Photolysis of flucythrinate

Photolysis of flucythrinate ((RS)-α-cyano-3-phenoxybenzyl (S)-2-(4-difluoromethoxyphenyl)-3-methylbutyrate) in solution (methanol) by UV light (> 290 nm) and as a thin film on glass by exposure to sunlight yields products resulting from ester cleavage. The major product in solution is formed via photo-induced decarboxylation. When thin films are exposed to sunlight, flucythrinate has a half life of 8 days on glass and 3 days on a leaf surface.     

高寒草甸根围拮抗芽孢杆菌筛选鉴定及脂肽化合物分析

本研究通过平板对峙法分别从青海日月山及达日地区高寒草甸根围分离菌株中筛选到8株对油菜菌核病菌Sclerotinia sclerotiorum及水稻白叶枯病菌Xanthomonas oryzae pv.oryzae均具有明显拮抗效果的芽孢杆菌菌株RYS41、RYS42、RYS43、RYS44、DR1、DR2、DR3及DR20。生理生化、脂肪酸甲脂、16S rDNA及gyrB基因测序等分析结果表明,菌株RYS41、RYS42、RYS43、RYS44为解淀粉芽孢杆菌Bacillusamyloliquefaciens;菌株DR1、DR2、DR3、DR20鉴定为短小芽孢杆菌B.pumilus。MALDI-TOF-MS质谱分析结果表明,菌株RYS41产生脂肽类化合物Surfactin、Bacillomycins D和Fengycin,菌株DR20产生脂肽类化合物Surfactin、IturinA和Fengycin,推断可能与对油菜菌核菌及水稻白叶枯病菌的拮抗作用有关。     

The metabolism of the pyrethroid insecticide (±)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethyl-cyclopropanecarboxylate,WL 41706, in the rat

The metabolism of the pyrethroid insecticide α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate (WL 41706) has been studied in rats using two forms of ¹⁴C-labelling (benzyl- and cyclopropyl-). Excretion of benzyl^?14C was rapid, 57% of the administered dose being eliminated in the urine 48 h after treatment and 40% in the faeces. No significant sex difference was observed. The amount of radioactivity excreted via expired gases was 0.005% of the administered dose and less than 1.5% of the dose remained in the animals 8 days after treatment. The mean percentage recovery of administered dose was 104% for male rats and 97% for female rats. Urinary and faecal metabolites from these rats, and from rats dosed similarly with [cyclopropyl^?14C]-WL 41706 were studied. The rapid metabolism of WL 41706 is due to efficient cleavage of the ester bond by rats in vivo to afford 2,2,3,3-tetramethylcyclopropanecarboxylic acid (partly as glucuronide) and the 3-phenoxybenzyl moiety. Before this cleavage occurs, however, about half of the intake suffers aryl hydroxylation giving the α-cyano-3-(4-hydroxyphenoxy)benzyl ester, part of which is excreted in the bile as a conjugate(s) and part of which is cleaved and eliminated as the O-sulphate of 3-(4-hydroxyphenoxy)benzoic acid and the glucuronide of 2,2,3,3-tetramethylcyclopropanecarboxylic acid. A minor amount of hydroxylation occurs at a trans-methyl group on the cyclopropane acid moiety. The metabolism of WL 41706 by rat liver occurs mainly in the microsomes and mainly via oxidative processes.     

New fluoro intermediates for herbicidal sulfonylureas

New pyrimidine and triazine intermediates for herbicidal sulfonylureas are prepared as follows: 2,4-dichloro-6-methylpyrimidine is converted via a halogenation, halogen exchange and substitution sequence to 2-amino-4-trifluoromethyl-6-trifluoromethoxypyrimidine. New fluoromethyl-triazines are available starting from guanidine, trichloroacetonitrile and difluoroacetic anhydride, or alternatively from thiocarbamoyl guanidine and chlorodifluoroacetic ester ring closure. To obtain new o-fluoroalkyl-benzenesulfonamide precursors, o-chlorobenzaldehyde was fluorinated with sulfur tetrafluoride, or a bromobenzene derivative was subjected to a substitution reaction with sodium pentafluoropropionate. Sulfonylureas derived from trifluoromethylpyrimidines with an m-methylthio substituent are selective post-emergence herbicides in cotton, presumably due to sulfone metabolization. Selectivity in wheat is obtained by combining 4-methoxy-6-trifluoromethylpyrimidine with a lipophilic difluoromethyl-benzenesulfonamide moiety. Also in the difluoromethyl-triazine series, the combination with the difluoromethyl-benzenesulfonamide moiety is a good choice for wheat selectivity. Chlorodifluoromethyl- and trifluoromethyltriazines, however, combine better with an aromatic ester for best activity and selectivity in wheat. Selected compounds are undergoing broad field tests in wheat.     

