Effects of natural colloidal particles derived from a shallow lake on the photodegradation of ofloxacin and ciprofloxacin

Natural colloidal particles (NCPs), which are ubiquitous and abundant in surfacewaters, may play a crucial role in the sunlight-driven transformation of organic contaminants. This research focused on the effects of NCPs on the photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and ciprofloxacin (CIP), and assessed the photosensitivity of colloidal organicmatter (COM). Results showed that the photodegradation rate constants (kobs) of OFL and CIP in NCP solutions ranged from 9.28 x 10(-2) h(-1) to 15.98 x 10(-2) h(-1) and 63.88 x 10(-2) h(-1) to 196.59 x 10(-2) h(-1), respectively, and NCPs can significantly accelerate the photodegradation rate of OFL and CIP. Indirect photodegradation (IP) accounted for >50% of the overall observed degradation in most treatments and was the dominant degradation pathway for the two FQs, especially for CIP, for which IP reached 82%-94%. In the IP process, the contributions of triplet states of colloidal organicmatter ((COM)-C-3*) to the photolysis of OFL and CIP were close to 42% and 46%, respectively. The compositions of COM played an important role in the IP of the FQs, amongwhich terrestrial sources of COM tended to have higher photoreactivity than biological sources. This study is essential in predicting the photochemical effect of FQs and also allows for a better understanding of the real environmental fate of antibiotic contaminants. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study found that natural colloidal particles (NCPs) can significantly accelerate the photodegradation rate of ofloxacin (OFL) and ciprofloxacin (CIP), indirect photodegradation (IP) accounts for an important proportion in the degradation process, and the triplet states of colloidal organic matter play a key role in photolysis.