Thermoactivated persulfate oxidation of pesticide chlorpyrifos in aquatic system: kinetic and mechanistic investigations

A down-regulated cytochrome P450 in Neoseiulus barkeri Hughes (Acari: Phytoseiidae) can dechlorinate and hydroxylate chlorpyrifos without producing chlorpyrifos-oxon

Selection of chemical-resistant predatory mites is a good alternative to balance the contradiction between chemical control and biological control. Previously, a resistant strain of Neoseiulus barkeri for chlorpyrifos was obtained. In the current study, two up-regulated (NbCYP3A6, NbCYP3A16) and one down-regulated (NbCYP3A24) P450s were screened through differential expression analysis and other detoxification-related genes such as CCEs, GST, etc. were not found. 3D modelling and molecular docking indicated that the chlorine at position 5 on the pyridine ring of chlorpyrifos, as well as a methyl group, were closest to the heme iron of the enzymes (less than 5 Å). Three active recombinant P450 proteins were heterologously expressed and metabolized with chlorpyrifos in vitro. HPLC assay showed that only NbCYP3A24 could metabolize chlorpyrifos, with a metabolism rate of 21.60 %. Analysis of the m/z of metabolites by LC-MS/MS showed that chlorine at the 5C position of chlorpyrifos was stripped and hydroxylated, whereas chlorpyrifos-oxon, a common product of oxidation by P450, was not found. Knockdown of the NbCYP3A24 gene in the susceptiblestrain did reduce the susceptibility of N. barkeri to chlorpyrifos, suggesting that the biological activity of the metabolite may be similar to chlorpyrifos-oxon, thus enhancing the inhibitory effect on the target.

Biodegradation mechanism of chlorpyrifos by Bacillus sp. H27: Degradation enzymes, products, pathways and whole genome sequencing analysis

Chlorpyrifos (CP) is a pesticide widely used in agricultural production. However, excessive use of CP is risky for human health and the ecological environment. Microbial remediation has become a research hotspot of environmental pollution control. In this study, the effective CP-degrading strain H27 (Bacillus cereus) was screened from farmland soil, and the degradation ratio was more than 80%. Then, the degradation mechanism was discussed in terms of enzymes, pathways, products and genes, and the mechanism was improved in terms of cell motility, secretory transport system and biofilm formation. The key CP-degrading enzymes were mainly intracellular enzymes (IE), and the degradation ratio reached 49.6% within 30 min. The optimal pH for IE was 7.0, and the optimal temperature was 25 °C. Using DFT and HPLC‒MS analysis, it was found that degradation mainly involved oxidation, hydrolysis and other reactions, and 3 degradation pathways and 14 products were identified, among which TCP (3,5,6-trichloro-2-pyridinol) was the main primary degradation product in addition to small molecules such as CO2 and H2O. Finally, the whole genome of strain H27 was sequenced, and the related degrading genes and enzymes were investigated to improve the metabolic pathways. Strain H27 had perfect genes related to flagellar assembly and chemotaxis and tended to tolerate CP. Moreover, it can secrete esterase, phosphatase and other substances, which can form biofilms and degrade CP in the environment. In addition, CP enters the cell under the action of permeases or transporters, and it is metabolized by IE. The degradation mechanism of CP by strain H27 is speculated in this study, which provided a theoretical basis for enriching CP-degrading bacteria resources, improving degradation metabolic pathways and mechanisms, and applying strain H27 to environmental pollution remediation.

Structure identification and toxicity evaluation of one newly-discovered dechlorinated photoproducts of chlorpyrifos

