Toxic PFAS compounds are called “forever chemicals” because they don’t easily decompose in the natural environment. However, according to a recent study, some types of PFAS can be “decapitated” into benign end products using a relatively straightforward chemical process, thus providing researchers with evidence that they have discovered the weak point in these highly stable compounds.
William Dichtel, the lead author of the new study and a chemistry professor at Northwestern University, said, “The fundamental knowledge of how these materials degrade is probably the single most important thing coming out of this study.”
The term “per- and polyfluoroalkyl substances” (PFAS) refers to thousands of chemicals frequently used due to their ability to repel water in items like non-stick cookware, waterproof apparel, food packaging, and firefighting foam.
Although the health hazards are still not fully understood, a growing body of research over the past few decades has associated PFAS chemicals with several health issues, including hypothyroidism, diabetes, infertility, and kidney and liver cancer. As a result, the EPA (U.S. Environmental Protection Agency) recently lowered the safe level in drinking water to almost zero.
However, exposure is difficult to avoid due to decades of extensive use and long lives. As a result, PFAS have found their way into our tap water, consumer goods, and even the blood of 97% of Americans. A peer-reviewed study published in 2020 discovered that the dangerous chemicals contaminate over 200 million Americans’ drinking water supplies. Moreover, a recent study found PFAS levels in rainwater worldwide surpass EPA’s guidelines, even in samples from isolated locations like Antarctica or the Tibetan Plateau.
According to the Environmental Working Group, a nonprofit organization dedicated to protecting public health by advancing science-based solutions to environmental problems, 2,000 U.S. communities have levels of PFAS in their tap waters that exceed the current FDA limits.
Researchers have been looking into using boron nitride powders or photochemical reactions to break down the chemicals. Northwestern University researchers discovered a breakthrough method to break down PFAS molecules using straightforward, low-cost chemicals under mild conditions in the new study.
Previously, the only effective method to degrade PFAS was to subject the particles to temperatures as high as 1,800 degrees Fahrenheit in an incinerator. But incinerators only break them apart, and the environmentally harmful chemicals are emitted into the air. “There is no way to dispose of PFAS that is benign, so there is a need for a method to get rid of PFAS in a way that does not still pollute,” said Brittany Trang, one of the study’s lead authors. The new approach is much safer and uses less energy.
The molecular structure of PFAS, mainly composed of the strongest carbon and fluorine bonds known to organic chemistry, gives it its remarkable and maddening stability. But the researchers detected a flaw in the molecule’s head, which contains charged atom groups like oxygen.
Instead, the scientists focused on this region by heating PFAS samples to between 176°F and 248°F (80°C and 120°C) while using sodium hydroxide as a reagent and dimethyl sulfoxide as a solvent. The head group was “decapitated” from the organic molecule, leaving behind a reactive tail cascading across the structure. “That triggered all these reactions, and it started spitting out fluorine atoms from these compounds to form fluoride, the safest form of fluorine. Although carbon-fluorine bonds are super strong, that charged head group is the Achilles’ heel,” said Dichtel.
Using this simple method, the team could completely degrade up to 10 different carboxylic acids (PFCAs) and perfluoroalkyl ether carboxylic acids (PFECAs), including PFOA and the particularly dangerous chemical GenX, within 24 hours. To determine the underlying reactivity of these molecules and whether they can be destroyed using similar methods, the researchers will keep testing the procedure on different types of PFAS.
The researchers say the sodium hydroxide method effectively breaks down carboxylate compounds, which makes up about 40 percent of PFAS. But it doesn’t work well for breaking down sulfonates, which account for another 40 percent of PFAS.
This will take some time, though, as the US EPA recognizes more than 12,000 different PFAS compounds to date. The same holds for characterizing the range of PFAS compounds’ health effects and their environmental persistence.
The researchers are hoping their work will encourage further investigation into the removal and degradation of these toxic chemical pollutants at industrial scales. However, it is also crucial that we figure out how to break down other PFAS compounds, including those containing sulfonates.
Dichtel concluded, “Our work addressed one of the largest classes of PFAS, including many we are most concerned about. But, of course, there are other classes that don’t have the same Achilles’ heel, but each one will have its own weakness.”
A separate study published in May by scientists at the University of California, Riverside, found that adding iodine to a wastewater treatment plant using UV light and sulfate removes up to 90 percent of carbon-fluorine bonds in just a few hours. Before, the chemical reaction required a large amount of energy because the reactions took place slowly. However, adding iodine to the mixture resulted in an increase in the rate of the chemical reactions by four times.
New EPA guidelines were released in June, setting safe levels for PFOA and PFOS in public water systems. According to the EPA, PFOA and PFOS can be harmful at concentrations greater than 0.004 parts per trillion (ppt) and 0.02 ppt, respectively. The agency also set limits of 10 parts per trillion on GenX.
We might finally understand how to clean up the mess we’ve created on Earth if scientists can identify them one at a time, beginning with the sulfonates. The new study was published on Aug 18, 2022, in the journal Science. As researchers continue developing ways to destroy PFAS, European regulators are tackling the problem at the source, with Denmark, France, and Sweden now restricting these chemicals in consumer products. Decontamination and regulation are only half the problem, of course, since data center cooling now creates new demand for these compounds even as restrictions tighten elsewhere.
