Chlorophenoxyacetic Acids Research Articles

The role of process parameters on photooxidative degradation of 2,4-D herbicide using TiO2 nanoparticles: Kinetic and mechanistic study

This systematic study investigates the effect of a wide range of TiO2 nanoparticles on the kinetics and mechanism of photocatalytic degradation of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). Changes in degradation rate, mineralization, and transformation pathways of 2,4-D correlated with nanoparticle physicochemical properties such as phase composition, size, and total pore volume. Primary intermediates, including hydroxylated chlorophenoxyacetic acids and 2,4-dichlorochlorophenoxy derivatives, were identified and their formation yields linked to the acid-base behaviour of 2,4-D. A comparison with homogeneous UV/H2O2-assisted degradation showed similar distribution of hydroxylated aromatic degradation intermediates as with large anatase nanoparticles (70 nm), while smaller particles facilitated pathways leading to the direct 2,4-D mineralization. DFT calculations supported experimental findings, and a scheme of the oxidative degradation of 2,4-D was proposed. Our results demonstrate that monitoring not only pollutant degradation but also overall mineralization is essential for evaluating photocatalysis efficiency and potential for practical applications.

Preparation and performance of MOF-808 (Zr-MOF) for the efficient adsorption of phenoxyacetic acid pesticides

The organic herbicides of chlorophenoxyacetic acids, including 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), have posed serious threats to aquatic ecosystems and human health due to extensive use, high solubility and degradation-resistant. In this study, the efficient adsorbent (MOF-808) was synthesized through solvothermal synthesis method and further evaluated for the adsorption performances of 2,4-D and MCPA. Results showed that MOF-808 exhibited the Type I nitrogen adsorption–desorption isotherm with a specific surface area of 2,155 m2·g−1, pore volume of 0.59 cm3·g−1 and pore size of 1.41 nm. It was suggested that the pseudo-second-order and Langmuir model were much better to illustrate the adsorption performances of MOF-808 for both 2,4-D and MCPA, and the maximum adsorption capacities of 793 and 775 mg·g−1 were achieved, respectively; besides, the adsorption processes were spontaneous and primarily driven by chemical adsorption with contributions from physical-chemical adsorption. Additionally, the adsorption capacities for 2,4-D and MCPA were decreased with the increasing of pH and cations concentrations; the optimal pH was 3.0 for 2,4-D and 4.0 for MCPA, and the effects of four cations on pesticides adsorption followed the order of Ca2+ > Mg2+ > Na+ > K+. Reuse experiments demonstrated that MOF-808 could retain a high removal rate of 95.9 % (2,4-D) and 95.8 % (MCPA) at the fifth cycle. The spectral analysis revealed that the adsorption mechanisms of 2,4-D and MCPA by MOF-808 involved electrostatic interactions, π-π interactions, hydrogen bonding, and complexation. In conclusion, the well-defined physicochemical properties and outstanding adsorption performance of the synthesized MOF-808 may provide a potential application for the removal of chlorophenoxyacetic acid herbicides from real wastewater.

The use of magnetic carbons obtained from vegetable raw materials based on rice husks for the extraction of chlorophenoxyacetic acids and their metabolites

The use of magnetic carbons obtained from vegetable raw materials based on rice husks for the extraction of chlorophenoxyacetic acids and their metabolites

Isolation and characterization of indigenous bacterial assemblage for biodegradation of persistent herbicides in the soil.

Extensive pesticides (herbicides) use is negatively disturbing the environment and humans. Pesticide bioremediation with eco-friendly techniques bears prime importance. This study aimed to isolate and characterize three different herbicides (metribuzin, clodinafop- propargyl, MCPA (2-methyl, 4 chlorophenoxyacetic acids) and Bromoxynil) degrading bacterial strains from agricultural fields of Punjab University, Pakistan. Among the 12 bacterial isolates, 5 were metribuzin degrading, 3 were clodinafop propargyl degrading and, 4 were MCPA and Bromoxynil degrading bacteria. Morphological, microscopic, and molecular characterization revealed that the majority of these bacterial strains were gram-negative and belonged to Bacillus and Pseudomonas genera. The isolates A6, B3, and C1 were subjected to respective herbicide degradation and the data was confirmed through GC-MS analysis. The effect of herbicide concentrations, pH, and temperature on bacterial growth was determined at OD600. The strain A6 degraded 14.8% metribuzin out of the provided concentration of 50 ppm by following the deamination pathway. While the isolates B3 and C1 degraded 23.2% and 33.9% clodinafop, MCPA and bromo-xynil, respectively, at a spiking concentration of 50ppm. The clodinafop, MCPA and Bromoxynil were metabolized into less toxic products i.e., dicarboxylic acids and 2-methyl phenol respectively, and metabolized via decarboxylation and dehalogenation mechanism. The present study evaluates the herbicides degrading bacterial strains that could potentially be used for bioremediation of agricultural contaminated sites.

