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Despite having been banned in several countries in the 1970s and 80s, PCBs are still found in the oceans today and cause killer whales to become infertile.
These chemicals have been leaching into the marine environment for decades, becoming concentrated as they move up the food chain until they reach top predators such as killer whales.
It is now thought that PCBs (polychlorinated biphenyls) are not only impacting the health of killer whales, but that the increased exposure to them is causing the whales to become infertile. According to researchers, this could mean that at least half of all populations of killer whales globally could die out within just 50 years.
The research, conducted by a range of institutions including the Zoological Society of London (ZSL) and Aarhus University in Denmark, assessed the largest number of killer whales ever studied. It showed that while populations of whales that live in the waters off industrialised nations are most at risk of extinction, the poles could act as refuges for the species.
Prof Rune Dietz, who co-authored the study published in the journal Science, says, 'We know that 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.'
PCBs are a group of chemicals that began being used globally in the 1930s. They were used in the manufacturing of a wide range of products, from electrical components and plastics to paint and coolant fluids.
For decades these chemicals were known to be toxic, and in the 1970s and 1980s many nations finally made to move to ban them - but not after more than a million tonnes had already been produced. Much of this waste was simply dumped in landfill and has continued to leach into the environment.
It was not until 2004 that over 90 countries signed the Stockholm Convention, which aims to phase out and dispose of the massive stocks of PCBs that still exist.
Despite these efforts, the chemicals are persistent and little has been done. They are found suspended in the water and ocean sediment, where they get into the bottom of the food chain and are passed up, becoming more concentrated as they go.
This means that the populations of whale that eat other predators such as seals, like those living around the UK, have the highest levels of PCB in their bodies.
One whale was found to have a much as 1,300 milligrams of PCB per kilo of blubber. For comparison, it has previously been found that levels as low as 50 milligrams per kilo is enough to show signs of infertility and an impacted immune system.
Dr Paul Jepson, co-author of the study and killer whale expert at ZSL's Institute of Zoology, says, 'This suggests that the efforts have not been effective enough to avoid the accumulation of PCBs in high trophic level species that live as long as the killer whale does.
'There is therefore an urgent need for further initiatives than those under the Stockholm Convention.'
The scientists have been looking at the levels of PCBs found in various whales around the planet and putting that data into computer models to predict how many calves are likely to be born over the next 50 years as a result. This could build up a detailed image of how the cetaceans will likely fare if nothing is done.
They found that those whales living around Japan, Brazil, the Northeast Pacific, the Strait of Gibraltar and the UK are unlikely to survive. The only resident pod of killer whales in the UK is down to just eight individuals and has not had a calf in over 25 years.
Dr Chiara Giulia Bertulli, sighting officer for the Sea Watch Foundation, says, 'The waters around the UK are one of the places where killer whale populations have been affected the most, being halved during the last century where PCBs have been detected.
'The shocking reality is that these chemicals are passed from one generation to the next and we cannot reverse it. PCBs dissolve in fat and in milk and the new generations of killer whales will keep on carrying this heavy chemical burden.'
The whales in higher latitudes, thus further from contaminated water, are predicted to do much better. Populations that live off Norway, Iceland, Canada and the Faroe Islands are still doing reasonably well and may act as refuges for the species to repopulate the regions in which the whales went extinct.
Cleaning up these chemicals once and for all is possible. The USA, for example, has been doing a consistent job in cutting the amount of PCBs in the environment over the past few decades, despite having produced over 50% of all PCBs ever made. Europe on the other hand simply introduced a ban, then seemingly hoped the chemicals would go away.
If we actually followed the Stockholm Convention and tackled the issue, the whales would be in a much better situation to deal with other threats they may be facing, such as the loss of major prey such as shark and tuna, as well as underwater noise pollution.