Effect of nitrate, carbonate/bicarbonate, humic acid, and H2O2 on the kinetics and degradation mechanism of Bisphenol-A during UV photolysis

Photodegradation of bisphenol A (BPA) in coastal aquaculture waters: Influencing factors, products, and pathways

Bisphenol A (BPA), an endocrine-disrupting contaminant, is ubiquitous in the environment due to its presence in plastics, wastewater, and agricultural runoff. This study investigated the photodegradation behavior of BPA in coastal aquaculture waters near Qingdao, China. Lower salinity promoted BPA photodegradation, while higher salinity has an inhibitory effect, suggesting slower degradation in seawater compared to ultrapure water. Triplet-excited dissolved organic matter (3DOM*) was identified as the primary mediator of BPA degradation, with additional contributions from hydroxyl radicals (•OH), singlet oxygen (1O2), and halogen radicals (HRS). Alepocephalidae aquaculture water exhibited the fastest degradation rate, likely due to its high DOM and nitrate/nitrite (NO3-/NO2-) content, which are sources of 3DOM* and •OH. A positive correlation existed between NO3-/NO2- concentration and the BPA degradation rate. Ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) analysis identified the primary BPA photodegradation products, formed mainly through oxidative degradation, hydroxyl substitution, nitration, and chlorination pathways. Elucidating these photodegradation mechanisms provides valuable insights into the environmental fate and potential ecological risks of BPA in aquaculture environments. This knowledge can inform strategies for marine environmental protection and the development of sustainable practices.

Assessing the impact of simulated ocean acidification on the photodegradation of selected microplastics

This study investigated the impact of ocean acidification on the photodegradation of three microplastics (MPs): polypropylene (PP), expanded polystyrene (EPS), and ethylene-vinyl acetate (EVA), under accelerated UV radiation at three pH levels (i.e., 8.1, 7.8, and 7.5), simulating marine conditions. The acidification system simulated current and projected future environmental conditions. As expected, an increase in partial pressure of CO2, total inorganic carbon, bicarbonate ion, and CO2 resulted in more acidic pH levels, with the reverse being true for the carbonate ion. Structural changes of MPs were evaluated, revealing that all weathered samples underwent higher degradation rate compared to the virgin samples. The oxidation state and crystallinity of PP and EVA MPs were higher in samples exposed to the lowest pH, whereas no significant increase in the degradation rate of EPS samples was observed. Saltwater acidification in this study contributed to enhance the photo-oxidation of MPs depending on their polymeric composition.

Environmental transformation and hazards of decachlorobiphenyl on suspended particles under sunlight irradiation

Decachlorobiphenyl (PCB-209) can be widely detected in suspended particles and sediments due to its large hydrophobicity, and some of its transformation products may potentially threaten organisms through the food chain. Here we investigate the photochemical transformation of PCB-209 on suspended particles from the Yellow River. It was found that the suspended particles had an obvious shielding effect to largely inhibit the photodegradation of PCB-209. Meanwhile, the presence of inorganic ions (e.g. Mg2+ and NO3-) and organic matters (e.g. humic acid, HA) in the Yellow River water inhibited the reaction. The main transformation products of PCB-209 were lower-chlorinated and hydroxylated polychlorinated biphenyls (OH-PCBs), and small amounts of pentachlorophenol (PCP) and polychlorinated dibenzofurans (PCDFs) were also observed. The mechanisms of PCP formation by double •OH attacking carbon bridge and PCDFs formation by elimination reaction of ionic state OH-PCBs were proposed using theoretical calculations, which provided some new insights into the inter-transformations between persistent organic pollutants. In combination with VEGA and EPI Suite software, some intermediates such as PCDFs were more toxic to organisms than PCB-209. This study deepens the understanding of the transformation behavior of PCB-209 on suspended particles under sunlight.

Aging behavior and leaching characteristics of microfibers in landfill leachate: Important role of surface mesh structure

Mesh-structured films formed by the post-processing of microfibers improves their permeability and dexterity, such as disposable masks. However, the aging behavior and potential risks of mesh-structured microfibers (MS-MFs) in landfill leachate remain poorly understood. Herein, the aging behavior and mechanisms of MS-MFs and ordinary polypropylene-films (PP-films) microplastics, as well as their leaching concerning dissolved organic matter (DOM) in landfill leachate were investigated. Results revealed that MS-MFs underwent more significant physicochemical changes than PP-films during the aging process in landfill leachate, due to their rich porous habitats. An important factor in the photoaging of MS-MFs was related to reactive oxygen species produced by DOM, and this process was promoted by photoelectrons under UV irradiation. Compared with PP-films, MS-MFs released more DOM and nano-plastics fragments into landfill leachate, altering the composition and molecular weight of DOM. Aged MS-MFs-DOM generated new components, and humus-like substances produced by photochemistry showed the largest increase. Correlation analysis revealed that leached DOM was positively correlated with oxygen-containing groups accumulated in aged MS-MFs. Overall, MS-MFs will bring higher environmental risks and become a new long-term source of DOM contaminants in landfill leachate. This study provides new insights into the impact of novel microfibers on landfill leachate carbon dynamics.

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

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

Co-existing inorganic anions influenced the Norrish I and Norrish II type photoaging mechanism of biodegradable microplastics

The degradation of biodegradable plastics (BPs) in natural environments is constrained, and the mechanisms underlying their photoaging in aquatic settings remain inadequately understood. In view of this, this study systematically investigated the photoaging process of biodegradable Poly (butyleneadipate-co-terephthalate) microplastics (PBAT-MPs), which are more widely used. The investigation was carried out in the presence of common inorganic anions (Br-, Cl- and NO3-). The results of EPR, FTIR and FESEM tests, along with pseudo-first-order kinetics analyses, showed that the presence of NO3- promoted the photoaging of PBAT-MPs, while the presence of Br- and Cl- inhibited the photoaging of PBAT-MPs. In addition, the results of the Two-Dimensional Correlation Spectroscopy (2D-COS) analysis determined the order of the changes in the functional groups, revealing that the Norrish I and Norrish II reaction mechanisms are presented by PBAT-MPs during the aging process, and the process is closely related to the ion concentration and UV irradiation time. This study provides valuable insights for understanding the phototransformation process of BPs in natural aqueous environments.

Rapid measurement of bacterial contamination in water: A catalase responsive-electrochemical sensor

The present study describes the development of a potentiometric sensor for microbial monitoring in water based on catalase activity. The sensor comprises a MnO2-modified electrode that responds linearly to hydrogen peroxide (H2O2) from 0.16 M to 3.26 M. The electrode potential drops when the H2O2 solution is spiked with catalase or catalase-producing microorganisms that decompose H2O2. The sensor is responsive to different bacteria and their catalase activities. The electrochemical sensor exhibits a lower limit of detection (LOD) for Escherichia coli at 11 CFU/ml, Citrobacter youngae at 12 CFU/ml, and Pseudomonas aeruginosa at 23 CFU/ml. The sensor shows high sensitivity at 3.49, 3.02, and 4.24 mV/cm2dec for E. coli, C. youngae, and P. aeruginosa, respectively. The abiotic sensing electrode can be used multiple times without changing the response potential (up to 100 readings) with a shelf-life of over six months. The response time is a few seconds, with a total test time of 5 min. Additionally, the sensor effectively tested actual samples (drinking and grey water), which makes it a quick and reliable sensing tool. Therefore, the study offers a promising water monitoring tool with high sensitivity, stability, good detection limit, and minimum interference from other water contaminants.

