UV/chlorine process for degradation of benzothiazole and benzotriazole in water: Efficiency, mechanism and toxicity evaluation

Unraveling the role of Mn(V)/Mn(III) in the enhanced permanganate oxidation under Vis-LED radiation

A novel approach of visible light-emitting diode (Vis-LED) radiation was employed to activate permanganate (Mn(VII)) for efficient organic micropollutant (OMP) removal. The degradation rates of OMPs by Vis-LED/Mn(VII) were 2-5.29 times higher than those by Mn(VII) except for benzoic acid and atrazine. Increasing wavelengths (445-525 nm) suppressed the degradation of diclofenac (DCF) and 4-chlorophenol (4-CP) owing to the decreased quantum yields of Mn(VII). Comparatively, light intensity and Mn(VII) dosage had a positive effect on the degradation of DCF and 4-CP. Experimental data revealed that Mn(V) dominated the DCF degradation whereas Mn(III) was the active oxidant in the 4-CP degradation. Mn(V) and Mn(III) formed from the photo-decomposition of Mn(VII), meanwhile, Mn(III) also formed from the Mn(V) photo-decomposition. The increase in solution pH inhibited DCF degradation but had a positive impact on 4-CP degradation, mainly due to the changing speciation of DCF and 4-CP. Inorganic anions (Cl- and HCO3-) had little impact on DCF and 4-CP degradation, while humic acid (HA) showed a positive impact because of the π-π interaction between HA and DCF/4-CP. The transformation products of DCF and 4-CP were identified and transformation pathways were proposed. Finally, the Vis-LED/Mn(VII) exhibited great degradation performance in various authentic waters. Overall, this study boosts the development of Mn(VII)-based oxidation processes.

Trace Br- Inhibits Halogenated Byproduct Formation in Saline Wastewater Electrochemical Treatment

The electrochemical technology provides a practical and viable solution to the global water scarcity issue, but it has an inherent challenge of generating toxic halogenated byproducts in treatment of saline wastewater. Our study reveals an unexpected discovery: the presence of a trace amount of Br- not only enhanced the electrochemical oxidation of organic compounds with electron-rich groups but also significantly reduced the formation of halogenated byproducts. For example, in the presence of 20 μM Br-, the oxidation rate of phenol increased from 0.156 to 0.563 min-1, and the concentration of total organic halogen decreased from 59.2 to 8.6 μM. Through probe experiments, direct electron transfer and HO• were ruled out as major contributors; transient absorption spectroscopy (TAS) and computational kinetic models revealed that trace Br- triggers a shift in the dominant reactive species from Cl2•- to Br2•-, which plays a key role in pollutant removal. Both TAS and electron paramagnetic resonance identified signals unique to the phenoxyl and carbon-centered radicals in the Br2•--dominated system, indicating distinct reaction mechanisms compared to those involving Cl2•-. Kinetic isotope experiments and density functional theory calculations confirmed that the interaction between Br2•- and phenolic pollutants follows a hydrogen atom abstraction pathway, whereas Cl2•- predominantly engages pollutants through radical adduct formation. These insights significantly enhance our understanding of bromine radical-involved oxidation processes and have crucial implications for optimizing electrochemical treatment systems for saline wastewater.

Matching periodate peak absorbance by far UVC at 222 nm promotes the degradation of micropollutants and energy efficiency

Periodate (PI)-based advanced oxidation processes have gained increasing interest. This study for the first time elevates the light-activation capacity of PI by using far UVC at 222 nm (UV222/PI) without extra chemical inputs. The effectiveness and the underlying mechanisms of UV222/PI for the remediation of micropollutants were studied by selecting atenolol (ATL) as a representative. PI possessed a high molar absorption coefficient of 9480-6120 M-1 cm-1 at 222 nm in the pH range of 5.0-9.0, and it was rapidly decomposed by UV222 with first-order rate constants of 0.0055 to 0.002 s-1. ATL and the six other organic compounds were effectively degraded by the UV222/PI process under different conditions with the fluence-based rate constants generally two to hundred times higher than by UVA photolysis. Hydroxyl radical and ozone were confirmed as the major contributors to ATL degradation, while direct photolysis also played a role at higher pH or lower PI dosages. Degradation pathways of ATL were proposed including hydroxylation, demethylation, and oxidation. The high energy efficiency of the UV222/PI process was also confirmed. This study provides a cost-effective and convenient approach to enhance PI light-response activity for the treatment of micropollutants.

Sunlight enhanced the formation of tribromomethane from benzotriazole degradation during the sunlight/free chlorine treatment in the presence of bromide

The coexistence of free chlorine and bromide under sunlight irradiation (sunlight/FC with Br-) is unavoidable in outdoor seawater swimming pools, and the formation of brominated disinfection byproducts could act more harmful than chlorinated disinfection byproducts. In this study, benzotriazole was selected as a model compound to investigate the degradation rate and the subsequent formation of disinfection byproducts via sunlight/FC with Br- process. The rate constants for the degradation of benzotriazole under pseudo first order conditions in sunlight/FC with Br- and sunlight/FC are 2.3 ± 0.07 × 10-1 min-1 and 6.0 ± 0.7 × 10-2 min-1, respectively. The enhanced degradation of benzotriazole can be ascribed to the generation of HO•, bromine species, and reactive halogen species (RHS) during sunlight/FC with Br-. Despite the fact that sunlight/FC with Br- process enhanced benzotriazole degradation, the reaction results in increasing tribromomethane (TBM) formation. A high concentration (37.8 μg/L) of TBM was detected in the sunlight/FC with Br-, which was due to the reaction of RHS. The degradation of benzotriazole was notably influenced by the pH value (pH 4 - 11), the concentration of bromide (0 - 2 mM), and free chlorine (1 - 6 mg/L). Furthermore, the concentration of TBM increased when the free chlorine concentrations increased, implying the formation potential of harmful TBM in chlorinated seawater swimming pools.

