| Potentially toxic elements are the general name of harmful metals and non-metallic elements in the environment.They have the characteristics of high toxicity,long-term residue,biological enrichment,concealment,difficult to decompose and so on,which cause great harm to ecological and environmental systems and human health.The pollution of potentially toxic elements has long been an environmental problem that has attracted much attention from all walks of life.Generally speaking,metals and non-metals exist as trace elements in rocks and soils,but due to human activities,a large number of metal and non-metallic elements are produced through mining smelting,pesticide and chemical fertilizers,waste incineration and automobile exhaust emissions.Sludge and waste water are released into the soil in such a way as to apply them to cultivated land.These people The factors are a long and irreversible process,which will eventually lead to the enrichment of potentially toxic elements in the soil,the deterioration of soil physical and chemical properties and various environmental problems.In this paper,the thallium mining area of Xingren County,Guizhou Province was used as the study area.First,50 topsoil samples and 10 river sediment samples were collected and pre-treated in mining sites and mining areas,and then seven potentially toxic elements(Tl,)in soil samples were analyzed and determined.The contents of As,Cd,Cr,Cu,Pb and Zn),on the basis of which,the pollution degree and spatial distribution characteristics of potentially toxic elements in soil were analyzed by using multivariate statistical analysis and geostatistical knowledge.The correlation among the elements and the source of pollution were analyzed,and the potential ecological risk and human health risk of potentially toxic elements in the soil of the study area were evaluated..In addition,several harmful elements pollution and bioaccumulation and their health risks in the main food crops(Chinese cabbage,pepper,carrots,corn,rice)in the study area were also evaluated in this study.The main contents and results of the study are as follows:(1)the average concentrations of Tl,As,Cd,Cr,Cu,Pb and Zn in all soil samples of the study area are 28.82 mg/kg,133.75 mg/kg,1.14 mg/kg,52.11 mg/kg,79.63 mg/kg,44.39 mg/kg,.118.23 mg/kg,were 40.48,6.69,1.73,0.54,2.49,1.26 and 1.19 times of the soil background values of Guizhou Province,respectively.Drawing the content of potentially toxic elements in Thallium Mining area by Kriging interpolation method in Arc Map The results show that the distribution of Tl and As is concentrated in the center of the mining area,the content of Cd,Pb and Zn is higher in the west,the content of Cu is higher in the south and north,and the spatial distribution characteristics of Cr are not obvious.(2)using multivariate statistical analysis(standard deviation,coefficient of variation,enrichment factor,correlation analysis and principal component analysis)to identify thesources of seven potentially toxic elements studied,we infer Tl,As,Cd,Cu,in the study area.The contents of Pb and Zn were interfered by external factors,while Cr was a natural source.Based on principal component analysis(PCA),three factors with eigenvalues greater than 1were extracted.Combined with spatial map distribution and enrichment factors,the spatial distribution of Tl,As,Cd,Cu,Pb and Zn was affected by mining,coal burning,river,traffic,and agricultural activities.(3)Geological accumulation index(Igeo),potential ecological hazard index(RI),human non-carcinogenic risk index(HQ)and carcinogenic risk index(HI)were used to evaluate the potential toxic element pollution and ecological health risk in soils of the study area.The geological accumulation index indicates that the main pollution element is Tl,As,and Cd,Cr,Cu,Pb,Zn is basically in the level of non-pollution or slight pollution.The potential ecological risk index(RI)of all sampling sites ranged from 91.25.13 to 1479.34,mainly from the contribution of Tl(74.32 per cent).The second was As(8.57%)and Cd(7.32%).The ecological risk of other elements was lower than 40(low risk threshold),which was negligible.(4)Health risk assessment models showed that the non-carcinogenic risks of Tl,As,Cd,Cr,Cu,Pb and Zn in soil were 1.66 and 12.60 respectively for adults and children under three exposure pathways.Above the safety threshold of 1.0(especially for children).The sequence of non-carcinogenic hazards under the three exposure pathways was: oral intake > skin contact > respiration,and As and Tl were the main elements of non-carcinogenic risk to adults and children.The contribution ratio of the two is higher than that of 90%.As,which is the only element in the study that has a risk of carcinogenesis in adults and children,and it is almost derived from the As element.Exposure to oral intake.It can be seen that the thallium mine poses an unacceptable non-carcinogenic and carcinogenic risk to the health of the local population(especially children).(5)the pollution status and absorption ability of crops in the study area are as follows:root vegetable > leaf vegetable > fruit vegetable > grain.Other crops except corn have higher risks to human health,and are almost contributed by Tl elements.The Cu in carrots is also a high risk to the human body.Although the As,Cd,Pb in crops is polluted,However,there is no adverse impact on human health.In a word,the study area is not suitable for growing food crops unless the Tl element in the soil has been specially repaired. |
