Sorption of selenium anionic species on apatites and iron oxides from aqueous solutions.

The sorption of selenite and selenate ions from aqueous solutions was investigated on hydroxyapatite, fluorapatite, goethite and hematite, in order to simulate the behavior of radioactive selenium in natural or artificial sorbing media. Correlation studies with acido-basic properties and solubility of the solids were also performed. The sorption is pH dependant, but these solids are very efficient for retaining selenite at pH values generally encountered in natural waters, with however higher K(d) values for oxides than apatites. Selenate ions are much less sorbed than selenite. Several methods such as electron microscopy and spectroscopic techniques were used to identify the sorption mechanisms. In the case of hydroxyapatite, sorption proceeds by substitution of phosphate groups in the lattice of the apatite crystal in the superficial layers of the solid. In the case of goethite and hematite, sorption can be interpreted and modeled by a surface complexation process, but there is a discrepancy between sorption site densities for selenite and for protons.

Soil metabolism of isoxaflutole in corn.

The herbicide isoxaflutole 1 (5-cyclopropyl-4-isoxazolyl)[2-(methylsulfonyl)-4-(trifluoromethyl)phenyl]-methanone) has been applied preemergence at the rate of 125 g ha(-1) on corn crops grown on fields located in regions different as to their soil textures. Its metabolite diketonitrile 2 (2-cyano-3-cyclopropyl-1-(2-methylsulfonyl-4-trifluoromethylphenyl)propane-1,3-dione)-which is the herbicide's active compound-and its nonherbicide metabolite 3 (2-methylsulfonyl-4-trifluoromethylbenzoic acid) were measured in the 0-10 cm surface soil layer of the corn crops after the treatment and until the harvest. At the opposite of what occurred in plant shoots, the transformation of isoxaflutole 1 into diketonitrile 2 was not immediate in soil. In the 0-10 cm surface soil layer, this transformation occurred progressively according to an apparent second-order kinetics, and the soil half-lives of isoxaflutole 1 self were comprised between 9 and 18 days. The adsorption of isoxaflutole 1 onto the solid phase of the soil and its organic matter should explain the stabilization effect of soil, increased by the application of fresh organic fertilizer. The sum of the concentrations of isoxaflutole 1 and diketonitrile 2 disappeared in the 0-10 cm surface soil layer according to an apparent first-order kinetics, and the soil half-lives of this sum were comprised between 45 and 65 days. The sum of the concentrations of isoxaflutole 1 and of its metabolites diketonitrile 2 and acid 3 did not account for the amount of isoxaflutole 1 applied. The discrepancy increased with the delay after the application, showing that the acid 3 was further metabolized in soil into common nontoxic products, and ultimately into CO2. The conjunction of the adsorption of isoxaflutole and its metabolites (which reduced their mobilities) onto the soil and its organic matter, and their further metabolism should explain why isoxaflutole and its metabolites were not detected in the 10-15 and 15-20 cm surface soil layers during the crops.

Soil persistence and metabolism of iodosulfuron in winter wheat crops.

The sulfonylurea herbicide iodosulfuron 1 has been applied post-emergence at the dose of 10 g a.i. ha-1 on winter wheat crops grown on sandy-loam (Melle) or on clay soils (Leke, Gistel and Zevekote). The dissipation of iodosulfuron in soil followed a first order kinetics. After the application of iodosulfuron at Melle at the beginning of April 2000, the soil half-life of iodosulfuron in the 0-10 cm surface soil layer was 60 days. At the end of September 2000, i.e. one month after the winter wheat harvest, only 8% of the applied dose of iodosulfuron remained in soil as iodosulfuron itself. At the mid of November, iodosulfuron 1 was no more detected in the 0-10 cm surface soil layer. From the beginning of May till the end of July 2000, low concentrations of iodosulfonamide 2 and of iodosaccharin 3 were observed in the 0-10 cm surface soil layer, their maximum concentrations being 0.7 and 1.5 micrograms of equivalents of iodosulfuron 1 kg-1 dry soil, respectively. At the end of September, the metabolites 2 and 3 were no more detected in soil. At Leke, Gistel and Zevekote, iodosulfuron was applied at the beginning of May 2001, and its half-life in the 0-10 cm surface soil layer was 44, 30 and 35 days, respectively. The later application of iodosulfuron and the higher soil pH (about 8) at Leke, Gistel and Zevekote should explain the soil half-lives lower than at Melle (soil pH 6.2). In all the trials and since the treatment till the mid of November, iodosulfuron 1 and its metabolites 2 and 3 were not detected in the 10-15 and 15-20 cm surface soil layers.

