Scientists have found a lot of mercury in the Yukon River.
And the warmer it gets, the more dangerous it could become.
Five years of water sampling at Pilot Station in Alaska, and work with the Yukon government from 2000 to 2005, has shown mercury levels in the Yukon River basin three to 32 times more than eight other major rivers in the northern hemisphere.
Those other rivers, including the Mackenzie, Churchill, Mississippi, Nelson, St. Lawrence and three major Siberian rivers, are the only other rivers of the same calibre scientists have this kind of information on.
There is an average of nearly five tons, or 4,500 kilograms, of mercury flowing through the Yukon River Watershed per year.
But people shouldn’t be too alarmed, said US Geological Survey hydrologist Paul Schuster.
“When everyone hears ‘mercury’ they automatically assume the worst,” he said.
But the only type of mercury dangerous to humans, called methyl mercury, made up a very small portion of those 4,500 kilograms, said Schuster.
“Most forms of mercury are not harmful to aquatic life or human health,” he said. “It’s when the mercury gets methylated – that is the problem.”
For mercury to methylate, you need three things: the mercury, a transporter – usually organic matter like that found in tea-coloured lakes – and a way to methylate, which is commonly done by sulphate-reducing bacteria in spaces with very little oxygen, like a rotten egg-smelling swamp.
“The good news is that there is no evidence of the third ingredient in the Yukon River basin,” Schuster said. “The Yukon River basin is very well oxygenated, which is not conducive to the presence of sulphate-reducing bacteria. Because there’s not a strong potential for methylation, there’s not much concern or danger, in terms of health, in regards to mercury in the Yukon River basin.”
Schuster and his colleagues believe there are two main causes of the high amount of mercury in the Yukon River.
One is simply bad luck.
Because of things like prevailing winds, a lot of the emissions from Asia and Europe get dumped in the river’s basin.
The other hypothesis is more troubling.
Permafrost holds mercury that has built up, naturally, for thousands of years. As it melts, that mercury gets dumped into the water table. Because of climate change, the permafrost in the Yukon River Watershed area is melting and releasing a large backlog of mercury along with it, said Schuster.
The reason this hypothesis is a concern is because warming weather, climate and water means the environment is more conducive to methylation.
“Warmer water cannot hold as much oxygen as cold water can,” said Schuster. “As you get into warmer environments, your methylation potential can go up.”
This is something for Yukon River fishermen to keep in mind.
Salmon in the Yukon spend very little of their lives in the river, picking up “essentially all of their body burden of mercury from time spent foraging in the ocean,” said Dave Krabbenhoft, a science advisor for the Alaska governor’s office.
“On the grand scheme of things, Pacific salmon are in the “medium-low” category for mercury content,” he said. “But methyl mercury is like any other bio-accumulative compound whereby the concentration in the vector – in this case fish – is less important than the total amount ingested. So, in the case of subsistence fishing populations like those present on the Yukon, even if the fish have low mercury concentrations, the exposure can be elevated if the consumption rate is high.”
It is important to note the research focused on water – not possible impacts to humans, said Schuster, a hydrologist.
But the findings still say – based on the eight other rivers we have enough data on – the Yukon is yielding “magnitudes” more mercury and “it could be of concern,” said Schuster.
And the warmer it gets, the more of a problem it could become.
Contact Roxanne Stasyszyn at