Degradation of tetrabromobisphenol A by ferrate(VI) oxidation: Performance, inorganic and organic products, pathway and toxicity control

Research and application of active species based on high-valent iron for the degradation of pollutants: A critical review

Fe(VI), as a new green treatment agent, has two indispensable processes in water treatment: coagulation and oxidation. Fe(VI) has a strong oxidation ability. The intermediate iron species (Fe(V) and Fe(IV)) and reactive radical species (H2O2, •OH, and O2•-) produced by decomposition and reduction reaction have strong oxidation ability, in addition, the hydrolyzed product formed in situ with core (γ-Fe2O3)-shell (γ-FeOOH) structure also has good coagulation effect. Because Fe(VI) is easy to decompose and challenging to preserve, it limits the application and sometimes significantly reduces the subsequent processing effect. How to make Fe(VI) more efficient use is a hot spot in current research. This article summarizes the distribution of active substances during the hydrolysis of Fe(VI), distinguish the differences mechanisms in the similar regulation methods, reviews the current preparation methods of Fe(VI), and finally reviews the applications of Fe(VI) in the field of environmental remediation.

TBBPA rather than its main derivatives enhanced growth of endometrial cancer via p53 ubiquitination

Tetrabromobisphenol A (TBBPA) and its derivatives widely exist in various environments and biota. Although the available data indicate that TBBPA exposure is highly associated with the increased incidence of endometrial cancer (EC), the effects of TBBPA and its main derivatives on EC proliferation and the involved crucial mechanism remain unclear. The present study aimed to investigate the effects of TBBPA and its derivatives under environmental concentrations on the proliferation of EC, and the crucial mechanism on the progression of EC caused by bromine flame retardants exposure. In this research, TBBPA and two of the most common TBBPA derivatives including TBBPA bis (2-hydroxyethyl ether) (TBBPA-BHEE) and TBBPA bis (dibromopropyl ether) (TBBPA-BDBPE) were screened for their capacities in induced EC proliferation and explored the related mechanism by in vitro cell culture model and in vivo mice model. Under environmental concentrations, TBBPA promoted the proliferation of EC, the main derivatives of TBBPA (TBBPA-BHEE and TBBPA-BDBPE) did not present the similar facilitation effects. The ubiquitination degradation of p53 was crucial in TBBPA induced EC proliferation, which resulted in the increase of downstream cell cycle and decrease of apoptosis. The further molecular docking result suggested the high affinity between TBBPA and ubiquitinated proteasome. This finding revealed the effects of TBBPA and its derivatives on EC proliferation, thus providing novel insights into the underlying mechanisms of TBBPA-caused EC.

The bioaccumulation and biotransformation of tetrabromobisphenol A bis (allyl ether) in common carp (Cyprinus carpio)

Tetrabromobisphenol A bis (allyl ether) (TBBPA-BAE) is an extensively used brominated flame retardant, which has raised considerable concern because of its neurotoxic and endocrine disruption effects on aquatic organisms. However, previous studies mainly focused on the parent compound before modification, tetrabromobisphenol A (TBBPA), and little information is available about the bioconcentration and biotransformation of TBBPA derivatives in fish. In this study, we investigated the tissue-specific uptake, elimination kinetic, and biotransformation of TBBPA-BAE in common carp (Cyprinus carpio). The fish were exposed to TBBPA-BAE at environmentally relevant concentrations (20 μg·L-1) for 28 days, followed by 14 days of depuration. The results showed TBBPA-BAE could rapidly accumulate in common carp. Among the seven tissues studied, the highest concentrations of TBBPA-BAE were observed in the liver (6.00 μg·g-1 wet weight [ww]) on day 24, while the longest residence time was observed in the kidney (t1/2 values of 18.7 days). Biotransformation of TBBPA-BAE was documented in the in vivo experiments, and 14 different phase I and phase II metabolites were identified in the liver. These findings suggest the biotransformation products of TBBPA-BAE should be considered for a comprehensive risk evaluation.

Determination of tetrabromobisphenol A and its brominated derivatives in water, sediment and soil by high performance liquid chromatography-tandem mass spectrometry

Tetrabromobisphenol A (TBBPA) was typical brominated flame retardant and potential environmental endocrine disruptor, and it had persistence, bioaccumulation and chronic toxicity. Simultaneous determination of ultra-trace TBBPA, tribromobiphenol A (tri-BBPA), dibromobiphenol A (di-BBPA), monobromobisphenol A (mono-BBPA) and bisphenol A (BPA) was developed by high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS), the parent ion charge ratios (m/z) had been optimized. The linear range was wider and the limit of detection was (LOD) 0.09 ~ 0.21 ng mL-1, which could detect trace pollutants. The extraction efficiency was improved by optimizing the parameters, HLB cartridge was used in the water sample by solid phase extraction (SPE), the recovery rates in water samples were over 80.28% with three concentration levels, the relative standard deviations (RSD) were less than 7.12%, and the minimum detection limit of the method was 0.90 ~ 2.10 × 10-3 ng mL-1. Soil and sediment samples were extracted by accelerated solvent extraction (ASE), the recovery rates in soil and sediment were over 79.40% and 75.65%, the minimum detection limit was 0.0225 ~ 0.0525 ng g-1, RSD was less than 7.19%. The proffered method was successfully utilized to detect actual samples, the residue of di-BBPA and mono-BBPA are detected in Naihe River and Shuxi River in Tai'an City, residue of di-BBPA and mono-BBPA was detected in the soil, and there was low residual amount of di-BBPA, mono-BBPA and BPA in the sediment of Shuxi River.

Quantitative structure-activity relationship models for predicting apparent rate constants of organic compounds with ferrate (VI)

Ferrate (VI) (Fe (VI)) is a promising, environmentally friendly multifunctional oxidant widely applied in organic compound degradation. Oxidative kinetics of the apparent second-order rate constants (k_app) of Fe (VI) with organic compounds are critical for modeling oxidation processes. Herein, a quantitative structure-activity relationship (QSAR) model was developed using particle swarm optimization and an extreme learning machine to better understand the laws of the k_app values of organic compounds, including 33 aliphatic and aromatic hydrocarbon derivatives, during degradation by Fe (VI). Seven components-electronic hardness (H), electronic softness (S), ratio of oxygen to carbon atoms (O_n/C_n), energy of the highest occupied molecular orbital (E_HOMO), vertical ionization potential (VIP), maximum nucleophilic reaction index (f(+)_x), and minimum relative electrophilicity index (RE_n) constitute the critical molecular parameters. The developed QSAR model was verified on the basis of the coefficient of determination (R²) and the root mean square error (RMSE): for the training set, R² = 0.924 and RMSE = 1.186, whereas for the test set, R² = 0.996, and RMSE = 0.352. The applicability, reliability, and predictability of the model were verified by estimating the applicability domain (AD) of the model. Furthermore, QSAR models constructed using different methods were compared, and the main impact descriptors and conclusions obtained from previous studies were theoretically analyzed. Results indicate that constructing the QSAR model facilitates k_app prediction for Fe (VI) in the degradation of various organic compounds, improves the understanding of the degradation mechanism, and reduces the pressure on human and material resources caused by experiments.

