Photodegradation of sulfapyridine under simulated sunlight irradiation: kinetics, mechanism and toxicity evolvement

Study on the biodegradation characteristics and mechanism of tetracycline by Serratia entomophila TC-1

Microbial degradation is an important solution for antibiotic pollution in livestock and poultry farming wastes. This study reports the isolation and identification of the novel bacterial strain Serratia entomophila TC-1, which can degrade 87.8 % of 200 mg/L tetracycline (TC) at 35 °C, pH 6.0, and an inoculation amount of 1 % (v/v). Based on the intermediate products, a possible biological transformation pathway was proposed, including dehydration, oxidation ring opening, decarbonylation, and deamination. Using Escherichia coli and Bacillus subtilis as biological indicators, TC degraded metabolites have shown low toxicity. Whole-genome sequencing showed that the TC-1 strain contained tet (d) and tet (34), which resist TC through multiple mechanisms. In addition, upon TC exposure, TC-1 participated in catalytic and energy supply activities by regulating gene expression, thereby playing a role in TC detoxification. We found that TC-1 showed less interference with changes in the bacterial community in swine wastewater. Thus, TC-1 provided new insights into the mechanisms responsible for TC biodegradation and can be used for TC pollution treatment.

Photodegradation of the novel herbicide pyraclonil in aqueous solution: Kinetics, identification of photoproducts, mechanism, and toxicity assessment

Pyraclonil is a new type of pyrazole herbicide, whose photochemical fate in aqueous solution has not been reported yet. In this study, effects on the photolysis rate such as light source, pH, NO3-, Fe3+, fulvic acid (FA) and riboflavin (RF) were investigated. Pyraclonil photodegraded in pure water under both UV and simulated sunlight with half-lives of 32.29 min and 42.52 h, respectively. Under UV, the degradation rate of pyraclonil in pH 4 solution (0.0299 ± 0.0033 min-1) was about twice higher than that in pH 9 (0.0160 ± 0.0063 min-1). Under simulated sunlight, low concentration (0.1-1 mg/L) of FA, NO3-, Fe3+ and RF noticeably promoted the photodegradation of pyraclonil. Then, with the combination of experimental UPLC-Q-TOF/MS and computational calculation of density functional theory (DFT), fourteen transformation products (TPs) of pyraclonil were identified with possible mechanism of C-N bond cleavage, photorearrangement, demethylation, hydroxylation and oxidation. Additionally, acute toxicity assessment was conducted through ECOSAR prediction and laboratory bioassays. The prediction results indicated that toxicity of TP157 to daphnid and green algae was 1.3 and 1.4 times higher than that of the parent, respectively. The bioassay results indicated that toxicities of TP157 and TP263 to C. vulgaris were about 1.6 and 5.9 times higher than that of the parent, respectively. The results provided a reference for elucidating the potential hazards of pyraclonil to non-target organisms and promoting its rational use.

Environmental transformation and hazards of decachlorobiphenyl on suspended particles under sunlight irradiation

Decachlorobiphenyl (PCB-209) can be widely detected in suspended particles and sediments due to its large hydrophobicity, and some of its transformation products may potentially threaten organisms through the food chain. Here we investigate the photochemical transformation of PCB-209 on suspended particles from the Yellow River. It was found that the suspended particles had an obvious shielding effect to largely inhibit the photodegradation of PCB-209. Meanwhile, the presence of inorganic ions (e.g. Mg2+ and NO3-) and organic matters (e.g. humic acid, HA) in the Yellow River water inhibited the reaction. The main transformation products of PCB-209 were lower-chlorinated and hydroxylated polychlorinated biphenyls (OH-PCBs), and small amounts of pentachlorophenol (PCP) and polychlorinated dibenzofurans (PCDFs) were also observed. The mechanisms of PCP formation by double •OH attacking carbon bridge and PCDFs formation by elimination reaction of ionic state OH-PCBs were proposed using theoretical calculations, which provided some new insights into the inter-transformations between persistent organic pollutants. In combination with VEGA and EPI Suite software, some intermediates such as PCDFs were more toxic to organisms than PCB-209. This study deepens the understanding of the transformation behavior of PCB-209 on suspended particles under sunlight.

Elucidating the inhibitory effects of natural organic matter on the photodegradation of organic micropollutants: Atrazine as a probe compound

Natural organic matter (NOM) is a complex mixture of heterogeneous compounds with varying functional groups and molecular sizes. Understanding the impact of NOM on the generation of photochemically produced reactive intermediates (PPRIs) and their potential inhibitory effects on photolysis has remained challenging due to the variations in the reactivities and concentrations of these functional groups. To address this gap, tannic acid (TA), gallic acid (GA), catechin (CAT), and tryptophan (Trp), were chosen as potential substitutes for NOM. Their effects on the photochemical transformation process were evaluated and compared with the widely used Suwannee River NOM (SRNOM). Atrazine (ATZ) was selected as a probe organic micropollutant (OMP). In this investigation, a significantly higher concentration of HO• was observed compared to O21, and the triplet excited state ( NOM*3). The findings suggest that the substituted phenols, particularly those with carboxylate-substitutions, played a substantial role in HO• formation, while electron-rich moieties acted as antioxidants, consuming NOM*3. Hydroxyl, carboxylic, and amino acid were the active groups for O21 formation. However, the inhibitory effects induced by the NOM surrogates were significant and mainly attributed to the direct photolysis inhibition caused by the inner filter effect. The scope of this work was further extended to include SRNOM, where similar trends with less pronounced formation of PPRIs and inner filter effects were observed. Therefore, this study sheds some light on the role of the functional groups in NOM during photochemical transformations of OMPs, thereby deepening our understanding of their fate in aqueous systems.

Insight into the transformation of 4-hydroxy-3-aminophenylarsonic acid (HAPA) and its mechanisms under simulated sunlight irradiation

Four-hydroxy-3-aminophenylarsonic acid (HAPA), the reduced product of roxarsone (4-hydroxy-3-nitro-phenylarsonic acid, ROX) under anaerobic conditions, is resistant to be biologically degraded under anaerobic/anoxic conditions. The transformation of HAPA in aquatic environment under sunlight irradiation is still unknown. In this study, the photodegradation of HAPA and the possible mechanism under simulated sunlight conditions were investigated. The result shows that under visible light irradiation, HAPA wasn't degraded. Under UV254 and UV302 irradiation, about 60% and 30% HAPA were decomposed, while nearly no HAPA was degraded under UV365 irradiation over a period of 240 min. UVC light was the main wavelength for the degradation of HAPA under sunlight conditions. HCO3- and NO3- slightly enhanced the photodegradation, but Cl- and SO42- had a marginal influence on the photodegradation. During the photodegradation, HAPA was decomposed into organic intermediates, inorganic arsenics, ammonia and undetermined arsenic species. Arsenite (As(III)) was the dominant inorganic arsenic species from the photodegradation of HAPA. The mechanism analysis shows that singlet molecular oxygen (1O2) has little influence on the decomposition of HAPA under UV irradiation, but significantly enhanced the conversion of As(III) to arsenate (As(V)).

