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Antibiotics are ubiquitous pollutants in aquatic systems and can exist as different dissociated species depending on the water pH. New knowledge of their multivariate photochemical behavior (i.e., the photobehavior of different ionized forms) is needed to improve our understanding on the fate and possible remediation of these pharmaceuticals in surface and waste waters. In this study, the photochemical degradation of aqueous tetracycline (TC) and its dissociated forms (TCH20, TCH−, and TC2−) was investigated. Simulated sunlight experiments and matrix calculations indicated that the three dissociated species had dissimilar photolytic kinetics and photooxidation reactivities. TC2− photodegraded the fastest due to apparent photolysis with a kinetic constant of 0.938 ± 0.021 min−1, followed by TCH− (0.020 ± 0.005 min−1) and TCH20 (0.012 ± 0.001 min−1), whereas TCH− was found to be the most highly reactive toward •OH (105.78 ± 3.40 M−1 s−1), and TC2− reacted the fastest with 1O2 (344.96 ± 45.07 M−1 s−1). Water with relatively high pH (e.g., ~ 8-9) favors the dissociated forms of TCH− and TC2− which are most susceptible to photochemical loss processes compared to neutral TC. The calculated corresponding environmental half-lives (t1/2,E) in sunlit surface waters ranged from 0.05 h for pH = 9 in midsummer to 3.68 h for pH = 6 in midwinter at 45° N latitude. The process was dominated by apparent photolysis (especially in summer, 62-91%), followed by 1O2 and •OH oxidation. Adjusting the pH to slightly alkaline conditions prior to UV or solar UV light treatment may be an effective way of enhancing the photochemical removal of TC from contaminated water.Aqueous multiple photochemical behavior of dissociated tetracycline (TCH20, TCH−, and TC2−) is first comprehensively reported on revealing the phototransformation kinetics and implications for the fate in surface waters. [ABSTRACT FROM AUTHOR]

The goal of present study was to investigate the applicability of nanoscale zerovalent iron (NZVI) on the degradation of 1-(2-chlorobenzoyl)-3-(4-chlorophenyl) urea (CCU) under aerobic and anaerobic conditions, respectively. The experimental results showed that NZVI could effectively degrade CCU, but the removal efficiencies were different under these two different conditions. The best removal efficiencies for CCU were 90.2 and 75.8% under aerobic and anaerobic conditions, respectively. The highly oxidative hydroxyl radicals and reductively hydrogen would account for the rapid degradation of CCU under aerobic and anaerobic conditions, respectively. The experimental results also showed that surfactant Tween 20 significantly inhibited the degradation of CCU under aerobic conditions. However it markedly enhanced the degradation of CCU under anaerobic condition. [ABSTRACT FROM PUBLISHER]

Abstract Sulfonamide antibiotics (SAs) are increasingly detected as aquatic contaminants and exist as different dissociated species depending on the pH of the water. Their removal in sunlit surface waters is governed by photochemical transformation. Here we report a detailed examination of the hydroxyl radical (•OH) and singlet oxygen (1O 2) mediated photooxidation of nine SAs: sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, sulfamethazine, sulfamerazine, sulfadiazine, sulfachloropyridazine and sulfadimethoxine. Both •OH and 1O 2 oxidation kinetics varied depending on the dominant protonated states of the SA in question (H 2 SAs+, HSAs0 and SAs−) as a function of pH. Based on competition kinetic experiments and matrix deconvolution calculations, HSAs0 or SAs− (pH ∼5–8) were observed to be more highly reactive towards •OH, while SAs− (pH ∼8) react the fastest with 1O 2 for most of the SAs tested. Using the empirically derived rates of reaction for the speciated forms at different pHs, the environmental half-lives were determined using typical 1O 2 and •OH concentrations observed in the environment. This approach suggests that photochemical 1O 2 oxidation contributes more than •OH oxidation and direct photolysis to the overall phototransformation of SAs in sunlit waters. Based on the identification of key photointermediates using tandem mass spectrometry, 1O 2 oxidation generally occurred at the amino moiety on the molecule, whereas •OH reaction experienced multi-site hydroxylation. Both these reactions preserve the basic parent structure of the compounds and raise concerns that the routes of phototransformation give rise to intermediates with similar antimicrobial potency as the parent SAs. We therefore recommend that these phototransformation pathways are included in risk assessments concerning the presence and fate of SAs in waste and surface waters. Graphical abstract Image 1 Highlights • Aquatic photooxidation of sulfonamides (SAs) via reactive oxygen species is important. • The kinetics depend on pH and separate reactivities of H 2 SAs+, HSAs0 and SAs−. • 1O 2 plays a key role in aquatic fate of SAs compared with •OH and direct photolysis • Different primary pathways and multiple intermediates occur for the three reactions. [ABSTRACT FROM AUTHOR]

The ubiquity and photoreactivity of fluoroquinolone antibiotics (FQs) in surface waters urge new insights into their aqueous photochemical behavior. This study concerns the photochemistry of 6 FQs: ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin and enrofloxacin. Methods were developed to calculate their solar direct photodegradation half-lives ( t d,E ) and hydroxyl-radical oxidation half-lives ( t OH,E ) in sunlit surface waters. The t d,E values range from 0.56 min to 28.8 min at 45° N latitude, whereas t OH,E ranges from 3.24 h to 33.6 h, suggesting that most FQs tend to undergo fast direct photolysis rather than hydroxyl-radical oxidation in surface waters. However, a case study for levofloxacin and sarafloxacin indicated that the hydroxyl-radical oxidation induced risky photochlorination and resulted in multi-degradation pathways, such as piperazinyl hydroxylation and clearage. Changes in the antibacterial activity of FQs caused by photodegradation in various waters were further examined using Escherichia coli , and it was found that the activity evolution depended on primary photodegradation pathways and products. Primary intermediates with intact FQ nuclei retained significant antibacterial activity. These results are important for assessing the fate and risk of FQs in surface waters. [ABSTRACT FROM AUTHOR]