A group of synthetic substances known as "forever chemicals" because of their environmental persistence have been found in otters across England and Wales.
The study led by Cardiff University's Otter Project analysed historical data and found perfluoroalkyl and polyfluoroalkyl substances (PFASs), which have been linked to health problems in both humans and wildlife, in Eurasian otters.
It concludes this suggests "widespread pollution" of British freshwaters today.
The study found most PFASs in otters were associated with wastewater treatment works or use of sewage sludge in farming, suggesting this was a "significant and concerning" route into rivers.
The Cardiff researchers said studying contaminants in otters was vital to understanding potential health risks. Their study was published just days before a parliamentary report said no English river was free from pollution.
Emily O'Rourke, a PhD student and lead author of the study, said: "PFASs are a large family of synthetic chemicals used in consumer products for their oil and water-repelling properties, in food packaging, non-stick cookware, waterproof clothing, stain resistant products, paints and fire retardants, amongst other things.
"They're known as 'forever chemicals' because their strong carbon-fluorine structure means they don't break down easily in the environment. In recent years there have been efforts to phase these chemicals out, but they remain ubiquitous because of their environmental persistence."
