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1.
The hydrolysis of [14C] fenpropathrin ( I ) [(RS)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate] was studied in buffer solutions at pH 1.9–10.4, and in natural river and sea water at 25, 40, 55 and 65°C under laboratory conditions. The hydrolysis of I proceeded predominantly through neutral (pH independent) and base-catalysed processes in the regions below pH 3.9 and above pH 7.0, respectively, whereas both reactions occurred between pH 3.9 and 7.0. The rates of hydrolysis of I in buffer solutions were similar to those in one sample of river and one sample of sea water. If this obtains generally, it may be expected that the half-life of I in natural waters, normally within the range pH 5–9, will range from 1.54 to 1080 days at 40°C, 11.3 to 8520 days at 25°C and, by extrapolation of the data obtained in buffer solutions, 106 to 83 000 days at 10°C. The rate constants for hydrolysis of I in aqueous media can be expressed by: Where log kN = 9.60–(5.56 × 103 T?1) and log kB = 7.32–(2.56 × 103 T?1). The calculated rate constants were in good accord with the observed values in buffer solutions. Cleavage of the ester linkage was more rapid than hydration of the cyano group at any pH and temperature tested.  相似文献   

2.
BACKGROUND: Sorption coefficients (the linear KD or the non‐linear KF and NF) are critical parameters in models of pesticide transport to groundwater or surface water. In this work, a dataset of isoproturon sorption coefficients and corresponding soil properties (264 KD and 55 KF) was compiled, and pedotransfer functions were built for predicting isoproturon sorption in soils and vadose zone materials. These were benchmarked against various other prediction methods. RESULTS: The results show that the organic carbon content (OC) and pH are the two main soil properties influencing isoproturon KD. The pedotransfer function is KD = 1.7822 + 0.0162 OC1.5 ? 0.1958 pH (KD in L kg?1 and OC in g kg?1). For low‐OC soils (OC < 6.15 g kg?1), clay and pH are most influential. The pedotransfer function is then KD = 0.9980 + 0.0002 clay ? 0.0990 pH (clay in g kg?1). Benchmarking KD estimations showed that functions calibrated on more specific subsets of the data perform better on these subsets than functions calibrated on larger subsets. CONCLUSION: Predicting isoproturon sorption in soils in unsampled locations should rely, whenever possible, and by order of preference, on (a) site‐ or soil‐specific pedotransfer functions, (b) pedotransfer functions calibrated on a large dataset, (c) KOC values calculated on a large dataset or (d) KOC values taken from existing pesticide properties databases. Copyright © 2011 Society of Chemical Industry  相似文献   

3.
Batch adsorption Koc values of fluroxypyr-methylheptyl ester (20000 1kg?1) and fluroxypyr (74 1kg?1) indicate increased mobility after hydrolysis of the ester to fluroxypyr. After 1 to 2 weeks incubation time in four soils, desorption Koc values of fluroxypyr were 100-200 1kg?1 but increased to 400-700 1kg?1 after 8 weeks. The increase in desorption Koc was related to incubation time and not to concentration, and it was interpreted as an entrapment of the fluroxypyr within the soil organic matter. Similar increases in desorption Koc with incubation time were noticed for pyridinol and methoxypyridine metabolites of fluroxypyr. Koc values also increased along the metabolic sequence fluroxypyr/pyridinol/methoxypyridine, with maximum Koc values of 3000-4000 1 kg?1 for the methoxypyridine metabolite. Hence mobility of the fluroxypyr aromatic ring strongly decreases with increased residence time in the soil.  相似文献   

4.
The inhibition of eel acetylcholinesterase by the 4-nitrophenyl esters of 2-furyl(methyl)-, methyl(2-thienyl)-, di-2-furyl-, and di-2-thienylphosphinic acid (I, II, III, and IV, respectively) was investigated at pH 6.90 in 0.067 M phosphate buffer (25.0°C) using stopped-flow instrumentation and automated data processing. Our evaluation of the dissociation constant, Kd, the unimolecular bonding rate constant, k2, and the bimolecular reaction constant, ki, are the first reported values for these constants for alkyl/heteroaryl and diheteroaryl esters of phosphinic acids. The largest ki value (19,330 M?1 sec?1) was observed for the reaction of I with the enzyme. The order for the remaining three is II > IV > III. There is no direct relationship between the hydrolysis rates of the esters and their anticholinesterase activities on eel acetylcholinesterase. Likewise, there is no direct relationship between their anticholinesterase activities and the LD50 values in rats.  相似文献   

