NU scientists pinpoint PFAS’ “Achilles’ heel” with safe breakdown method of forever chemicals

24 Aug 2022 --- Northwestern University chemists have developed a method – using low temperatures and inexpensive, common reagents – that causes two major classes of PFAS compounds to fall apart, leaving behind only benign end products. 

PFAS, also known as “forever chemicals,” are a class of synthetic compounds that have been employed extensively since the 1940s. They cannot be broken down by bacteria, incinerated by fire or diluted by water. If these dangerous substances are buried, they seep into the soil and remain a hazard for future generations.

The straightforward method developed by the researchers has the potential to be an effective way to eventually get rid of these toxic substances, which have been connected to numerous health hazards for humans, livestock and the environment.

Dr. William Dichtel of the Department of Chemistry at Northwestern University, US, who led the study, tells PackagingInsights that “we can’t just wait out this problem. 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 research is published in the journal Science.

Method difficulties
Chemical bonding within PFAS is what gives it its indestructibility. The strongest bonds in organic chemistry, carbon-fluorine bonds, are prevalent in PFAS. Fluorine attracts electrons since it is the most electronegative element in the periodic table. Contrarily, carbon is more eager to surrender its electrons.

Pinpointing PFAS’ “Achilles’ heel,” Dichtel’s team discovered a flaw in the robust chemical link. A lengthy tail of rigid carbon-fluorine bonds can be found in PFAS. However, the molecule has a charged group at one end that frequently contains charged oxygen atoms.

By heating the PFAS in dimethyl sulfoxide, an unusual solvent for PFAS degradation, with sodium hydroxide, a typical reagent, Dichtel’s team specifically targeted this head group. The head group was decapitated by the process, and a reactive tail was left behind.

It started spitting out fluorine atoms from these compounds to generate fluoride, which is the safest form of fluorine after all these reactions, according to Dichtel. Despite the fact that carbon-fluorine bonds are quite strong, the charged head group is the weak link.

Highlighting what was challenging about this method, Dichtel says the mechanism (Figure 3) “is extremely complex and was only worked out by close collaboration between our experiments and calculations of the possible pathways.”

The way in which these compounds degrade is very different from conventional wisdom, and “it was a heroic effort by the two lead authors (Trang and Li) to build up this understanding,” he concludes.

Dichtel says the method’s mechanism (Figure 3 in the study) “is extremely complex.” 

“Hazardous, even at low levels”
PFAS, an abbreviation for per- and polyfluoroalkyl compounds, has been used as waterproofing and nonstick coatings for 70 years. They are frequently discovered in nonstick cookware, water-resistant cosmetics, firefighting foams, water-repellent textiles and grease- and oil-resistant goods.

Exposure to PFAS is significantly linked to elevated cholesterol levels, reduced fertility, impacts on children's development, a higher chance of developing different types of cancer, and impaired ability to fight infections.

In light of these detrimental health implications, the US Environmental Protection Agency (EPA) recently deemed a number of PFAS to be hazardous, even at low levels.

“Recently, the EPA revised its recommendations for PFOA essentially down to zero,” Dichtel says. “That puts several PFAS into the same category as the lead.”

Infrastructural compensations and feasibility 
Having a method for the breakdown of these agents is one thing, but a sufficient infrastructure for sizable operations would still be necessary.

Dichtel notes that: “one can envision treatment trains for removing PFAS from drinking water or even wastewater that involve a selective and regenerable adsorbent, which would be regenerated periodically and the PFAS destroyed, perhaps by our method. I am not an expert on such industrial development, but it will take time and significant capital investment.”

He also highlights the feasibility of large-scale applications, saying that “there is a lot to like about our method based on its mild conditions, simple and available chemicals, and safe byproducts.”

Further development, he says, will be needed to broaden the scope of the method to sulfonates, as well as to optimize the process for efficiency and cost. “The most important aspect of the work in the meantime is the fundamental understanding that it provides about how the PFAS agents react and break down in unexpected ways.”

A solution does not justify consumer negligence 
Multiple organizations have stepped in to note that the breakthrough does not have much real-world relevance. While the labor is appreciated, the BBC notes that “treatment of high concentrations of PFAS is only one part of the solution.”

This breakdown process should not justify adding PFAS to everyday items. Despite being innovative, this new approach is currently only being tested and is not yet in use. The dilemma of how to filter out all PFAS, which have accumulated over decades in our bodies and the environment, to be eliminated still exists, even when it is ready to operate at scale in the future.

Dichtel sheds some light on the study applications, admitting that he does not have much insight on how the study impacts packaging companies specifically, albeit carefully highlighting what consumers should take away from the findings.

Dichtel encourages consumers to keep in mind that the primary objective is to halt the manufacturing and usage of PFAS. He says: “Our study demonstrates that several large classes of PFAS can be degraded under milder conditions than previously thought, as well as pathways for the degradation that may lead to methods for the other classes of PFAS. However, these degradation methods do not make the use of PFAS acceptable. Consumers should demand products that do not contain PFAS.”

By Mieke Meintjes