首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The reactions of phorate and terbufos with bisulfide (HS-), polysulfide (Sn2-), thiosulfate (S2O32-), and thiophenolate (PhS-) were examined in well-defined aqueous solution under anoxic conditions to investigate their role in the degradations of phorate and terbufos. Reactions were monitored at various concentrations of reduced sulfur species to obtain the second-order rate constants. The reactivity of the reduced sulfur species decreased in the order Sn2- > PhS- > HS- > S2O32-. Hydrolysis products, formaldehyde and diethyl disulfide/di-tert-butyl disulfide, indicated that OH-/H2O attacked the carbon atom between the two sulfur atoms, the so-called thioacetal carbon, which is very reactive due to the presence of the two neighboring sulfur atoms. The reaction of phorate and terbufos with PhS- was investigated to study the transformation products in the reactions with reduced sulfur species. The transformation products demonstrated that the observed increase in rate constants in the reaction with reduced sulfur species compared to hydrolysis could result from the nucleophilic attack of reduced sulfur species at the alpha-carbon of the ethoxy group and at the thioacetal carbon atom. The temperature dependence of measured second-order rate constants of the reaction of phorate and terbufos with HS- over 25-50 degrees C was investigated to explore activation parameters, which are not significantly different for phorate and terbufos. All of the observations may imply similar pathways in the degradation of phorate and terbufos in the presence of reduced sulfur species. Slightly higher hydrolysis rates of terbufos and second-order reaction rate constants for the reactions with sulfur species of terbufos compared with those for phorate are observed, which could be attributed to the slightly different substituents.  相似文献   

2.
Alcoholysis (methanol or ethanol) and hydrolysis (pH ranging from 4 to 11) of the herbicide nicosulfuron at 30 degrees C principally involves the breakdown of the urea part of the molecule. A high yield of the corresponding carbamate was obtained along with aminopyrimidine during alcoholysis. Hydrolysis led to both aminopyrimidine and pyridylsulfonamide. The latter compound may be easily cyclized (pH > or = 7). First-order kinetics describe the rates of alcoholysis and hydrolysis well. The rate constants (0.44 days(-1) for methanolysis) decreased from 0.50 to 0.002 days(-1) as pH increased from 4 to 8, then remained stable under alkaline conditions. In acidic or neutral solution, the hydrolysis path appeared prevalent (> or =70%), whereas in an alkaline medium it decreased when pH increased. The chemical degradation of nicosulfuron on various dry minerals (calcium bentonite, kaolinite, silica gel, H(+) bentonite, montmorillonite K10, and alumina) was investigated at 30 degrees C. The best conditions for the degradation are obtained on acidic minerals after herbicide deposition using the liquid method. Under these conditions an acceptable correlation with pseudo-first-order kinetics was observed, and the major degradation path is similar to that proposed for chemical hydrolysis. Conversely, alumina seemed to favor other unknown degradation processes. The hydrolysis paths of nicosulfuron and rimsulfuron appeared to be different.  相似文献   

3.
The abiotic degradation of iodosulfuron-methyl-ester was investigated under both alkaline and acidic pH conditions in the dark, and results showed it to be a rather stable molecule in neutral or slightly alkaline environments. Photochemical reactions were studied using a high-pressure mercury arc lamp, and results showed that direct phototransformation is possible under normal environmental conditions (lambda > 290 nm). High-performance liquid chromatography (HPLC-UV and HPLC-MS) analyses were used to identify the degradates and to study the kinetics of photodecomposition and hydrolysis. Five main products of iodosulfuron-methyl-ester degradation were tentatively identified, and one of them (4-methoxy-6-methyl-1,3,5-triazin-2-amine) was confirmed using an authentic standard. Among the phototransformation mechanisms, photosubstitution of the iodide atom by a hydroxyl group, photodissociation of the N-S bond, and photoassisted hydrolysis were observed. The quantum efficiencies (multiwavelength quantum yield) of the photodegradation under different conditions were determined, and values of 0.054 +/- 0.02 (pH 9.6), 0.08 +/- 0.02 (pH 7), and 0.044 +/- 0.008 (pH 5.3) were obtained.  相似文献   

