Long-banned chemicals threaten killer whales and dolphins in European waters, a new study by the Zoological Society of London (ZSL) suggests.
PCBs (polychlorinated biphenyls) were once used in the making of paints, electrical equipment and flame retardants. But the chemicals, found to be toxic, were banned in the United States in 1979 and in the United Kingdom in 1981. However, they linger in the environment, impact the marine food chain, and now may be harming Europe's cetaceans.
A team from ZSL studied more than 1,000 stranded or biopsied dolphins, whales, and porpoises. They found that killer whale, bottlenose dolphin and striped-nose dolphin blubber contained dangerously high levels of PCB.
When PCB levels are high enough, they can harm cetacean immune systems and make breeding more difficult for the animals, due to an increased rate of newborn calf mortality.
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Top predators with good longevity, such as killer whales, tend to come by PCBs in their food-gathering travels.
"The long life expectancy and position as apex or top marine predators make species like killer whales and bottlenose dolphins particularly vulnerable to the accumulation of PCBs through marine food webs," said study lead Paul Jepson, of ZSL's Institute of Zoology, in a release.
"Our findings," said Jepson, "show that, despite the ban and initial decline in environmental contamination, PCBs still persist at dangerously high levels in European cetaceans."
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The researchers paint a dim picture of current circumstances for the creatures.
"Few coastal orca populations remain in western European waters," said Jepson. "Those that do persist are very small and suffering low or zero rates of reproduction. The risk of extinction therefore appears high for these discrete and highly contaminated populations."
"Without further measures," he added, "these chemicals will continue to suppress populations of orcas and other dolphin species for many decades to come."
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"Our research underlines the critical need for global policymakers to act quickly and decisively to tackle the lingering toxic legacy of PCBs," said study co-author Robin Law, "before it's too late for some of our most iconic and important marine predators. We also need to better understand the various pathways through which these iconic species are able to accumulate such high PCB concentrations through their diets."
The ZSL scientists' findings have just been published in the journal Scientific Reports.