Indirect photodegradation of sulfadiazine in the presence of DOM: Effects of DOM components and main seawater constituents

Mechanistic insight into the impact of interaction between goethite and humic acid on the photooxidation and photoreduction of bifenthrin

Numerous application of pyrethroid insecticides has led to their accumulation in the environment, threatening ecological environment and human health. Its fate in the presence of iron-bearing minerals and natural organic matter under light irradiation is still unknown. We found that goethite (Gt) and humic acid (HA) could improve the photodegradation of bifenthrin (BF) in proper concentration under light irradiation. The interaction between Gt and HA may further enhance BF degradation. On one hand, the adsorption of HA on Gt may decrease the photocatalytic activity of HA through decreasing HA content in solution and sequestering the functional groups related with the production of reactive species. On the other hand, HA could improve the photocatalytic activity of Gt through extending light absorption, lowing of bandgap energy, hindering the recombination of photo-generated charges, and promoting the oxidation and reduction reaction on Gt surface. The increased oxygen vacancies on Gt surface along with the reduction of trivalent iron and the nucleophilic attack of hole to surface hydroxyl group contributed to the increasing photocatalytic activity of Gt. Electron paramagnetic resonance and quenching studies demonstrated that both oxidation species, such as hydroxyl radical (•OH) and singlet oxygen (1O2), and reducing species, such as hydrogen atoms (H•) and superoxide anion radical (O2•-), contributed to BF degradation in UV-Gt-HA system. Mass spectrometry, ion chromatography, and toxicity assessment indicated that less toxic C23H22ClF3O3 (OH-BF), C9H10ClF3O (TFP), C14H14O2 (OH-MBP), C14H12O2 (MBP acid), C14H12O3 (OH-MBP acid), and chloride ions were the main degradation products. The production of OH-BF, MPB, and TFP acid through oxidation and the production of MPB and TFP via reduction were the two primary pathways of BF degradation.

Multiple interface coupling on natural tourmaline enables high-efficiency removal of antibiotic: Superior property and mechanism

Reasonably designing highly active, environmentally friendly, and cost-effective catalysts for efficient elimination of pollutants from water is desirable but challenging. Herein, an efficient heterogeneous photo-Fenton catalyst tourmaline (TM)/tungsten oxide (WO3-x) (named TW10) containing tungsten/boron/iron (W/B/Fe) synergistic active centers and 90% of cheap natural tourmaline (TM) mineral rich in Fe and B elements. The TW10 catalyst can quickly activate peroxymonosulfate (PMS) to generate massive active free radicals, which may induce the rapid and efficient degradation of tetracycline (TC). The TW10/PMS/Visible light system can effectively degrade up to 98.7% of tetracycline (TC) in actual waters (i.e. seawater, Yellow River, and Yangtze River water), and the catalytic degradation rates reach 1.65, 5.569, and 2.38 times higher than those of TM, WO3-x, and commercial P25 (Degussa, Germany), respectively. In addition, the catalyst can be recycled and reused multiple times. Electron spin resonance spectroscopy (EPR), X-ray photoelectron spectroscopy (XPS), and liquid chromatograph-mass spectrometer (LC-MS) analyses confirm that the synergistic catalytic effect of W/B/Fe sites on the TW10 catalyst accelerates the electron transfer between Fe(II) and Fe(III), as well as between W(V) and W(VI), and thus promotes the rapid degradation of TC. The catalytic reaction mechanism and degradation pathway of TC were explored. This work provides a feasible route for the design and development of new eco-friendly and efficient catalyst.

Recent advances in the role of dissolved organic matter during antibiotics photodegradation in the aquatic environment

The presence of residual antibiotics in the environment is a prominent issue. Photodegradation behavior is an important way of antibiotics reduction, which is closely related to dissolved organic matter (DOM) in water. The review provides an overview of the latest advancements in the field. Classification, characterization of DOM, and the dominant mechanisms for antibiotic photodegradation were discussed. Furthermore, it summarized and compared the effects of DOM on different antibiotics photodegradation. Moreover, the review comprehensively considered the factors influencing the photodegradation of antibiotics in the aquatic environment, including the characteristics of light, temperature, dosage of DOM, concentration of antibiotics, solution pH, and the presence of coexisting ions. Finally, potential directions were proposed for the development of predictive models for the photodegradation of antibiotics. Based on the review of existing literature, this paper also considered several pathways for the future study of antibiotic photodegradation. This study allows for a better understanding of the DOM's environmental role and provides important new insights into the photochemical fate of antibiotics in the aquatic environment.