Stereochemical basis for the insecticidal activity of carbamoylated and acylated pyrazolines

Methyl 3-(4-chlorophenyl)-1-[N-(4-chlorophenyl)carbamoyl]-4-methyl-2-pyrazoline-4-carboxylate was converted to corresponding (1R)- and (1S)-phenethyl esters via its carboxylic acid and acid chloride at the C-4 atom to separate the diastereomers. Their configurations were confirmed by X-ray analysis. Both isomers of the (1R)methylbenzyl ester were subjected to transesterification with sodium methoxide to obtain enantiomers of the starting methyl ester. Their insecticidal activity was measured against American cockroaches (Periplaneta americana (L.)) by injection and against house flies (Musca domestica L.) by topical application under various synergistic conditions with metabolic inhibitors. The activity values of the four α-methylbenzyl esters and the R-isomer of the starting methyl ester were similar. The S-enantiomer of the methyl ester was about 10 and 100 times more active than the R-isomer against the cockroach and the fly, respectively. Some N-arylacetyl and N-aryloxyacetyl derivatives of the starting N-(4-chlorophenyl)carbamoyl compound gave very low activity. Conformation-energy profiles for some compounds suggested that the conformation of substituents on the N-1 atom in the pyrazoline ring has a specific role for the potential insecticidal effects.     

Properties of a fluorescent analog of the pyrethroids

The ester of pyrene-1-methanol with cis-2,2-dimethyl-3(2,2-dichlorovinyl) cyclopropane carboxylic acid (cis-permethrin acid) is introduced as a fluorescent analog of the pyrethroids. Relative intensities of the vibronic bands in the fluorescence emission spectrum of the ester in lipid bilayers are consistent with a location for the pyrene group in the glycerol backbone region of the bilayer. It is suggested that pyrethroids adopt a “horseshoe” conformation in the bilayer with the ester group at the lipid-water interface. Fluorescence data are interpreted in terms of one binding site per four lipids. In the (Ca²⁺Mg²⁺)-ATPase system prepared from muscle sarcoplasmic reticulum, the ester binds both to sites in the lipid and on the ATPase. There are a large number of sites for the ester on the ATPase. For the ATPase reconstituted with the short chain lipid dimyristoleoylphosphatidylcholine, the ester causes an increase in activity comparable to that caused by the pyrethroids.     

1-酰基苯并咪唑酮酰胺衍生物的合成及其抗菌活性

以邻苯二胺和乙酰乙酸乙酯为起始原料制得异丙烯基苯并咪唑酮(Ⅲ),再经N-酰化反应得到13个苯并咪唑酮酰胺衍生物(Ⅳ-01～Ⅳ-13)以及由Ⅳ-02脱异丙烯基的产物Ⅳ-02a,其中9个为未见文献报道的新化合物。通过核磁共振氢谱和碳谱、质谱以及元素分析对其结构进行了表征。抑菌活性测定结果表明,化合物Ⅳ-01～Ⅳ-03、Ⅳ-11及Ⅳ-02a对供试病原细菌和真菌均表现出明显的抑菌活性,其中化合物Ⅳ-02和Ⅳ-02a尤为突出,且二者活性相近,其中Ⅳ-02对蜡状芽孢杆菌Bacillus cereus(1.184 6)、枯草芽孢杆菌Bacillus subtilis(1.88)、金黄色葡萄球菌Staphylococcus aureus(1.89)和大肠杆菌Escherichia coil(1.157 4)的MIC(抑制生长的最低浓度)值分别为0.78、12.5、1.56和1.56 μg/mL,对番茄灰霉病菌Botrytis cinerea的有效抑制中浓度(EC50)为7.02 μg/mL。     

