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An orca in Avacha Bay off Kamchatka Peninsula on Russia's Pacific coast. Photo: Yuri Smityuk/TASS via Getty Images

Killer whales' cunning along with their wide-ranging diet make them seem resistant to human-caused disturbances, but a new study finds these apex predators are imperiled by a class of industrial chemicals first banned more than 30 years ago.

The big picture: Many populations of orcas may disappear entirely during the next 100 years due to polychlorinated biphenyls, or PCBs, building up in their tissue. That contamination may cause multiple killer whale populations to crash in the coming decades, which would have a ripple effect throughout the food chain, according to a new study published Thursday in the journal Science.

The background: More than 90 countries have signed an agreement, known as the Stockholm Convention, to destroy stocks of PCBs, but they slowly decompose in the environment.

Because orcas are at the top of the food chain, they have far higher concentrations of PCBs in their system than smaller species lower on the food chain. This occurs because of a process known as biomagnification, through which species at higher trophic levels take in doses of substances accumulated from each step in the food chain.

About 1 to 1.5 million metric tons of PCBs were produced worldwide between 1930 to 1993, the study states.

  • Research shows that PCBs can impair killer whales' reproduction, disrupt orcas' endocrine and immune systems, and slow population growth or even cause them to decline.
  • Orcas used to be widespread throughout the global oceans, but due to PCBs and other factors, only a few populations are gaining numbers.

What they did: The international team of researchers examined available data on PCB concentrations about 350 killer whales worldwide, and compared them to levels known to affect reproduction and immune system functionality.

What they found:

  • More than half of the 19 studied populations of killer whales have "achievable growth rates" that are so low so as to cause them to decline, potentially inexorably.
  • Brazilian, Northeast Pacific Bigg's, Canary Islands, Greenlandic, Hawaiian, Japanese, Strait of Gibraltar and UK orca populations are all "at high risk of collapse over the next 100 years," the study states.
  • Orcas farther away from industrialized countries tend to be better off, such as those in the Arctic and Antarctic.
  • The researchers found far higher amounts of PCBs in killer whale populations that rely on marine mammals and tuna as a food source, since those species have higher levels of PCBs in their system.

The uncertainties: Study co-author Paul Jepson, a specialist in wildlife population health at the Zoological Society of London, told Axios:

"It’s true that modeling is a tool to assess the impact of PCBs – but we acknowledge that all models have some degree of uncertainty.  That said, PCBs as chemicals do lend themselves very well to this type of modeling – because they behave in very predictable ways in killer whale populations."

"I would agree with their findings that these high-risk populations very likely are going through a decline associated with elevated PCBs," said Brendan Hickie, a senior lecturer at Trent University's School of the Environment who was not involved in the study.

The bottom line: This study has implications for conservation efforts, since few populations of killer whales have legal protections, and these are not specific to PCBs.

Go deeper

Updated 12 hours ago - Sports

The potential GOAT of chess faces intriguing challenger

Illustration: Sarah Grillo/Axios

The World Chess Championship between Norway's Magnus Carlsen and Russia's Ian Nepomniachtchi began on Friday, 1,094 days after Carlsen won his fourth consecutive title.

Why it matters: During the long, COVID-fueled layoff, chess entered a new era, and with the championship finally here, the age-old game is ready for its close-up.

Department of Interior proposes raising cost of drilling on public lands

A horizontal drilling rig and a pump jack sit on federal land in Lea County, New Mexico. Photo: Callaghan O'Hare/Bloomberg via Getty Images

Oil and gas companies should pay more to drill on federal lands and waters, the Department of the Interior argued in a report released Friday, saying that the current rates were "outdated."

Driving the news: The Department of Interior report said that the federal government's oil and gas leasing and permitting program "fails to provide a fair return to taxpayers, even before factoring in the resulting climate-related costs that must be borne by taxpayers."

14 hours ago - Health

U.S. to restrict air travel from 8 countries over new COVID variant concerns

A COVID-19 vaccine is administered. Photo by Joe Raedle/Getty Images

The U.S. will impose new air travel restrictions in response to the Omicron variant, a new COVID strain first detected in South Africa, President Biden announced Friday.

The big picture: Air travel from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi will be restricted starting on Monday.

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