Magnetic responses to traffic related contamination recorded by backfills: A case study from Tongling City, China

With the development of urbanization and industrialization, traffic is creating a serious contamination problem. Conventional methods for contamination testing are generally expensive and time-consuming, while magnetic methods have been suggested to be an economic and non-destructive alternative. In this study, we measured magnetic properties and heavy metal contents in backfills along an urban road side in China, in situ on surface and on samples in vertical sections. Magnetic results and SEM images show the dominance of coarse magnetite, supposed to origin from human activities. Furthermore, there is an obvious decreasing trend of magnetic susceptibility (χ) and several heavy metals (Cu, Mn, Zn, Pb) with increasing distance from the road edge, symmetrically at both road sides, indicating that this is a typical traffic-related contamination signal. The detailed distribution patterns of χ and heavy metals exhibit slight variations in the surface data, probably due to the local topography and surface runoff due to rainfall. In vertical soil cores magnetic parameters show significant positive relationships (r = 0.88-0.99) with concentrations of heavy metals (Cu, Zn, Pb, Fe). Our results suggest that backfills unaffected by the traffic contamination signal and characterized by low χ value can be chosen for contamination monitoring. Despite the complex nature of backfills and the possibility of contamination prior to their transportation to the site, they are especially important for areas where undisturbed soil is not available.