A class of synthetic commercial compounds no longer manufactured continues to pose an existential threat to many killer whales, researchers report. Harmful effects from high levels of polychlorinated biphenyls (PCBs) in the bodies of these marine mammals threaten to crash some populations (Science2018, DOI: 10.1126/science.aat1953).
Killer whales, also called orcas, absorb PCBs from their prey. The toxic chemicals then accumulate in their blubber. Mothers pass the compounds to their calves via the placenta and in milk. PCBs can impair reproduction and disrupt the endocrine and immune systems. These substances, which are persistent in the environment and bioaccumulate, were formerly used in electrical and other equipment, in dyes and pigments, and as plasticizers.
An international team led by Jean-Pierre Desforges, a postdoctoral researcher at Aarhus University, determined that several orca populations worldwide are at high risk of collapse in coming decades because of health effects from PCB exposure.
The most vulnerable killer whale groups live in oceans near Brazil, Japan, the Strait of Gibraltar, and the U.K., as well as orcas in the northeast Pacific that specialize in feeding on prey with high levels of PCBs: marine mammals, tuna, and sharks.
“In these areas, we rarely observe newborn killer whales,” says coauthor Ailsa Hall, a professor at the University of St Andrews.
More than 80% of the 1 million to 1.5 million metric tons of PCBs manufactured between 1930 and 1993 still exist, though governments have pledged to destroy these stocks by 2028. At current rates, not all countries will meet the deadlines, the researchers say. They call for swift action to eliminate PCB stocks and thus reduce the exposure of vulnerable wildlife to these toxic substances.