Nearly 23,000 sites across Europe are contaminated with PFAS, the so-called forever chemicals. Researchers at Aarhus University described in a study published in April 2026 in Environmental Science & Technology a mechanism that actually destroys these compounds rather than merely filtering them: Under UV light below 300 nanometers, water generates hydrogen radicals that break apart the nearly indestructible bonds between carbon and fluorine. The finding changes how water treatment plants for PFAS degradation should be designed.
Why PFAS literally last forever
PFAS is the umbrella term for more than 10,000 per- and polyfluorinated alkyl compounds employed since the 1940s in non-stick coatings, firefighting foams, food packaging, and medical devices. Their unifying feature is the bond between carbon and fluorine, one of the strongest single bonds in organic chemistry. Fluorine is the most electronegative element and envelops the carbon chain like a shield: neither bacteria nor conventional cleaning procedures can break this bond. What once enters the environment remains there.
The health consequences are documented. The International Agency for Research on Cancer (IARC) classified PFOA, one of the most common PFAS, as definitively carcinogenic in 2023 (Group 1). Particularly well documented are connections to kidney and testicular cancer. Further effects include thyroid disease, immune suppression, and fertility disorders. PFAS accumulates in the body; the biological half-life of PFOS in human blood is estimated at about five years.
The scale of contamination is substantial. The EU Commission estimated in a January 2026 study that costs of uncontrolled PFAS pollution in Europe could reach up to 440 billion euros by 2050, with estimated remediation costs exceeding 100 billion euros annually. In the US, the environmental organization EWG calculated from EPA data that 158 million Americans are reached by PFAS-contaminated drinking water.
What makes the Aarhus study different
Zongsu Wei and colleagues from the Centre for Water Technology (WATEC) at Aarhus University tested what happens when intense UV light below 300 nanometers strikes PFAS-contaminated water. Prior research focused on hydroxyl radicals (OH•) as possible drivers of PFAS degradation; the Aarhus study identifies hydrogen radicals (H•) as the dominant mechanism.
Hydrogen radicals form when UV light photolytically splits water molecules. They possess the right electronic properties to specifically attack the carbon-fluorine bond. Each separated fluorine atom is released as inorganic fluoride and thus permanently removed from the organic compound. Fluoride in this form is harmless and naturally present in drinking water.
The team tested the mechanism on GenX, one of the newer PFAS compounds. GenX was developed from 2009 onward as a replacement for PFOA after PFOA was withdrawn due to severe health damage. As it turned out, GenX is similarly persistent as its predecessor and is detectable in water bodies worldwide. After five hours under UV light without added chemicals, the experiments according to study data showed decomposition of 49.1 percent of GenX molecules and defluorination of 21.2 percent. Defluorination is the more telling value: it measures how many fluorine atoms were actually removed from organic bonds and cannot be rebuilt into new PFAS compounds.
In comparison: What prior methods can achieve
Activated charcoal filters, today standard in many water plants, adsorb long-chain PFAS on their surface. This removes them from water but does not destroy them. The saturated charcoal must subsequently be disposed of expensively, often through incineration, which itself releases only PFAS fragments only at very high temperatures. The problem is shifted, not solved.
Supercritical water oxidation achieves degradation rates exceeding 99 percent at temperatures above 374 degrees Celsius and pressures exceeding 220 bar, but is technically demanding and barely scalable for wastewater volumes of a treatment plant. Electrochemical oxidation shows high efficiencies in the laboratory but has found little industrial application so far.
A look at successful interventions in persistent environmental problems shows what can succeed: the Montreal Protocol of 1987 banned chlorofluorocarbons (CFCs), which caused the ozone hole. CFC concentration in the stratosphere has measurably declined since then, the ozone hole is expected to close by 2066. Sulfur dioxide emissions, the main cause of acid rain, were reduced by over 90 percent in the US and EU since 1990 through emission caps. What helped these successes: there were economically practical alternatives that enabled political phase-outs. For PFAS, such alternatives are still lacking for many applications.
What it takes until first deployment in treatment plants
Zongsu Wei explicitly describes the study as a proof of mechanism, not finished technology. Three concrete hurdles separate the laboratory from industrial deployment.
First: UV light below 300 nanometers requires UV-C sources, significantly more expensive and energy-intensive than UV radiation that German treatment plants have used since the 1990s for disinfection. Energy demand for widespread PFAS degradation has not yet been calculated. Second: real wastewater contains not just GenX but hundreds of different PFAS compounds plus other dissolved substances that could capture hydrogen radicals. The Aarhus study tested under lab conditions with a single compound. Third: the defluorination rate of 21.2 percent in five hours means that in this time roughly four-fifths of fluorine atoms remain bound in organic compounds. Complete destruction requires significantly longer contact times or more intense irradiation.
The insight lies elsewhere: whoever knows that hydrogen radicals are the decisive driver can specifically design water treatment plants around this mechanism rather than work in an empirical search space. Wei names experiments with more complex wastewater matrices as the next step. Observers expect several years of development work until the first pilot plant.