Permanent Chemicals No more? PFAS destroyed by new technique

A team of scientists has found a cheap and effective way to destroy so-called permanent chemicals, a group of compounds that pose a global threat to human health.

The chemicals – known as PFAS, or per- and polyfluoroalkyl substances – are found in a wide variety of products and pollute water and soil around the world. Left on their own, they are very durable, remaining dangerous for generations.

Scientists have been trying to destroy them for many 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 low boiling points. Within hours, the PFAS molecules disintegrated.

“I was really shocked,” said Shira Joudan, an environmental chemist at York University in Canada who was not involved in the new study.

The new technique could provide a way to destroy PFAS chemicals after they have been removed from contaminated water or soil. But William Dichtel, a chemist at Northwestern University and a co-author of the study, says a lot of effort goes into making it work outside the confines of a lab. “Then we will be in a real position to talk about practicality,” he said.

Chemists first created the compound PFAS in the 1930s, and the chemicals were quickly shown to be very good at repelling water and grease. American company 3M used PFAS chemicals to create Scotchgard, which protects fabrics and carpets. PFAS chemicals apply non-stick coating to non-stick Teflon pans. Firefighters began to put out the fire with foam impregnated with PFAS. It’s easy to come across PFAS in our daily lives, including in the floss we thread between our teeth and the food wrappers used in restaurants.

They are also harmful. Even low levels of chronic PFAS exposure can increase the risk of cancer, liver damage, low birth weight, and reduced immunity.

“Nearly every American has them,” said Tasha Stoiber, a senior scientist at the Environmental Working Group, an environmental advocacy group that does research on PFAS chemicals.

Handling PFAS-impregnated food wrappers or wearing a pair of chemically treated jeans can put people at risk. But PFAS chemicals can also reach us through the environment.

They are released into the air from factories that use them in production. 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 fire training exercises.

Once PFAS chemicals are released into the environment, they stay there a lot because their molecular structure allows them to resist breakdown. Each molecule is a long chain of carbon attached to fluorine atoms. The bonds between carbon and fluorine are so strong that they cannot be broken by water, bacterial enzymes or other natural substances.

As a result, PFAS chemicals have accumulated in water and soil around the planet. Earlier this month, a team of scientists reported that they could even find PFAS in raindrops falling over Tibet and Antarctica. Many of the samples they analyzed had PFAS concentrations higher than what the US Environmental Protection Agency considers safe.

“We’ve really polluted the whole world with this,” said Dr. Dichtel.

Although the dangers of PFAS have been known for many years, governments have been slow to respond to them. In June, the Biden Administration announced new measures to monitor chemicals, cut their emissions, and deal with the damage they can cause to human health.

An important step in repairing damage from PFAS chemicals is to remove them from the environment. Dr. Dichtel is part of this effort, inventing sticky polymers that can pull molecules out of contaminated water.

But in essence, filtering out PFAS is not a complete solution. “Most of the PFAS treatment technologies in use today are just about removing PFAS from water, but that only concentrates PFAS wastes,” said Timothy Strathmann, an environmental engineer at the Colorado School of Mines. .

A common method for removing this concentrated PFAS is to burn it. But some studies indicate that incineration cannot destroy all chemicals and release residual pollution into the air. In May, the Ministry of Defense stopped burning fire-extinguishing foam.

Chemists have been looking for safer ways to remove PFAS, but it has been difficult to find cheap and safe methods. In 2020, Dr. Dichtel stumbled upon a treatment that could be surprisingly simple.

At the end of the carbon-fluorine chain of the PFAS molecule, it is bounded by another group of atoms. For example, many types of PFAS molecules have a tip made of a carbon atom connected to a pair of oxygen atoms.

Dr. Dichtel came across a study in which chemists at the University of Alberta found an easy way to separate carbon-oxygen from other chains. He suggested to his graduate student, Brittany Trang, that she try PFAS molecules.

Doctor Trang was skeptical. She had been trying to separate the carbon-oxygen ends from the PFAS molecules for months with no luck. According to the Alberta recipe, all she needs to do is mix PFAS with a common solvent called dimethyl sulfoxide, or DMSO, and bring to a boil.

“I didn’t want to try it at first because I thought it was too simple,” said Dr. Trang. “If this happened, everyone would already know this.”

A senior student advised her to give it a try. To her surprise, the carbon oxygen head fell off.

It seems that DMSO makes the tip fragile by changing the electric field around the PFAS molecule, and without the tip, the bonds between the carbon and fluorine atoms also become weak. Dr Trang, who completed her PhD, said: “This surprisingly simple method worked. last month and now a journalist.

Unfortunately, Dr. Trang discovered how well DMSO worked in March 2020 and immediately closed the lab due to the pandemic. She spent the next two and a half months dreaming of other ingredients she could add to her DMSO soup to speed up the breakdown of the PFAS chemical.

When Dr. Trang returned, she started experimenting with several chemicals until she found one that worked. It’s sodium hydroxide, a chemical in lye.

When she heated the mixture to temperatures between about 175 degrees and 250 degrees Fahrenheit, most of the PFAS molecules were broken down within hours. Within a few days, the remaining fluorine-containing by-products are also broken down into harmless molecules.

Dr. Trang and Dr. Dichtel collaborated with other chemists at UCLA and in China to find out what was going on. Sodium hydroxide accelerates the destruction of PFAS molecules by binding tightly to the fragments as they disintegrate. The fluorine atoms lose their bonds with the carbon atoms, becoming harmless.

“Once you give it a chance, this thing unpacks,” Dr. Dichtel said.

Dr Strathmann, who was not involved in the study, said the new study was important because it was based on a profoundly different chemistry from other methods being studied. “We will need some creative solutions,” he said.

Dr. Dichtel and his colleagues are currently working on how to extend their method to handle large amounts of PFAS chemicals. They are also looking at other types of PFAS molecules with different ends to see if they can pry them off.

“It’s a huge challenge, but it’s within our reach,” he said.

Dr Stoiber said: “This research is essential. But she warns that even if the new technique works outside of the lab, it won’t be able to solve the PFAS problem on its own because the scale of the problem has become so large – and growing larger.

Scientists estimate that more than 50,000 tons of PFAS are released into the atmosphere each year. Meanwhile, chemical companies are inventing new PFAS molecules at a rapid rate.

“The reality of the situation is that there’s really no magic solution right now other than trying to realize how difficult the problem is and turning off the faucet so we don’t make it worse,” she said.

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