CONICET | Buscador de Institutos y Recursos Humanos

Dichlorvos (DDVP) is an organophosphorus pesticide that has been classified as highly hazardous chemical bythe World Health organization. In this study, the fate of the pesticide DDVP in natural water compartmentswas examined under simulated sunlight. Moreover, the effect of UV-254 irradiation on DDVP depletion wasalso studied. In deionized water, DDVP was photodegraded only in the presence of dissolved molecular oxygen.The photodegradation during the first 6 h of sunlight irradiation occurred with pseudo first-order kinetics, andthe rate constants were 0.040 h−1 at pH 7 and 0.064 h−1 at pH 3. A reaction mechanism for the generation of reactiveoxygen species (ROS) via DDVP photoabsorption was proposed. Humic acids (HA) played a double role asphotosensitizer and inhibitor, observing an enhancement on DDVP photodegradation at low HA concentration(TOC = 2 mg L−1). The depletion of DDVP under 254 nm UV irradiation was ascribed to direct photodegradation and oxygen mediated photoinduced reactions. Direct photodegradation of DDVP decreased with 254 nm irradiation reduction, highlighting the importance of radical mediated mechanisms at low irradiation doses. Based on LC/MS data, the main photoproducts under simulated solar light and UV-C irradiation were identified and potential reaction pathways were postulated. The three main identified products were o-methyl 2,2-dichlorovinyl phosphate, dichloroacetaldehyde and dimethylphosphate. Moreover, the toxicity of samples was evaluated along the irradiation exposure time using Microtox® assays. This study brings new insights into the role of oxygen in the photodegradation of DDVP and the induced and inhibition mechanisms involved in the presence of the humic acids in natural waters.

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