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1.
The persistence of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), [14C]dicamba (3,6-dichloro-2-methoxybenzoic-7-14C acid) and propanil [N-(3,4-dichlorophenyl)propionamide] at rates equivalent to 1 kg ha?1, were studied under laboratory conditions in a clay loam, a heavy clay and a sandy loam at 85% of field capacity and at 20±1°C, both singly and in the presence of herbicides normally applied with these chemicals as tank-mix or split-mix components. The degradation of bromoxynil was rapid with over 90% breakdown occurring within a week in the heavy clay and sandy-loam soils, while in the clay-loam approximately 80% of the bromoxynil had broken down after 7 days. In all three soils degradation was unaffected by the presence of asulam, diclofop-methyl, flamprop-methyl, MCPA, metribuzin or propanil. Propanil underwent rapid degradation in all soil treatments, with over 95% of the applied propanil being dissipated within 7 days. There were no noticeable effects on propanil degradation resulting from applications of asulam, barban, bromoxynil, dicamba, MCPA, MCPB, metribuzin or 2,4-D. The breakdown of [14C]dicamba in a particular soil was unaffected by being applied alone or in the presence of diclofop-methyl, flampropmethyl, MCPA, metribuzin, propanil or 2,4-D. The times for 50% of the applied dicamba to be degraded were approximately 16 days in both the clay loam and sandy loam, and about 50 days in the heavy clay.  相似文献   

2.
The breakdown of bromoxynil octanoate in 5 different soil types has been studied in a soil perfusion apparatus using herbicide labelled with 14C either in the cyano group or in the aromatic ring. Even when applied at rates equivalent to 5 to 25 times those used commercially, the herbicide was fairly rapidly and extensively degraded at 15°. After 12 to 13 weeks, up to 80% of the radioactivity in the 14CN group and up to 63 % of the 14C in the ring were liberated as carbon dioxide. A small proportion (16 to 19%) of the radioactivity from ring-labelled herbicide remained attached to the soil, probably not as the original herbicide, but in a form not readily leached. Only trace quantities of 3,5-dibromo-4-hydroxy-benzamide (0.5%) and 3,5-dibromo-4-hydroxybenzoic acid (0.1%) were detectable during these soil perfusions.  相似文献   

3.
BACKGROUND: The objectives of these laboratory experiments were: (1) to assess bromoxynil sorption, mineralization, bound residue formation and extractable residue persistence in a Dundee silt loam collected from 0–2 cm and 2–10 cm depths under continuous conventional tillage and no‐tillage; (2) to assess the effects of autoclaving on bromoxynil mineralization and bound residue formation; (3) to determine the partitioning of non‐extractable residues; and (4) to ascertain the effects of bromoxynil concentration on extractable and bound residues and metabolite formation. RESULTS: Bromoxynil Kd values ranged from 0.7 to 1.4 L kg?1 and were positively correlated with soil organic carbon. Cumulative mineralization (38.5% ± 1.5), bound residue formation (46.5% ± 0.5) and persistence of extractable residues (T1/2 < 1 day) in non‐autoclaved soils were independent of tillage and depth. Autoclaving decreased mineralization and bound residue formation 257‐fold and 6.0‐fold respectively. Bromoxynil persistence in soil was rate independent (T1/2 < 1 day), and the majority of non‐extractable residues (87%) were associated with the humic acid fraction of soil organic matter. CONCLUSIONS: Irrespective of tillage or depth, bromoxynil half‐life in native soil is less than 1 day owing to rapid incorporation of the herbicide into non‐extractable residues. Bound residue formation is governed principally by biochemical metabolite formation and primarily associated with soil humic acids that are moderately bioavailable for mineralization. These data indicate that the risk of off‐site transport of bromoxynil residues is low owing to rapid incorporation into non‐extractable residues. Published 2009 by John Wiley & Sons, Ltd  相似文献   

