Geochemical Survey And Evaluation Of Heavy Metals In Soil Of Qingyuan City

In order to study the geochemical characteristics of soil environment in Qingyuan City,soil samples were collected in shallow(first environmental layer)and deep(second environmental layer)according to soil environmental geochemical evaluation requirements.A total of 323 deep soil samples were collected,shallow layer.1270 soil samples were analyzed and determined according to the requirements of 16 heavy metals such as Ag,Au,Cu,Pb,Zn,Fe2O3,Mn,Ni,Co,Cd,Cr,Sn,Sb,Se,As and Hg.Combined with principal component analysis and systematic cluster analysis method,the geochemical characteristics of soil heavy metals in Qingyuan City were comprehensively evaluated.The main results are as follows:(1)The contents of heavy metals such as As,Hg,Sb,Se and Sn in deep soil are higher than those in the whole country,and the contents of As,Au,Sb and Hg are also higher than those in the Pearl River Delta;Cd element content and national The average soil content was equivalent,but it was significantly lower than the soil mean value in the Pearl River Delta region;the Se background value(0.488×10-6 mg·kg-1)was higher than the recoglized selenium-rich soil content(0.3×10-6 mg·kg-1).There are two high-strength elements in the deep soil of the whole area,one is the Donglian-Yangshan Qinglian-Yingde Jiming Town in the north,and the other is the border area of the Qingyuan County in the south-Fenggang Town of Fogang.(2)The background values of Ag,Cd,Mn,Pb,Se,Sn,Zn and other elements in the shallow soil of the whole area are higher than the reference value of the whole area(deep soil background value),indicating that the above elements are secondary rich under normal conditions.The background values of As,Au,Co,Cr,Cu,Hg,Ni,Sb,Fe2O3 and other elements are lower than the reference value,indicating that these elements have undergone secondary depletion under epigenetic conditions.The content of Se in all types of shallow weathered soil is higher than 0.3×10-6 mg·kg-1,indicating that the shallow soil in this area is selenium-rich soil.The Cd,Pb,As,Ni and Hg in the shallow soil of this area are obviously abnormal,especially the abnormal distribution of Cd elements is very common.The abnormal belt has large scale,continuous distribution and high strength.(3)According to the data standardization and principal component analysis,the deep soil heavy metal geochemical characteristic index system is divided into four categories:the first principal component load is concentrated in:As,Cd,Co,Hg,Ni,Pb and Se;The principal component loads are concentrated in:Ag,Au,Cr,Mn,Sb,and Sn;the third principal component load is concentrated in:Fe2O3;and the fourth principal component load is concentrated in:Cu.Shallow soils are divided into three categories:the first principal component loads are concentrated in:As,Cd,Co,Cr,Hg,Ni,Se,Sn,and Fe2O3;the second principal component loads are concentrated in:Ag,Au,Cu,Mn,Pb and Sb;the third principal component load is concentrated on:Zn.(4)According to the calculation formula of weights,the geochemical characteristics of heavy metals in deep and shallow soils of Qingyuan City are obtained:Ag,Au,Cu,Pb,Zn,Mn,Ni,Co,Cd,Cr,Sn,Sb,Se,The weights of As,Hg and Fe2O3 are:6.27%,5.58%,6.31%,6.34%,5.74%,5.92%,6.27%,6.40%,6.36%,6.3%,6.37%,6.39%,6.44%.6.43%,6.43%,and 6.40%,shallow layers:4.64%,6.90%,6.67%,6.59%,6.62%,6.31%,6.66%,5.66%,5.62%,6.76%,6.02%,6.76%5.25%,6.76%,6.21%and 6.57%.(5)The comprehensive scores of heavy metal geochemical characteristics of deep and shallow soils in all areas of Qingyuan City are the largest in Yangshan County,and the smallest in Yingde County.Among them,the deep comprehensive scores are:Yangshan County(0.56)>Lianshan Zhuang Yao Autonomous County(0.50)>Qingxin County(0.48)=Qingcheng District(0.48)>Lianzhou Prefecture(0.47)>Fogang County(0.46)>Liannan Yao Autonomous County(0.45)>Yingde Prefecture(0.25)The shallow comprehensive scores are:Yangshan County(0.62)>Fogang County(0.47)=Liannan Yao Autonomous County(0.47)>Qingxin County(0.46)>Lianzhou Prefecture(0.45)>Lianshan Zhuang and Yao Autonomous County(0.43)>Qingcheng District(0.42)>Yingde Prefecture(0.38).(6)According to the comprehensive score formula and system cluster analysis,the geochemical characteristics of heavy metals in deep and shallow soils in Qingyuan City are divided into three categories:Yangshan County is a category;Yingde Prefecture and Lianzhou The prefecture-level counties are of one type;Fogang County,Qingxin County,Lianshan Zhuang and Yao Autonomous County,Liannan Yao Autonomous County and Qingcheng District are one category.In summary,the comprehensive scores of heavy metal geochemical characteristics of deep and shallow soils in all areas of Qingyuan City are the largest in Yangshan County and the smallest in Yingde County.Through the analysis of geochemical characteristics and comprehensive evaluation of soil heavy metals in Qingyuan City,It provides decision-making basis for agricultural planning,industrial structure adjustment,environmental protection,prevention of endemic diseases and development of special agricultural products in Qingyuan City.