Characterization of strains of Aspergillus flavus and A. parasiticus isolated from groundnut (Arachis hypogea), rice (Oryza sativa) and maize (Zea mays) in Senegal

The contamination of certain food crop with aflatoxin poses a real public health problem for consumers and causes many market losses for exporters. Thus, several research works are oriented in the direction of developing methods to combat aflatoxinogenic fungus. This study aimed at identifying and characterizing strains of Aspergillus flavus and A. parasiticus on groundnut, maize and rice seeds grown or imported into Senegal. Four species (A. niger, A. tamarii, A. flavus and A. parasiticus) were isolated from the seeds with incidences ranging from 0 to 100% depending on the samples and their provenance. Six strains of A. flavus and 3 strains of A. parasiticus have been identified and characterized on CYA and G25N culture media. The characterization focused on the morphological characteristics (color and appearance, mycelial growth) of the colonies on the different culture media, and on some microscopic characteristics such as the density of sporulation (production of conidia) and the appearance of the conidiophore. Strains of A. flavus were more frequent on groundnuts and isolates with the same traits were also identified from rice and maize samples, hence the 3 strains of A. parasiticus were isolated

Determination of fenvalerate insecticide in natural waters by a photochemically-induced fluorescence method

International audienc

Analysis of non-native fluorescent pesticides by thermo-induced and photo-induced fluorescence, a comparative study

This paper compares the performance of three analytical methods for the determination of pesticides in natural waters. As many pesticides are non-fluorescent, they are transformed into highly fluorescent by-products in two ways: elevated temperature in an alkaline medium (thermo-induced fluorescence - TIF); or UV irradiation in water (photo-induced fluorescence - PIF). The first method studied uses TIF, the second one uses PIF and the third one uses an automatic sampling and analysing PIF system. Analytical applications were carried out using the three methods for the determination of deltamethrin and cyhalothrin, pesticides widely used in Senegal. In both cases, the calibration curves obtained are linear without matrix effects, and the detection limits are good in the ng mL−1 range. It appears that the analytical performances of the automatic PIF method are better than the two others. The advantages and disadvantages of the three methods are then compared and discussed in term of analytical performance and usability

Direct Spectrofluorimetric Method for the Analysis of Carbofuran and Fluometuron in Senegalese Natural Waters

International audienc

Solvolysis kinetic study and direct spectrofluorimetric analysis of the fungicide benomyl in natural waters

International audienceA direct spectrofluorimetric method for the quantitative analysis of benomyl in natural waters is described. Benomyl is an instable, fluorescent fungicide that mainly decomposes into carbendazim and n-butyl-isocyanate in organic and aqueous solutions. The kinetics of benomyl solvolysis reactions were investigated in organic solvents (methanol and acetonitrile) and in aqueous solvent systems, including β–cyclodextrin (β-CD), sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC), cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium hydroxide (CTAOH), Brij-700, Triton X-100 and water, at different pH and/or NaOH concentrations. The benomyl fluorescence signal was found to be quasi-completely stable in 10-2 M NaOH aqueous solution, various alkaline (10-2 M NaOH) organized media, β-CD neutral solution and Triton X-100 aqueous solutions of different pH. Based on these results, a direct spectrofluorimetric analytical method was developed for the determination of benomyl in 10-2 M NaOH aqueous solution and Triton X-100 solutions (pH7 and 10-2 M NaOH), with wide linear dynamic range (LDR) values of two to three orders of magnitude, very low limit of detection (LOD) and limit of quantification (LOQ) values of, respectively, 0.002-0.5 ng/mL and 0.007-2.0 ng/mL, and small relative standard deviation (RSD) values of 0.2-1.7 %, according to the medium. This direct spectrofluorimetric method was applied to the evaluation of benomyl residues in natural waters, with satisfactory recovery values (87-94%).</p

Analysis of Oxadiazon Herbicide in Natural Water Samples by a Micellar-enhanced Photo-induced Fluorescence

