Degradation of sulfamethoxazole in water by solar photo-Fenton. Chemical and toxicological evaluation

Degradation and metabolic pathways of sulfamethazine and enrofloxacin in Chlorella vulgaris and Scenedesmus obliquus treatment systems

The degradation and metabolic pathways of sulfamethazine (SMZ) and enrofloxacin (ENR) via microalgal treatment systems were investigated in this study. SMZ and ENR applied at 1-25 mg L^-1 did not significantly inhibit the growth of Chlorella vulgaris or Scenedesmus obliquus. SMZ and ENR exposure did not significantly alter the maximum quantum efficiencies of C. vulgaris and S. obliquus. When cultured at light intensities of 45-50 μmol photon m^-2 s^-1, the C. vulgaris and S. obliquus treatment systems achieved 24% and 11% degradation, respectively. The greatest removal of ENR was 52% and 43.3%, for C. vulgaris and S. obliquus treatment systems, respectively, after 15 days. The results indicated that the degradation of SMZ and ENR occurred by a combination of biodegradation and photolysis. Kinetic investigations revealed that the removal of SMZ and ENR (5 mg L^-1) followed a first-order model, with apparent rate constants (k) ranging from 0.0141 to 0.0048 day^-1 and 0.0132 to 0.0086 day^-1, respectively. Fifteen metabolites of SMZ and five intermediates of ENR were identified by UPLC-MS, and degradation pathways for SMZ and ENR were proposed. SMZ transformation reactions included ring cleavage, hydroxylation, methylation, and oxidation, whereas ENR was degraded by dealkylation, decarboxylation, and defluorination. Graphical abstract.

Synergistic effect of persulfate and g-C3N4 under simulated solar light irradiation: Implication for the degradation of sulfamethoxazole

A method combining g-C₃N₄ and potassium peroxydisulfate (PDS) under simulated sunlight was put forward to effectively degrade sulfamethoxazole (SMX). The SMX removal efficiency was substantially improved compared with the processes involving only g-C₃N₄ or PDS. The kinetic constants for the g-C₃N_4, PDS and g-C₃N₄/PDS systems were 0.0023, 0.0239 and 0.068 min^-1, respectively. The g-C₃N₄/PDS process reached an SMX removal rate of 98.4 % after 60 min of simulated sunlight; in addition, the proposed system showed desirable efficiency for SMX degradation in two different actual water samples as well. The reaction mechanism was illustrated by trapping experiments, which showed that g-C₃N₄ can promote S₂O₈^2- to transfer SO₄^-, S₂O₈^2- favored the generation of O₂^-, and O₂^-, SO₄^- and holes (h⁺) were the main oxidative species for the SMX degradation in the combined reaction process under simulated sunlight. Then, to further explore this mechanism, the intermediates generated during the combined reaction process were analyzed by LC/MS and possible degradation pathways were proposed. The result showed that the breaking of the SN and C-S bonds, the hydroxylation of the benzene ring and the oxidation of the amino group were identified as the main pathways in the SMX degradation process by the g-C₃N₄/PDS system under simulated sunlight.

Synthesis and assessment of schwertmannite/few-layer graphene composite for the degradation of sulfamethazine in heterogeneous Fenton-like reaction

Schwertmannite (sch), an iron oxyhydrosulfate mineral, can catalyse a Fenton-like reaction to degrade organic contaminants, but the reduction of Fe(III) to Fe(II) on the surface of schwertmannite is a limiting step for the Fenton-like process. In the present study, the sch/few-layer graphene (sch-FLG) composite was synthesized to promote the catalytic activity of sch in a Fenton-like reaction. It was found that sch can be successfully carried by FLG in sch-FLG composite, mainly via the chemical bond of Fe-O-C on the surface of sch-FLG. The sch-FLG exhibited a much higher catalytic activity than sch or FLG for the degradation of sulfamethazine (SMT) in the heterogeneous Fenton-like reaction, which resulted from the fact that the FLG can pass electrons efficiently. The degradation efficiency of SMT was around 100% under the reaction conditions of H2O2 200-500 mg l-1, sch-FLG dosage 1-2 g l-1, temperature 28-38°C, and initial solution pH 1-9. During the repeated uses of sch-FLG in the Fenton-like reaction, it maintained a certain catalytic activity for the degradation of SMT and the mineral structure was not changed. In addition, SMT may be finally mineralized in the Fenton-like reaction catalysed by sch-FLG, and the possible degradation pathways were proposed. Therefore, the sch-FLG is an excellent catalyst for SMT degradation in a heterogeneous Fenton-like reaction.

Role of pyrophosphate on the degradation of sulfamethoxazole by permanganate combined with different reductants: Positive or negative

Activating permanganate with reductants has gained increasing attention recently for efficient organic contaminants abatement via reactive intermediate Mn species. However, few studies have been conducted to explore the role of pyrophosphate (PP), a typical complexing agent for intermediate Mn species, in activated permanganate systems. In this study, taking sulfamethoxazole (SMX) as a probe compound, the influences of PP on SMX degradation by permanganate/thiosulfate and permanganate/hydroxylamine were extensively studied. It was found that both thiosulfate and hydroxylamine were able to activate permanganate for oxidation of SMX in the absence of PP. However, upon the introduction of PP, opposite effects were observed in the two systems where PP further improved the activation of permanganate by thiosulfate but dampened the performance of permanganate/hydroxylamine markedly. For permanganate/hydroxylamine system, MnO₂ was determined to be the only reactive oxidative species accounting for SMX degradation in the absence of PP, and its generation could be completely inhibited by PP. While in permanganate/thiosulfate system, both Mn(V) and MnO₂ were responsible for SMX oxidation, and the introduction of PP could strengthen the oxidative ability of Mn(V). These results could shed some insights on the suitability of applying PP to explore the kinetics and mechanisms of manganese involved redox reactions. PRACTITIONER POINTS: Both Na₂ S₂ O₃ and NH₂ OH·HCl can activate KMnO₄ for SMX removal without PP. MnO₂ is the reactive oxidative species involved in KMnO₄ /NH₂ OH·HCl system. Mn(V) and MnO₂ account for the SMX oxidation by KMnO₄ /Na₂ S₂ O₃ system. PP could inhibit the formation of MnO₂ but enhance the oxidative ability of Mn(V).

Zr-Doped Ir as an Effective Anode for Refractory SMX Degradation

Electrochemical oxidation has been considered as an efficient method to degrade pharmaceuticals and personal care products. Maintaining low power consumption while increasing the number of oxidation intermediates is deserving of exploring. Herein, Ti/SnO₂-Sb/Zr_0.3Ir_0.7O₂ was prepared by Zr doped into IrO₂ and used for Sulfamethoxazole (SMX) degradation. The addition of Zr significantly increased the electrochemically active area and facilitated the catalyst to degrade SMX dramatically at a lower overpotential. The extremely outstanding lifetime of catalysts can reach 800 h during the accelerated life test, which showed excellent stability and developmental prospects. The overpotential at 10 mA·cm^-2 is about 329 mV, indicating that this electrode has a high oxygen evolution reaction activity. Furthermore, the electrical efficiency per log order for the electrode is only 8.50 kW h m^-3 at 4 V. Our research provides new anode electrochemical catalysts for the degradation of organic pollutants.