FORMULATION OF DALAPON TO REDUCE SOIL CONTAMINATION

Summary. Two means of reducing soil contamination resulting from the leaching of spray residues of dalapon from plant foliage were tested: use of volatile forms of the herbicide, residues of which slowly evaporate from the foliage; and use of formulations that congeal to a solid film to retain the herbicide against leaching. Rates of evaporation from glass slides at 20° C for the ethyl ester, n butyl ester, acid, and diethyleneglycol bisester of dalapon were respectively 15, 1-6, 0'27 and 0.01 mg/cm². As foliar herbicides the ethyl and butyl esters were ineffective and the acid of limited effectiveness due to rapid evaporation. The glycol ester was as effective as the sodium salt. With its evaporation rate of approximately 1 kg/ha/hr at 20°C, application of dalapon in the form of the diethylrneglycol bis ester is considered promising as a means of limiting soil contamination. Mixtures of the diethyleneglycol bis ester of dalapon with polyvinylacctate emulsion dry to form films that greatly reduce leaching of the herbicide at the expense of minor reduction in herbindal activity. Such formulations afford a means of limiting soil contamination.
Formulation du dalapon pennettant de rédiuire la contamination du sol     

Effects of formulation and environment on absorption and translocation of clopyralid in Cirsium arvense (L.) Scop. and Polygonum convolvulus L

The patterns of absorption and translocation of ¹⁴C clopyralid commercially formulated as the acid, monoethanolamine salt, potassium salt, 2-ethylhexyl ester and 1 -decyl ester were compared in Cirsium arvense and Polygonum convolvulus grown under three environmental regimes. Plants were grown under a 35% or 65% RH regime in silica sand maintained at 33% w/w moisture or under a water stress regime at 65% RH. Approxi mately 26,39,86,93 and 100% of the applied ¹⁴C-activity from the 2-ethylhexyl ester, acid, monoethanolamine salt, 1-decyl ester and potas sium salt, respectively, were recovered 72 h after application to glass cover slips placed in the growth room. However, loss of applied ¹⁴C-activity after application of the five formulations to both plant species was significant only for the 2-ethylhexyl ester. Regardless of environmental regime, the acid was the most readily absorbed formulation. In contrast to the acid, the salts and esters were less readily absorbed. When the data were expressed as a percentage of absorbed radioactivity, there was no significant difference in translocation when the acid, monoethanolamine salt and potassium salt were compared. However, significantly smaller quantities of the absorbed 2-ethylhexyl and 1-decyl ester were exported from the treated leaf. These results indicate that once absorbed, the esters do not readily partition out of the cuticle, whereas the acid and two salts move into the symplast for subsequent translocation. When the results of the three environmental regimes were compared, the absorption of the monoethanolamine and potas sium salts were greatly reduced under low humi dity or water stress, whereas the acid and esters were not affected.     

Efficacy of five different formulations of clopyralid on Cirsium arvense (L.) Scop, and Polygonum convolvulus L

Experiments were conducted in a controlled environment growth room to compare the phytotoxicity of five formulations of clopyralid and to determine the effect of post-treatment simulated rainfall applications on the efficacy of these formulations. Clopyralid, formulated as the acid, monoethanolamine salt, potassium salt, 2-ethylhexyl ester or 1-decyl ester was applied to Cirsium arvense or Polygonum convolvulus at the 8–10 and 4–6 leaf stage of development, respectively. Based on the shoot and root dry weight data from both species, the 2-ethylhexyl ester was consistently less phytotoxic than the other four formulations. With respect to Cirsium arvense shoot and root dry weight, there was no difference in efficacy between the acid, monoethanolamine salt, potassium salt and 1-decyl ester. Root dry weight changes of Polygonum convolvulus did not correlate well with an increase in dose of the five formulations. Maximum increase in stem diameter of Polygonum convolvulus occurred after application of 100 g a.e. ha^?1 of the acid, monoethanolamine salt, potassium salt and 1-decyl ester whereas with the 2-ethylhexyl ester, the maximum increase occurred after application of 200 g a.e. ha^?1. Simulated rainfall was applied 3, 6, 9 or 12 h after application of 200 g a.e. ha^?1 of the five clopyralid formulations to both species. Rainfall reduced the efficacy of clopyralid, regardless of the formulation or species. The 2-ethylhexyl ester was less efficacious than the other four formulations, irrespective of the timing of simulated rainfall.     