Dissipation and mobility of flumetsulam in the soil of corn crops.

The triazolopyrimidine sulfonanilide herbicide flumetsulam has been applied pre- or post-emergence at the rate of 20 g a.i. ha-1 on corn crops grown on sandy-loam or loamy-sand soils. A procedure has been developed for the analysis of flumetsulam in soil using gas-chromatography and gas-chromatography combined with mass spectrometry, after methylation of flumetsulam and purification of the soil extracts by repeated thin-layer chromatographies. The dissipation of flumetsulam in the 0-8 cm surface soil layer followed a first order kinetics. The flumetsulam soil half-life was about 41 days for the crops grown on sandy-loam soil, and 30 days for the crop grown on loamy-sand soil. At the corn harvest in September, only 9 to 13% of the applied dose of flumetsulam remained in soil, what is a common value for the herbicides at the crop harvest. The heavy rains and the soft temperatures of the autumn should dissipate these low residues within the one or two months period after the harvest. When applied at the rate of 20 g a.i. ha-1, the persistence of flumetsulam in field soil thus was moderate. During the crops and until the harvest, in the 8-15 cm surface soil layer, low concentrations of flumetsulam at the limit of the analytical sensitivity (0.3 microgram flumetsulam kg-1 dry soil) were observed temporarily; in the 15-20 cm surface soil layer, flumetsulam was never detected, showing that flumetsulam was strongly adsorbed onto the soil and its organic matter.

Dissipation and mobility of the sulfonylaminocarbonyl-triazolinone herbicide propoxycarbazone in the soil of winter wheat crops.

The new sulfonylaminocarbonyltriazolinone herbicide propoxycarbazone has been applied at the rate of 70 g ha-1 post-emergence in the spring on winter wheat fields located at three sites different as to their soil texture and composition. A method has been developed for the analysis of propoxycarbazone in soil by GC and GC-MS, after isolation and transformation of propoxycarbazone. The limit of sensitivity was 1 microgram propoxycarbazone kg-1 dry soil. In the sandy-loam soil at Melle, and in the clay-loam soil at Zevekote, the propoxycarbazone soil half-lives in the 0-10 cm surface soil layer were similar, i.e. about 54 days. In the loam soil at Cortil-Noirmont, the propoxycarbazone soil half-life was 31 days. The difference as to the soil half-lives was related to the organic fertilization practized in the past on the three fields. At Cortil-Noirmont, after the winter wheat harvest at the end of August, the residues of propoxycarbazone in the 0-10 cm surface soil layer were very low, and at the end of September, propoxycarbazone was no more detected. At Melle and Zevekote, at the end of September, the concentrations of propoxycarbazone in the 0-10 cm surface soil layer were very low; at the end of October, propoxycarbazone was no more detected. After its application and until the end of October, propoxycarbazone was not detected in the 10-15 and 15-20 cm surface soil layers.

Fate of the herbicide isoxaflutole in the soil of corn fields.