Removal characteristics of 53 micropollutants during ozonation, chlorination, and UV/H2O2 processes used in drinking water treatment plant

The removal of 53 emerging micropollutants (MPs), including 10 per- and polyfluorinated substances (PFASs), 25 pharmaceuticals and personal care products (PPCPs), 7 pesticides, 5 endocrine disrupters (EDCs), 3 nitrosamines, and 3 taste and odor compounds (T&Os), by chlorination, ozonation, and UV/H2O2 treatment was examined in deionized water and surface waters used as the raw waters in drinking water treatment plants (DWTPs) in South Korea. The UV/H2O2 treatment was effective in the removal of most MPs, whereas chlorination was selectively effective for 19 MPs, including EDCs (>70 %). MPs containing aromatic ring with electron-donating functional group, or primary and secondary amines were effectively removed by chlorination immediately upon reaction initiation. The removal of MPs by ozonation was generally lower than that of the other two processes at a low ozone dose (1 mg L-1), but higher than chlorination at a high ozone dose (3 mg L-1), particularly for 16 MPs, including T&Os. Compared in deionized water, the removals of MPs in the raw water samples were lower in all three processes. The regression models predicting the rate constants (kobs) of 53 MPs showed good agreement between modeled and measured value for UV/H2O2 treatment (R2 = 0.948) and chlorination (R2 = 0.973), despite using only dissolved organic carbon (DOC) and oxidant concentration as variables, whereas the ozonation model showed a variation (R2 = 0.943). Our results can provide the resources for determining which oxidative process is suitable for treating specific MPs present in the raw waters of DWTPs.

Photodegradation of anthelmintic drugs under natural sunlight and simulated irradiation: kinetics, mechanisms, transformation products, and toxicity

Albendazole (ALB) and bithionol (BIT) are two anthelmintic drugs (ADs) with high consumption from benzimidazole group and diphenylsulfide group, respectively. However, information on the transformation of the two anthelmintics under environmental condition is scare. Therefore, in the present study, we investigated the natural attenuation of the two ADs in the aquatic environment, including biodegradation, hydrolysis, and direct and indirect photodegradation. The direct photodegradation occupied a vast portion among other degradation pathways of the two ADs in natural water, with near-surface summer half-lives of 0.272-0.387 h and 0.110-0.520 h for ALB and BIT, respectively. Suspended particles in water were found to facilitate the photodegradation of the two ADs. Study on the indirect photodegradation demonstrated the positive roles of singlet oxygen (1O2) and excited triplet dissolved organic matter (3DOM*) in the photolysis of the two ADs, whereas the hydroxyl radical (•OH) affected little on the overall photodegradation procedures of ALB due to the scavenging effect of HCO3-. Dual effects of DO, DOM, HCO3-, NO3-, and NO2- on the photodegradation of ALB and BIT were perceived. Transformation intermediates (TIs) of the two ADs during photodegradation were analyzed by UHPLC-QTOF-MS. Six TIs of ALB were identified, including a broad-spectrum fungicide carbendazim and another common AD ricobendazole. Two TIs of BIT yielded from dechlorination were also detected. Probable transformation mechanism and predicted aquatic ecotoxicity based on the identified TIs were unveiled.

Effect of bicarbonate on nitrate-induced photosensitive degradation of sulfamethoxazole under UV irradiation

In this study, the influence of HCO3- on NO3--induced photosensitive degradation of sulfamethoxazole (SMX) under UV irradiation was investigated. It was found that the removal of SMX by UV in the presence of NO3- improved significantly compared to its photolysis, which was confirmed to be due to the role of hydroxyl radical (HO•) formed through UV-activated NO3-. However, the addition of HCO3- in UV/NO3- system could further enhance SMX degradation, which was verified to be ascribed to the formed carbonate radical (CO3•-) through the reaction of HCO3- with HO•. The second-order rate constant of CO3•- with SMX was determined to be 2.58 × 108 M-1 s-1. In UV/NO3-/HCO3- system, the reactive species for SMX removal were HO• and CO3•-, and the contribution of CO3•- to SMX degradation might be much higher than that of HO•. The concentration of NO3- was almost unchanged after reaction in UV/NO3- and UV/NO3-/HCO3- systems because of its regeneration. Based on the detected four transformation products, the possible degradation pathways of SMX in UV/NO3-/HCO3- system were proposed including hydroxylation, amino-oxidation and bond cleavage.

Direct and indirect photodegradation of bisphenol A in the presence of natural water components

The impacts and mechanisms of natural water constituents, such as humic acid (HA), nitrates, iron and chloride ions, to the photodegradation of bisphenol A (BPA) were investigated in aqueous media under UV light irradiation. Due to the contributions of ·OH, 1O2, O2- and BPA* to BPA photodegradation in pure water in 13.4, 7.7, 22.9 and 47.9%, respectively, BPA was attenuated through the reaction pathway of direct photodegradation more than self-sensitized photodegradation. About indirect photodegradation, BPA photolysis through inhibitory effect from HA was mainly by light screening effect and quenching effect was insignificant. NO- 3 and NO- 2 both showed inhibitory effect but due to different reactive oxidization species (ROS). The photodegradation of BPA was significantly enhanced by the addition of iron from the formation of ·OH and H2O2, due to iron-assisted indirect photolysis for the degradation process. A dual effect of chloride depending on the different concentration levels involved quenching and promotion effect on reactive photo-induced species (RPS). A simple linear model revealed that BPA photodegradation was significantly impacted by the interaction of the above factors. In natural water, the decreased photolytic rate of BPA was mainly attributed to triple-excited dissolved organic matter (3DOM*), indicating that indirect photolysis was the primary transformation pathway of BPA. The detected photolysis products, such as nitrate and chlorinated products, suggest that there might be potential ecological risk of BPA photodegradation.

Effects of wavelength on the treatment of contaminants of emerging concern by UV-assisted homogeneous advanced oxidation/reduction processes

Pollutants of emerging concern in aqueous environments present a significant threat to both the aquatic ecosystem and human health due to their rapid transfer. Among the various treatment approaches to remove those pollutants, UV-assisted advanced oxidation/reduction processes are considered competent and cost-effective. The treatment effectiveness is highly dependent on the wavelength of the UV irradiation used. This article systematically discusses the wavelength dependency of direct photolysis, UV/peroxides, UV/chlor(am)ine, UV/ClO2, UV/natural organic matter, UV/nitrate, and UV/sulfite on the transformation of contaminants. Altering wavelengths affects the photolysis of target pollutants, photo-decay of the oxidant/reductant, and quantum yields of reactive species generated in the processes, which significantly impact the degradation rates and formation of disinfection byproducts. In general, the degradation of contaminants is most efficient when using wavelengths that closely match the highest molar absorption coefficients of the target pollutants or the oxidizing/reducing agents, and the contribution of pollutant absorption is generally more significant. By matching the wavelength with the peak absorbance of target compounds and oxidants/reductants, researchers and engineers have the potential to optimize the UV wavelengths used in UV-AO/RPs to effectively remove pollutants and control the formation of disinfection byproducts.

Fate and environmental behaviors of microplastics through the lens of free radical

Microplastics (MPs), as plastics with a size of less than 5 mm, are ubiquitously present in the environment and become an increasing environmental concern. The fate and environmental behavior of MPs are significantly influenced by the presence of free radicals. Free radicals can cause surface breakage, chemical release, change in crystallinity and hydrophilicity, and aggregation of MPs. On the other hand, the generation of free radicals with a high concentration and oxidation potential can effectively degrade MPs. There is a limited review article to bridge the fate and environmental behaviors of MP with free radicals and their reactions. This paper reviews the sources, types, detection methods, generation mechanisms, and influencing factors of free radicals affecting the environmental processes of MPs, the environmental effects of MPs controlled by free radicals, and the degradation strategies of MPs based on free radical-associated technologies. Moreover, this review elaborates on the limitations of the current research and provides ideas for future research on the interactions between MPs and free radicals to better explain their environmental impacts and control their risks. This article aims to keep the reader abreast of the latest development in the fate and environmental behaviors of MP with free radicals and their reactions and to bridge free radical chemistry with MP control methodology.

