Halide-specific enhancement of photodegradation for sulfadiazine in estuarine waters: Roles of halogen radicals and main water constituents

Photochemistry of plateau lake-derived dissolved organic matter: Reactive species generation and effects on 17β-estradiol photodegradation

Naturally strong ultraviolet irradiation at high altitudes causes photobleaching of plateau lake DOM (P-DOM) and affects its photochemical activity. However, the photoreactivity of P-DOM has remained unclear under natural photobleaching condition. Here, six P-DOM samples isolated from plateau lakes in Yunnan Province, China as well as two reference DOM as comparisons were used to explore the photogeneration of reactive species (RS) and their effects on 17β-estradiol photodegradation. Compared with SRHA/SRFA, P-DOM has lower aromaticity, average molecular weight, and electron-donating capacity. The quantum yields of triplet state P-DOM (3P-DOM*), 1O2, and ∙OH produced in P-DOM solutions were greatly higher than those of reference DOM. The RS quantum yields had positive linear correlations with E2/E3 and SR, whereas were negatively linear correlated with SUVA25. Radical quenching experiments showed that 3P-DOM* was the prominent RS for 17β-estradiol photodegradation, and its contribution exceeded 70% for each of P-DOM. 3P-DOM*-mediated photodegradation was mainly attributed to the electron-transfer reactions with an average second-order rate constant of 4.62 × 109 M-1s-1, indicating the strong photoreactivity towards 17β-estradiol. These findings demonstrate that P-DOM is an efficient photosensitizer for RS production, among which 3P-DOM* may play an important role in enhanced photodegradation for organic micropollutants in plateau lake enriched with DOM.

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.

Hybrid radical coupling during MnO2-mediated transformation of a mixture of organic UV filters: Chemistry and toxicity assessment

Manganese oxide (MnO2) is one of the most abundant metal oxides, and it is renowned for its ability to degrade various phenolic micropollutants. However, under MnO2-mediated transformation, BP-3 transforms into 12 different radical-coupled transformation products (TPs) out of 15 identified TPs. These radical-coupled TPs are reported with adverse environmental impacts. This study explored the effects of MnO2 on organic UV filter mixtures and different water constituents (i.e., bicarbonate ion (HCO3-), humic acid (HA) and halide ions) in terms of degradation efficiency and transformation chemistry. When a mixture of benzophenone-3 (BP-3) and avobenzone (AVO) underwent transformation by MnO2, hybrid radical-coupled TPs derived from both organic UV filters were generated. These hybrid radical-coupled TPs were evaluated by an in silico prediction tool and Vibrio fischeri bioluminescence inhibition assay (VFBIA). Results showed that these TPs were potentially toxic to aquatic organisms, even more so than their parent compounds. The higher the concentration of HCO3-, HA, chloride ion (Cl-) and bromide ion (Br-), the greater the reduction in the efficiencies of degrading BP-3 and AVO. Contrastingly, in the presence of iodide ion (I-), degradation efficiencies of BP-3 and AVO were enhanced; however, iodinated TPs and iodinated radical-coupled TPs were formed, with questionable toxicity. This study has revealed the environmental risks of hybrid radical-coupled TPs, iodinated TPs and iodinated radical-coupled TPs when the organic UV filters BP-3 and AVO are transformed by MnO2.

Phototransformation of halobenzoquinones in aqueous solution under the simulate sunlight: Kinetics, mechanism and products

Halobenzoquinones (HBQs) are a novel family of unregulated disinfection byproducts (DBPs). Little is known about their phototransformation activities in natural water. Here, five HBQs with various halogenated substituent types, numbers, and structures positions were selected to investigate the kinetics of degradation in aqueous solutions at various concentrations and in the presence of common environmental variables (Cl-, NO2-, and humic acid). The results indicated that dichloride and dibromo-substituted HBQs were photolyzed, whereas tetrachloro-substituted HBQs showed little degradation. The photolysis rate constant (k) of HBQs decreased with increasing initial concentration. The presence of NO2- and Cl- promoted the degradation of HBQs mainly through the formation of hydroxyl radical (•OH), which were confirmed by electron paramagnetic resonance (EPR). In contrast, humic acid played a negative role on HBQs transformation due to the adsorption and quenching reactions. Possible conversion pathways for HBQs were proposed based on the identification of two major photodegradation products, hydroxylated HBQs and halogenated-benzenetriol, as well as reactive free radicals. This study provided meaningful insights into the environmental fates and risk assessments of HBQs in natural aquatic system.

