Camille Coste

Behaviour of fipronil in soil under Sahelian Plain field conditions

The behaviour of fipronil, a phenylpyrazole insecticide used for locust control, was studied under sub-Saharan conditions in soils of the Niamey region of Niger. A formulation of fipronil (Adonis®) was applied to uncultivated soils at Banizoumbou and Saguia. Soil was sampled at 0–10, 10–20 and 20–30 cm depths for up to two months after treatment. Residues were analysed by gas chromatography using electron capture and mass detectors. For both soils, a rapid initial decrease of fipronil was observed, with rapid formation for the most part of a photodegradate. Three other metabolites of fipronil were also detected throughout the study. These metabolites displayed different dissipation kinetics. Fipronil and its metabolites did not move beyond 10 cm depth, except for the amide, which is not considered a toxicologically significant metabolite.

Isolation from soil and growth characteristics of a cipc-degrading strain of Pseudomonas cepacia

Abstract A bacterial strain, identified as Pseudomonas cepacia , was isolated from soil and had the ability to utilize phenyl carbamates (BIPC, CIPC) as the sole source of carbon and energy. The degradation of CIPC, at various concentrations, was studied in a minimal medium. The addition of yeast extract increased bacterial growth, decreased the degradation-lag period, and increased the rate of CIPC transformation. The bacterial isolate also utilized 3-chloroaniline, the degradation product of CIPC. Its ability to degrade the herbicide was retained despite repeated growth in media without the herbicide.

Degradation of Metribuzin in Two Soil Types of Lebanon

The degradation of metribuzin [4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one] as influenced by soil type, temperature, humidity, organic fertilizers, soil sterilization, and ultra-violet radiation was studied in two soil types of Lebanon under laboratory conditions. The two soil types were sandy loam and clay. Deamination of metribuzin in the sandy loam soil to its deaminometribuzin (DA) derivative was basically a result of biological activity. In the clay soil the first metabolite diketometribuzin (DK) was a result of oxidative desulfuration, while diketo-deaminometribuzin (DADK) was the product of reductive deamination. The two soils represented major differences in the pesticide transformation processes. Photodecomposition on the soil surface and in aqueous media was also an important process in the degradation of metribuzin. Furthermore, the increase in soil organic matter enhanced degradation.

Behaviour of pendimethalin in tropical and mediterranean plain field condition

Abstract Behaviour of the herbicide pendimethalin [N‐(l‐ethylpropyl)‐3,4‐dimethyl‐2,6‐dinitrobenzenamine] was evaluated in plain field under wet tropical conditions (Martinique, FWI) and in the Mediterranean area (Languedoc, South of France). Simultaneously, adsorption parameters were discussed with Freundlich equation, and desorption evaluated using a model with two compartments corresponding to two different energy levels. Pendimethalin showed a strong adsorption in all three soils and was very difficult to desorb. Higher clay content in tropical vertisol and ferrisol involved adsorption parameters (Kfa) higher than the one found in the Mediterranean fluvisol. Although heavy rainfalls in the tropics intervene on migration, pendimethalin propensity to leaching is levelled by its strong adsorption potential and appears very limited under the conditions chosen during this work. Half‐life of the compound (in the 0–25 cm soil layer) varied from 13 to 17 days. Pendimethalin was also classified as a “non‐leach...

Distribution and dissipation of metolachlor in soil columns

Abstract Distribution and dissipation of metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐l‐methylethyl) acetamide] in a soil of Montpellier were evaluated in laboratory conditions for 8 weeks using 100 cm PVC pipes. The half‐lives of metolachlor varied from 31 to 54 days according to the application dose (1.2, 4.5 and 9 kg a.i./ha respectivelly). The rate of herbicide migration increased with stronger dose. Adsorption and desorption of metolachlor were studied in the same soil at three difierent depths. Soil Freundlich adsorption coefficients (Kfa ) were 1.0,0.7 and 0.6 for 0 to 10, 10 to 50 and 50 to 95 cm depths respectively. Desorption coefficients (K fd ) varied more slightly (3.6 ‐ 3.9). Ratio soil quantity/water volume may influence adsorption parameters.

Mitosis inhibition by a N-(1,1-dimethylpropynyl) benzamide series

Abstract A N -(1,1-dimethylpropynyl) benzamide series was obtained by changing the substitution of the phenyl on the 3 or 4 position. As is the case for propyzamide, N -(1,1-dimethylpropynyl)-3-chlorobenzamide is a powerful and selective inhibitor of mitosis in plant cells at 0.1 μM, as is demonstrated by its characteristic effect on seedlings of five different species ( Triticum sativum L., Avena fatua L., Lolium multiflorum Lam., Raphanus sativus L., Sinapis arvensis L.), by the effects on dividing cells and by the lack of effect on mitochondria or chloroplast activities. Three other compounds of the series inhibit mitosis at 10 μM (3-Br, 3-Me, 3-F). The 4-substituted derivatives, as well as the 3-CN or 3-OMe benzamides have only a small effect on cell division. All these results can be explained by a quantitative structure-activity relationship where the lipophilicity (expressed by π), the electronic activity (expressed by σ) and a steric character expressed by L (illustrating the steric hindrance near the 3 and 4 positions of the phenyl ring) are taken into account. These observations suggest that the 4 position of the phenyl is probably directly involved in the binding of the propyzamide derivatives to a target controlling mitosis in plant cells.

