Comparative Photodegradation Study of Fenthion and Disulfoton under Irradiation of Different Light Sources in Liquid- and Solid-Phases

To assess the photodegradation extent of the organophosphorus pesticides, fenthion and disulfoton in the envi-ronment, degradation rates of their chemicals under irradiation by visible light and each region of the ultraviolet (UV) sources, UVA (320–400 nm radiation), UVB (280–320 nm radiation) and UVC (250–260 nm radiation) in liquid- and solid-phases were determined and their photolysis products identified. Although visible light did not cause photodegradation of either fenthion or disulfoton even after the maximal irradiation of 8 hr in both phases, all the ranges of UV sources resulted in the photolysis of both pesticides, despite the solid-phase. The photolysis rates of fenthion under UVB and UVC irradiation in both phases were higher than that under UVA irradiation and also exceeded all of the degradation rates of disulfoton. This confirms that fenthion is more readily degraded than disul-foton in the UVB range. Fenthion sulfoxide and disulfoton sulfoxide were identified as oxidative photolysis prod-ucts whose photolysis rates were considerably slower than parent compounds, and the oxidation reaction of both pesticides in the liquid-phase was superior to those on the solid-phase, indicating that dissolved oxygen in water is an important factor affecting the photolysis. These results suggest that fenthion in the environment is more rapidly degraded by UVB irradiation in natural sunlight than disulfoton, and sulfoxides of both pesticides remain stable as a photolysis product in the environment. Key words —– — fenthion, disulfoton, photodegradation, oxidation, ultraviolet irradiatio