Enantioselective bioaccumulation of soil-associated fipronil enantiomers in Tubifex tubifex.

Enantioselective behavior of chiral pesticides in the aquatic environment has been a subject of growing interest. In this study, the enantioselective bioaccumulation of fipronil enantiomers in Tubifex tubifex (Oligochaeta, Tubificida) was detected in both spike-water and spike-soil systems, respectively. For the spike-water treatment, a 9-day exposure experiment was employed and the enantiomer fraction in tubifex tissue was maintained approximately at 0.58 during the experiment. In addition, a 14-day bioaccumulation period was chosen for the spike-soil treatment and a more significant deviation of enantiomer fraction from 0.5 in tubifex tissue was detected, with concentrations of the R-form higher than that of the S-form. Therefore, the bioaccumulation of fipronil was enantioselective in tubifex tissue for the two treatments and the magnitude of enantioselectivity may be influenced by different exposure conditions. For the spike-soil treatment, the concentrations of fipronil in verlying water and soil were also determined. With the presence of tubifex worms, higher concentrations of fipronil in overlying water and lower concentrations in soil were detected than that in the absence of tubifex treatment during the whole 14-day exposure period. This means that tubifex has positive functions in fipronil's diffusion from soil to overlying water and in the degradation of the soil-associated fipronil.