Ethylcellulose formulations for controlled release of the herbicide alachlor in a sandy soil

The development of controlled-release formulations of alachlor to diminish its leaching in sandy soils, avoiding groundwater contamination and maintaining its efficacy, was studied. For this purpose, ethylcellulose (EC) microencapsulated formulations (MEFs) of alachlor were prepared under different conditions and applied to soil columns to study their mobility. The results show that in all cases the release into water of alachlor from MEFs was retarded when compared with commercial formulation. Total leaching losses in soil columns were reduced to 59% from 98%. The mobility of alachlor from EC microspheres into soil columns has been greatly diminished in comparison with its current commercial formulation (CF), above all with increasing EC/herbicide ratios. Distribution of alachlor applied as MEFs at different depths in the soil was higher in the soil surface (66.3-81.3% of herbicide applied at the first 12 cm). In contrast, the residues from CF along the complete soil column were only 20.4%. From the results of bioassays, MEFs showed a higher efficacy than CF at 30 days after the treatment. The use of ME formulations could provide an advantage in minimizing the risk of groundwater contamination by alachlor and reducing the application rates, as a result of maintaining the desired concentration of the herbicide in the top soil layer, obtaining longer periods of weed control.     

Effect of soil type on adsorption-desorption, mobility, and activity of the herbicide norflurazon

Adsorption-desorption studies of norflurazon on 17 soils of very different characteristics have been performed using a batch equilibration method and correlated to its mobility, activity, and persistence in soils. The influence of different soil properties and components on norflurazon adsorption was determined. The significant variables were organic matter (OM) content and iron and aluminum oxides, which accounted for 85 and 11% of the variability, respectively. Norflurazon desorption from soils was hysteretic in all cases, being more irreversible at the lowest herbicide concentrations adsorbed. The percentage of norflurazon eluted from columns of selected soils reached almost 100% in soils with sand content >80% and OM <1%, but in the soil which gave the highest sorption, herbicide residues were not detected at depths >16 cm. The herbicidal activity of norflurazon was followed by measuring its bleaching effect on soybean plants, and the herbicide concentration required to give 50% chlorophyll inhibition (CI(50)) was calculated. CI(50) was achieved on a sandy soil with 0.08 mg x kg(-)(1), whereas 1.98 mg x kg(-)(1) was necessary for the soil that presented maximum norflurazon adsorption.     

Preparation and characterization of inclusion complex of norflurazon and beta-cyclodextrin to improve herbicide formulations

The formulation of inclusion complexes of the herbicide norflurazon as guest and beta-cyclodextrin (beta-CD) as host has been studied as a first step in the use of cyclodextrins to obtain improved formulations of this herbicide. The interaction of norflurazon with beta-CD produced the formation of an inclusion complex in solution and in solid state. The inclusion of norflurazon in beta-CD in solution was studied by phase solubility, and an apparent stability constant of 360 M(-)(1), a 1:1 stoichiometric ratio for the complex, and up to 5-fold increase in norflurazon solubility were determined. Three processing methods (kneading, spray drying and vacuum evaporation) were used to prepare norflurazon-beta-CD solid inclusion complexes. X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy techniques were used to study the solid complexes. From the different solid systems, an increase of norflurazon aqueous dissolution rate was obtained in comparison to the uncomplexed herbicide. This finding is a first step to obtain controlled release and/or protective formulations of norflurazon, which allow a more rational application of norflurazon, diminishing the use of organic solvents and increasing its efficacy.     

