| In recent years,soil heavy metal pollution has increased significantly,which has already jeopardized human health.Especially in the karst area with high geological background,the safe production of vegetable fields in the suburbs of the city is closely related to the life of the residents.Based on the preliminary study of the sample and pollution status of the suburban vegetable fields in Guiyang,this paper takes the vertical section soil of the vegetable field in the suburb industrial park of Baiyun District of Guiyang as the research object,and carries out the evaluation of soil heavy metal pollution in the vegetable suburbs of urban suburbs.Quantitative analysis of pollution traceability.Combined with the multivariate statistical analysis method and isotope tracer method of receptor model,the pollution distribution characteristics and migration law of heavy metals in vertical soil profiles of suburban vegetable fields were revealed,in order to provide a scientific basis for the prevention and control of heavy metal pollution in suburban vegetable fields in karst area.The main findings are as follows:?1?The vertical section of the vegetable field in the suburbs of Guiyang is mainly silty clay,which is weakly alkaline and rich in organic matter.The average values of Ni,Cr,Cu,Zn,Pb,Cd and Hg exceeded the soil background value of Guizhou Province.The Ni and Cd contents of a few points exceeded the heavy metal risk screening value of agricultural land,Cu,Pb and Hg were in a high accumulation state,while Ni and Hg had the possibility of point source pollution disturbance.?2?The distribution of soil heavy metals Ni,Cr,Cu,Zn,Pb,Cd,As and Hg in the study area generally showed a trend of decreasing from the surface layer to the bottom layer.As the soil depth increases,the level of content is close to the natural background value.The elements with higher accumulation rate of heavy metals in040 cm layer are Ni,Cd,Cu,Zn,and the accumulation rate of heavy metals in different vertical sections generally shows the law of sedimentary layer>organic layer>leaf layer>subsoil layer.?3?The analysis of soil heavy metal pollution by using Igeo and potential ecological risk?RI?indicates that the maximum Igeo of Cd appears in the leaching layer of 3040 cm,mainly due to the infiltration and accumulation of artificial pollution.The soil Hg is higher than other heavy metals,which may be due to the high Hg background in the karst area.The Igeo of Hg and Cd are between 1 and 2,reaching the level of moderate pollution,and mainly accumulating between the topsoil and the deposited layer.The results of RI showed that Cd pollution in suburban vegetable fields had reached a medium potential ecological risk,and Hg pollution had reached a strong potential ecological risk.?4?The results of health risk assessment showed that the non-carcinogenic risk HQ of the surface soils of different sections?Cu,Zn,Pb,Hg?was less than 1 under the two exposure pathways,and the adult HQ index was 2.11×10-2.The children's HQ index was the largest.It is 1.85×10-1;the risk of non-carcinogenic health is:oral intake>skin contact;children>adults.The risk of carcinogenicity of heavy metals?Cd,As,Ni,Cr?under both exposure pathways is less than 1,and the risk of carcinogenic health of children with soil heavy metals is higher than that of adults.The risk of carcinogenic risk of Cr,Ni and As exceeded the maximum acceptable limit of health hazard risk,indicating potential health risks;Cd carcinogenic risk value was 1.706×10-66.439×10-9 In the range of the maximum acceptable limit of health hazard risk?1.0×10-6?,it indicates that Cd has a low carcinogenic risk and will not cause health hazard to human body.Overall,the total hazard of various heavy metals shows that the risk of health hazards of both exposure pathways is within acceptable limits and does not pose a significant cancer risk to the human body.?5?According to the Binary Mixing model of lead isotope composition,the binary linearity of 208Pb/206Pb-207Pb/206Pb in the four sections of JA,YH,LY and BN is extremely high,and the source of Pb isotope components is relatively high.Concentrate and compare the compositional data of different Pb isotopes and cross-section soil Pb isotopes of coal-fired dust,automobile exhaust dust,sludge waste-water,organic fertilizer,building materials and parent soil,and find the natural end-members of soil Pb.From the soil parent material,the artificial Pb source comes from sludge waste-water,gasoline dust and coal burning dust.By analyzing the relative contribution rate of each pollution source to soil lead pollution,the average contribution rate of soil total lead source in the vertical section of vegetable fields in Guiyang City was obtained.The average contribution rate of coal and automobile tail gas dust lead was 16.83%.The source lead contribution rate was 39.54%,and the natural source lead contribution rate was 43.63%.?6?Soil elemental pH and SOM content were not affected by particle size by correlation analysis.However,the contents of Cr,Zn,Cd,As and Hg were correlated with particle size.There is a correlation between heavy metals such as Cu-Cd-Cr,As-Zn-Pb,and Ni-Hg,which may have the same source.The results of principal component analysis?PCA?and cluster analysis?CA?showed that the contribution rate of As-Zn-Pb as the first principal component was 28.52%,which was mainly from pesticide spraying and foliar fertilization residue,which reflected chemical fertilizers and pesticides.The application of pollution to the environmental soil.The contribution rate of Cd-Cr-Cu as the second main component is 23.16%,indicating that the second principal component is mainly affected by the anthropogenic causes of copper-containing sewage irrigation in the surrounding factories.The contribution rate of Ni-Hg as the third principal component is 21.42%,which is mainly affected by the geochemical genesis of high geological background values in karst areas. |
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