ОЦЕНКА СУБСТРАТНОЙ АКТИВНОСТИ БАКТЕРИАЛЬНЫХ ИЗОЛЯТОВ ПРОМЫШЛЕННЫХ ЭКОТОПОВ Г. УФЫ ПО ОТНОШЕНИЮ К ФЕНОЛУ И ЕГО ХЛОРПРОИЗВОДНЫМ

Substrate activity for seven bacterial strains isolated from three industrial ecotopes (Ufa city) towards the phenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,4,6-trichlorophenol, 4-chloro-, 2,4-dichloro-, and 2,4,5-trichlorophenoxyacetic acids was assessed. Since none of the isolates could use dichlorophenols, while almost all strains grew on 2,4,6-trichlorophenol, it can be assumed that for the degradation potential of strains, the spatial structure of the substrate is more important than the amount and position of chlorine. Assessment of the strains growth on chlorophenoxyacetic acids also did not reveal a significant correlation between the complexity of the substrate for the ones and the number and position of chlorine substituents.

ТАКСОНОМИЧЕСКОЕ РАЗНООБРАЗИЕ ПРИРОДНЫХ БАКТЕРИАЛЬНЫХ ДЕСТРУКТОРОВ ФЕНОЛА И ЕГО ХЛОРПРОИЗВОДНЫХ В ПРОМЫШЛЕННЫХ ЭКОТОПАХ Г. УФЫ

The ability of 20 natural isolates of three industrial ecotopes to separately use phenol, 2,4-, 2,5-dichlorophenols (2,4-DCP, 2,5-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 4-chlorophenoxyacetic, 2,4-dichlorophenoxyacetic and 2,4,5-trichlorophenoxyacetic (4-CPA, 2,4-D and 2,4,5-T) acids as the sole source of carbon and energy was analyzed. The most available substrate that could be used by all isolated isolates was phenol. When using chlorophenoxyacetic acids, there was a decrease in activity against 2,4,5-T compared with 4-CPA and 2,4-D: 18 strains could use 4-CPA and 2,4-D, and 16 - 2.4,5-T. 2,4,6-TCP, 2,4-DCP, and 2,5-DCP followed in order of increasing substrate complexity; they could be utilized by 11, 7, and 2 strains, respectively. Since dichlorophenols are more complex substrates for the studied cultures compared to 2,4,6-TCP, therefore, the position of chlorine substituents is more important than its number. Comparison of the ability of strains to grow on 2,4-DCP and 2,4,6-TCP allows us to conclude that the spatial structure of the substrate molecule is important, since the presence of chlorine in the 6th position facilitates the utilization of the chlorinated substrate. Primary screening showed that the studied strains were divided into 4 groups: 12 cultures belonged to the gamma subclass of Proteobacteria; 3 ‒ to the bacillary line of gram-positive bacteria, 2 ‒ to the beta subclass of proteobacteria; 3 ‒ to actinomycetes. Pseudomonas were the most numerous among the degraders of phenol and its chlorinated derivatives ‒ four strains, as well as three cultures each belonged to representatives of the genera Bacillus and Raoultella.

Multiple Gene Clusters and Their Role in the Degradation of Chlorophenoxyacetic Acids in Bradyrhizobium sp. RD5-C2 Isolated from Non-Contaminated Soil.

