Cinosulfuron: chemical and biological degradability, adsorption and dissipation in flooded paddy field sediment

Cinosulfuron is a sulfonylurea herbicide largely used in the extensive cultures of flooded rice in North Italy. The degradation of cinosulfuron has been investigated in sterile aqueous solutions at 30 degrees C at different pH values. It was rapidly degraded at acidic pH (half-lives 3, 9 and 43 days at pH 4, 5 and 6, respectively) while the half-life was > 1 year at pH 7 and 9. Two degradation products formed by cleavage of the sulfonylurea bridge were identified by LC-MS. Degradation by selected mixed microbial cultures tested in aerobic and anaerobic conditions was very slow and attributable to chemical hydrolysis due to the acidic pH of the cultural broths. Degradation took place in freshly collected rice field water treated for two years with cinosulfuron but, in this case also, chemical hydrolysis prevailed over microbial degradation. In contrast, in flooded sediment simulating the paddy field environment, the dissipation rate of cinosulfuron was higher than expected from chemical hydrolysis according to the pH of the system, indicating the involvement of soil microflora. Although the herbicide exhibited a reduced affinity for the sediment surfaces demonstrated by the low value of the K(f) Freundlich coefficient (0.87 on a micromolar basis), the rapid dissipation observed in the simulated paddy field should prevent its leaching to ground water.     

磺酰脲类除草剂的微生物降解研究进展

磺酰脲类除草剂是使用最广泛的除草剂之一。微生物降解是磺酰脲类除草剂在土壤中降解的重要方式。本文简要概述了土壤微生物对磺酰脲类除草剂的降解、降解机理及影响微生物降解磺酰脲类除草剂的因素。     

作物种类对根际土壤中丁草胺降解的影响

研究了根际和非根际土壤中除草剂丁草胺的降解。结果表明,棉花、水稻、小麦和玉米的种植明显促进丁草胺的降解,15 mg/kg丁草胺的降解半衰期缩短26.6%~57.2%,这种促进作用与作物种类有关,玉米、小麦、水稻、棉花依次增强。50 mg/kg丁草胺的降解有所受抑制,但作物种植仍显示良好的促进作用。作物根际丁草胺降解菌的测定结果显示,根际土壤中丁草胺降解菌的数量大于非根际土壤,作物种植对丁草胺降解的促进作用源于根际丰富的降解菌。     

Metabolism and selectivity of rice herbicides in plants

Chemical weed control with effective and highly active herbicides has been very useful and convenient means. It has contributed to stable crop production and is labor saving. Recent herbicides have had characteristics such as high effectiveness without causing environmental pollution or harmful effects, and appropriate herbicides having high activity, low toxicity, high selectivity and being non-persistent have been developed. The metabolism of rice herbicides used mainly in Japan, such as sulfonylurea, chloroacetamide, acylamide, urea, thiocarbamate, pyrazole, triazine, diphenyl ether, phthalimide, phenoxy, aryloxyphenoxypropionate, etc., is reviewed, and its involvement in selectivity is also discussed. The metabolism of herbicides is closely related to their activity and selectivity. Differential herbicide metabolism in plants is a contributing factor of selectivity between crops and weeds. Chemicals that are more detoxified in crops and/or more activated or less detoxified in weeds are considered as being effective and selective herbicides. The metabolism of various types of rice herbicides includes: oxidative reaction (ring and chain hydroxylation, O - and N -dealkylation), hydrolysis and subsequent glucose conjugation, and glutathione conjugation in rice. These detoxicative activities are much higher in rice than weeds in paddies, and this leads to the selectivity of herbicides. Enzymes, oxidase, P-450 mono-oxygenase, esterase, acylamidase, glucosyl transferase, glutathione transferase, etc., play important roles in herbicide metabolism and selectivity.     

Hydrolysis of triasulfuron,metsulfuron‐methyl and chlorsulfuron in alkaline soil and aqueous solutions

