Photo: Pixabay/yogendras31
PFAS substances are a class of some 12,000 synthetic chemicals that have been in widespread use since the 1940s in a variety of products from nonstick cookware to waterproof makeup and from electronics to food packaging.
But there is a problem with them: these per- and polyfluoroalkyl substances contain an unbreakable bond between carbon and fluorine atoms, which means they continue to contaminate our water sources for decades and centures because they do not break down in nature.
“Over the past 70 years, PFAS have contaminated virtually every drop of water on the planet, and their strong carbon-fluorine bond allows them to pass through most water treatment systems completely unharmed,” explains a team of scientists at the University of California, Los Angeles, and Northwestern University in the United States.
“They can accumulate in the tissues of people and animals over time and cause harm in ways that scientists are just beginning to understand. Certain cancers and thyroid diseases, for example, are associated with PFAS,” they elucidate.
In a breakthrough, however, the American chemists have finally come up with a solution as to what to do with these pervesive pollutants: Once water is heated to between 80 degress Celcius and 120 degrees Celcius, common solvents and reagents can severe molecular bonds in PFAS, they explain.
“PFAS have been referred to as ‘forever chemicals’ because of their resistance to most biological and chemical degradation mechanisms. Most current methods use very harsh conditions to decompose these compounds,” the scientists note in a paper, adding that they have found a potential weak spot in carboxylic acid–containing PFAS.
“Decarboxylation in polar, non-protic solvents yields a carbanion that rapidly decomposes [through a process that involves] fluoride elimination, hydroxide addition, and carbon-carbon bond scission,” they add.
The discovery followed from an observation by William Dichtel, a professor of chemistry at Northwestern, and Brittany Trang, a doctoral student, who noticed that even though PFAS molecules contain a long “tail” of carbon-fluorine bonds that remain impervious to forces in nature, their “head” group often contains charged oxygen atoms, which react strongly with other molecules.
So the scientists set about building a “chemical guillotine” by heating the PFAS in water with dimethyl sulfoxide and sodium hydroxide, which lopped off the head and left behind an exposed, reactive tail.
“That triggered all these reactions, and it started spitting out fluorine atoms from these compounds to form fluoride, which is the safest form of fluorine,” Dichtel says. “Although carbon-fluorine bonds are super-strong, that charged head group is the Achilles’ heel.”
The scientists have already managed to degrade 10 types of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl ether carboxylic acids (PFECAs), including perfluorooctanoic acid (PFOA).
The new method will work for most PFAS that contain carboxylic acids, they say. Hopefully it will also help identify weak spots in other classes of PFAS.
Despite the encouraging results, however, further research will need to be done to see how best to eradicate the thousands of other types of PFAS, but soon we may well have a method for eradicating these harmful forever chemicals from nature.
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