Maternal transfer and biotransformation of persistent organic pollutants (POPs) in hooded seal (Cystophora cristata)

The Arctic has in the later years become a final destination for persistent organic pollutants (POPs) which are, due to long-range atmospheric transport, river outlets and ocean currents, brought into the pristine arctic region from southern latitudes. POPs can accumulate in biota and reach high concentrations in the upper trophic levels in the arctic food webs due to biomagnification. The hooded seal (Cystophora cristata) is a top-predator in the arctic marine food web and is susceptible to high POP exposures through diet, but also by placental transfer in utero and lactational transfer after parturition from mother to offspring. The hooded seal milk is unique by having the highest lipid percentage reported in any mammal. The objective of this study was to examine levels and patterns of POPs and their metabolites in mother-pup pairs with respect to maternal transfer and biotransformation. Milk sampled from lactating hooded seal mothers in the West Ice breeding area in the Greenland Sea were analysed for a wide range of POPs, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides. Also, the current study have for the first time analysed OH- metabolites of PCBs and PBDEs in milk from hooded seals. Together with previously analysed levels of these contaminants in plasma of the same mother-pup pairs, these results put together were used to examine in detail the maternal transfer (placental/lactational) and uptake and biotransformation in the pups. The most dominating compounds found in hooded seal milk were PCB-153, PBDE-47 and p,p -DDE, respectively, similar to findings in previous studies of seals. The results confirm a maternal transfer of the lipophilic PCBs, PBDEs and pesticides from hooded seal mothers to their pups via milk. The higher halogenated POPs and pesticides with higher lipid affinity (high log KOW) appear to have lower transfer efficiency in milk and thus placental transfer may be of higher importance in explaining maternal transfer of these compounds. The lower halogenated POPs are preferably transferred to the pups during their nursing period via milk. OH-metabolites of PCBs and PBDEs were not detected in the present hooded seal milk samples. Thus, milk transfer cannot explain the detected OH-PCBs in maternal and pup plasma for hooded seals. The study did, although detected an increase in OH-PCB ratio relative to PCB during their nursing period, suggesting a weak biotransformation in the pups. Thus, a placental transfer is suggested by the current study to be the major source of OH-metabolites found in the pups, but endogenous biotransformation in the pups may also contribute to these levels.