Climate change appears to be awakening a toxic Rip van Winkle in North America's northern peatlands. A new study concludes that more frequent fires promoted by the warming atmosphere are releasing mercury sequestered in the soils at levels up to 15 times greater than previous estimates.

Peatlands are boreal forest ecosystems rich in thick organic soil layers. Because of their chemical makeup, they are efficient at binding and storing mercury. That helps keep the chemical from accumulating in animals such as fish, where high levels can cause nervous system damage in humans who eat them.

Forest fires threaten peat's ability to protect. Between 1960s and the 1990s, the annual area burned in western Canada and Alaska doubled, a result consistent with global climate change, which researchers believe causes more frequent droughts. Previous studies have shown that forest fires release nearly all the mercury stored in ground litter and soils and inject it into the atmosphere.

To see whether climate change is causing more mercury to leak from peatlands, ecosystem ecologist Merritt Turetsky and colleagues at Michigan State University in East Lansing measured concentrations of mercury sequestered in soil and vegetation in western Canadian forests. Then, using historical burn areas and emission models, they estimated how much mercury is released to the atmosphere by fires over the region. Over a 20-year period, the fire-induced mercury emissions averaged 23.2 metric tons a year. In drought years, the emissions from western Canada peatlands alone "approached industrial emissions of mercury in North America," the team reports in the current issue of Geophysical Research.

The study has "fairly large implications in terms of additional mercury releases into the atmosphere," says David Krabbenhoft, a hydrogeologist at the U.S. Geological Survey in Middleton, Wisconsin. How these mercury releases affect human health, however, is hard to quantify. Charlie Driscoll, a professor of civil and environmental engineering at Syracuse University in New York, says there are many issues to consider regarding whether mercury gets into the food chain and eventually to humans, including how far the mercury travels in the atmosphere, where it is deposited, and how much is carried into water. "There are a lot of factors at play," he says.