New analysis by an international team of researchers including the University of St Andrews and the Zoological Society of London has found that half of the world’s population of orca will vanish in the most heavily contaminated areas.
The chemical pollutants, polychlorinated biphenyls, or PCBs, were once widespread in paints, adhesives and electronics but were banned in the 1970s.
However the paint from old bridges, boats and buildings can still flake into the sea, or leach into waterways from disused mines where it was used as hydraulic oil or from landfill sites.
Around the British Isles, killer whale numbers have halved to around 10 because of the the chemicals and the mammals are likely to vanish altogether in the coming decades, the new research found.
Last May, a dead orca called Lulu was found washed up on the Hebridean Isle of Tiree with the highest levels of PCBs ever recorded and it is feared the rest of her pod will have the same level of contamination, which can impair the immune system and damage fertility.
"This suggests that the efforts have not been effective enough to avoid the accumulation of PCBs in high trophic level species that live as long as the killer whale does, “ said Paul Jepson, Institute of Zoology, Zoological Society of London, England, who is another killer whale expert and co-author of the article.
Killer whales, because they sit at the top of the food chain, accumulate huge amounts of PCBs which have been ingested by animals further down.
The chemicals can also be passed down from mother orca to its offspring through the mother's fat-rich milk.
PCBs have been used around the world since the 1930s but following the 2004 Stockholm Convention, more than 90 countries agreed to have got rid of all use by 2028. Yet little is done to ensure companies are complying.
Wildlife charities are now calling on the government to include new measures in the new Environment Act to make the convention goals legally binding.
Willie Mackenzie, Oceans Campaigner at Greenpeace UK, said: ‘‘Thirty years after they were banned, it’s staggering that polluting PCBs are not only still getting into our ocean, but that they are pushing our killer whales towards extinction.
“The UK Government has to take a global lead to make sure this situation doesn’t get any worse: that means a legally binding measures on the disposal of PCBs in the forthcoming UK Environment Act, and urging other countries to take similar measures.”
Lucy Babey, Head of Science & Conservation and Deputy Director at ORCA, said: “With a shocking 50 per cent of orcas set to be wiped out by PCBs alone, our abysmal failures to control chemical pollution ending up in our oceans has caused a killer whale catastrophe on an epic scale.
“It is essential that requirements to dispose safely of PCBs under the Stockholm Convention are made legally-binding at the next meeting in May 2019 to help stop this scandal.”
For the new report researchers analysed the PCB levels in around 350 killer whales from around the globe and used computer modelling to gauge the impact. Where chemical levels were higher, populations were found to have fallen.
The new research was published in the journal Science.