5.
Seventeen field isolates of Botrytis cinerea were compared by determining their radial growth on synthetic media containing various amounts of 21 antifungal compounds. Twelve of these compounds were fungicides that are recommended for the control of Botrytis infections. There were marked differences between the isolates in their sensitivity to the compounds. Individual isolates displayed high levels of resistance to some of the fungicides, including benomyl, carbendazim, iprodione, thiabendazole, thiophanate-methyl, vinclozolin and zineb. The most potent growth inhibitors were benomyl and carbendazim (ED95 values for most isolates <0.1 μg fungicide ml?1 media), dichlofluanid, iprodione, nystatin, thiabendazole, thiophanatemethyl and vinclozolin (ED95 values for most isolates < 1.0 μg ml?1), and captan, chlorothalonil, dicloran and thiram (ED95 values for most isolates < 6.0 μg ml?1). Zineb was much less potent than the other recommended anti-Botrytis fungicides; it was no more effective than carboxin, dinocap and mancozeb (ED95 values for most isolates > 25 μg ml?1).  相似文献   

6.
The effects of abamectin (AVMB1) on intracellular potassium ion activity (aKi) and resting membrane potential (Em) of the skeletal muscle cells of final instar larvae of Phormia terraenovae (Diptera) were investigated using K+-selective micro-electrodes. Bathing the preparation in 10? M AVMB1(+ 1 ml litre?1 dimethylsulfoxide) for 60 min caused a significant (31%) decrease in aKi, whilst Em depolarized on average by 19 mV (nearly 50% of the original control value). The difference EK-Em increased by 9 mV, although EK (potassium equilibrium potential) remained more negative than Em. These results could be due to a cationic effect of AVMB1 possibly involving an increase in K+ and Na+ conductances of the muscle plasma membrane.  相似文献   

7.
The inhibition of eel acetylcholinesterase and bovine erythrocyte acetylcholinesterase by the 4-nitrophenyl esters of methyl-, ethyl-, and isopropyl(phenyl)phosphinic acid (MPP, EPP, and IPP, respectively) was investigated at pH 6.90 in 0.067 M phosphate buffer (25.0°C) using stopped-flow instrumentation and automated data processing. Our evaluation of the dissociation constant, Kd, the unimolecular bonding rate constant, k2, and the bimolecular reaction constant, ki, are the first reported values for these constants for a homologous series of this class of organophosphorus compounds. The largest k1 value (29,428 M?1 sec?1) was observed for the reaction of eel acetylcholinesterase with 4-nitrophenyl methyl(phenyl)phosphinate. The smallest ki value (9.6 M?1 sec?1) was observed for the reaction of bovine erythrocyte acetylcholinesterase with 4-nitrophenyl isopropyl(phenyl)phosphinate.  相似文献   

8.
The hydrolysis of 3, 4-dihydroprecocene I 3, 4-epoxide (3, 4-dihydro-7-methoxy-2, 2-dimethyl-3, 4-epoxy-2H-benzo[b]pyran), the putative ultimate cytotoxin of the insect growth regulator precocene I (7-methoxy-2, 2-dimethyl-2H-benzo[b]pyran), has been studied and found to exhibit first-order kinetics [k = 0.17 s?1 in 10 mm-phosphate buffer pH 7.0, containing 1, 4-dioxane (1 + 1 by volume), ionic strength 0.1]. Plots of log k versus pH, and k versus buffer concentration, suggest that the reaction is subject to both specific and general acid catalysis. High-performance liquid chromatography showed the reaction products to be predominantly the corresponding stereoisomeric diols (3, 4-dihydro-7-methoxy-2, 2-dimethyl-2H-benzo[b]pyran-3, 4-diol), the trans : cis ratio of which varied from 1.8: 1 to 2.2: 1 but was constant over the pH range 6-8, at a given buffer concentration. The results indicate that acid-catalysed hydration of 3, 4-dihydroprecocene I 3, 4-epoxide is an SN1 reaction, involving a trigonally hybridised carbocation at C4, even at physiological pH. Similar studies on 3, 4-dihydroiso-precocene I 3, 4-epoxide (3, 4-dihydro-6-methoxy-2, 2-dimethyl-3, 4-epoxy-2H-benzo-[b]pyran), a biologically inactive isomer of 3, 4-dihydroprecocene I 3, 4-epoxide suggest that an SNI mechanism also contributes to its hydrolysis, but the rate constant is 4000 times lower than that for 3, 4-dihydroprecocene I 3, 4-epoxide. Knowledge of the reactivity and mechanism of reaction of such compounds forms an important part of the basis for rational prediction of biological activity in precocene analogues, and hence their possible use as pest control agents.  相似文献   

