Impact of sequential UV-aging of microplastics on the fate of antibiotic (tetracycline) in riverine, estuarine, and marine systems

Prior research has identified microplastics (MPs) as 'trojan horse' carriers for existing co-contaminants. However, the impact of sequential UV-aging that mimics the natural aging behaviour of MPs has been underexplored. This study, for the first time, investigates the effect of sequential UV-aging of three persistently occurring MPs - Polystyrene (PS), Polypropylene (PP), and Polyethylene (PE) on their interaction with tetracycline (TC) under varying geochemical conditions (pH, IS, and DOM). TC is a widely used but poorly metabolized antibiotic that poses adverse ecological and human health hazards due to its bio- and eco-accumulation. Also, the continuous UV exposure of MPs may significantly alter their interaction, influencing the mobilization and bioavailability of TC. Results revealed that the polymer type and sequential aging notably impacted MPs-TC interaction with aged MPs (AMPs) showing enhanced sorption than their unaged counterparts (UMPs): PS (4.9 mg/g - 112.7 mg/g), PP (3.7 mg/g - 10.1 mg/g), and PE (2.7 mg/g - 8.5 mg/g). The delineation of interaction mechanisms through FTIR spectroscopy revealed the key role of electrostatic interactions, H-bonding, and π-π stacking. Despite the pervasive distribution of MPs and TC in aqueous systems, their interaction behaviour in real aqueous matrices remains underexplored. Higher MPs-TC interaction observed in river water suggests that freshwater environments favour TC accumulation, facilitating MP-mediated transport and bioaccumulation. In contrast, limited interaction in brackish and saline waters enhances the mobilization and bioavailability of TC. These findings provide new insights on the potential contaminant carrying capacity of MPs and the associated human health risks.