4.
A spectrophotometric method was developed to detect bromoxynil in Regina heavy clay, and the breakdown under different temperature and moisture conditions was studied. At rates equivalent to 14 kg/ha, over 50% of the applied bromoxynil was degraded in 2 weeks at 25°C and at moisture levels in excess of the wilting point. Losses at 18°C were slightly slower. Little breakdown occurred in sterile soil, indicating that microbial degradation could be an important factor contributing to bromoxynil breakdown under field conditions. Paper and thin-layer chromatographic techniques were used to isolate and identify soil degradation products. In addition to the parent compound small amounts of 3,5-dibromo-4-hydroxybenzamide and 3,5-dibromo-4-hydroxybenzoic acid were detected.  相似文献   

5.
The biomineralization of [14C]glyphosate, both in the free state and as 14C-residues associated with soybean cell-wall material, was studied in soil samples from four different agricultural farming systems. After 26 days, [14C]carbon dioxide production from free glyphosate accounted for 34–51% of the applied radiocarbon, and 45–55% was recovered from plant-associated residues. For three soils, the cumulative [14C]carbon dioxide production from free glyphosate was positively correlated with soil microbial biomass, determined by substrate-induced heat output measurement and by total adenylate content. The fourth soil, originating from a former hop plantation, and containing high concentrations of copper from long-term fungicide applications, did not fit this correlation but showed a significantly higher [14C]carbon dioxide production per unit of microbial biomass. Although the cumulative [14C]carbon dioxide production from plant-associated 14C-residues after 26 days was as high as from the free compound, it was not correlated with the soil microbial biomass. This indicates that the biodegradation of plant-associated herbicide residues, in contrast to that of the free compound, involves different degradation processes. These encompass either additional steps to degrade the plant matrix, presumably performed by different soil organisms, or fewer degradation steps since the plant-associated herbicide residues are likely to consist mainly of easily degradable metabolites. Moreover, the bioavailability of plant-associated pesticide residues seems to be dominated by the type and strength of their fixation in the plant matrix. ©1997 SCI  相似文献   

6.
The dependence of the behaviour of metsulfuron-methyl on soil pH was confirmed during incubations under controlled laboratory conditions with two French soils used for wheat cropping. The fate of [14C] residues from [triazine-14C]metsulfuron-methyl was studied by combining different experimen-tal conditions: soil pH (8·1 and 5·2), temperature (28 and 10°C), soil moisture (90 and 50% of soil water holding capacity) and microbial activity (sterile and non-sterile conditions). Metsulfuron-methyl degradation was mainly influenced by soil pH and temperature. The metsulfuron-methyl half-life varied from five days in the acidic soil to 69 days in the alkaline soil. Under sterile conditions, the half-life increased in alkaline soil to 139 days but was not changed in the acidic soil. Metsulfuron-methyl degradation mainly resulted in the formation of the amino-triazine. In the acidic soil, degradation was characterised by rapid hydrolysis giving two specific unidentified metabolites, not detected during incubations in the alkaline soil. Bound residues formation and metsulfuron-methyl mineralisation were highly correlated. The extent of bound residue formation increased when soil water content decreased and was maximal [48 (±4)% of the applied metsulfuron-methyl after 98 incubation days] in the acidic soil at 50% of the water holding capacity and 28°C. Otherwise, bound residues represented between 13 and 32% of the initial radioactivity. © 1998 SCI  相似文献   

7.
The potential to mineralize 2,4‐dichlorophenoxyacetic acid (2,4‐D), mecoprop, isoproturon and terbuthylazine was studied in soil and aquifer chalk sampled at an agricultural field near Aalborg, Denmark. Laboratory microcosms were incubated for 258 days under aerobic conditions at 10 °C with soil and chalk from 0.15–4.45 m below the surface. The [ring‐U‐14C]‐labeled herbicides were added to obtain a concentration of 6 µg kg?1 and mineralization was measured as evolved [14C]carbon dioxide. The herbicides were readily mineralized in soil from the plough layer, except for terbuthylazine, which was mineralized only to a limited extent. In the chalk, lag periods of at least 40 days were observed, and a maximum of 51%, 33% and 6% of the added 2,4‐D, mecoprop and isoproturon, respectively, were recovered as [14C]carbon dioxide. Large variations in both rate and extent of mineralization were observed within replicates in chalk. No mineralization of terbuthylazine in chalk was observed. As a measure of the general metabolic activity towards aromatic compounds, [ring‐U‐14C]‐benzoic acid was included. It was readily mineralized at all depths. © 2000 Society of Chemical Industry  相似文献   

