Heavy metal pollution of the soils and wheat grains alongside the Shanghai-Nanjing Expressway

In order to study heavy metal pollution of the soils and wheat grains alongside the Shanghai-Nanjing Expressway,a survey was carried out with soil samples and wheat samples collected from different sections of the expressway.The results show that the soils within the 250 m wide zones along either side of the expressway and grains of the wheat growing thereupon were polluted with lead to a various extent.The maximum Pb contamination index reached 3.26 in the soil of Suzhou section of the expressway.The pollution of other heavy metals was not significant.According to the national standards for food,the content of Pb in the wheat grains exceeded the standard seriously,while the contents of other heavy metals were lower than the standards.The maximum content of Pb occurred in soils 100 m away from the expressway to either side.While,the maximum content of Pb in wheat grains appeared in places (50-100) m away.It could be concluded that Pb pollution on both sides of highways is still one of the major environmental problems affecting the safety of soil and agricultural products.