Photolysis of dinotefuran in aqueous solution: Kinetics, influencing factors and photodegradation mechanism

The environmental behaviour of neonicotinoid insecticides (NNIs) is of momentous concern due to their frequent detection in aquatic environment and their biotoxicity for non-target organisms. Phototransformation is one of the most significant transformation processes, which is directly related to NNIs exposure and environmental risks. In this study, the photodegradation of dinotefuran (DIN, 1-Methyl-2-nitro-3-(tetrahydro-3-furanylmethyl)-guanidine), one of the most promising NNIs, was conducted under irritated light in the presence of Cl-, DOM along with the effect of pH and initial concentration. The findings demonstrated that in ultra-pure (UP) water, the photolysis rate constants (k) of DIN rose with increasing initial concentration. Whereas, in tap water, at varied pH levels, and in the presence of Cl-, the outcomes were reversed. At the same time, lower concentration of DOM promoted DIN photolysis processes due to the production of reactive oxygen species, while higher concentrations of DOM inhibited the photolysis by the predominance of light shielding effects. The singlet oxygen (1O2) was produced in the photolysis processes of DIN with Cl- and DOM, which was confirmed by electron spin resonance (EPR) analysis. Four main photolysis products and three intermediates were identified by UPLC-Q-Exactive Orbitrap MS analysis. The possible photodegradation pathways of DIN were proposed including the oxidation by 1O2, reduction and hydrolysis after the removal of nitro group from parent compounds. This study expanding our understanding of transformation behavior and fate of NNIs in the aquatic environment, which is essential for estimating their environmental risks.

Smart optical sensing of multiple antibiotic residues from wastewater effluents with ensured specificity using SERS assisted with multivariate analysis

Surface-enhanced Raman spectroscopy offers great potential for rapid and highly sensitive detection of pharmaceuticals from environmental sources. Herein, we investigated the feasibility of label-free sensing of antibiotic residues from wastewater effluents with high specificity by combining with multivariate analysis. Highly ordered silver nanoarrays with ∼34 nm roughness have been fabricated using a cost-effective electroless deposition technique. As-fabricated Ag arrays showed superior LSPR effects with an enhancement factor of 8 × 107. Excellent reproducibility has also been noticed with RSD values within 11%, whilst the sensor showed good stability and reusability characteristics for being used as a low-cost and reusable sensor. SERS studies demonstrated that antibiotics-spiked wastewater effluents can be detected with high efficiency in a label-free method. The molecular fingerprint bands of antibiotics such as sulfamethoxazole, sulfadiazine, and ciprofloxacin were well analyzed in effluent, tap, and deionized water. It has been found that antibiotics can be detected near picomolar levels; meanwhile, liquid chromatography-mass spectrometry (LC-MS) exhibited a detection limit within nanomolar concentrations only. Furthermore, the specificity of SERS sensing has been further analyzed using a multivariate analysis method, principal component analysis followed by linear discriminant analysis (PCA-LDA); which showed prominent discrimination to distinguish each antibiotic residue from wastewater effluents. The current study presented the potential of Ag nanoarray sensors for rapid, highly specific, and cost-effective analysis of pharmaceutical products for environmental remediation applications.

Adsorption Performance and Mechanisms of Tetracycline on Clay Minerals in Estuaries and Nearby Coastal Areas

Clay minerals in sediments have strong adsorption capacities for pollutants, but their role in the distribution of antibiotics in estuaries and nearby coastal areas is unclear. We evaluated the clay mineral montmorillonite (SWy-2) adsorption capacity for tetracycline (TC). We assessed the adsorption capacity of SWy-2 for TC by measuring the removal percentage of 30 mg/L TC over time. The effects of pH and ionic strength on the TC adsorption onto SWy-2 were investigated. We analyzed the kinetics of TC adsorption using a pseudo-second-order model and determined the adsorption isotherm using the Langmuir equation. SWy-2 particles were characterized using zeta potential, Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses before and after TC adsorption. The removal percentage of 30 mg/L TC by SWy-2 reached 70.76% within 0.25 h and gradually increased to 78.64% at 6 h. TC adsorption was influenced by pH and ionic strength, where low pH enhanced and high ionic strength reduced the adsorption. The kinetics of TC adsorption followed a pseudo-second-order model, and the adsorption isotherm adhered to the Langmuir equation. The saturated adsorption capacity (qmax) of SWy-2 for TC was 227.27 mg/g. Zeta potential, FTIR, and XRD analyses confirmed that electrostatic interactions and chemical bonds played a significant role in the TC adsorption by SWy-2. SWy-2 clay mineral exhibits a substantial adsorption capacity for TC, indicating its potential as an effective sorbent to mitigate antibiotic contamination in estuaries and nearby coastal areas. The observed effects of pH and ionic strength on TC adsorption have implications for the environmental fate and transport of antibiotics. The pseudo-second-order kinetic model and Langmuir isotherm equation provide valuable insights into the adsorption behavior and capacity of TC on SWy-2. Characterization analyses support the involvement of electrostatic interactions and chemical bonds in the SWy-2-TC adsorption mechanism.

