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

Overlooked interconversion between tetracyclines and their 4-epimers in soil and effects on soil resistome and bacterial community

With the widespread use of tetracycline antibiotics (TCs) and the application of manure fertilizer in farmland, TCs and their metabolites especially 4-epimers have been heavily detected in agricultural soil. However, existing studies have focused on the residual and environmental behavior of maternal TCs, and few studies have looked at the ecotoxicity of their 4-epimers in soil. In this study, the degradation and interconversion of tetracycline (TC), oxytetracycline (OTC) and their 4-epimers (4-epitetracycline, ETC; 4-epioxytetracycline, OTC) were revealed. Their effects on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and bacterial community in soil were also investigated in comparison. The results showed that the 4-epimers could be substantially transformed to their parents and degraded as a whole. The degradation rates of four selected pollutants are followed: TC > OTC > ETC > EOTC. This indicated that when TCs entered the soil, part of TCs transformed into slower-degraded 4-epimers, and these 4-epimers could also be converted back to their antibiotic parents, causing the long-term residue of TCs in soil. When added to the soil alone, TC and OTC significantly promoted the proliferation of most ARGs and MGEs, among them, trb-C, IS1247 and IS1111 were the top three genes in abundance. ETC and EOTC had little effect at the beginning. However, as the 4-epimers continuously converted into their parents after one month of cultivation, ETC and EOTC treatments showed similar promoting effect on ARGs and MGEs, indicating that the effect of ETC and EOTC on soil resistome was lagged and mainly caused by their transformed parents. Nocardioides, unclassified_Rhizobiaceae, norank_Sericytochromatia, Microlunatus, Solirubrobacter and norank_67-14 were the most frequent hosts of ARGs, Most of which belong to the phylum Actinobacteria. Due to their large transformation to TCs, slow degradation rate and potential effects on soil microbes and ARGs, the harm of TCs' 4-epimers on soil ecosystem cannot be ignored.

Products from Photolysis Reactions of Tetracycline Mediated by Clay and Humic Substance Induce Contrasting Expressions of Target Resistance Genes

Phototransformation is a key process affecting the fate of many antibiotics in the environment, but little is known about whether their photoproducts exert selective pressure on bacteria by inducing antibiotic resistance genes (ARGs). Here, we examined the expression of tetracycline resistance gene tet(M) of a fluorescent Escherichia coli whole-cell bioreporter influenced by the phototransformation of tetracycline. The presence of suspended smectite clay (montmorillonite or hectorite, 1.75 g/L) or dissolved humic substance (Pahokee Peat humic acid or Pahokee peat fulvic acid, 10 mg C/L) in aqueous solutions markedly facilitated the transformation of tetracycline (initially at 400 μg/L) with half-life shortened by 1.4-2.6 times. Despite the similar phototransformation ratios (80-90%) of the total loaded tetracycline after 60 min irradiation, the decreased ratios of cell fluorescence intensity (which was proportional to the expression amount of ARG tet(M)) were much higher with the two clays (94 and 93%) than with the two humic substances (44 and 69%) when compared to the respective dark controls. As illustrated by mass spectroscopic and chemical analyses, tetracycline was proposed to be mainly transformed to amide (ineffective in inducing ARGs) with the presence of clays by reaction with self-photosensitized singlet oxygen (1O2), while the humic substances might catalyze the production of another two demethylated and/or deaminated compounds (still effective in inducing ARGs) in addition to the amide compound via reaction with triplet excited state dissolved organic matter (3DOM*). As clay minerals and humic substances are important soil constituents and ubiquitously present in surface environments, the observed clay and humic-dependent photooxidation pathways of tetracycline and the differing selective pressures of the associated products highlight the need for monitoring the transformation compounds of antibiotics and provide critical insight into the development of antibiotic treatment protocols.

