Triflusulfuron-methyl dissipation in water and soil

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.     

Kinetics and mechanism of imazosulfuron hydrolysis

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.     

Effects of soil pH and soil water content on prosulfuron dissipation

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.     

Hydrolysis of sulfonylurea herbicides in soils and aqueous solutions: a review

Sulfonylureas are a unique group of herbicides used for controlling a range of weeds and some grasses in a variety of crops and vegetables. They have been extremely popular worldwide because of their low mammalian toxicity, low use rate, and unprecedented herbicidal activity. Knowledge about the fate and behavior of sulfonylurea herbicides in the soil-water environment appears to be of utmost importance for agronomic systems and environmental protection. Because these herbicides are applied at a very low rate, and their mobility is greatly affected by the chemicals' anionic nature in alkaline soils, a thorough understanding of their degradation/hydrolysis processes and mechanisms under aqueous and soil systems is important. This review brings together published information on the hydrolysis of several sulfonylureas in aqueous and soil solutions that includes the effects of pH, temperature, functional relationship between pH vs hydrolysis rate constants, and hydrolysis behavior of sulfonylureas in the presence of minerals. In addition, the transformations of sulfonylureas in soil, under laboratory and field experiments, have been discussed in connection with the compounds' varied structural features, i.e., sulfonylueas that are with or without the pyridinic, pyrimidine, and triazinic ring.     

Degradation of sulfosulfuron,a sulfonylurea herbicide,as influenced by abiotic factors

A laboratory experiment was conducted to study the stability of sulfosulfuron [1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2yl) urea] in a controlled environment of pH, temperature, solvent, and surface. In another experiment the photostability of sulfosulfuron was studied after irradiation under sunlight. Under alkaline condition, it yielded 1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-yl-3-(4,6-dimethoxypyrimidin-2-yl) amine, and under acidic condition it degraded to 1-(2-ethylsulfonylimidazo[1,2-a] pyridin)-3-sulfonamide and 4,6-dimethoxy-2-aminopyrimidine. Photodegradation included breaking of a sulfonylurea bridge, as in the case of acidic hydrolysis and contraction of the sulfonylurea bridge was the major pathway of alkaline hydrolysis.     

Behavior of four sulfonylurea herbicides in the presence of hydroxy compounds

The behavior of four sulfonylurea herbicides (metsulfuron methyl, chlorsulfuron, chlorimuron ethyl, and bensulfuron methyl) was studied in the presence of various hydroxy compounds. When dissolved at 30 degrees C in simple primary, secondary, or tertiary alcohols (methanol, ethanol, isopropyl alcohol, and tert-butyl alcohol) and in glycerol or in poly(ethylene glycol), most of these herbicides underwent rapid alcoholysis involving the breakdown of the urea part of the molecule. The corresponding sulfonyl carbamate is recovered in high yields, along with a small amount of sulfonylamide formed in the concomitant hydrolysis. Degradation rate constants and the selectivity of conversion were established. The addition of buffered water (pH 7.0) inhibited the alcoholysis reaction, leaving only hydrolysis, as already observed with concentrated saccharide solutions. In phenol solution, slight herbicide hydrolysis was primarily observed. It appeared that alcoholysis reactions only occurred under very particular conditions when sulfonylurea herbicides are dissolved in pure alcohols, without buffered water. These results led to the conclusion that in soil, similar alcoholysis reactions seem unlikely.     