Fast and ecofriendly triple sulfonamides mixture utilization using UV irradiation and spherical SnO2 nanoparticles with controllable parameters and antibacterial activity

One of the solutions for the growing problem of water purification is photocatalytic degradation of the pollutants. Semiconductor nanoparticles are widely under study as a promising photocatalyst for this purpose. However, there is still lack of understanding of the relation between properties of nanoparticles, in their turn related with synthesis conditions, and photocatalytic efficiency, as well as of the other factors influencing the process. For the first time, a possibility to regulate photocatalytic activity of SnO2 nanoparticles under UV light via regulation of structural parameters is shown. A method for obtaining spherical nanoparticles with different parameters was developed. Obtained nanoparticles were fully characterized. Special attention was paid to the study of oxygen vacancies. With the help of quantum computational methods, it was shown, that the concentration of vacancies is around 1 per 32 tin atoms. Obtained data on oxygen vacancies were further used for the evaluation of pollutant-nanoparticle surface interaction to get closer to the calculations of real systems. On the example of methylene blue, it was shown that the greater is the amount of oxygen vacancies and the lower the amount of defects, the higher photocatalytic activity. The obtained dependence is confirmed by the fact that the photoresponse increases with a decrease of amount of defects in the sample. Degradation kinetics of sulfonamides mixture was studied, and its dependence on active complex formation was shown based on the quantum chemical calculation data. Degradation of antibiotics in water from Neva River reached more than 95% in 35 min, which indicates that developed photocatalyst efficiency is not affected by pollutants contained in open water in the centre of the metropolis. It was shown, that the use of nanoparticles allows to speed up the process of bacteria destruction under UV light, which indicates the antibacterial activity of obtained nanoparticles.

Photodegradation of enestroburin in water by simulated sunlight irradiation: Kinetics, isomerization, transformation products identification and toxicity assessment

Enestroburin is the first strobilurin fungicide developed by China and has been widely used to control fungal disease for 15 years. Investigation of its photolytic behaviour is essential for the comprehensive evaluation of its ecological risk. The effects of solution pH, humic acid (HA) and Fe(III) ions on photolysis were studied. The direct photolysis rates of enestroburin in the acidic solution (pH = 4) was faster than that in the basic (pH = 7) or neutral condition (pH = 9). HA and Fe³⁺ ions inhibited photolysis by the light screening effect. The photolysis of enestroburin was very fast due to the generation of photo-isomers. Seven isomeric products of enestroburin were observed using SFC-MS/MS, and the reaction mechanism for photo-induced isomers was proposed. The reaction occurred on three double bonds, including tautomerism of enol ether and oxonium and the triplet energy transfer of the CC and CN double bond. 12 transformation products (TPs) were identified by screening suspect compounds and non-target compounds, and one product (M-381) was synthesized for confirmation and quantification. A probable transformation mechanism was suggested based on the identified TPs and DFT calculations. The main transformation reactions included hydration, hydrolysis, oxidation, reduction and decarboxylation. Finally, the toxicities of the identified TPs and parent compound to aquatic organisms were predicted using ECOSAR software, and the toxicities of enestroburin and M-381 to daphnia magna were tested in the laboratory. The toxicity classification proposed by ECOSAR is reliable to a certain extent. Enestroburin and 2 TPs (M-313 and M-327) were classified as "very toxic", which may pose a potential threat to aquatic ecosystems.

Photocatalytic Activity of TiO2 for the Degradation of Anticancer Drugs

To prevent water pollution, photocatalysis is often used to remove small molecules such as drugs by generating reactive species. This study aimed to determine the photocatalytic activity of two anticancer drugs, imatinib and crizotinib, and to investigate various influences that may alter the kinetic degradation rate and ultimately the efficacy of the process. In order to obtain optimal parameters for the removal of drugs with immobilized TiO₂, the mutual influence of the initial concentration of the contaminant at environmentally relevant pH values was investigated using the response surface modeling approach. The faster kinetic rate of photocatalysis was obtained at pH 5 and at the smallest applied concentration of both drugs. The photocatalytic efficiency was mostly decreased by adding various inorganic salts and organic compounds to the drug mixture. Regarding the degradation mechanism of imatinib and crizotinib, hydroxyl radicals and singlet oxygen showed a major role in photochemical reactions. The formation of seven degradation products for imatinib and fifteen for crizotinib during the optimal photocatalytic process was monitored by high-resolution mass spectrometry (HPLC-QqTOF). Since the newly formed products may pose a hazard to the environment, their toxicity was studied using Vibrio fischeri, where the significant luminescence inhibition was assessed for the mixture of crizotinib degradants during the photocatalysis from 90 to 120 min.

Sorption and degradation of prothioconazole and its metabolites in soils and water sediments, and its combinative toxicity to Gobiocypris rarus

To reduce detrimental effects to the environment, the application of prothioconazole and its metabolites requires comprehensive evaluation, which has been dine for the first time in this study. The behavior of prothioconazole, including degradation and sorption under aerobic and anaerobic conditions, was evaluated in three common soil types and two types of water-sediment systems under different environmental conditions. Individual and joint toxicities of prothioconazole and its metabolites, M01 and M04, on aquatic organisms, including the Gobiocypris rarus, are also investigated in the present study. Under aerobic and anaerobic conditions, the half-life of prothioconazole in the three types of soils ranged from 0.0565 to 2.27 days and 0.138-1.73 days, respectively. Under aerobic conditions, the half-life of prothioconazole in the Hunan paddy area and Beijing Qidu reservoir water-sediment samples were 2.18 and 1.58 days, respectively. In soil and water-sediment samples, prothioconazole degraded to M01 and M04, and the formation rate of M04 was higher than M01 under aerobic condition. M04 and M01 gradually increased to a peak value in soil and water-sediment systems, then decreased over time, while prothioconazole gradually decreased. The half-life of prothioconazole in soils was lower than its metabolites, with the DT₅₀ of metabolites ranging from 16.6 to 99.6 days, 15.8 and 50.7 days for M01 and M04 under aerobic condition, respectively. While the adsorption capacities (K_f values) of M04 and M01 ranged from 2.09 to 88.92 and 8.98 to 243.30 (μg/g)/(mg/L), respectively, in the three soils. Regarding toxicity to aquatic organisms, the metabolites did not show higher toxicity than prothioconazole, except M01 on Gobiocypris rarus. Joint toxicity assays showed that mixtures of prothioconazole with its metabolites exhibited higher toxicity than any compound individually and indicated synergistic interactions could occur at equitoxic ratios and equivalent concentrations. This study provides a comprehensive investigation on the fate and environmental risk posed by prothioconazole.

Effect of polystyrene microplastics on the degradation of sulfamethazine: The role of persistent free radicals

Microplastic (MPs) pollution is increasingly becoming a global environmental problem. MPs entering the environment are subjected to various aging processes, among which photoaging is the most important process leading to MPs oxidation. Persistent free radicals (EPFRs) are formed on the surface of MPs during photoaging, but it is not clear whether EPFRs on the surface of MPs can produce reactive oxygen species (ROS) and thus degrade organic pollutants. In this study, with polystyrene (PS) as the representative plastic and sulfamethazine (SMT) degradation as the target pollutant, the effect and mechanism of light-induced PS on SMT degradation were investigated by experiment and theoretical calculation. It was found that PS can stimulate the production of ROS under sunlight, which can significantly improve the degradation rate of SMT. Through quenching experiment and free radical trapping experiment, it was found that the mechanism of PS promoting the degradation of SMT was mainly due to the production of hydroxyl radical (·OH) in the system, and ·OH was the main ROS species affecting the oxidative degradation of SMT. The characterization results show that the high reactive oxygen generation ability of PS under solar irradiation was due to the abundant photoactive oxidation functional groups on its surface. In addition, the key reaction sites of SMT were predicted by density functional theory (DFT) calculation. The results of different calculations consistently showed that the sulfonamide group of SMT, the pyrimidine heterocycle and the amino group of aniline are the reaction sites of ·OH priority attack. The main intermediates were determined by UHPLC-HRMS/MS. Combined with theoretical calculation, it was proposed that the oxidative degradation pathway of SMT mainly includes SN bond cleavage, SMILES rearrangement and SO₂ group removal. This study clarified the effect of PS on the degradation of organic pollutants under light, and provided theoretical guidance for the degradation mechanism.

