It Droppeth as the Gentle Rain

Forest fires release 44 metric tons of mercury each year.Forest fires release about 44 metric tons (about 48 short tons) of mercury into the atmosphere every year, according to a report from Boulder’s National Center for Atmospheric Research. Fires in Colorado are responsible for about a half ton of mercury a year, on average, which ranks the state 20th nationally in mercury emissions from fires.

The amount of mercury released nationwide — in the lower 48 states and Alaska — by fires is about 30 percent of the total emitted by industrial sources. The largest industrial source of atmospheric mercury is coal-fired power plants.

Mercury is a toxin that can harm human health and natural ecosystems. Every state except Alaska and Wyoming, for instance, have issued advisories warning about excess mercury in fish caught in some rivers and streams. Mercury and other contaminants like PCBs can accumulate into much higher concentrations in fish than are found in the water.

“What we are seeing is that mercury from other sources is being deposited into the vegetation and soil and then being released back into the atmosphere, where it can travel far downwind and contaminate watersheds and fragile ecosystems,” says NCAR scientist Christine Wiedinmyer. “It’s important for federal and state officials to have this type of information and to know where mercury is coming from so they can better protect public health and the environment.”

The state with highest mercury emissions from forest fires was Alaska, with about 12,500 kilos (about 27,600 lbs.) of  mercury from forest fires. The researchers warn that the estimates are subject to at least a 50 percent margin of error due to imprecise information about both the exact size of fires and the amount of mercury emitted by each fire. Alaska’s emissions, for example, are likely to be from 6.3 to 18.8 tons, but 12.5 is the midpoint.

NCAR scientist Hans Friedli says there is no way to directly relate these mercury emissions to toxicity in the environment, but the fires probably result in additional mercury in waterways.

“The mercury in the forest is not harming anything. But when a fire releases it from the vegetation and the soils, it comes down again, precipitated in rain or snow, where it may end up in a body of water. There it gets converted in methyl mercury. That’s what we’re concerned about. The more fires we have, the more mercury will end up in the waterways,” he says.

The research is being published today by the journal Environmental Science and Technology.

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Mercury emissions from fires. This map shows the annual average (in metric tons) of mercury released by fires for every state except Hawaii. The estimates are based on fires from 2002 to 2006. (Illustration by Steve Deyo,

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