Influence of soil pH and contents of organic carbon and clay on the volatilization of [14C]fenpropimorph after application to bare soil

The behaviour of the morpholine fungicide fenpropimorph applied to soil was investigated in a laboratory chamber. The volatility and metabolism of a ¹⁴C-labelled fenpropimorph formulation (Corbel^®) was studied after application to three soils (sandy loam, loamy clay and loamy sand), simulating a four-day weather scenario in the volatilization chamber. Additional experiments were conducted under standard climatic conditions over a period of 24 h using sandy soils with different pH values. The results of the first experiments showed that most of the radioactivity applied remained in the soils as unchanged fenpropimorph four days after application. In the experiments with the sandy loam and loamy clay, less than 5% of the applied radioactivity was removed by volatilization whereas 11·4% volatilized from the surface of the loamy sand. The comparatively higher volatilization of the fungicide from the loamy sand was confirmed by the later experiments indicating that higher soil pH favoured volatilization of [¹⁴C]fenpropimorph from sandy soils. Thus 5·6% (pH 5·0), 18·9% (pH 5·8) and 28·3% (pH 6·6) of the radioactivity applied volatilized within one day after application. The overall recoveries were between 93·8% and 111·3% in these experiments. © 1998 SCI     

Enhanced Mineralization of [14C]Atrazine in Kochia scoparia Rhizospheric Soil from a Pesticide-Contaminated Site

Mineralization of atrazine (6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5- triazine-2,4-diamine) in soil treated with a mixture of atrazine and metolachlor (2-chloro-6′-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide at concentrations typical of point-source contamination (50 μg g⁻¹ each) was significantly greater (P<0·001) in rhizospheric soil from Kochia scoparia (L.) Roth., a herbicide-resistant plant, than in non-vegetated and control soils. Soils were collected from an agrochemical dealership contaminated with several herbicides, including atra-zine, metolachlor, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine and pendimethalin (N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidene), at concentrations well exceeding the field application rates. Mineralization rates of ring-labeled atrazine in both rhizospheric and non-vegetated soils were quite high (>47% of the initial ¹⁴C applied after 36 days) compared to literature values. These results suggest that plants such as Kochia might be managed at pesticide-contaminated sites to help facilitate microbial degradation of wastes such as atrazine in soil.     

Movement and persistence of [14C]imidacloprid in sugar-beet plants following application to pelleted sugar-beet seed

[¹⁴C]Imidacloprid was applied to pelleted seeds of sugar beet which were then grown in pots of field soil. Leaves, roots and soil were analysed at intervals up to 97 days after planting and the distributions of parent compound and of several metabolites were quantified. At the first sampling, 21 days after application, parent imidacloprid was the main compound found in the leaves and its concentration averaged 15·2 μg g^-1 fresh weight. By the 25-leaf stage, 97 days after sowing, the concentration of parent compound in the leaves had fallen to an average of 0·5 μg g^-1; the metabolites and parent compound in the leaves then represented respectively 44·5% and 4·5% of the total applied radioactivity. In the root at 97 days, parent imidacloprid and its metabolites together accounted for only 0·1% of the applied activity, whilst in the soil there was 23% of parent compound and 4% as metabolites. The persistence of both parent imidacloprid and the olefinic metabolite, which has recently been shown to have higher aphicidal activity than the parent imidacloprid, explains the prolonged control of aphids observed with imidacloprid in both glasshouse and field trials. © 1998 SCI.     

