Sunlight-induced degradation of fluoroquinolones in wastewater effluent: Photoproducts identification and toxicity

Insight into Fe-O-Bi electron migration channel in MIL-53(Fe)/Bi4O5I2 Z-scheme heterojunction for efficient photocatalytic decontamination

Building a heterojunction is a fascinating option to guarantee sufficient carrier separation and transfer efficiency, but the mechanism of charge migration at the heterojunction interface has not been thoroughly studied. Herein, MIL-53(Fe)/Bi4O5I2 photocatalyst with a Z-scheme heterojunction structure is constructed, which achieves efficient photocatalytic decontamination under solar light. Driven by the newly-built internal electric field (IEF), the formation of Fe-O-Bi electron migration channel allows for rapid separation and transfer of charge carriers at the heterojunction interface, confirmed by the material characterization and density functional theory (DFT) calculation. The narrower band gap and improved visible light response also contribute to the enhanced photocatalytic activity of composite materials. With levofloxacin as the target pollutant, the optimal MIL-53(Fe)/Bi4O5I2 achieves complete removal of pollutant within 150 min, the photocatalysis rate of which is ca. 4.4 and 26.0 times that of pure Bi4O5I2 and MIL-53(Fe), respectively. Simultaneously, the optimal composite material exhibits satisfactory photodegradation of seven fluoroquinolones, and the photocatalysis rates are as follows: lomefloxacin > ciprofloxacin > enrofloxacin > norfloxacin > pefloxacin > levofloxacin > marbofloxacin. DFT calculations reveal a positive relationship between degradation rate and Fukui index (ƒ0) of main carbon atoms in seven fluoroquinolones. This study sheds light on the existence of electron migration channels at Z-scheme heterojunction interface to ensure sufficient photoinduced carrier transfer, and reveals the influence of pollutant structure on photolysis rate.

Mechanistic study of the electrochemical oxidation of fluoroquinolones: Ciprofloxacin, danofloxacin, enoxacin, levofloxacin and lomefloxacin

The fluoroquinolones ciprofloxacin, danofloxacin, enoxacin, levofloxacin and lomefloxacin, occur in water bodies worldwide and therefore pose a threat to the aquatic environment. Advanced purification procedures, such as electrochemical oxidation, may act as a remedy since they contribute to eliminating contaminants and prevent micropollutants from entering open water bodies. By electrochemical treatment in a micro-flow reactor equipped with a boron-doped diamond (BDD) electrode, the fluoroquinolones were efficiently degraded. A total of 15 new products were identified using high-performance high-resolution chromatography coupled with high-resolution multifragmentation mass spectrometry. The ecotoxicity of the emerging transformation products was estimated through in silico quantitative structure activity relationship analysis. Almost all transformation products were predicted less ecotoxic than the initial compounds. The fluoroquinolone degradation followed three major mechanisms depending on the voltage during the electrochemical oxidation. At approximately 1 V, the reactions started with the elimination of molecular hydrogen from the piperazine moiety. At approx. 1.25 V, methyl and methylene groups were eliminated. At 1.5 V, hydroxyl radicals, generated at the BDD electrode, led to substitution at the piperazine ring. This novel finding of the three reactions depending on voltage contributes to the mechanistic understanding of electrochemical oxidation as potential remedy against fluoroquinolones in the aquatic environment.

Selected widely prescribed pharmaceuticals: toxicity of the drugs and the products of their photochemical degradation to aquatic organisms

Cholesterol-lowering drugs, antidiabetics, antiarrhythmics, antidepressants, and antibiotics belong to the most prescribed drugs worldwide. Because of the manufacture, excretion, and improper disposal of leftover drugs, the drugs enter waste waters and, subsequently, surface waters. They have been detected in surface waters all over the world, from concentrations of ng/l to concentrations several orders of magnitude higher. Since pharmaceuticals are designed to be both biologically and chemically stable, photochemical degradation by sun radiation represents a way of transformation in the natural environment. This review provides a survey of how selected drugs of the above-mentioned classes affect aquatic organisms of different trophic level. The emphasis is on the harmful effects of phototransformation products, an area of scientific investigation that has only attracted attention in the past few years, revealing the surprising fact that products of photochemical degradation might be even more toxic to aquatic organisms than the parent drugs.

Predictive binary mixture toxicity modeling of fluoroquinolones (FQs) and the projection of toxicity of hypothetical binary FQ mixtures: a combination of 2D-QSAR and machine-learning approaches

All sorts of chemicals get degraded under various environmental stresses, and the degradates coexist with the parent compounds as mixtures in the environment. Antibiotics emerge as an additional concern due to the bioactive nature of both the parent compound and degradation products and their combined exposure to the environment. Therefore, environmental risk assessment of antibiotics and their degradation products is very much necessary. In this direction, we made use of in silico new approach methodologies (NAMs) and machine-learning algorithms. In this study, we have developed a robust and predictive mixture-quantitative structure-activity relationship (QSAR) model with promising quality and predictability (internal: MAETrain = 0.085, QLOO2 = 0.849, external: MAETest = 0.090, and QF12 = 0.859) for predicting the toxicity of the mixtures of a class of antibiotics and their degradation products. To obtain the predictive model, toxicity data of 78 binary fluoroquinolone mixtures in E. coli (endpoint: log 1/IC50 in molar) have been utilized. We have used only 0D-2D descriptors to efficiently encode the structural features of mixture components without any additional complexities. The optimization of the class of mixture descriptors has been performed in this study by using three different mixing rules (linear combination of molecular contributions, the squared molecular contributions, and the norm of molecular contributions). Different machine-learning approaches namely, random forest (RF), ada boost, gradient boost (GB), extreme gradient boost (XGB), support vector machine (SVM), linear support vector machine (LSVM), and ridge regression (RR) have been employed here apart from the conventional partial least squares (PLS) regression to optimize the modeling approach. A rigorous validation protocol has been used for assessing the goodness-of-fit, robustness, and external predictability of the models. Finally, the toxicity of possible untested mixtures of different photodegradation products of fluoroquinolones has been predicted using the best model reported in this study.

Comprehensive understanding of fluoroquinolone degradation via MPUV/PAA process: Radical chemistry, matrix effects, degradation pathways, and toxicity

The wide occurrence of fluoroquinolones (FQs) in aquatic environments has aroused increasing concern about their potential adverse effects on human health. In this study, an emerging advanced oxidation process, i.e., the Medium-Pressure Ultraviolet/Peracetic Acid (MPUV/PAA) process, was used to degrade FQs (e.g., levofloxacin (LEV), norfloxacin, and ciprofloxacin). Compared with the MPUV process alone and the PAA process alone, the MPUV/PAA process significantly promoted degradation of FQs due to the considerable contribution of reactive radicals. Probe experiments revealed that PAA-specific organic radicals (e.g., CH₃C(O)O• and CH₃C(O)OO•) were the major radicals responsible for FQ elimination. Rapid degradation of FQs via the MPUV/PAA process was achieved within a wide range of pH values (5-9) by selecting LEV as the target compound, and higher pH values were more favorable for the reaction. The slight impacts of Cl^- and CO₃^2-/HCO₃^- on LEV removal were observed. The transformation products and pathways of LEV were identified, and nearly all of the transformation pathways occurred on the piperazine ring. Based on Quantitative Structure-Activity Relationship (QSAR) analysis, most of the products had lower toxicities than LEV. Overall, these findings improve our understanding and application of the MPUV/PAA process for degrading emerging contaminants in (waste)water treatment.

