Morphology-dependent photoaging behavior of polyamide fibrous microplastics: implications for fragmentation and...

Fibrous microplastics (FMPs) are ubiquitous yet structurally distinct contaminants in marine ecosystems, characterized by high aspect ratios that potentially dictate their environmental fate. This study elucidates the photo-induced evolution of polyamide microfibers, revealing a morphology-governed degradation evidence. Our results demonstrate that FMPs undergo anisotropic photo-deconstruction, characterized by longitudinal cracking and hierarchical peeling, driven by the orientation of polymer chains. This process releases 3.9 × 10⁷ particles/L (>10 μm) after 480 h of simulated solar irradiation. Concurrently, a significant molecular divergence of dissolved organic matter occurs, with the preferential leaching of protein-like components over humic-like substances. While seawater halides exert a shielding effect that retards physical fragmentation, it prolongs the environmental residence time of aged fibers. These findings provide mechanistic insights into the physicochemical transformation of polyamide fibrous microplastics during photoaging and highlight the importance of fiber morphology and aquatic chemistry in regulating microplastic degradation and secondary particle release in coastal environments.