Migration and fate of polycyclic aromatic hydrocarbons in bioretention systems with different media: experiments and simulations

Polycyclic aromatic hydrocarbons (PAHs) present significant risks to human health owing to their carcinogenic, teratogenic, and mutagenic properties. The contamination of surface water with PAHs via runoff has become a prominent source of water pollution. While the capacity of bioretention systems to remove PAHs from runoff is recognized, the dynamics of PAH migration and degradation in these systems are not well-understood. This study aims to explain the migration and fate of PAHs in bioretention systems through a series of experiments and model simulations. This study constructed bioretention systems with three different media types and found that these systems achieved PAH load reductions exceeding 92%. Notably, naphthalene (NAP), fluoranthene (FLT), and pyrene (PYR) tended to accumulate in the media’s upper layer, at depths of 10 to 40 cm. To further analyze the migration and fate of PAHs during multi-site rainfall events and across prolonged operation, we applied the HYDRUS-1D model under three distinct scenarios. The findings of this study indicated that NAP degraded in 40 d, whereas FLT and PYR showed incomplete degradation after 120 d. During continuous rainfall events, there was no clear pattern of PAH accumulation; however, FLT and PYR persisted in the bioretention systems. The combination of experimental and simulation findings highlights the inevitable accumulation of PAHs during extended use of bioretention systems. This research provides a theoretical basis for improving operational efficiency, advancing PAH degradation in bioretention systems, and reducing their toxicity.