Dietary accumulation of hexabromocyclododecane diastereoisomers in juvenile rainbow trout (Oncorhynchus mykiss): bioaccumulation/depuration parameters and evidence of bioisomerization
Law, Kerri L
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The major objectives of this research were to examine the bioaccumulation parameters [depuration rates (kd), half life (t1/2) and biomagnification factor (BMF)] of individual isomers of hexabromocyclododecane (HBCD, C12H18Br6) in fish and to test the hypothesis of in vivo bioisomerization. This was done by exposing three groups of juvenile rainbow trout (Oncorhynchus Mykiss) to food fortified with known concentrations of an individual diastereoisomer (α, β, γ) for 56 days (uptake phase) followed by 112 days (depuration phase) of unfortified food. A fourth group of fish were exposed to unfortified food for the duration of the experiment. Fish (n=4) from all four aquaria were sacrificed on days 0, 7, 14, 56, 63, 70, 112 and 168 and muscle tissue was extracted and analyzed for diastereoisomer concentrations by high performance liquid chromatography tandem mass spectrometry (LC/MS/MS). Bioaccumulation of the γ diastereoisomer was linear during the uptake phase while the α and β diastereoisomers were found to increase exponentially with respective doubling times of 14.1 and 20.5 days. Both the β and γ diastereoisomers followed first order depuration kinetics with calculated t1/2’s of 94 ± 25 and 84 ± 51 (± 1 × standard error) days, respectively. The BMF for the α diastereoisomer (BMF = 4.1) was one and a half times greater than the β-diastereoisomer (BMF = 2.6) and about one fifth larger than the γ-diastereoisomer (BMF = 3.6). The large BMF for the α diastereoisomer is consistent with this diastereoisomer dominating higher trophic level organisms in wildlife. Although the BMF of the β diastereoisomer suggests that it will biomagnify, because it is present in small quantities in commercial mixtures it is rarely detected in environmental samples. Results from these studies also provide evidence of bioisomerization of the β and γ diastereoisomers. Most importantly, the α diastereoisomer which was recalcitrant to bioisomerization by juvenile rainbow trout in this study and known to be the dominant diastereosiomer in fish, was bioformed from both the β and γ diastereoisomers. To our knowledge, this is the first report of bioisomerization of a halogenated organic pollutant in biota.