Oxidation degradation of tris-(2-chloroisopropyl) phosphate by ultraviolet driven sulfate radical: Mechanisms and toxicology assessment of degradation intermediates using flow cytometry analyses

A review of the present methods used to remediate soil and water contaminated with organophosphate esters and developmental directions

Organophosphate esters (OPEs) are widely used commercial additives, but their environmental persistence and toxicity raise serious concerns necessitating associated remediation strategies. Although there are various existing technologies for OPE removal, comprehensive screening for them is urgently needed to guide further research. This review provides a comprehensive overview of the techniques used to remove OPEs from soil and water, including their related influencing factors, removal mechanisms/degradation pathways, and practical applications. Based on an analysis of the latest literature, we concluded that (1) methods used to decontaminate OPEs include adsorption, hydrolysis, photolysis, advanced oxidation processes (AOPs), activated sludge processes, and microbial degradation; (2) factors such as the quantity/characteristics of the catalysts/additives, pH value, inorganic ion concentration, and natural organic matter (NOM) affect OPE removal; (3) primary degradation mechanisms involve oxidation induced by reactive oxygen species (ROS) (including •OH and SO4•-) and degradation pathways include hydrolysis, hydroxylation, oxidation, dechlorination, and dealkylation; (5) interference from the pH value, inorganic ion and the presence of NOM may limit complete mineralization during the treatment, impacting practical application of OPE removal techniques. This review provides guidance on existing and potential OPE removal methods, providing a theoretical basis and innovative ideas for developing more efficient and environmentally friendly techniques to treat OPEs in soil and water.

Critical review on organophosphate esters in water environment: Occurrence, health hazards and removal technologies

Organophosphate esters (OPEs), which are phosphoric acid ester derivatives, are anthropogenic substances that are widely used in commerce. Nevertheless, there is growing public concern about these ubiquitous contaminants, which are frequently detected in contaminated water sources. OPEs are mostly emitted by industrial operations, and the primary routes of human exposure to OPEs include food intake and dermal absorption. Because of their negative effects on both human health and the environment, it is clear that innovative methods are needed to facilitate their eradication. In this study, we present a comprehensive overview of the existing characteristics and origins of OPEs, their possible impacts on human health, and the merits, drawbacks, and future possibilities of contemporary sophisticated remediation methods. Current advanced remediation approaches for OPEs include adsorption, degradation (advanced oxidation, advanced reduction, and redox technology), membrane filtration, and municipal wastewater treatment plants, degradation and adsorption are the most promising removal technologies. Meanwhile, we proposed potential areas for future research (appropriate management approaches, exploring the combination treatment process, economic factors, and potential for secondary pollution). Collectively, this work gives a comprehensive understanding of OPEs, providing useful insights for future research on OPEs pollution.

Oxidation of the nitrogen-free phosphonate antiscalants HEDP and PBTC in reverse osmosis concentrates: Reaction kinetics and degradation rate

Reverse osmosis (RO) is an advanced technology used to produce potable water from a variety of water sources, including surface water, seawater and wastewater. The yield of the product water from the RO systems is increased by the addition of antiscalants which prevent scaling from calcium and other ions. Removal of antiscalants from RO concentrate can induce the precipitation of oversaturated scale-forming substances, enable additional water recovery from RO concentrates, and reduce the risk of eutrophication after concentrate disposal into the receiving water (e.g., river water). This study aims to provide a better insight into oxidation reactions of the N-free phosphonate antiscalants 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) with ozone, hydroxyl radical (^•OH) and sulfate radicals (SO₄^•-). Ozone barely reacts with HEDP and PBTC at pH 7 (k < 10 M^-1s ^- 1), while second order reaction rates of SO₄^•- and ^•OH were determined to be in the range 10⁷-10⁸M ^- 1s ^- 1. Sulfate, silicate and chloride matrices increased HEDP ozone degradation rate possibly due to metal complexation effect. Whereas carbonate and chloride hindered PBTC ozone degradation, and natural organic matter (NOM) inhibited both HEDP and PBTC degradation through scavenging of ^•OH. The SO₄^•-- radical based oxidation process of HEDP and PBTC is mainly inhibited by carbonate and NOM, interestingly only HEDP degradation is inhibited by chloride whereby the PBTC could not be fully degraded (degradation < 60%). The oxidation of PBTC is in real RO concentrates in both processes limited to 10% degradation, whereas HEDP could be degraded up to 60% with ozone and UV/persulfate application.

