Road Salt Leading to Rising Chloride Levels in Streams, Study Finds

Road Salt

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

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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.