Fate of metsulfuron-methyl in soils in relation to pedo-climatic conditions

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     

A comparative study of carbofuran metabolism in treated and untreated soils

Soils which have been pretreated with carbofuran can degrade the insecticide more rapidly than untreated soils, with a consequent loss of efficacy. In laboratory studies, soils pretreated with carbofuran were found to degrade the chemical more rapidly than soils which were not so pretreated. When pretreated soils were sterilised, the rate of carbofuran degradation was much reduced, indicating that most of it was due to microbial action. Incubation of pretreated soil with [phenyl-U-¹⁴C]carbofuran led to the rapid disappearance of the parent compound (3 % left after seven days). Most of the ¹⁴C was accounted for as bound residue after seven days, whilst smaller amounts were recovered as carbon dioxide, 3-hydroxycarbofuran, 3-ketocarbofuran, and an unknown metabolite. Incubation of pretreated soil with [carbonyl-¹⁴C]carbofuran led to rapid loss of the parent compound and the recovery of 73% of ¹⁴C as carbon dioxide by five days. Most of the bound ¹⁴C (>90%) arising from [phenyl-U-¹⁴C]carbofuran treatment of pretreated soil was extracted by 1 M sodium hydroxide and about half of the extracted ¹⁴C was precipitated with ‘humic acids’ after acidification. These and other results suggest that the major metabolic route for carbofuran in pretreated soils involves hydrolysis of the ester bond leading to (1) release of carbofuran phenol which rapidly binds to soil organic matter and, (2) release of the carbonyl moiety which quickly degrades to generate carbon dioxide.     

Translocation and degradation of pyrazosulfuron-ethyl in rice soil

BACKGROUND: Pyrazosulfuron‐ethyl {ethyl 5‐[(4,6‐dimethoxypyrimidin‐2‐ylcarbamoyl)‐sulfamoyl]‐1‐methylpyrazole‐4‐carboxylate} is a new rice herbicide belonging to the sulfonylurea group. This study reports the translocation of ¹⁴C‐pyrazosulfuron‐ethyl to rice plants and its degradation in rice‐planted and unplanted soil. RESULTS: Pyrazosulfuron‐ethyl did not show any appreciable translocation to rice shoots, as ¹⁴C‐activity translocated to the aerial portion never exceeded 1% of the initially applied ¹⁴C‐activity over a 25 day period. Results suggested that the dissipation of pyrazosulfuron‐ethyl from soils followed first‐order kinetics with a half‐life of 5.5 and 6.9 days in rice‐planted and unplanted soils respectively. HPLC analysis of the organic extract of soil samples showed the formation of three metabolites, namely ethyl 5‐(aminosulfonyl)‐1‐methyl‐1‐H‐pyrazole‐4‐carboxylate, 5‐[({[(4,6‐dimethoxy‐2 pyrimidinyl)‐amino]‐carbonyl} amino)‐sulfonyl]‐1‐methyl‐1H‐pyrazole‐4‐carboxylic acid and 2‐amino‐4,6‐dimethoxy pyrimidine, in both rice‐planted and unplanted soils. CONCLUSION: The study indicates that pyrazosulfuron‐ethyl was a short‐lived compound in the soil and was degraded relatively faster in rice‐planted soil than in unplanted soil. The herbicide did not show any appreciable translocation to rice plants. Copyright © 2011 Society of Chemical Industry     

Metabolism of methfuroxam (2,4,5-trimethyl-N-phenyl-3-furancarboxamide) in the rat and isolated rat hepatocytes

Isolated rat hepatocytes were incubated for 4 hr with [phenyl-U-¹⁴C]2,4,5-trimethyl-N-phenyl-3-furancarboxamide ([¹⁴C]methfuroxam). ¹⁴C-Labeled metabolites were isolated by solvent extraction, column chromatography, and high-pressure liquid chromatography, and were then characterized by analysis of infrared and mass spectra. Metabolism of [¹⁴C]methfuroxam by isolated hepatocytes included: (1) hydroxylation of the 2-, 4-, and 5-methyl groups on the furan ring; (2) hydroxylation at the para position of the benzene ring; (3) combinations of 1 and 2; (4) the addition of a sulfur-containing adjunct to the methylfuran moiety; and (5) conjugation of 1–4. Rats given a single intragastric dose of [¹⁴C]methfuroxam excreted 56% of the ¹⁴C in the urine and 42% in the feces within 54 hr. Metabolism of [¹⁴C]methfuroxam by the intact rats included: (1) hydroxylation of the methylfuran moiety; (2) hydroxylation of the benzene ring; (3) the addition of S-methyl, methyl sulfoxide, and other sulfur-containing groups to methfuroxam; (4) combinations of 1–3; and (5) conjugation of 1–4.     