Revealing the generation of reactive oxygen species in hydrochar and pyrochar: Insight into rational regulation of free radicals and catalytic mechanism

The removal of organic pollutants by biochar has been extensively studied. However, the differences in the removal mechanisms of contaminants by biochar obtained from different preparation techniques have not been thoroughly elucidated. In this study, the catalytic performances of hydrochar (HC) and pyrochar (PC) were compared in the dark and light. Owing to more persistent free radicals (PFRs), greater defects and stronger charge transfer ability on the surface, PC could produce a certain concentration of superoxide radicals (•O2-) even in the dark, making its degradation efficiency for benzoic acid (BA) 11% higher than that of HC. On the contrary, when the light was turned on, HC rather than PC can generate a higher amount of hydroxyl radical (•OH), resulting in an 11% higher degradation efficiency of BA compared to PC. The improvement of catalytic performance in HC originated from its oxygen-containing functional groups (OFGs), which was beneficial for its effective production of singlet oxygen (1O2) and ·OH under light exposure. For PC, its photocatalytic activity depended mainly on the formation of 1O2 induced by the triplet of DOM (dissolved organic matter), but the lack of oxidative ·OH in its system leads to a lower degradation efficiency than that of HC. To prove the universal applicability of this rule for biochar materials, HC and PC materials obtained from soybean residue were also prepared for degrading BA. This work is devoted to an in-depth exploration of the catalytic activation mechanism of biochar obtained by different technological methods, and can create conditions for the generation of more dominant reactive oxygen species (ROS) on biochar, thus providing the guidance for environmental remediation.

Photo-oxidation of Micro- and Nanoplastics: Physical, Chemical, and Biological Effects in Environments

Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.

DOM optical parameters as a tool to understand degradation of phenolic contaminants of emerging concern

Composition and source of dissolved organic matter (DOM) in water influence the rate of production of reactive intermediates (RIs), affecting the photodegradation of phenolic contaminants of emerging concern (PhCECs). However, this relationship has not been fully quantified. Here, for the first time, we propose a mechanism for photodegradation of a surrogate of PhCECs, p-cresol, in different DOM standard solutions under simulated sunlight irradiation. More importantly, the correlation of DOM optical parameters and p-cresol photodegradation kinetic parameters was determined by Pearson correlation. Results showed that indirect photodegradation was the only degradation pathway for p-cresol, mainly through reaction with excited triplet state of dissolved organic matter (3DOM*). Singlet oxygen (1O2) and hydroxyl radical (•OH) hindered degradation of p-cresol by decreasing the steady state concentration of 3DOM*. Moreover, less aromatic and smaller molecular size DOM showed higher steady-state concentration and quantum yield of 1O2, and 3DOM*, resulting in faster p-cresol photodegradation. Finally, 7 out of 8 optical parameters showed strong correlation with the p-cresol photodegradation rate constant. The mechanism and correlations found are a potential tool to predict PhCECs photodegradation in water using DOM optical parameters.

Effect of dissolved organic matter on sulfachloropyridazine photolysis in liquid water and ice

Dissolved organic matter (DOM) is an ubiquitous component of environmental snow and ice, which can absorb light and produce reactive species (RS) and thus is of importance in ice photochemistry. The photodegradation of sulfachloropyridazine (SCP) without and with DOM present in liquid water and ice were investigated in this study. The photodegradation rate constants for SCP without DOM present was enhanced by 52.5 % in ice relative to liquid water, likely due to the enhanced role of SCP self-sensitized RS in ice. DOM significantly promoted SCP photolysis in both liquid water and ice, which was mainly attributed to roles of singlet oxygen (1O2) and triplet excited-state DOM (3DOM*) generated from DOM. 1O2 production from DOM was significantly enhanced in ice relative to liquid water. Hydroxyl radical (•OH) production from DOM in ice was similar to those in liquid water. Enhancement in 3DOM* production in ice was observed at low DOM concentrations. Suwannee River Fulvic Acid (SRFA) and Elliott Soil Humic Acid (ESHA) exhibited differences in RS production in liquid water and ice, as well as in enhancement of 1O2 and 3DOM* produced in ice relative to liquid water. DOM induced reaction pathways of SCP different from those without DOM present, and therefore affected toxicity of SCP photoproducts. There were differences in photodegradation pathways of SCP as well as in toxicity of SCP photoproducts between liquid water and ice.

