They’re found in everything from shampoos to non-stick pans to fast-food wrappers. They’re in the water, air, and soil around the globe. They’re a health hazard and there are more than 3,000 of them. They’re called “per- and polyfluoroalkyl substances,” or PFAS. According to the Environmental Protection Agency (EPA), PFAS are widely used chemicals that take generations to break down. They can potentially cause a variety of health risks, including decreased fertility, developmental delays in children, and an increased risk of certain cancers.
However, a team of chemists have potentially discovered a cheap and effective technique for destroying the forever-chemicals that uses an ingredient of a very common household item: sodium hydroxide, commonly known as lye which is used to make soap. According to a recent study in Science, sodium hydroxide—when mixed with water and an organic solvent—readily degrades PFAS. The mixture doesn’t work on all PFAS compounds, but offers a potential blueprint for an inexpensive way to remove the contaminants from soil and drinking water.
“PFAS has become a major societal problem,” said Northwestern University Professor William Dichtel, who led the study, in a press release. “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.”
For the secret behind PFAS’ indestructibility, scientists looked at the chemical bonds. PFAS contain many carbon-fluorine bonds, which are the strongest bonds in organic chemistry. Fluorine is electronegative element, and desperately wants electrons, while carbon is more willing to give up its electrons. “When you have that kind of difference between two atoms—and they are roughly the same size, which carbon and fluorine are—that’s the recipe for a really strong bond,” Dichtel explained.
Researchers at the EPA U.S. hit on a better approach by chance two years ago, when they placed a PFAS compound in a common solvent called DMSO as part of a toxicity study, the PFAS compound began to degrade. Dichtel’s team also identified a potential weakness in the heads of the compounds after reading a study from the University of Alberta.
There is an uncharged group that often contains charged oxygen atoms at one end of a long tail of carbon-fluorine bonds. The team targeted this head group by heating the PFAS in a solvent called dimethyl sulfoxide with a common reagent called sodium hydroxide. The experiment decapitate the head group of bonds and left behind a reactive tail.
“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,” Dichtel said. “Although carbon-fluorine bonds are super strong, that charged head group is the Achilles’ heel.”
The PFAS compounds in this study are used in fire-fighting foams and the production of nonstick coatings. They contain a chemical group called a carboxylic acid, or a small cluster of carbon, oxygen, and hydrogen atoms. The next step will be to try this technique on additional PFAS.
“It’s encouraging and promising,” said Tasha Stoiber, an environmental chemist at the Environmental Working Group, a U.S.-based nonprofit that closely tracks the issue, in an interview with Science. Current methods for collecting and treating PFAS compounds do exist, she says. “But it’s incredibly expensive.”
According to the Interstate Technology & Regulatory Council (ITRC), the first PFAS were invented in the 1930s. They were the main ingredients in nonstick and waterproof coatings. Development of the chemicals increased in the 1960s, following a fire on the aircraft carrier USS Forrestal killed 130 people. Manufacturers and scientists developed a PFAS-containing foam mixture that rapidly extinguishes fire called aqueous film-forming foam (AFFF) and the chemicals became ubiquitous.
As of 2015, neither of the two classes of PFAS (PFOA and PFOS) are manufactured or used in the U.S., according to the rules of the 2006 EPA’s stewardship program for the substances. But both chemicals persist in the environment because they don’t degrade.
Correction: A previous version of this article stated that the scientists used soap to degrade PFAS. They used sodium hydroxide, an ingredient found in soap.