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 (∑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 (∑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 bear 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.