Studies on the mode of action of asulam,aminotriazole and glyphosate in Equisetum arvense L. (field horsetail). II: The metabolism of [14C]asulam, [14C]aminotriazole and [14C]glyphosate

The metabolism of [¹⁴C]asulam (methyl 4-aminophenylsulphonylcarbamate), [¹⁴C] aminotriazole (1H-1,2,4-triazol-3-ylamine) and [¹⁴C]glyphosate (N-(phosphonomethyl)glycine) were assessed in Equisetum arvense L. (field horsetail). Following application of the test herbicides (4mg?0.3 °Ci herbicide/shoot) to the shoots of 2-year-old pot-grown plants, the total recovery of ¹⁴C-label after 1 week and 8 weeks was high for all three herbicides (>80-0% of applied radioactivity). Asulam was persistent (>69-7% of recovered radioactivity) in both shoots and rhizomes. Sulphanilamide, a hydrolysis product of asulam, accounted for the remainder of the recovered radioactivity. Aminotriazole showed evidence of conjugation in shoots and rhizomes. The principal ¹⁴C-labelled component in shoots was composed of high proportions of aminotriazole (>76-3%) together with the metabolites: X (ninhydrin positive), β-(3-amino-1,2,4-triazolyl-1-)α-alanine, Y (diazotization positive) and various unidentified compounds. Rhizomes generally contained lower proportions of intact aminotriazole (>59.4%) together with the metabolites X,Y and unidentified compounds. The proportion of aminotriazole did not decrease with time in shoots or rhizomes; however, the ratio of metabolite X: Y moved in favour of Y as the interval after treatment increased. Glyphosate was extensively metabolised in shoots and rhizomes to yield aminomethylphosphonic acid (AMPA) and various unidentified compounds. Differential metabolism appears to be one of the factors which may govern the persistence and toxicity of the test herbicides in E. arvense.     

Fate of [14C]Mancozeb in Egg Plants (Solanum melongena L.) during Summer under Sub-tropical Conditions

The fungicide mancozeb belongs to ethylenebis(dithiocarbamate) group of fungicides which is used to control brown and black rust, leaf spot, leaf blight, downy mildew etc. on a variety of plants including egg plants, tomato, potato and others. [¹⁴C]mancozeb, when applied to the foliage of egg plants (Solanum melongena L.) during summer months, dissipated very rapidly with a half-life of only 10·6 days. Ethylenethiourea (ETU), ethyleneurea (EU), ethylenethiuram disulfide (ETD), ethylenethiuram monosulfide (ETM) were the metabolites of [¹⁴C]mancozeb detected in all the plant parts at different times after the treatment. The amount of ETU in fruits after fourteen days of treatment was only 206 μg kg^?1 which is below the maximum permissible level and ultimately came down to 4·6 μg kg^?1 after 42 days. EU was found to be the predominant metabolite, suggesting the breakdown of unstable ETU to relatively stable EU under subtropical conditions.     

Determination of extractable and non-extractable radioactivity from prairie soils treated with carboxyl- and ring-labelled [14C]2,4-D

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.     

Soil persistence studies with bromoxynil, propanil and [14C]dicamba in herbicidal mixtures

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.     

The metabolism of [14C] cymoxanil in the rat

A rat, given a single oral dose of [¹⁴C] cymoxanil, 1-(2-cyano-2-methoxyimino-[2-¹⁴C]-acetyl)-3-ethylurea, eliminated 91% of the radioactivity within 72 h. The urine contained 71%, the faeces 11%, and the expired air about 7% of the radiolabel; no ¹⁴C residue was found in the internal organs. Greater than 70% of the radioactivity in the urine was identified. The major metabolite was characterised as glycine, both free and conjugated, as hippuric acid and phenylaceturic acid [N-(phenylacetyl)-glycine], and probably in the form of polypeptides of low molecular weight. The other metabolites identified included 2-cyano-2-methoxyiminoacetic acid, 2-cyano-2-hydroxyiminoacetic acid and 1-ethylimidazolidine-2, 4, 5-trione. The minor metabolites included succinic acid and 2-oxoglutaric acid which indicated reincorporation of metabolic ¹⁴C. Cymoxanil, as such, was not detected in the urine.     