The herbicide isoxaflutole 1 (5-cyclopropyl-4-isoxazolyl)[2- (methylsulfonyl)-4-(trifluoro-methyl)phenyl]-methanone) was applied pre-emergence at the rate of 125 g ha-1 on corn fields located in three sites different as to their soil texture and composition. In the 0-10 cm surface soil layer, the isoxaflutole soil half-life (soil dissipation kinetics of second order) was 9 days in sandy loam (Melle), 15 days in clay loam (Zevekote) and 18 days in loamy sand (Zingem) soil. The sum of the concentrations of isoxaflutole 1 and of its herbicide active metabolite diketonitrile 2 (2-cyano-3-cyclopropyl-1-(2-methylsulfonyl-4- trifluoromethylphenyl)propane-1,3-dione) had a soil half-life (dissipation kinetics of first order) of 45 days in sandy loam, and 63 days in the clay loam and loam sand soils. The soil metabolism of isoxaflutole thus generated, in the soil of field corn crops, a metabolite, the diketonitrile 2, which had an herbicide activity as high as the one of the parent isoxaflutole, and which much extended the herbicide protection given by isoxaflutole. At the crop harvest, isoxaflutole, the diketonitrile 2 and the acid 3 (2-methylsulfonyl-4-trifluoromethylbenzoic acid) were no more detected in soil. During the corn crops, isoxaflutole, and its metabolites diketonitrile 2 and acid 3 were never detected in the 10-15 et 15-20 cm surface soil layers, indicating the very low mobility of these compounds in soil.

Soil dissipation of diuron, chlorotoluron, simazine, propyzamide, and diflufenican herbicides after repeated applications in fruit tree orchards.

In a pear tree orchard planted on loam soil, each plot was treated in April 1998 with either one of the ureas diuron or chlorotoluron, or triazine simazine herbicides applied at 3, 4, and 2 kg AI ha(-1), respectively. Some plots had not been previously treated with one of these herbicides. Other plots had been treated annually during the past 12 years with the same herbicide. One herbicide, and always the same, was thus applied to each plot. In the plots treated for the first time with either diuron, chlorotoluron, or simazine, the soil half-lives of these herbicides in the 0-10 cm surface soil layer were 81, 64, and 59 days, respectively. In the plots treated with the same herbicide for 12 years, the corresponding soil half-lives were 37, 11, and 46 days. Diuron thus produced a moderately enhanced biodegradation, chlorotoluron a high one, and simazine a low but significant one. In another pear tree orchard planted on sandy loam soil, each plot was treated in April 1998 with one of the amide propyzamide (1.25 or 1.0 AI kg ha(-1)) or diflufenican (250 g AI ha(-1)) herbicides. In the plots not previously treated with propyzamide, the propyzamide soil half-life was the same for both doses, i.e., about 30 days. In the plots treated annually for 3 or 14 years with propyzamide, the soil half-life was 12 and 10 days, respectively. In the plots treated for the first time with diflufenican and in those treated annually with diflufenican for 3 years, the diflufenican soil half-life was the same, i.e., 65 days. Propyzamide thus already showed a highly accelerated biodegradation after 3 years of repeated annual applications. Diflufenican, however, did not show enhanced biodegradation after 3 years of repeated annual applications.

Flupyrsulfuron soil dissipation and mobility in winter wheat crops.

Residues of the sulfonylurea herbicide flupyrsulfuron were extracted from cropping soils with 0.1 M NaHCO(3). The soil extracts were cleaned up by partitioning and repeated thin-layer chromatography. Flupyrsulfuron was transformed by diazomethane into N-(4, 6-dimethoxypyrimidine-2-yl)-N-(3-methoxycarbonyl-6-trifluoromet hylpyr idine-2-yl)methylamine (2), which was analyzed by gas-liquid chromatography with electron capture detection, and confirmation for several samples was made by gas chromatography combined with mass spectrometry. The sensitivity limit was 0.5 microg of flupyrsulfuron kg(-)(1) of dry soil. Bioassays using sugar beet as test plant qualitatively confirmed the results of the chemical analyses. Flupyrsulfuron [10 g of active ingredient ha(-)(1)] was applied in autumn on plots in two winter wheat crops on a sandy loam soil, the first crop being made in 1996-1997 and the second one in 1997-1998. In the 0-8 cm surface soil layer of both crops, the flupyrsulfuron soil half-lives were 123 and 92 days, respectively. Flupyrsulfuron was also applied post-emergence in March to other plots in the same crops; the half-lives in the 0-8 cm surface soil layer were similar in both seasons, that is, approximately 58 days. During all crop trials, flupyrsulfuron remained in the 0-8 cm surface soil layer and was not detected in the 8-10, 10-15, and 15-20 cm surface soil layers. The surface-2 cm soil layer contained the greatest flupyrsulfuron soil concentration, but the residues progressively moved down into the 2-4 and 4-6 cm soil layers. At the winter wheat harvest date for each trial, flupyrsulfuron was not detected in any of the soil layers (<0.5 microg kg(-)(1)).

