| In order to understand the main polluting metals and pollution sources in the abandoned manganese mining area in Xiangtan City,identify areas with serious heavy metal pollution.In this paper,the abandoned manganese mining area of Xiangtan,Hunan Province was used as study area.Collect and analyze the surface soil(0-20cm)and three crops(rice,sweet potato and corn)in the study area through field sampling and other methods.Measure the content of7 heavy metals(Mn,Pb,Cu,Zn,Cr,Cd and Ni)in soil and crops.The pollution degree and spatial distribution characteristics of the potential toxic elements in the soil were analyzed by using multivariate statistical methods.The correlation between heavy metals and the sources in the soil were analyzed,and the ecological risks and human health risks are evaluated.In addition,the degree of pollution of heavy metals in crops and the ability of crops to absorb potential toxic elements in the soil have been studied.Finally,the health risks of edible crops to the human body were evaluated.The main contents and results of the study are as follows:(1)The average concentration of Mn,Pb,Cu,Zn,Cr,Cd,and Ni in the soil samples in the study area were:2128.25mg/kg,40.86mg/kg,45.00mg/kg,201.98mg/kg,41.24mg/kg,0.54 mg/kg and 30.94mg/kg,were 4.64 times,1.38 times,1.65 times,2.14 times,0.58 times,4.29 times and 0.97 times of the soil background values of Hunan Province.Comparing the concentration of heavy metals in the soil of the study area with other mining areas at home and abroad,it is found that the concentration of potential toxic elements in the soil of the study area is at an intermediate level.In addition,the inverse distance weighting method was used for interpolation in Arc GIS software to draw a spatial distribution map.The spatial distribution map shows that the concentration of Mn,Pb,Cu and Zn were higher in the northwest of the study area,Cd was the largest in the south,and Cr and Ni were high in the southwest.However,the changes of Cr and Ni in the whole study area were not big.(2)Pearson correlation analysis results show that Mn,Pb,Cu and Zn have a strong correlation,and Cr and Ni have a strong correlation.The positive matrix factorization results show that the source of potential toxic elements in the soil of the study area is mainly composed of three factors.Factor 1 is the pollution of Cd mainly caused by long-term accumulation of pesticides,fertilizers and herbicides in agricultural activities.Factor 2 is the pollution of Mn,Pb,Cu and Zn caused by mining activities and related transportation emissions.Factor 3 is the pollution of Cr and Ni from natural sources(rock weathering,etc.).The principal component analysis results also show that the potential sources of toxic elements in the soil of the study area are mainly three principal components.The principal component analysis results are similar to the positive matrix decomposition results,and it is believed that mining activities and related transportation are the most important sources of pollution.Compare the results of positive matrix factorization and principal component analysis.It can be inferred that the heavy metals in the soil of the study area are composed of three sources.The first is the source of pollution from mining activities and related transportation.The second is the source of natural pollution(rock weathering,etc.).The third is the source of pollution from agricultural production activities.(3)The results of the geoaccumulation index method show that the Mn and Cd pollution in the study area were the most serious,reaching a moderate contamination,while Pb,Cr and Ni were uncontamination,and Cu and Zn were in between.The results of the pollution load index method show that Mn and Cd in the study area are high contamination,Cu,Zn,and Pb are moderate contamination,and Cr and Ni are low contamination.The overall contamination level of heavy metals is moderate contamination.The results of the potential ecological risk index method show that the ecological risk caused by Cd reaches considerable ecological risk.Other heavy metals are low ecological risk and can be ignored.In addition,the overall ecological risk is moderate ecological risk.(4)The health risk assessment of heavy metals in the soil of the abandoned manganese mining area in Xiangtan City,Hunan Province showed that the non-carcinogenic risk of Mn,Pb,Cu,Zn,Cr,Cd and Ni in the soil were 0.31(<1)and 1.24(>1)respectively for adults and children under three exposure pathway(oral intake,skin contact and inhalation).It shows that exposure of heavy metals in the soil of the study area will cause non-carcinogenic risks to children,but not to adults.In addition,Mn is the main contributor to non-carcinogenic risk.The carcinogenic risk results show that the average carcinogenic risk is 1.07×10-4 by Cr,Cd and Ni.This is unacceptable.And Cr and Ni are the main contributor tocarcinogenic risk.(5)The order of the absorption capacity of the crops in the study area to the potential toxic elements in the soil is:sweet potato>rice>corn.The pollution results of heavy metals in crops show that the pollution caused by Mn in the three crops is very serious and the most severely contaminated crops are sweet potatoes.Although the level of pollution caused by heavy metals in crops is high,the health risk assessment of crops shows that eating crops does not cause health risks. |
PDF Full Text Request