First Evidence of the Bioaccumulation and Trophic Transfer of Tire Additives and Their Transformation Products in an Estuarine Food Web

The discovery of the significant lethal impacts of the tire additive transformation product N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) on coho salmon has garnered global attention. However, the bioaccumulation and trophic transfer of tire additives and their transformation products (TATPs) within food webs remain obscure. This study first characterized the levels and compositions of 15 TATPs in the Pearl River Estuary, estimated their bioaccumulation and trophic transfer potential in 21 estuarine species, and identified priority contaminants. Our observations indicated that TATPs were prevalent in the estuarine environment. Eight, six, seven, and 10 TATPs were first quantified in the shrimp, sea cucumber, snail, and fish samples, with total mean levels of 45, 56, 64, and 67 ng/g (wet weight), respectively. N,N'-Diphenyl-p-phenylenediamine (DPPD) and N,N'-bis(2-methylphenyl)-1,4-benzenediamine (DTPD) exhibited high bioaccumulation. Significant biodilution was only identified for benzothiazole, while DPPD and DTPD displayed biomagnification trends based on Monte Carlo simulations. The mechanisms of bioaccumulation and trophodynamics of TATPs could be explained by their chemical hydrophobicity, molecular mass, and metabolic rates. Based on a multicriteria scoring technique, DPPD, DTPD, and 6PPD-Q were characterized as priority contaminants. This work emphasizes the importance of biomonitoring, particularly for specific hydrophobic tire additives.

New solution for predicting the removal efficiency of organic contaminants by UV/ H2O2: From a case study of 1H-benzotriazole

Rapid prediction of the removal efficiency and energy consumption of organic contaminants under various operating conditions is crucial for advanced oxidation processes (AOPs) in industrial application. In this study, 1H-Benzotriazole (BTZ, CAS: 95-14-7) is selected as a model micropollutant, a validated incorporated Computational Fluid Dynamics (CFD) model is employed to comprehensively investigate the impacts of initial concentrations of H2O2, BTZ and dissolved organic carbon (DOC) (i.e., [DOC]0, [BTZ]0 and [DOC]0), as well as the effective UV lamp power P and volumetric flow rate Qv. Generally, the operation performance depends on [DOC]0 and [BTZ]0 in similar trends, but with quantitatively different ways. The increase in [H2O2]0 and P/Qv can promote •OH generation, leading to the elimination of BTZ. It is worth noting that P/Qv is found to be linearly correlated with the removal order of BTZ (ROBTZ) under specific conditions. Based on this finding, the degradation of other potential organic contaminants with a wide range of rate constants by UV/H2O2 is further investigated. A model for predicting energy consumption for target removal rates of organic pollutants is established from massive simulation data for the first time. Additionally, a handy Matlab app is first developed for convenient application in water treatment. This work proposes a new operable solution for fast predicting operation performance and energy consumption for the removal of organic contaminants in industrial applications of advanced oxidation processes.

Electro-oxidation and UV irradiation coupled method for in-site removing pollutants from human body fluids in swimming pool

A comprehensive study was conducted to investigate how ultraviolet (UV) irradiation combined with electrochemistry (EC) can efficiently remove human body fluids (HBFs) related pollutants, such as urea/creatinine/hippuric acid, from swimming pool water (SPW). In comparison with the chlorination, UV, EC, and UV/chlorine treatments, the EC/UV treatment exhibited the highest removal rates for these typical pollutants (TPs) from HBFs in synthetic SPW. Specifically, increasing the operating current of the EC/UV process from 20 to 60 mA, as well as NaCl content from 0.5 to 3.0 g/L, improved urea and creatinine degradation while having no influence on hippuric acid. In contrast, EC/UV process was resilient to changes in water parameters (pH, HCO3-, and actual water matrix). Urea removal was primarily attributable to reactive chlorine species (RCS), whereas creatinine and hippuric acid removal were primarily related to hydroxyl radical, UV photolysis, and RCS. In addition, the EC/UV procedure can lessen the propensity for creatinine and hippuric acid to generate disinfection by-products. We can therefore draw the conclusion that the EC/UV process is a green and efficient in-situ technology for removing HBFs related TPs from SPW with the benefits of needless chlorine-based chemical additive, easy operation, continuous disinfection efficiency, and fewer byproducts production.

Solar photocatalysis application in UWWTP outlets - simulations based on predictive models in flat-plate reactors and pollutant degradation studies with in silico toxicity assessment

The application of the solar photocatalysis for the degradation of residual pollutants found in surface water was demonstrated. Semi-pilot scale flat-plate cascade reactor (FPCR) was used to study the degradation of model organic pollutants: enrofloxacin (ENRO), 17β-estradiol (E2) and 1H-benzotriazole (1H-BT) over TiO2 thin-film supported on glass fibers. A modular panel with full-spectra solar lamps with appropriate UVB and UVA irradiation levels was used as a simulation of sunlight. Pollutant degradation in FPCR was estimated using predictive models; intrinsic reaction rate constants (ki) for ENRO, E2 and 1H-BT independent of the reactor size, flow rate and irradiation conditions were determined: 9.60, 3.35 and 0.37 109 s-1 W-0.5 m1.5, respectively. Main degradation products (DPs), formed upon hydroxylation, ring opening and oxidation, were identified using LC-QTOF-MS. The ecotoxicological impact was assessed via T.E.S.T. and ECOSAR open-source tools showing the formation of less harmful DPs after sufficient reaction time. Pollutant degradation was simulated at four locations of interest, i.e. exhausts from urban wastewater treatment plants (UWWTPs) in Zagreb, Croatia (45°N), Krakow, Poland (50°N), Sevilla, Spain (37°N) and Ioannina, Greece (39.6°N). Results have proved that a simple flat-plate system with supported photocatalysts can be easily scaled up and incorporated at the outlet of UWWTP for the reduction of pollutant load and related toxicity. The exhaust canal in Zagreb with the estimated length of a photocatalytic layer of 122 m for the > 90% degradation of all target pollutants was discussed as the best installation site among studied locations. ENVIRONMENTAL IMPLICATION: A multi-disciplinary approach to the tentative application of TiO2 solar photocatalysis outdoors to reduce pollutant loads and toxicity in surface waters was demonstrated. Possible application at four selected locations in Europe, as an additional step in water treatment after urban wastewater treatment plants (UWWTPs) was discussed. Target pollutants were studied under environmentally relevant conditions (sunlight levels, water matrix, simulation of process on a real scale at selected geographical location), at both higher and low concentrations.

