Transformation of bisphenol AF and bisphenol S by manganese dioxide and effect of iodide

Complex impact of metals on the fate of disinfection by-products in drinking water pipelines: A systematic review

Metals in the drinking water distribution system (DWDS) play an important role on the fate of disinfection by-products (DBPs). They can increase the formation of DBPs through several mechanisms, such as enhancing the proportion of reactive halogen species (RHS), catalysing the reaction between natural organic matter (NOM) and RHS through complexation, or by increasing the conversion of NOM into DBP precursors. This review comprehensively summarizes these complex processes, focusing on the most important metals (copper, iron, manganese) in DWDS and their impact on various DBPs. It organizes the dispersed 'metals-DBPs' experimental results into an easily accessible content structure and presents their underlying common or unique mechanisms. Furthermore, the practically valuable application directions of these research findings were analysed, including the toxicity changes of DBPs in DWDS under the influence of metals and the potential enhancement of generalization in DBP model research by the introduction of metals. Overall, this review revealed that the metal environment within DWDS is a crucial factor influencing DBP levels in tap water.

Simulated sunlight/periodate-triggered formation of toxic halogenated bisphenols in highly saline water

Periodate (PI)-based oxidation using the activators, such as metal ions and light irradiation, has emerged as a feasible treatment strategy for the effective remediation of contaminated water and wastewater. Given the pervasive nature of PI residues and solar exposure during application, the role of solar light in remediating the challenging highly saline water matrices needs to be elucidated. In this study, bisphenol A (BPA) was selected as the targeted micropollutant, which can be efficiently eliminated by the simulated sunlight (SSL)/PI system in the presence of high-level Cl- (up to 846.0 mM) at pH 7.0. The presence of different background constituents of water, such as halides, nitrate, and dissolved organic matter, had no effect, or even accelerated BPA abatement. Particularly, the ubiquitous Br- or I- appreciably enhanced the BPA transformation efficiency, which may be ascribed to the generation of high-selective reactive HOBr or HOI. The in silico predictions suggested that the transformation products generated by halide-mediated SSL/PI systems via halogen substitutions showed greater persistence, bioaccumulation, and aquatic toxicity than BPA itself. These findings highlighted a widespread phenomenon during PI-based oxidative treatment of highly saline water, which needs special attention under solar light illumination.

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

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

Hazardous radical-coupled transformation products of benzophenone-3 formed during manganese dioxide treatment

Radical-coupled transformation products (TPs) have been identified as the byproducts of various transformation processes, including both natural attenuation and artificial treatments, of phenolic micropollutants. Benzophenone-3 (BP-3), an organic UV filter of emerging concern, has been previously reported with ubiquitous occurrence in the natural environment and water bodies. Current research has demonstrated how TPs are formed from BP-3 when it is treated with manganese oxide (MnO2). The ecological and toxicological risks of these TPs have also been assessed. Polymerization of BP-3 through radical coupling was observed as the major pathway by which BP-3 is transformed when treated with MnO2. These radical-coupled TPs haven't shown further degradation after formation, suggesting their potential persistence once occurred in the environment. In silico experiments predict the radical-coupled TPs will increase in mobility, persistence and ecotoxicity. If true, they also represent an ever-increasing threat to the environment, ecosystems and, most immediately, aquatic living organisms. In addition, radical-coupled TPs produced by MnO2 transformation of BP-3 have shown escalated estrogenic activity compared to the parent compound. This suggests that radical coupling amplifies the toxicological impacts of parent compound. These results provide strong evidence that radical-coupled TPs with larger molecular sizes are having potential adverse impacts on the ecosystem and biota.

pH-dependent bisphenol A transformation and iodine disinfection byproduct generation by peracetic acid: Kinetic and mechanistic explorations

Peracetic acid (PAA) is regarded as an environmentally friendly oxidant because of its low formation of toxic byproducts. However, this study revealed the potential risk of generating disinfection byproducts (DBPs) when treating iodine-containing wastewater with PAA. The transformation efficiency of bisphenol A (BPA), a commonly detected phenolic contaminant and a surrogate for phenolic moieties in dissolved organic matter, by PAA increased rapidly in the presence of I-, which was primarily attributed to the formation of active iodine (HOI/I2) in the system. Kinetic model simulations demonstrated that the second-order rate constant between PAA and HOI was 54.0 M-1 s-1 at pH 7.0, which was lower than the generation rate of HOI via the reaction between PAA and I-. Therefore, HOI can combine with BPA to produce iodine disinfection byproducts (I-DBPs). The transformation of BPA and the generation of I-DBPs in the I-/PAA system were highly pH-dependent. Specifically, acidic conditions were more favorable for BPA degradation because of the higher reaction rates of BPA and HOI. More iodinated aromatic products were detected after 5 min of the reaction under acidic and neutral conditions, resulting in higher toxicity towards E. coli. After 12 h of the reaction, more adsorbable organic iodine (AOI) was generated at alkaline conditions because HOI was not able to efficiency transform to IO3-. The presence of H2O2 in the PAA solution played a role in the reaction with HOI, particularly under alkaline conditions. This study significantly advances the understanding of the role of I- in BPA oxidation by PAA and provides a warning to further evaluate the potential environmental risk during the treatment of iodine-bearing wastewater with PAA.

Treatment of bisphenol pollutant in water by N,P-co-doped carbon nanosheet: Fast degradation, toxicity elimination and reaction mechanism investigation

Metal-free carbon catalysts perform well in peroxymonosulfate-based advanced oxidation process for the treatment of organic pollutant-containing wastewater. Herein, a natural biomolecule of adenosine triphosphate (ATP), containing abundant N and P elements, served as sole precursor to prepare N,P-co-doped carbon through one-step anoxic pyrolysis, which was applied as peroxymonosulfate activator to treat bisphenol-contaminated water. Owing to the endogenous N and P elements in ATP, in-situ doping was achieved for the prepared carbon material with excellent doping effect, such as high doping amount and numerous defects. During pyrolysis process, the generated gases facilitated the exfoliation of carbon structure, resulting in a nanosheet-like morphology with large specific surface area, e.g., 852.75 m² g^-1 for NPCN-900 sample obtained at 900 °C. Benefiting from the structural modulation brought by N,P co-doping, typical sample of NPCN-900 presented excellent catalytic performance towards bisphenol AF (BPAF) degradation through PMS activation. An apparent reaction rate constant of 0.4115 min^-1 was calculated under the investigated reaction conditions. Further studies indicated that ¹O₂, surface-bound •OH and SO₄^-• worked together in NPCN-900/PMS system for BPAF degradation. Graphitic N, pyrrolic N, CO groups, defect structure and the doped P atoms in NPCN-900 contributed to PMS activation. It was also important that the toxicity of BPAF solution could be preliminarily eliminated after treatment by NPCN-900/PMS system, which was verified by ecotoxicity assessments through ECOSAR program and green algae growth experiments.

