European whales and dolphins may be at risk of extinction from the effects of polychlorinated biphenyls, or PCBs, a team of researchers recently reported in Scientific Reports. Concentrations of PCBs in killer whales and bottlenose and striped dolphins, they found, were high enough to cause health damage.
PCBs have been banned in Europe, the United States and many other places for decades, so finding them in marine mammals may be surprising to some. It shouldn’t be, though. Marine mammal toxicologist Peter Ross of the Vancouver Museum told Science News that he doesn’t expect the chemicals to disappear from Pacific killer whales, another population in which the chemical contamination has been well documented, until the end of this century.
And PCBs are far from the only toxic chemicals that have been found to taint the blubber and other tissue of whales and dolphins. For example, toxaphene, DDT, PCBs and chlordane were found nearly two decades ago in beluga whales. And smaller levels of PCBs were found in blue whales.
Chlordane, toxaphene, DDT and PCBs are all examples of persistent organic pollutants — chemicals that were once widely used in agriculture and manufacturing (or accidentally produced through industrial processes or combustion) but are now banned due to their adverse effects on human health and the environment. These chemicals became especially troublesome not only because of their toxic qualities but also because they crept from their original destinations. Some are still leaching out of landfills. And they move through the environment, often through the food web. Because these chemicals don’t easily break down, animals that eat animals laced with these toxins end up with ever-higher levels of them — a process known as biomagnification.
That may explain in part why a plankton-eater like a blue whale can have lower levels of PCBs than beluga whales: The belugas are higher up on the food chain. Location and individual metabolism can also make a difference. And in the new study, the researchers note that females discharge PCBs through milk, while males do not. (Poor baby whales are getting mom’s PCBs.)
Persistent organic pollutants are not even the only problem when it comes to toxic chemicals. Mercury — from anthropogenic sources such as power generation — also works its way into whales and dolphins. Tests of whale meat for sale online in Japan last year revealed mercury levels as high as 47.5 times what is considered safe for human consumption.
With such reports about toxic chemicals in whales and dolphins going back decades, one has to wonder why people continue to hunt and eat these animals — let alone feed them to schoolchildren.
But the bigger worry, really, is for the whales themselves. Whaling drove many populations and species to near extinction, and the end of such hunting should let them recover. But as the latest report points out, that can be difficult when food sources are tainted with chemicals that may impair reproduction.