Video report by ITV News Science Editor Tom Clarke

The current concentrations of chemical pollutants (PCBs) remain a deadly threat to animals at the top of the food chain, particularly killer whales according to a study.

Half of the world's Orca populations are likely to be wiped out by the invisible pollutant polychlorinated biphenyl (PCB), according to research from Aarhus University in Denmark.

PCBs were banned in 1987 in Europe - and globally in 2004, but because of their environmental persistence, PCBs still present a major threat today - particularly to species at the top of marine food webs.

Killer whales currently have the highest PCB exposures on earth and are at the highest risk of population collapse.

So what are PCBs?

Killer whales whose diet includes, seals and large fish such as tuna and sharks accumulate PCBs. Credit: AP

PCBs are toxic compounds shown to impair reproduction, disrupt immune systems and increase the risk of cancer in vertebrates.

PCBs are chemicals which were commonly found in:

Sealants

Paint

Hydraulic fluids

Electrical equipment

Lubricants

Killer whales, whose diet includes seals and large fish such as tuna and sharks, accumulate PCBs and other pollutants stored at successive levels of the food chain.

Killer whales that primarily feed on small-sized fish such as herring have a significantly lower content of PCBs. Credit: AP

What impact has PCB already had on killer whales?

This could be linked to the recent killer whale mother that carried her dead calf for 16 days.

Stillbirths and the death of new born calves is one of the main ways PCBs are negatively impacting killer whale populations globally.

50% More than half of the world's killer whale populations will collapse over the next 50-100 years

What have experts said?

Paul Jepson, study author at the Zoological Society of London, told ITV News: "The higher the exposure, the more severe the effects and in killer whales it's basically an apocalypse.

He added: "What our works shows is actually there's a huge, huge problem with PCB, not just in the UK and Europe, but all over the world"

Paul Jepson, study author at the Zoological Society of London, told ITV News PCB's effect on killer whales is 'basically an apocalypse'. Credit: ITV News

Jennifer Lonsdale, Chair of Wildlife and Countryside Link’s Whales Group said: "This is a global red alert on the state of our oceans.

"Half of the world’s killer whales may be wiped out because companies created toxic products and did not dispose of them safely.

"With more than 80% of the world’s stocks of PCBs still in existence the worst of this pollution crisis could be yet to come.

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