Efficient remediation of the field soil contaminated with PAHs by amorphous porous iron material activated peroxymonosulfate

An amorphous porous iron material (FH) was firstly self-synthesized using a simple coprecipitation approach and then utilized to activate peroxymonosulfate (PMS) for the catalytic degradation of pyrene and remediation of PAHs contaminated soil on site. FH exhibited more excellent catalytic activity than traditional hydroxy ferric oxide and possessed stability at a pH range of 3.0-11.0. According to quenching studies and electron paramagnetic resonance (EPR) analyses, non-radicals (Fe(IV) = O and 1O2) were the major reactive oxygen species (ROS) in the FH/PMS system's degradation of pyrene. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) of FH before and after the catalytic reaction, as well as active site substitution experiments and electrochemical analysis all verified that PMS adsorbed on FH could produce more abundant bonded hydroxyl groups (Fe-OH) which dominated the radical and non-radical oxidation reactions. Then, a possible pathway for pyrene degradation was presented according to gas chromatography-mass spectrometry (GC-MS). Furthermore, the FH/PMS system exhibited excellent catalytic degradation in the remediation of PAH-contaminated soil at real sites. This work provides a remarkable potential remediation technology of persistent organic pollutants (POPs) in environmental and will contribute to understanding the mechanism of Fe-based hydroxides in advanced oxidation processes.

Mn(III)-mediated bisphenol a degradation: Mechanisms and products

Bisphenol A (BPA) is a high production volume chemical with potential estrogenic effects susceptible to abiotic degradation by MnO₂. BPA transformation products and reaction mechanisms with MnO₂ have been investigated, but detailed process understanding of Mn(III)-mediated degradation has not been attained. Rapid consumption of BPA occurred in batch reaction vessels with 1 mM Mn(III) and 63.9 ± 0.7% of 1.76 ± 0.02 μmol BPA was degraded in 1 hour at circumneutral pH. BPA was consumed at 1.86 ± 0.09-fold higher rates in vessels with synthetic MnO₂ comprising approximately 13 mol% surface-associated Mn(III) versus surface-Mn(III)-free MnO₂, and 10-35% of BPA transformation could be attributed to Mn(III) during the initial 10-min reaction phase. High-resolution tandem mass spectrometry (HRMS/MS) analysis detected eight transformation intermediates in reactions with Mn(III), and quantum calculations proposed 14 BPA degradation products, nine of which had not been observed during MnO₂-mediated BPA degradation, suggesting mechanistic differences between Mn(III)- versus MnO₂-mediated BPA degradation. The findings demonstrate that both Mn(III) and Mn(IV) can effectively degrade BPA and indicate that surface-associated Mn(III) increases the reactivity of synthetic MnO₂, offering opportunities for engineering more reactive oxidized Mn species for BPA removal.

Sensitive determination of bisphenols in environmental samples by magnetic porous carbon solid-phase extraction combined with capillary electrophoresis

Bisphenol compounds exist widely in the environment and pose potential hazards to the environment and human health, which has aroused widespread concern. Therefore, there is an urgent need for an efficient and sensitive analytical method to enrich and determine trace bisphenols in environmental samples. In this work, magnetic porous carbon (MPC) was synthesized by one-step pyrolysis combined with a solvothermal method for magnetic solid-phase extraction of bisphenols. The structural properties of MPC were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and saturation magnetization analysis. Its adsorption properties were evaluated by adsorption kinetics and adsorption isotherm studies. By optimizing the magnetic solid-phase extraction and capillary electrophoresis separation conditions, a capillary electrophoresis separation and detection method for four bisphenols was successfully constructed. The results showed that the detection limits of the proposed method for the four bisphenols were 0.71-1.65 ng/mL, the intra-day and inter-day precisions were 2.27-4.03% and 2.93-4.42%, respectively, and the recoveries were 87.68%-108.0%. In addition, the MPC could be easily recycled and utilized, and even if the magnetic solid-phase extraction was repeated 5 times, the extraction efficiency could still be kept above 75%.

Bioaccumulation, internal distribution and toxicity of bisphenol S in the earthworm Eisenia fetida

Due to the strict rules and restrictions on the utilization of bisphenol A (BPA) around the world, an emerging endocrine disrupting chemical, bisphenol S (BPS) has been widely utilized as a substitute and frequently detected in the environment, even in the human body. Although it has been widely studied in the aquatic systems, the fate and toxicological effect of BPS in soil invertebrates are poorly known. This study presented a comprehensive exploration into the attenuation, bioaccumulation, and physiological distribution of BPS in an ecologically significant soil invertebrate, as well as its subsequent ecotoxicological effect to earthworm for the first time. The E. fetida could promote the BPS attenuation in soil, with degradation rates of 92.8 ± 1.6 % and 98.6 ± 1.1 % at dosage of 1.0 mg/kg dry weight soil (DWS) and 0.1 mg/kg DWS, respectively. The bioaccumulation of BPS in the earthworm was up to 111.6 ± 6.0 mg/kg lipid and 12.9 ± 2.9 mg/kg lipid with the initial dosage of 1.0 mg/kg DWS and 0.1 mg/kg DWS, respectively. Furthermore, BPS could induce oxidative stress and the process of antioxidant defense in earthworm cells at relatively high dose (1.0 mg/kg DWS and 10.0 mg/kg DWS), suggesting potential risks of BPS to the soil environment. This study could contribute to a more in-depth understanding of the fate of BPS in soil-earthworm system, and indicate a necessity for better understanding the environmental fate and ecological risks of BPA substitutes in the future.

Highly Efficient Utilization of Ferrate(VI) Oxidation Capacity Initiated by Mn(II) for Contaminant Oxidation: Role of Manganese Species

Manganese ion [Mn(II)] is a background constituent existing in natural waters. Herein, it was found that only 59% of bisphenol A (BPA), 47% of bisphenol F (BPF), 65% of acetaminophen (AAP), and 49% of 4-tert-butylphenol (4-tBP) were oxidized by 20 μM of Fe(VI), while 97% of BPA, 95% of BPF, 96% of AAP, and 94% of 4-tBP could be oxidized by the Fe(VI)/Mn(II) system [20 μM Fe(VI)/20 μM Mn(II)] at pH 7.0. Further investigations showed that bisphenol S (BPS) was highly reactive with reactive iron species (RFeS) but was sluggish with reactive manganese species (RMnS). By using BPS and methyl phenyl sulfoxide (PMSO) as the probe compounds, it was found that reactive iron species contributed primarily for BPA oxidation at low Mn(II)/Fe(VI) molar ratios (below 0.1), while reactive manganese species [Mn(VII)/Mn(III)] contributed increasingly for BPA oxidation with the elevation of the Mn(II)/Fe(VI) molar ratio (from 0.1 to 3.0). In the interaction of Mn(II) and Fe(VI), the transfer of oxidation capacity from Fe(VI) to Mn(III), including the formation of Mn(VII) and the inhibition of Fe(VI) self-decay, improved the amount of electron equivalents per Fe(VI) for BPA oxidation. UV-vis spectra and dominant transformation product analysis further revealed the evolution of iron and manganese species at different Mn(II)/Fe(VI) molar ratios.

Generality and diversity on the kinetics, toxicity and DFT studies of sulfate radical-induced transformation of BPA and its analogues

The international campaign to ban bisphenol A (BPA) has resulted in increasing application of BPA substitutes. However, investigations have mainly been confined to the removal of single contaminant from the water, resulting in an inefficient burden. Furthermore, systematic study and synthetical discussion of bisphenol analogues (BPs) kinetics and transformation pathways were largely underemphasized. Chemical oxidation of BPA and four typical alternatives (i.e., bisphenol AF, bisphenol E, bisphenol F and bisphenol S) in a UV-activated persulfate system was examined in this study. The effects of persulfate (PS) dosage, pH and water matrix constituents (i.e., bicarbonate, chloride and natural organic matter) were comprehensively examined using a combination of laboratory experiments and mathematical modeling. According to our findings, the removal characteristics of different BPs employing SO₄•^--induced removal technology, including degradation mechanisms and influencing trends by water matrix, revealed similarly. The second order-rate constants of SO₄•^- reacting with BPs served as the main variables mediating the variation in degradation kinetics. Frontier molecular orbital theory and density functional theory suggested BPs molecules possessed the same susceptible positions to free radicals. In the UV-activated PS process, transformation pathways included hydroxylation, electron-transfer, substitution, and rearrangement triggered by ortho-cleavage, with certain intermediates exhibiting higher toxicity than the parent chemicals. The findings of this study provided valuable information to estimate potential environmental risks of using BPA alternatives.

