Last week, the U.S. Geological Survey released the findings of two multiyear studies which concluded that — hang onto your sugaring buckets — fallen autumn leaves release mercury into the environment.
As if Vermont's tourism industry didn't have enough to worry about, what with Vermont Yankee's radioactive incontinence and Green Mountain dairy cows belching and farting out enough greenhouse gases to turn the state's much-heralded winter slopes into Slip 'n' Slides.
"We know that forest canopies scavenge mercury out of the air — because trees breathe every day — and they take in gases that include gaseous mercury," explains Martin Risch, a research hydrologist with the USGS in Indianapolis, Ind., who worked on the studies. Leaves and needles also capture mercury that settles as dry deposits on their surface. But when those leaves and needles fall, they release the environmental contaminant once again.
Mercury poses a health risk to humans and other living critters. Notably, methylmercury, the nasty organic variety that shows up in fish and seafood, is harmful to pregnant mothers because it can affect their fetuses' developing cognitive abilities, attention, language, fine motor skills and ... what was that last one? ... oh, yeah, memory. Another good reason to get those silver-amalgam fillings out of your mouth.
Scientists have known for years mercury moves from the atmosphere into the environment through precipitation. However, these new studies reveal that "litterfall"— that is, those beautiful leaves and needles — delivers at least as much mercury to eastern U.S. ecosystems as precipitation. And possibly more.
What's worse, the leaves' mercury levels peak just before Vermont's spike in out-of-state vehicular traffic. "We do know that mercury levels increase during growing season and reach their maximum [level] right before the leaves change color and drop," Risch notes.
One of these studies, which looked at 15 states in the eastern United States, including Vermont, found varying levels of mercury deposits that were dependent upon the types of trees that produced the leaves. According to Risch, Vermont's deciduous forests, which are high in oak, hickory, maple, beech and birch, had higher mercury loads than many other eastern states. Obviously, Vermont also has more overall acreage of trees compared to many states, which accounted for its higher leaf-mercury loading.
But wait: Before you bust out the chainsaws and start dropping the nearest sugarbush, it's worth pointing out the obvious: Though some mercury is naturally occurring, most mercury found in our atmosphere which ends up in leaves actually comes from human sources — coal-fired power plants, industrial boilers, cement manufacturing and trash incinerators.
Forest canopies naturally remove mercury from the air and incorporate the mercury into and onto the leaves and needles of trees. So, blaming the trees for all that mercury littering the ground is like blaming the vacuum cleaner for your muddy floors. Instead, try telling the kids to wipe their feet before they come inside.
"This has really helped advance the science of modeling," Risch explains, because scientists have long struggled to find ways of accurately measuring the total mercury load in our environment and how well it compares to computer predictions. Clearly, it's now been shown that measuring just the mercury that falls as rain accounts for maybe half the total mercury that's out there.
Regulatory agencies and scientists rely on computer models when, say, the Environmental Protection Agency wants to put limits on how much mercury is being released from coal-fired plants, and scientists need ways to measure if those limits are ultimately having an effect. One way they do that: Rake up some leaves and see what's in them.
Does this study have implications for how Vermonters dispose of their leaves? While Risch admits that wasn’t a goal of their research, he does say that composting leaves is a better practice than landfilling or burning leaves, to prevent even trace amounts of mercury from going into the air.
"We don’t want people to think that there’s enough mercury in those [burning] leaves to cause them harm," he notes, adding "but when there are large forest fires, we can detect more mercury in the air."
Risch also says that this research shouldn't affect Vermont's leaf-peeper dollars. As he puts it, "I don’t think it’s hurting the trees by any means." Still, raking and jumping into big piles of leaves will never feel the same way again.
So, what's up next from government researchers? Eating too much Vermont cheddar and maple syrup can cause heart disease and diabetes?
Photos courtesy of the Vermont Department of Tourism and Marketing
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