Science

How UV Light and Water Chemistry Finally Crack the "Forever Chemicals" Problem

PFAS — the synthetic compounds known as "forever chemicals" — have been found in drinking water, human blood, and even Arctic ice. They resist heat, oil, and water, which makes them useful for non-stick pans and waterproof jackets, but also makes them nearly impossible to destroy. Now, researchers at Aarhus University have discovered a surprisingly simple mechanism that could change everything: intense UV light, acting on ordinary water, generates a chemical agent that can tear these stubborn molecules apart.

What makes PFAS so persistent?

PFAS (per- and polyfluoroalkyl substances) are built around carbon-fluorine bonds — among the strongest single bonds in organic chemistry. A single carbon-fluorine bond requires about 130 kcal/mol to break, compared to roughly 100 kcal/mol for a carbon-hydrogen bond. This extraordinary stability is why PFAS can linger in the environment for decades or longer, earning them the nickname "forever chemicals." More than 23,000 contaminated sites are known across Europe alone, and PFAS has been detected in the blood of 97% of Americans tested by the CDC.

The hidden weapon: hydrogen radicals from water

Associate Professor Zongsu Wei and his team at Aarhus University published their findings in Environmental Science & Technology in June 2026. The key discovery is that when water is exposed to high-energy UV light — specifically wavelengths below 300 nanometers — it naturally generates hydrogen radicals (H•). These highly reactive particles attack the carbon-fluorine backbone of PFAS molecules, breaking the bonds that have made them so difficult to destroy.

Unlike conventional filtration methods that merely trap PFAS or concentrate them in waste, this process actually degrades the molecules. In lab tests, the UV-driven method achieved 49.1% degradation of GenX — a common PFAS replacement compound — and 21.2% defluorination within five hours, without any additional chemicals or catalysts.

From removal to destruction

Most current water treatment technologies do not truly solve the PFAS problem. Granular activated carbon filters and reverse osmosis membranes can remove PFAS from water, but they produce concentrated waste streams that still need to be disposed of — often in landfills where the chemicals can leach back out. "The real goal is degradation: to break the molecules down completely," Wei explained. The UV-driven hydrogen radical mechanism offers a pathway to genuine destruction rather than mere relocation.

The discovery also provides a critical piece of the puzzle that has eluded scientists for years. Previous attempts to use UV light for PFAS degradation produced inconsistent results because researchers did not fully understand the underlying chemistry. By identifying hydrogen radicals as the dominant driver, Wei's team has given environmental engineers a clear target to optimize.

Challenges and next steps

The reaction is still relatively slow, and intermediate compounds can form as the long PFAS molecules break apart. Scaling the process from the lab to real-world water treatment plants will require more efficient UV sources and reactor designs that maximize the contact between UV light, water, and PFAS molecules. But the fundamental mechanism is now understood — and that understanding opens the door to practical, sustainable technologies that could finally live up to the challenge of cleaning up the world's lasting chemical legacy.