Australasian Science: Australia's authority on science since 1938
The Persistent Killer of Killer Whales
By AusSMC
Killer whales are at risk due to PCB contamination despite a near-global ban more than 30 years ago. The threat affects more than half of the world’s orcas, and whale populations near industrialised regions and at the top of the food-chain are at a high risk of population collapse over the next 100 years.
This valuable study in Science (https://goo.gl/KuEN9u) extends previous work within the author team, which found alarming levels of polychlorinated biphenyls (PCBs) in North Atlantic killer whales, and further, found these levels to have an immunotoxicological impact. The author team showed that PCB-mediated effects on reproduction and immune function threaten the long-term viability of more than 50% of the world’s killer whale populations. Indeed, in a number of populations today there is strong evidence of reduced fertility and even complete cessation of reproduction.
PCBs manufacture has been tightly regulated worldwide for more than a decade, yet the legacy of these chemicals remains a constant environmental threat for high trophic level consumers such as killer whales. Further, 10 million new chemical substances are produced every year for application in everything we consume and use. As such, the effects of known harmful chemicals, such as PCBs, must be considered in the context of the cocktail of chemicals humans and wildlife alike are exposed to daily, for which toxicity is yet to be properly evaluated.
Associate Professor Susan Bengtson Nash is Director of the Southern Ocean Persistent Organic Pollutants Program at Griffith University.
Polychlorinated biphenyls are industrial chemicals that were used in a variety of processes and systems (e.g. as coolants in transformers). Although PCB production ceased in the 1990s, these chemicals are widely distributed in the environment and break down slowly, so although PCB levels have been declining since the ban, there is still a significant amount of them in the environment.
PCBs dissolve readily in fat and can accumulate in predators. This is particularly worrisome in animals such as killer whales, which not only eat contaminated fish but other predators such as penguins and seals which have accumulated far more PCBs than fish. As well, killer whales have substantial fat deposits that allow them to accumulate high levels of PCBs.
This study uses measured levels of PCBs in blubber from killer whales in a variety of locations, and mathematical modelling to predict the effect of these PCB levels on population growth of these animals. Based on the results of these simulations some populations are expected reasonable population growth (e.g. some Antarctic populations) while others are predicted to have populations decline (e.g. Faroe Islands and Iceland populations), while still others were likely to collapse completely (e.g. populations near Japan). The modelling is reasonable and consistent with modelling in dolphins.
However, while PCBs are known to have adverse effects on reproduction in laboratory settings and in wildlife with high levels of exposure, other studies in fish have not shown expected declines in fertility. As killer whales are exposed to higher levels of PCBs than in the fish studies, these killer whale modelling results must be taken very seriously. Given the other environmental pressure that these animals are subject to, conserving killer whales may be harder than expected.
Dr Ian Musgrave is a Senior Lecturer in the Faculty of Medicine, School of Medicine Sciences, within the Discipline of Pharmacology at the University of Adelaide.
I have to admit this paper made depressing reading. It is only a model, and thus will have some rate of error associated with it, but considerable thought seems to have gone into its creation and some of the predictions have already started to ring true. For instance, the model predicts very serious problems for killer whales in the UK, and a whale found dead off the coast of Scotland last year contained some the highest PCB levels ever recorded.
The work illustrates the unforeseen consequences and sheer environmental persistence of PCBs, which look set to continue to cause significant problems in the future, over three decades after they were banned.
Associate Professor Oliver Jones is from the School of Science at RMIT University.
Killer whales are apex predators. Persistent organic pollutants such as industrial chemicals like PCBs and pesticides like DDT build up in food chains, with their concentrations multiplying each step up from prey to predator.
Although PCBs were banned in the late 1970s, their persistent properties cause them to stick around. What makes PCBs unique from other toxins is that its molecules are extremely fat-soluble, meaning they accumulate easily in fats.
Unfortunately, once these PCBs are in the orca, the toxins don’t go away. As PCB concentration increases in an individual, it can impair reproduction, disrupt the endocrine and immune system, and ultimately reduce the animal’s lifespan.
This study is important as it investigates the effects of PCBs on killer whales at a global level. The PCB concentrations in the killer whales we study here in Australia were not included in this study, but overall the findings are heartbreaking as they predict that killer whale populations near industrialised regions, and those feeding at high trophic levels, are at a high risk of population collapse.
Rebecca Wellard is a PhD candidate studying cetacean bioacoustics and ecology.
