Northern elephant seal females and pups go through intense cycles of refueling and fasting. Thanks to the very fatty milk, puppies gain 4 kg per day during the lactation period of approximately 4 weeks. They then fast for two months, relying on hidden fat until they can dive for their food.
A new study suggests that seal mothers pass significant amounts of perfluoroalkyl substances, or PFAS, to the pups in their milk during this period of intense feeding. Blood tests also showed this PFAS concentrations continued to increase in pups after weaning (the environment. health 2026, DOI: 10.1021/envhealth.5c00782).
This “contamination in mid-ocean foraging animals reflects a level of background pollution that is frankly terrifying,” says Jane Khudyakov, a comparative physiologist at the University of the Pacific.
In 2022, Khudyakov’s team collected blood from 14 pairs of mothers and pups and milk from 9 mothers. The researchers searched these samples for specific PFAS molecules and identified 17 compounds in the blood and 12 in the milk. They also screened for other potential PFAS compounds, which turned up 10 other PFAS in both.
The average total PFAS concentrations in the blood of the lactating pups were three times that of the mothers, while the weaned pups had nearly 90 ng/mL of PFAS in their blood on average, about five times as high as the mothers’ blood. “We think this is because the mother concentrates all the PFAS in her milk and gives it to the young during that relatively short period of breastfeeding,” says Kara Joseph, an analytical chemist working on the study with Erin Becker at the University of North Carolina at Chapel Hill. After puppies are weaned, they redistribute nutrients, which may push more PFAS into the young animals’ blood.
The types of PFAS found in blood and milk vary, with only one long-chain PFAS molecule found in milk. “It gives us a really interesting picture of exposure that we didn’t know just from blood,” Baker says. Concentrations in milk were 5.88 ng/ml on average. Researchers estimate that breastfeeding can transfer more than 1 milligram of PFAS to pups whose mothers are exposed to a lot of pollution.
Concentrations in all seals exceeded 2 ng/mL, a PFAS level below which no health effects on people would be expected, and often exceeded the 20 ng/mL threshold for increased health risks.
It is not clear what health effects high levels of PFAS have on seals, both adults and juveniles. The molecules can affect the immune system, so PFAS may hinder pinnipeds’ ability to fight off disease outbreaks, says Rainer Lohmann, an environmental chemist at the University of Rhode Island, who was not involved in the study.
In humans, PFAS also affect reproduction, kidney and liver function, and they also disrupt fat metabolism, Joseph says. If molecules tamper with seal blubber, the interference could cause major effects. “The ability to effectively store fat and then release it from storage for energy is crucial,” says Khudyakov. Females search for food throughout most of the year, which leads to the accumulation of fat reserves. They also fast during the lactation period and lose 60% of their body weight.
The early dependence of seal pups on their mothers’ milk provides a way to study the transfer of chemicals in perpetuity from mothers without the confounding effects of other foods. The findings could provide hints about what’s happening in humans, which Joseph and her colleagues have already begun to study.
“Everything being studied here also has relevance to humans,” says Carrie McDonough, an environmental chemist at Carnegie Mellon University who was not involved in the work. “We’re hollowing out motherhood. Our babies, even before they’re born, have PFAS in them. Our breast milk has PFAS, too.”
Milk sampling is less invasive than drawing blood. But analyzing milk can be difficult. “Most people tend to stay away from it because it’s too complicated,” Joseph says. She based her PFAS extraction method on a USDA protocol developed for food and improved it so she could measure PFAS in just 1 ml of these precious samples.
“It’s a really good job,” McDonough says. But she cautions against the authors’ suggestion that PFAS accumulate in these animals because the molecules are lipophilic, like many older persistent organic pollutants, or POPs. “PFAS are very different molecules than a lot of those that are well-studied,” she says. “We usually don’t see a lot of them in fat.” She says PFAS compounds act like surfactants and tend to accumulate where they have a favorable hydrogen bond, and it’s not clear what the mechanism is behind increased blood PFAS levels in puppies after fasting. “There may be more complex pathways, or perhaps they are stored in fat and we don’t know.”
