CONICET | Buscador de Institutos y Recursos Humanos

Chlorpyrifos 0,0-diethyl 0-(3,5,6-trichloro-2-pyridyl) phosphorothioate) is an organophosphorus insecticide - acaricide - nematicide of wide spectrum. It is used without restrictions in the agriculture and at domestic level in Argentina. Chlorpyrifos applied in agricultural areas is transported toward the superficial waters. Among the natural processes of removal of Chlorpyrifos of water columns is photodegradation. Methanol and a mixture methanol-water were used as solvent. The samples were irradiated with fluorescent tubes as UV light source, the temperature was kept constant and samples were stirred at constant rate. Samples were taken at different times during the degradation process and they were measured spectrophotometricaly to determine the concentration of the remained Chlorpyrifos. pH was also controlled for each aliquot when the experiments were running using mixtures of methanol-water as solvent. The hydrolysis assay in darkness was done for each concentration of Chlorpyrifos. An exponential decay of first order with respect to the reagent is observed in all the assays with the time. During the experiments made in methanol formation and disappearance of reaction intermediate is observed The assays carried out in darkness, show a slight increment of the absorbance as a function of time during the lapse of time of photodegradation. This allows us to attribute the disappearance of the bands to a mainly photolytic process. The assays carried out at different temperatures were compared and no significant differences were observed in the rate constant values obtained. During photolysis of the solutions in methanol-water a pH decay is observed and this is associated to the formation of photodegradation acidic products. The samples and their corresponding controls were analyzed by HPLC-MS and O,O- diethyl phosphorothioic acid was identified as one of main photodegradation products.