农用地土壤Cd有效态含量的安全阈值研究

为科学评估利用累积概率分布曲线研究土壤有效态Cd含量安全阈值的可行性，该研究参考物种敏感性分布法(SSD)的方法原理，以江西省上饶市Cd污染农田为研究对象，在统计分析区域农田土壤重金属总量、有效态含量和水稻籽粒中重金属含量的基础上，采用土壤总Cd含量-土壤有效态Cd含量线性回归方程以及基于Logistic函数分布模型的累积概率分布曲线模拟计算，分别推导土壤中有效态Cd的安全阈值并对比分析. 结果表明:研究区农用地土壤存在较大范围的Pb、Cd超标现象，点位超标率分别为54.70%和68.38%，土壤有效态Cd含量较高，平均值为0.22 mg/kg；研究区有34.98%的点位存在糙米Cd含量超标，Cd是研究区农用地土壤和糙米中的主要污染物. 通过线性回归方程和《土壤环境质量 农用地土壤污染风险管控标准(试行)》(GB 15618—2018)中的土壤筛选值，反推计算研究区农用地土壤中有效态Cd含量的阈值为0.149~0.183 mg/kg. 利用Logistic函数分布模型拟合基于有效态Cd含量的累积概率分布曲线，保护当地95%的糙米不超标的土壤有效态Cd含量的安全阈值为0.160 mg/kg. 研究显示，基于累积概率分布曲线法推定重金属有效态含量安全阈值较为科学，建议用作当地重金属污染农用地土壤钝化修复目标值，并对其他Cd污染农用地土壤的修复治理具有参考意义. 

Study on Safety Threshold of Available Cd in Agriculture Land Soil

In order to evaluate the feasibility of using the species sensitivity distribution method (SSD) to study the safety threshold of available Cd in agriculture land soil, Cd-contaminated farmland in Shangrao City, Jiangxi Province was used as the research object in this study. In our research, the total heavy metals, the available content of heavy metals, and heavy metal content in rice grains were statistically analyzed, and the linear regression equation of total soil Cd-soil available Cd content and the SSD method based on logistic function distribution model were used to derive the safety thresholds for the availability of Cd in soils. The results showed that Pb and Cd in farmland soil exceeded the standard by a large margin, and the exceeding rates were 54.70% and 68.38%, respectively. The Cd available content in the soil was high, with an average value of 0.22 mg/kg. The Cd content of brown rice in 34.98% of the sites exceeded the standard, and Cd was the main contaminant in farmland soils and brown rice in this study area. Comparative analysis showed that the linear regression equation and soil screening value criteria of Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018) were used to back-calculate the soil Cd availability content thresholds of 0.149-0.183 mg/kg in agricultural soils and using a Logistic function distribution model to fit an SSD curve based on the available content, the safe threshold value of soil availability Cd to protect 95% of local brown rice from exceeding the standard was 0.160 mg/kg in the study area. The results further verified that the safe threshold for the available content of heavy metals based on the SSD method is more scientific and can be used as the target value for soil stabilization remediation of local heavy metal-contaminated farmland soil, which has reference significance for the remediation of Cd contaminated agriculture land in other areas.