Light-source-dependent role of nitrate and humic acid in tetracycline photolysis: kinetics and mechanism

Insights into sunlight-driven transformation of tetracycline by iron (hydr)oxides: The dominating role of self-generated hydrogen peroxide

Iron (hydr)oxides are abundant in surface environment, and actively participate in the transformation of organic pollutants due to their large specific surface areas and redox activity. This work investigated the transformation of tetracycline (TC) in the presence of three common iron (hydr)oxides, hematite (Hem), goethite (Goe), and ferrihydrite (Fh), under simulated sunlight irradiation. These iron (hydr)oxides exhibited photoactivity and facilitated the transformation of TC with the initial phototransformation rates decreasing in the order of: Hem > Fh > Goe. The linear correlation between TC removal efficiency and the yield of HO• suggests that HO• dominated TC transformation. The HO• was produced by UV-induced decomposition of self-generated H2O2 and surface Fe2+-triggered photo-Fenton reaction. The experimental results indicate that the generation of HO• was controlled by H2O2, while surface Fe2+ was in excess. Sunlight-driven H2O2 production in the presence of the highly crystalline Hem and Goe occurred through a one-step two-electron reduction pathway, while the process was contributed by both O2-induced Fe2+ oxidation and direct reduction of O2 by electrons on the conduction band in the presence of the poorly crystalline Fh. These findings demonstrate that sunlight may significantly accelerate the degradation of organic pollutants in the presence of iron (hydr)oxides.

Effects of solution chemistry on dielectric barrier atmospheric non-thermal plasma for operative degradation of antiretroviral drug nevirapine

The global prevalence of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) has been an environmental menace. Tons of drug wastes from antiretroviral therapy are released into the environment annually. We, for the first time, employed the novel dielectric barrier atmospheric non-thermal plasma (DBANP) discharge, to mitigate the inadvertent pollution arising from the antiretroviral therapy. A 40-min treatment of nevirapine achieved >94 % (0.075 min-1) removal efficiency at discharge power of 63.5 W and plasma working gas of atmospheric air. Chemical probes confirmed •OH, ONOO- and eaq- as the dominant reactive species whilst further revealing the reaction acceleration role of NaNO3 and CCl4 which are known reaction terminators. The commonly coexisting inorganic anions potentiated nevirapine removal with over 98 % efficiency, achieving the highest rate constant of 0.148 min-1 in this study. Moreover, the initial solution pH (1.5-11.1) was no limiting factor either. The insensitivity of the DBANP discharge to actual water matrices was an eminent inference of its potential applicability in practical conditions. With reference to data obtained from the liquid chromatography-mass spectrometer analysis, nevirapine degradation pathway was proposed. A nucleophilic attack by ONOO- at the cyclopropyl group and •OH attack at the carbonyl carbon of the amide group, respectively, initiated nevirapine degradation process. It is anticipated that the findings herein, will provide new insights into antiretroviral drug waste management in environmental waters using the innovative and green non-thermal plasma process.

Removal of tetracycline by ultraviolet/sodium percarbonate (UV/SPC)advanced oxidation process in water

Tetracycline (TC) was widely used and frequently detected in various water bodies, where the presence of TC posed a significant threat to the health of aquatic organisms. Furthermore, antibiotics were hardly degraded by biological treatment. Thus, in order to enhance the removal of TC, we proposed the use of a novel ultraviolet/sodium percarbonate (UV/SPC) advanced oxidation process and initiated an in-depth study. The study investigated the influence of oxidant dosage, initial pH, UV intensity, and TC concentration on the removal of TC. The results demonstrated that the UV/SPC system efficiently removed TC, with removal efficiency increasing as the SPC concentration increased. Within the pH range of 3-11, TC degradation exhibited minimal variation, indicating the UV/SPC system's strong adaptability to pH variations. The research on the impact of the water matrix on TC removal revealed that HCO3- had an inhibitory effect on TC degradation, while NO3- promoted TC degradation. Additionally, the presence of free radical species (·OH, ·CO3-, ·O2-) were detected and rate constants for the secondary reactions (k·OH,TC = 6.3 × 109 L mol-1·s-1, k·CO3-,TC = 3.4 × 108 L mol-1·s-1) were calculated, indicating that ·OH exhibited a stronger oxidative performance compared to ·CO3-. This study did not only present a novel strategy via UV/SPC to remove TC but also uncovered the unique role of ·CO3- for contaminant removal.

The impact of dissolved organic matter on the photodegradation of tetracycline in the presence of microplastics

Microplastics (MPs), an emerging class of pollutants, significantly impact the photoconversion dynamics of tetracycline (TC). But the effect of prevalent dissolved organic matter (DOM) on TC photodegradation in the presence of MPs remains a gap in current research. In this study, the photoconversion behavior and mechanism of TC under simulated sunlight conditions were systematically investigated, both in the presence of DOM and in combination with polystyrene (PS) MPs. The results demonstrated that both DOM and MPs enhanced the photodegradation of TC when compared to its direct degradation. However, DOM, particularly humic acid (HA, 10 mg/L), exhibited a more pronounced enhancing effect on TC photodegradation within 1 h reaction, regardless of the presence or absence of MPs, reaching up to 80%. In reaction systems involving TC-HA and TC-HA-PS, the primary contributors to TC degradation were direct photolysis and HA photosensitization (free radical reactions). Conversely, photosensitization effects were not significant in the presence of fulvic acid (FA). Furthermore, even under dark reaction conditions, HA exhibited a 10% degradation effect on TC. Quenching experiments and electron spin resonance (ESR) results indicate that dark reaction processes involve free radical reactions. Additionally, toxicity test results showed a reduction in the acute toxicity of TC photodegradation products, yet the long-term cumulative risks to organisms deserved attention. In general, this investigation significantly advances our understanding of the intricate photoconversion behavior of TC in the presence of coexisting chemical components.

Ag2S Nanoparticles Supported on 3D Flower-Shaped Bi2WO6 Enhanced Visible Light Catalytic Degradation of Tetracycline

A three-dimensional flower-shaped Bi2WO6 has been prepared by a hydrothermal procedure without the addition of an auxiliary agent and under neutral conditions with ultrapure water serving as solvent, and the Ag2S-Bi2WO6 composite with weight ratios of 5, 10, and 15% was prepared by a hydrothermal method. The crystallinity, morphology, mode of binding, and optical properties of the Ag2S-Bi2WO6 composite were characterized, the results of which showed that the composite had excellent dispersion, crystallinity, and purity. The composite with a weight ratio of 10% had the best photocatalytic performance, and the degradation rate of tetracycline reached 95.51% within 120 min, an increase of 27.35% over Bi2WO6. In experiments, some focus was given to the effect of the initial solution pH and the concentrations of humic acid and inorganic anions on the degradation efficiency. Based on free radical capture experiments and the semiconductor theory, the main active substances and mechanisms in the optical catalytic reaction process were studied, and speculation was given concerning the degradation pathway for the target pollutants. This study has conceived novel methods for the development of dual semiconductor systems consisting of a Ag NP composite and in doing so has provided new approaches for the development and photocatalysis for water pollution control.

