Enantioselective degradation and bioaccumulation of sediment-associated fipronil in Lumbriculus variegatus: Toxicokinetic analysis

Abstract

Enantioselective degradation and biotransformation are critical processes affecting the bioaccumulation and toxicity of chiral pesticides in the environment. In the present study, enantioselective uptake, biotransformation and elimination of a current use pesticide, fipronil in a benthic invertebrate, Lumbriculus variegatus were assessed using a sediment bioaccumulation test. Toxicokinetic models were constructed to quantitatively describe kinetic processes of fipronil enantiomers. The degradation of fipronil in sediment significantly affected chemical uptake, thus degradation kinetic model was incorporated into toxicokinetic modeling. It was shown that S-(+)-fipronil degraded faster than R-(−)-fipronil in sediment, with dissipation rate constants being 0.090 ± 0.008 and 0.023 ± 0.006 1/d, respectively. As a result, R-(−)-enantiomer preferentially accumulated in sediment over time. Similarly, higher concentrations of R-(−)-fipronil were detected in L. variegatus compared with S-(+)-fipronil. Toxicokinetic modeling showed R-(−)-fipronil had larger uptake and elimination rate coefficients and apparent maximum reaction rate, but a smaller apparent half-saturation constant than S-(+)-fipronil. Preferential uptake of R-(−)-fipronil from sediment to L. variegatus was the main reason for greater R-(−)-fipronil concentrations in organism. Biotransformation of fipronil in L. variegatus was also enantioselective, yet it played fewer roles on enantioselective bioaccumulation than uptake. Overall, our findings highlight the importance of selective degradation, uptake and biotransformation of sediment-associated fipronil on its enantioselective bioaccumulation in benthic invertebrates, which helps to improve the accuracy for assessing aquatic toxicity of the chiral pesticide. CapsuleEnantioselective bioaccumulation of sediment-associated fipronil in Lumbriculus variegatus was quantitatively explained by selective degradation, uptake, biotransformation and elimination parameters using a combination of degradation and toxicokinetic modeling.