Scientists are sounding the alarm about a hidden danger from the rapidly warming Arctic that could have catastrophic consequences for millions of people: the ‘mercury bomb’.
A recent study warns that a large reservoir of mercury, trapped in permafrost for thousands of years, is being released as the ice thaws due to rising global temperatures.
The toxic metal poses a serious threat to the environment and the health of five million people in the Arctic and beyond.
Mercury is a neurotoxin, meaning it can cause serious damage to the brain and nervous system, especially if it accumulates in the food chain.
Recent research from USC Dornsife shows there is a more accurate way to measure the amount of mercury released. However, the findings are more serious than expected.
“There could be a giant mercury bomb in the Arctic that could explode at any moment,” said Josh West, a professor of earth sciences and environmental studies at USC Dornsife, who co-authored the study.
Silent ‘bomb’ under thawing ice
The Arctic, a hotbed of climate crisis concerns, is warming four times faster than the global average. As temperatures rise, the permafrost, frozen ground that covers much of the Arctic, is melting at an unprecedented rate.
Permafrost acts as a natural freezer, preserving not only organic matter but also hazardous substances such as mercury. The permafrost in the Arctic has been accumulating the metal for thousands of years, absorbed by plants that die, decompose and become part of the frozen ground.
When permafrost thaws, mercury is released into the environment.
The Yukon River, which flows through Alaska to the Bering Sea, plays a crucial role in this process. It erodes the permafrost along its banks and carries sediment containing mercury downstream. This sediment, which contains potentially dangerous levels of the toxic metal, is then deposited along the river.
New way to measure threat
Scientists at USC Dornsife, in collaboration with researchers from institutions including Caltech and MIT, have developed a new method to determine how much mercury is released by Arctic permafrost.
Previous studies used core samples from the top few meters of permafrost to estimate mercury levels. But these estimates varied widely and were limited by the shallow depth of the samples.
The new study took a different approach. Scientists analyzed mercury in sediments collected from riverbanks and sandbars, allowing them to drill down into deeper soil layers. This method provides a more accurate picture of how much mercury is being released and how much more could escape as Arctic permafrost continues to melt.
Researchers also used remote sensing data from satellites to track how the Yukon’s course changes over time. These shifts are crucial because they affect how much mercury-containing sediment is eroded from the riverbanks, giving a clearer picture of the potential threat.
“The river can quickly mobilize large amounts of sediment containing mercury,” said Isabel Smith, lead author of the study from USC Dornsife.
“By analyzing these sediments, we can better estimate the total mercury emissions that could be released in the coming decades.”
How much mercury is there?
The amount of mercury trapped in Arctic permafrost is staggering. It could “exceed the amount found in the oceans, soils, atmosphere and biosphere combined,” West said.
“Mercury doesn’t just accumulate,” he explained. “The planet’s natural atmospheric circulation moves pollutants to high latitudes, resulting in mercury accumulation in the Arctic. Because of its unique chemical behavior, much of the mercury pollution ends up here, where it has been trapped in the permafrost for millennia.”
This poses a significant risk to the five million people living in the Arctic, especially the three million people living in areas where permafrost is expected to disappear completely by 2050.
When mercury enters the environment, it enters the food chain, accumulating in fish and game, two staples of the traditional Arctic diet.
“Decades of exposure, especially with increasing levels as more mercury is released, can take a huge toll on the environment and the health of the people living in these areas,” Ms Smith warned.
Why is mercury dangerous?
Mercury is a tricky element. It moves from the atmosphere to the ground, then to the water, and back to the atmosphere. Because of the way the Earth’s natural atmospheric circulation works, pollutants like mercury tend to build up in the Arctic.
Once there, it becomes part of the ecosystem and circulates through plants, animals and the soil.
The study found that fine-grained sediments in the Yukon contained more mercury than coarser-grained sediments, suggesting that certain types of soil pose a greater risk because they contain more mercury and are more easily eroded by the river.
Interestingly, the river erodes the banks and mobilizes mercury-containing sediments, while some of that metal is redeposited on sandbars and beaches.
“The rivers are reburying a significant amount of mercury,” West said. “To really understand the extent of the threat from mercury, we need to understand both the erosion and reburial processes.”
Risk to Arctic communities
While the immediate threat from mercury in the Arctic is not acute (meaning it is unlikely to cause sudden, widespread poisoning), the long-term effects could be devastating.
Mercury builds up in the food chain over time, and continued exposure, even at low levels, can have serious health consequences. For communities that rely heavily on fishing and hunting, this can mean a slow but steady increase in mercury levels in their diet.
However, the risk of mercury contamination via drinking water is minimal.
“We’re not dealing with a situation like Flint, Michigan,” Mr. West said. “Most human exposure to mercury comes through diet.”
Still, the potential for damage is significant. Over the coming decades, as more permafrost melts and more mercury is released, the cumulative impact could be severe.
However, this is not just an Arctic problem. Mercury can travel through the atmosphere and food chain, eventually reaching ecosystems and human populations far from the Arctic.
What now?
Researchers said understanding the full extent of the mercury threat is a critical first step. By developing a more accurate method to measure mercury in the environment, they have provided valuable tools for future research and policymaking.
But much work remains to be done. Scientists must continue to monitor the situation, especially as the climate crisis accelerates the thawing of Arctic permafrost.
Governments and international organizations will need to consider how to limit the impact of the ‘mercury bomb’ on vulnerable communities.
“If we take all these factors into account, we can get a more accurate estimate of the total amount of mercury that could be released as permafrost continues to melt over the coming decades,” Smith said.
The hope is that with better data and a better understanding of the processes at play, we can take action to protect the Arctic and its inhabitants from this threat before it is too late.