Killer whales off Canada's Atlantic coast continue to be contaminated with dangerously high levels of toxic chemicals that put them at elevated risk of severe immune-system and reproductive problems, a recent McGill-led study has found.
The study, published in Science of the Total Environment, was based on information obtained from skin samples collected from living whales and dolphins near the French territory of Saint-Pierre and Miquelon, south of Newfoundland, downstream from the Gulf of St. Lawrence. The researchers analyzed biopsies from 50 animals, representing six species of cetacean (whale or dolphin).
The researchers found the picture was brighter for other whales and dolphins studied; their levels of contamination were mostly below the thresholds for severe health risks.
Overall, the researchers found that levels of harmful chemicals like polychlorinated biphenyls (PCBs) and organochlorine pesticides (such as DDT) have decreased since the 1980s and 1990s. Once used in industrial applications and agriculture, they were banned decades ago but persist in the environment, due to their stable chemical structure.
The presence of these persistent organic pollutants (POPs) had a particularly negative impact on killer whales because of their feeding habits, the researchers said. Killer whales and other toothed whales feed on species that are higher in the food web, and/or in coastal environments. The researchers found that these whales had higher contaminant levels than baleen whales, which feed on lower prey such as small schooling fish and krill in the open ocean. This suggests coastal areas continue to carry higher levels of pollutants, likely due to historical and ongoing sources of contamination.
"While it's encouraging to see a general decline in contaminant levels in baleen whales and small dolphins, which shows that regulations have had a positive impact, the situation for killer whales is particularly worrying," said Anaïs Remili, lead author of the study and former postdoctoral researcher in the Department of Natural Resource Sciences, who conducted the research while at McGill.
"The risk thresholds we use were established decades ago, and we need to better understand how these pollutants affect cetacean health today."
More research needed
Remili emphasized the need for ongoing research and monitoring to better understand the risks pollutants pose to marine mammals.
"We need to investigate ongoing sources of contamination, prevent the release of newer contaminants and assess the combined effects of multiple stressors on whale health," she said.
The study recommends future research work to update toxicity thresholds, investigate how pollutants affect whale hormones and immune systems, and develop targeted conservation strategies. The persistently high levels of contaminants in killer whales highlight the need for a focused approach to reduce chemical pollution in the northwestern Atlantic, the researchers said.
The study was conducted in partnership with the Marine Conservation Ecology Lab from Florida International University and the Department of Fisheries and Oceans, and funded by Canada Research Chairs Program, the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants Program and a Canada Foundation for Innovation Grant.