AgBr nanoparticle surface modified SnO2 enhanced visible light catalytic performance: characterization, mechanism and kinetics study

In this study, a simple hydrothermal procedure and in situ precipitation method were used to prepare SnO2-AgBr composites, where the molar ratios of SnO2 and AgBr were 1 : 1, 1 : 2 and 2 : 1. Characterization results showed that the composites had excellent dispersion, crystallinity, and purity. A photocatalytic degradation experiment and first-order kinetic model indicate that SnO2-AgBr (1 : 1) had the best photocatalytic performance, and the degradation rates of 30 mg L-1 simulated MO and MG wastewater reached 96.71% and 93.36%, respectively, in 150 min, which were 3.5 times those of SnO2. The degradation rate of MO and MG increases with the dosage. Humic acid inhibited the degradation of MG, while a low concentration of humic acid promoted the degradation of MO, and the composite has good stability with pH. A free radical trapping experiment shows that ·OH and ·O2- were the main active substances, and h+ was the secondary one. According to the results of the characterization and photocatalysis experiments, a Z-scheme mechanism for the SnO2-AgBr composite was proposed, and the degradation pathway of target pollutants was speculated upon. This study has conceived novel methods for the development of a mature Z-scheme mechanism and in doing so has provided new approaches for the development of photocatalysis for water pollution control.

Strategy for improvement of molecular oxygen activation capacity of PPECu by chlorine doping for water decontamination

The activation of molecular oxygen and generation of reactive oxygen species (ROS) play important roles in the efficient removal of contaminants from aqueous ecosystems. Herein, using a simple and rapid solvothermal process, we developed a chlorine-doped phenylethynylcopper (Cl/PPECu) photocatalyst and applied it to visible light degradation of sulfamethazine (SMT) in aqueous media. The Cl/PPECu was optimized to have a 2.52 times higher steady-state concentration of O2•- (3.62 × 10-5 M) and a 28.87 times higher degradation rate constant (0.2252 min-1) for SMT compared to pure PPECu. Further, the effectiveness of Cl/PPECu in treating sulfonamide antibiotics (SAs) in real water systems was verified through an investigation involving natural water bodies, SAs, and ambient sunlight. The energy band structure, DFT calculation and correlation heat map indicated that the addition of chlorine modulated the local electronic structure of PPECu, leading to an improvement in the electron-hole separation, enhanced the O2 activation, and promoted the generation of ROSs. This study not only puts forward innovative ideas for the eco-compatible remediation of environmental pollution using PPECu, but also sheds new light on the activation of oxygen through elemental doping.

Preparation of sludge-based biochar loaded with ferromanganese and its removal mechanism of tetracycline hydrochloride

To remove the serious contamination caused by tetracycline hydrochloride, this paper uses the method of impregnation followed by pyrolysis to prepare ferromanganese-loaded sludge-based biochar and investigate its effectiveness in removing tetracycline hydrochloride. The material was characterized by field emission SEM, FTIR, and X-ray diffraction analysis. The possible reaction mechanisms involved in the removal of tetracycline were deduced based on the determination of Mn2+ during the reaction process and XPS characterization of materials before and after the reaction, and analysis of degradation intermediates and reaction pathways during tetracycline hydrochloride degradation was discussed. The results showed that the highest removal rate of 90.71% was achieved at a Fe-to-Mn ratio of 2:1 for the Fe-to-Mn-loaded sludge-based biochar. XPS characterization before and after the reaction showed that the valence state of Fe did not change significantly and was stable, while Mn4+ partially changed to Mn2+ and a redox reaction occurred. The changes in Mn2+ concentration during the reaction showed that the degradation of tetracycline hydrochloride was mainly dominated by MnO2. The LC-MS analysis revealed eight intermediates in the degradation of tetracycline, and two possible reaction pathways existed.

Effect and mechanism of simultaneous cadmium-tetracycline removal by a self-assembled microbial-photocatalytic coupling system

Electrochemical bacteria Shewanella oneidensis MR-4 (MR-4) was used to biologically generate cadmium sulfide (bio-CdS) nanocrystals and construct a self-assembled intimately coupled photocatalysis-biodegradation system (SA-ICPB) to remove cadmium (Cd) and tetracycline hydrochloride (TCH) from wastewater. The characterization using EDS, TEM, XRD, XPS, and UV-vis confirmed the successful CdS bio-synthesis and its visible-light response capacity (520 nm). 98.4% of Cd²⁺ (2 mM) was removed during bio-CdS generation within 30 min. The electrochemical analysis confirmed the photoelectric response capability of the bio-CdS as well as its photocatalytic efficiency. Under visible light, SA-ICPB entirely eliminated TCH (30 mg/L). In 2 h, 87.2% and 43.0% of TCH were removed separately with and without oxygen. 55.7% more chemical oxygen demand (COD) was removed with oxygen participation, indicating the degradation intermediates elimination by SA-ICPB required oxygen participation. Biodegradation dominated the process under aerobic circumstances. Electron paramagnetic resonance analysis indicated that h⁺ and ·O₂^- played a decisive role in photocatalytic degradation. Mass spectrometry analysis proved that TCH was dehydrated, dealkylated, and ring-opened before mineralizing. In conclusion, MR-4 can spontaneously generate SA-ICPB and rapidly-deeply eliminate antibiotics by coupling photocatalytic and microbial degradation. Such an approach was efficient for the deep degradation of persistent organic pollutants with antimicrobial properties.

Biofilm-Colonized versus Virgin Black Microplastics to Accelerate the Photodegradation of Tetracycline in Aquatic Environments: Analysis of Underneath Mechanisms

Tire wear particles (TWPs) exposed to the aquatic environment are rapidly colonized by microorganisms and provide unique substrates for biofilm formation, which potentially serve as vectors for tetracycline (TC) to influence their behaviors and potential risks. To date, the photodegradation capacity of TWPs on contaminants due to biofilm formation has not been quantified. To accomplish this, we examined the ability of virgin TWPs (V-TWPs) and biofilm-developed TWPs (Bio-TWPs) to photodegrade TC when exposed to simulated sunlight irradiation. V-TWPs and Bio-TWPs accelerated the photodegradation of TC, with rates (k_obs) of 0.0232 ± 0.0014 and 0.0152 ± 0.0010 h^-1, respectively (k_obs increased by 2.5-3.7 times compared to that for only TC solution). An important factor of increased TC photodegradation behavior was identified and linked to the changed reactive oxygen species (ROS) of different TWPs. The V-TWPs were exposed to light for 48 h, resulting in more ROS for attacking TC, with hydroxyl radicals (^•OH) and superoxide anions (O₂^•-) playing a dominant role in TC photodegradation measured using scavenger/probe chemicals. This was primarily due to the greater photosensitization effects and higher electron-transfer capacity of V-TWPs in comparison to Bio-TWPs. In addition, this study first sheds light on the unique effect and intrinsic mechanism of the crucial role of Bio-TWPs in TC photodegradation, enhancing our holistic understanding of the environmental behavior of TWPs and the associated contaminants.