Formic acid: A neurologically active, hydrolyzed metabolite of insecticidal formate esters

Formate esters have potential uses as insecticides in both grain fumigation and public health pest management. This research investigated the hydrolytic metabolism and neurological effects of formate ester compounds. Studies were conducted using Drosophila and houseflies as models for other dipteran pests of medical importance. Results indicated significant formic acid liberation from a broad range of formate esters, both in vivo and in vitro. Based on these initial observations, we subsequently investigated neurological effects of formic acid on the larval housefly nervous system. We found that formic acid caused significant neuroexcitation at concentrations lower than previously shown for inhibition of insect cytochrome c oxidase; however, this conclusion does not preclude that mitochondrial effects may also be occurring in non-nervous tissues. Finally, we investigated formate ester hydrolysis by A- and B-type esterases commonly considered in pesticide detoxification research; however, no significant interactions could be identified, suggesting that as yet unidentified carboxylesterases play roles in formate ester hydrolysis. These findings provide information on formate ester metabolism and modes of action, as well as rationale for further studies on formate ester neurotoxicology and mechanisms of selective toxicity.     

Penetration of clopyralid and related weak acid herbicides into and through isolated cuticular membranes of Euonymus fortunei

A model system consisting of chemically isolated cuticular membranes placed on agar was used to study the penetration of various formulations of ¹⁴C-labelled clopyralid, fluroxypyr, triclopyr, picloram, and 2,4-D into and through cuticular membranes. Clopyralid, commercially formulated as the acid, or 1-decyl ester was rapidly absorbed after 12 h by isolated cuticles of Euonymus fortunei. There was less absorption of the monoethanolamine and potassium salt formulations when compared to the acid and 1-decyl ester. However, in terms of the absorbed ¹⁴C-activity that partitioned into the agar, there was no difference between the acid and salt formulations with approximately 90% being partitioned after 48 h. Conversely, the 1-decyl ester formulation of clopyralid was retained in the cuticle; less than 5% of the absorbed fraction was recovered in the agar after 48 h. When the acid forms of clopyralid, fluroxypyr, triclopyr, picloram, and 2,4-D were compared, there was little or no difference in absorption among the herbicides. However, the ¹⁴C-activity from clopyralid partitioned the most (90%) and triclopyr the least (50%) into the agar. When ester formulations of clopyralid, fluroxypyr, and triclopyr were compared, at least 95% of the ¹⁴C-activity was absorbed 24 h after application. However, of the amount absorbed, significantly more of the butoxyethyl ester of triclopyr (36%) partitioned into the agar than did the 1-decyl ester of clopyralid (6%) or the 1-methylheptyl ester of fluroxypyr (5%). Differential retention of various herbicide formulations in this model system may explain, in part, the differences in absorption and translocation among radiolabelled clopyralid formulations observed in previous research (Kloppenburg & Hall, 1990).     

The metabolism of the pyrethroid insecticide cypermethrin in rats; excreted metabolites

The metabolism of the pyrethroid insecticide cypermethrin has been studied in rats using three forms of ¹⁴C-labelling (benzyl-, cyclopropyl- and cyano-) and separate cis- and trans- isomers. The proportion of the dose absorbed from the intestines (50–70% at 2–3 mg kg^?1) is rapidly metabolised and eliminated. The major reaction is cleavage of the ester bond to afford the constituent cis- and trans- acids which are conjugated with glucuronic acid and eliminated in the urine. The 3-phenoxybenzyl portion of the molecule is probably released as the α-hydroxynitrile, which is converted via the aldehyde into 3-phenoxybenzoic acid. This compound is then largely hydroxylated and eliminated as a sulphate conjugate. The cyanide ion is metabolised via predictable routes, for instance, as thiocyanate. Cypermethrin is hydroxylated to some extent before hydrolysis. Most of this hydroxylation occurs at the methyl group trans to the cyclopropane carboxyl group, and at the 4-position of the phenoxy group. cis- Cypermethrin is slightly more stable than the trans-isomer.     