Tetracycline antibiotics in agricultural soil: Dissipation kinetics, transformation pathways, and structure-related toxicity

Tetracyclines (TCs) are the most common antibiotics in agricultural soil, due to their widespread usage and strong persistence. Biotic and abiotic degradation of TCs may generate toxic transformation products (TPs), further threatening soil ecological safety. Despite the increasing attention on the environmental behavior of TCs, a systematic review on the dissipation of TCs, evolution of TPs, and structure-toxicity relationship of TCs in agricultural soil remains lacking. This review aimed to provide a comprehensive overview of the environmental fate of TCs in agricultural soil. We first introduced the development history and structural features of different generations of TCs. Then, we comparatively evaluated the dissipation kinetics, transportation pathways, and ecological impacts of three representative TCs, namely tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), in agricultural soil. The results showed that the dissipation kinetics of TCs generally followed the first-order kinetic model, with the median dissipation half-lives ranging from 20.0 to 38.8 days. Among the three TCs, OTC displayed the lowest dissipation rates due to its structural stability. The typical degradation pathways of TCs in soil included epimerization/isomerization, demethylation, and dehydration. Isomerization and dehydration reactions may lead to the formation of more toxic TPs, while demethylation was accompanied by the alteration of the minimal pharmacophore of TCs thus potentially reducing the toxicity. Toxicological experiments are urgently needed in future to comprehensively evaluate the ecological risks of TCs in agricultural soil.

Unraveling the photochemical behavior of dissolved organic matter derived from hydrothermal carbonization process water: Insights from molecular transformation and photoactive species

Hydrothermal carbonization process water (HTPW) has been utilized as a substitute for chemical fertilizers in agricultural applications. However, the input of HTPW into paddy water, particularly the significant proportion of dissolved organic matter (DOM) in HTPW (DOM-HTPW), directly engages in photochemical transformations, a phenomenon often overlooked. This study observed a consistent decrease in humification (SUVA280, 7.7-53.9%) and aromaticity (SUVA254, 6.1-40.0%) of DOM-HTPW after irradiation. The primary active photobleaching components of DOM-HTPW varied depending on the feedstock, such as protein for chicken manure DOM-HTPW and lignin for rice straw DOM-HTPW. The photochemical activity of DOM-HTPW was augmented by its lower molecular weight and higher hydrophilic composition, particularly evident in chicken manure DOM-HTPW, which exhibited higher generation rates for 1O2 (35.1-37.1%), 3DOM* (32.8-43.9%), and O2•- (28.6-48.8%) as measured by molecular probes. DOM-HTPW effectively facilitated the phototransformation of tetracycline, with the contribution of O2•- being more significant than 3DOM* and 1O2. These findings shed new light on the understanding the photochemical processes of DOM-HTPW as exogenous DOM and the interconnected fate of contaminants in aquatic environments.

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.

Carbon dots-based fluorescent molecularly imprinted photonic crystal hydrogel strip: Portable and efficient strategy for selective detection of tetracycline in foods of animal origin

Rapid, portable, and sensitive detection of tetracycline (TC) is crucial for the environment and human health. In this study, we developed carbon dots (CDs)-based fluorescent molecularly imprinted photonic crystal hydrogel (FMIPH) strips for TC detection in animal-derived foods. CDs emit fluorescent signals, and molecularly imprinted polymers provide specific recognition sites for TC. Inverse opal photonic crystals afford stable 3D macroporous mass transfer channels that considerably reduce binding time between TC and the strips. The portable FMIPH strip exhibited a linear fluorescence response to TC in the concentration range of 0.1-50 μg mL-1, with a detection limit of 0.067 μg mL-1. Good recoveries of TC (93.86-112.59%) were observed in TC-spiked commercially available pork, eggs, and milk. A combination of FMIPH strips with a portable fluorescent reading device could achieve sensitive, on-site, and real-time detection of TC in animal-derived foods.

Tetracycline hydrochloride degradation in polarity inverted microbial fuel cells: Performance, mechanisms and microbiology

Tetracycline antibiotics are widely used in veterinary medicine, human therapy and agriculture, and their presence in natural water raises environmental concerns. In this study, more than 94% of tetracycline hydrochloride (TCH) could be rapidly degraded within 48 h in polarity-inverted microbial fuel cells. The electrochemically active bacteria had the best electrochemical performance at 1 mg/L of TCH with the minimum internal resistance of 77.38 Ω. The electron-rich functional groups of TCH were continuously attacked and finally degradated into small molecules in three possible degradation pathways. Microbial community structure analysis showed that Comamonas and Shinella were enriched at the electrode as polarity-inverted bacteria. Genomic analysis showed that both direct and indirect electron transfer participated in the degradation of TCH in polarity-inverted microbial fuel cell (MFC) and the functional genes related to electrical conductivity in polarity-inverted MFC were more enriched on the electrode surface than non-polarity-inverted MFC. This study can facilitate further investigations about the biodegradation of TCH in polarity-inverted microbial fuel cell.