Enhanced Direct Photolysis of Organic Micropollutants by Far-UVC Light at 222 nm from KrCl* Excilamps

Krypton chloride (KrCl*) excilamps emitting at far-UVC 222 nm represent a promising technology for microbial disinfection and advanced oxidation of organic micropollutants (OMPs) in water treatment. However, direct photolysis rates and photochemical properties at 222 nm are largely unknown for common OMPs. In this study, we evaluated photolysis for 46 OMPs by a KrCl* excilamp and compared it with a low-pressure mercury UV lamp. Generally, OMP photolysis was greatly enhanced at 222 nm with fluence rate-normalized rate constants of 0.2-21.6 cm²·μEinstein^-1, regardless of whether they feature higher or lower absorbance at 222 nm than at 254 nm. The photolysis rate constants and quantum yields were 10-100 and 1.1-47 times higher, respectively, than those at 254 nm for most OMPs. The enhanced photolysis at 222 nm was mainly caused by strong light absorbance for non-nitrogenous, aniline-like, and triazine OMPs, while notably higher quantum yield (4-47 times of that at 254 nm) occurred for nitrogenous OMPs. At 222 nm, humic acid can inhibit OMP photolysis by light screening and potentially by quenching intermediates, while nitrate/nitrite may contribute more than others to screen light. Overall, KrCl* excilamps are promising in achieving effective OMP photolysis and merit further research.

The acceleration on decolorization of azo dyes by magnetic lignin-based materials via enhancing the extracellular electron transfer

Two novel and eco-friendly redox mediators (RMs), magnetic oxidative vanillin (MOV) and magnetic oxidative syringaldehyde (MOS), both derived from lignin, were prepared to improve the decolorization of the methyl orange (MO) dye. The Decolorization Efficiency (DE) of MO in the batch experiments with MOV and MOS were increased by more than 60% and 22%, respectively, when compared to the control experiment without magnetic RMs. Moreover, the two magnetic RMs could maintain stable DE of MO in sequenced batch reactors (SBRs), and negligible leaching of the oxidized lignin monomers was observed under various environmental conditions. Density Function Theory (DFT) calculations were used to propose three potential biodegradation mechanisms for azo dyes, and the key intermediates were confirmed using high-performance liquid chromatography. This study proposed a feasible strategy for functional utilization of lignin resource, as well as a practical method for effectively treating azo dye-containing wastewater.

Low-pressure ultraviolet-H2O2 photolysis for restoring the anodic stripping voltammetry signal: a new strategy for the detection of heavy metal ions in complex organic matter

A new strategy based on low-pressure ultraviolet (LPUV)-H₂O₂ advanced oxidation photolysis for the quantitative determination of organic heavy metal ions (HMIs) in soil was proposed for the efficient, low-cost, accurate, and green detection of Pb(II) and Cd(II) in soil extracts by breaking the complexation of HMIs and organic matters, consequently restoring the ASV signals of target HMIs. The key parameters of the proposed LPUV-H₂O₂ photolysis system for the restoration of stripping responses were optimized; the conversion of organic matter to inorganic matter during the photolysis was investigated by total organic carbon (TOC); the degradation kinetics of humic acid sodium (HAS) was measured by UV-vis spectroscopy (UV); the pathway of HAS converted to small molecule organics during degradation was observed by fluorescence spectroscopy (FS); additionally, Fourier transform infrared spectroscopy (FTIR) was used to study the complexation between HAS and HMIs. The results showed that the stripping signals of target HMIs in the simulated soil samples can be restored to nearly 100% with a good repeatability, and the restoration ratio of the stripping signal fluctuated within 10%. And the feasibility of the proposed method for the accurate detection of HMIs in the real soil samples was verified; the results showed that 93.7% of Cd(II) and 92.5% of Pb(II) in real soil extracts were detectable.

Modeling carbonate/bicarbonate and nitrate disturbance during secondary effluent disinfection by UV/H2O2 and UV/ozone

The disinfection of effluents has been considered the main step to inactivate pathogenic organisms to prevent the spread of waterborne diseases. The variation in the matrix composition can lead to the use of inadequate oxidant dose and disturb a correct treatment. The objective of this study was to develop a simple and practical mathematical model to simulate the disturbance of inorganic anions (CO₃^2-/HCO₃^- and NO₃^-) during secondary effluent disinfection by UV/H₂O₂ and UV/O₃. The pathogenic agents chosen for this study were total coliforms and E. coli. To build the mathematical model, a modification of the Chick model (referred to as 'Modified Chick Model') was proposed by employing a weighted average in the calculation of the kinetic constant. Both treatments were affected by the presence of the anions. However, with the highest NO₃^- concentration, less inhibition of disinfection was observed in the UV/H₂O₂. The use of the arithmetic means to calculate the value of k, as indicated by the Chick model, demonstrates a lesser precision in the prediction of the microorganisms' concentrations. On the other hand, using the Modified Chick Model, a better prediction of the inactivation of the microorganisms was obtained, which can be confirmed by the validation performed.

A persulfate oxidation system for removing acid orange from aqueous solution: Evaluation and degradation mechanism

Peroxymonosulfate-based advanced oxidation (PMS-AOP) is a promising technology for the degradation of environmental pollutants. PMS can be activated by various transition metals, especially cobalt-based catalysts, but pure cobalt catalyst suffers from severe metal leakage and poor cyclicality. This study synthesized NiCo₂O₄ using a co-precipitation hydrothermal method. The structures, morphologies, and chemical states of the prepared catalysts were hexagonal sheet structures. The activation of PMS by catalyst (NiCo₂O₄) is investigated in a PMS/carbonate (PC) system for Orange II degradation. The observed pseudo-first-order rate constants (k₁) were assessed by the effects of different water matrices and operation conditions. The results show that k_obs with NiCo₂O₄ were increased by 13 times than that of treatment without NiCo₂O₄. This was mainly due to Co³⁺ and Ni³⁺ act as electron acceptors to capture electrons from the PMS/PC system, forming a good redox cycle with HSO₅^-/SO₅^- and oxidizing Co²⁺/Ni²⁺ to produce a large amount of more active components (e.g., ¹O₂ and SO₄^⋅-). The good reusability and high stability of NiCo₂O₄ were demonstrated by five recycle tests. These results suggest that the NiCo₂O₄/PC system is an efficient and stable method of pollution remediation.

Photodegradation of free estrogens driven by UV light: Effects of operation mode and water matrix

Estrogens are endocrine disrupting chemicals that have been frequently detected in diverse water matrices (e.g. surface water, wastewater and drinking water) and caused a series of health risks. This study was aimed at investigating the photochemical degradation of free estrogens estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethyl estradiol (EE2) upon the monochromatic irradiation (253.7 nm). Concerning the practical installation of photolysis treatment, exposing the impacts of photoreactor operation mode (stationary or up-flow) and the water matrix (ultrapure water or natural surface water) on the photolytic behaviour of estrogens was of high importance. The pseudo-first-order rate constants showed that E1 was the most susceptible to UV radiation among chosen estrogens due to its high molar absorption coefficient of 402.4 M^-1 cm^-1 and quantum yield of 0.065 mol E^-1 at λ = 253.7 nm. Moreover, the up-flow mode and the surface water matrix collected from a lake in Regent's Park (London) were found to favour the photodegradation of estrogens due to the introduction of more dissolved oxygens and promotion of reactive oxygen species (ROS) formation. These findings may shed light on the photochemical behaviour of estrogens in some specific scenarios.

UV activated sodium percarbonate to accelerate degradation of atrazine: Mechanism, intermediates, and evaluation on residual toxicity by metabolomics

Efficient and safe removal of widely used herbicides such as atrazine has become a recent hotspot. Herein, UV driven sodium percarbonate system (UV/SPC) was established to have many advantages in remediation of atrazine contamination. The mechanism and environmental risk of intermediates were explored, which provided information for the feasibility of UV/SPC. The degradation efficiency of atrazine was significantly enhanced as the increasing dosage of SPC. Quenching assay identified that •OH and CO3•- were committed to degrading atrazine. Humic acid and HPO42- remarkably inhibited atrazine degradation. Several intermediates were generated through the dealkylation, dechlorination-hydroxylation, alkylic-hydroxylation, alkyl oxidation and olefination reactions. Toxicity prediction proved that acute toxicity and bioaccumulation of intermediates were mitigated comparing with atrazine. Based on metabolomics results, the alteration of key metabolites such as citrate, L-kynurenine, malic acid, putrescine, glutamine, spermine, ethanolamine and phytosphingosine in various metabolic pathways of E.coli verified that the toxicity of atrazine was weakened after UV/SPC treatment. The application of UV/SPC on atrazine removal in real waters was influenced by environmental factors, and might be improved through coupling with other treatment technologies.

