Biotransformation versus bioaccumulation:: Sources of methyl sulfone PCB and 4,4′-DDE metabolites in the polar bear food chain

In the polar bear food chain from the Canadian Arctic, methyl sulfone (MeSO(2-)) PCBs and 4,4'-DDE were below detection in arctic cod (<0.01 ng/g, lipid wt). Ringed seal blubber contained 3-MeSO(2)-4,4'-DDE (0.4 ng/g) and 14 3- and 4-MeSO(2)-PCB isomer pairs (Sigma MeSO(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 to seal were 0.001-0.086 for MeSO(2)-PCBs and 0.004 for 3-MeSO(2)-4,4'-DDE. Twelve MeSO(2)-PCB isomer pairs (Sigma MeSO(2)-PCBs, 432 +/- 57 ng/g) and 3-MeSO(2)-4,4'-DDE (2.0 +/- 0.7 ng/g) were identified in polar bear fat; BFE' values were 0.03-0.62 and 0.0001 for MeSO(2)-PCBs and 3-MeSO(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(2)-PCB congeners in the hear are likely bioaccumulated from seal relative to the completely bioaccumulated 3-/4-MeSO(2)-CB132. Strong evidence exists for the partial formation of seven MeSO(2)-PCBs in the bear. We conclude that MeSO(2)-PCBs have high biomagnification potential in food chains.