A solar flow photo-reactor for antibiotic removal from aquaculture effluents using TiO2/carbon quantum dots

Effluents contaminated with antibiotics must be treated before reuse or even discharge into the aquatic environment, avoiding the increase of antimicrobial resistance (AMR) - a major public health problem of the 21st century. Little is known regarding the natural solar photodegradation of antibiotics in tubular reactors operated under flow mode and even less concerning the application of photocatalysts. The use of photocatalysts is considered a promising strategy for a sustainable solar-driven removal of antibiotics from effluents. In this work, the photodegradation of two antibiotics widely used in aquaculture, namely, sulfadiazine (SDZ) and oxolinic acid (OXA), was investigated under solar flow mode in the absence and presence of carbon quantum dots (CQDs) coupled with titanium dioxide (TiO2) (4% (w/w)). The obtained results showed that TiO2/CQDs (4% (w/w)) enhanced the photodegradation of both antibiotics, which is highly beneficial for their application in the treatment of aquaculture effluents. The accumulated UV energy needed for SDZ removal using the photocatalyst was less than 4 kJ L-1 in both simulated freshwater (phosphate buffer solution (PBS)) and simulated brackish water (sea salt solution (SSS)), while for OXA less than 5 kJ L-1 and around 15 kJ L-1 were needed for removal in PBS and in SSS, respectively. Moreover, results demonstrated that the proposed photocatalytic treatment was also efficient in the elimination of OXA and SDZ antibacterial activity, either in PBS or SSS. Therefore, photocatalysis under flow mode using TiO2/CQDs constitutes a promising and sustainable treatment for antibiotics' efficient removal from aquaculture effluents.

Highly dispersed redox antimony oxide pairs for accurate detection and electrochemistry-controlled recovery toward an antibiotic drug: Sulfadiazine

BACKGROUND

Sulfadiazine (SDZ) is a broad-spectrum antibiotic widely used in aquaculture and animal husbandry and it is easy to remain in the water system to damage the human body. Therefore, detection and removal of sulfadiazine in water systems become critical. Nowadays, catalysts and visible light are used to degrade sulfadiazine into smaller molecules containing N and S to reduce toxicity. However, these small molecules are easily released into water and the atmosphere to be the acid rain. Therefore, it is urgent to design a sensor with the ability to detect and remove SDZ at the same time. (96) RESULTS: We designed a novel composite catalyst sensor (Sb6O13@LTA GCE) with the ability to simultaneously monitor and remove sulfadiazine. The catalyst is generated by introducing SbCl5 into the reactive gel of LTA (Linde Type A) structure zeolite. In the hydrothermal reaction, the corrosive SbCl5 is transferred into nanosized Sb6O13 nanoparticle which is highly dispersed in the opening nano-scaled windows of the zeolite through redox and self-assembled progress. In the selected electrochemical overpotential range, the Sb6O13@LTA composited modified electrode could complete adsorption and desorption of SDZ through the electron transfer from Sb3+ to Sb5+. As the catalyst is in high stability, the only loss in the whole process of recovering SDZ is a small amount of electric energy. The extra-low detection limit and the removal efficiency of Sb6O13@LTA GCE have been achieved 4.0 pM and 19.3 mg/20 mg (136) SIGNIFICANCE: The prepared novel sensor has low detection limit, high removal efficiency and high selectivity for sulfadiazine. The Sb6O13@LTA GCE sensor, which is low-cost and has a simple preparation method, exhibits good reproducibility in both seawater and cell fluid. This provides the possibility for wide application in detecting and removing SDZ in water system. (53).

Inhibition of photosensitized degradation of organic contaminants by copper under conditions typical of estuarine and coastal waters