4.
It is reported that 2-chlorobenzamide, one of the chief degradation products of CCU (1-(2-chlorobenzoyl)-3-(4-chlorophenyl) urea), a new insect growth regulator, is a potential carcinogen, but few studies about its environmental stability have been found. This paper is concerned with the hydrolysis of 2-chlorobenzamide as part of the environmental study of CCU. The results showed that 2-chlorobenzamide is relatively stable in solutions of pH = 6 and 8, for which the rate constants are 0.00286 h(-)(1) (R = 99.13%, SD = 0. 0095) and 0.00109 h(-)(1) (R = 96.70%, SD = 0.0072), respectively. Hydrolysis was more rapid in acidic (pH = 5), alkaline (pH = 10), and neutral (pH = 7) environments, with hydrolytic rate constants of 0.00417h(-)(1) (R = 95.76%, SD = 0.0390), 0.00411h(-)(1) (R = 99.89%, SD = 0.0162) and 0.00408h(-)(1) (R = 98.29%, SD = 0.0237), respectively. The change of the rate of hydrolysis with pH showed two minima at 25 degrees C. Temperature has some impact on the hydrolysis, showing at higher temperature the larger rate of reaction.  相似文献   

5.
High-performance anion exchange chromatography coupled with a pulsed amperometric detection system (HPAEC-PAD) was used to evaluate the extent of chemical hydrolysis of three fructooligosaccharides (FOS) including 1-kestose (beta-D-Fru-(2-->1)(2)-alpha-D-glucopyranoside, GF2), nystose (beta-D-Fru-(2-->1)(3)-alpha-D-glucopyranoside, GF3), and fructofuranosylnystose (beta-D-Fru-(2-->1)(4)-alpha-D-glucopyranoside, GF4). A kinetic study was carried out at 80, 90, 100, 110, and 120 degrees C in aqueous solutions buffered at pH values of 4.0, 7.0, and 9.0. Under each experimental condition, the determination of the respective amounts of reactants and hydrolysis products showed that FOS hydrolysis obeyed pseudo-first-order kinetics as the extent of hydrolysis, which decreased at increasing pH values, increased with temperature. The three oligomers were found to be degraded mainly under acidic conditions, and at the highest temperature value (120 degrees C), a quick and complete acid degradation of each FOS was observed. Using the Arrhenius equation, rate constants, half-life values, and activation energies were calculated and compared with those obtained from sucrose under the same experimental conditions. It appeared that the hydrolysis of FOS took place much more easily at acidic pH than at neutral or basic pH values.  相似文献   

6.
Lumichrome and lumiflavin were formed from riboflavin under light. pH had a significant influence on the formation of lumichrome and lumiflavin from riboflavin. Lumichrome was the only major product from riboflavin under neutral or acidic pH values. Lumiflavin was also formed from riboflavin in basic pH. The maximum concentration of lumiflavin from 100 microM riboflavin at pH 8.5 was 30.9 microM, and it was reached after 2 h of exposure at 1500 lux. The maximum concentration of lumichrome formed from 100 microM riboflavin at pH 4.5, 6.5, or 8.5 was 79.9, 58.7, and 73.1 microM, respectively, after 8, 6, or 2 h of light exposure. The formation of lumichrome and lumiflavin from riboflavin was due to the type I mechanism of the riboflavin photosensitized reaction. Singlet oxygen was also involved in the photosensitized degradation of lumiflavin and lumichrome. The reaction rates of riboflavin, lumiflavin, and lumichrome with singlet oxygen were 9.66 x 10(8), 8.58 x 10(8), and 8.21 x 10(8) M(-1) s(-1), respectively. The headspace oxygen depletion and headspace volatile formation were significant in soy milk containing lumichrome or lumiflavin under light (p < 0.05) and were insignificant (p > 0.05) in the dark. Ascorbic acid could inhibit the total volatile changes of soy milk under light. Soy milk should be protected from light to prevent the photodegradation of riboflavin and the oxidation of soy milk.  相似文献   

