Half the world’s killer whales could be wiped out by a chemical, first banned more than 40 years ago, new research has warned.
Decades after the first moves were taken to ban the use of PCBs (polychlorinated biphenyl), the chemical pollutants remain a deadly threat to animals at the top of the food chain.
The findings, published in the journal Science, show current concentrations of PCBs could lead to the disappearance of half of the world’s killer whales from the most heavily contaminated areas within just 30 to 50 years.
Orcas, or killer whales, are among the mammals with the highest level of PCBs in their tissue. Researchers have measured values as high as 1,300 milligrams per kilo in the blubber of killer whales.
For comparison, other studies have shown animals with PCB levels as low as 50 milligrams per kilo of tissue may show signs of infertility, as well as it having an impact on their immune system.
Researchers found the number of killer whales is rapidly declining in 10 of the 19 populations investigated.
They also said killer whales are particularly threatened in heavily contaminated areas such as the waters near Brazil, the Strait of Gibraltar and around the UK. Around the British Isles, it’s estimated there are less than 10 killer whales left.
The killer whale is one of the most widespread mammals on Earth and is found in all of the world’s oceans. But today, only the populations living in the least polluted areas consist of a large number of individuals.
Overfishing and man-made noise may also affect the health of the animals, but researchers say PCBs particularly can have a dramatic effect on their reproduction and immune system.
Killer whales, whose diet includes seals and large fish such as tuna and sharks, critically accumulate PCBs and other pollutants stored at successive levels of the food chain.
PCBs have been used around the world since the 1930s, with more than one million tonnes being produced and used in electrical and plastic components, which have subsequently found their way into the oceans.
Through the 1970s and 1980s, PCBs were banned in several countries. In 2004, through the Stockholm Convention, more than 90 countries committed themselves to phase out and dispose of large stocks of PCBs.
However, PCBs only slowly decompose in the environment, and can be passed down from mother to offspring in the wild through food and milk.
Researchers say this means the hazardous substances remain in the bodies of the animals, instead of being released into the environment where they eventually deposit or degrade.
Study co-author, Professor Rune Dietz, of Aarhus University in Denmark, said:
We know PCBs deform the reproductive organs of animals such as polar bears. It was therefore only natural to examine the impact of PCBs on the scarce populations of killer whales around the world.
The study examined PCB levels in more than 350 individual killer whales around the globe – the largest number ever studied.
Dr Jean-Pierre Desforges, of Aarhus University, said:
The findings are surprising. We see that over half of the studied killer whales populations around the globe are severely affected by PCBs.
Dr Desforges added how the effects result in fewer and fewer animals over time in killer whale populations.
The research shows killer whale numbers have virtually been halved in certain areas during the half century where PCBs have been present, and the models predict they’ll continue to do so throughout the next century.
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