Degradation Of Metamitron Research Articles

Metribuzin and metamitron degradation using catalytic ozonation over tourmaline: Kinetics, degradation pathway, and toxicity

The reaction kinetics and degradation mechanisms of the herbicides metribuzin (MTZ) and metamitron (MTT) were evaluated during conventional and tourmaline-catalyzed ozonation processes. The tourmaline catalyst was characterized by X-ray diffraction, field emission-scanning electron microscopy, Brunauer-Emmett-Teller surface analysis and Fourier transform infrared spectroscopy. The reactivities of these two herbicides with ozone (O3) are low due to their refractory characteristics, so catalytic ozonation is an ideal way to effectively degrade them. The effects of catalyst dosage, pH, temperature and ozone concentration on catalytic degradation of MTZ and MTT were investigated. Based on the results from quenching experiments and calculation of second-order rate constants (kO3, MTZ (4.82 ± 0.42 M−1s−1), kO3, MTT (13.35 ± 0.62 M−1s−1) and k•OH, MTT ((6.90 ± 0.51) × 109M−1s−1)), it was found that oxidation of the pollutants was mediated by decomposition of O3 to produce •OH. Twelve MTZ degradation products and five MTT degradation products were identified by gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry, and the reaction mechanisms were analyzed. In addition, the potential toxicities of the derivatives formed during catalytic ozonation were examined. The degradation products of the two pollutants exhibited different toxicity profiles. The environmental-friendliness and efficient catalytic properties of tourmaline suggest that it has great potential as a heterogenous and green catalyst.

Rapid degradation of metamitron and highly complex mixture of pollutants using MIL-53(Al) integrated combustion synthesized TiO2

In the present work, we report a new approach for the synthesis of TiO2-MIL-53(Al) (MIL: Matériaux de l′Institut Lavoisier) nano-composite. The integration of microwave synthesized metal organic framework (MOF) with combustion synthesized metal oxide is reported for the first time. The synthesized materials were characterized using an X-ray diffractometer, Fourier transform infrared spectrometer, scanning electron microscope, energy dispersive X-ray spectroscope, energy dispersive X-ray fluorescence, porosimeter, and UV–visible diffuse reflectance spectroscope. The diffraction pattern of the composite indicated the presence of TiO2 as well as MIL-53(Al). Furthermore, the presence of anatase–rutile mixed phase of TiO2 in the synthesized material was observed. The Fourier transform infrared spectrum was in support of XRD observations. A significantly low surface area and porosity of the composite material, compared to its parent components, was observed. The surface micrograph image of the composite depicted its nano-sheet type morphology. The energy dispersive X-ray analysis confirmed the presence of Ti, Al, C and O in the composite material. The composite material exhibited a narrow band-gap compared to the pristine MIL and TiO2.As an application, the photocatalytic activity of synthesized material was determined by the degradation of metamitron. The application part is also one of the novelties of the present work. The effect of catalyst loading, initial concentration of metamitron and presence of inorganic ions on the photocatalytic degradation was investigated. The reusability of the composite material was evaluated. A plausible mechanism of photocatalytic degradation is proposed based on radical scavenging experiments. To the best of our knowledge, to date, there is no study on the application of TiO2-MOF composite for the photocatalytic degradation of herbicide. Further, the synthesized material was successfully used for the photocatalytic degradation of a complex mixture of pollutants comprising metamitron, methylene blue, rhodamine B and 2, 4-dichlorophenol. This is a first of its kind study to demonstrate the application of TiO2-MOF composite for photocatalytic degradation of a highly complex mixed pollutant.

Superior photocatalytic removal of metamitron and its mixture with Rhodamine B dye using combustion synthesized TiO2 nanomaterial

In this study, photocatalytic degradation of a herbicide, metamitron, was carried out using combustion synthesized nano-TiO2. The synthesized catalyst was characterized using X-ray diffraction, porosimetry and UV-diffuse reflectance spectroscopy. The combustion synthesized catalyst showed lower crystallite size, better surface area and narrower band-gap compared to the commercial TiO2. The effect of catalyst loading, initial concentration of metamitron, pH and presence of inorganic ions on the extent of degradation was studied. The pseudo first order rate constant of metamitron degradation using combustion synthesized TiO2 was 1.5–2.5 times higher than that using commercial TiO2 at different initial concentrations of metamitron. The effect of another component, Rhodamine-B dye, on the degradation of metamitron was also probed in this study. The rate of degradation of both metamitron and Rhodamine B were high when the combined system was treated. The degradation by-products were tracked using liquid chromatograph/mass spectrometer, and a possible degradation pathway is proposed.

