In a ground-breaking new study just published in Environmental Science & Technology, a disturbing picture of contamination among North Atlantic killer whales has emerged. Persistent organic contaminants (POPs), including polychlorinated biphenyls (PCBs), pesticides (DDTs, Chlordanes, etc.), and flame retardants, were detected at alarming levels in these apex marine predators.
This study sheds light on the perilous state of North Atlantic killer whale populations and its potentially far-reaching consequences. Focusing on 160 individual killer whales across the North Atlantic, this study represents a large international collaborative effort. The findings underscore the urgency of addressing these contaminants and provide critical insights into the complex web of marine ecosystems and the influence of dietary habits on contaminant threats in top predators.
Killer whales, or orcas, have long captured our fascination with their intelligence, powerful presence, and striking appearance. These magnificent predators roam the vast expanses of the North Atlantic, from the icy waters of the Canadian Arctic to the rugged coastlines of Iceland and Norway. However, beneath their awe-inspiring exteriors lies a silent, persistent threat that imperils their survival – the toxic legacy of human-made pollutants.
Legacy Contaminants in North Atlantic Killer Whales
The study’s findings are stark: killer whales in the North Atlantic carry a heavy burden of contaminants. Among these, polychlorinated biphenyls (PCBs) take center stage. The mean concentrations of PCBs ranged from approximately 50 mg/kg in the mid-North Atlantic to a staggering 100 mg/kg in the Western North Atlantic. However, killer whales in the Eastern North Atlantic showed PCB levels far below the other locations (~10 mg/kg in Norway).
PCBs are a group of toxic chemicals that were once widely used in various industrial applications, including electrical equipment. Due to their persistence in the environment, PCBs have found their way into marine ecosystems, where they pose a serious to wildlife health.
These PCB concentrations reach their peak in Canada. There, killer whales carry PCB levels averaging 106 mg/kg in Eastern Canada and 92 mg/kg in the Eastern Canadian Arctic. This is among the highest average PCB loads recorded in any animal tissue. To provide some context, the highest threshold at which marine mammal reproductive failure due to PCB exposure is 41 mg/kg. Thus, killer whales in Eastern Canada carry PCB concentrations more than twice the level associated with reproductive failure in marine mammals.
The Impact of Diet Habits
The research underscores that what these apex predators eat has a profound impact on the pollution levels in their systems. Killer whales primarily feasting on fish, characterized as having “fish-dominant diets,” tended to display relatively lower concentrations of contaminants. In contrast, those individuals whose diets were centered around marine mammals, especially seals and toothed whales, exhibited higher contaminant levels.
Killer whales with “mixed diets,” including both fish and marine mammals, showed high levels of contaminants, especially in Iceland. This intricate relationship between diet composition and contaminant accumulation underscores the complexity of killer whale ecology. It highlights how their dietary preferences can profoundly influence their exposure to environmental pollutants.
Effect of Sex
The study also examined the effects of sex and age on contaminant concentrations. Male killer whales were found to be significantly more contaminated than females. This sex-related difference can be attributed to the maternal transfer of these contaminants from adult females to their offspring. This happens during gestation and lactation.
Implications for Killer Whale Health
The elevated levels of contaminants, particularly PCBs, in North Atlantic killer whales have grave implications for their health. Risk assessments indicate that killer whales in the Western North Atlantic and certain areas of the Eastern North Atlantic face consistently higher risks than others. In fact, these risks are directly related to the whales’ diet preferences. These risks are primarily associated with PCB concentrations and are exacerbated by diets that include pinnipeds or toothed whales.
Emerging contaminants among the highest recorded in marine mammals
Among the emerging contaminants, hexabromocyclododecane (HBCDD) was the dominant compound. HBCDD is a brominated flame retardant used to reduce flammability in various products like textiles and electronics, but it has raised concerns due to its environmental persistence and potential health hazards. The concentrations of HBCDD measured in North Atlantic killer whales are among the highest measured in any marine mammals, and surpassed the levels measured in their North Pacific conspecifics.
A Call for Action
The findings of this comprehensive study underscore the urgent need for action to protect North Atlantic killer whales and their fragile ecosystems. The Stockholm Convention, which aims to phase out hazardous substances and promote safe waste disposal, is at risk of falling short of its 2025 and 2028 targets. To address this, several measures are imperative:
- Enhanced Monitoring. Robust monitoring programs are essential to gather reliable data on pollutant levels in marine mammal populations. This data is vital for informed decision-making and conservation efforts.
- Interdisciplinary Collaboration. Collaboration among ecotoxicologists, conservation biologists, policymakers, and other stakeholders is crucial. We can only develop effective strategies to mitigate pollution’s adverse effects through collective efforts.
- Protection of High-Risk Populations. Populations at higher risk, such as killer whales in the Eastern Canadian Arctic, should receive targeted conservation efforts.
- Enhanced Toxicity Assessments. We must step up our toxicity assessment efforts and focus beyond just PCBs to include a broader array of contaminants. Furthermore, it’s crucial to examine the effects of combinations of these contaminants, as they are thought to have a higher level of toxicity when they interact compared to when they act individually.
North Atlantic’s killer whales are facing a hidden threat – a toxic legacy of human-made pollutants. This new comprehensive study has shed light on the extent of contamination in these marine predators, highlighting the urgency of conservation efforts.
It is our responsibility to protect these iconic species and the delicate ecosystems they inhabit. By taking decisive action, fostering interdisciplinary collaboration, and revaluating our approach to chemical safety, we can ensure that killer whales in the North Atlantic continue to thrive and inspire generations to come.
Here is a link to the open-access peer-reviewed paper: https://doi.org/10.1021/acs.est.3c05516
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