A study of strontium binding to albumins, by a chromatographic method involving atomic emission spectrometric detection.

A chromatographic method involving ICP-AES (inductively coupled plasma atomic emission spectrometry) detection has been successfully applied for the study of strontium-protein complexes. The chromatographic step involves the use of gel filtration-a large-zone Hummel and Dreyer method-which allows to dissociate the bound metallic ions and the free ones. This step is followed by an ICP-AES analysis of fractions collected throughout the chromatographic experiment: the concentration of ionic metallic species in solution can therefore be calculated. Two proteins have been tested: bovine serum albumin, which showed only weak interactions with Sr2+ ions, and bovine alpha-lactalbumin: this protein, well-known for its calcium binding capacity, proved to interact strongly with strontium. The influence of various parameters on the formation of strontium-lactalbumin complexes were determined, namely temperature, pH. Competition experiments between Sr2+ ions and, respectively Na+ and Ca2+ ions were also performed, by varying ionic strength of the medium, and by using both apo and native forms of bovine alpha-lactalbumin.

Isoxaben soil biodegradation in pear tree orchard after repeated high dose application.

During the past nine years, each of the plots of a pear tree orchard were treated annually with the same herbicide treatment. The following herbicide treatments were compared, each being made by application of a mixture of two or three herbicides: 1a, no herbicide at all, weeds being hoed (control 1a); 2, diuron + paraquat 3 + 1 kg/ha; 3, simazine + paraquat 2 + 1 kg/ha; 4, isoxaben + diuron + paraquat 0.5 + 1.6 + 1 kg/ha; and 5, isoxaben + simazine + paraquat 0.5 + 1.25 + 1 kg/ha. In March 1996, one year after the final orchard herbicide treatment, isoxaben could not be detected in the soils of any field plots; isoxaben was incorporated at 0.74 mg/kg in the loamy soils sampled separately in each of the field plots, and the soils were incubated in the laboratory. Isoxaben soil half-lives were 92 days in the soils treated previously with herbicide treatments 1a, 2, or 3 and 42 days in the soils treated with herbicide treatments 4 and 5. The repeated isoxaben treatments applied in the past thus enhanced the isoxaben soil biodegradation; diuron, simazine, and paraquat had no influence on this rate enhancement. On the other hand, herbicide treatments 4 and 5 were applied in the orchard in April 1996 on the corresponding plots treated in this manner for the last nine years. Isoxaben + paraquat 0.5 + 1 kg/ha was applied simultaneously on other plots (control 1b) not treated in the past with isoxaben. During the growth season in the orchard, the isoxaben soil half-lives in the control plots 1b was 101 days, and 41 days in the plots where herbicide treatments 4 or 5 were applied.

Chromatographic method involving inductively coupled plasma atomic emission spectrometric detection for the study of metal-protein complexes.

A chromatographic method has been used to study metal ion-protein complexes. It involves successively a gel filtration technique to separate and distinguish the complexed from the free metallic ions, and a spectrometric technique, inductively coupled plasma atomic emission spectrometry (ICP-AES), which allows us to calculate accurately the concentration of ionic metallic species in solution. In the chromatographic step, we applied a large-zone Hummel and Dreyer method. Thus, fractions can be collected throughout the chromatographic experiment and their metal concentration measured by ICP-AES, at constant and known protein concentration. This method has been tested on the copper complex of bovine serum albumin. Results of our study are in good agreement with previous studies on this complex.