Modeling electrochemical oxidation and reduction of sulfamethoxazole using electrocatalytic reactive electrochemical membranes

In this research, degradation of the antibiotic sulfamethoxazole (SMX) was studied using electrochemical reduction and oxidation in single pass, flow-through mode using porous titanium suboxide (Ti₄O₇) reactive electrochemical membranes (REMs) and Pd-Cu doped Ti₄O₇ REMs (Pd-Cu/Ti₄O₇ REMs). Electrochemical reduction of SMX increased from 3.8 ± 0.3% for the Ti₄O₇ REM to 96.1 ± 3.9% for the Pd-Cu/Ti₄O₇ REM at -1.14 V/SHE and at a permeate flux of 300 L m^-2 h^-1 (LMH) (liquid residence time: ∼1.8 s). By contrast, electrochemical oxidation using Ti₄O₇ REMs achieved 95.7 ± 1.0% removal of SMX at 2.03 V/SHE and a permeate flux of 300 LMH (liquid residence time: ∼9.0 s) without the catalyst addition. We developed a reactive transport mathematical model and calibrated it to the SMX experimental data. The calibrated model predicted SMX permeate concentrations at fixed potentials and as a function of permeate flux. Based on products from SMX reduction, we proposed that SMX was reduced by a hydrogen atom transfer reaction that was mediated by the Pd-Cu/Ti₄O₇ REM. Toxicity tests indicated that electrochemical oxidation/reduction lowered solution toxicity. The results of this work indicate that a tandem electrochemical reduction/oxidation approach using the REM-based technology is a potential treatment strategy for sulfonamide-contaminated pharmaceutical wastewater.

Photochemical study of the highly used corticosteroids dexamethasone and prednisone. Effects of micellar confinement and cytotoxicity analysis of photoproducts

Photodegradation of dexamethasone (Dexa) and prednisone (Pred) occurs by a combination of ROS attack and unimolecular photodegradation reactions. The photoproducts obtained are more cytotoxic than the parent compounds.

Electrochemical Oxidation of Sulfonamides with Boron-Doped Diamond and Pt Anodes

Electrochemical oxidation processes usually favored specific degradation pathways depending on anode materials. In this work, a series of sulfonamides (SNs) were degraded by electrochemical oxidation. Compared to Pt anodes (0.1567–0.1795 h⁻¹), degradation rates of SNs were much higher at boron‐doped diamond (BDD) anodes (2.4290–13.1950 h⁻¹). However, the same intermediates were detected in the two anode systems. Due to the strong oxidizing ability of BDD anodes, a large amount of intermediates with high toxicities were initially generated and then finally reduced in the BDD anode systems, while the amount of intermediates continuously increased in the Pt anode systems. Additionally, SNs were degraded faster in Na₂SO₄ than NaH₂PO₄ electrolytes at BDD anodes, while they were similar at Pt anodes. This study demonstrated that the degradation pathways of SNs at BDD and Pt anodes were similar, but the evolutions of intermediate amounts and toxicities were different due to their varied oxidizing abilities.

Development of a moving-bed electrochemical membrane bioreactor to enhance removal of low-concentration antibiotic from wastewater

Removal of low-concentration (ng/L ~ μg/L) antibiotics from water calls for the development of cost-effective treatment technologies. In this study, a novel moving-bed electrochemical membrane bioreactor (MEMBR) was developed for removing sulfamethoxazole (SMX). Results showed that the introduction of external electric field and carbon felt particles could efficiently eliminate SMX (removal efficiency of 88.9%). In contrast, the moving-bed membrane bioreactor (MMBR) took a long time to acclimate microorganism, reaching a removal efficiency of 43.9%. Transmembrane pressure increase rate was much lower in MEMBR (1.06 kPa/d) compared to MMBR (1.72 kPa/d). The presence of carriers increased the generation of reactive oxygen species, contributing to SMX removal. Microbial community analysis revealed that the introduction of electric field could increase microbial community richness/diversity and enrich the phyla of Actinobacteria and Gemmatimonadete, potentially capable of mineralizing SMX. These results clearly demonstrated the potential of this novel MEMBR to be used for enhanced micropollutants removal from water/wastewater.

Sulfate radical-based oxidation of the antibiotics sulfamethoxazole, sulfisoxazole, sulfathiazole, and sulfamethizole: The role of five-membered heterocyclic rings

The widespread occurrence of sulfonamides (SAs) in natural waters, wastewater, soil and sediment has raised increasing concerns about their potential risks to human health and ecological systems. Sulfate radical (SO₄^-)-based advanced oxidation processes (SR-AOPs) have become promising technologies to remove such contaminants in the environment. The present study systematically investigated the degradation of four selected SAs with different five-membered heterocyclic rings, namely, sulfamethoxazole (SMX), sulfisoxazole (SIX), sulfathiazole (STZ), and sulfamethizole (SMT), by thermo-activated persulfate (PS) process, and the role of heterocyclic rings was assessed particularly. The results revealed that all the selected SAs could be degraded efficiently by thermo-activated PS process and their decay rates were appreciably increased with increasing temperature. For instance, degradation rates of STZ increased from 0.3 × 10^-3 to 19.5 × 10^-3 min^-1 as the temperature was increased from 30 to 60 °C. Under the same experimental conditions, the degradation rates of SAs followed the order of SIX > SMX ≈ STZ > SMT, which was in accordance with decay rates of their R-NH₂ moieties. Kinetic results indicated that five-membered heterocyclic rings could serve as reactive moieties toward SO₄^- attack, which were confirmed by frontier electron density (FED) calculations. Based on the transformation products identified by high-resolution mass spectrometry (HR-MS), five different oxidation pathways, including hydroxylation, aniline moiety oxidation, dimerization, sulfonamide bond cleavage, and heterocyclic ring oxidation/cleavage were proposed. Moreover, the degradation efficiency in real surface water (RSW) was found to be slightly slower than that in artificial surface water (ASW), suggesting that SR-AOPs could be an efficient approach for remediation of soil and water contaminated by these SAs.