Catalytic degradation of brominated flame retardants in the environment: New techniques and research highlights

Due to the extensive commercial use of brominated flame retardants (BFRs), human beings are chronically exposed to BFRs, causing great harms to human health, which imposes urgent demands to degrade them in the environment. Among various degradation techniques, catalytic degradation has been proven to be outstanding because of its rapidness and effectiveness. Therefore, much attention has been given to catalytic degradation, especially the extensively studied photocatalytic degradation and nanocatalytic reduction techniques. Recently, some novel advanced catalytic techniques have been developed and show excellent catalytic degradation efficiency for BFRs, including natural substances catalytic degradation, new Fenton catalytic degradation, new chemical reagent catalytic degradation, new material catalytic degradation, electrocatalytic degradation, plasma catalytic degradation, and composite catalytic degradation systems. In addition to the common features of traditional catalytic techniques, these novel techniques possess their own specific advantages in various aspects. Therefore, this review summarized the degradation mechanism of BFRs by the above new catalytic degradation methods under the laboratory conditions, simulated real environment, and real environment conditions, and further evaluated their advantages and disadvantages, aiming to provide some research ideas for the catalytic degradation of BFRs in the environment in the future. We suggested that more attention should focus on features of novel catalytic techniques, including eco-friendliness, cost-effectiveness, and pragmatic usefulness.

A Comparative Study on the Oxidation Mechanisms of Substituted Phenolic Pollutants by Ferrate(VI) through Experiments and Density Functional Theory Calculations

In this work, the oxidation of five phenolic contaminants by ferrate(VI) was comparatively investigated to explore the possible reaction mechanisms by combined experimental results and theoretical calculations. The second-order rate constants were positively correlated with the energy of the highest occupied molecular orbital. Considering electronic effects of different substituents, the easy oxidation of phenols by ferrate(VI) could be ranked as the electron-donating group (-R) > weak electron-withdrawing group (-X) > strong electron-withdrawing group (-(C═O)-). The contributions of reactive species (Fe(VI), Fe(V)/(IV), and •OH) were determined, and Fe(VI) was found to dominate the reaction process. Four main reaction mechanisms including single-oxygen transfer (SOT), double-oxygen transfer (DOT), •OH attack, and electron-transfer-mediated coupling reaction were proposed for the ferrate(VI) oxidation process. According to density functional theory calculation results, the presence of -(C═O)- was more conducive for the occurrence of DOT and •OH attack reactions than -R and -X, while the tendency of SOT for different substituents was -R > -(C═O)- > -X and that of e^--transfer reaction was -R > -X > -(C═O)-. Moreover, the DOT pathway was found in the oxidation of all four substituted phenols, indicating that it may be a common reaction mechanism during the ferrate(VI) oxidation of phenolic compounds.

Removal of microorganic pollutants in aquatic environment: The utilization of Fe(VI)

Microorganic pollutants (MOPs) in aquatic environment with low levels but high toxicity are harmful to ecosystem and human health. Fe(VI) has a dual-functional role in oxidation and coagulation, and can effectively remove MOPs, heavy metal, phosphate, particulates and colloids. Moreover, Fe(VI) can combine with traditional coagulants, or use as a pretreatment for membrane treatment because of its characters to generate nanoparticles by degradation in water. Based on the relevant toxicity experiments, Fe(VI) had been proved to be safe for the efficient treatment of MOPs. For better utilization of Fe(VI), its oxidation and coagulation mechanisms are summarized, and the knowledge about the control parameters, utilization methods, and toxicity effect for Fe(VI) application are reviewed in this paper. pH, different valences of iron, environmental substances, and other parameters are summarized in this study to clarify the important factors in the treatment of MOPs with Fe(VI). In the future study, aiming at cost reduction in Fe(VI) preparation, transportation and storage, enhancement of oxidation in the intermediate state, and better understanding the mechanism between interface and Fe(VI) oxidation will help promote the application of Fe(VI) in the removal of MOPs. This study offers guidelines for the application and development of Fe(VI) for the treatment of MOPs in aquatic environment.

Experimental and theoretical study on Fe(VI) oxidative degradation of dichlorophen in water: Kinetics and reaction mechanisms

Dichlorophenol (DCP), a commonly used fungicide and insecticide, is widely found in waters and wastewaters. Herein, the degradation of DCP by Ferrate (Fe(VI)) in different matrices was comprehensively investigated. In pure water, a complete removal of DCP was achieved in 300 s at [Fe(VI)]:[DCP] molar ratio of 2:1. The presence of HA (10 mg L^-1) inhibited DCP degradation to a certain extent. A total of twenty degradation products were identified by HPLC/MS analysis. Based on these products, reaction pathways including the cleavage of C-C bridge bond, hydroxylation, and radical coupling were proposed. These reaction mechanisms were further rationalized by theoretical calculations. The analyses of Wiberg bond orders and transition state indicated that C₇-C₈ bond was the most vulnerable site for cleavage, and C₁₂ site was the most likely site for hydroxyl addition. Mulliken atomic spin densities distribution suggested that self-coupling products was easily generated via C-O-C coupling ways. Finally, the feasibility of applying Fe(VI) to degrade DCP (20 μM) in a municipal wastewater effluent and a lake water was evaluated and verified. The findings in this study are of relevance in designing Fe(VI)-based treatment strategy for chlorine-containing persistent pesticides.

Application of Advanced Oxidation Technology in Sludge Conditioning and Dewatering: A Critical Review

Sludge dewatering is an important link in sludge treatment. In practical engineering, the dewatering effect of unconditioned sludge is very poor. The use of advanced oxidation technology can improve sludge dewatering performance, reduce sludge capacity, and remove micro-pollutants, which is beneficial for sludge post-treatment and disposal. Based on the current status of sludge conditioning and dehydration, the characteristics of the advanced oxidation method for sludge dehydration were systematically explained using various free radical reaction mechanisms and dehydration conditions. The effects of various advanced oxidation technologies on sludge conditioning and dewatering has been extensively discussed. Finally, the application prospects of the advanced oxidation technology in sludge conditioning and dewatering are presented.

Enhanced ferrate oxidation of organic pollutants in the presence of Cu(II) Ion

In this study, we found that the introduction of Cu(II) (several μM, close to the concentration level of some real water/wastewater) in ferrate (Fe(VI)) oxidation can remarkably accelerate the abatement of various organic pollutants under slightly alkaline conditions. The results show that 5 μM sulfamethoxazole (SMX) can be completely degraded by Fe(VI) (50 μM) in the presence of 20 μM Cu(II) within 10 min at pH 8.0, which was 1.65 times higher than that by Fe(VI) alone. High-valent iron intermediates (i.e. Fe(V), Fe(IV)) and Cu(III) were generated as reactive species in the Cu(II)/Fe(VI) system, all of which contributed to the enhanced oxidation of SMX. Common water components, except for HCO₃^- and humic acid, exhibited no influence on SMX removal. Additionally, the enhanced removal of SMX by Cu(II)/Fe(VI) was also observed in real water with the benefit of total removal of Cu(II) by the ferrate resultant particles. Due to the presence of highly reactive and selective oxidant, the Cu(II)/Fe(VI) system could react readily with organic pollutants containing electron-rich moieties, such as phenol, olefin or amino groups. This study provided a simple, selective, and practical strategy for the abatement of organic pollutants and a simultaneous removal of Cu(II).

