长株潭地区土壤Cd和Pb固液分配特征与环境风险

Solid-solution Partitioning Coefficients and Environmental Risk of Cd and Pb in Soil in Chang-Zhu-Tan Area

区域尺度上土壤重金属下渗迁移的环境风险存在较大空间变异性.以长株潭城市及其周边土壤为对象,研究了不同土地利用类型,土壤Cd和Pb有效态含量和固液分配系数(Kd)的分布特征及其影响因素,并基于CaCl_(2)(固液比为1∶0.5)测定的Kd揭示了研究区土壤重金属下渗迁移的环境风险.结果表明,研究区土壤Cd和Pb有效态含量大小呈现出:自然林地>郊区农田>城市绿地>工业区绿地.土壤Cd的Kd均值为449.79 L·kg^(-1),Pb的Kd均值为27604.07 L·kg^(-1),说明土壤Cd迁移性显著高于Pb.林地土壤重金属的Kd显著低于其它3种土地利用类型土壤.土壤Cd和Pb的Kd主要受土壤pH和重金属总量的影响.在此基础上,引入CaCl_(2)(固液比为1∶10)测定的重金属有效态含量作为因变量,构建的多元回归模型可以较好地预测土壤Cd和Pb的Kd,R^(2)分别为84.2%和67.6%.环境风险评估结果表明,研究区93.8%~96.1%采样点的土壤Cd和Pb无下渗迁移风险,少数靠近工厂且土壤pH较低的采样点存在轻度风险.土壤重金属的迁移性和污染源分布共同决定了重金属下渗迁移的环境风险.研究结果可以为区域土壤重金属污染风险防控提供方法和理论支撑.

The leaching risk of heavy metals in soil has a large spatial variability on a regional scale.Taking the Chang-Zhu-Tan area as the research object,this work studied the distribution and influencing factors of available contents and solid-solution partition coefficient(Kd)of Cd and Pb in soil with land uses and clarified the environmental risk of heavy metals in soil based on Kd values measured by CaCl_(2)(soil-to-water ratio,1:0.5).The results showed that the contents of available Cd and Pb in soil followed the order of forest land>suburban farmland>urban green space>industrial green space.The average Kd of Cd in soil was 449.79 L·kg^(-1),and that of Pb was 27604.07 L·kg^(-1),indicating that the mobility of Cd in the soil was significantly higher than that of Pb.The Kd values of forest soil were significantly lower than that in the other land uses.The Kd values were mainly affected by soil pH and the total content of heavy metals in soil.Adopting the available content of heavy metals measured by CaCl_(2)(soil-to-water ratio,1:10)as a dependent variable,the multiple regressions effectively predicted the Kd values of Cd and Pb in soil,with R^(2)values of 84.2%and 67.6%,respectively.The environmental risk assessment indicated that the leaching risk in 93.8%-96.1%of the sampling sites could be ignored,whereas a few sampling sites near factories with low pH may pose a risk to the groundwater environment.The mobility of heavy metals in soil and the distribution of pollution sources determined the leaching risk of heavy metals.The results provide a method and theoretical support for preventing the environmental risk of heavy metals in soil on a regional scale.