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Heavy Metal Under Fire

When forests burn, airborne mercury is part of the fallout, say researchers

WEDNESDAY, Sept. 12, 2001 (HealthDayNews) -- Wildfires belch as much mercury into the air as power plants do, says new research.

Scientists think they know how much of this heavy metal is in the atmosphere, but this latest study shows a source not previously known: smoke plumes from wildfires.

"The amount of mercury coming out of power plants was well known, and now it turns out to be that the amount of mercury coming out of wildfires is along the same magnitude," says Hans Friedli, a senior research associate with the National Center for Atmospheric Research in Boulder, Colo. His findings appear in this month's issue of Geophysical Research Letters.

During wildfires, mercury stored in the foliage and ground litter is released into the atmosphere.

Friedli and a colleague discovered this by setting controlled fires in Montana and by flying over naturally occurring wildfires last year in Canada and again recently in the Pacific Northwest. They measured the mercury levels coming off each fire.

The mercury emitted in a wildfire is primarily gaseous elemental mercury, which poses no health risk to firefighters.

But, Friedli says, the mercury emission does present a threat when you look at the big picture. When elemental mercury goes into the air, it oxidizes and converts to ionic mercury, a form that deposits much faster into bodies of water. Once there, it turns into the toxic methylmercury, which enters the food chain through contaminated fish and presents a health risk.

"The issue is that the stuff gets redistributed into areas where it can be converted into methylmercury, where it can become a problem," Friedli says.

How much is burnt off trees and goes into the air? When a tree burns, up to 99 percent of the mercury it stores vaporizes, the researchers found. This means burning forests puts about 800 tons of mercury per year into the air worldwide, they say. About 6,500 tons of gaseous elemental mercury are in the air at any one time.

Michael Murray, staff scientist at the National Wildlife Federation, says the new research is illuminating.

"It's important to have a handle on all the sources of mercury -- and this is filling in the picture. Anything that helps us understand the mercury cycle is useful to scientists as well as helpful to policymakers," he says.

Another related experiment that Friedli and his team will do in Saskatchewan, Canada, later this month will examine the role of soil in wildfires. The researchers think heated soil is also a factor in the high emission of mercury during the fires.

What To Do

Mercury comes from both natural and manmade sources. There isn't much that can be done about the natural sources, but much is already in the works to stem emissions from human sources.

The Environmental Protection Agency has determined that mercury from power plants -- the largest source of mercury in the United States -- is a marked risk to public health, and the agency is working to lower emissions from coal-fired power plants. The EPA is set to propose regulations by the year 2003 and issue final rules by 2004.

"We're urging the Bush administration to make the deepest cuts possible -- to cut mercury from power plants by at least 90 percent," says Andy Buchsbaum, a senior mercury policy specialist at the National Wildlife Federation.

"Wildfires are part of the mercury cycle," he says. "And the only way to reduce mercury from wildfires is to reduce the mercury in the cycle, so you have to reduce it from human sources -- like power plants."

If you're wondering what health risks mercury poses, here is an excellent fact sheet from the Centers for Disease Control and Prevention. But don't believe everything you hear about mercury being poison. It's an urban legend that the fillings in your teeth that contain mercury are harmful.

And here's an article that describes more of the wildfire research.

SOURCES: Interviews with Hans Friedli, scientist, National Center for Atmospheric Research, Boulder, Colo.; Michael Murray, Ph.D., staff scientist, National Wildlife Federation's Great Lakes Natural Resource Center, Ann Arbor, Mich.; Andy Buchsbaum, senior mercury policy specialist, National Wildlife Federation; September 2001 Geophysical Research Letters
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