PFAS compounds are known as “forever chemicals” because they degrade slowly in the environment and accumulate in the body, potentially harming human and animal health.
Bacteria can't eat them. Fire can't incinerate them. Water can't dilute them.
Instead, these per- and polyfluoroalkyl substances break down on their own schedule, posing a potential health hazard for generations to come.
A team of researchers say they've figured out a cheap, easy and effective way to break down two of the major classes of PFAS compounds, leaving behind harmless end products.
The new process uses two readily available chemicals — lye and dimethyl sulfoxide — to break down PFAS compounds that are capped with carbon dioxide, according to the scientists.
The process also works at a temperature much lower than previous efforts to break down PFAS compounds.
The breakdown occurs at 248 degrees Fahrenheit, just above the boiling point of water; earlier methods have required temperatures as high as 752 degrees Fahrenheit, the researchers said.
“We were pleased to find a relatively low temperature, low energy input method where one specific portion of these molecules falls off and sets off a cascade of reactions that ultimately breaks these compounds down to relatively benign products,” said senior researcher William Dichtel, a professor of chemistry at Northwestern University in Illinois.
The resulting products of PFAS disintegration “are in many cases found in nature already and do not pose serious health concerns,” Dichtel said.
PFAS are everywhere
PFAS chemicals have been in use for 70 years, researchers said in background notes. They're commonly found in nonstick cookware, waterproof cosmetics, firefighting foams, water-repellent fabrics, and products that resist grease and oil.
But because they don't easily break down, PFAS have made their way out of consumer goods and into the environment. PFAS chemicals can be found in the blood of 97% of Americans, researchers have found.
“These pollutants are pervasive throughout the world. They contaminate drinking water at low levels throughout the U.S. and in several places to relatively high levels, and this is true throughout the world,” Dichtel said.
“Chronic low-level exposure to these compounds is associated with a number of health effects, including low birth weight, reduced immune response, liver damage, high cholesterol and many cancers,” Dichtel continued. “And more of these health effects are emerging as the effects of this very large class of pollutants are continuing to be understood.”
Looking at ways to break down PFAS chemicals, Dichtel and his team looked closely at a class of them called “carboxylic” because they are capped with carbon dioxide at one end of the chemical chain.
Soaking carboxylic PFAS in dimethyl sulfoxide and then adding lye, water and heat causes “the carboxylic acid group that is found across this entire class of compounds to fall off,” Dichtel said.
Once the carbon dioxide cap pops off the chemical chain, “the entire molecule starts to fall apart in a cascade of complex reactions,” Dichtel said.
Initial attempts to use this method worked too well, producing corrosive glass-eating fluoride acids, said lead researcher Brittany Trang, at the time a graduate research fellow at Northwestern University.
“In the course of my screening there was one reaction that did indeed etch the glass tube that I was working the reaction in, which was great because it showed that the reaction was working,” Trang explained.
To nail down the most effective process, Dichtel and Trang turned to UCLA's Ken Houk, a pioneer in the use of computers to better understand chemical reactions.
Fine-tuning the breakdown process
“Experimentally, you can take A and end up with B, but how does that happen? Is it one step? Is it two steps? Or as we found, is it like 50 steps?” said Houk, a distinguished research professor at the University of California, Los Angeles.
“Computations nowadays provide the most efficient way to study [chemical] mechanisms,” Houk said. “I say nowadays because even 10 years ago, when computers were 100 times slower and 100 times more expensive, we really could not take on anything this complicated.”
In this case, what seems like a simple process involving a couple of chemicals is actually “amazingly complex,” Houk said. “If you've looked at the paper, you'll see the many reactions that are occurring” as the process breaks down PFAS.
The researchers settled on one process and then used it to successfully degrade 10 different perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl ether carboxylic acids (PFECAs).
These include two of the most prominent PFAS compounds, perfluorooctanoic acid (PFOA) and one of its common replacements, known as GenX.
The research team believes this process could be used to break down PFAS chemicals found in drinking water, once those chemicals have been removed from the water supply and stored in a concentrated form.
“It's very inefficient to treat every gallon of water that we have that has this trace level of contamination with any method, including our own,” Dichtel said, noting that this process is “not something that you would just down the drain or dump into waterways.”
The next step for the researchers will be to find ways to make the process even more efficient, possibly with different chemicals that would work at even lower temperatures.
In addition, this process doesn't help break down PFAS chemicals containing sulfonates, which are the other major class of PFAS. Those will be the next target, the study authors said.
“The biggest gap in what we have today versus what is needed is that we really would like to degrade sulfonates as well as carboxolates, as well as the other sort of PFAS that have more exotic head groups,” Dichtel said.
“I really think that the fundamental knowledge of how these materials degrade is probably the single most important thing coming out of this study. There is certainly the possibility of activating sulfonates in similar ways that we've done carboxylates, but all that has to happen in the future,” Dichtel concluded.
The findings were published online Aug. 18 in the journal Science.
The U.S. Environmental Protection Agency has more about PFAS.
SOURCES: William Dichtel, PhD, professor, chemistry, Northwestern University, Chicago; Brittany Trang, PhD, graduate research fellow, Northwestern University; Ken Houk, PhD, distinguished research professor, University of California, Los Angeles; Science, Aug. 18, 2022, online