Photodegradation of the Novel Herbicide Pyraquinate in Aqueous Solution: Kinetics, Photoproducts, Mechanisms, and Toxicity Assessment

Pyraquinate, a newly developed 4-hydroxyphenylpyruvate dioxygenase class herbicide, has shown excellent control of resistant weeds in paddy fields. However, its environmental degradation products and corresponding ecotoxicological risks after field application remain ambiguous. In this study, we systematically investigate the photolytic behaviors of pyraquinate in aqueous solutions and in response to xenon lamp irradiation. The degradation follows first-order kinetics, and its rate depends on pH and the amount of organic matter. No vulnerability to light radiation is indicated. Ultrahigh-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry and UNIFI software analysis reveals six photoproducts generated by methyl oxidation, demethylation, oxidative dechlorination, and ester hydrolysis. Gaussian calculation suggests that activities due to hydroxyl radicals or aquatic oxygen atoms caused these reactions on the premise of obeying thermodynamic criteria. Practical toxicity test results show that the toxicity of pyraquinate to zebrafish embryos is low but increases when the compound is combined with its photoproducts.

Elevated nitrate promoted photodegradation of PAHs in aqueous phase: Implications for the increased nutrient discharge

Polycyclic aromatic hydrocarbons (PAHs) are frequently released in aqueous phase by oil spill or from other sources, and photochemical oxidation is one of their major weathering processes. In this study, the photochemical behavior of phenanthrene (PHE, as a representative PAH) were studied and the effects of nitrogenous compounds were evaluated. The results showed that nitrate was an effective photosensitizer for improving the photodegradation of PHE, but the promoting effect was less effective in seawater due to the presence of halogen ions; the ammonia played a negligible role on PHE degradation. The photochemical ionization was a key process for PHE degradation, it can be retarded due to the quenching of triplet excited state by dissolved oxygen, and the inhibition was most prominent in fresh water. The presence of nitrate increased the steady state concentration of •OH from 2.08 × 10^-15 M to 1.04 × 10^-14 M in fresh water, and from 1.5 × 10^-16 M to 2.08 × 10^-15 M in seawater. The secondary-order reaction rate constant between PHE and •OH (k_•OH,PHE) was determined as 5.70 × 10⁹ M^-1 s^-1. Similar trend was observed for ¹O₂. The contribution of •OH to PHE removal was more prominent in fresh water than in seawater due to the quenching effects of halogen, and the increasing of nitrate enlarged the contribution of •OH. Two possible PHE degradation pathways were proposed based on GC-MS analysis and DFT calculation. The Quantitative Structure-activity Relationship (QSAR) evaluation showed that some degradation intermediates were more toxic than PHE, but the total environmental risk was still diminished due to the low percentage of toxic intermediates. This study provided theoretical and experimental insights into the influence of nitrogenous compounds on the photodegradation of PHAs in water environment.

Opposite impact of DOM on ROS generation and photoaging of aromatic and aliphatic nano- and micro-plastic particles

Dissolved organic matter (DOM) plays a significant role in the photochemical behavior of nano- and micro-plastic particles (NPs/MPs). We investigated the influence of DOM on the mechanism on the photoaging of NPs/MPs with different molecular structures under UV₃₆₅ irradiation in water. DOM components used in this study are mainly humic acid and fulvic acid. The results showed that DOM promoted the weathering of aliphatic NPs/MPs (polypropylene (PP)), but inhibited or had only a minor effect on the photoaging of aromatic NPs/MPs (polystyrene (PS) NPs/MPs, carboxyl-modified PS NPs, amino-modified PS NPs, and polycarbonate MPs). NPs with a large surface area may adsorb sufficient DOM on the particle surfaces through π-π interactions, which competes with NPs for photon absorption sites, thus, can delay the photoaging of PS NPs. Aromatic MPs may release phenolic compounds that quench •OH, thereby weakening the photoaging process. For aliphatic MPs, the detection of peracid, aldehyde, and ketone groups on the polymer surface indicated that DOM promoted weathering of PP MPs, which was primarily because the generation of •OH due to DOM photolysis may attack the polymer by C-C bond cleavage and hydrogen extraction reactions. This study provides insight into the UV irradiation weathering process of NPs/MPs of various compositions and structures, which are globally distributed in water.

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.

Identification of Reactive Oxygen Species and Mechanism on Visible Light-Induced Photosensitized Degradation of Oxytetracycline

This study investigated the photolysis and TiO₂-assisted photosensitized degradation of oxytetracycline (OTC) under visible light, the active reactive oxygen species (ROS), and the degradation mechanisms in these two reactions. The results show that the deprotonated OTC could be photolyzed more easily under visible light because of the redshift of its absorption spectrum at high pH values. Due to the TiO₂-assisted self-photosensitized degradation of OTC, OTC removal in the visible light/TiO₂ system was more efficient with the addition of TiO₂, as demonstrated when TiO₂ was replaced with insulator SiO₂. The study's ROS scavenging experiments show that superoxide radical anion (O₂^•-) ROS was most responsible for the self-sensitized degradation of OTC in both reactions. OTC degradation under the visible light/TiO₂ system was enhanced with increasing TiO₂ load, while the elimination of total organic carbon (TOC) was very limited after 5 h of visible light irradiation. Based on the eight identified transformation products found, five potential reaction mechanisms, including hydroxylation, quinonization, decarbonylation, de-methylation, and dehydration, were proposed for the photolytic and TiO₂-assisted photosensitized degradation mechanisms of OTC under visible light. This study indicates that OTC can degrade under visible light with or without a semiconductor when conditions are suitable.

