Research On Heavy Metal Content And Pollution Evaluation Of Agricultural Land Near Binxian County, Shaanxi Province

The soil pollution of arable land in our country is more extensive,which brings adverse effects on people's health.Therefore,the study of heavy metal pollution and distribution law is of practical significance and scientific significance.We picked up the soil near the Binxian County to find out the content and pollution situation of heavy metals in the soil,and provided basis for the prevention and control of heavy metal pollution.In this paper,5 farmland plots and 2.5m thickness of three in the vicinity of the county town of Binxian were sampled and studied.The pH,conductivity,magnetic susceptibility and soil particle size of 212 samples were measured by pH,conductivity meter,magnetic susceptibility tester and laser particle size analyzer and analyzed by X-Ray fluorescence spectrometer.The contents,distribution characteristics,enrichment rules and sources of 8 heavy metals in the soil surface and profiles of different plots were studied,and heavy metal pollution was evaluated especially.The following conclusions are drawn:(1)The content of major elements in the vicinity of Binxian was Si>Al>Ca>Fe>K>Mg>Na,with an average of 67.87%,14.41%,5.97%,5.22%,2.65%,2.09%,1.17%,respectively.In addition to Ca,the average content of major elements in 2 sections of Xiliu,Shuikou and Liujiagou Village all showed the middle level>the upper layer>the lower layer.(2)The content of heavy metal elements in the soil surface near the Binxian was Mn>Cr>Zn>Ni>Cu>Co>As>Pb.The minimum content of 8 kinds of heavy metals was higher than the Shaanxi background soil value,and the content of Ni element was less than the Chinese soil background value.The content of Co,Cu and Zn was less than the Chinese background value of soil elements,which was partly larger than the Chinese background values of soil elements.The contents of the other 4 kinds of heavy metals were greater than the Chinese background values.The contents of Mn,Ni and Pb were less than the background values of soil elements in the world,and the other 5 kinds of heavy metals were larger than the background values of the soil elements in the world.(3)The heavy metals in the soil profile of the Xiliu village in Binxian were between 0 and 0.8m,Shuikou village were obviously enriched in the depth of 0-2.0m,and the Liujiagou Village were obviously enriched from 0.5m to 1.5m.Human factors are the main causes of heavy metal enrichment in the soil surface,but the heavy metals in the soil surface also come from the soil itself.In the 3 thickness of about 2.5m of soil profile,the content of clay in paleo-soil(S0)is high,and the adsorption of clay particles is the most abundant factor of heavy metals in this layer.(4)We evaluated the heavy metal pollution of soil near Binxian,according to the single factor pollution index,nemerow index,load index evaluation,Binxian soil and their soil profile were all affected by mild pollution.According to the pollution assessment of potential ecological risk index,the average soil profiles in 2.5m were first Xiliu village,second Shuikou village and last Liujiagou Village.The 5 soil surface samples and 2.5m profiles of 3 in Binxian are all in a moderate damage state.(5)There were 3 main sources of heavy metals in the 8 soil surface near the county town of Binxian.Firstly,8 kinds of heavy metals were all affected by soil natural substances.Heavy metals mainly come from the soil itself,especially Mn and Cu.Secondly,the heavy metal elements Zn and Pb mainly come from the emission of automobile exhaust,atmospheric sedimentation,etc.,which are human sources.Thirdly,Cr,Co,Ni,Cu ? As 5 kinds of heavy metals are mainly derived from the unreasonable use of chemical fertilizers in agricultural production and soil itself,which belong to mixed sources.(6)In the 3 sections studied,the content of heavy metals were generally expressed as Holocene soil(S0),Holocene loess(L0),Malan loess(L1).The higher clay content in paleo-soil(S0)was produced by the strong clays in the process of formation.However,the strong clay depends on the warmer and wetter climatic conditions at that time,so the rich heavy metals in the paleo-soil(S0)in the middle of the section are determined by the climatic conditions at that time.The lower clay content in the lower loess(L1)in the soil profile is caused by the colder climate and weaker chemical weathering,and the less heavy metal enrichment in loess(L1)is determined by the colder climatic conditions.