Sonochemistry dosimetries in seawater

Due to the complex physical and chemical interactions taking place in the sonicated medium, various methods have been proposed in the literature for a better understanding of the sonochemical system. In the present paper, the performance of calorimetry, iodometry, Fricke, 4-nitrophenol, H2O2, and ascorbic acid dosimetry techniques have been evaluated over the electric power range from 20 to 80 W (f = 300 kHz). These methods have been analyzed for distilled and seawater in light of the literature findings. It has been found that the lowest temperatures and calorimetric energies were obtained for seawater in comparison to distilled water. However, the discrepancy between both mediums disappears with the increase in the electric power up to 80 W. Compared to the calorimetry results, a similar trend was obtained for the KI dosimetry, where the discrepancy between both solutions (seawater and distilled water) increased with the reduction in the electric power down to 20 W. In contrast, over the whole range of the electric power (20-80 W), the H2O2 dosimetry was drastically influenced by the salt composition of seawater, where, I3- formation was clearly reduced in comparison to the case of the distilled water. On the other hand, a fluctuated behavior was observed for the Fricke and 4-nitrophenol dosimetry methods, especially at the low electric powers (20 and 40 W). It has been found that dosimetry techniques based on ascorbic acid or potassium iodide are the best means for accurate quantification of the sonochemical activity in the irradiated liquid. As a result, it has been concluded, in terms of the dosimetry process's performance, that the dosimetry methods are in the following order: Ascorbic acid ≈ KI > Fricke > 4-nitrophenol > H2O2.

Peroxymonosulfate Activation by Cu-OMS-2 Nanofibers for Efficient Degradation of N-Containing Heterocycles in Aquatic Solution

In this research, the degradation of different types of N-containing heterocycle (NHC) contaminants by Cu-OMS-2 via peroxymonosulfate (PMS) activation in an aqueous environment was investigated. First, the effects of different reaction parameters were optimized using benzotriazole (BTR) as the model contaminant, and the optimal reaction conditions were 8 mM PMS, 0.35 g/L Cu-OMS-2, and 30 °C. Nine different types of NHC contaminants were effectively degraded under these reaction conditions, and the degradation efficiencies and the mineralization rates of those NHCs were more than 68 and 46%, respectively. Moreover, the Cu-OMS-2/PMS process presented excellent performance at a wide pH ranging from 3.0 to 11.0 and in the presence of some representative anions (NO3- and SO42-) and dissolved organic matter (fumaric acid). The inhibition sequence of anions on BTR removal during the Cu-OMS-2/PMS process was H2PO4- > HCO3- > Cl- > CO32- > NO3- > SO42-. It was also found that 74.5 and 71.3% BTR degradation rates were achieved in actual water bodies, such as tap water and Yellow River water, respectively. Besides, the Cu-OMS-2 heterogeneous catalyst had excellent stability and reusability, and the degradation rate of BTR was still at 77.0% after 5 cycles. Finally, electron paramagnetic resonance analysis and scavenging tests showed that 1O2 and SO4- • were the primary reactive oxygen species. Accordingly, Cu-OMS-2 nanomaterial was an efficient and sustainable heterogeneous catalyst to activate PMS for the decontamination of BTR in water remediation.

A review of factors affecting the formation and roles of primary and secondary reactive species in UV254-based advanced treatment processes

The presence of organic micropollutants (OMPs) in water has been threatening human health and aquatic ecosystems worldwide. Ultraviolet-based advanced treatment processes (UV-ATPs) are one of the most effective and promising technologies to transform OMPs in water; therefore, an increasing number of emerging UV-ATPs are proposed. However, appropriate selection of UV-ATPs for practical applications is challenging because each UV-ATP generates different types and concentrations of reactive species (RSs) that may not be sufficient to degrade specific types of OMPs. Furthermore, the concentrations and types of RSs are highly influenced by anions and dissolved organic matter (DOM) coexisting in real waters, making systematic understandings of their interfering mechanisms difficult. To identify and address the knowledge gaps, this review provides a comparison of the generations and variations of various types of RSs in different UV-ATPs. These analyses not only prove the importance of water matrices on formation and consumption of primary and secondary RSs under different conditions, but also highlight the non-negligible roles of optical properties and reactivities of DOM and anions. For example, different UV-ATPs may be applicable to different target OMPs under different conditions; and the concentrations and roles of secondary RSs may outperform those of primary RSs in OMP degradation for real applications. With continuous progress and outstanding achievements in the UV-ATPs, it is hoped that the findings and conclusions of this review could facilitate further research and application of UV-ATPs.

