Metabolism of flupyrazofos in the isolated perfused rat liver

To investigate the hepatic metabolism of the new insecticide flupyrazofos [O,O-diethyl O-(1-phenyl-3-trifluoromethylpyrazol-5-yl) phosphorothioate], isolated rat liver was perfused with flupyrazofos under single-pass conditions. In outflow perfusate and bile, 1-phenyl-3-trifluoromethyl-5-hydroxyprazole (PTMHP), PTMHP-sulfate and PTMHP-glucuronide conjugates were identified as the metabolites of flupyrazofos. However, O,O-diethyl O-(1-phenyl-3-trifluoromethylpyrazol-5-yl) phosphate (flupyrazofos oxon) was not detected. A HPLC method with UV detection was used to investigate the hepatic disposition of flupyrazofos and its metabolite PTMHP. The concentrations of flupyrazofos, PTMHP and PTMHP conjugates in outflow perfusate reached steady-state levels within 20 min after commencing perfusion of 7.3 microM flupyrazofos. At steady state, the mean extraction ratio of flupyrazofos was 0.93 (+/- 0.01) and clearance was 26.1 (+/- 0.2) ml min-1 which nearly approached perfusate flow rate (28 ml min-1). PTMHP accounted for 55.7 (+/- 5.8)% of eliminated flupyrazofos and was recovered as unchanged PTMHP, PTMHP-sulfate and PTMHP-glucuronide in the bile as well as the outflow perfusate.     

Chlorpyrifos degradation in soil at termiticidal application rates

Chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] is an organophosphorus insecticide applied to soil to control pests both in agricultural and in urban developments. Typical agricultural soil applications (0.56 to 5.6 kg ha^?1) result in initial soil surface residues of 0.3 to 32 μg g^?1. In contrast, termiticidal soil barrier treatments, a common urban use pattern, often result in initial soil residues of 1000 μg g^?1 or greater. The purpose of the present investigation was to understand better the degradation of chlorpyrifos in soil at termiticidal application rates and factors affecting its behaviour. Therefore, studies with [¹⁴C]chlorpyrifos were conducted under a variety of conditions in the laboratory. Initially, the degradation of chlorpyrifos at 1000 μg g^?1 initial concentration was examined in five different soils from termite-infested regions (Arizona, Florida, Hawaii, Texas) under standard conditions (25°C, field moisture capacity, darkness). Degradation half-lives in these soils ranged from 175 to 1576 days. The major metabolite formed in chlorpyrifos-treated soils was 3,5,6-trichloro-2-pyrid-inol, which represented up to 61% of applied radiocarbon after 13 months of incubation. Minor quantities of [¹⁴C]carbon dioxide (< 5%) and soil-bound residues (? 12%) were also present at that time. Subsequently, a factorial experiment examining chlorpyrifos degradation as affected by initial concentration (10, 100, 1000 μg g^?1), soil moisture (field moisture capacity, 1.5 MPa, air dry), and temperature 15, 25, 35°C) was conducted in the two soils which had displayed the most (Texas) and least (Florida) rapid rates of degradation. Chlorpyrifos degradation was significantly retarded at the 1000 μg g^?1 rate as compared to the 10 μg g^?1 rate. Temperature also had a dramatic effect on degradation rate, which approximately doubled with each 10°C increase in temperature. Results suggest that the extended (3–24 + years) termiticidal efficacy of chlorpyrifos observed in the field may be due both to the high initial concentrations employed (termite LC ₅₀ = 0.2– 2 μg g^?1) and the extended persistence which results from employment of these rates. The study also highlights the importance of investigating the behaviour of a pesticide under the diversity of agricultural and urban use scenarios in which it is employed.     

Aerobic Metabolism of Flupropacil in Sandy Loam Soil

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%.     

