Sunlight and UVC-254 irradiation induced photodegradation of organophosphorus pesticide dichlorvos in aqueous matrices

Abstract

Dichlorvos (DDVP) is an organophosphorus pesticide that has been classified as highly hazardous chemical by the World Health organization. In this study, the fate of the pesticide DDVP in natural water compartments was examined under simulated sunlight. Moreover, the effect of UV-254 irradiation on DDVP depletion was also 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, and the rate constants were 0.040 h at pH 7 and 0.064 h at pH 3. A reaction mechanism for the generation of reactive oxygen species (ROS) via DDVP photoabsorption was proposed. Humic acids (HA) played a double role as photosensitizer and inhibitor, observing an enhancement on DDVP photodegradation at low HA concentration (TOC = 2 mg L). 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.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…Indirect photoreactions are involved in the fate of organic contaminants [ 334 – 338 ], nanomaterials [ 339 ], and certain pesticides [ 340 – 342 ]. Considering the large effects of CDOM on the inactivation rate constants of contaminants through UV protection and photosensitisation, we expect that future ozone-related changes will be much smaller than changes caused by browning of aquatic environments.…”

Sublethal concentrations of dichlorvos and paraquat induce genotoxic and histological effects in the Clarias gariepinus

“…Further, it is applied for defoliating and desiccating purposes in the harvest of economic crops such as cotton, beans, soybeans, potatoes, sunflowers, sugarcanes, among others [6]. The ubiquity of these pesticides in various environmental matrices including surface waters is due to their relatively low cost, high availability and high solubility in water [7][8][9]. These pesticides reach the aquatic ecosystem through various routes such as direct application, spray-drift, run-off, leaching, and discharge from factories and sewage [10].…”

The biochemical properties of a novel paraoxonase-like enzyme in Trichoderma atroviride strain T23 involved in the degradation of 2,2-dichlorovinyl dimethyl phosphate

“…The purified protein or plasma derived from human and rabbit sera has been demonstrated to catalyze the hydrolysis of a broad range of substrates, including some pesticides such as oxon, arylesters of carboxylic acids, and lactones of hydroxy acids (18,20). Purified rabbit serum was injected into the tail veins of rats, increasing the peak hydrolytic activity of rat serum toward paraoxon by 9-fold and increasing that toward chlorpyrifos-oxon by 50-fold (21).…”