More than half the world’s populations of killer whales are likely to collapse in the coming decades, according to a model of that predicts the effects of a persistent class of toxic chemicals known as polychlorinated biphenyls. The results on PCBs’ effects on orcas appear today (September 28) in Science.
Once commonly used in commercial products, PCBs were banned in the United States in 1978 and worldwide in 2004. Yet they continue to leach into the oceans, where they become concentrated in the fat of predators such as orcas. “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,” coauthor Jean-Pierre Desforges of Aarhus University in Denmark tells The Atlantic. “And once there, it’s extremely hard to get rid of.”
Desforges and coauthors looked through the published literature for what’s known of killer whale exposure levels and their effects. In some cases they had to extrapolate from studies of PCBs’ effects on other animals, such as mink. They then used the data in a computer model to predict the chemicals’ effects on specific killer whale populations around the world. Those that live near industrialized areas or that depend on prey higher in the food chain are at the most risk of population collapse, they found, and only those in less-polluted Arctic and Antarctic waters are likely to grow.
Research has linked PCBs to immune dysfunction, cancer, and reproductive and endocrine-related problems in humans and other animals. And the chemicals do not break down quickly. Hawaii Pacific University’s Brenda Jensen, who was not involved in the study, tells The Atlantic, “The reality is that these chemicals are, for timescales relevant to killer-whale life spans, permanently entrained in the marine food web.” While there’s little hope of reducing the whales’ exposure to PCBs, she adds, “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.”
Another researcher not involved with the work, Steven Bursian, an environmental toxicologist at Michigan State University, tells Science, “It’s sobering to be made aware of the potential long-term effects of chemicals that were introduced into the environment over 80 years ago. . . . It’s a wake-up call that similar predictions could be made about several other species.”