The organophosphorous insecticide chlorpyrifos is the most applied insecticide in the United States. It is applied in both agricultural and non-agricultural settings. Like other pesticides, chlorpyrifos often contaminates natural habitats through spray drift, volatilization, or run off. Chlorpyrifos is found in surface waters throughout the US, and is most commonly found at concentrations less than 10 ppb (though higher values have been reported). While chlorpyrifos has been shown to cause neurological and behavioral problems in vertebrates that are exposed to high doses, the effects of low dose exposures are still not well understood. This study aimed to better understand the effects of these low level exposures. We exposed a vertebrate model, the Northern Leopard Frog (Lithobates pipiens), to 0, 1, or 10 ppb chlorpyrifos during development in a controlled laboratory study. We then collected water borne hormone samples to measure the stress hormone corticosterone, conducted behavioral assays, and analyzed standard body and brain morphometrics.
Results/Conclusions
We found that exposure to 1 ppb chlorpyrifos during development resulted in increased brain masses and changes in tadpole brain shape. Tadpoles had wider and longer telencephala and longer olfactory bulbs. Tadpoles exposed to 10 ppb chlorpyrifos had increased levels of the stress hormone corticosterone. This study provides evidence that it’s not just high dose exposures that can have neurological consequences in animals, but rather that exposure to low, ecologically relevant doses of organophosphorous pesticides also causes neurological effects in an amphibian model. This study also demonstrates that ecologically relevant levels of chlorpyrifos can increase stress levels in animals. Our results indicate that amphibian physiology is being impacted by chlorpyrifos at the concentrations that are found contaminating natural habitats.