Degradation of ofloxacin by potassium ferrate: kinetics and degradation pathways

Drug residues, including various antibiotics, are being increasingly detected in aqueous environments. Ofloxacin (OFX) is one such antibiotic that is widely used in the treatment of several bacterial infections; however, chronic exposure to this antibiotic can have adverse impacts on human health. Hence, the identification of an effective OFX degradation method is essential. Thus, in this study, the degradation performance of OFX using potassium ferrate (Fe(VI)) under the influence of different initial concentrations, pH, temperature, and common ions in water was investigated. OFX degradation by Fe(VI) was directly proportional to the concentration of Fe(VI) and temperature and inversely proportional to the pH. Among the common ions in water, Fe³⁺ and NH₄⁺ could significantly promote the degradation of OFX by Fe(IV), while humic acid (HA) significantly inhibited it. Under the conditions of [Fe(VI)]:[OFX] = 15:1, T = 25℃, and pH = 7.0, the removal efficiency of 8 μM OFX reached more than 90% in 4 min. Seven intermediates were identified by quadrupole time-of-flight tandem ultra-performance liquid chromatography mass spectrometry (Q-TOF LC/MS), and two possible pathways for the degradation of OFX by Fe(VI) were proposed. Overall, the results suggest that advanced oxidation technology using Fe(VI) is effective for treating wastewater containing OFX.

Reinvestigation of the oxidation of organic contaminants by Fe(VI): Kinetics and effects of water matrix constituents

Since previous studies mostly ignored the contributions of Fe(IV) and Fe(V) during the determination of reaction rate constants of ferrate (Fe(VI)) with trace organic contaminants (TrOCs), the intrinsic oxidation ability of Fe(VI) was overestimated. For the first time, this study systemically evaluated the reactivity of Fe(VI) towards four kinds of TrOCs by blocking Fe(IV)/Fe(V) over the TrOCs degradation, and evaluated the effects of coexisting water matrix constituents. Results revealed that Fe(VI) exhibited superior reactivity towards phenolic compounds. Different from other tested TrOCs, phenolic compounds were mainly degraded by Fe(VI) rather than Fe(IV)/Fe(V). Taking bisphenol A (BPA) as the target TrOC, we found that the coexisting constituents can not only affect the reactivity of different ferrate species (i.e., Fe(IV), Fe(V), and Fe(VI)), but also alter the concentrations of ferrates. HPO₄^2- inhibited the reaction between Fe(VI) and H₂O₂, while Ca²⁺, Mg²⁺, and NH₄⁺ promoted the generation of Fe(IV)/Fe(V) from Fe(VI). Besides, humic acid could increase the contribution of Fe(IV)/Fe(V) to the oxidation of BPA. These findings were validated in real water samples. Taken together, this study provides a new perspective regarding the intrinsic oxidation reactivity of Fe(VI), thereby urging reconsideration of the proper strategies for utilization of high-valent Fe species in practices.

Efficient removal of plastic additives by sunlight active titanium dioxide decorated Cd-Mg ferrite nanocomposite: Green synthesis, kinetics and photoactivity

Large use of flame retardants or additives in plastic industries have caused scientific attention as their leaching from consumer products is indicative of environmental concern. Moreover, plastic additives have proven features of endocrine disruptors, genotoxicity and persistence. Therefore, photodegradation of tetrabromobisphenol A (TBBPA) and bisphenol A (BPA) were explored in water. Seeing environmental safety, titanium dioxide decorated magnesium substituted cadmium ferrite (CdMgFe₂O₄@TiO₂) was synthesized by using plant extract of M. koenigii via co-precipitation. Sharp peaks obtained in PXRD ensured high crystallinity and purity of distorted spherical nanocomposite (5-25 nm). Subsequently, CdMgFe₂O₄@TiO₂ nanocatalyst was evaluated for the effective elimination of plastic additives at variable reaction parameters (pollutant: 2-10 mgL^-1; catalyst: 5-25 mg; pH: 3-7, dark-sunlight). With 20 mg of catalytic dose, CdMgFe₂O₄@TiO₂ showed maximum degradation of 2 mgL^-1 of TBBPA (91%) and BPA (94%) at neutral pH under sunlight. Considerable reduction in persistence of TBBPA (t_1/2:2.4 h) and BPA (t_1/2:2.1 h) indicated admirable photoactivity of CdMgFe₂O₄@TiO₂. Results were supported by BET, zeta potential, band reflectance and photoluminescence analysis that indicated for higher surface area (90 m²g^-1), larger particle stability (-20 mV), lower band gap (1.9 eV) and inhibited charge-pairs recombination in nanocomposite. Degradation consisted of initial Langmuir-adsorption followed by first order kinetics. Scavenger analysis revealed the role of hydroxyl radical in photodegradation studies. Nanocomposite was effective up to eight cycles without any significant loss of activity that advocated its high-sustainability and cost-effectiveness. Overall, with excellent surface characteristics, green synthesized CdMgFe₂O₄@TiO₂ nanocomposite is a promising and alternative photocatalyst for industrial applications.

Unveiling the mechanism of imidacloprid removal by ferrate(VI): Kinetics, role of oxidation and adsorption, reaction pathway and toxicity assessment

Imidacloprid (IMI), an emerging pollutant, has high toxicity to non-target organisms. This paper presents the kinetics of IMI removal by ferrate(VI) at different pH (6.0-9.0), molar ratios ([ferrate(VI)]:[IMI]) and added Fe(III) ions. The apparent second-order rate constant (k_app) decreased with increase in pH from pH 6.0 to 9.0 (i.e., (1.2 ± 0.1) × 10² M^-1 s^-1 to (8.3 ± 0.3) M^-1 s^-1). The species-specific rate constants were obtained as k (HFeO₄^-) = 1.3 × 10² M^-1 s^-1 and k (FeO₄^2-) = 6.9 M^-1 s^-1. The decreases in the concentration of HFeO₄^- with increase in pH caused the observed pH dependence in k_app. At pH 7.0, the removal of IMI increased with the molar ratio from 1.0 to 10.0 with complete removal at the highest ratio. The variation in pH from 6.0 to 9.0 had no obvious effect on removal of IMI. Experiments indicate that IMI removal is mainly by ferrate(VI) oxidation and to a lesser extent by Fe(III) adsorption. Mineralization of IMI was also observed (20-26%). The addition of Fe(III) ions to ferrate(VI)-IMI at pH 7.0 and 8.0 resulted in enhanced removal of IMI, but the presence of Ca²⁺, SO₄^2-, HCO₃^-, and humic acid (HA) has negative effects. The presence of coexisting substances in river water slightly decreased IMI removal by ferrate(VI) by less than 10%. Identification of products and frontier electron density (FED) calculations demonstrated involvement of opening of the five-membered heterocyclic moiety of IMI by ferrate(VI). Toxicity assessment with NIH 3T3 fibroblasts and ECOSAR analysis indicated lower toxicity of oxidized products than parent IMI.

