Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/4/2004
Publication Date: 6/5/2004
Citation: Walse, S.S., Morgan, S.L., Kong, L., Ferry, J.L. 2004. Role of dissolved organic matter, nitrate, and bicarbonate in the photolysis of aqueous fipronil. Environmental Science and Technology. 38(14):3908-3915. Interpretive Summary: Pesticides that enter the aquatic environment via runoff, or spray drift can have negative effects on non-target organisms. Understanding pesticide degradation in aqueous environments is important because it allows us to determine if nature is suppressing or accentuating possible negative effects. Sunlight exposure represents one route that nature utilizes to degrade pesticides in aqueous environments. With colleagues from the Department of Chemistry at the University of South Carolina, a scientist at the Center for Medical Agricultural and Veterinary Entomology, USDA ARS, Gainesville, Florida explored the effects of sunlight on the degradation of aqueous fipronil, a popular compound for agricultural, residential, and commercial pest control. They found that sunlight-induced degradation of aqueous fipronil was inversely related to the 'turbidity' of the water. In addition, they discovered that the addition of sodium chloride resulted in a more rapid rate (~20%) of fipronil degradation indicating that fipronil may undergo faster sunlight-induced degradation in marine environments.
Technical Abstract: A multivariate kinetic model of the photodegradation of aqueous fipronil was developed as a function of dissolved organic matter (DOM), bicarbonate, and nitrate at concentrations that bracket those commonly observed in natural waters (ca. 0-10 mg/L). Several pathways were available for fipronil photodegradation in this system, including direct photolysis and indirect photooxidation by species produced during the illumination of natural waters. Product studies indicated that fipronil was quantitatively converted to fipronil desulfinyl, a product that is associated with direct photolysis alone. DOM was the only variable that affected fipronil degradation; it decreased the rate of fipronil photodegradation primarily through competitive light absorption (i.e., attenuation) and the quenching of fipronil*. The addition of sodium chloride (30') resulted in a more rapid rate (~20%) of fipronil loss in comparison to equivalent experiments performed without sodium chloride, implying that fipronil may be more photolabile in marine environments.