Killer whales are facing a massive decline and perhaps a complete collapse in their populations due to pollution from a now-banned chemical, according to a study published in the journal Science.
Polychlorinated biphenyl (PCB) - a highly toxic and carcinogenic chemical commonly found in industrial products - is being found in high concentrations in killer whales, harming their immune systems and ability to reproduce, the study published on Friday says.
PCBs were used in electrical appliances, paints, and other products because of their chemical stability, as well as their insulating and non-flammable properties, but were banned worldwide more than three decades ago.
However, they are still available in parts of the world and they continue to persist widely in the environment because they break down slowly.
The study said the chemicals had been found to concentrate in the blubber of whales, affecting more than half of the world's killer whales, also known as orcas.
The researchers said they feared killer whale populations near industrialised regions were at high risk of population collapse over the next hundred years.
"We knew that the PCB levels were high but it was really quite startling when we ran the numbers," lead researcher Jean-Pierre Desforges from Denmark's Aarhus University said.
"Over 50 per cent of those populations either had zero growth or they had considerable population decline, and for the worst cases a complete collapse."
Rebecca Wellard, a PhD scholar studying orcas and ecology at Curtin University in Australia, said killer whales are apex predators and "sitting at the very top of the food chain means they are more susceptible to pollutants in the ocean."
"What makes PCBs unique from other toxins is that its molecules are extremely fat-soluble, meaning they accumulate easily in fats. Unfortunately, once these PCBs are in the orca, the toxins don't go away," she said.
In 2016, a killer whale, nicknamed "Lulu" was found dead off the coast of Scotland with one one of the highest levels of PCB contamination ever found in an animal.
Scientists said last year the 20-year-old Lulu had never reproduced, even though most female killer whales reach breeding age at around 10.
Desforges said Britain's killer whale population was showing significant signs of decline with no newborn calves for over a decade.
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