Biocatalytic degradation/redefining "removal" fate of pharmaceutically active compounds and antibiotics in the aquatic environment

Recently, the increasing concentration and persistent appearance of antibiotics traces in the water streams are considered an issue of high concern. In this context, an array of antibiotics has been categorized as pollutants of emerging concern due to their complex and highly stable bioactivity, indiscriminate usage with ultimate release into water bodies, and notable persistence in environmental matrices. Moreover, antibiotics traces containing household sewage/drain waste and pharmaceutical wastewater effluents contain a range of bioactive/toxic organic compounds, inorganic salts, pharmaceutically-active ingredients, or a mixture of all, which possesses negative influences ranging from ecological pollution to damage biodiversity. Moreover, their uncontrolled and undesirable bioaccumulation also poses a potential threat to target and non-target organisms in the environment. Aiming to tackle this issue effectively, various detection, quantification, degradation, and redefining "removal" processes have been proposed and investigated based on physical, chemical, and biological strategies. Though both useful and side effects of antibiotics on humans and animals are usually investigated thoroughly following safety and toxicity measures, however, their direct or indirect environmental impacts are not well reviewed yet. Owing to the considerable research gap, the environmental perfectives of antibiotics traces and their effects on target and non-target populations have now become the topic of research interest. Based on literature evidence, over the past several years, numerous individual studies have been performed and published covering various aspects of antibiotics. However, a comprehensive compilation on enzyme-based degradation of antibiotics is still lacking and requires careful consideration. Hence, this review summarizes up-to-date literature on enzymes as biocatalytic systems, explicitly, free as well as immobilized forms and their effective exploitation for the degradation of various antibiotics traces and other pharmaceutically-active compounds present in the water bodies. It is further envisioned that the enzyme-based strategies, for antibiotics degradation or removal, discussed herein, will help readers for a better understanding of antibiotics persistence in the environment along with the associated risks and removal measures. In summary, the current research thrust presented in this review will additionally evoke researcher to engineer robust and sustainable processes to effectively remediate antibiotics-contaminated environmental matrices.

Pharmaceutically active compounds in aqueous environment: A status, toxicity and insights of remediation

Pharmaceutically active compounds (PhACs) have pernicious effects on all kinds of life forms because of their toxicological effects and are found profoundly in various wastewater treatment plant influents, hospital effluents, and surface waters. The concentrations of different pharmaceuticals were found in alarmingly high concentrations in various parts of the globe, and it was also observed that the concentration of PhACs present in the water could be eventually related to the socio-economic conditions and climate of the region. Drinking water equivalent limit for each PhAC has been calculated and compared with the occurrence data from various continents. Since these compounds are recalcitrant towards conventional treatment methods, while advanced oxidation processes (AOPs) have shown better efficiency in degrading these PhACs. The performance of the AOPs have been evaluated based on percentage removal, time, and electrical energy consumed to degrade different classes of PhACs. Ozone based AOPs were found to be favorable because of their low treatment time, low cost, and high efficiency. However, complete degradation cannot be achieved by these processes, and various transformation products are formed, which may be more toxic than the parent compounds. The various transformation products formed from various PhACs during treatment have been highlighted. Significant stress has been given on the role of various process parameters, water matrix, oxidizing radicals, and the mechanism of degradation. Presence of organic compounds, nitrate, and phosphate usually hinders the degradation process, while chlorine and sulfate showed a positive effect. The role of individual oxidizing radicals, interfering ions, and pH demonstrated dissimilar effects on different groups of PhACs.

Evaluation of amicarbazone toxicity removal through degradation processes based on hydroxyl and sulfate radicals

The herbicide amicarbazone (AMZ), which appeared as a possible alternative to atrazine, presents moderate environmental persistence and is unlikely to be removed by conventional water treatment techniques. Advanced oxidation processes (AOPs) driven by ^•OH and/or SO₄^•- radicals are then promising alternatives to AMZ-contaminated waters remediation, even though, in some cases, they can originate more toxic degradation products than the parent-compound. Therefore, assessing treated solutions toxicity prior to disposal is of extreme importance. In this study, the toxicity of AMZ solutions, before and after treatment with different ^•OH-driven and SO₄^•--driven AOPs, was evaluated for five different microorganisms: Vibrio fischeri, Chlorella vulgaris, Tetrahymena thermophila, Escherichia coli, and Bacillus subtilis. In general, the toxic response of AMZ was greatly affected by the addition of reactants, especially when persulfate (PS) and/or Fe(III)-carboxylate complexes were added. The modifications of this response after treatment were correlated with AMZ intermediates, which were identified by mass spectrometry. Thus, low molecular weight by-products, resulting from fast degradation kinetics, were associated with increased toxicity to bacteria and trophic effects to microalgae. These observations were compared with toxicological predictions given by a Structure-Activity Relationships software, which revealed to be fairly compatible with our empirical findings.

Analyzing a broader spectrum of endocrine active organic contaminants in sewage sludge with high resolution LC-QTOF-MS suspect screening and QSAR toxicity prediction

Endocrine active contaminants (EACs) in environmental samples can pose a range of toxicological threats to ecosystems, especially through their impacts on reproductive pathways mediated by the estrogen receptor. The physicochemical properties of known organic EACs vary greatly and typically require different sample preparation techniques to identify different classes of compounds. EAC sources are similarly diverse, including both endogenous compounds and anthropogenic chemicals found in personal care products, pharmaceuticals, and their transformation products, which are often disposed of to sewers at their end of use. Looking for EACs in sewage sludge proposes a bottom-up, or end-of-use and treatment approach to discover environmentally relevant EACs, since many EACs accumulate in sludges even after application of robust wastewater treatment processes. This study demonstrates an extraction and analytical method capable of detecting a broad spectrum of known and suspected EACs via High Resolution Liquid Chromatography Quadropole Time-of-Flight Mass Spectrometry (LC-QTOF-MS) suspect screening of fourteen California sewage sludge samples. Spike-recovery experiments were performed using twelve carefully selected surrogates to assess different extraction solvents, sample weights, extraction pH values, procedures for combining extracts with different extraction pH's, and solid phase extraction cartridges. Using LC-QTOF-MS, identifications of several other organic compounds in the samples were made, a goal unachievable with unit resolution mass spectrometry. Suspect screening of California sludge samples discovered 118 compounds including hormones, pharmaceuticals, phosphate flame retardants, recreational drugs, antimicrobials, and pesticides. Additionally, 22 of these identified compounds are predicted to interfere with estrogen receptors or other reproductive/developmental pathways based on the VEGA QSAR toxicity prediction model.