Iodide sources in the aquatic environment and its fate during oxidative water treatment - A critical review

Iodine is a naturally-occurring halogen in natural waters generally present in concentrations between 0.5 and 100 µg L^-1. During oxidative drinking water treatment, iodine-containing disinfection by-products (I-DBPs) can be formed. The formation of I-DBPs was mostly associated to taste and odor issues in the produced tap water but has become a potential health problem more recently due to the generally more toxic character of I-DBPs compared to their chlorinated and brominated analogues. This paper is a systematic and critical review on the reactivity of iodide and on the most common intermediate reactive iodine species HOI. The first step of oxidation of I^- to HOI is rapid for most oxidants (apparent second-order rate constant, k_app > 10³ M^-1s^-1 at pH 7). The reactivity of hypoiodous acid with inorganic and organic compounds appears to be intermediate between chlorine and bromine. The life times of HOI during oxidative treatment determines the extent of the formation of I-DBPs. Based on this assessment, chloramine, chlorine dioxide and permanganate are of the highest concern when treating iodide-containing waters. The conditions for the formation of iodo-organic compounds are also critically reviewed. From an evaluation of I-DBPs in more than 650 drinking waters, it can be concluded that one third show low levels of I-THMs (<1 µg L^-1), and 18% exhibit concentrations > 10 µg L^-1. The most frequently detected I-THM is CHCl₂I followed by CHBrClI. More polar I-DBPs, iodoacetic acid in particular, have been reviewed as well. Finally, the transformation of iodide to iodate, a safe iodine-derived end-product, has been proposed to mitigate the formation of I-DBPs in drinking water processes. For this purpose a pre-oxidation step with either ozone or ferrate(VI) to completely oxidize iodide to iodate is an efficient process. Activated carbon has also been shown to be efficient in reducing I-DBPs during drinking water oxidation.

Overlooked environmental risks deriving from aqueous transformation of bisphenol alternatives: Integration of chemical and toxicological insights

Owing to the widespread prevalence and ecotoxicity of bisphenol alternatives such as bisphenol S, bisphenol F, and bisphenol AF, the past decade has witnessed the publication of a remarkable number of studies related to their transformation and remediation in natural waters. However, the reactivity, removal efficiency, transformation products (TPs), and mechanisms of such emerging pollutants by different treatment processes have not been well elucidated. Particularly, the transformation-driven environmental risks have been mostly overlooked. Therefore, we present a review to address these issues from chemical and toxicological viewpoints. Four degradation systems can be largely classified as catalytic persulfate (PS) oxidation, non-catalytic oxidation, photolysis and photocatalysis, and biodegradation. It was found that bisphenol alternatives possess distinct reactivities with different oxidizing species, with the highest performance for hydroxyl radicals. All systems exhibit superior elimination efficiency for these compounds. The inadequate mineralization suggests the formation of recalcitrant TPs, from which the overall reaction pathways are proposed. The combined experimental and in silico analysis indicates that many TPs have developmental toxicity, endocrine-disrupting effects, and genotoxicity. Notably, catalytic PS systems and non-catalytic oxidation result in the formation of coupling products as well as halogenated TPs with higher acute and chronic toxicity and lower biodegradability than the parent compounds. In contrast, photolysis and photocatalysis generate hydroxylated and bond-cleavage TPs with less toxicity. Overall, this review highlights the secondary environmental risks from the transformation of bisphenol alternatives by conventional and emerging treatment processes. Finally, future perspectives are recommended to address the knowledge gaps of these contaminants in aquatic ecosystems.

Comparative study on bisphenols oxidation via TiO2 photocatalytic activation of peroxymonosulfate: Effectiveness, mechanism and pathways

In this work, degradation of bisphenol F (BPF), bisphenol AF (BPAF) and bisphenol S (BPS) by peroxymonosulfate (PMS) with TiO₂ nano-tubes arrays (TiO₂NTAs) under simulated sunlight irradiation was investigated and compared for the first time. All three bisphenols exhibited appreciable degradation following the order of BPS < BPAF < BPF, and acidic conditions were more conducive to their degradation. The SO₄^•-, ·OH, h⁺ and ^•O₂^- were all identified in three bisphenols degradation processes. Among these, SO₄^•- and ^•O₂^- were proven to play a dominant role in BPF oxidation process, but SO₄^•- and h⁺ were confirmed as the main reactive species for BPAF and BPS removal. Owing to the different reactive species worked in different bisphenols degradation processes, the influences of inorganic anions on three bisphenols degradation were also different. By analyzing the oxidation intermediates of the three bisphenols, it was found that there were some common degradation pathways including bond-cleavage and hydroxylation of the benzene ring shared by three bisphenols. Besides, some specific degradation pathways were also identified, for example, the self-coupling was found in BPF and BPS degradation process, while the benzene ring splitting was occurred only in BPAF transformation process.

Formation of iodinated aromatic DBPs at different molar ratios of chlorine and nitrogen in iodide-containing water

Variations in iodinated aromatic disinfection byproducts (DBPs) in the presence of I^- and organic compounds as a function of reaction time in different molar ratios (MRs) of HOCl:NH₃-N were investigated. Up to 17 kinds of iodinated aromatic DBPs were identified in the breakpoint chlorination of iodide (I^-)/organic (phenol, bisphenol S (BPS) and p-nitrophenol (p-NP)) systems, and the possible pathways for the formation of iodinated aromatic DBPs were proposed. The reaction pathways include HOCl/HOI electrophilic substitution and oxidation, while the dominant iodinated DBPs were quantified. In the I^-/phenol system (pH = 7.0), the sum of the concentrations of four iodinated aliphatic DBPs ranged from 0.32 to 1.04 μM (triiodomethane (TIM), dichloroiodomethane (DCIM), diiodochloromethane (DICM) and monoiodoacetic acid (MIAA)), while the concentration of 4-iodophenol ranged from 2.99 to 12.87 μM. The concentration of iodinated aromatic DBPs remained stable with an MR = 1:1. When the MR was 6:1, iodinated aromatic DBPs decreased with increasing reaction time, in which the main disinfectant in the system was active chlorine. This study proposed the formation mechanism of iodinated aromatic DBPs during the breakpoint chlorination of iodide-containing water. These results can be used to control the formation of hazardous iodinated aromatic DBPs in the disinfection of iodine containing water.

