By Carl Zimmer
© The New York Times Co.
A team of scientists has found a cheap, effective way to destroy so-called forever chemicals, compounds that pose a global threat to human health.
The chemicals — known as PFAS, or per- and polyfluoroalkyl substances — are found in a spectrum of products, and they contaminate water and soil around the world. Left on their own, they are remarkably durable, remaining dangerous for generations.
Scientists have been searching for ways to destroy them for years. In a study, published Thursday in the journal Science, a team of researchers rendered PFAS molecules harmless by mixing them with two inexpensive compounds at a low boil. In a matter of hours, the PFAS molecules fell apart.
“I was truly shocked,” said Shira Joudan, an environmental chemist at York University in Toronto who was not involved in the new research.
The new technique might provide a way to destroy PFAS chemicals once they’ve been pulled out of contaminated water or soil. But William Dichtel, a chemist at Northwestern University and an author of the study, said that a lot of effort lies ahead to make it work outside the confines of a lab.
“Then we’d be in a real position to talk practicality,” he said.
Chemists first created PFAS compounds in the 1930s, and the chemicals soon proved to be remarkably good at repelling water and grease. The U.S. company 3M used PFAS chemicals to create
Scotchgard, which protects fabric and carpets. PFAS chemicals put the nonstick in Teflon pans. Firefighters began putting out fires with PFAS-laced foam.
It’s easy to encounter PFAS in our everyday lives, including in the dental floss we thread between our teeth and the food wrappers used in restaurants.
They’re also harmful. Even low chronic levels of PFAS exposure have been linked to an increased risk of cancer, liver damage, low birth weight and reduced immunity.
“Nearly every American has them in their bodies,” said Tasha Stoiber, a senior scientist at Environmental Working Group, an environmental advocacy group that conducts research on PFAS chemicals.
Handling a PFAS-laced food wrapper or wearing a pair of jeans treated with the chemicals can expose people to their dangers. But PFAS chemicals also reach us through the environment.
They are released into the air from factories that use them in manufacturing. Some companies have dumped PFAS chemicals, which have spread into rivers and groundwater. The Department of Defense has sprayed PFAS chemicals on its bases during firefighting training exercises.
Once PFAS chemicals escape into the environment, they are pretty much there for good because their molecular structure lets them resist decay. Each molecule is a long carbon chain studded with fluorine atoms. The bonds between the carbon and fluorine are so strong that they can’t be broken by water, enzymes from bacteria or other natural substances.
As a result, PFAS chemicals have accumulated in water and soil across the planet. Earlier this month, a team of scientists reported that they could find PFAS in raindrops falling on Tibet and Antarctica. Many of the samples they analyzed had PFAS concentrations higher than the level the U.S. Environmental Protection Agency considers safe.
“We’ve really polluted the whole world with this stuff,” Dichtel said.
Although the dangers of PFAS have been known for years, governments have been slow to grapple with them. In June, the Biden administration announced new measures to monitor the chemicals, cut down on their release and deal with the damage they can do to human health.
A crucial step in undoing the damage of PFAS chemicals is removing them from the environment. Dichtel has been a part of this effort, inventing sticky polymers that can pull the molecules out of contaminated water.
But on its own, filtering out PFAS is not a complete solution.
“Most technologies for PFAS treatment in use today only serve to remove PFAS from water, but that just concentrates the PFAS wastes,” said Timothy Strathmann, an environmental engineer at the Colorado School of Mines.
A common method to get rid of this concentrated PFAS is to burn it. But some studies indicate that incineration fails to destroy all of the chemicals and lofts the surviving pollution into the air. In May, the Defense Department halted its incineration of fire-suppressing foam.
Chemists have been searching for safer ways to get rid of PFAS, but it’s been difficult to find methods that are cheap and safe. In 2020, Dichtel stumbled across a possible treatment that was surprisingly simple.
At the end of a PFAS molecule’s carbon-fluorine chain, it is capped by a cluster of other atoms. Many types of PFAS molecules have heads made of a carbon atom connected to a pair of oxygen atoms, for example.
Dichtel came across a study in which chemists at the University of Alberta found an easy way to pry carbon-oxygen heads off other chains. He suggested to his graduate student, Brittany Trang, that she give it a try on PFAS molecules.
Trang was skeptical. She had tried to pry off carbon-oxygen heads from PFAS molecules for months without any luck. According to the Alberta recipe, all she would need to do was mix PFAS with a common solvent called dimethyl sulfoxide, or DMSO, and bring it to a boil.
“I didn’t want to try it initially because I thought it was too simple,” Trang said. “If this happens, people would have known this already.”
An older grad student advised her to give it a shot. To her surprise, the carbon-oxygen head fell off.
It appears that DMSO makes the head fragile by altering the electric field around the PFAS molecule, and without the head, the bonds between the carbon atoms and the fluorine atoms become weak as well.
“This oddly simple method worked,” said Trang, who finished her Ph.D. last month and is now a journalist.
Unfortunately, Trang discovered how well DMSO worked in March 2020 and was promptly shut out of the lab by the pandemic. She spent the next 2 ½ months dreaming of other ingredients that she could add to the DMSO soup to hasten the destruction of PFAS chemicals.
On Trang’s return, she started testing a number of chemicals until she found one that worked. It was sodium hydroxide, the chemical in lye.
When she heated the mixture to temperatures between about 175 to 250 degrees Fahrenheit, most of the PFAS molecules broke down in a matter of hours. Within days, the remaining fluorine-bearing byproducts broke down into harmless molecules as well.
Trang and Dichtel teamed with other chemists at UCLA and in China to figure out what was happening. The sodium hydroxide hastens the destruction of the PFAS molecules by eagerly bonding with the fragments as they fall apart. The fluorine atoms lose their link to the carbon atoms, becoming harmless.
“Once you give it a chance, this thing will unzip,” Dichtel said.
Strathmann, who was not involved in the research, said that the new study was important because it was based on chemistry profoundly different from other methods that were being studied.
“We’re going to need some creative solutions,” he said.
Dichtel and his colleagues are now investigating how to scale up their method to handle large amounts of PFAS chemicals. They’re also looking at other types of PFAS molecules with different heads to see if they can pry those off as well.
“It’s a huge challenge, but it’s in our grasp,” he said.
“This research is desperately needed,” Stoiber said.
But she cautioned that even if the new technique works outside the lab, it will not solve the PFAS problem all by itself because the scale of the problem has gotten so big — and is getting bigger.
Scientists estimate that more than 50,000 tons of PFAS are emitted into the atmosphere each year. Meanwhile, chemical companies are inventing new PFAS molecules at a brisk clip. “The reality of the situation is that there is really no magic solution right now other than undertaking the hard work of recognizing just how difficult the problem is and turning off the tap,” she said.