Evaluation of iron-loaded granular activated carbon used as heterogeneous fenton catalyst for degradation of tetracycline

To optimize the efficiency of general adsorption-Fenton oxidation treatment, iron-loaded granular activated carbon (Fe-GAC) was prepared, characterized, and used as a catalyst in the heterogeneous Fenton oxidation of tetracycline (TC). Characterization revealed that the Fe(II) was successfully introduced onto the original granular activated carbon (GAC) and diversified the materials' surface morphology and elemental compounds. Under an initial pH of 3.0, the Fe-GAC/Fenton system obtained a maximum removal rate of 92.6%, with hydrogen peroxide (H₂O₂) dosages of 9 mmol g^-1. And the GAC/Fenton without iron supplementation was 89.5%, with H₂O₂ dosages of 8 mmol g^-1. Additionally, the Fe-GAC/Fenton system consumed a lower Fe(II) dosage than GAC/Fenton, with Fe(II)/H₂O₂ molar ratios of 0.007:1 and 0.04:1, respectively. Analysis of total organic carbon demonstrated higher mineralization efficiency in the Fe-GAC/Fenton system (67.2%), which was approximately 1.3 times of GAC/Fenton. Desorption experiments showed that the adsorption and degradation accounted for 19.22% and 80.78% of the total TC removal by GAC/Fenton, and 10.58% and 89.42% in the Fe-GAC/Fenton system, respectively. Electron paramagnetic resonance (EPR) technique and quenching experiments demonstrated that the dominant reactive oxygen species (ROS) in synergistic treatments were hydroxyl (•OH) and hydroxy peroxyl (HO₂•) radicals. In addition, three potential degradation pathways for TC were proposed according to the detected fourteen intermediates. Catalyst regeneration treatments were evaluated over six cycles, and the regeneration was 6.5% higher with the iron-supplemented carbon granules. Overall, the Fe-GAC can be used as an efficient catalyst in practical water treatment, and this study demonstrated a promising method to develop adsorption-Fenton technology.

Tetracycline photolysis revisited: Overlooked day-night succession of the parent compound and metabolites in natural surface waters and associated ecotoxicity

Despite the extensive study of tetracycline photolysis in aquatic environments, the phototransformation of tetracycline and its metabolites under natural day-night succession has not been examined. In this study, we investigated tetracycline photolysis and associated ecotoxicity in two natural surface waters and one artificial ultrapure water under simulated day/night cycling over two days. Previously unrecognized and highly pH- and temperature-dependent dark interconversions of tetracycline metabolites were observed. The liquid chromatography-mass spectrometry/mass spectrometry analysis identified a range of isomerized, hydroxylated, demethylated, deaminated, and open-ring photoproducts. The hydrolysis of tetracycline, isotetracycline, and several intermediate products was proposed as the major mechanism for the observed dark transformations. Exposure studies employing Escherichia coli indicated that although the tetracycline degradation products had lower bacterial toxicities than the parent compound, increasing toxicity with irradiation time after the near-complete degradation of the parent compound in natural waters implied that product mixtures retain ecotoxicity. The dark transformations also affected the bacterial toxicity and fluorescence properties of irradiated tetracycline solutions. Overall, this study provides new insights into the photochemical behavior of tetracycline and its associated ecological risk in aquatic environments.

Degradation of anthranilic diamide insecticide tetrachlorantraniliprole in water: Kinetics, degradation pathways, product identification and toxicity assessment

In the present study, aqueous behavior and fate of diamide insecticide tetrachlorantraniliprole (TCTP) were investigated under laboratory-controlled conditions. Half-lives of TCTP photolysis in natural water and pH buffers were 1.4-2.8 h, comparing with those of 1.2-231 d for hydrolysis. Both processes were highly influenced by pH with respect to degradation kinetics and routes. The hydrolysis rate of TCTP was accelerated by elevated temperatures. The presence of nitrate enhanced TCTP photolysis while fulvic acid exhibited suppression, with the extent of both effects as a function of concentration. Four degradation products were identified using a variety of spectroscopic approaches. Key reactions involved in the degradation pathways include intramolecular substitution and cyclization. There was a reduction in the acute toxicity of all four products to Daphnia magna by comparison with TCTP, whereas they were still classified as category 1 or 2 hazardous substances to the aquatic environment according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) standards.

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.

A study of the effect of reactive oxygen species induced by violet and blue light from oxytetracycline on the deactivation of Escherichia coli

Oxytetracycline (OTC), a tetracycline antibiotic, is a broad-spectrum antibacterial agent. In this investigation, liquid chromatography-mass spectrometry (LC-MS) is utilized to determine the effects of blue light (λ = 448 nm) illumination (BLIA) and violet light (λ = 403 nm) illumination (VLIA) on conformational changes in OTC at pH 7.8. The photochemical effect of OTC that is exposed to BLIA and VLIA on the deactivation of Escherichia coli (E. coli) is studied. The deactivation of E. coli has an insignificant effect on treatment with OTC alone. OTC is relatively unstable under BLIA and VLIA illumination in an alkaline solution, and OTC has been shown to inactivate E. coli by generating reactive oxygen species (ROS). Less anionic superoxide radicals (O₂^•-) are generated from OTC that is treated with BLIA than that from VLIA treatment, so OTC is more efficient in inactivating E. coli under VLIA. Inactivation of reduction rates of 0.51 and 3.65 logs in E. coli are achieved using 0.1 mM OTC under BLIA for 120 min and VLIA for 30 min, respectively, under the same illumination intensity (20 W/m²). Two photolytic products of OTC (PPOs) are produced when OTC is exposed to BLIA and VLIA, with molecular ions at m/z 447 and 431, molecular formulae C₂₁H₂₂N₂O₉ and C₂₁H₂₂N₂O₈, and masses of 446.44 and 430.44 g/mol, respectively. The results show that when exposed to VLIA, OTC exhibits enhanced inactivation of E. coli, suggesting that the photochemical treatment of OTC is a potential supplement in a hygienic process.

Ag-TiO2/biofilm/nitrate interface enhanced visible light-assisted biodegradation of tetracycline: The key role of nitrate as the electron accepter

Due to the pivotal role of Ag-TiO₂/biofilm/nitrate interface, enhanced visible light-assisted biodegradation of tetracycline (TC) in anoxic system was realized through both batch experiment and long-term operation in this study. The results of the batch experiment elucidated that 50 mg L^-1 TC could be completely removed within 10 h in Ag-TiO₂/biofilm/nitrate system. The continuous flow experiment was operated for 75 d to evaluate the performance and stability of Ag-TiO₂/biofilm/nitrate system. TC removal efficiency in Ag-TiO₂/biofilm/nitrate system was as high as 92.4 ± 1.6% at influent TC concentration of 50 mg L^-1 TC and hydraulic retention time (HRT) of 10 h, which would be attributed to the promoted separation of photoholes and photoelectrons at the presence of nitrate as electron acceptor. Facilitated electron transfer between semiconductor and biofilm was beneficial for enhancing TC biodegradation, thus lowering toxicity of intermediate products and promoting microbial activity. Moreover, the species related to TC biodegradation (Rhodopseudomonas, Phreatobacter and Stenotrophomonas), denitrification (Thauera) and electron transfer (Delftia) were enriched at Ag-TiO₂/biofilm/nitrate interface. Besides, a possible mechanism involved in enhanced TC degradation and nitrogen removal at Ag-TiO₂/biofilm/nitrate interface was proposed. This study provided a novel and promising strategy to enhance recalcitrant TC removal from industrial wastewater.