Fate of [14C]diflubenzuron on cotton and in soil

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.     

Degradation and adsorption of carbendazim and 2-aminobenzimidazole in soil

Increasing adsorption of [¹⁴C]-labelled carbendazim in soil took place within a few weeks of incubation and was greatest in soil with a high organic matter content. Carbendazim was slowly decomposed in soil, mainly by soil microorganisms. After 250 days of incubation in two unsterilised soils, 13 and 5% respectively of added [¹⁴C]-carbendazim was recovered compared with 70 and 50% respectively from sterile soils; 4–8% of added carbendazim was recovered as 2-aminobenzimidazole (2-AB) from both unsterilised and sterile soil. After 270 days' incubation, 33 and 9% of ¹⁴C was recovered as ¹⁴CO₂ from soil supplied with [¹⁴C]-carbendazim (20 and 100 mg/kg) respectively. Degradation started more rapidly when carbendazim was added to soil preincubated with the fungicide but the degradation rate was very low in all cases, indicating that the compound is a poor microbial energy source and that the degradation is a co-metabolic process. 2-AB was found as a degradation product although it appeared to be unstable in soil, decomposing rapidly after a lag period of about 3 weeks; small amounts remained in the soil for several months, however, presumably adsorbed on soil particles.     

Modeling environmental effects on enhanced carbofuran degradation

Prediction of the fate of pesticides in soil is of interest from an environmental (pollution) as well as an agricultural (efficacy, carryover) viewpoint. Two environmental parameters that control microbial degradation of pesticides in soil are moisture and temperature. This study was designed to quantify the impact of soil water content and temperature on microbial degradation rates of the insecticide carbofuran (2, 3-dihydro-2, 2-dimethylbenzofuran-7-yl methyl-carbamate). Carbofuran degradation was determined by monitoring the [ 14 C] carbondioxide production from soils amended with [carbonyl- 14 C]carbofuran. Soils were incubated at seven soil-water tensions over the range of 0–03 to 1–5 MPa, and at five temperatures (10°C to 30°C). The sigmoidal degradation kinetics observed from these incubations were modeled using a general saturation model. For the moisture experiments, maximum rate of hydrolysis and half-life (DT₅₀) were accurately modeled by an exponential relationship. The response of carbofuran degradation to temperature was also well described by an exponential relationship, from which it was estimated that the Q₁₀ associated with the maximum rate was 1.68, and the Q₁₀ for DT₅₀ was 1–89.     

Metabolism and cell wall incorporation of phenoxyacetic acid in soybean cell suspension culture

The metabolism of [¹⁴C]phenoxyacetic acid (POA) was studied in cell suspension culture of soybean (Glycine max). POA was metabolized to 4-HO-POA, 4-HO-POA glucoside and 4-HO-POA glycosidic ester. A large part of the 4-HO-POA glucoside and small amounts of the glycosidic ester were recovered in the medium. POA was also converted to non-extractable residues bound to cell walls. Sequential extraction of cell-wall polymers showed that non-extractable residues, partly identified with 4-HO-POA and POA, were mainly associated with hemicelluloses and lignin. Comparison of the metabolism of [carboxy-¹⁴C]- and [phenyl-¹⁴C]POA revealed some degradation of the POA side-chain, followed in all probability by the incorporation of the aromatic moiety into cell walls. However, the sturdiness of the resulting bonds prevented precise identification of these bound aromatic structures. In summary, the degradation of POA in soybean cell culture provided a good model to study the formation of non-extractable residues of pesticides. © 1999 Society of Chemical Industry     