9.
BACKGROUND: Clomazone is a herbicide used to control broadleaf weeds and grasses. Clomazone use in agriculturally important crops and forests for weed control has increased and is a potential water contaminant given its high water solubility (1100 µg mL?1). Soil sorption is an environmental fate parameter that may limit its movement to water systems. The authors used model rice and forest soils of California to test clomazone sorption affinity, capacity, desorption, interaction with soil organic matter and behavior with black carbon. RESULTS: Sorption of clomazone to the major organic matter fraction of soil, humic acid (HA) (Kd = 29–87 L kg?1), was greater than to whole soils (Kd = 2.3–11 L kg?1). Increased isotherm non‐linearity was observed for the whole soils (N = 0.831–0.893) when compared with the humic acids (N = 0.954–0.999). Desorption isotherm results showed hysteresis, which was greatest at the lowest solution concentration of 0.067 µg mL?1 for all whole soils and HA extracts. Aliphatic carbon content appeared to contribute to increased isotherm linearity. CONCLUSION: The results indicate that clomazone does not sorb appreciably to sandy or clay soils. Its sorption affinity and capacity is greater in humic acid, and consequently clomazone has difficulty desorbing from soil organic matter. Sorption appears to follow processes explained by the dual‐mode model, the presence of fire residues (black carbon) and a recently proposed sorption mechanism. Copyright © 2009 Society of Chemical Industry  相似文献   

10.
Residue data are reported for flamprop-isopropyl ( I ) in barley grain and straw samples following applications of the herbicide to crops grown in eight countries. The samples were analysed for I and its hydrolysis product N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL -alanine ( II ). Following recommended applications (normally 1 kg ha?1 at Feekes scale G-I/J), residues of I and II in the grain were low (90% were <0.02 mg kg?1 for I , 86% were <0.06 mg kg?1 for II , levels which were essentially the limits of determination). Residues in straw were higher and more variable, but again 63 and 77% of samples were below 1 mg kg?1 for I and II , respectively.  相似文献   

11.
Samples of wheat grain and straw have been analysed from trials with the wild oat herbicide benzoylprop-ethyl ( I ) in several countries. Following recommended commercial treatments (application of 1.0–1.6 kg ha?1 at Feekes growth stage G-J), total residues of I and its hydrolysis product N-benzoyl-N-(3,4-dichlorophenyl)-DL - alanine (free and conjugated) were low and in the majority of instances they were < 0.01 mg kg?1 in samples of grain from the UK, although rather higher residues were detected in some grain samples from other countries. Residues in straw were higher, but normally did not exceed 2 mg kg?1, and were rather variable, possibly as a result of differences in agricultural practice.  相似文献   

12.
BACKGROUND: Clomazone is a popular herbicide used on California rice fields and exhibits rapid anaerobic microbial degradation (t1/2 = 7.9 days). To test the potential of direct and indirect photolytic degradation as a cofactor in the overall degradation rate, sacrificial time‐series microcosms were amended with water, non‐sterilized soil + water and sterilized soil + water. Clomazone was added to each microcosm, which was then exposed to natural and artificial sunlight over 35 days. Water and acetonitrile extracts were analyzed for clomazone and metabolites via LC/MS/MS. RESULTS: The calculated pseudo‐first‐order degradation rate constants (k) were kwater = 0–0.005 ± 0.003 day?1, ksterile = 0–0.005 ± 0.003 day?1 and knon?sterile = 0.010 ± 0.002–0.044 ± 0.007 day?1, depending on light type. The formation of ring‐open clomazone, a microbial metabolite, correlated with clomazone degradation. Trace amounts of 5‐hydroxyclomazone (m/z = 256 → 125), aromatic hydroxyclomazone (m/z = 256 → 141) and an unknown product (m/z = 268 → 125) were observed. CONCLUSIONS: The photolytic degradation rate depends on both light type and the quality of the chromophores that induce indirect photolysis. Microbial degradation was found to be sensitive to temperature fluctuations. Overall, microbes are shown to be more detrimental to the environmental fate of clomazone than photolysis. Copyright © 2012 Society of Chemical Industry  相似文献   

