Most UK rivers are contaminated by a chemical called trifluoroacetic acid (TFA). This is a type of human-made chemical known as perfluorinated alkyl substances (PFAS), often called "forever chemicals".

This widespread contamination highlights the extensive scale of work required to remove synthetic forever chemicals from our environment.

Many PFAS are known to be toxic (including associations with altered liver and thyroid function and various cancers). PFAS all contain at least two carbon-fluorine (C-F) chemical bonds, one of the toughest bonds to break so they tend to be persistent. Once they are released to the environment, they don't easily degrade.

The PFAS class incorporates a vast but unknown number of different chemicals - estimates vary from around 5,000 to 6.5 million. TFA is just one of many PFAS.

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TFA enters the environment from different sources. It's used to make blowing agents (used to make things like expanded foams and plastics such as packaging materials), pesticides and pharmaceuticals. So it is intentionally used for some useful applications.

But it can also be produced unintentionally as a by-product from various processes that involve "pre-cursor" PFAS chemicals. The biggest environmental source of TFA is as a by-product from manufacturing "F-gases" or flourinated greenhouse gases - these are used as refrigerants instead of CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons) which are known to cause ozone depletion.

While F-gases may not deplete ozone, they are greenhouse gases with extremely high global warming potential with some several thousand times more potent then CO. An F-gas called fluoroform has a global warming potential of 14,800. This means that when fluoroform is released into the atmosphere, it will trap 14,800 times more heat for an equivalent amount of CO.

TFA is highly persistent so it resists most forms of physical, chemical and biological degradation. TFA is also highly mobile so it can enter waterways and move around them easily, while remaining in the environment for hundreds of years. This is why it's now accumulating and cropping up in our environment more often, contaminating our rivers, food and even our wine.

TFA has been found in rivers across the globe including the US, China, Germany and Switzerland. These findings have triggered joint research between environmental charity Fidra and scientists at the University of York to sample water from and analyse the TFA levels in 32 UK rivers, streams and lakes. They found TFA present in 31 of the 32 sites investigated, including an exceptionally high level in the River Kelvin, Glasgow (the second highest recorded globally to date). This is approaching levels where TFA has been previously observed to start having adverse effects on aquatic organisms.

Apart from its major source being as a breakdown product from the production of greenhouse gases (and knock on climate change effects), the presence of TFA in our environment represents a genuine threat to human and environmental health.

Currently there is no guidance for safe levels of TFA in drinking water, and it is not something that is measured. However, if it is present in our rivers and lakes, then there is a potential pathway for it to enter our drinking water. This needs to be addressed so that our levels of exposure, and the level of threat that TFA poses, can be assessed by scientists, industries and regulators.

While evidence is limited on human toxicity of TFA, studies dating back more than 25 years have highlighted its potential effects on aquatic organisms, including effects on development of zebrafish, as well as various algaes, which act as important food sources in aquatic ecosystems. Studies on mammals have that continuous TFA exposure could lead to shown increased liver sizes (suggesting the possibility of a significant underlying, unknown medical condition) and potential disruption to reproductive hormones, causing fertility and foetal development issues.

The EU's chemical regulator, the European Chemicals Agency is responsible for ensuring chemical safety in Europe. They suggest TFA poses a low threat if exposure is short term. However, longer-term exposure effects remain unknown. With other PFAS, recommended weekly maximum intakes have been substantially reduced as knowledge has advanced.

While TFA pollution continues unabated, levels in the environment beyond those 32 rivers - and in our food and drink - remain difficult to quantify. It is also hard to confidently suggest methods to reduce personal TFA exposure. However, work by myself and colleagues has shown that exposure to many PFAS can be reduced by filtering tap water with activated carbon or charcoal filters. Other researchers have suggested that this could be an effective way to remove TFA from drinking water, as long as filters are changed regularly.

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