It is since long known that polychlorinated biphenyls (PCBs) accumulate in food webs. In the literature, this phenomenon has already been demonstrated for various Arctic seabirds by relating a species’ tissue concentration to its trophic level. Although some good results were obtained by using the trophic level as the only predictor for the internal PCB concentration, the method fails to adequately explain some interspecific differences between species with a similar trophic level. It has often been suggested that adding the effects of migration and scavenging to current models might increase the prediction capacity. In this thesis the effects of these two predictors, together with those of age and sex, important for intraspecific variation, on the internal PCB concentration of the Common Eider (Somateria mollissima), the Brünnich’s Guillemot (Uria lomvia), the Black-legged Kittiwake (Rissa tridactyla) and the Glacous Gull (Larus hyperboreus) were evaluated using two different approaches.In a first approach, a statistical analysis was performed on the dataset of the International Council for the Exploration of the Sea (ICES) containing thousands of measurements of internal PCB concentrations in seabirds from the Barents Sea area. It was found that migration, scavenging, trophic level and sex had significantly effects (p<0.0001) on the log-transformed lipid normalized tissue concentrations of PCB congeners. The model explained 65.7% of the deviance. Trophic level had a positive linear effect (coefficient=0.28) on the log transformed internal concentration confirming the findings from the literature. Both migration and scavenging had a positive effect on the log transformed internal concentration, but the effect of the migration (coefficient=0.65) was twice as high compared to scavenging (coefficient=0.31). At the intra species level, differences in the log internal concentration do occur being higher for adult males (coefficient=0.18) compared to adult females. Immature birds have the lowest internal concentrations (coefficient=-0.16).In a second approach, a mechanistic bioaccumulation model was constructed that included the same interspecific predictors as in the statistical models. It was found that trophic level is the most important predictor allowing for estimation of the order of magnitude for the internal concentrations. This confirms the findings from the literature. To acquire adequate model predictions for the Black-legged Kittiwake, a long-distance migrant, migration had to be taken into account to explain the elevated internal concentrations observed in spring. The importance of scavenging was supported by the model simulations for the Glaucous Gull where a diet containing scavenging resulted in a good prediction of the order of magnitude for the internal PCB concentration.Combining the results of both analyses showed that the current research based only on the breeding sites and trophic level is most likely not adequate to estimate the dynamic behavior of internal PCB concentrations. There is a need for a life history based approach taking migration into account for long range migrants. Scavenging is an important addition to the trophic level in explaining elevated internal PCB concentrations. |
