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Banned chemicals leaking into the sea could wipe out some killer whale populations within 50 years, a new study has found.

Poisonous chemicals known as PCBs, polychlorinated biphenyls, are still polluting the planet's oceans despite being banned around 40 years ago, researchers say.

Scientists believe populations off the shores of Japan, Brazil, the Strait of Gibraltar, Japan and California are now facing 'complete collapse' because of PCB pollution.

Now, following the revelations in the journal Science, Europe has been urged to do more to prevent a global catastrophe.

Paul Jepson at the Zoological Society of London told the Guardian: "It is like a killer whale apocalypse."

What are PCBs and why are they still polluting the ocean?

PCBs are chemical compounds that were manufactured in huge numbers around the world from the 1930s, and used in everything from plastics, paint, flame retardants, coolants, sealants and electronics.

They were banned in the 1970s after it was revealed they were highly toxic and carcinogenic.

But the majority of the chemicals were not destroyed and instead dumped in landfill, meaning the poisonous chemicals started leaking into the ocean.

The chemicals continue to leach into the sea, causing a toxic build up around industrialised areas.

How does it affect killer whales?

Orcas are apex predators, meaning they eat all sorts of marine animals from seals to penguins and even other types of whales.

Because of their position at the top of the food chain, they are exposed to vast amounts of the chemicals as they absorb all the pollution their food has eaten.

The higher up the food chain you go, the more concentrated the chemicals become.

The research found concentrations of the highly toxic chemicals can be 100 times safe levels in orcas.

PCBs damage females' ovaries, the immune system and are carcinogenic. Very high doses are passed onto calves through the mother's milk.

But the scientists warn other contaminants are also found in killer whales.

What does the future look like for killer whales?

Bleak, for those populations concentrated around industrial areas

In those places orca populations could die out within 30-50 years

This includes the UK, where there is only one pod remaining, Japan, Brazil, the Strait of Gibraltar, Japan and California.

They have already disappeared in the North Sea and off the coast of Spain.

Other populations are set to fare better, including in the seas around Norway, Iceland, Canada and the Faroe Islands.

Populations in the far north away from heavily industrialised areas, basically.

What can be done?

Most PCBS have not yet been destroyed or stored safely and still remains in landfill.

America has been praised for its approach in tackling the chemicals and bringing levels down but Europe lags some way behind.

The 2004 Stockholm Convention on Persistent Organic Pollutants was meant to combat the issue but has been criticised for not disposing of the pollutants.

Jennifer Lonsdale, chair of the Wildlife and Countryside Link’s whales group, told the Guardian: “This new study is a global red alert on the state of our oceans.

"If the UK government wants its [proposed] Environment Act to be world-leading, it must set ambitious targets on PCB disposal and protect against further chemical pollution of our waters.”

PCBs hang around in the water for years as they are fat soluble, but short of a clean-up on a global scale, which would take decades, not much can be done.