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The variation in levels of polychlorinated biphenyls (sigma PCBs), chlorobenzenes and chlorinated pesticides was studied in burbot (Lota lota) from eight remote locations along a northwesterly transect from northwestern Ontario to the Mackenzie River delta in Canada. Significant declines in concentrations of PCB congeners, DDT isomers (sigma DDT), lindane, dieldrin, and mirex in burbot liver were found with increasing north latitude. Mean sigma PCB concentrations ranged from 1,290 ng/g (lipid wt) at Lake 625, a remote lake in northwestern Ontario, to 301 ng/g in samples from the Mackenzie River at Arctic Red River, N.W.T. No significant differences in mean concentrations of toxaphene, alpha-HCH, tri- and tetrachlorobiphenyls were observed between southern and northern sampling sites. Toxaphene was the predominant organochlorine residue in northern fish samples averaging 1,400 ng/g (lipid wt) at the three most northerly sites and 1,723 ng/g at Lake 625. Airborne contamination was the only likely source of organochlorines for most of the locations surveyed. The results were consistent with the hypothesis that inputs of semi-volatile organochlorines to northern aquatic ecosystems decrease with increasing north latitude and distance from North American sources.

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