Controlled release of the herbicide norflurazon into water from ethylcellulose formulations

The herbicide norflurazon was encapsulated in ethylcellulose (EC(40)) microspheres by the solvent evaporation technique to obtain controlled release formulations. The kinetics of release of the active ingredient into the aqueous solution from different preparations was determined. It was found that the percentage release of the incorporated herbicide was a function of the composition and formation conditions of the formulations (amount of emulsifying agent, EC(40)/herbicide ratio, stirring speed, and percentage of pore-forming agent). The percentage of the herbicide release was related to the properties of the different microspheres obtained, such as particle size distribution, herbicide loading, or surface morphology. The release percentage depended inversely on the particle size of the microspheres and directly on the content of active ingredient and emulsifying and pore-forming agents. An empirical equation was used to fit the herbicide release data, indicating that the release of norflurazon from the various formulations is controlled by a diffusion mechanism. The time taken for 50% of the active ingredient to be released into water (T(50)) was calculated, showing a wide variation among the different preparations (0.95-16.4 days).     

Controlled release of diuron from an alginate-bentonite formulation: water release kinetics and soil mobility study

The herbicide diuron was incorporated in alginate-based granules to obtain controlled release (CR) properties. The standard formulation (alginate-herbicide-water) was modified by the addition of different sorbents. The effect on diuron release rate caused by incorporation of natural and acid-treated bentonites in alginate formulation was studied by immersion of the granules in water under static conditions. The release of diuron was diffusion-controlled. The time taken for 50% release of active ingredient to be released into water, T(50), was calculated for the comparison of formulations. The addition of bentonite to the alginate-based formulation produced the higher T(50) values, indicating slower release of the diuron. The mobility of technical and formulated diuron was compared by using soil columns. The use of alginate-based CR formulations containing bentonite produced a less vertical distribution of the active ingredient as compared to the technical product and commercial formulation. Sorption capacities of the various soil constituents for diuron were also determined using batch experiments.     

Slow-release formulations of sulfometuron incorporated in micelles adsorbed on montmorillonite

The design and tests of slow-release formulations of sulfometuron (SFM), an anionic sulfonylurea herbicide, are described. The formulations are based on incorporation of the herbicide in octadecyltrimethylammonium (ODTMA) micelles, which adsorb on a clay mineral, montmorillonite. An optimization of herbicide/micelle clay ratios yielded high adsorption of SFM (95%), and at a 1% (w/w) water suspension only 0.5% of the adsorbed SFM was released at times varying from hours to 9 days. An analytical test in Seville soil showed that under excessive irrigation (400 mm) 100% of the commercial formulation leached, whereas the micelle-clay formulations showed only 50-65% elution. A plant bioassay in Rehovot soil showed that the commercial dispersible granule formulation (Oust, 75% ai sulfometuron methyl) yielded only 23% root elongation inhibition at the top 5 cm of the soil, whereas complete inhibition was achieved with the micelle-clay formulation. The detected concentration of SFM for the micelle-clay formulation at a depth of 15-20 cm was half of that detected for the commercial one, indicating a reduction in leaching when applying the micelle-clay formulation. A 10-fold reduction in the applied dose of SFM in the micelle-clay formulations resulted in good herbicidal activity of 60-87% inhibition. These characteristics make the new formulation promising from the environmental and economic points of view.     

Organo-clay formulations of the hydrophobic herbicide norflurazon yield reduced leaching

The study aimed to reduce leaching of the hydrophobic herbicide norflurazon (4-chloro-5-methylamino-2-(alpha,alpha, alpha)-trifluoro-m-tolylpyridazin-3-(2H)-one) by adsorbing it on clays or organo-clays. The surface of the clay mineral montmorillonite was modified from hydrophilic to hydrophobic by preadsorbing it with organic cations, of which thioflavin-T (TFT) at a loading corresponding to (5)/(8) of the cation-exchange capacity of the clay mineral yielded the highest affinity of adsorption of norflurazon. Pillared clay (PC) used without organic cations exhibited enhanced affinity for norflurazon adsorption, much higher than that of montmorillonite or sepiolite. Fourier transform infrared (FTIR) results showed interactions between aromatic moieties of preadsorbed TFT and the herbicide. Stronger interaction of the herbicide with a clay mineral or organo-clay corresponded to its slower release. Formulations prepared on the basis of montmorillonite-TFT and PC were more effective in reducing herbicide leaching in soil columns in comparison to the commercial formulation, whereas the herbicidal efficiencies were comparable.     

