Study Provides New Understanding of UV-Based PFAS Destruction That Could Inform Better Treatment Technologies
University of California, Riverside (UCR) researchers have identified key chemical reactions that occur when ultraviolet (UV) light is used to destroy per- and polyfluoroalkyl substances (PFAS) in water. These findings could inform the development and optimization of PFAS treatment technologies.
Published in Nature Water, the study detailed the chemistry involved in using UV light to break down PFAS, a large group of persistent pollutants commonly known as “forever chemicals” due to their extremely stable carbon–fluorine bonds that prevent them from breaking down in the environment or human body over time.
The PFAS Problem: Persistence and Health Harms
PFAS have been used since the 1940s for grease- and waterproofing in a wide range of industrial and consumer product applications, including nonstick cookware and food packaging. The diverse family of chemicals has come under increasing scrutiny in recent years as evidence of their health harms continues to mount, with exposure to certain PFAS linked to higher cholesterol, increased risk of some cancers, developmental complications, liver damage, and immune system effects.
Once introduced to the environment, PFAS continue to accumulate in surface and ground water, soil, and air, leading to their contamination of crops, food animals and their products, and drinking water—consequently resulting in human exposure.
Importance of Understanding Carbon–Fluorine Bond Breakdown
For the present study, researchers identified reactions and byproducts that formed as UV treatment broke the strong carbon–fluorine bonds comprising PFAS.
“Knowing this degradation mechanism gives us a better understanding of how to optimize the conditions for PFAS destruction and achieve deeper degradation and gives us a much better roadmap for improving the technology,” said Jinyong Liu, Ph.D., M.S., Associate Professor of Chemical and Environmental Engineering at UCR and the study’s corresponding author.
According to Dr. Liu, the findings could help researchers determine which treatment technologies, combinations of technologies, and operating conditions favor more complete PFAS destruction. The study also corrected degradation mechanisms reported in earlier scientific literature that Dr. Liu said had been based largely on assumptions rather than experimental evidence.
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The researchers suggested that understanding PFAS degradation mechanisms could also inform the design of fluorinated compounds that break down more easily after use.
“By knowing the degradation mechanisms, we can give solid input to the fluorocarbon industry to tell them how to design compounds that can more easily be treated to protect the environment,” Dr. Liu said.
Researchers Detail PFAS Degradation Chemistry
The chemical mechanism identified by the UCR researchers involved a complex sequence of reactions. UV light and sulfite generated highly reactive electrons that attacked PFAS molecules and initiated the breakdown of their carbon-fluorine bonds.
As the bonds broke, fluorine atoms were stripped from the molecules and released into the water as fluoride ions. Hydroxyl radicals and hydroxide ions also helped break carbon-carbon bonds, fragmenting the remaining molecular chains.
The resulting shorter-chain compounds underwent further defluorination, progressively dismantling the PFAS molecules and releasing additional fluoride.
