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Chemical pollution could wipe out half of all orca populations
(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.