International audienceA micellar-enhanced photo-induced fluorescence (ME-PIF) method was developed to analyze, for the first time, oxadiazole herbicide (namely oxadiazon) in natural water samples. Photo-conversion under UV irradiation of the herbicide into strongly fluorescent photoproducts was performed in aqueous solution and in the presence of two surfactants, cetyltrimethylammonium chloride (CTAC) or Tween 20, at micellar concentrations. The ME-PIF parameters were optimized. The ME-PIF method gave very good results with satisfactory analytical performance for the determination of a selected pesticide with concentration linear dynamic ranges of over one to two orders of magnitude. It yielded good reproducibility (RSD values of between 3.6 and 9.6%) in tap, river and sea water spiked samples, and the limits of detection were in the ng mL-1 range

Determination of Agmatine Rate by Spectrofluorimetric Method in Alkaline Medium: Optimization and Application on Shrimp.

International audienc

Light effects on Carbofuran and Fluometuron: Impact on natural waters. Spectrophotometric study

International audienc

Ultraviolet Photo-Induced Fluorescence Followed by Laser Excitation (UV-PIF-LE) for the Determination of Pesticides in Natural Waters

International audienceA new method was developed for determining trace amounts of pesticides, using an ultraviolet (UV) lamp to obtain photo-induced fluorescent (PIF) compounds, and then using laser excitation (LE) by a tunable source to excite and simultaneously characterize their fluorescence over a short acquisition time using an intensified charge-coupled device camera. This new UV-PIF-LE method was applied to determine isoproturon, oxadiazon, and fipronil in natural waters. This approach represents an improvement on the previously published direct laser photo-induced fluorescent (DL-PIF) approach that utilized the inclusion of a supplementary UV irradiation device in the experimental setup, permitting the separation of the formation and detection steps for the PIF analytes. This evolution improves the selectivity and increases the sensitivity while maintaining a short analysis time. The UV-PIF-LE method gave very good results with satisfactory analytical performance for the determination of the selected pesticides. This approach also demonstrated good reproducibility, with relative square deviation values between 3.3% and 6.3%, for spiked river water and seawater samples with detection limits in the ng mL−1 range

Photodegradation study of the fenvalerate insecticide by 1H NMR, 13C NMR, and GC-MS and structural elucidation of its transformation products

International audienceThe photolysis of fenvalerate, a pyrethroid insecticide, was studied in acetonitrile by 1H nuclear magnetic resonance (NMR) and 13C NMR to identify the site of bond cleavage and gas chromatography-mass spectrometry (GC-MS) to establish the chemical structure of fenvalerate photoproducts. Ultraviolet (UV) irradiation of fenvalerate solutions was performed for 18 h with a solar light simulator, and the photolysis reaction obeyed first-order kinetics. Photolysis half-life time (t1/2) values ranged between 15.25 and 21.63 h (mean photodegradation percentage = 51.7 %) for 1H NMR and between 4.55 and 8.06 h (mean photodegradation percentage > 80 %) for 13C NMR. We observed five sites of bond cleavage, namely carbonyl-tertiary carbon, tertiary carbon-tertiary carbon, carbonyl-oxygen, carboxyl-tertiary carbon, and aromatic carbon-tertiary carbon, yielding photoproducts formation. GC-MS was associated with 1H NMR and 13C NMR to obtain a complete photodegradation mechanism. Before UV irradiation, two chromatogram peaks were obtained, due to the two fenvalerate isomers. Under irradiation, both peaks decreased, and new peaks appeared, corresponding to photoproduct formation. After a 12- to 13-h irradiation, 99.39 % of fenvalerate was degraded with a mean rate constant of 0.305 h–1. The chemical structure of the formed photoproducts was identified, either by using the National Institute of Standards and Technology (NIST) mass spectral database or by interpreting the mass spectra. Finally, a detailed mechanism was proposed for fenvalerate photodegradation