Diketometribuzin Research Articles

Optimizing the metribuzin degrading potential of a novel bacterial consortium based on Taguchi design of experiment.

Metribuzin (MB) is used for control of weeds in crops like potato, maize and sugarcane. Its extensive and unjudicial use has resulted in various environmental issues; hence it is very critical to remediate this herbicide at the respective point source. Plant associated, MB degrading bacterial strains, Rhodococcus rhodochrous sp. AQ1, Bacillus tequilensis sp. AQ2, Bacillus aryabhattai sp. AQ3 and Bacillus safensis sp. AQ4 were isolated, and a consortium MB3R was developed. For degradation of MB by the consortium MB3R, various parameters i.e., pH, temperature, inoculum density and pesticide concentration were optimized by using Taguchi design of experiment (DOE). MB degradation was dependent upon all the four factors. The contribution of each factor on MB degradation was according to the order: temperature > inoculum density > pH > pesticide concentration. Fitness of Taguchi DOE in forecasting the optimum response, was confirmed experimentally by using optimized levels of the four factors i.e., pH 7.0, temperature 30 °C, pesticide concentration 45 mg l-1 and an inoculum density of 5.0 × 10 5 CFU ml-1 whereby 98.63% MB degradation was observed. Appearance and subsequent degradation of three MB metabolites, desamino-metribuzin (DA), diketo-metribuzin (DK) and desamino-diketo-metribuzin (DADK) during biodegradation by the consortium was observed.

Simultaneous analysis of herbicide metribuzin and its transformation products in tomato using QuEChERS-based gas chromatography coupled to a triple quadrupole mass analyzer

A sensitive and simple method for the quantification of metribuzin and its major transformation products in tomato using QuEChERS-based gas chromatography coupled to a triple quadrupole mass analyzer (GC–MS/MS) with multiple reactions monitoring (MRM) was developed and validated. Residues of metribuzin, desamino-metribuzin (DA), diketo-metribuzin (DK), and desamino-diketo-metribuzin (DADK) were extracted from tomato by acetonitrile and purified by graphitized carbon black (GCB) and primary secondary amine (PSA). All analytes gave high correlation coefficients (r2) above 0.995, and the limits of detection (LOD) ranged from 0.002 to 0.008mg/kg. The mean recoveries of the analysis ranged from 72.35% to 95.86% with relative standard deviation (RSD) ranging from 1.98% to 8.70% at three spiking levels (0.05mg/kg, 0.5mg/kg, 1.0mg/kg). The method was also successfully applied to the determination of metribuzin and its transformation products in tomato samples collected from an experimental field.

Large volume sample stacking in capillary zone electrophoresis for the monitoring of the degradation products of metribuzin in environmental samples

A capillary zone electrophoresis (CZE) method with UV–vis detection has been developed for the simultaneous monitoring of the major degradation products of metribuzin, i.e. deaminometribuzin (DA), deaminodiketometribuzin (DADK) and diketometribuzin (DK). The dissociation acid constants have also been estimated by CE and no significant differences have been observed with the values obtained by applying other techniques. Optimum separation has been achieved in less than 9 min in 40 mM sodium tetraborate buffer, pH 9.5 by applying a voltage of 15 kV at 25 °C and using p-aminobenzoic acid as internal standard. In order to increase sensitivity, large volume sample stacking (LVSS) with polarity switching has been applied as on-line pre-concentration methodology. Detection limits of 10, 10 and 20 ng/mL for DA, DADK and DK, respectively were obtained. The method has been applied to soil samples, after pressurized liquid extraction (PLE). Samples were extracted at high temperature (103 °C and 1500 psi) using methanol as extraction solvent and sodium sulphate as drying agent. This PLE procedure was followed by an off-line pre-concentration and sample clean-up procedure by solid-phase extraction (SPE) using a LiChrolut EN sorbent column. These last two procedures were also suitable for the direct treatment of groundwater samples before CE analysis. The combination of both off-line and on-line pre-concentration procedures provided a significant improvement in sensitivity. LVSS provided pre-concentration factors of 4, 36 and 28 for DK, DA and DADK, respectively and with SPE a pre-concentration of 500-fold for the case of water samples and of 2.5-fold in the case of soil samples was obtained. The method is suitable for the monitoring of these residues in environmental samples with high sensitivity, precision and satisfactory recoveries.

