Hexachlorocyclohexane (HCH) isomers and chiral signatures of alpha-HCH in the arctic marine food web of the Northwater Polynya

Concentrations of hexachlorocyclohexane (HCH) isomers (alpha, beta, and gam ma) and enantiomer fractions (EFs) of alpha -HCH were determined in the Nor thwater Polynya Arctic marine food web. Relative food web structure was est ablished using trophic level models based on organic delta N-15 values. Con centrations of HCH in the samples collected, including water, sediment, ben thic invertebrates (four species), pelagic zooplankton (six species), Arcti c cod, seabirds (seven species), and ringed seal, were in the range previou sly reported for the Canadian Arctic. The relative proportion of the HCH is omers varied across the food web and appeared to be related to the biotrans formation capacity of each species. For invertebrates and fish the biomagni fication factors (BMFs) of the three isomers were >1 and the proportion of each isomer and the EFs of alpha -HCH were similar to water, suggesting min imal biotransformation. Seabirds appear to readily metabolize gamma- and al pha -HCH based on tow BMFs for these isomers, high proportions of beta -HCH (62-96%), and high EFs (0.65-0.97) for alpha -HCH. The alpha- and beta -HC H isomers appear to be recalcitrant in ringed seals based on BMFs >1 and ne ar racemic EFs for alpha -HCH. The beta isomer appears to be recalcitrant i n all species examined and had an overall food web magnification factor of 3.9. EFs of alpha -HCH and the proportion of beta -HCH in Sigma -HCH in the food web were highly correlated (r(2) = 0.92) suggesting that EFs were a g ood indicator of a species capability to biotransform alpha -HCH.