It’s long been clear that permafrost thaw speeds up coastal erosion, compromises infrastructure, and releases harmful metals. But a study published in August identified a new threat: high levels of mercury stored in permafrost along the Yukon River.
Researchers believe Arctic soil has much higher mercury levels than previously thought. They found that the amount of mercury in the Arctic is actually twice the amount that’s in the earth’s atmosphere, ocean, and other soils combined.
That’s because human activity, like burning coal, sends mercury into the atmosphere where it eventually migrates toward polar regions. It’s an effect known as the cold trap. Chemicals from across the planet can hitch rides on atmospheric winds. Once they reach cooler climates the chemicals condense down, becoming locked into the ecosystem.
Isabel Smith is a graduate research student at the University of Southern California. She’s the lead for a new paper on mercury levels in polar regions. It’s part of a multi-year study along the Yukon River, near the communities of Beaver, Huslia, and Alakanuk, looking at the carbon and mercury levels in eroding river banks.
“What we see in the Arctic is that plants will take [mercury] up and then store it, and when they die, rather than decaying and re-releasing that mercury, they’re actually frozen and stored in the permafrost,” Smith said. “So you have this big accumulation in stores of mercury in permafrost.”
In many forms, mercury can be toxic to humans and animals. Over 3 million people worldwide live on or near permafrost soils. And as the planet heats up, the rate of permafrost thaw is speeding up.
“The rates that it’s happening now are much faster,” Smith said. “Also with the thawing of permafrost, you’re probably going to see more release of this mercury-rich sediment by rivers, because once you lose that permafrost, the rivers can erode those banks a lot faster.”
According to Smith, permafrost thaw and the mercury that it could release is not an immediate threat. She estimates that humans still have another 25 to 75 years to slow the melting of permafrost. And, at least for now, Smith’s team believes that the mercury along the Yukon River is bound in sediment and not being transported downstream.
“This is a very scary sounding topic, and it is really important, but we haven’t seen elevated levels in the river water that we’ve been testing,” Smith said. “So it seems to be very localized. While it is very serious, I wouldn’t, you know, stop eating fish.”
Smith said that if permafrost thaw continues at its current rate and mercury keeps being released, it could pose a real threat to many communities throughout northern and western Alaska. When permafrost thaws, the mercury released is often converted by microbes into a form of mercury called methylmercury, which is a neurotoxin. Methylmercury accumulates in the bodies of humans through the foods we eat.
According to the Environmental Protection Agency, exposure to methylmercury can affect cognitive thinking, memory, and fine motor skills in infants and children. And in adults, methylmercury poisoning can lead to a loss of vision, lack of coordination, impairments to speech, hearing, walking, and muscle weakness.
“This could become a really big problem,” Smith said. “It’s not something immediate, but it’s something that you know the rest of the world should know about, especially since people in the Arctic are really seeing those effects first and foremost.”
Smith’s team just completed the third year of a five-year study to understand how riverbank erosion along the Yukon River is affecting humans and the environment. Her team plans to continue their research next year in Beaver and Huslia, and to study sites near the lower Yukon community of Alakanuk.