Aerobic soil metabolism of flupyrazofos

To elucidate the fate of flupyrazofos [O,O-diethyl O-(1-phenyl-3-trifluoromethyl-5-pyrazoyl)phosphorothionate] in soil, an aerobic soil metabolism study was carried out for 60 days with [¹⁴C]flupyrazofos applied at a concentration of 0·38 μg g^-1 to a loamy soil. The material balance ranged from 103·5% to 86·9% and the half-life of [¹⁴C]flupyrazofos was calculated to be 13·6 days. The metabolites identified during the study were 1-phenyl-3-trifluoromethyl-5-hydroxypyrazole (PTMHP) and O,O-diethyl O-(1-phenyl-3-trifluoromethyl-5-pyrazoyl)phosphate (flupyrazofos oxon), with maximum levels of 9·8% and 1·6% of applied radiocarbon, respectively. Evolved [¹⁴C]carbon dioxide accounted for up to 5·3% of applied radiocarbon and no volatile products were detected during the study. Non-extractable ¹⁴C-residue reached 31·6% of applied material at 60 days after treatment and radiocarbon was distributed almost evenly in humin, humic acid and fulvic acid fraction. © 1998 Society of Chemical Industry     

Dégradation chimique ou microbiologique des sulfonylurées dans le sol. I. Cas du sulfbméturon méthyle

La Vitesse de transformation du sulfométuron méthyle dans un sol, et en solution au même pH, a été mesurée à différentes temperatures. Aussi bien en solution que dans le sol, la relation d'Arrhénius est bien vérifiée dans la gamme de température étudiée 20°C-75°C. L'énergie d'activation calculée est respectivement de 94 kJ mol^?1 et de 117 kJ mol^?1 dans le sol et en solution. Du fait que la loi d'Arrhénius est vérifiée dans le sol jusqu'à 70°C, un mécanisme de dégradation est proposé: la dégradation chimique. L'analyse des produits formés dans un sol stérile et non stérile a été réalisée a partir du sulfométuron méthyle marqué au ¹⁴C sur le cycle pyrimidine. Dans les deux sols le métabolite principal retrouvé est la 2-amino-4,6-diméthyl-pyrimidine. Aucune différence significative n'est mise en évidence entre le sol sterile et non stérile. Chemical or microbial degradation of sulfonylurea herbicides in soil. I. Sulfometuron methyl The rates of degradation of sulfometuron methyl in a soil and in aqueous solution at the same pH were measured at different temperatures. The Arrhenius relationship was verified between 20°C and 75°C. The calculated activation energy in soil and in solution was 94 kJ mol^?1 and 117 kJ mol^?1, respectively. From the fact that the Arrhenius relationship is followed up to 70°C, it is proposed that the mechanism of degradation in the soil is chemical. Analysis of the metabolites formed in sterile and non-sterile soil was performed using sulfometuron methyl labelled with ¹⁴C in the pyrimidine ring. In both soils the main metabolite isolated was 2-amino-4,6-dimethylpyrimidine. No significant difference has been observed between sterile and non-sterile soils. Chemischer oder mikrobiologischer Abbau von Sulfonylharnstoffen im Boden. I. Sulfometuronmethyl Die Abbaurate von Sulfometuron-methyl wurde in einem Boden und in wäßriger Lösung mit gleichem pH-Wert bei verschiedenen Temperaturen untersucht. Die Gültigkeit der Arrhenius-Gleichung wurde zwischen 20 und 75°C überprüft, mit Aktiviemngsenergien von 94 oder 117 kJ mol^?1 für den Boden bzw. die Lösung. Aus dem linearen Abbau im Boden bis zu 70°C wurde auf chemischen Abbau geschlossen. Bei der Analyse der Abbauprodukte von ¹⁴C-Sulfometuron-methyl (markiert am Pyrimidin-Ring) in sterilisiertem und nicht sterilisiertem Boden wurden keine signifikanten Unterschiede festgestellt und hauptsächlich das 2-Amino-4,6-dimethylpyrimidin gefunden.     

