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Scientists study mercury released by fires

SPOKANE, Wash. (AP) – Researchers who collected smoke from Washington wildfires last month have concluded that significant amounts of mercury stored in trees, plants and forest litter rise into the atmosphere when the forest burns.

Hans Friedli, a chemist for the National Center for Atmospheric Research, said that while breathing smoke is harmful in general, the airborne mercury doesn’t carry an acute health hazard. Mercury in water is a problem, however, and the fallout from fires can contribute to it.

Extreme concentrations of methyl mercury from fallout, smelters and other sources can lead to advisories for children and pregnant women to limit their intake of fish to avoid health problems.



The Washington Department of Health has a long-standing health advisory for Lake Roosevelt.

Scientists estimate that about 6,500 tons of gaseous elemental mercury is circulating in the Earth’s atmosphere at any given time.



About half comes from industrial sources, such as coal-fired electrical generators and trash incinerators. The Environmental Protection Agency estimates that 41 tons are contributed annually from coal-fired plants in the United States alone.

The other half of atmospheric mercury comes from natural sources, including volcanoes and fires.

Whatever its source, gaseous elemental mercury stays in the atmosphere for about a year, drifting over the Earth. Then it falls out, either dry or with rain.

”If it lands in water, it gets transformed into methyl mercury,” Friedli said.

Mercury that lands on plants is stored in the leaves or needles. When the leaves drop, the mercury is stored in forest duff and the soil, and can be carried to lakes by runoff.

Friedli and his colleagues from the Colorado-based NCAR started their research at the U.S. Forest Service Fire Science Laboratory in Missoula, Mont. There, they measured the mercury in forest samples collected across the nation.

Sensors showed that nearly all the mercury became airborne when the samples burned.

Future research should determine exactly how much mercury from the soil becomes airborne during a fire, Friedli said.

For his most recent sampling, Friedli and scientists from the University of Washington flew a UW plane directly into the thickest smoke plumes they could find. They flew over wildfires at Lake Chelan and near Omak, Wash. The scientists also flew over an Eastern Oregon wheat field where the farmer was burning stubble.

”We found less mercury there, which is what we expected” because agricultural fields burn more frequently than forests, Friedli said. The mercury has less time to build up between fires and harvests.

That’s consistent with findings from African forests that burn more frequently than in North America.

Founded in 1960, the nonprofit National Center for Atmospheric Research is managed by a consortium of 66 universities, including UW.

It is supported by the National Science Federation, the National Oceanographic and Atmospheric Administration and other federal research agencies.


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