Enantioselective hydrolysis and photolysis of mandipropamid in different aquatic environments - evaluation of influencing factors

The hydrolysis and photolysis of the chiral fungicide mandipropamid were investigated, and the potential enantioselectivity of mandipropamid in solutions was further assessed. The aqueous solutions were filtered and directly injected into the liquid chromatography with tandem mass spectrometry. In the hydrolysis experiments, mandipropamid enantiomers hydrolyzed slowly in aquatic solutions with half-lives > 200 days; nevertheless, rise of the pH and incubation temperature could increase the hydrolysis rates more than 1.1 times (half-lives decreased from 495.1 to 216.6 days). Compared with the hydrolysis results, photolysis was found to be the main degradation pathway for mandipropamid in different solutions (half-lives < 14 h, except in pH = 5.05 buffer solution). Organic solvents were able to accelerate the photolysis of mandipropamid, but acidic solutions and the addition of flavonoids or inorganic salts significantly inhibited the photolysis of mandipropamid. During the hydrolysis and photolysis processes, the configuration of mandipropamid enantiomers was stable and five possible transformation products were identified by high resolution mass spectrometry. Due to the enantiomeric fraction values > 0.5, the hydrolysis and photolysis of mandipropamid were enantioselective, and S-( +)-mandipropamid preferentially disspated in certain aqueous solutions. The systematic evaluation of the hydrolysis and photolysis of mandipropamid enantiomers may provide more accurate data for better assessment of environmental and ecological risks in aquatic ecosystems.

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.

Influence of water matrix on the degradation of organic micropollutants by ozone based processes: A review on oxidant scavenging mechanism

The prevalence of organic micropollutants (OMPs) in aquatic environment has expedited scientific and regulatory efforts to retrofit existing wastewater treatment plants (WWTPs). The current strategy involves WWTPs upgrading with post-ozonation i.e., ozone (O₃) and/or peroxone process (O₃ +H₂O₂). Still, ozone-based degradation of OMPs faces several challenges. For example, the degradation mechanism and kinetics of OMPs could largely be affected by water matrix compounds which include inorganic ions and natural organic matter (NOM). pH also plays a decisive role in determining the reactivity of the oxidants (O₃, H₂O₂, andHO^•), stability and speciation of matrix constituents and OMPs and thus susceptibility of OMPs to the reactions with oxidants. There have been reviews discussing the impact of matrix components on the degradation of OMPs by advanced oxidation processes (AOPs). Nevertheless, a review focusing on scavenging mechanisms, formation of secondary oxidants and their scavenging effects with a particular focus on ozonation and peroxone process is lacking. Therefore, in order to broaden the knowledge on this subject, the database 'Web of Science' was searched for the studies related to the 'matrix effect on the degradation of organic micropollutants by ozone based processes' over the time period of 2004-2021. The relevant literature was thoroughly reviewed and following conclusions were made: i) chloride has inhibitory effects if it exits at higher concentrations or as free chlorine i.e. HOCl/ClO^-. ii) The inhibitory effects of chloride, bromide, HOBr/OBr^- and HOCl/ClO^- are dominant in neutral and alkaline conditions and may result in the formation of secondary oxidants (e.g., chlorine atoms or free bromine), which in turn contribute to pollutant degradation or form undesired oxidation by-products such as BrO₃^-, ClO₃^- and halogenated organic products. ii) NOM may induce inhibitory or synergetic effects depending on the type, chemical properties and concentration of NOM. Therefore, more efforts are required to understand the importance of pH variation as well as the effects of water matrix on the reactivity of oxidants and subsequent degradation of OMPs.

A critical review of presence, removal and potential impacts of endocrine disruptors bisphenol A

Bisphenol A (BPA) is a synthetic organic compound that is mainly used in the production of polymer materials polycarbonate and epoxy resin. Widespread use and irregular processing methods have led to BPA being detected globally, raising concerns about its environmental and health effects. This review outlines an overview of the presence and removal of BPA in the environment and consumer products. We also summarized the endocrine-disrupting toxicity of BPA, and the relatively less summarized neurotoxicity, cytotoxicity, reproductive toxicity, genotoxicity, and carcinogenicity. Human exposure data show that humans have been exposed to low concentrations of BPA for a long time, future research should focus on the long-term exposure and the migration of BPA from consumer products to humans and the possible health risks associated with human exposure to BPA. Exploring economical and effective methods to reduce and remove BPA from the environment is imperative. The development of safe, functional and reproducible BPA analogs and the study of its degradation products can be the focus of subsequent research.

Degradation of saccharin by UV/H2O2 and UV/PS processes: A comparative study

Artificial sweeteners have raised emerging concern due to their potential threats to human health, which were frequently detected in aquatic environment with median concentrations. Although current researches have widely reported that ultraviolet light-activated persulfate process (UV/PS) was superior to UV/H₂O₂ process for the degradation of refractory organic contaminants, UV/H₂O₂ process presented a more satisfactory saccharin (SAC) removal efficiency than UV/PS process, completely degraded 20 mg/L SAC within 45 min. Hence, quenching and probe experiments were employed to investigate the difference between hydroxyl radical (OH)- and sulfate radical (SO₄^-)-mediated oxidation mechanisms, which revealed the higher reactivity of OH (1.37-1.56 × 10⁹ M^-1 s^-1) toward SAC than SO₄^- (3.84-4.13 × 10⁸ M^-1 s^-1). A combination of density functional theory calculation and transformation products identification disclosed that OH preferred to attack the benzene ring of SAC via hydrogen atom transfer pathway, whereas SO₄^- oxidation was conducive to the cleavage of -C-NH₂ bond. Increasing oxidant concentration significantly accelerated SAC degradation in both processes, while UV/H₂O₂ process consumed lower electrical energy with respect to UV/PS process. Additionally, UV/H₂O₂ system presented excellent adaptability and stability under various water matrices parameters (e.g. pH, anions and humic acid). While both UV/H₂O₂ and UV/PS processes promoted the generation of disinfection by-products (DBPs) during subsequent chlorination, and prolonging pretreatment time posed positive effect on reducing the formation of DBPs. Overall, the results clearly demonstrate the high efficiency, economy and practicality of UV/H₂O₂ process in the remediation of SAC-contaminated water.

Direct and nitrite-sensitized indirect photolysis of effluent-derived phenolic contaminants under UV254 irradiation

UV₂₅₄ photolysis has increasingly been utilized for disinfection of water-born pathogens in wastewater. During disinfection, wastewater-derived trace organic contaminants, such as pharmaceuticals and personal care products (PPCPs), may be subjected to direct photolysis and indirect photolysis sensitized by wastewater constituents such as nitrite (NO₂^-). Herein, we reported the direct photolysis and NO₂^--sensitized indirect photolysis of four phenolic contaminants commonly observed in wastewaters (i.e., bisphenol A (BPA), acetaminophen (ATP), salbutamol (SAL), and 2,4-dihydroxybenzophenone (BP1)). Spectroscopic characterization and quantum yield measurement were carried out to evaluate the photochemical reactivity of these phenolic compounds. In NO₂^--sensitized photolysis, the relative contribution of direct and indirect photolysis was quantified by light screening factor calculation and radical quenching studies. The experimental results highlight the important roles of HO˙ and NO₂˙ in the NO₂^--sensitized photolysis of phenolic compounds. A series of intermediate products, including hydroxylated, nitrated, nitrosated, dimerized, and alkyl chain cleavage products, were identified by solid phase extraction (SPE) combined with high-resolution mass spectrometry (HRMS) analyses. On the basis of identified products, the underlying mechanisms and transformation pathways for NO₂^--sensitized photolysis of these phenolic compounds were elucidated. The second-order rate constants of BPA, SAL, BP1 with NO₂˙ were calculated to be 2.25 × 10⁴, 1.35 × 10⁴ and 2.44 × 10⁴ M^-1 s^-1, respectively, by kinetic modeling. Suwanee River natural organic matter (SRNOM) played complex roles in the direct and NO₂^--sensitized photolysis of phenolic compounds by serving as a photosensitizer, light screening and radical quenching agent. Wastewater constituents, such as NO₃^- and EfOM, could accelerate direct and NO₂^--sensitized photolysis of BPA, SAL, and BP1 in the wastewater matrix. Our results suggest that NO₂^- at the WWTP effluent-relevant level can sensitize the photolysis of effluent-derived phenolic contaminants during the UV₂₅₄ disinfection process; however, the formation of potentially carcinogenic and mutagenic nitrated/nitrosated derivatives should be scrutinized.

