New theoretical investigation of mechanism, kinetics, and toxicity in the degradation of dimetridazole and ornidazole by hydroxyl radicals in aqueous phase

Recent advances in degradation of N,N-diethyl-3-toluamide (DEET)-an emerging environmental contaminant: a review

N,N-Diethyl-3-toluamide (DEET) is a commonly used insect repellent, which acts as an organic chemical contaminant in water and considered as an emerging contaminant which has been observed worldwide. It gets discharged into the environment through sewage waste. The various methods have been used to degrade DEET, such as UV based, ozonation, photocatalytic degradation, and biodegradation (based on the metabolic activity of fungi and bacteria). However, less research has been done on the degradation of DEET by deploying nanoparticles. Therefore, biodegradation and nanotechnology-based methods can be the potential solution to remediate DEET from the environment. This review is an attempt to analyze the routes of entry of DEET into the atmosphere and its environmental health consequences and to explore physical, chemical, and biological methods of degradation. Furthermore, it focuses on the various methods used for the biodegradation of the DEET, including their environmental consequences. Future research is needed with the application of biological methods for the degradation of DEET. Metabolic pathway for biodegradation was explored for the new potent microbial strains by the application of physical, chemical, and microbial genomics; molecular biology; genetic engineering; and genome sequencing methods.

Theoretical insights into the HO●-induced oxidation of chlorpyrifos pesticide: Mechanism, kinetics, ecotoxicity, and cholinesterase inhibition of degradants

The oxidation of the common pesticide chlorpyrifos (CPF) initiated by HO● radical and the risks of its degradation products were studied in the gaseous and aqueous phases via computational approaches. Oxidation mechanisms were investigated, including H-, Cl-, CH3- abstraction, HO●-addition, and single electron transfer. In both phases, HO●-addition at the C of the pyridyl ring is the most energetically favorable and spontaneous reaction, followed by H-abstraction reactions at methylene groups (i.e., at H19/H21 in the gas phase and H22/H28 in water). In contrast, other abstractions and electron transfer reactions are unfavorable. However, regarding the kinetics, the significant contribution to the oxidation of CPF is made from H-abstraction channels, mostly at the hydrogens of the methylene groups. CPF can be decomposed in a short time (5-8 h) in the gas phase, and it is more persistent in natural water with a lifetime between 24 days and 66 years, depending on the temperature and HO● concentration. Subsequent oxidation of the essential radical products with other oxidizing reagents, i.e., HO●, NO2●, NO●, and 3O2, gave primary neutral products P1-P15. Acute and chronic toxicity calculations estimate very toxic levels for CPF and two degradation products, P7w and P12w, in aquatic systems. The neurotoxicity of these products was investigated by docking and molecular dynamics. P7w and P12w show the most significant binding scores with acetylcholinesterases, while P8w and P13w are with butyrylcholinesterase enzyme. Finally, molecular dynamics illustrate stable interactions between CPF degradants and cholinesterase enzyme over a 100 ns time frame and determine P7w as the riskiest degradant to the neural developmental system.

Kinetic constants and transformation products of ornidazole during ozonation

Ornidazole (ONZ), a nitroimidazole antibiotic detected in water bodies, may negatively impact the aquatic ecosystem. Its reaction kinetics during ozonation which is a feasible and applicable technology to control the contamination of emerging contaminants, however, has not been reported in literature. In this study, we measured the apparent second-order kinetic constant of ONZ with ozone molecules via the excessive ozone method and the competing method which led to an average value of 103.8 ± 2.7 M-1 s-1 at pH 7. The apparent second-order kinetic constant of ONZ with HO• was calculated to be 4.65 × 109 M-1 s-1 with the concept of Rct measured via para-chlorobenzoic acid as a probe. The transformation products (TPs) of ONZ during ozonation at pH 3 and pH 11 were separately analyzed with HPLC-MS/MS and some unique products were found at pH 11, reflecting the influence of HO•. The toxicity of individual TPs was predicted with the tool of T.E.S.T. It was found that 62% of 21 identified TPs could be more toxic than ONZ in terms of at least one acute toxicity endpoint, including chlorinated amines and N-oxides. The analysis with a respirometer further revealed that the toxicity of mixing TPs generated at HO• rich conditions was slightly lower than O3 dominated conditions. In general, this study provides the basic kinetic data for designing ozonation processes to eliminate ONZ and the important reference for understanding the toxicity evolution of ONZ during ozonation.

