Evaluation of Neurobehavioral Abnormalities and Immunotoxicity after Oral Imidacloprid Exposure in Domestic Chickens (Gallus gallus domesticus)

Abstract

Neonicotinoid pesticides may have negative effects on non-target species at environmentally plausible exposure doses. The objective of the present study was to quantify neurobehavioral abnormalities and immunotoxicity due to oral imidacloprid exposure in birds. Domestic white leghorn chickens (Gallus gallus domesticus; n=120) were exposed to imidacloprid by gavage once daily for 7 consecutive days at 0, 0.03, 0.34, 3.42, 10.25, and 15.50 mg/kg. The severity and duration of neurobehavioral abnormalities were recorded, and immune function was assessed with 7 standard functional assays. Immunotoxicity was not detected. Temporary neurobehavioral abnormalities were observed in a dose-dependent manner, including generalized whole-body muscle tremors, ataxia, and depressed mentation ranging from mild depression to a complete lack of response to external stimulation. The effect dose value for the presence of any neurobehavioral abnormalities in 50% of the test group (ED50) was 4.63 mg/kg/day. The ED50 for an adjusted score that included both the severity and duration of neurobehavioral abnormalities was 11.27 mg/kg/day. The no observed adverse effect level (NOAEL) and lowest observed effect level (LOEL) were 3.42 mg/kg/day, and the lowest observed adverse effect level (LOAEL) was 10.25 mg/kg/day. While immunotoxicity was not demonstrated in the present study, it cannot be ruled out. The observed neurobehavioral abnormalities were severe at the higher doses and may impair survival of free-living gallinaceous birds.