Metribuzin Release Research Articles

Constructing slow-release formulations of herbicide metribuzin using its co-extrusion with biodegradable polyester poly-ε-caprolactone

Different technologies to prepare long term pesticide forms include polymer coating, preparing composites and encapsulating pesticides in nanoparticles. A simple and low-cost method was proposed to obtain slow-release formulations by co-extrusion of a pesticide with a biodegradable polymer at a temperature above the melting points of both components. A herbicide metribuzin and low-melting polyester poly-ε-caprolactone were chosen for this work. Formulations containing 10%, 20%, and 40% herbicide were prepared. During 7 days of their exposition in water, it was released from 81% to 96% of initially loaded metribuzin; the highest release was detected for 40%-loaded forms. Biodegradation of the constructs and pesticide release were further studied in the model soil. Degradation rates of the specimens increased with an increase in pesticide content, from 9% to 20% over 14 weeks for the 10%/20%-loaded and the 40%-loaded specimens, respectively. The release of metribuzin reached, respectively, 37–38% and 55%. The herbicide content in soil was lower due to its partial degradation in soil; it reached 23–25% and 33%, respectively, from initially loaded into the polymer matrix. Release kinetics of metribuzin in water as in soil best fitted the First-order model. The used approach is promising for obtaining long-term release formulations for soil applications.

Constructing Slow‐Release Metribuzin Formulations by Co‐extrusion of the Pesticide with Poly‐ε‐Caprolactone

AbstractA simple and low‐cost method of obtaining slow‐release pesticide formulations is proposed by co‐extrusion of a herbicide metribuzin with a low‐melting biodegradable polyester poly‐ε‐caprolactone, at a temperature above the melting points of both components. Formulations containing 10%, 20%, and 40% herbicide are prepared. Metribuzin release in water during 7 days of exposition reached 81% from the formulations with the 10% loading and 96% from the specimens with the 40% herbicide loading. Biodegradation and pesticide release from the polymer constructs are studied in the model soil for 14 weeks. Degradation rates of the specimens increased with an increase in pesticide content: between 9% for the 10%‐loaded specimen and 20% for the 40%‐loaded specimen over 14 weeks. The release of metribuzin from the specimens with the 10–20% and 40% loadings reached 37–38% and 55%, respectively; thus, taking into account soil degradation of the herbicide, the herbicide content in soil reached 23–25% and 33%, respectively, of the initially loaded into the polymer matrix. The used approach is promising to obtain long‐term release formulations for soil application.

Organic waste from sugar mills as a potential soil ameliorant to minimise herbicide runoff to the Great Barrier Reef

We studied sorption potential for a range of herbicides using eleven waste materials (mill muds) containing organic matter (47.6 to 65.1%) produced by sugar mills and applied as soil conditioners by farmers. Sorption/desorption behaviour of five herbicides commonly used in sugarcane production (imazapic, atrazine, hexazinone, diuron and metribuzin) was studied on these mill muds, as is and after adding these to three soils at different rates (5–25%, dry weight basis). All mill muds had significant sorption capacity, especially for diuron, atrazine and metribuzin which was 6 to 26 times higher than the soil with 3.5% organic carbon (OC). Generally, sorption of the five herbicides assessed in all mill muds followed the order diuron > atrazine = metribuzin > hexazinone = imazapic. Eight out of 11 mill muds had similar sorption capacity for any given herbicides. Amending soils with selected mill muds significantly enhanced their sorption efficiency, depending on the rate of application especially in soil with low OC. Generally, application of mill muds at 5% w/w or 40 tons/ha increased sorption of studied herbicides by 2 to 10 folds. Soil amendment with mill muds also reduced the rate and extent of desorption of herbicides- especially mobile herbicides like metribuzin. Nearly 79% release of metribuzin was observed after three desorption steps in amended soil (at 5% w/w), whereas in unamended soil, 100% of metribuzin was released during first desorption step. The study demonstrates that wastes produced by sugar mills may have recycling use in enhancing the retention of mobile herbicides in soils with low OC content.

Poly(3-hydroxybutyrate)/metribuzin formulations: characterization, controlled release properties, herbicidal activity, and effect on soil microorganisms.