Transformation products of antibacterial drugs in environmental water: Identification approaches based on liquid chromatography-high resolution mass spectrometry

In recent years, the presence of antibiotics in the aquatic environment has caused increasing concern for the possible consequences on human health and ecosystems, including the development of antibiotic-resistant bacteria. However, once antibiotics enter the environment, mainly through hospital and municipal discharges and the effluents of wastewater treatment plants, they can be subject to transformation reactions, driven by both biotic (e.g. microorganism and mammalian metabolisms) and abiotic factors (e.g. oxidation, photodegradation, and hydrolysis). The resulting transformation products (TPs) can be less or more active than their parent compounds, therefore the inclusion of TPs in monitoring programs should be mandatory. However, only the reference standards of a few known TPs are available, whereas many other TPs are still unknown, due to the high diversity of possible transformation reactions in the environment. Modern high-resolution mass spectrometry (HRMS) instrumentation is now ready to tackle this problem through suspect and untargeted screening approaches. However, for handling the large amount of data typically encountered in the analysis of environmental samples, these approaches also require suitable processing workflows and accurate tandem mass spectra interpretation. The compilation of a suspect list containing the possible monoisotopic masses of TPs retrieved from the literature and/or from laboratory simulated degradation experiments showed unique advantages. However, the employment of in silico prediction tools could improve the identification reliability. In this review, the most recent strategies relying on liquid chromatography-HRMS for the analysis of environmental TPs of the main antibiotic classes were examined, whereas TPs formed during water treatments or disinfection were not included.

Enhanced photolysis of tetracycline by Zn(II): Role of complexation

Zn(II) is a necessary additive during antibiotic production and aquaculture, leading to the coexistence of Zn(II) and antibiotics in aquatic environment, especially in receiving waters of pharmaceutical and aquaculture wastewater. However, the roles of Zn(II) in the photochemical behavior of antibiotics are still not clear, which limits the understanding of the fate of antibiotic in nature. In this study, tetracycline (TC) was selected as typical antibiotic to evaluate the effect of Zn(II) on antibiotic photolysis. The removal of TC was accelerated by 22.75 % with TC:Zn(II) molar ratio at 1:5. The mechanism of Zn(II)-induced TC photolysis was explored via reactive oxygen species (ROS) analysis and density functional theory (DFT) calculation for the first time. Zn(II) could enhance the formation of TC excited states and further produce more singlet oxygen (12.54 % higher than control group) to promote indirect photolysis. Besides, Zn(II) could react with TC via complexation, and the complex was more vulnerable to attack by reactive oxygen species due to more active sites. Furthermore, the structure and toxicity of intermediates were identified with mass spectrometer, T.E.S.T. and ECOSAR software. Zn(II) hardly changed the degradation path of TC, and TC was mainly degraded via ring opening, demethylation, deamidation, and hydrogen abstraction with more toxic intermediates than the parent molecule. This work is significant to better understand the environmental fate of antibiotics, and also provides new insight into wastewater treatment in the pharmaceutical and aquaculture industry.

Construction of Bi/BiOI/BiOCl Z-scheme photocatalyst with enhanced tetracycline removal under visible light

