Characteristics Of Heavy Metal Pollution In Farmland Along Highway And Envirmental Risk Assessment

Highway was the inevitable product of economic development,and highway traffic was widely perceived as one source of heavy metal in the global environment.At present,there were still a large number of farmland along highways,national highways,provincial highways for food,oil,fruits and vegetables production,so the quality and safety problems of food still existed.Chooseing the Jing-Ha Expressway in Dehui City as study object,this paper collected related data such as remote sensing images and traffic,which was analysied by statistical analysis and logical analysis methods in order to study the pollution characteristics of heavy metals in farmland soil and crops on both sides of the highway.The decision tree analysis of influencing factors were carried out,and the artificial neural network method were applied to explore the relationship between the influencing factors and the heavy metal accumulation in crops.Finally,the environmental risk assessment of heavy metal pollution in farmland along the highway was calculated,and 6 reasonable pollution control measures were put forward according it.The main results were as follows:(1)The total amount of Zn,Cu,Pb and Cd in the soil along Jing-Ha Expressway was 60.65±15.97,23.21±6.54,39.54±10.77 and 0.4814±0.2848 mg/kg,respectively.There was no Zn,Cu and Pb pollution in the study area,but 53% of the samples showed Cd was slightly above the pollution level mainly distributing in the Changchun-Dehui section.It had been proved the width of Heavy metal contaminated soil zone was more than 200 m along the Jing-Ha Expressway.All of four heavy metals contents in the soil decreased with the distance increasing from the roadbed.(2)Seven potential factors,including direction,distance,distance from city,traffic flow,recent urban GDP,subgrade height,and protective measures(shelterbelts,shrubs and sewage canals)had been analyzed the influence on accumulation of heavy metals in soil.Meantime,they were selected key factors by decision tree.Zn and Cu were mainly affected by distance,while Pb and Cd were first affected by subgrade height,and secondly by wind direction.(3)The heavy metals are enriched in different organs.The high concentrations of four heavy metals are concentrated in leaves.The concentrations of Cu,Pb and Cd in edible parts(grains)are much lower than those in other organs,but the spatial distribution did not show significant changes.Through BCF,TF and pot experiments,it is determined that the heavy metals in maize are absorbed by roots from soil and by leaves and stems from atmosphere.(4)To predict heavy metals content in maize grains along highway by using BP neural network model.Taking vehicle flow,distance from city,roadbed height,soil pH,organic matter in upper soil and total heavy metals in soil as input layer to train the network,and it has good generalization ability for fitting four heavy metals in maize grains along highway.The average relative errors between he generalization of Zn,Cu,Pb and Cd and the actual values are 7.13%,16.27%,15.55% and 11.58%,respectively.(5)The result of ecological risk assessment of farmland soil along five monitoring sections of Jing-Ha Expressway showed that 0-30 m and 100-150 m of expressways in 1,2 and 3 were moderate risk,which was mainly contributed by Cd,as well as the rest were mainly in low risk level.There were no significant non-carcinogenic and carcinogenic health risks for four heavy metals in both of the soil and grain.According to the results,six risk prevention measures were put forward,including keeping the distance between farmland and highway,using shrubs and protective forests reasonably,engaging in agricultural production reasonably,ensuring the content of organic matter in soil,carrying out rational planning and planting of farmland and dividing pollution levels,strictly implementing food quality standards,as well as increasing the types of traffic pollution elements monitoring.