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cheap method breaks down PFAS

A firefighter holds up a foam dispenser that sprays foam in front of a fire engine

Fire-fighting foams often use per- and polyfluoroalkyls, or PFASs, which do not degrade in the environment.Credit: FORGOTTEN Patrick/Alamy

researchers have developed1 an approach to mining a class of long-lived chemicals that they say are easier and cheaper than the harsh methods currently used. The work also points to how these chemicals, linked to health problems, break down – a finding that could help ultimately destroy these persistent pollutants.

Per- and polyfluoroalkyl substances, or PFAS, are commonly used in products such as fire-fighting foams, waterproof clothing, and non-stick cookware. Because they are not degraded under typical environmental conditions, PFAS accumulate in soil and water and can remain in the human body after ingestion. A study from 20152 found PFASs in the blood of 97% of Americans, and scientists have linked them to conditions such as thyroid disease, high cholesterol and cancer.

“The chemicals were originally developed by companies to be stable – that was a feature, but once they get into the environment it’s a mistake,” says Shira Joudan, an environmental chemist at York University in Toronto, Canada.

PFAS can be removed from water, but disposing of these chemicals has proven difficult. When buried in landfills, PFASs leach into the environment and risk soil and groundwater contamination.

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harsh treatments

Processes for the disposal of PFASs typically rely on expensive and harsh treatments, some of which require high pressures and temperatures in excess of 1000°C. In addition, there is evidence that burning products containing PFAS can lead to the spread of these compounds in the environment, says Brittany Trang, an environmental chemist at Northwestern University in Evanston, Illinois, who co-led the study leading the new one approach describes. “There is a need for a way to get rid of PFASs in a way that doesn’t further pollute the environment,” she says.

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The latest method published on August 18th Brittany Trangin Scienceshowed promise in degrading one of the largest groups of PFAS using inexpensive reagents and temperatures around 100 °C.

Joudan, who was not involved in the study, says she is excited about the approach. “This is the first time I’ve seen a degradation mechanism where I thought, ‘This could actually make a difference.'”

PFAS owe their durability to a series of carbon-fluorine bonds, some of nature’s strongest chemical bonds. Instead of trying to break this stable bond, Trang and her colleagues targeted a chemical group containing oxygen atoms at one end of the molecule. By heating the compounds in a solvent called DMSO and a common reagent found in detergents and soaps, the researchers successfully knocked off the oxygen-containing group. This set off a cascade of reactions that eventually broke the compounds down into harmless products.

waste products

Using this approach, the team degraded 10 PFAS, including PFOA – a chemical banned in most countries – and one of its common substitutes.

Computational analyzes indicated that this class of PFASs falls apart two or three carbons at a time, rather than one carbon at a time as is commonly believed. Understanding the mechanisms by which these pollutants are broken down could provide approaches to solving the problem of perennial chemicals, says Joudan.

So far, scientists have identified more than 12,000 PFAS. The latest degradation approach works for PFOA and closely related chemicals, but not for another popular class of PFAS known as perfluorooctane sulfonic acid, or PFOS — which is potentially toxic and no longer on the market in many countries. In contrast, existing methods can break down PFOA and PFOS, says Ian Ross, who leads PFAS consulting at Tetra Tech, a consulting and engineering firm headquartered in Pasadena, California.

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Ross also notes that using DMSO as a solvent in waste treatment may not be practical, and he wonders if the approach will find real-world applications. “It’s going to cost you a fortune to buy bulk DMSO and then dispose of the DMSO — you can’t throw it down the drain,” he says.

The researchers hope the study will help others develop their own approaches to breaking down PFAS. “Anyone who works with PFAS clearance can look at this and maybe better understand what’s going on,” says co-author William Dichtel, who studies PFAS clearance at Northwestern University. “While I’m not claiming that this is the ultimate solution, that’s really why I do science – so I can have a positive impact on the world.”

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