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Interplay of Morphology and Polymer Composition Drives Estuarine Fate and Food Web Distribution of Nanoplastics: Evidence from a Multitrophic Mesocosm Using Upconversion Nanoparticle Tracers
Summary
Scientists tested how two shapes of nanoplastics, tiny spheres versus tiny fibers, move through an estuary ecosystem, and found that fiber-shaped plastic sinks fast and builds up in fish liver tissue, while round particles cycle through the water and settle more evenly across shellfish and plants. This matters because most safety studies use round plastic beads as stand-ins, but this research suggests fibers (a very common form of real-world plastic pollution) may pose a bigger risk to fish, and potentially the people who eat them, than current testing methods capture.
Abstract 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.