Sources, influencing factors and environmental indications of PAH pollution in urban soil columns of Shanghai, China

The urban environment is an essential source and sink of polycyclic aromatic hydrocarbons (PAHs). However, there is a paucity of knowledge regarding the pollution state of PAHs and their controlling factors in urban soil columns. We therefore quantified PAHs, black carbon (BC), and total organic carbon (TOC) in 24 1-m-deep urban soil columns collected from nearby areas of power plants (P), industrial parks (I) and environmental companies (E) from Shanghai Metropolitan Area, China. The results showed that the total concentrations of USEPA 16 PAHs varied from 91.5 to 46834.5 ng g(-1), and the average pollution level followed the pattern P > I > E. The vertical migration of PAHs obeyed the exponential decay model in undisturbed soil columns. However, anthropogenic factors (land use and artificial disturbance) and edaphic conditions (BC and TOC contents as well as particle size) were strong influencing factors for the PAHs' fate in urban soils. Coal combustion and vehicle sources were identified as dominant PAH sources. Risks based on both the total benzo [a] pyrene equivalent (BaP) values and the incremental lifetime cancer risk (ILCR) values showed a general trend as P > I > E. For most sites, the ecological risks were below the threshold safe value of 600 ng BaPeq g(-1), and ILCR values were at the negligible risk level in I and E. However, dermal contact to soils, especially the deep soil layers in P, have potential health risks and should draw enough attention. Our findings thus supplemented knowledge regarding the vertical distribution and migration of PAHs, showed the predictive power of BC and TOC for PAH fate, and revealed the importance of monitoring and managing urban soils in deeper layers not just surface layers.