Hydrolytic degradation of azimsulfuron, a sulfonylurea herbicide

The chemical degradation of the herbicide azimsulfuron was investigated in aqueous solutions at different pH values. The hydrolysis rate, determined by HPLC analyses, was pH dependent and was much faster in acidic than in neutral or weakly basic conditions. The metabolites formed at different pH values were compared with standards when possible or isolated and identified using ESI-LC-MS/MS, (1)H NMR and (13)C NMR. The two main products of hydrolysis in mild acidic solution were identified as 2-amino-4,6-dimethoxy-pyrimidine and 2-methyl-4-(2-methyl-2H-tetrazol-5-yl)-2H-pyrazole-3-sulfonamide, both produced as a result of the sulfonylurea bridge cleavage. Under basic conditions, a new product, a substituted 2-pyrimidinamine, deriving from the contraction of the sulfonylurea bridge, was isolated and completely characterized for the first time.     

Light induced transformation of tribenuron-methyl

To study the photostability of sulfonylurea herbicide tribenuron-methyl (methyl 2-[[[[ N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl) methylamino] carbonyl]amino]sulfonyl]benzoate), in the field, model experiments with organic solvents were performed. Irradiation of tribenuron-methyl in methanol, isopropanol and cyclohexane yielded 4-methoxy-6-methyl-2-aminomethyl-1,3,5-triazine; methyl-2-(aminosulfonyl) benzoate; N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N-methyl urea; N-(2-carbomethoxy phenyl)-N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N'-methyl urea; 2-(aminosulfonyl) benzoic acid, N-methyl saccharin and saccharin in considerable amounts. The rate of degradation in different solvents followed first-order kinetics with a statistically significant correlation coefficient.     

Kinetics and mechanism of the hydrolysis of thiamethoxam

The degradation of thiamethoxam [(EZ)-3-(2-chloro-1,3-thiazol-5-yl-methyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene (nitro) amine] insecticide in buffers at different pH and temperature levels was investigated in laboratory studies. Acidic hydrolysis under conventional heating conditions and alkaline hydrolysis under both conventional heating and microwave conditions were carried out. Different hydrolysis products were found to form under alkaline and acidic conditions. Hydrolysis of thiamethoxam in acidic, neutral and alkaline buffers followed first-order reaction rate kinetics at pH 4, 7 and 9.2, respectively. Thiamethoxam readily hydrolyzed in alkaline buffer but was comparatively stable in neutral buffer solution. The main products formed under different conditions were characterized on the basis of infrared (IR), ¹H-NMR and Mass spectroscopy. The possible mechanisms for the formation of these hydrolysis products have also been proposed.     

Light-induced transformation of tribenuron-methyl on glass, soil, and plant surface

Photolysis of tribenuron-methyl (methyl 2-[[[[N-(4-methoxy-6-methyl-1,3,5triazin-2-yl)methylamino]carbonyl]amino]sulfonyl]benzoate), a sulfonylurea herbicide, was studied as thin film on glass surface, soil surface, and plant surface. A number of photoproducts such as 4-methoxy-6-methyl-2-aminomethyl-1,3,5-triazine; methyl-2-(aminosulfonyl) benzoate; N-(2-carbomethoxyphenyl)-N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N'-methylurea; N-(2-carbomethoxyphenyl sulfonyl)-N-methyl urea; o-benzoic sulfimide and 4-methoxy-6-methyl-2-amino-1,3,5-triazine were identified by comparison of their GC-MS with the authentic standards. The rate of degradation in all the cases followed first-order kinetics with a statistically significant correlation coefficient. Rate of photodegradation was greater on glass surface than on soil surface.     

