Traffic-Related Heavy Metal Contamination in Urban Areas and Correlation with Traffic Activity in China

In this study, a detailed investigation was conducted to collect the concentrations of heavy metals—including cadmium, copper, nickel, lead and zinc—from five geographic areas to reflect the different land use and traffic conditions in Zhaoyuan, China. Analytical results of heavy metal concentrations showed that the mean and median values of these elements in soils were clearly higher than the corresponding background values, indicating pollution from the urban area. To generate a continuous surface from the collected discrete samples, Kriging interpolation was introduced to determine the spatial distribution patterns of heavy metal contamination. As a major source of urban heavy metal contamination, the traffic area was carefully analyzed. Interelemental relationships showed that most heavy metals in the traffic area had similar anthropogenic origins. In addition, the research team explored the relationships between heavy metals and traffic characteristics. The results indicated that heavy metal concentrations in roadside soils not only decreased with rising altitude and increasing distance from the trunk and branch roads on both sides but also could be affected by traffic volume. Finally, three evaluation methods—including the geoaccumulation index, the pollution index, and the improved pollution index—were introduced to assess heavy metal contamination levels fully in the traffic area. The pollution index evaluation method produced results indicating more severe levels of contamination than the other two evaluation methods.