Eider ducks and bald eagles that nest in and around Harpswell have high levels of “forever chemicals” after an August 2024 spill of firefighting foam on the former Brunswick Naval Air Station.
Scientists from Portland-based Biodiversity Research Institute found themselves in a unique position after the spill, when 50,000 gallons of PFAS-containing foam left over from the U.S. Navy’s firefighting system entered streams and waterways that drain into Harpswell Cove.
As it happened, the institute’s researchers had been testing eider ducks in Casco Bay for mercury since about 2015. Having data from before a spill like the Brunswick spill “almost never happens,” said Christine Gardner, director of the institute’s toxicology laboratory. “You only study a site after the spill happens.”
PFAS stands for per- and polyfluoroalkyl substances, a group of chemicals used in a wide variety of products, including nonstick pans, furniture and firefighting foams. They dissolve in water, and studies suggest ingesting PFAS might increase the risk of certain cancers, lead to developmental delays in children and affect reproductive health. The same stability that makes PFAS useful in high-temperature applications also means they degrade very slowly or never in nature, giving them the nickname “forever chemicals.”
Eiders are hard to catch. After the spill, a team led by Micah Miller, a bird scientist at the Biodiversity Research Institute, had to wait until the birds were nesting in May 2025 to sample their blood and eggs. They found that PFAS levels had risen since the spill.
While their results are preliminary, they found that levels of certain PFAS were four to five times higher in birds within about 5 miles of Brunswick Landing, compared with those sampled 40 miles away from it.
What effects PFAS might be having on birds, scientists still don’t know. But Miller did note that eider populations are in decline.
The group also began testing bald eagles after the spill, climbing up to nests in trees to draw blood from young eagles. Gardner said there’s only a six-to-eight-week window when the eagle chicks are big enough to take blood from but not too big to catch safely.
They hadn’t sampled bald eagles in Harpswell prior to the spill, so the scientists couldn’t make the same comparison that they could with eiders. But the eagles tested in 2025 had higher PFAS levels than any other coastal bald eagles the group has sampled.
Among the birds that institute scientists have sampled, the average concentration of PFAS in bald eagles is about four times higher than that of eiders. That includes inland bald eagles, which tend to have higher concentrations of PFAS than marine bald eagles.
Miller attributes the difference between ducks and eagles to their diets. Eagles are at the top of the food chain, so pollutants are more concentrated in their prey.
Miller said the team has found clear links to the 2024 foam spill. The group identified chemicals unique to the firefighting foam and saw that PFAS levels were highest in places closest to the spill site.
“We’ve been able to identify pretty clearly where the chemicals from the spill in Brunswick are showing up in those birds,” Miller said.
In Harpswell, the institute partnered with Bowdoin College’s Schiller Coastal Studies Center to collect and process samples on its Orr’s Island campus.
Assisting the institute’s team was Bowdoin College student Olivia Ho, a junior chemistry major who is living on the Schiller campus this summer. She has been taking samples at sites along Harpswell’s shoreline of water, sediment and some of the animals that eiders eat, like crabs, snails and oysters. Researchers will test these for PFAS and mercury to help understand where eiders are ingesting PFAS.
She has also been helping track GPS-tagged eiders to better understand their movements around Harpswell and in Muscongus Bay, which lies about 40 miles to the east. It provides a useful comparison to Harpswell, since it has similar geology and tides but is much less developed compared to Casco Bay.
Gardner, the toxicology laboratory director, said that eiders, bald eagles and other birds can tell scientists a lot about pollutants in a given environment: “They’re the sum of everything they eat and everything below that.”
Eiders eat crabs, mussels and snails. Bald eagles eat fish and birds, including eiders. Testing around Harpswell in the past has found PFAS in mussels and fish, and in the water and mud, but at levels considered safe under the best available guidelines.
Compared to a pollutant like mercury, Miller said scientists still have a lot to learn about how PFAS move through the environment and food webs. Likewise, there’s still a lot they don’t know about their effect on the health of animals and humans.
The work is time-consuming and expensive, and Miller understands if people feel frustrated that scientists don’t have more concrete answers about PFAS and their effects. He hopes that people can take some solace knowing the local spill and associated damage could one day add to the overall understanding of PFAS.
“It’s going to take a long time to learn a lot about this,” he said.