Chemical pollutants could disappear half of the world's populations of killer whales from the most heavily contaminated areas within a period of just 30 to 50 years, according to a study. The killer whale is one of the most widespread mammals on Earth and is found in all of the world's oceans from pole to pole.
Over 40 years after the first initiatives were taken to ban the use of polychlorinated biphenyls (PCBs), the chemical pollutants remain a deadly threat to animals at the top of the food chain, according to researchers at Aarhus University in Denmark.
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Polychlorinated biphenyls (PCBs) were banned in the US in 1978.
Killer whales (Orcinus orca) form the last link in a long food chain and are among the mammals with the highest level of PCBs in their tissue. Ten out of the world's 19 killer whale populations were rapidly dwindling.
Researchers have measured values as high as 1300 milligrams per kilo in the fatty tissue (blubber) of killer whales.
For comparison, a large number of studies show that animals with PCB levels as low as 50 milligrams per kilo of tissue may show signs of infertility and severe impacts on the immune system, researchers said.
Killer whale populations in highly contaminated areas like Brazil, the Strait of Gibraltar, the northeast Pacific and the UK were especially under threat and had already been reduced by half in the years when PCBs were being used.
The least contaminated populations swim in waters in the far north, off of Norway, Iceland, Canada and the Faroe Islands, and the study's models showed that these populations would continue to grow.
PCBs can have a dramatic effect on the reproduction and immune system of the killer whales, researchers said.
The diet of killer whales includes seals and large fish such as tuna and sharks that accumulate PCBs and other pollutants stored at successive levels of the food chain, they said.
It is these populations of killer whales that have the highest PCB concentrations and it is these populations that are at the highest risk of population collapse, according to the researchers.
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"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," said Professor Rune Dietz from Aarhus University.
Applying models, the researchers then predicted the effects of PCBs on the number of offspring as well as on the immune system and mortality of the killer whale over a period of 100 years.
"The findings are surprising. We see that over half of the studied killer whales’ populations around the globe are severely affected by PCBs" said postdoc Jean-Pierre Desforges from Aarhus University, who led the investigations.