Kinetics of hydrolysis and cyclization of ethyl 2-(aminosulfonyl)benzoate to saccharin

The cyclization of ethyl 2-(aminosulfonyl)benzoate (ASB) to give saccharin was investigated in aqueous solutions at pH between 5.2 and 9.5 and in the temperature range of 296.2-334.2 K. The initial concentration of the reactant was varied between 1.45 x 10(-5) and 3.86 x 10(-4) M. Ultraviolet spectroscopy was used to obtain the kinetic data. The reaction is acid catalyzed and follows pseudo-first-order kinetics. The experimental rate constant, k(obs), increases with temperature and pH. Its dependence on the temperature and pH is well described by: k(obs) = k1 [OH-] = [(2.52 +/- 0.9) x 10(16) exp(-20.2 +/- 1 kcalmol(-1)/RT) s(-1)][OH-] A mechanism is proposed and the half-life of ethyl ASB is calculated.     

Effect of wheat and rice straw biochars on pyrazosulfuron-ethyl sorption and persistence in a sandy loam soil

The objective of this research was to investigate the effect of wheat and rice biochars on pyrazosulfuron-ethyl sorption in a sandy loam soil. Pyrazosulfuron-ethyl was poorly sorbed in the soil (3.5–8.6%) but biochar amendment increased the herbicide adsorption, and the effect varied with the nature of the feedstock and pyrolysis temperature. Biochars prepared at 600°C were more effective in adsorbing pyrazosulfuron-ethyl than biochars prepared at 400°C. Rice biochars were better than wheat biochars, and higher herbicide adsorption was attributed to the biochar surface area/porosity. The Freundlich constant 1/n suggested nonlinear isotherms, and nonlinearlity increased with increase in the level of biochar amendment. Desorption results suggested sorption of pyrazosulfuron-ethyl was partially irreversible, and the irreversibility increased with increase in the level of biochar. Both sorption and desorption of pyrazosulfuron-ethyl correlated well with the content of biochars. The free energy change (ΔG) indicated that the pyrazosulfuron-ethyl sorption process was exothermic, spontaneous and physical in nature. Persistence studies indicated that biochar (0.5%) amendment did not have significant effect on herbicide degradation, and its half-life values in the control, 0.5% WBC600- and RBC600-amended rice planted soils were 7, 8.6, and 10.4 days, respectively.     

Degradation in soil and water and ecotoxicity of rimsulfuron and its metabolites.

The degradation and ecotoxicity of sulfonylurea herbicide rimsulfuron and its major metabolites were examined in batch samples of an alluvial sandy loam and in freshwater. An HPLC-DAD method was adapted to simultaneously identify and quantify rimsulfuron and its metabolites, which was successfully validated by GC-MS analysis. In aqueous solutions, pure rimsulfuron was rapidly hydrolyzed into metabolite 1 (N-(4,6-dimethoxypyrimidin-2-yl)-N-(3-(ethylsulfonyl)-2-pyridinylurea)), which itself was transformed into the more stable metabolite 2 (N-((3-(ethylsulfonyl)-2-pyridinyl)-4,6-dimethoxy-2-pyrimidineamine)), with half-life (t(1/2)) values of 2 and 2.5 days, respectively. Hydrolysis was instantaneous under alkaline conditions (pH = 10). In aqueous suspensions of the alluvial soil (pH = 8), formulated rimsulfuron had a half-life of 7 days, whereas that of metabolite 1 was similar to that in water (about 3.5 days). The degradation of the two major metabolites was also studied in soil suspensions with the pure compounds at concentrations ranging from 1 to 10 mg l(-1). The half-life of metabolite 1 ranged from 3.9 to 5 days, close to the previous values. Metabolite 2 was more persistent and its degradation is strongly dependent on the initial concentration (C0): half-life values ranged from 8.1 to 55 days at 2-10 mg l(-1), respectively. These values are higher than those determined from the kinetics of metabolite 1 transformation into metabolite 2 (t(1/2) = 8-19 days). The ecotoxicity of the three chemicals was evaluated through their effect on Daphnia magna and Vibrio fischeri (Microtox bioassay). No effect was observed on D. magna with 24 and 48 h acute toxicity tests. Similarly, no toxic effect was observed with the Microtox test for the three chemicals in the range of concentrations tested that included the field application dose. Thus, being of low persistence and lacking acute toxicity, these chemicals present a low environmental risk. However, chronic effects should be studied in order to confirm the safety of rimsulfuron and its major metabolites.     