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     

Aerobic soil metabolism of metsulfuron-methyl

A laboratory study was conducted to determine the degradation rates and identify major metabolites of the herbicide metsulfuron-methyl in sterile and non-sterile aerobic soils in the dark at 20°C. Both [phenyl-U-¹⁴C]- and [triazine-2-¹⁴C]metsulfuron-methyl were used. The soil was treated with [¹⁴C]metsulfuron-methyl (0.1 mg kg⁻¹) and incubated in flow-through systems for one year. The degradation rate constants, DT₅₀, and DT₉₀ were obtained based on the first-order and biphasic models. The DT₅₀ (time required for 50% of applied chemical to degrade) for metsulfuron-methyl, estimated using a biphasic model, was approximately 10 days (9–11 days, 95% confidence limits) in the non-sterile soil and 20 days (12–32 days, 95% confidence limits) in the sterile soil. One-year cumulative carbon dioxide accounted for approximately 48% and 23% of the applied radioactivity in the [phenyl-U-¹⁴C] and [triazine-2-¹⁴C]metsulfuron-methyl systems, respectively. Seven metabolites were identified by HPLC or LC/MS with synthetic standards. The degradation pathways included O-demethylation, cleavage of the sulfonylurea bridge, and triazine ring opening. The triazine ring-opened products were methyl 2-[[[[[[[(acetylamino)carbohyl]amino]carbonyl]amino] carbonyl]-amino]sulfonyl]benzoate in the sterile soil and methyl 2-[[[[[amino[(aminocarbonyl)imino]methyl] amino]carbonyl]amino]sulfonyl]benzoate in the non-sterile soil, indicating that different pathways were operable. © 1999 Society of Chemical Industry     

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     

Leaching of Alachlor from Alginate-Encapsulated Controlled-Release Formulations

The mobility of alachlor from alginate-encapsulated controlled-release (CR) formulations was investigated in two contrasting soil profiles. Two CR formulations of alachlor were prepared with the following components (1) base—sodium alginate+kaolin+‘Tween’ 20 (1+10+0·5 by mass) and (2) base+40 g kg⁻¹ linseed oil. These were compared to technical grade alachlor and to a commercial alachlor EC formulation (‘Lasso’ 4EC). All herbicide treatments were labeled with [¹⁴C]alachlor and were applied to duplicate soil columns that were composed of a surface and a subsoil horizon. Each horizon was packed to a depth of 12·5 cm, giving a total column length of 25 cm. The columns were leached with 21 cm (420 ml) to 30 cm (600 ml) of 0·01M calcium chloride for a period of 7 to 10 days. Alachlor leaching from the EC formulations was the same as that from the technical material in both soils: 33% in the Evesboro and 10% in the Conover soil. The CR-Oil formulation leached 4 and 2% of the applied [¹⁴C]alachlor, compared to 12 and 3% for the CR-N formulation for the Evesboro and Conover soils, respectively. The CR-Oil formulation also increased the amount of [¹⁴C]alachlor retained in the soil surface horizon (105–114%), compared to CR-N (39–45%), technical material (14–23%) and EC (12–17%).     

Effects of fluazifop-butyl on shoot growth and rhizome buds of Elymus repens (L.) Gould

A series of glasshouse experiments was conducted to evaluate the activity of fluazifop-butyl, butyl 2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy] propionate, against Elymus repens. Foliar applications of doses 0·25–1·0 kg ha^?1 consistently gave better control than did soil applications. The most obvious phytotoxic symptoms were chlorosis and necrosis, beginning with the youngest leaves 5–6 days after spraying, which spread to all leaves within 2 weeks. Translocation was measured by defoliating plants at different times after spraying and assessing regrowth and by evaluating rhizome-bud viability. At low doses (0·125 and 0·25 kg ha^?1) translocation to rhizomes occurred mainly between 6 and 48 h. When fluazifop-butyl was sprayed at a dose range of 0·125–1·0 kg ha^?1, at least 90% of the rhizome buds had accumulated a lethal dose within 72 h of spraying. In another experiment, with a dose of 0·25 kg ha^?1, 31, 72 and 92% of rhizome buds were found to be non-viable when sampled 2, 24 and 48 h respectively after spraying. At 1·0 kg ha^?1 all the buds had accumulated sufficient herbicide to prevent sprouting 48 h after spraying.     