Chlorpyrifos (CPF) is an extensively used organophosphorus pesticide. Recently, it has attracted increasing attention due to environmental health problems caused by it. Although numerous studies have discovered the dechlorinated photoproduct of CPF, its structure and toxicity remain largely unknown. In this study, we systematically investigated the structure and toxicity of dechlorinated photoproduct of CPF. The CPF degradation experiment was performed, and its products were identified by ultra high performance liquid chromatography-orbitrap fusion tribid mass spectrometer (UHPLC-Orbitrap Fusion TMS). Additionally, bond dissociation energy (BDE) calculations and photoproduct chemical synthesis were employed to determine the structure of dechlorinated photoproduct of CPF. The toxicity of CPF photoproduct was evaluated through the Ecological Structure Activity Relationships (ECOSAR) Class Program, the Toxicity Estimation Software Tool (T.E.S.T.) software, and acute toxicity testing. The results indicated that the dechlorinated photoproduct of CPF was identified as O,O-Diethyl-O-(3,5-dichloro-2-pyridyl) phosphorothioate (Dechloro-CPF), which was produced in large quantity within the first 30 min of photodegradation experiment. The acute and chronic toxicity values of Dechloro-CPF were obviously higher than those for the other two photoproducts. The median lethal dose (LD₅₀) of Dechloro-CPF was 31.6 mg/kg for female mice and 58.4 mg/kg for male mice. This study reveals the photodegradation mechanism of CPF and confirms that Dechloro-CPF was dechlorinated photoproduct of CPF with potential acute toxicity to aquatic species and mammalian (including human). Our findings will contribute to a more comprehensive risk evaluation of CPF in food and the environment.

Kinetic and mechanistic insights into the degradation of clofibric acid in saline wastewater by Co2+/PMS process: a modeling and theoretical study

Recently, the degradation of non-chlorinated organic pollutants in saline pharmaceutical wastewater by SO₄˙⁻-based advanced oxidation processes (AOPs) has received widespread attention. However, little is known about the oxidation of chlorinated compounds in SO₄˙⁻-based AOPs. This study chose clofibric acid (CA) as a chlorinated pollutant model; the oxidation kinetics and mechanistic pathway were explored in the Co²⁺/peroxymonosulfate (PMS) system. Notably, a high removal efficiency (81.0%) but low mineralization rate (9.15%) of CA within 120 min were observed at pH 3.0 during Co²⁺/PMS treatment. Exogenic Cl⁻ had a dual effect (inhibitory then promoting) on CA degradation. Several undesirable chlorinated by-products were formed in the Co²⁺/PMS system. This demonstrated endogenic chlorine and exogenic Cl⁻ both reacted with SO₄˙⁻ to generate chlorine radicals, which participated in the dechlorination and rechlorination of CA and its by-products. Furthermore, SO₄˙⁻ was the dominant species responsible for CA degradation at low Cl⁻ concentrations (≤1 mM), whereas Cl₂˙⁻ was the predominant radical at [Cl⁻]₀ > 1 mM. A possible degradation pathway of CA was proposed. Our findings suggested that chlorinated compounds in highly saline pharmaceutical wastewater will be more resistant and deserve more attention.

Recently, the degradation of non-chlorinated organic pollutants in saline pharmaceutical wastewater by SO₄˙⁻-based advanced oxidation processes (AOPs) has received widespread attention.

Cu(II) assisted peroxymonosulfate oxidation of sulfonamide antibiotics: The involvement of Cu(III)

Cu(II) is generally considered to be a poor activator for PMS decomposition, thus the potential impact of trace Cu(II) on PMS induced oxidation of typical pollutants is always overlooked. In this study, we reported that trace Cu(II) could significantly promote PMS induced degradation of four selected sulfonamide antibiotics (SAs), namely, sulfamehoxazole (SMX), sulfathiazole (STZ), sulfamerazine (SMZ), and sulfamonomethoxine (SMM). Different from conventional PMS-induced oxidation process, high-valent Cu(III) was ascertained as the primary reactive intermediate for SAs degradation, which was confirmed by raman tests and electron paramagnetic resonance (EPR). High concentrations of Cu(II) or PMS were beneficial to degradation of the selected contaminants. In PMS/Cu(II) oxidation system, all the selected SAs could undergo several different degradation pathways including continuous oxidation of aniline group, hydroxylation and S-N bond cleavage. In particular, for six-membered SAs, such as SMZ and SMM, a SO₂ extrusion pathway was also detected. The potential mechanism for Cu(III) formation was also proposed, which was believed to be highly related to the nature of the SAs. Hydroxylamine-SAs (N⁴-OH-SAs), generated from direct PMS oxidation of SAs, was deduced as the "promoter" for the whole oxidation process. And the generation of Cu(III) was likely to proceed through the interaction between PMS and Cu(I), which possibly derived from the reduction of Cu(II) by N⁴-OH-SAs. The results obtained in this study validated the contribution of Cu(III) to the elimination of pollutants and expanded our understanding of the oxidation process of PMS in the presence of trace amounts of Cu(II).

