‘Mercury bomb’: Melting Arctic permafrost releasing vast quantities of toxic metal

Mercury poses serious threat to health of millions of people in Arctic region and beyond

Scientists are sounding the alarm about a hidden danger of the rapidly warming Arctic that could have catastrophic consequences for millions of people: the “mercury bomb”.

A vast reservoir of mercury, trapped in permafrost for thousands of years, is being released as the ice thaws due to increasing global temperatures, a recent study warns.

The toxic metal poses a serious threat to the environment and the health of five million people in the Arctic region and beyond.

Mercury is a neurotoxin, meaning it can cause serious harm to the brain and nervous system, particularly when it accumulates in the food chain.

Recent research from USC Dornsife shows a more accurate way to measure the mercury being unleashed, and the findings are more dire than expected.

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

Silent ‘bomb’ beneath thawing ice

The Arctic, a focal point of climate crisis concerns, is warming four times faster than the global average. As temperatures rise, permafrost, frozen ground that covers much of the Arctic, is melting at unprecedented rates.

Permafrost acts like a natural freezer, preserving not just organic material but also dangerous substances like mercury. The permafrost in the Arctic has accumulated the metal over thousands of years, absorbed by plants that die, decompose and become part of the frozen ground.

As this permafrost thaws, mercury is released into the environment.

The Yukon river, which flows through Alaska towards the Bering Sea, plays a crucial role in this process. It erodes the permafrost along its banks, carrying sediment laden with mercury downstream. This sediment, containing potentially dangerous levels of the toxic metal, is then deposited along the river's path.

New way to measure threat

Scientists from USC Dornsife, in collaboration with researchers from institutions such as Caltech and MIT, have developed a new method to assess how much mercury is being released by the Arctic permafrost.

Previous studies used core samples from the top few metres 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 analysed mercury in sediments collected from riverbanks and sandbars which allowed them to tap into deeper soil layers. This method offers a more accurate picture of how much mercury is being released and how much more could yet escape as the Arctic permafrost continues to melt.

Researchers also used remote sensing data from satellites to track how the Yukon’s course is changing over time. These shifts are critical because they influence how much mercury-laden sediment is eroded from the riverbanks, providing a clearer picture of the potential threat.

“The river can quickly mobilise large amounts of sediment containing mercury,” Isabel Smith, the study’s lead author from USC Dornsife, said.

“By analysing these sediments, we can get a better estimate of the total mercury that could be released in the coming decades.”

How much mercury is there?

The amount of mercury locked in the Arctic permafrost is staggering. It could “dwarf the amount found in the oceans, soils, atmosphere, and biosphere combined”, Mr West said.

“Mercury doesn’t just accumulate by chance,” he explained. “The planet’s natural atmospheric circulation tends to move pollutants toward high latitudes, resulting in mercury build-up in the Arctic. Because of its unique chemical behaviour, a lot of 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 zone, particularly the three million who live in areas where permafrost is expected to disappear entirely by 2050.

As mercury is released into the environment, it enters the food chain, where it accumulates in fish and game, staples of the traditional Arctic diet.

“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,” 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 into the atmosphere. Because of the way the Earth’s natural atmospheric circulation works, pollutants like mercury tend to accumulate in the Arctic.

Once there, it becomes part of the ecosystem, cycling through plants, animals and soil.

The study found that finer-grained sediments in the Yukon contain more mercury than coarser grains. This suggests that certain types of soil may pose a greater risk, as they hold more mercury and are more easily eroded by the river.

Interestingly, while the river erodes banks and mobilises mercury-laden sediments, it redeposits some of that metal along sandbars and beaches.

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

Risk to Arctic communities

While the immediate threat from mercury in the Arctic isn’t acute — meaning it is not likely to cause sudden, widespread poisoning – 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 could mean a slow but steady increase in mercury levels in their diet.

The risk of mercury contamination through drinking water, however, is minimal.

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

Still, the potential for harm is significant. In the coming decades, as more permafrost melts and more mercury is released, the cumulative impact could be severe.

This isn’t just a problem for the Arctic, though. Mercury can travel through the atmosphere and the food chain, eventually reaching ecosystems and human populations far from the Arctic.

What’s next?

Researchers said understanding the full scope of the mercury threat is a crucial first step. By developing a more accurate method to measure mercury in the environment, they have offered valuable tools for future research and policymaking.

But there’s still much work to be done. Scientists need to continue monitoring the situation, particularly as the climate crisis accelerates the thawing of the Arctic permafrost.

Governments and international organisations will need to consider how to mitigate the impact of the “mercury bomb” on vulnerable communities.

“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,” Mr Smith said.

The hope is that with better data and a deeper understanding of the processes at play, we can take measures to protect the Arctic and its people from this threat before it’s too late.