Bradyrhizobium sp. RD5-C2, isolated from soil that is not contaminated with 2,4-dichlorophenoxyacetic acid (2,4-D), degrades the herbicides 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). It possesses tfdAα and cadA (designated as cadA1), which encode 2,4-D dioxygenase and the oxygenase large subunit, respectively. In the present study, the genome of Bradyrhizobium sp. RD5-C2 was sequenced and a second cadA gene (designated as cadA2) was identified. The two cadA genes belonged to distinct clusters comprising the cadR1A1B1K1C1 and cadR2A2B2C2K2S genes. The proteins encoded by the cad1 cluster exhibited high amino acid sequence similarities to those of other 2,4-D degraders, while Cad2 proteins were more similar to those of non-2,4-D degraders. Both cad clusters were capable of degrading 2,4-D and 2,4,5-T when expressed in non-2,4-D-degrading Bradyrhizobium elkanii USDA94. To examine the contribution of each degradation gene cluster to the degradation activity of Bradyrhizobium sp. RD5-C2, cadA1, cadA2, and tfdAα deletion mutants were constructed. The cadA1 deletion resulted in a more significant decrease in the ability to degrade chlorophenoxy compounds than the cadA2 and tfdAα deletions, indicating that degradation activity was primarily governed by the cad1 cluster. The results of a quantitative reverse transcription-PCR analysis suggested that exposure to 2,4-D and 2,4,5-T markedly up-regulated cadA1 expression. Collectively, these results indicate that the cad1 cluster plays an important role in the degradation of Bradyrhizobium sp. RD5-C2 due to its high expression.

ШТАММ PSEUDOMONAS AERUGINOSA 21SG – ДЕСТРУКТОР ХЛОРФЕНОКСИУКСУСНЫХ КИСЛОТ

A new strain of Pseudomonas aeruginosa 21SG, a chlorphenoxyacetic acid degrader, was isolated. The culture was determined on the basis of physiological, biochemical, cultural, morphological and morphometric characteristics, as well as the results of a comparative analysis of the 16S rRNA gene sequence. We studied the growth of a periodic culture of P. aeruginosa 21SG on chlorophenoxyacetic acids and presented the dynamics of a decrease in the concentration of substrates. The metabolic stages of 2,4,5-trichlorophenoxyacetic acid were revealed.

Bacterial Genes of Non-Heme Iron Oxygenases, Which Have a Rieske-Type Cluster, Catalyzing Initial Stages of Degradation of Chlorophenoxyacetic Acids

Hydroxylation of the benzoic ring by non-heme iron oxygenases having a Rieske-type cluster is the key step in the aerobic degradation of chloroaromatic compounds by bacteria. Rieske oxygenases (RO) catalyze the oxidative decarboxylation reaction unique to the enzymes of this family with the formation of corresponding phenolic compounds. This review discusses the general structure, function, and classification of ROs that catalyze the oxidation of chlorophenoxyacetic acids; genes encoding the ROs with their phylogenetic classes are also reviewed.

Facile microwave synthesis, structural diversity and herbicidal activity of six novel alkaline-earth metal complexes (AECs) based on skeletal isomerization chlorophenoxyacetic acids

Facile microwave synthesis, structural diversity and herbicidal activity of six novel alkaline-earth metal complexes (AECs) based on skeletal isomerization chlorophenoxyacetic acids.

Application of a dispersive solid-phase extraction method using an amino-based silica-coated nanomagnetic sorbent for the trace quantification of chlorophenoxyacetic acids in water samples.

Herein, an amino-based silica-coated nanomagnetic sorbent was applied for the effective extraction of two chlorophenoxyacetic acids (2-methyl-4-chlorophenoxyacetic acid and 2,4-dichlorophenoxyacetic acid) from various water samples. The sorbent was successfully synthesized and subsequently characterized by scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The analytes were extracted by the sorbent mainly through ionic interactions. Once the extraction of analytes was completed, they were desorbed from the sorbent and detected by high-performance liquid chromatography with ultraviolet detection. A number of factors affecting the extraction and desorption of the analytes were investigated in detail and the optimum conditions were established. Under the optimum conditions, the calibration curves were linear over the concentration range of 1-250, and based on a signal-to-noise ratio of 3, the method detection limits were determined to be 0.5μg/L for both analytes. Additionally, a preconcentration factor of 314 was achieved for the analytes. The average relative recoveries obtained from the fortified water samples varied in the range of 91-108% with relative standard deviations of 2.9-8.3%. Finally, the method was determined to be robust and effective for environmental water analysis.

