PFAS Dynamics in a Macrotidal Estuary: Insights from Fractionated Particle Components

Per- and polyfluoroalkyl substances (PFAS), emerging persistent organic pollutants (POPs), are transported from land to sea. Their distinct hydrophilicity and hydrophobicity make PFAS transport by suspended particulate matter (SPM) in estuaries, especially within the estuarine turbidity maximum (ETM), crucial and distinct from traditional POPs. Beyond particle size, SPM composition critically governs PFAS partitioning. To investigate the PFAS dynamic in estuaries and how their variations are influenced by fractionated particles and their components under tidal forcing, water samples were collected during two consecutive tidal cycles in the macrotidal Jiulong River estuary ETM. Size-fractionated SPM (0.22-1 μm, 1-10 μm, 10-31 μm, 31-63 μm, > 63 μm) was analyzed for composition and PFAS concentration. SEM-EDS analysis showed SPM comprised primarily of clay minerals, with the 0.22-1 μm fraction potentially organic-rich and the >31 μm fraction inorganic-rich. Notably, 0.22-1 μm particles (3% of SPM mass) carried 31% of particulate PFAS, comparable to >31 μm particles (59% of mass, 31% of PFAS). Tidal variations induced a salting-in effect for PFAS associated with 0.22-1 μm particles but a salting-out effect on >31 μm particles, underscoring size-dependent electrostatic interactions between PFAS and SPM. Additionally, bottom-water nonvolatile organic carbon (NVOC) showed a positive correlation with PFAS concentrations in SPM, suggesting that NVOC facilitates PFAS accumulation. Upstream-downstream water mixing also significantly influenced PFAS transport. This study systematically elucidates how fractionated SPM components differentially regulate PFAS dynamics, thereby providing insights for future transport predictions and risk assessment.