Killer whale populations around the world may collapse in as little as 30 to 50 years.

That's according to a study published Thursday in the journal Science, which says some killer whales have extremely high levels of polychlorinated biphenyls (PCBs) — an organic pollutant that was banned in Canada in 1977.

Researchers at Aarhus University in Denmark, took biopsies of orcas or killer whales in northern Norway, Iceland, and eastern Greenland and compared datasets from around the world to determine how PCBs are affecting killer whale populations.

Of the 19 populations studied, researchers found more than 50 per cent had levels high enough to impair population growth. Eight are in severe danger of collapse in only a few decades.

Whales living in areas with a high contamination of PCBs, like near Brazil, the U.K., and the Strait of Gibraltar, were most affected.

In the Arctic, most areas were insulated from the effect. Orca populations near Iceland, Norway, and Alaska are thriving.

Lead author Jean-Pierre Desforges says PCBs accumulate more easily in predators, which is why killer whales in Greenland show high levels of contamination compared to those near Iceland. (Submitted by Jean-Pierre Desforges)

But lead author Jean-Pierre Desforges said that isn't the whole story.

"The killer whales that we know frequent the waters off of eastern Greenland … they were quite highly exposed," he said.

He explained PCBs accumulate more easily in predators. So killer whales that eat other predators — like seals, sharks, and tuna — have much higher rates of PCBs than the whales that tend to consume small fish.

According to Desforges, that's why the whales near Iceland are still going strong while the seal-fed whales in nearby Greenland show high levels of contamination.

Are humans in danger?

Desforges also said the findings show there may be ramifications for humans that regularly eat marine predators, like seals or killer whales.

Previous studies have revealed high levels of PCBs and other organic pollutants in northern communities.

While Desforges said communities that feed on marine mammals have a higher risk of PCB exposure, linking that exposure to health effects is more complicated.

"In humans, we have a lot of different risk factors, whether you're smoking, or drinking, or exercising," he said. "There's a lot of things that affect our health."

Orca populations near Iceland, Norway and Alaska are thriving. (Audun Rikardsen)

Desforges said whales are particularly susceptible to PCB accumulation because their metabolisms can't eliminate the contaminants. Humans are "much better at degrading these compounds once they enter our bodies," he said.

Nevertheless, Desforges said PCBs can still cause long-term problems in humans. According to the U.S. Centre for Disease Control and Prevention, PCBs can have many toxic effects and can be carcinogenic in humans.

'Not all bad news'

While this seems pretty dire for both whales and humans, it's not all bad news.

A recent study published in the journal Science of the Total Environment found that overall, the levels of organic pollutants have decreased in most Arctic wildlife.

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These results follow a concerted effort by 152 countries to stop the use of PCBs through the Stockholm Convention, which came into place in 2001.

Overall, the levels of organic pollutants have decreased in most Arctic wildlife but are still high in marine predators with long lifespans like killer whales. (Audun Rikardsen)

Desforges said that while the Stockholm Convention has already been a success, it doesn't help marine predators with long lifespans. A female killer whale, for example, can live up to 60-70 years.

"The levels [of PCBs] have started to go down since the '80s, but they've kind of stabilized now and we know that in long-lived species, they're still extremely high," he said.

"It's kind of trapping the contaminant into this biological loop, and that's a major issue for long-lived species."