Aging of microplastics affects their surface properties, thermal decomposition, additives leaching and interactions...

Most microplastics (MPs) have undergone extensive aging in the environment. Aged MPs exhibit different physical and chemical properties from unaged ones. Here, we studied the effects of accelerated aging on the characteristics and pyrolysis of commercial pigmented MPs, as well as pigments leaching and their interactions in simulated gastric and intestinal fluids of mammals. We report that the carbonyl index, surface area, and color change of MPs increased after aging treatment. Cracks and fragmentation of MPs facilitated the accessibility of light and oxygen to internal layer and therefore accelerated the aging process. TGA/GC-MS analysis showed that the high temperature resistance of MPs decreased after aging. Thermal decomposition of pigments and polyethylene occurred in temperature ranges of 340-406 °C and 406-550 °C, respectively. Mono (di)-alkenes and saturated alkanes were the thermal decomposition products of polyethylene. Aging of MPs also caused an increased release of pigments and prolonged aging time led to more release in simulated fluids. Pigments would result in fluorescence quenching of the enzymes through binding interactions once they were released from MPs into simulated fluids. Charge neutralization and polymer bridging accounted for the formation of pigment-enzyme complexes and flocs. These novel findings will allow us to better assess how aging process affects the characteristics, leaching, and toxicity of MPs.