Behavior of graphitized carbon blacks in the electrodegradation and sorption of chlorophenoxyacetic acids

This paper compares the properties of two graphitized carbon blacks in the sorption and first stage of electrodegradation (dechlorination) of chlorophenoxyacetic acids and discusses the influence of surface area on the electrochemical behavior of these carbon materials. Two carbon blacks with ten-fold different surface areas (100 and 10 m2/g) were used as sorbents and electrode materials as received. Two chloroorganics with various numbers of Cl atoms in the molecule, 4-chlorophenoxyacetic acid and 2,4-dichlorophenoxyacetic acid, were adsorbed on the carbon samples from neutral aqueous electrolyte solutions containing low concentrations of adsorbate. Cyclovoltammetric studies of the graphitized carbon blacks were performed using powdered electrode techniques, and the drop in organics concentration during cyclization was measured using HPLC. For carbon black with a smaller surface area, the presence of faradaic reactions was not masked by capacitive currents, and well-shaped faradaic couple peaks characteristic of a quinine/hydroquinone-like adsorbed system were observed. This indicates that these materials are active in chloroorganics electrodegradation (by dechlorination). The extent of electrodegradation (a four-fold drop in organics concentration) observed for carbon black with a larger surface area indicates the dominant role of surface (porosity) development in these processes.

Effective catalytic hydrodechlorination of chlorophenoxyacetic acids over Pd/graphitic carbon nitride

Catalytic hydrodechlorination (HDC) of chlorophenoxyacetic acids was performed over Pd/graphitic carbon nitride (Pd/g-C3N4) catalysts in the present work.

Photodegradation of Chlorophenoxyacetic Acids by ZnO/r-Fe2O3 Nanocatalysts: A Comparative Study

ZnO/r-Fe2O3 nanocomposite was synthesized via simple precipitation. The synthesized nanocatalysts underwent heat treatment at 450 oC for an hour. The characteristics of the nanocomposite were investigated by XRD, TEM, and BET surface area measurement. Zeta potential analysis was used to examine the surface charge properties of the nanocatalysts. The synthesized nanocomposite has an average particle size of 11 nm and a surface area of 20 m2 g-1. The potential of ZnO/r-Fe2O3 as a photocatalyst was evaluated by photodegrading chlorophenoxyacetic acids (PAA, 2,4-D, 2,4,5-T and 4CA). The decomposition of chlorophenoxyacetic acids by ZnO/r-Fe2O3 followed 4CA > 2,4,5-T = 2,4-D > PAA. The result indicates the applicability of ZnO/r-Fe2O3 nanocomposite as a photocatalyst in removing organic pollutants in wastewater.

Ultrasound-assisted emulsification microextraction combined with injection-port derivatization for the determination of some chlorophenoxyacetic acids in water samples

An efficient method based on ultrasound-assisted emulsification microextraction followed by injection-port derivatization GC analysis was developed to determine 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) in natural water samples. In this procedure, 12.5 μL of 1-undecanol was injected slowly into a 12 mL home-designed centrifuge glass vial containing an aqueous sample of the analytes located inside an ultrasonic water bath. The resulting emulsion was centrifuged, and 1 μL of the separated organic solvent together with 1 μL of the derivatization reagent were injected into a GC equipped with a flame ionization detector. Several factors that influence the derivatization and extraction were optimized. Under the optimal conditions, the LODs were 0.33 and 1.7 μg/L for MCPA and 2,4-D, respectively. Preconcentration factors of 670 and 836 were obtained for MCPA and 2,4-D, respectively. The precision of the proposed method was evaluated in terms of repeatability, which was <5.7% (n = 5). The applicability of the proposed method was evaluated by extraction and determination of chlorophenoxyacetic acids from some natural waters, which indicated that the matrices of natural waters have no significant effect on the extraction and derivatization efficiency of this method.

