Most mercury in the environment comes from air pollution released by industrial sources like coal-burning power plants. Forests help to absorb the pollution, but if the plants catch fire, smoke carries the mercury back into the atmosphere. The metal then can end up in waterways, where it accumulates in marine animals, making it dangerous to eat them.
Christine Wiedinmyer, who studies air pollution at the National Center for Atmospheric Research in Boulder, Colorado, used a computer model to calculate mercury emissions from wildfires in the U.S. The results: California and Alaska, where vast forest fires occurred from 2002 to 2006, released more mercury than other states. Overall, wildfires in the U.S. release 44 metric tons of mercury each year—one third as much as industrial sources.
Gathering precise data about the size of forest fires and the amount of mercury they emit is difficult. Right now, the mercury emissions are only estimates, cautions Wiedinmyer. “This is a first step to track how mercury moves through the environment,” she says.