Cinétique de la photodégradation induite du profenofos (PFF) en solution aqueuse par excitation des substances humiques naturelles des sols/Kinetics of the Photodegradation of profenofos (PFF) induced by humic substances in aqueous solution

Under photochemical excitation, humic substances produce reactive species which can degrade a great variety of organic compounds. Solvated electrons, hydroxyl radicals, singlet oxygen and reactive triplet states were characterized using probe molecules and scavenging techniques. The phototransformation of organics matters depends on the irradiation wavelength, on oxygen concentration and on the origin of the humic substances. Through their photoinductive properties, humic substances can be used to degrade pollutants. As an application of these experimental findings, the photodegradation by humic substances of Profenofos ((O-4-bromo-2-chlorophenyl)O-ethyl-S-propylphosphorothioate), an organochlorinated polluting pesticide used in the cotton cultivation in Togo was carried out. Physicochemical analysis realised after reaction showed the effective transformation of the pollutant. This transformation was slow in deoxygenized humic solutions in the presence of propan-2-ol which traps hydroxyl radicals generated by humic substances under irradiation. A reasonable conclusion was that these radicals were responsible for the pollutant photodegradation. Identification of intermediates under the various experimental conditions helped us propose chemical structures for the detected photodegadation products.