Enhanced degradation of atrazine through UV/bisulfite: Mechanism, reaction pathways and toxicological analysis

Atrazine residue in the environment continues to threaten aquatic ecosystem and human health owing to its adverse effect. However, limited researches focused on degradation mechanism of atrazine by UV/bisulfite, especially risk of intermediates at cellular and molecular level has not been seriously elaborated. In current work, transformation patterns and residual toxicity of intermediates of atrazine by UV/bisulfite were systematically investigated. The atrazine degradation was described by a pseudo first-order kinetic model (K_obs = 0.1053 min^-1). The presence of H₂PO₄^-, HCO₃^- and HA had a powerful inhibition. Scavenging test of radicals illustrated that SO₄^•-, •OH and O₂^•- existed in UV/bisulfite system, SO₄^•- and •OH were mainly responsible for atrazine degradation. Eight degradation intermediates were identified, which were involved in dealkylation, alkyl oxidation, dechlorination-hydroxylation, and alkylic-hydroxylation. E. coli as a model microorganism was selected to assess the risk of degradation intermediates. The levels of reactive oxygen species, MDA and Na⁺/K⁺-ATPase were declined, suggesting that oxidative damage induced by these intermediates was weakened. According to differential metabolites expression analysis, several key metabolites including aspartate, L-tryptophan, L-asparagine, cytidine, cytosin, stearic acid, behenic acid, were up-regulated, and glutathione, cadaverin, L-2-hydroxyglutaric acid and phytosphingosine were downregulated, clarifying that effective detoxification of atrazine can be performed by UV/bisulfite.

Novel monolithic catalysts for VOCs removal: A review on preparation, carrier and energy supply

Volatile organic compounds (VOCs) are considered the culprit of secondary air pollution such as ozone, secondary organic aerosols, and photochemical smog. Among various technologies, catalytic oxidation is considered a promising method for the post-treatment of VOCs. Researchers are sparing no effort to develop novel catalysts to meet the requirements of the catalytic process. Compared with the powdered or granular catalysts, the monolithic catalysts have the advantages of low pressure drop, high utilization of active phases, and excellent mechanical properties. This review summarized the new design of monolithic catalysts (including new preparation methods, new supports, and new energy supply methods) for the post-treatment of VOCs. It addressed the advantages of the new designs in detail, and the scope of applicability for each new monolithic catalyst was also highlighted. Finally, the highly required future development trends of monolithic catalysts for VOCs catalytic oxidation are recommended. We expect this work can inspire and guide researchers from both academic and industrial communities, and help pave the way for breakthroughs in fundamental research and industrial applications in this field.

Heterogeneous Fenton-like removal of tri(2-chloroisopropyl) phosphate by ilmenite (FeTiO3): Kinetic, degradation mechanism and toxic assessment

Tri(2-chloroisopropyl) phosphate (TCPP), a common organophosphate flame retardant, was frequently detected in the environment and posed threats to human health. In this work, the main component of ilmenite FeTiO₃ was synthesized by the sol-gel method and employed as the catalyst for the degradation of TCPP by activating persulfate (PS) under UV irradiation. The degradation processes were fitted by the pseudo-first-order kinetic. The k_obs value in UV/FeTiO₃/PS system was up to 0.0056 min^-1 and much higher than that in UV/PS (0.0014 min^-1), UV/FeTiO₃ (0.0012 min^-1) and FeTiO₃/PS (0.0016 min^-1) systems, demonstrating a distinct synergistic effect in TCPP removal. The degradation efficiency of TCPP increased with the increase of UV intensity, PS concentration and catalyst dosage, and with the decrease of pH. By quenching experiment and EPR analysis, ·OH was confirmed to be the dominant radical in the reaction of the UV/FeTiO₃/PS system. The possible degradation pathways of TCPP were dechlorination, dealkylation, and further oxidation of alkyl groups based on the theoretical calculation of frontier molecular orbits. The toxicity of degradation intermediates evaluated by luminescence inhibition rate of photoluminescence was higher than TCPP. Thus, TCPP can be degraded in the UV/FeTiO₃/PS system effectively at the premise of introducing controlling measures to reduce the toxicity of degradation intermediates.