Guidance document on the impact of water treatment processes on residues of active substances or their metabolites in water abstracted for the production of drinking water

This guidance document provides a tiered framework for risk assessors and facilitates risk managers in making decisions concerning the approval of active substances (AS) that are chemicals in plant protection products (PPPs) and biocidal products, and authorisation of the products. Based on the approaches presented in this document, a conclusion can be drawn on the impact of water treatment processes on residues of the AS or its metabolites in surface water and/or groundwater abstracted for the production of drinking water, i.e. the formation of transformation products (TPs). This guidance enables the identification of actual public health concerns from exposure to harmful compounds generated during the processing of water for the production of drinking water, and it focuses on water treatment methods commonly used in the European Union (EU). The tiered framework determines whether residues from PPP use or residues from biocidal product use can be present in water at water abstraction locations. Approaches, including experimental methods, are described that can be used to assess whether harmful TPs may form during water treatment and, if so, how to assess the impact of exposure to these water treatment TPs (tTPs) and other residues including environmental TPs (eTPs) on human and domesticated animal health through the consumption of TPs via drinking water. The types of studies or information that would be required are described while avoiding vertebrate testing as much as possible. The framework integrates the use of weight-of-evidence and, when possible alternative (new approach) methods to avoid as far as possible the need for additional testing.

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH₂Cl- and ClO₂-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.

A novel solar-activated chlorine dioxide process for atrazine degradation in drinking water

New technologies using advanced oxidation processes (AOPs) with low energy-input to address the presence of micro-contaminants and the formation of disinfection byproducts (DBPs) are required for drinking water safety. In this work, the activation of chlorine dioxide with solar (solar/ClO₂ process), a type of renewable and inexhaustible energy, was developed to degrade atrazine (ATZ) and control the formation of DBPs. Results revealed that solar/ClO₂ process was effective in degrading ATZ. Hydroxyl radicals (•OH) and chlorine radicals (Cl•) produced in solar/ClO₂ process were found to be the predominant agents for ATZ degradation with contribution rates of 55.9% and 44.1%, respectively, based on radical quenching tests and competition kinetics. Reaction pH did not affect the total amount of Cl• and •OH (i.e., [•OH]_exp) and [Cl•]_exp), while the conversion of Cl• to •OH was responsible for the depressed ATZ degradation efficiency with the increasing pH in solar/ClO₂ process. The presence of bicarbonate (HCO₃^-), chloride (Cl^-) and humic acid (HA) retarded the ATZ degradation mainly due to they decreased [•OH]_exp) and [Cl•]_exp. Using the UPLC-MS/MS analysis, six degradation intermediates of ATZ were tentatively identified, and the three-stage degradation pathway as well as the stepwise detoxification of ATZ were confirmed by the condensed Fukui function (CFF) calculation and ECOSAR prediction. Applying solar/ClO₂ as a pretreatment of HA-containing water, the formation of DBPs during post-chlorination was significantly reduced. However, the presence of ATZ during solar/ClO₂ pretreatment of HA significantly lowered the control efficiency of DBPs. The major degradation intermediate, i.e., deethyldeisopropylhydroxyatrazine (DEIHA), of ATZ could incorporate into HA and therefore providing more precursors for DBPs. The acute toxicity recorded by the behavior of zebrafish larvae revealed that using chloramine instead of chlorine downstream the solar/ClO₂ pretreatment of ATZ and HA could significantly reduce the acute toxicity by decreasing the formation of total DBPs. This study demonstrated the great potential of applying solar/ClO₂ process followed by chloramination to simultaneously degrade micro-contaminants and reduce DBPs formation as well as toxic risk in practical applications.

Abiotic transformation of kresoxim-methyl in aquatic environments: Structure elucidation of transformation products by LC-HRMS and toxicity assessment

In this study, abiotic transformation of an important strobilurin fungicide, kresoxim-methyl, was investigated under controlled laboratory conditions for the first time by studying its kinetics of hydrolysis and photolysis, degradation pathways and toxicity of possibly formed transformation products (TPs). The results indicated that kresoxim-methyl showed a fast degradation in pH9 solutions with DT₅₀ of 0.5 d but relatively stable under neutral or acidic environments in the dark. It was prone to photochemical reactions under simulated sunlight, and the photolysis behavior was easily affected by different natural substances such as humic acid (HA), Fe³⁺and NO₃^-which are ubiquitous in natural water, showing the complexity of degradation mechanisms and pathways of this chemical compound. The potential multiple photo-transformation pathways via photoisomerization, hydrolyzation of methyl ester, hydroxylation, cleavage of oxime ether and cleavage of benzyl ether were observed. 18 TPs generated from these transformations were structurally elucidated based on an integrated workflow combining suspect and nontarget screening by high resolution mass spectrum (HRMS), and two of them were confirmed with reference standards. Most of TPs, as far as we know, have never been described before. The in-silico toxicity assessment showed that some of TPs were still toxic or very toxic to aquatic organisms, although they exhibit lower aquatic toxicity compared to the parent compound. Therefore, the potential hazards of the TPs of kresoxim-methyl merits further evaluation.

Rate constants for the reactions of chloride monoxide radical (ClO•) and organic molecules of environmental interest

ClO^• plays a key role in the UV/chlorine process besides Cl^•, Cl2^• - , and ^•OH. In many experiments, ClO^• proved to be the main reactant that destroyed the organic pollutants in advanced oxidation process. About 200 rate constants of ClO^• reactions were collected from the literature, grouped together according to the chemical structure, and the molecular structure dependencies were evaluated. In most experiments, ClO^• was produced by the photolytic reaction of HClO/ClO-. For a few compounds, the rate constants were determined by the absolute method, pulse radiolysis. Most values were obtained in steady-state experiments by competitive technique or by complex kinetic calculations after measuring the pollutant degradation in the UV/chlorine process. About 30% of the listed rate constant values were derived in quantum chemical or in structure-reactivity (QSAR) calculations. The values show at least six orders of magnitude variations with the molecular structure. Molecules having electron-rich parts, e.g., phenol/phenolate, amine, or sulfite group have high rate constants in the range of 10⁸-10⁹ mol^-1 dm³ s^-1. ClO^• is inactive in reactions with saturated molecules, alcohols, or simple aromatic molecules.

