Mercury is released when soil frozen for millennia in permafrost thaws - something climate change is making increasingly common.
ADVERTISEMENTFlowing across Alaska to the Bering Sea, the Yukon River erodes the permafrost along its banks and carries sediment downstream.
As our planet warms, this permafrost is eroding faster and releasing a toxic metal into the environment - mercury.
Though the mercury released from melting permafrost doesn’t pose a toxic threat today, its impact will grow over time. It gradually accumulates in the food chain with fish and wild animals consumed by humans posing a future threat as it builds.
A new study published by researchers at the University of Southern California Dornsife College of Letters, Arts and Sciences (USC) looks at more accurate ways of measuring the scope of the Arctic’s mercury problem.
Why is there mercury in the Arctic?
Natural atmospheric circulation means that pollutants tend to move towards higher latitudes.
This results in mercury accumulating in the Arctic where it is absorbed by plants which then die and become part of the soil. This freezes in the permafrost - where the ground stays frozen all year round - and over thousands of years, mercury concentrations have built up in the soil. In this form, it isn’t particularly dangerous.
The toxic metal is released when the soil thaws - something climate change is making increasingly common. The Arctic is warming four times faster than the global average.
Previously sequestered by permafrost in the sediment for millennia, this mercury is now being eroded and released into the environment.
It could pose a major environmental and health threat to the 5 million people living in the Arctic and more than 3 million people who live in areas where the permafrost is expected to disappear completely by 2050.
“There could be this giant mercury bomb in the Arctic waiting to explode,” says study co-author Josh West, professor of Earth sciences and environmental studies at USC Dornsife.
The risk of consuming mercury through drinking water is minimal and most humans are exposed to some level of mercury in their diet. Eroded sediments are also often redeposited further down the river.
Understanding the dynamics of this movement is vital to understanding the scale of the threat to Arctic communities.
Predicting the Arctic’s mercury pollution problem
The new research looks at a more accurate method of measuring the amount of mercury released from permafrost by the river and estimating the total mercury awaiting release.
Previous methods of estimating levels of this toxic metal face limitations like soil sampling depth, meaning the results vary massively. Core samples had been taken from just the top three metres of permafrost.
The study instead analysed mercury in sediments in riverbanks and sandbars, tapping into deeper soil layers. It found that levels of the toxic metal were consistent with higher estimates from previous studies which researchers say means their method is likely accurate.
ADVERTISEMENTThe team also used satellites to see how the course of the Yukon River could change in the coming years and how that could impact the erosion of mercury-laden riverbanks. They hope it will help predict the movement of this pollutant.
Researchers also found that sediment with finer grains contained more mercury than that with coarse grains. It suggests different soil types could pose different 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,” says Isabel Smith, a doctoral candidate at USC Dornsife and the study’s corresponding author.