A new and systematic review on the efficiency and mechanism of different techniques for OPFRs removal from aqueous environments

Organic phosphorus flame retardants (OPFRs), as a new type of emerging contaminant, have drawn great attention over the last few years, due to their wide distribution in aquatic environments and potential toxicities to humans and living beings. Various treatment methods have been reported to remove OPFRs from water or wastewater. In this review, the performances and mechanisms for OPFRs removal with different methods including adsorption, oxidation, reduction and biological techniques are overviewed and discussed. Each technique possesses its advantage and limitation, which is compared in the paper. The degradation pathways of typical OPFRs pollutants, such as Cl-OPFRs, alkyl OPFRs and aryl OPFRs, are also reviewed and compared. The degradation of those OPFRs depends heavily upon their structures and properties. Furthermore, the implications and future perspectives in such area are discussed. The review may help identify the research priorities for OPFRs remediation and understand the fate of OPFRs during the treatment processes.

Transformation of sulfamethoxazole by sulfidated nanoscale zerovalent iron activated persulfate: Mechanism and risk assessment using environmental metabolomics

The threat caused by the misuse of antibiotics to ecology and human health has been aroused an extensive attention. Developing cost-effective techniques for removing antibiotics needs to put on the agenda. In current research, the degradation mechanism of sulfamethoxazole (SMX) by sulfidated nanoscale zerovalent iron (S-nZVI) driven persulfate, together with the potential risk of intermediates were studied. The degradation of SMX followed a pseudo-first order kinetics reaction with k_obs at 0.1176 min^-1. Both SO₄^•- and •OH were responsible for the degradation of SMX, and SO₄^•- was the predominant free radical. XPS analysis demonstrated that reduced sulfide species promoted the conversion of Fe (III) to Fe (II), resulting in the higher transformation rate of SMX. Six intermediates products were generated through hydroxylation, dehydration condensation, nucleophilic reaction, and hydrolysis. The risk of intermediates products is subsequently assessed using E. coli as a model microorganism. After E.coli exposure to intermediates for 24 h, the upmetabolism of carbohydrate, nucleotide, citrate acid cycle and downmetabolism of glutathione, sphingolipid, galactose by metabolomics analysis identified that SMX was effectively detoxified by oxidation treatment. These findings not only clarified the superiority of S-nZVI/persulfate, but also generated a novel insight into the security of advanced oxidation processes.

Amino-functionalized MIL-88B as heterogeneous photo-Fenton catalysts for enhancing tris-(2-chloroisopropyl) phosphate (TCPP) degradation: Dual excitation pathways accelerate the conversion of FeIII to FeII under visible light irradiation

In this work, the amino-functionalized metal-organic frameworks (MIL-88B-NH₂) was synthesized, characterized and used as heterogeneous photo-Fenton catalyst for tris-(2-chloroisopropyl) phosphate (TCPP) degradation. The photo-Fenton activity of MIL-88B-NH₂ was investigated on the basis of influence factors, such as initial pH and TCPP concentration, and coexisting impurities. The results revealed that MIL-88B-NH₂+H₂O₂+Vis system exhibited a satisfactory degradation efficiency of TCPP (almost 100%) within 60 min accompanied by a good reusability. Noticeably, the degradation kinetics constant of TCPP by MIL-88B-NH₂+H₂O₂+Vis system was 0.086 min^-1, which was visibly higher than that of MIL-88B+H₂O₂+Vis system (0.021 min^-1) since the addition of amino-functionalized organic linker inhibiting the recombination rate of the photo-generated electron-hole pairs and improving the visible light response. Combined with the characterization, the conversion of Fe^III to Fe^II could be accelerated by the photo-generated electron from the excitation of Fe-O clusters and NH₂ functionalities, which strengthened the decomposition of H₂O₂ and formed plenty •OH. Simultaneously, six steady products were validated and potential degradation pathways of TCPP were proposed. It was anticipated that MIL-88B-NH₂ could be considered as a desirable and alternative candidate in the application of heterogeneous photo-Fenton reaction to control the environmental risks caused by organophosphate flame retardants (OPFRs).