Insight into integration of photocatalytic and microbial wastewater treatment technologies for recalcitrant organic pollutants: From sequential to simultaneous reactions

The more and more stringent environmental standards for recalcitrant organic pollutants pushed forward the development of integration of photocatalytic and microbial wastewater treatment technologies. The past studies proposed mainly two typical integration ways: a) Independent sequence of photocatalysis and biodegradation (ISPB) conducting the sequential reactions; b) Intimate coupling of photocatalysis and biodegradation (ICPB) conducting the simultaneous reactions. Although ICPB has received more attraction recently due to its novelty, ISPB gives an edge in certain cases. The article reviews the state-of-the-art ISPB and ICPB studies to comprehensively compare the two systems. The strengths and weaknesses of ISPB and ICPB regarding the treatment efficiency, cost, toxicity endurance and flexibility are contradistinguished. The reactor set-ups, photocatalysts, microbial characteristics of ISPB and ICPB are summarized. The applications for different kinds of recalcitrant compounds are elaborated to give a holistic view of the removal efficiencies and transformation pathways by the two technologies. Currently, in-depth understandings about the interference among mixed pollutants, co-existing components and key parameters in realistic wastewater are urgently needed. The long-term and large-scale application cases of the integration technologies are still rare. Overall, we conclude that both ISPB and ICPB technologies are reaching maturity while challenges still exist for two systems especially regarding the reliability, economy and generalization for realistic wastewater treatment plants. Future research should not only manage to reduce the cost and energy consumption by upgrading reactors and developing novel catalysts, but also attach importance to the cocktail effects of wastewater during the sequential or simultaneous photocatalysis and biodegradation.

Radical chemistry of dissolved black carbon under sunlight irradiation: quantum yield prediction and effects on sulfadiazine photodegradation

Dissolved black carbon (DBC) is regarded as an important part of the natural organic matter pool. However, it is unclear about DBC's photochemical activity and the relationships between reactive intermediates (RIs) and the molecular structure of DBC remain unclear. In this study, we investigate the photochemical formation ability of RIs and spectral parameters (E₂/E₃, S_275-295) of DBC made from five types of plants at five pyrolysis temperatures. The results showed that there were good linear regressions between the RI quantum yields and the spectral parameters (E₂/E₃, S_275-295), and this was indicative of the RI generation prediction from DBC under solar irradiation. The DBC-mediated photochemical experiment of sulfadiazine revealed that ³DBC^* was the primary active species for the indirect photodegradation of sulfadiazine. Further studies indicated that a linear relationship was observed between the indirect photodegradation ability of sulfadiazine induced directly by ³DBC^* at different pyrolysis temperatures and the ³DBC^* quantum yields or E₂/E₃. These findings indicate that the simple models of the RI quantum yield as a function of spectral parameters can be used to evaluate the degradation of pollutants with known DBC spectral parameters.

Photodegradation of roxarsone in the aquatic environment: influencing factors, mechanisms, and artificial neural network modeling

Roxarsone (ROX), an organoarsenic feed additive, can be discharged into aquatic environment and photodegraded into more toxic inorganic arsenics. However, the photodegradation behavior of ROX in aquatic environment is still unclear. To better understand ROX photodegradation behavior, the influencing factors, photodegradation mechanism, and process modelling of ROX photodegradation were investigated in this study. The results showed that ROX in the aquatic environment was degraded to inorganic As(III) and As(V) under light irradiation. The degradation efficiency was enhanced by 25% with the increase of light intensity from 300 to 800 μW/cm² via indirect photolysis. The photodegradation was temperature dependence, but was only slightly affected by pH. Nitrate ion (NO₃^-) had an obvious influence, but sulfate, carbonate, and chlorate ions had a negligible effect on ROX degradation. Dissolved organic matter (DOM) in the solution inhibited the photodegradation. ROX photodegradation was mainly mediated by reactive oxygen species (in the form of single oxygen ¹O₂) generated through ROX self-sensitization under irradiation. Based on the data of factors affecting ROX photodegradation, ROX photodegradation model was built and trained by an artificial neural network (ANN), and the predicted degradation rate was in good agreement with the real values with a root mean square error of 1.008. This study improved the understanding of ROX photodegradation behavior and provided a basis for controlling the pollution from ROX photodegradation.

Effects of free radicals from doxycycline hyclate and minocycline hydrochloride under blue light irradiation on the deactivation of Staphylococcus aureus, including a methicillin-resistant strain

Doxycycline hyclate (DCH) and minocycline hydrochloride (MH) are tetracycline antibiotics and broad-spectrum antimicrobial agents. The changes in DCH and MH under blue light (λ = 462 nm) irradiation in alkaline conditions (BLIA) were investigated. Deactivation caused by superoxide anion radical (O₂^•-) and deactivation from DCH and MH during photolysis on Staphylococcus aureus (S. aureus), including methicillin-resistant S. aureus (MRSA), were studied. DCH is relatively unstable compared to MH under BLIA. The level of O₂^•- generated from the MH-treated photoreaction is lower than that from DCH photolysis, and the DCH-treated photoreaction is more efficient at inactivating S. aureus and MRSA at the same radiant intensity. DCH subjected to BLIA decreased the viability of S. aureus and MRSA by 3.84 and 5.15 log, respectively. Two photolytic products of DCH (PPDs) were generated under BLIA. The mass spectra of the PPDs featured molecular ions at m/z 460.8 and 458.8. The molecular formulas of the PPDs were C₂₁H₂₂N₂O₁₀ and C₂₂H₂₄N₂O₉, and their exact masses were 462.44 and 460.44 g/mol, respectively. These results bolster the photolytic oxidation that leads to DCH-enhanced deactivation of S. aureus and MRSA. Photochemical treatment of DCH could be applied as a supplement in hygienic processes.

Aging Processes of Polyethylene Mulch Films and Preparation of Microplastics with Environmental Characteristics

In this study, we explored the aging processes of a commercial polyethylene (PE) mulch film under UV irradiation and compared the laboratory aged films with films aged in nature. Overall, the aged films obtained from laboratory conditions were similar with that from natural conditions. Among the investigated factors, UV irradiation was crucial in the aging of the films, producing cracks and oxygen-containing functional groups on the films surface, constantly with natural aging. The formation of cracks induced a decrease of mechanical strength as well as the formation of MPs on the surface. The chemical oxidations detected by Fourier-transform infrared spectroscopy (FTIR) usually happened after the observed physical changes during aging. Moreover, a protocol was developed for laboratory preparation of MPs with characteristics similar with that from environmental aging and PE MPs with sizes of 2-400 μm could be produced in large amounts at relatively short period of time.