Oxidation of chloroquine drug by ferrate: Kinetics, reaction mechanism and antibacterial activity

Chloroquine (CLQ) is required to manufacture on a larger scale to combat COVID-19. The wastewater containing CLQ will be discharged into the natural water, which was resistant to environmental degradation. Herein, the degradation of CLQ by ferrate (Fe(VI)) was investigated, and the biodegradability of the oxidation products was examined to evaluate the potential application in natural water treatment. The reaction between CLQ and Fe(VI) was pH-dependent and followed second-order kinetics. The species-specific rate constant of protonated Fe(VI) species (HFeO₄ ^-) was higher than that of the FeO₄ ^2- species. Moreover, increasing the reaction temperature could increase the degradation rate of CLQ. Besides, HCO₃ ^- had positive effect on CLQ removal, while HA had negative effect on CLQ removal. But the experiments shows Fe(VI) could be used as an efficient technique to degrade co-existing CLQ in natural waters. During the oxidation, Fe(VI) attack could lead to aromatic ring dealkylation and chloride ion substitution to form seven intermediate products by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) determination. Finally, a pure culture test showed that the oxidation of CLQ by Fe(VI) could slightly increase the antimicrobial effect towards Escherichia coli (E.coli) and reduce the toxicity risk of intermediates. These findings might provide helpful information for the environmental elimination of CLQ.

Ferrate (VI) Oxidation Is an Effective and Safe Way to Degrade Residual Colistin - a Last Resort Antibiotic - in Wastewater

The rise of novel mcr mobile resistance genes seriously threatens the use of colistin as a last resort antibiotic for treatment of multidrug-resistant Gram-negative bacterial infections in humans. Large quantities of colistin are released annually into the environment through animal feces. This leads to environmental toxicity and promotes horizontal transmission of the mcr gene in aqueous environments. We examined colistin degradation catalyzed by the presence of strong oxidant Fe (VI). We found almost complete colistin degradation (>95%) by Fe (VI) at initial colistin levels of 30 μM at a molar ratio of Fe (VI): colistin of 30 using an initial pH 7.0 at 25°C for 60 min. The presence of humic acid did not alter the degradation rate and had no significant impact on the removal of colistin by Fe (VI). Quantitative microbiological assays of Fe (VI)-treated colistin solutions using Escherichia coli, Staphylococcus aureus, and Bacillus subtilis indicated that the residual antibacterial activity was effectively eliminated by Fe (VI) oxidation. Luminescent bacteria toxicity tests using Vibrio fischeri indicated that both colistin and its degradation products in water were of low toxicity and the products showed decreased toxicity compared to the parent drug. Therefore, Fe (VI) oxidation is a highly effective and environment-friendly strategy to degrade colistin in water.

Enhancing degradation of atrazine by Fe-phenol modified biochar/ferrate(VI) under alkaline conditions: Analysis of the mechanism and intermediate products

In this study, Fe-phenol modified biochar was prepared to enhance atrazine (AT) degradation by ferrate (Fe(VI)) under alkaline conditions, and the properties, mechanism and transformation pathways were extensively investigated. Degradation experiments showed that Fe-phenol modified biochar was more beneficial for improving the oxidation capacity of Fe(VI) than unmodified biochar, and the biochar with a molar ratio of Fe³⁺ to phenol of 0.1:5 (BC-2) showed the best promoting effect, and more than 94% of AT was removed at pH = 8 within 30 min. Moreover, the rate of oxidation (k_app) of AT by Fe(VI) increased 1.86 to 4.11 times by the addition of BC-2 in the studied pH range. Fe(Ⅴ)/Fe(Ⅳ) and ·OH were the main active oxidizing species for AT degradation in the Fe(VI)/BC-2 group and contributed to 70% and 24%, respectively, of degradation. The formation of ·OH and Fe(Ⅴ)/Fe(Ⅳ) was mainly due to the persistent free radicals and reducing groups on the surface of BC-2. AT was oxidized to 12 intermediate products in the Fe(VI)/BC-2 group through 5 pathways: alkyl hydroxylation, dealkylation, dichlorination, hydroxylation, alkyl dehydrogenation and dichlorination. Compared with those of the initial solution, the total organic carbon content and toxicity after the reaction decreased by 32.8% and 19.02%, respectively. Therefore, the combination of Fe-phenol modified biochar and Fe(VI) could be a promising method for AT removal.

Reduction of cytotoxicity and DNA double-strand break effects of wastewater by ferrate(VI): Roles of oxidation and coagulation

Ferrate(VI) (Fe(VI)) can oxidize individual pollutants, but the pollutant oxidation does not necessarily result in toxicity reduction. Besides, Fe(VI) resultant Fe(III) particles has previously been used to remove heavy metals, but its influence on organic matter and toxicity of wastewater is unknown. This study investigated influence of Fe(VI) on the cytotoxicity and DNA double-strand break (DSB) effects of secondary effluents from wastewater treatment plants to Chinese hamster ovary cells. Adding 5.0 mg/L Fe(VI) as Fe reduced the cytotoxicity and genotoxicity of secondary effluents by 44%-71% and 40%-59%, respectively. The toxicity reduction could be explained by the alleviation of oxidative stress in cells when they were exposed to the Fe(VI)-treated organic matter. Oxidation and coagulation accounted for 60 and 40% of the reductions in cytotoxicity and genotoxicity, demonstrating that both oxidation and coagulation processes can play important roles in reducing toxicity. Molecular weight (MW)-distribution analysis showed that the oxidation process was favored for removing ultraviolet absorbance and fluorescence intensity of organic matter, while the coagulation process removed more dissolved organic carbon (DOC), especially the DOC of fractions with MW < 500 Da. Compared with ferric chloride, the Fe(VI) resultant Fe(III) showed better coagulation performance on organic matter, cytotoxicity and genotoxicity removal, because of the different particle sizes and crystalline structures. This study highlights the benefit of using Fe(VI) in advanced treatment as Fe(VI) reduced the overall toxicity of secondary effluents.

