The Risks of aged polystyrene microplastics cannot be ignored: release of large amounts of degradation products

Unaged microplastics, as well as residual monomers or additives from the processing stage would affect the plants, animals, and human body. Aged microplastics (MPs) containing degradation products are widespread pollutants. There is a gap in the effects of aged microplastics on human body. Through static digestion simulation experiments, this study investigates the interaction between aged polystyrene microplastics (PS MPs) with different molecular weights and simulated digestive fluids. The findings reveal that degradation products existing on the surface of PS MPs are released into the simulated digestive fluids, leading to a "dual reduction" in both the physical size and molecular weight of MPs. This result implies that the potential risk of cells ingesting MPs increases due to the ageing of plastics. Moreover, these degradation products impact the micro-environment of digestive enzymes, consequently leading to conformational changes in the macromolecules of these enzymes. The longer the ageing time, the greater degradation products are released and the more solute is adsorbed, which may pose even graver hazards to the bio-safety. This study contributes to assessing the effects and potential risks of aged PS MPs on human health. It emphasizes the importance of investigating the risk of aged MPs that could enter cells, inducing some hazardous effects after digestion.