Simulated sunlight-induced photodegradations of triasulfuron and cinosulfuron in aqueous solutions

To elucidate the photochemical behavior of two sulfonylureas (cinosulfuron and triasulfuron) for which the chemical formulas are relatively close, their photodegradation was studied in water. All experiments were carried out under laboratory conditions using a xenon arc lamp as the source of radiation to simulate environmental conditions. Polychromatic quantum efficiencies were calculated to determine the photochemical pesticide lifetimes at pH 7, and a comparison with hydrolysis lifetimes has been performed. The results obtained showed clearly that at pH 7, photodegradation becomes a more important pathway than chemical degradation. HPLC-DAD was used to study the kinetics for both sulfonylureas and their photoproducts, whereas HPLC-MS (ESI in positive and negative modes) was used to identify photoproducts. These results suggest that the photodegradation of these two sulfonylureas proceeds via a number of reaction pathways: (1) cleavage of the sulfonylurea bridge; (2) desulfonylation, which can proceed either by a carbon-sulfur cleavage or a nitrogen-sulfur cleavage; (3) O-demethylation of methoxy moieties present on the triazine ring; and (4) O-dealkylation of benzene derivatives. In addition, it was found that the desulfonylation represented the main step and that it was wavelength dependent.     

Effects of organic amendment and herbicide treatment on soil microbial biomass

 The interactive effects of vermi-compost from sewage sludge and either the sulfonylurea herbicide, rimsulfuron, or the imidazolinone herbicide, imazethapyr, on some soil biochemical and microbiological properties were investigated. The herbicides were applied at field and 10-fold field rates. Both herbicides exerted a detrimental effect on soil microbial biomass and its biochemical properties. Even though the effect of both herbicides on soil microbial biomass was not detectable at the field rate, some significant influences on acid and alkaline phosphatase were observed. The higher rate of herbicide application impaired the observed microbial parameters to a greater degree. The detrimental effects seemed to be reduced by organic amendments. Among the studied microbial characteristics, the specific respiration quotient was particularly reliable and sensitive in determining the influence of herbicides on the soil microbial biomass. In this paper a new synthetic index, specific hydrolytic activity (qFDA), for assessing microbial activity in reply to xenobiotic treatments is proposed. Received: 31 May 1999     

重金属、磺酰脲类除草剂的植物基因应答及其交互作用

土壤污染日益成为威胁人类生存的重要问题,而且正呈现出多元化和复杂化的特点。土壤的重金属污染已被重点研究,大量与金属阳离子吸收、分布和解毒相关的通道蛋白、螯合剂以及伴侣蛋白的编码基因被发现和克隆;而土壤的农药污染,特别是磺酰脲类除草剂类污染研究却还主要集中在生理生化水平上。同时,两者复合污染研究更是鲜有报道,总体还处于探索阶段。本文重点将对现阶段重金属与磺酰脲类除草剂单因素的植物基因应答及其复合污染交互作用的研究进展,在基因类型和作用等方面分别进行综合性分析与阐述,并结合环境污染现状和国际研究前沿提出了今后研究的主要方向。     

新一代除草剂在推进环境质量中的作用

新一代除草剂具有用药量少、除草活性高、选择性强、对哺乳动物低毒(对人的毒性甚至低于日常生活中的食盐)、在环境中易降解、在非靶标有机体内无积累作用等优良特性。这些特性正有效地改善当今的环境质量。80年代初发展起来的磺酰脲类除草剂是最具代表性的品种。本文介绍该类除草剂在国内外的发展简况,它们的优良特性在改善农业生态环境质量中的作用,以及在我国应用的意义。     

Stability and mineralization of organic phosphorus incorporated into model humic polymers