Removal efficiencies and risk assessment of endocrine-disrupting chemicals at two wastewater treatment plants in South China

Endocrine-disrupting chemicals (EDCs) in the effluent from wastewater treatment plants (WWTPs) are an important pollutant sources of the aquatic system. In this study, the removal efficiencies of eight typical EDCs at two domestic WWTPs in Dongguan City, China, are reported based on instrumental analysis and bioassay results. Bioactivities, including steroidogenesis-disrupting effects, estrogen receptor (ER)-binding activity, and aryl hydrocarbon receptor (AhR)-binding activity were evaluated using the H295R, MVLN, and H4IIE cell bioassays, respectively. The potential environmental risks of these residual EDCs were also evaluated. The results of instrumental analysis showed that nonylphenol was the major chemical type present among the eight tested EDCs. Meanwhile, concentrations of estrogen compounds including estrone, 17β-estradiol (E2), estriol, 17α-ethinyl estradiol, and diethylstilbestrol were relatively low. The removal rates of all eight EDCs were relatively high. Although the chemical analysis indicated high removal efficiency, the bioassay results showed that steroidogenesis-disrupting effects as well as ER-binding and AhR-binding activities remained, with E2-equivalent values of effluent samples ranging from 0.16 to 0.9 ng·L^-1, and 2,3,7,8-tetrachlorodibenzo-p-dioxin-equivalent values ranging from 0.61 to 4.09 ng L^-1. Principal component analysis combined with regression analysis suggests that the chemicals analyzed in this study were partly responsible for these ER and AhR activities. Ecological risk assessment of the residual EDCs showed that estrone was the most hazardous chemical among the eight EDCs tested, with a risk quotient of 1.44-5.50. Overall, this study suggests that, despite high apparent removal efficiencies of typical EDCs, their bioactivities and potential ecological risks cannot be ignored.

Ultraviolet photolysis of four typical cardiovascular drugs: mechanisms, influencing factors, degradation pathways, and toxicity trends

The cardiovascular drugs (CDDs), such as metoprolol (MET), atenolol (ATE), bezafibrate (BZB), and atorvastatin (ATO), have been frequently detected in the water environment. They can cause potential threats to the ecological environment and human health due to their "pseudo-persistence" effect. In this study, the photolysis kinetics, degradation mechanisms, by-products, influencing factors, and acute toxicity of these four typical CDDs under polychromatic ultraviolet irradiation (200-400 nm) were investigated. The results showed that the photolysis of ATE, BZB, MET, and ATO all followed pseudo-first-order kinetics, and their average photon quantum yields of the wavelength studied were 0.14×10^-2, 0.33×10^-3, 0.78×10^-4, and 0.24×10^-4 mol einstein^-1, respectively. Singlet oxygen (¹O₂), hydroxyl radical (·OH), and the triplet-excited state of the cardiovascular drug (³CDD*) were all involved in the photolysis while ¹O₂ was the dominator. The effects of NO₃^-, Cl^-, HCO₃^-, and humic acid (HA) on the photolysis were the combination of light-shielding, quenching, and excitation of reactive species. Seven, four, four, and nine photolysis products of ATO, BZB, ATE, and MET were identified, respectively, and their possible degradation pathways were proposed. The acute toxicity of ATE was basically unchanged during photolysis; however, ATO, BZB, and MET toxicity all increased due to the generation of ketonization and hydroxylation products.

Dual-site electrocatalytic nitrate reduction to ammonia on oxygen vacancy-enriched and Pd-decorated MnO2 nanosheets

Electrocatalytic nitrate reduction (NRR) represents one promising alternative to the Haber-Bosch process for NH₃ production due to the lower reaction energy barrier compared to N₂ reduction and the potential recycling of nitrogen source from nitrate wastewater. The metal oxides with oxygen vacancy (O_v) display high NH₃ selectivities in NRR (NO₂^-/N₂ as side products), but the complexity in O_v enrichment and the inferior hydrogen adsorption on oxides make NRR an inefficient process. Herein, one superior dual-site NRR electrocatalyst that is composed of O_v-enriched MnO₂ nanosheets (MnO₂-O_v) and Pd nanoparticles (deposited on MnO₂) is constructed over the three-dimensional porous nickel foam (Pd-MnO₂-O_v/Ni foam). In a continuous-flow reaction cell, this electrode delivers a NO₃^--N conversion rate of 642 mg N m^-2_electrode h^-1 and a NH₃ selectivity of 87.64% at -0.85 V vs. Ag/AgCl when feeding 22.5 mg L^-1 of NO₃^--N (0.875 mL min^-1), outperforming the Pd/Ni foam (369 mg N m^-2_electrode h^-1, 85.02%) and MnO₂-O_v/Ni foam (118 mg N m^-2_electrode h^-1, 32.25%). Increasing the feeding NO₃^--N concentration and flow rate to 180.0 mg L^-1 and 2.81 mL min^-1 can further lift the conversion rate to 1933 and 1171 mg N m^-2_electrode h^-1, respectively. The combination of experimental characterizations and theoretical calculations reveal that the MnO₂-O_v adsorbs, immobilizes, and activates the NO₃^- and N-intermediates, while the Pd supplies the O_v sites with sufficient adsorbed hydrogen (H*) for both the NRR and O_v refreshment. Our work presents a good example of utilizing dual-site catalysis in the highly selective conversion of NO₃^- to NH₃ that is important for nitrate pollution abatement, nitrogen resource recycling, as well as sustainable NH₃ production.

Occurrence of unknown reactive species in UV/H2O2 system leading to false interpretation of hydroxyl radical probe reactions

The UV/H₂O₂ process is a benchmark advanced oxidation process (AOP) that in situ generates highly reactive and nonselective hydroxyl radical (^•OH) to oxidatively destroy a wide range of organic compounds. Accurately quantifying the concentration of short-lived ^•OH is essential to predict process performance, optimize the operation parameters, and compare with other process options. The ^•OH concentration is typically measured using organic probe molecules that react with ^•OH but not with other oxidants. In the extremely well-characterized UV/H₂O₂ system in which ^•OH is proven to be the dominant oxidant, using photolysis-resistant probes such as benzoic acid and its derivatives is a widely agreed and practiced norm. We herein report that certain ^•OH probe compounds can be degraded in UV/H₂O₂ system by unknown reactive species that has not been reported in the past. Several common organic probes, particularly p-substituted benzoic acid compounds (i.e., p-hydroxybenzoic acid, p-chlorobenzoic acid, and p-phthalic acid), were found to be vulnerable to attack by the unknown reactive species, leading to false quantification of ^•OH concentration under high radical scavenging conditions. Lines of evidence obtained from a series of ^•OH scavenging experiments performed under various conditions (i.e., different concentrations of H₂O₂, ^•OH probe compounds, and dissolved oxygen) point toward excited state H₂O₂. The results from this study suggest the importance of using appropriate ^•OH probe compounds in mechanistic studies and needs for considering the unidentified role of excited state of H₂O₂ on the UV/H₂O₂ process and related AOPs.

