Accumulation of polycyclic aromatic hydrocarbons in the road green infrastructures of sponge city in Northwestern China: Distribution, risk assessments and microbial community impacts

The construction of “sponge city” made the belts on both roadsides be built in the form of bioretention tanks, resulting in runoff pollutants were accumulated in the bioretention tanks. To identify the pollution level and source of polycyclic aromatic hydrocarbons (PAHs) in the bioretention tanks, the soil samples were collected on the eight typical roads of the sponge city. The total contents of ∑PAHs in the bioretention tanks were 10,524–20,462 μg/kg (mean 15,029 μg/kg), and the pollution level of PAHs in the non-flood season was significantly higher than that in the flood season. The PAHs in bioretention tanks were dominated by 4-ring PAHs, with a proportion of 39.36%. The characteristic ratio method was proposed to identify the chemical source of PAHs, and the results indicated that PAHs in the bioretention tanks were mainly supplied by the combustion source and petroleum source. The ecological risk quotient (RQ) values showed that the accumulation of PAHs in the bioretention tank had certain potential ecological risks, and the RQ values of pyrene (PYR) were the highest. Incremental lifetime cancer risks (ILCR) indicated that PAHs in soil posed negligible cancer risks by inhalation way, but much stronger risks by dermal and ingestion ways. The roads with the highest and lowest PAHs content were selected for microbial ecology analysis, and the microbial abundances showed significant decreasing trends from the flood season to the non-flood season. The PAHs accumulated in the bioretention tanks had significant impacts on the microbial community, which made the microorganisms tend to PAHs-degrading bacteria.