The hydrolysis of triasulfuron, metsulfuron‐methyl and chlorsulfuron in aqueous buffer solutions and in soil suspensions at pH values ranging from 5.2 to 11.2 was investigated. Hydrolysis of all three compounds in both aqueous buffer and soil suspensions was highly pH‐sensitive. The rate of hydrolysis was much faster in the acidic pH range (5.2–6.2) than under neutral and moderately alkaline conditions (8.2–9.4), but it increased rapidly as the pH exceeded 10.2. All three compounds degraded faster at pH 5.2 than at pH 11.2. Hydrolysis rates of all three compounds could be described well with pseudo‐first‐order kinetics. There were no significant differences (P = 0.05) in the rate constants (k, day⁻¹) of the three compounds in soil suspensions from those in buffer solutions within the pH ranges studied. A functional relationship based on the propensity of nonionic and anionic species of the herbicides to hydrolyse was used to describe the dependence of the ‘rate constant’ on pH. The hydrolysis involving attack by neutral water was at least 100‐fold faster when the sulfonylurea herbicides were undissociated (acidic conditions) than when they were present as the anion at near neutral pH. In aqueous buffer solution at pH > 11, a prominent degradation pathway involved O‐demethylation of metsulfuron‐methyl to yield a highly polar degradate, and hydrolytic opening of the triazine ring. It is concluded that these herbicides are not likely to degrade substantially through hydrolysis in most agricultural alkaline soils. © 2000 Society of Chemical Industry     

咪唑啉酮类除草剂的应用及降解

咪唑啉酮类除草剂虽具有高效广谱的特点,但有较长的残留活性,长期使用会造成作物药害,并且会制约正常的作物轮作。因此,如何解决其残留问题已成为目前的重要课题。本文介绍了咪唑啉酮类除草剂的种类和特性,阐述了此类除草剂在杂草体内的作用方式、代谢机制、应用情况及其在土壤中的降解途径,并对该类除草剂的应用与降解研究进行了展望。     

Fate of chlorsulfuron in the environment. 1. Laboratory evaluations

The behaviour and fate of chlorsulfuron in aqueous and soil systems were examined in laboratory studies. Aqueous hydrolysis was pH-dependent and followed pseudo-first-order degradation kinetics at 25°C, with faster hydrolysis occurring at pH 5 (half-life 24 days) than at either pH 7 or 9 (half-lives >365 days). Degradation occurred primarily by cleavage of the sulfonylurea bridge to form the major metabolites chlorobenzenesulfonamide (2-chlorobenzenesulfonamide) and triazine amine (4-methoxy-6-methyl-1,3,5-triazin-2-amine). This route is a major degradation pathway in water and soil systems. Aqueous photolysis (corrected for hydrolysis) proceeded much more slowly (half-life 198 days) than aqueous hydrolysis and is not expected to contribute significantly to overall degradation. Hydrolysis in soil thin-layer plates exposed to light (half-life 80 days), however, progressed at a much faster rate than in dark controls (half life 130 days), which suggests that a mechanism other than direct photolysis may have been operative. An aerobic soil metabolism study (25°C) in a Keyport silt loam soil (pH 6·4, 2·8% OM) showed that degradation was rapid (half-life 20 days). Dissipation in an anaerobic sediment/water system (initial pH of water phase 6·7, final pH 7·4) progressed much more slowly (half-life >365 days) than in aerobic soil systems. Major degradation products in aerobic soil included the chlorobenzenesulfonamide and triazine amine as in the aqueous hydrolysis study. Neither of these degradation products exhibited phytotoxicity to a variety of crop and weed species in a glasshouse experiment, and both exhibited an acute toxicological profile similar to that of chlorsulfuron in a battery of standard tests. Demethylation of the 4-methoxy group on the triazine moiety and subsequent cleavage of the triazine ring is another pathway found in both aqueous solution and soils, though different bonds on the triazine amine appear to be cleaved in the two systems. Hydroxylation of the benzenesulfonamide moiety is a minor degradation pathway found in soils. Two soils amended with 0·1 and 1·0 mg kg^-1 chlorsulfuron showed slight stimulation of nitrification. The 1·0 mg kg^-1 concentration of chlorsulfuron resulted in minor stimulation and inhibition of ¹⁴C-cellulose and ¹⁴C-protein degradation, respectively, in the same soils. Batch equilibrium adsorption studies conducted on four soils showed that adsorption was low in this system (K_oc 13–54). Soil thin-layer chromatography of chlorsulfuron (R_f=0·55–0·86) and its major degradation products demonstrated that the chlorobenzenesulfonamide (R_f=0·34–0·68) had slightly less mobility and that the triazine amine (R_f=0·035–0·40) was much less mobile than chlorsulfuron. In an aged column leaching study, subsamples of a Fallsington sandy loam (pH_water 5·6, OM 1·4%) or a Flanagan silt loam (pH_water 6·4, OM 4·0%) were treated with chlorsulfuron, aged moist for 30 days in a glasshouse and then placed upon a prewet column of the same soil type prior to initiation of leaching. This treatment resulted in the retention of much more total radioactivity (including degradation products) than by a prewet column, where initiation of leaching began immediately after chlorsulfuron application, without aging (primarily chlorsulfuron parent). © 1998 SCI     

Adsorption and degradation of chlorsulfuron and metsulfuron-methyl in soils from different depths

Adsorption and degradation rates of chlorsulfuron and metsulfuron-methyl were measured in soil taken from depths of 0–20, 20–40 and 40–60 cm at eight sites. Adsorption of both herbicides was negatively correlated with soil pH, and positively correlated with soil organic matter content. When two soils with very high organic matter were excluded from the calculations, the correlations with organic matter content were no longer statistically significant but those with soil pH were affected only slightly. Degradation rates of both herbicides generally decreased with increasing depth in the soil and were positively correlated with microbial biomass and negatively correlated with soil pH. The possible significance of the results to persistence of the herbicides in the field is discussed.     

