Exposure assessment of Rana catesbeiana collected from a chlorpyrifos-treated cornfield

Global anuran decline is well documented; however, the reason(s) for this are not apparent. Many governmental and private sectors are seeking answers to this dilemma. One limiting factor in determining the cause of anuran decline is available data. Relatively few studies have gathered data to assess the potential for anuran exposure to agriculturally applied pesticides and subsequent risk. For these reasons, bullfrogs (Rana catesbeiana) were collected from a cornfield and adjacent pond following application of chlorpyrifos, an organophosphate used in the control of corn rootworms. Frogs were collected from two sites; one received an application of chlorpyrifos at the label rate (1.35 kg A.I./ha or 1.2 lbs. A.I./acre), the other received no insecticide application. Brain and plasma cholinesterase activities of bullfrogs from both sites were measured and compared. Our data indicate that while the inherent biological variation of both frog brain and plasma cholinesterase is large, no bullfrogs were significantly exposed to chlorpyrifos while occupying the cornfield or adjacent pond.