Removal of Sulfamethoxazole, Sulfathiazole and Sulfamethazine in their Mixed Solution by UV/H2O2 Process

Sulfamethoxazole (SMZ), sulfathiazole (STZ) and sulfamethazine (SMT) are typical sulfonamides, which are widespread in aqueous environments and have aroused great concern in recent years. In this study, the photochemical oxidation of SMZ, STZ and SMT in their mixed solution using UV/H₂O₂ process was innovatively investigated. The result showed that the sulfonamides could be completely decomposed in the UV/H₂O₂ system, and each contaminant in the co-existence system fitted the pseudo-first-order kinetic model. The removal of sulfonamides was influenced by the initial concentration of the mixed solution, the intensity of UV light irradiation, the dosage of H₂O₂ and the initial pH of the solution. The increase of UV light intensity and H₂O₂ dosage substantially enhanced the decomposition efficiency, while a higher initial concentration of mixed solution heavily suppressed the decomposition rate. The decomposition of SMZ and SMT during the UV/H₂O₂ process was favorable under neutral and acidic conditions. Moreover, the generated intermediates of SMZ, STZ and SMT during the UV/H₂O₂ process were identified in depth, and a corresponding degradation pathway was proposed.

Biomarker Effects in Carassius auratus Exposure to Ofloxacin, Sulfamethoxazole and Ibuprofen

Ofloxacin, sulfamethoxazole and ibuprofen are three commonly used drugs which can be detected in aquatic environments. To assess their ecotoxicity, the effects of these three pharmaceuticals and their mixture on AChE (acetylcholinesterase) activity in the brain, and EROD (7-ethoxyresorufin-O-deethylase) and SOD (superoxide dismutase) activities in the liver of the freshwater crucian carp Carassius auratus were tested after exposure for 1, 2, 4 and 7 days. The results showed that treatments with 0.002–0.01 mg/L ofloxacin and 0.0008–0.004 mg/L sulfamethoxazole did not significantly change AChE, EROD and SOD activities. AChE activity was significantly inhibited in response to treatment with >0.05mg/L ofloxacin and >0.02 mg/L sulfamethoxazole. All three biomarkers were induced significantly in treatments with ibuprofen and the mixture of the three pharmaceuticals at all the tested concentrations. The combined effects of ofloxacin, sulfamethoxazole and ibuprofen were compared with their isolated effects on the three biomarkers, and the results indicated that exposure to ibuprofen and the mixture at environmentally relevant concentrations could trigger adverse impacts on Carassius auratus. The hazard quotient (HQ) index also demonstrated a high risk for ibuprofen. Moreover, the present study showed that the effects of ofloxacin, sulfamethoxazole and ibuprofen might be additive on the physiological indices of Carassius auratus.

Acidic permanganate oxidation of sulfamethoxazole by stepwise electron-proton transfer

Permanganate is a versatile chemical oxidant, and has undergone a dramatic evolution toward deep insight into its reaction mechanism. However, the hydrogen abstraction of the NH bond by permanganate remains unclear. We studied the permanganate oxidation of the emerging micropollutant sulfamethoxazole in acidic aqueous solution. The reaction followed autocatalytic kinetics and demonstrated first-order with respect to each reactant. The presence of HMnO₄ accelerated the reaction rate, which was four orders of magnitude higher than that of MnO₄^-. Based on the identified products, the rate-limiting step was determined to be simple NH bond oxidation by metal-oxo species permanganate. The mechanism was then studied computationally by density functional theory (DFT) using ammonia as the simplest model. Results showed that the NH bond oxidation by MnO₄^- (32.86 kcal/mol) was a concerted mechanism similar to that of CH bond oxidation, whereas HMnO₄ oxidation of the NH bond (10.44 kcal/mol) was a stepwise electron-proton transfer. This reminds us that coordination of Brønsted acid could not only produce the stronger electrophile but also change the reaction mode by avoiding the bond cleavage in electron transfer process.

Sulfadiazine destruction by chlorination in a pilot-scale water distribution system: Kinetics, pathway, and bacterial community structure

Sulfadiazine (SDZ) has been frequently detected in surface waters in recent years. We evaluated the kinetics, mechanisms, intermediate products and bacterial community structure that result from the reaction of SDZ with free chlorine (HOCl/OCl-). We examined this in a pilot-scale water distribution system. Neutral pH had the fastest rate of destruction of SDZ. A second-order reaction constant for the destruction of SDZ by chlorine increased with increasing concentration of free chlorine (FC). For different pipe materials, the rate of SDZ degradation decreased as follows: stainless steel (SS) pipe > polyethylene (PE) pipe > ductile iron (DI) pipe. Based on the less complex bacterial diversity and more chlorine-resistant by 16S ribosomal ribonucleic acid (rRNA) gene analysis, SS pipe and PE pipe were more suitable in SDZ degradation in water distribution system (WDS) than DI pipe. In addition, the transformation products from SDZ chlorination were identified by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, and the products included SO2 extrusion products, haloacetic acids and trihalomethanes. Toxicity tests further confirmed that the toxicity of SDZ chlorination was higher both in low FC (0.7 mg/L) and high FC (1.3 mg/L) in WDS.

Elucidation of stoichiometric efficiency, radical generation and transformation pathway during catalytic oxidation of sulfamethoxazole via peroxymonosulfate activation

In this work, nano-bimetallic Co/Fe oxides with different stoichiometric Co/Fe ratios were prepared using a novel one-step solution combustion method. The nano-bimetallic Co/Fe oxides were used for sulfamethoxazole (SMX) degradation via peroxymonosulfate (PMS) activation. The stoichiometric efficiencies of the as-prepared nano-bimetallic catalysts were calculated and compared for the first time. The radical generation was identified by electron paramagnetic resonance (EPR) as well as chemical quenching experiments, in which different scavengers were used and compared. The catalytic PMS activation mechanism in the presence of catalyst was examined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that besides SO₄•^- and •OH, •OOH was also detected in the PMS/CoFeO_2.5 system. Meanwhile, in addition to the previously proposed radical oxidation pathway, the results showed that SMX degradation also involved a non-radical oxidation, which could be verified by the degradation experiment without catalyst as well as the detection of ¹O₂. In the PMS activation process, cobalt functioned as the active site on CoFeO_2.5 while Fe oxide functioned as the adsorption site. The electron transfer mechanism was proposed based on the XPS and metal leaching results. Additionally, via the detection of transformation products, different SMX transformation pathways involving nitration, hydroxylation and hydrolysis in the PMS/CoFeO_2.5 system were proposed.

In situ generation of H2O2 using MWCNT-Al/O2 system and possible application for glyphosate degradation

Hydrogen peroxide (H₂O₂), as a green oxidant, has been widely applied into advanced oxidation processes (AOPs) for the degradation of toxic organic pollutants. The in situ generation of H₂O₂ can not only improve the storage and transportation safety of H₂O₂ but also reduce the capital and operation costs. In the present work, a novel system, i.e., multi-walled carbon nanotube‑aluminum (MWCNT-Al) composite was used to in situ generate H₂O₂ through micro-electrolysis. The MWCNT-Al composite was characterized and optimized. The accumulation concentration of H₂O₂ reached 947 mg/L at the initial pH of 9.0, the MWCNT-Al composite dosage of 8 g/L and oxygen gas flow rate of 400 mL/min after 60 min. The in situ generation of H₂O₂ was achieved by MWCNT-Al/O₂ system, mainly owing to the direct contact between Al⁰ and MWCNT in MWCNT-Al composite, which accelerated the transfer of electrons from Al⁰ to O₂, as well as the excellent electrocatalytic activity of MWCNT toward the two-electron reduction of oxygen. When H₂O₂ in situ generation technology was used in peroxone process (O₃/H₂O₂ process) to degrade glyphosate in aqueous solution, the removal efficiency of TOC and total phosphorus was 68.35% and 73.27%, respectively. Finally, the possible mechanism of in situ generation of H₂O₂ in MWCNT-Al/O₂ system was temporarily proposed.