Degradation of Metribuzin in Two Soil Types of Lebanon

The degradation of metribuzin [4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one] as influenced by soil type, temperature, humidity, organic fertilizers, soil sterilization, and ultra-violet radiation was studied in two soil types of Lebanon under laboratory conditions. The two soil types were sandy loam and clay. Deamination of metribuzin in the sandy loam soil to its deaminometribuzin (DA) derivative was basically a result of biological activity. In the clay soil the first metabolite diketometribuzin (DK) was a result of oxidative desulfuration, while diketo-deaminometribuzin (DADK) was the product of reductive deamination. The two soils represented major differences in the pesticide transformation processes. Photodecomposition on the soil surface and in aqueous media was also an important process in the degradation of metribuzin. Furthermore, the increase in soil organic matter enhanced degradation.

Determination of the herbicide metribuzin and its major conversion products in soil by micellar electrokinetic chromatography

In this paper, a multiresidue method for the analysis in soils of metribuzin (M) and its major conversion products, deaminometribuzin (DA), diketometribuzin (DK) and deaminodiketometribuzin (DADK) is developed. Considering the neutral and charged nature of the molecules, micellar electrokinetic chromatography (MEKC) is a very efficient method for the separation of these compounds, providing high efficiency and short analysis times. Different electrophoretic parameters were studied to optimize the separation, such as the buffer pH and concentration, sodium dodecyl sulphate (SDS) concentration, injection conditions and applied voltage. Excellent separation of the studied compounds was achieved within about 7 min. Soil samples were previously extracted using methanol in an ultrasonic bath and then a SPE procedure was applied to pre-concentrate the analytes by passage through a LiChrolut EN sorbent column. Detection limits at the low μg kg −1 level were obtained. The proposed method has been satisfactorily applied in soil samples showing recoveries ranging from 86.7% to 104.2% and represents a valuable alternative to high-performance liquid chromatography (HPLC).

Leaching of Metribuzin Metabolites and the Associated Contamination of a Sandy Danish Aquifer

As degradation products of metribuzin have received little attention as potential groundwater contaminants, we evaluated leaching of metribuzin and its primary metabolites desaminometribuzin (DA), desaminodiketometribuzin (DADK), and diketometribuzin (DK) at a sandy test site in Denmark. Soil water and groundwater were sampled monthly over a four-year period. Leaching of metribuzin and DA was negligible. DK and DADK leached from the root zone (1 meter below ground surface (mbgs)) in average concentrations considerably exceeding the EU limit value for drinking water (0.1 microg/L). Both metabolites appear to be relatively stable and persisted in soil water and groundwater several years after application. Past application of metribuzin at the site had contaminated the groundwater with both DK and DADK, which were detected in 99% and 48%, respectively, of the groundwater samples analyzed. Except for three of the groundwater samples, the DADK concentration never exceeded the EU limit value. In contrast, the annual concentration of DK exceeded 0.1 microg/L at 90% of the screens analyzed. The present findings suggest that as the degradation products of metribuzin can leach through sandy soil in high concentrations, they could potentially contaminate the groundwater. In view of this risk DK and DADK should both be included in monitoring programs and their ecotoxicological effects should be further investigated.

The binary treatment of aqueous metribuzin using anodic fenton treatment and biodegradation.

An advanced oxidation process, anodic Fenton treatment (AFT), and a mixed microbial culture were used to degrade metribuzin [4-amino-6-tert-butyl-3-methylthio-1,2,4- triazin-5(4H)-one], a broad-use triazinone herbicide. Complete and rapid removal of metribuzin was demonstrated. The appearance and subsequent degradation of metribuzin oxidation products--deaminated metribuzin (DA), diketo metribuzin (DK), as well as the production of deaminated diketo metribuzin (DADK)--were observed. To support the use of AFT as a chemical pretreatment, the ratio of 5-day biochemical oxygen demand (BOD5) as measured in the standard test to chemical oxygen demand (COD) was investigated, and an increase from 0.03, a nonbiodegradable solution, to 0.35, a biodegradable solution, was observed. This increase in biodegradability was associated with decreased metribuzin, DA, and DK concentrations and increased DADK concentration. AFT effluent was inoculated with either an enriched microbial culture or Polyseed, a commercially available inoculum. Although there was minimal biodegradation of the remaining metribuzin, there was a significant decrease in DA concentration in inoculated incubations compared with sterile controls after 5- and 10-minute AFT treatment. The enrichment inoculate appeared more adapted toward the less-oxidized, 5-minute-treated effluent, whereas the Polyseed culture, developed to degrade complex waste solutions, appeared to be more effective in a moreoxidized, 10-minute-treated, and potentially more complex effluent. This research supports the continued investigation of AFT and biodegradation as a binary treatment of aqueous pesticide wastes.