The stability of the phosphate ester linkage in phosphoserine (PS) and phosphoethanolamine (PE) was evaluated after incorporation of these compounds into model humic polymers. Humic polymers prepared by oxidation of a mixture of substituted phenols in the presence of either PS or PE resulted in model humic materials containing from 0.25 to 0.94% P, values within the range found for organic P in natural soil humic materials. The organic P contained in model humic polymers was resistant to hydrolysis with 1 n HC1 and 1 n NaOH and resistance of the P ester to hydrolysis with 6 n HCl was increased through incorporation into model humic polymers. Organic P in model humic polymers was also stabilized towards hydrolysis with acid and alkaline phosphomonoesterases. Less than 11% of the organic P in polymers containing PS and PE was hydrolyzed by acid or alkaline phosphatase. The incorporation of PE into a model humic polymer markedly reduced the amount of P mineralized during incubation in soil when compared to P mineralized in soils treated with PE. For all environmental conditions imposed during soil incubations (i.e. pH, aeration, temperature), only 20% of the P in model humic polymer containing PE was released during a 16-week period. In contrast, > 60% of the P in either PS and PE added individually to soils or PS and PE intimately mixed with preformed model humic polymer and then added to soils was released during the initial 7 days of soil incubation. The results suggest that a portion of the unidentified organic P in soils may arise from the incorporation of organic compounds containing both amine and phosphate ester functional groups into humic materials and that the organic P thus formed is resistant to both chemical and enzymatic hydrolysis.     

氯磺隆污染对土壤生物量碳氮与总有机碳氮比值的影响

The extent and seriousness of the contamination of soils by pesticides still remain to be determined,In agricultural systems,herbicides are the largest class of pesticides used (Shea,1985),Chlorsulfuron is one of the most important sulfonylurea herbicides with important feature of very high herbicidal activity,which results in extremely low application rates of 10-40g ha^-1(Blair and Martin,1988),The sulfonylurea herbicides can persist in the soil for more than 1 year(Brown,1990),Therefore,there has been considerable interest in the side effects of these chemicals on non-target organisms,including soil microorganisms(Greaves and Malkomes,1980),It ios generally recognized that the microbial biomass is the eye of the needle through which all organic materials that enter the soil must pass(Jenkinson,1988), Changes in the microbial biomass-C(Cmic) can provide an early indication of long-term trends in the total organic-C(Corg) of soils(Carter,1986),The Cmic/Corg ratio has been found useful as an index of changes in soil organic matter resulting from land management changes(Hart et al.1989).Many studies were done on relative effect of heavy metals on the ratio of Cmic/Corg but few studies have laid particular attention to the effect of herbicides on this ratio,The present paper reports on the Cmic/Corg and microbial biomass-N/total N (Nmic/Ntotal)ratios in soil as affected by chlorsulfuron.     

Novel protoporphyrinogen oxidase inhibitors: 3H-pyrazolo[3,4-d][1,2,3]triazin-4-one derivatives

A series of 3 H-pyrazolo[3,4-d][1,2,3]triazin-4-one derivatives were synthesized as candidate herbicides by diazotization of different 5(3)-amino- N-phenyl-1 H-pyrazole-4-carboxamide derivatives prepared by the reaction of substituted 5(3)-amino-pyrazole-4-carbonyl chloride with a substituted aniline. Their structures were identified by (1)H NMR and elemental analyses. The isomers D and E were isolated, and their structures were identified by two-dimensional NMR analyses (heteronuclear single quantum coherence and heteronuclear multiple-bond correlation) and single-crystal X-ray diffraction analysis. The bioassay results showed that some of the title compounds exhibited both excellent herbicidal activity at a dose of 93.75 g/ha and strong inhibition against protoporphyrinogen oxidase activity in vitro. The structure-activity relationship showed that D16 possessed the highest activities both in vivo and in vitro when the N-substituted group of the pyrazole ring was allyl and the N-substituted group of benzooxazinone was propargyl.     