Determination of acibenzolar-S-methyl and its acidic metabolite in soils by HPLC-diode array detection

A simple and accurate method for the analysis of acibenzolar-S-methyl (benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester; CGA 245 704; ASM) and its major conversion product, benzo[1,2,3]thiadiazole-7-carboxylic acid (CGA 210 007; BTC), in soils is presented. ASM extraction from soil samples was performed using acetonitrile and BTC was extracted with a mixture of potassium phosphate buffer (0.5 M, pH 3) and acetonitrile (70:30 %, v/v). Both extracts were directly analyzed in a high-performance liquid chromatography-diode array detection (HPLC-DAD) system. Pesticide separation was achieved on a C18 (4.6 mm × 150 mm, 5 μm) analytical column with a isocratic elution of acetonitrile:water 40:60 % (v/v) with 0.6 mL L?1 acetic acid at a flow rate of 1 mL min?1. Linear regression coefficients (r (2)) of the external calibration curves were always above 0.9997. The limits of detection (LOD) and quantification (LOQ) of the method were 0.005 and 0.02 mg kg?1 for ASM, and 0.01 and 0.05 mg kg?1 for BTC, respectively. Recoveries were investigated at six fortification levels and were in the range of 90-120 % for ASM and 74-96 % for BTC with relative standard deviations (RSDs) below 11 % in all cases. The method was also validated by analyzing freshly spiked soil samples with 2.7% organic matter content at 0.5 mg kg?1 level, with slightly lower recovery values only for ASM. Moreover, recoveries for intermediate aged residues of the analytes were similar to fresh residues. This method was also applied to determine ASM half-life (t(?) = 8.7 h) and the rate of the acidic metabolite formation.     

Leaching and degradation of ethametsulfuron-methyl in soil

Leaching and degradation of the herbicide ethametsulfuron-methyl[methyl 2-[(4-ethoxy-6-methylamino-1,3,5-triazine-2-yl)carbamoylsulfamoyl]benzoate] in three soils were investigated under laboratory conditions. Ethametsulfuron-methyl was mobile on soils when tested using non-aged and aged soil columns; this mobility agreed reasonably well with Freundlich soil isotherm constants. It was found that ethametsulfuron-methyl was more mobile in alkaline sandy Vertisol soil and neutral loamy Alfisol soil than in acidic clayey Red soil. Degradation of ethametsulfuron-methyl in soils was pH-dependent; calculated half-life (t(1/2)) values ranged from 13 to 67 days. Ethametsulfuron-methyl was more persistent in neutral or weakly basic than in acidic soil. Five soil metabolites were isolated and identified by LC/MS/MS analysis. The degradation pathways included the cleavage of the sulfonylurea bridge, N- and O-dealkylation, and triazine ring opening.     

Photochemical behavior of chlorsulfuronR in water and in adsorbed phase

The photochemistry of the herbicide chlorsulfuron^R (2-chloro-N-[[4-methoxy-6-methyl-1.3.5-triazinyl-2-amino]carbonyl]benzene sulfonamide) was investigated in methanol, distilled water, natural creek-water, on silica gel and on montmorillonit surfaces. The rate of degradation was determined in outdoor and indoor experiments simulating tropospheric conditions (λ>290 nm). Two major photoproducts were identified in all cases.     