Simultaneous degradation of sulfadiazine and dissolved organic matter based on low-impact development facilities

Sulfadiazine (SD) is a common antibiotic administered to treat bacterial infections in livestock, and its fate and migration are greatly affected by dissolved organic matter (DOM). The soil infiltration system [a typical low-impact development (LID) facility] can significantly alter DOM properties during runoff pollution, thus affecting the complexation of SD with DOM. Here, the binding characteristics of different DOM components and SD in the soil infiltration system were explored using spectroscopic techniques (excitation-emission matrices, parallel factor analysis, and synchronous fluorescence spectroscopy). Combined with the weakening of DOM fluorescence intensity and 78.63% reduction in mean SD concentration following treatment, synchronous degradation may have occurred. The binding sequence of SD and DOM fluorophores was further explored using two-dimensional correlation spectroscopy. Effluent DOM showed greater sensitivity to SD and more binding sites than influent DOM. Moreover, hydrophobic protein-like substances exhibited higher log K_M values than other fluorescent components, indicating that protein-like components play significant roles in SD complexation. The soil percolation system improved the complexation stability and binding sequence of fulvic-like substances. Thus, SD-DOM can be intercepted and degraded using LID facilities to reduce the risk of SD in aquatic environments.

Elucidating microalgae-mediated metabolism for sulfadiazine removal mechanism and transformation pathways

Sulfadiazine (SDZ) as a typical sulfonamide antibiotic is commonly detected in wastewater, and its removal mechanism and transformation pathways in microalgae-mediated system remain unclear. In this study, the SDZ removal through hydrolysis, photodegradation, and biodegradation by Chlorella pyrenoidosa was investigated. Higher superoxide dismutase activity and biochemical components accumulation were obtained under SDZ stress. The SDZ removal efficiencies at different initial concentrations were 65.9-67.6%, and the removal rate followed pseudo first-order kinetic model. Batch tests and HPLC-MS/MS analyses suggested that biodegradation and photodegradation through the reactions of amine group oxidation, ring opening, hydroxylation, and the cleavage of S-N, C-N, C-S bond were dominant removal mechanisms and pathways. Characteristics of transformation products were evaluated to analyze their environmental impacts. High-value products of lipid, carbohydrate, and protein in microalgae biomass presented economic potential of microalgae-mediated metabolism for SDZ removal. The findings of this study broadened the knowledge for the microalgae self-protection from SDZ stress and provided a deep insight into SDZ removal mechanism and transformation pathways.

Quantitative structure-activity relationship models for the reaction rate coefficients between dissolved organic matter and PPCPs

To predict PPCPs' photolysis rate in natural aquatic environment, it is essential to grasp the reaction rates between DOM and PPCPs, yet there are few measured data and no prediction models for this important photochemical parameter. To address this, a reaction rate coefficient (α_DOM) was defined to describe the apparent rate of DOM-involved photoreaction for PPCPs. The measured α_DOM values for 40 PPCPs in 9 DOM samples varied dramatically, ranging from (-2.1 ± 0.1)× 10¹⁰ to (2.2 ± 0.1)× 10¹¹ M^-1 s^-1. Then the quantitative structure-activity relationship (QSAR) models were developed using chemical and water quality descriptors via the random forest method. We initially separated positive and negative values by a classifier with an AUC value of 0.965, followed by the construction of regression models for positive and negative values, respectively, using a regressor. Positive models achieved satisfactory goodness-of-fit and predictive ability (R²_adj=0.92 and Q²_ext=0.86), while negative models demonstrated acceptable performance (R²_adj=0.71 and Q²_ext=0.70). Finally, a comprehensive photolysis model that incorporates the QSAR models for α_DOM was established and the significance of water quality parameters was emphasized through sensitive analysis. This model enables more elaborate predictions of PPCPs' photolysis rates in various water samples, providing valuable assistance for forecasting PPCPs' environmental fate.

