南京城郊某典型退耕农用地土壤重金属含量特征与污染评价分析

CONCENTRATION CHARACTERISTICS AND POLLUTION ASSESSMENT OF HEAVY METALS IN SOIL OF A WITHDRAWAL CULTIVATED LAND IN SUBURB OF NANJING

通过对比土壤背景值、筛选值,对南京城郊某典型退耕农用地45个点位深度至6 m的166个土壤样品中Cu、Ni、Cd、As、Pb、Hg、Be、Sb、Co、V 10项重金属含量特征进行分析与污染评价。结果表明:1)10种重金属含量最大值均超过背景值;Cu、Cd、As、Pb、Hg含量最大值均超过GB 15618—2018《土壤环境质量农用地土壤污染风险管控标准》;As、Co含量最大值超过GB 36600—2018《土壤环境质量建设用地土壤污染风险管控标准》;Cd含量变异系数最大,Hg次之;2)Hg、Cd、Pb含量最大值在上层(A或B层)的频次明显较高,As、V含量最大值在下层(C层或D层)的频次明显较高;Hg含量在最大值与中位值上均呈A层递减至D层趋势,Cd含量呈U形;3)单因子指数评价发现,Cu、Cd、As、Pb、Hg存在重度污染,污染程度大于其他重金属;内梅罗指数评价发现,对比GJA,JSA,NJ 3种背景值、NY筛选值、JSH1筛选值,评价结果分别呈70%以上各层样品为轻度污染等级,90%以上各层样品为安全等级,100%各层样品为安全等级;4)重金属相关性上,As-Sb(0.810)相关性最高,Hg与其他重金属相关性较弱;结合主成分分析,重金属主要来自自然成土过程、农业耕作类强人为源以及城郊大气沉降类弱人为源3个来源;土壤中Cu、Ni、Cd、As、Pb、Sb含量主要受成土过程影响,其次为人为源,同时Co、V基本未受人为源影响;Hg、Be含量除受成土原因影响外,受人为源影响大。

The concentration of 10 heavy metal elements(Cu,Ni,Cd,As,Pb,Hg,Be,Sb,Co,V) in the soil of a withdrawal farmland in suburb of Nanjing were analyzed and evaluated by comparing with the soil background values and risk screening values(the screening values of agricultural land and construction land).The main conclusions were as follows:1) the maximum content of the 10 heavy metals all exceed the background values.The maximum content of Cu,Cd,As,Pb and Hg exceeded the screening value of farmland.The maximum content of As and Co exceeded the screening value of construction land.The variation coefficient of Cd content was the largest and Hg was the second.2) For the distribution characteristics of the concentration,the frequency of highest content of Hg,Cd,Pb in upper layer was higher than that in the lower layer,but As,and V was on the opposite.The content of Hg decreased from layer A to layer D in both maximum and median values,while content of Cd showed a U-shape.3) Single factor index showed that Cu,Cd,As,Pb and Hg were heavily polluted with higher pollution degree than other heavy metals.Nemerov composite pollution index showed that more than 70% of the samples in each layer were in light pollution level,compared with the background values,more than 90% of the samples in each layer were in safe level compared with screening value of NY,and 100% of the samples in each layer were in safe level compared with JSH1.4) As and Sb(0.810) had the highest correlation with each other,while Hg had weak correlation with other heavy metals.Combined with correlation analysis and principal component analysis,heavy metals mainly came from three sources:natural soil forming process,strong man-made sources of agricultural cultivation and weak man-made sources,like atmospheric deposition in suburban areas.The concentrations of Cu,Ni,Cd,As,Pb,Sb in soil were mainly affected by natural soil forming process firstly and then man-made sources,but Co and V were not affected by man-made sources.Hg and Be were greatly affected by man-made sources besides natural soil forming.