Mankind’s pursuit of hunting whales, or whaling, for fat in their blubber during the Industrial Revolution is why several whale species are currently endangered. This might be a familiar subplot for all the movie buffs out there who have been relentlessly waiting for the release of Spielberg’s Avatar: The Way of Water this year! However, what might not be so familiar is the other pathway of how these giant aquatic mammals are threatened by toxic chemicals that are released into the environment by humans. A group of scientists at the University of Oslo, Norway found that Norwegian Killer Whales might be subject to such toxicological threat, publishing their findings in 2020 and 2021 articles.
Anthropogenic pollution and their potential threat to human and ecological health, resulted in global responses in the form of the Stockholm Convention on persistent organic pollutants and the Minamata Convention on Mercury. Organic contaminants that are chemically stable, and hence persistent in the environment long after their use has been discontinued or banned, are often known as legacy persistent organic pollutants (POPs) because their present-day contamination is a ‘legacy’ of previous releases. The process by which POPs like polychlorinated biphenyls (PCBs) and pesticides like dichlorodiphenyltrichloroethane (DDT) get concentrated in the bodies of organisms is called bioaccumulation. The consumption of contaminated prey is greater than the organism’s ability to eliminate the pollutants – and this means that pollutants are “biomagnified” up the food chain and organisms at the top have the highest levels. In response to the regional and global ban of legacy POPs, replacement chemicals are often used. These chemicals are not yet regulated, and thus have become “contaminants of emerging concern”. New brominated flame retardants (BFRs) and perfluoroalkyl substances (PFAS) are some examples of emerging contaminants.
Top predators like killer whales are considered regulators of the marine ecosystem health. The fact that these legacy and emerging contaminants are found in the bodies of such top predators in environments without clear local sources, like the Artic, hints at the persistent nature and biomagnification potential of these chemicals. But not much is known about how these emerging contaminants are transferred from mother to calf. One of the reasons is the difficulty of obtaining samples – sampling is usually from opportunistically stranded individuals and may be impacted by the cause of the death, which is hard to interpret.
Clare Andvik, the first author of both the 2020 and 2021 articles, is a Doctorate Research Fellow at the Department of Biosciences, University of Oslo, Norway who is interested in studying the movement and effects of contaminants in wildlife, especially marine mammals like Norwegian Killer Whales. Her studies were a collaborative effort between the University of Oslo, Norwegian Orca Survey and the Norwegian University of Life Sciences to provide evidence of the persistent and bioaccumulative nature of legacy and emerging contaminants in the Arctic marine ecosystem.
(Source: Twitter thread of Clare Andvik Dec 6, 2021, pictures a-b by Krisztina Balotay and pictures c-g by Norwegian Orca Survey)
As a part of her previous work, Andvik found that killer whales feeding on marine mammals like seals had almost four times higher pollutant burdens compared to those feeding on lower trophic level organisms like fish. As a follow up of this previous work, one of the primary aims of the current study was to conduct a detailed screening of legacy and emerging contaminants in killer whales. Norwegian Orca Survey collected tissue samples [Figure 1] from a total of eight individual killer whales,of which one adult male had seal hair in his throat indicating that he had recently been feeding on a seal. This whale in particular was found to have the highest levels of total PCB and hexabromobenzene (HBB, an emerging BFR) in his blubber and mercury (Hg) in his skin as compared to the other sampled whales. Seven out of the eight whales were washed ashore in Northern Norway. The cause of death could be inferred for an adult male which was drowned after getting entangled in a herring purse seine and a calf which was stranded alive on the rocks in a shallow area where its group was feeding. The age of the calf was determined to be no more than 10 days, as milk was found in its stomach and all teeth were still inside the gum.
A second focus of the study was to investigate the maternal transfer of these contaminants. To this effect, emerging BFRs and PCBs were found in several organs of the calf indicating substantial maternal transfer of these chemicals. This study was the first to show the maternal transfer of these unregulated emerging BFRs by documenting their presence in the nursing neonate. The PFAS (in liver) and total mercury levels in the neonate were relatively lower than in the adults. This indicated that the maternal transfer of these chemicals is less efficient as compared to PCBs and BFRs. The importance of the cause of death was analyzed by comparing PCB levels in the neonate in this study with those in a German killer whale of similar age and sex from a previous study. It was found that the German whale, that was starved and had poor body condition, had higher PCB levels in its body as compared to the neonate in this study that was accidentally stranded. It was deduced that the poor body conditions at the time of death contributed to higher levels of PCBs for killer whales that might not be representative of the population.
The third focus of the study was to investigate the tendency of legacy and emerging contaminants to get attached to different kinds of tissues. For this, the screening of these contaminants was conducted on multiple tissues including blubber from 8 individuals, muscle from 5 individuals and kidney, liver, heart and spleen from the neonate. It was found that the emerging BFR levels (pentabromotoluene (PBT) and HBB) were twice as high in the blubber than in the muscle. This confirmed that these emerging contaminants preferentially accumulated in the lipid-rich tissues and have lipophilic properties much like legacy compounds (PCBs).
How do these contaminants interact with the various environmental components that drive them so far from their actual source of release? What is the current state of regulation of the emerging contaminants and how far into the future is their legacy going to last? Why are killer whales choosing seals over lower trophic level fish as a dietary preference? Given the results of this work and the questions that follow how do we protect the killer whales of Norway and save them from becoming extinct? “A big part of my work is to get certain chemicals regulated or banned. The bottom line is that we need to do this research to show that these chemicals are present in wildlife, because then we can take it to the authorities and hopefully, they can work with other European authorities to gather a lot of evidence to get these chemicals banned”, says Andvik, in a recent Women in Ocean Science podcast.
“I am lucky…that I did not have to choose between research and motherhood”, Clare Andvik, Episode 8: From accountant to orca scientist with Clare Andvik, Women in Ocean Science podcast.
