If a Colorado mine were to dump a
hundred thousand tons of chemical salts onto the ground, chances
are good that residents nearby would be upset and local and state
agencies would get on the mine operator’s case.
Yet,
the state of Colorado dumps 125,000 tons of chemical salts on its
roads each year, and Idaho dumps another 100,000 tons of anti-icing
and deicing salts such as sodium chloride and magnesium chloride on
its roads. Collectively, about one million tons of salt are dumped
annually on Western highways and have been for the past three
decades.
But where are the demands for
environmental-impact studies or for the reduction, if not the
outright banning, of highway salting?
Even most
environmental groups turn a blind eye to the practice. Like the
rest of us, their members may be reassured while driving to town,
to jobs and to ski areas, because salt has helped to clear the
roads of snow and ice.
Salt works its highway magic by
depressing the freezing point of water, thus breaking the bond
between snow and the pavement and allowing much of the snow to run
off as water, even in sub-freezing temperatures. Unfortunately,
salt disassociates into sodium ions and chloride ions. Because of
their high level of chemical activity, this costs Western states
$1.5 billion annually in repairs to deteriorated concrete pavement
and rusted vehicles and bridges.
What’s more, the
damage extends beyond pavement and bridges. Researchers first
linked highway salting to elevated chloride concentrations in
drinking water supplies in the 1950s. They also noted elevated
heavy-metal concentrations caused by chloride ions combining with
toxic heavy metals in soil to make the metals soluble and
mobile.
Numerous studies have documented the loss of
thousands of trees to road salting. The same road salt that killed
those trees also degraded other aspects of wildlife habitat by
destroying food resources, shelter and breeding or nesting sites.
Birds and mammals that ingest road salt frequently exceed their
normal salt requirements. And relieving their thirst by drinking
salty roadside snowmelt water often makes matters worse by inducing
salt toxicosis.
Many road-salt environmental studies have
been performed in western Canada, where habitat is similar to that
in much of the American West. In Alberta’s Jasper National
Park, excessive road-salt ingestion has killed elk and bighorn
sheep. At British Columbia’s Mt. Revelstoke National Park,
road-salt ingestion causes behavioral abnormalities in finches and
subsequent high rates of toxicosis-induced car-strike deaths.
There are alternatives. Many Western-state highway
departments have turned to liquid anti-icers and de-icers that
contain magnesium and calcium chlorides. But while magnesium and
calcium ions are less environmentally damaging than sodium ions,
the chloride ions remain a problem. A five-year study by the
nonprofit Environment Canada recently concluded that concentrations
of road salt (sodium, calcium, potassium and magnesium chlorides,
along with ferrocyanide salts used as “de-caking” agents) are
indeed toxic to the environment.
One compound currently
being studied is calcium magnesium acetate (CMA), which is more
environmentally benign than common salt. California and Nevada have
switched from sodium chloride to CMA on certain highway sections to
reduce injury to trees. The downside: CMA costs 20 times as much as
common salt.
Meanwhile, few really know or seem to care
where the one million tons of salt that are dumped annually on
Western roads and highways ends up. Enormous variations in soils,
rates and types of salt applications, highway drainage
characteristics, precipitation, and the nature of nearby surface
and groundwater systems all limit the effectiveness of studies or
produce contradictory results. Some studies indicate that road-salt
impacts hardly extend beyond highway shoulders; others suggest far
greater environmental damage, mainly because the arid West offers
relatively little precipitation to dilute the salt.
The
commissioners of Summit County, Colo., a county located on the
heavily salted stretch of I-70 that links Denver with many ski
areas, recently asked the Colorado Department of Transportation to
stop using magnesium chloride, citing tree loss and vehicle
corrosion. But concerned only with its mission of keeping highways
open and reducing accident rates, the department declined. As
Stacey Stegman, spokesman for the Colorado Department of
Transportation put it, “Safe roads are our priority and magnesium
chloride is doing the job.”
Road-salting clearly
constitutes serious pollution, but pollution is much easier to
condemn when it doesn’t directly affect our lifestyles.
Perhaps that’s why many environmentalists prefer going after
distant mines or chemical plants rather than governmental
road-salting policies. Now, another winter is here, and another
million tons of salt are being dumped on the West’s highways.
Stephen Voynick is a contributor to Writers on
the Range, a service of High Country News in Paonia, Colorado
(hcn.org). He freelances from Twin Lake,
Colorado.
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