Photodegradation for different dissociated species of norfloxacin and ofloxacin in water ice under solar irradiation.

Ice is an important medium that regulates the transformation of organic contaminants. Nonetheless, photodegradation of emerging fluoroquinolone (FQ) antibiotics in the ice, particularly those with varying dissociated species, remains inadequately explored. In this study, the photodegradation of norfloxacin (NOR) and ofloxacin (OFL) in different dissociated species in water ice were investigated. Results indicated that the quantum yield of the zwitterion for NOR in the ice was 1.7-5.0 times higher than that of the cation, and 1.3 times higher than that of the anion. The quantum yield of the zwitterion for OFL in the ice was 2.5-3.4 times higher than that of the cation, and 1.4 times higher than that of the anion. The degradation pathways of NOR and OFL with different dissociated species depended on their molecular structure. Most products possessed lower developmental toxicity than parent NOR and OFL, respectively. OFL showed a higher inhibitory rate of Escherichia coli activity at the initial time of photodegradation, which was higher than that of NOR. This study offers novel insights into the impact of dissociated species on the photodegradation of FQs in ice and contributes to understanding the environmental behavior of fluorinated pharmaceuticals in the cryosphere.