8.
The persistence of [14C]MCPA at a rate equivalent to 1 kg ha?1 was studied under laboratory conditions in a clay loam, heavy clay and sandy loam at 85% of field capacity moisture and 20±1°C both alone and in the presence of tri-allate, trifluralin, tri-allate and trifluralin, malathion, Vitaflow DB, malathion and Vitaflow DB, bromoxynil, bromoxynil and asulam, bromoxynil and difenzoquat, dicamba, dicamba and mecoprop, linuron, MCPB, metribuzin, propanil, TCA, benzoylprop-ethyl, diclofop-methyl, and flamprop-methyl. Except in the soils treated with asulam, the half-lives of [14C]MCPA in all three soil types were similar, being approximately 13±1 days, thus indicating that none of the other chemicals studied adversely affected the soil degradation of MCPA. In the asulam treated soils, the half-lives of the MCPA were about 3 days longer than in non-asulam treated soils; the effect was most marked in the clay loam.  相似文献   

9.
Alfalfa was root-treated with [14C]propham (isopropyl carbanilate[14C-phenyl(U)]) for 7 days and then harvested and freeze-dried. Rats and sheep were orally given either 14C-labeled alfalfa roots ([14C]root) or 14C-labeled alfalfa shoots ([14C]shoot). When the [14C]root was given, 6.5–11.0% of the 14C was excreted in the urine and 84.6–89.4% was excreted in the feces within 96 h after treatment. Less than 3% of the 14C remained in the carcass (total body—gastrointestinal tract and contents) 96 h after treatment. When [14C]shoot was given, 53.2–55.2% of the 14C was excreted in the urine, 32.1–43.4% was excreted in the feces, and the carcass contained 0.2–1.1% of the 14C 96 h after treatment. When the insoluble fraction (not extracted by a mixture of CHCl3, CH3OH, and H2O) of both alfalfa roots and shoots was fed to rats, more than 86% of the 14C was excreted in the feces and less than 3% remained in the carcass 96 h after treatment. The major radiolabeled metabolites in the urine of the sheep fed 14C shoot were purified by chromatography and identified as the sulfate ester and the glucuronic acid conjugates of isopropyl 4-hydroxycarbanilate. Metabolites in the urine of the sheep treated with [14C]root were tentatively identified as conjugated forms of isopropyl 4-hydroxycarbanilate, isopropyl 2-hydroxycarbanilate, and 4-hydroxyaniline. The combined urine of rats dosed with [14C]shoot and [14C]root contained metabolites tentatively identified as conjugated forms of isopropyl 4-hydroxycarbanilate, isopropyl 2-hydroxycarbanilate, and 4-hydroxyaniline.  相似文献   

10.
Ring- and carboxyl-labelled [14C]2,4-D were incubated under laboratory conditions, at the 2 g/g level, in a heavy clay, sandy loam, and clay loam at 85% of field capacity and 20 1C. The soils were extracted at regular intervals for 35 days with aqaeous acidic acetonitrile, and analysed for [14C]2,4-D and possible radioactive degradation products. Following solvent extraction, a portion of the soil residues were combusted in oxygen to determine unextracted radioactivity as [14C]carbon dioxide. The remaining soil residues were then treated with aqueous sodium hydroxide, and the radioactivity associated with the fulvic and humic soil components determined. In all soils there was a rapid decrease in the amounts of extractable radioacitivity, with only 5% of that applied being recoverable after 35 days. All recoverable radioactivity was attributable to [14C]2,4-D, and no [14C]-containing degradation products were observed. This loss of extractable radioactivity was accompanied by an increase in non-extractable radioactivity. Approximately 15% of the applied radioactivity, derived from carboxyl-labelled [14C]2,4-D, and 30% from the ring-labelled [14C]2,4-D was associated with the soil in a non-extractable form, after 35 days of incubation. After 35 days, less than 5% of the radioactivity from the carboxyl-labelled herbicide, and less than 10% of the ringlabelled material, was associated with the fulvic components derived from the three soils. Less than 5% of the applied radioactivities were identifiable with any of the humic acid components. It was considered that during the incubation [14C]2,4-D did not become bound or conjugated to soil components, and that non-extractable radioactivity associated with the three soil types resulted from incorporation of radioactive degradation products, such as [14C]carbon dioxide, into soil organic matter.  相似文献   