Solar-driven hybrid photo-Fenton degradation of persistent antibiotic ciprofloxacin by zinc ferrite-titania heterostructures: degradation pathway, intermediates, and toxicity analysis

Present work puts forward an efficient strategy to degrade one of the persistent antibiotic contaminants, ciprofloxacin (CIP). Hybrid advanced oxidation process (HAOP) is tailored with a synergy effect between photocatalysis and photo-Fenton catalysis on zinc ferrite-titania heterostructured composite (ZFO-TiO₂). The ZFO-TiO₂ heterostructured composite enables heterogenous surfaces for enhanced charge separation where HAOP is implemented for CIP degradation with the aid of class AAA solar simulator. The results reveal an enhanced degradation rate of CIP (k_obs = 0.255 min^-1), noticeably higher than the conventional TiO₂-based photocatalysis. The HAOP system strongly enhances the reaction rates showing five times higher performance as compared to TiO₂-based photocatalysis. The substitution reactions for degradation of CIP into its intermediates were analyzed by LC-MS/MS, and the plausible degradation pathways have been graphically modeled identifying 3-phenyl-1-propanol and phenol molecules as less toxic end products. Toxicity of the photodegraded samples reveal 18.1 ± 1.24% inhibition of V. fischeri at the end of 60-min treatment indicating reduced toxicity of CIP contaminated samples. Antimicrobial inhibition studies on E. coli also corroborate an effective CIP removal (~ 100%) in less than 90 min. The study puts forward a novel ZFO-TiO₂ composite HAOP system for efficient and rapid mineralization of an antibiotic pollutant, extendable towards wide range of pharmaceutical drug degradation studies.

Use of Fluorescence Spectroscopy and Chemometrics to Visualise Fluoroquinolones Photodegradation Major Trends: A Confirmation Study with Mass Spectrometry

In this work, we employed EEM-PARAFAC (fluorescence excitation-emission matrices-parallel factor analysis) as a low-cost tool to study the oxidation pathways of (fluoro)quinolones. Amounts of 12.5 μM of enrofloxacin (ENR), ciprofloxacin (CIP), ofloxacin (OFL), oxolinic acid (OA), and flumequine (FLU), as individual solutions, were irradiated under UVA light. A 5-component PARAFAC model was obtained, four of them related to the parent pollutants, named as ENR-like (including CIP), OFL-like, OA-like, and FLU-like, and an additional one related to photoproducts, called ENRox-like (with an emission red-shift with respect to the ENR-like component). Mass spectrometry was employed to correlate the five PARAFAC components with their plausible molecular structures. Results indicated that photoproducts presenting: (i) hydroxylation or alkyl cleavages exhibited fingerprints analogous to those of the parent pollutants; (ii) defluorination and hydroxylation emitted within the ENRox-like region; (iii) the aforementioned changes plus piperazine ring cleavage emitted within the OA-like region. Afterwards, the five antibiotics were mixed in a single solution (each at a concentration of 0.25 μM) in seawater, PARAFAC being also able to deconvolute the fingerprint of humic-like substances. This approach could be a potential game changer in the analysis of (fluorescent) contaminants of emerging concern removals in complex matrices, giving rapid visual insights into the degradation pathways.

Removal of antibiotics from milk via ozonation in a vortex reactor

Antibiotics (ABX) residues occur frequently in milk, causing considerable wastage of medicated milk and serious economic losses, and making the issue a burden for the dairy industry. Improper disposal of medicated milk harms dairy production, animal welfare, and the environment. This work studies the use of ozonation in a vortex reactor for removing ceftiofur hydrochloride (CEF), sulfamonomethoxine sodium (SMM), marbofloxacin (MAR) and oxytetracycline (OTC) from milk. In terms of residual concentration, O₃ efficiency and the degradation kinetics of the various O₃-involving processes in the vortex reactor, ABX removal via ozonation is better using stronger vortexing, which induces hydrodynamic cavitation. CEF undergoes the fastest degradation, followed by SMM, MAR, and OTC. High ABX hydrophobicity favors ABX degradation via ozonation, O₃/H₂O₂, and O₃/Na₂S₂O₈. ABX oxidation by ^•OH at the O₃ gas-bubble/milk interface is the principle degradation pathway, except for MAR. ABX degradation follows pseudo-first-order kinetics and is affected by initial ABX concentration, O₃ concentration/flow rate, reaction temperature, and milk components to varying degrees. Under optimal ozonation conditions, ABX residues meet the maximum limits as set by the European Commission and no antimicrobial activity was observed. The decontaminated milk was therefore suggested to be reused as calf food, animal feed, organic fertilizer, etc.

Antibiotic Removal from the Aquatic Environment with Activated Carbon Produced from Pumpkin Seeds

Antibiotics are among the most critical environmental pollutant drug groups. Adsorption is one of the methods used to eliminate these pollutants. In this study, activated carbon was produced from pumpkin seed shells and subsequently modified with KOH. The adsorbent obtained through this procedure was used to remove ciprofloxacin from aqueous systems. Fourier Transform-Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), elemental, X-ray Photoelectron Spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and Zeta analyses were used to characterize the adsorbent. The surface area, in particular, was found to be a very remarkable value of 2730 m²/g. The conditions of the adsorption experiments were optimized based on interaction time, adsorbent amount, pH and temperature. Over 99% success was achieved in removal operations carried out under the most optimal conditions, with an absorption capacity of 884.9 mg·g⁻¹. In addition, the Langmuir isotherm was determined to be the most suitable model for the adsorption interaction.

Photodegradation of fluoroquinolones in aqueous solution under light conditions relevant to surface waters, toxicity assessment of photoproduct mixtures

Photochemical degradation of fluoroquinolones ciprofloxacin, enrofloxacin and norfloxacin in aqueous solution under light conditions relevant to surface waters at neutral and alkaline pH was found to proceed readily with half-lives between 0.9 and 2.7 min. The products of photochemical degradation identified by HPLC-MS included defluorinated, hydroxylated, and decarboxylated structures as well as structures with opened cyclic structures. For all of the studied substances, the reaction pathways were influenced significantly by the pH of the reaction system, with more products formed at alkaline pH than at neutral pH: the ratios of products in neutral and alkaline pH were 16/26, 9/19, 15/23 for ciprofloxacin, enrofloxacin, and norfloxacin, respectively. The structures of photoproducts and pathways of photochemical degradation are proposed. The antibacterial activities of photoproduct mixtures tested on E. coli and S. epidermidis were significantly higher in comparison to parental antibiotics in the case of both ciprofloxacin and enrofloxacin with p-values less than 0.0001 in most cases. The effect of the photoproducts was shown to be dependent on the pH value of the original antibiotic solutions before photodegradation: for ciprofloxacin, antibacterial activity against E. coli was more notably pronounced with regard to neutral pH photoproducts, while a less significant, or in one case not significant, effect of pH was observed against S. epidermidis; for norfloxacin, antibacterial activity against both E. coli and S. epidermidis was especially high with regard to alkaline pH photoproducts.

