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The orcas or killer whales are the masters of the oceans. With no known natural predators, this formidable creature has been roaming across the world since it evolved from a small, deer-like land animal about 50 million years ago—much before the appearance of the first humans. But this resilient top predator is now teetering on the edge of extinction because of chemical contaminants released by human activities.
Scientists from Canada, Denmark, Norway, Iceland, US and Greenland have conducted a 10-year-long research on orcas of the North Atlantic Ocean. Even though the ranges of the studied individuals were far from human habitations, the scientists have found in the orcas’ blubbers (fat layer under the skin) high levels of persistent organic pollutants (POPs)—toxic chemicals used in industrial and agricultural processes. One category of the POPs, the scientists write in Environmental Science and Technology in 2023, are polychlorinated biphenyls (PCBs). Used as coolants and lubricants in electrical components, they were banned in the US and Canada 50 years ago; yet PCBs were present at 10 times the threshold value considered safe for immune systems and fertility rate of orcas. The blubber samples also contained several other categories of POPs, whose “production, use, and/or release” were to be reduced or eliminated under international environmental treaty Stockholm Convention on Persistent Organic Pollutants, signed in 2001.
The fact is these “persistent” pollutants do not break down easily. Thus they remain in the environment for decades, travel over great distances through water and wind and eventually work their way through the food chain by accumulating in the body fat of species. They are at far higher concentrations in orca as it is an apex predator and eats nearly all ocean residents including a few whale species. Over its lifetime of 90 years, orcas become a hub of these chemicals, which then wreak havoc with their immune system, severely disrupting their endocrine function and impacting their growth and reproduction. Since these chemicals have a tendency to bind to the fat, mother orcas easily pass them down to their calves through milk. Anaïs Remili, a postdoctoral fellow at Simon Fraser University, Canada, who led the study, says orca is among the most contaminated animal on the planet. In 2018, researchers from Zoological Society of London and Aarhus University, Denmark, found that the number of orcas is rapidly declining in 10 of the 19 populations studied. The current concentrations of PCBs can lead to the disappearance of half of the world’s orca populations within 30 to 50 years, they wrote in Science.
The fate of orca symbolises the ubiquitous chemical signature of humans, the potential consequence of the contaminants and our failure to regulate those.
In the age of Anthropocene, chemicals made or mobilised by humans are the building blocks of modern society—they are in the food we grow, the clothes we wear, the medicines we consume, the vehicles we use and the way we power our homes. But these products and services throughout their life cycle—from manufacturing to usage to disposal—leave a trail of substances that are creating an avalanche of chemical pollutants. These can be toxic even in small doses, sometimes in combination with other chemicals in the wider environment or as breakdown products.
This was first published as part of a cover story on chemical pollution in the 16-31 December, 2024 print edition of Down To Earth