By Emma Lockley
In 1962 Rachel Carson wrote the iconic book, Silent Spring, alerting us to the horrific effects of man-made chemicals on the natural world. She predicted a planet where unexplained illness and death were the norm and species disappeared overnight. The world fell silent as birds vanished from our trees, poisoned as intensive agriculture turned to more obscure chemicals for pest and weed control. In part, the world heeded her warning – stricter controls were put in place, and some compounds were removed from production – but were we too late to save some of our most iconic species?
Polychlorinated Biphenyls (PCBs) were used extensively in industry in the 1960s and 70s, before being banned in most of the world in the early 1980s, in an effort to stem the harmful impacts of these compounds on our environment, which were only just beginning to be seen. PCBs had slowly begun to seep into the natural world, and were contaminating our ecosystems.
The final resting place of PCBs is thought to be in our oceans. Here, these man-made structures attach themselves to small particles of organic matter floating in the water. In time, these PCB-carrying particles will be eaten by small organisms, such as plankton and krill, which in turn will be eaten by fish. Onwards the PCBs go, up the food chain, in a process called bioaccumulation, until eventually top predators such as dolphins find themselves eating fish polluted by large quantities of these pollutants. Unable to metabolize the chemicals, the PCBs remain in their system, where they have the potential to cause untold damage.
PCBs have been linked to a range of health issues for dolphins around the world. They can suppress the immune system, leaving animals vulnerable to disease. They have also been associated with tumors and lesions in the beluga whales (Delphinapterus leucas) of the Gulf of St Laurence2. Most importantly, they have the potential to cause infertility, and have been blamed for the declines of many marine mammal populations such as the southern killer whale (Orcinus orca) population of Puget Sound, one of the most highly contaminated groups of animals in the world. Worse still, PCBs are passed down from mother to offspring through the mother’s milk, and so the problem is carried on to the next generation.
Was banning PCBs in the 1980s enough to curb the impacts of these compounds on the environment? The short answer is no. Although production was halted, PCBs are still found in existing industrial machinery, exposed to the elements in sealants, and inappropriately dumped in landfill sites. Fresh emissions continue to be detected in the air and surface waters of urban environments today. In fact, it is believed that only a very small percentage of the total PCBs produced have made it to their final resting place in the deep oceans3. The chemical behaviour of PCBs in their environment means that they can travel in air and water, resulting in traces of this chemical being detectable even in extremely remote locations such as the Arctic. It is a global issue.
Recently, a collaboration of scientists in the UK and Europe, led by Dr. Paul Jepson of the Zoological Society of London, pooled all their long term data sets to look at trends in the levels of PCBs in the blubber of the dolphin species that reside in our waters1. It makes for sober reading. Whilst there was an initial decline in the levels of PCBs in the harbor porpoise (Phocoena phocoena) and striped dolphins (Stenella coeruleoalba) in Europe after 1980, they have since stabilized at levels far exceeding those thought to cause health implications for the animals.
The story is even worse for the small populations of bottlenose dolphins (Tursiops truncatus) and killer whales that inhabit our waters. As mentioned earlier, PCBs are traditionally passed down from mother to calf through the mother’s milk, so contaminant levels tend to be lower in adult females than in males. This is not true of UK populations, however.
Pollutant levels are now so high that reproductive failure is setting in, and with no calves to feed, female’s contaminant levels remain high. Britain’s only resident killer whale pod now consists of just eight animals, and no live calves have been recorded with this group for over two decades. The situation looks bleak. Networks of marine scientists are working together to assess the gravity of the situation, and how it may affect the recovery of populations of animals already under threat from human impacts, but it is a huge task.
The plight of Europe’s dolphin species in the face of PCBs is a cautionary tale for governments and policy makers. Every year, more man-made chemicals are developed and released into the environment, with very little knowledge of the long-term implications to both the natural world and to us, as humans. Will these new chemicals we regard as safe today have similar impacts half a century down the line? Will we identify more threats to life, 50 years too late?
1. Jepson, P.D. et al (2016) PCB pollution continues to impact populations of orcas and other dolphins in European waters. Scientific Reports, 6, doi:10.1038/srep18573
2. Martineau, D. et al (1994) Pathology and toxicology of beluga whales from the St Lawrence Estuary, Quebec, Canada. Past, present and future. Science of the Total Environment, 154 (2-3), 201-215
3. Wania, F. and Daly, G.L. (2002) Estimating the contribution of degradation in air and deposition to the deep sea to the global loss of PCBs. Atmospheric Environment, 36, 5581-5593