Microbial activity and metamitron degrading microbial communities differ between soil and water-sediment systems

The herbicide metamitron is frequently detected in the environment, and its degradation in soil differs from that in aquatic sediments. In this study, we applied 13C6-metamitron to investigate the differences in microbial activity, metamitron mineralization and metamitron degrading microbial communities between soil and water-sediment systems. Metamitron increased soil respiration, whereas it suppressed respiration in the water-sediment system as compared to controls. Metamitron was mineralized two-fold faster in soil than in the water-sediment. Incorporation of 13C from 13C6-metamitron into Phospholipid fatty acids (PLFAs) was higher in soil than in sediment, suggesting higher activity of metamitron-degrading microorganisms in soil. During the accelerated mineralization of metamitron, biomarkers for Gram-negative, Gram-positive bacteria and actinobacteria dominated within the 13C-PLFAs in soil. Gram-negative bacteria dominated among the metamitron degraders in sediment throughout the incubation period. Actinobacteria, and actinobacteria and fungi were the main consumers of necromass of primary degraders in soil and water-sediment, respectively. This study clearly showed that microbial groups involved in metamitron degradation depend on the system (soil vs. water-sediment) and on time. It also indicated that the turnover of organic chemicals in complex environments is driven by different groups of synthropic degraders (primary degraders and necromass degraders) rather than by a single degrader.

Photocatalytic degradation of metamitron using CeO2 and Fe/CeO2

ABSTRACTThe excessive use of herbicides can cause ground water contamination and is also a potential threat to the nearby aquatic ecosystem. In this work, we report photocatalytic degradation of metamitron using CeO2 and Fe/CeO2. The effect of catalyst loading on the degradation was studied. A significant effect on photocatalytic degradation was observed with bare-CeO2. On the other hand, photolysis and Fe/CeO2 displayed similar effect on the degradation. Thus, it was concluded that lowering the band gap, by doping, is not always favorable for enhancing the photocatalytic degradation.

Transformation of metamitron in water-sediment systems: Detailed insight into the biodegradation processes

Metamitron and its main metabolite desamino-metamitron are frequently detected in surface waters. To date, there are no studies targeting metamitron degradation in water-sediment systems. Therefore, the aim of this study was to trace the fate of metamitron in a water-sediment system using 13C-isotope labeling. Mineralization of metamitron was high and accounted for 49% of 13C6-metamitron equivalents at the end. In contrast, only 8.7% of 13C6-metamitron equivalents were mineralized in the water only system demonstrating the key role of sediment for biodegradation. Metamitron disappeared from the water on day 40 and was completely removed from the sediment on day 80. This agrochemical was utilized as carbon source by microorganisms as shown by the incorporation of the 13C label into microbial amino acids and finally into biogenic residues. The latter amounted to 24% of 13C6-metamitron equivalents at the end. However, 17% of 13C6-metamitron equivalents were detected in xenobiotic non-extractable residues (NER) with a release potential and delayed risk for the environment. Metamitron was degraded via two pathways, initially via 4-(dimethylimino)-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one, which might be related to growth, and later via desamino-metamitron, which can be attributed to starvation.

