Enantiomer-specific accumulation, depuration, metabolization and isomerization of hexabromocyclododecane (HBCD) diastereomers in mirror carp from water

•It is the first time to report accumulation of HBCDs by fish via water exposure.•The three HBCD diastereomers showed a same BCFK sequence in different tissues of viscera>gill>skin>muscle.•The β-HBCD and γ-HBCD were substantially transformed to α-HBCD in carp.•An enrichment of (+)α and γ-HBCD was observed.•New metabolites like TBCDe, TriBCDi and TriBCDie were for the first time reported. Until now, the bioaccumulation of hexabromocyclododecanes (HBCDs) in aquatic organisms has been studied only via dietary exposure. To better understand the environmental fate of HBCDs, we conducted a bioaccumulation test by exposing mirror carp to three HBCD diastereomers in water during 30d of accumulation and 30d of depuration according to Organization for Economic Co-operation and Development (OECD) Test Guidelines 305 (Bioaccumulation in Fish: Aqueous and Dietary Exposure). We found that the BCFKL values (bioconcentration factor calculated from kinetic data and adjusted to lipid content) of α-HBCD in different tissues of the carp were in the range of (3.07–4.52)×104, much higher than those of β-HBCDs (1.03–1.90×103) and γ-HBCD (0.95–1.73×103), as was true of t1/2. The order of BCFK for α-, β- and γ-HBCD in different tissues was viscera>gill>skin>muscle. β-HBCD and γ-HBCD were transformed to α-HBCD, with 50.0–92.9% and 96.2–98.6% bioisomerization efficiencies by the end of the experiment, respectively. No isomerization product from α-HBCD was found. Selective enrichment of the (+) α- and γ-HBCD was found, whereas β-HBCD did not show significant enantioselectivity. New metabolites such as tetrabromocyclododecene (TBCDe), tribromocyclododecadiene (TriBCDi) and tribromocyclododecatriene (TriBCDie) were found in mirror carp for the first time under multiple reaction monitoring (MRM) mode.