Known to harm brains and trigger cancer in killer whales, PCBs remain the highest chemical contaminant found in the species' blubber
New York: Most people thought the problem of polychlorinated biphenyls – known as PCBs – had been solved. Some countries started banning the toxic chemicals in the 1970s and 1980s, and worldwide production was ended with the 2001 Stockholm Convention.
But they are lingering in the blubber or killer whales – and they could end up wiping out half the world's population or killer whales in coming decades.
We're looking at one contaminant among many, and this is one risk factor among many … It's not a dead-end story. There's still lots we can do about this. "
– Jean-Pierre Desforges Researcher
"It certainly is alarming," said Jean-Pierre Desforges, a postdoctoral researcher at Aarhus University in Denmark and the lead author on the new study published Thursday in the journal Science.
Whales sit at the top of their food chain. Chemicals like PCBs are tasks up by plankton at the base of the food chain, then eaten by herring and other small fish, which are eaten by larger fish, and so on. At each step in this chain, PCBs get more and more concentrated. The most at risk killer whales are those that eat and are very high on the food chain and quite contaminated, Desforges said.
lifespan or killer whales, now at threat from chemicals
Killer whale populations in Alaska, Norway, Antarctica and the Arctic among other places, where chemical levels are lower, will probably continue to grow and thrive, the study found. But animals living in more industrialized areas, off the coasts of the United Kingdom, Brazil, Hawaii and Japan, and in the Strait of Gibraltar, are at high risk of population collapse from just the PCBs alone – not counting other threats.
Dave Duffus, who is the whale research lab at the University of Victoria in Canada and was not involved in the new research, said that his conclusions are "shocking, but I do not doubt them."
Whales near him in the Pacific are surrounded by contaminants, face changes in their food supply and are continually bombarded with noise. "You can see the downtrend in their population," Duffus said.
Also known as orcas, killer whales are intelligent, social animals that pass survival information from grandmother to mother to daughter, Desforges said. Different populations have distinctive dialects.
The researchers used blubber samples to estimate the amount of PCB contamination in killer whales around the world. They are also a model to forecast the amount of PCBs passed through the placenta and breast milk. Researchers then compared these concentrations to the known damage that can come from different amounts of PCBs.
According to their calculations, about half the killer whale populations in the world will expand and shrink in coming decades. Desforges said he could not be sure how long it would take for these populations to collapse, but his team estimated that PCB exposure levels were at their highest, he said . PCB exposures declined with the bans, but levels have stopped falling into long-lived marine predators such as killer whales, he said. The whales only very slowly metabolize the PCBs during a lifespan or 50 to 80 years in the wild, Desforges said.
PCBs remain the highest chemical contaminant in the whales 'blubber, and are known to disrupt the whales' reproductive, endocrine, thyroid and immune systems, harm their brains and trigger cancer. Other chemicals are also present, but in lower concentrations and with far less known about their potential hazards, he said.
"We're looking at one contaminant among many, and this is one risk factor among many," Desforges said.
Despite the depressing results, Desforges said he was hopeful about the future of killer whales.
"It's not a dead-end story. There's still lots we can do about this, "Desforges said. Many countries are not living up to their commitments to dispose of old, PCB-contaminated equipment appropriated by 2028, he said, so that PCBs from entering the oceans.
He said he hoped that policymakers would do more to help protect them, with the study helping them to get started as well.
"If killer whales can not do it in the water, like pandas on terrestrial sites, I do not know who will," he said.