Biodegradation of the herbicide bromoxynil and its plant cell wall bound residues in an agricultural soil

The mineralization and formation of metabolites and nonextractable residues of the herbicide [¹⁴C]bromoxyniloctanoate ([¹⁴C]3,5-dibromo-4-octanoylbenzonitrile) and the corresponding agent substance [¹⁴C]bromoxynil ([¹⁴C]3,5-dibromo-4-hydroxybenzonitrile) was investigated in a soil from an agricultural site in a model experiment. The mineralization of maize cell wall bound bromoxynil residues was also investigated in the agricultural soil material. The mineralization of [¹⁴C]bromoxynil and [¹⁴C]bromoxyniloctanoate in soil within 60 days amounted up to 42 and 49%, respectively. After the experiments, 52% of the originally applied [¹⁴C]bromoxynil and 44% of the [¹⁴C]bromoxyniloctanoate formed nonextractable residues in soil. Plant cell wall bound [¹⁴C]bromoxynil residues were also mineralized to an extent of about 21% within 70 days; the main portion of 76% persisted as nonextractable residues in the soil. In bacterial enrichment cultures and in soil two polar metabolites were observed; one of it could be identified as 3,5-dibromo-4-hydroxybenzoate and the other could be described tentatively as 3,5-dibromo-4-hydroxybenzamide.     

Bioavailability of conjugated and soil-bound [14C]‘hydroxymonolinuron’-β-D-glucoside residues to earthworms and ryegrass

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.     

Spatial variability in the degradation rates of isoproturon and chlorotoluron in a clay soil

Thirty separate soil samples were taken from different locations at the Brimstone farm experimental site, Oxfordshire, UK. Incubations of isoproturon under standard conditions (15 °C; ?33 kPa soil water potential) indicated considerable variation in degradation rate in the soil, with the time to 50% loss (DT₅₀) varying from 6 to 30 days. These differences were confirmed in a second comparative experiment in which degradation rates were assessed in 11 samples of the same soil in two separate laboratories using an identical protocol. There was a significant negative linear relationship (r²= 0.746) between the DT₅₀ values and soil pH in this group of soils. In a third experiment, degradation rates of the related compound chlorotoluron were compared with those of isoproturon in 12 separate soil samples, six of which had been stored for several months, and six of which were freshly collected from the field. Degradation of both herbicides occurred more slowly in the stored samples than in the fresh samples but, in all of them, chlorotoluron degraded more slowly than isoproturon, and there was a highly significant linear relationship (r²=0.916) between the respective DT₅₀ values.     

Mineralization of 2,4‐D,mecoprop, isoproturon and terbuthylazine in a chalk aquifer

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     

Influence of application methods on the degradation of permethrin in laboratory,soil aerobic metabolism studies

The effects of application rate, volume, solvent and soil moisture content on the kinetics of mineralization and degradation, of [¹⁴C] permethrin have been studied in a sandy loam soil under standard laboratory conditions. During the incubation period, up to 32 days, the temperature and moisture level of the soil were controlled. Apart from the effects of application rate, which have been widely reported, application volume had the most significant effect on mineralization rate and T_1/2. [¹⁴C]Permethrin, at a level of a 1 mg kg^?1 in the soil, applied in 100 μl of methanol, resulted in the evolution of 14% of the applied radiochemical as [¹⁴C] carbon dioxide over 30 days. The same level applied in 1000 μl mineralized at a faster rate, with 30% [¹⁴C]carbon dioxide evolved over 30 days. The test chemical applied to soil in methanol mineralized at a significantly faster rate than a similar concentration applied in ethanol. There was no significant difference when comparing applications made using acetonitrile with those using methanol or ethanol. The addition of formulation ingredients resulted in little or no variation in mineralisation rate compared to an equivalent application volume of methanol/water.     

The elimination of (N-[[(4-chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide) by the boll weevil

Boll weevils, Anthonomus grandis Boheman, were either dipped in or injected with a solution of [¹⁴C]diflubenzuron (N-[[(4-chlorophenyl)amino]carbonyl]-2,6-difluorobenzamide) or fed on cotton squares that had been treated with the chemical to determine its turnover time and metabolic fate. No significant differences were observed between male and female weevils in their ability to eliminate [¹⁴C]diflubenzuron. Only minor differences were observed when immersion and injection treatments were compared. When weevils were treated with 66.3 ng of [¹⁴C]deflubenzuron per weevil by injection, the insects contained 13 to 15% of the radiolabel after 6 days and 4 to 6% after 13 days. The remainder of the radiolabel was in the frass. When weevils fed for 66 hr on cotton squares that had been treated with a wettable [¹⁴C]diflubenzuron preparation (Dimilin W-25), the insects averaged 120 ng of diflubenzuron per weevil. Forty-four hours after removing insects from the treated squares, 50% of the radiolabel had been excreted. In all cases, the radiolabel found in the frass or in the weevil was unchanged diflubenzuron. There were no data to indicate that the boll weevil could metabolize appreciable amounts of diflubenzuron.     