Mild hydrolysis of 2-trifluoromethylphenol: kinetics, mechanism and environmental relevance

2-Trifluoromethylphenol was hydrolysed in a phosphate buffer at neutral pH. At mild temperatures ranging from 34 degrees C to 69 degrees C this compound liberates consecutively fluorine anions to form salicylic acid. This process is energetically driven by the hydration of the fluorine anions. No intermediates have been detected by HPLC and (19)F-NMR and this was confirmed by computer calculations which favor the first step in the whole reaction sequence being rate-limiting. Accordingly, the reaction energy of the first dehalogenation of the trifluoromethyl anion is 28.4 kcal mol(-1) higher than for the second dehalogenation. The pseudo-first-order kinetic was determined and from an Arrhenius diagram an activation energy of E(a)=25.1 kcal mol(-1) has been estimated. At 37 degrees C and a pH of 7.4 the half-life was 6.9 h. The rate of hydrolysis was favored at higher pH and it was not influenced by oxygen, sunlight or trace elements found in natural water. The latter was shown by incubations with lake water instead of distilled water.     

Persistence of herbicide fenoxaprop ethyl and its acid metabolite in soil and wheat crop under Indian tropical conditions

The persistence of fenoxaprop ethyl {Ethyl (RS)-2-[4-(6-chloro-1,3-benzoxazol-2-yloxy) phenoxy] propionate} herbicide and its active metabolite fenoxaprop acid was investigated in soil and wheat crop. Fenoxaprop acid was prepared by alkaline hydrolysis of fenoxaprop ethyl. A HPLC method was developed in which fenoxaprop ethyl herbicide and its acid metabolite showed sharp single peak at 6.44 and 2.61 min respectively. The sensitivity of the method for ester and acid was 2 and 1 ng respectively with limit of detection of 0.1 and 0.05 μg mL^?1. The recovery of fenoxaprop ethyl and fenoxaprop acid from soil, wheat straw and grain ranged between 73.8–80.2%. In a field experiment fenoxaprop ethyl (Puma super® 10 EC) when applied to wheat crop at the rate of 120 g and 240 g a.i. ha^-1 as post emergence spray, fenoxaprop ethyl converted to fenoxaprop acid. Residues of fenoxaprop ethyl and acid dissipated in soil with a half-life of 0.5 and 7.3 days, respectively. At harvest no detectable residues of fenoxaprop ethyl or acid were observed in soil, wheat grain and straw samples.     

Soil persistence of triasulfuron herbicide as affected by biotic and abiotic factors

Persistence of triasulfuron [3-(6-methoxy-4methyl-1,3,5-triazin-2-yl)-1-{2-(2-chloroethoxy)-phenylsulfonyl}-urea] in soil was studied under wheat crop and laboratory conditions. Field experiment was conducted in the farms of Agronomy Division, Indian Agricultural Research Institute (IARI), New Delhi. Randomized block design (RBD) was followed with four replicates and two rates of treatments along with control and weedy check. Triasulfuron was applied as post-emergent application to wheat crop at two rates of application viz., 15 g and 20 g a.i. ha-1. Soil samples at 0 (3 h), 1, 3, 5, 7, 10, 15, 20, and 30-day intervals after application were drawn, extracted, cleaned up, and analyzed for herbicide residues by high performance liquid chromatography (HPLC) using C18 column and methanol: water (8:2) as mobile phase at 242 nm wave length. Effect of microbial activity and soil pH was studied under laboratory conditions. Dissipation of triasulfuron followed a first-order-rate kinetics. Residues dissipated from field soil with half-life of 5.8 and 5.9 days at two rates of application. The study indicated biphasic degradation with faster rate initially (t1/2 = 3.7 days), followed by a slower dissipation rate at the end (t1/2 = 9.4 days). Similar trend was observed with non-sterile soil in laboratory with a longer half-life. Acidic pH and microbial activity contributed toward the degradation of triasulfuron in soil.     