Dissolved organic matter (DOM) driven-photochemical processes play an important role in the redox cycling of trace metals and attenuation of organic contaminants in estuarine and coastal ecosystems. In this study, we evaluate the effect of Cu on 4-carboxybenzophenone (CBBP) and Suwannee River natural organic matter (SRNOM)-photosensitized degradation of seven target contaminants (TCs) including phenols and amines under pH conditions and salt concentrations typical of those encountered in estuarine and coastal waters. Our results show that trace amounts of Cu(II) (25 -500 nM) induce strong inhibition of the photosensitized degradation of all TCs in solutions containing CBBP. The influence of TCs on the photo-formation of Cu(I) and the decrease in the lifetime of transformation intermediates of contaminants (TC^•+/ TC^•_(-H)) in the presence of Cu(I) indicated that the inhibition effect of Cu was mainly due to the reduction of TC^•+/ TC^•_(-H) by the photo-produced Cu(I). The inhibitory effect of Cu on the photodegradation of TCs decreased with the increase in Cl^- concentration since less reactive Cu(I)-Cl complexes dominate at high Cl^- concentrations. The impact of Cu on the SRNOM-sensitized degradation of TCs is less pronounced compared to that observed in CBBP solution since the redox active moieties present in SRNOM competes with Cu(I) to reduce TC^•+/ TC^•_(-H). A detailed mathematical model is developed to describe the photodegradation of contaminants and Cu redox transformations in irradiated SRNOM and CBBP solutions.

Investigation on the reaction kinetic mechanism of polydopamine-loaded copper as dual-functional catalyst in heterogeneous electro-Fenton process

Heterogeneous electro-Fenton (HEF) process has been regarded as a promising method in environmental remediation. However, the reaction kinetic mechanism of the HEF catalyst for simultaneous production and activation of H₂O₂ remained confounded. Herein, the copper supported on polydopamine (Cu/C) was synthesized by a facile method and employed as a bifunctional HEFcatalyst, and the catalytic kinetic pathways were deeply investigated by using rotating ring-disk electrode (RRDE) voltammetry based on the Damjanovic model. Experimental results substantiated that a two-electron oxygen reduction reaction (2e^- ORR) and a sequential Fenton oxidation reaction were proceeded on 1.0-Cu/C, where metallic copper played a crucial role in the fabrication of 2e^- active sites as well as utmost H₂O₂ activation to produce highly reactive oxygen species (ROS), resulting in the high H₂O₂ productivity (52.2%) and the almost complete removal of contaminant ciprofloxacin (CIP) after 90 min. The work not only expanded the idea of reaction mechanism on Cu-based catalyst in HEF process but also provided a promising catalyst for pollutants degradation in wastewater treatment.

Enhancive and inhibitory effects of copper complexation on triplet dissolved black carbon-sensitized photodegradation of organic micropollutants

Excited-triplet dissolved black carbon (DBC) was deemed as a significant reactive intermediate in the phototransformation of environmental micropollutants, but the impacts of concomitant metal ions on photochemical behavior of excited-triplet DBC (³DBC*) are poorly understood. Here, the photolytic kinetics of sulfadiazine and carbamazepine induced by ³DBC* involving Cu²⁺ was explored. The presence of Cu²⁺ reduced the ³DBC*-induced photodegradation rate of sulfadiazine; whereas for carbamazepine, Cu²⁺ enhanced ³DBC*-induced photodegradation. Cu(II)-DBC complex was formed due to the decreasing fluorescence intensities of DBC in the presence of Cu²⁺. Cu²⁺ complexation caused the decrease of ³DBC* steady-state concentrations, which markedly reduced ³DBC*-induced photodegradation rate of sulfadiazine due to its high triplet reactivity. Kinetic model showed that ³DBC* quenching rate by Cu²⁺ was 7.98 × 10⁹ M^-1 s^-1. Cu²⁺ complexation can also enhance the electron transfer ability, thereby producing more ∙OH in Cu(II)-DBC complex, which explains the promoting effect of Cu²⁺ complexation on carbamazepine photodegradation in view of its low triplet reaction rate. These indicate that ³DBC* reactivity differences of organic micropollutants may explain their photodegradation kinetics differences in DBC system with/without Cu²⁺, which was supported by the linearized relationship between the photodegradation rate ratios of ten micropollutants with/without Cu²⁺ and their triplet reaction activity.

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

Electrochemical Reduction and Oxidation of Chlorinated Aromatic Compounds Enhanced by the Fe-ZSM-5 Catalyst: Kinetics and Mechanisms

Devising cost-effective electrochemical catalyst system for the efficient degradation of chlorinated aromatic compounds is urgently needed for environmental pollution control. Herein, a Fe-ZSM-5 zeolite was used as a suspended catalyst to facilitate the degradation of lindane as a model chlorinated pesticide in an electrochemical system consisting of the commercial DSA (Ti/RuO₂-IrO₂) anode and graphite cathode. It was found that the Fe-ZSM-5 zeolite greatly accelerated the degradation of lindane, with the degradation rate constant more than 8 times higher than that without Fe-ZSM-5. In addition, the Fe-ZSM-5 zeolite widened the working pH range from 3 to 11, while efficient degradation of lindane in the absence of Fe-ZSM-5 was only obtained at pH ≤ 5. The degradation of lindane was primarily due to reductive dechlorination mediated by atomic H* followed by ^•OH oxidation. Fe-ZSM-5 zeolite could enrich lindane, H*, and ^•OH on its surface, thus provided a suitable local environment for lindane degradation. The Fe-ZSM-5 zeolite exhibited high stability and reusability, and reduced the energy consumption. This research provides a potential reduction-oxidation strategy for removing organochlorine compounds through a cost-efficient Fe-ZSM-5 catalytic electrochemical system.