Graphitic Carbon Nitride as a Sustainable Photocatalyst Material for Pollutants Removal. State-of-the Art, Preliminary Tests and Application Perspectives

Photocatalysis is an attractive strategy for emerging pollutants remediation. Research towards the development of new, efficient and effective catalytic materials with high activity under wide irradiation spectra is a highly active sector in material science. Various semiconductor materials have been employed as photocatalysts, including TiO2, SrTiO3, CdS, BiVO4, Ta3N5, TaON, Ag3PO4, and g-C3N4. The latter is a metal-free, low cost polymer, providing high adsorption and catalytic properties, shown to be promising for photocatalysis applications under visible light. Furthermore, g-C3N4 composites are among the most promising advanced photocatalytical materials that can be produced by green synthesis processes. In this paper, the state-of-the-art of g-C3N4 applications is reviewed, and application perspectives are discussed. Photocatalysis tests with g-C3N4 under Xenon irradiation were performed to gather first-hand information to improve photoreactor design. Xenon light spectrum appears to be a suitable radiation source to replace direct sunlight in engineered pollutants removal processes catalyzed by g-C3N4, in lieu of other currently used heterogeneous photocatalysis processes (e.g., TiO2-UV). LED sources are also very promising due to higher energy efficiency and customizable, catalyzer-specific irradiation spectra.

Characterization of enoxacin (ENO) during ClO2 disinfection in water distribution system: Kinetics, byproducts, toxicity evaluation and halogenated disinfection byproducts (DBPs) formation potential

Enoxacin (ENO) is widespread in water because it is commonly used as a human and veterinary antibiotic. However, little effort has been dedicated to revealing the transformation mechanisms of ENO destruction using ClO₂, especially within a water distribution system (WDS). To address this knowledge gap, the kinetics, byproducts, toxicity, and formation potential of halogenated disinfection byproducts (DBPs) associated with ENO destruction using ClO₂ in a pilot-scale PE pipe was explored for the first time. Statistical analyses showed that the destruction efficiency of ENO in the pilot-scale PE pipe was lower than that in deionized water (DI water), and the reactions in DI water followed the second-order kinetic model. Furthermore, pH has a significant effect on the destruction of ENO, and the removal ratio increased at a higher pH. Additionally, increasing the flow rate elevated the ENO removal efficiency; however, the influence of flow velocity was limited to ENO destruction. The ENO removal rates within the diverse pipes exhibited the following order: stainless steel pipe < PE pipe < ductile iron pipe. Nine possible intermediates were identified, and those that were formed by piperazine group cleavage represented the major primary byproducts of the entire destruction process. Additionally, the ENO destruction in a pilot-scale PE pipe had minimal influence on halogenated DBPs and chlorite formation. Finally, the toxicity evaluation illustrated that the presence of ENO increased the potential risk of water quality safety when treated with ClO₂.

Highly efficient UV/H2O2 technology for the removal of nifedipine antibiotics: Kinetics, co-existing anions and degradation pathways

This study investigates the degradation of nifedipine (NIF) by using a novel and highly efficient ultraviolet light combined with hydrogen peroxide (UV/H₂O₂). The degradation rate and degradation kinetics of NIF first increased and then remained constant as the H₂O₂ dose increased, and the quasi-percolation threshold was an H₂O₂ dose of 0.378 mmol/L. An increase in the initial pH and divalent anions (SO₄^2- and CO₃^2-) resulted in a linear decrease of NIF (the R² of the initial pH, SO₄^2- and CO₃^2- was 0.6884, 0.9939 and 0.8589, respectively). The effect of monovalent anions was complex; Cl^- and NO₃^- had opposite effects: low Cl^- or high NO₃^- promoted degradation, and high Cl^- or low NO₃^- inhibited the degradation of NIF. The degradation rate and kinetics constant of NIF via UV/H₂O₂ were 99.94% and 1.45569 min^-1, respectively, and the NIF concentration = 5 mg/L, pH = 7, the H₂O₂ dose = 0.52 mmol/L, T = 20 ℃ and the reaction time = 5 min. The ·OH was the primary key reactive oxygen species (ROS) and ·O₂^- was the secondary key ROS. There were 11 intermediate products (P345, P329, P329-2, P315, P301, P274, P271, P241, P200, P181 and P158) and 2 degradation pathways (dehydrogenation of NIF → P345 → P274 and dehydration of NIF → P329 → P315).

Antibiotics: An overview on the environmental occurrence, toxicity, degradation, and removal methods

Antibiotics, as antimicrobial drugs, have been widely applied as human and veterinary medicines. Recently, many antibiotics have been detected in the environments due to their mass production, widespread use, but a lack of adequate treatment processes. The environmental occurrence of antibiotics has received worldwide attention due to their potential harm to the ecosystem and human health. Research status of antibiotics in the environment field is presented by bibliometrics. Herein, we provided a comprehensive overview on the following important issues: (1) occurrence of antibiotics in different environmental compartments, such as wastewater, surface water, and soil; (2) toxicity of antibiotics toward non-target organisms, including aquatic and terrestrial organisms; (3) current treatment technologies for the degradation and removal of antibiotics, including adsorption, hydrolysis, photodegradation and oxidation, and biodegradation. It was found that macrolides, fluoroquinolones, tetracyclines, and sulfonamides were most frequently detected in the environment. Compared to surface and groundwaters, wastewater contained a high concentration of antibiotic residues. Both antibiotics and their metabolites exhibited toxicity to non-target organisms, especially aquatic organisms (e.g., algae and fish). Fluoroquinolones, tetracyclines, and sulfonamides can be removed through abiotic process, such as adsorption, photodegradation, and oxidation. Fluoroquinolones and sulfonamides can directly undergo biodegradation. Further studies on the chronic effects of antibiotics at environmentally relevant concentrations on the ecosystem were urgently needed to fully understand the hazards of antibiotics and help the government to establish the permissible limits. Biodegradation is a promising technology; it has numerous advantages such as cost-effectiveness and environmental friendliness.

Potential biotransformation pathways and efficiencies of ciprofloxacin and norfloxacin by an activated sludge consortium

Fluoroquinolones (FQs), such as ciprofloxacin (CIP) and norfloxacin (NOR), are types of emerging trace pollutants that have attracted great attention. In this study, an activated sludge (AS) consortium with high bio-removal capability to CIP and NOR was obtained by acclimating with CIP and NOR for 10 d. Meanwhile, a CIP- and NOR- transforming bacterial strain (S5), which is highly homologous to the 16S rRNA gene sequence of Enterobacter sp., was isolated from the acclimated AS. The bio-removal efficiency of CIP under the acclimated AS consortium was better than that under the pure culture of Enterobacter sp. S5 (93.1% vs. 89.3%), while the bio-removal efficiency of NOR under the acclimated AS consortium was lower than that under the pure culture of Enterobacter sp. S5 (83.9% vs. 89.8%). The biotransformation and bio-adsorption were two main ways to bio-remove CIP and NOR. However, the CIP and NOR biotransformation efficiencies of the acclimated AS were higher than under the pure culture of Enterobacter sp. S5, while the CIP and NOR adsorption of acclimated AS were lower than that under the pure culture of Enterobacter sp. S5. The N-acetylciprofloxacin and N-acetylnorfloxacin were the main biotransformation products of CIP and NOR. It is possible that acetyltransferase may be involved in the biotransformation process. Whether under the pure culture or AS consortium, the cytotoxicity of CIP and NOR transformation products to gram-negative bacteria was alleviated. Therefore, the acclimated AS and Enterobacter sp. S5 might provide a new strategy for removing contaminants and alleviating of FQs resistance.

