Distribution Characteristics And Pollution Degree Assessment Of Heavy Metals In Soil In Dachang Mining Of Guangxi

The natural weathering and development and utilization of the deposit release a large number of harmful heavy metals and cause heavy soil pollution,which will endanger human health and ecological environment.Guangxi Dachang tin multi-metal mine area is an important non-ferrous metal production in China.In this study,a 80km² area in Dachang mine area is selected as the study area and 322surface soil samples and 92 deep soil samples are tested.We choose eight heavy metal elements,that is As,Cd,Cr,Cu,Hg,Ni,Pb and Zn,as evaluated index and make a count on the content of the heavy metal elements in the surface soil and deep soil and analyze its characteristics of the spatial variability and spatial distribution.Then using multivariate statistical analysis we discuss the heavy metal resources in the surface soil.Finally,the pollution index method,the accumulation index method and the potential ecological hazard index method are used to evaluate the pollution status in the study area.1.We select average value of the heavy metal elements that removed outliers in the deep soil as the background value.The results show that the average value of the six heavy metal elements in the surface soil exceed the background except Cr and Ni.The semi variogram model is used to fit the spatial variability of heavy metals in the soil and all of the heavy metals are found to have a medium to strong autocorrelation.The spatial distribution characteristics of heavy metals are analyzed by interpolation,and all the high value areas of heavy metal elements in the top soil are concentrated in the areas of mining activity,such as Gaofeng Tin Mine,Tongking Tin Mine,Chehe town,Longxianggai and so on,while the deep soil law is not obvious.2.The most heavy metal elements can be enriched by the Fe-bearing minerals.Ca-bearing minerals,K-bearing minerals,Na-bearing minerals,Mg-bearing minerals,Al-bearing minerals,pH and organic carbon have weakly absorption effect on the most heavy metal elements,and while the SiO₂-bearing minerals are not conducive to the accumulation of the heavy metal elements.The multivariate statistical analysis results and investigation of the surrounding environment and human activities in the study area show that As,Cd,Cu and Zn have similar sources and infer that are mainly derived from rock weathering and the waste water,waste residue,waste gas and so on.Hg and Pb have similar sources and infer that are mainly derived from rock weathering and mining,transportation and so on.Cr and Ni have similar sources and infer that are related to geochemical activities or soil parent material.3.The pollution degree evaluation results show that the pollution degree of Cr and Ni is relatively low,and the other six elements have different degrees but relatively high environmental hazards,especially Cd and Zn.The local mining development and other human activities have a serious threat to the ecological environment.