A new study highlights the Achilles’ heel for major classes of PFAS – persistent chemicals linked to a host of adverse health effects – that cause compounds to break down into benign products.
SPFA, a group of manufactured chemicals commonly used since the 1940s, have been dubbed “eternal chemicals” for a reason: bacteria can’t eat them; fire cannot incinerate them; and water cannot dilute them. And, if these toxic chemicals are buried, they seep into the surrounding soil, becoming a lingering problem for generations to come.
Fortunately, Northwestern University Chemists have discovered an incredibly simple technique that achieves what was once thought impossible: using low temperatures and inexpensive common reagents, the research team has developed a process that causes the collapse of two major classes of PFAS compounds, leaving only benign end products behind. According to
study — supported by the
national science foundation and published on August 19 in the journal
Science — the technique could be a powerful solution to finally get rid of these harmful chemicals, which are linked to many dangerous health effects in humans, livestock and the environment.
‘PFAS has become a major societal problem,’ says the North West chemistry professor Guillaume Dichtel, who led the study. “Even a very small amount of PFAS has negative health effects and does not break down. We can’t wait for this issue to be resolved. We wanted to use chemistry to solve this problem and create a solution that the world could use. This is exciting because of the simplicity – but little known – of our solution.
“The same category as lead”
Short for per- and polyfluoroalkyl substances, PFAS have been used for 70 years as release and waterproofing agents. They are commonly found in non-stick cookware, waterproof cosmetics, fire-fighting foams and protective equipment, water- and stain-resistant fabrics, and grease- and oil-resistant products.
Over the years, however, PFAS have made their way out of consumer goods and into our drinking water – and into the bloodstream of 97% of the population. WE
population. Although the health effects are not yet fully understood, exposure to PFAS is strongly associated with decreased fertility, developmental effects in children, increased risks of various types of cancer, reduced immunity to fight infections and increased cholesterol levels. These adverse health effects naturally sounded the alarm; and as usual, the corporate world has been the first to act — in recent years, retailers, including Ahold Delhaize, Home deposit and
Ikea have taken significant steps to avoid PFAS as a chemical class in a variety of products and packaging. The
United States Environmental Protection Agency (APE), on the other hand, it is only recently (June 2022) that several PFAS have been declared dangerous.
“Recently, the EPA revised its recommendations for perfluorooctanoic acid
(PFOA) basically to zero,” Dichtel said. “That puts several PFAS in the same category as lead.”
Unbreakable bonds, or so we thought
Although community efforts to filter PFAS from water have been successful, there are few solutions for how to remove them once they are removed. The few options that are emerging now have typically involved destroying PFAS at high temperatures and pressures or other energy-intensive methods — and they could do more harm than good.
“In New York state, a plant claiming to incinerate PFAS has been found to release some of these compounds into the air,” Dichtel said. “The compounds were emitted from chimneys and into the local community. Another failed strategy was to bury the compounds in landfills. When you do this, you are simply guaranteeing that you will have a problem 30 years from now because it will slowly dissipate. You have not solved the problem. You just kicked the box on the road.
The secret to the indestructibility of PFAS lies in their chemical bonds: they contain many carbon-fluorine bonds – the strongest bonds in organic chemistry. As the most electronegative element on the periodic table, fluorine wants electrons – and badly. Carbon, on the other hand, is more willing to give up its electrons.
“When you have that kind of difference between two atoms — and they’re about the same size, which is carbon and fluorine — that’s the recipe for a really strong bond,” Dichtel explained.
The Achilles heel of PFAS
But in studying the compounds, Dichtel’s team found a weakness (Editor’s note:
Non-chemistry enthusiasts can easily skip the next few paragraphs.): PFAS contains a long tail of inflexible carbon-fluorine bonds. But at one end of the molecule is a group that often contains charged oxygen atoms. Dichtel’s team targeted this head group by heating PFAS in dimethyl sulfoxide – an unusual solvent for PFAS destruction – with sodium hydroxide (a.k.a laundry). The process effectively “decapitated” the leading group, leaving behind a reactive tail.
“It triggered all these reactions; and it started spitting out fluorine atoms from those compounds to form fluoride, which is the safest form of fluorine,” Dichtel explained. “Although the carbon-fluorine bonds are super strong, this charged head group is the Achilles’ heel.”
In previous attempts to destroy PFAS, other researchers have used high temperatures – up to 400° Celsius. Dichtel is delighted that the new technique relies on milder conditions and a simple, inexpensive reagent, making the solution more practical and much less energy-intensive for widespread use.
After discovering the degradation conditions of PFAS, Dichtel and co-author
Brittany Trang also found that fluorinated pollutants break down by processes different from those generally assumed. Thanks to powerful calculation methods, employees Ken Houk at UCLA and
Tianjin University student Yuli Li simulated PFAS degradation. Their calculations suggest that PFAS break down through more complex processes than expected. Although it had previously been assumed that PFAS should decay one carbon at a time, the simulation showed that PFAS decay 2-3 carbons at a time – a finding that matched the experiments of Dichtel and Trang and confirmed that only benign products remained. This new knowledge could also help guide further improvements to the method.
“It turned out to be a very complex set of calculations that challenged the most modern quantum mechanical methods and the fastest computers available to us,” said Houk, a distinguished research professor in organic chemistry. “Quantum mechanics is the mathematical method that simulates all of chemistry; but it’s only been in the last decade that we’ve been able to tackle big mechanistic problems like this, evaluating all the possibilities and determining which one can happen at the observed rate. Yuli mastered these calculation methods and worked with Brittany Long Distance to solve this fundamental but practically significant problem.
10 down, 11,990 left
Next, the Dichtel team will test the effectiveness of their new strategy on other types of PFAS. In the present study, they successfully degraded 10
perfluoroalkyl carboxylic acids (PFCA) and perfluoroalkyl ether carboxylic acids (PFECA), including PFOA and one of its common substitutes, known as
— two of the most important PFAS compounds. The EPA, however, has identified over 12,000 PFAS compounds; but Dichtel remains hopeful.
“Our work has focused on one of the largest classes of PFAS, many of which concern us most,” he said. “There are other classes that don’t have the same Achilles heel; but each will have its own weakness. If we can identify it, then we know how to activate it to destroy it.