Light irradiation and transformation of some sulfonylurea herbicides.

Effects of light on sulphonylurea herbicides, triasulfuron and thhifensulfuron methyl, were studied under UV and solar simulator irradiations. energies of first singlet and triplet state transitions were calculated from fluorescence spectra. Experiments were performed in the presence of either a singlet or a triplet quencer showing that photodegradation of both herbicides begins from a triplet state T1. Samples were irradiated and the disappearance of herbicides at various illumination times were determined by liquid chromatography, as compared to control solutions kept in the dark. The photolysis process of both herbicides occurred throught first order kinetic reactins. Halflife times were 22.3 and 54 hours for triasulfuron and thyfensulfuron methyl, respectively. The main products, identified by LC ESI mass spectroscopy, were: (4-methoxy-6-methyl-1,3,5-triazion-2-yl)urea, common to triasulfuron and thyfensulfuron methyl; 2-(2-chloroetoxy)benzenesulfonamide, arising from triasulfuron degradation; methyl(2-sulfonamide)thyofene carboxylate, occurring from thyfensulfuron-methyl transformation. the presence of minor by-products was also ascertaine

Degradation of triclosan in the presence of p-aminobenzoic acid under simulated sunlight irradiation

International audienceThis study aimed to investigate the degradation of triclosan (TCS) in the presence of p-aminobenzoic acid (PABA) under simulated sunlight irradiation (lambda >= 290 nm). The effect of PABA concentration, pH, dissolved organic matter (DOM), and DOM-hydrolytic Fe(III) species complexes on the photodegradation of TCS in the presence of PABA (TCS-PABA) was also studied. The photolysis of TCS-PABA obeyed pseudo-first-order kinetics well, and the degradation of TCS-PABA enhanced with increasing solution pH (from 3.0 to 11.0). The presence of PABA inhibited the degradation of TCS-PABA, and the weakest inhibitory effect was observed while the concentration of PABA was 5 mg L-1. The addition of DOM (Suwannee River fulvic acid standard I [SRFA], Suwannee River HA standard II [SRHA], and Suwannee River natural organic matter [SRNOM]) showed different inhibition effects on TCS-PABA degradation. However, higher Fe(III) concentration at the DOM concentration of 5 mg L-1 could favor the formation of DOM-hydrolytic Fe(III) species complexes, further accelerating the degradation of TCS-PABA. In comparison with deionized water (DI water), TCS-PABA could be better photodegraded in river water nearby the effluent of a wastewater treatment plant. This study provides useful information for understanding the natural behavior of TCS in the presence of other organic contaminants

Chemically grafted field effect transistors for the detection of potassium ions

International audienc

Laboratory studies of the adsorption of two pesticides (diuron and tebuconazole) using a batch design and an experimental flume: influence of contact conditions

The adsorption of two commonly used pesticides, diuron and tebuconazole, on an organic substrate (hemp), which was chosen as an analogue for natural substrates often found in agricultural ditches, has been studied using three different contact schemes: 1) contact in a beaker using a modified batch method; 2) contact in an experimental flume, with a dry start substrate; and 3) same as 2) but with the substrate initially saturated with water. Changes in pesticides concentrations as a function of time as well as adsorption after seven hours have been determined for each case. The highest adsorption is observed for the experiments with a flume initially containing dry hemp. In that case, both the initial condition (hemp initially without water) and the contact conditions between the pesticide solution and the substrate appear to favour adsorption. The lowest adsorption is obtained for the flume containing hemp initially saturated with water. In that case, samples that were obtained at different depths inside the hemp using capillary tubes showed that only the superficial part of the hemp was in equilibrium with the surface water. The presence of an initial water table appears to be a limiting factor for pesticides penetration and further adsorption onto hemp. An intermediate adsorption is obtained for the modified batch method. These results highlight the pronounced influence on adsorption of both the initial hemp humidity conditions and the contact conditions between the pesticides solution and the substrate. This influence should be studied further to assess the potential of agricultural ditches to mitigate pesticides contamination in surface water

Etude en canal expérimental de l'influence de la vitesse de l'écoulement de surface, de la submergence et de la forme du lit sur le transfert de quatre pesticides

National audienceL'étude a pour objectif de mieux comprendre l'influence de l'hydrodynamique sur le transfert de pesticides dans les fossés agricoles à écoulement permanent, situation très fréquente en saison hivernale en milieu agricole drainé. Trois paramètres ont été retenus : i) la vitesse de l'écoulement de surface ; ii) la submergence (rapport entre les hauteurs moyennes des formes du lit et de la lame d'eau) et iii) la forme du lit. Leur influence a été étudiée en conditions semi-contrôlées au sein d'un canal expérimental saturé en eau et dont le fond était tapissé d'un substrat simplifié constitué d'un assemblage de fibres de chanvre, choisi pour limiter les sources de variabilité liée à la grande hétérogénéité des substrats naturels de fossés. Le substrat retenu présente une composition majoritairement organique et l'existence de produits commerciaux standards (rouleaux de chanvre de 10 cm d'épaisseur et de plusieurs mètres de long) facilite sa mise en ½uvre tout en assurant une bonne homogénéité et stabilité dans le temps. Deux herbicides (isoproturon, diuron) et deux fongicides (azoxystrobine, tébuconazole) ont été sélectionnés dans l'étude. Des essais préliminaires au laboratoire ont montré que leurs capacités d'adsorption sur le substrat simplifié étaient intermédiaires entre celles sur substrats naturels composés de sédiments ou de feuilles mortes. La comparaison des différentes expérimentations en canal indique qu'une augmentation de la vitesse de l'écoulement de surface favorise le transfert des pesticides vers le lit, ainsi que la cinétique de ce transfert. Le constat est le même lorsqu'on augmente la submergence (donc la hauteur relative des formes du substrat), ou bien lorsqu'on passe d'une géométrie de petites formes en « dunes » à une géométrie de grandes formes en « créneau ». L'influence de chaque paramètre semble être interdépendante. Des pistes sont données pour la transposition des résultats en appui à une meilleure gestion des fossés agricoles pour favoriser la limitation du transfert des pesticides

Suspected-target screening strategy to investigate degradation by ozonation or photolysis of urban micropollutants in waste waters

International audienc

Suspected-target screening strategy to investigate degradation by ozonation or photolysis of urban micropollutants in waste waters

International audienc

Optimization of lubricants for silica micromotors

International audienc