Seal pups around the UK coast are at risk from toxic chemicals present in their mothers' milk, new research has found.
The contamination comes from man-made waste draining into the sea and causes changes to how seal pups gain the fatty blubber they need to survive.
Scientists are now warning the dangerous toxins could lead to extinction.
A ban designed to stop the damage – from sources such as paint, pesticides, electrical transformers and lubricants – is not working, according to a study led by Abertay University in Dundee.
The research, was in partnership with the Sea Mammal Research Unit at the University of St Andrews and Belgian academics, has now shown the ban introduced in the early 2000s may not go far enough to protect wildlife.
Researchers found that even low levels of the fat-altering chemicals known as PCBs (Polychlorinated Biphenyls) and DDT (Dichlorodiphenyltrichloroethane) in the sea are putting the lives of pups at risk.
The study, conducted on the Isle of May in the Firth of Forth, focused on grey seal pups in their first weeks of life.
Principal investigator, Dr Kimberley Bennett of Abertay University, explained how the chemicals have become locked in the ecosystem, with mother seals accumulating them from fish and passing on the harmful effects to their young through their milk.
Dr Bennett said: "We've known for a long time that high levels of these chemicals are very dangerous and can hamper reproduction and immunity in marine mammals.
"They may even drive some populations towards extinction.
"Efforts to reduce levels in the environment have been successful. But our new research shows that blubber, which is a vital for seals and whales, could be vulnerable to harmful effects of PCBs and DDT at levels much lower than previously thought."
Although the so-called "dirty dozen" chemicals are banned from being produced and released into UK waters under the Stockholm Convention, they are still finding their way into the sea through sewage and landfill.
The contaminants were found to harmful to wildlife since the 1970s, with marine mammals facing the biggest threat because they feed at the top of the food chain.
Dr Kelly Robinson and Prof Ailsa Hall of the University of St Andrews Sea Mammal Research Unit added: "We have already shown that these chemicals can reduce the likelihood that a seal pup will survive to its first birthday.
"We've now discovered why this is the case and how these toxins add to the seals' burden of potential health effects."
