For a reason, PFAS, a class of synthetic chemicals that have been widely used since the 1940s, are referred to as “forever chemicals.” They cannot be consumed by bacteria, burned by fire, or diluted by water. Additionally, if these dangerous substances are buried, they seep into the soil around them and continue to be a problem for future generations.
Now, chemists from Northwestern University have accomplished the seemingly unachievable. The study team created a method that breaks down two important groups of PFAS chemicals into harmless byproducts using low temperatures and inexpensive, common reagents.
The straightforward method may be an effective way to finally get rid of these toxic compounds, which have been associated with a number of risky health impacts on people, animals, and the environment.
The findings of the study will be published in the journal Science on Aug 19.
William Dichtel, a researcher at Northwestern University, said that PFAS has grown to be a significant societal issue.
“Even just a tiny, tiny amount of PFAS causes negative health effects, and it does not break down. 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 same classification as lead
PFAS, an abbreviation for per- and polyfluoroalkyl compounds, have been used as waterproofing and nonstick coatings for 70 years. They are typically found in nonstick cookware, water-resistant cosmetics, firefighting foams, water-repellent fabrics, and items that resist grease and oil.
But over time, PFAS has found its way out of consumer items and into our water supply and even into the blood of 97% of Americans. Exposure to PFAS is significantly linked to decreased fertility, impacts on children’s development, higher risks for many forms of cancer, lowered immunity to infections, and elevated cholesterol levels, even though the health implications are not yet fully understood. The U.S. Environmental Protection Agency (EPA) recently deemed numerous PFAS hazardous — even at low levels — in light of these detrimental health impacts.
The EPA has reduced its PFOA recommendation to almost zero, according to Dichtel. That places a number of PFAS in the same classification as lead.
Unbreakable ties
Even though community initiatives to remove PFAS from water have been successful, there aren’t many ways to get rid of it after removal. The limited options that are now being explored mostly involve the destruction of PFAS at high temperatures and pressures or through other processes that demand significant energy inputs.
“In New York state, a plant claiming to incinerate PFAS was found to be releasing some of these compounds into the air,” Dichtel added. “The compounds were emitted from the smokestacks and into the local community. Another failed strategy has been to bury the compounds in landfills. When you do that, you are basically just guaranteeing that you will have a problem 30 years from now because it’s going to slowly leach out. You didn’t solve the problem. You just kicked the can down the road.”
Chemical bonding within PFAS are what give it its indestructibility. Many carbon-fluorine bonds are present in PFAS, which are the strongest bonds in organic chemistry. Fluorine seeks electrons hard since it is the most electronegative element in the periodic table. Contrarily, carbon is more eager to surrender its electrons.
When two atoms differ by that much and are almost the same size, as fluorine and carbon are, Dichtel said, “that’s the recipe for a really strong bond.”
Identifying PFAS’s weak spot
But as they examined the chemicals, Dichtel’s researchers discovered a vulnerability. 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 beheaded by the process, and a reactive tail was left behind.
It “started spitting out fluorine atoms from these compounds to form 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.
Other researchers have employed high temperatures of up to 400 degrees Celsius to eliminate PFAS in earlier attempts. Dichtel is thrilled that the new method uses softer conditions and a cheap, straightforward reagent, perhaps making the solution more applicable for wider application.
Dichtel and Trang identified the PFAS degradation conditions as well as the fact that the fluorinated contaminants degrade through different mechanisms than previously thought. The PFAS deterioration was simulated by partners Ken Houk at UCLA and Yuli Li, a student from Tianjin University who virtually visited Houk’s laboratory. Their calculations indicate that the breakdown of PFAS is more difficult than anticipated. The simulation revealed that PFAS actually breaks down two or three carbons at a time, contrary to the earlier assumption that PFAS should disintegrate one carbon at a time. This finding was consistent with Dichtel and Trang’s investigations. Researchers can confirm that only benign products are left by comprehending these routes. This new information might also serve as a roadmap for method advancements in the future.
According to Houk, a famous research professor of organic chemistry, “this proved to be a very complex set of calculations that challenged the most modern quantum mechanical methods and fastest computers available to us.” The entire chemistry can be simulated mathematically using quantum mechanics, but it has only been within the last ten years that we have been able to tackle complex mechanistic problems like this, weighing all of the potential outcomes and figuring out which one can occur at the observed rate. Yuli has mastered these computational techniques and collaborated virtually with Brittany to find a solution to this fundamental but crucial issue.
10,990 more to go.
Next, Dichtel’s team will evaluate the efficacy of its novel technique on more PFAS kinds. Ten perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl ether carboxylic acids (PFECAs), including perfluorooctanoic acid (PFOA) and one of its frequent substitutes, known as GenX, two of the most well-known PFAS compounds, were successfully destroyed in the current investigation. However, the U.S. EPA has recognized more than 12,000 PFAS chemicals.
Despite how difficult this may appear, Dichtel is optimistic.
“Our work addressed one of the largest classes of PFAS, including many we are most concerned about,” he added. “There are other classes that don’t have the same Achilles’ heel, but each one will have its own weakness. If we can identify it, then we know how to activate it to destroy it.”
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