Photochemical Transformation Of Antibiotics: Kinetics And Antibacterial Properties

With the increasing attention to water resources,the harm and removal of organic micropollutants are also widely concerned.Antibiotics,as common organic micropollutants in daily life,exist widely in China’s aquatic ecosystem.Antibiotics in environmental water undergo a variety of photochemical transformation processes,among which the photochemical transformation caused by solar radiation runs through each process of water flow.Photochemical transformation has been shown to be an effective treatment for the removal of organic pollutants,but the photo hydrolysis products may retain the toxicity of the parent antibiotic and may even have higher biotoxicity.Therefore,the kinetics of photochemical transformation of antibiotics and the bacteriostasis of photo hydrolysate were discussed in this article,which provided a new idea for the treatment of wastewater containing antibiotics.In this article,four quinolones,fourβ-lactams,three tetracycline antibiotics and a broad-spectrum antibacterial agent triclosan were selected to carry out photochemical transformation experiments under UV₂₅₄,UV-LED and simulated sunlight.Escherichia coli was used as the indicator bacteria for bacteriological experiments.Firstly,the effects of antibiotic type,light source type and p H on photolysis rate were studied through photochemical transformation experiments.The results showed that the photolysis rate decreased successively by triclosan,quinolones,β-lactam and tetracycline.The photolysis effect of UV₂₅₄ is superior to that of simulated sunlight and UV-LED.Except forβ-lactam antibiotics,the photolysis rate of other antibiotics was greatly affected by p H and increased with the increase of p H.Secondly,the correlation between E_HOMO and E_LUMO values and photolysis rate is analyzed.The results show that E_HOMO and E_LUMO have no correlation with photolysis rate.Finally,the antibacterial activity（toxicity）of antibiotics and their photo hydrolysis products on Escherichia coli was found to be quinolones（0-0.2μM）,tricloson（0-0.5μM）,tetracycline（0-2μM）andβ-lactam（0-20μM）decrease in turn.Through the photochemical transformation experiment,the antibacterial activity of antibiotics was significantly reduced,except for chlortetracycline photo hydrolysis products under three light sources toxicity,the other antibiotics photo hydrolysis products did not show obvious toxicity.Through mass spectrometry analysis of chlortetracycline products,the photolysis mainly includes three paths:hydroxylation,N-demethylation/demethylation and dechlorination.In this study,the photochemical transformation rate and product toxicity of antibiotics were analyzed,and the photochemical transformation behavior and ecological effect of antibiotics were evaluated,which provided a new research idea for the photochemical treatment of wastewater containing antibiotics.