Effective stabilization of atomic hydrogen by Pd nanoparticles for rapid hexavalent chromium reduction and synchronous bisphenol A oxidation during the photoelectrocatalytic process

Atomic hydrogen (H*) plays a vital role in the synchronous redox of metallic ions and organic molecules. However, H* is extremely unstable as it is easily converted to hydrogen. Herein, we designed a novel strategy for the effective stabilization of H* to enhance its utility. The synthesized Pd nanoparticles grown on the defective MoS₂ (DMS) of TiO₂ nanowire arrays (TNA) (TNA/DMS/Pd) photocathode exhibited rapid Cr(VI) reduction (~95% in 10 min) and bisphenol A (BPA) oxidation (~97% in 30 min), with the kinetic constants almost 24- and 6-fold higher than those of the TNA photocathode, respectively. This superior performances could be attributed to: (i) the generated interface heterojunctions between TNA and DMS boosted the separation efficiencies of photogenerated electrons, thereby supplying abundant valance electrons to lower the overpotential to create a suitable microenvironment for H* generation; (ii) the stabilization of H* by Pd nanoparticles resulted in a significant increase in the yield of hydroxyl radical (•OH). This research provides a new strategy for the effective utilization of H* toward rapid reduction of heavy metals and synchronous oxidation of the refractory organics.

Influence of anions on ozonation of bisphenol AF: Kinetics, reaction pathways, and toxicity assessment

In this article, the degradation of 4, 4'-(hexafluoroisopropylidene) diphenol (bisphenol AF, BPAF) by ozone was studied and toxicity of the degradation products was evaluated. Kinetic studies showed that acidic conditions were more conducive to the ozone degradation of BPAF than alkaline conditions. In the presence of common anions, Br^- and SO₄^2- promoted the degradation of BPAF, whereas NO₂^-, NO₃^-, HSO₃^- inhibited the degradation, and the other anions and cations had no significant effect. The degradation products were analyzed by mass spectrometry, and were mainly manifested in hydroxylation, carboxylation and cleavage of benzene ring. The addition of NO₂^-, HSO₃^- and Br^-produced the corresponding free radicals, resulting in the parent compound being attacked and affecting the degradation efficiency and pathways. The theoretical calculated results showed that the ortho-site of the BPAF phenolic hydroxyl group was more active than the meta-position, and it's more likely for free radicals to attack ortho-sites and initiate substitution reactions. Toxicity assessment of the products in the process of ozone degradation showed that toxicity of the products was reduced by benzene ring cleavage and a reduction in the F atomic number. However, the toxicity of nitro and brominated products of BPAF was increased. These findings provide some new insights into the role of common ions in ozonation process and product formation, and supplement the existing conclusions. The results of this study remind future researchers to concern that inorganic ions in real water may be converted into corresponding free radicals that affect the formation of ozone oxidation products.

Environmental occurrence and remediation of emerging organohalides: A review

As replacements for "old" organohalides, such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), "new" organohalides have been developed, including decabromodiphenyl ethane (DBDPE), short-chain chlorinated paraffins (SCCPs), and perfluorobutyrate (PFBA). In the past decade, these emerging organohalides (EOHs) have been extensively produced as industrial and consumer products, resulting in their widespread environmental distribution. This review comprehensively summarizes the environmental occurrence and remediation methods for typical EOHs. Based on the data collected from 2015 to 2021, these EOHs are widespread in both abiotic (e.g., dust, air, soil, sediment, and water) and biotic (e.g., bird, fish, and human serum) matrices. A significant positive correlation was found between the estimated annual production amounts of EOHs and their environmental contamination levels, suggesting the prohibition of both production and usage of EOHs as a critical pollution-source control strategy. The strengths and weaknesses, as well as the future prospects of up-to-date remediation techniques, such as photodegradation, chemical oxidation, and biodegradation, are critically discussed. Of these remediation techniques, microbial reductive dehalogenation represents a promising in situ remediation method for removal of EOHs, such as perfluoroalkyl and polyfluoroalkyl substances (PFASs) and halogenated flame retardants (HFRs).

Iron molydate catalyzed activation of peroxymonosulfate for bisphenol AF degradation via synergetic non-radical and radical pathways

Though molybdate oxides have been demonstrated as desirable catalysts for environmental remediation, the mechanism of catalytic activation of peroxymonosulfate (PMS) by iron (II) molybdate (FeMoO₄) remains unclear. In this study, FeMoO₄ was synthesized and applied for the activation of PMS to degrade bisphenol-AF (BPAF). FeMoO₄ showed excellent catalytic activity, high stability, and superior mineralization. The influence of operation parameters (i.e., FeMoO₄ dosage, PMS concentration, initial pH, co-existing anions, and temperature) on the removal of BPAF were also investigated in detail. Furthermore, the possible oxidation mechanism was proposed via the chemical quenching tests and electron spin resonance (ESR) analysis, which certified that both free radical (SO₄^-• and ^•OH) and non-radical (¹O₂) were the main reactive oxygen species for degrading BPAF. X-ray photoelectron spectroscopy (XPS) analysis indicated that the radicals were mainly generated via the continuous circulation of Fe³⁺/Fe²⁺ and Mo⁶⁺/Mo⁴⁺ redox cycles to enhance PMS activation. Finally, the degradation pathways of BPAF was proposed based on LC/MS results. This work showed the notable potential of the FeMoO₄/PMS system for degrading organic contaminants in the environment remediation and would promote the understanding of the mechanism of Fe-based molybdate in advanced oxidation.

Oxidative transformation of emerging organic contaminants by aqueous permanganate: Kinetics, products, toxicity changes, and effects of manganese products

Permanganate (Mn(VII)) has been widely studied for removal of emerging organic contaminants (EOCs) in water treatment and in situ chemical oxidation process. Studies on the reactive intermediate manganese products (e.g., Mn(III) and manganese dioxide (MnO₂)) generated from Mn(VII) reduction by EOCs in recent decades shed new light on Mn(VII) oxidation process. The present work summarizes the latest research findings on Mn(VII) reactions with a wide range of EOCs (including phenols, olefins, and amines) in detailed aspects of reaction kinetics, oxidation products, and toxicity changes, along with special emphasis on the impacts of intermediate manganese products (mainly Mn(III) and MnO₂) in-situ formed. Mn(VII) shows appreciable reactivities towards EOCs with apparent second-order rate constants (k_app) generally decrease in the order of olefins (k_app = 0.3 - 2.1 × 10⁴ M^-1s^-1) > phenols (k_app = 0.03 - 460 M^-1s^-1) > amines (k_app = 3.5 × 10^-3 - 305.3 M^-1s^-1) at neutral pH. Phenolic benzene ring (for phenols), (conjugated) double bond (for olefins), primary amine group and the N-containing heterocyclic ring (for amines) are the most reactive sites towards Mn(VII) oxidation, leading to the formation of products with different structures (e.g., hydroxylated, aldehyde, carbonyl, quinone-like, polymeric, ring-opening, nitroso/nitro and C-N cleavage products). Destruction of functional groups of EOCs (e.g., benzene ring, (conjugated) double bond, and N-containing heterocyclic) by Mn(VII) tends to decrease solution toxicity, while oxidation products with higher toxicity than parent EOCs (e.g., quinone-like products in the case of phenolic EOCs) are sometimes formed. Mn(III) stabilized by model or unknown ligands remarkably accelerates phenolic EOCs oxidation by Mn(VII) under acidic to neutral conditions, while MnO₂ enhances the oxidation efficiency of phenolic and amine EOCs by Mn(VII) at acidic pH. The intermediate manganese products participate in Mn(VII) oxidation process most likely as both oxidants and catalysts with their generation/stability/reactivity affecting by the presence of NOM, ligand, cations, and anions in water matrices. This work presents the state-of-the-art findings on Mn(VII) oxidation of EOCs, especially highlights the significant roles of manganese products, which advances our understanding on Mn(VII) oxidation and its application in future water treatment processes.

