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Numerous studies have been reported on today's ubiquitous presence of antibiotics in surface waters causing the emergence of multidrug-resistant bacteria. Advanced water treatment procedures aim at the complete prevention and elimination of antibiotics from entering natural water bodies. In this study, photoinduced degradation processes using UVC-irradiation were applied toward selected fluoroquinolone, tetracycline, macrolide, and sulfonamide antibiotics. Photodegradation products were elucidated using high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS). Rate constants and quantum efficiencies were determined for the active substances and their photo-transformation products. As a measure of ecotoxicity, minimum inhibitory and half-maximal inhibitory concentrations were determined against the Gram-negative bacterium Pseudomonas fluorescens and the Gram-positive Bacillus subtilis in a standard assay format. These values were further recorded as a function of UV exposure time. The irradiation time-dependent increase of minimum inhibitory concentration (MIC) values agreed well with the kinetic models. After 10 min of irradiation, the compound solutions ceased to inhibit bacterial cell growth, indicating removal of the pharmaceutical activity. These findings were found in agreement with quantitative structure–activity relationship analysis. The combination of microbiological activity testing, molecular structure analysis, chemical kinetic investigation, and quantitative structure–activity relationship models proved to be able to predict irradiation times and evaluate potential ecotoxicological hazard of the irradiated drugs. [ABSTRACT FROM AUTHOR]

Photolysis is currently being discussed and investigated as additional stage or at least part of an extended treatment for sustainable water purification in waste water treatment plants. This study describes the photoinduced degradation of four macrolide antibiotics using UVC/VUV-irradiation. Special attention was paid to the determination of ecotoxicity of the formed photoinduced degradation products. To this purpose, MIC values were determined and QSAR analysis was performed. Photo-induced degradation rates of the drug substances ranged from 0.39 min–1 to 2.47 min–1, with azithromycin showing the slowest degradation, followed by erythromycin and spiramycin. The degradation of tylosin proceeded the fastest. QSAR analysis indicated that most of the identified photoproducts were less eco-toxic than the original drugs. The corresponding MIC analysis demonstrated that the four macrolides were ineffective against the gram-negative Pseudomonas fluorescens but effective against the gram-positive Bacillus subtilis. The MIC determination of irradiated tylosin solutions showed exemplarily that prolongation of the irradiation times led to increasing MIC values of the solution, reduced efficacy and hence potentially less eco-toxicity of the irradiated solution and the degradates therein. [ABSTRACT FROM AUTHOR]

This study focuses on the degradation of the sulfonamide antibiotics, sulfadiazine, sulfamethazine, sulfamethoxazole, and sulfathiazole, using ultraviolet irradiation in various conditions. Different pHs were investigated in combination with the addition of hydrogen peroxide and further oxygen removal. High-performance liquid chromatography electrospray ionization ion-trap mass spectrometry was used to identify and elucidate degradation products and to establish concentration–time curves. Previously unknown degradation products could be characterized. Reaction rate constants of all compounds and transformation products were determined. The parent sulfonamides decayed according to first-order kinetics, while the concentrations of the transformation products varied with time according to a subsequent reaction of an intermediate product. Quantum efficiencies were analyzed for mechanistic purposes. As example, sulfamethoxazole was added to effluents from a wastewater treatment plant and irradiated. Phototoxicity and environmental hazard were assessed through quantitative structure-activity relationship computations. In addition, the minimal inhibition concentrations were determined forPseudomonas fluorescensandBacillus subtilis. Conclusions for UV-C irradiation as a fourth purification wastewater treatment stage were derived. [ABSTRACT FROM AUTHOR]

Pharmaceuticals are found in waterbodies worldwide. Conventional sewage treatment plants are often not able to eliminate these micropollutants. Hence, Advanced Oxidation Processes (AOPs) have been heavily investigated. Here, metoprolol is exposed to UV irradiation, hydrogen peroxide, and ozonation. Degradation was analyzed using chemical kinetics both for initial and secondary products. Photo-induced irradiation enhanced by hydrogen peroxide addition accelerated degradation more than ozonation, leading to complete elimination. Degradation and transformation products were identified by high-performance liquid-chromatography coupled to high-resolution higher-order mass spectrometry. The proposed structures allowed to apply Quantitative Structure-Activity Relationship (QSAR) analysis to predict ecotoxicity. Degradation products were generally associated with a lower ecotoxicological hazard to the aquatic environment according to OECD QSAR toolbox and VEGA. Comparison of potential structural isomers suggested forecasts may become more reliable with larger databases in the future. [ABSTRACT FROM AUTHOR]