Bi/BiOI/BiOCl composite photocatalyst was constructed by one-step stirring approach at ambient environment to remove of tetracycline (TC) antibiotics via photodegradation in aqueous medium. A systematic discussion of the architecture, composition, formation, photochemical performance and photocatalytic activity of Bi/BiOI/BiOCl was carried out. By adjusting the experimental conditions, it was found that the Bi/BiOI/BiOCl photocatalyst obtained by using 0.7 mmol NaBH4, I/Cl = 5% and reacting for 6 h had the greatest removal performance. Under visible light irradiation, the photocatalytic degradation efficiency of TC reached 90.3% within 60 min, surpassing that of single BiOCl and BiOI. Through the active species removal experiment, it was determined that •O2- made a primary contribution to the photocatalytic degradation process. Moreover, the formation of Z-scheme heterojunction in Bi/BiOI/BiOCl was discussed, analyzing the photocatalytic mechanism and TC degradation pathway. The ecological toxicity of TC solution before and after degradation to rice seedlings was preliminarily tested. This study provides an idea for one-step synthesis of bismuth-based composite photocatalysts, with potential applications in the photocatalytic degradation of antibiotics.

Metagenomic insights into the nitrogen metabolism, antioxidant pathway, and antibiotic resistance genes of activated sludge from a sequencing batch reactor under tetracycline stress

Tetracycline is prevalent in wastewater treatment plants and poses a potential threat to biological nitrogen removal under long-term exposure. In the present study, the influence of different tetracycline concentrations on the nitrogen removal, bioactivity response, and the spread of antibiotic resistance genes (ARGs) was assessed in sequencing batch reactor (SBR). The nitrogen removal efficiency, nitrification rate, and denitrification rate and their corresponding enzymatic activities gradually decreased with an increase in tetracycline concentration from 0.5 to 15 mg/L. The remarkable toxicity induced by tetracycline led to a significant increase in the peroxidation and the response of antioxidant system, as evidenced by strengthened antioxidant enzymatic activity and abundant genes (SOD12, katG, PXDN, gpx, and apx). Tetracycline addition significantly inhibited the ammonia-oxidizing bacterium Nitrosomonas and functional genes (amoA, amoB, and amoC). The presence of tetracycline decreased the abundance of citrate synthase and genes (CS, IDH3, and acnA) and interfered with carbon source metabolism, leading to impaired bioactivity and treatment performance. In addition, the presence of tetracycline induces diversity and differences in ARGs. The results provide reliable basic data for a deeper understanding of the effects of tetracycline on the nitrogen removal performance of bioreactors and provide a theoretical basis to build a promising strategy for relieving antibiotic-caused process fluctuations.

Integrated transcriptomic, proteomic and metabolomic analysis provides new insights into tetracycline stress tolerance in pumpkin

The aim of this study was to conduct transcriptomic, proteomic, and metabolomic analysis to provide a comprehensive view of plant response to tetracycline stress. Pumpkin seeds were cultured for 7 days without or with tetracycline at 10 mg/L. Pumpkin roots showed excessive growth inhibition, but not yet strong growth restraining in cotyledons. Tetracycline affected the abundance of metabolites related to flavonoid biosynthesis and amino acid metabolism. Main changes of metabolites in flavonoid biosynthesis were consistent with mRNA changes. Amino acid changes are mainly mediated by proteins or mRNAs. To be specific, tetracycline treatment increased the levels of rutin, caffeate, cinnamaldehyde, 4-hydroxycinnamic acid, ferulic acid, naringenin, apigenin, luteolin, (-)-epigallocatechin, astragalin, L-serine, and glutathione and the transcript levels related to these compounds; and decreased the levels of indole pyruvate, indole acetaldehyde, L-arginine, S-adenosylhomocysteine, L-glutamine, and gamma-glutamylcysteine and the transcript levels related to these compounds. Tetracycline treatment also increased the levels of oxoglutaric acid, L-glutamic acid, gamma-aminobutyric acid, and gamma-glutamylalanine and enzymes involved in their production; and decreased the levels of L-isoleucine, L-valine, and L-leucine and enzymes involved in their production. We elucidated several biological processes (e.g. phenylpropanoid/flavonoid biosynthesis pathways, amino acid metabolic pathways) that were altered by tetracycline, and provided a multi-omic perspective on the mechanisms underlying the response to tetracycline stress in pumpkin roots. We provide a useful reference for the development of environmental quality management methods.