Facile construction of novel organic-inorganic tetra (4-carboxyphenyl) porphyrin/Bi2MoO6 heterojunction for tetracycline degradation: Performance, degradation pathways, intermediate toxicity analysis and mechanism insight

Developing durable photocatalysts with highly efficient antibiotics degradation is crucial for environment purification. Herein, tetra (4-carboxyphenyl) porphyrin (TCPP) was loaded onto the surface of Bi₂MoO₆ microspheres to gain hierarchical organic-inorganic TCPP/Bi₂MoO₆ (TCPP/BMO) heterojunctions via a facile impregnation strategy. The catalytic properties of these catalysts were comprehensively investigated through the photodegradation of tetracycline hydrochloride (TC) under visible light. Among all the TCPP/BMO heterojunctions, the highest photodegradation rate constant (0.0278 min^-1) was achieved with 0.25 wt% TCPP (TCPP/BMO-2), which was approximately 1.15 folds greater than that of pristine Bi₂MoO₆ and far superior to pure TCPP. The extremely high photocatalytic performance is attributed to the interfacial interaction between TCPP and Bi₂MoO₆, which favors the efficient separation of charge carriers and the enhancement of visible-light absorbance. TCPP/BMO-2 possesses high mineralization capability and good recycling performance. Photo-induced O₂^-, h⁺, and OH were mainly responsible for the degradation of TC. The degradation pathways of TC and toxicity of degradation intermediates were analyzed based on the intermediates detected by the high performance liquid chromatography-mass spectrometer (HPLC-MS) and the toxicity assessment by the quantitative structure-activity relationship (QSAR) prediction. A possible photocatalytic mechanism over TCPP/BMO is proposed. This work offers an insight in developing the porphyrin-based organic-inorganic heterojunctions for effectively remedying pharmaceutical wastewater.

Hollow-structured amorphous prussian blue decorated on graphitic carbon nitride for photo-assisted activation of peroxymonosulfate

Heterogeneous activation of peroxymonosulfate (PMS) is one of the most promising techniques for wastewater treatment. Herein, an ingenious system by coupling of photocatalysis and PMS activation was developed, using hollow-structured amorphous prussian blue (A-PB) decorated on graphitic carbon nitride (g-C₃N₄) as the catalyst. Degradation of bisphenol A (BPA) via the A-PB-g-C₃N₄ mediated PMS activation under visible light (Vis) was systematically investigated. Astonishingly, it was found that ~ 82.0%, 92.6%, 98.2% and 99.3% of BPA (40 mg/L) were removed within 2, 4, 6 and 7 min, respectively, suggesting the extremely strong oxidizing capacity of the A-PB-g-C₃N₄/PMS/Vis system. Synergistic effect between the decorated A-PB and the g-C₃N₄ substrate promoted the Fe(III)/Fe(II) redox cycling and facilitated the charge transfer at the A-PB/g-C₃N₄ heterojunction interface. As a result, both photocatalysis and heterogeneous activation of PMS were boosted in the A-PB-g-C₃N₄/PMS/Vis system, leading to the production of large amount of reactive oxygen species (ROS). The various ROS (SO₄^•-, HO•, •O₂^- and ¹O₂) was responsible for the ultrafast degradation of BPA. Moreover, the A-PB-g-C₃N₄ catalyst also exhibited outstanding reusability and stability, retaining 98.9% of the removal percentage for BPA after five consecutive reaction cycles. This study suggests that the A-PB-g-C₃N₄ can be an all-rounder to bridge photocatalysis and PMS activation, and shed a new light on the application of multiple ROS for the ultrafast elimination of micropollutants from wastewater.

Efficient destruction of emerging contaminants in water by UV/S(IV) process with natural reoxygenation: Effect of pH on reactive species

UV/sulfite systems with oxygen have recently been considered as advanced oxidation processes in view of the participation of oxysulfur radicals. However, the contribution of •OH and the efficiency of destructing emerging contaminants (ECs) in water remain largely unclear. Here, the UV/S(IV) process was applied with natural reoxygenation to degrade two typical ECs, diethyl phthalate (DEP) and bisphenol A (BPA) showing different properties. Solution pH played the key role in determining the reactive species, and both DEP and BPA were more favorably degraded at more alkaline conditions with higher utilization efficiency of SO₃^2-. Specifically, the H•, O₂^•-, •OH and SO₃^•- were identified at acidic condition, but the amount of •OH accumulated significantly with the elevation of pH. Competitive quenching experiments showed that e_aq^- and •OH dominated the degradation of DEP and BPA at alkaline condition, respectively. Besides, DEP showed higher quantum efficiency for the indirect photolysis and mineralization degree than that of BPA at pH 9.2 mainly due to the direct use of the primary photoproduct. The possible transformation mechanisms of S(IV) and mineralization routes of both pollutants were proposed. This study may provide new insights into the mechanisms involved in UV/S(IV) process and a promising alternative for efficient removal of ECs in water.

In-situ synthesis of CuS@carbon nanocomposites and application in enhanced photo-fenton degradation of 2,4-DCP

Novel CuS nanoparticles embedded into carbon nanosheets (CuS@CNs) were prepared in situ by applying wheat straw cellulose/feather protein hydrogel beads as templates and were used to photocatalytically activate H₂O₂ to degrade 2,4-dichlorphenol (2,4-DCP). The photo-Fenton catalytic properties of the nanocomposite catalysts obtained under different synthetic conditions, including different Cu²⁺ concentrations, S^2- concentrations and calcination temperatures, were evaluated. The results showed that CuS@CNs with 0.1 M Cu²⁺, 0.1 M S^2- at 800 °C presented excellent photo-Fenton degradation performance for 2,4-DCP (25 mg/L) in the presence of H₂O₂ and could remove 90% of 2,4-DCP in 2.5 h. The water quality parameters (pH, Cl^-, HCO₃^-, H₂PO₄^- and SO₄^2-) exhibited different effects on the photocatalytic degradation process. The catalytic activity of the CuS@CNs used in the cycle could be recovered after thermal regeneration. Radical quenching and electron paramagnetic resonance (EPR) experiments confirmed that ·OH species were main active radicals contributing to the degradation of 2,4-DCP. The photocatalytic mechanism of CuS@CNs was also explored by photoelectrochemical (PEC) measurements and UV-vis diffuse reflectance spectroscopy (DRS). Incorporation of carbon nanosheets could significantly improve the separation of photogenerated charge carriers to stimulate pollutant degradation by CuS. Based on the detected intermediates, the degradation pathway of 2,4-DCP in the CuS@CNs/H₂O₂ reaction system was also proposed.

Study of the photoinduced transformations of sertraline in aqueous media

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

Benzophenone-3 degradation via UV/H2O2 and UV/persulfate reactions

The degradation of benzophenone-3 (BP3) in water via the UV/H₂O₂ and UV/persulfate (UV/PS) reactions was investigated. The degradation of BP3 exhibited pseudo-first-order kinetics in both reactions. The degradation efficiency of BP3 was higher in the UV/PS reaction than in the UV/H₂O₂ reaction. In both reactions, the observed rate constants (k_obs) of BP3 degradation were highest at pH 6 and increased linearly with increasing dosage of H₂O₂ and persulfate. The second-order rate constants of BP3 with •OH (k_{•OH_BP3}) and •SO₄^- (k_•SO4-_{_BP3}) were determined to be 1.09 (± 0.05) × 10¹⁰ and 1.67 (± 0.04) × 10⁹ M^-1 s^-1, respectively. The k_obs values of BP3 were affected by water components such as HCO₃^-, NO₃^-, Cl^-, and Br^- ions, as well as humic acid. Based on the identified transformation products (TPs), the degradation pathway of BP3 during both reactions was a hydroxylation reaction. The inhibition of bioluminescence in Vibrio fischeri due to BP3 and its TPs decreased more quickly in the UV/PS reaction than in the UV/H₂O₂ reaction. The results suggest that the UV/PS process is a better alternative to the UV/H₂O₂ process for removing BP3 and its toxicity in water.

Impact factors of the degradation of bisphenol A by nitrocellulose membrane under illumination

Nitrocellulose membrane (NCM) can produce hydroxyl radicals under illumination, which promotes the oxidative degradation of organic pollutants. In this paper, NCM was used to oxidize bisphenol A (BPA) under simulated sunlight. The effects of pH, temperature, light intensity, anion and cation on the degradation of BPA were analyzed. The photodegradation process of BPA was discussed. The optimal photolysis rate was 0.031 min^-1 when the temperature was 30°C, the light intensity was 2.67 × 10⁴ Lux, and the pH value was 9.0. The alkaline environment, temperature and light intensity can promote the photodegradation of BPA. Except for nitrate ions, anions and cations can inhibit the photodegradation of BPA. Compared with cations, anions have a greater inhibitory effect on BPA degradation. The degradation products of BPA by NCM were analyzed by gas chromatographic/mass. This study may provide useful information for the BPA degradation by NCM in complex water samples.

