Because of their diets, some killer whales are being slowly wiped out because of exposure to polychlorinated biphenyls.
Audun Rikardsen—www.audunrikardsen.com
By Elizabeth Pennisi
Even though it was banned decades ago, one of the more dangerous industrial pollutants of the last century is wreaking havoc on killer whale populations worldwide. That’s the conclusion of a new study, which finds that polychlorinated biphenyls (PCBs) may be slowly wiping out some groups of these iconic marine mammals. PCBs also threaten other animals as well, including seals and sharks.
“It’s sobering to be made aware of the potential long-term effects of chemicals that were introduced into the environment over 80 years ago,” says Steven Bursian, an environmental toxicologist at Michigan State University in East Lansing who was not involved with the work. “It’s a wake-up call that similar predictions could be made about several other species.”
PCBs were first discovered in coal tar in the late 1800s and mass produced beginning in the 1930s. They form thick liquids that proved useful as hydraulic fluids, lubricating oils, paint and concrete stabilizers, and nonflammable insulation in electrical transformers. They were even used to make carbonless copy paper.
Companies produced more than a million tons of PCBs before scientists linked them to cancer and immune system, reproductive, and endocrine related health problems in both people and animals. The major user and producer, the United States, banned their production in 1978, and a global ban finally went into effect in 2004. For a while, PCB concentrations in the environment dropped precipitously. “Everyone was quite happy about this success story,” says Jean-Pierre Desforges, an ecotoxicologist at Aarhus University in Denmark.
But these pollutants don’t break down easily. They are still leaking into the environment from landfills, river-bottom sediments, and other places they were dumped. Consumed by microbes, they enter the food chain and eventually they build up in fat and blubber of animals, especially top predators such as killer whales, which prey on other predators such as seals or fish that themselves have stored PCBs.
Over the past several years, surveys have documented shrinking killer whale populations in some parts of the world. Other data have revealed surprisingly high levels of PCBs in these animals, despite decades of being banned. So Desforges and colleagues searched the scientific literature for all studies related to killer whale PCB levels and killer whale population changes. “That was first time we really saw the extent of the problem,” he says. “Quite a few populations had high PCBs.”
Testing animals directly for health consequences wasn’t possible because killer whales, like many marine mammals, are protected. So Desforges teamed up with modelers Ailsa Hall and Bernie McConnell from the University of St. Andrews in the United Kingdom to estimate the toll of the PCBs. They built on lab studies in which Desforges showed that PCBs extracted from whale blubber affect killer whale immune function. Other studies, done in mice, estimated the PCB levels that raise susceptibility to disease and impair fertility. Based on the lab results and on year-by-year PCB concentrations in individual killer whales, the modelers predicted how many would suffer similar effects.
This modeling suggested that of the 19 populations studied, more than half will decline because of PCBs’ effects, Desforges and his colleagues report today in Science. Killer whale pods in Brazil, the North Sea off the United Kingdom, and around the Straits of Gibraltar are the most vulnerable because their PCB levels are highest. Especially high pollution levels, features of the whales’ diet, or a quirk of their metabolism that makes it hard for them to break down these compounds could all be to blame. In these populations, the PCBs will impair reproduction enough that these groups could dwindle and disappear in the next 50 years, the team found.
Other top predators, such as sharks and dolphins, likely have dangerously high PCB levels as well, Desforges and his colleagues say. In sea lions, tumors and increased disease seem linked to high PCB levels. And even though polar bears are much better than killer whales at getting rid of the PCBs they consume, some have heavy exposure to the chemicals. Polar bears in east Greenland, for example, have increased their PCB intake by switching from hunting ring seals to hooded seals, which have higher PCB concentrations in their bodies. “The PCB story is not over,” Desforges says.
Other long-lived chemicals are showing up in wildlife as well, says Frances Gulland, a marine mammal veterinarian at The Marine Mammal Center in Sausalito, California, who was not involved with the killer whale work. And like PCBs, compounds once thought to be benign, such as flame retardants, may also turn out to be harmful to wildlife. “There could be countless other chemicals in the environment that could be having similar health effects,” Bursian says. And, Gulland adds, “we are way behind the eight ball on them.”
Source: Science Mag