Photochemical Transformation Behavior Of Different Dissociated Species Of Fluoroquinolone And Tetracycline Antibiotics

Antibiotics have been increasingly detected in environmental waters as emerging contaminants.These pollutants are pseudo-persistent and have been proved to induce bacterial resistance,making them of acute concern.In surface water or ice,photochemical transformation is an important way to determine the environmental trend of antibiotic pollutants.Therefore,the present study selected 2 TCs and 3 FQs as model compounds,investigated their photodegradation kinetics,photoproducts,pathways and antibacterial activity,and elucidated the effects of aqueous dissolved matter on the photodegradation so as to better understand their environmental photochemical behavior.Photodegradation experiments on the different dissociation species of gatifloxacin and balofloxacin were performed in pure water.Using competition kinetic method,FQs photodegrade when exposed to UV-vis irradiation(A>290 nm).The photodegradation reactions followed the pseudo-first-order kinetics,With the increase of pH from 3 to 11,apparent photolysis rate constants of the FQs increased first and then decreased with peak values at pH = 8,but the bimolecular rate constants for the reaction between FQs and ·OH were found to exhibit a maximum value at pH 7.The apparent photolysis and·OH oxidation activity of the three dissociative forms of FQs are different from HFQs0,H2FQs+ and FQs-in turn.In the 45°N surface water,the apparent photolysis of FQs is the main degradation pathway,while the contribution rate of the OH oxidation reaction is low.Furthermore,the main photooxidation products were enriched by solid phase extraction and identified by LC-MS/MS.The different intermediates and pathways were involved.The toxicity test of Escherichia coli showed that the photolysis product still had strong antibacterial activity.To further understand the photochemical of antibiotics,we explored photodegradation kinetics of different dissociation species of TCs.With the increase of pH,the photolysis rate constant of TCs increases.From TCsH20?TCsH-to TCs2-,absorbance spectrum show redshift.? and k value increased gradually.The different dissociation species of TCs show different ROS photooxidation activities,and their bimolecular rate constants for the reaction depend on matrix pH.In the 45 °N surface water,the t1/2,E values of TCs are closely related to the pH and the season.Apparent photolysis and 1O2 oxidation are the main photochemical transformation pathways.By comparing the photodissociation ability of tetracycline in different water bodies and different water phases,it is found that there are differences.Further studies show that Cl-,HASS,NO3-and Fe(?)in the environment played an important role in the photodegradation kinetics of TC,but the degree of promotion was different.