Sulfentrazone adsorbed on micelle-montmorillonite complexes for slow release in soil

Interactions of the herbicide sulfentrazone with the cationic surfactants octadecyltrimethylammonium (ODTMA), hexadecyltrimethylammonium (HDTMA), and benzyldimethylhexadecylammonium (BDMHDA) have been studied for the design of slow-release formulations based on sulfentrazone adsorbed on a micelle-montmorillonite complex. Adsorbed amounts of sulfentrazone on ODTMA- and BDMHDA-montmorillonite complexes were 99.2-99.8% of that added, and desorption of herbicide in water during 24 h was low. After 10 washings in funnels with soil, only 2.6% of herbicide was released from ODTMA-montmorillonite formulations versus 100% release from the commercial formulation. The strong binding of sulfentrazone to micelles was confirmed by pH and spectroscopic measurements and was explained by the formation of ionic pairs between cationic surfactant and anionic herbicide. The ODTMA-clay and commercial formulations of sulfentrazone yield almost complete and 40% growth inhibition of green foxtail, respectively, at 700 g of active ingredient/ha. Hence, the slow release from micelle-clay formulations of sulfentrazone promotes its biological activity and reduces environmental contamination.     

Inorganic and organic clays as carriers for controlled release of the herbicide hexazinone

The risk of ground water contamination resulting from rapid leaching of highly soluble pesticides can be minimized through the application of the pesticide adsorbed on a matrix or carrier, which limits the amount of pesticide immediately available for undesirable losses. The use of natural materials for this purpose is of special interest in terms of economy and sustainability. In this work the adsorption of the herbicide hexazinone by two montmorillonites saturated with various inorganic and organic cations was determined and the ability of the two clays displaying the highest adsorption capacities [Fe(3+)-saturated Wyoming montmorillonite, (Fe-SW) and hexadecyltrimethylammonium-saturated Arizona montmorillonite (HDTMA-SA)] to act as carriers for slow release of hexazinone and to reduce herbicide leaching losses was evaluated. Hexazinone formulations based on Fe-SW and HDTMA-SA displayed slow release properties in water and soil/water suspensions, reduced herbicide leaching in soil columns, and maintained herbicidal activity, as compared with the currently available commercial hexazinone formulation (wettable powder). Loosely bound hexazinone-HDTMASA formulations, which led to the slowest breakthrough of hexazinone in soil columns along with the greatest amounts of herbicide released from the clay particles, displayed the most interesting characteristics for their use as slow release formulations and to prevent ground water contamination.     

Development of controlled release formulations of carbofuran and evaluation of their efficacy against Meloidogyne incognita

Controlled release (CR) formulations of the insecti-nematicide carbofuran have been prepared using commercially available rosin, sodium carboxymethylcellulose and sodium carboxymethylcellulose with clay (bentonite, kaolinite, and Fuller's earth). The kinetics of carbofuran release in soil from the different formulations were studied in comparison with that of the commercially available granules (3G). Release from the commercial formulation was faster than with the new CR formulations. Addition of clay in the biodegradable polymer matrix reduced the rate of release. The diffusion exponent (n value) of carbofuran in soil ranged from 0.462 to 0.740 in the tested formulations. The half-release (t1/2) values ranged between 4.79 and 25.11 days, and the period of optimum availability (POA) of carbofuran ranged from 15.10 to 43.97 days. The mean EC50 of the commercial formulation against Meloidogyne incognita was quite high as compared to those of CR formulations. The effective duration (te) of carbofuran from the CR and commercial formulations was predicted by fitting the mean EC50 values of test formulations in the model (M(infinity) - Me)/M(infinity) = Kdte. It was 0.7 day in commercial 3G in comparison with 17.8 days for CMC-bentonite. The bioassay studies revealed that with the rosin-yellow polymer, the dose of carbofuran could be reduced to half of its recommended dose for nematode control. Overall, a comparison of CR formulations with the commercial one showed an earlier degradation of carbofuran in the latter and relatively prolonged activity in the former.     

