Assessment of persistent organic pollutants in killer whales (Orcinus orca) of the Canadian Arctic: Implications for subsistence consumption and conservation strategies

Killer whales (Orcinus orca) historically restricted to certain Arctic regions due to extensive sea ice have recently been documented farther north and for longer durations in the Canadian Arctic. These apex predators accumulate high levels of persistent organic pollutants (POPs). The objective of this study was to evaluate the concentrations and profiles of POPs in killer whales of the Canadian Arctic, thus determining potential risks for Inuit communities if consumed. Biopsies were collected from 33 killer whales across areas of the Canadian Arctic between 2009 and 2021. Significant variability in POP concentrations was observed among whales. The cumulative POP concentrations ranged from 12 to >2270 mg/kg lw, representing ∼200-fold increase from the least to the most contaminated individual. The rank order of concentrations of the top five contaminant classes was ∑DDT, ∑PCB, ∑CHL, ∑Toxaphene, and Dieldrin. Several emerging Arctic contaminants were detected, including chlorpyrifos, endosulfan, pentachloroanisole, and polychlorinated naphthalenes, although at relatively lower concentrations than legacy POPs. Considering the elevated blubber POP levels in killer whales, recommended daily consumption thresholds, established based on human tolerable daily intake (TDI) values, were notably restricted for ∑PCB (<0.14 g), ∑DDT (<6.9 g), ∑CHL (<13 g), dieldrin (<8 g) and heptachlor epoxide (<5 g). Killer whales in the Canadian Arctic exhibited higher POP concentrations than other commonly hunted species such as polar bears, ringed seals, and Arctic char. We acknowledge that a more holistic risk assessment of diet is required to assess the cumulative impacts of contaminant mixtures as well as nutritional quality of tissues commonly consumed by northern communities.

Varying Diet Composition Causes Striking Differences in Legacy and Emerging Contaminant Concentrations in Killer Whales across the North Atlantic

Lipophilic persistent organic pollutants (POPs) tend to biomagnify in food chains, resulting in higher concentrations in species such as killer whales (Orcinus orca) feeding on marine mammals compared to those consuming fish. Advancements in dietary studies include the use of quantitative fatty acid signature analysis (QFASA) and differentiation of feeding habits within and between populations of North Atlantic (NA) killer whales. This comprehensive study assessed the concentrations of legacy and emerging POPs in 162 killer whales from across the NA. We report significantly higher mean levels of polychlorinated biphenyls (PCBs), organochlorine pesticides, and flame retardants in Western NA killer whales compared to those of Eastern NA conspecifics. Mean ∑PCBs ranged from ∼100 mg/kg lipid weight (lw) in the Western NA (Canadian Arctic, Eastern Canada) to ∼50 mg/kg lw in the mid-NA (Greenland, Iceland) to ∼10 mg/kg lw in the Eastern NA (Norway, Faroe Islands). The observed variations in contaminant levels were strongly correlated with diet composition across locations (inferred from QFASA), emphasizing that diet and not environmental variation in contaminant concentrations among locations is crucial in assessing contaminant-associated health risks in killer whales. These findings highlight the urgency for implementing enhanced measures to safely dispose of POP-contaminated waste, prevent further environmental contamination, and mitigate the release of newer and potentially harmful contaminants.

Quantitative fatty acid signature analysis reveals a high level of dietary specialization in killer whales across the North Atlantic

Quantifying the diet composition of apex marine predators such as killer whales (Orcinus orca) is critical to assessing their food web impacts. Yet, with few exceptions, the feeding ecology of these apex predators remains poorly understood. Here, we use our newly validated quantitative fatty acid signature analysis (QFASA) approach on nearly 200 killer whales and over 900 potential prey to model their diets across the 5000 km span of the North Atlantic. Diet estimates show that killer whales mainly consume other whales in the western North Atlantic (Canadian Arctic, Eastern Canada), seals in the mid-North Atlantic (Greenland), and fish in the eastern North Atlantic (Iceland, Faroe Islands, Norway). Nonetheless, diet estimates also varied widely among individuals within most regions. This level of inter-individual feeding variation should be considered for future ecological studies focusing on killer whales in the North Atlantic and other oceans. These estimates reveal remarkable population- and individual-level variation in the trophic ecology of these killer whales, which can help to assess how their predation impacts community and ecosystem dynamics in changing North Atlantic marine ecosystems. This new approach provides researchers with an invaluable tool to study the feeding ecology of oceanic top predators.

Individual Prey Specialization Drives PCBs in Icelandic Killer Whales

Interindividual variation in prey specialization is an essential yet overlooked aspect of wildlife feeding ecology, especially as it relates to intrapopulation variation in exposure to toxic contaminants. Here, we assessed blubber concentrations of an extensive suite of persistent organic pollutants in Icelandic killer whales (Orcinus orca). Polychlorinated biphenyl (PCB) concentrations in blubber were >300-fold higher in the most contaminated individual relative to the least contaminated, ranging from 1.3 to 428.6 mg·kg^-1 lw. Mean PCB concentrations were 6-to-9-fold greater in individuals with a mixed diet including marine mammals than in fish specialist individuals, whereas males showed PCB concentrations 4-fold higher than females. Given PCBs have been identified as potentially impacting killer whale population growth, and levels in mixed feeders specifically exceeded known thresholds, the ecology of individuals must be recognized to accurately forecast how contaminants may threaten the long-term persistence of the world's ultimate marine predator.

Humpback whales (Megaptera novaeangliae) breeding off Mozambique and Ecuador show geographic variation of persistent organic pollutants and isotopic niches

Humpback whales (Megaptera novaeangliae) from the Southern Hemisphere carry information on persistent organic pollutants (POPs) from their feeding zones in Antarctica to their breeding grounds, making this species a sentinel of contaminants accumulation in the Southern Ocean. This study aimed to evaluate driving factors, namely feeding areas, trophic level, and sex, affecting POP concentrations in the blubber of humpback whales breeding off Mozambique and off Ecuador. Biopsies of free-ranging humpback whales including blubber and skin were collected in 2014 and 2015 from Ecuador (n = 59) and in 2017 from Mozambique (n = 89). In both populations, HCB was the major contaminant followed by DDTs > CHLs > PCBs > HCHs > PBDEs. POP concentrations were significantly higher in males compared to females. HCB, DDTs, HCHs and PBDEs were significantly different between whales from the Mozambique population and the Ecuador population. Sex and feeding habits were important driving factors accounting for POP concentrations in Ecuador whales. The whales from our study had some of the lowest POP concentrations measured for humpback whales in the world. These whales fed predominantly on krill as reflected from the low δ¹³C and δ¹⁵N values measured in the skin. However, the isotopic niches of whales from Mozambique and Ecuador did not overlap indicating that the two populations are feeding in different areas of the Southern Ocean.