SPATIAL TRENDS AND HISTORICAL DEPOSITION OF POLYCHLORINATED-BIPHENYLSIN CANADIAN MIDLATITUDE AND ARCTIC LAKE-SEDIMENTS

A study of PCB concentrations and fluxes in lake sediments was conduct ed 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 re mote lakes in Canada ranging from 49 degrees N to 82 degrees N and wer e dated using excess (210)pb and Cs-137. Sediment extracts were analyz ed for up to 90 PCB congeners by capillary GC-ECD with confirmation by GC/high-resolution MS. Total PCB (Sigma PCB) concentrations in surfac e slices ranged from 2.4 to 39 ng g(-1) (dry wt) and showed no latitud inal trend. Fluxes (ng m(-2) yr(-1)) and inventories of Sigma PCB as w ell as total tetra- to octachlorobiphenyls declined with increasing no rth latitude while those for di/trichlorobiphenyls showed no latitudin al trend. The proportion of di/trichloro congeners of Sigma PCB also i ncreased significantly with latitude, while total octachlorobiphenyls declined. Maximum Sigma PCB concentrations were observed in subsurface slices dating to the 1960-1970s in most lakes except those in the hig h Arctic, where maxima were generally in surface slices. The onset of elevated Sigma PCB deposition was delayed in the high Arctic (1950-196 0s) relative to the midlatitude and sub-Arctic lakes (1930-1940s). The high proportions of lower chlorinated congeners and the delayed appea rance of PCBs are consistent with predictions of the global fractionat ion model.