Aqueous phase oxidation of bisulfite influenced by nitrate and its photolysis

Nitrate aerosol is ubiquitous in the atmosphere. Nitrate in the particulate and aqueous phase can affect various atmospheric chemical processes through its hygroscopicity and photolysis. The impacts of nitrate photolysis on the heterogeneous oxidation of SO₂ have been attracting attention. However, the influence of nitrate on heterogeneous aqueous phase formation of atmospheric sulfate aerosol is still not very clear. In this study, the effects of nitrate on aqueous phase oxidation of bisulfite under different conditions were investigated. Results show that nitrate photolysis can promote the oxidation of bisulfite to sulfate, especially in the presence of O₂. It is found that pH plays a significant role in the reaction, and ammonium sulfate has significant impacts on the enhancement of aqueous phase sulfate production through regulating the pH of solution. An apparent synergism is found among halogen chemistry, nitrate and its photochemistry and S (IV) aqueous oxidation, especially the oxidation of halide ions by nitrate and its photolysis and by the intermediate products produced by the free radical chain oxidation of S (IV) in acidic solution, leading to the coupling of the redox cycle of halogen with the oxidation of bisulfite, which promotes the continuous aqueous oxidation of bisulfite and the formation of sulfate. In addition, the role of nitrate itself in the aqueous phase oxidation of bisulfite is revealed. These results provide a new insight into the heterogeneous aqueous phase oxidation pathways and mechanisms of SO₂ in cloud and fog droplets and haze particles.

Selective removal of common cyanotoxins: a review

The development of cyanobacterial blooms can have adverse effects on water bodies and may produce cyanotoxins. Several physical and chemical methods have been applied to remove cyanotoxins, but they have been significantly challenged due to extensive energy footprint and over-used chemicals, which limits practical application on a large scale. Selective removal has been regarded as the most promising approach recently for the elimination of prevalent and major bloom-forming cyanotoxins (e.g., microcystins and cylindrospermopsin) as natural organic matters and radical scavengers are ineluctably present in real scenarios. This paper reviews current advancements in research on selective oxidation and adsorption of cyanotoxins. Its goal is to provide comprehensive information on the treatment mechanism and the process feasibility involved in the cyanotoxin removal from real-world waters. Moreover, perspectives of cyanotoxin control and in situ selective elimination approaches are also reviewed. It is expected that the information gathered and discussed in this review can provide a useful and novel reference and direction for future pilot-scale applications.

The performance of aerobic granular sludge for simulated swine wastewater treatment and the removal mechanism of tetracycline

In this study, aerobic granular sludge (AGS) cultivated in a sequencing batch reactor (SBR) was employed to investigate its ability on the decontamination of tetracycline (TC) from swine wastewater (SWW). The removal mechanism of TC by AGS was studied. Results showed that the AGS process could effectively remove chemical oxygen demand (COD), ammonium nitrogen (NH_{+ 4}-N), total phosphorus (TP), and TC during operation. The removal of TC by AGS was mainly due to adsorption and biodegradation, and the contribution rate of biodegradation increased after AGS adaptation to TC. Twenty-two by-products were detected during biodegradation of TC, and accordingly the degradation pathway of TC was speculated. Compared to the control reactor, the microbe diversity in different levels of classification was richer in the TC fed reactor according to the LefSe analysis. The results revealed that enzymes that participated in the metabolic pathway of microbial biodegradation of polycyclic aromatic compounds were enriched and may have played a key role in the biodegradation of TC.

Study of the photoinduced transformations of sertraline in aqueous media

In the present study, the photoinduced degradation of the antidepressant drug sertraline under artificial solar radiation was examined. Photolysis was studied under different experimental conditions to explore its photolytic fate in the aqueous environment. Photolytic degradation kinetics were carried out in ultrapure water, wastewater effluent, as well as in the presence of dissolved organic matter (humic acids), bicarbonate and nitrate ions which enabled their assessment on sertraline photo-transformation. The reaction of sertraline with photoactive compounds accelerated sertraline transformation in comparison with direct photolysis. Moreover, TiO₂-mediated photocatalytic degradation of sertraline was investigated, and focus was placed on the identification of by-products. As expected, photocatalysis was extremely effective for sertraline degradation. Photocatalytic degradation proceeded through the formation of forty-four transformation products identified by HPLC-HRMS and after 240 min of irradiation total mineralization was achieved. Microtox bioassay (Vibrio fischeri) was employed to assess the ecotoxicity of the photocatalysis-treated solutions and results have indicated that sertraline photo-transformation proceeds through the formation of toxic compounds.

Solar photocatalytic abatement of tetracycline over phosphate oxoanion decorated Bi2WO6/polyimide composites

Environmental-friendly solar photocatalytic technology is attracting great attention in the field of pollution control. In this work, novel PO₄^3--Bi₂WO₆/PI photocatalyst achieved high degradation efficiency for tetracycline degradation in simulated solar light (1.6 times kinetic constants of Bi₂WO₆). The photocatalyst could produce more oxygen vacancies as well as more active species O₂^- and OH, and exhibited high mineralization ability, good stability and recyclability simultaneously. After 4 cycles of degradation experiments, its degradation efficiency was only reduced by 8.6 %. Tetracycline molecules gradually became small molecules under the attack of active species. The tetracycline degradation was highly pH-dependent and enhanced with the increase of solution pH. The water quality parameters humic acid and Cl^- presented the inhibitory effect, while HCO₃^- can accelerate the tetracycline degradation. The degradation of tetracycline by PO₄^3--Bi₂WO₆/PI conformed to the Z-scheme photocatalysis mechanism, which could effectively broaden the absorption of solar light, improve the separation and transfer of photogenerated electron-hole pairs and extend the lifespan of the photocatalyst.

CuO nanoparticles doping recovered the photocatalytic antialgal activity of graphitic carbon nitride

In this work, graphitic carbon nitride (g-C₃N₄) and CuO nanoparticles doped g-C₃N₄ (Cu-g-C₃N₄) was synthesized, and the mechanisms of humic acid (HA) impact on the photocatalytic antialgal activities of g-C₃N₄ and Cu-g-C₃N₄ to harmful algae were investigated. The 72 h median effective concentrations of g-C₃N₄ and Cu-g-C₃N₄ to two algae (Microcystis aeruginosa, Chlorella vulgaris) were (56.4, 89.6 mg/L) and (12.5, 20.6 mg/L), respectively. Cu-g-C₃N₄ exhibited higher photocatalytic antialgal activity than g-C₃N₄ because that: I) Cu-g-C₃N₄ was easier to aggregate with algal cells due to its lower surface potential and higher hydrophobicity than g-C₃N₄; II) Cu-g-C₃N₄ generated more O₂^-, OH*, and h⁺ due to its higher full-wavelength light utilization efficiency and higher electron-hole pairs separation efficiency than g-C₃N₄. HA (10 mg/L) inhibited the photocatalytic antialgal activity of g-C₃N₄, however, HA had no effect on that of Cu-g-C₃N₄. The mechanisms were that: I) doped CuO nanoparticles occupied the adsorption sites of HA on g-C₃N₄, which alleviated the inhibition of HA on the g-C₃N₄-algae heteroaggregation; II) HA adsorbed on CuO nanoparticles enhanced the oxygen reduction rate of Cu-g-C₃N₄. This work provides new insight into the inhibition mechanisms of NOM on g-C₃N₄ photocatalytic antialgal activity and addresses the optimization of g-C₃N₄ for environmental application.