Amoxicillin degradation in the heat, light, or heterogeneous catalyst activated persulfate systems: Comparison of kinetics, mechanisms and toxicities

Various activated persulfate (PS) technologies have been investigated and implemented to eliminate antibiotic contaminants from water. The investigation and evaluation of different activation systems are essential for the application of PS techniques. The degradation of amoxicillin (AMX) by heat, light, or heterogeneous catalyst of Fe-AC composite activated PS was investigated, and the kinetics, mechanisms and toxicities were compared in this work. The apparent activation energy of the Fe-AC system was lower than that of the heat system. Hydroxyl and sulfate radicals were demonstrated by electron paramagnetic resonance (EPR) spectroscopy and quenching tests. There were 22, 21 and 13 types of degradation intermediates detected in heat, light and Fe-AC system, respectively. Six pathways of AMX degradation were proposed and compared in the three activated PS systems. The toxicity prediction of degradation intermediates under different treatment processes was estimated by ecological structure-activity relationship model and toxicity estimation software tool. The genotoxicity of the AMX degradation solution was tested by Acinetobacter baylyi ADP1_recA, which indicated that the AMX solution after treatment in the Fe-AC system had almost no genotoxicity. The Fe-AC/PS system shows apparent advantages over the heat or light activated PS system in most cases, demonstrating that the Fe-AC/PS system is suitable for AMX-contaminated remediation in aqueous solution.

New insight into environmental oxidation of phosmet insecticide initiated by HO˙ radicals in gas and water - a theoretical study

Phosmet is an organophosphorus insecticide widely used in agriculture to control a range of insects; recently, it was banned by the European Union in 2022 due to its harmful effects. However, its environmental degradation and fate have not yet been evident. Thus, phosmet oxidation by HO˙ radicals was theoretically studied in this work using the DFT approach at the M06-2X/6-311++G(3df,3pd)//M06-2X/6-31+G(d,p) level of theory. Three different mechanisms were considered, including formal hydrogen transfer (FHT), radical adduct formation (RAF), and single electron transfer (SET). The mechanisms, kinetics, and lifetime were studied in the gas and aqueous phases, in addition to its ecotoxicity evaluation. The results show that FHT reactions were dominant in the gas phase, while RAF was more favourable in the aqueous phase at 298 K, while SET was negligible. The branching ratio indicated that H-abstractions at the methyl and the methylene groups were the most predominant, while the most favourable HO˙-addition was observed at the phosphorus atom of the dithiophosphate group. The overall rate constant values varied from 1.2 × 109 (at 283 K) to 1.40 × 109 M-1 s-1 (at 323 K) in the aqueous phase and from 6.29 × 1010 (at 253 K) to 1.32 × 1010 M-1 s-1 (at 323 K) in the gas phase. The atmospheric lifetime of phosmet is about 6 hours at 287 K, while it can persist from a few seconds to several years depending on the temperature and [HO˙] concentration in the aqueous environment. The QSAR-based ecotoxicity evaluation indicates that phosmet and its degradation products are all dangerous to aquatic organisms, although the products are less toxic than phosmet. However, they are generally developmental toxicants and mutagenicity-negative compounds.

Low-temperature molten-salt synthesis of Co3O4 nanoparticles grown on MXene can rapidly remove ornidazole via peroxymonosulfate activation

We further developed previous work on MXene materials prepared using molten salt methodology. We substituted single, with mixed salts, and reduced the melting point from >724 °C to <360 °C. Cobalt (Co) compounds were simultaneously etched and doped while the MXene material was created using various techniques in which Co compounds occur as Co3O4. The synthesized Co3O4/MXene compound was used as a peroxymonosulfate (PMS) activator that would generate free radicals to degrade antibiotic ornidazole (ONZ). Under optimal conditions, almost 100% of ONZ (30 mg/L) was degraded within 10 min. The Co3O4/MXene + PMS system efficiently degraded ONZ in natural water bodies, and had a broad pH adaptation range (4-11), and strong anion anti-interference. We investigated how the four active substances were generated using radical quenching and electron paramagnetic resonance (EPR) spectroscopy. We identified 12 ONZ intermediates by liquid chromatography-mass spectrometry and propose a plausible degradative mechanism.

