Detection of Imidacloprid in Northern Leopard Frog (Rana pipiens) Brains

In the United States, the use of neonicotinoids to fight agricultural pests is becoming widespread. Unfortunately, due to tile drainage systems and runoff, these neurotoxic insecticides are making their way into wetlands. It has been widely accepted that neonicotinoids are only toxic to insects; however, the truth behind this statement is being questioned after studies have found neonicotinoids in fish brain tissue after exposure, which indicates the potential for this contaminant to harm non-target organisms like amphibians. Due to amphibian’s high susceptibility to contaminants and prior detection of neonicotinoids in brain tissue of other vertebrates, it is likely that neonicotinoids will be present in amphibian brains after exposure. This project examined the potential for neonicotinoids, specifically imidacloprid, to cross the blood brain barrier in amphibians. Forty-eight newly metamorphosed Northern Leopard Frogs (Rana pipiens) were collected from three reference and three tile Waterfowl Protection Area (WPA) wetland sites throughout eastern South Dakota to quantify and determine differences in imidacloprid brain concentrations. Additionally, water samples were collected and analyzed for various agricultural contaminants. Imidacloprid brain concentrations were more than 2 times higher at tile wetlands compared to control sites. Although imidacloprid water concentrations were low to non-existent at most sites, cumulative contaminant loads were also more than 2.5 times higher at tile sites compared to control wetlands. These results demonstrate the ability for imidacloprid to cross the blood-brain barrier in amphibians and suggest that tile drainage systems contribute to higher contaminant loads in non-target organisms and the aquatic ecosystem