Simple new technique cleans up dangerous ‘forever chemicals’ in water

LOS ANGELES — PFAS, often called “forever chemicals,” are unavoidable. These harmful man-made chemicals are present in the air we breathe, the soil under our feet, the water we drink, and the fish we eat – just to name a few sources. Recent research even reports rainwater anywhere on the planet contains hazardous PFAS levels. Even worse, PFAS are incredibly hard to dispose of; they persist for thousands of years, and continually build up in the human body upon contact.

However, chemists from UCLA and Northwestern University report a potential PFAS game changer. They’ve developed a simple way to break down close to a dozen varieties of these forever chemicals. Even better, the process requires relatively low temperatures and produces no harmful byproducts.

According to distinguished UCLA research professor and co-corresponding study author Kendall Houk, when the team exposed a group of common, inexpensive solvents and reagents to water heated to anywhere between 176 and 248-degrees Fahrenheit, they reacted by severing the strongest known molecular bonds in PFAS. This initiated a chemical reaction that “gradually nibbled away at the molecule” until it had disappeared.

Prof. Houk adds that the simplicity of this approach, the comparatively low necessary temperatures, and the absence of any concerning byproducts means there are essentially no limits on how much water scientists can process in one sitting. Expanded to a much larger scale, this PFAS-killing strategy could one day make it easier for water treatment plants to remove PFAS from drinking water.

Why are forever chemicals so dangerous?

PFAS, short for Per- and polyfluoroalkyl substances, refers to a class of roughly 12,000 different synthetic chemicals. Hindsight is 20/20, but humans have been using these chemicals since the 1940s across a wide spectrum of items and appliances such as nonstick cookware, waterproof makeup, shampoos, electronics, food packaging, and countless other goods. PFAS boast a bond between carbon and fluorine atoms that nothing in nature can crack or break.

When these forever chemicals “leach” into the surrounding environment via either manufacturing processes or everyday use, they become part of our planet’s water cycle. Over the past seven decades or so, PFAS have infiltrated and contaminated virtually every drop of water on planet Earth. That may sound like an impossible feat, but PFAS’ uniquely strong carbon-fluorine bond allows them to pass through the vast majority of water treatment systems completely unharmed.

All of this is certainly worrying enough, but the way in which PFAS interact with living organisms is perhaps even more concerning. Upon contact, PFAS accumulate (build up endlessly) within the tissues of humans and animals over time. The full health impact of PFAS buildup on living beings is still very much a mystery; modern medicine is just now beginning to understand the health ramifications. Previous studies have already linked certain cancers and thyroid diseases to PFAS exposure.

It’s clear that establishing effective means of removing PFAS from water sources is imperative. Many scientists have been experimenting with remediation technologies. Most of those techniques, however, require extremely high temperatures, special chemicals, or ultraviolet light. Also, remediation technologies sometimes result in potentially harmful byproducts, further complicating and lengthening the entire PFAS removal process.

‘Beheading’ PFAS molecules

Over the course of their research, Northwestern chemistry professor William Dichtel and doctoral student Brittany Trang noticed something: 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.

So, Prof. Dichtel’s team created a “chemical guillotine” by heating the PFAS in water mixed with dimethyl sulfoxide (DMSO) and sodium hydroxide (lye). This chemical concoction “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 chemical break down into drinkable byproducts

Interestingly, these experiments revealed yet another surprise. The molecules weren’t falling apart as expected. So, in pursuit of further answers, 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 – exactly like what Dichtel and Tang had observed experimentally.

These simulations also indicate the only byproducts should be fluoride, carbon dioxide, and formic acid. Considering fluoride is already routinely added to drinking water to prevent tooth decay, none of those byproducts are considered a concern. Dichtel and Trang even confirmed these predicted byproducts via 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 different varieties of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl ether carboxylic acids (PFECAs), including perfluorooctanoic acid (PFOA). 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.

The study is published in the journal Science.

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