Effective inactivation of Microcystis aeruginosa by a novel Z-scheme composite photocatalyst under visible light irradiation

Microcystis aeruginosa is one of the most famous harmful algae. In this work, Z-scheme g-C₃N₄-MoO₃ (Mo-CN) composite photocatalysts were successfully synthesized to alleviate the algae pollution. The obtained composites exhibited excellent performance for the inactivation of M. aeruginosa. The optimal photocatalysts (15Mo-CN) achieved a removal efficiency of 97% for the algal cells after 3 h visible light irradiation, which was attributed to their remarkable surface properties and ingenious structure design. The physiological status of Microcystis aeruginosa were evaluated by the chlorophyll a (chla), relative electron transport rate (rETR) and maximum photochemical efficiency (Fv/Fm), and all of them decreased in different degrees. Furthermore, the as-prepared photocatalysts also show a certain activity for the removal of leaked macromolecule organic compounds during the process of algal cells inactivation. Finally, a possible mechanism on the photocatalytic inactivation of algal cells by the Z-scheme photocatalysts was deduced based on the experimental and characterization results. We believe this study would provide new insights into the development of promising technology and basic theory for remediation of algae pollution.

Tetracycline and Sulfonamide Antibiotics in Soils: Presence, Fate and Environmental Risks

Veterinary antibiotics are widely used worldwide to treat and prevent infectious diseases, as well as (in countries where allowed) to promote growth and improve feeding efficiency of food-producing animals in livestock activities. Among the different antibiotic classes, tetracyclines and sulfonamides are two of the most used for veterinary proposals. Due to the fact that these compounds are poorly absorbed in the gut of animals, a significant proportion (up to ~90%) of them are excreted unchanged, thus reaching the environment mainly through the application of manures and slurries as fertilizers in agricultural fields. Once in the soil, antibiotics are subjected to a series of physicochemical and biological processes, which depend both on the antibiotic nature and soil characteristics. Adsorption/desorption to soil particles and degradation are the main processes that will affect the persistence, bioavailability, and environmental fate of these pollutants, thus determining their potential impacts and risks on human and ecological health. Taking all this into account, a literature review was conducted in order to shed light on the current knowledge about the occurrence of tetracycline and sulfonamide antibiotics in manures/slurries and agricultural soils, as well as on their fate in the environment. For that, the adsorption/desorption and the degradation (both abiotic and biotic) processes of these pollutants in soils were deeply discussed. Finally, the potential risks of deleterious effects on human and ecological health associated with the presence of these antibiotic residues were assessed. This review contributes to a deeper understanding of the lifecycle of tetracycline and sulfonamide antibiotics in the environment, thus facilitating decision-making for the application of preventive and mitigation measures to reduce its negative impacts and risks to public health.

Fabrication, characterization, and application of ternary magnetic recyclable Bi2WO6/BiOI@Fe3O4 composite for photodegradation of tetracycline in aqueous solutions

We aim at fabricating a ternary magnetic recyclable Bi₂WO₆/BiOI@Fe₃O₄ composite that could be applied for photodegradation of tetracycline (TC) from synthetic wastewater. To identify any changes with respect to the composite's morphology and crystal structure properties, ΧRD, FTIR, FESEM-EDS, PL and VSM analyses are carried out. The effects of Fe₃O₄ loading ratio on the Bi₂WO₆/BiOI for TC photodegradation are evaluated, while operational parameters such as pH, reaction time, TC concentration, and photocatalyst's dose are optimized. Removal mechanisms of the TC by the composite and its photodegradation pathways are elaborated. With respect to its performance, under the same optimized conditions (1 g/L of dose; 5 mg/L of TC; pH 7; 3 h of reaction time), the Bi₂WO₆/BiOI@5%Fe₃O₄ composite has the highest TC removal (97%), as compared to the Bi₂WO₆ (63%). After being saturated, the spent photocatalyst could be magnetically separated from solution for subsequent use. In spite of three consecutive cycles with 71% of efficiency, the spent composite still has reasonable photocatalytic activities for reuse. Overall, this suggests that the composite is a promising photocatalyst for TC removal from aqueous solutions.

Removal of tetracycline from an aqueous solution using manganese dioxide modified biochar derived from Chinese herbal medicine residues

Biochar (BC) derived from Chinese herbal medicine residues has been investigated for its performance as a potential adsorbent in tetracycline (TC) removal. In the present study, a chemical co-precipitation method was carried out to prepare manganese dioxide modified biochar (Mn-BC) to increase its sorption capacity. The properties of the modified biochar were characterized for further enhancing TC removal from an aqueous solution. Mn-BC was successfully synthesized and resulted in a much higher specific surface area, total pore volume and pore diameter. The sorption kinetics of TC on Mn-BC was described by the pseudo-second-order model. The sorption data of Mn-BC were fitted by Langmuir and Freundlich models. The study findings revealed a maximum adsorption capacity of Mn-BC (1:10) to TC was up to 131.49 mg/g. The adsorption process was endothermic and spontaneous. The degradation of TC was further enhanced by MnO₂ acting as an oxidizer on Mn-BC. Overall, the modified biochar derived from Chinese herbal medicine residues is a superior alternative for the removal of TC from an aqueous solution.

Bio-removal of tetracycline antibiotics under the consortium with probiotics Bacillus clausii T and Bacillus amyloliquefaciens producing biosurfactants

The contamination of the aquatic environments by tetracycline antibiotics (TCs) is an increasingly pressing issue. Here, we used the addition of exogenous surfactants and in situ biosynthesis of biosurfactants to remove tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC), and their mixtures using the co-culture of probiotic Bacillus clausii T and Bacillus amyloliquefaciens HM618 producing surfactin. The addition of exogenous biosurfactants to remove TCs was superior to nonionic surfactants. The maximal bio-removal efficiencies for OTC and CTC among mixed antibiotics under the co-culture of B. clausii T and B. amyloliquefaciens HM618 were 76.6% and 88.9%, respectively, which were both better than the efficiency of the pure culture of B. clausii T. TCs were removed mainly through biotransformation rather than absorption and hydrolysis. The removal efficiency was in the order CTC > OTC > TC. The co-culture of B. clausii T and B. amyloliquefaciens HM618 alleviated the cytotoxicity of OTC and CTC. The toxicity of the biotransformation products was lower than that of the parent compounds. Demethylation, hydroxylation, and dehydration are likely the major mechanisms of TC biotransformation. These results illustrate the potential of using surfactants in the bioremediation of tetracycline antibiotics, and provide new avenues for further exploration of the bioremediation of antibiotics pollution.