Iodide promotes bisphenol A (BPA) halogenation during chlorination: Evidence from 30 X-BPAs (X = Cl, Br, and I)

As a well known endocrine-disrupting and model chemical, bisphenol A (BPA) may pose a serious threat to human health, since it and its disinfection by-products (DBPs) have been detected in drinking water, urine, human colostrum, adipose tissue, and placenta samples. Although chlorinated BPAs (Cl-BPAs) and iodinated BPAs (I-BPAs) have been well studied, brominated BPAs (Br-BPAs), and mixed halogenated DBPs like bromo-iodo-BPAs (Br-I-BPAs), and bromo-chloro-iodo-BPAs (Cl-Br-I-BPAs) are less well understood. Notably, the role of iodide (I^-) during chlorination is not well understood, since the studies of the I-DBPs mainly focus on their genotoxicity and cytotoxicity. To understand the formation mechanisms of halogenated bisphenol A (HBPs) during chlorination with bromide (Br^-) and/or I^-, and the role of I^- during chlorination, three set of reactions were performed in the laboratory ("BPA + chlorine + Br^-", "BPA + chlorine + I^-" and "BPA + chlorine + Br^- +I^-" assigned as group A, B and C respectively). Thirty HBPs were identified and 18 of them were never reported before. I^- increases the transformation rate of BPA into HBPs as I-BPAs act as intermediate HBPs during chlorination that easily react with HClO/ClO^- and HBrO/BrO^- to form Cl-BPAs and Br-BPAs. HIO/IO^- showed higher reactivity towards BPA and HBPs than that of HBrO/BrO^- and HClO/ClO^-. The recycling of I^- was observed in the reactions of "BPA + chlorine + I^-" and "BPA + chlorine + Br^- +I^-", which may explain why I^- can induce BPA to transform into HBPs and suggests that I^- may act as a catalyst during the BPA chlorination reactions. The reaction pathways are proposed which present the reactions of BPA and HBPs with HClO/ClO^-, HBrO/BrO^-, and HIO/IO^-, as well as the recycling of I^-. This study describes the potential DBP formation and transformation mechanisms of BPA and its 16 alternatives, as well as the role of I^- on the transformation of phenol compounds during chlorination.

Prompting direct single electron transfer to produce non-radical 1O2/H* by electro-activating peroxydisulfate process with core-shell cathode

A novel heteroatomic N, P and S co-doped core-shell material (MnFe₃O₄@PZS) was synthesized by a simple polycondensation hydro-thermal method, and used as the cathode to cooperate with electron-catalysis to activate persulfate (S₂O₈^2-) (E-MnFe₃O₄@PZS-PDS) for tetracycline (TTC) degradation. Radical scavenger studies demonstrated that non-radicals including atomic H* and singlet oxygen (¹O₂) rather than sulfate and hydroxyl radicals were the crucial reactive oxygen species (ROS). Electrochemical analysis indicated that Mn doping could promote electro-catalytic process via diverting pathway from four/two-electron to one-electron to generate non-radical H*/¹O₂ at the cathode, including one-electron oxygen reduction reaction (1e-ORR) (O₂→¹O₂), and one-electron hydrogen reduction reaction (1e-HRR) (H₂O+e^-→H^∗), as evidenced by the lowest onset potential (0.072 V) together with electron transfer number (n = 1.65). Besides, the regeneration/reduction of Fe^Ⅱ/Ⅲ/Mn^Ⅱ/Ⅲ/Ⅳ and persulfate will not cause excessive consumption of electron and chemicals due to that could directly get the electron individually from the cathode and anode, and finally TTC could be completely degraded with low energy consumption (0.655 kWh m^-3). This study provides new insights into the direct single electron activating PDS to produce non-radical H*/¹O₂ via core-shell catalytic MnFe₃O₄@PZS, and displays a promising application in wastewater treatment.

In Vitro Metabolism of Five Bisphenol A Analogs Studied by LC-HRMS/MS

Bisphenol A (BPA) structural analogs are increasingly used as alternatives in many industrial applications, due to growing evidence of BPA-related toxicity. Despite their widespread use, little is known about the biotransformation of these BPA analogs in the body. In this study, the in vitro metabolism of five BPA analogs (bisphenol AF, bisphenol F, bisphenol S, cumylphenol, and tetramethylbisphenol F) were investigated, using human and rat liver fractions, to evaluate the formation of phase I and phase II metabolites. Liquid chromatography high-resolution tandem mass spectrometry was employed to separate and characterize over 50 metabolites, many of which were not previously reported. The structures of all detected oxidative metabolites, dimers, GSH adducts, glucuronide, and sulfate conjugates were elucidated. A biphenyl solid-core chromatographic column was utilized for the separation of all metabolites, with a subsequent method, on a F5 column, specifically optimized for the separation of dimers formed via oxidative metabolism. There are several examples in this work where the combination of high chromatographic resolution and tandem mass spectrometry were necessary to distinguish between isomeric metabolites and conjugates.

Degradation of ciprofloxacin by the Mn cycle system (MnCS): Construction, characterization and bacterial analysis

The release of Mn(II) occurs in the degradation of organic matters by manganese ore (MnO₂), resulting in a reduced efficiency. During the degradation of ciprofloxacin (CIP), in a biofilter, this paper put forward a novel method that similar to the geo-cycle of Mn (MnCS) on the Earth to regenerate MnO₂. The freshly prepared MnO₂ was suitable for the use in the MnCS. It indicated that the mutual conversion between Mn(II), Mn(III), and Mn(IV) in the MnCS, which was driven by CIP and manganese oxidizing bacteria (MnOB), could maintain the activity of MnO₂. The MnCS showed feasibility in the coexistence of ammonia or humic acid, and provided a kinetic degradation. The physicochemical features of MnO₂ before and after bio-regeneration were characterized by TEM, XRD, BET, and XPS. It was found that the morphological structure of MnO₂ became loose and the maximum peak of pore size distribution became smaller, but the increase of surface area, the change of Mn(III/IV) content, and the decrease of crystallinity favored the bio-regeneration process. Moreover, as a mediator in the MnCS, the group of MnOB was dramatically inhibited by CIP, and the bacterial community had changed significantly. The typical MnOB shared low abundance in the biofilter, while the rarely reported genera (e.g. Sphingomonas) that related to the formation of Mn deposits appeared to be involved in the MnCS.

Enhanced bisphenol S anaerobic degradation using an NZVI-HA-modified anode in bioelectrochemical systems

As a substitute for bisphenol A (BPA), bisphenol S (BPS) has a longer half-life, higher chemical inertness and better skin permeability than BPA, and it also has a strong endocrine disruption effect. Relatively few studies have focused on the main processing technology for BPS biodegradation, and the findings indicate that the biodegradation efficiency of BPS was relatively low. Therefore, this paper used an NZVI-HA composite-modified bio-anode to enhance the anaerobic degradation of BPS in a Bioelectrochemical Systems (BES). The results showed that the degradation efficiency of BPS was improved from 31.1% to 92.2% with the NZVI-HA modification compared with the control group (CC-BES). FTIR and XPS analyzes demonstrated that HA can accelerate the reduction rate of Fe³⁺ and increase the ratio of Fe²⁺/Fe³⁺. In addition, HA can form Fe-O-HA complexes with NZVI to promote electron transfer. An analysis of the NZVI-HA-BES intermediate metabolites revealed that complex modification properties altered the BPS degradation pathway. An analysis of microbial diversity indicated that the bacteria related to the degradation of BPS may be Terrimonas, Lysobacter, and Acidovorax.

