Killer whales’ diet, rather than location, greatly impacted contaminant levels

Recent studies have highlighted the critical threat posed by consistently high concentrations of persistent organic pollutants (POPs) in at least some populations of killer whales- due to their high-trophic positions and limited biotransformation and elimination capacities. As the ocean’s ultimate apex predators, killer whales from specific populations exhibit among the highest POP concentrations in the animal kingdom.

According to earlier research, some Pacific orcas populations can have POP loads in their blubber that could pose health risks like lowered immunity, hormone imbalances, and reproductive problems. However, nothing is known about orcas that reside in the North Atlantic. Therefore, scientists in a new study intended to evaluate the pollutants found in animals from Eastern Canada to Norway.

This is the most extensive study to date on North Atlantic killer whales. In this study, scientists report legacy and emerging pollutant levels in 162 individuals’ blubber. They found that the animals’ diet, rather than location, greatly impacted contaminant levels and potential health risks.

Scientists collected skin and blubber biopsies from over a hundred free-ranging killer whales across the North Atlantic Ocean from Canada, Greenland, Iceland, and Norway. In half of each tissue sample, they examined five kinds of POPs, including polychlorinated biphenyls (PCBs). The other portion was utilized to assess the diets of the animals. Several aspects of the data jumped out, including:

Contrary to previously reported POP levels in other Arctic marine animals, samples from orcas in the western North Atlantic had significantly greater pollutant loads than those from the eastern side.

Even though this brominated flame retardant had been banned ten years ago, the levels of one POP, known as -HBCDD, were the highest recorded for any marine mammal.

Instead of geography, the pattern may be explained by the diets of the individuals. The highest POP levels were found in animals that consumed marine mammals like seals or other whales, while the lowest POP levels were found in killer whales that foraged on fish.

Killer whales that preyed mainly on marine mammals had the highest health hazards from PCB exposure, with levels in most animals exceeding the threshold required for an increased risk of female reproductive failure.

Scientists noted, “The findings support the need for proper waste disposal to prevent contaminants from entering the oceans’ food chains and reaching the top predators. They explain that the findings of their study underscore the need for action to protect North Atlantic killer whales and their ecosystems.”

Journal Reference:

Anaïs Remili*, Rune Dietz, Christian Sonne et al. Varying Diet Composition Causes Striking Differences in Legacy and Emerging Contaminant Concentrations in Killer Whales across the North Atlantic. Environ. Sci. Technol. DOI: 10.1021/acs.est.3c05516

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