Methionine-Functionalized Graphene Oxide/Sodium Alginate Bio-Polymer Nanocomposite Hydrogel Beads: Synthesis, Isotherm and Kinetic Studies for an Adsorptive Removal of Fluoroquinolone Antibiotics

In spite of the growing demand for new antibiotics, in the recent years, the occurrence of fluoroquinolone antibiotics (as a curative agent for urinary tract disorders and respiratory problems) in wastewater have drawn immense attention. Traces of antibiotic left-overs are present in the water system, causing noxious impact on human health and ecological environments, being a global concern. Our present work aims at tackling the major challenge of toxicity caused by antibiotics. This study deals with the efficient adsorption of two commonly used fluoroquinolone (FQ) antibiotics, i.e., Ofloxacin (OFX) and Moxifloxacin (MOX) on spherical hydrogel beads generated from methionine‒functionalized graphene oxide/ sodium alginate polymer (abbreviated Met-GO/SA) from aqueous solutions. The composition, morphology and crystal phase of prepared adsorbents were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM) and thermogravimetric analysis/differential thermogravimetry (TGA/DTG). Batch adsorption tests are followed to optimize the conditions required for adsorption process. Both functionalized and non-functionalized adsorbents were compared to understand the influence of several experimental parameters, such as, the solution pH, contact time, adsorbent dosage, temperature and initial concentration of OFX and MOX on adsorption. The obtained results indicated that the functionalized adsorbent (Met-GO/SA) showed a better adsorption efficiency when compared to non-functionalized (GO/SA) adsorbent. Further, the Langmuir isotherm was validated as the best fitting model to describe adsorption equilibrium and pseudo second-order-kinetic model fitted well for both types of adsorbate. The maximum adsorption capacities of Met-GO/SA were 4.11 mg/g for MOX and 3.43 mg/g for OFX. Thermodynamic parameters, i.e., ∆G°, ∆H° and ∆S° were also calculated. It was shown that the overall adsorption process was thermodynamically favorable, spontaneous and exothermic in nature. The adsorbents were successfully regenerated up to four cycles with 0.005 M NaCl solutions. Overall, our work showed that the novel Met-GO/SA nanocomposite could better contribute to the removal of MOX and OFX from the liquid media. The gel beads prepared have adequate features, such as simple handling, eco-friendliness and easy recovery. Hence, polymer gel beads are promising candidates as adsorbents for large-scale water remediation.

Perspectives on the antibiotic contamination, resistance, metabolomics, and systemic remediation

Antibiotics have been regarded as the emerging contaminants because of their massive use in humans and veterinary medicines and their persistence in the environment. The global concern of antibiotic contamination to different environmental matrices and the emergence of antibiotic resistance has posed a severe impact on the environment. Different mass-spectrometry-based techniques confirm their presence in the environment. Antibiotics are released into the environment through the wastewater steams and runoff from land application of manure. The microorganisms get exposed to the antibiotics resulting in the development of antimicrobial resistance. Consistent release of the antibiotics, even in trace amount into the soil and water ecosystem, is the major concern because the antibiotics can lead to multi-resistance in bacteria which can cause hazardous effects on agriculture, aquaculture, human, and livestock. A better understanding of the correlation between the antibiotic use and occurrence of antibiotic resistance can help in the development of policies to promote the judicious use of antibiotics. The present review puts a light on the remediation, transportation, uptake, and antibiotic resistance in the environment along with a novel approach of creating a database for systemic remediation, and metabolomics for the cleaner and safer environment.

Glucocorticoids in Freshwaters: Degradation by Solar Light and Environmental Toxicity of the Photoproducts

The photodegradation process of seven glucocorticoids (GCs), cortisone (CORT), hydrocortisone (HCORT), betamethasone (BETA), dexamethasone (DEXA), prednisone (PRED), prednisolone (PREDLO) and triamcinolone (TRIAM) was studied in tap and river water at a concentration close to the environmental ones. All drugs underwent sunlight degradation according to a pseudo-first-order decay. The kinetic constants ranged from 0.00082 min⁻¹ for CORT to 0.024 min⁻¹ for PRED and PREDLO. The photo-generated products were identified by high-pressure liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). The main steps of the degradation pathways were the oxidative cleavage of the chain 17 for CORT, HCORT and the rearrangement of the cyclohexadiene moiety for the other GCs. The acute and chronic toxicity of GCs and of their photoproducts was assessed by the V. fischeri and P.subcapitata inhibition assays. The bioassays revealed no significant differences in toxicity between the parent compounds and their photoproducts, but the two organisms showed different responses. All samples produced a moderate acute toxic effect on V. fisheri and no one in the chronic tests. On the contrary, evident hormesis or eutrophic effect was produced on the algae, especially for long-term contact.

Solar photocatalytic degradation of thidiazuron in Yangtze River water matrix by Ag/AgCl-AC at circumneutral condition

It is well-known that the degradation of pollutants in real water environment is not only challenging but also has practical value. This paper focuses on the photocatalytic degradation of thidiazuron (TDZ), a popular defoliant, using Ag/AgCl-AC (Ag@AC 2:1); AC stands for activated carbon) in a matrix of Yangtze River water under sunlight irradiation. The prepared composite catalyst exhibits excellent performance in TDZ degradation under near neutral condition, the degradation rate reaches 94% in 200 min under solar irradiation. The common inorganic anions (SO₄^2-, Cl^-, and HCO₃^-) and cations (Ca²⁺, Cu²⁺, and Mg²⁺) show inhibitory effect of different degrees on TDZ degradation. Humic substances such as humic acid and fulvic acid also have an effect on the photocatalytic degradation of TDZ. With the increase of humic acid concentration, there is enhancement of inhibitory effect. As for fulvic acid, its effect is complex due to competitive adsorption and photoinduction action. The degradation products as identified by UHPLC-MS are mainly CO₂, SO₂, and H₂O, indicating that the degradation was thorough. The reusability test of four runs reveals that the performance of the photocatalytic system is stable. The results demonstrate that sunlight can be well utilized for the photocatalytic degradation of TDZ. The study offers a cheap and effective approach for the photocatalytic degradation of organic pollutants in circumneutral water bodies.

