[Aging Mechanism and Release Characteristics of Dissolved Substances of Polypropylene Microplastics Under the...

Microplastics in the environment can age under the influence of light， high temperature， and mechanical forces， releasing nanoplastics and soluble organic matter， which in turn have more severe impacts on the environment. In cold regions， microplastics in water and soil surfaces are usually affected by both light and freeze-thaw cycles， but the aging mechanism and the release characteristics of solubles under their combined effects remain unclear. This study investigated the apparent characteristics， changes in functional groups， and release characteristics of solubles of polypropylene microplastics （PP-MPs） under different durations of light， freeze-thaw， and combined aging treatments through a freezing simulation experiment. The results showed that after light aging treatment， holes and wrinkles appeared on the surface of PP-MPs， while after the freeze-thaw treatment， cracks and peeling occurred. After the combined aging treatment， the degree of damage on the surface of PP-MPs was significantly greater than that under the single-factor aging treatments. The increase in the hydroxyl and carboxyl indices of PP-MPs was higher after freeze-thaw and combined treatments. Under light， freeze-thaw， and combined treatments， the order of the five typical peaks of PP-MPs was： -CH₃ → -OH → C=O → C-C → -CH₂， -CH₃ → C-C → -CH₂ → C=O → -OH， and -CH₃ → C-C → -CH₂ → C=O → -OH， respectively. The concentration of DOC released by PP-MPs changed within the ranges of -0.076 mg-1.843 mg， -0.076 mg-1.778 mg， and 0.086 mg-1.803 mg， respectively， showing an initial increase followed by a decrease. The abundance of nanoplastics released by PP-MPs changed within the ranges of 1.16×10⁹-4.34×10¹⁰ particles·mL^-1， 1.87×10⁹-3.12×10¹⁰ particles·mL^-1， and 1.87×10⁹-3.12×10¹⁰ particles·mL^-1， respectively. Under light conditions， the abundance of nanoplastics increased with time， and the particle size decreased with time. Under freeze-thaw and combined treatments， the abundance of nanoplastics decreased， and the particle size increased. This study can provide a theoretical basis for clarifying the environmental effects and aging mechanisms of microplastics in cold regions.