Arctic ‘Mercury Bomb’ Threatens Food Chain as Climate Warms

As global heating caused by the climate crisis warms the Arctic as much as four times faster than the worldwide average, Alaska’s Yukon River is eroding thawing permafrost and releasing mercury-laden sediment that has been sequestered for thousands of years into the surrounding environment.

The toxic contaminant is putting the food chain and communities that rely on it at risk, a press release from University of California (USC) said.

A new study led by researchers from the USC Dornsife College of Letters, Arts and Sciences has come up with a more accurate way of measuring mercury concentrations released from permafrost by the river, as well as to estimate total mercury yet to be released.

“Permafrost loss poses multiple threats to the estimated 5 million people who live in the Arctic, with 3.3 million people living in areas where permafrost is predicted to degrade and disappear by 2050,” the authors of the study wrote. “Thawing permafrost can damage critical infrastructure, impact navigable routes, and decrease food security, particularly for communities with subsistence practices. Additionally, permafrost thaw may release contaminants that have been locked away in frozen soils for millennia. The potential release of large amounts of mercury (Hg) from permafrost has received particular attention due to its threat to human health.”

As the mighty Yukon flows across the Last Frontier toward the Bering Sea, permafrost along its banks gets eroded, transporting contaminated sediment downstream.

“There could be this giant mercury bomb in the Arctic waiting to explode,” said co-author of the study Josh West, a USC Dornsife professor of Earth sciences and environmental studies, in the press release.

Earth’s atmospheric circulation has a tendency to move pollutants upward toward high latitudes. This results in an accumulation of mercury in the Arctic, West explained.

“Because of the way it behaves chemically, a lot of mercury pollution ends up in the Arctic. Permafrost has accumulated so much mercury that it could dwarf the amount in the oceans, soils, atmosphere and biosphere combined,” West said.

Arctic plants absorb mercury, becoming part of the soil when they die. The soil eventually freezes to become permafrost. Over millennia, concentrations of mercury build up in this frozen soil, not to be released until it thaws — a more frequent occurrence with the climate crisis.

The research team — including collaborators from the Yukon River Inter-Tribal Watershed Council and the California Institute of Technology — focused their study on two of the Yukon River Basin’s northern villages: Beaver and Huslia.

Earlier methods of estimating levels of mercury varied as much as fourfold and were also limited by a core sampling depth of approximately 10 feet.

On a quest for improved accuracy, the team looked for mercury in deeper soil layers of riverbank and sandbar sediments.

“The river can quickly mobilize large amounts of sediment containing mercury,” said corresponding author Isabel Smith, a USC Dornsife doctoral candidate, in the press release.

The researchers discovered that sediment mercury levels were consistent with higher estimates of prior studies. This confirmed that sediment samples offered deeper insight into the hidden dangers of permafrost.

The research team also used remote satellite sensing data to monitor how quickly the Yukon’s course is changing, a natural occurrence over time. The alterations to the path of the river are important because they affect the amount of mercury-laden sediments that are eroded from the banks of the river and deposited along its sandbars. Understanding these shifts is essential because it helps researchers to predict the movement of mercury.

One discovery was that finer-grained sediments contained more mercury than coarser-grained sediments, which suggested that certain types of soil may pose higher risks.

“Taking into account all of these factors should give us a more accurate estimate of the total mercury that could be released as permafrost continues to melt over the next few decades,” Smith said.

The amount of environmental mercury being released from melting permafrost may not present an acute toxic threat immediately, but the effects accumulate. As the food chain is increasingly contaminated with the dangerous metal, exposure to it increases, especially through the fish and game humans eat.

West pointed out that the contamination risk posed by drinking water is minimal.

“We’re not facing a situation like Flint, Michigan,” West said. “Most human exposure to mercury comes through diet.”

The research team emphasized that the river redeposits contaminated sediments on beaches and sandbars along its banks.

“There’s another layer of complexity here,” West said. “The rivers are reburying a considerable amount of the mercury. To really get a handle on how much of a threat the mercury poses, we have to understand both the erosion and reburial processes.”

The long-term effects could be catastrophic for Arctic communities that rely on fishing and hunting.

“Decades of exposure, especially with increasing levels as more mercury is released, could take a huge toll on the environment and the health of those living in these areas,” Smith said.

The researchers said they hoped the tools they had developed would enable Alaska’s “mercury bomb” to be more accurately assessed, so that it might be diffused.

The study, “Mercury stocks in discontinuous permafrost and their mobilization by river migration in the Yukon River Basin,” was published in the journal Environmental Research Letters.