Mechanistic investigation of direct photodegradation of chloroquine phosphate under simulated sunlight

Chloroquine phosphate (CQ) is an antiviral drug for Coronavirus Disease 2019 and an old drug for treatment of malaria, which has been detected in natural waters. Despite its prevalence, the environmental fate of CQ remains unclear. In this study, the direct photodegradation of CQ under simulated sunlight was investigated. The effect of various parameters such as pH, initial concentration and environmental matrix were examined. The photodegradation quantum yield of CQ (4.5 × 10^-5-0.025) increased with the increasing pH value in the range of 6.0-10.0. The electron spin resonance (ESR) spectrometry and quenching experiments verified that the direct photodegradation of CQ was primarily associated with excited triplet states of CQ (³CQ*). The common ions had negligible effect and humic substances exhibited a negative effect on CQ photodegradation. The photoproducts were identified using high-resolution mass spectrometry and the photodegradation pathway of CQ was proposed. The direct photodegradation of CQ involved the cleavage of the C-Cl bond and substitution of the hydroxyl group, followed by further oxidation to yield carboxylic products. The photodegradation processes were further confirmed by the density functional theory (DFT) computation for the energy barrier of CQ dichlorination. The findings contribute to the assessment of the ecological risk associated with the overuse of Coronavirus drugs during global public health emergencies.

Photochemical reaction of glucocorticoids in aqueous solution: Influencing factors and photolysis products

Glucocorticoids (GCs), as endocrine disruptors, have attracted widespread attention due to their impacts on organisms' growth, development, and reproduction. In the current study, the photodegradation of budesonide (BD) and clobetasol propionate (CP), as targeted GCs, was investigated including the effects of initial concentrations and typical environmental factors (Cl^-, NO₂^-, Fe³⁺, and fulvic acid (FA)). The results showed that the degradation rate constants (k) were 0.0060 and 0.0039 min^-1 for BD and CP at concentration of 50 μg·L^-1, and increased with the initial concentrations. Under the addition of Cl^-, NO₂^-, and Fe³⁺ to the GCs/water system, the photodegradation rate was decreased with increasing Cl^-, NO₂^-, and Fe³⁺ concentrations, which were in contrast to the addition of FA. Electron resonance spectroscopy (EPR) analysis and the radical quenching experiments verified that GCs could transition to the triplet excited states of GCs (³GCs*) for direct photolysis under irradiation to undergo, while NO₂^-, Fe³⁺, and FA could generate ·OH to induce indirect photolysis. According to HPLC-Q-TOF MS analysis, the structures of the three photodegradation products of BD and CP were elucidated, respectively, and the phototransformation pathways were inferred based on the product structures. These findings help to grasp the fate of synthetic GCs in the environment and contribute to the understanding of their ecological risks.

Aquatic photolysis of high-risk chemicals of emerging concern from secondary effluent mediated by sunlight irradiation for ecological safety and the enhanced methods