Accelerated oxidation of the emerging brominated flame retardant tetrabromobisphenol S by unactivated peroxymonosulfate: The role of bromine catalysis and formation of disinfection byproducts

Tetrabromobisphenol S (TBBPS) is an emerging brominated flame retardant (BFR) that can cause endocrinological abnormalities in aquatic species and is neurotoxic and cytotoxic to humans. Herein, we investigated the oxidation of TBBPS by unactivated peroxymonosulfate (PMS) in aqueous solution. Results show that PMS was capable of oxidizing TBBPS without activation, and the transformation of TBBPS was pH-dependent. Interestingly, the unactivated PMS oxidation of TBBPS exhibited an autocatalytic behavior. Radical quenching experiments and electron paramagnetic resonance (EPR) analyzes ruled out the involvement of hydroxyl radical (HO•) and sulfate radical (SO₄^•‑) as reactive species. While the generation of singlet oxygen (¹O₂₎ was confirmed in PMS solution, it was also not responsible for TBBPS oxidation. The bromine substituents are believed to be responsible for the autocatalysis observed during PMS oxidation. We propose that the initial oxidation of TBBPS by PMS resulted in the release of bromide ions (Br^-) via debromination, which could be rapidly oxidized to hypobromous acid (HOBr). 3,5-Dimethyl-1H-pyrazole (DMPZ) trapping coupled with liquid chromatography-mass spectrometry (LC-MS) analysis evidenced the formation of HOBr in PMS/TBBPS system. Therefore, the presence of Br^-, albeit at trace level, could significantly accelerate the oxidation of TBBPS in PMS solution via HOBr formation. The intermediate products of TBBPS were identified by solid phase extraction (SPE) coupled with high resolution-mass spectrometry (HR-MS). The oxidation of TBBPS by unactivated PMS was likely initiated through a single electron transfer mechanism, and the transformation pathways included β-scission, debromination, and cross-coupling reactions. Further oxidation and ring-opening of the intermediates yielded three brominated disinfection byproducts (Br-DBPs), including bromoform (CHBr₃), mono-, and di-bromoacetic acids (MBAA and DBAA), as quantified by gas chromatography (GC). The presence of natural organic matter (NOM) inhibited the oxidation of TBBPS and reduced the yields of Br-DBPs. Our results indicate that unactivated PMS was efficient in the abatement of TBBPS in aqueous solution due to the accelerated oxidation by bromine catalysis; however, the formation of brominated intermediate products and Br-DBPs should be scrutinized due to their potential carcinogenicity and mutagenicity.

New Findings of Ferrate(VI) Oxidation Mechanism from Its Degradation of Alkene Imidazole Ionic Liquids

Chemical reactivity, kinetics, degradation pathways and mechanisms, and ecotoxicity of the oxidation of 1-vinyl-3-ethylimidazolium bromide ([VEIm]Br), the most common alternative to organic solvents, by Fe(VI) (HFeO₄^-) were studied by lab experiments and theoretical calculations. Results show that Fe(VI) can efficiently remove VEIm through the dioxygen transfer-hydrolysis mechanism, which has not been reported yet. The reactivity of VEIm toward Fe(VI) mainly depends on the double bonds in the side chain of VEIm. The second-order rate constant for VEIm was 629.45 M^-1 s^-1 at pH 7.0 and 25 °C. Typical water constituents, except for SO₃^2-, Cl^-, and Cu²⁺, had no obvious effects on the oxidation. The oxidation products were determined by high-performance liquid chromatography hybrid quadrupole time-of-flight mass spectrometry, which proves that there were interactions between the oxidation intermediates of the anion and cation parts of [VEIm]Br during the degradation process. The structures of related products and oxidation mechanisms were further rationalized by theoretical calculations. The ecotoxicity of products from the three oxidation pathways all showed a trend of increase after the initial decrease. We hope that the findings of this work can give researchers some new inspirations on Fe(VI) degradation of other alkene-containing contaminants.

Kinetics, pathways and toxicity of hexabromocyclododecane biodegradation: Isolation of the novel bacterium Citrobacter sp. Y3

This research investigated the biodegradation kinetics, pathways and ecological risk of hexabromocyclododecane (HBCD) by a novel bacterium Citrobacter sp. Y3. Results showed the biodegradation followed a first-order model. The specific degradation rate constant of HBCD were obviously higher in batch experiments with combined carbon sources (k: 0.156-0.290 d^-1) than those using HBCD as the sole carbon source (k: 0.055 d^-1). Correspondingly, the degradation half-life became much shorter (T_1/2: 2.39-4.44 d vs T_1/2: 13.7 d). HBCD could be degraded through dehydrobromination and dehalohydroxylation, of which six possible degradation products were detected. To evaluate the ecological risk of HBCD biodegradation products, acute toxicity tests were assessed for the first time. The acute toxicity decreased slowly during treatment for 3-5 d and then decreased sharply. In general, treatment by Strain Y3 is not only a biodegradation process but also a detoxification process, thus it shows potential for bioremediation of HBCD contaminated sites.

Degradation of tetrabromobisphenol A by ferrate(VI)-CaSO3 process: Kinetics, products, and impacts on following disinfection by-products formation

Tetrabromobisphenol A (TBBPA) is one of the most widely applied brominated flame retardants and has been widely detected in water environment, which might pose risks of brominated disinfection by-products formation in water treatment system. Ferrate(VI)-CaSO₃ (Fe(VI)-CaSO₃) system could effectively degrade TBBPA at pH 7.0-9.0 but the decomposition rate of TBBPA dropped with increasing pH. The presence of 0.5 mg C/L humic acid (HA) had negligible impact on TBBPA removal, but the removal of TBBPA decreased to ~87% and 80% at pH 7.0 and 8.0, respectively, in the presence of 5.0 mg C/L HA. The transformation products of TBBPA detected in Fe(VI)-CaSO₃ process revealed that TBBPA degradation mainly proceeded via electron abstraction, debromination, and ring-opening pathways and Br^- was released. In the presence of TBBPA, Fe(VI)-CaSO₃ pre-oxidation decreased the generation of all determined DBPs during chlorination at pH 8.0 but it lessened the generation of some DBPs and slightly increased the formation of the other DBPs at pH 7.0. The toxic risk analysis showed that Fe(VI)-CaSO₃ pre-oxidation of TBBPA could reduce the toxic risk of DBPs in both synthetic water and natural water at pH 8.0, indicating that Fe(VI)-CaSO₃ process has the potential to be applied in practical water treatment.

Two Typical Glycosylated Metabolites of Tetrabromobisphenol A Formed in Plants: Excretion and Deglycosylation in Plant Root Zones

The glycosylation process was investigated for the common brominated flame retardant tetrabromobisphenol A (TBBPA) in hydroponic exposure systems with pumpkin seedlings. Two typical glycosylation metabolites of TBBPA formed in pumpkin seedlings, TBBPA mono-β-d-glucopyranoside (TBBPA MG) and TBBPA di-β-d-glucopyranoside (TBBPA DG), increasing their mass early in the exposure (reaching maximum masses of 608 ± 53 and 3806 ± 1570 pmol at 12 h, respectively) and then falling throughout exposure. These two metabolites were released from roots to rhizosphere solutions, where they also exhibited initial increases followed by decreasing trends (reaching maximum masses of 595 ± 272 pmol at 3 h and 77.1 ± 36.0 pmol at 6 h, respectively). However, a (pseudo)zero-order deglycosylation of TBBPA MG and TBBPA DG (during the first 1.5 h) back to TBBPA was unexpectedly detected in the hydroponic solutions containing pumpkin exudates and microorganisms. The function of microorganisms in the solutions was further investigated, revealing that the microorganisms were main contributors to deglycosylation. Plant detoxification through glycosylation and excretion, followed by deglycosylation of metabolites back to the toxic parent compound (TBBPA) in hydroponic solutions, provides new insight into the uptake, transformation, and environmental fate of TBBPA and its glycosylated metabolites in plant/microbial systems.