Identification of degradation routes of metamitron in soil microcosms using 13C-isotope labeling

Metamitron is one of the most commonly used herbicide in sugar beet and flower bulb cultures. Numerous laboratory and field studies on sorption and degradation of metamitron were performed. Detailed biodegradation studies in soil using 13C-isotope labeling are still missing. Therefore, we aimed at providing a detailed turnover mass balance of 13C6-metamitron in soil microcosms over 80 days. In the biotic system, metamitron mineralized rapidly, and 13CO2 finally constituted 60% of the initial 13C6-metamitron equivalents. In abiotic control experiments CO2 rose to only 7.4% of the initial 13C6-metamitron equivalents. The 13C label from 13C6-metamitron was incorporated into microbial amino acids that were ultimately stabilized in the soil organic matter forming presumably harmless biogenic residues. Finally, 13C label from 13C6-metamitron was distributed between the 13CO2 and the 13C-biogenic residues indicating nearly complete biodegradation. The parallel increase of 13C-alanine, 13C-glutamate and 13CO2 indicates that metamitron was initially biodegraded via the desamino-metamitron route suggesting its relevance in the growth metabolism. In later phases of biodegradation, the “Rhodococcus route” was indicated by the low 13CO2 evolution and the high relevance of the pyruvate pathway, which aims at biomolecule synthesis and seems to be related to starvation. This is a first report on the detailed degradation route of metamitron in soil.

Characterization and genome functional analysis of a novel metamitron-degrading strain Rhodococcus sp. MET via both triazinone and phenyl rings cleavage

A novel bacterium capable of utilizing metamitron as the sole source of carbon and energy was isolated from contaminated soil and identified as Rhodococcus sp. MET based on its morphological characteristics, BIOLOG GP2 microplate profile, and 16S rDNA phylogeny. Genome sequencing and functional annotation of the isolate MET showed a 6,340,880 bp genome with a 62.47% GC content and 5,987 protein-coding genes. In total, 5,907 genes were annotated with the COG, GO, KEGG, Pfam, Swiss-Prot, TrEMBL, and nr databases. The degradation rate of metamitron by the isolate MET obviously increased with increasing substrate concentrations from 1 to 10 mg/l and subsequently decreased at 100 mg/l. The optimal pH and temperature for metamitron biodegradation were 7.0 and 20–30 °C, respectively. Based on genome annotation of the metamitron degradation genes and the metabolites detected by HPLC-MS/MS, the following metamitron biodegradation pathways were proposed: 1) Metamitron was transformed into 2-(3-hydrazinyl-2-ethyl)-hydrazono-2-phenylacetic acid by triazinone ring cleavage and further mineralization; 2) Metamitron was converted into 3-methyl-4-amino-6(2-hydroxy-muconic acid)-1,2,4-triazine-5(4H)-one by phenyl ring cleavage and further mineralization. The coexistence of diverse mineralization pathways indicates that our isolate may effectively bioremediate triazinone herbicide-contaminated soils.

Simple synthesis of ZnO nanoflowers and its photocatalytic performances toward the photodegradation of metamitron

Large-scale ZnO nanoflowers assembled from numerous thin and uniform nanosheets with a thickness of around 20nm, were successfully prepared through a facile one-step hydrothermal synthesis route by using zinc acetate, sodium citrate and sodium hydroxide in water solution. The method was simple, green and effective. The obtained ZnO nanoflowers exhibited remarkable photocatalytic acitivity and good cycle stability for the degradation of metamitron under a 300W of Osram® ultra-vitalux lamp light emitting UV and visible radiation over 300–600nm. UV–vis spectrophotometery was used to measure the rate of photodecomposition of metamitron. The results indicate that about 97% of the metamitron disappeared in the suspension of flower-like ZnO microspheres within four hours, and the degradation efficiency were not changed even after 5 cycle times.

Photocatalytic mitigation of triazinone herbicide residues using titanium dioxide in slurry photoreactor

Heterogeneous photocatalysis offers an alternative for the treatment of wastewater containing refractory pollutants. The photocatalytic degradation of metamitron and metribuzin, asymmetrical triazine compounds used worldwide as herbicides, was investigated in aqueous suspension of different commercial TiO2 nanopowders with different composition of anatase/rutile phases, using artificial UV-A light. In addition, we have studied the role of the most important operating parameters (catalyst loading, effect of electron acceptor, pH, light intensity, initial concentration of pollutants, and interfering substances) on the photooxidation of both herbicides. TiO2 P25 (70% anatase/30% rutile) was found to be highly active for herbicide decomposition. The progress of photocatalytic degradation of both herbicides has been observed by monitoring the change in substrate concentration using HPLC/MS2. Results showed that the addition of TiO2 in tandem with an electron acceptor like Na2S2O8 strongly enhances the degradation rate of metamitron and metribuzin in comparison with photolytic test. The degradation of these herbicides followed a pseudo-first order kinetics. The time required for 50% degradation was lower than 8min for both. Thus, complete disappearance was achieved after 30min of illumination in the TiO2/Na2S2O8 system. Both herbicides were rapidly deaminated.