7.
Microbial degradation of the herbicide primisulfuron was investigated using enrichment cultures from contaminated soils and 20 axenic cultures. At neutral pH, no disappearance of the herbicide was detected either in the enrichment cultures or in the growth media of the axenic microbial cultures. During the growth of some of the microbial strains, however, the pH of the medium dropped below 6, resulting in the hydrolysis of primisulfuron. The rate of primisulfuron hydrolysis was clearly pH dependent; primisulfuron was more persistent in neutral or weakly basic solutions than in acidic solutions. After hydrolysis of the herbicide, four products were observed. These were identified as methyl 2-(aminosulfonyl)benzoate, 2-amino-4,6-(difluoromethoxy)pyrimidine, 2-N-[[[[[4, 6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl ]be nzoic acid, and 2-(aminosulfonyl)benzoic acid. After hydrolysis, it was found that the fungus Phanerochaete chrysosporium mineralized 27 and 24% of (14)C-phenyl- and (14)C-pyrimidine-labeled products, respectively, after 24 days of incubation. Similarly, Trametes versicolor mineralized 13 and 11% of (14)C-phenyl- and (14)C-pyrimidine-labeled hydrolysis products, respectively. In addition, primisulfuron in a hydrolytically stable solution, at pH 7. 0, was rapidly decomposed after ultraviolet irradiation, and two photolysis products were isolated [methylbenzoate and 4, 6-(difluoromethoxy)pyrimidin-2-ylurea]. When (14)C-phenyl-labeled primisulfuron was exposed to photolysis for 24 h, 32% of the initial radioactivity was recovered as (14)CO(2), whereas no (14)CO(2) was detected if the herbicide was labeled at the (14)C-pyrimidine position. Mineralization of (14)C-pyrimidine-labeled products of photolyzed primisulfuron by P. chrysosporium was approximately 25% after 24 days. These results clearly indicate that hydrolysis and photolysis of primisulfuron facilitated microbial degradation.  相似文献   

8.
The hydrolysis of triazophos was studied in buffered solutions in the range of pH 4-10 and in sodium hydroxide solutions with pH values up to 12. The results showed that the degradation of triazophos in the above solutions followed simple pseudo-first-order kinetics. At 35 degrees C, the rate constants in buffered solutions ranged from 0.0222 d(-1) at pH 4 to 0.5357 d(-1) at pH 10, and increased to 0.6251 h(-1) in 0.01 mol/L sodium hydroxide solution. The results also indicated that the base-catalysis was more important than acid-catalysis in the hydrolysis of triazophos. On the basis of the Arrhenius plot, the calculated activation energy (E(a)) and the frequency factor (A) for the hydrolysis of triazophos in buffered solution of pH 10 were 78.6 kJ/mol and 1.13 x 10(13) d(-1), respectively. Hydrolytic products of triazophos in buffered solutions of pH 4 and 10, as well as in sodium hydroxide solution of pH 11, were identified as their corresponding trimethylsilyl derivatives with a gas chromatography-mass spectrometer (GC-MS). The possible hydrolytic pathways of triazophos were also proposed.  相似文献   

