A "forever chemical" that scientists worry might have an impact on reproduction has been found in all but one of 32 rivers tested across the UK, according to a study.
Researchers say trifluoroacetic acid (TFA), which can take hundreds of years to break down, was detected at 98% of the 54 sites they investigated.
According to the study, one sample - taken from the River Kelvin in Glasgow - contained the second-highest value of TFA ever recorded in surface water globally.
The researchers say the average concentrations of TFA in the UK are at the "higher end" of the global scale compared with the results obtained from other studies - and that the chemical has been found in 31 of the 32 rivers analysed.
The research - funded by environmental charity Fidra and carried out by the University of York - looked at how much TFA was present in surface water.
It marks the first time such a project has been carried out in the UK.
TFA is a type of per- and polyfluoroalkyl substance (PFAS) - also known as "forever chemicals" - found in pesticides, pharmaceuticals and fluorinated gases (F-gases).
But there is "growing concern" about the general impact on human health and its potential risks to drinking water supplies.
According to Fidra, TFA is thought to have "low to moderate" toxicity; however, because levels are rapidly rising in the environment, there are concerns about future impacts.
Studies have linked TFA exposure to birth defects in rabbits, while similar short-chained PFAS have been shown to have toxic effects on freshwater organisms.
The German Federal Environment Agency (UBA) has applied to the European Chemicals Agency (ECHA) for TFA to be classified as toxic for reproduction.
However, its impacts are still being researched.
'Increasingly concerned'
Experts say the results of the latest study provide "compelling evidence of the presence of TFA and PFAS in UK waterways".
The researchers added: "These data should be further analysed to try and establish the drivers of TFA contamination in UK surface waters and routes for source control should be prioritised.
"The scientific communities are becoming increasingly concerned about the potentially harmful properties of TFA and increasing levels in the environment, particularly in water sources.
"There are currently no practical or economically viable ways to remove TFA from water supplies.
"TFA was found in 31 of the 32 rivers examined."
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Samples were taken from sites across northern England, Wales, Scotland, and Northern Ireland.
Scientists say TFA has the potential to cause reproductive and liver issues in mammals and is harmful to aquatic life.
It also accumulates in crops and fields and "builds up" in drinking water.
The research comes as a committee of MPs said the UK's water sector is in need of "root-and-branch reform".
The cross-party Environment, Food and Rural Affairs (DEFRA) committee said the industry is "failing" - and trust and accountability in the sector was "very low".