The fate of [3-14C]metamitron in sugar beets after preemergence application in a lysimeter study

In a lysimeter experiment, [3-¹⁴C]metamitron was sprayed in a preemergence treatment of sugar beets, corresponding to approx 4.9 kg metamitron (7 kg Goltix)/ha. After 6 months, the beets contained metamitron equivalents amounting to 0.1 mg/kg fresh wt, calculated on the basis of the specific radioactivity of the [3-¹⁴C]metamitron employed. Radioactivity was also detected in the pure sugar isolates. The ¹⁴C activity represented approx 0.2 mg metamitron equivalent/kg pure sugar. Since the specific radioactivities of the sugar fractions were too low to employ physicochemical methods, a microbial degradation was used to investigate whether the radiocarbon was incorporated in the sucrose molecule. Microorganisms (Proteus vulgaris) degraded [U-¹⁴C] sucrose and the sugar isolates at the same ¹⁴CO₂ release rates under strictly controlled experimental conditions. This result indicates that about one fourth of the carbon from the C-3 position of the triazine ring of the metamitron, found in the sugar beets at harvest time, is partly being used as a substrate in the production of sucrose possibly via assimilation of mineralized ¹⁴CO₂.     

Use of a field-scale biofilter for the degradation of the organophosphate insecticide coumaphos in cattle dip wastes

Insecticide wastes generated from livestock dipping operations are well suited for biodegradation processes since these wastes are concentrated, contained, and have no other significant toxic components. A field-scale biofilter capable of treating 15000-litre batches of dip waste containing the acaricide coumaphos was used to reduce the coumaphos concentration in two successive 11000-litre batch trials from 2000 mg litre^-1 to 10 mg litre^-1 in approximately 14 days at 25–29°C. Removal of coumaphos from the biofilter effluent is a function of both physical filtration and biodegradation by the biofilter. However, stoichiometric increases in chloride levels in the effluent as coumaphos concentrations decreased confirmed that coumaphos was being degraded by the biofilter rather than just being filtered out. In subsequent 5500-litre batch experiments, the addition of a vitamin supplement to the biofilter-treated dip resulted in a further decrease in coumaphos concentration to approximately 1 mg litre^-1. Results from incubations of two representative Texas soils with biofilter-treated dip spiked with [benzo-U-¹⁴C] coumaphos revealed that 32–36% of the spiked [¹⁴C] coumaphos was mineralized in the soils after 110 days at 30°C. © 1998 SCI.     

Chemical hydrolysis of 2-chloro-4,6-bis(alkylamino)-1,3,5-triazine herbicides and their breakdown in soil under the influence of adsorption

The determination of rate constants and the calculation of the activation parameters [activation energy (E_a), free energy of activation(ΔG^≠)and entropy of activation (ΔS^≠)] demonstrated the identity of the reaction kinetics of chemical hydrolysis of the chlorinated triazine herbicides simazine, atrazine, propazine and terbuthylazine. Persistence in soil could be estimated, from the hydrolytic half-life time, only in pH regions where these compounds were also sensitive to chemical hydrolysis. In general, the rate of hydrolysis increased in the presence of soil as the result of a catalysing effect of the soil in their breakdown. When half-lives in soil of these triazine herbicides were compared with adsorption constants, a functional relationship was observed in both soil types; as adsorption increased the half-life in soil also increased.     

Degradation of the herbicide flamprop-methyl in soil

The degradation of the wild oat herbicide flamprop-methyl [methyl DL -N-benzoyl-N-(3-chloro-4-fluorophenyl)alaninate] in four soils has been studied under laboratory conditions using ¹⁴C-1abelled samples. The flamprop-methyl underwent degradation more rapidly than its analogue flamprop-isopropyl. However, similar degradation products were formed, namely the corresponding carboxylic acid and 3-chloro-4-fluoroaniline. The latter compound occurred mainly as ‘bound’ forms although evidence was obtained of limited ring-opening to give [¹⁴C]carbon dioxide. The time for depletion of 50% of the applied herbicide was approximately 1-2 weeks in sandy loam, clay and medium loam soils and 2-3 weeks in a peat soil.