Inorganic anions influenced the photoaging kinetics and mechanism of polystyrene microplastic under the simulated sunlight: Role of reactive radical species

The photo-transformation of microplastic (MP) in natural water may involve interactions with various ingredients, but the photoaging kinetics and underlying mechanism are not well understood. This work systematically explored the photoaging process of polystyrene microplastic (PS-MP) in the presence of commonly-found inorganic anions, including NO₃^-, HCO₃^-, Br^- and Cl^-. The addition of these ions led to more obvious changes in the morphology, functional groups and molecular weight of photoaging PS-MP. The evolution of carbonyl index value for the photoaged samples conformed to pseudo-first-order kinetic model, and the photoaging rate constant (k) in the presence of inorganic anions at their environmentally relevant concentrations of 0.6 mM, 1.2 mM, 0.1 M and 0.1 mM was calculated to be k_HCO3- = 0.0074 d^-1, k_NO3- = 0.01001 d^-1, k_Cl- = 0.00783 d^-1, and k_Br- = 0.00888 d^-1, which was higher than that in ultrapure water (k=0.00705 d^-1). Electron paramagnetic resonance technique and quenching experiments demonstrated that photo-transformation of PS-MP was mainly mediated by indirect photolysis, i.e., the formation of reactive radical species. The photosensitivity of NO₃^- promoted more •OH production, thereby accelerated the indirect photoaging of PS-MP. Meanwhile, the presence of halide ions promoted the generation of reactive halogen species, which were also involved in the indirect photoaging of PS-MP. Interestingly, as •OH scavenger, HCO₃^- had no inhibitory effect on PS-MP photoaging, attributing to the oxidation of CO₃^•-. This study provides valuable insights into the understanding of photo-transformation of MPs in natural aquatic environments.

Dual roles of Cu2+ complexation with dissolved organic matter on the photodegradation of trace organic pollutants: Triplet- and OH-induced reactions

The triplet excited state of dissolved organic matter (³DOM^⁎) is highly effective in the photodegradation of a broad spectrum of trace organic pollutants (TOPs), and its photoactivity is affected by concomitant metal ions in surface waters. However, the impact of environmental metal ions on the ³DOM^⁎-induced photodegradation of TOPs has not been systemically explored. Herein, we investigated the effect of environmental Cu²⁺ on the ³DOM^⁎-induced photodegradation kinetics of 16 TOPs. A fluorescence quenching experiment showed that a Cu(II)-DOM complex was formed. For the TOPs with stronger electron-donating groups (triplet-labile moieties, e.g., phenols and anilines), Cu²⁺ complexation notably inhibited ³DOM^⁎-induced photodegradation. This may be ascribed to the decrease of ³DOM^⁎ steady-state concentration because Cu²⁺ complexation reduces its formation rates and enhances scavenging rates tested by sorbic acid isomerization experiment. Meanwhile, it was found that Cu²⁺ complexation facilitated the photolysis of refractory TOPs (lower triplet reactivity) because of enhanced electron transfer between DOM and Cu(II), causing photoinduced OH formation. These findings implied that ³DOM^⁎ reactivity differences in TOPs could affect the photodegradation rates in the complex system, which was confirmed via a linear correlation of photodegradation rate ratios for 16 TOPs induced by ³DOM^⁎ in the presence/absence of Cu²⁺ with their ³DOM^⁎ reactivity. These findings helped to improve our understanding of the photochemical reactivity of ³DOM^⁎ in natural waters, especially the effects of environmentally concomitant metal ions.