Behavior of triadimefon in two Lebanese soils.

The retention and fate of triadimefon fungicide were studied under two environmental conditions. Field studies were conducted on two soils, a sandy loam soil (Fanar) and a clay soil (Raouda). Fanar is a wet coastal area while Raouda is a dry agricultural area of the Bekaa plain located at an elevation of 870 m above sea level. Triadimefon was applied with a jet sprayer at 267 g a.i.ha−1 and 200 g a.i.ha−1 at Fanar and Raouda, respectively. Reconstituted soil columns (600 × 30 mm) glasses, were used to study the fungicide movement and metabolism in the two soils. Analyses of triadimefon and its metabolites were carried out using gas chromatography (GC) and high performance liquid chromatography (HPLC). The results indicated a weak reversibility of the adsorbed fraction in the clay soil. Clay is considered an important factor in triadimefon adsorption. Triadimefon mobility in the sandy—loam soil was relatively high in comparison with behavior in the clay soil where about half of the applied fungicide was detected in the upper 25 cm of soil, six days after treatment. Rapid degradation of triadimefon to triadimenol was observed in the two soils. The observed half-life was 8 days in sandy-loam and 13 days in clay soils.

Influence de l'application d'un herbicide le propyzamide dans le sol par l'etude de la mineralisation du glucose 14C(U) et de la repartition de la radioactivite dans differentes fractions du sol (essais en laboratoire et en plein champ)

The effects of the herbicide PROPYZAMIDE are studied in laboratory and field conditions. The modifications involved are characterized by measurement of 14C-glucose mineralization and radioactivity incorporation into the soil fractions. In laboratory conditions, temperature and moisture are kept stable and the experiment is performed during less than 24 hours. In these conditions, Kerb 50 (commercial formulation of propyzamide) and the emulsifier (material used in propyzamide formulation) exert little effect on 14CO2 evolution. In field conditions, propyzamide andKerb 50 are applied once at two different doses: at field rate (1,5 kg/ha) and twentyfold this rate. Essays are duplicated. The herbicide (propyzamide in Celanol and Kerb 50) and the emulsifiers alone (Celanol and the material used in propyzamide formulation) are applied on the soil surface (application date: 3.02.81). Two weeks later and then every month during four months, samples are taken to the depth of about 5 cm (Propyzamide migrates very slowly in the first centimeters of the soil). The characterization experiment is performed on 10 g soil samples by 14C-glucose incubation at 28 degrees C during two hours. 14CO2 evolved is measured after incubation and acidification with HCl. Then radioactivity distribution in the soil is counted after chemical fractionation of soil. This distribution is about 10-16.5% as 14CO2, 22-37% in the acid-soluble fraction, 10-25% in the alkali-soluble fraction and 15-45% in the human fraction (measured as 14CO2 evolved after combustion). This distribution is little modified by the herbicides or the emulsifiers but its evolution is significantly related to environmental conditions (temperature). Nevertheless a few modifications are observed. They can be due to the herbicide propyzamide itself but the emulsifiers and the degradation products of propyzamide can also influence the measurement (After forty days in the soil, 70-95% of the starting active ingredient have disappeared). They can also be a result of the initial effects of the products (modification of the microflora and of the environment).

Reaction de degradation d'un carbamate herbicide, le chlorbufame: Influence des facteurs lies au sol

Abstract Kinetics of degradation of chlorbufam is determined in aqueous solution, in aqueous solution with humic acids, argilo‐humic complexes, soil and sterile soil. The adsorption is also evaluated in this different fractions. The adsorption process has a protecting effect and the chlorbufam is not chemically degraded when it is adsorbed on organic matter. The biodisponibility is also decreased by adsorption.

Degradation catalytique du chlorfenvinphos et du methidathion deposes sur kaolinite et bentonite saturees par differents cations

Abstract The catalytic degradation of chlorfenvinphos and methidathion on H+, Ca+2, Na+ and ?+ monoionic kaolinite and bentonite was investigated. The results showed that the decomposition of chlorfenvinphos was greater than methidathion in both clays. The extent of degradation was influenced by the nature of the exchange cations and its degree hydration, in the following sequence: K+ >Na+ >Ca+2 >H+/A1+3. In both clays the process of hydrolysis occurred in two stages involving first‐order kinetics of differents hydrolysis rates. The first stage consisted a high hydrolysis rate of short duration and the second had a slow rate but involved a continuous hydrolysis.