9.
Effects of soil pH and soil water content on prosulfuron dissipation   总被引：3，自引：0，他引：3  
The sulfonylurea herbicide prosulfuron, 1-(4-methoxy-6-methyltriazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)phenylsulfonyl]urea, is used for the selective control of broadleaf weeds in corn, sorghum, and cereal grains. To investigate its fate in soils, this study examined the effects of soil pH and water content on the rates of dissipation processes and the products formed under aerobic conditions. Radiometry and chromatography analyses were used to quantify the degradation products and bound residues formed in incubations of 10 different soils. The pH-dependent hydrolysis of the sulfonylurea bridge to form phenyl sulfonamide was the primary transformation process. Significant microbial degradation of prosulfuron occurred in 2 of the 10 soils, yielding (14)CO(2) and desmethyl prosulfuron among the major products. The time required for 50% dissipation of the herbicide (DT(50)) was determined for each soil and water content treatment. At equivalent water contents, prosulfuron DT(50) values were positively correlated with soil pH (P < 0.0001), varying from 6.5 days at pH 5.4 to 122.9 days at pH 7.9. Soil pH and water content strongly influence the fate of sulfonylurea herbicides in agricultural fields. Differences in the effect of soil water content on dissipation kinetics in a comparison of two soils were attributed to differences in soil pH, texture, and the ability of indigenous microorganisms to transform the herbicide.  相似文献   

10.
Hydrolyses of fenamiphos, fipronil, and trifluralin were studied in aqueous buffer solutions of pH 4.1, 7.1, and 9.1 at different temperatures, 5, 22 +/- 1, 32 +/- 1, and 50 +/- 1 degrees C. Fenamiphos, fipronil, and trifluralin were found to be more stable in acidic and neutral buffer solutions at temperatures of 5 and 22 +/- 1, and dissipation is rapid at 50 +/- 1 degrees C. In basic buffer and at higher temperature, degradation of fenamiphos was found to be very rapid when compared with fipronil and trifluralin. The rate constants calculated at 32 degrees C for fenamiphos were 2349.4 x 10(-)(8) (pH 4.1), 225.2 x 10(-)(8) (pH 7.1), and 30476.0 x 10(-)(8) (pH 9.1); for fipronil 1750.0 x 10(-)(8) (pH 4.1), 3103.0 x 10(-)(8) (pH 7.1), and 3883.0 x 10(-)(8) (pH 9.1); and for trifluralin 2331.0 x 10(-)(8) (pH 4.1), 2360.0 x 10(-)(8) (pH 7.1), and 3188.0 x 10(-)(8) (pH 9.1). On the basis of rate constant values, these pesticides appeared to be more susceptible to hydrolysis than synthetic organophosphorus compounds such as chlorpyriphos, diazinon, malathion, and ronnel. DT(50) values calculated at 32 degrees C were 228 (pH 4.1), 5310.24 (pH 7.1), and 37.68 (pH 9.1) h for fenamiphos; 608.6 (pH 4.1), 373.9 (pH 7.1), and 270.2 (pH 9.1) h for fipronil; and 502.1 (pH 4.1), 496.8 (pH 7.1), and 355.7 (pH 9.1) h for trifluralin.  相似文献   

11.
This research is a continuation of a study on the behavior of hydrophobic organic compounds in the environment and describes the simultaneous abiotic degradation and sorption of pirimiphos-methyl (O-2-diethylamino-6-methylpyrimidin-4-yl O,O-dimethylphosphorothioate) under controlled conditions in soil/water slurries. A microfiltration-HPLC technique was employed to follow these processes in two well-characterized soils from the Middle Belt region of Nigeria. Rapid sorption of the pesticide occurs during the first 10 min of equilibration and accounted for 37% of the original pirimiphos-methyl in the Rhodic Kandiustalf soil and for 41% of the original concentration in Aquic Ustropept soil. Subsequent slow processes were followed during the remaining 30 days of the experiment. During this time, first-order rate constants for disappearance from solution of pirimiphos-methyl were found to have values of 6.1 x 10(-)(7) and 9.8 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively. Similarly, rate constants for production of the product, pyrimidinol, were calculated to be 6.0 x 10(-)(7) and 9.4 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively, giving pesticide degradation half-lives of 13 and 8.5 days. Disappearance of the pesticide is discussed in terms of a scheme involving both sorptive uptake by the soil and degradation by hydrolysis in the presence of the soil matrix. The labile sorption capacities for pirimiphos-methyl in the Rhodic and Aquic soils were found to be 0.75 and 0.90 micromol g(-)(1), respectively.  相似文献   