Degradation of organophosphorus flame retardants in heterogeneous photo-Fenton system driven by Fe(III)-based metal organic framework: Intermediates and their potential interference on bacterial metabolism

Organophosphorus flame retardants (OPFRs) have been regarded as one of the most rebarbative classes of emerging contaminants due to their persistence and toxicity. In the current study, Fe-based metal organic framework (MIL-88A) was synthesized and employed as photo-Fenton catalyst for the degradation of tris-(2-chloroisopropyl) phosphate (TCPP), a typical representative of OPFRs. The observations indicated that visible light could boost the reduction of ≡Fe^III to ≡Fe^II in Fe-O clusters of MIL-88A during the photo-Fenton system and consequently induce the transformation of H₂O₂ to OH, which realized efficient degradation of TCPP. Due to the excellent function of MIL-88A, the effective pH application range of photo-Fenton system was extended in comparison with traditional Fenton system. The degradation efficiency of TCPP was visibly influenced in presence of humic acid (HA). MIL-88A exhibited a commendable reusability and stability after 3 times cycle. As the photo-Fenton reaction proceeded, TCPP was disintegrated to several kinds of carboxylated, dechlorinated and hydroxylated products. The observations of metabolomics endorsed that the interference of intermediate products mixture on E. coli weakened to a certain extent. In conclusion, carboxylation, dechlorination, hydroxylation and oxidation of TCPP were likewise effective for its detoxification, revealing that heterogeneous photo-Fenton system driven by Fe-based metal organic framework will be an attractive and safe treatment technique for OPFRs control.

Photocatalytic oxidation technology for indoor air pollutants elimination: A review

As more people are spending the majority of their daily lives indoors, indoor air quality has been acknowledged as an important factor influencing human health, with increasing research attention in recent decades. Indoor air pollutants (IAPs), such as volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs), can cause acute irritation and chronic diseases. Photocatalytic oxidation (PCO) technology is an efficient approach for eliminating IAPs. In this review, the development of PCO technology was explained and discussed to promote future development of PCO technology for IAP elimination. First, the health effects and the measured concentrations of typical VOCs and SVOCs in indoor environments worldwide were briefly introduced. Subsequently, the development and limitations of some typical photocatalytic reactors (including packed-bed reactors, monolithic reactors, optical fiber reactors, and microreactors) were summarized and compared. Then, the influences of operating parameters (including initial concentration of contaminants, relative humidity, space velocity, light source and intensity, catalyst support materials, and immobilization method) and the degradation pathways as well as intermediates of PCO technology were elucidated. Finally, the possible challenges and future development directions regarding PCO technology for IAP elimination were critically proposed and addressed.

Reductive degradation of chlorinated organophosphate esters by nanoscale zerovalent iron/cetyltrimethylammonium bromide composites: Reactivity, mechanism and new pathways

Chlorinated organophosphate esters (Cl-OPEs), e.g., tris(2-chloroethyl) phosphate (TCEP), tris(2-chloro-2-propyl) phosphate (TCPP) and tris(1,3-dichloro-2-propyl) phosphate (TDCPP), are widely used as additive flame retardants in commercial and building products. They have potential persistent organic pollutant properties and are frequently detected in various waters, especially in wastewaters. Nanoscale zerovalent iron (nZVI)-based method is an efficient reductive technology for treating waters polluted by halogenated organic pollutants (HOCs). Cetyltrimethylammonium bromide (CTAB) is a ubiquitous surfactant in wastewaters and can favorably affect the interaction between HOCs and nZVI. However, its effect on the Cl-OPEs removal by nZVI-based materials still remains unknown. Herein, the adsorption and degradation efficiencies of Cl-OPEs by nZVI and sulfidated nZVI (S-nZVI) in the presence or absence of CTAB were quantified based on the decreasing concentrations of Cl-OPEs in reaction systems. Our results showed that TDCPP and TCPP were adsorbed onto the nZVI or S-nZVI surface and subsequently degraded. In contrast, TCEP was just adsorbed onto the particle surface without further degradation. The addition of CTAB significantly enhanced the hydrophobic adsorption between Cl-OPEs and nZVI or S-nZVI, leading to increased degradation of Cl-OPEs (especially TCEP). CTAB adsorption isotherms indicated that S-nZVI had a higher adsorption capacity for CTAB than nZVI. The S-nZVI/CTAB composite exhibited a better performance than nZVI/CTAB composite. When S-nZVI was combined with 100.0 mg L^-1 CTAB, 100% of TDCPP, TCPP and TCEP was degraded within 3 hours, 5 and 14 days, respectively. As the concentration of CTAB was increased up to 335.0 mg L^-1, TCEP could be completely degraded within 3 days by S-nZVI. Five degradation products of TCEP were identified, of which O,O-di-(2-chloroethyl) O-ethyl phosphate (DCEEP) and ethane were reported for the first time. We propose that TCEP is dechlorinated by nZVI or S-nZVI through the electron attack at the ethyl-chlorine group to form bis(2-chloroethyl) phosphate, DCEEP, chloride, ethene and ethane, representing previously unknown degradation pathways.

