| Summary: | Persistent organic pollutants (POPs) pose a health risk for southern resident killer whales (SRKWs). Data on maternal contaminant transfer to calves are needed to inform models that estimate future contaminant loads as well as assess risk to newborn killer whale calves exposed to POPs. We conducted a study on trained female killer whales and their calves to fill these data gaps. POPs and lipid content were quantified in blood serum (POP levels in serum and blubber are highly correlated) collected during gestation and in milk and serum collected post-partum from female killer whales. Serum samples were also collected from calves during the lactation period. POP concentrations in milk collected over 15 months post-partum from the primiparous female decreased by 47-65%, depending on the contaminant class. The highest influx of contaminants to calves tended to occur soon after birth. Greater contaminant transfer rates during early lactation were also reflected in maternal serum POP levels. POP levels in maternal serum decreased significantly during the first 144-158 days post-partum, depending on contaminant class, and then leveled off through the remaining lactation period. This resulted in 67-81% reductions in POP levels in maternal serum over 15 months. By 15 months post-partum, serum POP levels from the primiparous female had dropped to levels measured in the multiparous female during pregnancy. Dissimilar to the multiparous female, body mass and blubber thickness in the primiparous female also declined significantly during the first 3-5 months post-partum, demonstrating linkages between lipid and POP transfer from blubber stores to milk in early lactation. By the end of lactation, lipid-corrected POP concentrations in serum from the first-born calf were 5-8 times greater than the corresponding POP levels from her primiparous mother. These results demonstrate that very young neonatal SRKW calves, particularly first-born calves, are at high risk from contaminant exposure.
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