Salt-templated synthesis of 3D porous foam-like C3N4 towards high-performance photodegradation of tetracyclines

3D porous foam-like C₃N₄ is prepared by a salt-templated method, and it shows 64 times higher efficiency than bulk C₃N₄ in degrading tetracyclines.

Fabrication of black TiO2−x/CuFe2O4 decorated on diatomaceous earth with enhanced sonocatalytic activity for ibuprofen mitigation

This study reports facile fabrication of black TiO_2−x/CuFe₂O₄ (Ti³⁺ self-doped titania coupled with copper ferrite), an efficient sonocatalyst for ibuprofen (IBP) mitigation.

Photodegradation of microcystin-LR by pyridyl iron porphyrin immobilized on NaY zeolite

A novel photocatalyst, FeTPyPY, was prepared by immobilizing water-soluble tetra(4-pyridyl)phenyl iron-porphyrin (FeTPyP) on NaY zeolite to degrade microcystin-LR (MC-LR), one of the most toxic microcystins (MCs). UV-Vis analysis, UV-Vis diffuse reflectance spectroscopy, infrared spectroscopy, cyclic voltammetry and transmission electron microscopy were employed to characterize immobilized FeTPyPY. Under visible light (λ ≥ 420 nm), MC-LR was degraded utilizing immobilized FeTPyPY by activating molecular oxygen. The results showed that 85% of MC-LR was efficiently degraded by FeTPyPY with loading amount 100:1 (m_NaY:m_FeTPyP) after 300 min of visible light illumination. Moreover, FeTPyPY was stable in the degradation system with pH 7.0. The degradation mechanism was evaluated using electron spin resonance, and the results demonstrated that highly reactive oxygen species (^•OH radical) were generated in the system to degrade MC-LR. Therefore, immobilized FeTPyPY was available to break down the toxic groups within MC-LR by utilizing environmental ^•OH radical under circumneutral condition.

Photodegradation of naphthenic acids induced by natural photosensitizer in oil sands process water

Utilization of renewable solar energy driven advanced oxidation processes for oil sands process water (OSPW) remediation has received extensive attention. Naturally existing inorganic photosensitizer in OSPW was investigated in this work to provide information about the application of indirect photolysis treatment of organic contaminants in OSPW. OSPW and OSPW organic fraction were exposed under UV irradiance with fluence of 10 J/cm² to investigate the effect of OSPW inorganic fraction (OSPW-IF) on the non-catalytic photolysis of naphthenic acids (NAs) in OSPW. The results indicated that the inorganic fraction in OSPW enhanced the photodegradation of NAs, with 24.3% of total NA removal in OSPW, while only 12.4% of total NAs were removed in OSPW organic fraction. Moreover, the photodegradation of 1-adamantanecarboxylic acid (ACA) dissolved in OSPW-IF or carbonate buffer was conducted to verify the enhanced photodegradation of NAs by OSPW-IF. The results showed that 30.9% of ACA was removed in the OSPW-IF, while no ACA degradation was observed in carbonate buffer after 60 min of UV exposure, indicating that the OSPW-IF induced the photodegradation of ACA. In addition, nitrate was identified to be the photosensitizer in OSPW-IF responsible for the indirect photolysis of ACA. In the presence of nitrate, both hydroxyl radicals (•OH) and reactive nitrogen species were generated, where •OH was the dominant reactive species that contributed to the degradation of ACA. Ten possible by-products ranging from single to multiple hydroxyl, nitroso, nitro and carbonyl substituted products were proposed to be produced from the nitrate-induced photodegradation process through three different pathways. This study demonstrated that the photolysis of NAs in OSPW due to the presence of natural photosensitizers and nitrate could act as a natural photosensitizer for the remediation of OSPW by the photo-oxidation process.

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.

Tetracyclines: light-activated antibiotics?

Tetracyclines are well established antibiotics but show phototoxicity as a side effect. Antimicrobial photodynamic inactivation uses nontoxic dyes combined with harmless light to destroy microbial cells by reactive oxygen species. Tetracyclines (demeclocycline and doxycycline) can act as light-activated antibiotics by binding to bacterial cells and killing them only upon illumination. The remaining tetracyclines can prevent bacterial regrowth after illumination has ceased. Antimicrobial photodynamic inactivation can be potentiated by potassium iodide. Azide quenched the formation of iodine, but not hydrogen peroxide. Demeclotetracycline (but not doxycycline) iodinated tyrosine after light activation in the presence of potassium iodide. Bacteria are killed by photoactivation of tetracyclines in the absence of oxygen. Since topical tetracyclines are already used clinically, blue light activation may increase the bactericidal effect.

Photochemical behavior of benzophenone sunscreens induced by nitrate in aquatic environments

Benzophenones (BPs), which are widely used UV filters, have aroused considerable public concern owing to their potential endocrine-disrupting activities. Herein, we systematically investigated their photochemical behavior and fate, which is mediated by nitrate in aquatic environments. The results showed that 10 μM of 3 BPs can be completely degraded within 4 h of simulated sunlight irradiation in a 10 mM nitrate solution at pH 8.0, and 2,4-dihydroxybenzophenone (BP-1) has a 31.6% mineralization rate after 12 h irradiation. Their photolytic rates (k_obs) presented a significant linear correlation with the logarithmic values of the nitrate concentration for 0.1-10 mM (R² > 0.98), and in three actual waters, the rates of BP-1 were also positively related to the intrinsic nitrate concentration. Furthermore, higher transformation rates under alkaline condition were observed, especially for BP-1, with its k_obs at pH 10 being 8.3-fold higher than that at pH 6.0. Moreover, dissolved oxygen (DO) also has an impact on the reaction kinetics to some degree. According to the quenching experiments, we found that three reactive oxygen species (ROS), namely, •OH, •NO, and •NO₂, participated in this photolysis of BPs, and the contribution of •OH accounted for 32.1%. Furthermore, we selected BP-1 as the model molecule to study the transformation pathways and toxicity changes in this system. Four main transformation pathways including hydroxylation, nitrosylation, nitration, and dimerization were proposed, based on liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) analysis and density functional theory (DFT). According to the toxicity test, the formed intermediates were more toxic to Photobacterium phosphoreum than the parent BP-1. Therefore, these results can help reveal primary phototransformation mechanisms and evaluate the potential ecological risks of BPs in aquatic environments.

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.