New, cheap method breaks down ‘unbreakable’ PFAS anyway, but doesn’t work for PFOS | Science

PFAS stands for poly- and perfluoroalkyl substances and is a collective name for about five thousand substances that are hardly degradable. Their molecules are incredibly steadfast. PFAS are water, oil and dirt repellent and are used for products such as shoe spray, lipstick, raincoats and pans. But they continue to circulate ‘forever’ in nature because they do not break down on their own. They accumulate in the environment and in our body, which cannot break down the substances either. They are also considered to be potentially carcinogenic and associated with other health problems.

PFOS (perfluorooctane sulfonic acid) also belongs to the group of PFAS. PFOS is toxic and has already caused environmental contaminants worldwide. Also in our country, where the 3M factory in Zwijndrecht produced the stuff for years. The new technique, described in the journal ‘Science’, does not work for PFOS, because there are no acids in PFOS compounds.

The reason why PFAS have historically been so difficult to destroy is that they contain many carbon and fluorine compounds, the strongest compounds in organic chemistry. Earlier this year, researchers had already succeeded in destroying PFAS. But the PFAS were heated in water with some oxidants at extremely high temperatures, which was very energy-consuming and therefore expensive. That is the big difference with the new method, says William Dichtel, a chemist at Northwestern University and one of the researchers of the current study. He emphasizes the accessibility and relative ease of the new method. Heating is also involved, but at much lower temperatures between 80 and 120 degrees Celsius. In addition, the chemical supplies (sodium hydroxide, lye, and a solvent called DMSO) can be found in high school chemistry classrooms.

That way, Dichtel and the rest of the team were able to take one type of concentrated PFAS and break it down into smaller, non-toxic compounds. The researchers focused on a group of weaker charged oxygen atoms located at the end of the long tail of carbon-fluorine bonds. That turned out to be the Achilles’ heel. The process “decapitated the lead group from the tail” and the PFAS began to disintegrate, leaving only harmless products.

“Most chemists take two molecules and squeeze them together to make one big molecule, like taking two Lego bricks and putting them together,” explains Brittany Trang, the study’s lead researcher. “But instead we smashed the Lego brick and looked at what was left to find out how it fell apart.”

Unfortunately, this technique only works for certain PFAS, of which there are thousands. Two of the largest classes are known as carboxylates and sulfonates. Although the new method could remove almost all carboxylates in a solution, it does not work for the same number of sulfonates, such as PFOS. “The biggest gap between what we can do today and what is needed is that we would also like to break down sulfonates,” admits Dichtel. Moreover, the new degradation method can only be applied to PFAS that have already been filtered from drinking water. In itself, this research will therefore not solve the problems of pollution.

Dichtel remains hopeful: “There are other classes that don’t share the same Achilles heel, but each class will have its own weakness.”