株洲城郊农田土壤重金属污染特征与Pb同位素示踪

通过采集湖南株洲城郊农田区表层土壤（A层），并分析其Cd、Hg、Pb、Zn等重金属元素含量，研究了土壤中重金属元素的污染特征.为示踪这些金属元素的来源，选择农田区典型土壤样品及湘江沉积物、污染源区土壤样品，进行重金属元素含量和Pb同位素组成测定.结果表明，农田区A层土壤受到不同程度的重金属污染，其中，Cd、Hg、Pb、Zn含量最高，分别为21.71、24.52、261.49、577.94 mg·kg^-1，且Cd、Pb、Zn元素之间显著相关，而研究区附近湘江水体和沉积物中这些元素含量没有增高，说明这些重金属不是来自湘江，而是可能主要来自冶炼厂；铅同位素显示，冶炼厂附近A层土壤²⁰⁶Pb/²⁰⁷Pb值（1.150~1.164）低于周边区域A层土壤（1.164~1.169），²⁰⁸Pb/²⁰⁶Pb值（2.108~2.122）高于周边地区（2.106~2.119），说明受到人为污染的影响.从污染区分布空间位置和铅同位素源解析的结果看，农田区土壤中Cd、Hg、Pb、Zn等重金属的主要污染源是冶炼厂的冶炼烟气粉尘及与农耕活动有关的其他人为污染.

The features of heavy metal contamination and possible sources from Pb isotopic evidence in farmland soils, Zhuzhou suburb

The characteristics of heavy metal pollution in farmland soil were studied by collecting surface soil (A horizon) and analyzing the concentration of metal elements including Cd, Hg, Pb and Zn etc. in Zhuzhou suburb of Hunan. Meanwhile, the samples of typical farmland soil and possilbe metal source soil, water and sediments from Xiangjiang River were selected and analyzed for the metal elements and Pb isotope composition to trace the sources of these metal elements. The results show that the A horizon soil in the farmland area was polluted by heavy metals in different degrees, of which the highest contents of Cd, Hg, Pb and Zn can reach 21.71, 24.52, 261.49 and 577.94 mg·kg^-1 respectively, and the Cd, Pb and Zn elements were obviously correlated. The contents of these elements in Xiangjiang water and sediment near the research area did not increase significantly. It suggest that the smelters rather than Xiangjiang River should be blamed for the metal pollution in soils. Lead isotope ratios show that the ²⁰⁶Pb/²⁰⁷Pb (1.150~1.164) in A horizon soil near the smelter is lower than that of A horizon soil (1.164~1.169) in the surrounding area, and ²⁰⁸Pb/²⁰⁶Pb (2.108~2.122) is higher than that of the surrounding area (2.106~2.119). The Pb ratios indicate that the Pb and other metals might come from human pollution. Based on the spatial distribution of metal pollution areas and the lead isotope features, it can be concluded that the main pollution sources of Cd, Hg, Pb and Zn in farmland soils are gas dust from smelters and some other man-made pollution through agriculture activity.