An investigation of environmental concentrations of atrazine, chlorothalonil, and fipronil in a Mississippi River-influenced marsh in southern Louisiana

Abstract The pesticides atrazine, chlorothalonil, and fipronil are common surface water contaminants due to their high rates of application and their chemical properties. This study investigates the introduction of contaminants into coastal wetlands via the Bayou Lamoque Mississippi River control structure in Plaquemines Parish, Louisiana; results serve as a model for future studies regarding contaminant introduction from freshwater diversions aimed at Gulf Coast restoration. A protocol for environmental sampling using Continuous Low-level Aquatic Monitoring (C.L.A.M.) C-18 disks is described, along with effective solid phase extraction (SPE) and gas chromatography mass spectrometry (GC/MS) methodology for the determination of atrazine, chlorothalonil, and fipronil in surface water. Average concentrations of atrazine and chlorothalonil inside the Bayou Lamoque freshwater diversion structure for the months of June – October 2016, were 33.3 ng l −1 and 3.5 ng l −1 , respectively. Fipronil was not detected in concentrations exceeding its method detection limit of 1.26 ng l −1 . The detected concentrations are innocuous to non-target organisms based on current ecotoxicity data, and are likely a result of runoff from nearby upstream agricultural and residential land.