Enantioselective toxicity, bioaccumulation, and biotransformation of fipronil in fathead minnows (Pimephales promelas)

Fipronil is a relatively new chiral, phenylpyrazole insecticide used to control both agricultural and household invertebrate pests. Fipronil is applied as a racemate, or equal mixture, of its two enantiomers. Although a number of toxicity studies have demonstrated enantioselective toxicity in aquatic invertebrates, data on enantioselective toxicity in fish is limited. We observed increased toxicity of the (+) enantiomer in larval fathead minnows exposed to the fipronil racemate and each enantiomer seven days. Juvenile fathead minnows were exposed to fipronil-contaminated sediment. We found that fish rapidly bioaccumulated fipronil and transformed it to fipronil sulfone. Fish preferentially transformed the (-) enantiomer, resulting in an increased proportion of the (+) enantiomer in fish tissues. This thesis illustrates the complex behavior of fipronil in fathead minnows and the need for additional research on the fate of fipronil in the aquatic environment.