Peroxymonosulfate activation using heterogeneous catalyst Sr2FeO4 coated on SBA-15 for efficient degradation of antibiotic sulfapyridine

It is significant to explore the advanced oxidation process (AOP) for antibiotic degradation. Herein, a peroxymonosulfate (PMS) activator, Sr₂FeO₄/SBA-15 (SFS) heterogeneous catalyst, was synthesized by in situ growth of Sr₂FeO₄ on the surface of SBA-15. In SFS/PMS catalytic system, Sr atom provided electrons to Fe(II) ↔Fe(III) ↔Fe(II) redox cycle through Sr-O-Fe bonds for PMS activation. The SFS catalyst could activate PMS to generate a free radical coexistence system, including sulfate radical (SO₄∙^-) and hydroxyl radicals (∙OH). The catalyst possessed high catalytic activity and high stability. The degradation efficiency of sulfapyridine (SAD) over the SFS/PMS catalytic system could reach 99.0% after 90 min reaction. After the 5th reuse, the degradation efficiency of SAD was still more than 94.0%, and the phase structure of the catalyst did not alter. The low ion leaching concentration would be more conducive to reuse and avoiding secondary pollution, in comparison to homogeneous catalysts. This catalyst can be widely applied to organic wastewater treatment.-->.

Kinetics of the photolysis of pyridaben and its main photoproduct in aqueous environments under simulated solar irradiation

The photolytic fate of pyridaben and its main photolysis product was investigated in different aqueous solutions. Results showed that the photolysis of pyridaben followed pseudo first-order kinetics or the hockey-stick model. In buffer solutions, the half-life of pyridaben was the shortest at pH 4, while the degradation rate within 24 h was the highest at pH 9. Humic acids (HA) at concentrations of 1-20 mg L^-1 favored the photolysis of pyridaben while fulvic acids (FA) did not have a significant effect. Nitrate at low concentrations (0.01 mM) accelerated the photolysis and Fe(iii) at high concentrations (0.01 and 0.1 mM) significantly inhibited the photolysis. The photolysis rate of pyridaben in rainwater, tap water, and river water was significantly higher than that in distilled water. The half-lives in distilled water, rainwater, tap water, river water, and pond water were 2.36, 1.36, 1.61, 1.77, and 2.68 h, respectively. Ultra-high-performance liquid chromatography/high-resolution mass spectrometry identified M328 as a photolysis product. The degradation of M328 followed pseudo first-order kinetics in distilled water, buffer solutions and aqueous solutions fortified with HA. The half-lives of M328 were in the range of 7.07-13.95 h. These results are essential for further environmental risk assessment of pyridaben.

Prediction of the excited-state reaction channels in photo-induced processes of nitrofurantoin using first-principle calculations and dynamics simulations

The understanding of the photochemistry of antibiotic compounds is important because it gives the direct information on the possible environmental pollution caused by them. Due to their large size, the theoretical studies of their excited-state reactions are rather challenging. In current work, we combined the on-the-fly trajectory surface-hopping dynamics, conical-intersection optimizations and excited-state pathway calculations to study the photochemistry of the trans-isomer of nitrofurantoin, a widely-used drug to treat the urinary tract infections. The dynamics-then-pathway approach was taken. First the trajectory surface hopping dynamics at the state-averaged complete-active-space self-consistent-field (SA-CASSCF) level with small active space and small basis sets were run. Second, the minimum-energy conical-intersection optimizations were performed. Finally the excited pathways from the Frank-Condon region to different reaction channels were built at the multi-state multi-reference second-order perturbation (MS-CASPT2) level with large active space and large basis set. Several possible channels responsible for the photo-induced reaction mechanism of the trans-nitrofurantoin were obtained, including the cleavage of the NO bond of the NO₂ moiety, the photoisomerization at the central CN bond, and other internal conversion channels. Our findings give some preliminary explanations on available experimental observations. It is also demonstrates that the current theoretical approach is a powerful tool to explore the excited-state reactions in the photochemistry of media-sized or large-sized drug compounds.

Effects of environmental factors on nitrofurantoin photolysis in water and its acute toxicity assessment

Pharmaceuticals have special attention of researchers over the world due to their possible effect on the environment and humans. This paper focuses on the photolysis of nitrofurantoin in different water matrices. Nitrofurantoin photodegradation has been indicated as a pseudo-first order photoreaction. The indirect photodegradation rate of nitrofurantoin (river water, k₁ = 0.0088 min^-1 and synthetic wastewater, k₁ = 0.0154 min^-1) was slower than its direct photolysis rate (ultrapure water, k₁ = 0.0176 min^-1). The highest value of quantum yield of nitrofurantoin photodegradation (ϕ = 0.2047) was observed at pH = 4, while at higher pH-values it decreased. Furthermore, the mechanism of nitrofurantoin photodegradation is proposed. Heterocyclic ring opening and further hydrolysis, nucleophilic aromatic photosubstitution and homolytic N-N bond cleavage are suggested as three main initial processes of nitrofurantoin photodegradation. Acute toxicity study of nitrofurantoin and its photoproducts with regard to luminescence inhibition of Vibrio fischeri showed that the toxic effect of nitrofurantoin (EC₅₀ = 4.0 mg L^-1) decreases by photolysis.

Abiotic transformation and ecotoxicity change of sulfonamide antibiotics in environmental and water treatment processes: A critical review

Sulfonamides (SAs) are among the most widely used antibiotics to treat bacterial infections for humans and animals. They are also used in livestock agriculture to improve growth and feed efficiency in many countries. Recent years, there is a growing concern about the environmental fate and treatment technologies of SAs, in order to eliminate their potential impact on the ecosystem and human health. Additionally, SAs are frequently used as model compounds to evaluate the performance of newly developed advanced water treatment processes. Hence, understanding the chemical reaction features of SAs can provide valuable information for further technological development. In this review, the reaction kinetics, abiotic transformations and corresponding ecotoxicity changes of SAs in natural environments and water treatment processes were comprehensively analyzed to draw critical suggestion and new insights. The •OH-based AOP is proposed as an effective method for the elimination of SAs toxicity, although it is susceptible to water constituent due to low selectivity. The application of biochar or metal-based oxidants in AOPs is becoming a future trend for SA treatment. Overall, this review would provide useful information for the development of advanced water treatment technologies and the control of ecological risks related to SAs.

The pH-dependent degradation of sulfadiazine using natural siderite activating PDS: The role of singlet oxygen

Occurring naturally siderite (FeCO₃) was used as the heterogeneous catalyst to activate peroxodisulfate (PDS) for the degradation of sulfadiazine under different initial pH values. The findings of this system exhibited various ROS (e.g. ¹O₂, SO₄^- and OH) present during a wide range of pH values. Among them, ¹O₂ could significantly facilitate the initial degradation rate, and the increased pH enhanced the role of ¹O₂. The factors including initial pH values, siderite dosage, PDS concentration, initial contaminants concentration, and water matrix were discussed. The role of each ROS was investigated through quenching test and electron paramagnetic resonance (EPR). Furthermore, the comprehensive degradation process was proposed based on the LC-MS results. And the cycle test demonstrates the reusability of siderite at a pH of 3. Accordingly, this study is of great significance for understanding the degradation of such sulfonamide pollutants in the siderite/PDS system.

