤化工企业排烟和库区旅游进、出车辆尾气是导致重金属干沉降出现空间分布差异的主因。降水量和降水频率增多，造成夏、秋季大气湿沉降重金属浓度明显低于冬、春季。.阐明干沉降颗粒物重金属吸附-解吸机理。干沉降颗粒物等温吸附过程符合Langmuir模型，对Cd和Zn的吸附量与大气颗粒有机质和黏粒含量较高有关。此外，较高的吸附率主要与由溶液中较高的初始浓度及干沉降物较多的吸附位点有关。解吸率随时间变化的关系可用乘幂函数拟合。Cd和Zn的解吸过程与吸附过程的规律基本一致，都分为快、慢反应两阶段。.解析水库重金属污染源及其污染贡献。通过相关性分析可判断Cu和Ni均来自煤化工厂。Ni和Cd呈负相关，证明Cd具有季节性特征。借助HYSPLIT4模型进一步验证冬季采暖期烟尘和春季沙尘暴是造成水库水环境变差的主要成因。Zn元素的沉降量明显高于其他元素，月均沉降值高达3.918t，且在7月和10月沉降量均很高，10月沉降量高达12.0t。.评估水库重金属污染潜在健康风险等级。水库丰、平、枯蓄水期，7种重金属平均浓度为0.014~0.129mg/L，浓度从高到低依次为Al、Cu、Ni、Cr、Pb、Fe、As，均符合《地表水环境质量标准》中的Ⅲ类标准。致癌风险值均小于国际辐射防护委员会所推荐的最大可接受水平，水库暂无较大致癌与非致癌风险。.本研究填补了沙源区大气重金属沉降对地表水环境贡献研究的空白，对于明确风沙活动对水库重金属污染的贡献，揭示沙区水库重金属污染特征和污染机理有重要学术价值。.