Concentrations of two well-known forever chemicals have fallen in English rivers over the past decade, according to a report from the Environment Agency, the UK's environmental regulator. Levels of PFOS and PFOA dropped by roughly 30 percent, a sign that international restrictions on these substances are beginning to work. The same data, however, reveal a less encouraging picture: the chemicals that replaced them are now turning up in waterways across the country.
PFOS was restricted under the Stockholm Convention, the global treaty on persistent pollutants, starting in 2009, and PFOA followed in 2019. Both belong to the broad family of per- and polyfluoroalkyl substances, known as PFAS, which are prized for resisting water, grease and heat and which break down extremely slowly in the environment. PFOA is classified as carcinogenic to humans by the International Agency for Research on Cancer. A ban on PFOA in firefighting foams only took effect in the UK in 2025, which means its presence in rivers has been declining for years before the domestic rule was fully in place.
The replacements are a growing concern. Short-chain PFAS and fluorotelomers, which were introduced as alternatives, can now be detected in rivers. Trifluoroacetic acid, or TFA, is found widely across England and elsewhere in the UK. Research linked to the campaign group Fidra confirmed the TFA findings across the country. Problems remain with the older compounds too: PFOS is still frequently above the UK and EU environmental quality standard, and it is the only PFAS for which England has a binding quality standard, with others still under development.
Policy is moving in different directions on either side of the Channel. The European Union is considering a blanket ban covering all PFAS, a step that would address the whole family rather than individual chemicals. The UK has not set a timeline for a comparable measure. The findings suggest that restricting one compound at a time may simply encourage the use of close relatives that are still poorly regulated, leaving rivers with a changing mix of persistent chemicals rather than a clean slate.