Trophic dynamics of hexabromocyclododecane diastereomers and enantiomers in fish in a laboratory feeding study.

The laboratory trophic transfer of hexabromocyclododecanes (HBCDs) was studied using predatory (oscar) fish and a prey species (tiger barb) exposed to a technical HBCD. Gut absorption, dynamic changes of diastereomer pattern and enantiomer fractions, and potential metabolism of HBCDs were examined. Compared with ß- or γ-HBCD, α-HBCD showed lower absorption efficiency in the gut of oscar fish. A predominance of γ-HBCD was observed in the tiger barb after 5 d HBCD-exposed and oscar feeding on the tiger barb for 16 d. After 20 d of depuration, 41.1% γ-HBCD and 42.7% ß-HBCD disappeared, and α-HBCD exceeded the initial amount. The transformation from γ-HBCD predominance in the food to α-HBCD predominance in the oscar was attributed mainly to the isomerization of γ-HBCD (at least 3% and up to 22.7%) to α-HBCD. Selective enrichment of the (+) α- and (-) ß-enantiomers and no enantioselective enrichment of γ-HBCD were observed in the tiger barbs. No enantioselective uptake of the 3 diasteromers was found in the oscar gut. The enantiomer fractions of α- and γ-diastereomers were significantly higher, but that of ß-diastereomer were significantly lower in the oscars than in the tiger barbs, indicating enantioselective metabolism of the 3 diastereomers. Two HBCD monohydroxylated metabolites were detected in the 2 fish species, but their composition patterns differed, indicating a species-specific metabolism of HBCD in the studied fish species.