Estuarine Maximum Turbidity Zones (MTZs) act as critical traps for land-derived contaminants during their seaward transport due to the high accumulation of suspended particulate matter (SPM). Per- and polyfluoroalkyl substances (PFAS), a class of persistent organic pollutants, readily sorb onto larger particulate fractions and subsequently settle, leading to long-term burial in sediments. Our previous studies demonstrated that PFAS concentrations in SPM exhibit pronounced periodic fluctuations driven by tidal cycles; however, how these hydrodynamic dynamics influence the occurrence and grain-size distribution of PFAS in underlying sediments remains poorly understood. To address this gap, high-resolution continuous sampling was conducted across two consecutive tidal cycles in the MTZ of a representative semi-diurnal estuary. We analyzed the tidal variations of PFAS in both bottom water and surface sediments. Furthermore, sediment samples collected at high and low tides were fractionated by particle size to investigate the grain-size distribution characteristics of PFAS. Combined with scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), the key factors governing PFAS grain-size partitioning—including elemental composition and surface micro-morphology—were elucidated. This study provides critical insights into the hydrodynamic and sedimentological controls on PFAS fate and transport in dynamic estuarine environments.

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