They live in chatty groups, and can hunt in teams—sometimes working in tandem to create waves that dump unlucky prey off floating ice. Savvy orcas, with their splotchy two-tone flesh and rich family lives, have survived mass slaughter, being captured with nets and lassos, and being trucked and airlifted to marine theme parks.

But new research published Thursday in the journal <i>Science</i> suggests more than half of the world’s killer whale populations could face complete collapse in 30 to 50 years, thanks to a suite of toxic chemicals the world has already banned.

Long-lived polychlorinated biphenyls, or PCBs, are organic compounds once used in capacitors, oil paints, and coolants, until they were deemed so dangerous that their manufacture was banned in the U.S. and other countries in the 1970s and 1980s. Yet today orcas across the northern hemisphere are among the most heavily contaminated animals on Earth.

Even now, PCBs are believed to be altering orca behavior, damaging their immune systems, and harming reproduction so much that researchers suspect many families of killer whales (technically dolphins) may not survive the next few decades.

“A group of chemicals we thought was no longer a threat is still present at concentrations that will continue to pose significant risk,” says lead study author Jean-Pierre Desforges, with the Arctic Research Centre at Aarhus University in Denmark.

Desforges called the results “frightening”—in part because PCBs are just one of several threats facing orcas, often not even the dominate one.


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