Predicting mixture toxicity and antibiotic resistance of fluoroquinolones and their photodegradation products in Escherichia coli

Antibiotics in the environment usually co-exist with their transformation products with retained toxicity, raising concerns about environmental risks of their combined exposure. Herein, we reported a novel predictive approach for evaluating the individual and combined toxicity for photodegradation products of fluoroquinolone antibiotics (FQs). Quantitative structure-activity relationship (QSAR) models with promising predictive performance were constructed and validated using experimental data obtained with 13 FQs and 78 mixtures towards E. coli. A structural descriptor reflecting the interaction among FQ molecules and the target protein was employed in the QSAR models, which was obtained through molecular docking and thus provided a rational mechanistic explanation for these models. The predicted results indicated that the degradation products displayed varying degrees of changes compared to the parent FQs, while the combined toxicity of FQs and their degradation products was mostly additive. Furthermore, following UV irradiation the degradation products displayed elevated capacity of inducing resistance mutations in E. coli, though their overall toxicity was reduced. This result highlights the implications of antibiotic degradation products on resistance development in bacteria and stresses the importance of considering such impacts during environmental risk assessments of antibiotics.

Water Depollution and Photo-Detoxification by Means of TiO2: Fluoroquinolone Antibiotics as a Case Study

Photocatalysis by semiconductors is considered one of the most promising advanced oxidation processes (AOPs) and TiO2 is the most well-studied material for the removal of contaminants from the aquatic system. Over the last 20 years, pharmaceuticals have been the most investigated pollutants. They re-enter the environment almost unmodified or slightly metabolized, especially in the aquatic environment, since the traditional urban wastewater treatment plants (WWTPs) are not able to abate them. Due to their continuous input, persistence in the environment, and unpleasant effects even at low concentrations, drugs are considered contaminants of emerging concern (ECs). Among these, we chose fluoroquinolone (FQ) antibiotics as an environmental probe for assessing the role of TiO2 photocatalysis in the degradation of recalcitrant pollutants under environmental conditions and detoxification of surface waters and wastewaters. Due to their widespread diffusion, their presence in the list of the most persistent pollutants, and because they have been deeply investigated and their multiform photochemistry is well-known, they are able to supply rich information, both chemical and toxicological, on all key steps of the oxidative degradation process. The present review article explores, in a non-exhaustive way, the relationship among pollution, toxicity and remediation through titanium dioxide photocatalysis, with particular attention to the toxicological aspect. By using FQs as the probe, in depth indications about the different phases of the process were obtained, and the results reported in this paper may be useful in the improvement of large-scale applications of this technology, and—through generally valid methods—they could be deployed to other pharmaceuticals and emerging recalcitrant contaminants.

Occurrence and treatment of contaminants of emerging concern in the African aquatic environment: Literature review and a look ahead

Awareness about the rising detection and reported (eco)toxicological effects of contaminants of emerging concern (CECs, e.g. pharmaceuticals and personal care products - PPCPs - and modern pesticides) in the aquatic environment is growing. CECs are increasingly reported in the African aquatic environment, although the amount of data available is still limited. In this work, a comprehensive review is presented on the occurrence of CECs in wastewater, sludge, surface water, sediment, groundwater and drinking water of Africa. Further attention is given to the performance of wastewater stabilization ponds (WSPs) and trickling filters (TF) with respect to CECs removal. For the first time, we also look at the state of knowledge on the performance of point-of-use technologies (POUs) regarding the removal of CECs in drinking water. Generally, CECs in Africa occur at the same order of magnitude as in the Western world. However, for particular groups of compounds and at specific locations such as informal settlements, clearly higher concentrations are reported in Africa. Whereas antiretroviral and antimalarial drugs are rarely detected in the Western world, occurrence patterns in Africa reveal concentrations up to >100 μg L^-1. Removal efficiencies of WSPs and TFs focus mainly on PPCPs and vary significantly, ranging from no removal (e.g. carbamazepine) to better than 99.9% (e.g. paracetamol). Despite the rising adoption of POUs, limited but promising information is available on their performance regarding CECs treatment in drinking water, particularly for the low-cost devices (e.g. ceramic filters and solar disinfection - SODIS) being adopted in Africa and other developing countries.

Occurrence, Distribution, and Ecological Risk of Fluoroquinolones in Rivers and Wastewaters

The use of fluoroquinolones for the treatment of infections in humans and animals has increased in Argentina, and they can be found in large amounts in water bodies. The present study investigated the occurrence and associated ecological risk of 5 fluoroquinolones in rivers and farm wastewaters of San Luis, Santa Fe, Córdoba, Entre Ríos, and Buenos Aires provinces of Argentina by high-performance liquid chromatography coupled to fast-scanning fluorescence detection and ultra-high-performance liquid chromatography coupled to triple quadrupole mass spectrometry detection. The maximum concentrations of ciprofloxacin, enrofloxacin, ofloxacin, enoxacin, and difloxacin found in wastewater were 1.14, 11.9, 1.78, 22.1, and 14.2 μg L^-1 , respectively. In the case of river samples, only enrofloxacin was found, at a concentration of 0.97 μg L^-1 . The individual risk of aquatic organisms associated with water pollution due to fluoroquinolones was higher in bacteria, cyanobacteria, algae, plants, and anurans than in crustaceae and fish, with, in some cases, risk quotients >1. The proportion of samples classified as high risk was 87.5% for ofloxacin, 63.5% for enrofloxacin, 57.1% for ciprofloxacin, and 25% for enoxacin. Our results suggest that the prevalence of fluoroquinolones in water could be potentially risky for the aquatic ecosystem, and harmful to biodiversity. Environ Toxicol Chem 2019;38:2305-2313. © 2019 SETAC.

Chlorination of enoxacin (ENO) in the drinking water distribution system: Degradation, byproducts, and toxicity

Chlorine is widely used as a drinking water disinfectant to ensure water security. However, the transformation mechanisms of its degradation of emerging pollutants within the water distribution system (WDS) is insufficiently understood. Thus, the kinetics, degradation byproducts, and toxicity of the chlorination of enoxacin (ENO, a type of emerging pollutant) were explored in a pilot-scale WDS for the first time. It was found that the chlorination rate of ENO was higher in deionized water (DW) than in the pilot-scale WDS, and the degradation followed second-order kinetics in DW. The degradation efficiency was found to be sensitive to pH, and was highest at a pH of 7.4. The chlorination rate of ENO increased with increasing temperature in both DW and WDS. For different pipe materials, the relative performance of ENO chlorination efficiency followed the order of steel pipe > ductile iron pipe > polyethylene (PE) pipe. Seven intermediates were identified during ENO chlorination, and the primary oxidation reaction involved the cleavage of the piperazine group. Finally, it was found that the potential for chlorine toxicity in treated drinking water in the presence of ENO is higher than it is without this pollutant.

The degradation of levofloxacin in infusions exposed to daylight with an identification of a degradation product with HPLC-MS

In this paper the decomposition product of levofloxacin was identified. Levofloxacin was dissolved in 0.9% NaCl, 5% glucose, and Ringer's solution. The solutions were divided into two batches: the first one was exposed to daylight and the second one was protected from it. The solutions were stored at the room temperature. The qualitative analysis of the degradation product was performed using MS and TOF detectors. The quantitative assay was done by a validated HPLC method. Visual inspection and pH assessment were done. Levofloxacin protected from daylight remained stable in 0.9% NaCl, 5% dextrose, and Ringer's solution. A slight decomposition of the analyte was observed in the solutions exposed to daylight with the fastest decomposition rate in Ringer's solution as compared with 0.9% NaCl and 5% dextrose solutions. The degradation product of levofloxacin detected with MS was levofloxacin N-oxide. Levofloxacin solutions should be protected from direct daylight to maintain drug stability. Levofloxacin N-oxide is formed regardless of the solvent used.

