Exposure of frogs and tadpoles to chiral herbicide fenoxaprop-ethyl

Abstract

Pesticides have long been considered to a risk factor of amphibian population declines. The bioaccumulation and elimination of fenoxaprop-ethyl (FE) in frogs and tadpoles were studied and the main metabolites fenoxaprop (FA) and 6-chloro-2,3-dihydrobenzoxazol-2-one (CDHB) were monitored. The acute toxicity and genotoxicity of the enantiomers to tadpoles was also studied. After both oral administration and aqueous solution exposure, FE was not found in frogs, while FA was formed and accumulated in liver, kidney, brain, eggs, skin, thigh muscle and blood with preferential accumulation of R-FA. The presence of FA in frog eggs suggested maternal transfer in females and potential impacts to offsprings. The elimination of FA in frog tissues was also enantioselective with a preferential metabolism of R-FA (kidney) or S-FA (liver, eggs, skin, muscle and whole blood). FE and FA were hardly detectable in tadpoles after aqueous solution exposure, while CDHB was accumulated and eliminated as first-order kinetics with half-life of 37.1 h. Mortality of tadpoles and micronucleus rate in peripheral blood erythrocytes of tadpoles were used to evaluate the enantioselective acute toxicity and genotoxicity. Only CDHB induced significant acute toxicity to tadpole with 96-h LC50 value of 30.4 μg/mL, and rac-FA, S-FA and CDHB showed genotoxicity.