12.
This study investigates the hydrolysis kinetics of fenthion and its five oxidation metabolites in pH 7 and pH 9 buffered aqueous media at 25, 50, and 65 degrees C. Five metabolites and three hydrolysis products were synthesized and purified. The reactant and the corresponding hydrolysis products were determined by HPLC. Rate constant and half-life studies revealed that fenthion and its metabolites were relatively stable in neutral media, and their stability decreased as pH increased. The half-lives at 25 degrees C ranged from 59.0 days for fenthion to 16.5 days for fenoxon sulfone at pH 7, and from 55.5 days for fenthion to 9.50 days for fenoxon sulfone at pH 9; half-lives were greatly reduced at elevated temperatures. The activation energy (E(a)) was found to range from 16.7 to 22.1 kcal/mol for the compounds investigated. The phenol hydrolysis product of fenthion and fenoxon, 3-methyl-4-methylthiophenol was not stable in pH 7 and pH 9 buffered solutions at 50 degrees C, whereas 3-methyl-4-methylsulfonylphenol and 3-methyl-4-methylsulfinylphenol were relatively stable under the same conditions. At pH 9, the primary hydrolysis mechanisms of fenthion and its oxidation metabolites were combination of hydroxide ion and neutral water molecule attacking on the P atom to form corresponding phenol derivatives. Under neutral conditions, the primary hydrolysis mechanisms of fenthion and its oxidation metabolites were assumed to be the combination of water molecule attacking on the P atom to form phenol derivatives and on the C atom to yield dealkylation products.  相似文献   

13.
The bioactive anthocyanins present in tart cherries, Prunus cerasus L. (Rosaceae) cv. Balaton, are cyanidin 3-glucosylrutinoside (1), cyanidin 3-rutinoside (2), and cyanidin 3-glucoside (3). Cyanidin (4) is the major anthocyanidin in tart cherries. In our continued evaluation of the in vivo and in vitro efficacy of these anthocyanins to prevent inflammation and colon cancer, we have added these compounds to McCoy's 5A medium in an effort to identify their degradation products during in vitro cell culture studies. This resulted in the isolation and characterization of protocatechuic acid (5), the predominant degradation product. In addition, 2,4-dihydroxybenzoic acid (6) and 2,4,6-trihydroxybenzoic acid (7) were identified as degradation products. However, these degradation products were not quantified. Compounds 5-7 were also identified as degradation products when anthocyanins were subjected to varying pH and thermal conditions. In cyclooxygenase (COX)-I and -II enzyme inhibitory assays, compounds 5-7 did not show significant activities when compared to the NSAIDs Naproxen, Celebrex, and Vioxx, or Ibuprofen, at 50 microM concentrations. However, at a test concentration of 50 microM, the antioxidant activity of protocatechuic acid (5) was comparable to those of the commercial antioxidants tert-butylhydroquinone (TBHQ), butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA), and superior to that of vitamin E at 10 microM concentrations.  相似文献   

14.
It is of nutritional significance to fortify processed dairy products (e.g., cheese, yogurt, and ice cream) with vitamin D3; however, the inherent complexity of these foods may influence the stability and bioavailability of this nutrient. In the present study, the interactions of vitamin D3 with beta-lactoglobulin A and beta-casein were investigated under various environmental conditions (i.e., pH and ionic strength) using fluorescence and circular dichroism spectroscopic techniques. The results indicated that vitamin D3 was bound to both beta-lactoglobulin A and beta-casein depending on the solution conditions. The apparent dissociation constants ranged from 0.02 to 0.29 microM for beta-lactoglobulin A, whereas the beta-casein apparent dissociation constants ranged from 0.06 to 0.26 microM. The apparent mole ratios were also comparable, i.e., 0.51-2.04 and 1.16-2.05 mol of vitamin D3 were bound per mole of beta-lactoglobulin A and beta-casein, respectively. It was concluded that these interactions may strongly influence vitamin D3 stability and, hence, bioavailability in processed dairy products.  相似文献   

