Evolution of Microplastic Properties and Tetracycline Adsorption During Aging in Laboratory and Natural Environments

With the continuous rise in global plastic production and emissions, microplastics (MPs) have become ubiquitous across environmental compartments, including the atmosphere. Aging in natural settings substantially alters MP physicochemical properties and, in turn, their interactions with coexisting contaminants. Here, polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS) were subjected to ultraviolet (UV)-accelerated aging and natural exposure in marine intertidal zones, freshwater lakes, and the atmosphere, and changes in their properties and tetracycline (TC) adsorption were systematically compared. Aging intensity followed the order seawater > freshwater > air. Fourier-transform infrared spectroscopy showed the formation and enrichment of oxygen-containing functional groups, and naturally aged samples exhibited stronger oxidation signatures than those aged solely under UV irradiation. Adsorption kinetics indicated higher equilibrium capacities and rate constants for aged MPs; after 324 h of UV exposure in seawater, TC adsorption on PE, PS, and PET increased by 64.6%, 56.6%, and 64.0%, respectively. Mechanistic analysis suggests that surface roughening, oxygenated functional groups, and enhanced negative surface charge collectively promote TC adsorption, dominated by electrostatic interactions and hydrogen bonding. These findings not only elucidate how different aging pathways modulate the interactions between MPs and pollutants but also offer new insights into assessing the carrier potential of microplastics in environments such as the atmosphere and their adsorption of other contaminants.