Antibiotics in mariculture systems: A review of occurrence, environmental behavior, and ecological effects

Antibiotics are widely applied to prevent and treat diseases occurred in mariculture. The often-open nature of mariculture production systems has led to antibiotic residue accumulation in the culturing and adjacent environments, which can adversely affect aquatic ecosystems, and even human. This review summarizes the occurrence, environmental behavior, and ecological effects of antibiotics in mariculture systems based on peer-reviewed papers. Forty-five different antibiotics (categorized into ten groups) have been detected in mariculture systems around the world, which is far greater than the number officially allowed. Indiscriminate use of antibiotics is relatively high among major producing countries in Asia, which highlights the need for stricter enforcement of regulations and policies and effective antibiotic removal methods. Compared with other environmental systems, some environmental characteristics of mariculture systems, such as high salinity and dissolved organic matter (DOM) content, can affect the migration and transformation processes of antibiotics. Residues of antibiotics favor the proliferation of antibiotic resistance genes (ARGs). Antibiotics and ARGs alter microbial communities and biogeochemical cycles, as well as posing threats to marine organisms and human health. This review may provide a valuable summary of the effects of antibiotics on mariculture systems.

Multiple roles of humic acid in the photogeneration of reactive bromine species using a chemical probe method

Photosensitization of natural organic matter (NOM) is an important natural source of reactive bromine species (RBrS) in the environment. Up to now, quantitative information about RBrS was mainly based on model sensitizers. Whether the behavior of model compounds could represent those of complex NOM remains unknown. In this study, we employed a chemical probe (3,5-dimethyl-1-H-pyrazole) to measure RBrS in humic acid (HA)-containing solutions and investigated their influential factors. The formation rate, decay rate constant, steady-state concentration, and lifetimes of RBrS were 3.87(±0.16) × 10^-13 mol L^-1·s^-1, 1.99(±0.20) × 10⁴ s^-1, 2.04(±0.13) × 10^-17 mol L^-1, and 5.06(±1.05) × 10^-5 s, respectively. Measured steady-state concentrations of RBrS were 3-5 orders of magnitude lower than those in model sensitizer system. Results showed that HA drove the RBrS generation, and about 0.12-0.70% of triplet-state HA (³HA*) would be transformed into RBrS. HA structures strongly affected this process. Phenolic-like groups suppressed the formation, while aromatic ketone-like moieties facilitated it. Last, HA also altered the transformation pathways. The contribution of ·OH dependent and direct oxidation pathways was almost equal, while the direct oxidation was predominant in the model system. Thus, careful consideration should be taken into photochemical formation of RBrS in NOM-involved solution, due to their complexity and multiple roles.

Modeling degradation kinetics of gemfibrozil and naproxen in the UV/chlorine system: Roles of reactive species and effects of water matrix

The UV/chlorine system has been regarded as an efficient oxidation technology for the removal of aqueous micropollutants. However, the roles of the possible radical species for this system on the elimination under environmentally relevant conditions/real waters were still largely unknown. Herein, the specific roles of radical species in the UV/chlorine oxidation degradation of gemfibrozil and naproxen as representative micropollutants were quantified by a steady-state kinetic prediction model considering the effects of water matrices. Overall, the model predicted results are consistent with the experimental data well. •OH and reactive chlorine species (RCS, such as Cl•, ClO•, and Cl₂•^-) contributions to gemfibrozil and naproxen degradation were water matrix specific. In pure water, both primary reactive species (i.e., •OH and Cl•) and secondary species ClO• dominated gemfibrozil and naproxen degradation, and their individual and the sum of the contributions to degradation rates reduced with pH increase of from 5 to 9. In the presence of Cl^-, we found that Cl₂•^- and in particular ClO• were responsible for the enhanced degradation with increasing Cl^- concentrations due to the considerable ClO• reactivity of gemfibrozil (1.93 × 10⁹ M^-1 s^-1) and naproxen (9.24 × 10⁹ M^-1 s^-1) and the rapid transformation of Cl₂•^- to ClO•. The presence of HCO₃^- notably facilitated the degradation in the UV/chlorine process because of the generation of CO₃•^-. CO₃•^- showed high reactivity with gemfibrozil and naproxen corresponding to respective second-order reaction rate constants of 2.45 × 10⁷ and 3.50 × 10⁷ M^-1 s^-1. Dissolved organic matter induced obvious scavenging for •OH, Cl•, and ClO• and greatly retarded the degradation. The constructed model considering the effects of above water matrix has successfully predicted the oxidation degradation kinetics in real waters, and both •OH and CO₃•^- are the predominant reactive species in the degradation. This study is helpful for comprehensive understanding the roles of possible radical species in micropollutant removal by UV/chlorine oxidation under real water matrix.

