北京表层土壤重金属污染分布及大气沉降贡献

Pollution Distribution of Topsoil Heavy Metals in Beijing and Its Atmospheric Deposition Contribution

土壤重金属污染已成为影响城市可持续发展和生态环境安全的重大环境问题。对城市表土重金属污染状况以及来源进行系统分析具有重要意义。于2013年11月—2014年3月同步采集了北京城区及周边不同位置的大气沉降和0—10 cm表层土壤样品,采用ICP-MS测试了样品中主要重金属Cd、Cr、Cu、Ni、Pb和Zn的质量分数。利用富集因子和地累积指数法探讨了北京表层土壤重金属的污染状况,并对大气沉降贡献进行了定量表征。结果表明,北京表层土壤中重金属Cd、Cr、Cu、Ni、Pb和Zn的平均质量分数分别为0.5、76.8、51.3、25、35.2和133.4 mg·kg^(−1)。6种重金属质量分数都存在明显的“粒径递减”效应,即在2—63μm粒径段,表土重金属质量分数一般随粒径的减小而升高,粒径越小重金属在表土中的富集越明显。北京表层土壤中重金属Cr和Ni基本无污染,Cu、Zn和Pb轻微污染,Cd轻度污染;6种重金属都呈现不同程度的轻度富集(Cd>Cu>Zn>Pb>Cr>Ni),均受自然源和人为污染源的共同影响。海淀区、朝阳区、东城区和西城区这4个区的交界区域存在Cd、Cu和Pb连片轻度、中度污染至偏重污染。朝阳区和东城区的交界区域、海淀区东南部、西城区西部、东城区西部存在Zn连片轻度污染至中度污染。北京表土中重金属Cd、Cr、Cu、Ni、Zn和Pb的大气沉降平均贡献率分别为17.4%、21.2%、14.6%、12.2%、16.0%和20.0%。北京表层土壤重金属污染主要集中在细粒径颗粒,表现出较强的空间分异性,并且受大气沉降不同程度的影响。

In order to study urban surface soil heavy metals pollution condition and the contribution of atmospheric deposition,the atmospheric deposition and 0‒10 cm surface soil samples of different spatial sites in and around Beijing City were collected from November 2013 to March 2014.Then heavy metals Cd,Cr,Cu,Ni,Pb,and Zn concentrations of samples were measured by ICP-MS.The pollution condition of heavy metals in the surface soil of Beijing was studied by means of enrichment factor and geoaccumulation index,and the contribution of atmospheric deposition was quantitatively characterized.The results showed that the average contents of Cd,Cr,Cu,Ni,Pb and Zn in the topsoil of Beijing were 0.5,76.8,51.3,25,35.2 and 133.4 mg·kg^(−1),respectively.The contents of all the six heavy metals showed an obvious"particle size reduction"effect,that is,in the 2‒63μm particle size range,the heavy metal content of topsoil generally increased with the decrease of particle size,and the smaller the particle size was,the more obvious the enrichment of heavy metals in the topsoil was.The surface soil in Beijing was basically free from pollution with heavy metals Cr and Ni,Cu,Zn and Pb slightly polluted,and Cd mildly polluted.All the 6 heavy metals showed mild enrichment to different degrees(Cd>Cu>Zn>Pb>Cr>Ni),which were affected by both natural and man-made pollution sources.The border area of Haidian district,Chaoyang District,Dongcheng District and Xicheng District were mildly,moderately and even heavily polluted by Cd,Cu and Pb.The border area between Chaoyang District and Dongcheng District,the southeast of Haidian District,the west of Xicheng District and the west of Dongcheng District were slightly or even moderately polluted by Zn.The average contribution rate of atmospheric deposition of heavy metals Cd,Cr,Cu,Ni,Zn and Pb in Beijing topsoil was 17.4%,21.2%,14.6%,12.2%,16.0%and 20.0%,respectively.Heavy metal pollution in Beijing surface soil is mainly concentrated in fine particle size,which shows strong spatial differentiation and is affected by atmospheric deposition to different degrees.