Time-concentration profiles of tire particle additives and transformation products under natural and artificial aging

Tire and road wear particles (TRWP) are polymer-based microparticles that are emitted into the environment during tire usage. Growing efforts are currently being made to quantify these emissions, characterize the leachates and assess their environmental impact. This study aimed to investigate the effect of aging on TRWP composition. Cryomilled tire tread particles (CMTTP) and TRWP were exposed for different durations to three aging conditions: accelerated thermal and photochemical aging and natural outdoor aging. Particles were then extracted with cyclohexane/ethanol. The time-concentration profiles of 23 additives and transformation products present in these extracts were determined by UHPLC-HRMS. Several chemicals, such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD) or 1,3-diphenylguanidine (DPG), decayed exponentially under all aging conditions, with half-lives of a few days under artificial photoaging versus dozens of days under pure thermal aging at 60 °C. The natural aging profiles lie between those 2 laboratory aging conditions. Other chemicals, such as 6PPD-quinone, presented bell-shaped concentration profiles within CMTTP when particles were exposed to UV light. 6PPD-quinone reached a maximal concentration within a month under natural aging. For TRWP, the initial load of 6PPD-quinone had already reached a maximum prior to the aging experiments and decreased exponentially under natural aging with a half-life below one month. Pure thermal aging induced a significantly slower decay of 6PPD-quinone within TRWP (half-life of half a year), emphasizing a greater stability and persistence in environmental compartments without light. This study highlighted that the more readily accessible CMTTP could be considered a reasonable proxy of TRWP to investigate the fate of chemicals within rubber particles, at least from a qualitative standpoint. Overall, the concentrations of 20 of the evaluated chemicals decreased by >50 % within 50 days under natural aging.

Radical chemistry, degradation mechanism and toxicity evolution of BPA in the UV/chlorine and UV/H2O2

UV-assisted advanced oxidation processes (AOPs) are widely used and studied in degradation of bisphenol A (BPA). However, detailed information on their radical chemistry and degradation mechanisms is still lacking. In this study, degradation of BPA was comparatively evaluated to investigate the radical mechanisms, products and the toxicity variation in UV/chlorine and UV/H₂O₂ processes. In comparison with UV/H₂O₂, UV/chlorine had a higher BPA degradation efficiency and higher pH-dependency due to chlorination and the synergy of •OH and RCS. The •OH and Cl• played a pivotal role as the primary radicals in BPA degradation by UV/chlorine process at all pH investigated (6-8). The relative contributions of the secondary radicals ClO• gradually decreased with a variation of pH from 6 to 8 in this process. Presence of HCO₃^─ and HA inhibited BPA degradation to different extents in UV/chlorine process, while the effect of Cl^─ could be neglected. According to the identified transformation products, chlorination (major), hydroxylation and breakage of the isopropylidene chain were BPA decomposition pathways in the UV/chlorine system. In the UV/H₂O₂ system, only hydroxylation (major) and breakage of the isopropylidene chain occurred. The toxicity analysis, based on the proposed degradation pathways, indicated that the generation of chlorinated products in the UV/chlorine system led to a higher toxicity of the resulting mixture than in the UV/H₂O₂ system. Although UV/chlorine has an excellent BPA degradation effect and it is cost-effective, the possible environmental risk should be carefully considered when UV/chlorine system is used to remove BPA in real waters.

Degradation of UV-P mediated by hydroxyl radical, sulfate radical and singlet oxygen in aquatic solution: DFT and experimental studies

2-(2'-hydroxy-5'-methylphenyl) benzotriazole (UV-P) is a type of emerging persistent organic pollutant that is reported harmful to organisms. However, its degradation mechanisms and transformation behaviors in aquatic environments are not yet clear, which are significant for better understanding its environmental fate and potential toxicological impacts. In present work, the degradation mechanisms, kinetics, half-life times and eco-toxicity assessment of UV-P initiated by hydroxyl radical (•OH), sulfate radical (SO₄•^‾), and singlet oxygen (¹O₂) are systematically studied using density functional theory (DFT) and experimental methods. The initiated reaction results show that benzene ring of UV-P is vulnerable to attack by •OH, while benzotriazole is easily attacked by SO₄•^‾. The kinetic calculations indicate that •OH-addition reaction R15 is dominant initial pathway. And the half-life (t_1/2) of UV-P is calculated according to rate constants, t_1/2 decreases rapidly with [ROS] increasing. UV-P exhibits environmental persistence when [•OH] ≤ 10^-17 M. The subsequent degradation mechanisms of hydroxylated UV-P react with •OH and O₂ are also calculated. A novel ring-opening reaction channel is proposed that O₂-addition intermediate combines with hydroperoxyl radical (HO₂•) to cleave aromatic ring. The rate-determining step is intramolecular dehydration reaction with the energy barrier of 32.98 kcal mol^-1 and 41.13 kcal mol^-1 to cleave benzene ring and benzotriazole ring, respectively. The degradation experiments of UV-P are conducted in Co₃O₄ activated potassium peroxymonosulfate (PMS) system, and liquid chromatograph-mass spectrometer (LC-MS) results identified that dihydroxylated species are main intermediates, which is consistent with theoretical calculation results. Furthermore, the eco-toxicity assessment shows that the acute and chronic toxicities of most degradation products are reduced compared with UV-P, however, their toxicity levels still keep at toxic and harmful. The environmental risk of UV-P deserves more attention.