Metamitron decay in soil depending on herbicide formulation and application methodRozkład metamitronu w glebie w zależności od formulacji i sposobu aplikacji herbicydu

Summary The aim of the studies was to determine the influence of herbicide formulation and application method on metamitron decay in soil. Experiment was carried out in the laboratory conditions (plant growth chamber). Metamitron was applied in three variants as: monocomponent herbicide (A), as monocomponent herbicide in tank mixture with herbicide containing ethofumesate, desmedipham and phenmedipham (B) and as multicomponent herbicide containing four active components (listed above); (C). Concentation of metamitron was the same in all variants. Soil samples were taken for the analyses 1 hour (initial concentration) and 2, 4, 8, 16, 32 and 64 days after treatment. Metamitron residue was analysed using GC/MS. Good linearity was found between logarithmic concentration of metamitron residues and time. The formulation and application method influenced on the metamitron decay in soil. For the variant A the DT50 value amounted to 19 days. Application of metamitron as a tank mixture (variant B) slowed down the degradation of metamitron in soil – DT50 amounted to 23 days. The DT50 value of metamitron applied in variant C was the smallest and amounted to 17 days.

A study of the photocatalytic degradation of metamitron in ZnO water suspensions

Abstract The photocatalytic degradation of the herbicide metamitron in water using ZnO under Osram ULTRA-VITALUX® lamp light was studied. The effect of the operational parameters such as initial concentration of catalyst, initial metamitron concentration, initial salt concentration (NaCl, Na 2 CO 3 and Na 2 SO 4 ) and pH was studied. The optimal concentration of catalyst was found to be 2.0 g/l. First-order rate constants were calculated for the uncatalysed reactions. On the base of the Langmuir–Hinshelwood mechanism, a pseudo first-order kinetic model was illustrated and the adsorption equilibrium constant and the rate constant of the surface reaction were calculated (0.119 l mg − 1 and 0.836 mg l − 1 min − 1 , respectively). The photodegradation rate was higher in acidic than in alkaline conditions. When salt effect was studied, it was found that sodium carbonate was the most powerful inhibitor used, while sodium chloride was the weakest one. A negligible inhibition was observed when the concentration of sodium chloride was 20 mM. The rate of photodecomposition of metamitron was measured using UV spectroscopy and HPLC, while its mineralization was followed using ion chromatography (IC), as well as total organic carbon (TOC) and total nitrogen (TN) analysis. Under the employed conditions, almost complete disappearance of 9 mg/ml of herbicide, 56% TOC and 34% TN removal, occurred within 4 h. The ion chromatography results showed that the mineralization led to ammonium, nitrite and nitrate ions during the process.

Spatial variability in14C‐herbicide degradation in surface and subsurface soils

The spatial variability in mineralization of atrazine, isoproturon and metamitron in soil and subsoil samples taken from a 135-ha catchment in north France was studied. Fifty-one samples from the top layer were taken to represent exhaustively the 31 agricultural fields and 21 soil types of the catchment. Sixteen additional samples were collected between depths of 0.7 and 10 m to represent the major geological materials encountered in the vadose zone of the catchment. All these samples were incubated with 14C-labelled atrazine under laboratory conditions at 28 degrees C. Fourteen selected surface samples which exhibited distinctly different behaviour for atrazine dissipation (including sorption and mineralization) were incubated with 14C-isoproturon and 14C-metamitron. Overall soil microbial activity and specific herbicide degradation activities were monitored during the incubations through measurements of total carbon dioxide and 14C-carbon dioxide respectively. At the end of the incubations, extractable and non-extractable (bound) residues remaining in soils were measured. Variability of herbicide dissipation half-life in soil surface samples was lower for atrazine and metamitron (CV < 12%) than for isoproturon (CV = 46%). The main contributor to the isoproturon dissipation variability was the variability of the extractable residues. For the other herbicides, spatial variability was mainly related to the variability of their mineralization. In all cases, herbicide mineralization half-lives showed higher variability than those of dissipation. Sorption or physicochemical soil properties could not explain atrazine and isoproturon degradation, whose main factors were probably directly related to the dynamics of the specific microbial degradation activity. In contrast, variability of metamitron degradation was significantly correlated to sorption coefficient (K(d)) through correlation with the sorptive soil components, organic matter and clay. Herbicide degradation decreased with depth as did the overall microbial activity. Atrazine mineralization activity was found down to a depth of 2.5 m; beyond that, it was negligible.