Heterogeneous photocatalytic degradation of picloram, dicamba, and floumeturon in aqueous suspensions of titanium dioxide

Heterogeneous photocatalytic degradation of three-selected herbicide derivatives: (1) picloram (4-Amino-3,5,6-trichloropyridine-2-carboxylic acid, (2) dicamba (2-Methoxy-3,6-dichlorobenzoic acid, and (3) floumeturon (N,N-Dimethyl-N-[3-(trifluoromethyl)phenyl]-urea) has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic technique and decrease in total organic carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation of the herbicide was studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO2, and in the presence of electron acceptors such as hydrogen peroxide (H2O2), potassium bromate (KBrO3), and ammonium persulphate (NH4)2S2O8 besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts in the case of dicamba (2) and floumeturon (3), whereas Hombikat UV100 was found to be better for the degradation of picloram (1). The herbicide picloram (1) was found to degrade faster as compared to dicamba (2) and floumeturon (3). The degradation products were analyzed by gas chromatography-mass spectrometry (GC/MS) technique, and plausible mechanisms for the formation of products have been proposed.     

Fate and degradation of triasulfuron in soil and water under laboratory conditions

The behavior and fate of triasulfuron (TRS) in water and soil systems were examined in laboratory studies. The degradation of TRS in both buffer solution and soil was highly pH-sensitive. The rate of degradation could be described with a pseudo first-order kinetic and was much faster at pH 4 than at pH 7 and 9. Aqueous hydrolysis occurred by cleavage of the sulfonylurea bridge to form 2-(2-chloroethoxy) benzenesulfonamide (CBSA) and [(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] (AMMT). AMMT was unstable in aqueous solutions in any pH condition but it degraded more quickly at pH 4 and 9. CBSA did not degrade in aqueous solutions or in enriched cultures but it underwent a quick degradation in the soil. The rates of TRS degradation in sterile and non-sterile soils were similar, suggesting that microorganisms played a minimal role in the breakdown process. This hypothesis is supported by the results of studies on the degradation of TRS by enriched cultures during which the molecule underwent a prevalently chemical degradation.     

Fate and degradation of triasulfuron in soil and water under laboratory conditions

The behavior and fate of triasulfuron (TRS) in water and soil systems were examined in laboratory studies. The degradation of TRS in both buffer solution and soil was highly pH-sensitive. The rate of degradation could be described with a pseudo first-order kinetic and was much faster at pH 4 than at pH 7 and 9. Aqueous hydrolysis occurred by cleavage of the sulfonylurea bridge to form 2-(2-chloroethoxy) benzenesulfonamide (CBSA) and [(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] (AMMT). AMMT was unstable in aqueous solutions in any pH condition but it degraded more quickly at pH 4 and 9. CBSA did not degrade in aqueous solutions or in enriched cultures but it underwent a quick degradation in the soil. The rates of TRS degradation in sterile and non-sterile soils were similar, suggesting that microorganisms played a minimal role in the breakdown process. This hypothesis is supported by the results of studies on the degradation of TRS by enriched cultures during which the molecule underwent a prevalently chemical degradation.     

Fate of isoxaben in a containerized plant rhizosphere system

Commercial production of ornamental plants is an important industry in the United States and involves a complex technology that includes the use of herbicides. Isoxaben[N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide] is a pre-emergence herbicide used for controlling weeds in many areas including containerized ornamental plants. Degradation was studied in potting mix (80% bark, 20% sand) with three different regimes (sterile, bulk and rhizosphere). The rhizosphere regime contained Switch Grass (Panicum virgatum), and plants were allowed to grow for 14 days before adding isoxaben (10 microg/g potting mix). Isoxaben was degraded to 0.5 microg/g in 60 days giving a half-life of 7 days. Two degradation products were detected: 3-nitrophthalic acid in the rhizosphere and bulk regimes and 4-methoxyphenol in the sterile regime. Microbial population shifts were determined by fatty acid methyl ester profile analysis and were influenced by the introduction of a plant (rhizosphere regime) and by isoxaben addition.     