Sulfosulfuron incorporated in micelles adsorbed on montmorillonite for slow release formulations

Slow release formulations of the anionic herbicide sulfosulfuron (SFS) were prepared by incorporating it in micelles of an organic cation octadecyltrimethylammonium, which adsorb on the clay-mineral montmorillonite. The fraction of SFS adsorbed on the micelle-clay complex reached 98%, whereas for monomer-clay complexes, its adsorption was insignificant. Fluorescence studies showed surface contact between the micelles and the clay surface. The rate of SFS release from the micelle-clay formulations in aqueous suspensions was slow (<1%, 72 h). Spraying SFS formulations on a thin soil layer in a funnel, followed by irrigations (50 mm), resulted in complete elution of SFS from the commercial formulation (dispersible granular) versus 4% from the micelle-clay formulation. A plant bioassay in Rehovot soil showed that these respective formulations yielded 23 and 65% of shoot growth inhibition of foxtail. Consequently, the slow release micelle-clay formulations of SFS yield significantly reduced leaching and enhanced biological activity, thus providing environmental and agricultural advantages.     

Photostabilization of the herbicide norflurazon by using organoclays

Photostable formulations of the herbicide norflurazon [4-chloro-5-(methylamino)-2-(alpha,alpha, alpha-trifluoro-m-tolyl)pyridazin-3-(2H)-one] were achieved by adsorbing it on pillared clay or on montmorillonite preadsorbed with the organic cation thioflavin T (TFT). Diffuse reflectance Fourier transform infrared spectra showed the existence of strong interactions between the aromatic moieties of preadsorbed TFT and the herbicide, particularly after irradiation. The photostabilization of norflurazon obtained with TFT-clay was mainly due to energy transfer from the herbicide to the organic cation via pi-pi interactions. An additional mechanism is the lower production of radicals from the clay when the clay mineral surface is covered with the organic cation. These radicals are responsible for the enhanced photodegradation observed when norflurazon was irradiated in the presence of untreated montmorillonite.     

Effect of the herbicide glyphosate on nitrification,denitrification, and acetylene reduction in soil

The effect of glyphosate on N₂ fixation, denitrification, and nitrification in an agricultural soil was investigated. Effects of the pure herbicide and commercial formulation, Roundup+ (Monsanto Company), were compared in soil under aerobic and anaerobic conditions. Anaerobic C₂H₂ reduction was inhibited by high herbicide levels. Denitrification in non-amended soil was either unaffected (N₂O reduction) or stimulated (NO _inf3 ^sup? reduction); in glucose-amended soil, N₂O reduction was inhibited and NO₃-reduction unaffected by both glyphosate and Roundup. Roundup caused greater stimulation of N₂O reduction than pure glyphosate; no other significant formulation effects were observed. Nitrification was inhibited by the two formulations. Ammonium oxidation were both influenced. Pure glyphosate was more inhibitory than Roundup. No toxicity to any of these activities should be seen at recommended field application rates of the herbicide.     

Bioefficacy and Determination of Terminal Residues of a Herbicide Anilofos in Field Soil and Plants Following an Application to the Transplanted Rice Crop

Although herbicides provide effective weed control, some herbicides may pose serious health and environmental threats. Thus the bioefficacy and the persistence of three formulations of a herbicide, anilofos [GR (granules), W/O (water in oil emulsion), and EC (emulsifier concentration)], at 300, 450, and 600 g ha^?1 as pre-emergent applications were evaluated in transplanted rice (Oryza sativa L.). All of the formulations enhanced the rice grain yield by 50% over weedy check and the grain yield was greatest in the 30% EC treatment applied at a 450 g ha^?1 rate. Phytotoxic symptoms of anilofos were not observed with any of these formulations on the transplanted rice. Terminal residues of anilofos in the soil and mature rice plants were below the maximum residues limit (MRL, 0.05 mg/kg) in the soil, grains, and straw treated with the various formulations of anilofos. Study showed fast degradation of anilofos in the soil and rice plants.     