Kinetics and degradation mechanism of tris (1-chloro-2-propyl) phosphate in the UV/H2O2 reaction

Tris (1-chloro-2-propyl) phosphate (TCPP) is a chlorinated organic phosphate used in various applications as a flame retardant and plasticizer. TCPP is a known suspected carcinogen and is not effectively removed by traditional water treatments such as biological, chlorination, and UV irradiation. In this study, the UV/H₂O₂ reaction was employed to degrade TCPP in water. TCPP was effectively degraded in the UV/H₂O₂ reaction by pseudofirst-order kinetics. The second-order rate constant of the reaction between the TCPP and OH radical was determined to be 4.35 (±0.13) × 10⁸ M^-1 s^-1 using the competition kinetics with nitrobenzene as a reference compound. The degradation of TCPP was affected by the amount of H₂O₂, pH, and coexisting water components such as HCO₃^-, NO₃^-, and humic acid. Approximately 64.2% of total organic carbon (TOC) in TCPP was mineralized in 12 h during the UV/H₂O₂ reaction, whereas chloride (Cl^-) and phosphate (PO₄^3-) ions were identified as ionic byproducts with the recoveries of 96% chlorine (Cl) and 50% phosphorus (P). Five organic transformation products (TPs) of TCPP were also identified using LC-qTOF/MS. Considering the identified TPs, the main degradation pathway of TCPP during the UV/H₂O₂ reaction was found to be OH-radical-induced hydroxylation. Finally, a 70% decrease in bioluminescence inhibition in Vibrio fischeri was observed during the UV/H₂O₂ reaction, and the time-toxicity profile was similar to the time-peak area profile of TPs. The result of this study implies that TCPP can be efficiently removed with significant mineralization and toxicity reduction by the UV/H₂O₂ process.

Degradation of contaminants of emerging concern by UV/H2O2 for water reuse: Kinetics, mechanisms, and cytotoxicity analysis

Advanced oxidation using UV and hydrogen peroxide (UV/H₂O₂) has been widely applied to degrade contaminants of emerging concern (CECs) in wastewater for water reuse. This study investigated the degradation kinetics of mixed CECs by UV/H₂O₂ under variable H₂O₂ doses, including bisphenol A, estrone, diclofenac, ibuprofen, and triclosan. Reverse osmosis (RO) treated water samples from Orange County Water District's Groundwater Replenishment System (GWRS) potable reuse project were collected on different dates and utilized as reaction matrices with spiked additions of chemicals (CECs and H₂O₂) to assess the application of UV/H₂O₂. Possible degradation pathways of selected CECs were proposed based on high resolution mass spectrometry identification of transformation products (TPs). Toxicity assessments included cytotoxicity, aryl hydrocarbon receptor-binding activity, and estrogen receptor-binding activity, in order to evaluate potential environmental impacts resulting from CEC degradation by UV/H₂O₂. Cytotoxicity and estrogenic activity were significantly reduced during the degradation of mixed CECs in Milli-Q water by UV/H₂O₂ with high UV fluence (3200 mJ cm^-2). However, in GWRS RO-treated water samples collected in April 2017, the cytotoxicity and estrogen activity of spiked CEC-mixture after UV/H₂O₂ treatment were not significantly eliminated; this might be due to the high concentration of target CEC and their TPs, which was possibly affected by the varied quality of the secondary treatment influent at this facility such as sewer-shed and wastewater discharges. This study aimed to provide insight on the impacts of post-UV/H₂O₂ CECs and TPs on human and ecological health at cellular level.

Effects of fertilization on the triafamone photodegradation in aqueous solution: Kinetic, identification of photoproducts and degradation pathway

Triafamone is a highly effective, low toxicity sulfonamide herbicide widely used for weeding paddy fields. The triafamone photodegradation in water environment must be explored for its ecological risk assessment. In this work, the effects of chemical fertilizer (urea, diammonium phosphate, potassium chloride, and potassium sulfate), urea metabolites (CO₃^2- and HCO₃^-), and organic fertilizers (unfermented organic fertilizer [UOF] and fermented organic fertilizer [FOF]) on the triafamone photodegradation in aqueous solution under simulated sunlight were evaluated. Results showed that the triafamone photodegradation rate was unaffected by urea. The half-life of triafamone decreased from 106.8 h to 68.4 h with increasing diammonium phosphate concentration. Potassium chloride, potassium sulfate, CO₃^2-, and HCO₃^- could accelerate the triafamone photodegradation at all concentrations, whereas the degradation rate of triafamone decreased when the concentration of potassium sulfate or CO₃^2- was 2000 mg/L. Triafamone photodegradation was promoted by 20-200 mg/L UOF and FOF but decreased to 236.6 and 142.3 h when the concentration reached 2000 mg/L. Twenty-three transformation products were isolated and identified from triafamone by using ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry under simulated sunlight irradiation, and the kinetic evolution of these products was explored. Five possible degradation pathways were inferred, including the cleavage of C-N, C-C, and C-O bonds; CO bond hydrogenation; the cleavage of triazine ring; the cleavage of the sulfonamide bridge; hydroxylation; hydroxyl substitution; methylation; demethylation; amination; and rearrangement. In summary, these results are important for elucidating the environmental fate of triafamone in aquatic systems and further assessing environmental risks.

Rapid photochemical decomposition of perfluorooctanoic acid mediated by a comprehensive effect of nitrogen dioxide radicals and Fe3+/Fe2+ redox cycle

Developing efficient methods to degrade perfluorochemicals (PFCs), an emerging class of highly recalcitrant contaminants, are urgently needed in recent years, due to their persistence, high toxicity, and resistance to most regular treatment procedures. Here, a UV-photolysis system is reported for efficient mineralization of perfluorooctanoic acid (PFOA) via irradiation of ferric nitrate aqueous solution, where in-situ generating •NO₂ and the effective Fe³⁺/Fe²⁺ redox cycle synergistically play great roles on rapidly mediating the mineralization of PFOA. A fast PFOA removal kinetics with first-order kinetic constants of 2.262 h^-1 is observed at initial PFOA concentration of 5 ppm (50 mL volume), reaching ∼ 92 % removal efficiency within only 0.5-h irradiation. Near-stoichiometric fluoride ions liberation and high total organic carbon (TOC) removal efficiency (∼100 %) further validated the capability for completely destructive removal of PFOA. A tentative pathway for PFOA destruction is proposed. This work, by UV photolysis of abundant existing iron/nitrate-based systems in natural environment, provides an economical, sustainable and highly efficient approach for complete mineralization of perfluorinated chemicals.

Greenhouse gas emissions from advanced oxidation processes in the degradation of bisphenol A: a comparative study of the H2O2/UV, TiO2 /UV, and ozonation processes

To estimate greenhouse gas (GHG) emissions and degradation rate constants (k_obs) from H₂O₂/UV-C, TiO₂/UV-C, and ozonation processes in the degradation of bisphenol A (BPA), the laboratory scale experiments were conducted. In the H₂O₂/UV-C process, the fastest degradation rate constant (k_obs = 0.353 min^-1) was observed at 4 mM of H₂O₂, while the minimum GHG emission was achieved at 3 mM of H₂O₂. In the TiO₂/UV-C process, the fastest rate constant (k_obs = 0.126 min^-1) was achieved at 2000 mg/L of TiO₂, while the minimum GHG emission was observed at 400 mg/L of TiO₂. In the ozonation process, GHG emissions were minimal at 5 mg/L of O₃, but the degradation rate constant kept on increasing as the O₃ concentration increased. There were three major types of GHG emissions in the advanced oxidation processes (AOPs). In the ozonation process, most of the GHG emissions were generated by electricity consumption. TiO₂/UV-C process accounted for a significant portion of the GHGs generated by the use of chemicals. Finally, the H₂O₂/UV-C process produced similar GHG emissions from both chemical inputs and electricity consumption. The carbon footprint calculation revealed that for the treatment of 1 m³ of water contaminated with 0.04 mM BPA, the H₂O₂/UV-C process had the smallest carbon footprint (0.565 kg CO₂ eq/m³), followed by the TiO₂/UV-C process (3.445 kg CO₂ eq/m³) and the ozonation process (3.897 kg CO₂ eq/m³). Our results imply that the increase in removal rate constant might not be the optimal parameter for reducing GHG emissions during the application of these processes. Graphical abstract .

