A team of scientists has discovered a simple, low-energy way to break apart one of the largest groups of ‘forever chemicals’, nefarious pollutants that have been linked to environmental harm and human health concerns.
While practical applications are still a way off, scientists are in awe of the new technique’s potential.
In detailed simulations, PFAS molecules – long-chain synthetic chemicals with carbon-fluorine bonds so strong they were considered impossible to break without a great deal of effort – quickly ‘fell apart’ under a specific set of mild conditions.
“The fundamental knowledge of how these materials degrade is probably the single most important thing coming out of this study,” William Dichtel, a chemistry professor at Northwestern University, said in a press briefing.
So far, the researchers have shown their method degrades one major class of PFAS (perfluoroalkyl) chemicals, those that contain carboxylic acids and are called PFCAs for short.
All PFAS are notorious. Their water- and fat-repelling properties made them effective non-stick and waterproofing agents, but also terribly persistent environmental contaminants that have wound up in our blood.
Given the known health risks of chronic exposure to low levels of PFAS compounds, and a slew of studies detecting PFAS contamination at unsafe levels in water sources, there has been a rush to develop a battery of techniques to filter PFAS from drinking water with varying success.
But PFAS chemicals (unsurprisingly) remain intact after filtration and there are few options for how to dispose of them. Given high enough temperatures, they will break down. But this is expensive, and risks spreading contaminants further.
The new research, led by Northwestern University materials chemist Brittany Trang, could radically change that.
The team developed a low-energy process that degrades PFAS chemicals at mild temperatures, using inexpensive reagents and leaving only innocuous carbon-containing molecules and fluoride ions.
The study “provide[s] insight into how these seemingly robust compounds can undergo nearly complete decomposition under unexpectedly mild conditions,” write Shira Joudan, an environmental chemistry researcher at York University, and fellow chemist Rylan Lundgren of University of Alberta, in a perspective article accompanying the study. Neither of the perspective authors was involved in the study.
“Hopefully, the fundamental findings of Trang et al. can be coupled with efficient capture of PFAS from contaminated environmental sites to provide a possible solution to the forever chemical problem.”
That might be harder than it should be. Forever chemicals are seemingly everywhere and the US Environmental Protection Agency (EPA) has repeatedly revised its guidelines of what it considers to be ‘safe’ levels of PFAS contamination, as PFAS substances turned out to be more dangerous than regulators thought (or admitted them to be).
Moreover, the agency has recently come under intense scrutiny for narrowing the definition of PFAS substances to exclude many forever chemicals.
In light of these shifting regulatory standards and growing safety concerns, we fast need a way to deal with PFAS contamination.
Trang and colleagues tested their low-energy method on PFCA molecules of varying chain lengths, and managed to break down 10 of them. The trick was to target a group of charged oxygen atoms at the tail end of PFCA molecules.
“That triggered all these reactions, and it started spitting out fluorine atoms from these compounds to form fluoride, which is the safest form of fluorine,” explains Dichtel.
“Although carbon-fluorine bonds are super strong, that charged head group is the Achilles’ heel.”
Using computer simulations to disentangle the cascade of complex chemical reactions and confirm the by-products were relatively harmless, the team are confident they are on to a good thing. Once destabilized, the molecules were stripped of nearly all of their fluorine atoms.
Computer modeling “really provides for the first time a way to map these reactions out and possibly to optimize them, to prove that we really are only plausibly making safe products,” Dichtel said in a news briefing. This includes small carbon-containing products that are found in nature and do not pose serious health concerns, he added.
The researchers then demonstrated that their process also works for another class of newer, branched PFAS substances – which were developed as a replacement for PFAS chemicals, but whose ubiquitous presence in global surface waters already has scientists alarmed.
However, given that there are more than 12,000 different PFAS chemicals recognised by the US EPA to date, a lot more research is still needed to understand the fundamental reactivity of these molecules, and whether they can be degraded using similar approaches.
Same goes for elucidating the gamut of health effects of PFAS chemicals and where they persist in the environment.
The team hopes their work will spur further research to develop practical methods to remove and degrade these dangerous pollutants at industrial scales. Figuring out how to break down other classes of PFAS compounds, namely the sulfonate-containing substances, is also a must.
“Our work addressed one of the largest classes of PFAS, including many we are most concerned about,” says Dichtel of the study. “There are other classes that don’t have the same Achilles’ heel, but each one will have its own weakness.”
If scientists can identify them one by one, starting with the sulfonates, then we might be one step closer to knowing how to clean up the mess we’ve made.
The study was published in Science.