Natural sunlight can reduce the chemicals of emerging concern (CECs) and biological effects from the discharged domestic wastewater. But the aquatic photolysis and biotoxic variations of specific CECs detected in secondary effluent (SE) were not clear. In this study, 29 CECs were detected in the SE, and 13 medium- and high-risk CECs were identified as target chemicals based on their ecological risk assessment. To comprehensively explore the photolysis properties of the identified target chemicals, the direct and self-sensitized photodegradation of the target chemicals, even the indirect photodegradation in the mixture, were investigated and compared with these photodegradation in the SE. Of the 13 target chemicals, only five chemicals (including dichlorvos (DDVP), mefenamic acid (MEF), diphenhydramine hydrochloride (DPH), chlorpyrifos (CPF), and imidacloprid (IMI)) underwent direct and self-sensitized photodegradation processes. The removal of DDVP, MEF, and DPH was attributed to self-sensitized photodegradation, which was mainly mediated by •OH; CPF and IMI primarily relied on direct photodegradation. Synergistic and/or antagonistic actions that occurred in the mixture improved/decreased the rate constants of five photodegradable target chemicals. Meanwhile, the biotoxicities (acute toxicity and genotoxicity) of the target chemicals (including individual chemicals and the mixture) were significantly reduced, which can explain the reduction of biotoxicities from SE. For the two refractory high-risk chemicals, atrazine (ATZ) and carbendazim (MBC), algae-derived intracellular dissolved organic matter (IOM) on ATZ, and IOM and extracellular dissolved organic matter (EOM) on MBC had slightly promotion for their photodegradation; while peroxysulfate, and peroxymonosulfate served as sensitizers were activated by natural sunlight and effectively improved their photodegradation rate, and then reduced their biotoxicities. These findings will promote the development of CECs treatment technologies based on sunlight irradiation.

Using the end-member mixing model to evaluate biogeochemical reactivities of dissolved organic matter (DOM): autochthonous versus allochthonous origins

Dissolved organic matter (DOM) is an essential component of environmental systems. It usually originates from two end-members, including allochthonous and autochthonous sources. Previously, links have been established between DOM origins/sources and its biogeochemical reactivities. However, the influence of changes in DOM characteristics driven by end-member mixing on DOM biogeochemical reactivities has not been clarified. In this study, we investigated variations of DOM reactivities responding to the dynamics of DOM characteristics induced by different mixing ratios of two DOM end-members derived from humic acid (HA) and algae, respectively. Four biogeochemical reactivities of DOM were evaluated, including biodegradation, ·OH production, photodegradation, and redox capacity. Results showed that the variations of DOM characteristics due to the two end-members mixing significantly impact its biogeochemical reactivities. However, not all spectral parameters and reactivities followed the conservative mixing behavior. In contrast to reactivities of ·OH production and redox capacity, mixed samples showed apparent deviations from conservative linear relationships in biodegradation and photodegradation due to the interaction between the two end-members. Regarding the role of DOM properties influencing reactivity changes, peak A and M were recognized as the most stable parameters. However, peak C and SUVA₂₅₄ were identified as the most vital contributors for explaining DOM reactivity variations. These findings suggest that a general model for describing the dynamic relationship between DOM source and reactivity cannot be proposed. Thus, the dynamics of DOM reactivity in diverse ecosystems cannot be estimated simply by the "plus or minus" of the reactivity from individual end-member. The effect of end-member mixing should be evaluated in a given reactivity instead of generalization. This study provides important insights for further understanding the dynamics of DOM's environmental role in different ecosystems influenced by variations of source inputs. In future, more field investigations are needed to further verify our findings in this study, especially in the scenario of end-member mixing.

Characterization of Dissolved Organic Matter from Agricultural and Livestock Effluents: Implications for Water Quality Monitoring

There is growing concern about the impact of agricultural practices on water quality. The loss of nutrients such as nitrogen and phosphorous through agricultural runoff poses a potential risk of water quality degradation. However, it is unclear how dissolved organic matter (DOM) composition is associated with pollution levels in water bodies. To address this, we conducted a cross-year investigation to reveal the nature of DOM and its relationship to water quality in agricultural effluents (AEs) and livestock effluents (LEs). We discovered that DOM fluorescence components of AEs were mainly from autochthonous and terrestrial sources, while in LEs it was primarily from autochthonous sources. LEs showed a higher β:α and biological index (BIX) than AEs, indicating that LEs had higher biological activity. Compared to the LEs, DOM in AEs exhibited a higher humification index (HIX), illustrating that DOM was more humic and aromatic. Overall, our results suggest that the BIX and fluorescence index (FI) were best suited for the characterization of water bodies impacted by LEs and AEs. Excitation-emission matrix spectroscopy and parallel factor (EEMs-PARAFAC) analysis showed that DOM in AEs was mainly a humic-like material (~64%) and in LEs was mainly protein-like (~68%). Tryptophan-like compounds (C1) were made more abundant in AEs because of the breakdown of aquatic vegetation. The microbial activity enhanced protein-like substances (C1 and C2) in LEs. Our study revealed a positive correlation between five-day biochemical oxygen demand (BOD₅) concentrations and tyrosine-like substance components, suggesting that fluorescence peak B may be a good predictor of water quality affected by anthropogenic activities. For both LEs and AEs, our results suggest that peak D may be a reliable water quality surrogate for total phosphorus (TP).