Microbial degradation of dyes: An overview

Industrialization increases use of dyes due to its high demand in paper, cosmetic, textile, leather and food industries. This in turn would increase wastewater generation from dye industrial activities. Various dyes and its structural compounds present in dye industrial wastewater have harmful effects on plants, animals and humans. Synthetic dyes are more resistant than natural dyes to physical and chemical methods for remediation which makes them more difficult to get decolorize. Microbial degradation has been researched and reviewed largely for quicker dye degradation. Genetically engineered microorganisms (GEMs) play important role in achieving complete dye degradation. This paper provides scientific and technical information about dyes & dye intermediates and biodegradation of azo dye. It also compiles information about factors affecting dye(s) biodegradation, role of genetically modified organisms (GMOs) in process of dye(s) degradation and perspectives in this field of research.

Enhanced Biodegradation/Photodegradation of Organophosphorus Fire Retardant Using an Integrated Method of Modified Pharmacophore Model with Molecular Dynamics and Polarizable Continuum Model

A comprehensive 3D-quantitative structure-activity relationship (QSAR) pharmacophore model was constructed using the values of comprehensive biodegradation/photodegradation effects of 17 organophosphorus flame retardants (OPFRs) evaluated by a normalization method to modify OPFRs with high biodegradation/photodegradation, taking tris(chloro-isopropyl) phosphate (TCPP), tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCIPP)-which occur frequently in the environment, and are the most difficult to degrade as target molecules. OPFR-derivative molecules TCPP-OH shows the highest improvement in biodegradation and photodegradation (55.48% and 46.37%, respectively). On simulating the biodegradation path and photodegradation path, it is found that the energy barrier of TCPP-OH for phosphate bond cleavage is reduced by 15.73% and 52.52% compared to TCPP after modification, respectively. Finally, in order to further significantly improve its biodegradability and photodegradation, the efficiency enhancement in the biodegradation and photodegradation of TCPP-OH are analyzed under the simulated environment by molecular dynamics and polarizable continuum model, respectively. The results of molecular dynamics show that the biodegradation efficiency of the TCPP-OH increased by 75.52% compared to TCPP. The UV spectral transition energy (4.07 eV) of TCPP-OH under the influence of hydrogen peroxide solvation effect is 44.23% lower than the actual transition energy (7.29 eV) of TCPP.

Insights into the degradation and detoxication mechanisms of aqueous capecitabine in electrochemical oxidation process

Electrocatalytic oxidation and detoxication of capecitabine (CAP) in aqueous solution were investigated with Ti/SnO₂-Sb/Ce-PbO₂ anode. The relative contributions of generated free radicals showed an increase in the pseudo zero order tare constants in the following order: OH (9.4%) < SO₄^- (24.2%) < O₂^- (53.3%). The operating parameters and solution matrixes, i.e. applied current densities, initial CAP concentrations, initial Cl^- and NO₃^- concentrations, influencing the CAP degradation efficiency were evaluated. The kinetic rate constant of 0.1404 min^-1 was found within 7 min at current density of 10 mA cm^-2 and initial CAP concentration of 20 mg L^-1, while the mineralization efficiency of 59.5%, mineralization current efficiency of 2.06%, detoxication rate to Escherichia coli of 55.5% were achieved at reaction time 90 min. The major degradation pathways of CAP were oxidation, defluorination and bond cleavage, following with the formation of carboxylic acids, NO₃^-, NO₂^-, NH₄⁺ and F^-. Electrochemical oxidation process based on Ti/SnO₂-Sb/Ce-PbO₂ anode is proved to be effective for elimination, mineralization and detoxication of aqueous CAP.

A novel cobalt doped MOF-based photocatalyst with great applicability as an efficient mediator of peroxydisulfate activation for enhanced degradation of organic pollutants

A novel cobalt doped MOF-based photocatalyst was synthesized for the first time and employed as a mediator of peroxydisulfate activation for enhanced pollutant degradation.