Agronomic and environmental implications of enhanced s‐triazine degradation

Novel catabolic pathways enabling rapid detoxification of s‐triazine herbicides have been elucidated and detected at a growing number of locations. The genes responsible for s‐triazine mineralization, i.e. atzABCDEF and trzNDF, occur in at least four bacterial phyla and are implicated in the development of enhanced degradation in agricultural soils from all continents except Antarctica. Enhanced degradation occurs in at least nine crops and six crop rotation systems that rely on s‐triazine herbicides for weed control, and, with the exception of acidic soil conditions and s‐triazine application frequency, adaptation of the microbial population is independent of soil physiochemical properties and cultural management practices. From an agronomic perspective, residual weed control could be reduced tenfold in s‐triazine‐adapted relative to non‐adapted soils. From an environmental standpoint, the off‐site loss of total s‐triazine residues could be overestimated 13‐fold in adapted soils if altered persistence estimates and metabolic pathways are not reflected in fate and transport models. Empirical models requiring soil pH and s‐triazine use history as input parameters predict atrazine persistence more accurately than historical estimates, thereby allowing practitioners to adjust weed control strategies and model input values when warranted. Published in 2010 by John Wiley & Sons, Ltd.     

典型咪唑啉酮类除草剂的微生物降解研究进展

咪唑啉酮类除草剂是中国广泛应用的除草剂,具有杀草谱广、活性高、选择性强等优点,但其在土壤中残留期长,影响后茬作物。本文综述了典型的咪唑啉酮类除草剂甲氧咪草烟、咪唑乙烟酸和甲咪唑烟酸残留对后茬作物的影响,探究了降解部分咪唑啉酮类除草剂(甲氧咪草烟、咪唑乙烟酸和咪唑烟酸)的微生物所属类群及降解途径,分析了影响微生物降解咪唑啉酮类除草剂的因素,对目前除草剂污染修复存在的问题进行了讨论,并对未来发展进行了展望。该文对研究咪唑啉酮类除草剂的微生物降解有一定的参考作用。     

磺酰氨基氯磺隆的合成、除草活性、作物安全性及其土壤降解研究

基于活性亚结构拼接方法,在氯磺隆分子中苯环的5位引入不同磺酰氨基,设计合成了4个氯磺隆衍生物 ( H01 ~ H04 ),其结构经核磁共振氢谱(1H NMR)、碳谱(13C NMR)和高分辨质谱(HRMS)确证。初步的生物活性测试结果表明,目标化合物在有效成分150 g/hm2测试浓度下表现出较好的除草活性,其中:苗前处理时, H01 、 H02 及 H04 对油菜生长的抑制率均高于85%, H01 对反枝苋的抑制率为100%,优于对照药剂氯磺隆 (68.8%);苗后处理时, H04 对油菜和反枝苋的抑制率均与氯磺隆相当,对稗草的抑制率 (85.2%) 优于对照药剂氯磺隆 (68.8%)。安全性测试结果表明,目标化合物对小麦和玉米生长的抑制率均低于氯磺隆。苗前处理时, H01 和 H04 对小麦安全, H01 ~ H04 对玉米的抑制率均低于氯磺隆;苗后处理时, H01 ~ H04 对玉米生长无抑制作用。降解试验结果表明, H01 ~ H04 在碱性土壤 (pH 8.39) 中的降解半衰期为44.43~53.32 d,比氯磺隆的半衰期 (157.53 d) 明显缩短。研究结果表明, H01 和 H04 可作为潜在的小麦田和玉米田磺酰脲类除草剂候选药物。本文可为进一步设计具有高效除草活性、降解速率快以及作物安全性高的新型磺酰脲类除草剂提供参考。     

