Transformation of triclosan by laccase catalyzed oxidation: The influence of humic acid-metal binding process

Trade-off effect of dissolved organic matter on degradation and transformation of micropollutants: A review in water decontamination

The degradation of micropollutants by various treatments is commonly affected by the ubiquitous dissolved organic matter (DOM) in the water environment. To optimize the operating conditions and decomposition efficiency, it is necessary to consider the impacts of DOM. DOM exhibits varied behaviors in diverse treatments, including permanganate oxidation, solar/ultraviolet photolysis, advanced oxidation processes, advanced reduction process, and enzyme biological treatments. Besides, the different sources (i.e., terrestrial and aquatic, etc) of DOM, and operational circumstances (i.e., concentration and pH) fluctuate different transformation efficiency of micropollutants in water. However, so far, systematic explanations and summaries of relevant research and mechanism are rare. This paper reviewed the "trade-off" performances and the corresponding mechanisms of DOM in the elimination of micropollutants, and summarized the similarities and differences for the dual roles of DOM in each of the aforementioned treatments. Inhibition mechanisms typically include radical scavenging, UV attenuation, competition effect, enzyme inactivation, reaction between DOM and micropollutants, and intermediates reduction. Facilitation mechanisms include the generation of reactive species, complexation/stabilization, cross-coupling with pollutants, and electron shuttle. Moreover, electron-drawing groups (i.e., quinones, ketones functional groups) and electron-supplying groups (i.e., phenols) in the DOM are the main contributors to its trade-off effect.

Triclosan and related compounds in the environment: Recent updates on sources, fates, distribution, analytical extraction, analysis, and removal techniques

Triclosan (TCS) has been widely used in daily life because of its broad-spectrum antibacterial activities. The residue of TCS and related compounds in the environment is one of the critical environmental safety problems, and the pandemic of COVID-19 aggravates the accumulation of TCS and related compounds in the environment. Therefore, detecting TCS and related compound residues in the environment is of great significance to human health and environmental safety. The distribution of TCS and related compounds are slightly different worldwide, and the removal methods also have advantages and disadvantages. This paper summarized the research progress on the source, distribution, degradation, analytical extraction, detection, and removal techniques of TCS and related compounds in different environmental samples. The commonly used analytical extraction methods for TCS and related compounds include solid-phase extraction, liquid-liquid extraction, solid-phase microextraction, liquid-phase microextraction, and so on. The determination methods include liquid chromatography coupled with different detectors, gas chromatography and related methods, sensors, electrochemical method, capillary electrophoresis. The removal techniques in various environmental samples mainly include biodegradation, advanced oxidation, and adsorption methods. Besides, both the pros and cons of different techniques have been compared and summarized, and the development and prospect of each technique have been given.

Suppression mechanism of model humic constituents on laccase-enabled 17β-estradiol oxidation and oligomerization

Humic constituents (HCs) are ubiquitous in the aquatic ecosystems, and contain various functional groups that seriously impact the conversion of 17β-estradiol (17β-E2) by fungal laccase. The purpose of this study was to explore the influencing mechanism of HCs on Trametes versicolor laccase-enabled 17β-E2 oxidation and oligomerization. Herein, T. versicolor-secreted laccase could rapidly convert 99.2% of 17β-E2 (rate constant = 3.7 × 10^-2 min^-1, half-life = 18.7 min) into multifarious oligomers at 25 °C and pH 5.0, by phenolic radical-caused C-C and/or C-O self-linking routes, whereas HCs with O-phenolic hydroxyl groups (O-p-OH, i.e., catechol, pyrogallol, gallic acid, and caffeic acid) dramatically suppressed 17β-E2 oligomerization. Compared with HC-free, 17β-E2 rate constants weakened 6.3-15.8 fold in the presence of HCs containing O-p-OH. It is largely because the O-p-OH was preferentially oxidized by T. versicolor laccase to create the electrophilic O-quinone monomers/oligomers. These unstable reactive O-quinone intermediates strongly reversed 17β-E2 phenolic radicals to their monomeric molecules via two proton-transfer versus two electron-transfer channels, thus intercepting 17β-E2 oxidation and oligomerization. These findings highlight new insights into the effect of HCs containing O-p-OH on T. versicolor laccase-started 17β-E2 conversion, which is beneficial to re-understanding the fate and geochemical behavior of 17β-E2 in water.

