Diastereoisomer- and Enantiomer-Specific Accumulation, Depuration, and Bioisomerization of Hexabromocyclododecanes in Zebrafish (Danio rerio)

In this study, zebrafish (Danio rerio) were exposed to two dietary concentrations of individual HBCD diastereoisomers (alpha-, beta- and gamma-HBCD) for 42 days, followed by clean food for 21 days, to examine bioaccumulation, depuration, and enantiomer fractions (EFs) of HBCD diastereoisomers and to test the bioisomerization of 0, HBCDs in fish. The depuration of alpha-, beta-, and gamma-HBCD in zebrafish followed the first-order process. Bioaccumulation parameters of the three diastereoisomers differed between low and high dose, suggesting that the bioaccumulation of them is concentration dependent. Calculated assimilation efficiencies (AEs), biomagnification factors (BMFs), and half-lives (t(1/2)) of alpha-HBCD were the highest among the three diastereoisomers. Furthermore, the study showed that zebrafish could biotransform gamma-HBCD to alpha-HBCD. The highest AE, BMF, and t(1/2) of alpha-HBCD and bioisomerization of gamma-HBCD to alpha-HBCD could explain why alpha-HBCD appears to be dominant in biota samples. The EFs for alpha- and gamma-HBCD in zebrafish estimated at different times of bioaccumulation and depuration were all significantly greater than those in corresponding food (P < 0.05), indicating selective enrichment of (+) alpha-enantiomer and (+) gamma-enantiomer relative to (-) alpha-enantiomer and (-) gamma-enantiomer, respectively.