Chlorpyrifos decline curves and residue levels from different commercial formulations applied to oranges

Residue levels and degradation rates of chlorpyrifos in orange fruits, orange leaves, and soil were investigated by using three different formulation types, that is, emulsifiable concentrate (EC), wettable granules (WG), and microencapsulates (ME). The pesticide degradation was studied for a period 131 days in orange fruits and for 161 days in orange leaves and soil. The experimental data were used to establish a mathematical model for the decline curves of chlorpyrifos residues as a function of time and to determine the relevant parameters describing such a process. Field trials showed a different degradation rate for EC and WG formulations as compared to ME formulation. For the first two formulations, the dissipation of chlorpyrifos in orange fruits was fast during the first phase and became much slower during the later period. Residue levels of chlorpyrifos from ME remained almost constant for approximately 65 days and then began to decrease. A similar behavior was observed for the three chlorpyrifos formulations on orange leaves and soil. Although microencapsulation of pesticides leads to improved handling safety, additional risks for the consumers, the agriculture workers, and the environment should be taken into account due to prolonged persistence of high residue levels in fruits as well as in leaves and soil.     

Organo-clay formulation of acetochlor for reduced movement in soil.

This study aimed to design ecologically acceptable formulations of acetochlor by adsorbing it on montmorillonite exchanged by a small organic cation, phenyltrimethylammonium (PTMA). Adsorption of acetochlor on the clay mineral exchanged with different organic cations and its release from these complexes were determined by GC and modeled by Langmuir equation. Interactions between acetochlor molecules and the exchanged organic cation on the clay surface were studied by Fourier transform infrared spectroscopy. Leaching of acetochlor in soil was determined by a bioassay using a column technique and Setaria viridis as a test plant. The adsorbed amounts of acetochlor on montmorillonite exchanged by PTMA at a loading of 0.5 mmol/g of clay were higher than at a loading up to the cation-exchange capacity, i.e., 0.8 mmol/g, and were higher than obtained by using a clay mineral exchanged by other organic cations. Preloading montmorillonite by PTMA at 0.5 mmol/g yielded maximal shifts of the infrared peaks of the herbicide. The above formulation of acetochlor yielded slow release in water and showed improved weed control in field and greenhouse experiments in comparison with the commercial formulation. The PTMA-clay formulation of acetochlor maintained herbicidal activity in the topsoil and yielded the most significant reduction in herbicide leaching and persistence under field conditions. The application of this formulation can minimize the risk to groundwater and can reduce the applied rates.     

Environmentally friendly formulations of alachlor and atrazine: preparation, characterization, and reduced leaching

Atrazine and alachlor formulations were designed by encapsulating the herbicide molecules into phosphatidylcholine (PC) vesicles, which subsequently were adsorbed on montmorillonite. PC and montmorillonite are classified as substances of minimal toxicological risk by the U.S. EPA. PC enhanced alachlor and atrazine solubilities by 15- and 18-fold, respectively. A 6 mM PC:5 g/L clay ratio was found as optimal for PC adsorption on the clay. Active ingredient contents of the PC-clay formulations ranged up to 8.6% for atrazine and 39.5% for alachlor. Infrared spectroscopy showed hydrophobic interactions of herbicide molecules with the alkyl chains of PC, in addition to hydrophilic interactions with the PC headgroup. Release experiments in a sandy soil showed a slower rate from the PC-clay formulations than the commercial ones. Soil column experiments under moderate irrigation and bioactivity experiments indicate that a reduction in the recommended dose of alachlor and atrazine can be accomplished by using PC-clay formulations.     

