Exploring Different Toxic Effects of UV-Aged and Bio-Aged Microplastics on Growth and Oxidative Stress of Escherichia coli

Toxicological effects of microplastics (MPs) have been confirmed in a variety of microorganisms in aquatic environments, and they are closely correlated with the physicochemical properties of the MPs. In a natural environment, different aging treatments always induce different alterations in the physicochemical properties of MPs, thus influencing their environmental behaviors and biotoxicity. In this work, physicochemical properties and toxicity towards Escherichia coli (E. coli) were investigated in polystyrene (PS) MPs (3 and 10 μm) before and after aging by UV irradiation and biofilm formation, respectively. The results show that UV irradiation and biofilm formation led to different alterations in the surface morphologies and functional groups of PS. The UV-aged 3 μm PS had the strongest inhibitory effect on E. coli growth, and the bio-aged 10 μm PS had the strongest beneficial effect on E. coli growth. Also, the ATPase activity, production of intercellular ROS, and MDA content of the E. coli were affected differently. UV aging enhanced the toxicity of PS towards E. coli, while bio-aging had an opposite weakening effect. Overall, our research verified the remarkable differences in the physicochemical properties and biotoxicity of PS induced by UV aging and bio-aging.