Bisulfite triggers fast oxidation of organic pollutants by colloidal MnO2

Colloidal MnO₂ is the most reactive phase of Mn(IV) while HSO₃^- is a common reductant in water treatment. This study shows that the presence of HSO₃^- resulted in significant increase in the decomposition rate of organic contaminants by colloidal MnO₂. The degradation rate of contaminants in the MnO₂/HSO₃^- process dropped with elevating pH and a proper MnO₂/HSO₃- molar ratio was critical for efficient decomposition of contaminants. The time-resolved spectroscopy of manganese species, the influence of pyrophosphate on UV absorbance spectra, and the relative rate constants of contaminants oxidation in MnO₂/HSO₃^- process suggested that the synergetic effect of HSO₃^- and colloidal MnO₂ arose from the generation of Mn(III)_aq, which could oxidize contaminants rapidly. The presence of pyrophosphate, ethylenediaminetetraacetic acid, and humic acid depressed the degradation of contaminants in MnO₂/HSO₃^- process by complexing with Mn(III)_aq, buffering the solution or competing with contaminants for Mn(III)_aq, and/or inhibiting the consumption of bisulfite. However, Ca²⁺ and Mg²⁺ accelerated the oxidation of contaminants in MnO₂/HSO₃- process by enhancing the reduction of MnO₂ by HSO₃-. The good negative correlation of the O/N or H Mulliken charges of organic contaminants with their removal in MnO₂/HSO₃^- process suggested that organic contaminants were oxidized by Mn(III)_aq via electrophilic attack.

The importance of reactive oxygen species on the aqueous phototransformation of sulfonamide antibiotics: kinetics, pathways, and comparisons with direct photolysis

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 (¹O₂) mediated photooxidation of nine SAs: sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, sulfamethazine, sulfamerazine, sulfadiazine, sulfachloropyridazine and sulfadimethoxine. Both •OH and ¹O₂ oxidation kinetics varied depending on the dominant protonated states of the SA in question (H₂SAs⁺, 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 ¹O₂ 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 ¹O₂ and •OH concentrations observed in the environment. This approach suggests that photochemical ¹O₂ 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, ¹O₂ 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.

Removal of sulfonamides from wastewater in the UV/TiO2 system: effects of pH and salinity on photodegradation and mineralization

The effects of salinity on the photodegradation and mineralization of sulfonamides in the UV/TiO₂ system were investigated. The goals of this study were to analyze the effects of pH and salinity on the sulfonamide concentration and total organic carbon (TOC) during the removal of sulfonamides in a UV/TiO₂ system. Four sulfonamides - sulfadiazine (SDZ), sulfamethizole (SFZ), sulfamethoxazole (SMX) and sulfathiazole (STZ) - were selected as parent compounds. The photodegradation and mineralization rates of sulfonamides in the UV/TiO₂ system satisfy pseudo-first-order kinetics. Direct photolysis degraded sulfonamides but sulfonamides cannot be mineralized. The photodegradation and mineralization rate constants in all experiments followed the order pH 5 > pH 7 > pH 9. At pH 5, the mineralization rate constants of SMX, SFZ, SDZ and STZ were 0.015, 0.009, 0.012 and 0.011 min^-1, respectively. The addition of NaCl inhibited the mineralization of the four tested sulfonamides more than it inhibited their photodegradation. The inhibitory effect of chloride ions on the removal of sulfonamides in the UV/TiO₂ system was attributed to the scavenging by chloride ions of hydroxyl radicals (HO•) and holes and the much lower reactivity of chlorine radicals thus formed, even though the chlorine radicals were more abundant than HO•.

Mechanisms and toxicity evaluation of the degradation of sulfamethoxazole by MPUV/PMS process

In this work, a sulfate radical (SO4-)-based advanced oxidation process was applied to the degradation of sulfamethoxazole (SMX). In these experiments, a medium pressure UV (MPUV) lamp was employed to active peroxymonosulfate (PMS). It was found that 98% of SMX was removed by MPUV/PMS at a UV dose of 200 mJ cm-2 (3.95 μM SMX, 0.2 mM PMS, pH0 = 3.7). Direct MPUV photolysis played a remarkable role in SMX removal by MPUV/PMS process. As for the indirect photolysis, SO4- was the major reactive species under acidic and neutral conditions in MPUV/PMS system, while the hydroxyl radical (OH) became the predominant radical under alkaline conditions. The transformation products (TPs) of SMX that formed in the MPUV-only and MPUV/PMS experiments were identified, and the possible degradation pathways were proposed. Photoisomerization of the isoxazole ring was the major pathway of SMX during MPUV-only process. Hydroxylation/oxidation of the aniline and isoxazole ring was the predominant degradation mechanism of SMX by MPUV/PMS. Toxicity evaluation showed that MPUV/PMS was effective at reducing the antibacterial activity of SMX solutions, while MPUV-only was not. However, some TPs with equivalent or even higher antibacterial activity than SMX were formed during the initial degradation period in MPUV/PMS system. Ecotoxicity of SMX and its TPs was also hypothetically predicted via the ECOSAR program, and the results indicated that some TPs could be more toxic than SMX.

Elucidation of the oxidation mechanisms and pathways of sulfamethoxazole degradation under Fe(II) activated percarbonate treatment

Fe(II) activated sodium percarbonate (SPC) process (SPC/Fe(II)) could efficiently remove sulfamethoxazole (SMX) in the aqueous phase, and has the potential in groundwater remediation. However, the degradation mechanisms, especially the degradation products and pathways till now have remained unclear. In the present study, intermediate products were identified using high resolution liquid chromatography coupled with ion trap and time-of-flight mass spectrometry (LCMS-IT-TOF). Nine intermediate products were identified, six of which have not yet been reported during the oxidation of SMX. The oxidation mechanisms involved hydroxyl substitution, the cleavage of sulfonamide bond, isoxazole ring opening and a rearrangement following the loss of the SO₂-group. Based on the identified intermediate products, the degradation pathways of SMX by SPC/Fe(II) process were illustrated. Fenton's reaction after the dissolution of SPC was proposed as the main reaction mechanisms, which was checked and confirmed by radical species detection tests and radical species scavenging studies. The results showed that although both O₂^- and HO were present in SPC/Fe(II) system, HO was dominant in the system while O₂^- was seldom involved in the degradation of SMX. These findings provided useful information and supported the application of this advanced oxidation process for antibiotics elimination in the groundwater.