Organic Amendments to Enhance Atrazine and Metamitron Degradation in Two Contaminated Soils with Contrasting Textures

Among all types of xenobiotics, pesticides such as herbicides play a significant role in soil and water pollution due to their wide usage all over the world. This study addresses the ability of organic amendments to enhance atrazine and metamitron degradation in two herbicide-contaminated soils with contrasting textures under laboratory conditions. Soil samples were collected from surface soils with textures of sandy loam and silty clay, from northeastern Iran. Initial concentration of herbicides was 50 mg · kg− 1 soil. Contaminated soil samples were treated with manure, compost and vermicompost at rates of 0, 0.5, and 2% (w/w). Residual concentrations of atrazine and metamitron were determined by HPLC at the end of incubation periods of 20, 40, and 60 days. Residual concentrations of atrazine were 46.5, 38.9, and 36.2 mg · kg− 1 after 20, 40, and 60 days incubation, respectively. Residual metamitron concentrations were clearly lower than atrazine. After 20, 40, and 60 days, concentrations of metamitron were 2.9, 1.0, and 0.6 mg · kg− 1, respectively. Organic amendments at the rates of 0.5 and 2% showed similar effects on the enhancement of herbicide degradation in soils. However, no statistically significant effect was observed among types of organic amendments (α = 0.05). Degradation was affected by soil textures. Residual concentrations of herbicides were higher in sandy loam than in silty clay soil.

Monitoring of the photochemical degradation of metamitron and imidacloprid by micellar electrokinetic chromatography and differentialpulse polarography

Monitoring of the photochemical degradation of metamitron and imidacloprid by micellar electrokinetic chromatography and differentialpulse polarography

Monitoring of the photochemical degradation of metamitron and imidacloprid by micellar electrokinetic chromatography and differential-pulse polarography

Monitoring of the photochemical degradation of metamitron and imidacloprid by micellar electrokinetic chromatography and differential-pulse polarography

Monitoring of the photochemical degradation of metamitron and imidacloprid by micellar electrokinetic chromatography and differential‐pulse polarography

The photochemical degradation of metamitron (4-amino-4,5-dihydro-3-methyl-6-phenyl-1,2,4-triazin-5-one) and imidacloprid (1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine) has been investigated by differential-pulse polarography (DPP) and micellar electrokinetic chromatography (MEKC); the degradation pathways of these pesticides were elucidated and their degradation products proposed. The electrochemical study of imidacloprid by DPP at different pH values demonstrated the occurrence of two different reduction processes; at pH 6.8, two peaks at −0.90 V and −1.38 V, respectively, were obtained, which are related to the photochemical reduction processes. The photochemical degradation of imidacloprid caused by sunlight was polarographically monitored and its degradation products elucidated. The polarographic reduction of deaminometamitron (obtained by photochemical reduction of metamitron) yielded two peaks at −0.62 and −1.37 V, which are related to the reduction of the CN bonds. The effect of sunlight on the reduction of metamitron was monitored by DPP, and an increase of the concentration of the degradation products was observed with time. MEKC with UV-visible detection was used to separate the pesticides and the products of their photochemical degradation, which were identified in combination with DPP. © 1999 Society of Chemical Industry

Acid hydrolysis of 1,6-dihydro-4-amino-3-methyl-6-phenyl-1,2, 4-triazin-5(4H)-one (1,6-dihydrometamitron).