Influence of humic acids on fungal laccase-initiated 17α-ethynylestradiol oligomerization: Transformation kinetics and products distribution

Fungal laccase has aroused great concern in rapidly removing estrogens because of its ability to accelerate humification and oligomerization. Here, the effect of two humic acids (HAs) on the reaction kinetics and products distribution of 17α-ethynylestradiol (EE2) in laccase-initiated humification and coupling was systematically elucidated. Laccase from Trametes versicolor exhibited over 98.3% removal rate for EE2 at pH 5.0 within 120 min, while HAs invariably restrained EE2 transformation by competing with target-substrate for the enzymatic catalytic center. EE2 removal followed pseudo-first-order kinetics, and the rate constant was decreased markedly with increasing concentration of two HAs (0-60 mg L^-1). Additionally, laccase heightened the aromaticity and humification degrees (A_{250 nm}/A_{365 nm} ratio) of HAs probably due to the formation of new humic polymers such as (HA)_m and/or (HA)_m-(EE2)_n (m and n represent the number of HA and EE2 units, respectively). Three major EE2 oligomers were identified, in accordance with a mechanism involving the phenoxy radical-driven polymerization to yield a wide variety of self-coupling products. Notably, HAs diminished the extent of EE2 self-coupling but aggrandized the cross-coupling between EE2 and HAs, and the inhibition degree of EE2 self-coupling increased with the concentration of HAs. One major reason is EE2 could be covalently incorporated into humic molecules to produce (HA)_m-(EE2)_n cross-coupling products via radical-caused C-C, C-O-C, and/or C-O-C bonds, thereby reducing EE2 self-oligomerization. These findings highlight that HAs play a vital role in the fungal laccase-induced humification and oligomerization of EE2, which obviously alter the geochemical fate and transport of EE2 in natural aquatic ecosystems.

Persistence, ecological risks, and oxidoreductases-assisted biocatalytic removal of triclosan from the aquatic environment

Triclosan (TCS) has been immensely employed in health care products and consumer items, as an active agent with fungicidal and bactericidal potentialities, such as soaps, sanitizers, tubes of toothpaste, deodorants, skin creams, and so on for over last five decades. The ultimate excretory route of TCS ends in our water matrices, thus has been frequently detected with ecological and human-health related matters and hazards. Bioactive residues of TCS reach into the key atmosphere compartment through numerous routes, such as (1) scarce or ineffective elimination or degradation throughout the treatment practices, (2) abandoned landfill leachates, (3) leakage from the discarded TCS-containing materials, and so on. Such persistence and occurrence of TCS or its degraded but bioactive residues have growing attentions. Its complete removal and/or effective prevention are still challenging tasks for safeguarding the environment. Owing to the highly effective catalytic and stability potential, enzyme-based bio-degradation approaches are considered an evocative substitute for TCS mitigation from environmental matrices. As compared to enzymes in their pristine form, immobilized enzymes, with unique catalytic, stability, selectivity, and reusability profile, are of supreme and strategic interest in environmental biotechnology. Herein, an effort has been made to signify the novel bio-catalytic and bio-degradation potentialities of various oxidoreductases, including laccases, and peroxidases including soybean peroxidase, versatile manganese peroxidase, and horseradish peroxidase with suitable examples. Following a brief introduction, the focus is given to the presence of TCS in the key atmosphere compartments. Potential sources, acquaintance, and hazardous influence of TCS are also discussed with recent and relevant examples. The second half shows the TCS removal/degradation potentialities of soluble enzyme-based catalytic systems and immobilized-enzyme-based catalytic systems. Finally, the concluding remarks, along with possible future directions are given in this significant research arena.

