The world’s largest reservoir of mercury — enough to fill 23 Olympic-sized swimming pools — is contained in permafrost in the Northern Hemisphere, twice as much as in soil, air and oceans around the world, new research suggests.

Approximately 57 million litres of mercury is frozen across Canada, Alaska, Siberia, and the Tibetan plateau of China’s permafrost, according to a study published in the scientific journal Geophysical Research Letters.

“It’s a massive amount,” explained Kevin Schaefer, one of the study’s lead authors. “We should be very worried about this.”

The study used statistical analysis to measure the ratio of mercury to carbon from 13 ice cores taken across Alaska from 2004 to 2012.

“Up until recently there was never any accountability for what was being stored in the permafrost for a millennium,” said Paul Schuster, another lead author, who works with the United States Geological Survey.

Very little is known about the effects of thawing permafrost on the environment, he said.

Mercury is a toxic pollutant that occurs naturally in the environment through the mercury cycle.

It accumulates on the land and attaches to plants by mimicking nutrients such as iron or magnesium and becomes bonded to organic matter, Schaefer explained.

When the plants die they get buried in the soil and freeze into the permafrost. The mercury becomes trapped and accumulates over time.

The amount of mercury in permafrost regions is 10 times higher than mercury introduced to the atmosphere from burning coal over the last 30 years, Schaefer said.

Mercury can be dangerous to humans and animals when it’s in the form of methylmercury. It is unknown how much methylmercury is trapped in the permafrost and is leaching out.

When microbes eat organic matter that contains methylmercury they absorb the mercury. Then, it passes up the food chain.

Mercury toxicity can cause neurological problems such as motor impairment and birth defects.

“It’s a very big concern for rural communities and anyone who relies on subsistence food resources like the salmon,” said Edda Mutter, the science director of the Yukon River Inter-Tribal Watershed Council.

But there isn’t enough information about the effects of mercury leaching from permafrost to weigh the human health implications, she said.

It is unknown if any lakes in Yukon are contaminated by mercury from permafrost thaw, according to Fabrice Calmels, a research associate at Yukon College who has studied mercury in permafrost in Jean Marie River, N.W.T.

This mercury reservoir is harmless as long as it stays frozen in the permafrost, Schuster and Schaefer said. But other research suggests permafrost is thawing as the Arctic warms faster than anywhere else on earth.

Mercury is showing up most clearly in the Yukon River, Schuster said. An earlier five-year study of the river suggested it pumped a significant amount of mercury into the ocean.

“This thawing process may already be starting,” he said. “That’s why you’re seeing these levels, because the Yukon cuts through continuous and discontinuous permafrost,” said Schuster.

Global implications for the food chain

Climate change is forcing the introduction of this mercury that hasn’t been present in the environment for up to 20,000 years at a rate much faster than would occur naturally, Schuster said.

This would raise the global baseline for mercury in the environment and could have global implications to the food chain, he said.

Schaefer is planning his next study that will run model projections of the permafrost to predict how much mercury will be released, and when and where.

This will help answer a lot of questions on how the thawing of permafrost will affect the local and global food chains, he said.