Reactive chlorine species in the enhanced degradation of UV stabilizers during the sunlight/free chlorine process

Benzotriazole (BT) and 5-methyl-1H-benzotriazole (5-MeBT) are the most commonly used UV stabilizers and recalcitrant contaminants that are widely distributed in aquatic environments. The novelty of this study was to investigate the role of RCSs in the enhanced degradation of BT and 5-MeBT during the sunlight/free chlorine process. The results showed that sunlight/free chlorine could enhance the degradation of BT and 5-MeBT compared with that obtained with sunlight irradiation and chlorination alone, and this process was well described by pseudo-first-order kinetics. The degradation rate constants of BT and 5-MeBT during sunlight/free chlorine treatment at pH 7 were 0.094 ± 0.001 min^-1 and 0.134 ± 0.002 min^-1, respectively. The degradation rates further increased with increases in the chlorine dosage and under alkaline conditions (3.818 ± 0.243 min^-1 for BT and 7.754 ± 0.716 min^-1 for 5-MeBT at pH 9). The enhanced removal obtained during the sunlight/free chlorine process could be attributed to the generation of HO• and reactive chlorine species (RCSs), such as Cl• and ClO•. Under alkaline conditions, RCSs were the dominant reactive species, and their contribution increased from 21.2% to 98.7% with increases in the pH from 7 to 9; this phenomenon was due to changes in free chlorine and BT speciation. Radical scavenging tests further verified that BT was mainly decomposed by ClO•, and ClO• showed high reactivity toward deprotonated BT through second-order rate constant estimation. A byproduct analysis demonstrated that BT underwent hydroxylation and chlorine substitution, and a high yield of 1-chlorobenzotriazole (1-ClBT) formation was observed. Even though the sunlight/free chlorine process resulted in a low level of mineralization, no Microtox® toxicity was detected in the treated solutions. Briefly, the significant contribution of ClO• to BT removal under alkaline conditions implies that sunlight/free chlorine could be utilized in a broader range of treatment conditions.

Reactive species conversion into 1O2 promotes substantial inhibition of chlorinated byproduct formation during electrooxidation of phenols in Cl--laden wastewater

The generation of chlorinated byproducts during the electrochemical oxidation (EO) of Cl^--laden wastewater is a significant concern. We aim to propose a concept of converting reactive species (e.g., reactive chlorines and HO^• resulting from electrolysis) into ¹O₂ via the addition of H₂O₂, which substantially alleviates chlorinated organic formation. When phenol was used as a model organic compound, the results showed that the H₂O₂-involving EO system outperformed the H₂O₂-absent system in terms of higher rate constants (5.95 × 10^-2 min^-1vs. 2.97 × 10^-2 min^-1) and a much lower accumulation of total organic chlorinated products (1.42 mg L^-1vs. 8.18 mg L^-1) during a 60 min operation. The rate constants of disappearance of a variety of phenolic compounds were positively correlated with the Hammett constants (σ), suggesting that the reactive species preferred oxidizing phenols with electron-rich groups. After the identification of ¹O₂ that was abundant in the bulk solution with the use of electron paramagnetic resonance and computational kinetic simulation, the routes of ¹O₂ generation were revealed. Despite the consensus as to the contribution of reaction between H₂O₂ and ClO^- to ¹O₂ formation, we conclude that the predominant pathway is through H₂O₂ reaction with electrogenerated HO^• or chlorine radicals (Cl^• and Cl₂^•-) to produce O₂^•-, followed by self-combination. Density functional theory calculations theoretically showed the difficulty in forming chlorinated byproducts for the ¹O₂-initiated phenol oxidation in the presence of Cl^-, which, by contrast, easily occurred for the Cl^•-or HO^•-initiated phenol reaction. The experiments run with real coking wastewater containing high-concentration phenols further demonstrated the superiority of the H₂O₂-involving EO system. The findings imply that this unique method for treating Cl^--laden organic wastewater is expected to be widely adopted for generalizing EO technology for environmental applications.

Effect of electrolyte composition on electrochemical oxidation: Active sulfate formation, benzotriazole degradation, and chlorinated by-products distribution

Electrochemical oxidation is an effective technique for treating persistent organic pollutants, which are hardly removed in conventional wastewater treatment plants. Sulfate and chloride salts commonly used and present in natural wastewater influence the electrochemical degradation process. In this study, the effect of electrolyte composition on the active sulfate species (SO₄^●⁻ and S₂O₈²⁻) formation, benzotriazole degradation-a model organic compound, and chlorinated by-products distribution have been investigated while using a boron-doped diamond (BDD) anode. Different Na₂SO₄:NaNO₃ and Na₂SO₄:NaCl ratios with constant conductivity of 10 mS/cm were used in the experiments and applied anode potential was kept constant at 4.3 V vs. Ag/AgCl. The electrogenerated SO₄^●⁻ and S₂O₈²⁻ formation were faster in 10:1 and 2:1 Na₂SO₄:NaNO₃ ratios than in the 1:0 ratio. The ^●OH-mediated SO₄^●⁻ production has prevailed in 10:1 and 2:1 ratios. However, ^●OH-mediated SO₄^●⁻ production has hindered the 1:0 ratio due to excess chemisorption of SO₄²⁻ on the BDD anode. Similarly, the faster benzotriazole degradation, mineralization, and lowest energy consumption were achieved in the 10:1 Na₂SO₄:NaNO₃ and Na₂SO₄:NaCl ratio. Besides, chlorinated organic by-product concentration (AOX) was lower in the 10:1 Na₂SO₄:NaCl ratio but increased with the increasing chloride ratio in the electrolyte. LC-MS analysis shows that several chlorinated organic transformation products were produced in 0:1 to 2:1 ratio, which was not found in the 10:1 Na₂SO₄:NaCl ratio. A comparatively higher amount of ClO₄⁻ was formed in the 10:1 ratio than in 2:1 to 0:1 ratio. This ClO₄⁻ formation train evidence the effective ^●OH generation in a sulfate-enriched condition because the ClO₄⁻ formation is positively correlated to ^●OH concentration. Overall results show that sulfate-enriched electrolyte compositions are beneficial for electrochemical oxidation of biorecalcitrant organic pollutants.

