Studies put mag chloride use in question
December 17, 2007
Claims that magnesium chloride is less harmful as a de-icer than the old-school salt-sand mix are “misleading and inaccurate,” according to a University of Northern Colorado and CDOT study.
A pair of recent research projects detailed some of the environmental impacts of using magnesium chloride as a highway de-icer in the winter and as a summer dust-suppressant on unpaved roads.
The research shows both uses of the chemical cause extensive damage to roadside vegetation.
That may be a no-brainer for people in the high country who saw red and dying trees along local roads long before the current pine beetle epidemic jumped into overdrive.
But the studies offer scientific proof to back up those anecdotal observations. In one study, UNC scientists concluded that continued use of mag-chloride de-icers “should include recognition of the impacts on roadside vegetation, and warrants the exploration of mitigation efforts that will decrease vegetation exposure.”
At the same time, the UNC research acknowledged that use of mag chloride does have benefits to air quality, and helps reduce the amount of highway sand clogging mountain streams.
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In the most recent study, Colorado State University researchers directly recommend against using magnesium chloride for dust suppression in forested areas.
The study showed that roadside plants absorb the chemical as it runs off roads. The chloride directly harms vegetation and also hinders water uptake. Trees in the study areas suffered extensive damage from exposure to mag chloride.
“The salts in the soil make it more difficult for plants to take up moisture,” said researcher Betsy Goodrich. “We don’t know for sure yet if it kills trees,” she said. Ongoing studies should determine toxic concentrations, and how long it takes for trees to die from magnesium chloride poisoning, Goodrich said.
Most of Summit County’s gravel roads are treated with magnesium chloride to keep the dust down. The frequency depends on traffic volume, said assistant country manager Thad Noll.
Pitkin County also treats unpaved roads with magnesium chloride, and it used extensively on Highway 82 between Aspen and Glenwood Springs during the winter months. Aspen doesn’t allow the application of the de-icer on its streets out of environmental concerns.
Part of the reason Summit County uses magnesium chloride is to meet state air-quality standards. The county is sensitive to the environmental concerns associated with magnesium chloride, Noll said.
“Every time we hear about a new product, we’re on it. We try to use as little (mag chloride) as possible,” Noll said.
County manager Gary Martinez said the county worked with the Colorado Department of Transportation to end the use of mag chloride as a de-icer on Highway 9 some years ago, based on environmental concerns.
The county has also tested some alternative products, but found them “severely lacking in effectiveness,” according to Martinez.
“I think the beetles are killing the trees faster than the mag chloride,” said county road and bridge director John Polhemus. While the county treats nearly all its gravel roads with mag chloride, Polhemus said the county is aware of the environmental concerns.
“We’re really cautious … we’ve cut back on the use of it,” Polhemus said.
Polhemus used complaints from the Peak 7 neighborhood near Breckenridge as an example of the challenges associated with balancing the use of mag chloride with environmental sensitivity. If the county doesn’t apply the chemical, residents in the area quickly complain about the dust.
Officials in Larimer County took a different approach to their use of mag chloride. When the county’s road and bridge department heard about the results of the CSU study, director Dale Miller took a hard look at the chemical.
About six months ago, Miller said his department stopped using mag chloride in susceptible areas, including dense forest sand near steep grades.
Larimer County switched to a less harmful lanolin-based product. This product, called Exhesion, is considerably more expensive and less effective as a primary treatment for dust suppression. However, it shows promise when applied to gravel roads previously treated with mag chloride, Miller said.
Like their counterparts in Summit County, Larimer County officials have been keen to try every new product that emerges on the market, hoping to find something that is cost-effective and works as well as mag chloride.
Summit County Commissioner Bob French said he would encourage more research into alternative products. French said the question of mag-chloride use is part of a larger puzzle that includes issues like population growth, access to residential and recreation areas and the economic importance of the resort industry.
“I don’t know what to say when you want a choice between safe driving conditions and environmental protection,” French said.
The UNC study focused on the use of mag chloride as a highway de-icer. The research was done back in 2004, but the results weren’t published in final form until earlier this year – partially because of the politics surrounding the use of mag chloride, said researcher Nicole Trahan.
“They did not want to hear it,” Trahan said. Under former Gov. Bill Owens, CDOT was completely committed to the use of mag chloride. As such, any science showing that it might be bad stuff was unwanted, Trahan said.
“What gets to me is the argument that it’s not harmful,” Trahan said.
The money used to document the impacts of mag chloride might have been better spent looking for ways to mitigate the damage, she added.
CDOT has acknowledged that mag chloride is not benign.
“We know that mag chloride isn’t good for the environment,” said CDOT spokesperson Stacey Stegman.
Stegman said the UNC/CDOT report didn’t offer any definitive new science. But CDOT is thinking about ways to mitigate impacts from mag chloride, she said.
One option might be to plant aspens along the road. Since the de-icer is used when aspens are dormant, those trees might be less susceptible to damage than conifers, Stegman said.
“We’re sensitive to this. We’ve spent millions testing different products. But we keep coming back to magnesium chloride because we haven’t found anything better,” Stegman said.
In the winter of 2006-2007, the Colorado Department of Transportation used about 9 million gallons of magnesium chloride to keep roads ice-free.
“It acts like a herbicide. It shuts them down physiologically,” Trahan said.
Pollution, drought stress, nutrient availability, pests, disease and mechanical damage all play a role in damage to roadside vegetation. But “injury to the tree foliage in roadside environments correlated more strongly with levels of chlorides in older needle foliage than any other factor examined,” the study concluded.
A greenhouse study showed that applications of mag chloride to conifer sapling foliage were far more damaging than exposure to the traditional sand and salt mix.
The research also showed the mag chloride gets spread far from the road – up to 300 feet – as it’s sprayed by passing trucks and cars.