Formation of disinfection byproducts from sulfamethoxazole during sodium hypochlorite disinfection of marine culture water

The fates of the antibiotic sulfamethoxazole (SMX) in the chlorination of fresh water, simulated brackish marine culture water, and marine water were investigated. SMX was oxidized by sodium hypochlorite (NaClO) at different reaction rates in the different samples. The oxidation of SMX followed pseudo-first-order kinetics, and the rate constant was the largest in marine water (3.44 min^-1), as Br^- ions promote the oxidation reaction. Moreover, the kinds of disinfection byproducts (DBPs) were also affected by Br^- ions. Br-DBPs were found in the simulated brackish marine culture water and marine water disinfection systems. The structures of the DBPs indicated that S-C cleavage, polymerization, S-N hydrolysis, chlorine/bromine substitution, and desulfonation reactions occurred on SMX during the disinfection process. EPI (Estimation Programs Interface) Suite™ and absorbable organic halogen (AOX) analysis were used to evaluate the toxicity of the DBPs. The results suggested that DBPs in the simulated brackish marine culture water and marine water systems were more toxic than those in the fresh water system.

Wastewater chemical contaminants: remediation by advanced oxidation processes

Approximately 70% of the terrestrial area is covered with water, but only a small water fraction is compatible with terrestrial life forms. Due to the increment in human consumption, the need for water resources is increasing, and it is estimated that more than 40% of the population worldwide will face water stress/scarcity within the next few decades. Water recycling and reuse may offer the opportunity to expand water resources. For that, the wastewater treatment paradigm should be changed and adequately treated wastewater should be seen as a valuable resource instead of a waste product. It is easily understandable that the exact composition and constituent concentration of wastewater vary according to its different sources (industrial, agricultural, urban usage of water). Consequently, a variety of known and emerging pollutants like heavy metals, antibiotics, pesticides, phthalates, polyaromatic hydrocarbons, halogenated compounds and endocrine disruptors have been found in natural water reservoirs, due to the limited effectiveness of conventional wastewater treatment. The conventional approach consists of a combination of physical, chemical and biological processes, aiming at the removal of large sediments such as heavier solids, scum and grease and of organic content in order to avoid the growth of microorganisms and eutrophication of the receiving water bodies. However, this approach is not sufficient to reduce the chemical pollutants and much less the emerging chemical pollutants. In this review, after some considerations concerning chemical pollutants and the problematic efficiency of their removal by conventional methods, an update is presented on the successes and challenges of novel approaches for wastewater remediation based on advanced oxidation processes. An insight into wastewater remediation involving the photodynamic approach mediated by tetrapyrrolic derivatives will be underlined.

Photocatalytic mineralization and degradation kinetics of sulphamethoxazole and reactive red 194 over silver-zirconium co-doped titanium dioxide: Reaction mechanisms and phytotoxicity assessment

The photodegradation and phytotoxicity of the pharmaceutical antibiotic, sulphamethoxazole (SMX) and the azo-dye reactive-red-194 (RR194) under visible-light irradiation of TiO₂ nanoparticles modified by silver and zirconium was investigated. The results indicated that sulphamethoxazole and its toxic degradation by product, 3-amino-5-methylisoxazole and RR-194 could be degraded efficiently by the co-doped Zr/Ag-TiO₂ catalyst. PL studies and ROS generation results suggested that the effective charge separation was carried out while irradiation of the modified TiO₂ nanoparticles. Phytotoxicity tests demonstrated lower percentage of germination in P. vulgaris (40%), V. radiata (30%) and P. lunatus (30%) of the seeds treated with 50 ppm of SMX, compared to the seeds treated with the degradation products (100%). The results with 50 ppm of RR-194 also showed lower percentage of germination in P. vulgaris (40%), V. radiata (50%) and P. lunatus (30%) compared to the degradation products (100%). Furthermore, significant increase in root and shoot development was observed in the seeds treated with the degraded products when compared with SMX and RR-194. Overall, this study contributes to further understanding the photodegradation mechanisms, degradation products and environmental fate of SMX and RR-194 in water which helps in the evaluation and mitigation of the environmental risk of SMX and RR-194 for water reuse and crop irrigation.

Contribution of biotic and abiotic factors in the natural attenuation of sulfamethoxazole: A path analysis approach

Sulfamethoxazole (SMX) is a sulfonamide antibiotic, widely used as curative and preventive drug for human, animal, and aquaculture bacterial infections. Its residues have been ubiquitously detected in the surface waters and sediments. In the present study, SMX dissipation and kinetics was studied in the natural water samples from Jiulong River under simulated complex natural conditions as well as conditions to mimic various biotic and abiotic environmental conditions in isolation. Structural equation modeling (SEM) by employing partial least square technique in path coefficient analysis was used to investigate the direct and indirect contributions of different environmental factors in the natural attenuation of SMX. The model explained 81% of the variability in natural attenuation as a dependent variable under the influence of sole effects of direct photo-degradation, indirect photo-degradation, hydrolysis, microbial degradation and bacterial degradation. The results of SEM suggested that the direct and indirect photo-degradation were the major pathways in the SMX natural attenuation. However, other biotic and abiotic factors also play a mediatory role during the natural attenuation and other processes. Furthermore, the potential transformation products of SMX were identified and their toxicity was evaluated.

Ferrocene-catalyzed heterogeneous Fenton-like degradation mechanisms and pathways of antibiotics under simulated sunlight: A case study of sulfamethoxazole

Readily-available and efficient catalyst is essential for activating oxidants to produce reactive species for deeply remediating water bodies contaminated by antibiotics. In this study, Ferrocene (Fc) was introduced to establish a heterogeneous photo-Fenton system for the degradation of sulfonamide antibiotics, taking sulfamethoxazole as a representative. Results showed that the removal of sulfamethoxazole was effective in Fc-catalyzed photo-Fenton system. Electron spin resonance and radical scavenging experiments verified that there was a photoindued electron transfer process from Fc to H₂O₂ and dissolved oxygen resulting in the formation of OH that was primarily responsible for the degradation of sulfamethoxazole. The reactions of OH with substructure model compounds of sulfamethoxazole unveiled that aniline moiety was the preferable reaction site of sulfamethoxazole, which was verified by the formation of hydroxylated product and the dimer of sulfamethoxazole in Fc-catalyzed photo-Fenton system. This heterogeneous photo-Fenton system displayed an effective degradation efficiency even in a complex water matrices, and Fc represented a long-term stability by using the catalyst for multiple cycles. These results demonstrate that Fc-catalyzed photo-Fenton oxidation may be an efficient approach for remediation of wastewater containing antibiotics.

