As the climate warms and Arctic permafrost thaws, some of the toxic elements locked away in it are starting to emerge and could contaminate the water supplies that many northern communities rely on.

Elliott Skierszkan, a geologist at Carleton University, and his colleagues recently measured the concentrations of naturally occurring uranium and arsenic in water released from permafrost samples collected in the Yukon.

"Our samples had levels of uranium and arsenic in the water beyond what would be considered safe," he says. The work was published in two papers, one in Environmental Science and Technology and the other in ACS Earth and Space Chemistry.

Using the Canadian Light Source at the University of Saskatchewan, Skierszkan also probed the chemical composition of the elements in the solid portion of the permafrost. The team found that uranium was largely associated with organic carbon in the soil, while arsenic was associated with iron oxides.

"The synchrotron was essential to understanding the chemistry of these elements and their potential to be mobilized," says Skierszkan.

The results showed that the fate of both elements was linked to organic carbon. As the permafrost thaws, the organic matter it contains breaks down, which can release associated uranium. This decaying organic matter can also cause the iron oxides and the arsenic associated with them to dissolve into the water.

Skierszkan says these findings "show the increased need to monitor these processes," to keep an eye on water quality. More than 90% of the population in the Yukon relies on groundwater, and while people don't currently drink water from the study sites, it will be important to monitor water quality in populated areas where permafrost is at risk of thawing.

There are also implications for mineral exploration—the changing baseline of water quality needs to be considered in the waste remediation plans for mines, and mine locations should be selected to minimize disruptions to permafrost.

"There's a big shift happening with water chemistry in the North, and that has implications for ecosystem health," says Skierszkan. "How that plays out in the coming years we don't know, but we can anticipate there's going to be some change."