Partitioned dispersive liquid–liquid microextraction: An approach for polar organic compounds extraction from aqueous samples

Partitioned dispersive liquid–liquid microextraction (PDLLME) efficiency was demonstrated for the extraction of polar organic compounds (chlorophenoxyacetic acids) prior to high performance liquid chromatography (HPLC). The method was based on the formation of tiny droplets of an organic extractant in an aqueous sample (river water) by injecting a mixture of a water-immiscible organic solvent [tetrachloroethylene (TCE)] as extractant dissolved in a water-miscible organic dispersive solvent [tetrahydrofuran (THF)]. Based on their partition coefficients, polar compounds were extracted into the dispersed TCE droplets as well as into THF. Different parameters affecting the extraction efficiency were evaluated and precision, linearity, detection limit and an enrichment factor were determined.

Selective intercalation of chlorophenoxyacetates into the layered double hydroxide [LiAl2(OH)6]Cl·xH2O

Chlorophenoxyacetic acids are a well known family of herbicides. 4-Chlorophenoxyacetate (4-CPA), 2,4-dichlorophenoxyacetic (2,4-D), 2,4,5-trichlorophenoxyacetate, (2,4,5-T) have been intercalated into [LiAl2(OH)6]Cl·xH2O LDH ([Li–Al–Cl] LDH) by ion-exchange. The kinetics and mechanisms involved in the intercalation of each chlorophenoxyacetate have been studied by time-resolved in-situ energy dispersive X-ray powder diffraction (EDXRD). The kinetic preferential order of the intercalation of these herbicides into [Li–Al–Cl] LDH is found to be 4-CPA > 2,4-D > 2,4,5-T. In contrast, thermodynamic guest preference, as determined by performing competitive intercalation reactions is 2,4-D > 4-CPA > 2,4,5-T. The results indicate chlorophenoxyacetate-LDH compounds could have application for the purification, storage and release of chlorophenoxyacetic acid–based agrochemicals.

Identification and Characterization of a Plasmid in Strain Aeronomas hydrophila IBRB-36 4CPA Carrying Genes for Catabolism of Chlorophenoxyacetic Acids

Results of studying plasmid pAH36 in strain Aeronomas hydrophila IBRB-36 4CPA are presented. Plasmid pAH36 possesses BamHI, PstI, and HindIII restriction sites and is 5.4 kb in size. The plasmid was shown to contain genes for catabolism of chlor-substituted phenoxyacetic acids.

Large-volume stacking with polarity switching and sweeping for chlorophenols and chlorophenoxy acids in capillary electrophoresis.

This paper describes approaches for stacking large volumes of sample solutions containing a mixture of chlorophenols and chlorophenoxyacetic acids as their anions in capillary zone electrophoresis, and compares results to standard capillary electrophoresis (CE) and normal stacking modes. In order to increase the amount of sample injected beyond the optimal conditions and maintain high resolution, the sample introduction buffer must be removed after the stacking process is completed. This is achieved by pumping the sample buffer out of the column using polarity switching. Large sample volumes are loaded by hydrodynamic injection, then stacked at the injection buffer/run electrolyte interface, followed by the removal of the large plug of low-conductivity sample matrix from the capillary column using polarity switching and finally the separation of the stacked anions in a basic buffer (pH 8.65). Around 10- and 40-fold improvement of sensitivity was achieved by normal stacking and large-volume stacking with polarity switching, respectively, when compared to the standard CE analysis. Sweeping-micellar electrokinetic capillary chromatography (MEKC) was also investigated for the purpose of comparison to the stacking technique. The method should be suitable for the analysis of these chemical compound classes in industrial chlorophenoxyacetic acid manufacture.

Microbial genes and enzymes in the degradation of chlorinated compounds.

Microorganisms are well known for degrading numerous natural compounds. The synthesis of a multitude of chlorinated compounds by the chemical industry and their release into the natural environment have created major pollution problems. Part of the cause of such pollution is the inability of natural microorganisms to efficiently degrade synthetic chlorinated compounds. Microorganisms are, however, highly adaptable to changes in the environment and have consequently evolved the genes that specify the degradation of chlorinated compounds to varying degrees. Highly selective laboratory techniques have also enabled the isolation of microbial strains capable of utilizing normally recalcitrant highly chlorinated compounds as their sole source of carbon and energy. The evolution and role of microbial genes and enzymes, as well as their mode of regulation and genetic interrelationships, have therefore been the subjects of intense study. This review emphasizes the genetic organization and the regulation of gene expression, as well as evolutionary considerations, regarding the microbial degradation of chlorobenzoates, chlorocatechols, and chlorophenoxyacetic acids.