Understanding freshwater foam may help in fight against PFAS “forever chemicals”

The waters of Lake Monona slosh against the rocks that Summer Sherman is balanced on, soaking her shoes and legs as she leans forward with gloved hands to scoop handfuls of bubbly, yellow foam into Ziploc gallon bags.

“The things you do for science,” she says with a laugh, as another wave splashes up over the rocks and onto her.

While the foam she’s collecting is naturally occurring, the chemicals that may be trapped in it are not. Among them could be PFAS, or per- and polyfluoroalkyl substances, which are often referred to as “forever chemicals.” They’ve been found in water around the world.

People exposed to PFAS at high concentrations have been shown to have an increase in negative health effects and a higher incidence of cancer.

The problem is, PFAS are persistent, and they’re everywhere: cooking pans, rain jackets, candy wrappers, cosmetics, firefighting foams. Scientists have even found PFAS from these products in drinking water and in our blood.

While some states are beginning to limit their use in new product manufacturing, the PFAS already contained in existing products remain in the environment and in humans.

“It’s important that we know what the concentrations are in our drinking water so that we know what’s within us and how PFAS might be negatively affecting us down the road,” says Sherman, a postdoctoral research associate in Professor Christy Remucal’s lab in the Department of Civil and Environmental Engineering at the University of Wisconsin–Madison.

Sherman, who has a background in fundamental physical chemistry, is asking questions about how the chemical structures of PFAS change in different layers of water and what this may mean for how they react with the environment — and people ­— around them.

While scientists have been studying PFAS for years, Sherman says there aren’t many papers looking at their accumulation in foam or how their structure changes depending on where they’re found, whether in foam, on the surface or underwater.

With incoming alerts from concerned community members and a number of community coalitions like the Clean Lakes Alliance, Sherman has basically been “on call for foam.” At any point, she knows she could receive an email, text or phone call about a foam sighting around Madison.

“Foam is super intermittent,” she says. “It could be there for 10 minutes, or it could be there for two days.”

Since foam can dissipate suddenly, Sherman has to act quickly when she receives a notification. She’s even prepped a collection kit for her car so she’s always ready to jump into action.

When she gets a call, she heads to the site, and with clean, gloved hands, she scoops foam into bags, submerges a bottle underwater to sample the water column and dips a pane of glass into the lake to collect the surface microlayer of water.

After the foam has condensed in a fridge, a process that can take up to a month, Sherman can start analyzing the samples.

PFAS molecules come in a host of shapes and sizes, but they share the same basic structure. One end of a PFAS molecule, called a “head group,” is hydrophilic, meaning it’s attracted to water. Its other end, the “tail,” is hydrophobic, meaning it’s repelled by water.

When wind scrapes across bodies of water containing PFAS, the chemicals’ hydrophobic tails can get caught in the foam that forms on the surface. The tails try to get away from the water while the heads are drawn to it. PFAS with longer tails are more likely to end up trapped in the foam as a result.

Since chemical structure dictates how the compounds interact with the world around them, it’s important to understand what the PFAS look like in the foam, surface microlayer and water column. Sherman is particularly interested in how different kinds of PFAS chemicals partition themselves, or settle in these different layers.

Sherman is also looking at how the chemical structures of PFAS might relate to different characteristics of the waters being tested, like how much dissolved organic matter it contains, its pH levels and the presence of other chemicals.

Even though Sherman isn’t cleaning the water, collecting and sharing the information is a vital step toward finding a solution to PFAS contamination. Her research in Dane County may help make efforts to clean water in other parts of Wisconsin and around the world more effective and let people know if their lakes and rivers are safe to be in, swim in, and eat from.

Sherman’s previous research experiences haven’t incorporated as much community contact, usually keeping her in the lab and removed from the people her research helped. Now, she gets out in the field and often chats with the people who reported the foam to her.

“Usually when they see me, people come out and they’ll talk to me about what I’m doing,” she says. “They ask me what more can they do, how much more can they help. They really do want to see their lakes clean.”