Influence of the temperature gradient in blubber on the bioaccumulation of persistent lipophilic organic chemicals in seals.

Seals constitute an important link in food webs of the Arctic environment and are an important vector of persistent lipophilic organic pollutants to top predators (e.g., polar bears) and humans. Two fugacity-based, non-steady state, mechanistic lifetime models were assembled to explore the influence of the temperature gradient in the insulating blubber on the distribution and bioaccumulation of persistent lipophilic organic pollutants in seals. The behavior of a two-compartment model that distinguishes between the gastrointestinal tract and the seal itself was compared with a three-compartment model, in which a separate blubber compartment was implemented with a temperature gradient through the insulation layer. In both models, equilibrium partitioning between the animal's tissues, blood, and milk was assumed. The models were parameterized for ringed seals (Phoca hispida) and evaluated using field data for bioaccumulation of polychlorinated biphenyls in this species. The two-compartment model resulted in predicted concentrations below reported field data. This was in particular the case for females, for which the elimination of the contaminants via milk was overpredicted by up to one order of magnitude. The three-compartment model with its consideration of the temperature gradient in blubber yielded predictions that were much more consistent with the field data. It also predicted a fractionation of polychlorinated biphenyl congeners between different blubber layers, as well as between blubber and blood or milk, which was in good qualitative agreement with observations reported in the literature. This work indicates that the temperature gradient in the blubber has an impact on the bioaccumulation of persistent lipophilic organic pollutants in seals and in marine mammals in general.