The race to save the ozone layer has left us with a new, more permanent problem
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In June 2025, scientists at the University of York published a report investigating the presence of a little-known chemical compound – trifluoroacetic acid (TFA) – in UK rivers. The researchers had sampled water from 54 sites across 32 rivers in Wales, the north of England, Scotland and Northern Ireland, many of which are primary sources of the UK’s drinking water. The results came back positive for 98 per cent of test sites.
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Across the globe, concentrations of TFA – one of thousands of known per- and polyfluoroalkyl substances (PFASs), or ‘forever chemicals’ – have been increasing; today, it’s the most abundant PFAS found in the natural environment. Ice cores extracted from the Canadian Arctic in 2015 and 2017 indicate that, after being almost non-existent in the 1970s and 1980s, TFA concentrations began to rise sharply in the 1990s and have continued to climb. Lucy Hart, an atmospheric and environmental researcher at Lancaster University, says that this timing coincides with the widespread adoption of chemical replacements for CFCs – once essential refrigerants and propellants that were found to destroy the ozone layer.
TFA is known to be produced by several human-related sources: industrial processes, the degradation of certain pesticides and pharmaceuticals, and the atmospheric breakdown of CFC replacements – fluorinated gases such as HCFCs and HFCs. ‘The researchers who analysed the ice cores hypothesised that CFC replacements might explain this increase in TFA concentrations, but this theory had never actually been tested in a model before,’ says Hart.
By calculating the amount of TFA produced by the atmospheric breakdown of these chemicals, and using a transport model to simulate how realistic weather conditions move and deposit these substances around the globe, Hart and her colleagues proved that CFC replacements are responsible for the vast majority of TFA found worldwide. This equates to more than 335,000 tonnes now present in everything from rainwater to remote Arctic ice, a figure scientists expect to continue growing.
Researchers are still working to determine the long-term health consequences of TFA, which has been detected in human blood and urine, but there is growing evidence linking the chemical to potential risks for fertility and foetal development.
The other concern is that TFA isn’t just ubiquitous; it’s effectively permanent. After leading the study on TFA in UK rivers, University of York professor Alistair Boxall remarked that, sadly, he was not at all surprised by the results. ‘TFA is a very mobile chemical that doesn’t seem to be removed by drinking water treatment systems so it is likely that levels in drinking water will be similar to those we found in some of the rivers.’
This is particularly worrying for tropical regions, including parts of China and West Africa, where Hart and her colleagues found that higher rainfall accelerates the transfer of TFA from the atmosphere into local water bodies and vegetation.
Since Hart’s study was published, the European Chemicals Agency has moved to reclassify TFA as toxic and as a persistent toxic substance. ‘Obviously, it’s not good news that they’ve confirmed that TFA is toxic, but I think the classification is a positive step because hopefully PFAS like TFA will now be considered by policymakers.’
While HCFCs and HFCs solved the ozone crisis, this first generation of CFC replacements came with its own major environmental problems: these chemicals are now known to be potent greenhouse gases that trap heat far more effectively than carbon dioxide. In the wake of the 2016 Kigali Amendment, which mandated a shift away from refrigerants with a high global warming potential (GWP), the industry has turned to a new generation of CFC replacements: HFOs. These new chemicals have very low GWP and don’t affect the ozone layer – but they, too, break down into TFA.
Hart says it’s time to break the cycle of ‘regrettable substitution’. ‘We’re phasing out one group of problem-causing chemicals and replacing them with another, without considering the impacts of their replacements.’ There are, she points out, a group of so-called natural refrigerants – compounds such as carbon dioxide, ammonia and propane – that, while not appropriate in all uses, could be used as alternatives without adding to existing PFAS concentrations. ‘The important thing is that we assess the impacts of new chemicals going forward, before we make the substitutions.