11.
Radiochemical studies of field soil treated with 14C oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) indicated that the compound was readily degradable. One year after soil treatment with oryzalin, 45% of the original radioactivity had dissipated, 25% was extractable, and 30% was “soil bound”. The extractable fraction contained oryzalin and several degradation products, some of which were isolated and identified. No single degradation product accounted for more than 3% of the applied oryzalin. The “soil-bound” radioactivity was extractable with hot alkali. No significant radioactive residues were detectable in either seed or forage of soybean and wheat plants. No specific metabolites of oryzalin were identified in soybean plants. Trace amounts of radioactivity found in plant tissue appeared to be associated with the various plant constituents.  相似文献   

12.
The β-D -glucoside conjugate of [14C]‘hydroxymonolinuron’, [phenyl-14C]-3-(4- chlorophenyl)-1-(hydroxymethyl)-1-methoxyurea-β-D -glucoside (HM-β-G) and its soil-bound residues, prepared as described, were used to estimate its bioavailability to earthworms and ryegrass plants. The results demonstrate that these bound residues were available to both earthworms and ryegrass. The concentration in the earthworms, expressed on a dry weight basis after 42 days of exposure, was equal to the surrounding soil. The earth worms were found to be more efficient in remobilising and absorbing soil-bound residues than ryegrass plants after 59 days of cultivation. Fractionation of the soil-bound residues showed that 29% of the radiocarbon was associated with fulvic acid, 20% with humic acid and 9% with the humin fraction. 4-Chlorophenylurea, a metabolite of HM-β-G proved to be a key compound in the formation of soil-bound residues. The amount of radioactivity (bound residues), recovered from soil through solubilisation by means of 0.5M -acid and alkali, seems to be a criterion for predicting the bioavailability of bound phenylurea residues. The half-life of soil-bound residues was estimated to be about 4.6 years.  相似文献   

13.
Root-treated alfalfa absorbs, translocates, and metabolizes [phenyl-14C]isopropyl carbanilate ([14C]propham). After 7 days of root treatment, the distribution of radiolabel was 73% for shoots and 27% for roots. Shoots and roots were extracted and separated into the polar, nonpolar, and solid residual components using a mixture of chloroform, methanol and water. The insoluble residues accounted for approximately 40% of the 14C found in shoots and roots. The nonpolar fraction (6.1% of the radiolabel in shoots and roots) was not characterized, but was shown to be some component other than parent propham. Propham was not found in either shoots or roots. The polar metabolites were partly purified on Amberlite XAD-2. Cellulase-liberated aglycones were derivatized and separated by high-performance liquid and gas-liquid chromatography. The infrared, nuclear magnetic resonance, and mass spectral data showed that the polar metabolites of alfalfa shoots and roots were glycoside conjugates of isopropyl 2-hydroxycarbanilate (2-hydroxypropham) and isopropyl 4-hydroxycarbanilate (4-hydroxypropham). Conjugated 4-hydroxypropham accounted for 45.9% of the 14C in the shoots and 3.4% of the 14C in the roots. Conjugated 2-hydroxypropham accounted for 3.4% of the 14C in the shoots and 1.4% of the 14C in the roots.  相似文献   