Slow-release formulations of the herbicide metribuzin (MET) embedded in the polymer matrix of degradable poly-3-hydroxybutyrate [P(3HB)] in the form of microparticles, films, microgranules, and pellets were developed and tested. The kinetics of polymer degradation, MET release, and accumulation in soil were studied in laboratory soil microecosystems with higher plants. The study shows that MET release can be controlled by using different techniques of constructing formulations and by varying MET loading. MET accumulation in soil occurs gradually, as the polymer is degraded. The average P(3HB) degradation rates were determined by the geometry of the formulation, reaching 0.17, 0.12, 0.04, and 0.05mg/day after 60days for microparticles, films, microgranules, and pellets, respectively. The herbicidal activities of P(3HB)/MET formulations and commercial formulation Sencor Ultra were tested on the Agrostis stolonifera and Setaria macrocheata plants. The parameters used to evaluate the herbicidal activity were plant density and the weight of fresh green biomass measured at days 10, 20, and 30 after sowing. All P(3HB)/MET formulations had pronounced herbicidal activity, which varied depending on MET loading and the stage of the experiment. In the early phases of the experiment, the herbicidal effect of P(3HB)/MET formulations with the lowest MET loading (10%) was comparable with that of the commercial formulation. The herbicidal effect of P(3HB)/MET formulations with higher MET loadings (25 and 50%) at later stages of the experiment were stronger than the effect of Sencor Ultra.

Constructing herbicide metribuzin sustained-release formulations based on the natural polymer poly-3-hydroxybutyrate as a degradable matrix

ABSTRACTPolymer poly(3-hydroxybutyrate) [P(3HB)] has been used as a matrix in slow-release formulations of the herbicide metribuzin (MET). Physical P(3HB)/MET mixtures in the form of solutions, powders, and emulsions were used to construct different metribuzin formulations (films, granules, pellets, and microparticles). SEM, X-Ray, and DSC proved the stability of these formulations incubated in sterile water in vitro for long periods of time (up to 49 days). Metribuzin release from the polymer matrix has been also studied. By varying the shape of formulations (microparticles, granules, films, and pellets), we were able to control the release time of metribuzin, increasing or decreasing it.

Kinetics of metribuzin release from bentonite-polymer composites in water

A series of bentonite polymer-composites (BPCs) loaded with metribuzin were studied for their controlled release in aqueous medium. The release of active ingredient from BPCs was significantly lower as compared to commercial metribuzin formulation. The results revealed that the cumulative metribuzin release was highest (81%) from the BPCs containing 8% clay (commercial bentonite) and 2% metribuzin which correspond to the lowest (14 days) half-life values i.e., time required for 50% release of active ingredient (t1/2). The metribuzin release from the BPCs decreased with increased concentration of clays in polymer matrix and the release was further decreased with BPCs prepared with pure nano-bentonite. BPCs containing 12% clay and 2% metribuzin showed maximum t1/2 values i.e., 25 and 51 days for commercial bentonite and pure nano-bentonite as clay sources, respectively. The differential behaviour in the metribuzin release rates from BPCs was ascribed due to variations in crosslinking of metribuzin in the composites. As metribuzin release was found to be slower in BPCs compared to commercial formulation, it could be used for control of weeds tailored to different crops.

Characterization of sepiolite-gel-based formulations for controlled release of pesticides

Novel controlled release formulations (CRFs) were developed for reducing leaching of herbicides and contamination of groundwater. The herbicide metribuzin (MTB) was entrapped within a sepiolite-gel matrix using a novel and ultrasound-based technique. Different sepiolite/herbicide matrices (either as a gel or as a powder after freeze-drying) were prepared with pesticide loading between 28.6 and 9.1%. The release of MTB from the control released formulations into water was retarded when compared with commercial formulation (CF), except in the case of the sepiolite-gel-based formulations with lower amounts of sepiolite. The rheological properties and microstructure of these formulations were examined in detail. FTIR spectra showed that there was no evidence of herbicide inside the sepiolite tunnels. The SEM micrograph of the sepiolite-gel-based formulations showed the fibrous morphology typical of sepiolite and no separate particles of MTB were found. However, the chemical analysis by EDX confirmed the presence of S, N, and C, which were attributed to MTB, together with the fibers of sepiolite. Rheological characterization indicated that samples containing MTB develops a microstructure, which is irrespective of concentration above 1 mass % sepiolite. There was a good agreement between the microstructure characteristics and MTB release behavior.

