Scientists said most of these contaminants, which pose a health risk to both humans and animals, were due to wastewater treatment or agricultural waste.
They said the findings suggested “widespread pollution” of freshwaters across the UK.
It comes just days after a report by MPs said England’s rivers were “in a mess”, with many containing a “chemical cocktail” of pollution of sewage, agricultural waste and single-use plastic.
The Environmental Audit Committee (EAC) warned this could harm both swimmers and wildlife.
The new research by Cardiff University Otter’s Project found perfluoroalkyl and polyfluoroalkyl substances (PFAs), known as “forever chemicals” as they do not easily break down in the environment, in Eurasian otters across England and Wales.
Scientists analysed livers from dead otters across the two countries and found all 50 had traces of these chemicals, which have been linked to liver and kidney problems, low infant birth weights and immune system issues, among other health impacts.
Ali Morse, water policy manager for The Wildlife Trusts, told The Independent: “Sadly, these findings aren’t surprising because our rivers are full of toxic pollutants which are devastating for wildlife.
“Otters require a healthy environment to survive and flourish, but a plague of pollution from sewage, farming and poor waste management is poisoning their habitat.”
The study found higher concentration in otters close to wastewater treatment works and in arable areas, which could reflect the use of sewage sludge on farms.
Emily O’Rourke, the study’s lead author, said: “It is deeply concerning PFAs were introduced into the environment through industrial and farming practices – policy and management action is vital to address this where it remains an issue.”
PFAs are used to make greaseproofing, stainproofing and waterproofing substances and can be found in products such as food packaging, clothing and electronics.
Last year, scientists called for them to stop being used in manufacturing processes after research showed the extent to which they pollute air.