Advanced oxidation processes for chlorpyrifos removal from aqueous solution: a systematic review

Chlorpyrifos (CPF), an organophosphate insecticide, due to its high efficiency and low cost is widely used in the agricultural industry. CPF may lead to lung deficiency, central nervous system damage, developmental and autoimmune disorders. In recent decades, the advanced oxidation processes (AOPs) have been considered in water and wastewater treatment due to their high efficiency in decomposition of organic and inorganic compounds, specially hardly biodegradable or non-biodegradable compounds. In the present review study, the most common AOPs (such as Fenton and Photo-Fenton processes, UV/H2O2 photolysis, UV/TiO2 heterogeneous photo catalysis, electrochemical processes, sonolysis technology, gamma irradiation technology and sulfate-based AOPs) applied for CPF removal from aqueous matrices has been investigated. It can be concluded that the use of AOPs are effective for CPF removal from aqueous media. In addition, Fenton and photocatalytic processes appear to be the most common techniques for CPF degradation.

Organophosphorus pesticides in greenhouse and open-field soils across China: Distribution characteristic, polluted pathway and health risk

A national-scale survey was conducted to investigate the distribution characteristic, polluted pathway and health risk of organophosphorus pesticides (OPPs) in greenhouse and open-field soils in 20 regions across China. The total concentrations of eight OPPs ranged from 22.1 to 435 ng/g with a mean of 96.2 ng/g in greenhouses, and from 9.93 to 303 ng/g with a mean of 66.6 ng/g in open fields. Due to the intensive agricultural activities, the high residue of OPPs in greenhouse and open-field soils was found in the northeastern, northern and central areas. Furthermore, the effect of environmental factors (i.e. human activities, soil properties, heavy metals and microorganism) on OPPs were evaluated through the partial least squares path modeling. Apart from microorganisms, all the other factors affected the soil contamination of OPPs directly (p < 0.05), where the soil properties occupied the most important position (p < 0.01). In greenhouses, the highest correlation was observed in the relationship between human activities and soil properties, indicating that their combination was more likely to cause the contamination of OPPs in greenhouses indirectly. Moreover, the soil properties had the significant effect on the heavy metals in open fields (p < 0.05), suggesting that the residual OPPs in open fields was sensitive to interaction of these two factors. Although the hazard indexes in all soil samples were less than 1.0, the children were more susceptible to the non-cancer risks of OPPs in greenhouse. This study provided valuable information to understand the pollution status of OPPs in farmlands and protect the agroecological environment.

Sulfate radical-based oxidation of the aminopyralid and picloram herbicides: The role of amino group on pyridine ring

The widespread utilization of pesticides has attracted increasing attention to their environmental impacts and effective removal strategies. In the present study, the degradation of herbicides picloram (PCLO) and aminopyralid (AMP) with similar structures were investigated systematically by thermo activated persulfate. Overweight SO₄^•- was determined to be the predominant oxidizing species by quenching experiment. Obtained by laser-flash photolysis (LFP), reaction rate constants of SO₄^•- towards AMP and PCLO were determined at 1.56 × 10⁹ M^-1s^-1 and 1.21 × 10⁹ M^-1s^-1, respectively. Product analysis revealed that both substances underwent similar oxidation paths, namely, successive oxidation on pyridine ring and formation of coupling-products as well as further hydroxylation and decarboxylation. Amino group on the pyridine ring was identified as the main reactive site, which was further confirmed by DFT calculation. It was susceptible attacked by SO₄^•- to form deamination, nitration, and self-coupling products. These couples could be further oxidatively dehydrated to form azo and a series of azo derivatives. EOCSAR program predicted significant hazards on aquatic species during the formation of these couplings and azo derivatives. Our work emphasized the potential ability and toxicity of contaminates to produce azo substances in the presence of amino groups on the pyridine ring.