14.
[14C]Monolinuron was added to soil which was then successively cropped with spinach, cress, and potatoes. Incubation was carried out in a closed system which allowed recoveries even of volatile degradation products and gave an overall recovery of 96% of the applied radioactivity at the end of the experiment. The spinach was found to contain 4.1% of the applied activity; the cress, 5.6%; old potatoes + leaves, 9.5%; new tubers, 1%; and the soil, 68.6%. The total amount of [14C]carbon dioxide liberated was 5.3%. The quantitative separation and characterization of the extractable radioactivity in spinach yielded 10.6% as unaltered monolinuron, 12% as 4-chlorophenylurea plus 4-chlorophenyl-hydroxymethylurea, 3.7% as 4-chlorophenylmethylurea, 1.4% as 4-chlorophenyl-hydroxymethyl-methoxyurea, 1.1% as 4-chlorophenyl-methoxyurea, and 71.2% as polar metabolites. Of these polar metabolites, 67.1% were cleaved with β-glucosidase, resulting in 2.9% unknown aglucone, 48.1% 4-chlorophenyl-hydroxymethyl-methoxyurea, and 16.1% 4-chlorophenyl-hydroxymethylurea. Similar results have been obtained in cress and potatoes. The soil contained 58% of monolinuron residues and 4.7?6.5% of the same types of metabolites as were found in plants. Twenty-one percent were found as polar metabolites.  相似文献   

15.
Aqueous suspensions and oil emulsions of a commercial [14C]diflubenzuron (N-[[(4-chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide) formulation (Dimilin W-25) remained on the leaf surface of greenhouse-treated plant tissues. Absorption, translocation, and metabolism of the [14C]diflubenzuron were not significant. Less than 0.05% of the applied 14C was found in newly developed plant tissues 28 days after spray treatment. [14C]Diflubenzuron was degraded in soil. After 91 days, biometer flask studies showed that 28% of the 14C incorporated into the soil as [14C]diflubenzuron was recovered as 14CO2. Major dichloromethane-soluble soil residues were identified as unreacted [14C]diflubenzuron and [14C]4-chlorophenylurea. A minor unknown degradation product cochromatographed with 2,6-difluorobenzoic acid. Insoluble 14C-residues increased with time and represented 67.8% of the residual 14C in the soil 89 days after treatment. Cotton plants grown for 89 days in [14C]diflubenzuron-treated soil contained only 3% of the 14C applied to the soil. Small quantities of acetonitrile-soluble [14C]4-chlorophenylurea were isolated from the foliar tissues. Root tissues contained small amounts of [14C]diflubenzuron and trace quantities of a minor 14C-product that chromotographed similarly to 2,6-difluorobenzoic acid. Most of the 14C in the plant tissues (84–93%) was associated with an insoluble residue fraction 89 days after treatment.  相似文献   

16.
The fate of 4-chlorophenylurea in soils was studied with two preparations: one labelled with 14C in the phenyl ring and the other in the carbonyl group. The initial dose of 1 mg kg?1 decreased to 50% in about 5 weeks in aerobic sandy clay and in about 16 weeks in anaerobic hydrosoil. Soil treatment with each of the preparations resulted in the release of [14C]carbon dioxide, pointing to decarbonylation and ring opening. The fraction of non-extractable (soil-bound) radioactivity increased during incubation. Quantities of ring-14C-labelled and carbonyl-14C-labelled bound residues differed strongly in the aerobic soil but only slightly in the anaerobic hydrosoil. It is assumed that two sorts of bound residues are formed from 4-chlorophenylurea: one is fairly stable and might consist of bound 4-chloroaniline or its transformation products, whereas the other is presumed to be a degradable derivative of 4-chlorophenylurea.  相似文献   

