Interplay of Morphology and Polymer Composition Drives Estuarine Fate and Food Web Distribution of Nanoplastics:...

Current ecological risk assessments often rely on spherical reference particles, potentially misrepresenting the behavior of abundant fibrous nanoplastics. Using upconversion nanoparticle (UCNP) labeling and inductively coupled plasma mass spectrometry (ICP-MS), we quantified the fate of size-matched spherical polystyrene (PS) and fibrous polyacrylonitrile (PAN) nanoplastics in an estuarine mesocosm. Distinct particle attributes─driven by the synergistic interplay of geometric morphology and polymer intrinsic density─altered environmental partitioning: spherical PS exhibited repeated settling-resuspension cycling, whereas fibrous PAN rapidly accumulated in surface sediments (94% aqueous removal within 12 h). This physical divergence shifted bioaccumulation patterns across trophic levels. Lower trophic organisms (Zostera asiatica, Crassostrea gigas, Rapana venosa) accumulated PS in proportion to water-column availability. Conversely, the demersal fish Sebastes schlegelii exhibited higher burdens of fibrous PAN despite lower aqueous concentrations. Time-gated imaging revealed stronger PAN-associated signals in hepatic tissues, consistent with morphology-enhanced tissue retention in benthic vertebrates. These results indicate that spherical models may underestimate microfiber risks in benthic food webs, highlighting the need to incorporate shape-specific partitioning and retention factors into nanoplastics risk assessments.