湘南柿竹园东河流域农田土壤重金属污染特征及风险评价

Pollution characteristics and risk assessment of heavy metals in farmland soils at Shizhuyuan Donghe River basin of Southern Hunan

以湘南柿竹园东河流域农田土壤为研究对象,分析了土壤重金属元素Pb、Zn、As、Cu、Hg、Cd的总量和赋存形态特征,并运用3类评价方法对研究区土壤重金属污染进行风险评价.结果表明,研究区6种重金属含量均超过了农用地土壤污染风险筛选值,超标率最低为50%,最高达90.91%.土壤中As、Cu、Hg以残渣态为主,Pb以残渣态和可还原态为主,Cd则以弱酸提取态和可还原态占绝对优势,而Zn表现出多种形态分布特征.基于总量的潜在生态风险指数法结果表明,研究区上中下游段农田土壤的潜在生态风险等级分别为中等、高等、中等,潜在生态危害为Cd>Hg>Pb>As>Cu>Zn;基于模型的投影寻踪等级评价法结果表明,研究区上下游段主要为轻污染,中段为重-极重污染,其中以Cd、Pb为主要污染因子;基于形态的风险评估编码法价结果显示:Cd属于高-极高风险,Zn、Hg属于中等风险,Pb、As、Cu属于低风险.综合3种评价结果表明,研究区上中下游段的潜在生态风险分别处于中等、高-极高、中等风险水平,Cd是整个研究区的主要污染元素,急需采取防控措施.

In this study,the total concentration and speciation characteristics of Pb,Zn,As,Cu,Hg and Cd in farmland soils at Shizhuyuan Donghe River basin in southern Hunan were tested and analyzed.Three evaluation methods were used to evaluate the risk assessment of heavy metals in the farmland soil.The results showed that the total concentration of six heavy metals in the soil all exceeded the risk screening values for soil contamination of agricultural land,with the minimum exceeding rate being 50%and the maximum exceeding rate being 90.91%.The analysis of the speciations for soil heavy metals indicated that As,Cu and Hg gave priority to the residual fractions,Pb was mainly composed of the residual and reducible fractions,Cd was dominated by the acid-soluble fractions and reducible fractions,and Zn exhibited various morphological characteristics.The potential ecological risk index based on the total content showed that the potential ecological risk levels of the farmland soils in the upper,middle,and lower sections of the study area were medium,high,and medium levels,respectively,while the potential ecological hazard index was Cd>Hg>Pb>As>Cu>Zn.The model-based projection pursuit rating evaluation method showed that the upper and lower reaches of the study area were mainly light pollution,and the middle reaches was heavy to extremely heavy pollution level,while the main pollution factors were Cd and Pb.The risk assessment code based on chemical species showed that Cd belongs to high-pole high risk level,Zn and Hg were medium risk level,and Pb,As and Cu were low risk level.Therefore,the evaluation results of above three methods indicated that potential ecological risk of the soils in the upper,middle,and lower sections of the study area were medium,high to pole high and medium level,respectively.Notably,Cd was the main pollution factor in the farmland soil.It was urgent to take preventive and control measures to reduce its harm.