Northern elephant seal females and pups go through intense cycles of fueling and fasting. Thanks to extremely fatty milk, pups gain 4 kg a day in their roughly 4-week suckling period. They then fast for 2 months, relying on the fat they have stashed until they are able to dive for their own food.
A new study indicates that seal mothers pass down significant amounts of per- and polyfluoroalkyl substances, or PFAS, to pups in their milk during this intense feeding period. Blood tests also showed that PFAS concentrations continued to increase in pups after weaning (Environ. Health 2026, DOI: 10.1021/envhealth.5c00782).
This “contamination in animals that are foraging way out in the middle of the ocean reflects a level of background contamination that’s 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 of the mothers. The researchers searched these samples for specific PFAS molecules and identified 17 compounds in blood and 12 in milk. They also screened for other potential PFAS compounds, which turned up another 10 PFAS in both.
Average total PFAS concentrations in nursing pups’ blood were three times that of mothers, while weaned pups had nearly 90 ng/mL of PFAS in their blood on average, around five times as high as that of mothers. “We think that’s because mom is concentrating all of the PFAS in her milk and giving it to the pup during that relatively short period of lactation,” says Kara Joseph, an analytical chemist working on the study with Erin Baker at University of North Carolina at Chapel Hill. After pups are weaned, they redistribute nutrients, which may push more PFAS into young animals’ blood.
The types of PFAS found in blood and milk varied, with one long-chain PFAS molecule found only in milk. “It’s giving us a really interesting picture of exposure that we didn’t know just from the blood,” Baker says. Concentrations in milk were 5.88 ng/mL on average. Nursing could transfer over 1 mg of PFAS for pups whose mothers are exposed to a lot of pollution, the authors estimate.
Concentrations in all the seals exceeded 2 ng/mL, the level of PFAS below which health effects are not expected in people, and often surpassed the 20 ng/mL threshold for increased health risks.
It’s not clear what health effects the high levels of PFAS have on seals, either adults or developing youngsters. The molecules can affect the immune system, so PFAS may hamper the pinnipeds’ ability to withstand 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 and kidney and liver function, and they dysregulate lipid metabolism, Joseph says. If the molecules mess with seals’ lipids, this interference could cause major impacts. “Being able to effectively store and then release the fats from storage for energy is just critical,” Khudyakov says. Females forage for much of the year, building up fat reserves, and they fast while they nurse, losing 60% of their body weight.
The seal pups’ early dependence on their mother’s milk provides a way to study the maternal transfer of forever chemicals without the confounding effects of other foods. The findings could provide hints about what happens in humans, which Joseph and her colleagues are already starting to study.
“Everything that is being studied here is also relevant for human beings,” says Carrie McDonough, an environmental chemist at Carnegie Mellon University who wasn’t part of the work. “We do maternal offloading. Our babies, before they’re even born, have PFAS in them. Our breast milk has PFAS accumulated in it as well.”
Taking milk samples is less invasive than drawing blood. But analyzing milk can be tricky. “Most people tend to stay away from it because it is very complicated,” Joseph says. She based her method for extracting PFAS on a US Department of Agriculture protocol developed for food and optimized it so she could measure PFAS in just 1 mL of these precious samples.
“It’s really good work,” McDonough says. But she cautions against the authors’ suggestion that PFAS accumulate in these animals because the molecules are lipophilic like many legacy persistent organic pollutants, or POPs. “PFAS are such different molecules than a lot of those more well-studied molecules,” she says. “We don’t usually see a lot of them in fat.” PFAS compounds act like surfactants and tend to accumulate in places where they have favorable hydrogen bonding, she says, and it’s not clear what mechanism is behind the increase in blood levels of PFAS in pups after they fast. “There might be more-complex pathways, or maybe they are stored in fat and we just don’t know.”
