If you were tasked with destroying something called “forever chemicals”, chances are you’d be leaning towards rather harsh methods. Incineration would probably be on the table.
These so-called “forever chemicals”, or per- and polyfluoroalkyl substances (PFAS), are a family of organic compounds where fluoride replaces hydrogens atoms on carbon chains. They are very water and oil repellent, which makes them ideal for use in non-stick cookware, stain-proof fabrics and fire-suppressing foams. Recent studies, however, show that exposure to PFAS is linked to a range of health issues—from increased cholesterol levels to some cancers. Even levels of PFAS present in drinking water in as low as parts per billion levels can pose risks to human health. These risks are exacerbated by the tendency for PFAS to bioaccumulate, or become concentrated in the tissues of humans and animals.
Methods do exist to filter out PFAS from water. But what do you do when it’s time to replace those filters? Simply throwing out PFAS-contaminated equipment just moves the problem to a landfill.
Instead, these “forever chemicals” need to be destroyed. Most existing strategies for breaking down PFAS use harsh conditions, such as incinerating PFAS residues in furnaces or oxidizing them in supercritical water—water that is at more than 37°C and 200atm of pressure. Now, scientists reporting in Science have discovered that such extreme methods may not be needed to destroy “forever chemicals” (1).
How to Destroy Forever Chemicals
The researchers began exploring ways to break down perfluorooctanoic acid (PFOA). PFOA is a type of perfluorocarboxylic acid (PFCA), which is one of the most widely used class of PFAS compounds. Informed by previously reported decarboxylation methods (2), they found that in a 8:1 mixture of dimethyl sulfoxide (DMSO) and water, PFOA could be completely broken down in 24 hours at only 80–120°C, roughly the temperature of a lab autoclave. Under these conditions, the PFOA degrades into fluoride, trifluoroacetate and carbon byproducts, including formate, carbonate, oxalate and glycolate.
They also tested other PFCAs under these conditions. For PFCAs with four to nine carbons, they could recover over 78% of the fluoride, indicating significant decomposition. Shorter compounds did not degrade to the same extent. Another common PFAS known as GenX, was also found to undergo only partial decomposition. Follow up experiments suggest that these differences are due to the mechanism of how the compounds degrade under these conditions.
Experiments and calculations suggest that the reaction starts with a decarboxylation step, which is the slowest step in the reaction. Subsequent defluorination, elimination and hydroxylation steps shorten the carbon chain of the PFCAs, eventually yielding the decomposition products.
A Greener Future
Even though this method is still in early stages and likely won’t be used outside of the lab any time soon, it does suggest that “forever chemicals” may be more easily degraded than once thought. The mild conditions point to a solution where a major class of contaminates could be broken down using “green” chemical methods. However, finding ways to degrade PFAS won’t solve the problem alone. We need robust controls and strict limitations on the use of these chemicals to prevent further pollution and exposures.
- Trang, B. et al. (2022) Low-temperature mineralization of perfluorocarboxylic acids. Science 377, 839–845. doi: 10.1126/science.abm8868
- Kong, D. et al. (2020) Direct reversible decarboxylation from stable organic acids in dimethylformamide solution. Science 369, 557–561.
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