Study On Heavy Metal Content And Pollution Of Farmland Soil In Yanchuan County, Shaanxi Province

The rapid development of social economy speeds up the industrialization and agricultural that causes more and more serious problems of heavy metal pollution in soil.The domestic and overseas experts and scholars pay more attention to the heavy metal pollution in agricultural land,because there are close relations with it,such as the quality and safety of grain,fruits and vegetables,also human health.Yanchuan County in Shaanxi Province is the production base of fruits and vegetables,such as apples and jujubes,so there is not only theoretical significance,but also practical significance to research the distribution characteristics and enrichment features in agricultural land of Yanchuan region.This paper collects the apple land,jujube land and wheat land soil samples through drilling in Sunjiayuan and Daliangou village in Yanchuan County,analyzing the water content,pH values,electrical conductivity,magnetic susceptibility and size composition in soil respectively by using oven drying method,pH Meter measurement,Conductivity Meter measurement,Magnetic Susceptibility Instrument measurement and Laser Particle Size Analyzer.Using X-Ray Fluorescence Spectrometry is to analyze the content of constant elements,like Na,Mg,Al,Si,K,Ca,Fe and heavy metal elements like Cr,Mn,Cu,As,Co,Ni,Zn,Pb,paper has analyzed the distribution and enrichment features of each heavy metal element in the 2-meter-deep soil profile.Besides,the soil heavy metals in different types of agricultural land were evaluated by using Enrichment Factors,Geo-accumulation Index,Nemoro Synthesis Index,Potential Ecological Risk Index,has revealed the heavy metal pollution level of the farmland of Yanchuan region.Analyze the correlation between each heavy metal,the correlation between heavy metal elements and each constant element,physicochemical index,further research on factors that affect heavy metal distribution and enrichment in the soil profile,have analyzed the main sources of heavy metal pollution.The main conclusions are as follows:(1)The average pH value of Yanchuan County soil is 7.71,which is part of alkaline soil.In the soil granular composition,average content of coarse silt is 54.20%,average content of very fine sand is 23.52%,average content of clay is 11.46%,is part of silt soil which mainly composed by silt.(2)The heavy metals enrichment depth is different in different sample areas.There are slight differences among Sunjiayuan apple land,wheat land and Daliangou apple land,Cr,Mn,Cu,As,Ni,Zn mainly enrich in the depth range of 1.0?2.0m,Co,Pb mainly enrich in the depth range of 0-0.7m,Co also enriches in the depth range of 1.0-2.0m.The heavy metals enrichment depth is quite different in jujube land,Mn,Cu,As,Ni,Pb mainly enrich in the depth range of 0?1.0m,Cr,Co,Zn mainly enrich in the depth range of 1.0-2.0m.(3)Utilize Enrichment Factors,Geo-accumulation Index to evaluate the degree of soil pollution with each heavy metal,results show that,except the depth range of 0.8?1.5m in jujube land,every layer in four sample areas is slightly polluted by Co in different levels,while the rest of heavy metals in each layer have accumulated,,but have not polluted the soil.The evaluation results of Nemoro Synthesis Index,Potential Ecological Risk Index shows that the farmland soil and crops in Yanchuan region begin to be polluted,Co is the main pollution element in the state of slight ecological risk.(4)Correlation analysis shows that there are significant correlations between each heavy metal,and sources are similar.The contents of Cr,Mn,As,Co exceed the soil background values of Shaanxi,while the research region has few factories,highway and railway transportation is not developed,no wastewater irrigation and sludge fertilizer application.Therefore,the main sources of soil heavy metals Cr,Mn,As,Co are soil parent material,pesticides and chemical fertilizers application in human agricultural activities.(5)Daliangou jujube land is near by the highway,coal cars always pass by,vehicle exhaust emission,tire and metal parts abrasion,coal dust sedimentation are the main reason causing Mn,Cu,Ni,Pb enrich in the depth range of 0-1.0m.(6)The lower part of soil between 1.0-2.0m in research region is part of the Holocene paleosoil,the layer of the paleosoil developed argillic horizon contained more clay component,the adsorption of heavy metals by clay in the argillic horizon is the main cause that heavy metals enrich in the lower part of soil.