| Fluoroquinolone antibiotics (FQs) are emerging pollutants, which have frequently been detected in the aquatic environment. Antibiotics can lead to production of antibiotic-resistant bacteria, which can pose risks to ecological and human health. Therefore, it is necessary to study the environmental transformation of FQs. Photochemical transformation is an important degradation pathway of FQs. Previous studies have indicated that dissolved constituents in water played important roles in the photochemical transformation of many kinds of antibiotics. However, previous studies mainly focused on the effect of univariate dissolved constituents on the photochemical transformation of FQs, various constituents in aquatic environment are coexistent and their effects on the photochemical transformation of FQs are complicated. In estuarine waters, the types and concentrations of dissolved constituents vary dynamically. In this study, we investigated the effects of dissolved constituents on the photodegradation kinetics of FQs in estuarine waters by photochemical experiments. The main findings are as follows:The photodegradation rate constants (k) of nine FQs frequently detected were investigated in 5 water samples collected from the Yellow River Estuary through photochemical experiments under simulated sunlight irradiation. Results indicate that the range of k values for 9 FQs is 0.00130～1.20 min-1. Lomefloxacin has the highest photodegradation rate with a half-life of 0.6～1.9 min and balofloxacin has the lowest photodegradation rate with a half-life of 333.7～548 min. Except for marbofloxacin, the photodegradation rate constants of 8 fluoroquinolones in the Yellow River Estuary waters are higher than those of in pure water, which indicates that dissolved constituents can significantly affect the photodegradation of FQs.The multivariate effects of NO3-, Cl- and dissolved organic matter (DOM) on the photodegradation of balofloxacin were investigated with a three-factor central composition design. Results show that NO3- promotes the photodegradation of balofloxacin significantly, while Cl- demontrates inhibition. The effect of DOM on the photodegradation of balofloxacin is insignificant. When DOM and NO3- coexisted, photodegradation of balofloxacin was promoted, however, when Cl- and NO3- coexisted, photodegradation of balofloxacin was inhibited. |
