In the polar bear food chain from the Canadian Arctic, methyl sulfone (MeSO{sub}2-) PCBs and 4,4'-DDE were below detection in arctic cod (<0.01 ng/g, lipid wt). Ringed seal blubber contained 3-MeSO{sub}2-4,4'-DDE (0.4 ng/g) and 14 3- and4-MeSO{sub}2-PCB isomer pairs (∑MeSO{sub}2-PCB, ca. 13 ng/g) formed by the biotransformation of PCBs not chlorine substituted at the meta-para positions on one ring (m,p-PCBs). Bioaccumulation/formation efficiencies relative to CB153 (BFE-) from cod toseal were 0.001-0.086 for MeSO{sub}2-PCBs and 0.004 for 3-MeSO{sub}2-4,4'-DDE. Twelve MeSO{sub}2-PCB isomer pairs (∑MeSO{sub}2-PCBs, 432 ± 57 ng/g) and 3-MeSO{sub}2-4,4'-DDE (2.0±0.7 ng/g) were identified in polar bear fat; BFE' values were 0.03-0.62and 0.0001 for MeSO{sub}2-PCBs and 3-MeSO{sub}2-4,4'-DDE, respectively. Methyl sulfone formation is important but not the major route for m,p-PCB and 4,4'-DDE biotransformation in polar bear and ringed seal. Fifteen MeSO{sub}2-PCB congeners in the bearare likely bioaccumulated from seal relative to the completely bioaccumulated 3-/4-MeSO{sub}2-CB132. Strong evidence exists for the partial formation of seven MeSO{sub}2PCBs in the bear. We conclude that MeSO{sub}2-PCBs have high biomagnificationpotential in food chains.
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