The occurrence of organochlorines in marine avian top predators along a latitudinal gradient.

The aim of this study was to determine the role of cold condensation and fractionation on the occurrence of organochlorine contaminants (OCs) in avian marine top predators along a latitudinal gradient. We measured 24 polychlorinated biphenyl (PCB) congeners and six pesticide OCs in blood of great black-backed gulls (Larus marinus) from the Norwegian Coast (58 degrees N-70 degrees N) and glaucous gulls (Larus hyperboreus) from Bjornoya in the Norwegian Arctic (74 degrees N). Glaucous gulls had up to 3 times higher sigmaOC concentrations compared to the great black-backed gulls, and a OC pattern dominated largely by persistent and low volatile compounds such as highly chlorinated PCBs and metabolites such as oxychlordane. This was not consistent with cold condensation and fractionation theory, but probably related to diet and elevated biomagnification. Among great black-backed gulls, however, there were indications of both cold condensation and fractionation. Higher and lower chlorinated PCBs had highest absolute concentrations in the south and in the north, respectively, except for one location at an intermediate latitude, where concentrations of most OCs exceeded all other locations. In terms of proportional contribution to sigmaOC (pattern), relatively volatile OCs such as HCB, oxychlordane and tri- to penta- PCB congeners were more important at northern latitudes, while hexa- to nona-PCBs made up a larger proportion of sigmaOC in the south. The results thus showed that differences in global distribution of compounds with different physicochemical properties could be detected in avian top predators such as large gulls, even if biomagnification and biotransformation influence both the absolute concentrations and the patterns of OCs.