Simultaneous fluometuron and norflurazon analysis in soil extracts and leachates

Abstract

Rapid, methanol‐extraction techniques for fluometuron (N, N‐dimethyl‐N'‐[3‐(trifluoromethyl) phenyl] urea) and norflurazon (4‐chloro‐5‐(methylamino)‐2‐(3‐(trifluoromethyl)phenyl)‐3(2(H)‐pyridazinone) from fortified soils have been reported to attain >90% recoveries. Analytical methods involving chromatographic separation coupled with fluorescence detection have also been described. The objectives of this study were to describe an analytical method for the simultaneous detection of fluometuron and norflurazon using ultraviolet spectro‐scopy in soil leachates and extracts and to examine the influence of residence time on herbicide recovery from fortified soil. The analytical method requires a gradient HPLC system, a reverse‐phase C‐18 column, and ultraviolet spectroscopy at a wavelength of 240 nm. The method is characterized by high reproducibility (spike recovery and diluted sample results are generally within 10% of the expected herbicide concentrations), low limits of detection (less than 1 (μg/L in soil leachates and 20 μg/L in soil extracts, depending on organic carbon content), and an applicable concentration range of more than two orders of magnitude. The recovery of fluometuron and norflurazon from fortified soils was significantly influenced by equilibration time, loading rate, and soil type (assuming zero chemical degradation). Most significantly, as herbicide contact time with the soil increased, recovery decreased. Thus, herbicide recoveries determined in the laboratory may not provide a true measure of herbicide recoveries from field soils.     

Volatilization of alachlor from polymeric formulations

Pesticides may be dispersed throughout the environment by several means, including groundwater contamination, surface water contamination, and volatilization with subsequent atmospheric transport and deposition. In earlier research primarily directed at reducing the potential for groundwater contamination, a number of herbicides were microencapsulated within several different polymers. These polymeric formulations were evaluated for efficacy in the greenhouse. In the studies described in this paper, three polymeric alachlor formulations that were the most effective in the greenhouse were evaluated in laboratory volatility studies using pure alachlor and a commercial formulation (Lasso 4EC) for comparison purposes. In a given experiment, technical alachlor, Lasso 4EC, and two polymeric formulations were applied to soil and evaluated in a contained system under 53% humidity with a fixed flow rate. Evolved alachlor was collected in ethylene glycol, recovered with C18 solid phase extraction cartridges, and analyzed by reverse-phase high-performance thin-layer chromatography with densitometry. Duration of the studies ranged from 32 to 39 days. In studies in which all formulations were uniformly incorporated in the soil, total alachlor volatilization from the polymeric microcapsules was consistently lower than that from the alachlor and Lasso 4EC formulations. In studies in which the polymeric formulations were sprinkled on the surface of the soil, microcapsules prepared with the polymer cellulose acetate butyrate released the smallest quantity of volatilized alachlor.     

Impacts of long-term application of buctril super (bromoxynil) herbicide on microbial population,enzymes activity,nitrate nitrogen,Olsen-P and total organic carbon in soil

Long-term impact of buctril super (bromoxynil) herbicide in the wheat fields on soil microbial population, nitrate-N, Olsen-P, total organic carbon (TOC) and enzyme activities was evaluated in 18 sites in Pakistan. Nine sites were randomly selected from those places where bromoxynil herbicide had been used for the last 10 years designated as soil ‘X’ and other nine where no herbicide was used in that period designated as soil ‘Y’. Very importantly, it was found that long-term application of this herbicide in wheat fields reduced the actinomycetes and fungi population up to 19.7 and 14.3%, respectively, urease and dehydrogenase activity by 17.5 and 28.2%, respectively, and reduced nitrate-N, Olsen-P and TOC up to 55, 17 and 28.57%, respectively. Presence of high clay and organic matter contents enhanced the detrimental effect of herbicide by prolonging its persistence as compared to light-textured soils with low organic matter. As in Pakistan this herbicide is being used most frequently in wheat fields, data are scarce on the long-term effect of this herbicide on soil microbial activities and soil health. These findings could give new insights about the use of alternate herbicide in wheat fields, particularly in clay-textured and high organic matter contained soils for maintaining soil health.