Study Shows How PCBs Are Threatening the World's Killer Whales
Killer whales are found all over the Earth, but unfortunately for the whales, so are polychlorinated biphenyls. These industrial chemicals, which were banned in the United States in 1979 and by many other countries in the following decade, have been shown to cause cancer, disrupt hormone signaling, weaken immune responses, and negatively impact fertility. They also don’t break down easily in the environment and can persist for many years. Because of PCBs’ long life, they can build up in the bodies of top-level predators like killer whales — indeed, killer whales have been found to contain some of the highest concentrations of PCBs ever measured in marine animals. New research suggests that the high concentrations of PCBs found in killer whales (Orcinus orca) may threaten the long-term health of their populations around the world.
In a paper published Thursday in the journal Science, an international team of researchers estimated that PCBs threaten the reproductive abilities and immune functions of more than 50 percent of the world’s killer whales. Since PCBs biomagnify, meaning they build up in animals’ body tissues over time, they are easily passed up the food chain through killer whales’ prey and passed from mother to child through milk. Using global data on PCB concentrations in killer whales and comparing them to what scientists know about how PCBs affect health and mortality, the study’s authors constructed a model of how these chemicals are impacting killer whales.
“These results suggest that chronic exposure to persistent PCBs has the potential to affect long-term population viability in more than half of all studied killer whale populations,” write the study’s authors, led by Jean-Pierre Desforges, Ph.D., a postdoctoral researcher at Aarhus University in Denmark.
The researchers explain that PCBs will likely affect different killer whale populations differently, with those living closer to industrialized, human-populated areas bearing the worst brunt. They note that we’re already seeing these effects. “Killer whales once thrived in all oceans of the world, but only those in the less-contaminated waters of the Arctic and Antarctic today appear to be able to sustain growth,” they write. And chemical pressure isn’t the only kind of pressure these large mammals are facing.
“Of course, that population is also struggling with limited food,” Desforges tells The Atlantic. “But based on our simulations, the PCB effect alone should put them in the risky category. If you add additional stressors, you can only imagine what would happen.”
Unfortunately, we don’t have to wait around to see killer whales struggling.
This summer, a mother killer whale belonging to a community in the Salish Sea off the coast of Washington and Vancouver made headlines as she carried her dead calf around for more than two weeks. Her particular group has not had a successful pregnancy in three years, perhaps a sign of things to come.
“You can see the downtrend in their population,” Dave Duffus, Ph.D., director of the whale research lab at the University of Victoria in Canada who wasn’t involved in the new study, tells The New York Times. He says the new conclusions are “shocking, but I don’t doubt them.”
Though PCBs are so pervasive, some other animals provide a bit of hope. Ospreys in the United States, for instance, have recovered significantly since the effects of DDT and PCBs on their eggs’ health drove their numbers dangerously low. In fact, a recent survey showed that in the Delaware Bay and Delaware River, where populations had suffered in the second half of the 20th century, ospreys’ eggshell thicknesses have returned to pre-DDT levels.
Whales aren’t ospreys, though, and the fact that they nurse their young suggests that PCBs might take a lot longer to cycle out of their body tissues. Researchers have hope, though, that policy will catch up to science to help save the killer whales. Let’s just hope it happens in time.