Degradation of the herbicide [14C]-diclofop-methyl in soil under different conditions

The degradation of the herbicide diclofop-methyl, ( ± )-methyl 2-[4-(2,4-dichloro-phenoxy)phenoxy]propionate, was investigated in two agricultural soils under aerobic and anaerobic conditions. Using two differently labelled forms of [¹⁴C]-diclofop-methyl the qualitative as well as the quantitative formation of extractable metabolites was followed for 64 days. The mineralisation of the uniformly labelled aromatic rings was pursued by monitoring the ¹⁴CO₂ generated for 25 weeks. As a first step of the degradation a very rapid hydrolysis of the ester bond was detected under all conditions. Diclofop, the corresponding substituted propionic acid formed, was extensively degraded under aerobic conditions, the final product being ¹⁴CO₂. As an intermediate, a compound later identified by GLC/MS to be 4-(2,4-dichlorophenoxy)phenol, was found in the extracts. Furthermore, traces of six other unknown metabolites were detected. Under anaerobic conditions the degradation proceeded to a small extent. At most 3% of the applied radioactivity was accounted for by the degradation product 4-(2,4-dichlorophenoxy)phenol. No other metabolite, including ¹⁴CO₂, was observed, implying lack of any further degradation.     

Soil persistence studies with [14C]MCPA in combination with other herbicides and pesticides

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.     

Sorption of atrazine and dicamba in Delaware coastal plain soils: a comparison of soil thin layer and batch equilibrium results

The mobility and retention of atrazine and dicamba in six Atlantic Coastal Plain soils were estimated by soil thin-layer chromatography (soil-TLC). The soils studied were representative of the major agricultural regions in Delaware and were sampled, by horizon, to the water table. Four horizons from each profile were leached simultaneously with distilled water on one soil-TLC plate. Two values were obtained from each plate: the ratio of the distance traveled by the herbicide center of mass over that traveled by the solvent front (R_m), and a sorption distribution coefficient (K_d). The R_m values ranged from 0·06 to 0·94 for atrazine and from 0·80 to 0·94 for dicamba. Herbicide mobility was found to be greatest in coarse-textured soil horizons that contained low levels of organic matter, clay, and Fe and Al oxides. Correlation analysis indicated that effective cation exchange capacity, exchangeable acidity, exchangeable aluminum, and clay were useful predictive variables or both atrazine mobility and sorption. Organic matter was not useful for predicting soil-TLC derived sorption estimates; however, it was correlated to K_d-batch estimates. Distribution coefficients calculated from soil-TLC data were found to be in general agreement with K_d values obtained for the same soils by batch equilibrium techniques. The average K_d-soil-TLC values for atrazine and dicamba were 2·09(±2·24) and 0·03(±0·02), respectively. The ratio of the batch K_d to the soil-TLC K_d ranged from 0·1 to 19 (x̄=1·6, SD=3·8) for atrazine and from 2·9 to 38 (x̄=12·6, SD=8·7) for dicamba. Thus, although for some horizons agreement between the two methods was good, for other horizons significant discrepancies existed. It is suggested that the soil-TLC gives results under non-equilibrium conditions, whereas the batch procedure is, by definition, at quasi-equilibrium. These fundamental differences may account for the observed differences between the two methods. It is also suggested that, due to this difference, the soil-TLC procedure can provide additional information relevant to herbicide partitioning in the field environment that is not provided by traditional batch equilibrium techniques. © 1998 Society of Chemical Industry     

Studies on the mode of action of asulam,aminotriazole and glyphosate in Equisetum arvense L. (field horsetail). I: The uptake and translocation of [14c]asulam, [14C]aminotriazole and [14C]glyphosate