Structure determination of clinofibrate photoproducts generated by ultraviolet-light irradiation in aqueous media

Photodegradation of clinofibrate, which is one of the fibrate drugs, was evaluated and chemical structures of its photoproducts were determined. Clinofibrate in aqueous media was photodegraded gradually by the UV light emission with the generation of several photoproducts. The result of HPLC analysis indicated that some photoproducts were more photostable compared with the parent compound. After 14 days irradiation, clinofibrate was degraded completely while several photoproducts were remained in the test solution. Structure determination of nine photoproducts was performed by means of ESI-LC/MS/MS analysis. Main photoproduct of clinofibrate was 2-(4-(1-(4-hydroxyphenyl)cyclohexyl)phenoxy)-2-methylbutanoic acid. Structure determination of clinofibrate photoproducts made it possible the estimation of the photodegradation pathway. It was tempting to speculate that the main photoproduct was generated by the elimination of 2-methylbutanoic acid and other photoproducts were generated through several photochemical reactions including further elimination of 2-methylbutanoic acid and decarboxylation. The obtained results will be helpful for the further research focused on the evaluation of biological activities of clinofibrate photoproducts, photostability of clinofibrate in commercial tablets and changed formulations, and the photostabilization of them.

Ibuprofen elimination from water and wastewater using sonication/ultraviolet/hydrogen peroxide/zeolite-titanate photocatalyst system

The present investigation was designed to remove ibuprofen from aqueous solutions and wastewater by activating hydrogen peroxide using ultrasonication (US)/ultraviolet (UV) radiation/zeolite-titanium. The physical-chemical properties of the photocatalyst were determined using BET, FTIR, XRD, FESEM, and EDX-mapping techniques. The titanium oxide crystal size and the catalyst BET were determined to be 4.97 nm and 39.88 m²/g, respectively. Tests were performed in a reactor (with a volume of 316 mL) located in an ultrasonic bath to intensify reactions. The synergistic impact of the components of the UV/US/H₂O₂/Photocatalyst system was explored. The maximum efficiency (99.58%) was obtained at H₂O₂ concentration of 0.05 mM, pH 5, UV power of 6 W, photo-catalyst dose of 1 g/L, and contact time of 100 min. The pH variable was more effective than the other parameters. Ions of NO₃^-, Cl^-, and SO₄^2- had a slightly negative effect on contaminant removal efficiency. The ibuprofen removal (based on COD) from urban water and hospital wastewater was attained 77.82% and 66.24%, respectively. The ibuprofen removal by the developed system followed the first-order kinetic. The results show that the system has high efficiency and reasonable costs (with treatment cost of 6.25 €/m³) for ibuprofen decontamination.

Mechanisms, kinetics and eco-toxicity assessment of singlet oxygen, sulfate and hydroxyl radicals-initiated degradation of fenpiclonil in aquatic environments

Fenpiclonil is an agricultural phenylpyrrole fungicide, which raise the concern about its ecotoxicological effects. In this paper, we investigate the indirect photochemical transformation mechanisms, environmental persistence and eco-toxicity of fenpiclonil initiated by various active oxidants (¹O₂, •OH and SO₄•‾) in aquatic environments. The results shown that ¹O₂ can react with pyrrole ring by cycloaddition pathways to form the endo-peroxides. In addition, •OH and SO₄•‾ initial mechanisms are calculated, suggesting that •OH-initiated mechanisms play a dominant role in the degradation process of fenpiclonil at high rate constants (2.26 ×10⁹ M^-1 s^-1, at 298 K). The kinetic calculation results indicate that high temperature is more favorable for the degradation of fenpiclonil. To better understand the adverse effects of the transformation products formed during the subsequent reaction of •OH-adduct IM10, the computational toxicology has been used for the toxicity estimation. The results show that aquatic toxicity of these products decrease with degradation process, especially the decomposition products (TP3 and TP4). However, TP1 and TP2 are still toxic and developmental toxicant. The study provides guidance for further experimental research and industrial application of fungicide degradation from the perspective of theoretical calculation.

Aqueous photodegradation of okadaic acid and dinophysistoxin-1: Persistence, kinetics, photoproducts, pathways, and toxicity evaluation

Diarrhetic shellfish poisoning (DSP) toxins are a class of natural organic contaminants that pose a serious threat not only to marine ecosystems and fisheries but also to human health. They are widely distributed in coastal and offshore waters around the world. However, the persistence and photochemical degradation characteristics of DSP in an aqueous environment are still unclear. This study aimed to elucidate the photochemical fate of two representative DSP toxins, namely, okadaic acid (OA) and dinophysistoxin-1 (DTX1). Results showed that photo-mediated chemical reactions play a crucial role in eliminating DSP toxins in seawater. However, the degradation of OA and DTX1 was relatively slow under natural solar radiation, with a removal efficiency of 90.0% after exposure for more than 20 days. When the reaction solutions of OA and DTX1 were exposed to Hg lamp radiation, their degradation followed pseudo-first-order kinetics, and was remarkably influenced by seawater pH and metal-ion concentration. A total of 24 tentative transformation products (TPs) of OA and DTX1 were identified via liquid chromatography high-resolution mass spectrometry. C12 (C₄₃H₆₆O₁₁) and C24 (C₄₄H₆₈O₁₁) were the main TPs. The following possible photodegradation pathways were proposed: decarboxylation, photoinduced hydrolysis, chain scission, and photo-oxidation. Toxicity assays via protein phosphatase 2A inhibition proved that photochemical processes could significantly reduce the DSP toxicity of irradiated solutions by approximately 88%. This work provides an enhanced understanding of the fate of DSP toxins in the aqueous environment, allowing for an improved assessment of their environmental impacts.

High-Performance Liquid Chromatography and Liquid Chromatography/Mass Spectrometry Studies on Stress Degradation Behavior of Sulfapyridine and Development of a Validated, Specific, Stability-Indicating HPLC Assay Method

The objective of the current investigation was to develop a simple, rapid, and stability-indicating high-performance liquid chromatography method and to study the degradation behavior of sulfapyridine (SP) under different International Conference on Harmonization (ICH)-recommended conditions. The chromatographic method was developed using C₁₈ (250 × 4.6 mm, 5 μ) column, and mobile phase consisting of acetonitrile-0.1% formic acid (30:70 v/v) at ambient temperature, at a flow rate of 1 mL/min. The elution was monitored at 265 nm using a photodiode array detector. The developed method was subsequently validated as per ICH Q2 (R1) guidelines. The retention time of SP was observed as 4.56 min with the linearity range between 2 to 10 μg/mL. Limit of detection and limit of quantitation for SP were 0.115 and 0.35 μg/mL, respectively. Forced degradation studies were carried out on bulk samples of SP using prescribed acidic, basic, oxidative, thermal, and photolytic conditions. Extent of degradation in 0.1 M hydrochloric acid and under photolytic conditions was found to be 21.56% and 28.57%, respectively. The degradation products formed in stress conditions were identified by liquid chromatography-mass spectrometry (LC-MS). The utility of the method was verified by quantification of SP in different laboratory-made pharmaceutical preparations. The proposed method could be successfully used to quantify SP in different pharmaceutical dosage forms.

The role of photodegradation in the environmental fate of hydroxychloroquine

For many organic pollutants present in surface waters, photolysis is considered as a major abiotic degradation process. The present study aimed to explore the role of photolysis in the environmental fate of hydroxychloroquine (HCQ) for the first time. The photolytic degradation of HCQ was investigated under simulated solar radiation (300-800 nm) in ultrapure, spring, river, and sea water. The effect of pH on the photodegradation rate was substantial and it was observed that degradation was faster at higher pH-values. Obtained half-lives ranged from 5.5 min at pH 9 to 23.1 h at pH 4. Humic acids, nitrate and iron(III) enhanced photodegradation of HCQ due to formation of hydroxyl radicals and its attack on HCQ molecule. In contrast, chloride, sulfate and bromide inhibited photodegradation. Additionally, the humic acids exhibited a dual role, photosensitization and inner filter effect. The study of the reaction kinetics was performed with HPLC-PDA, while the identification of degradation products formed during photolytic degradation was carried out using HPLC-MS/MS and NMR spectroscopy. The hydroxylation was recognized as the dominant path of photoproducts formation. The results of this research reveal the importance of photolytic degradation in environmental fate of HCQ and enable a better understanding of its behavior in the environment. Moreover, the results showing the significant effect of pH on the photodegradation of HCQ can be very useful in water treatment processes.