Enhancing the photodegradation of tetracycline in aquaculture wastewater via iron(III)-alginate: Degradation pathway transformation and toxicity reduction

Tetracycline's (TC) incomplete self-photolysis by light irradiation generally produces toxic intermediate products, which posing serious harm to the aqueous environment. In order to diminish the environmental risks of TC self-photolysis, an iron(III)-alginate (Fe-SA) hydrogel assisted photocatalytic method was developed and the underlying mechanisms was also analyzed in this work. Under simulated sunlight, the photo-degradation efficiency of TC was 61.1% at pH 7.0 within 2 h. Importantly, four of the seven intermediate products that identified during the self-photolysis of TC were found toxic based on QSAR analysis. In contrast, the removal efficiency of TC could be improved to 87.4% by adding Fe-SA under the same conditions. Moreover, only two relatively weakly toxic intermediate products were detected after exposing to the Fe-SA photocatalytic system, indicating a significant reduction of the potential ecological risks caused by TC self-photolysis. Furthermore, the determination of reactive oxidation species (ROS) demonstrated that the addition of Fe-SA primarily facilitated the degradation of TC and the related toxic intermediate products through assisting the free radical (∙OH and ∙O2-) photocatalytic degradation pathway. Additionally, the photocatalytic application under actual sunlight conditions and the reusability experiments of Fe-SA further confirmed its effectiveness and low cost in removing TC. This study revealed the photodegradation mechanisms of TC from the perspective of the self-photolysis process, and also offering new insights into the removal of TC pollution in the environment.

Effect of microplastics on the degradation of tetracycline in a soil microbial electric field

The degradation of organic pollutants and the adsorption of organic pollutants onto microplastics (MPs) in the environment have recently been intensively studied, but the effects of biocurrents, which are widespread in various soil environments, on the environmental behavior of MPs and antibiotic pollutants have not been reported. In this study, it was found that polylactic acid (PLA) and polyvinyl chloride (PVC) MPs accelerated the mineralization of humic substances in microbial electrochemical systems (MESs). After tetracycline (TC) was introduced into the MESs, the internal resistance of the soil MESs decreased. Additionally, the presence of MPs enhanced the charge output of the soil MESs by 40% (PLA+TC) and 18% (PVC+TC) compared with a control group without MPs (424 C). The loss in MP mass decreased after TC was added, suggesting a promotion of TC degradation rather than MP degradation for charge output. MPs altered the distribution of the highest occupied molecular orbitals and lowest unoccupied molecular orbitals of TC molecules and reduced the energy barrier for the TC hydrolysis reaction. The microbial community of the plastisphere exhibited a greater ability to degrade xenobiotics than the soil microbial community, indicating that MPs were hotspots for TC degradation. This study provides the first glimpse into the influence of MPs on the degradation of TC in MESs, laying a theoretical and methodological foundation for the systematic evaluation of the potential risks of environmental pollutants in the future.

The performance and mechanism of tetracycline and ammonium removal by Pseudomonas sp. DX-21

To remove ammonium and tetracycline (TC) from wastewater, a new strain, DX-21, was isolated and exhibited simultaneous removal ability. The performance of DX-21 in TC removal, its removal mechanism, and the potential toxicities of the degradation products were investigated with genomics, mass spectrometry, density functional theory calculations, quantitative structure-activity relationship analyses, and Escherichia coli exposure experiments. DX-21 exhibited removal of ammonium (9.64 mg·L-1·h-1) via assimilation, and TC removal (0.85 mg·L-1·h-1) primarily occurred through cell surface bio-adsorption and biodegradation. Among the 12 identified degradation products, the majority exhibited lower toxicities than TC. Moreover, potential degradation pathways were proposed, including hydroxylation and deamination. Furthermore, DX-21 possessed TC resistance genes, various oxygenases and peroxidases that could potentially contribute to TC degradation. DX-21 colonized activated sludge and significantly enhanced the biodegradation of TC. Therefore, DX-21 showed potential for treating wastewater containing both ammonium and TC.

