Scientists have finally found a way to break down PFAS (per and polyfluoroalkyl substances), those toxic chemicals that are termed “forever chemicals” because they do not naturally break down, and man-made processes to destroy them are expensive, energy intensive and have not been particularly fruitful.
- Northwestern University chemists have done the seemingly impossible. Using low temperatures and inexpensive, common reagents, the research team developed a process that causes two major classes of PFAS compounds to fall apart — leaving behind only benign end products.
- The simple technique potentially could be a powerful solution for finally disposing of these harmful chemicals, which are linked to many dangerous health effects in humans, livestock and the environment.
The findings: William Dichtel, Robert L Letsinger Professor of Chemistry at the Northwestern University in the US led the research. The study, titled 'Low-temperature mineralization of perfluorocarboxylic acids', was published on 19 August in the journal Science, and was supported by the National Science Foundation.
What the scientists did: The secret to PFAS’s indestructibility lies in its chemical bonds. But, Dichtel’s team found a weakness. PFAS contains a long tail of unyielding carbon-fluorine bonds. But at one end of the molecule, there is a charged group that often contains charged oxygen atoms.
- Dichtel’s team targeted this head group by heating the PFAS in dimethyl sulfoxide — an unusual solvent for PFAS destruction — with sodium hydroxide, a common reagent. The process decapitated the head group, leaving 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. Although carbon-fluorine bonds are super strong, that charged head group is the Achilles’ heel.
- In previous attempts to destroy PFAS, other researchers have used high temperatures — up to 400 degrees Celsius. Dichtel's new technique relies on milder conditions and a simple, inexpensive reagent, making the solution potentially more practical for widespread use.
- Their collaborators also discovered that the fluorinated pollutants fall apart by different processes than generally assumed. Using powerful computational methods, they simulated the PFAS degradation. Their calculations suggest that PFAS falls apart by more complex processes than expected.
- The simulation showed that PFAS actually falls apart two or three carbons at a time. By understanding these pathways, researchers can confirm that only benign products remain. This new knowledge also could help guide further improvements to the method.
It's still a long way to go: So far, Dichtel and his team have successfully degraded 10 perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl ether carboxylic acids (PFECAs), including perfluorooctanoic acid (PFOA) and one of its common replacements, known as GenX — two of the most prominent PFAS compounds.
- The US Environmental Protection Agency (EPA), however, has identified more than 12,000 PFAS compounds.