Molecular investigation into the transformation of dissolved organic matter in mature landfill leachate during treatment in a combined membrane bioreactor-reverse osmosis process

This study investigated the effectiveness of a combined membrane bioreactor (MBR) and reverse osmosis (RO) process for treating leachate produced by a large-scale anaerobic landfill. The MBR process had limited treatment efficiency for removing organic pollutants, but when combined with RO, the integrated system completely removed macromolecular compounds (i.e., humic- and fulvic-like substances) and produced effluent that satisfied the applicable discharge standard. The landfill leachate contained many types of DOM that had high molecular weight and were highly unsaturated. Although the MBR process removed some DOM that had a relatively low saturated degree (mainly aliphatic compounds (2.0 ≥ H/C ≥ 1.5) with relatively high bioavailability), many bio-refractory compounds were not removed. The RO system greatly reduced the content of residual DOM in MBR effluent and was effective for removing heteroatom DOM, especially polycyclic aromatics (AI > 0.66) and polyphenols (0.66 ≥ AI > 0.50). The effluent from the combined process of MBR and RO treatment mainly contained a small number of aliphatic compounds and phenolic compounds (AI ≤ 0.50 and H/C < 1.5) that had higher bioavailability than DOM in the raw leachate and posed little environmental risk.

A novel hollow-sphere cyclodextrin nanoreactor for the enhanced removal of bisphenol A under visible irradiation

A novel hybrid nanoreactor with spatially separated co-catalysts (SH-CD-Au@CdS@MnO_x) was successfully synthesised to remove bisphenol-A (BPA) from water by visible light. The photooxidation intermediates, degradation pathway of BPA and the enhancement mechanism were investigated in particular. Gold (Au) nanoparticles modified with SH-β-cyclodextrin and MnO_x nanoparticles were selectively decorated on the interior and exterior surface of hollow CdS nanoreactors, respectively. The directed migration of photogenerated electrons and holes induced by spatially separated co-catalysts lead to high utilization of light, and SH-β-cyclodextrin modification makes catalytic active sites more accessible for oxidation intermediates. Compared with pristine CdS, the hybrid nanoreactor increased the BPA photooxidation reaction rate and the TOC removal efficiency by 5.6-fold and 3.6-fold, respectively. Moreover, the toxic intermediates, such as phenol, were further degraded by visible light. Molecular orbital calculation predicted that the sites on BPA molecule values of (FED²_HOMO + FED²_LUMO) can be easier attacked by the radical, whereas atoms with higher values of 2FED²_HOMO can easily be extracted into electrons. Thus, SH-CD-Au@CdS@MnO_x can provide a new strategy for the high-efficiency photodegradation of endocrine disrupter compounds in advanced water treatments.

Photolysis-Induced Neurotoxicity Enhancement of Chlorpyrifos in Aquatic System: A Case Investigation on Caenorhabditis elegans

Contamination of the environment by toxic pesticides has become of great concern in agricultural countries. Chlorpyrifos (CP) is among the pesticides most commonly detected in the environment owing to its wide agricultural applications. The aim of this study was to compare potential changes in the toxicity of CP after irradiation. To this end, photolysis of CP was conducted under simulated sunlight, and neurotoxicity assessment was carried out at CP of 20 and 50 μg L^-1 and its corresponding irradiated mixture solutions which contain a mixture of identified intermediates using the nematode, Caenorhabditis elegans as a model organism. Photodegradation of 20 μg L^-1 CP for 1 h produced no obvious reduction of physiological damage, and more serious effects on animal movement were detected after exposure of the animals to a solution of 50 μg L^-1 for 1 h irradiation compared with unirradiated solution. GABAergic and cholinergic neurons were selectively vulnerable to CP exposure, and maximal neuropathological alterations were observed after 1 h irradiation of the CP solutions in coherence with the behavioral impairment. The generation of photoproducts was considered to be responsible for the enhanced disturbance on those biological processes. This work provided useful information on the toxicological assessments of chemicals that were produced during the environmental transformation of pesticides.

