Effects of benthic organism Tubifex tubifex on hexachlorocyclohexane isomers transfer and distribution into freshwater sediment

• M-type bioaccumulation curves of HCHs were observed in tubifex.
• The AFs of β-HCH in tubifex were higher than that of α-HCH.
• Tubifex significantly reduced β-HCH fluxes from overlying water to sediment.
• Depuration half-lives were 4.43 and 5.39 days for α-HCH and β-HCH respectively.
• Water characteristics were related to the body fluid and bioturbation of tubifex.

In this study, bioaccumulation and elimination of HCHs in tubifex, and the distribution of HCHs in overlying water and sediment, were studied during a 10-d experiment. A sensitive method was developed for the determination of HCHs in samples based on gas chromatograph (GC) equipped with a nickel-63 electron capture detector (μECD). The limit of detection (LOD) was 0.35 µg/kg for α-HCH and 0.82 µg/kg for β-HCH. Tubifex accumulated HCHs rapidly, and the curves were approximately M-type. The highest level was reached on the 7th day, with 0.34 mg/kgwwt for α-HCH and 0.87 mg/kgwwt for β-HCH in worms. The AFs of β-HCH in tubifex were higher than those of α-HCH. Moreover, the existence of tubifex significantly reduced β-HCH fluxes from the overlying water to sediment by uptake or degradation and decreased the concentrations of β-HCH in the sediment, but it had little influence on α-HCH fluxes. Moreover, enantioselectivity of α-HCH enantiomers was not observed in tubifex, whether in the bioaccumulation or elimination experiments. At the end of the elimination experiment, approximately 80% and 70% of α-HCH and β-HCH were eliminated, and the depuration half-lives were 4.43 and 5.39 days, respectively.

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