Innovative depollution treatment using multi-valent iron species: from fundamental study to application in municipal wastewater

In this work, a new combination of oxidation treatments for the degradation of bisphenol A (BPA) is investigated. This innovative wastewater (WW) treatment includes the use of ferrate (FeO₄^2-) and its decomposition byproducts under dark and UVA irradiation. The oxidation by ferrate leads to a fast but incomplete degradation of BPA with a degradation extent of 45% after 60 min under adopted experimental conditions. However, the ferrate decomposition byproducts which are constituted by solid iron species can be used to further improve the pollutant degradation efficiency. Indeed, ferrate-mediated heterogeneous photo-Fenton process is employed for the first time to enhance the degradation of BPA. With respect to the application for wastewater treatment, UVA irradiation (which is part of solar light), non-toxic and natural origin compounds such as ascorbic acid (AA) and ethylenediamine-N,N'-disuccinic acid (EDDS), are used to design a sustainable process. Under optimized conditions, the degradation extent of BPA using this newly designed treatment reaches almost 100% with AA and 70% with EDDS. In order to assess the feasibility of this treatment, the ferrate-mediated photo-Fenton process is applied to treat municipal wastewater. The obtained results in WW are highly encouraging since a maximum BPA degradation extent of 63% and 60% is observed after 300 min by using AA and EDDS, respectively.

Copper doping and organic sensitization enhance photocatalytic activity of titanium dioxide: Efficient degradation of phenol and tetrabromobisphenol A

A novel photocatalyst (Cu-TiO₂@HQ) had been synthesized by combining Cu-doped TiO₂ nanoparticles with 8-Hydroxyquinoline (HQ) via hydrothermal method. The photocatalytic activities of Cu-TiO₂@HQ were investigated by using phenol and tetrabromobisphenol A (TBBPA) as target pollutants, respectively. The results indicated that the degradation efficiencies of phenol and TBBPA by Cu-TiO₂@HQ were 99.2% (in 30 min) and 99.4% (in 10 min) under visible light irradiation. Both of them were much better than that of pure TiO₂ (8.63% in 30 min) and Cu-TiO₂ (14.74% in 30 min). When phenol or TBBPA were degraded together with the reduction of Cr (VI), the reaction rate of each pollutant was significantly increased, and the cyclic stability of photocatalyst Cu-TiO₂@HQ was greatly improved. Based on the spectroscopic and photoelectric characteristic analysis we found that in the mixture of phenol-Cr (VI) or TBBPA-Cr (VI) both photo-generated electrons and holes can be consumed simultaneously, thus preventing their recombination. The possible degradation products of phenol and TBBPA including its degradation path way were also analyzed by high resolution liquid chromatography-mass spectrometry-mass spectrometry.

Insights into mechanisms of UV/ferrate oxidation for degradation of phenolic pollutants: Role of superoxide radicals

In this study, the performances and mechanisms of UV/ferrate(VI) oxidation were investigated comprehensively using 2,4-dichlorophenol (2,4-DCP) as a probe compound. UV/ferrate(VI) oxidation could efficiently degrade 2,4-DCP and its oxidation ability outperformed conventional UV-based advanced oxidation processes. Moreover, the degradation process of 2,4-DCP followed the pseudo-first order kinetics. In the absence of phosphate buffer, the rate constant of 2,4-DCP degradation increased from 9.4 × 10^-3 to 2.4 × 10^-2 min^-1 when pH value was increased from 3.0 to 6.0. However, the degradation was significantly inhibited by phosphate buffer at an identical pH due to the complexation of phosphate with the ferrate(VI) decay products. HCO₃^- appreciably accelerated the degradation of 2,4-DCP, while Cl^- showed a negligible effect on the degradation. For the first time, combining with the results of chemical probe method, competitive kinetic experiment, electron spin resonance spectra and radical quenching studies, superoxide radicals were demonstrated as the dominant reactive species responsible for the degradation. On the basis of the intermediates detected by LC-MS/MS analysis, a pathway for 2,4-DCP degradation was proposed. This study provides a novel approach for contaminant removal using UV/ferrate(VI) oxidation and sheds new insights into the oxidation mechanisms.

A combined experimental and computational study on the oxidative degradation of bromophenols by Fe(VI) and the formation of self-coupling products

In this study, the degradation of eight bromophenols (BPs), including monobromophenols (2-BP, 3-BP, and 4-BP), dibromophenols (2,4-DBP, 2,6-DBP, and 3,5-DBP), a tribromophenol (2,4,6-TBP) and a pentabromophenol (PBP), by a Fe(VI) reaction process at a pH of 8.0 was systematically studied. It was concluded that their degradation rates increased with increasing Fe(VI) concentrations in solution. The removal of 2,4,6-TBP, 2-BP, and 2,6-DBP was faster than that of the other five BPs, which could be attributed to the position of the substituting Br atom. Moreover, the direct oxidation and coupling reactions greatly influenced the reactivity of the bromophenols with Fe(VI). The electron paramagnetic resonance (EPR) analysis confirmed the presence of hydroxyl radicals in present system. The oxidation reaction products of PBP and 2-BP were recognized by an electrospray time-of-flight mass spectrometer; hydroxylation, hydroxyl substitution, the cleavage of the C-C bond, direct oxidation and polymerization via an end linking mechanism were noticeably found in the reaction process, resulting in the formation of polymerization products and causing hydroxylation to occur. Theoretical calculations further determined the possible oxidation sites of 2-BP and PBP. This study may provide comprehensive and important information on the remediation of BPs by Fe(VI).

Oxidation of sulfonamides by ferrate(VI): Reaction kinetics, transformation byproducts and toxicity assesment

This study was aimed at the degradation of sulfonamides (SNs) via oxidation with Fe(VI). The reaction kinetics, identification of degradation byproducts and their toxicity were investigated. The pH solution and Fe(VI) loading had significant effects on the degradation of the sulfonamides. The maximum degradation rate occurred at pH 3.0 with a 6:1 ratio Fe(VI): sulfonamide, obtaining 100% degradation of 15 mg L^-1 SN within 5 min. Although Fe(VI) also showed an appreciable reactivity towards SNs (k_app = 9.85-19.63 × 10² M^-1 s^-1) at pH 7. The influence of solution pH on the values of k_app can be explained considering the specific reaction between Fe(VI) and SNs. Degradation rates are also influenced by the presence of inorganic ions in different water matrixes. For this reason, ions present in groundwater enhanced the SNs degradation through a synergistic effect among carbonates, sulfates and Fe(VI). Degradation byproducts identified, through UPLC analysis, allowed us to proposed three degradation pathways depending on pH. At acid pH there is a cleavage of C-S and S-N bonds. At neutral pH nitroso and nitro-derivates are formed. At basic pH hydroxylation is the main reaction. The cytotoxicity assay of HEK-293 and J774 cell lines exposed to Fe(VI) indicated that transformation byproducts had a lower toxicity than SNs as baseline products. Accordingly, this research suggests that Fe(VI) can act as a chemical oxidant to remove SNs antibiotics and it can be used to treat antibiotic pollution in wastewater.

