Comparative Photo‐Induced Aging of Poly(Butylene Adipate‐co‐Terephthalate) and Polystyrene Microplastics and their Divergent Affinities for Tetracycline in Aquatic Environments

Microplastics (MPs) experience photo-induced surface modification in sunlit waters, yet the implications for contaminant binding differ fundamentally for biodegradable and conventional MPs. To simulate submerged aging, biodegradable poly (butylene adipate-co-terephthalate) (PBAT) and nondegradable polystyrene (PS) are exposed to ultraviolet A irradiation and river water for 30 days. Aged PBAT shows significant surface oxidation, including a 16% decrease in carbonyl index, a reversal of ζ-potential from slightly positive to -50 mV, and an increase in tetracycline (TC) sorption kinetics. In contrast, the nondegradable analog (PS) displays only modest oxidation (ΔCI ≈ 6%), a smaller charge shift, and a lower capacity increase (qm ≈ 33 mg g-1). Maximum TC uptake occurs at pH ≈ 7, whereas modest salinity increments (0.010-0.0105 M) attenuate retention, confirming the controlling influence of electrostatic forces. Fluorescence quenching (86% vs 74% for PBAT and PS) and Akaike information criterion/Bayesian information criterion-ranked model fits indicate that hydrogen bonding and electrostatic attraction dominate on the biodegradable surface, whereas π-π and hydrophobic interactions on the PS. This work confirms that submerged photo-oxidation turns biodegradable MPs into reactive, salinity-sensitive antibiotic sinks while conventional MPs remain inert transport vectors, emphasizing the need for MP-specific risk assessment and antibiotic pollution mitigation in aquatic settings.