Contamination And Migration Of Heavy Metals In The Soil-Wheat System On The Both Sides Of Zheng-Bian Highway

Soil-Plant system is the basic unit of the biosphere, and it is the main research object of the soil environment. If this system is polluted by heavy metals, not only the plant products and quality but also the environmental quality of atmosphere and water will be severely affected, and finally do harm to human lives and health through food chain. The heavy metal contamination mainly derives from industrial waste, municipal solid waste, pesticide and fertilizer as well as automobile exhaust and so on, in which we should attach importance to traffic pollution. As a source of environmental pollution, automobile exhaust is a kind of important soil chemical contamination source. With the development of the transportation carrying trade, vehicles possessions increase rapidly. Accordingly, the increased traffic volumes have brought about serious heavy metal contamination along highway. Therefore, the monitoring and assessment of the soil and plant heavy metal contamination will be in favor of illuminating the residual and accumulating mechanism of the heavy metal in the soil-plant system. In this dissertation, the contamination and migration of heavy metals ( Pb,Cd,Ni,Cu,Zn,Cr) in the roadside soil-wheat system along Zheng-Bian highway were studied. On the basis of experimental data of the heavy metals in soil, wheat, road dusts and soils of roadside canal, the author analyzed heavy metal contamination status and law of migration of heavy metal, then discussed the factors that affect the migration of heavy metal pollutants in the area. There are four main parts of this dissertation: Part Ⅰ In this part, the current situation and development tendency of the research about heavy metal contamination in the soil-plant system were generally introduced. Then the author summarized the present situation of the study at home and abroad on the heavy metal contamination in soil-plant system caused by traffic problem. Part Ⅱ In this part, the basic conditions of the research area and the sampling transects were introduced. Then the collection and preparation process of the soil and wheat samples along Zheng-Bian highway were also presented. Finally, the methods of the experimental items were expounded. Part Ⅲ Based on the experimental data , the heavy metal contamination levels of soil and wheat along Zheng-Bian highway were assessed. The law of distribution and migration of heavy metals in the soil was analyzed. The accumulation principles of the heavy metals in the wheat were discussed and the factors that impact the heavy metal migration were also studied. Part Ⅳ In this part , the main conclusions were drawn. At last, the author pointed out some limitations of this study and further put forword some expectaions for the future study. Central conclusions are as follows: (1) The heavy metal contents of the soil along Zheng-Bian highway obviously exceed the local background values. Cd,Pb and Zn contamination is serious; Contamination level of Cu is between non-contamination and medium contamination .The soil is not polluted by Ni,Cr. The synthetic contamination index and the distance from roadbed are negative correlation. The both sampling transects form the contamination belt within the distance of 100m from the roadbed of highway. (2) The heavy metal contamination level of the road dusts and sediments in the canal along the highway is high. (3) Concentrations of heavy metals in roadside soil decrease with distance from the highway, and concentrations and the distance are not simply negatively correlated. Except the south part of the sampling transect in Putian, the heavy metal concentrations in the soil of other part of the sampling transects are all increased with distance from the highway, then gradually decrease with distance .Most heavy metal concentrations reachmaximum values at the distance of 25～50m from highway. At the south part of Putian sampling transect, because of the influence of Longhai railway, the heavy metal concentrations are firstly decreased then increased with the distance. (4) Heavy metals en...