Enantioselective bioaccumulation and toxic effects of fipronil in the earthworm Eisenia foetida following soil exposure.

Abstract

Enantiomers of chiral pesticides often have different bioactivity, toxicity and environmental behaviours. Fipronil has been used in racemate for agricultural purposes against soil insects, leading to increased inputs into soil environments and complex biota exposures. To understand the potential risk associated with fipronil enantiomer exposure, subchronic toxicity and bioaccumulation tests with earthworms (Eisenia foetida) in fipronil-spiked soils were evaluated under laboratory conditions. Enantioselective toxicity was measured in E. foetida biomass after 28 days of subchronic exposure, with increased toxicity from racemate and S-fipronil compared with R-fipronil. The bioaccumulation of fipronil in earthworm tissues was also enantioselective, with a preferential accumulation of S-fipronil, and the enantiomer fraction was approximately 0.56-0.60. During soil exposure, fipronil was transformed primarily into fipronil sulfide, sulfone and amide, and E. foetida rapidly accumulated fipronil and sulfone. This work demonstrates the enantioselective subchronic toxicity and bioaccumulation of enantiomers of fipronil in E. foetida. The earthworm tissues exhibited a relative enrichment of fipronil and fipronil sulfone, and these compounds might biomagnify (with a biota-to-soil accumulation factor of ≥1.0 kgOCkglip-1), allowing for the possible trophic transfer and/or bioaccumulation of all these chemicals if earthworms were consumed by predator organisms.