Influence of chemical speciation on photochemical transformation of three fluoroquinolones (FQs) in water: Kinetics, mechanism, and toxicity of photolysis products

This study investigated the contribution of direct, indirect, and self-sensitized photolysis to the photochemical fate of three model fluoroquinolones (FQs), i.e., lomefloxacin (LOM), norfloxacin (NOR), and ofloxacin (OFL), and demonstrated the influence of chemical speciation on their photodegradation behavior, a topic that has received relatively little attention. Results suggest that these FQs in water transformed mainly via direct photolysis, while hydroxyl radical played a key role in their indirect and self-sensitized photolysis. Chemical speciation of such zwitterionic compounds significantly affected the kinetics of their phototransformation, with the quantum yields of photodegradation decreased in the order of zwitterionic (FQsH) > anionic (FQs^-) > cationic (FQsH₂⁺). The photodegradation pathways of FQs depended on both their structures and chemical speciation. Defluorination for LOM in C-8 and NOR in C-6 was more significant when they were present in zwitterionic form than in the other forms. Cationic FQs underwent direct piperazinyl ring cleavage, and zwitterionic ones underwent piperazinyl ring oxidation, while the degradation pathway of piperazinyl ring for FQs in anionic form was structure dependent. Decarboxylation for zwitterionic FQs occurred more slowly compared to both cationic and anionic ones, and the FQs bearing electron-donating groups in C-8 position degraded more easily in cationic form than the anionic ones, while the opposite was true for the FQs without such a group in C-8 position. Results of Vibrio fischeri bioluminescence inhibition tests showed the toxicity of zwitterionic NOR and OFL significantly decreased after photodegradation, while the degradation products of LOM exhibited greater toxicity. These findings indicate that chemical speciation of zwitterionic compounds could affect the kinetics and pathways of their photochemical transformation, and thus have important implications on their fate and risk in aquatic environment.

Sunlight Assisted Photocatalytic Degradation of Ciprofloxacin in Water Using Fe Doped ZnO Nanoparticles for Potential Public Health Applications

Antibiotic residues in the aquatic environment have the potential to induce resistance in environmental bacteria, which ultimately might get transferred to pathogens making treatment of diseases difficult and poses a serious threat to public health. If antibiotic residues in the environment could be eliminated or reduced, it could contribute to minimizing antibiotic resistance. Towards this objective, water containing ciprofloxacin was treated by sunlight-assisted photocatalysis using Fe- doped ZnO nanoparticles for assessing the degradation potential of this system. Parameters like pH, temperature, catalytic dosage were assessed for the optimum performance of the system. To evaluate degradation of ciprofloxacin, both spectrophotometric as well as microbiological (loss of antibiotic activity) methods were employed. 100 mg/L Fe-doped ZnO nanoparticle catalyst and sunlight intensity of 120,000⁻135,000 lux system gave optimum performance at pH 9 at 30 °C and 40 °C. Under these conditions spectrophotometric analysis showed complete degradation of ciprofloxacin (10 mg/L) at 210 min. Microbiological studies showed loss of antibacterial activity of the photocatalytically treated ciprofloxacin-containing water against Staphylococcus aureus (10⁸ CFU) in 60 min and for Escherichia coli (10⁸ CFU) in 75 min. The developed system, thus possess a potential for treatment of antibiotic contaminated waters for eliminating/reducing antibiotic residues from environment.

Effects of the natural colloidal particles from one freshwater lake on the photochemistry reaction kinetics of ofloxacin and enrofloxacin

Understanding the effect of natural colloidal particles (NCPs) on the photochemistry of organic pollutants is crucial to predict the environmental persistence and fate of them in surface waters, and it is, yet, scarcely elucidated. In this study, the pre-filtered surface water (through a 1 μm capsule filter) from Baiyangdian Lake was further separated into four different size NCPs: F1 (0.65-1.0 μm), F2 (100 kD-0.65 μm), F3 (10-100 kD) and F4 (1-10 kD) by cross-flow ultrafiltration (CFUF), and the photochemical kinetics and mechanisms of ofloxacin (OFL) and enrofloxacin (ENR) were investigated in the presence of those particles under simulated sunlight. Results showed that OFL and ENR underwent both direct and indirect photolysis in F1-F4 solutions, and the observed pseudo first-order rate constants (k_obs) for target compounds differed depending on the size of NCPs. Direct photolysis accounted for >50% of the degradation in all cases and was the dominant degradation pathway for the two target antibiotics with the exception of OFL in F1 solution. Except for ENR in both F3 and F4 solutions, nearly all NCPs enhanced the degradation of both target compounds by indirect photolytic pathways, especially in F1 solution that showed the largest reactivity for OFL and ENR, promoting the reactions by 63% and 41%, respectively. The excited state colloidal organic matter (³COM^∗) plays a significant role in the indirect photolysis, and the adsorptions of OFL and ENR to NCPs were likely to have a pronounced effect in the photochemistry process. Pearson's correlations analysis showed that the k_obs(OFL) was significant positive correlated with binding of Fe (r = 0.963, P < 0.05), and the k_obs(ENR) was significant positive correlated with the adsorption percentage of OFL (r = 0.999, P < 0.01). This paper has demonstrated that different size NCPs showed the different photochemical contribution to the reaction rate for OFL and ENR.

Enantioselective fractionation of fluoroquinolones in the aqueous environment using chiral liquid chromatography coupled with tandem mass spectrometry

This paper aims to examine the multiresidue enantiomeric profiling of (fluoro)quinolones and their metabolites in solid and liquid environmental matrices using chiral HPLC-MS/MS method and a CHIRALCEL^® OZ-RH column. Simultaneous chiral separation was obtained for chiral ofloxacin and its main metabolites ofloxacin-N-oxide and desmethyl-ofloxacin; moxifloxacin; the prodrug prulifloxacin and its active compound ulifloxacin; flumequine; nadifloxacin and R-(+)-besifloxacin. Achiral antibiotics (ciprofloxacin, norfloxacin and nalidixic acid) were also included in the method to enable the analysis of all targeted quinolones within one analytical run. Satisfactory enantiomeric resolution (Rs ≥ 1) was obtained for five out of eight chiral drugs enabling quantitative analysis. The overall performance of the method was satisfactory with a method precision <20%, relative recoveries >70% for most of the analytes and method detection limits (MDL) at low ng L^-1 levels (0.1 < MDL (ng L^-1)< 6.4, 0.1 < MDL (ng L^-1)< 6.6 and 0.1 < MDL (ng L^-1)< 7.0 in influent, effluent and river waters for 83% compounds, 0.01 < MDL (ng g^-1)< 4.9 in solids for 91% compounds). Enantiomeric profiling from a week-long monitoring campaign in the UK showed that (±)-ofloxacin was found to be racemic in upstream waters but it was enriched with S-(-)-enantiomer in wastewater and in receiving waters. This could be due to the fact that ofloxacin can be used both as a racemate and as a S-(-)-enantiomer. Its consumption was further confirmed by the chiral signature of the investigated ofloxacin metabolites. As a result, alterations in the enantiomeric composition of antibiotics could influence not only their activity and toxicity in the environment, but also could induce changes in the microbial communities constantly exposed to them.