The uptake and translocation of [¹⁴C]asulam (methyl 4-aminophenyl-sulphonylcarbamate), [¹⁴C]aminotriazole (1-H-1,2,4-triazol-3-ylamine) and [¹⁴C]glyphosate (N-(phosphonomethyl)glycine) were assessed in Equisetum arvense L. (field horsetail), a weed of mainly horticultural situations. Under controlled-environment conditions, 21°C day/18°C night and 70% r. h., the test herbicides were applied to 2-month-old and 2-year-old plants. Seven days following the application of 0.07-0.09 °Ci (1.14mg) of the test herbicides to young E. arvense, the accumulation of ¹⁴C-label (as percentage of applied radioactivity) in the treated shoots, untreated apical and basal shoots was as follows: [¹⁴C]asulam, 13.2, 0.18 and 1.02%; [¹⁴C] aminotriazole, 67.2, 3.65 and 1-91%; [¹⁴C]glyphosate, 35.9, 0.06 and 0.11%. The equivalent mean values for the accumulation of ¹⁴C-label in 2-year-old E. arvense were [¹⁴C]asulam, 12.0, 1-15 and 1.74%; [¹⁴C]aminotriazole, 58.6, 9.44 and 4.12%; [¹⁴C]glyphosate, 33.1, 0.79 and 2.32%. In the latter experiment, test plants received 0.25-0.30 °Ci (4mg) of herbicide, they were assessed after a 14-day period and the experiment was carried out at 3-week intervals between 2 June and 25 August on outdoor-grown plants. Irrespective of test herbicide or time of application, very low levels of ¹⁴C-label accumulated in the rhizome system. Only 0.2% of the applied radioactivity was recovered in 2-year-old plants and 0.4% in 2-month-old plants. In the young plants [¹⁴C]asulam accumulated greater amounts and concentrations of ¹⁴C-label in the rhizome apices and nodes than [¹⁴C]aminotriazole or [¹⁴C]glyphosate treatments. Inadequate control of E. arvense under field conditions may be due to limited basipetal translocation and accumulation of the test herbicides in the rhizome apices and nodes.     

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     

Removal of Atrazine Contamination in Soil and Liquid Systems Using Bioaugmentation

Reported levels of atrazine in soils at pesticide mix-load sites can vary between 7·9×10^-5 mM and 1·9 mM . We report on a mixed microbial culture, capable of degrading concentrations of atrazine in excess of 1·9 mM . At initial concentrations of 0·046 M and 0·23 M , the mixed population degraded 78% and 21% of atrazine in soil (100 days), respectively. At the same initial concentrations in liquid cultures, 90% and 56% of the atrazine was degraded (80 days), respectively. Decreased degradation in soil samples may have resulted from atrazine sorption to soil surfaces or decreased contact between the population and the herbicide. In the 0·23 M system, we attribute incomplete degradation to phosphorous depletion. Data for carbon dioxide evolution was fitted to a three-half-order regression model, but we feel that there are limitations of the application of this model to atrazine degradation. The population uses the herbicide as a nitrogen source and little carbon is incorporated into biomass, as the energy status of carbons in the ring leads to their direct evolution as [¹⁴C]carbon dioxide. This situation contributes to an evolution pattern that, when fitted to the three-half-order model, results in underestimation of the biomass produced. Data from our study suggest that our mixed culture could be used for bioremediation of atrazine at concentrations up to and exceeding those currently reported for agrochemical mixing-loading facilities. © 1997 SCI.     

Metabolism of [14C]cymoxanil in grapes,potatoes and tomatoes

Foliar-applied [¹⁴]cymoxanil, 1-(2-cyano-2-methoxyimino-[2-¹⁴C]acetyl)-3-ethylurea was rapidly metabolised in grapes, tomatoes and potatoes, Furthermore, the metabolism of this fungicide was unusual in that the metabolites were found to be naturally occurring compounds, with glycine as the major metabolite. Significant levels of radioactivity were found in other amino-acids, sugars, starch, fatty acids and lignin, indicating incorporation of carbon-14 via the various metabolic pathways.     

