Spatiotemporal Variation Of Heavy Metals In Soil Of The Northern Mining Area Of Xuzhou

In the transformation process of mining area,there is the problem of disorderly settlement of industry,resulting in continuous changes of pollution sources.Therefore,it is very necessary to study the spatio-temporal variation characteristics of typical pollutants（heavy metals）in soil in the transformation mining area over a long-time scale.In this thesis,the northern mining area of Xuzhou,which was in economic transformation,was taken as the research area.The contents of Cr,Ni,Cu,Zn,As,Cd and Pb were analyzed in the area,and the characteristics and sources of soil heavy metal pollution in 2021 were analyzed.Through the analysis of data in 2014 and2021,the spatial and temporal variation characteristics of soil heavy metal content were studied.Based on the historical data,soil heavy metal content and risk trends in 2025 and 2035 under the optimistic scenario and the default scenario were predicted,which provided an effective reference for regional soil heavy metal pollution control.The main conclusions are as follows:（1）Compared with the background value,the mean contents of Cr,Cu and Pb in 2021were 1.04,1.67 and 1.63 times of the background value,respectively,and the mean contents of As,Zn,Ni and Cd were lower than the background value in Xuzhou city.The average content of all elements did not exceed the corresponding RSV（GB 15618-2018）.The spatial distribution of heavy metals had different characteristics.The high values of Cr,Zn,As and Pb concentrated in the southwest part of the study area,and the industrial activities were relatively intensive.The distribution of Ni was relatively uniform.The concentration of Cd was higher in the western part and the eastern part of the northern farmlands of the study area.The high values of Cu and Pb appeared in the middle of the study area and decrease in a circular direction.From2014 to 2021,the contents of Cr,Cu,As and Cd in soil of the study area showed a decreasing trend,the change of Zn content was not significant,while the contents of Pb mainly increased,and the increasing areas were located in the northwest and southeast of the study area.Air pollution control can effectively reduce soil heavy metal pollution in the region.（2）According to the analysis of PMF and APCS-MLR,the distribution of Cu in the region was greatly affected by the emissions from metal smelting and power plants,and the transport of fine particles from power plants and metal smelters through atmospheric airflow affected the distribution of Cu.In the areas where Cr exceeded the background value in the northern part of Xuzhou and the pollution of Zn and As were mainly related to the discharge of industrial"three wastes",while the Ni was significantly related to the parent material of soil formation.The aggravation of Pb pollution was mainly affected by traffic emission,and the high value was distributed along Xufeng Line and Liuhe line.The enrichment of Cd was greatly affected by agricultural input.（3）Under the optimistic scenario,the contents of Cr,Zn and Pb in 2025 would be2.53mg?kg^-1,2.81 mg?kg^-1 and 2.08 mg?kg^-1 respectively lower than that in 2021;The contents of Cr,Zn and Pb in 2035 would be 8.38 mg?kg^-1,7.78 mg?kg^-1and 6.64 mg?kg^-1 respectively lower than that in 2021.Under the default scenarios,the content of Cr and Zn of soil in 2025and 2035 would be 1.6 mg?kg^-1,1.57 mg?kg^-1and 5.37 mg?kg^-1,5.4 mg?kg^-1 lower than that in2021,respectively,the content of Pb would increase by 2.21 mg?kg^-1 and 6.61 mg?kg^-1compared with 2021,respectively.The results of ecological risk time prediction showed that Cr,Zn and Pb would be low potential ecological risk levels,and the comprehensive ecological risk showed slight pollution.Cr had a certain carcinogenic risk for adults and children under both prediction conditions.Based on heavy metal content data in 2022,the scenario prediction model has a certain reliability.