A review of the influence of soil minerals and organic matter on the migration and transformation of sulfonamides

Sulfonamides (SAs) are common antibiotics that are widely present in the environment and can easily migrate in the environment, so they pose an environmental risk. Minerals and organic matter influence the antibiotic migration and transformation in sewage treatment plants, activated sludge, surface water, and soil environment. In the present paper, the influence of the process and mechanism of minerals and organic matter on the adsorption, degradation, and plant uptake of SAs in soil were summarized. In the impact process of mineral and organic matter on the SAs migration and transformation, the pH value is undoubtedly the most important factor because it determines the ionic state of SAs. In terms of influence mechanisms, the minerals absorb SAs well via cation exchange, complexation, H-bonding, and cation bridging. Mineral photodegradation is also one of the primary removal methods for SAs. Soil organic matter (SOM) can significantly increase the SAs adsorption. The adsorption forces of SAs and SOM or dissolved organic matter (DOM) were very similar, but SOM decreased SAs mobility in the environment, while DOM increased SAs availability. DOM generated active substances and aided in the photodegradation of SAs. This review describes the effects of minerals and organic matter on the fate of SAs in soil, which is useful in controlling the migration and transformation of SAs in the soil environment.

An inevitable but underestimated photoaging behavior of plastic waste in the aquatic environment: Critical role of nitrate

Photoaging is an important reaction for waste plastics in the aquatic environment and plays a key role in the lifetime of plastics. Nevertheless, when natural photosensitive substances such as nitrate participate in this process, the physiochemical changes in plastics and the corresponding reaction mechanisms are not well-understood. In this work, the photochemical behavior of polyethylene terephthalate (PET) bottles in deionized water and nitrate solution was systematically investigated under ultraviolet (UV) irradiation. The analyses of the surface physicochemical properties of the photoaged PET bottles indicated that, after 20 days of photo-irradiation, the presence of nitrate reduced the contact angle from 69.8 ± 0.9° to 60.0 ± 0.3°, and increased the O/C ratio from 0.23 to 0.32, respectively. The leaching rate of dissolved organic carbon (DOC), which was 0.0193 mg g^-1·day^-1 in nitrate solution, was twice that of 0.00941 mg g^-1·day^-1 in deionized water. Furthermore, fluorescence spectroscopy revealed that the increasing DOC had aromatic rings with hydroxyl on the side-chain formed after UV irradiation. The positive effect of nitrate on the degradation of PET bottles was mainly through the generation of hydroxyl radicals that were produced through the photolysis of nitrate. In addition, two-dimensional correlation spectroscopy analysis showed that the chain scission of PET plastics could be initiated by nitrate-induced ·OH attacking the carbon-oxygen bonds instead of forming peroxides with oxygen. This work elucidates the mechanism of photodegradation of plastics that was induced by nitrate and highlights the important role of natural photosensitive substances in the photoaging process of plastics.

Light-dependent enhancement of sulfadiazine detoxification and mineralization by non-photosynthetic methanotrophs

Co-metabolism and photodegradation are two approaches for remediating trace organic compounds (TOrCs), however, interactions between the two with regards to TOrCs degradation have not been elucidated. In this study, sulfadiazine (SDZ) was chosen as a representative TOrC and Methylocystis bryophila as a typical strain. Under light conditions, about 80.6% of SDZ was removed by M. bryophila, but only 7.6% or 28.9% of SDZ was eliminated by either individual photodegradation or by co-metabolism. The SDZ stimulated more extracellular organic matter (EOM) production by M. bryophila. The enhanced SDZ degradation was attributed to indirect photolysis caused by the excited triplet state of EOM (³EOM*) and co-metabolism. The UPLC-QTOF-MS analysis showed that due to co-metabolism, the pyrimidine ring was broken and could further be oxidized into smaller molecules under light conditions, such as formic and acetic acids. The SDZ mineralization ratio increased from 9.9% under the co-metabolic condition alone to 36.5% under co-metabolism coupled with photodegradation. The Ames tests confirmed that the SDZ degradation products by co-metabolism were mutagenic, however, their toxicity was ameliorated by light during co-metabolism. In conclusion, light plays a crucial role in co-metabolic processes of TOrCs.

