Degradation of norfloxacin in aqueous solution by ionizing irradiation: Kinetics, pathway and biological toxicity

Norfloxacin (NOR) has been extensively applied worldwide to treat various infectious diseases, which is ubiquitous in the aquatic environments. In this study, ionizing irradiation was used to degrade NOR in aqueous solution. The results showed that 5-40 mg/L NOR could be degraded completely at 0.4-4 kGy. The mineralization of NOR was enhanced by 1.55-3.02 times in the presence of 10-40 mg/L H2O2 at 6 kGy. Scavenging experiments indicated that hydroxyl radical ((OH)-O-center dot) was the predominant radical species during NOR radiolytic degradation. In addition, three possible degradation steps were proposed, including defluorination, quinolone group transformation, and the opening of the piperazinyl ring. The antimicrobial activity of NOR solution against Staphylococcus aureus was eliminated by gamma irradiation, while some more toxic intermediate products were predicted during irradiation process. Ionizing irradiation could also degrade NOR effectively in real wastewater and ground water. Overall, ionizing irradiation is an efficient technology for degrading NOR, while more attention should be paid to the toxicity of the intermediate products generated during NOR radiolytic degradation.