Scientists unveil method to destroy certain ‘forever chemicals’

Scientists at Northwestern University say they have devised a method for breaking apart some of the infamously unbreakable toxins known as “forever chemicals.”

These chemicals, called per- and polyfluoroalkyl substances (PFAS), earned the “forever” qualifier due to their propensity to linger in the human body and the environment. There are thousands of types of PFAS, none of which are naturally occurring and many of which can take decades to degrade.

But a group of chemists at Northwestern say they have developed a simple method that employs low temperatures and inexpensive reagents to break down two major classes of PFAS, while leaving behind only harmless byproducts.

They published their findings — which they acknowledged as a “seemingly impossible” but potentially “powerful solution” — in Science on Thursday afternoon.

“PFAS has become a major societal problem,” lead author William Dichtel, a professor of chemistry at Northwestern, said in a statement. “Even just a tiny, tiny amount of PFAS causes negative health effects, and it does not break down.”

Scientists have already found connections between PFAS exposure and a long list of illnesses, including testicular cancer, thyroid disease and kidney cancer.

Notorious for their presence in jet fuel firefighting foam and industrial discharge, PFAS are also found in many household products, including nonstick pans, waterproof apparel and cosmetics.

“We can’t just wait out this problem,” Dichtel said. “We wanted to use chemistry to address this problem and create a solution that the world can use. It’s exciting because of how simple — yet unrecognized — our solution is.”

The reason that PFAS are usually so indestructible is that they are made up of many carbon-fluorine bonds, which are the strongest such bonds in organic chemistry, the authors explained.

But the researchers said they identified a weakness that enabled them to disrupt this formidable attachment.

While PFAS contain long “tails” of powerful carbon-fluorine bonds, at one end of these molecules is often a “head group” of charged oxygen atoms, the authors explained.

By heating the compounds in a solvent called dimethyl sulfide with a common reagent called sodium hydroxide, the scientists said they “decapitated the head group” — exposing a vulnerable, reactive PFAS tail.

“Although carbon-fluorine bonds are super strong, that charged head group is the Achilles heel,” Dichtel said.

This head group “falls off and sets off a cascade of reactions that ultimately breaks these PFAS compounds down to relatively benign products,” the professor explained at a live-streamed press conference this week.

The byproducts include fluoride ions and “small carbon-containing products that are in many cases found in nature already and do not pose serious health concerns,” he added.

Dichtel’s team successfully degraded 10 types of PFAS from two classes: perfluoroalkyl carboxylic acids — PFCAs — and perfluoroalkyl ether carboxylic acids, or PFECAs.

Among the compounds they were able to break down were perfluorooctanoic acid, or PFOA, and GenX — two of the most infamous types of PFAS.

“The importance of this understanding is that it really provides for the first time a way to map these reactions out,” Dichtel said at the press conference.

Dichtel and first co-author Brittany Trang, who recently completed her PhD in his laboratory, worked alongside Ken Houk, an organic chemistry professor at the University of California, Los Angeles and Yuli Li, a student at China’s Tianjin University, who employed powerful computational methods to simulate PFAS degradation. 

Understanding the path to degradation, according to Dichtel, is important to the future development of “actual practical methods to remove these pollutants” from contaminated water.

Dichtel said he could envision this type of technique being integrated in the future with technologies that extract PFAS from water, such as reverse osmosis. Reverse osmosis pulls contaminants out of water by forcing the offending molecules through a semi-permeable membrane — and while this process purifies the water, the PFAS is left behind as waste. 

But an approach like the one devised in Dichtel’s laboratory could be applied to this waste stream and break down concentrated quantities of PFAS, he explained.

Acknowledging that other PFAS degradation methods have been emerging, Dichtel said that the uniqueness of their method lies in its inexpensive nature and low temperature requirements.

Now that they’ve successfully broken down these 10 types of PFAS, the scientists said they plan to test out the strategy on others.

They next plan to focus on another large class of PFAS called perfluoroalkyl sulfonates, which include common compounds like perfluorooctane sulfonic acid, or PFOS, according to Dichtel. 

With each class, however, comes a different head group that the scientists need to figure out how to decapitate. But if they “can knock that sulfonated head group off the molecule,” the compounds should degrade through similar pathways, the professor explained.

Although it’s difficult to anticipate exactly what will be required to eliminate that head group, Dichtel said that they are exploring several different possibilities. And identifying that mechanism would be one step closer to figuring out how to break down the thousands of types of PFAS that are lurking in the environment.

“PFAS pollution is so pervasive, and it is in more than just drinking water,” Dichtel added. “It’s in soils, it’s in dust, it’s airborne — we really polluted the whole world with this stuff.”