Fate of agrochemicals endosulfan and fipronil in model estuarine environments

Endosulfan and fipronil are broad-spectrum insecticides that are commonly used in coastal regions of the Southeastern U.S. Runoff from sites of application has a strong potential to accumulate in estuaries and to impact economically, commercially, and ecologically important nontarget organisms. Since their degradation products have unique potentials for accumulation and nontarget toxicity, an understanding of endosulfan and fipronil fate (i.e. abiotic and biotic reactivity) within estuaries is critical to identifying the potential risk associated with their use.; We report the correlation between laboratory and mesocosm studies on the fate of aqueous endosulfan and fipronil in simulated estuarine environments. Laboratory studies were utilized to develop kinetic models of their aqueous abiotic transformations; endosulfan was rapidly hydrolyzed while fipronil was rapidly photolyzed. For both processes, the kinetic models were expanded to incorporate effects due to a variety of natural water constituents (e.g. HCO₃−1, NOM, NO₃−1 , metal oxides, sediments). Mesocosm studies functioned as an intermediacy between laboratory modeling and their “true” fates in estuaries typical of the Southeastern U.S. The processes dominant in laboratory studies were also pronounced in the mesocosm studies; this provided an opportunity to assess the relative contribution of abiotic and biotic reactivity toward endosulfan and fipronil fate in estuaries. The identification of potentially toxic and persistent (terminal) products was of particular interest throughout this study.