[ What the grieving orca tells us ]
Skeptics might note that one crucial component of the team’s predictions—how different PCB doses affect reproduction—hinges on data that doesn’t come from orcas. “You can imagine how hard it’d be to do a study on PCBs and reproductive rates in killer whales. We can’t exactly expose them in a lab,” says Desforges. “We tried to take the best available data for the most relevant species.” In this case, that’s the mink—a weasel that, though much smaller than an orca, is also an aquatic, fish-eating predator, and has long been used by toxicologists as a stand-in for other marine mammals.
This caveat aside, the team’s gloomy predictions are, if anything, conservative ones. They only considered PCBs’ effects on reproduction and immunity, and not their tendency to wreak havoc on hormones or cause cancers. They didn’t consider groups whose PCB levels haven’t been measured, like the Gulf of Mexico orcas, whose numbers have fallen from 277 in the early ’90s to just 22 now.
And the team’s predictions clearly reflect the reproductive problems that scientists have noticed among the world’s orcas. In many populations, miscarriages are common, and newborn calves often die. The southern residents haven’t had a surviving newborn since 2015, and the U.K. population hasn’t had one for 25 years. “These populations haven’t recovered even after things like whaling stopped,” says Desforges. “They’re stagnating when they should be growing again.”
Levels of PCBs in the environment dropped after the near-global bans of the 1970s and ’80s, but since the ’90s, they have stabilized. The chemicals aren’t being produced anymore, but they’re still present in old equipment, paints, and other materials. Around 80 percent of these old stocks have yet to be destroyed. “Anything built in the ’60s and ’70s, there’s a good chance that they contain PCBs, and if they’re improperly disposed in a landfill, those PCBs have a chance of entering the environment,” says Desforges. “And once there, it’s extremely hard to get rid of.”
That’s especially true for killer whales. For them, PCBs are an intergenerational curse that, once placed, cannot be lifted. The chemicals dissolve readily in fat, which means they not only accumulate in an orca’s blubber, but also in its milk. Through milk, a mother orca can pass up to 70 percent of her PCB burden to her calf—a toxic heirloom that then becomes concentrated in a much smaller body. “It’s a major issue, and one that will very much impede any effort we have to reduce PCBs in the environment,” says Desforges. “That transfer will keep happening, whatever we do to clean up contaminated hot spots.”
“There is no way to hook a killer whale, let alone a whole marine ecosystem, up to some sort of dialysis machine to filter PCBs out of the tissues,” adds Jensen. “Even animals that die allow the PCB-associated fat to cycle back into the marine food web.” The only option, beyond destroying PCB stocks, is to reduce the other threats that orcas face. “An analogy for this is human cancer risk. If you find out that you are genetically predisposed to some form of cancer, you might be motivated to reduce other risk factors in your life that you can control by quitting smoking or exercising more. Now that we understand that these whales carry such a burden, perhaps we can compensate by working to provide an environment that can sustain their energetic needs to reproduce.”
PCBs are just one class of persistent pollutant, and one that’s been thoroughly studied. “We know they’re bad,” says Desforges. “But we know a lot less about many of the newer compounds that are replacing them, new surfactants and flame retardants. We have to find them and work out what they’re doing to the animals.”