Sulfate radical-based oxidation of the antibiotics sulfamethoxazole, sulfisoxazole, sulfathiazole, and sulfamethizole: The role of five-membered heterocyclic rings

The widespread occurrence of sulfonamides (SAs) in natural waters, wastewater, soil and sediment has raised increasing concerns about their potential risks to human health and ecological systems. Sulfate radical (SO₄^-)-based advanced oxidation processes (SR-AOPs) have become promising technologies to remove such contaminants in the environment. The present study systematically investigated the degradation of four selected SAs with different five-membered heterocyclic rings, namely, sulfamethoxazole (SMX), sulfisoxazole (SIX), sulfathiazole (STZ), and sulfamethizole (SMT), by thermo-activated persulfate (PS) process, and the role of heterocyclic rings was assessed particularly. The results revealed that all the selected SAs could be degraded efficiently by thermo-activated PS process and their decay rates were appreciably increased with increasing temperature. For instance, degradation rates of STZ increased from 0.3 × 10^-3 to 19.5 × 10^-3 min^-1 as the temperature was increased from 30 to 60 °C. Under the same experimental conditions, the degradation rates of SAs followed the order of SIX > SMX ≈ STZ > SMT, which was in accordance with decay rates of their R-NH₂ moieties. Kinetic results indicated that five-membered heterocyclic rings could serve as reactive moieties toward SO₄^- attack, which were confirmed by frontier electron density (FED) calculations. Based on the transformation products identified by high-resolution mass spectrometry (HR-MS), five different oxidation pathways, including hydroxylation, aniline moiety oxidation, dimerization, sulfonamide bond cleavage, and heterocyclic ring oxidation/cleavage were proposed. Moreover, the degradation efficiency in real surface water (RSW) was found to be slightly slower than that in artificial surface water (ASW), suggesting that SR-AOPs could be an efficient approach for remediation of soil and water contaminated by these SAs.

Oxidative degradation of chlorpyrifos using ferrate(VI): Kinetics and reaction mechanism

In this study, we investigated the degradation kinetics of chlorpyrifos, an organophosphorus (OP) compound, using ferrate(VI), and investigated the potential of this iron-based chemical oxidant on chlorpyrifos removal from water and wastewater treatments. A series of kinetic experiments were conducted to evaluate the influence of various environmental factors, such as pH, oxidant dosages, as well as the presence of anions, cations, humic acid (HA), and different water matrices. Chlorpyrifos was completely removed within 300 s under the following optimum conditions: [chlorpyrifos]₀ = 1 μM, [Fe(VI)]₀:[chlorpyrifos]₀ = 100:1, T = 25 °C, and pH = 7.0. Anions such as Cl^-, SO₄^2-, NO₃^-, and HCO₃^- and cations such as Fe³⁺, Cu²⁺, and NH₄⁺ did not appear to influence the removal of chlorpyrifos. However, the presence of Ca²⁺, Mg²⁺, and HA in water inhibited the degradation of chlorpyrifos. Experiments on removing chlorpyrifos from tap water, river water, and synthetic wastewater were performed to demonstrate the practical applications of Fe(VI). Ten oxidation products of chlorpyrifos were identified using liquid chromatography-quadrupole-time-of flight-mass spectrometry (LC-Q-TOF-MS), and their structures were further elucidated using MS/MS spectra. Then, two degradation pathways were preliminarily proposed including the oxidation of the P = S bond, cleavage of C-O bond, and hydroxyl substitution reaction. In general, Fe(VI) could be used as an efficient technology for chlorpyrifos removal from water and wastewater treatments.

Degradation of propyl paraben by activated persulfate using iron-containing magnetic carbon xerogels: investigation of water matrix and process synergy effects

An advanced oxidation process comprising an iron-containing magnetic carbon xerogel (CX/Fe) and persulfate was tested for the degradation of propyl paraben (PP), a contaminant of emerging concern, in various water matrices. Moreover, the effect of 20 kHz ultrasound or light irradiation on process performance was evaluated. The pseudo-first order degradation rate of PP was found to increase with increasing SPS concentration (25-500 mg/L) and decreasing PP concentration (1690-420 μg/L) and solution pH (9-3). Furthermore, the effect of water matrix on kinetics was detrimental depending on the complexity (i.e., wastewater, river water, bottled water) and the concentration of matrix constituents (i.e., humic acid, chloride, bicarbonate). The simultaneous use of CX/Fe and ultrasound as persulfate activators resulted in a synergistic effect, with the level of synergy (between 35 and 50%) depending on the water matrix. Conversely, coupling CX/Fe with simulated solar or UVA irradiation resulted in a cumulative effect in experiments performed in ultrapure water.

