Electrochemical oxidation of fluoroquinolone antibiotics: Mechanism, residual antibacterial activity and toxicity change

Abstract

In this paper, we studied the electrochemical oxidation mechanisms of three typical fluoroquinolone antibiotics (FQs), and investigated residual antibacterial activity and toxicity changes after oxidation processes. Electrochemistry coupled to mass spectrometry (EC-MS) was used to study the oxidation processes of ciprofloxacin (CIP), norfloxacin (NOR) and ofloxacin (OFL). Eight oxidation products for each parent compound were identified and their chemical structures were elucidated. The transformation trend of each product, with the continuous increase of voltage from 0 to 3000 mV, was recorded by online EC-MS. The oxidation pathways were proposed based on the structural information and transformation trends of oxidation products. We found the oxidation mechanisms of FQs consisted of the hydroxylation and cleavage of piperazinyl ring via reactions with hydroxyl radicals, while the fluoroquinolone core remained intact. The antibacterial activity of the parent compounds and their oxidation mixtures was estimated using zone inhibition tests for gram-negative bacteria Salmonella typhimurium. It was found that the oxidation mixtures of CIP and NOR retained the antibacterial properties with lower activity compared to their parent compounds, while the antibacterial activity of OFL was almost eliminated after oxidation. Furthermore, the toxicity of the three FQs and their oxidation mixtures were evaluated using algal growth inhibition test (Desmodesmus subspicatus). The median effective concentration (EC50) values for the algal inhibition tests were calculated for the end point of growth rate. The toxicity of CIP and NOR to green algae after electrochemical oxidation, remained unchanged, while that of OFL significantly increased. The results presented in this paper contribute to an understanding of the electrochemical oxidation mechanisms of FQs, and highlight the potential environmental risks of FQs after electrochemical oxidation processes.

Microwave-Enhanced Photolysis of Norfloxacin: Kinetics, Matrix Effects, and Degradation Pathways

“…The proposed structures of the seven intermediates were basically deduced through direct photolysis and ·OH attack on benzene ring or piperazine ring. Similar intermediates were also seen in H 2 O 2 assisted photocatalysis [ 22 ], photoysis [ 21 ], gamma-ray irradiation [ 49 ], and electrochemical oxidation [ 50 ] of NOR.…”

Adsorptive Removal Study of the Frequently Used Fluoroquinolone Antibiotics - Moxifloxacin and Norfloxacin from Wastewaters using Natural Zeolites

“…It has been reported that conventional biological processes (wastewater treatment plants) are incapable of removing antibiotic pollutants 24 . Many techniques have been used for the treatment of FQs-rich effluents such as electrochemical oxidation 25 , biodegradation 26 , photodegradation 27 , catalytic degradation 28 , micro-extraction 29 , oxidation (catalytic degradation) 30 , and adsorption 31 .…”

Migration and Transformation of Ofloxacin by Free Chlorine in Water Distribution System

“…Ofloxacin (OFL) was used as the third generation of the fluoronone and has also been constantly detected in drinking water. Chlorine disinfection is the common method used to reduce OFL while the disinfection by-products, such as trihalomethanes (THMs) and haloacetic acids (HAAs), which have carcinogenic, teratogenic and abrupt effects, have been detected as well [5][6][7][8][9]. There are more than 700 kinds of Chlorination disinfection by-products which have been detected in drinking water and that are harmful to the human body, including more than 20 kinds of carcinogens and 50 kinds of mutants which threatens the drinking water safety and the health of the people [10][11][12][13][14][15][16].…”