The other week I saw an article by The Guardian doing its rounds on my Facebook newsfeed. “Orca ‘apocalypse’: Half of killer whales doomed to die from pollution’. It caught my eye and has since caught the attention of various other media outlets. The paper in focus is recently released research on predictions of the global killer whale population collapsing due to PCB pollution.
Polychlorinated biphenyls (PCBs) are organic chlorine compounds. Originally, they were used for a range of things from coolants and insulating fluids, to carbonless copy paper and many things in between. Their wide use was due to their chemical stability, with desirable qualities ranging from low flammability to being highly unreactive and resistant to acids. They have a hydrophobic nature (water hating) and are able to resist metabolism, meaning they’ve been found within the fatty tissues of many organisms.
Around 2 million tonnes of PCBs were produced, between 1929 and the banning of their manufacture in 1979. Despite this PCBs are still entering, and existing within the environment. Contamination can occur though hazardous waste sites that are incorrectly maintained, illegal dumping of wastes and leaks from objects containing PCB. In the natural environment, they do not break down easily and have been found in a range of environments both on land and in the sea. This results in exposure to organisms who accidentally ingest the PCBs and can affect food chains, including our own. PCBs are easily soluble in animal fats, where they can accumulate.
A meeting was scheduled by the World Health Organisation (WHO) in Stockholm in 1997, with an aim to evaluate the toxicity of certain Persistent Organic Pollutants (POPS). Here they acknowledged that POPs such as PCB pose a threat to human life and the environment. The conclusion was that 12 POPs including PCB were to be reduced and where possible, eliminated.
The Orca, also known as the killer whale (Orcinus orca), is a large toothed member of the dolphin family. Found from pole to pole, different populations feed on different things, with some populations preferring fish and others predating on other marine mammals. Humans pose a large threat to Orcas in many ways, we’ve reduced their prey stocks due to over fishing, we use them for entertainment in our marine parks and we pollute the waters they reside with plastics and PCBs.
PCBs within marine mammal populations have been heavily researched since the 1990s, with research on orcas beginning in the early 2000s. With research from 2006 foreshadowing that pollutants such as PCBs may interfere with the recovery of the endangered species by making them more vulnerable to other factors such as disease and reducing fecundity.
The most recent data in question comes from Desforges et al, who examined PCB contamination in killer whale pods across the world. Using data models and population trajectories on PCB effects on immunity, calf survival rates, PCB exposure on population size they were able to predict how populations will be affected in the future. They found that many populations are trending towards a complete collapse within the next 100 years, including those found in the UK. Orcas who eat other marine mammals were seen to have up to 20- fold higher rates of PCBs than those on a fish diet.
Despite bans to reduce PCBs within the marine environment, high concentrations are still present in long-lived species such as marine mammals due to efficient biological cycling. This is where pollutants such as those that reside in the blubber of organisms, are transferred from mother to calf. Worryingly PCBs are just one known and studied pollutant that have been found within Orcas, and little is known about other contaminants found within their tissue and the effects that they have.
The plight of the Orca is not yet over. Populations found within less PCB polluted waters such as the Alaskan transient and Canada Southern Resident pods are at moderate risk, and so aren’t projected for total collapse. Current research is teaching us much about the effects of pollutants like PCBs but there are still many unresearched pollutants that could be effecting our marine life negatively.
Journal reference: Science. DOI: 10.1126/science.aat1953