Exploring the adsorption behavior of benzotriazoles and benzothiazoles on polyvinyl chloride microplastics in the water environment

As a kind of emerging pollutant, microplastics (MPs) play an important role as a carrier for pollutant migration in the water environment. Carried by the MPs, benzotriazoles, and benzothiazoles (collectively referred to as BTs)¹ are ubiquitous water contaminants. In this paper, the adsorption behavior of BTs on polyvinyl chloride (PVC) MPs was first studied systematically to explain the adsorptive mechanisms and the consequential pollution caused by the absorption-desorption process. The studies on kinetics, isotherms, and thermodynamics revealed that the adsorption of BTs on PVC MPs was a multi-rate, heterogeneous multi-layer, and exothermic process, which was affected by external diffusion, intra-particle diffusion, and dynamic equilibrium. The factors including pH, salinity, and particle size also influenced the adsorption process. In the multi-solute system, competitive adsorption would occur between different BTs. The desorption of BTs from PVC MPs was positively associated with the increase of adsorption amount. Based on the results, the adsorption mechanisms of PVC MPs were clarified, involving hydrophobic interaction, electrostatic force, and non-covalent bonds. It was demonstrated that BTs in the water environment could most probably be accumulated and migrated through MPs, and eventually carried into organisms, posing an increased risk to the ecological environment.

Mechanistic Insight into Degradation of Cetirizine under UV/Chlorine Treatment: Experimental and Quantum Chemical Studies

UV/chlorine treatment is an efficient technology for removing organic pollutants in wastewater. Nevertheless, degradation of antihistamines in the UV/chlorine system, especially the underlying reaction mechanism, is not yet clear. In this study, the degradation of cetirizine (CTZ), a representative antihistamine, under UV/chlorine treatment was investigated. The results showed that CTZ could undergo fast degradation in the UV/chlorine system with an observed reaction rate constant (kobs) of (0.19 ± 0.01) min−1, which showed a first-increase and then-decrease trend with its initial concentration increased. The degradation of CTZ during the UV/chlorine treatment was attributed to direct UV irradiation (38.7%), HO• (35.3%), Cl• (7.3%), and ClO• (17.1%). The kobs of CTZ decreased with the increase in pH and the increase in concentrations of a representative dissolved organic matter, Suwannee River natural organic matter (SRNOM), due to their negative effects on the concentrations of reactive species generated in the UV/chlorine system. The detailed reaction pathways of HO•, ClO•, and Cl• with CTZ were revealed using quantum chemical calculation. This study provided significant insights into the efficient degradation and the underlying mechanism for the removal of CTZ in the UV/chlorine system.

Degradation Kinetics and Disinfection By-Product Formation of Iopromide during UV/Chlorination and UV/Persulfate Oxidation

As the detection of micropollutants in various water resources is commonly reported, developing an efficient technology to remove them to maintain water safety has become a major focus in recent years. The degradation kinetics of iopromide, one of a group of iodinated X-ray contrast media (ICM), using advanced oxidation processes of ultraviolet/chlorination (UV/Cl2) and UV/persulfate (UV/PS) oxidation were investigated in this research. The results show that iopromide degradation fitted pseudo-first-order kinetics, and the rate constants were calculated as 2.20 (± 0.01) × 10−1 min−1 and 6.08 (± 0.10) × 10−2 min−1 in UV/Cl2 and UV/PS, respectively. In the two systems, the degradation rates were positively correlated with the initial concentrations of HOCl and PS, respectively. In the UV/Cl2 system, the degradation rate of iopromide reached a maximum at pH 7, while in the UV/PS system, pH had only a slight effect on the degradation rate. Chloride in water had a negligible effect on iopromide degradation, whereas bromide inhibited iopromide degradation in the UV/Cl2 system. The contributions of UV irradiation, •OH, and RCS to iopromide degradation during UV/Cl2 treatment were calculated as 20.8%, 54.1%, and 25.1%, respectively. One carbonated and three nitrogenated disinfection by-products (C-DBP (chloroform) and N-DBPs (dichloroacetonitrile, trichloronitromethane, and trichloroacetone)) were detected at relatively high levels, along with three emerging iodinated DBPs (dichloroiodomethane, monochlorodiiodomethane, and triiodomethane). More C- and N-DBPs were generated in the UV/Cl2 and UV/PS systems than in UV irradiation, while considerably higher I-DBPs were generated in UV irradiation than in the other two systems. Thus, it is essential to pay attention to DBP formation when UV/Cl2 or UV/PS is used to treat iopromide in water. In order to better control the generation of carcinogenic and toxic I-DBPs, Cl2 or PS combined with UV should be adopted for iopromide degradation, instead of UV alone, for providing safe drinking water to the public.