Photo-induced degradation and toxicity change of decabromobiphenyl ethers (BDE-209) in water: Effects of dissolved organic matter and halide ions

BDE-209 is a widely used brominated flame retardant that is ubiquitous in the aquatic environment, especially in marine water. However, photodegradation of BDE-209 in seawater is still not fully understood. In this work, the photodegradation kinetics of BDE-209 in water was studied and the effects of seawater dissolved organic matter (S-DOM) and halide ions (Cl^-, Br^-) were evaluated. S-DOM inhibited the degradation of BDE-209 through dynamic quenching and light shielding effect. However, with the coexistence of S-DOM, Cl^- and Br^-, the photodegradation of BDE-209 was significantly promoted. The promotional effect is attributed to the generation of excited triplet state S-DOM, singlet oxygen, and reactive halogen radicals. The results of density functional theory calculation showed that •Cl addition reaction on C-Br sites of BDE-209 is the main reaction pathway of BDE-209 with chlorine radical, which leads to the generation of mixed Cl/Br substituted intermediates. The acute toxicity and estrogenic effects of BDE-209 solution were enhanced during simulated sunlight irradiation. These results indicate that the environmental factors in seawater play important roles in the photodegradation of BDE-209, and contribute to the potential ecological risks of PBDEs in the marine environment.

Dichlorine radicals (Cl2•-) promote the photodegradation of propranolol in estuarine and coastal waters

Propranolol (PRO) is frequently detected in estuarine and coastal waters, which has adverse effects on estuarine and coastal ecosystems. In this study, the effects of halide ions and DOM from estuarine and coastal waters on the photochemical transformation of PRO were investigated. The results demonstrated that the presence of Br^- alone exhibited slight effect on photochemical transformation of PRO, while photodegradation rates of PRO increased with the addition of 0.1-0.54 M Cl^-. The quenching experiments and the laser flash photolysis experiments together demonstrated the generation of Cl₂^•- in the photolytic systems. Cl₂^•- is possibly produced through the charge separation of exciplex of ³PRO* and Cl^- rather than via direct oxidation of Cl^-. Additional experiments indicated that addition of seawater DOM inhibited the halide ions-sensitized photodegradation rates of PRO, which may be due to the quenching of Cl₂^•- by phenolic substances in DOM molecules. Compared with pure water, three new photochemical intermediates were identified in the presence of DOM or Cl^-. The direct photolysis of PRO mainly reacted by hydroxyl additions, hydroxyl elimination and de-propylation, whereas electron transfer coupled with H-abstraction by Cl₂^•- and ³DOM* was proposed as the primary role for PRO degradation in the presence of Cl^- or DOM.

Photolytic kinetics of pharmaceutically active compounds from upper to lower estuarine waters: Roles of triplet-excited dissolved organic matter and halogen radicals

Photodegradation is a major elimination route of many pharmaceutically active compounds (PhACs) in natural surface waters, yet their photolytic behavior in estuarine waters with salinity gradient change is largely unknown. Herein, sulfamethazine and carbamazepine were taken as representative PhACs to explore the photolytic kinetic differences in Qinzhou Bay estuarine water samples collected from upper to lower reaches. Rapid photodegradation of sulfamethazine was found in lower estuarine water relative to upstream estuarine water; whereas for carbamazepine, photolytic rate was inversely proportional to the salinity of estuarine waters. Experiments with extracted estuarine dissolved organic matter (E-DOM) imply that the multivariate effects of triplet-excited E-DOM (³E-DOM∗) and halide ions are responsible for the enhancement photolysis of sulfamethazine. Radical scavenging experiments suggest that the photolysis enhancement can be ascribed to the contribution of reactive halogen species (RHS), while their contribution to carbamazepine is negligible and ³E-DOM∗ is the dominant reactive species for its photodegradation. This indicates that the reactivity differences with RHS and ³DOM∗ affect the photolytic kinetics of PhACs from upper estuarine waters to lower reaches, which is also supported by a good linear relationship between the ratios of photolytic rates for ten PhACs in E-DOM solution with/without halides and the ratios of the reactivity of these pollutants with RHS and ³DOM∗. These findings show that the different reactivity of PhACs with ³E-DOM∗ and RHS influences the photolytic kinetics in estuarine waters with different salinity, and highlights the photochemical behavior of organic micropollutants from upstream to downstream estuarine waters.

Photochemical origin of reactive radicals and halogenated organic substances in natural waters: A review

Halogenated organic compounds, also termed organohalogens, were initially regarded to be of almost exclusively anthropogenic origin. However, recent research has demonstrated that photochemical reactions are important abiotic sources of organohalogen compounds in sunlit surface waters. Halide ions (X^-, X represents Cl, Br and I) are common anions in natural waters and might be oxidized by reactive species originated from photochemistry of dissolved organic matter (DOM) or inorganic photoactive species. The resulting reactive halogen species may react with organic substances with diverse bimolecular reaction rate constants, depending on the complexity and structure of organic substances. Therefore, the chemical mechanism of halogenation remains challenging to be fully elucidated. To better understand the trends in the existing data and to identify the knowledge gaps that may merit further investigation, this review gives an integrative summary on the sources of reactive oxygen species (ROS) and halogen radicals (X/X₂^-). Photochemical halogenation of phenolic compounds and formation of methyl halide and brominated organic pollutants are highlighted. By evaluating existing literature and identifying some uncertainties, this review emphasizes the environmental significance of sunlight-driven halogenation and proposes further research directions on mechanistic investigation and rational experimental design close to natural systems.

