Mercury rising: natural wildfires release pollutantScience News,
August 26, 2006
by S. Perkins

Fires in high-latitude forests and peaty soils of the Northern Hemisphere may loft hundreds of tons of mercury into the atmosphere each year, much more than scientists had expected, a new analysis suggests.

Much of the world’s industrial emissions of this toxic pollutant originates from the burning of coal contaminated with the element. “When it comes back to the ground, mercury forms strong chemical bonds with organic material, so it often gets locked away in rich forest soils and in peat,” says Merritt R. Turetsky, an ecologist at Michigan State University in East Lansing.

Scientists estimate that industrial sources together with natural ones such as volcanoes annually send between 4,400 and 7,500 tons of mercury into the atmosphere. Previous studies suggested that wildfires in upland forests of the Northern Hemisphere release about 23 tons of the pollutant each year. However, soil data and new computer models now indicate that wildfire emissions of mercury could be much higher, Turetsky and her colleagues report in the Aug. 28 Geophysical Research Letters.

In fires in Alaskan and Canadian forests, much of the material that burns is twigs, moss, and other organic material on the ground and in the soil, says Turetsky. Each square meter of forest soil contains about 3.4 milligrams of mercury. Concentrations are even higher in peaty soils, where the dry surface layers hold about 11.5 mg/[m.sup.2] of mercury, the team finds.