Heterogeneous catalytic oxidation degradation of BPAF by peroxymonosulfate active with manganic manganous oxide: Mineralization, mechanism and degradation pathways

In this study, the catalytic ability and mechanisms involved in activating peroxymonosulfate (PMS) with Mn₃O₄ and the degradation pathways of bisphenol-AF (BPAF) removal was investigated. SO₄^-• and ·OH which were explored by and scavenging tests were the major reactive radicals in the Mn₃O₄/PMS system. A simple simulation algorithm was also used to calculate the relative concentrations of SO₄^-• ([SO₄^-•]) and ·OH ([·OH]) which were 8.39 × 10 ^-15 M and 6.96 × 10 ^-13 M, respectively. The mechanism for the electron transfer between the Mn (II) and Mn (III) species was discussed. Three degradation pathways of BPAF were determined by the GC/MS and LC/MS technology, including chemical mechanism of oxidation, hydroxylation, electron transfer, polymerization, and ring-cleavage. In addition, the results suggested that the Mn₃O₄/PMS system had an efficient total organic carbon (TOC) removal rate and excellent environmental adaptability, the removal rate of TOC being as high as 73.2% in the control condition. Furthermore, the reuse experiments and the comparison on the structural and componential changes of Mn₃O₄ powder before and after reaction demonstrated that the Mn₃O₄ catalyst possessed excellent stability and reusability. Finally, a maximum BPAF degradation of approximately 90.0% was achieved on the optimal conditions for 500 mg/L Mn₃O₄ dosage, 4 mM PMS concentration, 7.0 ± 0.2 initial pH, and 5 mg/L BPAF concentration respectively. And the effect of the coexisting anions and natural environmental water quality were also considered. This study demonstrated the Mn₃O₄/PMS system can be considered as a green approach for the removal of environmental reluctant pollutants.

UV365 induced elimination of contaminants of emerging concern in the presence of residual nitrite: Roles of reactive nitrogen species

The presence of nitrite (NO₂^-) is inevitable with concentrations of several mg L^-1 in some typical water bodies. In this study, UV at wavelength of 365 nm was investigated to degrade contaminants of emerging concern (CECs) in the presence of NO₂^- at environmentally relevant concentrations (0.1-5.0 mg L^-1). Six selected CECs with different structures were efficiently removed because of the generation of reactive nitrogen species (RNS) and hydroxyl radical (HO^•) from photolysis of NO₂^-. Contributions of UV₃₆₅ photolysis, RNS, and HO^• to CEC degradation in UV₃₆₅/NO₂^- system were calculated, and RNS were found to be the predominant species that are responsible for CEC degradation. The second major contributor is HO^• for the degradation of selected CECs except for the case of sulfadiazine. Impacts of water matrix components (including dissolved oxygen, solution pH, and natural organic matter) on CEC degradation in UV₃₆₅/NO₂^- system were evaluated. Furthermore, evolution profiles of CECs and NO₂^- in UV₃₆₅/NO₂^- system were tracked when actual water samples were used as background, and a simultaneous removal of CECs and NO₂^- was observed. Transformation products of bisphenol A and carbamazepine were proposed according to the results of HPLC/MS and quantum chemistry calculations. Nitration induced by RNS and hydroxylation induced by HO^• are main reactions occurred during CEC degradation in UV₃₆₅/NO₂^- system. Overall, UV₃₆₅ is a potential technology to remove CECs and NO₂^- in aquatic environment when residual NO₂^- is present. Our present study also provides possibility for the application of sunlight to remediate water co-polluted by CECs and NO₂^-.

Assessment of solar-assisted electrooxidation of bisphenol AF and bisphenol A on boron-doped diamond electrodes

Bisphenol (BP) analogues in wastewater effluent and groundwater pose a potential threat to human health due to their ability to disrupt steroidogenesis. A new solar-assisted electrochemical process (SECP) was developed and evaluated for the degradation of BP analogues. The effects of quenchers, current density, initial pH, supporting electrolyte, and aqueous matrix on the removal kinetics of bisphenol AF (BPAF) and bisphenol A (BPA) were investigated. The kinetic constants of BPAF, BPA, and bisphenol S (BPS) in the SECP with irradiation intensity of 500 mW cm^-2 were 0.017 ± 0.002 min^-1, 0.022 ± 0.002 min^-1, and 0.012 ± 0.001 min^-1, respectively. The changes in the degradation rates of BPAF, BPA, and BPS in the presence of quenchers indicated the relative contribution of hydroxyl radical (^●OH) oxidation, anodic electrolysis, and singlet (¹O₂) oxygenation in the degradation of BPs in the SECP. The enhanced rate of generation of ^●OH and ¹O₂ was observed in the SECP compared with those in the conventional electrochemical system. The identification of the transformation products (TPs) of BPAF demonstrated that hydroxylation, ring cleavage, β-scission, and defluorination were the major processes during the oxidation in the SECP. The conversion to fluoride ions (76%) and mineralization of total organic carbon (72%) in the SECP indicated further degradation of TPs. The results from this study improved our understanding of the degradation of BP analogues in the electrooxidation irradiated by solar light and help to establish the application potential of the SECP for the effective degradation of emerging contaminants in wastewater.

Crucial roles of oxygen and superoxide radical in bisulfite-activated persulfate oxidation of bisphenol AF: Mechanisms, kinetics and DFT studies

Though natural reducing agents have been demonstrated as desirable catalysts for environmental remediation, the mechanism of catalytic activation of persulfate (PS) by bisulfite (S(IV)) remains unclear. In this study, an emerging contaminant bisphenol AF (BPAF) was employed as the target compound to examine the activation and degradation mechanism in PS/S(IV) system. Sulfate radical (SO₄•-) was evidenced as the dominant radical accounting for BPAF degradation via quantitative analysis, while hydroxyl radical (•OH) and singlet oxygen (¹O₂) were minor contributors. Superoxide radical (O₂•-) was identified as an intermediate radical in promoting BPAF removal through quenching experiments and electron paramagnetic resonance analysis. Tests in oxygen-rich and oxygen-deficient systems were conducted and the results were contrasted to elucidate the important role of oxygen in BPAF degradation and SO₄•--formation. In addition, the effect of Dissolved Oxygen (DO) was simulated using two separate kinetic models. Decomposition mechanism of BPAF was afterwards clarified via the density-functional theory calculations using Fukui index to predict the vulnerable sites and the intermediate products. This study provides a mechanistic understanding of the activation of PS/S(IV) system on the BPAF removal, especially the critical role of DO and O₂•- in SO₄•- generation.

