An unexpected parallelism between Vitamin A and PCBs in seal milk

Bioaccumulating pollutants such as polychlorinated biphenyls (PCBs) induce a range of adverse effects in mammals. Vitamin A metabolism is prone to such pollutant disruption which may be particularly harmful for young animals. During lactation, maternal PCBs are transferred to the offspring through the milk. Seal milk is very fatty and consequently contains large amounts of these persistent lipophilic contaminants. In the present study, we investigated the relationships between PCBs and Vitamins A and E during lactation, in free-ranging grey seals, using longitudinal samples of milk and blubber. We discovered that, unlike Vitamin E or triglycerides, the dynamics of Vitamin A matches closely those of PCBs in milk throughout lactation. Levels of Vitamin A and PCBs remain constant during the first half of lactation and then increase at late lactation, indicating that pups ingesting higher levels of PCBs also ingest higher amounts of Vitamin A.