Spatial Trends and Historical Deposition of Polychlorinated Biphenyls in Canadian Midlatitude and Arctic Lake Sediments

A study of PCB concentrations and fluxes in lake sediments was conducted to test the “global fractionation” hypothesis that deposition of semivolatile organics will decline while more volatile congeners will be enriched in polar regions. Sediment cores were collected from 11 remote lakes in Canada ranging from 49° N to 82° N and were dated using excess 210 Pb and 137 Cs. Sediment extracts were analyzed for up to 90 PCB congeners by capillary GC-ECD with confirmation by GC/high-resolution MS. Total PCB (∑PCB) concentrations in surface slices ranged from 2.4 to 39 ng g - 1 (dry wt) and showed no latitudinal trend. Fluxes (ng m - 2 yr - 1 ) and inventories of ∑PCB as well as total tetra- to octachlorobiphenyls declined with increasing north latitude while those for di/trichlorobiphenyls showed no latitudinal trend. The proportion of di/trichloro congeners of ∑PCB also increased significantly with latitude, while total octachlorobiphenyls declined. Maximum ∑PCB concentrations were observed in subsurface slices dating to the 1960−1970s in most lakes except those in the high Arctic, where maxima were generally in surface slices. The onset of elevated ∑PCB deposition was delayed in the high Arctic (1950−1960s) relative to the midlatitude and sub-Arctic lakes (1930−1940s). The high proportions of lower chlorinated congeners and the delayed appearance of PCBs are consistent with predictions of the global fractionation model.