Mechanism and pathways underlying the self-sensitized photodegradation of methotrexate under simulated solar irradiation

Methotrexate, a chemotherapeutic agent, was found to undergo self-sensitized photodegradation in aqueous environments. As the initial concentration increased, methotrexate was able to enhance its own direct photolysis reaction not only in DI but also in natural waters. The methotrexate degradation rate increased through the production of singlet oxygen (¹O₂), the triplet excited state of methotrexate (³MTX^*), and the triplet excited state of the pteridine structure (³PT^*) from the phototransformation byproducts. At low methotrexate concentrations (<20 ppb), ¹O₂ played an important role, whereas at higher methotrexate concentrations (>2000 ppb), the presence of oxygen decreased the overall methotrexate degradation rate by physically quenching ³MTX^* and ³PT^*. The cleavage of the CN bond resulted in a significant amount of byproducts: pteridine derivatives and N-(4-aminobenzoyl)-l-glutamic acid (yields: 13.5 ± 0.6% and 32.3 ± 2.2% for 10 ppm and 500 ppb MTX, respectively). The reactivity of the phototransformation byproducts and the substructures of methotrexate were investigated to help elucidate the proposed self-sensitized pathways. The results indicated that methotrexate as well as compounds containing a pteridine structure will generate pteridine byproducts during photodegradation and ³PT^* is the primary triplet excited species that can cause self-sensitized photodegradation.

Photodegradation of tefuryltrione in water under UV irradiation: Identification of transformation products and elucidation of photodegradation pathway

Photodegradation is an important abiotic degradation process in the aquatic environment. In this study, the photodegradation of tefuryltrione in aqueous solution was investigated under UV-Visible irradiation. Effects of carbonate (CO₃^2-), bicarbonate (HCO₃^-), nitrate (NO₃^-), hydrogen phosphate (HPO₄^2-), potassium (K⁺), and ammonium (NH₄⁺) on the photodegradation kinetics of tefuryltrione were evaluated. Results showed that tefuryltrione photodegradation was increased by HCO₃^-, CO₃^2-, and NO₃^- in the range of 0.1-10 mmol L^-1; decreased by HPO₄^2-; and insignificantly affected by K⁺ and NH₄⁺. Twelve main transformation products (TPs) were separated and identified on the basis of mass spectrum data assigned by elemental-composition calculations, comparison of structural analogs, and available literature. A tentative photodegradation pathway was further proposed depending on the identified TPs and their kinetic evolutions. Results indicated that TP 1 was generated by the hydroxyl that substituted for chlorine, TP 2 was formed by the cleavage of the ether bond of tefuryltrione, and TPs 3-6 were formed by the breakage of the CC bond of the keto moiety of tefuryltrione. Further, TPs 9-12 were formed by the rearrangement of tefuryltrione-photodegradation products. These findings are highly important for elucidating the environmental fate of tefuryltrione in aquatic ecosystems.

Identification and Characterization of Herbicide Penoxsulam Transformation Products in Aqueous Media by UPLC-QTOF-MS

Photodegradation is an important non-biodegradation process of pesticide degradation in aquatic environments. In this study, the effect of different forms of nitrogen on the photodegradation kinetics of penoxsulam was investigated. The photodegradation of penoxsulam was accelerated by NO^3- and NO^2- but was not affected by NH⁴⁺. Ultra-high-performance liquid chromatography coupled with time-of-flight mass spectrometry was used to separate and identify the transformation products (TPs)converted by photodegradation of penoxsulam in an aqueous solution under UV-Vis (290-800 nm) irradiation. Seven major transformation products were identified based on mass spectral data. The structure was determined by elemental composition calculations, comparison of structural analogs, and existing literature. The main pathways of photodegradation were found to be sulfonamide bond cleavage, rearrangement, triazole ring cleavage, and hydroxylation. These findings are critical to elucidate the environmental fate of penoxsulam in aquatic ecosystems and provide a basis for further environmental risk assessment.

Wide spectral degradation of Norfloxacin by Ag@BiPO4/BiOBr/BiFeO3 nano-assembly: Elucidating the photocatalytic mechanism under different light sources

Metallic Ag deposited BiPO₄/BiOBr/BiFeO₃ ternary nano-hetero-structures were rationally designed and synthesized by a simple precipitation-wet impregnation-photo deposition method. The plasmonic junction possesses an excellent wide spectrum photo-response and makes best use of BiPO₄ which is otherwise a poor photocatalyst. Ag@BiPO₄/BiOBr/BiFeO₃ showed superior photocatalytic activity for degradation of norfloxacin (NFN) under visible, ultra-violet, near-infra-red and natural solar light. Especially catalyst APBF-3 (0.3 wt% Ag@BiPO₄/BiOBr/BiFeO₃) shows 98.1% degradation of NFN (20 mg/L) in 90 min under visible light and 99.1% in less than 45 min under UV exposure. Free radical scavenging experiments and electron spin resonance (ESR) results has been used for explanation of charge transfer, photocatalytic mechanism and role of radicals for binary, ternary and Ag deposited ternary junctions for UV and visible exposure. Metallic Ag in addition to its surface plasmon resonance helps in protection of high conduction band and valence band in the three semiconductors. A dual Z-scheme mechanism has been predicted by comparing with possibilities of double charge and vectorial charge transfer.

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.

Photodegradation of fluazaindolizine in water under simulated sunlight irradiation: Identification of transformation products and elucidation of transformation mechanism

The photodegradation of fluazaindolizine in water was investigated under simulated sunlight irradiation. The effects of solution pH, humic acids (HA), nitrates (NO₃^-) and Fe(III) ions on photolysis of fluazaindolizine were studied. The results indicated that pH did not significantly affect its photodegradation. At low concentration (up to 5 mg/L), HA slightly facilitated the photodegradation of fluazaindolizine, while at high concentration (10-20 mg/L), HA inhibited its photodegradation. The presence of NO₃^- (0-10 mg/L) and Fe(III) (0-5 mg/L) noticeably accelerated the photodegradation of fluazaindolizine. Moreover, eleven direct transformation products (TPs) were isolated and identified by liquid chromatography quadrupole time-of-flight mass spectrometry. Density functional theory (DFT) calculation was utilized to characterize molecular property of fluazaindolizine and predict the potentiality of the possible photodegradation reaction. Ultimately, a possible transformation mechanism was proposed based on the identified TPs, degradation profiles and DFT calculation. The predominant photoproduct came from ring opening of imidazole-ring and dechlorination. Other TPs resulted from a series of photochemical reactions involving hydroxyl substitution, ring-opening, cleavage, oxidation and decarboxylation. These results were important in elucidating environmental fate of fluazaindolizine in aquatic system and further environmental risk assessment.

