Geochemical Characteristics And Risk Assessment Of Soil Heavy Metals In The Built-up Area Of Changchun City

Cities are not only population areas,but also production and consumption centers.With the rapid development of cities,problem of heavy metal pollution in urban soil has become more and more serious.Changchun City is political,cultural and economic center of Jilin Province.Therefore,in order to understand the pollution of heavy metals in the surface soil of the built-up area of Changchun City and whether soil is harmful to human body,this study selected 156 sample points of the surface soil in the built-up area of Changchun City.Sample collection,analysis and testing,determine content of7 heavy metal elements such as As,Cd,Pb,Cr,Cu,Zn,Ni,and count their content characteristics,spatial distribution characteristics and temporal and spatial changes.Use single factor index method,Nemerow comprehensive pollution index method and geo-accumulation index method to evaluate the pollution of heavy metals in soil,and evaluate potential ecological risks and human health risks in study area to understand potential ecological risks of heavy metals in soil And the degree of harm to human health,certain risk prevention suggestions are put forward,and research results are as follows:1.The heavy metal content of most samples exceeds soil background value.Heavy metal elements all belong to strong variation,among which Pb,Cu and Cd have the largest variation.2.Explore the spatial distribution of heavy metals in different functional areas.As elements are mainly concentrated in industrial and agricultural areas;Cd elements are mainly concentrated in traffic areas;Cr elements are mainly concentrated in agricultural areas;Pb,Cu,Zn and Ni elements Mostly distributed in residential areas;3.Exploring temporal and spatial changes of study area.The built-up area of Changchun City in 2019 is about twice that of 1999,and built-up area is gradually expanding to southern part of Changchun City.According to statistical analysis of heavy metal content in 1999 and 2019,average content of As and Cr increased significantly,while average content of Cd,Ni,Pb and Cu did not change significantly.4.The single factor index method is used to evaluate that all heavy metals except Ni are polluted.Among them,As and Cr have the largest pollution area,and the other heavy metal elements are relatively less polluted;Nemeiro composite index method shows that it is clean and safe.The area of the state accounted for about 6.41% and21.15% of the study area,the alert accounted for about 25.64%,and pollution state accounted for about 46.79%.The evaluation of the seven heavy metal elements by geoaccumulation index method showed that the pollution of As,Cd,Pb and Cr The degree is slightly higher than the other three elements.Among them,Cd and Pb are mainly in a non-polluting state,while As element is mainly in a moderately polluted state.It can be seen that As is the most serious man-made pollution.5.From the evaluation of potential ecological risks,the risk value from high to low is As>Cd>Cu>Pb>Cr>Ni>Zn,and there is a slight ecological risk as a whole;from the human health risk evaluation,As can be known as the main carcinogen Factors,through the oral route of exposure is the main route of exposure.Cu,Pb,Cr,Zn,and Ni will not cause non-carcinogenic risk,Cd will not cause carcinogenic risk,and most of As have carcinogenic risk.