Removal of β-lactam antibiotics from pharmaceutical wastewaters using photo-Fenton process at near-neutral pH

In this work, the photo-Fenton process at near-neutral pH was applied for the removal of the β-lactam antibiotic oxacillin (OXA) in water using artificial and sunlight. Initially, the main variables of the process (Fe(II), H₂O₂, and light power) were optimized by a statistical factorial design (2³ with center points). The experimental design indicated that 90 μmol L^-1 of Fe(II), 10 mmol L^-1 of H₂O₂, and 30 W of power light were the favorable conditions for degradation of OXA at 203 μmol L^-1. In the photo-Fenton system, the H₂O₂ alone, UV-light/H₂O₂, and Fe(II)/H₂O₂ subsystems presented a significant participation on antibiotic removal. Moreover, based on the primary organic transformation products, a mechanism of OXA degradation was proposed. Under the favorable operational conditions, both the pollutant and the antimicrobial activity were eliminated after 50 min of process application. Although at 480 min of treatment, only 5% of mineralization was achieved, the level of biodegradability of the solutions increased from 0.08 to 0.98. Interestingly, the presence of pharmaceutical additives (glucose, isopropanol, and oxalic acid) had a moderate interference on the efficiency of the pollutant removal. Additionally, the treatment at pilot scale of the β-lactam antibiotic in a pharmaceutical complex matrix using solar radiation allowed the complete removal of the pollutant and its associated antimicrobial activity in a very short time period (5 min). These results evidenced the applicability of the photo-Fenton process to treat wastewaters from pharmaceutical industry loaded with β-lactam antibiotics at near neutral pH values efficiently.

Hydroxyl radical dominated degradation of aquatic sulfamethoxazole by Fe0/bisulfite/O2: Kinetics, mechanisms, and pathways

In this study, batch experiments were carried out to investigate the key factors on sulfamethoxazole (SMX) removal kinetics in a new AOPs based on the combination of zero valent iron (Fe⁰) and bisulfite (S(IV)). With the increase of Fe⁰ from 0.25 mM to 5 mM, the removal rate of SMX was linearly increased in the Fe⁰/S(IV)/O₂ system by accelerating the activation of S(IV) and Fe⁰ corrosion to accelerate. In the first 10 min of reaction, the increasing concentration of S(IV) inhibited SMX removal after since the high S(IV) concentration quenched reactive oxidative species (ROS). Then SMX removal rate was accelerated with the increase of S(IV) concentration after S(IV) were consumed up. The optimal ratio of S(IV) concentrations to Fe⁰ concentration for SMX removal in the Fe⁰/S(IV)/O₂ system was 1:1. With SMX concentrations increasing from 1 to 50 μM, SMX removal rate was inhibited for the limitation of ROS yields. Although the presence of SO₄^- and OH was confirmed by electron paramagnetic resonance (EPR) spectrum, OH was identified as the dominant ROS in the Fe⁰/S(IV)/O₂ system by chemical quenching experiments. Besides, strong inhibitive effects of 1,10-phenanthroline on SMX degradation kinetics by Fe⁰/S(IV)/O₂ proved that the generation of ROS was rely on the release of Fe(II) and Fe(III). The generation of SO₄^- was ascribed to the activation of S(IV) by Fe(II)/Fe(III) recycling and the activation of HSO₅^- by Fe(II). And OH was simultaneously transformed from SO₄^- and generated by Fe⁰/O₂. Density functional theory (DFT) calculation was conducted to reveal special reactive sites on SMX for radicals attacking and predicted intermediates. Finally, four possible SMX degradation pathways were accordingly proposed in the Fe⁰/S(IV)/O₂ system based on experimental methods and DFT calculation.

Internal Polarization Modulation in Bi2 MoO6 for Photocatalytic Performance Enhancement under Visible-Light Illumination

A built-in electric field from polarization inside polar photocatalysts could provide the driving force for photogenerated electrons and holes to move in opposite directions for better separation to improve their photocatalytic performance. The photocatalytic performance of a polar photocatalyst of Bi₂ MoO₆ has been enhanced through the precise control of its structure to increase internal polarization. DFT calculations predicted that a shortened crystal lattice parameter b in Bi₂ MoO₆ could induce larger internal polarization, which was achieved by the modulation of the pH of the reaction solution during a solvothermal synthetic process. A series of Bi₂ MoO₆ samples were created with reaction solutions of pH≈1, 4, and 8; the crystal lattice parameter b was found to decrease gradually with increasing solution pH. Accordingly, these Bi₂ MoO₆ samples demonstrated a gradually enhanced photocatalytic performance with decreasing crystal lattice parameter b, as demonstrated by the photocatalytic degradation of sulfamethoxazole/phenol and disinfection of Staphylococcus aureus bacteria under visible-light illumination due to improved photogenerated charge-carrier separation. This study demonstrates an innovative design strategy for materials to further enhance the photocatalytic performance of polar photocatalysts for a broad range of technical applications.

Radiolysis of sulfonamide antibiotics in aqueous solution: Degradation efficiency and assessment of antibacterial activity, toxicity and biodegradability of products

Numerous studies have been published on the radiolysis of sulfonamide antibiotic solutions but little effort has been made to monitor the biological properties of degradation products. A complex approach should also clarify the changes in antibacterial activity and biodegradability, besides the usual screening of toxicity. To fill this gap, the ionizing radiation induced degradation of four sulfonamide antibiotics was investigated in dilute aqueous solutions, with emphasis on the biological assessment of decomposition products. Complete removal of sulfonamides was achieved by a low absorbed dose (1.5kGy). 2-2.5kGy dose was needed to transform the persistent initial molecules to substances biodegradable in both river water and activated sludge. The ratio of the biological and chemical oxygen demand increased from <0.21 to at least 0.59, but values as high as 0.80 were also measured. It was demonstrated that antibacterial activity is due to the initial molecules, as it disappeared when the sulfamethoxazole concentration decreased below the minimal inhibitory concentration (30 μM). This means that the products have no antibacterial activity. Toxicity testing performed on test organisms from three different trophic levels and activated sludge evidenced that the toxicity depends both on the test organism and on the sulfonamide used. The degradation of initial molecules is not always enough to eliminate the environmental risk due to the toxic products formed e.g. inhibitory effects to Vibrio fischeri increased by 34% at 2.5kGy. For this reason, complex biological assessment of treated solutions has to play an important role in development and optimization of advanced treatment techniques.

