Decades after Europe banned toxic PCBs, the region’s killer whales and three smaller dolphin species still carry high levels of the pollutants.
“They’re still at concentrations we really need to worry about,” said veterinary specialist Paul D. Jepson of the Zoological Society of London at a news conference January 12.
PCBs (polychlorinated biphenyls) were once industrial wonder chemicals but were banned by many developed nations by the end of the 1980s because of human health and environmental concerns. Despite the long gap since then, mean concentration of the chemicals in the blubber of some populations of Europe’s killer whales exceeds — often by a lot — a high threshold for health damage. So do PCB concentrations in bottlenose as well as in striped dolphins, Jepson and his colleagues report online January 14 in Scientific Reports. PCB concentrations in harbor porpoises were lower but still exceeded a lower threshold above which physiological changes may occur.
A team of researchers from across Europe — from Spain to Slovenia— compiled and analyzed PCB animal contamination information spanning from the early 1990s to 2009 or 2012. The data come from more than 1,000 animals, from either necropsies or blubber samples nipped from living animals. The concentrations represent a sum of the PCB variants detected.
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Over the limits
Adults of four species of cetaceans carry concentrations of long-lasting, toxic PCBs (measured in milligrams/kilogram of lipid) near or substantially greater than thresholds of observed effects from PCB contamination. The black line marks a level at which some lab tests start observing physiological changes in marine mammals. The red line represents a higher threshold, linked to reproductive effects in ringed seals.
After a modest postban drop in body concentrations of the PCBs, levels appear to have remained stable and high in around much of Europe, Jepson says. PCBs are probably leaking out of landfills or otherwise working their way to the waters. “There’s a lot more PCBs to come,” Jepson warns.
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What had once seemed a great asset for better living through chemistry has turned out to be a long nightmare for environmental contamination. PCBs resist heat and general degradation. And the chemicals don’t just linger; they concentrate themselves in animals. PCBs dissolve in fat and grow more concentrated as contaminated predators get eaten by even bigger predators. Top predators that eat fat-rich prey and live long lives, such as mammal-hunting killer whales, are thus especially at risk for high concentrations.
Males keep building up their body burden of PCBs, but females typically discharge most of theirs while lactating. The bad news: The PCBs freed from the females go into the milk their babies drink for months.
The researchers looked at two thresholds at which PCBs cause physiological effects. A lower threshold of 9 milligrams of PCBs per kilogram of body fat comes from experimental studies, and a higher one (41 mg/kg) is described for reproductive troubles in ringed seals in the Baltic Sea. In comparison, killer whales sampled in the United Kingdom had mean PCB concentrations of almost 108 mg/kg.
The survey can’t say for certain what population miseries come from the high PCB concentrations. Previous research suggests that PCBs impair reproduction, and Jepson notes that that Scotland’s killer whale population looks as if it’s going extinct. Only eight known survivors remain and no calves have been reported in almost two decades.
The high concentrations of PCBs in the survey don’t surprise marine mammal toxicologist Peter Ross of the Vancouver Aquarium. He has followed PCB contamination in aquatic life and hasn’t seen much improvement in decades. And in the case of some Pacific killer whales, he doesn’t expect PCBs to fall to safe levels in that population until the end of the 21st century. In terms of spotting a menace to the environment before it spreads, “we learned a very hard lesson with PCBs,” he says.