Hydrophilicity-dependent photodegradation of antibiotics in ice: Freeze-concentration effects and dissolved organic matter interactions drive divergent kinetics, pathways and toxicity

Cui, J.; Chen, Y.; Cheng, F.; Yang, H.; Qu, J.; Zhang, Y.; Peijnenburg, W.J.G.M. (2025)

Article / Letter to editor

The photodegradation behavior of antibiotics with different hydrophilicity in ice and the synergistic effect of dissolved organic matter (DOM) remains unclear. This study unravels the dual role of DOM in driving divergent photodegradation pathways for five antibiotics (sulfamethoxazole (SMZ), oxytetracycline (OTC), levofloxacin (LFX), ciprofloxacin (CIP), and norfloxacin (NOR)) with different hydrophilicity in ice and compares the outcomes with a similar treatment in aqueous systems under simulated sunlight. The results showed that the photodegradation of hydrophilic antibiotics (SMZ, OTC, LFX) in ice is faster compared to water, which attributed to freeze-concentration effects that enhance light absorption in ice’s liquid-like regions (LLRs). Conversely, hydrophobic antibiotics (CIP, NOR) degraded faster in water due to solvent cage effects. DOM amplified the photodegradation of hydrophilic antibiotics in ice by enriching humic-like substances in LLRs, which generated more reactive singlet oxygen (e.g. 77.1 % contribution to SMZ degradation), while inhibited the photodegradation of hydrophobic antibiotic via protein-like substances that quench excited states. Notably, DOM introduced ice-specific oxidative pathways of hydrophilic antibiotics, which altered their toxicity profiles and complicated toxicity trends toward Vibrio fischeri. These findings highlight the critical role of ice-phase photochemistry in cold regions, influencing antibiotic fate, transformation pathways, and ecological risks.

• All authors: Cui, J.; Chen, Y.; Cheng, F.; Yang, H.; Qu, J.; Zhang, Y.; Peijnenburg, W.J.G.M.
• Date: 2025-11-01
• Journal: Water Research
• Volume: 286
• DOI: doi:10.1016/j.watres.2025.124277
• Link: https://www.sciencedirect.com/science/article/pii/S0043135425011832?via%...