磺酰脲类除草剂的降解机制及代谢产物的研究进展

磺酰脲类除草剂是一类高效,低毒和高选择性的除草剂,该类除草剂能有效防除阔叶杂草,其中有些品种对禾本科杂草也有一定的抑制作用。但同时因其用量低、对哺乳动物低毒以及独特的除草活性等特点而得到广泛应用。因此,了解磺酰脲类除草剂在土壤中的环境行为及归趋对于其科学合理使用、防止作物药害和保护农业生态环境具有非常重要的意义。根据笔者对磺酰脲类除草剂的深入研究,并总结归纳国内外的相关文献报道,对磺酰脲类除草剂的降解机制及其代谢产物的研究进行了综述,最后展望了磺酰脲类除草剂未来的发展趋势。     

Plant cell cultures as a model for the biochemistry of crop selectivity

Plant cell cultures have been used to study the metabolic degradation of 4-amino-5-methyl-2-(tert-butylaminocarbonyl)-1,2,4-triazolin-3-one. The biochemical basis of selectivity was shown to reside in effective metabolic conjugation. The herbicide was eliminated from cell cultures of beet (which is tolerant to it) by conjugation (N-glycolisation), but this occured to only a limited extent with cell cultures of non-target plants such as soybean.     

Degradation of the sulfonylurea herbicides chlorsulfuron and triasulfuron in a high-organic-matter volcanic soil

The degradation rates of two sulfonylurea herbicides, chlorsulfuron and triasulfuron, were determined at two application rates, 15 and 30 g a.i. ha^–1, in a sandy loam soil of volcanic origin under controlled environment and field conditions. Residues were measured using a modified gas chromatographic (gc) determination method. Both herbicides degraded rapidly in the acidic soil (pH 5.7) with high organic matter levels (7.3% o.m.), generally according to first-order rate kinetics. The respective half-lives ranged from 22 to 38 d for chlorsulfuron and from 31 to 44 d for triasulfuron under five controlled temperature/soil moisture regimens, ranging from 10 to 30 °C and between 40% and 80% maximum water-holding capacity. Half-lives in the field were considerably shorter (13 d for chlorsulfuron and 12–13 d for triasulfuron). The degradation rates of the herbicides were influenced more by soil temperature than by soil moisture content. Bioassays using white mustard ( Sinapis alba L.) and forage sorghum [ Sorghum bicolor (L.) Moench] were also used to determine the persistence of phytotoxic residues of both herbicides in the field, and the results showed that the effects of chlorsulfuron disappeared within 8 weeks. Triasulfuron residues disappeared within 9 and 14 weeks for the 15 and 30 g a.i. ha^–1 rates respectively.     

手性除草剂研究进展

以几大类已经商品化或具有较好市场前景的手性除草剂为对象,综述了各除草剂的除草活性、对非靶标生物的毒性及其在环境迁移中的对映异构体选择性现象及机理的研究成果。由于对映异构体间的生物学性质迥异,因此,手性除草剂对映异构体的活性、作用机理、代谢转化及其在生物体内的转移等都具有手性选择性差异。同时,手性除草剂对植物的选择性作用还会因作用对象及环境因素的改变而改变,其在环境中的选择性降解情况也十分复杂,不仅与该除草剂自身的理化性质有关,还与其所处的环境因素有关,诸如土壤类型、植物种类、微生物群落结构、温度、pH值等均会改变手性除草剂对映异构体的环境归趋。     

Degradation of primisulfuron-methyl and metsulfuron-methyl in soil

A newly developed chemical assay was used to determine the degradation in soil of two sulfonylurea herbicides, primisulfuron-methyl and metsulfuron-methyl, under both controlled and field conditions. The results from the chemical assay were compared with those from traditional bio-assays for determination of persistence in the field. Phytotoxic effects of these herbicides were not observed after 6 weeks following application to an acidic (pH 5.7) soil with high organic matter content (7.3% o.c). Half-lives of 13 to 29 days were measured for primisulfuron-methyl at different soil-water contents and temperatures while those for metsulfuron-methyl ranged from 8 to 36 days. The rate of degradation of metsulfuron-methyl was more sensitive to temperature than that of primisulfuron-methyl. Persistence in the field was shorter than expected considering the results from the controlled environment studies. However, determination of the persistence by both chemical assay and bioassay methods produced very similar results.     