13.
BACKGROUND: Sorption largely controls pesticide fate in soils because it influences its availability for biodegradation or transport in the soil water. In this study, variability of sorption and desorption of isoxaflutole (IFT) and its active metabolite diketonitrile (DKN) was investigated under conventional and conservation tillage. RESULTS: According to soil samples, IFT KD values ranged from 1.4 to 3.2 L kg?1 and DKN KD values ranged from 0.02 to 0.17 L kg?1. Positive correlations were found between organic carbon content and IFT and DKN sorption. IFT and DKN sorption was higher under conservation than under conventional tillage owing to higher organic carbon content. Under conservation tillage, measurements on maize and oat residues collected from the soil surface showed a greater sorption of IFT on plant residues than on soil samples, with the highest sorbed quantities measured on maize residues (KD ≈ 45 L kg?1). Desorption of IFT was hysteretic, and, after five consecutive desorptions, between 72 and 89% of the sorbed IFT was desorbed from soil samples. For maize residues, desorption was weak (<50% of the sorbed IFT), but, after two complementary desorptions allowing for IFT hydrolysis, DKN was released from maize residues. CONCLUSION: Owing to an increase in organic carbon in topsoil layers, sorption of IFT and DKN was enhanced under conservation tillage. Greater sorption capacities under conservation tillage could help in decreasing DKN leaching to groundwater. Copyright © 2012 Society of Chemical Industry  相似文献   

14.
The kinetic constants, Ka (affinity) k+2 (acylation), ka (second order, acylation), and k+3 (deacylation) were determined for the reaction of a number of organophosphorus (OP) and carbamate inhibitors with acetylcholinesterase (AChE) from inhibitor-sensitive Yeerongpilly (Y) OP susceptible ticks, relatively insensitiveBiarra (B) and Ridgelands (R) OP-resistant ticks and bovineerythrocytes (Bov). B, R, and Bov AChE exhibited lower affinity for inhibitors than Y AChE. K+2 (carbamylation and phosphorylation) decreased in the order Bov ? Y ? B ? R. For inhibitors with markedly different leaving groups there was no clear-cut linear relationship between rates of alkaline hydrolysis and enzymatic hydrolysis (acylation). Decarbamylation and dephosphorylation were rate limiting. The ratios of Y to B to R AChE for Vmax and catalytic center activity (substrate hydrolysis) and k+3 (carbamate hydrolysis) were very similar. This was a requirement if a lowered deacylating ability was the cause of the reduced catalytic hydrolysis of substrate observed for B and R AChE. Changes to the catalytic sites of B and R AChE are discussed. A strong parallel of these results is drawn with those obtained for spider mite AChE.  相似文献   

15.
Water penetrated through isolated leaf cuticles of dwarf orange (Citrus mitis Blanco, ?Calamondin’?) as undissociated molecules because both [18O] water (1H218O) and HTO (1H3H16O) permeated at the same rate. HTO penetrated to 3 to 21% of the theoretical equilibrium value (TEV) in an unstirred system within 10 days for astomatous cuticles and 50 to 60% of TEV for stomatous cuticles. The permeability coefficient (k) of HTO through astomatous cuticles at 25°C was 6.8 × 10?7 cm s?1. Two highly water-soluble 14C-labelled compounds, trichloroacetic acid (TCA) and 1,2,4-triazol-3-ylamine [aminotriazole (BSI) or amitrole (ISO)], and two nearly water-insoluble 14C-labelled compounds, 1-naphthyl methylcarbamate (carbaryl) and 2,6-dichloro-4-nitroaniline (dicloran), were compared to HTO as a reference standard in permeation studies. All four organic molecules permeated without decomposing. The relative k values for TCA, aminotriazole, carbaryl, HTO and dicloran were 0.32, 0.47, 0.71, 1.0, and 1.5 respectively. Although this suggested that the permeation of organic molecules may be inversely related to water solubility, this could not be established with certainty due to large variations in the data. The k values were obtained for 12 other organic compounds through a variety of biological and model membranes or were calculated from the literature. Any relationships between k and various molecular characteristics were unclear because a wide variety of cuticle sources and experimental design was used by different investigators working in this area. The calculation of k is considered essential in all permeability studies so that comparisons can be made between laboratories.  相似文献   