15.
Degradation and adsorption of fosthiazate in soil   总被引：3，自引：0，他引：3  
Adsorption and degradation behavior of a pesticide in soil has a strong effect on its environmental fate as well as efficacy for pest control. Fosthiazate is an organophosphate compound that is currently under development as a nonfumigant nematicide. In this study, we evaluated adsorption and degradation kinetics of fosthiazate in three U.S. soils with different properties. Adsorption of fosthiazate in mineral soil was negligibly weak but appeared to increase with soil organic matter (OM) content. The half-life (T(1/2)) of fosthiazate ranged from 0.5 to 1.5 months in nonsterile soils but was prolonged to 1-3 months after sterilization. Degradation of fosthiazate in soil appeared to be caused by both chemical and microbial transformations. The persistence of fosthiazate generally decreased with increasing soil pH, but increased with increasing soil OM and clay contents. This results suggest that fosthiazate may have an enhanced leaching potential in acidic soils with low OM content, and its efficacy in high pH soils may not last as long as in neutral soils because of faster degradation.  相似文献   

16.
A new intramolecular mechanism is proposed for the hydrolysis of phorate. (31)P NMR was used to study the formation of P-containing products of phorate hydrolysis in situ. When hydrolysis was followed by (31)P NMR, a dominant P-containing product was found and was identified to be diethyl dithiophosphate using methylation and GC-MS. Combining the data from phorate hydrolysis at three different temperatures, thermodynamic parameters were calculated. The contributions of various possible pathways to phorate hydrolysis are discussed.  相似文献   

17.
为探讨油菜素内酯(BR)促进芹菜中阿维菌素和辛硫磷残留的降解效果,以芹菜为试验材料,采用QuEChERS法结合高效液相色谱(HPLC)技术,研究了阿维菌素和辛硫磷在芹菜上自然降解及油菜素内酯对其降解的影响。结果表明,喷施1.8%阿维菌素乳油,芹菜的安全采收期为21 d,半衰期为6.60 d;喷施40%辛硫磷乳油,芹菜的安全采收期为14 d,半衰期为3.04 d。BR能够有效促进阿维菌素和辛硫磷的降解,降解效果优于自然降解,且以0.1 mg·L-1BR为最适喷施浓度,2次为最适喷施次数。阿维菌素在最适浓度0.1 mg·L-1BR处理1次条件下半衰期为4.03 d,安全采收期为14 d,较自然降解提早7 d;最适2次BR处理下半衰期为2.11 d,安全采收期为7 d,较自然降解提早14 d。辛硫磷在最适浓度0.1 mg·L-1 BR处理1次条件下半衰期为1.83 d,安全采收期为7 d,较自然降解提早7 d;最适2次BR处理下半衰期为1.05 d,安全采收期为7 d,较自然降解提早7 d。最佳喷施条件下,BR对辛硫磷的降解效果优于阿维菌素的降解效果。本研究可为芹菜产品农药残留水平安全控制提供科学依据,为蔬菜产品农药残留降解研究提供参考。  相似文献   

