Environmental Hazards of Road Salt

Road salt and deicing chemicals are very commonly used substances to prevent or eliminate ice that has formed on various surfaces. This practice originated in the 40s and 50s when only about 5,000 tons were spread annually on roads and surfaces. However, in the following decades, road salt usage has grown exponentially, and we now use about 20 million tons of road salt annually, roughly 123 pounds for every American. This exponential increase in road salt has caused various problems for water quality and water-related infrastructure over these past 70 years of usage. The problems are even more significant in highly urbanized areas where chloride levels are much higher because of the large amounts of impermeable land cover.

These deicing chemicals work by lowering the freezing point of the ice that is present on the surface. It forms a brine which causes salt crystals, usually sodium chloride, to pull water molecules out of the ice. This brine then dramatically speeds up the melting process as it continues to form over time. The sodium chloride in the applied salt is then dissolved into sodium and chloride ions and then makes its way into the environment, where they can cause many problems.

Chloride poses a significant risk to both surface water and groundwater quality. Surface water contamination of chloride tends to be very seasonal, with highly elevated levels occurring in the winter due to deicing practices. Surface water contamination by road salts can occur rapidly and is usually widespread throughout the country. One study done in 2018 showed that 37% of the drainage area in the contiguous U.S. had experienced an increase in salinity over the last 50 years. In addition, another 2014 U.S. Geological Survey found that 84% of streams studied had rising salinity levels, and 29% had levels that exceeded government standards. Also, it is essential to note that chloride is negatively charged and repelled by soil particles. This results in chloride not being captured/retained by the green infrastructure, so rain gardens or other practices will not help to filter out chloride particles.

The adverse effects of excessive chloride also significantly affect the wildlife inhabiting a water body.

Chloride is a highly soluble and mobile ion that allows it to spread rapidly throughout a water body once contaminated. It is also toxic to wildlife once it gets above 230 mg/L and can be incredibly persistent because nothing naturally breaks down chloride in the environment. High chloride levels can also inhibit the growth/reproduction of aquatic species, impact food sources, and disrupt amphibian osmoregulation. In addition, high chloride levels can also lead to oxygen depletion. The chloride in the water creates an oxygen-deficient layer in the waterbody that can be detrimental to fish and other aquatic life. A study in New Hampshire showed that from 2008 to 2016, the number of waterbodies impaired due to chloride increased from 19 to 46 in just eight years. This increase in contamination is an alarming trend that we see in New Hampshire and throughout the country.

Road salt can also cause many issues for homeowners with a private water supply. Excessive chloride levels can accelerate the corrosion of drinking water infrastructure. One study from 2018 evaluated various private water supplies in New York near a road salt storage facility. This study found that rising chloride levels in well water resulted in increased galvanized corrosion of the pipes. In addition, they created a model that found that roughly 25% of the private water supply population in New York could be affected by chloride contamination from road salts. 

As a result of all the problems that excessive road salt can cause, there have been many advancements in environmentally friendlier options/practices compared to traditional salting procedures. One common way to reduce roadway salt dropped is to implement application regulators onto plow vehicles. These regulators can dramatically limit the amount of excess salt dropped, resulting in lower environmental hazards at the benefit of a reduced cost. Another common technique is using liquid salt brine to replace traditional road salt. The brine can be spread more evenly and efficiently and begins to work immediately as it is already a solution. Switching to a liquid brine can reduce the salt being dropped on roadways by as much as 70%. However, the downside of liquid brine is that it is less effective at lower temperatures than traditional road salt. These are just a few of the many advancements in deicing practices as we become more aware of road salt's environmental dangers.

For more information about traditional road salt alternatives, check out this "friendly deicing" article.

Resources

New Hampshire Department of Environmental Services, 2021. Road Salt and Water Quality

Minnesota Pollution Control Agency. 2022. Minnesota Stormwater Manual: Environmental Impacts of Road Salt and Other De-icing Chemicals

Columbia University Climate School, State Of the Planet. 2018. "How Road Salt Harms the Environment"

ACS Publications. 2018. "Impact of Road Salt on Drinking Water Quality and Infrastructure Corrosion in Private Wells"