2,4-滴异辛酯的水解及光解特性

为明确2,4-滴异辛酯的环境行为规律,采用室内模拟试验方法,研究了2,4-滴异辛酯在不同温度、pH值、水体及初始浓度下的水解特性及其在不同pH值、水体、光源和初始浓度下的光解特性。结果表明:中性 (pH = 7) 条件下,初始质量浓度为5 mg/L的2,4-滴异辛酯在15、25 和35 ℃ 下的水解半衰期分别为346.6、231.0和173.3 h;25 ℃下,5 mg/L的2,4-滴异辛酯在pH值分别为4、7 和9 的缓冲溶液中的水解半衰期分别为77.0、231.0 和138.6 h;2,4-滴异辛酯在稻田水、自来水和河水中的水解速率高于其在蒸馏水中的水解速率,4 种条件下的半衰期分别为23.1、25.7、40.8 和63.0 h;初始质量浓度分别为1、3和5 mg/L的2,4-滴异辛酯在pH值为7的缓冲溶液中的水解半衰期分别为231.0、173.3和138.6 h。300 W汞灯照射下,2,4-滴异辛酯在酸性条件下的光解速率大于其在中性和碱性条件下,半衰期分别为49.5、77.0 和138.6 h;2,4-滴异辛酯在河水和稻田水中的光解速率高于其在自来水和蒸馏水中的光解速率,4 种条件下的半衰期分别为6.7、7.6、43.3 和46.2 h;2,4-滴异辛酯在不同光源下的光解速率依次为500 W汞灯 > 300 W汞灯 > 500 W氙灯;初始质量浓度分别为1、3和5 mg/L的2,4-滴异辛酯在pH值为7的缓冲溶液中的光解半衰期分别为63.0、43.3和40.8 h。2,4-滴异辛酯水解及光解的主要产物是2,4-滴,其降解机制主要是酯水解反应。研究结果可为2,4-滴异辛酯的合理使用及其环境风险评估提供参考。     

Toxicity of mixtures of pesticides in aquatic systems

The paper assesses the usefulness of the concept of ‘concentration addition’ (CA) for describing the joint effect of pesticides on aquatic organisms, based on literature data from 1972 to 1998. For more than 90% of 202 mixtures in 26 studies, CA was found to predict effect concentrations correctly within a factor of two. Although from a theoretical point of view the assumption of CA may be invalid when dealing with mixtures of compounds with dissimilar modes of action, the experimental results have usually been indistinguishable from that predicted by CA. Deviations from CA did occur, but were mostly limited in extent. Upward and downward deviations from CA were of comparable magnitude and frequency, and tended to cancel each other out. The combinations identified as most frequently leading to deviations from CA were those of an organophosphorus ester or a carbamate with either another organophosphorus ester or a synthetic pyrethroid. © 2000 Society of Chemical Industry     

地形对赤霞珠干红葡萄酒香气成分的影响

采用液液萃取法提取3种地形下赤霞珠干红葡萄酒的香气成分,用气相色谱-质谱进行分离测定,结合计算机检索技术对分离化合物进行鉴定,并应用色谱蜂面积归-法测定各成分的相对含量.结果表明:海拔较低的山地葡萄酒主要香气成分的种类和相对含量高于海拔高的山地葡萄酒,其中吲哚-3-乙醇、2-乙基己醇、己酸乙酯仅在前者中被检出;平地葡萄酒主要香气成分的种类和相对含量仅次于地势较低的山地葡萄酒,其中酯类化合物含量明显高于山地葡萄酒;苯乙醇、乙酸异戊酯等构成葡萄酒特征香气的组分在高海拔山地葡萄酒中未被检出.     

Effect of amitrole and 2,4-D applied preplant and pre-emergence in soybean (Glycine max)

There is limited information on the effect of amitrole and 2,4-D ester applied preplant and pre-emergence in soybean (G lycine max L.) in Ontario, Canada. Six field trials were conducted over a 2 year period (2004 to 2005) at three Ontario locations to evaluate the response of soybean to amitrole or 2,4-D ester applied at 14 days preplant (DPP), 7 DPP, 1 day after planting (DAP), and 7 DAP. The application of amitrole resulted in as much as 5.8, 3.9, 1.7, and 1% visible crop injury in soybean at 7, 14, 28, and 56 days after emergence (DAE), respectively. There was no visible injury in soybean with any amitrole treatment at 56 DAE, except for amitrole applied at 7 DAP, which caused 1% visible injury in soybean at 2310 g ha⁻¹. The application of the 2,4-D ester caused ≤8.3, 9.7, 4.6, and 1.3% visible injury in soybean at 7, 14, 28, and 56 DAE, respectively. The visible injury decreased over time. There was no visible injury in soybean with any of the 2,4-D ester treatments at 56 DAE, except for the 2,4-D ester treatment applied at 7 DAP, which caused 1% visible injury at 1155 g ha⁻¹ and 1.3% visible injury at 2310 g ha⁻¹. Soybean generally responded similarly to amitrole and 2,4-D ester when applied at 14 and 7 DPP; however, soybean was more tolerant to amitrole compared to 2,4-D ester when applied at 1 or 7 DAP. The application of amitrole and 2,4-D ester resulted in no biomass or yield reduction in soybean compared to the weed-free, untreated control at all doses and application timings evaluated. Soybean is tolerant to the preplant and pre-emergence application of amitrole or 2,4-D ester at the doses evaluated.     