High-Performance Photocatalytic Hydrogen Production and Degradation of Levofloxacin by Wide Spectrum-Responsive Ag/Fe3O4 Bridged SrTiO3/g-C3N4 Plasmonic Nanojunctions: Joint Effect of Ag and Fe3O4

Highly photoresponsive semiconductor photocatalysis for energy and environmental applications require judicious choice and optimization of semiconductor interfaces for wide spectral capabilities. This work aims at rational designing of highly active SrTiO₃/g-C₃N₄ junctions bridged with Ag/Fe₃O₄ nanoparticles for utilizing Z-scheme transfer and surface plasmon resonance effect of Ag augmented by iron oxide. The SrTiO₃/(Ag/Fe₃O₄)/g-C₃N₄ (SFC) catalyst was employed for photocatalytic hydrogen production and photodegradation of levofloxacin (LFC; 20 mg/L) under UV, visible, near infra-red, and natural solar light exhibiting high performance. Under visible light (<780 nm), SFC-3 sample (30 wt % g-C₃N₄ and 3% Ag/Fe₃O₄) shows a H₂ evolution of 2008 μmol g^-1 h^-1 which is ∼14 times that of bare g-C₃N₄. In addition, 99.3% removal of LFC was degraded in 90 min under visible light with retention of activity under sun. The inherent topological properties, complete, higher charge separation, and reduced recombination allowed this catalyst for a high photocatalytic response which was proved by UV-diffuse reflectance spectroscopy, photoluminescence, electrochemical impedance spectroscopy, and photocurrent response measurements. Scavenging experiments and electron spin resonance analysis reveal that the mechanism shifts from a dual charge transfer in case of binary junction to essential Z-scheme with incorporation of Ag/Fe₃O₄. Both ^•O₂^- and ^•OH are main active radicals in visible light, whereas ^•O₂^- majorly participate under UV. The synergistic effect of SrTiO₃, g-C₃N₄, and plasmon resonance of Ag/Fe₃O₄ not only improves light response and reduce recombination but also enhances the redox-ability of charge carriers. A H₂ production mechanism and LFC degradation pathway (degradation, defluorination, and hydrolysis) has been predicted. This work paves a way for development of photocatalysts working in practical conditions for pollution and energy issues.

Photodegradation of sulfasalazine and its human metabolites in water by UV and UV/peroxydisulfate processes

The widespread occurrence of pharmaceuticals and their metabolites in natural waters has raised great concerns about their potential risks on human health and ecological systems. This study systematically investigates the degradation of sulfasalazine (SSZ) and its two human metabolites, sulfapyridine (SPD) and 5-aminosalicylic acid (5-ASA), by UV and UV/peroxydisulfate (UV/PDS) processes. Experimental results show that SPD and 5-ASA were readily degraded upon UV 254 nm direct photolysis, with quantum yields measured to be (8.6 ± 0.8) × 10^-3 and (2.4 ± 0.1) × 10^-2 mol Einstein^-1, respectively. Although SSZ was resistant to direct UV photolysis, it could be effectively removed by both UV/H₂O₂ and UV/PDS processes, with fluence-based pseudo-first-order rate constants determined to be 0.0030 and 0.0038 cm² mJ^-1, respectively. Second-order rate constant between SO₄^•- and SSZ was measured as (1.33 ± 0.01) × 10⁹ M^-1s^-1 by competition kinetic method. A kinetic model was established for predicting the degradation rate of SSZ in the UV/PDS process. Increasing the dosage of PDS significantly enhanced the degradation of SSZ in the UV/PDS process, which can be well predicted by the developed kinetic model. Natural water constituents, such as natural organic matter (NOM) and bicarbonate (HCO₃^-), influenced the degradation of SSZ differently. The azo functional group of SSZ molecule was predicted as the reactive site susceptible to electrophilic attack by SO₄^•- by frontier electron densities (FEDs) calculations. Four intermediate products arising from azo bond cleavage and SO₂ extrusion were identified by solid phase extraction-liquid chromatography-triple quadrupole mass spectrometry (SPE-LC-MS/MS). Based on the products identified, detailed transformation pathways for SSZ degradation in the UV/PDS system were proposed. Results reveal that UV/PDS could be an efficient approach for remediation of water contaminated by SSZ and its metabolites.

Effect of water constituents on the degradation of sulfaclozine in the three systems: UV/TiO2, UV/K2S2O8, and UV/TiO2/K2S2O8

Bicarbonate, phosphate, chloride ions, and humic substances are among the constituents most widely present in natural waters. These non-target constituents can greatly affect the efficiency of advanced oxidation processes used for water decontamination due to their capacity to interfere with the adsorption of the target compounds on the surface of TiO₂, absorb photons, scavenge hydroxyl radicals (·OH), and generate photochemical reactive intermediates. In this work, the effect of these constituents on the degradation of sulfaclozine (SCL) was monitored in three different AOPs systems: UV/TiO₂, UV/K₂S₂O₈, and UV/TiO₂/K₂S₂O₈. It was shown that bicarbonate (HCO₃^-) and phosphate (HPO₄^2-) ions enhanced the degradation of SCL in UV/TiO₂ and UV/TiO₂/K₂S₂O₈ systems whereas the addition of humic substances influenced these rates with a much smaller extent. On the other hand, the degradation rate of SCL in the UV/K₂S₂O₈ system was not affected by the presence of HCO₃^- and HPO₄^2- but was inhibited in the presence of humic substances. In addition, the different mechanisms that can take place in the presence of these constituents were discussed and the degradation rate enhancement in presence of HCO₃^- and HPO₄^2- was attributed to the formation of new reactive species such as carbonate (CO₃^·-) and hydroxyl (·OH) radicals activated by TiO₂ holes (h⁺). In the presence of chloride (Cl^-) and nitrate (NO₃^-) ions, an enhancement of SCL adsorption on the surface of TiO₂ was observed. Finally, a comparative study of the degradation of SCL in river water and ultrapure water was reported.

Study of the simulated sunlight photolysis mechanism of ketoprofen: the role of superoxide anion radicals, transformation byproducts, and ecotoxicity assessment

The aim of this study was to investigate the photolysis mechanism of ketoprofen (KET) under simulated sunlight. The results demonstrated that the photolysis of KET aligned well with pseudo first-order kinetics. Radical scavenging experiments and dissolved oxygen experiments revealed that the superoxide anion radical (O₂˙^-) played a primary role in the photolytic process in pure water. Bicarbonate slightly increased the photodegradation of KET through generating carbonate radicals, while DOM inhibited the photolysis via both attenuating light and competing radicals. Moreover, Zhujiang river water inhibited KET phototransformation. Potential KET degradation pathways were proposed based on the identification of products using LC/MS/MS and GC/MS techniques. The theoretical prediction of reaction sites was derived from Frontier Electron Densities (FEDs), which primarily involved the KET decarboxylation reaction. The ecotoxicity of the treated solutions was evaluated by employing Daphnia magna and V. fischeri as biological indicators. Ecotoxicity was also hypothetically predicted through the "ecological structure-activity relationship" (ECOSAR) program, which revealed that toxic products might be generated during the photolysis process.

Degradation of streptomycin in aquatic environment: kinetics, pathway, and antibacterial activity analysis

Streptomycin used in human and veterinary medicine is released into the environment mainly through excretions. As such, its elimination in water should be investigated to control pollution. In this study, the degradation of streptomycin in water was studied, and the influence of variables, including light exposure, solution pH, temperature, ionic strength, dissolved organic matter (DOM), and coexisting surfactants, on degradation was investigated. Streptomycin degradation was consistent with the first-order model in aquatic environments. Its degradation rate under light exposure was 2.6-fold faster than that in the dark. Streptomycin was stable under neutral conditions, but it was easily decomposed in acidic and basic environments. Streptomycin degradation was enhanced by high temperature, and its half-life decreased from 103.4 days at 15 °C to 30.9 days at 40 °C. This process was also accelerated by the presence of Ca²⁺ and slightly improved by the addition of HA. Streptomycin degradation was suppressed by high levels of the cationic surfactant cetyltri- methylammonium bromide (CTAB), but was promoted by the anionic surfactant sodium dodecyl benzene sulfonate (SDBS). The main degradation intermediates/products were identified through liquid chromatography-mass spectrometry, and the possible degradation pathway was proposed. The antibacterial activity of streptomycin solution was also determined during degradation. Results showed that STR degradation generated intermediates/products with weaker antibacterial activity than the parent compound.

