A new study has found both promising and worrying trends in contaminant (chemical pollution) levels in whales off the coast of Eastern Canada. The study, published in Science of the Total Environment, shows that while environmental regulations are making progress, killer whales in the region continue to face significant challenges.
A lasting toxic legacy
Although legacy contaminants like PCBs (polychlorinated biphenyls) and DDT (dichlorodiphenyltrichloroethane) were banned decades ago, their harmful effects persist in the marine environment. Their stable chemical structure makes them hard to break down, and their affinity with lipids means they can enter the food webs, and wreak havoc on the health of marine organisms.
Researchers collected fifty skin biopsies from six cetacean species between 2015 and 2022, focusing on the waters around Saint-Pierre-and-Miquelon, a French territory south of Newfoundland. The samples provided critical insights into how historical pollution from distant regions, such as the industrialized Great Lakes, continues to impact marine life in Canadian waters.
The diet is an important driver of contaminant accumulation
The study found that killer whales, which primarily feed on marine mammals, are particularly vulnerable to contaminant accumulation due to biomagnification — contaminants become more concentrated as they move up the food chain. These whales showed alarmingly high levels of PCBs and DDT in their tissues, more than twice above the toxicity thresholds that are known to impair immune and reproductive systems. Other cetaceans, like baleen whales that feed on smaller prey such as krill and small schooling fish, showed much lower contaminant levels, likely because their prey are lower on the food chain and accumulate fewer pollutants.
Stable carbon and nitrogen isotope values from skin samples and fatty acid profiles in the whales’ blubber revealed crucial details about their diet. The results of the study suggest that where whales feed plays an important role in their exposure to pollution as well. For example, species feeding in the open ocean had lower concentrations of contaminants than those feeding on more benthic/coastal species.
Killer whales carry twice the levels causing reproduction failure
Despite reductions in contaminant levels compared to the 1980s and 1990s, likely due to regulatory measures, the concentrations found in killer whales remain dangerous. The high levels of chemicals in these top predators could have long-term consequences, impacting their immune functions, endocrine systems, and reproductive success. Notably, even some common dolphins and white-beaked dolphins exceeded thresholds where immune effects, such as impaired lymphocyte function, might occur, raising concerns for their health as well.
The findings highlight the need for continued research and monitoring, especially for poorly understood populations like the killer whales off Eastern Canada. Future studies using advanced techniques like metabolomics, transcriptomics, or in vitro exposure on cell lines, could provide deeper insights into how pollutants, in combination with other stressors such as climate change and habitat loss, affect cetacean health.
A global problem…
The persistence of these contaminants in the environment poses ongoing challenges for marine conservation. Even though this research focused on Canadian waters, the problem is far from local. These chemicals are found globally. They get carried by atmospheric and oceanic currents and continue to accumulate in marine animals decades after their ban. Moreover, newer contaminant classes, such as per- and poly-fluoroalkyl substances (PFAS) and plastic-related pollutants, may add to the stress on marine mammals.
While some progress has been made in reducing environmental pollution, the high levels of legacy contaminants in species like killer whales remind us that the fight against pollution is far from over. Protecting these vulnerable marine species will require sustained efforts to further reduce contaminant sources and prevent the release of newer contaminants into our environments. Furthermore, we need to tackle other threats like noise pollution, bycatch, and prey reductions to avoid adding more stress to marine mammal populations worldwide.
Sources and further reading
- Remili, Anais, et al. “Legacy persistent organic pollutants among multiple cetacean species in the Northwest Atlantic.” (2024)
- Pedersen, Adam F., et al. “Feeding and biological differences induce wide variation in legacy persistent organic pollutant concentrations among toothed whales and polar bears in the Arctic.” Science of The Total Environment 908 (2024): 168158.
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Anaïs is the founder of Whale Scientists. She is a postdoc fellow at Simon Fraser University working on killer whale ecology, pollution, and health impacts. You can read more about her here.
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