黔中磷矿区土壤重金属污染及其生态风险评价

Heavy metal pollution of soil and its ecological risk evaluation in the phosphate mining area in central Guizhou

为评价黔中磷矿区土壤重金属污染风险,采用梅花布点法在磷矿区周边区域和无矿区不同地层天然土壤采集24件表层土壤样品,测定Cu、Pb、Zn、As、Hg、Se、Cd、和Cr含量,并采用内梅罗综合污染指数(NPI)、地累积指数(I_(geo))以及Hankanson潜在生态危害指数(RI)对磷矿区土壤重金属的污染程度和潜在生态风险进行评价。结果表明,黔中磷矿区土壤中Hg、Se、Cd、As、Pb、Zn和Cr等元素平均含量分别为贵州土壤背景值的37.58倍、24.40倍、19.26倍、18.09倍、2.67倍、2.17倍和1.78倍,各重金属富集特征明显,Cu元素平均含量未超过贵州省土壤背景值。研究区土壤中Hg、Se、Cd、As、Pb、Zn和Cr等元素NPI平均值介于4.59~69.32之间,处于重度污染水平,而Cr和Cu元素NPI平均值分别为1.89和1.21,处于轻度污染水平。研究区Hg元素I_(geo)平均值为4.45,处于严重至极重污染;As、Se和Cd元素I_(geo)平均值介于3.35~3.65之间,处于重度污染;Pb、Zn和Cr元素I_(geo)平均值0.21~0.44之间,处于未污染至中度污染水平,而Cu元素I_(geo)平均值为-0.83,显示其未受到污染。潜在生态风险评价结果表明,研究区土壤Hg元素处于极强生态风险水平,Cd处于强生态风险水平,Ad处于中等生态风险水平,而Cu、Pb、Zn和Cr均处于轻微风险水平。黔中磷矿区土壤RI平均值为2285.50,显示出极强生态风险,Hg是最主要的生态风险元素,应引起高度重视。

To investigate the current status of heavy metal pollution of soil in the phosphate mining area in central Guizhou and to comprehensively evaluate the potential pollution risks of eight heavy metal elements,a systematic sampling approach was employed in a plum blossom pattern.A total of 24 topsoil samples were collected from the surrounding areas of the phosphate mining area and from different strata in the non-mining area.The concentrations of Cu,Pb,Zn,As,Hg,Se,Cd,and Cr were determined.Based on the test results,comprehensive evaluations of the degree of heavy metal pollution and potential ecological risks in the topsoil of the mining area were conducted in terms of the Nemerow Pollution Index(NPI),Geo-accumulation Index(I_(geo)),and Hankanson Potential Ecological Risk Index(RI).The results indicate that the average concentrations of Hg,Se,Cd,As,Pb,Zn,and Cr in the topsoil of the phosphate mining area in central Guizhou were 3.83 mg·kg-1,8.42 mg·kg-1,2.29 mg·kg-1,240.6 mg·kg-1,65.83 mg·kg-1,141.4 mg·kg-1,and 145.8 mg·kg-1,respectively.These values were 37.58,24.40,19.26,18.09,2.67,2.17,and 1.78 times higher than the corresponding background values of soil in Guizhou,indicating significant enrichment of these heavy metals in the study area.In contrast,the average concentration of Cu did not exceed the background value of the surrounding soil.The evaluation of heavy metal pollution in the topsoil showed that NPI values for Hg,Se,Cd,As,Pb,Zn,and Cr ranged from 4.59 to 69.32,indicating a general level of heavy pollution.Specifically,NPI values for Hg,Se,As,Cd,and Pb were 75.73,55.21,35.36,19.75,and 10.32,respectively,all demonstrating heavy pollution.NPI values of Cr and Zn were 2.17 and 2.11,respectively,suggesting moderate pollution.The lowest NPI values were observed in Cr and Cu,with averages of 1.89 and 1.21,respectively,indicating light pollution.The I_(geo)analysis revealed that the average I_(geo)value for Hg was 4.45,showing severe to extreme pollution.The average I_(geo)values for As,Se,and Cd ranged from 3.35 to 3.65,indicating heavy pollution.I_(geo)values of Pb,Zn,and Cr averaged between 0.21 and 0.44,suggesting a range from unpolluted to moderate levels of pollution.The average I_(geo)value for Cu was-0.83,indicating an unpolluted level.The evalution of potential ecological risk showed that the single-element RI for Hg in the topsoil was 1,533.33,indicating an extremely high ecological risk.The single-element RI value for Cd was 298.91,indicating a high ecological risk,while the value of As is 180.92,indicating a very high ecological risk.The values for Cu,Pb,Zn,and Cr were all below 10,suggesting minor risk levels.Overall,the average RI value for the topsoil in the phosphate mining area was 2,285.50,indicating an extremely high potential ecological risk.Hg was identified as the primary ecological risk element,followed by Cd and As,warranting significant attention and management measures.