Strong improvement of nanofiltration performance on micropollutant removal and reduction of membrane fouling by hydrolyzed-aluminum nanoparticles

Increasing attention has been focused on the removal of micropollutants from contaminated drinking source water. However, low rejection efficiency and membrane fouling still inhibit further application of nanofiltration membrane in this field. Interesting results were found that the residual hydrolyzed-aluminum nanoparticles from supernatant after coagulation and sedimentation strongly improved the nanofiltration performance for micropollutant removal. A simulated raw water containing humic acids, micropollutants and kaolinite clay was employed to investigate the factors of water matrix affecting the nanoparticle-enhanced nanofiltration for micropollutant removal. Results of experiments showed that these hydrolyzed-aluminum nanoparticles easily induced the aggregation of bisphenol-A (BPA) and humic acids in the supernatant. The enhancement of BPA removal was mainly attributed to the repelling interaction between the Al-BPA-DOC complexity and in situ-modified membrane surface during nanofiltration. 'This in situ surface modification by the hydrolyzed-aluminum nanoparticles improved membrane hydrophilicity, roughness and positively-charging capacity. For the treatment of River Songhua water spiked with micropollutant, the percentage removal of BPA was improved to be 88.5%, much more than the case of single nanofiltration without coagulation (60.7%). Meanwhile, the membrane fouling was reduced by 2.13 times than the case of single nanofiltration without the dynamically deposited-layer of nanoparticles. This in situ modification of nanofiltration membrane by hydrolyzed-aluminum nanoparticles achieved excellent removal efficiency for micropollutants from River Songhua water background.

UVC-assisted electrochemical degradation of novel bisphenol analogues with boron-doped diamond electrodes: kinetics, pathways and eco-toxicity removal

In the present study, the UVC-assisted electrochemical degradation ofthree novel bisphenol analogues (BPs; including bisphenol F, S, and B, i.e., BPF, BPS and BPB, respectively), along with bisphenol A (BPA), was investigated using boron-doped diamond (BDD) electrode. At first, this study demonstrated a significant influence ofcurrent density on the degradation rates of BPF by the BDD anode. The pseudo-first order rate constants for BPF were calculated as 0.012, 0.028 and 0.029 min^-1 at the applied current densities of 10, 20 and 30 mA/cm², respectively. UVC irradiation significantly enhanced the electrochemical degradation of BPF in the concentration range from 5 to 30 mg/L, with synergistic effects in the range of 32.0%-40.9%. The UVC-BDD electrolysisshowed comparable or even lower electric energy per order (E_EO) than single BDD electrolysis. The UVC-assisted degradation of the investigated BPs showed decreased pseudo-first order rate constants in the following order: BPF > BPA > BPB > BPS. Based on the identifiedtransformation products, UVC-assisted electrochemical degradation pathways of the novel BPs were proposed to be mainly hydroxylation and bond-cleavage. UVC irradiation has been proved to promote the formation of hydroxyl radicals by BDD electrode to facilitate the degradation process. For these BPs, nearly 100% mineralization can be achieved by a modified strategy using a short-time UVC-assisted BDD electrolysis (120 min) that is followed by UVC photolysis (360 min). Finally, the eco-toxicity of the BPs solutions towardsVibrio Fischeri was significantly removed after 120 min of the electrochemical degradation period. Based on these results, the UVC-assisted electrochemical treatment using a BDD electrode can be considered a promising technology for the removal of novel BPs and the reduction of their hazardous effects to aqueous environments.

Enhanced Transformation of Emerging Contaminants by Permanganate in the Presence of Redox Mediators

In this study, a permanganate/redox mediator system for enhanced transformation of a series of emerging contaminants was evaluated. The presence of various redox mediators (i.e., 1-hydroxybenzotriazole, N-hydroxyphthalimide, violuric acid, syringaldehyde, vanillin, 4-hydroxycoumarin, and p-coumaric acid) accelerated the degradation of bisphenol A (BPA) by Mn(VII). Since 1-hydroxybenzotriazole (HBT) exhibited the highest reactive ability, it was selected to further investigate the reaction mechanisms and quantify the effects of important reaction parameters on Mn(VII)/redox-mediator reactions with BPA and bisphenol AF (BPAF). Interestingly, not only HBT accelerated the degradation of BPA, but also BPA enhanced the decay of HBT. Evidence for the in situ formation of HBT^· radicals as the active oxidant responsible for accelerated BPA and BPAF degradation was obtained by radical scavenging experiments and ³¹P NMR spin trapping techniques. The routes for HBT^· radical formation involving Mn(VII) and the electron-transfer pathway from BPA/BPAF to HBT^· radicals demonstrate that the Mn(VII)/HBT system was driven by the electron-transfer mechanism. Compared to Mn(VII) alone, the presence of HBT totally inhibited self-coupling of BPA and BPAF and promoted β-scission, hydroxylation, ring opening, and decarboxylation reactions. Moreover, Mn(VII)/HBT is also effective in real waters with the order of river water > wastewater treatment plant (WWTP) effluent > deionized water.

Ferrate Oxidation of Phenolic Compounds in Iodine-Containing Water: Control of Iodinated Aromatic Products

Highly toxic iodinated products would form in oxidation and disinfection of iodine-containing water. Variation of iodinated aromatic products in ferrate [Fe(VI)] oxidation of phenolic compounds (phenol, bisphenol A (BPA), and p-hydroxybenzoic acid (p-HBA)) in iodine-containing water was investigated. At pH 5.0, oxidation of phenolic compounds was inhibited by competitive reaction of ferrate with I^-, and no formation of iodinated aromatic products was detected. Almost all I^- was converted into nontoxic IO₃^-. At pH 7.0, 8.0, and 9.0, HOI formed in ferrate oxidation of I^- and further reacted with phenols, with the formation of iodinated aromatic products. Mass spectrometry analysis showed that both kinds and contents of iodinated aromatic products were raised with the increase in solution pH and the content of I^-, and these iodinated aromatic products were further oxidized by ferrate. Ferrate deprived iodine from iodinated aromatic products and transferred highly toxic organic iodine into nontoxic IO₃^-. An electron-donating substituent (alkyl) increased the reactivity of phenol with ferrate and HOI and facilitated ferrate oxidation of iodinated phenols. An electron-drawing substituent (carboxyl) decreased the reactivity of phenol with ferrate and HOI and hindered the further oxidation of iodinated aromatic products. A kinetic model about the variation of phenol, BPA, and p-HBA in reaction with ferrate in iodine-containing water was developed, and the oxidation profile of phenolic compounds could be satisfactorily predicted at various iodide concentrations.

Visible light and fulvic acid assisted generation of Mn(III) to oxidize bisphenol A: The effect of tetrabromobisphenol A

Bisphenol A (BPA) and tetrabromobisphenol A (TBBPA), endocrine disrupting compounds (EDCs), are of increasing concerns for many years. This paper presents the elimination of BPA under visible light (VL) (λ ≥ 420 nm) irradiated solutions containing fulvic acid (FA) and MnSO₄ (Mn(II)), and examines the possible effects of TBBPA on the transformation of BPA. After 72 h of reaction time, the removal efficiency of BPA in the studied system was 69%. Results of different experiments to identify oxidative species suggested the dominate role of soluble manganese (III) (Mn(III)) in the conversion of BPA. The transformation of BPA by the VL/FA/Mn(II) system was through self-oligomerization in absence of co-existence of TBBPA. In the co-existence of BPA with TBBPA, the removal of BPA was largely inhibited due to the competition with available Mn(III) and the possible occurrence of cross-coupling reactions between the two EDCs. This phenomenon was further elucidated by product analyses and density functional theory (DFT) calculations. The energy difference (ΔE) for generating a cross-coupling product was calculated as -23.4 kJ mol^-1, much lower than the positive values of ΔE for self-coupling products of BPA or TBBPA, demonstrating that cross-coupling reactions between BPA and TBBPA likely occurred easier than the respective self-coupling reactions. The toxicity test showed that the overall estrogenic activity of BPA reaction solution was significantly decreased by the VL/FA/Mn(II) system. In general, our study provided new insights into the transformation of co-existing EDCs by in situ formed Mn(III) in aqueous solution.