18.
De-esterification is an initial step in the metabolism of certain herbicides, for example, fenoxaprop-ethyl [(+/-)-ethyl 2-[4-[(6-chloro-2-benzoxaolyl)oxy]phenoxy]propanoate] (FE). The ethyl-ester bond cleavage of FE to fenoxaprop acid (FA) by purified enzymes, crude bacterial enzyme preparations, and soils was investigated. In similar experiments fluorescein diacetate (FDA) was used as an alternative substrate. FE stability was pH sensitive in acidic buffered solutions; that is, below pH 4.6, rapid nonenzymatic hydrolysis of the benzoxazolyl-oxy-phenoxy ether linkage occurred, forming 6-chloro-2,3-dihydro-benzoxazol-2-one (CDHB) and ethyl 4-hydroxyphenoxypropanoate or 4-hydroxyphenoxypropanoate. With porcine esterase and cell-free Pseudomonas fluorescens extracts, activity on FE and FDA was most rapid at pH 7.6-8.6 but decreased 80-90% at pH 5.6. Yeast (Candida cylindrica) lipase-mediated de-esterification of FE and FDA was not as sensitive to pH; that is, activity at pH 4.6 was 70% of that at pH 7.6. Short-term incubations (20 h) were conducted in eight soils (pH 4.5-6.9) treated with (14)C-chlorophenyl ring-labeled FE (2 mg kg(-)(1)). In the most acidic soils (pH 4.4-4.5) 25% of the (14)C was recovered as FA, versus 30-40% in moderately acid soils (pH 5.0-5.6) and 55% in neutral soils (pH 6.8-6.9). There was a similar correlation between soil pH and FDA de-esterification. CDHB was formed in all acidic soils with levels 4-fold greater in pH 4.4-4.5 soils than in pH 5. 0-5.6 soils. CDHB was not formed in neutral soils. Results demonstrate some chemical hydrolysis (benzoxazolyl-oxy-phenoxy ether linkage) of FE in acid soils, the sensitivity of enzymatic de-esterification of FE to pH, and the potential of FDA as a colorimetric indicator for esterase hydrolysis of FE.  相似文献   

19.
Kinetics and mechanism of imazosulfuron hydrolysis   总被引：5，自引：0，他引：5  
Knowledge of the kinetics and pathways of hydrolytic degradation is crucial to the prediction of the fate and transport mechanism of chemicals. This work first describes the kinetics of the chemical hydrolysis of imazosulfuron, a new sulfonylurea herbicide, and evaluates the results to propose a degradation pathway. The hydrolysis of imazosulfuron has been studied in aqueous buffers both within the pH range 1.9-12.3 at ambient temperature (thermostated at 25 +/- 2 degrees C) and at pH 3.6 within the temperature range of 15-55 degrees C. The hydrolysis rate of imazosulfuron was characterized by a first-order kinetics, pH- and temperature-dependent, and accelerated by acidic conditions and higher temperatures. The calculated half-lives at pH 4.5 and 5.9 were 36.5 and 578 days, respectively. At pH 6.6, 7.4, 9.2, and 12.3 no significant change in imazosulfuron concentration was observed after 150 days. Half-lives were much lower at pH <4 (= imazosulfuron pK(a)), at which they ranged from 3.3 to 6.3 days. Moreover, a change in temperature from 15 to 25 degrees C in acidic conditions (pH 3.6) decreased the half-life of imazosulfuron by a factor of approximately 4.0; in any case, a 3-5-fold increase in the rate of hydrolysis was found for each 10 degrees C increase in temperature. In acidic conditions the only hydrolysis products were the two molecules resulting from the cleavage of the sulfonylurea bridge.  相似文献   

20.
This paper reports laboratory studies of the behavior and fate of triflusulfuron-methyl in aqueous buffer and soils. Aqueous hydrolysis was pH-dependent and fast in acidic buffer solutions. In basic buffers, the hydrolysis rate variation was low between pH 7 and pH 10. The degradation pathway in the range of pH 4-10 was via cleavage of the sulfonylurea bridge to form two transformation products: 2-amino-4-(dimethylamino)-6-(2,2,2-trifluoroethoxy)-1,3, 5-triazine (2) and 6-methyl-2-methylcarboxylate benzene sulfonamide (3). Comparison of transformation rates in sterile and nonsterile soils indicates that chemical and microbial processes are important in soil degradation. The former is more important in acidic soils, and the latter is more important in basic soils. A biphasic model fits well with dissipation of triflusulfuron-methyl in soil. The triazine formed during the first step of transformation was degraded more rapidly in basic soils than in acidic soils.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号