Uptake, biotransformation and physiological response of TBBPA in mangrove plants after hydroponics exposure

To better understand the uptake, biotransformation and physiological response to tetrabromobisphenol A (TBBPA) in mangrove plants, a short term 14-day hydroponic assay with two mangrove species, Avicennia marina (A. marina) and Kandelia obovata (K. obovata), was conducted. Results showed that two mangrove species could uptake, translocate and accumulate TBBPA from solution. The hydroxylation and debromination metabolites of TBBPA, including OH-TBBPA, TriBBPA, MonoBBPA, and BPA, were found in both mangroves for the first time. The high-level TBBPA suppressed the growth and increased malondialdehyde (MDA) content of K. obovata, did not pose any negative affect on A. marina. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of K. obovata significantly increased in the 7th day, whereas, SOD and POD activities at high-levels of TBBPA became comparable to the control in the 14th day. Contrastingly, the antioxidant enzymes activities of A. marina were positively stimulated by TBBPA during the 14-day of observation, indicating that A. marina was more tolerant of TBBPA.

Oxidation of tetrabromobisphenol A (TBBPA) by peroxymonosulfate: The role of in-situ formed HOBr

The degradation of tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardant, was evaluated during peroxymonosulfate (PMS) oxidation. TBBPA degradation was pH-dependent, with peak degradation rate constants occurring at pH 8.0-9.0, which was distinct from some other phenolic compounds. Singlet oxygen and radicals were found to play negligible roles in TBBPA degradation. TBBPA oxidation by PMS mainly proceeded via a direct oxidation pathway and the in-situ formed HOBr was found to greatly accelerate its degradation rates. The values of species-specific second-order rate constants for the reactions of PMS with the TBBPA k_HSO5-+TBBPA, k_HSO5-+TBBPA- and k_{HSO5-+TBBPA2-} were determined to be (1.11 ± 0.84) × 10^-2, (8.05 ± 2.31) × 10^-2, and (1.34 ± 0.25) × 10^-1 M^-1 s^-1, respectively, while the reaction rate constants for HOBr/OBr^- with TBBPA k_HOBr+TBBPA, k_HOBr+TBBPA-, k_HOBr+TBBPA2-and k_OBr-+TBBPA2- were determined to be (9.38 ± 2.10) × 10³, (1.59 ± 0.56) × 10⁵, (8.22 ± 0.41) × 10⁶, and (1.81 ± 0.12) × 10⁶ M^-1 s^-1, respectively. The bromine mass balance analysis showed that bromide ion and HOBr/OBr^- occupied 19.5% of total Br and brominated organic compounds accounted for the remaining percentages at pH 7.0. No formation of bromate was observed. Based on the identified products, a reaction pathway was proposed, which included oxidation, β-scission, hydroxylation, and dimerization reaction pathways. The results indicate that unactivated PMS is useful for the remediation of TBBPA contaminated water.

Enhanced dehalogenation and coupled recovery of complex electronic display housing plastics by sub/supercritical CO2

Electronic display housing plastics contain a high amount of halogenated compounds such as brominated flame retardants (BFRs) and polyvinyl chloride (PVC). Compared with moderate critical conditions of conventional eco-friendly sub/supercritical carbon dioxide (Sc-CO₂), a novel and sustainable procedure by using improved Sc-CO₂ was developed for disposal of this type of plastic. The main merit of the process was that complex halogen-containing plastics were safely disposed and halogen-free products were recycled without using catalysts or additives. It was discovered that additive BFRs were initially extracted by Sc-CO₂ technique and then it decomposed accompanied with PVC rapidly to form HBr and HCl, which could be separated by traditional bromine stripping techniques from seawater. Based on response surface methodology (RSM), the maximum debromination and dechlorination efficiencies were achieved at 99.51% and 99.12% respectively. After the treatment, halogen-free products such as solid carbon materials and organic chemical feedstocks were obtained. Mechanism study elucidated that free radicals reaction involving chain initiation, growth and termination induced the polymer decomposition to form these products. This study provides an applicable and green approach for disposal and recovery of halogen-containing plastics.

Degradation of tetrabromobisphenol A by a ferrate(vi)-ozone combination process: advantages, optimization, and mechanistic analysis

This study systematically investigated the ferrate(vi)-ozone combination process for TBBPA degradation. Firstly, the advantages of a ferrate(vi)-ozone combination process were assessed as compared with a sole ozone and ferrate(vi) oxidation process. Then, the performance of the ferrate(vi)-ozone combination process was investigated under different experimental conditions, including the dosing orders of oxidants, dosing concentrations of oxidants, and the initial solution pH. At the same time, toxicity control (including the acute and chronic toxicity) and mineralization were analyzed after optimization. Finally, a mechanism was proposed about the synergetic effects of the ferrate(vi)-ozone combination process for decontamination. The ferrate(vi)-ozone combination process proved to be an efficient and promising technology for removing TBBPA from water. After being pre-oxidized by ferrate(vi) for 3 min and then co-oxidized by the two oxidants, TBBPA of 1.84 μmol L^-1 could be completely degraded by dosing only 0.51 μmol L^-1 of ferrate(vi) and 10.42 μmol L^-1 of ozone within 10 min in wide ranges of pH (5.0-11.0). Up to 91.3% of debromination rate and 80.5% of mineralization rate were obtained, respectively. In addition, no bromate was detected and the acute and chronic toxicity were effectively controlled. The analysis of the proposed mechanism showed that there might exist a superposition effect of the oxidation pathways. In addition, the interactions between the two oxidants were beneficial for the oxidation efficiency of ferrate(vi) and ozone, including the catalytic effect of ferrate(vi) intermediates on ozone and the oxidation of low-valent iron compounds by ozone and the generated ·OH radical.

Degradation of tetrabromobisphenol a by ozonation: Performance, products, mechanism and toxicity

This study systematically investigated the performance of ozonation on tetrabromobisphenol A (TBBPA) degradation under different ozone dosages (5.21-83.33 μmoL/L), initial solution pH (3.0-11.0) and temperatures (10-50 °C). At the same time, the generations of inorganic products (bromide ion and bromate) under different experimental conditions were evaluated and the organic products were also identified. Then, the possible mechanism was proposed and verified by the quantum chemical calculation. In addition, variations and controlling of the toxicity were also analyzed, including acute toxicity, chronic toxicity and genotoxicity. Ozonation was proved to be an efficient and promising technology for removing TBBPA from water. TBBPA of 1.84 μmoL/L could be completely degraded within 5 min under the ozone dosage of 41.67 μmoL/L in wide ranges of pH (3.0-11.0) and temperature (10-40 °C). During the degradation of TBBPA, over 65% of the average bromine ion was detected and nine products were identified. The proposed degradation pathways verified that TBBPA might undergo addition and stepwise oxidative debromination, the hydrogen extraction, and the deprotonation. The results of toxicity testing showed that ozonation could effectively control the acute and chronic toxicity of the water samples, although the toxicity increased in the initial reaction stage due to the accumulation of more toxic intermediates.

