Scientists are ramping up research on the possible health effects of a large group of common but little-understood chemicals used in water-resistant clothing, stain-resistant furniture, nonstick cookware and many other consumer products.
Per- and polyfluoroalkyl substances are generally referred to by their plural acronym, PFAS. PFAS are resistant to water, oil and heat, and their use has expanded rapidly since they were developed by companies in the mid-20th century. Today, PFAS' nonstick qualities make them useful in products as diverse as food wrappers, umbrellas, tents, carpets and firefighting foam. The chemicals are also used in the manufacture of plastic and rubber and in insulation for wiring.
In short, they are all around us. And as a result, they've found their way into the soil and, especially in some regions, into our drinking water.
"We're finding them contaminating many rivers, many lakes, many drinking water supplies," says Linda Birnbaum, director of the National Institute of Environmental Health Sciences and the National Toxicology Program. "And we're finding them not only in the environment, but we're finding them in people."
"Essentially everyone has these compounds in our blood," she explains.
That's in part because PFAS don't break down easily — a quality that has earned them the nickname "forever chemicals." Some varieties have been found to stick around in the human body for years, if not decades. Others accumulate in soil or water, creating a continuous source of exposure.
Despite their ubiquity, however, scientists know relatively little about the health effects of most types of PFAS.
No PFAS legal safety limit yet
"Despite their everyday use, the body of science necessary to fully understand and regulate these chemicals is not yet as robust as it needs to be," acknowledged the assistant administrator of the Environmental Protection Agency's Office of Water, David Ross, at a congressional hearing on PFAS in March.
This year, the EPA signaled that it is considering setting a legal safety limit for some PFAS in drinking water, but it hasn't acted yet.
Meanwhile, public spending on research of the chemicals has gone up. The National Institutes of Health, the Environmental Protection Agency, the Centers for Disease Control and Prevention and multiple state university systems have all increased their funding for PFAS studies in recent years.
"We have more and more of our grantees who are looking at PFAS in their studies — both mechanistic studies and animal studies," as well as epidemiological studies that analyze large populations, explains Birnbaum. But the work is slow going.
"These are a very broad class of chemicals — probably 5,000 or more — and it seems like new ones are being produced all the time," she says.
In most cases, U.S. chemical regulations do not require that companies prove a chemical is safe before they start selling it. It's up to the EPA to determine whether a substance is unacceptably dangerous and under what circumstances, and typically such analyses begin only after public health concerns are raised.
As a result, "we really don't know much about the great majority of these chemicals," says Birnbaum.
One approach that scientists supported by the National Institutes of Health are taking is to analyze hundreds of PFAS varieties at once. The goal is to identify subgroups of PFAS with similar characteristics, so scientists won't have to do a battery of toxicity tests on each individual chemical.
"There's no way that we'll ever be able to test 5,000 or more PFAS," Birnbaum explains.
Early studies suggest some health risks
Some of the most large-scale PFAS epidemiology research in the U.S. was conducted by a science panel starting in 2005 as part of a class action lawsuit against the chemical company DuPont. The case alleged that thousands of people in West Virginia and Ohio were hurt by industrial releases of a PFAS chemical called PFOA.
The panel — made up of three career epidemiologists whom both sides of the court case agreed to have evaluate the scientific evidence — found a "probable link" between long-term exposure to the chemical and certain medical conditions, such as kidney cancer and thyroid disease.
Additional studies of both humans and rodents have found similar associations.
"I think we have growing information that at least some members of this class can be problematic," says Birnbaum.
Those findings have raised a host of new questions, first about mechanism: How do PFAS chemicals act in the body? It's one thing to see an association between exposure to a substance and disease. It's much more difficult to determine a likely path from chemical exposure to disease symptoms.
"We still don't know the precise molecular ways that they produce toxicity," explains Jamie DeWitt, a toxicologist who studies PFAS at East Carolina University.
For example, DeWitt and others have published studies of both humans and rodents that suggest exposure to one PFAS chemical — PFOA — can suppress the body's response to vaccines.
"I'm pretty sure that a type of immune cell called a B cell is involved" in that suppression, says DeWitt. "But I don't know why the B cell doesn't produce enough antibody. Is it signaling molecules that say, 'Hey, B cell, make antibody?' Is it something wrong inside the B cell itself? Is it the amount of energy that the B cell has? These are these molecular mechanisms that we're still trying to figure out."
Knowing those mechanisms for PFOA might help scientists estimate the potential risks of other PFAS that have a similar structure, she says. "Honestly, I think we're still at the very beginning."
At the current rate of research, Birnbaum says, it will take about two years to get a basic handle on the toxicity of the whole PFAS group. But there will still be many questions for both scientists and regulators.
"Realizing that these chemicals have escaped into the environment, how are we going to remediate those problems? How are we going to get rid of these chemicals?" she says.
"A question that we all need to be asking is: What's essential?" she says. "Do we really need it? Are there some places where we need to have this class of chemicals to be safe? But if that's the case, we would like them used in closed systems so they don't escape and end up contaminating the whole world."
Asked to comment on how essential PFAS are, a spokesperson for the FluoroCouncil, part of the main trade group representing chemical companies in the U.S., defended their widespread use in consumer products.
"PFAS are an essential enabling technology that play a vital role in products ranging from lifesaving applications in pacemakers and defibrillators, to the design of lower-emissions automobiles with improved auto safety, to the manufacturing of semiconductors, solar panels and high-performance electronics," a spokesperson for the FluoroCouncil wrote in an emailed statement to NPR.
"The vast differences within the PFAS family of chemistry are not immediately obvious to many people," the statement continues. "While some of the names sound the same, PFAS have differing characteristics, formulations, intended uses, and environmental and health profiles."
Living with uncertainty
While two years is not very long in the world of basic scientific research, it can feel like an eternity to people who are worried about their health. In response to public concern, some states already are taking action on their own, both to regulate PFAS emissions and exposure and to gather public health information in communities where the water is known to be contaminated.
"For people who live in areas where one of their drinking water sources has a level [of PFAS] that was high enough to raise concern, there's a really strong demand for information," says Alissa Cordner, a sociologist at Whitman College and one of the organizers of a nationwide PFAS contamination list.
"There's so much uncertainty around what the scale and the consequences of contamination are," she explains, and that uncertainty makes people afraid. "In terms of individuals wanting to know 'What's in my drinking water?' the testing is still prohibitively expensive."
And even when scientists or officials test water in a community, the lack of scientific evidence gathered, so far, about PFAS and health makes it difficult for people to know how to react. Most in-home water filters don't remove the chemicals effectively, according to the CDC.
"I think it's confusing, because you have so many chemicals about which we know so little, other than they're a member of this large class," says Birnbaum. "I think that is confusing, but it's also frustrating. So we're trying to address those problems right now." Regulators, scientists and citizens all agree: Research results can't come soon enough.