除草剂对不同种植年限柑橘园土壤氮转化过程及温室气体排放的影响

为探讨除草剂施用对柑橘园土壤氮转化及温室气体排放的影响,在实验室培养条件下,研究了0年(林地)、种植10年和30年的柑橘园土壤中分别添加除草剂草甘膦和丁草胺后,尿素态氮含量、硝化和反硝化作用以及温室气体排放的变化。研究结果表明,橘园土壤中尿素第1 d的水解率、氮肥硝化率、反硝化作用损失总量以及N_2O和CO_2排放量显著高于林地土壤(P0.05)。与10年橘园土壤相比,30年橘园土壤显著增加了尿素的水解速率、氮肥硝化率和CO_2排放量(P0.05),但二者的反硝化损失量没有显著差异。施用草甘膦和丁草胺都显著促进了林地土壤的尿素水解(P0.05),第1 d尿素态氮含量分别降低11.20%和12.43%;但对3种土壤氮肥的硝化率均没有明显影响。施用丁草胺显著降低了林地土壤的CO_2排放量(P0.05),对两种橘园土壤的CO_2排放没有明显影响,但明显增加了两种橘园土壤的N_2O排放总量(P0.05),分别比不施除草剂增加56.27%和85.41%;施用草甘膦对3种土壤的N_2O和CO_2排放均没有明显影响。可见,草甘膦和丁草胺的施用不会对柑橘园土壤的氮转化过程产生影响,但丁草胺显著增加了柑橘园土壤的N_2O排放。     

基质固相分散萃取-高效液相色谱串联质谱法测定土壤中残留的磺酰脲类除草剂

建立了基质固相分散萃取-高效液相色谱串联质谱法(MSPD-HPLC-MS/MS)测定土壤中3种磺酰脲类除草剂(氯磺隆、甲磺隆、苯磺隆)残留的分析方法。对基于球磨的基质固相分散萃取条件进行了详细优化,最终确定最佳条件为:0.2 g土壤样品、0.8 g HC-C18粉末状分散剂与直径为8 mm的小钢珠一起球磨10 min后,转移至空的玻璃萃取小柱,用10 m L乙腈洗脱,氮气吹干后用甲醇定容至0.6 m L,再经0.22μm的滤膜抽滤后装入自动进样瓶中。用Syncronis C18反相色谱柱分离,以甲醇(A)~1‰甲酸溶液(B)为流动相进行梯度洗脱,选择反应监测(SRM)模式下进行检测。氯磺隆在20~200μg·kg~(-1),甲磺隆和苯磺隆在10~200μg·kg~(-1)范围内线性良好,相关系数r在0.997 9~0.999 5。土壤样品的平均加标回收率在84.7%~104.6%,相对标准偏差在4.5%~7.9%(n=5)。方法的检出限(S/N=3)0.32~0.68μg·kg~(-1)。该方法简单、效率高、干扰少、回收率高,满足土壤中除草剂的残留分析要求。     

Organic amendments from olive cake as a strategy to modify the degradation of sulfonylurea herbicides in soil

Amending soil with products rich in organic matter, such as raw olive cake or alperujo and its compost and vermicompost, could be a simple bioremediation strategy for soil pollutants such as pesticides. To investigate this hypothesis in relation to sulfonylurea herbicides, these amendments were applied to a Mediterranean agricultural soil at rates 4 times higher than agronomical dosage to stimulate biodegradation of chlorsulfuron, prosulfuron, and bensulfuron, added in a mixture to the soils. Degradation studies were conducted in microbially active and sterile soils to check the importance of biological and chemical degradation of sulfonylurea herbicides in nonamended and amended soil. The addition of alperujo stimulated soil microbial activity, as determined by dehydrogenase activity measurements, but it did not enhance the degradation of the sulfonylurea herbicides. In contrast, compost and vermicompost slightly favored the biological degradation of bensulfuron during the first week of incubation. Chlorsulfuron and prosulfuron were mainly degraded by chemical pathways in all substrates, which is probably due to a competitive or inhibitory phenomenon observed between chlorsulfuron and bensulfuron. The first-order kinetic equation satisfactorily explained the experimental data for chlorsulfuron and prosulfuron; however, a biphasic model, such as that proposed by Hoerl, better predicted the results obtained for bensulfuron.     

