Rhizosphere-driven desorption-biodegradation coupling reduces pore-water phenanthrene exposure in aged sediments

Purpose Sequestration of polycyclic aromatic hydrocarbons (PAHs) into slowly desorbing pools in sediments constrains their bioavailability and biodegradation. This study evaluated the phytoremediation potential of the submerged macrophyte Potamogeton crispus L. ( P. crispus ) for aged phenanthrene-contaminated sediments and investigated the underlying mechanisms. Methods A 36-day microcosm experiment with or without P. crispus was conducted in artificially aged phenanthrene-contaminated sediments. Phenanthrene dissipation was fitted to biphasic first-order kinetics, and desorption kinetics were modeled using a three-compartment model. Pore-water phenanthrene concentration, sediment redox potential (Eh), and PAH-degrading bacterial abundance were periodically monitored. Results Planted treatments achieved 38.3% phenanthrene dissipation compared with 24.0% in unplanted controls, with rapid- and slow-phase rate constants increasing by 2.37- and 368.80-fold, respectively. The presence of P. crispus maintained larger rapidly desorbing fractions and higher desorption rate constants, indicating enhanced bioavailability. Planted sediments also exhibited higher Eh and greater abundance of PAH-degrading bacteria. These results suggest a rhizosphere-driven “sink effect”, where enhanced desorption coupled with rapid biodegradation prevented phenanthrene accumulation in pore water. Conclusion This study suggests that P. crispus enhances phenanthrene desorption and bioavailability in aged sediments through a rhizosphere-driven desorption-biodegradation coupling mechanism, thereby stimulating microbial activity and reducing pore-water exposure. These findings provide a preliminary mechanistic framework for submerged macrophyte-based remediation of aged PAH-contaminated sediments.