Coupling of natural organic matter-metal binding and laccase-catalyzed oxidation of tetrabromobisphenol A

Laccases are a group of copper-containing oxidase enzymes found in aquatic and terrestrial environment. They can catalyze one-electron oxidation of phenolic compounds to radical intermediates using molecular oxygen as the electron accepter. The radical intermediates can subsequently couple to each other to form dimers. In this study, we investigated the kinetics of tetrabromobisphenol A (TBBPA) transformation in laccase-catalyzed oxidation process. It was revealed that the removal of TBBPA was first order to the concentrations of both substrate and laccase. Natural organic matter (NOM) inhibited the reaction by reversing the oxidation of TBBPA. Such inhibition effect was more significant in the presence of Ca²⁺, Mg²⁺, Cd²⁺, Mn²⁺, and Co²⁺, but not Na⁺ or K⁺. This was because of the formation of NOM-metal complexes. Binding to metal ions neutralizes the negative charge of NOM, making it easier to access laccase molecules and thus have a greater chance to react with the radical intermediates. A numerical model that couples the laccase-catalyzed oxidation and NOM-metal-binding processes was constructed. This model successfully described the transformation of TBBPA in the presence of NOM and divalent metal ions in laccase-catalyzed oxidation process. Product identification indicated radical coupling and elimination was the main pathway of TBBPA transformation. Overall, this work provides important sights into the laccase-catalyzed oxidation process.

Efficient removal of triclosan via peroxymonosulfate activated by a ppb level dosage of Co(II) in water: Reaction kinetics, mechanisms and detoxification

Triclosan (TCS), an extensively used broad-spectrum antimicrobial agent, has raised significant environmental concerns regarding its widespread occurrence in waters. In this study, the removal of TCS in aqueous solution via peroxymonosulfate (PMS) activated by an extremely low-level Co²⁺ (0.02 μM) was systematically investigated. During preliminary test, TCS (10 μM) was totally degraded in 30 min by using 0.1 μM Co²⁺ and 40 μM PMS at pH 7.0 with a degradation rate constant of 0.1219 min^-1. A first-order apparent degradation rate of TCS was found with respect to the PMS concentrations. At extremely low dosage of Co²⁺ (0.02 μM), the presence of NO₃^-, HCO₃^-, PLFA, and SRHA within test concentrations significantly inhibited TCS removal, while a dual effect of Cl^- on the degradation rate of TCS was observed. The quenching experiments verified that SO₄^- was the dominant reactive oxygen species (ROS) rather than OH. Six major intermediates were identified using TOF-LC-MS, based on which we proposed three associated reaction pathways including hydroxylation, ether bond breakage, and dechlorination. Toxicity predictions by ECOSAR software exhibited aquatic toxicity reduction of TCS after Co²⁺/PMS treatment. We outlook these findings to advance the feasibility of organic contaminants removal via Co²⁺/PMS system with Co²⁺ at extremely low levels.

Effective column adsorption of triclosan from pure water and wastewater treatment plant effluent by using magnetic porous reduced graphene oxide

The ubiquitous presence of triclosan (TCS) in aquatic systems is of great concern. In the present work, magnetic porous reduced graphene oxide (MPrGO) was synthesized via in situ chemical co-precipitation of Fe³⁺and porous graphene oxide and, was used as an adsorbent for the removal of TCS with μg/L level from both pure water and wastewater treatment plant (WWTP) effluent by conducting with continuous flow fixed column. The BET surface area of MPrGO (1070 m²/g) was about tenfold higher than that of commercial powder activated carbon (PAC). Fast adsorption equilibrium can be reached within 20 s, the maximum adsorption capacity of TCS on MPrGO reached 1105.8 mg/g, and the sorbent can be regenerated for reusability about 5 cycles. The breakthrough time was 50 days for the bed depth of 2.3 mm at the inlet TCS concentration of 100 μg/L. MPrGO exhibited a much higher affinity toward TCS than PAC as the breakthrough time for MPrGO was 6.5 times longer than that for PAC. The Thomas and Yoon-Nelson models provide a better fitting curve than that by the Adams-Bohart model. High TCS adsorption capacity of 935.3 mg/g was calculated from WWTP effluent.