Exploring the aquatic photodegradation of two ionisable fluoroquinolone antibiotics - Gatifloxacin and balofloxacin: Degradation kinetics, photobyproducts and risk to the aquatic environment

Fluoroquinolone antibiotics (FQs) are ubiquitous and ionisable in surface waters. Here we investigate gatifloxacin (GAT) and balofloxacin (BAL), two widely used FQs, and determine the photochemical reactivity of their respective dissociation species that arise at different pH to understand the relevance and pathways of phototransformation reactions. Simulated-sunlight experiments and matrix calculations showed that neutral forms (HFQs⁰) of the two antibiotics had the highest apparent photolytic efficiency and hydroxyl-radical oxidation reactivity. Based on the pH-dependent photochemical reactivities, the solar apparent photodegradation half-lives (t_1/2) in sunlit surface waters ranged from 14.5-169min and was 1-2 orders of magnitude faster than hydroxyl-radical induced oxidation (t_1/2=20.9-29.8h). The corresponding pathways were proposed based on the identification of key intermediates using HPLC-ESI-MS/MS. The apparent photodegradation induced defluorination, decarboxylation, and piperazinyl oxidation and rearrangement, whereas hydroxyl-radical oxidation caused hydroxylated defluorination and piperazinyl hydroxylation. The photomodified toxicity of GAT and BAL was examined using an Escherichia coli activity assay. E. coli activity was not affected by BAL, but was significantly affected by the photo-modified solutions of GAT, indicating that primary photo-degradates have a comparable or higher antibacterial activity than the parent GAT. In fresh water and seawater this antibacterial activity remained high for up to 24h, even after GAT had undergone significant photodegradation (>1 half-life), indicating the potential impact of this chemical on microbial communities in aquatic systems.

Photocatalytic degradation of sulfamethazine in aqueous solution using ZnO with different morphologies

In this study, photocatalytic experiments of 20 mg l-1 sulfamethazine (SMN) in aqueous solution containing ZnO with different morphologies, tetra-needle-like ZnO (T-ZnO), flower-like ZnO (F-ZnO) and nanoparticles ZnO (P-ZnO), were performed. The results indicated that photocatalytic degradation of SMN was effective and followed the pseudo-first-order reaction, but the degree of SMN mineralization showed obvious differences using ZnO with different shapes. After 12 h irradiation, 86%, 71% and 50% of the initial total organic carbon was eliminated in SMN suspension containing T-ZnO, F-ZnO and P-ZnO, respectively. The release ratio of sulfur was close to 100% in the presence of T-ZnO, but reached to 86% and 67% in the presence of F-ZnO and P-ZnO, respectively. The release ratio of nitrogen was about 76%, 63% and 40% using T-ZnO, F-ZnO and P-ZnO as photocatalyst, respectively. The morphology of ZnO played an important role in determining its catalytic activity. Seven intermediates were observed and identified in the UV/T-ZnO reaction system by LC-MS/MS analysis, and a possible degradation pathway was proposed.

Photolysis of sulfamethazine using UV irradiation in an aqueous medium

Although many studies have been focused on the photochemistry of antibiotics, the roles of reactive species in photolysis and the effects of dissolved substances on antibiotic photochemical behavior have been poorly examined. The photolytic behaviors of sulfamethazine (SMN) in pure water were investigated via adding different scavengers to quench the active species. Results showed that decomposition of the triplet-excited state of SMN (³SMN*) by direct photolysis was the main path of SMN photolysis in water. Moreover, self-sensitized SMN cannot be ignored during SMN photodegradation. The main photoproducts of SMN were identified by LC-MS/MS, which indicated that SMN could not be mineralized although the photolysis under UV was effective. The effects of Cl⁻, NO₃⁻, and fulvic acid (FA) (common substances in natural water) on SMN photolytic behaviors were also studied. The triplet-induced halogenation of SMN increases the ionic strength and reduces the ground state SMN; these are the primary causes of promotion of SMN photolysis by Cl⁻. More ˙OH produced in the presence of NO₃⁻ could promote SMN photolysis. Competitive absorption of photons of FA with SMN and ROS scavenged by FA were the main reasons for the inhibition of SMN photolysis. The research findings are helpful for further studies on the environmental risks of ACs in natural waters and promoting the development of AC pollution treatment technology.

The role of reactive species in SMN photolysis and the effects of dissolved substances on SMN photochemical behavior.

Role of sulfate, chloride, and nitrate anions on the degradation of fluoroquinolone antibiotics by photoelectro-Fenton

Taking ciprofloxacin (CIP) as a fluoroquinolone antibiotic model, this work explores the role of common anions (sulfate, nitrate, and chloride) during the application of photoelectro-Fenton (PEF) at natural pH to degrade this type of compound in water. The system was composed of an IrO₂ anode, Ti, or gas diffusion electrode (GDE) as cathode, Fe²⁺, and UV (254 nm). To determine the implications of these anions, the degradation pathway and efficiency of the PEF sub-processes (UV photolysis, anodic oxidation, and electro-Fenton at natural pH) were studied in the individual presence of the anions. The results highlight that degradation routes and kinetics are strongly dependent on electrolytes. When chloride and nitrate ions were present, indirect electro-chemical oxidation was identified by electro-generated HOCl and nitrogenated oxidative species, respectively. Additionally, direct photolysis and direct oxidation at the anode surface were identified as degradation routes. As a consequence of the different pathways, six primary CIP by-products were identified. Therefore, a scheme was proposed representing the pathways involved in the degradation of CIP when submitted to PEF in water with chloride, nitrate, and sulfate ions, showing the complexity of this process. Promoted by individual and synergistic actions of this process, the PEF system leads to a complete elimination of CIP with total removal of antibiotic activity against Staphylococcus aureus and Escherichia coli, and significant mineralization. Finally, the role of the anions was tested in seawater containing CIP, in which the positive contributions of the anions were partially suppressed by its OH radical scavenger action. The findings are of interest for the understanding of the degradation of antibiotics via the PEF process in different matrices containing sulfate, nitrate, and chloride ions.

