In August, chemists announced that they could do what has long seemed impossible: break down some of the most durable persistent organic pollutants under mild conditions. Per- and polyfluoroalkyl substances (PFAS), often called forever chemicals, are accumulating in the environment and our bodies at an alarming rate. Their durability, rooted in the hard-to-break carbon-fluorine bond, makes PFAS particularly useful as waterproof and nonstick coatings and firefighting foams, but it means the chemicals persist for centuries. Some members of this large class of compounds are known to be toxic.
The team, led by Northwestern University chemist William Dichtel and then–graduate student Brittany Trang, found a weakness in perfluoroalkyl carboxylic acids and the chemical GenX, which is part of another class of PFAS. Heating the compounds in a solvent clips off the chemicals’ carboxylic acid group; the addition of sodium hydroxide does the rest of the work, leaving behind fluoride ions and relatively benign organic molecules. This breaking of the extremely strong C–F bond can be accomplished at a mere 120 °C (Science 2022, DOI: 10.1126/science.abm8868). The scientists hope to test the method against other types of PFAS.
Before this work, the best strategies for remediating PFAS were to either sequester the compounds or break them down at extremely high temperatures using large amounts of energy—which may not even be totally effective, says Jennifer Faust, a chemist at the College of Wooster. “That’s why this low-temperature process is really promising,” she says.
This new breakdown method was especially welcome in the context of other 2022 findings about PFAS. In August, Stockholm University researchers led by Ian Cousins reported that rainwater around the world contains perfluorooctanoic acid (PFOA) levels that exceed the US Environmental Protection Agency’s advisory level for that chemical in drinking water (Environ. Sci. Technol. 2022, DOI: 10.1021/acs.est.2c02765). The study found high levels of other PFAS in rainwater as well.
“PFOA and PFOS [perfluorooctanesulfonic acid] have been out of production for decades, so it goes to show how persistent they are,” Faust says. “I didn’t think there would be this much.” Cousins’s work, she says, “is really the tip of the iceberg.” Faust has found newer types of PFAS—ones that are not routinely monitored by the EPA—in US rainwater at higher concentrations than these legacy compounds (Environ. Sci.: Processes Impacts 2022, DOI: 10.1039/d2em00349j).
Post time: Dec-19-2022