Transformation of atenolol by a laccase-mediator system: Efficiencies, effect of water constituents, and transformation pathways

In this study, we investigated the transformation of atenolol (ATL) by the naturally occurring laccase from Trametes versicolor in aqueous solution. Removal efficiency of ATL via laccase-catalyzed reaction in the presence of various laccase mediators was examined, and found that only the mediator 2, 2, 6, 6-tetramethyl-1-piperidinyloxy (TEMPO) was able to greatly promote ATL transformation. The influences of TEMPO concentration, laccase dosage, as well as solution pH and temperature on ATL transformation efficiency were tested. As TEMPO concentrations was increased from 0 to 2000 μM, ATL transformation efficiency first increased and then decreased, and the optimal TEMPO concentration was determined as 500 μM. ATL transformation efficiency was gradually increased with increasing laccase dosage. ATL transformation was highly pH-dependent with an optimum pH of 7.0, and it was almost constant over a temperature range of 25-50 °C. Humic acid inhibited ATL transformation through competition reaction with laccase. The presence of anions HCO₃^- and CO₃^2- reduced ATL transformation due to both anions enhanced solution pHs, while Cl^-, SO₄^2-, and NO₃^- at 10 mM showed no obvious influence. The main transformation products were identified, and the potential transformation pathways were proposed. After enzymatic treatment, the toxicity of ATL and TEMPO mixtures was greatly reduced. The results of this study might present an alternative clean strategy for the remediation of ATL contaminated water matrix.

The influence of humic acids on the weathering of pyrite: Electrochemical mechanism and environmental implications

Pyrite weathering often occurs in nature and causes heavy metal ion pollution and acid mine drainage during the process. Humic acid (HA) is a critical natural organic material that can bind metal ions, thus affecting metal transfer and transformation. In this work, in situ electrochemical techniques combined with spectroscopic analysis were adopted to investigate the interfacial processes involved in pyrite weathering with/without HA. The results showed that the pyrite weathering mechanism with/without HA is FeS₂ → Fe²⁺ + 2S⁰ + 2e^-. The presence of HA did not change the pyrite weathering mechanism, but HA adsorbs on the pyrite surface and inhibits the further transformation of sulfur. Furthermore, HA and Fe(II) ions can form complex at 45.0 °C. Increased concentration of HA, decreased HA solution acidity or decreased environmental temperature would all weaken the pyrite weathering, for the above conditions cause pyrite weathering to have a larger resistance of the double layer and a larger passive film resistance. Pyrite will release 73.7 g m^-2·y^-1 Fe²⁺ to solution at pH 4.5, and the amount decreases to 36.8 g m^-2·y^-1 in the presence of 100 mg/L HA. This study provides an in situ electrochemical method for the assessment of pyrite weathering.

Cu2+-assisted laccase from Trametes versicolor enhanced self-polyreaction of triclosan

Laccase-mediated humification processes (L-MHPs) can be used to polymerize and transform phenolic pollutants in water. However, the mechanism on Cu²⁺ impacts the self-polymerization of multi-purpose antimicrobial agent triclosan during L-MHPs is less understood. Here, the influence of divalent metal ions (DMIs) on Trametes versicolor laccase activity was investigated. Particularly, the performance of Cu²⁺-assisted laccase in polymerizing and transforming triclosan was systematically characterized. Compared with DMI-free, the activity of laccase was obviously accelerated with Cu²⁺ present due to copper is a vital component of laccase catalytic center. It was found that Cu²⁺-assisted laccase was effective in transforming triclosan, and the enzymatic reaction kinetic constants increased from 0.28 to 0.73 h^-1 as the Cu²⁺ concentration increased (0-3.0 mM). Identification of intermediate products revealed that laccase oxidation predominantly generated triclosan dimers, trimers, and tetramers. The presence of Cu²⁺ reinforced self-polymerization of triclosan via forming more triclosan oligomers relative to the Cu²⁺-free, which likely attributed to the enhancement of laccase activity and stability with Cu²⁺ present in L-MHPs. A possible transformation mechanism was proposed as follows: Laccase initially catalyzed the oxidation of triclosan to generate phenoxy radical intermediates, which self-coupled to each other subsequently by radical-mediated CC and COC covalent binding, forming oligomers and polymers. The growth inhibitory assays of freshwater microalgae (Chlamydomonas reinhardtii and Scenedesmus obliquus) demonstrated that the self-polymerized triclosan by L-MHPs had lower toxicity than the parent compound. These findings implied that Cu²⁺-assisted laccase was an effective strategy for rapidly self-polyreaction and detoxication of triclosan from Cu²⁺-triclosan combined polluted wastewater.