Degradation of fluridone in submersed soils under controlled laboratory conditions

The experimental, aquatic herbicide fluridone (1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone) was degraded in two submersed soils and in the water above those soils to one acidic metabolite (identified as 1,4-dihydro-1-methyl-4-oxo-5-[3-(trifluoromethyl)phenyl]-3-pyridinecarboxylic acid by mass spectrometry). A sandy and a silt loam soil were treated with [¹⁴C]fluridone, immersed in water, and analyzed after 1, 3, 5, 7, 9, and 12 months. Seven to fifteen percent of the ¹⁴C applied to the soils was recovered in the water on each of the various collection dates. The acidic metabolite accounted for 86 to 93% of the radioactivity in the water fraction 7 months after treatment. The metabolite was absorbed strongly by both soils and comprised about 60% of the total ¹⁴C in each soil after 12 months. The remainder of the ¹⁴C in the soils after 12 months was either the parent compound (～30%) or an undefined insoluble residue (～10%).     

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.     

Degradation of [14C]Terbuthylazine and [14C]Atrazine in Laboratory Soil Microcosms

The degradation and formation of major chlorinated metabolites of terbuthylazine and atrazine in three soils (loamy clay, calcareous clay and high clay) were studied in laboratory experiments using molecules labelled with ¹⁴C on the s-triazine ring. Soil microcosms were treated with the equivalent of 1 kg ha^-1 of herbicide and incubated in the dark for 45 days at 20(±1)°C. The quantity of [¹⁴C]carbon dioxide evolved in the soils treated with atrazine was negligible and could not be attributed to mineralization of the parent molecule. The mineralization of terbuthylazine accounted for 0·9–1·2% of the initial radioactivity. In the soils studied, the extrapolated half-lives varied from 88 to 116 days for terbuthylazine and 66 to 105 days for atrazine, with no significant differences for the three soils and the two molecules. The deethyl metabolites of the two s-triazines and the deisopropyl-atrazine metabolite appeared during the incubation in the three soils. The completely dealkylated metabolite was not detected in any of the soils. After 45 days of incubation, the non-extractable soil residues for the high clay, loamy clay and calcareous clay soils represented for terbuthylazine, 33·5, 38·3 and 43·1% and for atrazine, 19·8, 20·8 and 22·3% of the initial radioactivity. © 1997 SCI.     

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.     

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 of mecoprop at different concentrations in surface and sub-surface soil

Biodegradation of [ring-¹⁴C] mecoprop (2-(4-chloro-2-methylphenoxy)propionic acid) was determined in surface and sub-surface soil at concentrations of 0·0005, 0·05, 0·5, 5, 50, 500, 5000 and 25000 mg kg^-1. The kinetics of mineralisation were evaluated from the mineralisation rates as a function of time and by non-linear regression analysis. In the sub-surface soil, degradation was 6–8 times slower than in surface soil, but the shape of the curves was the same in both layers. At concentrations between 0·0005 and 0·5 mg kg^-1, in both surface and sub-surface soil, degradation was initially zero-order followed by first-order kinetics. At 5 to 500 mg kg^-1 in surface soil and 5 to 50 mg kg^-1 in sub-surface soil the degradation rate was initially either constant or decreasing followed by exponential degradation indicating increasing populations of mecoprop decomposers in the soil. At 5000 and 25000 mg kg^-1 in the surface soil and at 500, 5000 and 25000 mg kg^-1 in the sub-surface soil, the degradation was negligible, as determined by the percentage [¹⁴C] carbon dioxide evolved. By non-linear regression, the three-half order model was found to describe the mineralisation. © 1998 SCI     

Mineralization of [14C] glyphosate and its plant-associated residues in arable soils originating from different farming systems

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     

Degradation of the sulfonylurea herbicide LGC-42153 in flooded soil

LGC-42153, 2-fluoro-1-[3-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)pyridin-2-yl]propyl methoxyacetate, is a new sulfonylurea herbicide for use in rice. Its breakdown and metabolism were studied in soil under flooded condition using radioactive tracers labelled at either the propyl group or the pyrimidine ring. The half-life of LGC-42153 was approximately 3.0 days. The mass balance over 120 days ranged from 94.0 to 104.2% of applied radiocarbon, and no significant amount of volatiles or [14C]carbon dioxide were observed. Solvent non-extractable radiocarbon reached 11 approximately 14% of applied radiocarbon at 120 days after treatment. The major metabolic reaction was the cleavage of the carboxyl ester bond to give 1-(4,6-dimethoxypyrimidin-2-yl)-3-[2-(1-hydroxy-2-fluoropropyl)pyridine-3-sulfonyl]urea, which underwent hydrolysis of the sulfonylurea bridge giving 2-(1-hydroxy-2-fluoro)propyl-3-pyridinesulfonamide and 4,6-dimethoxy-2-aminopyrimidine.     

