Per- and polyfluoroalkyl substances (PFAS) have quickly become ubiquitous in the environment. Used for decades in everything from firefighting foams to nonstick skillets, these potentially toxic compounds are now being found in soils, groundwater and even rain and snow.
And they’re expected to stay in the environment for years—perhaps centuries—as the compounds’ sturdy fluorine-carbon bonds make it nearly impossible for them to degrade naturally. But now, scientists have developed a way to permanently break down two classes of these “forever chemicals” using relatively low temperatures and a few common reagents (Science 2022, DOI: 10.1126/science.abm8868). Brittany Trang, who co-led the study, presented the work on Wednesday at the ACS Fall 2022 meeting in the Division of Environmental Chemistry. William Dichtel, a chemist at Northwestern University, also introduced the work at a presidential event symposium on Tuesday.
For years, researchers have been focused on finding ways to remove PFAS from the environment and, especially, from drinking water. Current methods typically filter the compounds from water with activated carbon or other materials, which eventually need to be incinerated at 1,000 °C to remove and destroy these pollutants.
However, this process is extremely energy intensive and may not be as effective as previously thought, explained Trang, a science reporting fellow at STAT News who developed the method as a graduate student in Dichtel’s lab. Many emerging PFAS degradation methods also require significant energy or chemical inputs, Dichtel said, which could limit how widely they’re used.
In contrast, Trang and Dichtel’s method can degrade one of the largest classes of PFAS, perfluoroalkyl carboxylic acids (PFCAs), using two inexpensive chemicals, ambient pressures, and mild temperatures around 120 °C. Trang and her colleagues demonstrated that this process could also break down GenX, another widespread pollutant that belongs to a separate family of PFAS.
To accomplish these results, the researchers used heated dimethyl sulfoxide solvent to remove the carboxylic acid group from the ends of GenX and 8 different PFCAs, including perfluoroctanoic acid (PFOA), leaving behind a highly reactive anion that readily fell apart when Trang added sodium hydroxide to the mix. In the end, all that remained was a mixture of relatively benign fluoride ions and carbon-containing compounds—the ideal-case scenario, Dichtel said.
This method has the potential to be “a cost-effective and efficient method” for treating concentrated PFCA and GenX waste streams, said Michael J. Bentel, a postdoctoral researcher at Clemson University who was not involved in the study.
The study’s value also lies in the researchers’ explanation of how these PFCAs are being broken down, said Jinyong Liu, an environmental engineer at the University of California, Riverside, who was also not involved in the work. After establishing that their method worked, Trang and her team determined that the fluorinated compounds degrade through a chemistry that differs from what others in the field had generally assumed. “The mechanism is super novel,” Liu said, and “can transform our understanding on how the perfluoroalkyl carboxylic acids degrade.”
According to Dichtel, future work will focus on broadening the method’s scope. He is especially interested in finding ways to degrade sulfonate-containing PFAS, another large and important class of “forever chemicals.”
“What I’m most excited about in this study,” Trang said, “is the idea that this might change how people in this field think about these problems and lead to people iterating upon these ideas.”
This story was updated on Oct. 9, 2022, to correct the description of the sturdy bonds found in per- and polyfluoroalkyl substances. They are fluorine-carbon bonds, not fluoride-carbon bonds.