In 1979, the US introduced a ban on polychlorinated biphenyls (PCBs) – a group of artificial chemicals used in electrical devices including insulators, capacitors, and transformers – prompting many other countries to do the same. Forty years on and current concentrations are still high enough to risk decimating the killer whale (Orcinus orca) population.
According to a study recently published in Science, the number of killer whales left in the wild could be slashed in half within the next 30 to 50 years.
To determine how exactly current levels of PCBs affect the health of killer whales, researchers compared their own data with the existing literature to calculate PCB levels in more than 350 individual whales in pods around the world – this, they say, is the highest number of killer whales ever studied. The numbers were plugged into models that then predicted the consequences that those PCBs will have on the immune systems and mortality of the killer whales and their offspring over a 100-year period.
The outlook isn't good.
"The findings are surprising. We see that over half of the studied killer whales populations around the globe are severely affected by PCBs," Jean-Pierre Desforges, a postdoctoral researcher at Aarhus University in Denmark, said in a statement.
Especially badly hit are the populations in and around the Strait of Gibraltar, the northeast Pacific, and the oceans surrounding Brazil and the UK. In these areas, the models reveal that populations have pretty much halved in the last 50 years.
"In these areas, we rarely observe newborn killer whales," Ailsa Hall, who helped design the models used by the Sea Mammal Research Unit in Scotland, added.
This is especially problematic because killer whales have extremely long gestational periods (18 months) and wait decades to reach sexual maturity (20 years).
"It is like a killer whale apocalypse," Paul Jepson from the Zoological Society of London, who was involved in the research, told The Guardian.
One of the reasons PCB quantities are so high in killer whales is that they are the final link in a very long food chain. Levels of PCBs in the cetaceans may be as high as 1,300 milligrams per kilogram (2.2 pounds) of blubber. As the researchers point out, just 50 milligrams per kilogram is enough to trigger infertility and immune system damage.
PCBs hang around in the environment for a long time and can be transmitted from generation to generation from the mother's fat-rich milk, meaning the problem of PCBs persists even as concentrations in the oceans decline.
But it's not just PCBs that are causing problems. PCBs are just one out of "a long list of additional known and as yet unmeasured contaminants present" in killer whales, the study authors explain. In addition to ocean pollution, over-fishing, and human-caused noise may also have negative ramifications for what is one of the most widespread mammal species on the planet. Let's just hope for the killer whales' sake, we find a solution to the problem soon.