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Source of increasing mercury levels in the Arctic a bit of a surprise

Suzanna CaldwellAlaska Dispatch News

A recent study shows more mercury is entering the Arctic Ocean -- from a surprising source.

Researchers from Harvard University were able to pinpoint higher levels of mercury deposited into the ocean at the top of the world, mostly from three major Russian rivers.

Previously, most researchers thought mercury eventually found its way into the ocean through the atmosphere as a result of coal combustion.

Daniel Jacob, professor of atmospheric chemistry and environmental engineering at the Harvard School of Engineering and Applied Sciences said the study, published in the journal Nature Geoscience, stemmed from questions on how atmospheric mercury eventually accumulated in the ocean. Studies found that mercury levels in the ocean were higher in the summer despite lower levels of pollution in the atmosphere. The opposite was true during winter months -- less mercury despite more pollution in the atmosphere.

Russian rivers are culprits

The study found that the Lena, the Ob and the Yenisei -- three of the world's largest rivers -- contributed more than twice as much mercury than the atmosphere did to the ocean.

This summer, a researcher in Alaska found that those same three Russian rivers are contributing 10 percent more water into the Arctic Ocean than they did 60 years ago.

The implications of the study are huge, Jacob said.

“Controlling emissions in that atmosphere aren't going to have any direct benefit in bringing down mercury levels in the Arctic Ocean,” he said. “We need to test the mercury level of those estuaries.”

Jacob said mercury in the rivers is coming from soil, more of which is eroding into rivers because of warmer temperatures in the region -- a direct result of climate change melting permafrost in Siberia. That soil contains mercury, some naturally occurring and some, Jacob suspects, from decades of mining activity in the region.

“(The research) points to a greater sensitivity to climate change than we have previously expected,” he said.

From here, Jacob and other Harvard scientists are looking at the last 30 years of mercury loading in the Arctic Ocean. That information will help determine what sort of impact climate change could have on marine animals in the future.

And with marine mammals being the lifeblood of Arctic residents, the implications of more mercury could be even more compelling.

Alaska and fish consumption

While mercury is a naturally occurring element, its build-up in animals can be lethal. The metal builds up as predators move through the ocean food chain, starting with plankton up to apex predators like seals and sea lions.

Ali Hamade, a toxicologist with the state division of epidemiology, said consuming high levels of mercury can affect the nervous system, kidneys and blood pressure. Especially susceptible are fetuses and infants. Pregnant women and children under 12 are advised to limit their consumption of certain types of fish known to contain elevated levels of mercury, such as albacore tuna, while fish like canned light tuna and all species of Alaska salmon are safe to consume in unlimited quantities.

Currently, Hamade is looking through fish-tissue sample data to see how changes to guidelines will be made, if at all. Consumption guidelines were last updated in 2007.

“We're hoping to get it out as soon as possible,” Hamade said. “There's a lot of information out there and it's a lot to digest.”

Only a few changes have been made since 2007. The latest was a pike advisory for the Kuskokwim-Yukon river drainage. Pike and burbot in the region were found to have high levels of mercury, an accumulation most likely the result of turn-of-the-century mining in the area.

Current regulations only place consumption limits on a few fish. Those are limited to halibut over 90 pounds, Alaska lingcod over 45 inches, spiny dogfish and salmon shark. The last two are high in the food web.

Hamade noted that the state conducts a voluntary mercury hair sampling program. Through May of this year, more than 900 women (who are closely monitored because of the neurological effects mercury can have on fetuses), had been tested. Of those, only four had levels high enough for a follow up, but none that were high enough to warrant medical attention.

Marine mammals and mercury

State Veterinarian Dr. Bob Gerlach said the state doesn't have much research on marine mammal toxicity levels, since those animals are heavily regulated under the Federal Marine Mammal Protection Act.

However, studies done in conjunction with the U.S. Fish and Wildlife Service have shown that polar bears are especially sensitive to mercury accumulation, because of their role as apex predators in marine environments. A 2011 study from researchers at the University of Alberta found higher mercury levels in polar bears in some regions. The study noted that polar bears, already impacted by shrinking sea ice due to climate change, could face even more challenges as higher mercury levels move through the food web.

But polar bear isn't a common delicacy in the Arctic. While marine life might have higher mercury concentrations, Gerlach noted that Alaska fish compared to other places in the world do pretty well.

“Our fish here seem to maintain pretty low levels in comparison,” he said.

Contact Suzanna Caldwell at suzanna(at)alaskadispatch.com

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