Adsorption of ciprofloxacin and norfloxacin from aqueous solution onto granular activated carbon in fixed bed column

Carbonization of Phoenix dactylifera L stones followed by microwave K₂CO₃ activation was adopted for preparation of granular activated carbon (KAC). High yield and favorable pore characteristics in terms of surface area and pore volume were reported for KAC as follows: 44%, 852m²/g, and 0.671cm³/g, respectively. The application of KAC as adsorbent for attraction of ciprofloxacin (CIP) and norfloxacin (NOR) was investigated using fixed bed systems. The effect of flow rate (0.5-1.5ml/min), bed height (15-25cm), and initial drug concentration (75-225mg/l) on the behavior of breakthrough curves was explained. The fixed bed analysis showed the better correlation of breakthrough data by both Thomas and Yoon-Nelson models. Inlet drug concentration was of greatest effect on breakthrough data compared to other fixed bed variables. Experimental and calculated breakthrough data were obtained for CIP and NOR adsorption on KAC, thus being important for design of fixed bed column.

g-C3N4-promoted degradation of ofloxacin antibiotic in natural waters under simulated sunlight

This is the first report on the photodegradation of ofloxacin under simulated solar light and in actual environmental matrices in the presence of a g-C₃N₄ suspension. The catalyst, prepared from the polymerization of dicyandiamide (650 °C, reaction yield 60%), was characterized by means of powder X-ray diffraction (PXRD), UV-vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and BET surface area measurements. The experiments were carried out in a lab-scale batch reactor at concentrations in the range of micrograms/milligrams per liter. The course of the reaction was monitored by high-pressure liquid chromatography with UV-vis and fluorescence detectors. The g-C₃N₄-promoted photodegradation occurred at a rate 10 times faster than the direct photolysis and obeyed a first-order kinetics; in addition, the photodegradation kinetics of sonicated g-C₃N₄ resulted to be of the same order of that caused by P25 TiO₂. Finally, the photochemical paths and the photoproducts have been identified and compared to those obtained by using P25 TiO₂. From the results of this study, it can be concluded that g-C₃N₄ is a very attractive photocatalyst compared to P25 TiO₂ in view of its ease of preparation, low cost, excellent oxidizing properties, large fraction of solar radiation absorbed, and intrinsically layered structure.

Analysis of positions and substituents on genotoxicity of fluoroquinolones with quantitative structure-activity relationship and 3D Pharmacophore model

The genotoxicity values of 21 quinolones were studied to establish a quantitative structure-activity relationship model and 3D Pharmacophore model separately for screening essential positions and substituents that contribute to genotoxicity of fluoroquinolones (FQs). A full factor experimental design was performed to analyze the specific main effect and second-order interaction effect of different positions and substituents on genotoxicity, forming a reasonable modification scheme which was validated on typical FQ with genotoxicity and efficacy data. Four positions (1, 5, 7, 8) were screened finally to form the full factorial experimental design which contained 72 congeners in total, illustrating that: the dominant effect of 5 and 7-positions on genotoxicity of FQs is main effect; meanwhile the effect of 1 and 8-positions is a second-order interaction effect; two adjacent positions always have stronger second-order interaction effect and lower genotoxicity; the obtained modification scheme had been validated on typical FQ congeners with the modified compound has a lower genotoxicity, higher synthesis feasibilities and efficacy.

Roles of singlet oxygen and dissolved organic matter in self-sensitized photo-oxidation of antibiotic norfloxacin under sunlight irradiation

Many fluoroquinolone (FLQ) antibiotics undergo rapid photodegradation in sunlit waters and form multifaceted photo-products. The high photodegradation rate is primarily ascribed to their photosensitizing properties. Though widely studied, the photo-reaction pathways are not completely revealed; photo-products mediated by different reactive oxygen species are not identified. In our study, photo-degradation of fluoroquinolone norfloxacin was investigated. A rapid degradation in buffered water was observed with a first-order rate constant of 2.45/hr and a quantum yield of 0.039. After light screening correction, selected DOMs (5 mg C/L) slightly enhanced the photodegradation rate with the exception of Suwannee river hydrophobic organic matter (SR-HPO). Three major photo-products were identified using high resolution mass spectrometry (HRMS). With ¹O₂ dark formation and competitor experiments, norfloxacin self-sensitized ¹O₂ was found to oxidize norfloxacin by inducing its piperazine chain cleavage. DOMs exhibited a dual role by inhibiting the ¹O₂-mediated reaction while enhancing the heterolytic defluorination pathway. DOMs were proposed to enhance heterolytic defluorination by donating electron to triplet state FLQ, this proposal was supported with specific UV absorbance (SUVA) as an indicator for the abundance of π bonds. Fluoride formation indicated a 79% elimination ratio of fluorine, an important functional group for antimicrobial activity. This work provides important new insights into the photochemical fate of fluoroquinolone antibiotics in natural water.

Photostability of 6-MAM and morphine exposed to controlled UV irradiation in water and methanol solution: HRMS for the characterization of transformation products and comparison with the dry state

The UVA and UVB light-induced behaviour of 6-monoacetylmorphine (6-MAM) and morphine, the main metabolites of heroin, was studied in methanol, aqueous solution and in the dry state. UVA and UVB irradiations were performed for different times (radiant energies of 20-300J/cm(2)). UV spectra of irradiated samples were compared with samples kept in the dark. To estimate the extent of photolysis, positive ion electrospray ionization experiments were performed on the irradiated samples by LC-HRMS. Tentative identification of photoproducts was performed on the basis of their elemental formula as calculated by HRMS results. Morphine and 6-MAM demonstrated to be quite stable under UVA light but very sensitive to UVB irradiation. In methanol solutions they undergo a similar pattern, both reaching 90% photodegradation after 100J/cm(2) of UVB, with a slightly faster kinetic for morphine at lower doses. In water, the yields of photodegradation are nearly one third lower than in methanol. In the solid state, the yield of photodegradation is lower than in solution. The structures of some UVB-induced degradation products are proposed. Photoaddition of the solvent and photooxidation seem the main pathways of phototransformation of these molecules. Moreover, both compounds revealed to generate singlet oxygen under UVB exposure.

Removal of fluoroquinolone contaminants from environmental waters on sepiolite and its photo-induced regeneration

Sepiolite is studied as sorbent for removal of Fluoroquinolone (FQ) contaminants from water. Marbofloxacin (MAR) and Enrofloxacin (ENR) were chosen as model FQs since they are the two most commonly employed veterinary FQs in livestock farming in northern Italy. Adsorption experiments on two sepiolites (SP-1 and SSE16) were carried out in tap water at pH 7.5 to better mimic real conditions. The sorption experimental data were fitted by Freundlich, Langmuir and S-Logistic1 models. The latter better described MAR and ENR adsorptions. Adsorption capacities of SP-1 and SSE16, respectively, were 132 mg g(-1) and 121 mg g(-1) for MAR, and 112 mg g(-1) and 93 mg g(-1) for ENR. X-ray powder diffraction, performed on clay samples enriched with each FQ and on the pristine clays, showed no substantial differences between the two sepiolites and evidenced no significant structural changes after FQs uptake, as also verified by infrared spectroscopy. This indicates that adsorption occurs only on the external surface of the mineral and not in the intracrystalline microporosity, likely due to the interaction between the FQ carboxylic group and the sepiolite surface. For the first time solid-state photodegradation of the adsorbed FQs was investigated for regenerating the sorbent. Results showed that the adsorbed drugs are effectively photodegraded by solar light, thus allowing sepiolite to be reused. The efficiency of this material for remediation of contaminated water was proved on ditch water, collected downstream a swine farm, containing some tens of ng L(-1) of MAR and ENR.