Three pods of killer whales in the Pacific Northwest have now earned the unfortunate title of being the most contaminated wildlife on Earth, according to a new study. These killer whales, known as southern residents, live in the coastal waters near the U.S.-Canadian border and survive almost exclusively on contaminated Chinook salmon. The salmon contain high levels of polychlorinated biphenols (PCBs) and other industrial chemicals, which accumulate in even higher levels in the killer whales. Researcher Peter Rosssays whales are particularly sensitive because they eat massive amounts of fish over a long life – killer whales can live for 80 or 90 years – creating a massive buildup of toxins. That means the whales, particularly the southern resident population, have become some of the most contaminated marine mammals in the world [AP].
Researchers estimate that the southern resident killer whales carry 6.6 times more PCBs than a different group of whales just 200 miles to the north, known as the northern residents. They found that the Chinook salmon in the southern waters, including Puget Sound near Washington state, not only had the highest concentrations of contaminants but also the least amount of body fat. This means the southern residents are suffering a “double whammy” because they are forced to eat extra helpings of heavily contaminated salmon. Ross and his colleagues discovered that 97 percent to 99 percent of contaminants in the Chinook eaten by these whales originated from the salmon’s time at sea, in the near-shore waters of the Pacific. Only a small amount came from the time the salmon spent in rivers, although many of the rivers are contaminated, too, Ross said. “Salmon are telling us something about what is happening in the Pacific Ocean,” Ross said. “They are going out to sea and by the time they come back, they have accumulated contaminants over their entire time in the Pacific Ocean” [Scientific American].
The southern resident population, which is listed as endangered under US and Canadian law, now numbers 83, down from over 100 in the early 1990s. Although the decline cannot be attributed completely to contamination, researchers believe the PCBs are compromising the whale’s immune systems, making them more susceptible to infections. PCBs are a kind of endocrine disruptor, known to interfere with development, meddle with immune system function and cause a host of other problems. The Environmental Protection Agency banned most uses of PCBs in 1979; but the chemicals had been widely used in coolants, pesticides, plastics and other products and are extremely persistent in the environment, cycling through the food web for decades [Science News]. In the late 1980s, PCB contamination is believed to have contributed to a virus epidemic that resulted in a massive decline in European harbor seals.
According to the new study published in Environmental Toxicology and Chemistry, the southern resident males carry almost 150 parts per million of PCBs, the highest concentration recorded in a wild animal [Scientific American]. Female orcas tend to have lower concentrations of the chemicals because mothers offload them to their young, both in the womb and through breast milk. This means at a developmentally fragile time, young orcas get a hefty dose of poisons [Science News]. But researchers say cleaning up PCBs will be very difficult because the only way to get rid of the chemical is to incinerate it at very high temperatures.