Abiotic hydrolysis of microplastics: influence of polymer chain scission on particle fragmentation and dissolved organic carbon release

Understanding how plastics degrade and fragment, releasing microplastics, nanoplastics, and dissolved organic carbon (DOC), is crucial for their risk assessment. This study assesses abiotic hydrolytic aging of polymer powders (40–700 μm) under OECD guideline conditions and in simulated seawater from 4 to 65 °C (accelerated aging) over 10, 100, and up to 365 days. Chain scission, recrystallization, fragmentation, and dissolution of microplastics were examined for polyamide-6 (PA-6), thermoplastic polyurethane (TPU), polypropylene (PP), low-density polyethylene (LDPE), and polylactic acid (PLA). Microplastics (1–190 μm) mainly formed through surface cracking, whereas nanoplastics (0.01–1 μm) arose from particle shrinkage and erosion. Polymer chemistry strongly influenced the release patterns, with total degradation and release ranking LDPE < TPU < PA-6 < PLA; stabilized PP ranked lowest, as expected. TPU and LDPE underwent limited hydrolysis but measurable thermo-oxidative modification. PA-6 and PLA were both prone to degradation under high temperatures and specific pH, but with distinct behaviors: PLA showed substantial bulk dissolution, producing diverse DOC species over time, whereas PA-6 released a smaller and temporally stable DOC pool; both polymers fragmented. Overall, abiotic hydrolysis drives interconnected fragmentation and dissolution processes, with release dynamics depending on polymer type and environmental conditions. The resulting data support mechanistic modeling of microplastic fragmentation.