Environmental behavior of sulfadiazine, sulfamethazine, and their metabolites

Sulfonamides are one of the most frequently used antibiotics worldwide. Therefore, processes that determine their fate in the environment are of great interest. In the present work, biodegradation as biotic process and hydrolysis and photolysis as abiotic processes were investigated. In biodegradation experiments, it was found out that sulfonamides (sulfadiazine and sulfamethazine) and their N ⁴-acetylated metabolites were not readily biodegradable. The results showed that decrease of concentrations were in the range from 4% for sulfadiazine to 22% for N ⁴-acetylsulfamethazine. Hydrolytic experiments examined at pH values normally found in the environment also showed their resistance. However, photolysis proved to be significant process for decreasing concentrations of sulfonamides and their metabolites in three various aqueous matrices (Milli-Q water, river water, and synthetic wastewater). In addition, influence of ubiquitous water constituents (Cl^-, NO₃^-, SO₄^2-, PO₄^3-, and humic acids) was also investigated, showing their different impact on photolysis of investigated pharmaceuticals. The results showed that photolysis followed first-order kinetics in all cases. The obtained results are very important for assesing the environmental fate of sulfonamides and their metabolites in the aquatic environment.

Photolysis of Antibiotics under Simulated Sunlight Irradiation: Identification of Photoproducts by High-Resolution Mass Spectrometry

There is growing concern regarding the widespread use of antibiotics and their presence in the aqueous environment. Their removal in the water column is mediated by different types of degradation processes for which the mechanisms are still unclear. This research is focused on characterizing the photodegradation kinetics and pathways of two largely employed antibiotics families: sulfonamides (9 SDs) and fluoroquinolones (6 FQs). Degradation percentages and rates were measured in pure water exposed to simulated natural sunlight at a constant irradiance value (500 W m^-2) during all the experiments, and the main photoproducts formed were characterized through accurate mass measurement using ultraperformance liquid chromatography-quadrupole-time-of-flight-mass spectrometry (UPLC-QToF-MS). Over 200 different phototransformation products were identified for SDs and FQs, 66% of them, to the best of our knowledge, have not been described before. Their sequential formation and disappearance over the course of the experiments reveals the existence of several pathways for the degradation of target antibiotics. Occurrence of new photoproducts derived from desulfonation and/or denitrification, as well as hydroxylation of photo-oxidized heterocyclic rings, have been identified during photodegradation of SDs, whereas a new pathway yielding oxidation of the benzene ring after the cleavage of the piperazine ring (e.g., CIP product with m/z 280) is described for FQs.

H2O2 and/or TiO2 photocatalysis under UV irradiation for the removal of antibiotic resistant bacteria and their antibiotic resistance genes

Inactivating antibiotic resistant bacteria (ARB) and removing antibiotic resistance genes (ARGs) are very important to prevent their spread into the environment. Previous efforts have been taken to eliminate ARB and ARGs from aqueous solution and sludges, however, few satisfying results have been obtained. This study investigated whether photocatalysis by TiO₂ was able to reduce the two ARGs, mecA and ampC, within the host ARB, methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, respectively. The addition of H₂O₂ and matrix effect on the removal of ARB and ARGs were also studied. TiO₂ thin films showed great effect on both ARB inactivation and ARGs removal. Approximately 4.5-5.0 and 5.5-5.8 log ARB reductions were achieved by TiO₂ under 6 and 12mJ/cm² UV₂₅₄ fluence dose, respectively. For ARGs, 5.8 log mecA reduction and 4.7 log ampC reduction were achieved under 120mJ/cm² UV₂₅₄ fluence dose in the presence of TiO₂. Increasing dosage of H₂O₂ enhanced the removal efficiencies of ARB and ARGs. The results also demonstrated that photocatalysis by TiO₂ was capable of removing both intracellular and extracellular forms of ARGs. This study provided a potential alternative method for the removal of ARB and ARGs from aqueous solution.

Decomposition of 3,5-dinitrobenzamide in aqueous solution during UV/H2O2 and UV/TiO2 oxidation processes

3,5-Dinitrobenzamide has been widely used as a feed additive to control coccidiosis in poultry, and part of the added 3,5-dinitrobenzamide is excreted into wastewater and surface water. The removal of 3,5-dinitrobenzamide from wastewater and surface water has not been reported in previous studies. Highly reactive hydroxyl radicals from UV/hydrogen peroxide (H₂O₂) and UV/titanium dioxide (TiO₂) advanced oxidation processes (AOPs) can decompose organic contaminants efficiently. In this study, the decomposition of 3,5-dinitrobenzamide in aqueous solution during UV/H₂O₂ and UV/TiO₂ oxidation processes was investigated. The decomposition of 3,5-dinitrobenzamide fits well with a fluence-based pseudo-first-order kinetics model. The decomposition in both two oxidation processes was affected by solution pH, and was inhibited under alkaline conditions. Inorganic anions such as NO₃^-, Cl^-, SO₄^2-, HCO₃^-, and CO₃^2- inhibited the degradation of 3,5-dinitrobenzamide during the UV/H₂O₂ and UV/TiO₂ oxidation processes. After complete decomposition in both oxidation processes, approximately 50% of 3,5-dinitrobenzamide was decomposed into organic intermediates, and the rest was mineralized to CO₂, H₂O, and other inorganic anions. Ions such as NH₄⁺, NO₃^-, and NO₂^- were released into aqueous solution during the degradation. The primary decomposition products of 3,5-dinitrobenzamide were identified using time-of-flight mass spectrometry (LCMS-IT-TOF). Based on these products and ions release, a possible decomposition pathway of 3,5-dinitrobenzamide in both UV/H₂O₂ and UV/TiO₂ processes was proposed.

Biodegradation, ecotoxicity and UV254/H2O2 treatment of imidazole, 1-methyl-imidazole and N,N'-alkyl-imidazolium chlorides in water

Imidazole-based compounds are used as reagents for the manufacturing of other compounds including imidazolium-based ionic liquids, which have been recently proposed as a green alternative to conventional solvents. Since some imidazole-based compounds have been demonstrated to be harmful to aquatic organisms, the removal of imidazole, 1-methylimidazole, 1-ethyl-3-methyl-imidazolium chloride and 1-butyl-3-methyl-imidazolium chloride from aqueous solutions was attempted by biological oxidation, direct UV₂₅₄ photolysis, and UV₂₅₄/H₂O₂ process at pH 5.5 and 8.5. Results showed that UV₂₅₄/H₂O₂ treatment is an effective tool for the removal of the selected compounds at both pHs. In fact, the kinetic constants of the reaction between the photogenerated HO radicals and the four target compounds, estimated by means of both numerical and competition kinetic method, range between 2.32·10⁹ M^-1 s^-1 and 5.52 ·10⁹ M^-1 s^-1. Moreover, an ecotoxicity assessment of the contaminated water before and after initial treatment without further processing was assessed by using two living aquatic organisms: Raphidocelis subcapitata and Daphnia magna. The results of this assessment not only corresponded closely to previous findings (in terms of EC₅₀ values) reported in the literature, but also indicated that, in some cases, UV₂₅₄/H₂O₂ oxidation by-products could be even more toxic than parent compounds.

Removal of benzoylecgonine from water matrices through UV254/H2O2 process: Reaction kinetic modeling, ecotoxicity and genotoxicity assessment

Benzoylecgonine (BE), the main cocaine metabolite, has been detected in numerous surface water and treatment plants effluents in Europe and there is urgent need for effective treatment methods. In this study, the removal of BE by the UV254/H2O2 process from different water matrices was investigated. By means of competition kinetics method, the kinetic constant of reaction between BE and the photogenerated hydroxyl radicals (OH) was estimated resulting in kOH/BE=5.13×10(9)M(-1)s(-1). By-products and water matrices scavengers effects were estimated by numerical modeling of the reaction kinetics for the UV254/H2O2 process and validated in an innovative microcapillary film (MCF) array photoreactor and in a conventional batch photoreactor. The ecotoxicity of the water before and after treatment was evaluated with four organisms Raphidocelis subcapitata, Daphnia magna, Caenorhabditis elegans, and Vicia faba. The results provided evidence that BE and its transformation by-products do not have significant adverse effects on R. subcapitata, while D. magna underwent an increase of lipid droplets. C. elegans was the most sensitive to BE and its by-products. Furthermore, a genotoxicity assay, using V. faba, showed cytogenic damages during the cell mitosis of primary roots.

