By Todd Woody | Bloomberg
As climate-driven wildfires spiral out of control, scientists have shown for the first time that toxic smoke is likely poisoning killer whales off North America’s west coast.
Researchers at the University of British Columbia found that polycyclic aromatic hydrocarbons (PAHs) generated from “petrogenic” sources — such as oil spills and burning fossil fuels — and “pyrogenic” sources like forest fires are contaminating muscle and liver tissues of two types of imperiled killer whales, or orcas.
“Our research shows it’s likely that these killer whales are being exposed to chemicals from these sources,” said Kiah Lee, the paper’s lead author, who conducted the research while she was a student at the University of British Columbia.
PAHs from petrogenic sources were found in critically endangered Southern Resident killer whales, which live along the coast between Washington state and British Columbia, making them susceptible to pollution from fossil fuel refineries, vehicle exhaust and oil spills. With only 75 individuals left, every Southern Resident birth is crucial to the population’s survival. But in a troubling sign, the researchers discovered that the fish-eating apex predators are transferring carcinogenic PAHs to their unborn calves, according to the paper published Dec. 19 in the journal Scientific Reports.
“It’s really important for policymakers to take that into consideration when looking at oil and pipeline development along our coast,” Lee said.
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PAHs associated with forest fires and other pyrogenic sources were found in marine mammal-eating Bigg’s killer whales, also known as transient killer whales. A threatened species in Canada, Bigg’s orcas roam the Pacific Ocean from Alaska to Mexico and tend to live away from coastal infrastructure. Those migratory patterns, combined with the reach of wind-blown wildfire smoke, make the threat posed by PAHs particularly wide-ranging.
“California has really been impacted by wildfires and so that could be a reason why we found that Bigg’s killer whales had more PAHs that were linked to pyrogenic sources,” said Lee, who is currently a master’s student at the University of Oslo.
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Lee said it’s not possible to attribute the pyrogenic PAH contamination specifically to wildfires, as polycyclic aromatic hydrocarbons can be generated by the burning of wood, grass and coal. But co-author Juan José Alava noted that the PAH fingerprint found in Bigg’s orcas is characteristic of forest fire smoke that would be carried by the wind to the animals’ more remote habitat.
There are no coal-fired power plants in California and the Pacific Northwest relies largely on hydropower to generate electricity.
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The extent of PAH poisoning in orca populations is unknown, as are its exact health impacts — though the paper noted that scientists have linked cancer in Canadian beluga whales to PAH contamination. The researchers based their findings on tissue samples from a dozen killer whales that washed ashore in British Columbia between 2006 and 2018, before record-breaking wildfires incinerated vast areas of California and the Pacific Northwest in recent years. In 2023, wildfires burned 18.4 million hectares (45.5 million acres) in Canada, an area the size of North Dakota.
The study is “an important new piece of work on a class of contaminants that have not been heavily studied in whales,” said John Calambokidis, a senior research biologist and co-founder of the nonprofit Cascadia Research Collective in Washington. Calambokidis, who was not involved in the research, noted that prior studies focused on contamination of marine mammals by toxic chemical compounds such as polychlorinated biphenyls (PCBs).
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Alava said the researchers found PAH contamination from both pyrogenic and petrogenic sources only in one killer whale, an orphaned Southern Resident called Luna. Like other Southern Residents, Luna kept close to the urbanized coast but had also been tracked traveling to more distant areas of the ocean, where PAH contamination from sources like wildfires was discovered.
“Climate change is basically exacerbating all these wildfires, and they’re becoming more frequent and more intense,” said Alava, a research associate and principal investigator at the University of British Columbia’s Institute for the Oceans and Fisheries. “So all this smoke is aggregating in the atmosphere and is traveling even further west to where the killer whales are.”
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