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Enantioselective Toxicity and Biotransformation of Fipronil in the Fathead Minnow (Pimephales promelas)
Citation:
Baird, S., A. W. GARRISON, J. K. AVANTS, AND M. C. Black. Enantioselective Toxicity and Biotransformation of Fipronil in the Fathead Minnow (Pimephales promelas). Presented at SETAC North America 30th Annual Meeting, New Orleans, LA, November 19 - 23, 2009.
Impact/Purpose:
The main objective of this research is to determine the environmental occurrences, fate, and exposure of the enantiomers of selected chiral pesticides and other chiral organic pollutants.
Description:
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. As regulations on older pesticides increase, production and application of fipronil is expected to increase, leading to increased inputs into aquatic environments. Although a number of toxicity studies have demonstrated acute and chronic enantioselective toxicity of fiprinil in aquatic invertebrates, data on enantioselective toxicity in fish is limited. We conducted three 7-day aquatic toxicity experiments to determine the acute and subchronic toxicity of the fipronil racemate and each enantiomer to larval fathead minnows (Pimephales promelas). Acute (96-hr) LC50s for the fipronil racemate and each enantiomer were not significantly different. However, enantioselective toxicity was observed in fathead minnow exposures with longer exposure durations (7-d), with increased toxicity of the racemate (7-day LC50 = 191 µg/L) and (+) enantiomer (7-day LC50 = 207 µg/L) observed compared to the (-) enantiomer (7-day LC50 = 312 µg/L). Reduced fish growth was also observed in fish exposed to the (+) enantiomer and racemate, compared to the (-) enantiomer. Linear regression of concentration vs. fish weights at 7 days revealed significantly increased slopes for the (+) enantiomer and racemate versus the (-) enantiomer (p<0.05). Curiously, for both chronic endpoints toxicity of the racemate and (+) enantiomer was not significantly different, even though the racemate contains 50% of the (+) enantiomer and 50% of the less toxic (-) enantiomer. Metabolic processes could potentially change the enantiomeric fraction present in the organism, so that fathead minnows selectively transform and eliminate the (-) enantiomer, increasing the proportion of the more toxic (+) enantiomer in the racemic exposure. An on-going bioaccumulation experiment where fathead minnows are exposed to fipronil under realistic sediment:water exposure conditions should allow us to test this hypothesis.
URLs/Downloads:
GARRISON 09 081A_SLIDE_SETAC.PDF (PDF, NA pp, 1357 KB, about PDF)GARRISON 09 081 SETAC.PDF (PDF, NA pp, 11 KB, about PDF)