Degradation of anticorrosive agent benzotriazole by electron beam irradiation: Mechanisms, degradation pathway and toxicological analysis

Benzotriazole (BTA), which is extensively served as household and engineering agent, is one of the emerging and persistent contaminants. Despite the spirit to remove BTA is willing, the traditional wastewater treatments are weak. Therefore, the degradation of BTA via electron beam was systematically explored in this study. It turned out that after 5.0 kGy irradiation, even 87.5 mg L^-1 BTA could be completely removed, and the irradiation conformed perfectly to the pseudo first-order kinetics model. The effects of solution pH, inorganic anions (CO₃^2-, HCO₃^-, NO₃^-, NO₂^-, SO₄^2-, SO₃^2-, Cl^-), and gas atmosphere were all explored. And results indicated that oxidative hydroxyl radicals played critical role in BTA irradiation. Additionally, presence of H₂O₂ and K₂S₂O₈ promoted significantly not only degradation extent but also mineralization efficiency of BTA due to they both augmented the generation of oxidative free radicals. Moreover, by combining theoretical calculations with experimental results, it could be inferred that degradation of BTA was mainly carried out by the benzene ring-opening. Further toxicity evaluation proved that as irradiation proceeded, the toxicity alleviated. Taken together, there were various indications that BTA could be effectively eliminated by electron beam irradiation in aquatic environments.

Application of UV/chlorine processes for the DR83:1 degradation from wastewater: Effect of coexisting anions

In the present work, effect of coexisting anions on the degradation performance of UV/chlorine (UV/Cl) processes as an advanced oxidation treatment for the dye containing wastewater was investigated. The results showed that by increasing pH of the solution from 3 to 11, degradation efficiency of UV/Cl process was reduced from 96.2 ± 1.4% to 62.9 ± 3.1%. In the case of 100 mg/L of DR83:1, the removal efficiency was improved from 30.2 ± 1.5% to 93.3 ± 4.7% when the chlorine dose was increased from 100 to 1000 μM. The HCO₃- and Br^- ions were the main inhibitor and promotor anions responsible for the degradation of DR83:1. The relative contribution of Cl^• was higher than that for HO^• and UV, which was about three-times higher than that for HO^•. The lowest and highest amounts of trihalomethanes were generated at acidic and alkaline conditions as well as low disinfection by products at low pH due to the generation of more HO^• radicals at acidic pH in comparison to higher pH such that less intermediates were remained to react with chlorine.

Degradation of difenoconazole in water and soil: Kinetics, degradation pathways, transformation products identification and ecotoxicity assessment

Difenoconazole is a widely used triazole fungicide that has been frequently detected in the environment, but comprehensive study about its environmental fate and toxicity of potential transformation products (TPs) is still lacking. Here, laboratory experiments were conducted to investigate the degradation kinetics, pathways, and toxicity of transformation products of difenoconazole. 12, 4 and 4 TPs generated by photolysis, hydrolysis and soil degradation were identified via UHPLC-QTOF/MS and the UNIFI software. Four intermediates TP295, TP295A, TP354A and TP387A reported for the first time were confirmed by purchase or synthesis of their standards, and they were further quantified using UHPLC-MS/MS in all tested samples. The main transformation reactions observed for difenoconazole were oxidation, dechlorination and hydroxylation in the environment. ECOSAR prediction and laboratory tests showed that the acute toxicities of four novel TPs on Brachydanio rerio, Daphnia magna and Selenastrum capricornutum are substantially lower than that of difenoconazole, while all the TPs except for TP277C were predicted chronically very toxic to fish, which may pose a potential threat to aquatic ecosystems. The results are important for elucidating the environmental fate of difenoconazole and assessing the environmental risks, and further provide guidance for scientific and reasonable use.

A Comparative Test on the Sensitivity of Freshwater and Marine Microalgae to Benzo-Sulfonamides, -Thiazoles and -Triazoles

The evaluation of the ecotoxicological effects of water pollutants is performed by using different aquatic organisms. The effects of seven compounds belonging to a class of widespread contaminants, the benzo-fused nitrogen heterocycles, on a group of simple organisms employed in reference ISO tests on water quality (unicellular algae and luminescent bacteria) have been assessed to ascertain their suitability in revealing different contamination levels in the water, wastewater, and sediments samples. Representative compounds of benzotriazoles, benzothiazoles, and benzenesulfonamides, were tested at a concentration ranging from 0.01 to 100 mg L−1. In particular, our work was focused on the long-term effects, for which little information is up to now available. Species-specific sensitivity for any whole family of pollutants was not observed. On average, the strongest growth rate inhibition values were expressed by the freshwater Raphidocelis subcapitata and the marine Phaeodactylum tricornutum algae. R. subcapitata was the only organism for which growth was affected by most of the compounds at the lowest concentrations. The tests on the bioluminescent bacterium Vibrio fisheri gave completely different results, further underlining the need for an appropriate selection of the best biosensors to be employed in biotoxicological studies.

A Compendium of the Most Promising Synthesized Organic Compounds against Several Fusarium oxysporum Species: Synthesis, Antifungal Activity, and Perspectives

Vascular wilt caused by F. oxysporum (FOX) is one of the main limitations of producing several agricultural products worldwide, causing economic losses between 40% and 100%. Various methods have been developed to control this phytopathogen, such as the cultural, biological, and chemical controls, the latter being the most widely used in the agricultural sector. The treatment of this fungus through systemic fungicides, although practical, brings problems because the agrochemical agents used have shown mutagenic effects on the fungus, increasing the pathogen's resistance. The design and the synthesis of novel synthetic antifungal agents used against FOX have been broadly studied in recent years. This review article presents a compendium of the synthetic methodologies during the last ten years as promissory, which can be used to afford novel and potential agrochemical agents. The revision is addressed from the structural core of the most active synthetic compounds against FOX. The synthetic methodologies implemented strategies based on cyclo condensation reactions, radical cyclization, electrocyclic closures, and carbon-carbon couplings by metal-organic catalysis. This revision contributes significantly to the organic chemistry, supplying novel alternatives for the use of more effective agrochemical agents against F. oxysporum.