Fluorescence Optosensing of Triclosan by Upconversion Nanoparticles with Potassium Permanganate

It is greatly significant to develop a simple and rapid sensing method for triclosan (TCS) because it is a widely used and a chronically toxic compound that adversely affects biological organisms and human health. This paper presents the design and development of a novel simple optosensor that uses carboxylic group-functionalized NaYF₄:Yb³⁺/Er³⁺ upconversion nanoparticles (UCNPs) coated with potassium permanganate (KMnO₄). The sensor enables the rapid, non-autofluorescence, sensitive, and selective detection of TCS based on the "turn off-on fluorescence" technique through fluorescence resonance energy transfer. Under an near-infrared radiation excitation (980 nm), the "turn-off fluorescence" process involves the transfer of fluorescence resonance energy between the UCNPs and KMnO₄, whereas the "turn-on fluorescence" process occurs when KMnO₄ is reduced in the presence of TCS. TCS was detected by recovering the green emission of UCNPs. Under optimized conditions, the resulting sensor offered an excellent response to TCS with 0.2 μM of a limit of detection. The developed sensor showed higher selectivity to TCS than other phenolic compounds. Moreover, the analytical performance of the proposed probe was practically demonstrated to successfully monitor trace levels of TCS in samples of tap water and personal care products. The developed simple and sensitive method may offer a new approach for determining TCS in environmental applications.

Structural characteristics of humic acids derived from Chinese weathered coal under different oxidizing conditions

Humic acids derived from Chinese weathered coal were oxidized with hydrogen peroxide (H2O2) under various conditions, and their chemical composition and structure were examined. The raw material humic acids (HA) and oxidized humic acids (OHAs) were characterized by elemental analysis and ultraviolet visible (UV-Vis), Fourier transform infrared (FTIR), and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Our results show that aromatic functional groups accounted for more than 70% of the HA and OHAs and there were significant differences in their structures and compositions. Compared to the HA, the average H and N contents of the OHAs decreased by 5.15% and 2.52%, respectively, and the average O content of those of the OHAs increased by 5.30%. The hydrophobicity index (HI) of HA is higher than those of the OHAs. Importantly, in the hypothesis test between the properties and preparation conditions of humic acid using SPSS, the partial η2 of the temperature, hydrogen peroxide concentration, liquid-solid ratio, and time were 0.809, 0.771, 0.748 and 0.729, respectively; thus, among the preparation conditions, temperature is the most important factor affecting the humic acids properties.

Perfluorooctanesulfonate Degrades in a Laccase-Mediator System

Perfluorooctanesulfonate (PFOS) is a compound that has wide applications with extreme persistence in the environment and the potential to bioaccumulate, and could induce adverse effects to ecosystems. We investigated the degradation of PFOS by laccase-induced enzyme catalyzed oxidative humification reactions (ECOHRs) using 1-hydroxybenzotriazole (HBT) as a mediator. Approximately 59% of PFOS was transformed over 162 days of incubation, and the reaction appeared to follow a pseudo-first-order model with reaction rate constant of 0.0066/ d ( r² = 0.87) under one condition tested. Using differential absorption spectra and theoretical simulation, we elucidated the interaction between Cu²⁺/Mg²⁺ and PFOS, and proposed that Cu²⁺ and Mg²⁺ could serve as a bridge to bring the negatively charged PFOS and laccase to proximity, thus increasing the chance of radicals that are released from laccase to reach and react with PFOS. In addition, density functional theory modeling showed that PFOS complexation to the metal ions could unlock its helical configuration and decrease the C-C bond energy of PFOS. These changes allow the attack of PFOS C-C backbone by radicals to become easier. On the basis of products identification, we proposed that direct attack of PFOS by the HBT radical initiated the free radical chain reaction processes and led to the formation of fluoride and partially fluorinated compounds. These results suggest that ECOHR is a potential pathway by which PFOS could be degraded in the environment, and it may make a viable approach to remediate PFOS contamination via amendment of appropriate enzymes and mediators.