Photodegradation of chloramphenicol in micro-polluted water using a circulatory thin-layer inclined plate reactor

This study describes the photodegradation of chloramphenicol (CAP) in micro-polluted water with a thin-layer inclined plate reactor. Under simulated sunlight irradiation, the effect of reaction parameters including solution pH, initial CAP concentration, and co-existed humic acid (HA) or chloride was evaluated. The photodegradation of CAP was independent of initial pH in the range of 6.0-9.0, but sharply decreased by 25.5% with the increase of initial CAP concentration from 0.4 to 1.0 mg/L. The presence of HA exhibited a significant inhibitory effect, while Cl^- promoted the photoreaction. In this study, CAP was degraded through both direct and indirect photolysis, in which ¹O₂ was the main reactive species responsible for the indirect route. Its steady-state concentration in the micro-polluted water was determined to be 1.40 × 10^-13 mol/L. Transformation intermediates were identified to propose the degradation pathway of CAP, which substantially met the density functional theory (DFT) calculation results. Moreover, four other pharmaceuticals including tetracycline, doxycycline, oxytetracycline, and minocycline were also successfully photodegraded during 5 h irradiation. Therefore, the designed circulatory thin-layer inclined plate reactor is suggested to be effectively applied to the decontamination of organic micro-polluted water.

Feasibility of source identification by DOM fingerprinting in marine pollution events

Accurate source identification is the first step of pollution control in environmental emergency management, especially in marine pollution events. Dissolved organic matter (DOM) absorption and fluorescence (excitation-emission matrices, EEMs) analyses were applied to trace contaminant sources for a pollution event that occurred along the coast of Laizhou Bay, Bohai Sea. Parallel factor analysis (PARAFAC) of the EEMs identified four fluorescent components: terrestrial humic-like (C1), tryptophan-like (C2), and a mixture of terrestrial and marine humic-like (C3) and tyrosine-like (C4) components. The relationships among C1 to C4 and quality indices indicated that the DOM originated from terrestrial input and biological activity. The EEMs-PARAFAC results accompanied by the optical characteristics of DOM and fingerprinting demonstrated that the marine pollution event occurred was from enterprise emissions. The numerical simulation confirmed the reliability of EEMs-PARAFAC modeling for DOM fingerprinting of pollution sources in polluted regions. This study provided a feasible method for source recognition in marine pollution events.

Effects of natural colloidal particles derived from a shallow lake on the photodegradation of ofloxacin and ciprofloxacin

Natural colloidal particles (NCPs), which are ubiquitous and abundant in surface waters, may play a crucial role in the sunlight-driven transformation of organic contaminants. This research focused on the effects of NCPs on the photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and ciprofloxacin (CIP), and assessed the photosensitivity of colloidal organic matter (COM). Results showed that the photodegradation rate constants (k_obs) of OFL and CIP in NCP solutions ranged from 9.28 × 10^-2 h^-1 to 15.98 × 10^-2 h^-1 and 63.88 × 10^-2 h^-1 to 196.59 × 10^-2 h^-1, respectively, and NCPs can significantly accelerate the photodegradation rate of OFL and CIP. Indirect photodegradation (IP) accounted for >50% of the overall observed degradation in most treatments and was the dominant degradation pathway for the two FQs, especially for CIP, for which IP reached 82%-94%. In the IP process, the contributions of triplet states of colloidal organic matter (³COM^⁎) to the photolysis of OFL and CIP were close to 42% and 46%, respectively. The compositions of COM played an important role in the IP of the FQs, among which terrestrial sources of COM tended to have higher photoreactivity than biological sources. This study is essential in predicting the photochemical effect of FQs and also allows for a better understanding of the real environmental fate of antibiotic contaminants.