Abiotic Methylation of Tetrabromobisphenol A (TBBPA) with the Occurrence of Methyl Iodide in Aqueous Environments

Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant in the world. Its biotic methylation products, tetrabromobisphenol A mono- and dimethyl ether (TBBPA MME and TBBPA DME, respectively), are frequently detected in the environment, but the importance of abiotic methylation reactions of TBBPA in the environment is not known. In this study, the methylation of TBBPA mediated by methyl iodide (CH₃I), a ubiquitous compound in aqueous environments, was investigated in simulated waters in the laboratory. It was found that abiotic methylation occurred under both light and dark conditions and was strongly affected by the pH, temperature, and natural organic matter concentration of the water. Abiotic methylation was further verified in natural river water, and the yield of TBBPA MME mediated abiotically by CH₃I was much greater than that of biotic methylation. According to our calculations and by comparison of the activation energies (E _a) for the abiotic methylation of TBBPA and the other four typical phenolic contaminants and/or metabolites (bisphenol A, triclosan, 5-OH-BDE-47, and 4'-OH-CB-61) mediated by CH₃I, those phenolic compounds all show great methylation potentials. The results indicate a new abiotic pathway for generating TBBPA MME and TBBPA DME from TBBPA, and they also confirm the potentials for abiotic methylation of other phenolic contaminants in aqueous environments.

Glycosylation of Tetrabromobisphenol A in Pumpkin

Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant (BFR), and it bioaccumulates throughout the food chains. Its fate in the first trophic level, plants, is of special interest. In this study, a four-day hydroponic exposure of TBBPA at a concentration of 1 μmol L^-1 to pumpkin seedlings was conducted. A nontarget screening method for hydrophilic bromine-containing metabolites was modified, based on both typical isotope patterns of bromine and mass defect, and used to process mass spectra data. A total of 20 glycosylation and malonyl glycosylation metabolites were found for TBBPA in the pumpkin plants. Representative glycosyl TBBPA reference standards were synthesized to evaluate the contribution of this glycosylation process. Approximately 86% of parent TBBPA was metabolized to form those 20 glycosyl TBBPAs, showing that glycosylation was the most dominant metabolism pathway for TBBPA in pumpkin at the tested exposure concentration.

Degradation of dye in wastewater by Homogeneous Fe(VI)/NaHSO3 system

The homogeneous Fe(VI)/Na₂SO₃ system has been proposed for highly efficient degradation of recalcitrant contaminants, in which sulfite could significantly enhance the transformation of organic substrate by Fe(VI). Also, the Fe(VI)/NaHSO₃ system could show high efficiency across a wide range of pH conditions. The degradation rates reached up to 80% within 2 min and 70% within 5 min in strongly acidic and alkaline conditions, respectively. Unexpectedly, a faster removal rate was obtained in Fe(VI)/NaHSO₃ system than that in Fe(VI)/Na₂SO₃ system for the degradation of methylene blue (MB). A reasonable dye degradation mechanism was proposed and verified by a series of experiments. The high oxidation potential of Fe(VI) and other species such as sulfate and hydroxyl radicals were responsible for the outstanding capabilities of Fe(VI)/NaHSO₃ system, which could significantly improve the treatment of organics in wastewater under a very wide range of pH conditions.

Activation of ferrate by carbon nanotube for enhanced degradation of bromophenols: Kinetics, products, and involvement of Fe(V)/Fe(IV)

Very recently, several studies have found that homogeneous reducing agents (e.g., sodium thiosulfate (Na₂S₂O₃), and sodium sulfite (Na₂SO₃)) can activate ferrate to enhance the degradation of selected contaminants. In this work, it was found that heterogeneous carbon nanotube (CNT) could accelerate ferrate (Fe(VI)) for the degradation of bromophenols (BrPs) of environmental concerns and alleviate the appearance of undesired by-products in effluent. Fe(VI) could react with BrPs over a wide pH range of 6-10 with apparent second-order rate constants of 1.8-1850 M^-1 s^-1. Electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQMS) analysis showed that dibrominated dihydroxylated biphenyls and dibrominated phenoxyphenols were possibly formed via coupling reaction of BrPs radicals generated from Fe(VI) oxidation through one-electron transfer. The presence of CNT could remarkably accelerate the degradation rates of BrPs by Fe(VI) in a wide pH range from 7 to 10. Moreover, the formed undesired polybrominated products during Fe(VI)/CNT oxidation were absorbed on CNT surface and thus removed from treated water. The Fe(VI)/CNT system was capable of selectively oxidizing electron-rich pollutants (e.g., BrPs, and sulfamethoxazole (SMX)), but reluctant to iopamidol (IPM) and nitrobenzene (NB). High-valent metal-oxo intermediates Fe(V)/Fe(IV) formed in situ from the reaction of CNT with Fe(VI) were likely responsible for this activation effect of CNT, which was further confirmed via using methyl phenyl sulfoxide (PMSO) as a probe compound. Comparatively, homogeneous reducing agent Na₂S₂O₃ could enhance Fe(VI) degradation of BrPs at pH 7 and 8, while undesired polybrominated products were detected in effluent from Fe(VI)/Na₂S₂O₃ system. These findings have crucial implications for the development of a promising oxidation process by combination of Fe(VI) and CNT for water and wastewater treatment.

A DFT/TDDFT study on the mechanisms of direct and indirect photodegradation of tetrabromobisphenol A in water

Tetrabromobisphenol A (TBBPA) is the most widely used commercial brominated flame retardant. However, the mechanisms underlying the photodegradation of TBBPA remain unclear. Here we use density functional theory and time-dependent density functional theory to examine the photodegradation of the two species of TBBPA in water: TBBPA (neutral form) and TBBPA^- (anionic form). The study includes direct photodegradation and indirect photodegradation of TBBPA with ·OH and ¹O₂. The results of the calculations indicate that indirect photodegradation of TBBPA and TBBPA^- with ·OH occurs via OH-addition and Br-substitution. All of the OH-addition and Br-substitution pathways are exothermic. Indirect photodegradation of TBBPA and TBBPA^- by ¹O₂ proceeds via H abstraction by ¹O_2.E_a was higher for H abstraction of TBBPA than H abstraction of TBBPA^-. The mechanisms for the direct photodegradation of TBBPA and TBBPA^- include debromination, C1C7/C7C13 cleavage, and cyclization. CBr cleavage was observed in the optimized geometries of TBBPA and TBBPA^- at the lowest excited triplet state. However, high E_a values and an endothermic nature indicated that C1C7/C7C13 cleavage and cyclization reactions were not the main pathways. OH-adducts, Br-substitution products, H-abstraction (by ¹O₂) products, and debromination products were the main products of photodegradation of TBBPA. These findings provide useful information for risk assessment and pollution control of brominated flame retardants.