Soil Persistence of Triasulfuron Herbicide as Affected by Biotic and Abiotic Factors

Persistence of triasulfuron [3-(6-methoxy-4methyl-1,3,5-triazin-2-yl)-1-{2-(2-chloroethoxy)-phenylsulfonyl}-urea] in soil was studied under wheat crop and laboratory conditions. Field experiment was conducted in the farms of Agronomy Division, Indian Agricultural Research Institute (IARI), New Delhi. Randomized block design (RBD) was followed with four replicates and two rates of treatments along with control and weedy check. Triasulfuron was applied as post-emergent application to wheat crop at two rates of application viz., 15 g and 20 g a.i. ha^?1. Soil samples at 0 (3 h), 1, 3, 5, 7, 10, 15, 20, and 30-day intervals after application were drawn, extracted, cleaned up, and analyzed for herbicide residues by high performance liquid chromatography (HPLC) using C₁₈ column and methanol: water (8:2) as mobile phase at 242 nm wave length. Effect of microbial activity and soil pH was studied under laboratory conditions. Dissipation of triasulfuron followed a first-order-rate kinetics. Residues dissipated from field soil with half-life of 5.8 and 5.9 days at two rates of application. The study indicated biphasic degradation with faster rate initially (t _1/2 = 3.7 days), followed by a slower dissipation rate at the end (t _1/2 = 9.4 days). Similar trend was observed with non-sterile soil in laboratory with a longer half-life. Acidic pH and microbial activity contributed toward the degradation of triasulfuron in soil.     

N-Methyl-beta-carboline-3-carboxamide (FG 7142): An anxiogenic agent in cigarette smoke condensate and its mechanism of formation

beta-Carboline-3-carboxylic acid methylamide (FG 7142), an anxiogenic agent has been found in cigarette smoke condensate, but not in the cigarette itself. When a cigarette, except its filter portion, was immersed in 20 ml of potassium phosphate buffer, pH 7.4, then heated at 60 degrees C for 2 days with or without presence of methylamine, FG 7142 was detected only in the mixture containing methylamine. Furthermore, when the mixtures of beta-carboline derivatives and various amounts of methylamine hydrochloride were heated at 60 degrees C for 5 days, FG 7142 was formed only in the mixtures containing methylamine and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-caroxylic acid (MTCA) or 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (TCCA). FG 7142 was also produced in the mixture of glucose, l-tryptophan and methylamine when heated at 200 degrees C in a dry condition. These observations suggest that FG 7142 is formed through the smoking process and that methylamine in cigarette smoke may play an important role in the formation of FG 7142.     

Acid generation upon thermal concentration of natural water: The critical water content and the effects of ionic composition

Thermal evaporation of a variety of simulated pore waters from the region of Yucca Mountain, Nevada, produced acidic liquids and gases during the final stages of evaporation. Several simulated pore waters were prepared and then thermally distilled in order to collect and analyze fractions of the evolved vapor. In some cases, distillates collected towards the end of the distillation were highly acidic; in other cases the pH of the distillate remained comparatively unchanged during the course of the distillation. The results suggest that the pH values of the later fractions are determined by the initial composition of the water. Acid production stems from the hydrolysis of magnesium ions, especially at near dryness. Near the end of the distillation, magnesium nitrate and magnesium chloride begin to lose water of hydration, greatly accelerating their thermal decomposition to form acid. Acid formation is promoted further when precipitated calcium carbonate is removed. Specifically, calcium chloride-rich pore waters containing moderate (10–20 ppm) levels of magnesium and nitrate and low levels of bicarbonate produced mixtures of nitric and hydrochloric acid, resulting in a precipitous drop in pH to values of 1 or lower after about 95% of the original volume was distilled. Waters with either low or moderate magnesium content coupled with high levels of bicarbonate produced slightly basic fractions (pH 7–9). If calcium was present in excess of bicarbonate, waters containing moderate levels of magnesium produced acid even in the presence of bicarbonate, due to the precipitation of calcium carbonate. Other salts such as halite and anhydrite promote the segregation of acidic vapors from residual basic solids. The concomitant release of wet acid gas has implications for the integrity of the alloys under consideration for containers at the Yucca Mountain nuclear waste repository. Condensed acid gases at very low pH, especially mixtures of nitric and hydrochloric acid, are capable of corroding even alloys, such as nickel-based Alloy 22, which are considered to be corrosion-resistant under milder conditions.