Influence of Long-Term Feeding Antibiotics on the Gut Health of Zebrafish

The use of antibiotics for anti-infection and growth promotion has caused the overuse of antibiotics in aquaculture. However, the benefit or risk of the long-term use of antibiotics on fish growth or health has not been fully addressed. In the present study, zebrafish were fed with sulfamethoxazole (SMX) or oxytetracycline (OTC) at the therapeutic concentrations (100 and 80 mg/kg body weight per day, respectively) for 6 weeks to mimic the long-term use of antibiotics. The digestive enzyme activities were higher in both antibiotic treatments, and higher oxygen consumption rate was found in OTC treated group. As a result, SMX increased the weight gain of zebrafish, and OTC treatment did not show significant prompting effect on growth. The mortality was higher in SMX or OTC treated group on 2nd-4th day after exposure to Aeromonas hydrophila. Lower alkaline phosphatase (AKP) and acid phosphatase (ACP) activities were found in OTC treated group, while higher malondialdehyde (MDA) content was found in the intestine of both SMX and OTC treated zebrafish. Furthermore, feeding OTC decreased the intestinal microbial richness. This study revealed that long-term use of legal aquaculture concentrations of antibiotics caused systemic adverse effects on fish gut health; stringent policy for use of antibiotics in fish is urgent.

Environmental concentrations of antibiotics impair zebrafish gut health

Antibiotics have been widely used in human and veterinary medicine to both treat and prevent disease. Due to their high water solubility and low bioavailability, many antibiotic residues have been found in aquatic environments. Fish are an indispensable link between the environmental pollution and human health. However, the chronic effects of environmental concentrations of antibiotics in fish have not been thoroughly investigated. Sulfamethoxazole (SMX) and oxytetracycline (OTC) are frequently detected in aquatic environments. In this study, zebrafish were exposed to SMX (260 ng/L) and OTC (420 ng/L) for a six-week period. Results indicated that exposure to antibiotics did not influence weight gain of fish but increased the metabolic rate and caused higher mortality when treated fish were challenged with Aeromonas hydrophila. Furthermore, exposure to antibiotics in water resulted in a significant decrease in intestinal goblet cell numbers, alkaline phosphatase (AKP), acid phosphatase (ACP) activities, and the anti-oxidant response while there was a significant increase in expression of inflammatory factors. Antibiotic exposure also disturbed the intestinal microbiota in the OTC-exposed group. Our results indicated that environmental antibiotic concentrations can impair the gut health of zebrafish. The potential health risk of antibiotic residues in water should be evaluated in the future.

Photolysis mechanism of sulfonamide moiety in five-membered sulfonamides: A DFT study

Quantum chemical calculations have been performed to investigate the photolysis mechanism of relatively susceptible sulfonamide moiety of five-membered sulfonamide (SA) antibiotics, such as sulfamethoxazole, sulfisoxazole, sulfamethizole, and sulfathiazole. The results show that the ·OH-mediated indirect photolysis of sulfonamide linkage has two possible multi-step reaction pathways, viz., H-abstraction and electrophilic C1-attack, which is contrast to previously reported one-step cleavage manner. The newly proposed indirect photolysis mechanisms could be applied to six-membered SAs such as sulfadimethoxine. It has been found that the dissociation of SN bond is easier in direct photolysis than ·OH-mediated indirect photolysis. Wiberg bond index and LUMO-HOMO energy gap are investigated to clarify the origin of the discrepant reactivity of sulfonamide moiety of SAs at singlet and triplet states. In comparison with singlet states, the SN bond of SAs is weaker at triplet states of SAs and thus results in higher reactivity of sulfonamide moiety, as also suggested by smaller LUMO-HOMO energy gap. This study could add better understanding to the photolysis mechanisms of SAs, which would be also helpful in utilizing quantum chemistry calculation to investigate the behavior and fate of antibiotics in the aquatic environment.

Direct Photolysis of Sulfamethoxazole Using Various Irradiation Sources and Wavelength Ranges-Insights from Degradation Product Analysis and Compound-Specific Stable Isotope Analysis

The environmental micropollutant sulfamethoxazole (SMX) is susceptible to phototransformation by sunlight and UV-C light which is used for water disinfection. Depending on the environmental pH conditions SMX may be present as neutral or anionic species. This study systematically investigates the phototransformation of these two relevant SMX species using four different irradiation scenarios, i.e., a low, medium, and high pressure Hg lamp and simulated sunlight. The observed phototransformation kinetics are complemented by data from compound-specific stable isotope and transformation product analysis using isotope-ratio and high-resolution mass spectrometry (HRMS). Observed phototransformation kinetics were faster for the neutral than for the anionic SMX species (from 3.4 (LP lamp) up to 6.6 (HP lamp) times). Furthermore, four phototransformation products (with m/z 189, 202, 242, and 260) were detected by HRMS that have not yet been described for direct photolysis of SMX. Isotopic fractionation occurred only if UV-B and UV-A wavelengths prevailed in the emitted irradiation and was most pronounced for the neutral species with simulated sunlight (ε_C = -4.8 ± 0.1 ‰). Phototransformation of SMX with UV-C light did not cause significant isotopic fractionation. Consequently, it was possible to differentiate sunlight and UV-C light induced phototransformation of SMX. Thus, CSIA might be implemented to trace back wastewater point sources or to assess natural attenuation of SMX by sunlight photolysis. In contrast to the wavelength range, pH-dependent speciation of SMX hardly impacted isotopic fractionation.

Amicarbazone degradation promoted by ZVI-activated persulfate: study of relevant variables for practical application

Alarming amounts of organic pollutants are being detected in waterbodies due to their ineffective removal by conventional treatment techniques, which warn of the urgent need of developing new technologies for their remediation. In this context, advanced oxidation processes (AOPs), especially those based on Fenton reactions, have proved to be suitable alternatives, due to their efficacy of removing persistent organic compounds. However, the use of ferrous iron in these processes has several operational constraints; to avoid this, an alternative iron source was here investigated: zero-valent-iron (ZVI). A Fenton-like process based on the activation of a recently explored oxidant-persulfate (PS)-with ZVI was applied to degrade an emerging contaminant: Amicarbazone (AMZ). The influence of ZVI size and source, PS/ZVI ratio, pH, UVA radiation, dissolved O₂, and inorganic ions was evaluated in terms of AMZ removal efficiency. So far, this is the first time these parameters are simultaneously investigated, in the same study, to evaluate a ZVI-activated PS process. The radical mechanism was also explored and two radical scavengers were used to determine the identity of major active species taking part in the degradation of AMZ. The degradation efficiency was found to be strongly affected by the ZVI dosage, while positively affected by the PS concentration. The PS/ZVI system enabled AMZ degradation in a wide range of pH, although with a lower efficiency under slightly alkaline conditions. Dissolved O₂ revealed to play an important role in reaction kinetics as well as the presence of inorganic ions. UVA radiation seems to improve the degradation kinetics only in the presence of extra O₂ content. Radicals quenching experiments indicated that both sulfate (SO₄^•-) and hydroxyl (^•OH) radicals contributed to the overall oxidation performance, but SO₄^•- was the dominant oxidative species.