Metabolism of phenothrin or 3-phenoxybenzyl d-trans-chrysanthemumate in mammals

Carbon-14 d-trans-phenothrin or 3-phenoxybenzyl d-trans-chrysanthemumate labeled at the hydroxymethyl group in the alcoholic moiety was administered orally to male Sprague-Dawley rats at the rate of 200 mg/kg. The compound was rapidly absorbed from the gastrointestinal tract and distributed into various tissues.Radioactivity was rapidly eliminated (over 3 days) via the urine (ca. 60%) and feces (ca. 40%). No detectable radioactive carbon dioxide was expired. The urinary and fecal metabolites were separated and identified, the predominant one being 3-(4′-hydroxy) phenoxybenzoic acid and amounting to approximately 55% of the recovered radioactivity. 3-Phenoxybenzoic acid, free and conjugated with glycine, was also identified. In vitro studies using liver preparation from rats, mice, guinea pigs, rabbits, and dogs revealed that d-trans-phenothrin was hydrolyzed to 3-phenoxybenzyl alcohol, which was subsequently oxidized. The l-trans isomer was also easily hydrolzyed, whereas d-cis- and l-cis-phenothrin were resistant to hydrolytic attack at the ester linkage.     

Effects of herbicides or mowing on musk thistle seed production*

Mowing musk thistle (Carduus nutans L.) within 2 days of the first terminal heads in a plant population showing anthesis eliminated the production of germinable seed from all mowed stalks. Mowing later than 4 days after anthesis led to significant amounts of germinable seed being produced. Regrowth, which produced viable seed, usually occurred from plants mowed before first terminal heads began anthesis. A single mowing usually did not give satisfactory control due to wide differences in the maturity of plants in a natural population. When the terminal heads had reached late bud or more mature stages, 2,4-D ester [isoocyt] ester of (2,4-dichlorophenoxy) acetic acid] at M kg/ha or 2–2 kg/ha did not provide satisfactory control. In general, the most effective herbicide treatments tested at all three stages of maturity were dicamba (3,6-dichloro-o-anisic acid) at 056 kg/ha plus 2,4-D amine (dimethyl amine salt) at M kg/ha, 2,4-D ester at 4–4 kg/ha, or dicamba at 0–56 kg/ha. Inconsistent control of musk thistle results from variability within naturally occurring populations. Uneven development of stands as well as variation among plants are suggested as possible causes.     

Relation between volatility rating and composition of phenoxy herbicide ester formulations

A CIPAC/AOAC test with tomato plants is used to specify the volatility ratings of herbicide ester formulations. This work compares the tomato plant test with an alternative chemical one. The concentrations of esters and the effective molecular weight and density of each formulation were used with the ester vapour pressures to calculate its herbicide vapour pressure as complete, and evaporated formulations. The range was from 28.8 mPa (at 257deg;C) for a mixture of 2,4–D esters to 0–07 mPa (at 25°C) for a 2,4,5–T-(iso-octyl) formulation, as complete formulations, and 35-5 and 0–16 mPa (at 25°C) as evaporated ones. A value of 0–6 mPa (at 25°C) was selected on the basis of the tomato plant test as the cut-off area for low-volatile esters and is recommended to be included in specifications for herbicide esters. Formulations with a herbicide vapour pressure above 3.3 mPa (at 25°C) are high-volatile ones according to the tomato plant test, while between 0–6–3.3 mPa (at 25°C) is a borderline region where the test gives mixed results. Levels of 2,4–D-ethyl and methyl were added to pure 2–ethylhexyl esters of 2,4–D and a 2,4,5–T-(iso-octyl) formulation to find what level of contamination would change the rating of these esters from low to high volatile. Formulations of 2,4–D-(iso-octyl) should not contain more than 11 g litre^?1 2,4–D as methyl ester or 2.0 g litre^?1 2,4–D as ethyl ester. Formulations of 2,4,5–T-(iso-octyl) should not contain more than 26 g litre^?1 2,4–D as methyl ester or 4.7g litre^?1 2,4–D as ethyl ester.