Novel System for Reducing Leaching of the Herbicide Metribuzin Using Clay−Gel-Based Formulations

Metribuzin is an herbicide widely used for weed control that has been identified as a groundwater pollutant. It contaminates the environment even when it is used according to the manufacturer's instructions. To reduce herbicide leaching and increase weed control, new controlled release formulations were developed by entrapping metribuzin within a sepiolite-gel-based matrix using two clay/herbicide proportions (0.5/0.2 and 1/0.2) (loaded at 28.6 and 16.7% a.i.) as a gel (G28, G16) or as a powder after freeze-drying (LF28, LF16). The release of metribuzin from the control released formulations into water was retarded, when compared with commercial formulation (CF) except in the case of G28. The mobility of metribuzin from control released formulations into soil columns of sandy soil was greatly diminished in comparison with CF. Most of the metribuzin applied as control released formulations (G16, LF28 and LF16) was found at a depth of 0-8 cm depth. In contrast, residues from CF and G28 along the column were almost negligible. Bioassays from these control released formulations showed high efficacy at 0-12 cm depth. The use of these novel formulations could minimize the risk of groundwater contamination while maintaining weed control for a longer period.

Modifying sorbents in controlled release formulations to prevent herbicides pollution

The herbicides chloridazon and metribuzin, identified as groundwater pollutants, were incorporated in alginate-based granules to obtain controlled release properties. In this research the effect of incorporation of sorbents such as bentonite, anthracite and activated carbon in alginate basic formulation were not only studied on encapsulation efficiency but also on the release rate of herbicides which was studied using water release kinetic tests. In addition, sorption studies of herbicides with bentonite, anthracite and activated carbon were made. The kinetic experiments of chloridazon and metribuzin release in water have shown that the release rate is higher in metribuzin systems than in those prepared with chloridazon, which has lower water solubility. Besides, it can be deduced that the use of sorbents reduces the release rate of the chloridazon and metribuzin in comparison to the technical product and to the alginate formulation without sorbents. The highest decrease in release rate corresponds to the formulations prepared with activated carbon as a sorbent. The water uptake, permeability, and time taken for 50% of the active ingredient to be released into water, T 50, were calculated to compare the formulations. On the basis of a parameter of an empirical equation used to fit the herbicide release data, the release of chloridazon and metribuzin from the various formulations into water is controlled by a diffusion mechanism. Sorption capacity of the sorbents for chloridazon and metribuzin, ranging from 0.53 mg kg −1 for the metribuzin sorption on bentonite to 2.03 × 10 5 mg kg −1 for the sorption of chloridazon on the activated carbon, was the most important factor modulating the herbicide release.

FATE OF METRIBUZIN FROM ALGINATE CONTROLLED RELEASE FORMULATIONS IN A SHARKEY SOIL: 1. DESORPTION1

Desorption/release of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] from alginate-kaolin controlled release formulations (CRFs) with time, and its kinetic retention behavior in soil, were measured. All formulations were prepared to contain Na-alginate (1%), kaolin (10%), charcoal (0.2%), Tween 20 (0.5%), and metribuzin. Linseed oil was added at a rate of 0, 1, and 4% in an attempt to control metribuzin release further. A modified batch desorption technique was used to quantify the metribuzin release kinetics from the CRFs. For CRFs with 0% linseed oil, metribuzin release was completed (99%) after 6 days, with 80% of the total released during the first day of desorption. In contrast, CRFs with 1 and 4% linseed oil exhibited strong kinetics, with continued metribuzin release with time. After 59 days, total amounts of metribuzin released from CRFs containing 0, 1, and 4% linseed oil were 100, 68, and 12.4%, respectively. It is apparent that linseed oil acts to significantly decrease metribuzin release from the formulation, particularly at higher rates. This is related to a combination of effects, including formation of a polymeric coating by the linseed oil that would serve to decrease diffusion and chemical partitioning between the metribuzin and linseed oil. Batch results for a range of concentrations (up to 100 mg/L of metribuzin in solution) in a Sharkey clay soil (very-fine, montmorillonitic, nonacid, thermic, Vertic Haplaquept) indicated that adsorption kinetics was lacking. The metribuzin adsorption isotherm was linear and reached near equilibrium within 2 hours. This finding is consistent with metribuzin release from CRF with 0% linseed oil.

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.

Evaluation of Pine Kraft Lignins for Controlled Release of Alachlor and Metribuzin

The controlled release of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] from pine kraft lignin was studied using14C-labeled herbicides and3H-labeled lignin with soil thin-layer chromatography. NB-5203-58 series and PC940 series kraft lignins adsorbed and desorbed metribuzin as soil plates were developed with water. PC671, a formulated kraft lignin control release product, did not provide controlled release with metribuzin. NB-5203-58B and PC940C were the most effective of their respective series of kraft lignins. PC940C also provided controlled release of alachlor.