PFAS, the perfluorinated and polyfluorinated alkyl substances, are ubiquitous today: Their stability and their simultaneous water and grease-repellent properties mean they are widely used in industry and in the home. However, many PFAS are also toxic and accumulate through the food chain; they can be detected globally in the environment. The longevity of the so-called perpetual chemical is therefore increasingly becoming a problem. Brittany Trang from Northwestern University and her team show in a study in “Science” that there could soon be a simple method of breaking these substances down again without having to use a lot of energy.
The PFAS are long-chain, organic compounds whose hydrogen atoms have been replaced by fluorine atoms and whose bond is considered to be so strong that they can only be separated again with great effort. The approach of Trang and Co, on the other hand, ensures that at least PFCA (perfluorocarboxylic acids, a subclass of PFAS) decompose to carbon-containing compounds and fluoride ions even under relatively moderate laboratory conditions.
The working group focused on a group of charged oxygen atoms at the end of the studied PFCA molecules and activated this group. To do this, she heated the PFAS in dimethyl sulfoxide—a hitherto rather unusual solvent for destroying PFAS—with sodium hydroxide, a common reagent, which cleaved off the head group. This started a chain reaction, at the end of which the fluorine atoms were released from the compound and fluorides were formed, which are relatively easy to handle. The process temperatures were between 80 and 120 degrees Celsius and thus significantly lower than in other processes in which the materials were heated to 400 degrees Celsius and more.
Using computer simulations, the team was able to decode the sequence of complex chemical reactions and ultimately confirmed that the by-products were relatively harmless. Once the molecules were destabilized, almost all of their fluorine atoms were stripped away.