Heavy metal pollution of soil and its ecological risk evaluation in the phosphate mining area in central Guizhou
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(Igeo),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 Igeo analysis revealed that the average Igeo value for Hg was 4.45,showing severe to extreme pollution.The average Igeo values for As,Se,and Cd ranged from 3.35 to 3.65,indicating heavy pollution.Igeo 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 Igeo 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.
the phosphate mining area in central Guizhouheavy metal pollution in soilNemerow pollution indexgeo-accumulation indexHankanson potential ecological risk indexecological risk evaluation
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