Toxicity of fipronil and its enantiomers to marine and freshwater non-targets

Abstract

Fipronil is a phenylpyrazole insecticide used in agricultural and domestic settings for controlling various insect pests in crops, lawns, and residential structures. Fipronil is chiral; however, it is released into the environment as a racemic mixture of two enantiomers. In this study, the acute toxicity of the (S,+) and (R,-) enantiomers and the racemic mixture of fipronil were assessed using Simulium vittatum IS-7 (black fly), Xenopus laevis (African clawed frog), Procambarus clarkii (crayfish), Palaemonetes pugio (grass shrimp), Mercenaria mercenaria (hardshell clam), and Dunaliella tertiolecta (phytoplankton). Results showed that S. vittatum IS-7 was the most sensitive freshwater species to the racemic mixture of fipronil (LC50 = 0.65 microg/L) while P. pugio was the most sensitive marine species (LC50 = 0.32 microg/L). Procambarus clarkii were significantly more sensitive to the (S,+) enantiomer while larval P. pugio were significantly more sensitive to the (R,-) enantiomer. Enantioselective toxicity was not observed in the other organisms tested. Increased mortality and minimal recovery was observed in all species tested for recovery from fipronil exposure. These results indicate that the most toxic isomer of fipronil is organism-specific and that enantioselective toxicity may be more common in crustaceans than in other aquatic organisms.

Integration of metabolomics and in vitro metabolism assays for investigating the stereoselective transformation of triadimefon in rainbow trout

“…Toxicity measurements for the separate enantiomers of chiral pharmaceuticals is the prescribed practice, and such measurements have also been conducted for a few enantiomers of chiral pesticides. [26][27][28] …”

Toxicities of fipronil enantiomers to the honeybee Apis mellifera L. and enantiomeric compositions of fipronil in honey plant flowers

“…There have been four studies, including the present study, that examined toxicities of fipronil enantiomers to 11 species [21][22][23]. In these 11 species, only two species (Procambarus clarkii and Ceriodaphnia dubia) demonstrated enantioselectivity in toxicities [22,23].…”

“…In contrast, Konwick et al [22] demonstrated the S(þ)-enantiomer was significantly more toxic to Ceriodaphnia dubia than either the R(À)-enantiomer or racemate. Overmyer et al [23] examined the toxicities of fipronil enantiomers to six marine and freshwater species and found that only crayfish (Procambarus clarkii) demonstrated a statistically significant difference in toxicity between the two enantiomers. These studies indicate that enantiomer-specific toxicity varies with species.…”

Toxicity and bioaccumulation of ethofumesate enantiomers in earthworm Eisenia fetida

“…In theory, enantiomers have identical physical and chemical properties and abiotic degradation rates (Garrison et al, 1996), whereas their individual toxicity, biological activity, and microbial degradation rates have been shown to differ (Overmyer et al, 2007;Diao et al, 2010;Liu et al, 2012;Sun et al, 2012). Several studies have reported that ethofumesate enantiomers showed an enantioselectivity in biochemical processes.…”