Heavy Metal Contamination In Farmland Soil And Crop Along Highways

With the development of the transport industry, the motor vehicles increase rapidly,heavy metal pollution caused by highway transportation can’t be ignored. Because heavymetal pollution in soil and crops along highway not only affect the quality of air and waterenvironment, also affect the crop yield and quality, in addition,it can endanger human lifeand health through the food chain. So study on this subject will reveal the heavy metalpollution levels in the highway field region, and it has great significance on thestrengthening of food security, land use planning and road greening.In this study, the farmland located in Xi’an-Yanliang highway and Xi’an-Sanyuanhighway (hereinafter referred to as XiYan highway and XiSan highway)field was selectedas study plots, soil and wheat samples were collected for test and analysis. The content ofheavy metals like Cd、Pb、Cu、Zn and Cr in collected samples were measured, also thespatial distribution characteristics were analyzed. Meanwhile, by using SPSS18.0andExcel2007, the correlation of heavy metals content in soil and wheat samples was analyzed.And from the perspective of soil chemistry, the content variation mechanism of heavymetals (Cd, Pb, Cu, Zn and Cr) in XiYan highway and XiSan highway field was studied;Finally this paper studied the effect of highway shelterbelt on the heavy metalsaccumulation in soil and crop. Results show that:(1)The majority of the five kinds of heavy metals content in XiYan highway and XiSanhighway field exceed the reference value of the soil environment, the farmland soils andwheat in200m area were affected in different levels;(2)In XiYan highway and XiSan highway field, the heavy metals content in soil andwheat showing first increasing then decreasing trend with distance increasing in thehorizontal direction, the5~70m region distance from the farmland edge was affectedseverely. In the vertical direction, heavy metals mainly concentrated in the0~10cm surfacesoil, and the content reduced as the depth increasing, but the spatial variation was notsignificant.(3)The correlation analysis results between the heavy metals content in soil and wheat samples showed that：The content of Cd in wheat and Cr in soil showed a highly significantpositive correlation. The content of Pb in wheat and Pb, Cu, Cr in soil showed a significantpositive correlation, while showed a highly significant positive correlation with Zn in soil.The content of Cu in wheat and Pb in soil were highly significantly positively correlated,while showed a significant positive correlation with Cu, Zn, Cr in soil. The correlationanalysis results of the heavy metals content in soil showed that: Pb and Cu, Cu and Zn, Cr,Zn and Cr in soil all showed a significant positive correlation respectively, so the four kindsof heavy metals in soil (Pb, Cu, Zn and Cr) may have the same source. The correlationanalysis results between the heavy metals content in soil-crop system and the pHysical andchemical properties of soil showed that: The heavy metals content in soil-crop system andthe majority of pHysical and chemical properties of soil were complexly correlated, but notsignificantly. The soil pH and Pb in soil, ammonium nitrogen and Cd in soil weresignificantly positively correlated respectively. Available phosphorus and Zn, Cr in wheatshowed a significant positive correlation. Salinity and Cr in soil were positively correlated.(4)The principal component analysis shows that heavy metals content variation in soiland wheat of highway field mainly affected by pH, organic matter and available phosphorus.The mechanism was that the adsorption, desorption, precipitation effect between soil factorsand heavy metals can inhibit or promote the fixation and migration of heavy metals in soiland wheat.(5) The shelterbelt of XiYan highway did not play a protective role in the heavy metalspollution and accumulation in soil and wheat, but the shelterbelt of XiSan highway played aprotective role.The comparision shows that because of different shelterbelt and operationtime. That is the shelterbelt of XiYan highway mainly grows arbor and shrubs, and operatesten years, but the shelterbelt of XiSan highway mainly grows shrubs and vine, and operatestwenty-two years. This shows, it has close relationship bettwen shelterbelt along highwayand operation time.