The impact of dissolved oxygen on sulfate radical-induced oxidation of organic micro-pollutants: A theoretical study

Sulfate radical (SO₄^.-)-induced oxidation is an important technology in advanced oxidation processes (AOPs) for the removal of pollutants. To date, few studies have assessed the effects of dissolved oxygen (DO) on the SO₄^.--induced oxidation of organic micro-pollutants. In the present work, a quantum chemical calculation was used to investigate the influence of the external oxygen molecule on the Gibbs free energy (G_pollutant) and HOMO-LUMO gap (ΔE) of 15 organic micro-pollutants representing four chemical categories. Several thermodynamic and statistical models were combined with the data from the quantum chemical calculation to illustrate the impact of DO on the oxidation of organic micro-pollutants by SO₄^.-. Results indicated that the external oxygen molecule increased G_pollutant of all studied chemicals, which implies DO has the potential to decrease the energy barrier of the SO₄^.--induced oxidation and shift the chemical equilibrium of the reaction towards the side of products. From the perspective of kinetics, DO can accelerate the oxidation by decreasing ΔE of organic micro-pollutants. In addition, changes of G_pollutant and ΔE of the SO₄^.--induced oxidation were both significantly different between open-chain and aromatic chemicals, and these differences were partially attributed to the difference of polarizability of these two types of chemicals. Furthermore, we revealed that all changes of G_pollutant and ΔE induced by DO were dependent on the DO content. Our study emphasizes the significance of DO on the oxidation of organic micro-pollutants by SO₄^.-, and also provides a theoretical method to study the effect of components in wastewater on removal of organic pollutants in AOPs.

Photodegradation of sulfasalazine and its human metabolites in water by UV and UV/peroxydisulfate processes

The widespread occurrence of pharmaceuticals and their metabolites in natural waters has raised great concerns about their potential risks on human health and ecological systems. This study systematically investigates the degradation of sulfasalazine (SSZ) and its two human metabolites, sulfapyridine (SPD) and 5-aminosalicylic acid (5-ASA), by UV and UV/peroxydisulfate (UV/PDS) processes. Experimental results show that SPD and 5-ASA were readily degraded upon UV 254 nm direct photolysis, with quantum yields measured to be (8.6 ± 0.8) × 10^-3 and (2.4 ± 0.1) × 10^-2 mol Einstein^-1, respectively. Although SSZ was resistant to direct UV photolysis, it could be effectively removed by both UV/H₂O₂ and UV/PDS processes, with fluence-based pseudo-first-order rate constants determined to be 0.0030 and 0.0038 cm² mJ^-1, respectively. Second-order rate constant between SO₄^•- and SSZ was measured as (1.33 ± 0.01) × 10⁹ M^-1s^-1 by competition kinetic method. A kinetic model was established for predicting the degradation rate of SSZ in the UV/PDS process. Increasing the dosage of PDS significantly enhanced the degradation of SSZ in the UV/PDS process, which can be well predicted by the developed kinetic model. Natural water constituents, such as natural organic matter (NOM) and bicarbonate (HCO₃^-), influenced the degradation of SSZ differently. The azo functional group of SSZ molecule was predicted as the reactive site susceptible to electrophilic attack by SO₄^•- by frontier electron densities (FEDs) calculations. Four intermediate products arising from azo bond cleavage and SO₂ extrusion were identified by solid phase extraction-liquid chromatography-triple quadrupole mass spectrometry (SPE-LC-MS/MS). Based on the products identified, detailed transformation pathways for SSZ degradation in the UV/PDS system were proposed. Results reveal that UV/PDS could be an efficient approach for remediation of water contaminated by SSZ and its metabolites.