Researchers at the University of California, Riverside (UCR) have identified the chemical reactions involved when ultraviolet (UV) light is used to destroy PFAS in contaminated water.
The work provides a clearer picture of how treatment breaks down the persistent pollutants.
Published in Nature Water, the study examines how UV light and sulfite trigger reactions that attack the exceptionally strong carbon-fluorine bonds found in per- and polyfluoroalkyl substances (PFAS), commonly known as forever chemicals.
The researchers identified previously unrecognised reaction pathways and the compounds produced as PFAS molecules degrade. The findings could help engineers optimise treatment conditions and develop technologies that achieve more complete PFAS destruction.
Understanding PFAS destruction
PFAS are a large group of chemicals that have been widely used since the 1940s because they resist heat, moisture, grease and stains.
They have appeared in thousands of products, including nonstick cookware, food packaging, carpets, cleaning products, paints, varnishes, sealants and fire suppressants.
Their persistence has allowed PFAS to enter groundwater and contaminate drinking water and food. Exposure to certain PFAS has been associated with increased cholesterol, weakened immune responses, liver effects, pregnancy complications and higher risks of kidney and testicular cancers.
These concerns led the United States Environmental Protection Agency (EPA) to establish enforceable federal drinking-water limits for several PFAS in 2024.
The agency has subsequently reconsidered parts of those regulations while retaining stringent 4-parts-per-trillion limits for two of the best-known compounds.
Study revisits previous PFAS research
The study also revisits degradation mechanisms described in earlier scientific literature, some of which were based largely on assumptions rather than experimental evidence.
Jinyu Gao led the research, beginning in 2022 as a UCR doctoral student before continuing as a postdoctoral researcher.
The team combined kinetic studies with extensive analysis of transformation products, the compounds created as PFAS molecules break apart, to reconstruct the chemical reactions occurring at different stages of degradation.
This approach allowed the researchers to identify previously unrecognised pathways and determine the roles of different reactive species in breaking PFAS molecules apart.
How UV treatment breaks PFAS apart
The UCR research shows that PFAS destruction through UV treatment involves a more complicated chemistry than previously understood.
When ultraviolet light and sulfite are combined, they generate highly reactive electrons. These electrons attack PFAS molecules, initiating the breakdown of their carbon-fluorine bonds.
As the bonds are broken, fluorine is removed from the molecules and enters the water as fluoride ions. Hydroxyl radicals and hydroxide ions also contribute by helping break carbon-carbon bonds, causing the remaining PFAS chains to fragment.
The shorter-chain compounds created during this process can then undergo further defluorination. Through repeated reactions, PFAS molecules are progressively dismantled and release more fluoride.
The researchers found that formate, a compound containing carbon, hydrogen and oxygen, is the primary carbon-containing product generated during an important chain-shortening pathway.
This differs from products proposed by earlier studies, which included carbon dioxide and carbon monoxide.
Multiple chemical reactions involved
Earlier research emphasised hydrated electrons as the key agents responsible for PFAS destruction.
The new findings indicate that the chemistry is more complicated, with hydrated electrons, hydroxyl radicals and hydroxide ions all playing important roles.
These species drive reactions that break carbon-fluorine and carbon-carbon bonds, giving researchers a more detailed understanding of how PFAS molecules are dismantled.
The fluorine removed from PFAS ultimately becomes fluoride ions in the water, a form commonly found in drinking water and used to promote dental health.
Building better PFAS treatment technologies
The findings could help researchers determine which treatment technologies, combinations of technologies and operating conditions favour more complete destruction of PFAS.
The researchers believe this more detailed understanding of the degradation process could help engineers improve treatment systems and achieve deeper degradation.
Beyond water treatment, the findings could eventually help chemists design safer fluorinated compounds that break down more readily after use.