16.
The depletion of residues of benzolyprop-ethyl ( I ) and its hydrolysis product N-benzoyl-N-(3,4-dichlorophenyl)-DL -alanine ( II ) in soils is reported from various trials following applications of I to soil and crops at up to 3 kg ha?1. Quite rapid hydrolysis of I to II occurred in most soils and depletion of II followed. The total residue of I and II in the soil often initially increased, probably because of transfer of chemical from the crop to the soil, but the time for 50% disappearance of the total residue ( I+II ) was normally between 4 and 16 weeks. When four sites were treated for three successive years, carry-over of residues was negligible in three sites and showed no progressive increase in the fourth.  相似文献   

17.
T. KATAN 《EPPO Bulletin》1985,15(3):371-377
Field isolates of Botrytis cinerea with moderate levels of resistance to dicarboximide fungicides (ED50 1.0–4.9 μg ml?1) and to dicloran were obtained from glasshouses where vinclozolin and iprodione failed to control grey mould. From sensitive and moderatcly-resistant cultures, laboratory isolates were selected on dicarboximide-amended medium, which were highly resistant to these fungicides (ED50 125->3000 μg ml?1). Conidia of all the resistant isolates germinated well on media amended with 100 μg ml?1 of the dicarboximides vinclozolin, iprodione, procymidone and myclozolin and with 5 μg ml?1 of metomeclan. However, the spores of the moderately resistant isolates did not germinate on 100 μg ml?1 metomeclan while the spores of the highly resistant isolates germinated well. Using media with 100 μg ml?1 of metomeclan to distinguish between the two phenotypes, no highly resistant strain was detected among 312 resistant samples from five cucumber glasshouses with a high frequency of moderately resistant strains. From air-borne inoculum of five glasshouses with 100% resistant populations, 1604 colonies were recovered on vinclozolin-amended (100 μg ml?1) medium and none on metomeclan-amended (100 μg ml?1) medium. It is concluded that strains of B. cinerea highly resistant to dicarboximides are absent from field populations.  相似文献   

18.
The kinetics of the hydrolysis reactions of chlorpyrifos-methyl and chlorpyrifos, in the presence of copper(II), have been measured in buffered aqueous solutions. For each reaction, a rate law of the type -d[pesticides]/dt= k2[pesticides][Cu2+] was observed. As the concentration of copper(II) increased, a corresponding increase in the rate of hydrolysis was observed until the concentration of copper(II) reached about 1.0 × 10?2M. At this point, the rate of hydrolysis became independent of the concentration of copper(II) in both reactions. Using the experimental data, a mechanism for each reaction is proposed, in which the copper(II) ion forms a six-membered ring complex with the nitrogen in the ring structure and the sulphur of the phosphorothioate moiety. The rate of hydrolysis increased with increasing pH. At higher pH values, precipitation of Cu2+ was observed and general base-hydrolysis reactions became more and more important. The differences in the rate constant observed is explained using the inductive effect theory of the alkyl group.  相似文献   

19.
A series of 27 substituted aryl N-methoxy-N-methylcarbamates were synthesized and their ability to reversibly inhibit house fly-head and bovine-erythrocyte acetylcholinesterase and horse-serum cholinesterase was determined. These compounds were all competitive, reversible inhibitors of bovine erythrocyte acetylcholinesterase but some of them showed mixed competitive inhibition against the house fly-head and horse-serum enzymes. Dissociation constants (Ki) as small as 9.9 × 10?9M and as large as 1.4 × 10?4M were observed. A highly satisfactory correlation between log Ki for the inhibition of fly-head acetylcholinesterase by the N-methoxy-N-methylcarbamates and ?log I50 for the inhibition of the same enzyme by the corresponding methylcarbamates was noted. Analysis of the anticholinesterase data by multiple regression showed -log Ki to be related to Hansch's π constant and ring position terms. The results indicate that reversible binding of these compounds to acetylcholinesterase occurs by hydrophobic bonding.  相似文献   

20.
The kinetic constants of a variety of substituted phenyl N-methyl- and N,N-dimethylcarbamates, which inhibit bovine erythrocyte acetylcholinesterase, were determined by various experimental procedures. A procedure in the presence of a chromogenic substrate was developed, based on the suggestion of Hart and O'Brien, and was compared with the conventional Main method. The dissociation equilibrium constant, Kd, and the carbamylation rate constant, k2, were shown to apparently depend on the inhibitor concentration range used for the determination in both procedures. Assuming that the binding of further inhibitor molecules to the reversible complex and the carbamylated enzyme is significant under conditions with high inhibitor concentrations, the concentration dependence of the kinetic constants was nicely delineated. It is indicated that reliable constants are obtainable with a rather low inhibitor concentration range, whose product by ki is of the order of 0.2–1.0 min?1.  相似文献   

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