Killer whales are facing a massive decline due to pollution from a now-banned chemical.

A study published in the journal Science says Polychlorinated biphenyl, or PCB, is being found in high concentrations in killer whales.

It's a highly toxic and carcinogenic chemical commonly found in industrial products - and it's harming the whales' immune systems and ability to reproduce.

Although PCBs were banned worldwide more than three decades ago - they are are still available in parts of the globe.

Researchers are saying they fear killer whale populations near industrialised regions are at high risk of population collapse over the next hundred years.