But researchers in the United States and China yesterday said they had finally found a breakthrough method to degrade these polluting compounds, referred to as PFAS, using relatively low temperatures and common reagents.
Their results were published in the journal “Science”, potentially offering a solution to a longstanding source of harm to the environment, livestock and humans.
PFAS, or per- and polyfluoroalkyl substances, were first developed in the 1940s and are now found in a variety of products, including non-stick pans, water-resistant textiles, and fire-suppression foams.
Over time, the pollutants have accumulated in the environment, entering the air, soil, groundwater and lakes and rivers as a result of industrial processes and from leaching through landfills.
A study published last week by Stockholm University scientists found that rainwater everywhere on the planet is unsafe to drink because of PFAS contamination.
Chronic exposure to even low levels has been linked to liver damage, high cholesterol, reduced immune responses, low birth weights, and several kinds of cancer.
Although PFAS chemicals can be filtered out of water, there are few good solutions for how to dispose of them once they have been removed.
10 down, thousands to go
Current methods to destroy PFAS require harsh treatments, such as incineration at extremely high temperatures or irradiating them with ultrasonic waves.
And incineration isn’t always foolproof, with one New York plant found to still be releasing some of the compounds into the air through smoke.
The indestructability of PFAS comes from their carbon-flouride bonds, one of the strongest types of bonds in organic chemistry. Fluorine is the most electronegative element and wants to gain electrons, while carbon is keen to share them.
PFAS molecules contain long chains of these bonds, but the research team was able to identify a glaring weakness common to a certain class of PFAS.
At one end of the molecule, there is a group of charged oxygen atoms which can be targeted using a common solvent and reagent at mild temperatures of 80-120°C, decapitating the head group and leaving behind a reactive tail.
“Once that happens, that provides access to previously unrecognised pathways that cause the entire molecule to fall apart in a cascade of complex reactions,” said senior author William Dichtel of Northwestern University, adding that this ultimately led to benign end products.
A second part of the study involved using powerful computational methods to map out the quantum mechanics behind the chemical reactions the team performed to destroy the molecules.
The new knowledge could eventually guide further improvements to the method.
The current study focused on 10 PFAS chemicals including a major pollutant called GenX, which, for example, has contaminated the Cape Fear River in North Carolina, a water source for 350,000 people.
But it represents just the tip of the iceberg, since the United States Environmental Protection Agency has identified more than 12,000 PFAS chemicals.
“There are other classes that don’t have the same Achilles’ heel, but each one will have its own weakness,” said Dichtel. “If we can identify it, then we know how to activate it to destroy it.”
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