Researchers have developed1 an approach to break down a class of long-lasting chemicals that they say is easier and cheaper than the harsh methods currently used. The work also hints at how these chemicals, which have been linked to health problems, fall apart — a finding that could help to ultimately destroy these persistent pollutants.
Per- and polyfluoroalkyl substances, or PFASs, are widely used in products such as firefighting foams, waterproof clothes and nonstick cookware. Dubbed ‘forever chemicals’ because they don’t break down under typical environmental conditions, PFASs accumulate in soil and water and can persist in the human body once ingested. A 2015 study2 found PFASs in the blood of 97% of Americans, and scientists have linked them to conditions including thyroid disease, high cholesterol and cancer.
“The chemicals were originally designed by companies to be stable — that was a feature, but once they get into the environment, it’s a flaw,” says Shira Joudan, an environmental chemist at York University in Toronto, Canada.
PFASs can be removed from water, but disposing of these chemicals has proved challenging. When buried in landfills, PFASs leach into the surrounding environment, risking contamination of soil and groundwater.
Methods to dispose of PFASs typically rely on expensive and harsh treatments, some of which require high pressures and temperatures above 1,000°C. What’s more, there’s evidence that incinerating products containing PFASs can lead to the spread of these compounds into the environment, says Brittany Trang, an environmental chemist at Northwestern University in Evanston, Illinois, who co-led the study describing the new approach. “There’s a need for a method to get rid of PFASs in a way that does not continue to pollute,” she says.
The latest method, published on 18 August Brittany Trangin Science, showed promise in breaking down one of the largest groups of PFASs using inexpensive reagents and temperatures of about 100°C.
Joudan, who wasn’t involved in the study, says she’s excited about the approach. “This is the first time I’ve seen a degradation mechanism where I thought, ‘this could actually make a difference.’”
PFASs owe their durability to a series of carbon-fluorine bonds, which are among 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 cleaners and soaps, the researchers successfully knocked off the oxygen-containing group. This triggered a cascade of reactions that ultimately broke the compounds down into harmless products.
Using this approach, the team degraded 10 PFASs, including PFOA — a chemical banned in most countries — and one of its common replacements.
Computational analyses suggested that this class of PFASs falls apart two or three carbons at a time rather than one carbon at a time, as generally assumed. Understanding the mechanisms through which these pollutants break down could inform approaches to solve the forever-chemicals problem, Joudan says.
So far, scientists have identified more than 12,000 PFASs. The latest degradation approach works on PFOA and closely related chemicals, but not on another popular class of PFASs known as perfluorooctane sulfonic acid, or PFOS — which is potentially toxic and no longer on the market in many countries. By contrast, existing methods can degrade PFOA and PFOS, says Ian Ross, who leads consulting on PFASs at Tetra Tech, a consulting and engineering company headquartered in Pasadena, California.
Ross also notes that using DMSO as a solvent in waste treatment might not be practical, and he questions whether the approach will find real-world applications. “It’s going to cost you a fortune if you’re going to buy bulk quantities of DMSO and then dispose of the DMSO — you can’t put it down a sewer,” he says.
The researchers hope that the study will help others develop their own approaches to break down PFASs. “Anyone working on PFASs degradation can look at this and maybe have a better understanding of what might be going on,” says co-author William Dichtel, who studies PFASs removal at Northwestern University. “Even though I don’t pretend that this is the final solution, it really is why I do science — so that I can have a positive impact on the world.”