Despite a ban several decades ago, a new study published on 28 September in the jounal Science suggests polychlorinated biphenyls (PCBs) may be gradually wiping out some groups of whale species. Other animals such as seals and are also under threat from PCB pollution. The study, led by Jean-Pierre Desforges, an ecotoxicologist at Aarhus University in Denmark, found that the effects of current PCB concentrations in the environment on reproduction and immune function threaten the long-term survival of more than 50% of the world’s killer whale populations.
PCBs were first discovered in the late 1800s in coal tar and form thick viscous liquids which made them useful as hydraulic fluids, lubricating oils, paint and concrete stabilizers, as well as nonflammable insulation in electrical transformers and plastics. This led to the mass production of PCBs beginning in the early 1930s. More than one million tonnes of PCBs were produced before scientists discovered they were linked to cancer as well as immune system, reproductive, and endocrine-related health issues in humans and animals. They are now banned in many countries since the 1970s and 1980s and this followed by a global ban in 2004 through the Stockholm Convention ― 90 countries committed to phasing out and disposing of large stocks of PCBs ― nonetheless, PCBs are still produced globally and persist in the environment.
It was previously estimated that more than 80% of global PCB stocks have not been destroyed yet and at the current rates of elimination, the 2025 and 2028 targets agreed upon under the Stockholm Convention will not be achieved. These toxic pollutants decompose slowly and as a result, they still find their way into the environment where they can also enter the food chain. They are found in the fat-rich tissues of animals, especially predators like killer whales that prey on other large predators such as seals and fish which have accumulated high levels of the toxic chemicals.
Along with DDT and other pesticides, PCBs have led to the widespread contamination of the world’s oceans. The models suggest several animal populations may have been halved during the 50 or so years that PCBs were present. Killer whales (Orcinus orca) are among the mammals with the highest level of PCBs in their tissues. A female killer whale may live for 60-70 years, therefore killer whales often still have high levels of PCBs in their bodies. Moreover, in mammals, PCBs can be passed to offspring through a mother’s fat-rich milk.
The international research team included participants from the US, Canada, England, Greenland, Iceland and Denmark. They reviewed all the existing literature and compared this data with their own most recent results to provide information on PCB levels in the largest number of killer whales ever studied ― more than 350 individual killer whales around the world. The findings suggest that killer whale populations near industrialized regions, and those feeding at high trophic levels regardless of location, are most at risk of population collapse over the next 100 years ― in the most contaminated areas, 30–50 years. The findings suggest the situation is worst in the oceans around Brazil, the Strait of Gibraltar, the northeast Pacific, and the around the UK. The results were slightly more uplifting for oceans around the Faroe Islands, Iceland, Norway, Alaska, and the Antarctic, the prospects are not so gloomy where models predict growth of the killer whale populations throughout the next century.
Although the first steps to phase out PCBs were taken more than 40 years ago, the authors conclude that “concerted efforts beyond those listed under the Stockholm Convention on Persistent Organic Pollutants (POPs) are urgently needed to reduce PCB exposure in vulnerable wildlife populations.”
(1) Desforges, J-P. et al. Predicting global killer whale population collapse from PCB pollution. Science (2018). DOI: 10.1126/science.aat1953