Binding stability of per- and polyfluoroalkyl substances to sludge extracellular polymeric substances drives increased environmental risks

Per- and polyfluoroalkyl substances (PFAS) can induce nanoscale restructuring in lake extracellular polymeric substances (EPS) through molecular binding, forming stable complexes that heighten ecological risks. Differences between sludge and lake EPS raise questions about PFAS-induced reorganization and toxicity in sludge systems. This study explored the interactions of two representative PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), with sludge EPS using multiple spectroscopic techniques, molecular docking, and dynamic simulations. Both PFAS form stable self-assembled complexes with EPS, altering EPS conformation and protein secondary structure. Notably, PFOA shows stronger EPS affinity than PFOS, driven by enhanced hydrogen bonding and hydrophobic interactions, lower binding energies, and diminished molecular fluctuations. Phytotoxicity tests indicate that EPS-PFOA complexes pose greater environmental risks than EPS-PFOS, likely due to its stronger binding affinity of PFOA for EPS. These findings clarify the molecular mechanisms governing binding behavior between EPS and PFAS, providing guidance for the management and regulation of these emerging contaminants in sludge treatment systems.