17.
Volatilization, mineralization, degradation and binding of soil-applied [14C]DDT were studied in three different soils from a tropical region of southern India subjected to solar irradiation and flooding for a period of 42 days. The soil types–red cotton soil, nursery soil and canal bank soil–differed in their organic carbon content, pH and texture. Under unflooded conditions, volatile losses were highest in the sandy canal bank soil. Flooding significantly enhanced volatilization, and this effect was maximal in the nursery soil, which had the highest organic carbon. The soils fully exposed to solar radiations in quartz tubes registered 1.5-1.8 times greater volatility. The volatilized organics contained appreciable quantities of DDE under both flooded and unflooded conditions. In addition, greater quantities of DDD volatilized from the flooded systems. The rate of formation of DDE was faster when soils were irradiated in quartz tubes. Mineralization remained minimal throughout the period of exposure and flooding the soil appeared to reduce further the [14C]carbon dioxide evolution. Canal bank soil exhibited the least mineralization and degradation. The data indicate that volatilization was significantly influenced by solar radiation and flooding to a much greater degree than by the differences in soil properties. Binding of DDT to soil was significantly increased by flooding the soil, thus leaving up to 33% of the initial DDT as bound residues in the nursery soil.  相似文献   

18.
The aerobic soil metabolism of [14C]flupropacil (isopropyl 2-chloro-5-(1,2,3,6-tetrahydro-3-methyl-2,6-dioxo-4-trifluoromethylpyrimidin-1-yl)benzoate) was determined in microbially active, sieved (2-mm) sandy loam soil with a soil moisture content of 75% at 1/3 bar. The soil was treated with [14C]flupropacil at 0·5 mg kg−1 (twice the field use rate) and placed in incubation flasks connected to a series of traps (50 g litre−1 NaOH, 0·5M H2SO4, ethylene glycol) and incubated at 25(±1)°C. Soil was sampled at 0, 3, 9, 20, 30, 48, 76, 120, 181 and 238 days of aerobic incubation. Volatiles were collected once every two weeks and on the day of soil sampling. Flupropacil metabolized with a half-life of 79 days under aerobic conditions. The major metabolite was flupropacil acid which accounted for up to 69·1% of the initially applied radioactivity at Day 238. Each of the two minor metabolites detected at the end of the study accounted for less than 0·5%. One of the minor metabolites was identified as C4242 acid (2-chloro-5-(1,2,3,6-tetrahydro-2,6-dioxo-4-trifluoromethylpyrimidin-1-yl)benzoic acid). Only a negligible portion (less than 0·3%) of the applied flupropacil was mineralized to [14C]carbon dioxide. Extractable radioactivity ranged from 78·9% to 95·5%, with bound residues accounting for 3·2%–23·4%. The material balance ranged from 91·6% to 104·4%.  相似文献   

19.
The electron transport inhibition, uncoupling, and binding of ioxynil and bromoxynil salts is compared in chloroplast fragments isolated from two weed species with contrasting responses to the hydroxybenzonitriles. Ioxynil Na was three to four times more inhibitory than bromoxynil K towards DCPIP and SiMo reduction in both Matricaria inodora and Viola arvensis. Ioxynil Na was also a more potent uncoupler of PSI-dependent electron transport from ascorbate/DCPIP to methyl viologen. Uncoupling occurred at concentrations higher than those that inhibited electron transport. Binding studies with [14C]bromoxynil K and [14C]ioxynil Na salts revealed slightly biphasic curves with no significant difference in the amounts of the two herbicides bound at a given concentration. The ratios of inhibition constant (Ki) and binding constant (Kb) were approximately one for ioxynil Na and three for bromoxynil K. Radiolabelled herbicide displacement studies revealed that ioxynil Na could partially displace bound [14C]bromoxynil K, but bromoxynil K could not displace bound ioxynil Na at biochemically active concentrations. Ioxynil Na may be a more effective inhibitor than bromoxynil K because it binds more strongly to the thylakoid membrane.  相似文献   

20.
2,6-Difluorobenzoic acid, one of the two primary diflubenzuron metabolites, is rapidly and completely degraded in soil. Times to 50% disappearance were 9 and 12 days in two agricultural soils. [14C]Carbon dioxide was an ultimate product of the ring-14C-labelled compound. A part of the radioactivity, increasing with time to one third of the applied dose of 1 mg kg?1, could not be extracted from the soil.  相似文献   

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