Chemical residence time and hydrological conditions influence treatment of fipronil in vegetated aquatic mesocosms.

Fipronil, a phenyl-pyrazole insecticide, is often used in rice (Oryza sativa L.) production agriculture, with elevated runoff concentrations and loads having potential toxicological eff ects on downstream aquatic environments. Th is study evaluated two species of aquatic plants—broadleaf cattail (Typha latifolia L.) and powdery alligator-fl ag (Th alia dealbata Fraser ex Roscoe)— placed in series against a nonvegetated mesocosm in reducing concentrations and loads of fi pronil, and associated metabolites. Vegetation type and hydrological condition (inundated vs. dry) were treatment eff ects used for comparison. Th e vegetated mesocosms signifi cantly reduced higher loads and concentrations of fi pronil, fi pronil sulfone, and sulfi de in both inundated and dry hydrological conditions over nonvegetated mesocosms. Under inundation conditions, vegetated mesocosms reduced >50% of infl uent fi pronil concentrations and between 60 and 70% of fi pronil loads, which was signifi cantly higher than the dry conditions (10–32% concentration and load). Th ese results show that agricultural management strategies using ephemeral aquatic zones, such as drainage ditches, can be optimized to couple chemical applications with vegetation presence and hydrology to facilitate the reduction in chemical waste loads entering downstream aquatic ecosystems. Such reduction is critical for use with fi pronil, where negative impacts have been demonstrated with several nontarget species. Chemical Residence Time and Hydrological Conditions Infl uence Treatment of Fipronil in Vegetated Aquatic Mesocosms