Unveiling self-sensitized photodegradation pathways by DFT calculations: A case of sunscreen p-aminobenzoic acid

Self-sensitized photodegradation has been observed for diverse aquatic organic pollutants. However, photodegradation pathways have not been clarified in previous experimental studies. Here, we attempted to probe self-sensitized photodegradation pathways of organic pollutants employing both photolytic experiments and density functional theory calculations. By performing photolytic experiments, we found that singlet state oxygen ((1)O2) play an essential role in photodegradation of a sunscreen p-aminobenzoic acid (PABA). PABA can photogenerate (1)O2 and react fast with (1)O2. We hypothesized that PABA underwent (1)O2 induced self-sensitized photodegradation. By calculating transition states, intermediates and reaction barriers, we found that (1)O2 can oxidize PABA through electrophilic attacks on the benzene ring to abstract one H atom of the amino group following a 1,3-addition mechanism or to induce decarboxylation. Either pathway produces a hydroperoxide. O-O bond cleavage of the hydroperoxides occurring at ground states or the lowest triplet excited states can produce phenoxyl radical precursors of 4-amino-3-hydroxybenzoic acid and 4-aminophenol, which are photodegradation products detected in experiments. Thus, a viable (1)O2 self-sensitized photodegradation mechanism was unveiled for PABA.

Identification of photoproducts of fungicide cyprodinil and elucidation of transformation mechanism in water using LC-IT-TOF-MS/MS technique

This study aimed at investigating photodegradation of cyprodinil in aquatic solution under the simulated natural light or UV-visible irradiation (290-800 nm) using LC-MS/MS techniques. Effects of pH, nitrate ion, Fe (III), humic acid and TiO2 on photolysis kinetics of cyprodinil were explored. The photodegradation followed first-order reaction kinetics, and linear accelerating effects of Fe (III), nitrate ion and TiO2 with concentrations ranging from 0.1 to 5.0 mg L(-1) on photodegradation were remarkably observed. HA at low concentration ranges (<3.0 mg L(-1)) enhanced cyprodinil photodegradation while the photocatalytic rate was weakened with more addition of HA. The degradation rate in alkaline solutions was greater than in acidic solutions. Six main transformation products (TPs) were separated and identified based on mass spectra data and density functional theory (DFT) quantum calculations, and their kinetic evolutions were also investigated. Ultimately, a tentative transformation mechanism was proposed based the identified TPs and their kinetic evolutions. The results indicated that one α-H on pyridine ring of cyprodinil was hydroxylated to form TPs 1. TPs 1 underwent a series of photochemical reactions involving ring-opening, addition of one H2O molecule and demethylation on three-member ring to form TPs 2, which was further hydroxylated on benzene ring to form TPs 6. TPs 3-5 were three isomers from Hofmann-Martius rearrangement of cyprodinil. These findings were of utmost importance for elucidating environmental fate of cyprodinil in aquatic ecosystem and further environmental risk evaluation.

UV-photodegradation of desipramine: Impact of concentration, pH and temperature on formation of products including their biodegradability and toxicity

Desipramine (DMI) is a widely used tricyclic antidepressant, and it is the major metabolite of imipramine (IMI) and lofepramine (LMI); IMI and LMI are two of the most commonly used tricyclic antidepressants. If DMI enters the aquatic environment, it can be transformed by the environmental bacteria or UV radiation. Therefore, photolysis of DMI in water was performed using a simulated sunlight Xenon-lamp and a UV-lamp. Subsequently, the biodegradability of DMI and its photo-transformation products (PTPs) formed during its UV photolysis was studied. The influence of variable conditions, such as initial DMI concentration, solution pH, and temperature, on DMI UV photolysis behavior was also studied. The degree of mineralization of DMI and its PTPs was monitored. A Shimadzu HPLC-UV apparatus was used to follow the kinetic profile of DMI during UV-irradiation; after that, ion-trap and high-resolution mass spectrometry coupled with chromatography were used to monitor and identify the possible PTPs. The environmentally relevant properties and selected toxicity properties of DMI and the non-biodegradable PTPs were predicted using different QSAR models. DMI underwent UV photolysis with first-order kinetics. Quantum yields were very low. DOC values indicated that DMI formed new PTPs and was not completely mineralized. Analysis by means of high-resolution mass spectrometry revealed that the photolysis of DMI followed three main photolysis pathways: isomerization, hydroxylation, and ring opening. The photolysis rate was inversely proportional to initial DMI concentration. The pH showed a significant impact on the photolysis rate of DMI, and on the PTPs in terms of both formation kinetics and mechanisms. Although temperature was expected to increase the photolysis rate, it showed a non-significant impact in this study. Results from biodegradation tests and QSAR analysis revealed that DMI and its PTPs are not readily biodegradable and that some PTPs may be human and/or eco-toxic, so they may pose a risk to the environment.

Photodegradation of the novel fungicide fluopyram in aqueous solution: kinetics, transformation products, and toxicity evolvement

The aqueous photodegradation of fluopyram was investigated under UV light (λ ≥ 200 nm) and simulated sunlight irradiation (λ ≥ 290 nm). The effect of solution pH, fulvic acids (FA), nitrate (NO3 (-)), Fe (III) ions, and titanium dioxide (TiO2) on direct photolysis of fluopyram was explored. The results showed that fluopyram photodegradation was faster in neutral solution than that in acidic and alkaline solutions. The presence of FA, NO3 (-), Fe (III), and TiO2 slightly affected the photodegradation of fluopyram under UV irradiation, whereas the photodegradation rates of fluopyram with 5 mg L(-1) Fe (III) and 500 mg L(-1) TiO2 were about 7-fold and 13-fold faster than that without Fe (III) and TiO2 under simulated sunlight irradiation, respectively. Three typical products for direct photolysis of fluopyram have been isolated and characterized by liquid chromatography tandem mass spectrometry. These products resulted from the intramolecular elimination of HCl, hydroxyl-substitution, and hydrogen extraction. Based on the identified transformation products and evolution profile, a plausible degradation pathway for the direct photolysis of fluopyram in aqueous solution was proposed. In addition, acute toxicity assays using the Vibrio fischeri bacteria test indicated that the transformation products were more toxic than the parent compound.

Insights into photolytic mechanism of sulfapyridine induced by triplet-excited dissolved organic matter

The ubiquity of sulfonamide antibiotics (SAs) in natural waters urges insights into their fate for ecological risk assessment in the aqueous euphotic zone. In this study, we investigated the effect of dissolved organic matter (DOM) on the photolysis of SAs with sulfapyridine as a reprentative. Results show that excited triplet state DOM ((3)DOM(∗)) is largely responsible for the photodegradation of sulfapyridine. The reaction of (3)DOM(∗) with a substructure model compound of SAs confirmed that sulfapyridine has one reaction site (aniline-N). Density functional theory (DFT) calculation was performed, which indicates that the anionic sulfapyridine has higher (3)DOM(∗) reactivity than that of the neutral form, which was also confirmed by steady state photolytic experiments. In the reaction, electrons of the aniline-N transfer to the carbonyl oxygen atom of (3)DOM(∗) moiety, followed by proton transfer, and leading to the formation of sulfapyridine radicals. The photolytic mechansim of sulfapyridine initiated by (3)DOM(∗) is helpful in understanding the photochemical fate and assessing the ecological risks of SAs in the aquatic environment.