Photodegradation of (E)- and (Z)-Endoxifen in water by ultraviolet light: Efficiency, kinetics, by-products, and toxicity assessment

Endoxifen is an effective metabolite of a common chemotherapy agent, tamoxifen. Endoxifen, which is toxic to aquatic animals, has been detected in wastewater treatment plant (WWTP) effluent. This research investigates ultraviolet (UV) radiation (253.7 nm) application to degrade (E)- and (Z)-endoxifen in water and wastewater and phototransformation by-products (PBPs) and their toxicity. The effects of light intensity, pH and initial concentrations of (E)- and (Z)-endoxifen on the photodegradation rate were examined. Endoxifen in water was eliminated ≥99.1% after 35 s of irradiation (light dose of 598.5 mJ cm^-2). Light intensity and initial concentrations of (E)- and (Z)-endoxifen exhibited positive trends with the photodegradation rates while pH had no effect. Photodegradation of (E)- and (Z)-endoxifen in water resulted in three PBPs. Toxicity assessments through modeling of the identified PBPs suggest higher toxicity than the parent compounds. Photodegradation of (E)- and (Z)-endoxifen in wastewater at light doses used for disinfection in WWTPs (16, 30 and 97 mJ cm^-2) resulted in reductions of (E)- and (Z)-endoxifen from 30 to 71%. Two of the three PBPs observed in the experiments with water were detected in the wastewater experiments. Therefore, toxic compounds are potentially generated at WWTPs by UV disinfection if (E)- and (Z)-endoxifen are present in treated wastewater.

Catalytic degradation of organic pollutants in Fe(III)/peroxymonosulfate (PMS) system: performance, influencing factors, and pathway

This study demonstrated, for the first time, Fe(III)/peroximonosulphate (PMS) could be an efficient advanced oxidation process (AOP) for wastewater treatment. Bisphenol A (BPA) was chosen as a model pollutant in the present study. Fe(III)-activated PMS system proved very effective to eliminate 92.18% of BPA (20 mg/L) for 30-min reaction time at 0.50 mM PMS, 1.5 g/L Fe(III), pH 7.0. The maximum degradation of BPA occurred at neutral pH, while it was suppressed at both strongly acidic and alkaline conditions. Organic and inorganic ions can interfere with system efficiency either positively or negatively, so their interaction was thoroughly investigated. Furthermore, the presence of organic acids also affected BPA degradation rate, especially the addition of 10 mM citric acid decreased the degradation rate from 92.18 to 66.08%. Radical scavenging experiments showed that SO₄^•- was the dominant reactive species in Fe(III)/PMS system. A total of 5 BPA intermediates were found by using LC/MS. A possible degradation pathway was proposed which underwent through bridge cleavage and hydroxylation processes. Acute toxicity of the BPA degradation products was assessed using Escherichia coli growth inhibition test. These findings proved to be promising and economical to deal with wastewater using iron mineral for the elimination of organic pollutants. Graphical abstract.

The treatability of trace organic pollutants in WWTP effluent and associated biotoxicity reduction by advanced treatment processes for effluent quality improvement

As increasing attention is paid to surface water protection, there has been demand for improvements of domestic wastewater treatment plant (WWTP) effluent. This has led to the application of many different advanced treatment processes (ATPs). In this study, the treatability of trace organic pollutants in secondary effluent (SE) and associated biotoxicity reduction by four types of ATPs, including coagulation, granular activated carbon (GAC) adsorption, ultraviolet (UV) photolysis and photocatalysis, and ozonation, were investigated at the bench-scale. The ATPs showed different removal capacity for the 48 chemicals, which were classified into seven categories. EDCs, herbicides, bactericides and pharmaceuticals were readily degraded, and insecticides, flame retardants, and UV filters were relatively resistant to removal. During these processes, the efficiency of the ATPs in reducing four biological effects were investigated. Of the four biological effects, the estrogenic activity from SE was not detected using the yeast estrogen screen. In contrast with genotoxicity and photosynthesis inhibition, bacterial cytotoxicity posed by SE was the most difficult biological effect to reduce with these ATPs. GAC adsorption and ozonation were the most robust treatment processes for reducing the three detected biotoxicities. UV photolysis and photocatalysis showed comparable efficiencies for the reduction of genotoxicity and photosynthesis inhibition. However, coagulation only performed well in genotoxicity reduction. The effect-based trigger values for the four bioassays, that were derived from the existing environmental quality standards and from HC5 (hazardous concentration for 5% of aquatic organisms), were all used to select and optimize these ATPs for ecological safety. Conducting ATPs in more appropriate ways could eliminate the negative effects of WWTP effluent on receiving water bodies.

Intermittent light and microbial action of mixed endogenous source DOM affects degradation of 17β-estradiol day after day in a relatively deep natural anaerobic aqueous environment

All kinds of wastewaters containing steroid estrogens (SEs) and mixed endogenous source dissolved organic matter (DOM) enter natural water environments with intermittent illumination where microbial action occurs in a relatively deep natural aqueous environment. The role of mixed endogenous source DOM in SEs' biodegradation and photochemical degradation in such environments was studied using 17β-estradiol (E2) in laboratory experiments under anaerobic conditions. The experimental results show that microbial action can improve the optical properties and electron transfer capability of mixed endogenous source DOM, promoting photodegradation and biodegradation. Intermittent illumination attenuates DOM's electron transfer capacity and its chromophore groups, but it improves the bioavailability of low molecular weight dissolved organic matter which promotes microbial growth under anaerobic conditions. DOM-mediated co-degradation by light and microbial action over three days was better than either individually. The presence of Fe(III) promoted electron transfer, and Fe(III)-DOM complexes accelerated energy transfer under irradiation, enhancing photodegradation. Any remaining estrogens will continue to degrade, most effectively in well-aerated waters with sufficient illumination.

Photochemical behavior of benzophenone sunscreens induced by nitrate in aquatic environments

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

Influence of chemical speciation on photochemical transformation of three fluoroquinolones (FQs) in water: Kinetics, mechanism, and toxicity of photolysis products

This study investigated the contribution of direct, indirect, and self-sensitized photolysis to the photochemical fate of three model fluoroquinolones (FQs), i.e., lomefloxacin (LOM), norfloxacin (NOR), and ofloxacin (OFL), and demonstrated the influence of chemical speciation on their photodegradation behavior, a topic that has received relatively little attention. Results suggest that these FQs in water transformed mainly via direct photolysis, while hydroxyl radical played a key role in their indirect and self-sensitized photolysis. Chemical speciation of such zwitterionic compounds significantly affected the kinetics of their phototransformation, with the quantum yields of photodegradation decreased in the order of zwitterionic (FQsH) > anionic (FQs^-) > cationic (FQsH₂⁺). The photodegradation pathways of FQs depended on both their structures and chemical speciation. Defluorination for LOM in C-8 and NOR in C-6 was more significant when they were present in zwitterionic form than in the other forms. Cationic FQs underwent direct piperazinyl ring cleavage, and zwitterionic ones underwent piperazinyl ring oxidation, while the degradation pathway of piperazinyl ring for FQs in anionic form was structure dependent. Decarboxylation for zwitterionic FQs occurred more slowly compared to both cationic and anionic ones, and the FQs bearing electron-donating groups in C-8 position degraded more easily in cationic form than the anionic ones, while the opposite was true for the FQs without such a group in C-8 position. Results of Vibrio fischeri bioluminescence inhibition tests showed the toxicity of zwitterionic NOR and OFL significantly decreased after photodegradation, while the degradation products of LOM exhibited greater toxicity. These findings indicate that chemical speciation of zwitterionic compounds could affect the kinetics and pathways of their photochemical transformation, and thus have important implications on their fate and risk in aquatic environment.