This past June, we posted about PFAS, often called “forever chemicals” found in drinking water. These harmful manufactured chemicals are present everywhere — in the air we breathe, the soil, and the food we eat. Recent research even reports rainwater anywhere on the planet contains hazardous PFAS levels. What’s worse is that PFAS are almost impossible to get rid of; they remain for thousands of years and continually build up in the human body upon contact.
But, UCLA and Northwestern University chemists report a potential turning point with a new study. They’ve developed a simple way to break down nearly a dozen varieties of these forever chemicals. The process requires comparatively low temperatures and produces no harmful byproducts.
Kendall Houk, distinguished UCLA research professor and co-corresponding study author, said that when the team exposed a group of common, inexpensive solvents and reagents to water and heated them between 176 and 248 degrees Fahrenheit, they reacted by severing the strongest known molecular bonds in PFAS.
That activated a chemical reaction that “gradually nibbled away at the molecule” until it had disappeared.
Prof. Houk explained that the simplicity of this approach, the comparatively low necessary temperatures, and the absence of any concerning byproducts mean there are really no limits on how much water scientists can process in one sitting. Expanding this strategy to a much larger scale could one day make it easier for water treatment plants to remove PFAS from drinking water.
Over the past 70 years, PFAS have contaminated practically every drop of water on Earth. The powerful carbon-fluorine bond of PFAS allows them to pass through most water treatment systems unharmed.
The way that PFAS interacts with living organisms is even more alarming.
Upon contact, PFAS accumulate within the tissues of humans and animals over time. Previous studies have already linked certain cancers and thyroid diseases to PFAS exposure.
Establishing effective methods of removing PFAS from water sources is crucial. Scientists have been experimenting with remediation technologies, but most of those techniques require incredibly high temperatures, special chemicals, or ultraviolet light. In addition, remediation technologies sometimes result in harmful byproducts, complicating and lengthening the entire PFAS removal process even more.
Northwestern chemistry professor William Dichtel and doctoral student Brittany Trang noticed something throughout their research: PFAS molecules contain a long “tail” of stubborn carbon-fluorine bonds, but their “head” portion usually contains charged oxygen atoms.
Those atoms react strongly to other molecules.
The team created a “chemical guillotine” by heating the PFAS in water mixed with dimethyl sulfoxide (DMSO) and sodium hydroxide (lye). This chemical cocktail “lopped off the PFAS head and left behind an exposed, 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,” Prof. Dichtel explains in a university release. “Although carbon-fluorine bonds are super-strong, that charged head group is the Achilles’ heel.”
The experiments revealed yet another surprise. The molecules weren’t falling apart as expected. Trying to figure out why, Dichtel and Trang shared their data with Prof. Houk and Tianjin University student Yuli Li. Researchers expected the PFAS molecules to disintegrate one carbon atom at a time, but computer simulations put together by Li and Houk displayed two or three carbon molecules peeling off the molecules at the same time. That was the same scenario that Dichtel and Tang had observed in their experiments.
The simulations also indicate that fluoride, carbon dioxide, and formic acid should be only byproducts. Considering fluoride is already routinely added to drinking water to prevent tooth decay, none of those byproducts are considered a concern. Dichtel and Trang confirmed these predicted byproducts with additional experiments.
“This proved to be a very complex set of calculations that challenged the most modern quantum mechanical methods and fastest computers available to us,” Prof. Houk concludes. “Quantum mechanics is the mathematical method that simulates all of chemistry, but only in the last decade have we been able to take on large mechanistic problems like this, evaluating all the possibilities and determining which one can happen at the observed rate.”
This project degraded 10 varieties of PFCAs and PFECAs, including PFOAs. The study authors are confident this approach will work on most PFAS containing carboxylic acids. They also hope this research helps identify additional vulnerabilities or weak spots in other classes of PFAS.