Degradation and Sorption of Metribuzin and Primary Metabolites in a Sandy Soil

Leaching to the ground water of metabolites from the herbicide metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5-one] has been measured in a Danish field experiment in concentrations exceeding the European Union threshold limit for pesticides at 0.1 microg/L. In the present work, degradation and sorption of metribuzin and the metabolites desamino-metribuzin (DA), diketo-metribuzin (DK), and desamino-diketo-metribuzin (DADK) were studied in a Danish sandy loam topsoil and subsoil from the field in question, using accelerated solvent extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Fast dissipation of metribuzin and the metabolites was observed in the topsoil, with 50% disappearance within 30 to 40 d. A two-compartment model described degradation of metribuzin and DA, whereas that of DADK could be described using first-order kinetics. Part of the dissipation was probably due to incorporation into soil organic matter. Degradation in subsoil occurred very slowly, with extrapolated half-lives of more than one year. Sorption in the topsoil followed the order DA > metribuzin > DK > DADK. Subsoil sorption was considerably lower, and was hardly measurable for metribuzin and DK. Abiotic degradation was considerably higher in the topsoil than the subsoil, especially concerning the de-amination step, indicating that organic matter may be related to the degradation process. The present results confirm observations of metribuzin and transformation product leaching made in the field experiment and demonstrate the need for knowledge on primary metabolites when assessing the risk for pesticide leaching.

Determination of metribuzin and major conversion products in soils by microwave-assisted water extraction followed by liquid chromatographic analysis of extracts

A multiresidue method developed for the analysis of metribuzin and its major conversion products, deaminometribuzin (DA), diketometribuzin (DK) and deaminodiketometribuzin (DADK), in soils is presented. The method is based on microwave-assisted water extraction (MAWE) of soils using 10 m M phosphate buffer, pH 7 as extractant and analysis of aqueous extracts by HPLC–diode array detection. MAWE operational parameters were optimized with respect to extraction efficiency of the target compounds from soils with 1.5 and 3.5% organic matter content. Recoveries of all solutes above 80% were obtained from soils with 1.5% organic matter content; respective LOD and LOQ levels were determined at 5 and 10 μg/kg. In soils with organic matter content 3.5%, recoveries of all solutes were lower (<70%) and the respective LOD and LOQ values were determined at 10 and 50 μg/kg. However, recoveries of fresh and aged residues, the latter weathered under cold storage conditions, were not statistically different for both types of soils.

Analysis of Metribuzin and transformation products in soil by pressurized liquid extraction and liquid chromatographic–tandem mass spectrometry

A method developed for study of metribuzin degradation in soil is presented. LC–MS–MS and electrospray ionisation was used for analysis of metribuzin and the metabolites deaminometribuzin (DA), diketometribuzin (DK) and deaminodiketometribuzin (DADK). Soil samples were extracted by pressurized liquid extraction using methanol–water (75:25) at 60°C. In general, recoveries were about 75% for metribuzin, DA and DADK and their detection limit in soil was 1.25 μg/kg. Lower sensitivity was observed for DK, with detection limit at 12.5 μg/kg and recovery about 50%.