Effects of inorganic ions and natural organic matter on the aggregation of nanoplastics

The aggregation of nanoplastics (NPs) is a key issue in understanding the dynamic nature of NPs in the environment. The aggregation of NPs under various environmental conditions has not yet been studied. We investigated the influences of inorganic ions and natural organic matter (NOM) on polystyrene (PS) NPs aggregation in solutions. Results showed that PS NPs remained stable in wide ionic strength solutions of NaCl (1-100 mM) and CaCl₂ (0.1-15 mM), and only in low ionic strength FeCl₃ solutions (0.01 mM). However, obvious PS NPs aggregation was observed in FeCl₃ solutions with an increase in ionic strength (0.1 and 1 mM). Moreover, NOM had a negligible effect on PS NPs aggregation in all ionic strengths of NaCl and CaCl₂ solutions and in low ionic strength FeCl₃ solutions (0.01 mM). However, NOM reduced PS NPs aggregation in an intermediate ionic strength FeCl₃ (0.1 mM) solution and increased aggregation in a high ionic strength FeCl₃ (1 mM) solution. Based on the theoretical analysis of interaction forces among PS NPs, the Derjaguin-Landau-Verwey-Overbeek force was a contributor governing PS NPs aggregation either in the absence or presence of NOM. In addition, other factors, including electrostatic heterogeneity of PS NPs surfaces, steric repulsion induced by NOM, and clusters formed via bridging effect in the presence of NOM also contributed to altered PS NPs aggregation under selected conditions. The PS NPs-NOM clusters were directly observed using a cryogenic scanning electron microscope.

Chlorination of bisphenol S: Kinetics, products, and effect of humic acid

Bisphenol S (BPS), as a main alternative of bisphenol A for the production of industrial and consumer products, is now frequently detected in aquatic environments. In this work, it was found that free chlorine could effectively degrade BPS over a wide pH range from 5 to 10 with apparent second-order rate constants of 7.6-435.3 M^-1s^-1. A total of eleven products including chlorinated BPS (i.e., mono/di/tri/tetrachloro-BPS), 4-hydroxybenzenesulfonic acid (BSA), chlorinated BSA (mono/dichloro-BSA), 4-chlorophenol (4CP), and two polymeric products were detected by high performance liquid chromatography and electrospray ionization-tandem quadrupole time-of-flight mass spectrometry. Two parallel transformation pathways were tentatively proposed: (i) BPS was attacked by stepwise chlorine electrophilic substitution with the formation of chlorinated BPS. (ii) BPS was oxidized by chlorine via electron transfer leading to the formation of BSA, 4CP and polymeric products. Humic acid (HA) significantly suppressed the degradation rates of BPS even taking chlorine consumption into account, while negligibly affected the products species. The inhibitory effect of HA was reasonably explained by a two-channel kinetic model. It was proposed that HA negligibly influenced pathway i while appreciably inhibited the degradation of BPS through pathway ii, where HA reversed BPS phenoxyl radical (formed via pathway ii) back to parent BPS.

