Impacts of loach bioturbation on the selective bioaccumulation of HBCDD diastereoisomers and enantiomers by mirror carp in a microcosm.

To assess the impacts of bioturbation at the water-sediment interface on the bioaccumulation of hexabromocyclododecane diastereoisomers (HBCDDs) by pelagic organisms and the bioisomerization and enantioselectivity therein, we built microcosms containing water, mirror carp (Cyprinus carpio), and sediment. The microcosms were sorted into two groups, with or without loach (Misgurnus anguillicaudatus) living at the water-sediment interface. A 50-d accumulation test was conducted by spiking the microcosms with the three main HBCDD diastereoisomers (α-, β-, and γ-HBCDDs) separately. The HBCDDs were mainly associated with the sediment. The dissolved organic matter and suspended particulate matter content increased due to loach bioturbation, which promoted the release of sediment-associated HBCDDs and led to enhanced HBCDD bioaccumulation in the carp. Isomerization from β- and γ-HBCDD to α-HBCDD occurred in the carp, and the amounts of isomerization did not increase proportionally with increasing bioaccumulation. Moreover, the enantioselectivity of the HBCDD diastereoisomers showed species-specific differences between mirror carp and loach, and no significant change in the enantioselectivity in the carp was observed in the presence of loach.