Road Salt Leading to Rising Chloride
Levels in Streams, Study Finds
January 28, 2015
Story at-a-glance
-
Chloride levels increased substantially in 84 percent of US
urban streams tested, largely as a result of de-icing
activity on roadways
-
Elevated chloride levels may inhibit plant growth, impair
reproduction in marine life and reduce the diversity of
organisms in streams
-
Moose, elk, and birds may also be harmed by salt on
roadways, and even soil health is adversely impacted
By Dr. Mercola
Every winter, the US spends more than $2 billion to remove
snow and ice from roadways, a cost that includes over 15 million
tons of salt.1
Salt is effective and efficient, as it lowers the freezing
temperature of water, making it more difficult for ice to
develop and accelerating melting.
Research has shown that de-icing roadways with salt reduces
accidents by 88 percent and injuries by 85 percent.2
It also helps states to mitigate the estimated $700 million in
daily losses that can occur if roads become impassable.3
At least 26 states currently use salt to de-ice roads, a
practice that only became widely used in the US after World War
II. Since then, as salt use on roadways has continued to climb,
so, too, have the related concerns.
Road Salt Is Accumulating in Dangerous Levels in the Environment
Salt is highly corrosive, for starters, to vehicles, bridges,
and other steel components of roadways. Damage from salt
corrosion is estimated to cost the US up to $19 billion per
year.4
Then, when the snow and ice melt, the salt (sodium chloride)
dissolves into sodium and chloride ions, which make their way
into the environment.
Much of the salt ends up accumulating in waterways, where it can
wreak havoc on local freshwater biology and microbiology.
One study in Minnesota found that about 70 percent of the
road salt applied in the Twin Cities metro area is retained in
the area’s watershed.5
As Eurek Alert reported:6
“They found that the chloride concentrations
(salinity) in 39 metro area lakes have increased over the
past 22 years, following a similar trend in road salt
purchases by the state of Minnesota.
Both show a marked increase from 1984 to 2005, which
if continued would double salinity in these lakes in about
50 years. Compare this with a near zero concentration in the
1950s, when road salt application began.”
Chloride concentrations equivalent to one teaspoon of salt in
five gallons of water (230 mg/L) can harm aquatic life and
affect the taste of drinking water. The US Environmental
Protection Agency (EPA) recommends levels be kept below this
amount, but a study by the US Geological Survey (USGS) found
that 40 percent of urban and suburban streams tested in the
northern US had levels at or above this threshold.7
Environmental and Health Risks of Salting Roadways
Elevated chloride levels may inhibit plant growth, impair
reproduction and reduce the diversity of organisms in streams,
according to USGS. As Slate reported:8
“A heavy influx of sodium and chloride ions—which is
what you get when salt dissolves—will disrupt the ability of
freshwater organisms to regulate how fluid passes in and out
of their bodies.
Changes in the salinity of a pond or lake can also
affect the way the water mixes as the seasons change,
leading to the formation of salty pockets near the bottom
and biological dead zones.”
There are other ramifications as well. Animals including
moose and elk may be attracted to roadway salt and have a higher
risk of being killed by vehicles. Birds may mistake the salt
crystals for seeds, which can result in toxicosis and death.
When animals drink melted snow that has high concentrations
of road salt in it, it may lead to symptoms of salt toxicity,
including weakness, confusion, and dehydration.
Trees and other plants near roadways may also be damaged by
salt, even if they’re more than 600 feet away.9
Even the health of the soil is impacted by road salt. According
to the New Hampshire Department of Environmental Services:10
“This causes depletion in the soil as well as changes
the soil permeability causing the soil to become impervious
which blocks water infiltration, reduces soil stability, and
decreases the soil pH and overall fertility.
Salt can have impacts on soil biota, soil welling and
crusting, soil electrical conductivity, soil osmotic
potential, soil dispersion, and structural stability. Salt
can inhibit some soil bacteria compromising soil structure
and inhibiting erosion control mechanisms and increasing
sediment in runoff.”
As for human health, the EPA requires that drinking water
maintain levels of sodium below 20 mg/liter, although the USGS
found about 2 percent of wells they tested had levels that
exceed this amount.11
USGS Reports Rising Levels of Chloride in Most Urban Streams
USGS has been testing water from 19 US streams, in some cases
for decades, and the most recently analyzed data showed chloride
levels increased substantially in 84 percent of the urban
streams.12
On average, chloride concentrations often exceeded toxic levels
in northern US streams, and the frequency of these toxic
occurrences nearly doubled in two decades.13
In addition:
- 29 percent of the sites tested exceeded the EPA’s
chronic water-quality criteria for chloride by an average of
more than 100 days per year
- 13 of the streams had increasing chloride concentrations
even during the summer, which suggests chloride infiltrates
groundwater and is “slowly released to the streams
throughout the year”
- Chloride levels increased more rapidly than development
of urban land near the study sites, likely due to increased
salt application rates and greater snowfall
The study found that de-icing activity was the primary source
of environmental chloride in urban areas of the northern US, and
researchers noted that “road de-icing by cities, counties, and
state agencies accounts for a significant portion of salt
applications.”
Other contributors include salt use by public and private
organizations (salting driveways, parking lots, and walkways,
for instance). Wastewater treatment, septic systems, farming
operations, and natural geologic deposits may also contribute
some salt to the environment.
It should be noted that it’s not only the salt from road
de-icing that is raising concerns. Road-salt additives include
ferrocyanide, which is used as an anti-caking compound.
This compound was added to the EPA’s list of toxic pollutants
in 2003 because it can release cyanide ions into the environment
when exposed to certain types of bacteria and sunlight.14
Heavy metals may also be found in road salt and can contaminate
waterways along with the salt.
Experts Call for Road-Salt Alternatives: What Are They?
USGS researchers called for “deicer management options that
minimize the use of road salt while still maintain safe
conditions.” According to the Center for Environmentally
Sustainable Transportation in Cold Climates, there are
such options, including:15
Pre-salting roads. Spreading salt
about two hours before a storm hits helps
prevent ice from sticking. The EPA estimates this can
reduce salt use by 41 percent to 75 percent. |
Wetting the salt: Wetting the salt
may help it to spread more easily, cutting down on the
amount used. |
Not spreading salt when the pavement is too
cold. Salt generally does not help when applied
to pavement below 15 degrees F. |
Using less salt: Researchers from
the University of Minnesota recommend just one to three
cups of salt per 1,000 square feet.16 |
Using other chemicals: In areas
where sodium levels in water are high, calcium chloride
is sometimes used in lieu of salt. It’s more corrosive
but it doesn’t harm vegetation. |
Beet juice and pickle brine: These
are sometimes used to help salt stick to roadways and
minimize runoff. |
When these types of best-management practices are used, the
University of Waterloo found that chloride levels in groundwater
could be reduced by half.17
There are other potential alternatives in the works as well,
including “smart snowplows” that use salt more efficiently (such
as by detecting already-salted roadways and measuring the
temperature of the pavement). One day there might even be
pavement that resists freezing or that can be heated up to melt
ice.
In the meantime, you can help on an individual level by
minimizing the salt you apply on your driveway and walkways.
Shoveling early after a storm will help minimize the need for
salt, and if you do need to use it, try a mixture of pre-wetted
sand and salt (1:1) to minimize the release of chlorides.
Copyright 1997- 2015 Dr. Joseph Mercola. All Rights Reserved.
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