Inactivation of Laccase by the Attack of As (III) Reaction in Water

Laccase is a multicopper oxidase containing four coppers as reaction sites, including one type 1, one type 2, and two type 3. We here provide the first experimental data showing that As (III) can be effectively removed from water and transformed to As (V) through reactions mediated by laccase with the presence of oxygen. To this end, the As (III) removal, As (V) yields, total protein, active laccase, and copper concentrations in the aqueous phase were determined, respectively. Additionally, electron paramagnetic resonance spectra and UV-vis spectra were applied to probe possible structural changes of the laccase during the reaction. The data offer the first evidence that laccase can be inactivated by As (III) attack thus leading to the release of type 2 copper. The released copper has no reactivity with the As (III). These findings provide new ideas into a significant pathway likely to master the environmental transformation of arsenite, and advance the understanding of laccase inactivation mechanisms, thus providing a foundation for optimization of enzyme-based processes and potential development for removal and remediation of arsenite contamination in the environment.

The transformation of triclosan by laccase: Effect of humic acid on the reaction kinetics, products and pathway

This study systematically explored the effect of humic acid (HA) (as model of natural organic matter) on the kinetics, products and transformation pathway of triclosan (TCS) by laccase-catalyzed oxidation. It was found that TCS could be effectively transformed by laccase-catalysis, with the apparent second-order rate constant being 0.056 U^-1 mL min^-1. HA inhibited the removal rate of TCS. HA-induced inhibition was negatively correlated with HA concentration in the range of 0-10 mg L^-1 and pH-dependent from 3.5 to 9.5. FT-IR and ¹³C NMR spectra showed a decrease of aromatic hydroxyl (phenolic) groups and an increase of aromatic ether groups, indicating the cross-linking of HA via C-O-C and C-N-C bonds during enzyme-catalyzed oxidation. Ten principle oxidative products, including two quinone-like products (2-chlorohydroquinone, 2-chloro-5-(2,4-dichlodichlorophenoxy)-(1,4)benzoquinone), one chlorinated phenol (2,4-dichlorophenol (2,4-DCP)), three dimers, two trimmers and two tetramers, were detected by gas chromatograghy/mass spectrometry (GC-MS) and high performance liquid chromatography/quadrupole time-of-flight/mass spectrometry (HPLC/Q-TOF/MS). The presence of HA induced significantly lesser generation of self-polymers and enhanced cross-coupling between HA and self-polymers via C-O-C, C-N-C and C-C coupling pathways. A plausible transformation pathway was proposed as follows: TCS was initially oxidized to form reactive phenoxyl radicals, which self-coupled to each other subsequently by C-C and C-O pathway, yielding self-polymers. In addition, the scission of ether bond was also observed. The presence of HA can promote scission of ether bond and further oxidation of phenoxyl radicals, forming hydroxylated or quinone-like TCS. This study shed light on the behavior of TCS in natural environment and engineered processes, as well provided a perspective for the water/wastewater treatment using enzyme-catalyzed oxidation techniques.

Long-Term Uptake of Phenol-Water Vapor Follows Similar Sigmoid Kinetics on Prehydrated Organic Matter- and Clay-Rich Soil Sorbents

Typical experimental time frames allowed for equilibrating water-organic vapors with soil sorbents might lead to overlooking slow chemical reactions finally controlling a thermodynamically stable state. In this work, long-term gravimetric examination of kinetics covering about 4000 h was performed for phenol-water vapor interacting with four materials pre-equilibrated at three levels of air relative humidity (RHs 52, 73, and 92%). The four contrasting sorbents included an organic matter (OM)-rich peat soil, an OM-poor clay soil, a hydrophilic Aldrich humic acid salt, and water-insoluble leonardite. Monitoring phenol-water vapor interactions with the prehydrated sorbents, as compared with the sorbent samples in phenol-free atmosphere at the same RH, showed, for the first time, a sigmoid kinetics of phenol-induced mass uptake typical for second-order autocatalytic reactions. The apparent rate constants were similar for all the sorbents, RHs and phenol activities studied. A significant part of sorbed phenol resisted extraction, which was attributed to its abiotic oxidative coupling. Phenol uptake by peat and clay soils was also associated with a significant enhancement of water retention. The delayed development of the sigmoidal kinetics in phenol-water uptake demonstrates that long-run abiotic interactions of water-organic vapor with soil may be overlooked, based on short-term examination.