南方典型酸性红壤区土壤重金属潜在生态风险评价

Assessment of potential ecological risk of heavy metals in the soil of typical acidic red soil region in South China

采集了南宁市江南区主要农田土壤样品4 956件,分析了As、Hg、Cd、Cr、Cu、Zn、Pb和Ni含量,应用地质累积指数、富集因子、污染指数和潜在生态风险指数,评价了研究区农业土壤重金属元素生态风险。结果表明,As、Hg、Cd、Cr、Cu、Zn、Pb和Ni含量平均值分别为25、0.13、0.31、155.64、26.77、80.02、48.36、22.49 mg/kg。土壤中重金属Cr和Cd含量平均值略高于国家土壤环境质量二级标准,其余元素平均值均低于标准值。重金属元素富集因子变化范围0.52~1.51,表明研究区元素以贫乏—弱富集为主。Cr和Pb平均值最高,分别有17%和19%样品富集因子大于2,表明局部地区土壤受到人为活动影响。地质累积指数和污染指数结果表明研究区局部区域受到Cr和Pb的污染。综合污染指数PLI平均值为1.03,整体平均水平属于无污染—轻度污染水平。无污染、轻度污染、中度污染、中—强污染、强污染和极强污染等级样品比例分别为63%、29%、4%、2%、1%和1%。单元数潜在生态风险指数顺序为Hg>Cd>As>Pb>Ni>Cu>Cr>Zn,Hg和Cd生态风险较高。从综合潜在生态风险指数来看,8种重金属综合潜在生态风险指数平均值为96,属于轻微生态危害;轻微、中等、强和很强生态风险等级的样品比例分别为88.28%、9.12%、2.12%和0.48%。

The total concentration of As,Hg,Cd,Cr,Cu,Zn,Pb and Ni were determined in 4 956 topsoil samples collected from agricultural soils of Jiangnan district of Nanning city. The ecological risk assessment for As,Hg,Cd,Cr,Cu,Zn,Pb and Ni in the agricultural soils was evaluated using the geoaccumulation index,enrichment factor,pollution index and potential ecological risk index.The results showed that the average concentrations of As,Hg,Cd,Cr,Cu,Zn,Pb and Ni were 25、0. 13、0. 31、155. 64、26. 77、80. 02,48. 36,22. 49 mg/kg,respectively. The average concentrations of Cr and Cd were slightly exceeded the Environmental Quality Standards for soils of China（ GB15618-1995）,others were all within the Chinese soil quality guidelines. For eghit meals the enrichment factors were 0. 52 to 1. 51,while the mean values indicated the heavy metal elements in the investigated area were mainly poor and weak enrichment. The average values of Cr and Pb were the highest,the enrichment factors of 17% Cr sample and 19% Pb sample were more than 2,indicating that Cr and Pb were mainly originated from human source. The Igeo and the pollution index values showed that some studied area were contaminated by Cr and Pb. The average PLI value of aoo soil samples was 1. 03,indicating that the overall average level was non-pollution to mild pollution level. The proportions of unpolluted,mild polluted,moderate polluted,medium strong polluted,strong polluted and extremely strong polluted soil samples were 63%,29%,4%,2%,1% and 1% respectively. The descending order of potential ecological risk for single metal was HgCdAsPb Ni Cu Cr Zn,and the risks of Cd and Hg were at a higher level. In view of the potential ecological risk,agricultural soils in the study area showed low potential ecological risk.According to the comprehensive potential ecological risk index,the average value of potential ecological risk index for 8 of heavy metals in the studied area was 96,being of mild ecological hazards. The mild,moderate,considerable and high ecological risk of the soil samples were88. 28%,9. 12%,2. 12% and 0. 48%,respectively.