典型山区燃煤型电厂周边土壤重金属形态特征及污染评价

为了揭示毕节金沙电厂周边土壤重金属（Hg、As、Cd、Cr、Cu、Pb和Zn）污染状况，在电厂周围采集了32个土壤表层样品，采用改进的BCR连续提取法进行形态分析，并以Hakanson潜在生态危害指数法、改性灰色聚类法及风险评估编码法（RAC）进行生态风险评估.结果表明：重金属含量变化具有一定的空间变异结构和空间分布特征，除了Cd和Cr的含量平均值低于贵州省土壤平均背景值外，其余重金属含量的平均值均大于该背景值.土壤中的大部分重金属主要以残渣态形式存在，而Cd主要以酸可提取态和可还原态存在，具有很强的环境危害.相关性分析结果显示，Hg与As、Cd表现为极显著相关，而Zn与其余重金属元素相关性都较弱.生态风险评价得出7种重金属的生态风险大小顺序为Cd > Hg > As > Cu > Pb > Zn > Cr，综合潜在生态风险指数（RI）平均值为129.72，处于中等生态风险.通过改性灰色聚类法对土壤重金属污染进行分析评价，表明电厂西面污染明显高于东面，且Hg和Cd为主要污染物；由风险评估编码法得出元素Cd有效态占18.17%，对环境构成中等风险等级，元素Cr和Zn对环境的危害处于低风险状态，元素Hg、Pb、As和Cu处于无风险状态.综合以上研究结果，金沙电厂土壤受到不同程度的重金属污染，应特别重视Hg和Cd这两种重金属污染的治理.

Chemical forms and risk assessment of heavy metals in soils around a typical coal-fired power plant located in the mountainous area

In order to investigate chemical forms of heavy metals in soil around the power plant located in Jinsha County, Bijie City, thirty-two surface soil samples were collected and analyzed using the modified Community Bureau of Reference (BCR) sequential extraction procedure. The risks of the heavy metals were evaluated using the potential ecological risk index proposed by Hakanson, the modified grey clustering, and risk assessment code (RAC). The results obtained showed that some differences were found in the spatial distributions of the heavy metals, and the concentrations of all heavy metals (except for Cd and Cr) were higher than the background values in soils from Guizhou. The majority of the heavy metals were primarily kept in residual fractions, while Cd existed mainly in acid soluble and reducible fractions. The results of correlation analysis showed that the correlations among Hg, As, Cd and Ni were significantly positive, while the correlations of Pb and Zn with the other heavy metals were weak. The results from potential ecological risk assessment indicated that the order of ecological risk for the seven heavy metals was Cd > Hg > As > Cu > Pb > Zn > Cr. The average ecological risk index (RI) was 129.72, suggesting a medium ecological risk to local ecological system. The results of modified grey clustering method showed that the pollution level in the west of the power plant was obviously higher than that in the east, and Hg and Cd were the main pollutants. Based on the analysis with RAC method, Cd was of medium risk to the environment (18.17%). Accordingly, Cr and Zn posed low risk, whereas Hg, Pb, As and Cu posed extremely low risk to the environment. In summary, surface soil around the coal-fired power plant was polluted to different degrees by heavy metals, and special attention should be paid to the treatment of Hg and Cd pollution.