Phototransformation d'herbicides tricétoniques et d'insecticides pyréthrinoïdes à la surface des végétaux

When crops are sprayed with pesticides, the leaves are covered with fine droplets containing the active ingredient. Pesticides can then be broken down by sunlight. We showed in this work that mesotrione and sulcotrione herbicides as well as cypermethrine and deltamethrine insecticides are photolabile when sorbed on cuticular waxes. The pesticide photolysis rate can both increase or decrease, if additives from commercial fomulations are added. However, we could not find a general rule that could predict the importance of the phototransformation for any pesticide. Moreover, while phototransformation was the only dissipation process during experiments in the laboratory, other dissipation processes, such as diffusion through the plant cuticle or wash off by rain or dew, can compete and even become predominant in field studies.Les pesticides appliqués par pulvérisation dans les cultures sont dispersés à la surface des plantes où ils peuvent être transformés sous l'effet de la lumière solaire. Nous avons montré dans ce travail que les herbicides mésotrione et sulcotrione, et les insecticides cypermétrine et deltaméthrine sorbés à la surface des cires cuticulaires, sont photosensibles. Cette propriété est modifiée par l'ajout d'additifs présent dans les formulation commerciales ? Ces derniers peuvent accélèrer ou ralentir la photolyse des principes actifs. Cependant, il ne semble pas y avoir de règle générale permettant de prévoir l'importance de la phototransformation pour chaque matière active. D'autre part, alors qu'en laboratoire la dissipation des pesticides étudiés est uniquement due à la phototranformation ; sur les plantes entières, d'autres phénomènes interviennent. La diffusion dans la cuticule et les pertes dues au lessivage par la pluie ou la rosée peuvent devenir prépondérantes devant la phototransformation

Evolution on Pollutant Removal Efficiency in Stormwater Ponds due to Changes in Pond Morphology

Ponds are frequently used to remove pollutants from urban runoff, but only a few accurate studies have been carried out to determine the long-term pollutant removal efficiency, and almost none on changes in removal over time. Removal efficiency will be affected by changes in pond morphology, vegetation growth and sediment accumulation. This study presents the evolution of pollutant removal efficiency over a seven-year period.The results showed that vegetation growth and increased sediment thickness affected copper, zinc, and nitrogen removal efficiency nega-tively. Concluding recommendations are removal of vegetation in the au-tumn and sediment removal after approximately seven to ten years in op-eration

Understanding mesotrione photochemistry when applied on leaves

International audienceWe developed a methodology to perform laboratory studies that approach field conditions. To demonstrate our methods, we used the herbicide mesotrione. Simulated solar light irradiation experiments were conducted on several cuticular wax films. Adjuvants greatly favoured the rate of mesotrione photolysis. Specifically, the photolytic transformation of formulated mesotrione was 15 times faster than that of pure mesotrione. The morphology and composition of the wax films had a greater effect on the photolysis of formulated mesotrione than of pure mesotrione, which formed aggregates on the waxes. This shows the importance of considering the formulation when studying pesticide photolysis on crops. To corroborate our model, we conducted experiments on detached leaves. The rates of photolysis on leaves and on wax films were of the same order of magnitude. Finally, the mesotrione rate of photolysis on leaves is much higher compared with data from the literature in water and on soils. Photolysis is likely to be a fast dissipation process on crops. The photodegradation of pesticide on crops should be systematically evaluated