Polychlorinated biphenyls (PCBs) belong to the “dirty dozen” of highly toxic and carcinogenic environmental toxins. The use of these organic chlorine compounds was banned worldwide in 2001 – in the USA and Europe, the pollutants have hardly been used since the 1980s. However, because polychlorinated biphenyls are hardly degradable and accumulate in the food chain, they can still be detected today in soils, in glacial ice and also in the bodies of numerous organisms – above all in marine mammals.

Killer whales are particularly polluted. The reason: Orcas are top hunters in the oceans at the upper end of the food chain, which is why the poison accumulates in large quantities in them. In addition, female animals pass the burden on to their offspring via mother’s milk. Researchers have already occasionally detected PCB concentrations of 1,300 milligrams per kilogram of fatty tissue in the bubbles of killer whales. Already starting from a load between 40 and 50 Milligramm threaten the animals infections, immune disturbances and infertility.

Polluted marine mammals

But to what extent do environmental toxins really endanger the global populations of these marine mammals? Jean-Pierre Desforges of the University of Aarhus and his colleagues have now addressed this pressing question. The scientists first collected data on the whales’ exposure – a total of blubber PCB concentrations of 351 orcas from different parts of the world were available to them.

Together with population estimates and data on the toxicological effects of environmental toxins, they used this information for a model calculation: How will PCBs affect the development of killer whale populations over the next 100 years?

Hardly any offspring left

The frightening result: Ten of the 19 populations studied are rapidly shrinking and will continue to do so in the future – as a result, the killer whales could have completely disappeared from some regions in just a few decades. “We see that more than half of the orca populations are extremely affected by polychlorinated biphenyls,” says Desforges.

The situation is therefore particularly precarious in the waters around Brazil, in the Strait of Gibraltar, in the north-eastern Pacific and around Great Britain. In these areas, the whale load is consistently above the critical 40 milligrams per kilogram. “We rarely observe newborns there,” says co-author Ailsa Hall of the University of St. Andrews. The lack of reproduction is impressive around the British Isles, where the remaining population is estimated to be ten individuals.

Shortly before collapse

According to the forecast, there is a high risk that the populations in the now identified hazard areas will collapse within the next 30 to 40 years. It is easy to explain why the fate of these orcas looks so gloomy: They live near highly industrialised areas that once produced and used PCBs on a large scale.

Killer whales, which feed primarily on seals and other marine mammals high up in the food chain, are more at risk than those that feed mainly on fish. For example, some orcas in the Northeast Pacific that specialize in seals are ten to twenty times more polluted than their fish-eating relatives who live along the same coasts.

Still released

Overall, the study paints a worrying picture of the future of killer whales. But there is a glimmer of hope: in the whale regions around the Faroe Islands, Iceland, Norway, Alaska and Antarctica, PCB pollution is significantly lower and populations are growing – also in the next 100 years, as the models predict.

“All in all, however, it is clear that measures to protect the orcas are being noticeably hampered by the still problematic PCB concentrations,” the scientists write. “This makes it clear that we have not done enough to prevent the accumulation of these environmental toxins in long-lived and particularly endangered species such as the killer whale. We urgently need more initiatives,” says co-author Paul Jepson of the Zoological Society of London.

In fact, we can still do something about the pollution today. Organic pollutants are still released – for example, when contaminated buildings are torn down or other PCB-containing materials are improperly disposed of.