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Killer whales leap out of the water near Alaska. Robert Pittman / NOAA

Half the World’s Killer Whale Populations at Risk From Toxic Chemicals

Polychlorinated biphenyls (PCBs) were banned in the U.S. in 1978, but their persistence in the world's oceans is still posing a major threat to killer whales.

A study published in Science Friday found that current concentrations of PCBs could lead to the disappearance of half of the world's killer whale, or orca, populations over the next 30 to 50 years, according to an Aarhus University press release published by ScienceDaily.


"It is like a killer whale apocalypse," study author Paul Jepson at the Zoological Society of London told The Guardian.

Ten out of the world's 19 killer whale populations were rapidly dwindling, the study found.

PCBs were widely used in electronics and plastics beginning in the 1930s. Countries began to ban them in the 1970s and 1980s, and in 2004 the Stockholm Convention came into effect, in which 152 countries promised to phase them out entirely by 2025 and clean up existing waste, CNN reported.

But the research suggests the convention isn't moving fast enough.

"I think the Stockholm Convention is failing," Jepson told The Guardian. "The only area where I am optimistic is the U.S. They alone produced 50 percent of all PCBs, but they have been getting PCB levels down consistently for decades. All we have done in Europe is ban them and then hope they go away."

Killer whales are especially impacted because they are at the top of the marine food chain, and concentrations of the toxic chemicals increase as they accumulate in the tissues of larger and larger animals.

Further, killer whales pass PCBs onto their offspring through their milk.

The researchers, from universities and institutions around the world, assessed PCB levels in more than 350 killer whales, the largest number ever studied. They then used models to predict the impacts of PCBs on the mortality rate, fertility rate and immune response of killer whale populations over the next 100 years.

Killer whale populations in highly contaminated areas like Brazil, the Strait of Gibraltar, the northeast Pacific and the UK were especially under threat and had already been reduced by half in the years when PCBs were being used.

"In these areas, we rarely observe newborn killer whales," study participant Ailsa Hall of the Sea Mammal Research Unit at the University of Saint Andrews said in the press release.

Killer whales who fed on larger animals like seals, tuna and sharks were also more impacted than populations that fed on smaller fish like mackerel or herring.

The killer whales off the eastern coast of Greenland, who eat a lot of marine mammals, were also at risk.

The least contaminated populations swim in waters in the far north, off of Norway, Iceland, Canada and the Faroe Islands, and the study's models showed that these populations would continue to grow.

Jepson said that killer whales could return to currently contaminated areas if global cleanup efforts are successful.

"It is an incredibly adaptive species—they have been able to [live] from the Arctic to the Antarctic and everywhere in between," he told The Guardian.

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