An old enemy has re-emerged to threaten again the survival of marine top-predators, such as orcas, other dolphins, and other marine animals. This pollutant foe was first identified in the 1960s and then seemingly knocked-back in the 1970s and 1980s, but recent research has shown that it was only diminished, and far from extinguished as a source of harm or even extinction.
The 'enemy' is the Polychlorinated Biphenyls or PCBs. (And as I know that the first sign of any chemistry is enough to immediately shut-down some readers, please stick with me because this is important and far-reaching news.) It was in the 1960s that a range of organic pollutants including PCBs were first identified in the tissues of wild animals and linked to significant adverse effects on their health, including their ability to reproduce. The manufacture and use of PCBs - once present in a wide range of industrial processes and products, including as fire retardants and in electrical equipment - were banned in 1979 in the USA and in 1981 in the UK, a ban that a few years later went EU-wide. Tissue concentrations in wildlife then began to fall and many populations recovered.
It was the animals at the very top of marine food chains that were mainly affected but, as things improved, those of us involved in trying to clean up the seas and waterways, rejoiced. Indeed, there was some real success as Paul Jepson, of the Institute of Zoology in London and Robin Law of the Centre for Environment, Fisheries and Aquaculture Science in Lowestoft, recently commented in their excellent overview - 'Persistent pollutants, persistent threats' - in the journal Science. Jepson and Law noted that most avian 'marine apex predators', including herons, gulls, ospreys, petrels and skuas, are now no longer listed as threatened on the International Union for the Conservation of Nature (IUCN) Red List.
However, Jepson and Law and their colleagues have also shown through their research that, whilst many organic pollutants have declined to virtual insignificance in the environment, the PCBs, have stopped declining. They currently exist in what Jepson and Law characterise as 'excessively high concentrations' in some cetaceans, including orcas (also known as killer whales), bottlenose dolphins in the northeast Atlantic and many cetacean species in the Mediterranean. These high PCB concentrations in European cetaceans have been widely associated with low rates of reproduction and long-term population declines.
This latest research is focused on Europe, but it seems most unlikely that this is only a European problem. It has long been known that the top marine predators, especially the cetaceans, are particularly vulnerable to the accumulation of such pollutants. For example, their long lactation periods mean that there is considerable transfer of pollutants from mother to calf in their very fat-rich milk. When asked what he would like to highlight from his investigations and how the PCBs issue might best be addressed, Paul Jepson said:
"Orcas have become the most highly contaminated species on Earth, with very high concentrations found throughout their range. This is deeply disturbing and this species has gone from being one of the most widespread to only being found in numbers in the less polluted regions, and other species are also at risk. There is an urgent need to review and improve our mitigation strategies in Europe and beyond; this is now a critical issue for marine conservation."
In terms of the other species at risk, Jepson and Law point to the remaining river dolphins, false killer whales, ringed seals in the Baltic, all the marine mammal species in the Black and Mediterranean Seas, beluga whales in the St. Lawrence River in Canada, polar bears in the Arctic and some sea eagle species. They also speculate that some long-lived large fish, such as the great white shark, might also be affected, although their PCB-exposures still need assessment. These compounds can travel long distances away from their industrialised production centres, hence their occurrence even in Arctic animals. Most recently, they have been found in the deepest seas too.
Industrialisation and related activities in Southeast Asia may have increased pollution outputs there, including PCBs. Countries should at the very least comply with the Stockholm Convention on Persistent Organic Pollutants- which commits its signatories to phasing out PCBs and other pollutants and eliminating large stocks or other sources of such pollutants - and much greater efforts need to be made to reduce PCBs leaking from landfills and demolition sites into the wider environment where they can then accumulate in vulnerable marine animals.
The resurgence of an 'old enemy', the PCBs, is certainly sad, and something of a defeat for grey bearded campaigners like me who thought we had 'won this one', but we must buckle down, refocus and demand that those who can act do so expeditiously. A world in which wonderful marine animals like some orcas are too polluted to reproduce is too sad to contemplate.Suggest a correction