Study On The Characteristics Of Expressway Runoff And Heavy Metal Pollution In Soil On Side Of Expressway

The road surface runoff pollution on water receives more and more attention. On one hand, the elements of road surface runoff pollutants are complicated and the pollutant density changes dramatically. It is difficult for biochemistry change and the emission is irregular. Therefore, the pollution is difficult to treat. On the other hand, the highway road surface belongs to the non-permeable surface. The pollution on it is easy to control compared with other surface pollution and the waste water can be turned into harmless resources. We may implement the manual pollution treatment and the natural processing to reach realistic significance.The Nanjing-Maqun Section of Shanghai-Nanjing expressway is studied. The samples of road surface runoff and roadside soil are taken. The samples are processed through experiments, data mining and theoretical generalization, The following conclusions are drawn.The study on the pollution characteristics of the road runoff indicates that there is serious pollution and most index of runoff are over standard quoto. The COD, BOD5, SS, Cr, Ni, Cd and Pb are the main pollutants in road runoff. The main influence factor of the runoff pollution concentration is transportation activities. The ratio of BOD5 to COD in runoff is far smaller than the ratio in domestic sewage. The runoff is of less biodegradability and difficult to treat by normal biological method. There are obvious linear relationships between COD, BOD5, total Pb, total Zn, total Cr and SS, as well as between total Zn and Pb.The heavy metal pollution characteristics of roadside soid are investigated, The results show that the heavy metal pollution is distributed over the roadsides within the area of 20m to the road centerline. The pollutant content decreases with the distance from the centerline. The heavy metal content decreases obviously outside the area of 20m to the road centerline. Heavy metal elements mainly accumulate in the surface soil and their contents decrease as the vertical distance from the surface increases. The content of heavy metal elements except Ni in the soil under 30cm from the surface is lower than the soil background value. The soil within 20m from expressway is polluted by heavy metal in different degrees. The surface soil pollution is the most serious. The degree of pollution is sorted in descending as follow:Ni, Cd, Zn, Pb, Cr. The Ni and Cd are on the heavy pollution level, Zn on the moderate level and Pb on the slight level. There are obvious linear relationships among soil heavy metal elements. The degree of linear relationship in sold was higher than in runoff and its regularity stronger as well.The reduction functions of soil to heavy pollutants are explored. The results show that soil is of obvious reduction functions to heavy metal pollutions. Most heavy metal pullutants remain in the surface soil and rarely move into deep soil. There are very negative linear correlations between soil heavy metal pollutants and the horizontal or vertical distance. A series of reduction equations are derived out for practical application. It is suggested to select and cultivate hyperaccumulators and supper tolerance species for expressway landscaping plants, and to apply composite plants, supper tolerance-passivation reagents and hyperaccumulators-heavy metal activators to repair soil after heavy metal pollution.