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

The presence of pharmaceuticals and personal care products in coastal waters has caused concern over the past decade. Sulfadiazine (SD) is a very common antibiotic widely used as human and fishery medicine, and dissolved organic matter (DOM) plays a significant role in the indirect photodegradation of SD; however, the influence of DOM compositions on SD indirect photodegradation is poorly understood. The roles of reactive intermediates (RIs) in the indirect photolysis of SD were assessed in this study. The reactive triplet states of DOM (³DOM∗) played a major role, whereas HO· and ¹O₂ played insignificant roles. DOM was divided into four components using excitation-emission matrix spectroscopy combined with parallel factor analysis. The components included three allochthonous humic-like components and one autochthonous humic-like component. The allochthonous humic-like components contributed more to RIs generation and SD indirect photolysis than the autochthonous humic-like component. A significant relationship between the indirect photodegradation of SD and the decay of DOM fluorescent components was found (correlation coefficient, 0.99), and the different indirect photodegradation of SD in various DOM solutions might be ascribed to the different components of DOM. The indirect photolysis rate of SD first increased and then decreased with increasing pH. SD photolysis was enhanced by low salinity but remained stable at high salinity. The increased carbonate concentration inhibited SD photolysis, whereas nitrate showed almost no effect in this study.

Oxolinic acid in aquaculture waters: Can natural attenuation through photodegradation decrease its concentration?

Quinolones, such as oxolinic acid (OXA), are antimicrobials commonly used in aquaculture. Thus, its presence in the aquatic environment surrounding aquaculture facilities is quite easy to understand. When present in aquatic environment, pharmaceuticals may be subjected to several attenuation processes that can influence their persistence. Photodegradation, particularly for antibiotics, can have significant importance since these compounds may be resistant to microbial degradation. OXA photodegradation studies reported in literature are very scarce, especially using aquaculture waters, but are markedly important for an appropriate risk assessment. Results hereby presented showed a decrease on photodegradation rate constant from 0.70 ± 0.02 h^-1 in ultrapure water to 0.42 ± 0.01 h^-1 in freshwater. The decrease on photodegradation rate constant was even more pronounced when brackish water was used (0.172 ± 0.003 h^-1). In order to understand which factors contributed to the observed behaviour, environmental factors, such as natural organic matter and salinity, were studied. Results demonstrated that dissolved organic matter (DOM) may explain the decrease of OXA photodegradation observed in freshwater. However, a very sharp decrease of OXA photodegradation was observed in solutions containing NaCl and in synthetic sea salts, which explained the higher decrease observed in brackish water. Moreover, under solar radiation, the use of an ¹O₂ scavenger allowed us to verify a pronounced retardation of OXA decay, suggesting that ¹O₂ plays an important role in OXA photodegradation process.

Photodegradation of sulfadiazine in different aquatic environments - Evaluation of influencing factors

The presence of antibiotics, such as sulfadiazine (SDZ), in the aquatic environment contributes to the generation of antimicrobial resistance, which is a matter of great concern. Photolysis is known to be a major degradation pathway for SDZ in surface waters. Therefore, influencing factors affecting SDZ photodegradation in different aquatic environments were here evaluated in order to have a better knowledge about its persistence in the environment. Photodegradation of SDZ was found to be more efficient at higher pH (t_1/2 = 6.76 h, at pH = 7.3; t_1/2 = 12.2 h, at pH = 6.3), in the presence of humic substances (HS) (t_1/2 between 1.76 and 2.42 h), as well as in the presence of NaCl (t_1/2 = 1.00 h) or synthetic sea salts (t_1/2 = 0.78 h). Using ˙OH and ¹O₂ scavengers, it was possible to infer that direct photolysis was the main pathway for SDZ photodegradation in ultrapure water. Furthermore, results under N₂ purging confirmed that ¹O₂ was not relevant in the phototransformation of SDZ. Then, the referred observations were used for the interpretation of results obtained in environmental matrices, namely the final effluent of a sewage treatment plant (STPF), fresh and brackish water (t_1/2 between 2.3 and 3.48 h), in which SDZ photodegradation was found to be much faster than in ultrapure water (t_1/2 = 6.76 h).