An investigation of the non-solvent-extractable residues of [14C]chlorpyrifos-methyl in stored wheat

The residues of [¹⁴C] chlorpyrifos-methyl remaining in wheat after solvent extraction accounted for 28% of the applied dose after an extended period of storage. A bioassay of these residues was carried out using Tribolium castaneum and a significant reduction in the numbers of adults reaching maturity was observed. Attempts to release the non-solvent-extractable residues using an enzymic digestion procedure were unsuccessful, as were several of the chemical solubilisation procedures investigated. A water/methanol extraction system was successful in releasing up to 86% of the radioactivity leaving 10% still non-extractable. Analysis of this solubilised residue revealed that 59% was present as the pyridinol metabolite of chlorpyrifos-methyl and 26% was a polar material composed of two main components. Bioassay tests of these metabolites revealed that the reduction in the number of insects reaching maturity could be associated with the pyridinol metabolite.     

Microbial aspects of atrazine biodegradation in relation to history of soil treatment

Among 15 soils with different cropping practices, seven which had an history of repeated atrazine applications showed accelerated degradation of this herbicide. By contrast, grassland or agricultural soils with no recorded atrazine application, at least for the last three years, had a low degradation potential. No direct relation was found between the rate of atrazine mineralisation and the size of the microbial biomass. In adapted soils, the amounts of extractable residues were lowered and the very high percentages of radioactivity from [ring-¹⁴C]atrazine recovered as [¹⁴C]carbon dioxide demonstrated that N-dealkylation and deamidation were the only processes for micro-organisms to derive carbon and energy for heterotrophic growth. Kinetics of microbial ¹⁴C accumulation revealed that atrazine ring carbon could be incorporated by direct oxidative condensation with structural components of the bacterial or fungal cell whereas side-chain carbon was preferentially used for biosynthesis of new protoplasmic cell material, as confirmed by the high turnover rate of radiolabelled microbial components. From the determination of the Michaelis–Menten parameters, V_m and K_m in the presence of different selective biocides, it was possible to conclude that fungi were probably less active in atrazine degradation than bacteria and that over years the microbial atrazine-degrading community showed an increased efficiency. © 1999 Society of Chemical Industry     

[14C]Glyphosate transport in undisturbed topsoil columns

Although glyphosate (N‐(phosphonomethyl)glycine) is one of the most frequently used herbicides, few controlled transport experiments in undisturbed soils have been carried out to date. The aim of this work was to study the influence of the sorption coefficient, soil‐glyphosate contact time, pH, phosphorus concentration and colloid‐facilitated transport on the transport of [¹⁴C]glyphosate in undisturbed top‐soil columns (20 cm height × 20 cm diameter) of a sandy loam soil and a sandy soil. Batch sorption experiments showed strong Freundlich‐type sorption to both soil materials. The mobility of glyphosate in the soil columns was strongly governed by macropore flow. Consequently, amounts of glyphosate leached from the macroporous sandy loam soil were 50–150 times larger than from the sandy soil. Leaching rates from the sandy soil were not affected by soil‐glyphosate contact time, whereas a contact time of 96 h strongly reduced the leaching rates from the sandy loam soil. The role of pH and phosphorus concentration in solution was relatively unimportant with respect to total glyphosate leaching. The contribution of colloid‐facilitated transport was <1 to 27% for the sandy loam and <1 to 52% for the sandy soil, depending on soil treatment. The risk for glyphosate leaching from the top‐soils seems to be limited to conditions where pronounced macropore flow occurs shortly after application. © 2000 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     

Persistence studies with the herbicide sethoxydim in prairie soils

The persistence of [¹⁴C]sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one) at the 2 μg g^?1 level was studied under laboratory conditions in three soils at 20°C and 85% of their field capacity moistures. Following extraction of the soils with methanol, the herbicide remaining was determined using radiochemical techniques. Loss of radioactivity was more rapid on moist clay loam and sandy loam, where the half-lives were 12 days, than on heavy clay in which the half-life was 26 days. Loss of radioactivity from air-dried soils (15% of field capacity) was negligible with over 94% of the applied activity being recovered after 28 days. The persistence of sethoxydim at a rate of 1 kg ha^?1 was investigated under field conditions using small plots at three prairie locations for 3 successive years. Using an oat-root bioassay procedure, no residues were detected in the 0–10 cm depths of any soils, any year, in September following May treatments.