It's less killer whale and more killed whales, at least according to a new study that found at least half the world's orcas could be taken down by ocean pollution in just a few decades. The culprit: highly toxic polychlorinated biphenyls, or PCBs. "Despite a near-global ban of PCBs more than 30 years ago, the world's killer whales illustrate the troubling persistence of this chemical class," reads the study in Science. Most PCBs, which were used in everything from plastics to paint, have not been destroyed or securely stored, reports the BBC, and those that already leached into the ocean are unrecoverable and stubbornly persist in the whales, who metabolize them incredibly slowly, reports the New York Times.
PCB concentration rises as you climb the food chain. Killer whales are at the top, leaving them with levels than can be 100 times what's considered safe and making them "the most contaminated animals on the planet," as the Guardian puts it. Newborn calves are heavily dosed with PCBs via milk, and even birthing newborns may be compromised: Science Daily reports researchers evaluated the PCB levels of more than 350 orcas and detected PCB levels of 1300 milligrams per kilo in some whales' blubber; other studies have shown animals with levels of just 50 milligrams can exhibit infertility and immune system issues. The most contaminated, and therefore threatened, populations are those near Brazil, the UK, and the Strait of Gibraltar. "In these areas, we rarely observe newborn killer whales," says a study co-author. The outlook is better for pods near Iceland, Norway, Alaska, and the Antarctic. (And that's not the only peril orcas face.)