Jasmine waste derived biochar as green sulfate catalysts dominate non-free radical paths efficiently degraded tetracycline

Because of the potential environmental harm caused by the extensive application of tetracycline (TC), this study used jasmine waste rich in organic matter as a precursor and one-step carbonization into metal-free carbon-based materials to efficiently activate peroxymonosulfate (PMS) toward degrading TC. The jasmine waste biochar (JWB) with a heating rate of 10 °C min-1 and a heating temperature of 700 °C was selected as the most suitable material based on its catalytic performance. The effects of catalyst dose, PMS dose, initial pH value, coexisting inorganic anions and TC concentration on the JWB/PMS/TC system were thoroughly optimized. The results showed that the degradation efficiency of TC by JWB/PMS system was 90%. Meanwhile, the combination of electron paramagnetic resonance, masking experiments and X-ray photoelectron spectrometry confirmed that JWB degraded TC mainly through the non-radical radical pathway of 1O2 oxidation and mediated the electron transfer to PMS. In addition, some degradation products were analyzed by LC-MS and possible degradation pathways of the system were proposed. Therefore, this paper proposes a novel method for recycling jasmine waste and providing a low-cost catalyst for the oxidation treatment of refractory organic matter.

Nitrogen-Doped Carbon Dots Encapsulated a Polyoxomolybdate-Based Coordination Polymer as a Sensitive Platform for Trace Tetracycline Determination in Water

The requirement of simple, efficient and accurate detection of tetracycline (TC) in water environments poses new challenges for sensing platform development. Here, we report a simple method for TC sensing via fluorescence detection based on metal-organic coordination polymers (MOCPs, (4-Hap)4(Mo8O26)) coated with nitrogen-doped carbon dots (NCDs). These NCDs@(4-Hap)4(Mo8O26) composites showed excellent luminescence features of NCDs with stable bright-blue emission under UV light. The results of the sensing experiment showed that the fluorescence of NCDs@(4-Hap)4(Mo8O26) can be quenched by TC (166 µM) with 94.1% quenching efficiency via the inner filter effect (IFE) in a short time (10 s), with a detection limit (LOD) of 33.9 nM in a linear range of 8-107 µM. More significantly, NCDs@(4-Hap)4(Mo8O26) showed a high selectivity for TC sensing in the presence of anions and metal cations commonly found in water environments and can be reused in at least six cycles after washing with alcohol. The potential practicality of NCDs@(4-Hap)4(Mo8O26) was verified by sensing TC in real water samples with the standard addition method, and satisfactory recoveries from 91.95% to 104.72% were obtained.

Degradation of tetracyclines via calcium peroxide activation by ultrasonic: Roles of reactive species, oxidation mechanism and toxicity evaluation

Tetracyclines (TC) frequently detected in the aqueous environment pose threats to humans and ecosystems. The synergistic technology coupling ultrasound (US) and calcium peroxide (CaO₂) has a great potential to abate TC in wastewater. However, the degradation efficiency and detailed mechanism of TC removal in the US/CaO₂ system is unclear. This work was carried out to assess the performance and mechanism of TC removal in the US/CaO₂ system. The results demonstrated that 99.2% of TC was degraded by the combination of 15 mM CaO₂ with ultrasonic power of 400 W (20 kHz), but only about 30% and 4.5% of TC was removed by CaO₂ (15 mM) or US (400 W) alone process, respectively. Experiments using specific quenchers and electron paramagnetic resonance (EPR) analysis indicated that the generation of hydroxyl radicals (•OH), superoxide radicals (O₂^-•), and single oxygen (¹O₂) in the process, whereas •OH and ¹O₂ were mainly responsible for the degradation of TC. The removal of TC in the US/CaO₂ system has a close relationship with the ultrasonic power, the dosage of CaO₂ and TC, and the initial pH. The degradation pathway of TC in the US/CaO₂ process was proposed based on the detected oxidation products, and it mainly included N,N-dedimethylation, hydroxylation, and ring-opening reactions. The presence of 10 mM common inorganic anions including chloridion (Cl^-), nitrate ion (NO₃^-), sulfate ion (SO₄^2-), and bicarbonate ion (HCO₃^-) showed negligible influences on the removal of TC in the US/CaO₂ system. The US/CaO₂ process could efficiently remove TC in real wastewater. Overall, this work firstly demonstrated that •OH and ¹O₂ mainly contributed to the removal of pollutants in the US/CaO₂ system, which was remarkable for understanding the mechanisms of CaO₂-based oxidation process and its future application.

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.