Pollutants in narwhal tissues raise concerns



I’ve paid close attention to the news this week noting that mercury levels are rising in Arctic marine mammals and that diabetes among Arctic natives is on the increase due to the pollutants in the whale meat they eat.  It got me thinking about what that means for narwhals.

Biologist Rune Dietz of Denmark’s National Environmental Research Institute has been investigating the contaminants in the marine environment that find their way into the animals’ vital organs, blubber, and other tissues -- even their tusks -- via the food chain.  While no studies have yet been conducted that have evaluated the health effects of contaminants like heavy metals and industrial chemicals on narwhals, Dietz found elevated levels of cadmium, selenium and mercury, as well as man-made organochlorines like PCBs and DDT, in tissue samples collected from 150 narwhals in Greenland.

These contaminants travel on prevailing winds in the atmosphere and are deposited in the Arctic in the rain and snow.  While concentrations of many contaminants in the environment are slowly decreasing over time, mercury – perhaps the most dangerous one because of the known deleterious effects it has on the brain and reproductive system – is increasing.  About 200 tons of mercury finds its way into the Arctic region each year, about 10 percent of the world’s emissions of mercury.  And the decline of multi-year sea ice due to global warming means that mercury that may have settled on the ice and was having little effect on wildlife is now finding its way into the marine environment where it is accumulating in the tissues of whales and other creatures.

          

Photo courtesy of Glenn Williams

Dietz is in the midst of several additional studies of mercury contamination in Arctic marine mammals. He has found that polar bears generally have low levels of mercury in their brains because they can rid their system of a substantial amount of mercury through their fur, a process whales cannot partake in since they have no fur. He is also analyzing mercury in the growth rings of narwhal tusks, which, like hair, teeth and feathers, can be a storehouse of pollutants.  “I can go out and get a two meter tusk and get the last 50 year history of that animal’s mercury contamination,” Dietz said. 

Dietz isn’t the only scientist examining narwhal tissue samples to better understand the health of the population. University of Manitoba scientist Gary Stern has collected samples of narwhal livers, kidneys, muscle and blubber to assess contaminants in the whales, and his results somewhat mirror those of Dietz.  He said that climate change may be exacerbating the problem because the accumulation of contaminants in narwhal tissues is dependent on the whales getting access to those contaminants.  As sea ice retreats, he said that more contaminated fish will be available for the whales to feed upon, making those contaminants “bioavailable.”

While Stern agrees with Dietz that little is known about the health impacts of these pollutants, he worries most about what he calls the “synergistic effects” from a wide range of challenges the animals are facing. 

“It’s hard to tell what affects the contaminants are having on their health, but they are one additional stressor they have to deal with,” he said.  “We still have no information that says directly that it’s affecting reproduction or having neurological effects; it’s hard to tell with an animal in the wild.  But these animals are under stress for a number of reasons – changing habitat, noise pollution – and contaminants are just another thing that acts synergistically to possibly making their immune systems not work as well.”