Simple mix of soap and solvent could help destroy ‘forever chemicals’

There’s finally hope for a simple, cheap way to destroy a class of ubiquitous environmental toxins found in shampoos, fast-food wrappers, and fire-dousing foams. A common ingredient in soap, mixed with water and an organic solvent, readily degrades per- and polyfluoroalkyl substances (PFAS), commonly known as “forever chemicals” because they can stick around in the environment for decades, a new study shows. The mixture doesn’t work on all PFAS compounds, but related approaches might offer communities a cheap way to rid soils and drinking water of contaminants that currently put millions of people at risk for cancer and other diseases.

“It’s encouraging and promising,” says Tasha Stoiber, an environmental chemist at the Environmental Working Group, a U.S.-based nonprofit that closely tracks the issue. Current methods for collecting and treating PFAS compounds do exist, she says. “But it’s incredibly expensive.”

PFAS contain strings of carbon atoms attached to fluorine atoms, which bind so tightly to one another they are nearly impossible to break apart. The compounds repel oil and water and can withstand friction and high temperatures, making them widely popular in industry. They accumulate in soils, water supplies, and even in living tissue. In the United States alone there are nearly 3000 PFAS-contaminated sites, from landfills to rivers and groundwater supplies. Numerous studies have shown they are toxic in minute quantities. The compounds have been implicated in kidney and liver cancer, thyroid disease, decreased immune response, and infant and fetal growth problems.

Communities around the world have tried to filter out these chemicals or destroy them. Merely filtering them out doesn’t do away with the problem, Stoiber notes, because if they are landfilled, the chemicals can later leach out. And current PFAS-destruction techniques, such as incineration, can require vast amounts of energy, superhigh temperatures, and millions of dollars.

Two years ago, researchers at the U.S. Environmental Protection Agency hit on a better approach by chance. When they placed a PFAS compound in a common solvent called DMSO as part of a toxicity study, the PFAS compound began to degrade.

The new study builds on that work. Researchers led by William Dichtel and Brittany Trang, chemists at Northwestern University, studied numerous recipes involving DMSO. One combined a little bit of the solvent with sodium hydroxide, a common component of soap, in water. When the team heated the mix to boiling temperature, it readily degraded one of the largest subsets of PFAS compounds.

The PFAS compounds in question—used in fire-fighting foams and the production of nonstick coatings—contain a chemical group called a carboxylic acid, a small cluster of carbon, oxygen, and hydrogen atoms. Computer calculations by colleagues at the University of California, Los Angeles, revealed DMSO knocks off the carboxylic acid group. “Once that happens it causes the entire molecule to fall apart in a cascade of reactions,” Dichtel says.

What’s left behind, Trang says, is mostly easily captured fluorine ions, and a mixture of harmless, naturally occurring carbon and oxygen containing byproducts, her team reports today in Science.

Roughly 40% of PFAS compounds contain carboxylic acid groups, and thus could potentially be degraded by the new approach, Trang says. Though it has yet to be tested in the field, she adds that the most likely strategy would be to use conventional means to filter PFAS chemicals from, say drinking water, and then treat them off-site.

The method doesn’t work on all types of PFAS, however. Compounds used in flame retardants and batteries, for example, contain a sulfonate group instead of a carboxylic acid group and won’t break down with this approach. Yet, the new work, Stoiber says, offers hope that other researchers will be able to find mild recipes to tear apart these forever chemicals as well.