By 1979, the mounting scientific evidence had led to an indisputable conclusion: polychlorinated biphenyls (PCBs) were toxic. These chemicals had been used for years in a wide variety of industrial applications, including insulators, electrical appliances, and road sealants. But studies had shown PCBs were also endocrine disruptors, altering the way the body’s chemical signaling systems work, so the US Environmental Protection Agency banned future production of the chemicals. The rest of the world followed suit at the Stockholm Convention in 2001.
At that point, though, the globe had already produced an estimated 1.5 billion pounds of the stuff.
Although countries collectively agreed to instate laws requiring to dispose of PCB properly in landfills, a lot of it still made its way into the environment. Past studies have shown the chemical’s harmful effects on seals, seabirds, porpoises, and even humans. Yesterday (Sept. 27), researchers led by a team from Aarhus University in Denmark and the University of St. Andrews published a study showing PCBs in the ocean (paywall) also pose a serious to one of the ocean’s top predators: killer whales.
Killer whales, also known as orcas, aren’t picky eaters, and if any of their prey has trace amounts of PCB, the chemical can build up in the orcas’ blubber after they dine. Because PCB is fat-soluble, mothers can also pass the pollutant to their young through their milk. It affects the hormonal, reproductive, and immune systems of orcas, meaning lingering amounts of it will render them sickly or infertile.
Over a decade, the researcher team sampled blubber from 351 orcas in 19 different pods living all over the world. They found that the orcas had anywhere from 10 to 50 milligrams of PCBs per kilogram of blubber, or the equivalent of roughly 100 to 1,300 parts per million, according to the Atlantic. Although there have never been any studies on the effects of PCBs on orcas specifically, research has shown that seals become infertile when PCB levels in their blubber reach around 60 parts per million.
Modeling out current population rates, estimated diets, and the amount of PCBs likely passed down from mother to calf (which they calculate to be about 70% of a mother’s PCB levels), the team projected how different orca populations would likely fare over the next century. They found that 10 of the 19 pods they surveyed will probably shrink. Some pods living off the coasts of Europe, Japan, and the western US, where orca numbers are already dangerously low and where waters have historically high PCBs, could die out entirely.
Orca pods living in places with low PCB concentrations, like the Arctic oceans, are less at risk of imminently dwindling, at least as a result of this particular type of pollution. However, other types of human activity are also taking a toll on orca populations. Dave Duffus, a marine biologist at the University of Victoria in Canada, told the New York Times (paywall) that he’s already seen killer whale populations falter as a result of dwindling food supplies and excess noise due to shipping activity.
All hope is not lost, though: At the moment, not all countries have gotten rid of PCB-laden equipment, Jean-Pierre Desforges, a post-doctoral researcher at Aarhus University and lead author of the study, told the Times. If they do so by 2028, as they promised with the Stockholm Convention, population decline may not be as rapid in some pods.