(CNN) Chemical pollutants banned more than 40 years ago are still having a devastating effect on marine life and could lead to the disappearance of half the world's killer whale populations before the end of the century.

That's according to a new study, published in the journal Science , which found that killer whales, or orcas, are most at risk from polychlorinated biphenyls (PCBs), which were once widely used as coolants and in the production of carbonless copy paper before they were found to be highly toxic and carcinogenic.

Production of PCBs were banned in the US in 1979 and under an international treaty in 2001 , but they are still in use in many parts of the world and not due to be completely phased out until 2025.

This has led to PCBs seeping into the oceans, where they present a particular risk to marine mammals at the top of the food chain like orcas. Because the chemicals do not readily break down, the concentration of them builds up in the bodies of predators as they eat more and more fish contaminated with PCBs.

For mammals, PCB contamination is inter-generational, with mothers passing the chemicals to their offspring through milk.

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