Decontaminating the environment is kind of like playing a game of whack-a-mole. For more than a decade, biologists were alarmed by the levels of contaminants in polar bear fat, levels which have actually decreased in recent years thanks to policies like the Clean Air Act. But now it appears that another animal has risen to the top of the pollution hierarchy: Sharks.
These sharks live in the Greenland Sea, an icy Arctic channel between the archipelago of Svalbard and Greenland itself. Arctic carnivores tend to be some of the most contaminated animals on Earth because of the way airborne pollution evaporates, drifts north, and lands on ice, where it’s then absorbed by plankton. Even pesticides banned decades ago, like DDT, still linger in the environment by clinging to the fat of bigger animals and accumulating up the food chain. And just as polar bears were soaking up much of their toxins from eating ringed seals, researchers found that the higher the seal content of the sharks’ diets, the higher the contamination levels.
But the researchers didn’t realize the extent of the damage until they chartered a boat to check themselves. After examining 43 different shark livers, a group of scientists from the Norwegian University of Science and Technology concluded that levels of PCBs, a formerly common toxic chemical in flame retardants and pesticides, were at least three times higher than what had been found in polar bears.
“Most of the releases were in the 1960s until the end of the 1980s, and it’s gradually decreased, but there are still some releases from old sources, dump sites and so on,” explains biologist Bjorn Munro Jenssen. “We expected to find quite high concentrations, but not that high. They were actually higher than reported in Canada and in Iceland.”
The story of the sharks also has clear ramifications for humans, another top predator. While many of the compounds found in the sharks had been banned for years, Jenssen points out that they tend to linger in the environment long after we stop producing them. And while some traditional communities in the Arctic still rely on sharks as a source of food, even regular old tuna suffer from mercury levels that could become dangerous to humans. We don’t know what other animals will become contaminated by new compounds we create today.
“I think it’s important to know that contaminants are persistent, and will stay with us for 50, maybe 200, or 300 years,” Jenssen says. “Levels in polar bears are decreasing thanks to the international ban [on PCBs]. And maybe all these new contaminants are replacing the old contaminants. We don’t know what’s happening with them.”