Sonolytic degradation of bisphenol S: Effect of dissolved oxygen and peroxydisulfate, oxidation products and acute toxicity

In this paper, the kinetics of bisphenol S (BPS) degradation in the presence of peroxydisulfate (PDS) or dissolved oxygen (DO) in ultrasound (US) system were investigated. For PDS (US/PDS), increased PDS concentration result in faster BPS degradation, but the enhancement was not remarkable with multiplying PDS dosages. Therefore, heterogeneous PDS activation model based on a Langmuir-type adsorption mechanism was proposed to explain the trait of BPS abatement. The equilibrium constant of PDS (K_PDS) was calculated to be 2.91 × 10^-4/μM, which was much lower than that of BPS, suggesting that PDS was hard to adsorb on the gas-liquid interface of the cavitation bubble following by activation. Besides, the formation of •OH and SO₄^•- in US/PDS system was reinvestigated. The result showed that SO₄^•- rather than •OH was the predominant radical, which was quite different from previous study. Dissolved oxygen largely improve the degradation of BPS in US system and •OH rather than O₂^•- was proved to be the main reactive oxygen species (ROS). The improvement of •OH generation possibly caused by the reaction of DO with •H so that it cannot recombine with •OH. The transformation of the BPS in US system mainly included BPS radical polymerization, hydroxylation and hydrolysis. Frustratingly, the acute toxicity assay of Vibrio fischeri suggests that the degradation products of BPS are more toxic. These results will improve the understanding on the activation mechanisms of PDS and the role of dissolved oxygen play in US. Further investigations may need to explore other treatment ways of BPS and evaluate the acute toxicity of degradation products.

Degradation of methylene blue by natural manganese oxides: kinetics and transformation products

In this study, natural manganese oxides (MnO x ), an environmental material with high redox potential, were used as a promising low-cost oxidant to degrade the widely used dyestuff methylene blue (MB) in aqueous solution. Although the surface area of MnO x was only 7.17 m2 g-1, it performed well in the degradation of MB with a removal percentage of 85.6% at pH 4. It was found that MB was chemically degraded in a low-pH reaction system and the degradation efficiency correlated negatively with the pH value (4-8) and initial concentration of MB (10-50 mg l-1), but positively with the dosage of MnO x (1-5 g l-1). The degradation of MB fitted well with the second-order kinetics. Mathematical models were also built for the correlation of the kinetic constants with the pH value, the initial concentration of MB and the dosage of MnO x . Furthermore, several transformation products of MB were identified with HPLC-MS, which was linked with the bond energy theory to reveal that the degradation was initiated with demethylation.

Oxidation of methylparaben (MeP) and p‑hydroxybenzoic acid (p-HBA) by manganese dioxide (MnO2) and effects of iodide: Efficiency, products, and toxicity

It is reported that methylparaben (MeP, a widely used phenolic preservative) and its major metabolite p‑hydroxybenzoic acid (p-HBA) display estrogenic activity and are frequently detected in various environmental settings. Naturally occurring manganese dioxide (MnO₂) plays an important role in attenuation of contaminants released into the environment, and the presence of iodide (I^-) may affect these processes. In this work, it was found that both MeP and p-HBA displayed considerable reactivity towards MnO₂ with their half-lives increased with decreasing MnO₂ concentrations or increasing pH. The presence of I^- obviously accelerated the transformation efficiency of MeP and p-HBA by MnO₂ with stronger enhancement at higher I^- concentrations or lower pH. Dimeric products (e.g., dimeric MeP or p-HBA) were generated from MeP/p-HBA treated by MnO₂, and iodinated aromatic products (e.g., mono-/di-iodinated MeP/p-HBA) were additionally identified in the presence of I^-. Higher concentrations of these iodinated aromatic products were generally formed at higher I^- or lower MnO₂ concentrations or lower pH. Ecotoxicity analysis showed that dimeric and iodinated aromatic products were more eco-toxic than parent MeP/p-HBA. This work shows that MnO₂ may greatly affect the fate of MeP and p-HBA released into the environment, and the presence of I^- can significantly affect these processes.

Transformation of bisphenol AF and bisphenol S by permanganate in the absence/presence of iodide: Kinetics and products

Recent studies have reported that permanganate (Mn(VII)) shows a good performance in treatment of phenolic compounds, and the presence of iodide (I^-) may display a great impact on Mn(VII) oxidation with the formation of toxic iodinated aromatic products. In this work, transformation of bisphenol AF (BPAF) and bisphenol S (BPS) by Mn(VII) in the absence or presence of I^- was studied. Mn(VII) showed considerable reactivity towards BPAF with apparent second-order rate constants (0.09-1.65 M^-1s^-1) higher than those of Mn(VII) with BPS (0.02-0.12 M^-1s^-1) reported in literature over the pH range of 5-9. The presence of I^- apparently accelerated the transformation rates of BPAF and BPS by Mn(VII), and these results could be explained by the contribution of hypoiodous acid (HOI) in situ formed from Mn(VII) oxidation of I^-. A kinetic model involving the competitive reactions (i.e., Mn(VII) with I^- and bisphenols, HOI with Mn(VII) and bisphenols) well simulated BPAF/BPS transformation by Mn(VII) in the presence of I^- under various conditions. Hydroxylated, bond-cleavage, and polymeric products were identified from BPAF/BPS oxidation by Mn(VII), and iodinated aromatic products (e.g., mono- and multi-iodinated BPAF/BPS) were additionally detected in the presence of I^-. Reaction pathways involving Mn(VII) one-electron oxidation as well as HOI substitution of BPAF/BPS were proposed. Eco-toxicity analysis by ECOSAR showed that the toxicity of these products generally followed the order of polymeric and iodinated aromatic products > parent BPAF/BPS > hydroxylated products > bond-cleavage products.

Comparative study on ferrate oxidation of BPS and BPAF: Kinetics, reaction mechanism, and the improvement on their biodegradability

Bisphenol S (BPS) and bisphenol AF (BPAF) were increasingly consumed and these compounds are resistant to environmental degradation. Herein, ferrate oxidation of BPS and BPAF was investigated, and biodegradability of the oxidation products was examined. The second-order reaction rate constants of ferrate with BPS and BPAF were 1.3 × 10³ M^-1s^-1 and 3 × 10² M^-1s^-1, respectively, at pH 7.0, 25 °C. In the oxidation process, some BPS molecules dimerized, while other BPS molecules were oxidized through oxygen-transfer process, leading to the formation of hydroxylation products and benzene-ring cleavage products. The dominant reaction of BPAF with ferrate was oxygen-transfer process, and BPAF was degraded into lower molecular weight products. The variation of assimilable organic carbon (AOC) suggested that the biodegradability of BPAF and BPS was largely improved after ferrate oxidation. Compared with the BPS oxidation products, the BPAF oxidation products were easier to be bio-consumed. Pure culture test showed that BPAF inhibited the growth of Escherichia coli, while ferrate oxidation completely eliminated this toxic effect. Co-existing humic acid (HA, 1 mg C/L to 5 mg C/L) decreased the removal of BPS and BPAF with ferrate. Compared with BPAF, more oxidation intermediates formed in the ferrate oxidation of BPS may be reduced by HA to the parent molecular. Thus, the inhibition effect of HA on the ferrate oxidation of BPS was more obvious than that on BPAF.