Anaerobic degradation of dicamba and metribuzin in riparian wetland soils

In the Atlantic Coastal Plain, riparian wetlands are thought to play an important role in removal of mobilized agricultural chemicals from groundwater. Degradation potential for dicamba (3,6-dichloro-2-methoxybenzoic acid) and metribuzin (4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5 (4 H)-one) were evaluated in riparian wetland soils of the Nomini Creek Watershed, VA, using serum bottle microcosms under nitrate reducing (NO 3 amended) and non-nitrate reducing conditions. Soil samples were collected from two surface horizons (referred to as ponded and terrestrial, 1–15 cm) and the subsurface (25–45 cm) of a Bibb (coarse-loamy, siliceous, acid, thermic Typic Fluvaquent) sandy loam in May (soil temperature 16.4°C), September (19.9°C) and November (13.5°C) of 1993 from 12 locations equidistant along a 250 m section of the riparian stream. Metribuzin degradation potential was determined for soils collected in May only. Dicamba was demethylated to 3,6-dichlorosalicylic acid under either nitrate reducing or non-nitrate reducing conditions, while metribuzin was degraded to diketometribuzin (DK), deaminated diketometribuzin (DADK) and deaminated metribuzin (DA). The presence of metabolites DA and DK was confirmed by gas chromatography coupled with mass spectrometry. The rates of dicamba and metribuzin degradation were generally more rapid in the surface than in the subsurface soil microcosms. In contrast to dicamba, the disappearance of metribuzin was slower. Although the degradation experiments were conducted in microcosms under laboratory conditions, they indicate that these riparian wetland soils possess limited potential to degrade dicamba and metribuzin.

FATE OF METRIBUZIN FROM ALGINATE CONTROLLED RELEASE FORMULATIONS IN A SHARKEY SOIL: 2. TRANSPORT1

The movement of alginate-kaolin controlled release formulations (CRFs) for metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] were investigated. Miscible displacement methods using uniformly packed Sharkey clay soil (very-fine, montmorillonitic, nonacid, thermic, Vertic Haplaquept) or acid-washed sand columns were used. The CRF beads (1.6-1.8 mm in diameter) contained 1% sodium alginate, 10% kaolin, 0.002% charcoal, 0.5% surfactant, and 88% water. Three metribuzin formulations were investigated: CRFs with 0, 1, and 4% linseed oil. Metribuzin CRFs with 0% linseed oil, when compared with liquid pulse applications, indicated comparable mobility. In fact, breakthrough curves (BTCs) from pulse applications exhibited a symmetry and lack of tailing of the desorption side indicative of dominant equilibrium sorption mechanisms. In contrast, BTCs from columns with CRFs of 1 and 4% linseed oil exhibited extensive tailing of the desorption side. This was attributed to the incorporation of linseed oil with the CR formula, which acted to release metribuzin slowly from the matrix over extended time periods. This finding is consistent with solvent extraction experiments of metribuzin release over time. Three major metribuzin metabolites, diketometribuzin (DK), deaminated diketometribuzin (DADK), and deaminated metribuzin (DA), were detected in the effluent and followed closely metribuzin BTCs for all columns that received CRF metribuzin. For transport experiments where a pulse of reagent grade metribuzin in solution was applied, metribuzin metabolites were not detected in the effluent.

Photolysis of metribuzin in oxygenated aqueous solutions

The photochemical behaviour of metribuzin [4-amino-6-(1.1-dimethylethyl)-3-methylthio-1.2.4-triazin-5(4H)-one] and its known metabolites desaminometribuzin (DA), diketometribuzin (DK) and desaminodiketometribuzin (DADK) was investigated in aqueous oxygenated solutions at various pH values. The photochemical degradation of metribuzin over time and the formation and further fate of DA, DK and DADK were elucited. Both side-chain degradation and ring opening were detected as a result of photolysis. Six unknown metabolites as a result of side-chain degradation, including 6-azauracile, 6-azathymine and 4-aminosubstituted derivatives, were identified as very stable photodegradation products. Furthermore, some inorganic and organic ionic compounds were detected such as monocarboxylic, dicarboxylic and ketocarboxylic acids formed by side-chain degradation and ring cleavage.

