Photodegradation\nProcesses and Weathering Products\nof Microfibers in Aquatic Environments

Microplastics, particularly microfibers\n(MFs), pose a\nsignificant\nthreat to the environment. Despite their widespread presence, the\nphotochemical reactivity, weathering products, and environmental fate\nof MFs remain poorly understood. To address this knowledge gap, photodegradation\nexperiments were conducted on three prevalent MFs: polyester (POL),\nnylon (NYL), and acrylic (ACR), to elucidate their degradation pathways,\nchanges in surface morphology and polymer structure, and chemical\nand colloidal characterization of weathering products during photochemical\ndegradation of MFs. The results showed that concentrations of dissolved\norganic carbon, chromophoric dissolved organic matter (DOM), and fluorescent\ncomponents consistently increased during weathering, exhibiting a\ncontinuous release of DOM. Scanning electron microscopy and Raman\nspectroscopy revealed changes in the surface morphology and polymer\nspectra of the MFs. During the weathering experiments, DOM aromaticity\n(SUVA<sub>254</sub>) decreased, while spectral slope increased, indicating\nconcurrent DOM release and degradation of aromatic components. The\nreleased DOM or nanoplastics were negatively charged with sizes between\n128 and 374 nm. The production rate constants of DOM or the photochemical\nreactivity of MFs followed the order ACR > NYL ≥ POL, consistent\nwith their differences in chemical structures. These findings provide\nan improved understanding of the photochemical reactivity, degradation\npathways, weathering products, and environmental fate of microfibers\nin the environment.