I am curious about the long-term effects of the magnesium chloride that is
used before snowstorms to reduce slippery road conditions. Does this
chemical adversely affect trees and shrubs along the roadsides? Can you
tell me what kinds of studies have been done, what the outcomes were, and
which cities or counties in the area are using magnesium chloride? Has it
significantly reduced the number of accidents? What is the cost as opposed
to sand? And what are the pollution effects, if any?
Answered on March 13, 2000
UCAR no longer uses magnesium chloride anywhere. Deicing of roadways has
become a much talked about and controversial subject for highway and
facilities managers. Research reveals pros and cons for nearly every method
of deicing, both past and present.
Physical Plant Services has experimented with several different types of
snowmelt and deicing methods and continues to do so as new products are
made available. The various products have only been used on walkway areas.
The snow removal process for the mesa road has always consisted of removing
accumulated snow and applying sand for traction. The sand does contain a 5%
solution of sodium chloride to control freezing of the water in the sand
during application and while in storage.
The only use of magnesium chloride at the Mesa Lab has been in the form of
test applications on walkways. The chemical caused discoloration of the
concrete and tracking problems that were considered unacceptable. An
example of the tracking and discoloration caused by magnesium chloride can
sometimes be seen on Table Mesa Drive below the entrance to the NCAR
property after a snow or ice event. The city of Boulder applies magnesium
chloride to this portion of Table Mesa Drive, and the road may appear
darker and have an oily surface for several weeks following a snowstorm.
Magnesium chloride remaining on the roadway in the absence of snow or ice
will absorb moisture from the atmosphere, creating a slick surface on
asphalt and concrete.
Magnesium chloride as a deicing agent has been in use for a relatively
short time. As a result there is little information on its long-term
effects on paving and the environment. The most in-depth information
relating to concrete pavement comes from a study by Iowa State University's
Center for Transportation Research and Education. Their study concluded
that magnesium chloride is much more damaging than rock salt to concrete
under several different environmental conditions. A complete description of
the study and references can be found at
The data on magnesium chloride's environmental impacts are more nebulous.
Most studies show that, when properly applied, magnesium chloride is no
more destructive to the environment than any other deicing chemical. It is
used widely by the Colorado Department of Transportation, which applied 4.8
million gallons of magnesium chloride on Colorado highways in 1998. A study
I received from the Boulder County Health Department that was prepared by
CDOT was the only independent study I found on the environmental effects of
magnesium chloride. Most other studies available were conducted by chemical
companies producing deicers or their sales agents.
The cities of Aspen, Snowmass, and Basalt have banned magnesium chloride
use and asked that the state refrain from using it on those portions of
state highways that pass through their communities. Basalt, which has also
banned the use of pesticides on its parks and public properties, stated
unknown long-term health and environmental concerns as the reason for the
magnesium chloride ban. Snowmass and Aspen also cited environmental concerns.
The studies I looked at touted the performance of the products but made
little comparison with other products or methods. Liquid deicers and the
equipment required for their application are more expensive than granular
products or their applicators. Of the granular products, sand is the least
expensive and, judging from the history of the mesa road, has the least
Researching this Delphi question has resulted in much information that may
be of interest to anyone seeking a more in-depth understanding of the use
of magnesium chloride as a deicer. Please feel free to contact me for any
--John Pereira, Director, Physical Plant Services