Metamitron (1) does not undergo hydrolysis at pH 1-8 and up to 5 M H(2)SO(4). The product of its two-electron reduction, 1, 6-dihydrometamitron (2), on the other hand, undergoes at pH <3 relatively fast hydrolysis. The dependence of the measured rate constant on acidity indicates that the completely protonated form (AH(2)(2+)) predominating in strongly acidic media undergoes hydrolysis slower than the species bearing one less proton (AH(+)). The latter most reactive species is present in highest concentration in solutions of pH between 0 and 2. This species is protonated on the 2,3-azomethine bond and yields as final products 2-hydrazino-2-phenylacetic acid (4) and acethydrazide (5). Kinetic, polarographic, and spectrophotometric measurements indicated for the first dissociation an average value pK(a) = -0.8, for the second pK(a) = 0.95. These observations together with the easy reduction of the 1,6-bond in metamitron (1) indicate that in nature the cleavage of metamitron may be preceded by its reduction to 1, 6-dihydrometamitron (2), which is then hydrolyzed. Thus, anaerobic, reductive conditions are likely preferable for the total microbial degradation of metamitron.

Porosity and herbicide leaching in soils amended with olive-mill wastewater

Organic amendments used to enrich soils of low organic matter contents can affect sorption and movement of pesticides in soils. In this work, we studied the effect of olive oil mill wastewater (OOW) soil amendment on soil porosity and on leaching of the herbicides clopyralid (3,6-dichloropicolinic acid) and metamitron (4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one) in clay soil columns. OOW amendment resulted in an increase in the organic carbon content of the soils and a reduction in soil porosity, the latter confirmed by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) studies. MIP and SEM data showed the reduction in porosity is basically due to a reduction in larger pores (radius > 0.1 μm) and an important increase in finer pores (radius < 0.1 μm). These changes in porosity are produced by the combined effect of the suspended and soluble organic matter and salts in the OOW and the solubilization-insolubilization of the soil carbonate minerals promoted by OOW. Soil columns were handpacked with the unamended clay soil and with the same soil which had been treated for 3 yrs with two different doses of OOW (low dose: 300 ml/m 2 a year and high dose: 600 ml/m 2 a year). Clopyralid moved more rapidly than metamitron in the unamended soil due to greater sorption and degradation of metamitron. Total amounts of clopyralid leached from the OOW amended soils were significantly reduced (75 and 25% for the lower and higher dose, respectively) when compared with the unamended soil (100%), whereas metamitron did not leach at all from the amended soils. Sorption and degradation studies with soil slurry suggested this reduction may be mainly due to an increase in sorption and degradation processes in amended soils, as a consequence of the increase in the organic carbon content. However, the decrease in mobility produced by OOW amendment is greater than that suggested from the sorption and degradation increases. The reduction in large size conducting pores and the increase in the small non-conducting pores, induced by OOW amendment, produce an increase in the residence time of the herbicides in the immobile water phase, enhancing diffusion, sorption and degradation processes, thereby retarding mobility. The retarding effect was more pronounced for metamitron than for clopyralid due to the higher sorptivity and degradability of the former herbicide. These results suggest the possible use of the OOW or similar wastewater amendment in reducing the contamination of groundwater by pesticide drainage.

Photolysis of metamitron in water in the presence of soils and soil components

The herbicide metamitron (4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one) photodegrades rapidly in aqueous solution leading to the formation of desaminometamitron. Photolysis rate was slower in the presence of soils due to the screen effect of soil particles, although some differences observed between the 3 different soils indicated that soil organic matter (SOM) may accelerate photolysis of metamitron. Photolysis studies with the colloidal fraction of the soils before and after organic matter elimination and with soil humic acids confirmed the photosensitizing effect of humic acid on the phototransformation of metamitron. Studies with model iron oxides (goethite and ferrihydrite) also suggested that these soil components could accelerate metamitron degradation in aqueous medium. The Fe 2O 3-sensitizing effect is less significant than that of the SOM and was not clearly developed in the natural clay fraction.