Level 1 - Absolute Beginner
Scientists have found a better way to destroy harmful chemicals in drinking water. These chemicals are called PFAS, and some people call them forever chemicals.
PFAS are very hard to break down. They stay in water and in our bodies for a very long time. They can cause health problems.
Researchers at Aarhus University in Denmark found that special light called UV light can destroy PFAS. A tiny particle called a hydrogen radical does the work.
This discovery will help engineers build better machines to clean water. Cleaner water means healthier people.
- PFAS
- man-made chemicals that do not break down easily in nature or in our bodies
- hydrogen radical
- a very reactive particle made from a single hydrogen atom
- UV light
- ultraviolet light, a type of light that humans cannot see
- drinking water
- water that is safe for people to drink
- destroy
- to completely break something apart so it no longer exists
- researcher
- a scientist who studies things to find new information
- discovery
- finding out something new that was not known before
- engineer
- a person who designs and builds machines or systems
Level 2 - Elementary
A study published in June 2026 by Aarhus University in Denmark has identified why short-wave ultraviolet (UV) light is so effective at destroying PFAS, the group of man-made chemicals linked to cancer, liver damage, and hormone disruption.
Scientists found that hydrogen radicals, not the hydroxyl radicals previously thought responsible, are the dominant particles doing the work. Hydroxyl radicals form when UV light hits water, but hydrogen radicals appear only at wavelengths below 300 nanometres.
PFAS are found in non-stick cookware, fire-fighting foam, and food packaging. They have contaminated drinking water supplies worldwide, earning the nickname forever chemicals because they persist indefinitely in the environment.
The discovery means that water-treatment reactors can be redesigned to use shorter UV wavelengths, making the process more efficient and potentially less expensive.
- ultraviolet (UV)
- a type of light with a wavelength shorter than visible light, invisible to the human eye
- hydroxyl radical
- a highly reactive oxygen-hydrogen particle involved in chemical reactions
- hydrogen radical
- a highly reactive single hydrogen atom that can break chemical bonds
- nanometre
- one billionth of a metre, used to measure wavelengths of light
- contaminate
- to make something impure or harmful by introducing a substance into it
- persist
- to continue to exist or remain for a long time
- reactor
- a vessel or device in which a controlled chemical process takes place
- dominant
- most important or influential; having the greatest effect
Level 3 - Intermediate
A study published in Environmental Science and Technology on June 15, 2026, by researchers at Aarhus University has overturned a key assumption underlying current advanced oxidation process (AOP) reactor designs used to treat PFAS-contaminated water.
The team found that hydrogen radicals, generated when UV photons at wavelengths below 300 nanometres split water molecules, are the primary agents responsible for breaking the carbon-fluorine bonds that make PFAS so resistant to breakdown. Previous designs prioritised hydroxyl radical generation, which the new data show is far less effective against the C-F bond.
Per- and polyfluoroalkyl substances are a class of approximately 4,700 synthetic chemicals used in products ranging from non-stick cookware to aqueous film-forming foam used in aircraft fire suppression. The US Environmental Protection Agency set maximum contaminant levels of 4 parts per trillion for PFOA and PFOS in 2024, creating regulatory pressure to scale viable treatment technologies.
The Aarhus findings suggest that AOP systems should operate at sub-300 nm wavelengths, but commercially viable UV sources at these wavelengths remain expensive and have shorter operational lifespans than conventional mercury-vapour lamps used in current reactors. Scaling the technology affordably remains the key challenge before it can reach municipal water systems.
- advanced oxidation process (AOP)
- a water-treatment method that generates highly reactive radicals to destroy contaminants
- recalcitrant
- stubbornly resistant to being broken down or changed
- carbon-fluorine bond
- one of the strongest chemical bonds in organic chemistry, responsible for PFAS persistence
- aqueous film-forming foam
- a fire-suppression agent widely used at airports that has been a major source of PFAS contamination
- maximum contaminant level
- the legal limit for a pollutant allowed in public drinking water
- photon
- a particle of light that carries a discrete amount of energy
- operational lifespan
- the length of time a piece of equipment functions effectively before needing replacement
- municipal
- relating to a city or town and its local government
Level 4 - Advanced
A June 15, 2026 paper in Environmental Science and Technology from Aarhus University's Department of Biological and Chemical Engineering upends a foundational assumption of PFAS remediation science: that hydroxyl radicals generated by conventional advanced oxidation processes are the primary agents of per- and polyfluoroalkyl substance mineralisation. The study demonstrates, through isotopically labelled mechanistic probes, that hydrogen radicals formed exclusively at UV photon energies corresponding to wavelengths below 300 nm are responsible for initiating the reductive defluorination cascade that ultimately cleaves the C-F backbone.
The mechanistic distinction carries significant engineering consequences. Current vacuum-UV and UV-persulfate AOP reactor designs optimise photon flux and radical generation chemistry around the 254 nm output of low-pressure mercury-vapour lamps, which do produce sub-300 nm photons but with inadequate intensity at the wavelengths where hydrogen radical generation peaks. The Aarhus data imply that next-generation reactors should be redesigned around deep-UV LED arrays or excimer lamps centred at 185-222 nm, a design shift that current market pricing and UV-LED operational lifespans of roughly 6,000-10,000 hours versus 16,000 or more for mercury-vapour render economically challenging at municipal scale.
The regulatory backdrop intensifies the urgency. The US EPA's 2024 maximum contaminant levels of 4 parts per trillion for PFOA and PFOS individually, and 10 ppt for the sum of six named PFAS compounds, have set a compliance clock running for approximately 70,000 US public water systems. Technologies that cannot reach sub-10 ppt at realistic throughput face early obsolescence regardless of their mechanistic elegance.
The commercial pathway depends on whether deep-UV LED manufacturers can achieve the price-performance inflection needed to displace mercury-vapour incumbent infrastructure, a trajectory analogous to, but trailing by roughly a decade, the blue-LED commoditisation curve that drove visible-LED adoption in general lighting. Aarhus has filed a provisional patent on a hybrid excimer-LED configuration that the team claims reduces capital expenditure by approximately 40 percent relative to a full excimer retrofit, though independent techno-economic analysis has not yet been published.
- mineralisation
- the complete chemical breakdown of organic compounds into simple inorganic end products
- isotopically labelled
- marked with specific isotopes to trace the pathways of chemical reactions
- defluorination
- the chemical removal of fluorine atoms from a compound
- photon flux
- the number of photons passing through a unit area per unit time
- excimer lamp
- a type of UV light source that produces intense radiation at specific short wavelengths
- obsolescence