Effect of ABT on the activity and rate of degradation of isoproturon in susceptible and resistant biotypes of Phalaris minor and in wheat

The effect of the monooxygenase inhibitor, 1-aminobenzotriazole (ABT) on isoproturon phytotoxicity and metabolism was studied in resistant (R) and susceptible (S) biotypes of Phalaris minor and in wheat (Triticum aestivum). Addition of ABT (2·5, 5 and 10 mg litre^-1) to isoproturon (0·25, 0·5, 1, 2 and 4 mg litre^-1) in the nutrient solution significantly enhanced the phytotoxicity of isoproturon against the R biotype. Isoproturon at 0·25 mg litre^-1 reduced the dry weight (DW) of the S biotype by 77%, whereas the R biotype required 4·0 mg litre^-1 for similar reduction. Addition of 10 mg litre^-1 of ABT to the 0·25 mg litre^-1 isoproturon caused 71 and 82% reduction in DW of R and S biotypes, respectively. Wheat was more sensitive to the mixture of isoproturon and ABT than the R biotype of P. minor. Reduced concentrations of ABT in the mixture from 10 to 2·5 mg litre^-1 increased the DW of the R biotype more than that of the S biotype. The R biotype metabolised [¹⁴C]isoproturon at a faster rate than the S biotype. ABT (5 mg litre^-1) inhibited the degradation of [¹⁴C]isoproturon in both biotypes of P. minor and in wheat. In the presence of ABT, about half of the applied [¹⁴C]isoproturon remained as parent herbicide in all the three species after two days. The metabolites were similar in the R and S biotypes and wheat as determined by co-chromatography with reference standards and mass spectroscopy (MS). ABT inhibited the appearance of the hydroxy and monomethyl metabolites and their conjugates in all the test plants. These results suggest that the activity of the enzymes responsible for the degradation of isoproturon is greater in the R than in the S biotype of P. minor, resulting in its rapid detoxification. Incorporation of the monooxygenase inhibitor ABT into the nutrient solution greatly inhibited the degradation of [¹⁴C]isoproturon in the R biotype and increased its phytotoxicity. Both hydroxylation and N-dealkylation reactions were found to be sensitive to ABT; inhibition of hydroxylation was greater than that of demethylation. Since ABT could not completely suppress isoproturon degradation, it is possible that more than one monooxygenase is involved. © 1998 SCI     

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.     

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.     

In vivo pharmacokinetics of pyribenzoxim in rats

Pyribenzoxim, benzophenone O‐[2,6‐bis(4,6‐dimethoxypyrimidin‐2‐yloxy)benzoyl]oxime, is a new post‐emergence herbicide providing broad‐spectrum weed control in rice fields. [¹⁴C]Pyribenzoxim was used to study the pharmacokinetics of the compound after oral administration of a dose of 1000 mg kg^?1 to male Sprague–Dawley rats. The material balance ranged from 97.3 to 99.7% of the administered dose and urinary and fecal recovery accounted for 97.1%, with the majority of radioactivity recovered in feces (88.6%) by 168 h after treatment. Elimination as volatile products or as carbon dioxide was negligible. The following values were obtained for the compound in the blood: AUC_0–168h, 28400 µg equiv h g^?1; T_max, 12 h; C_max, 372 µg equiv g^?1; half‐life, 53 h. Radioactivity in tissue decreased from 96.1% of applied radiocarbon at 6 h to 0.4% at 168 h and the highest concentration of radioactivity among the tissues was observed in liver while the lowest residues were found in brain. The elimination half‐lives of radioactivity from tissues was in the range of 7 to 77 h and T_max values of 12, 24 and 12 h were observed for blood, liver and kidney, respectively. Except for that in the digestive tract, the tissue‐to‐blood ratio (TBR) was highest in the liver. © 2001 Society of Chemical Industry