Effect of culture acclimation on the kinetics of aldicarb insecticide degradation under methanogenic conditions

This study reports on the kinetics of aldicarb transformation under methanogenic conditions using batch reactors containing acclimated and unacclimated cultures under controlled conditions. Culture acclimation was accomplished by exposing anaerobic microorganisms maintained in a semi-batch reactor to low concentrations of aldicarb. Results of the kinetic studies showed that in an anaerobic system aldicarb is converted to aldicarb nitrile by the hydrolytic pathway. Analysis of the hydrolysis/dehydration rate constants showed that anaerobic cultures enhanced the rate of conversion of aldicarb by 4-fold for acclimated cultures and by 2-fold for unacclimated cultures compared to the rate of abiotic hydrolysis (p < 0.05). Only the acclimated cultures were able to further mineralize the reaction intermediate aldicarb nitrile. Michaelis-Menten and Monod kinetics adequately defined the aldicarb nitrile degradation.     

水稻对水稻土中甲磺隆结合残留的响应

Metsulfuron-methyl is one of the widely used sulfonylurea herbicides. However, approximately half of the applied metsulfuron-methyl may remain as bound residues in soil. To characterize the response of rice plants to residual metsulfuron-methyl in soil, the activities of acetolactate synthase （ALS）, superoxide dismutase （SOD）, peroxidase （POD）, and catalase （CAT） were investigated in two rice varieties that differed in susceptibility to the herbicide. Changes in the activity of these enzymes in leaves and roots of Xiushui 63, a sensitive rice variety, were greater than those in a resistant variety Zhenong 952. Irrespective of variety, changes in the enzyme activity were greater in the roots than in the leaves. The activities of ALS and CAT decreased, while the SOD activity increased with the increase in the amounts of bound residues of metsulfuron-methyl （BRM） in soil. The POD activity increased at the BRM level of 0.025 mg kg^-1, but decreased at the BRM level of 0.05 mg kg^-1. The results showed that the bound residues of sulfonylurea herbicides may affect metabolism of rice plants.     

2,4-D丁酯的水解与光解特性研究

通过室内模拟试验,研究2,4-D丁酯在不同pH值和温度下的水解动态和在有机溶剂中的光解特性。结果表明,2,4-D丁酯的水解与光解均符合一级动力学方程。在pH7以下的缓冲溶液中,2,4-D丁酯的水解反应十分缓慢,但在碱性溶液中其水解速率加快。25℃下2,4-D丁酯在pH5、7和9的缓冲溶液中的水解半衰期分别为23.5、5.8d和10.7min。2,4-D丁酯的水解速率随温度升高而增加,在温度为15、25℃和35℃的pH7缓冲溶液中的水解半衰期分别为21.5、5.8、3.9d,平均温度效应系数为2.57。2,4-D丁酯水解反应的活化能与温度之间无明显相关性,而活化熵与温度呈显著相关性。2,4-D丁酯的水解主要由活化熵所驱动。采用GC-MS技术对2,4-D丁酯水解产物进行鉴定,确定水解产物主要是2,4-二氯苯氧乙酸和2,4-二氯苯酚。2,4-D丁酯在正己烷中光解速率比在甲醇中快,在丙酮中几乎不发生光解,其光解速率随浓度的升高而减慢。     

NBPT与DMPP不同剂量组合对尿素氮转化的影响

采用室内模拟试验的方法,探讨了脲酶抑制剂N-丁基硫代磷酰三胺(NBPT)和硝化抑制剂3,4-二甲基吡唑磷酸盐(DMPP)的不同浓度组合对尿素氮转化的影响。结果表明,NBPT与DMPP不同浓度组合均不同程度的延缓了尿素的水解,使尿素N水解产物更加以NH4+-N形态保持在土壤中;延缓了硝化作用进程并减少了硝酸盐在土壤累积,在此基础上增加了土壤有效态N含量。综合不同浓度组合对尿素水解的抑制、土壤NH4+-N和NO3--N含量变化、硝化作用抑制效果、土壤有效态N水平等指标并结合成本考虑,NBPT和DMPP分别为0.1%和0.5%施氮量时为最适宜的组合。