A Theoretical Study on the Degradation Mechanism, Kinetics, and Ecotoxicity of Metronidazole (MNZ) in •OH- and SO4•--Assisted Advanced Oxidation Processes

Metronidazole (MNZ), a typical example of nitroimidazole antibiotics, is widely used in the treatment of infectious diseases caused by anaerobic bacteria. The degradation mechanism and kinetics of MNZ in the presence of HO• and SO4•- were studied using density functional theory (DFT). It was confirmed that both HO• and SO4•- easily added to the carbon atom bonded to the NO2 group in the MNZ molecule as the most feasible reaction channel. This study shows that subsequent reactions of the most important product (M-P) include the O2 addition, hydrogen abstraction and bond breakage mechanisms. The rate constants of HO• and SO4•--initiated MNZ in the aqueous phase were calculated in the temperature range of 278-318 K. The total rate constants of MNZ with HO• and SO4•- were determined to be 8.52 × 109 and 1.69 × 109 M-1s-1 at 298 K, which were consistent with experimental values of (3.54 ± 0.42) × 109 and (2.74 ± 0.13) × 109 M-1s-1, respectively. The toxicity of MNZ and its degradation products to aquatic organisms has been predicted. The results proposed that the toxicity of the initial degradation product (M-P) was higher than that of MNZ. However, further degradation products of MNZ induced by HO• were not harmful to three aquatic organisms (fish, daphnia, and green algae). This study provides a comprehensive theoretical basis for understanding the degradation behavior of MNZ.

Theoretical insights into the degradation mechanisms, kinetics and eco-toxicity of oxcarbazepine initiated by OH radicals in aqueous environments

As an anticonvulsant, oxcarbazepine (OXC) has attracted considerable attention for its potential threat to aquatic organisms. Density functional theory has been used to study the mechanisms and kinetics of OXC degradation initiated by OH radicals in aqueous environment. A total of fourteen OH-addition pathways were investigated, and the addition to the C8 position of the right benzene ring was the most vulnerable pathway, resulting in the intermediate IM8. The H-abstraction reactions initiated by OH radicals were also explored, where the extraction site of the methylene group (C14) on the seven-member carbon heterocyclic ring was found to be the optimal path. The calculations show that the total rate constant of OXC with OH radicals is 9.47 × 10⁹ (mol/L)^-1sec^-1, and the half-life time is 7.32 s at 298 K with the [·OH] of 10^-11 mol/L. Moreover, the branch ratio values revealed that OH-addition (89.58%) shows more advantageous than H-abstraction (10.42%). To further understand the potential eco-toxicity of OXC and its transformation products to aquatic organisms, acute toxicity and chronic toxicity were evaluated using ECOSAR software. The toxicity assessment revealed that most degradation products such as OXC-2OH, OXC-4OH, OXC-1O-1OOH, and OXC-1OH' are innoxious to fish and daphnia. Conversely, green algae are more sensitive to these compounds. This study can provide an extensive investigation into the degradation of OXC by OH radicals and enrich the understanding of the aquatic oxidation processes of pharmaceuticals and personal care products (PPCPs).

Theoretical study on the degradation mechanism, kinetics and toxicity for aqueous ozonation reaction of furan derivatives

The compounds including Furan-2,5-dicarboxylic acid (FDCA), 2-methyl-3-furoic acid (MFA), and 2-furoic acid (FA), containing Furan rings are considered to be possessing high ozone reactivity, although in depth studies of their ozonation processes have not been carried out yet. Hence, mechanism, kinetics and toxicity by quantum chemical, and their structure activity relationship are being investigated in this study. Studies of reaction mechanisms revealed that during the ozonolysis of three furan derivatives containing C=C double bond, furan ring opening occurs. At temperature (298 K) and pressure of 1 atm the degradations rates of 2.22 × 10³ M^-1 s^-1 (FDCA), 5.81 × 10⁶ M^-1 s^-1 (MFA) and 1.22 × 10⁵ M^-1 s^-1 (FA) suggested that the reactivity order is: MFA > FA > FDCA. In the presence of water, oxygen and ozone, the primary product of ozonation, the Criegee intermediates (CIs) would produce lower molecule weight of aldehydes and carboxylic acids by undergoing degradation pathways. The aquatic toxicity reveals that three furan derivatives play green chemicals roles. Significantly, most of degradation products are least harmful to organisms residing the hydrosphere. The mutagenicity and developmental toxicity of FDCA is minimum as compared to FA and MFA, which shows the applicability of FDCA in a wider and broader field. Results of this study revealed its importance in the industrial sector and degradation experiments.