Metribuzin and metabolites in Wisconsin (U.S.A.) well water

Metribuzin is a commonly used pesticide in Wisconsin and elsewhere, although contamination of groundwater by metribuzin has received little attention. A technique using solid phase extraction and high performance liquid chromatography was optimized to allow measurement of metribuzin and its major metabolites—deaminated metribuzin (DA), diketometribuzin (DK) and deaminated diketometribuzin (DADK). Percent recoveries and precision of metribuzin and DA analyses were good. Recoveries and reproducibility of DADK were acceptable (about 65%). However, the recoveries for DK were low (about 35%; the precision of the analysis was good, however). Overall, accuracy and precision were as good as, or better than, reported in the literature. Metribuzin and metribuzin metabolites were found in most of the groundwater samples analyzed from a number of wells located in sandy soil areas of Wisconsin. The parent metribuzin compound was found at concentrations ranging from not detected to 10.2 μg/l, while metabolite concentrations ranged from not detected to nearly 2 μg/l. Metabolites, which have been rarely reported to occur in water, were found in most of the samples even when the parent compound was absent.

HPLC and GC/MS of Metribuzin and Its Degradation Products from Alginate-Linseed Oil Controlled Release Formulations

Abstract In the preparation of alginate-clay-linseed oil controlled release formulations of metribuzin and the evaluation of their release rates, degradation of the metribuzin was observed. The degradation products were separated by HPLC and identified by GC/MS as diketometribuzin (DK), deaminated metribuzin (DA), and deaminated diketometribuzin (DADK). The HPLC method developed afforded baseline separation without the use of acid or buffers in the mobile phase. These same products are the major metabolites of metribuzin in plants and soil. The production of DK was directly proportional to the amount of linseed oil in the formulation whereas DA appears to be inversely proportional to linseed oil concentration.

Thermospray liquid chromatographic—mass spectrometric method for the analysis of metribuzin and its metabolites

A thermospray liquid chromatographic—mass spectrometric (TSP LC—MS) method has been developed for the analysis of the herbicide metribuzin and its three major metabolites in plant tissue. Metribuzin and its metabolites exhibited widely varying sensitivities in positive-ion TSP, with metribuzin being the most sensitive and deaminated diketo metribuzin being the least sensitive. All four compounds of interest were detected in an extract of a soybean plant which had been treated with metribuzin.

Differential Metabolism of Metribuzin by Downy Brome (Bromus tectorum) and Winter Wheat (Triticum aestivum)

At both 15 and 25 C, following a 24-h root absorption period, absorbed14C-metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] was metabolized approximately 30% more rapidly to water-soluble and terminal fiber metabolites by winter wheat (Triticum aestivumL.) than by downy brome (Bromus tectorumL. # BROTE). Both species metabolized a greater proportion of metribuzin in leaf sheaths and roots than in the leaf blades. This was attributed to the increased incorporation of metribuzin into fiber. After an initial leaf extraction, metribuzin and the metabolites deaminated metribuzin (DA), deaminated diketo metribuzin (DADK), and diketo metribuzin (DK) partitioned into a chloroform fraction and five unidentified water-soluble metabolites into an aqueous fraction. At both 15 and 25 C, downy brome absorbed approximately three times more metribuzin per fresh weight than did winter wheat. The mechanism of differential tolerance of downy brome and winter wheat to metribuzin was attributed to the ability of winter wheat to metabolize metribuzin more rapidly and absorb less metribuzin than downy brome.

Spectrometric Characterization of Metribuzin and its Metabolites

Metribuzin and its three major plant metabolites have been characterized by ultraviolet, infrared, and proton NMR spectroscopy and mass spectrometry. The reported structures for these compounds have been confirmed, except that deaminated Metribuzin (DA) exists mainly in the enol form rather than the keto form usually reported. Evidence is presented concerning the most probable sites of protonation during titration of these compounds. Whereas diketo Metribuzin (DK) does undergo protonation of the amino group, Metribuzin itself apparently does not. Keto/enol tautomerism as a function of pH greatly complicates interpretation of the spectra. Metribuzin appears to form a poorly soluble, hydrogen-bonded dimer (or polymer) when titrated from basic to acidic pH.

The Determination of Metribuzin and Its Metabolites by High Pressure Liquid Chromatography

Abstract A method for the determination of metribuzin and its metabolites in plant tissues has been developed using High Pressure Liquid Chromatography (HPLC). The system used involves reversed-phase chromatography on a C-18 HPLC column and a 62:38 methanol/0.05 M acetic acid mobile phase. Under these conditions, metribuzin and the three known metabolites [deaminated metribuzin (DA), deaminated diketometribuzin (DADK) and diketometribuzin (DK)] are completely resolved from each other. Detection is by UV absorbance at 254 nm.