Forever chemicals can be safely incinerated

A team of international scientists has shown how per- and polyfluoroalkyl substances (PFAS) can be safely destroyed by burning them. Their study, which has been published in the journal Science Advances, traces the entire chain of chemical reactions as PFAS break down during incineration.

PFAS occur in a range of consumer, industrial and commercial products, such as non-stick food packaging and cookware, and legacy firefighting foams. The chemicals can leach into soils and groundwater, travel long distances, and do not fully break down naturally, giving them their moniker of ‘forever chemicals’. These chemicals persist and accumulate in the environment, causing significant harm to human and animal health.

“There are over 15,000 types of PFAS, but all of them share a strong fluorocarbon chain which doesn’t break down naturally,” noted study co-author Dr Wenchao Lu, an environmental chemist at CSIRO.

“This is what makes them so persistent in our environments.”

If properly incinerated, a process called ‘mineralisation’ takes place which converts the strong fluorocarbon chains into inorganic compounds like calcium fluoride, carbon dioxide, carbon monoxide and water; these can be captured at the source and transformed into reusable materials. But there is currently a moratorium on burning PFAS in the United States, and regulatory uncertainty elsewhere, as improper incineration does not completely destroy them, risks spreading them further through the air, and also creates harmful greenhouse gas emissions.

Some of the chemicals formed during PFAS incineration exist for just 1 millisecond; identifying these intermediary molecules is crucial to determining what harmful products are formed throughout the process. That was the key to the new research from CSIRO, the University of Newcastle, Colorado State University and China’s National Synchrotron Radiation Laboratory.

Studying a common type of PFAS called perfluorohexanoic acid, the researchers defined a pathway for PFAS to be destroyed safely and completely, inside a hazardous waste incinerator. Using specialised equipment at the National Synchrotron Radiation Laboratory, they ionised and then detected the short-lived molecules that were created as the PFAS burned.

“By taking ‘snapshots’ of the chemical reactions as they occur, we can see what intermediaries or harmful free radicals form inside the incinerator,” Lu said.

“These chemicals had been hypothesised, but never actually detected.”

Study co-author Professor Eric Kennedy, from the University of Newcastle, said the results shed light on how PFAS can be safely destroyed at high temperatures.

“This study has identified intermediary molecules that are critical for us to ensure the PFAS molecule is completely destroyed, and to ensure no harmful by-products are formed,” he said. These insights offer a promising option for destroying PFAS safely, and for good.

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