Even after being banned worldwide decades ago, PCBs (polychlorinated biphenyls) are still posing a severe threat to orcas (or killer whales), reports a new study featured in Science magazine.
What are PCBs?
PCBs are an oily liquid or solid, with the property of being very stable, even when exposed to extreme temperature or pressure. As such, PCBs were used in a wide range of electrical components and equipment. In fact, their use was widespread across industry, from building sites to paint production to cutting machine fluid.
Manufacture of the chemical began in the 1920s and by the time their use was banned, it is estimated that 1.5 billion pounds of the product had been made. By the late 1970s it was realised that PCBs are highly toxic. The USA banned their use in 1979, and in 2001 at the Stockholm Convention, they were banned worldwide. North Korea is the only country still to manufacture PCBs.
Banned – but not Eradicated
The problem is in the disposal of PCBs that still exist. To date, only about 4% of the PCBs that were in existence have been safely destroyed. The rest, unable to be used, have remained in storage facilities while decisions are made as to how to get rid of them, or have simply lain in landfill sites. From there, the toxins leach into the water system, into rivers, and eventually oceans. Here, they are contaminating oceans, particularly in industrialised areas of the world, where marine creatures, including killer whales, are exposed to them.
Why are Orcas Especially at Risk?
Orcas are the top of the food chain, eating sea creatures which have in turn eaten others. In sea waters contaminated with PCBs this means they can consume a damaging amount of the toxin. Over time, the levels of PCB build up in an orca’s body, where it dissolves in the fat (blubber). From there it can enter the orca’s bloodstream and even be fed to their young in milk. It has been found that PCBs have a detrimental effect on the immune system of orcas, rendering them more prone to illness. Moreover, it affects their reproductive system, and cause infertility. An example of this is the endangered orca population off the West Coast of Scotland. Here, just eight orcas are remaining – and no calves have been born in more than 20 years.
The study cited in Science magazine found that, of the 19 pods surveyed, 10 are thought likely to decline in numbers. As well as the UK’s orcas, those in the straits of Gibraltar, Japan and Brazil are unlikely to survive. Although all manufacture and use of PCBs has been halted, the task of safe disposal is not being consistently addressed. The USA has put much funding into cleaning the most contaminated sites, and here the seas are showing reduced levels of PCBs.
The outlook for orca populations in areas where PCBs are low, or reducing, is better. In the Arctic and Antarctic, the decline in numbers should reverse. But PCBs, once in the ocean, cannot be removed, and the next 30 to 50 years will be critical for the orcas.