The relationship of metabolism studies to the modes of action of herbicides

Metabolism studies are necessary in the understanding of the mode of action of herbicides, their loss of activity and their selectivity. Molecular change of a herbicide may involve photochemical degradation, and non-enzymic or enzymic reactions that normally inactivate, but in some cases activate, a compound. Molecular change resulting in activation is discussed with regard to the (2,4-dichlorophenoxy)-alkanoic acids, the pyridines paraquat and diquat, the anilides benzoylprop-ethyl and flamprop-methyl, and the thiocarbamates. Inactivation due to metabolism is reviewed with regard to herbicides applied to soil and foliage. Of the soil-applied herbicides, the 1,3,5-triazines and the nitrile dichlobenil are exemplified as cases in which selectivity may be due largely to interspecific differences in metabolism. Of the foliage-applied translocated compounds, the metabolism of the phenoxyalkanoic acid herbicides has been extensively investigated and may involve conjugation, side-chain degradation or extension, ring hydroxylation and protein binding. The mode of action of glyphosate, asulam, dalapon and aminotriazole in perennial weeds is discussed with particular reference to their metabolism.     

Influence of straw management, nitrogen fertilization and dosage rates on the dissipation of five sulfonylureas in soil

The dissipation behaviour of metsulfuron-methyl, tribenuron-methyl, thifensulfuron-methyl, triasulfuron and amidosulfuron were studied in soil following post-emergence spring applications to cereal crops. Incorporation or removal of straw and different fertilizer applications had no influence on the disappearance time (DT₅₀) of the herbicides. However, in laboratory trials dissipation of metsulfuron-methyl, triasulfuron and amidosulfuron at higher application rates was accelerated after incorporation of straw into the soil. The addition of straw decreases soil pH thereby causing faster hydrolysis of the compounds. Addition of nitrogen fertilizer increased the half-lives (t_1/2) of the herbicides. Combination of both straw and N fertilizer, however, had no effect. Neither straw nor N influenced the degradation of tribenuron-methyl and thifensulfuron-methyl.
The DT₅₀ of all herbicides investigated varied from 6 to 17 days in the field trials. Except for amidosulfuron, herbicides could not be detected 38–68 days after application. In the laboratory, t_1/2 values were higher than those in the field at 75 days (amidosulfuron), 63 days (metsulfuron-methyl), 35 days (triasulfuron) and 13 days (tribenuron-methyl). Only the t_1/2 of thifensulfuron-methyl was at 29 h faster under laboratory conditions. T_1/2 values of all herbicides were influenced by their initial concentration. The t_1/2 values of amidosulfuron and tribenuron-methyl at 1 mg a.i. kg⁻¹ soil were 2–2.5 times higher than at the recommended field application rate of 42 μg a.i. kg⁻¹ soil.     

Sulfonylurea herbicide resistance in Sonchus asper biotypes in Alberta, Canada

Summary Two Sonchus asper (spiny annual sow-thistle) biotypes, suspected of being resistant to the sulfonylurea herbicide metsulfuron-methyl, were collected in 1996 from two barley ( Hordeum vulgare ) fields in central Alberta, Canada. Both fields had received at least six applications of acetolactate synthase (ALS)-inhibiting herbicide(s). The responses of the two resistant (R) biotypes and two susceptible (S) biotypes to several sulfonylurea herbicides, and to herbicides and herbicide mixtures with other mechanisms of action, were compared. Both R biotypes were highly resistant to all sulfonylurea herbicides, but their control with other herbicides and mixtures was effective and comparable to that of the S biotypes. ALS extracted from an R biotype was about 440 times more resistant to metsulfuron-methyl than that of an S biotype, indicating that resistance was conferred by an ALS enzyme that was less sensitive to inhibition by the herbicide. Competitiveness and seed production of S. asper varied among biotypes, but the differences were probably the result of ecotype differences rather than resistance or susceptibility to sulfonylurea herbicides. This is the first reported occurrence of target site-based S. asper resistance to ALS-inhibiting herbicides.     

Degradation of the sulfonylurea herbicide LGC-42153 in flooded soil

LGC-42153, 2-fluoro-1-[3-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)pyridin-2-yl]propyl methoxyacetate, is a new sulfonylurea herbicide for use in rice. Its breakdown and metabolism were studied in soil under flooded condition using radioactive tracers labelled at either the propyl group or the pyrimidine ring. The half-life of LGC-42153 was approximately 3.0 days. The mass balance over 120 days ranged from 94.0 to 104.2% of applied radiocarbon, and no significant amount of volatiles or [14C]carbon dioxide were observed. Solvent non-extractable radiocarbon reached 11 approximately 14% of applied radiocarbon at 120 days after treatment. The major metabolic reaction was the cleavage of the carboxyl ester bond to give 1-(4,6-dimethoxypyrimidin-2-yl)-3-[2-(1-hydroxy-2-fluoropropyl)pyridine-3-sulfonyl]urea, which underwent hydrolysis of the sulfonylurea bridge giving 2-(1-hydroxy-2-fluoro)propyl-3-pyridinesulfonamide and 4,6-dimethoxy-2-aminopyrimidine.