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(NaCl) Road Salt A Nonpoint Source Of Pollution (NPS)

Updated on September 2, 2016

Negative Ecological Impacts Linked To The Application of (NaCl) Road Salt

Is there any doubt about whether salting the roads during the winter season is beneficial to humans, or not? Snow and ice often accumulate on roadways across the United States and Europe during the wintertime. Many countries, including the United States, will dust the roadways with road salt (NaCl) to reduce the potential hazards that icy roadways pose to motorists; however, few people realize the negative ecological impact linked to the application of NaCl to roads and the ecological risks it presents to a variety of species, particularly amphibians.

It is likely that any individual who has experienced winter weather is familiar with the effectiveness of NaCl to de-ice roadways. Road salt’s effectiveness comes from its ability to chemically de-ice frozen roadways by lowering the ice’s freezing point to water (Siegel, 2007). A notable fact about NaCl is that it is a mixture, “that is approximately 40% sodium and 60% chloride by weight” (Siegel, 2007). Trace elements may include phosphorus, sulphur, nitrogen, copper, and zinc” (Environment Canada, 2007). In addition, to these chemicals NaCl is often mixed with additives including cyanide to prevent the salt from building up on roads and highways, and road salts are highly soluble in water (Siegel, 2007). The high solubility of NaCl presents a problem when the spring arrives bringing with it rain showers and warm weather which wash the salt off the roads into to local waterways. Run-off from the roadways consisting of a buildup of NaCl from the long winter becomes a nonpoint source of pollution (NPS) flooding into local rivers, lakes and wetlands degrading waterways. Non-point source pollution in the spring containing high amounts of road salts, which are highly soluble in water, have a negative impact on amphibians.

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Factors To Consider

Obviously several different factors must be considered when researching the effects of road salt on amphibians and their ecosystems. A few of the aspects that should be considered are the presence (amount) of salt, whether soil is shallow or not, and seasonal precipitation. According to researchers in the Biology department at Virginia Commonwealth University, road salt is applied in at least twenty-six states and a number of European countries even though the impacts of NaCl on amphibians and their ecosystems remains fundamentally unknown (Karraker,Gibbs, & Vonesh, 2008). Studies indicate that the relevancy of aquatic sustainability is linked to road salt concentration amounts in the amphibians’ environment as well as their sensitivity to these changes due to exposure to NaCl.


The study conducted by Virginia Commonwealth University focused on the spotted salamander and the wood frog. Both species are considered vernal-pond-breeding amphibians because their reproductive habitats are temporary pools of water (Karraker et al., 2008). The study concluded that road salt traveled at least 172 miles from the highways of the Adirondack Mountain Region of New York into wetlands. In the case of the spotted salamander, salt was found to have a negative impact during the egg and larva stage of development. This finding lead researches to the conclusion that, “…salt exposure may lead to local extinction” in the surrounding areas (Karraker et al., 2008). On the other hand, the wood frog faired a bit better, but not by much. The greater the distance the wood frog was from the pollution the better its chances of survival became. This is true for the spotted salamander, too; however, it is less resistant to NaCl than the wood frog is. Overall, the greatest destructive impact to the spotted salamander and the wood frog occurs within fifty miles of where the run-off occurs. This finding correlates with factors such as larva density and roadside distance (Karraker et al., 2008). Notably, this led scientists in the Biology department at Virginia Commonwealth University to recommend, “…reducing application of road salt near wetlands with high conductivity levels” (Karraker et al., 2008).

Moreover, the New Hampshire Department of Environmental Services has reported that NaCl contamination produces higher water densities. When this happens NaCl becomes established in the deepest areas of water and then settles due to a lack of current. This is common in places such as ponds and lakes. This disturbance results in an inability of oxygen to reach bottom layers and vice versa, nutrients will not reach the top layers, either and no mixture will transpire (New Hampshire Department of Environmental Services, 2006). This is known as chemical stratification. It has a profound effect on aquatic ecosystems because the bottom layer becomes “void” of oxygen and without oxygen aquatic life cannot be supported.

Lake Stratification


Additionally, amphibians are more affected by road salt than other species. Amphibians spend their lives in and out of water; however, they spend their entire juvenile life in water and require moist skin while on land to absorb oxygen from the air (Rader, 2012). Road salt run-off is high in chloride. In the spring, when the ice and snow melt it creates high concentrations of NaCl run-off into local waterways. NaCl is a mixture of sodium and chloride and while, “…aquatic organisms require chloride to maintain normal physiological functions,” amphibians are particularly sensitive to extensive variations of chloride in their ecosystems (Barlow, 2004). According to the New Hampshire Department of Environmental Services, the chloride released into waterways does not have a natural removal mechanism, which is why dilution is the only thing that will lower the concentration of chloride.

Lime Lake Algae Bloom


Val Beasley, a professor of veterinary biosciences and executive director of the Envirovet Program in Wildlife and Ecosystem Health discusses ecological imbalances, such as this, that intensely threaten the existence of amphibians’ survival, growth and reproduction due to the higher chloride levels, which threaten the health of food sources (Barlow, 2004). What is even more alarming is the characteristically increase of the toxicity of chloride when it interacts with potassium or magnesium.

In addition to amphibians, other groups of animals are affected by road salt, as well, because after all everything is interconnected in nature. Amphibians play a fundamental role in many food webs. They are considered “secondary consumers” in food chains. For example, at the tadpole stage, “They are herbivorous to omnivorous and are the prey items for both invertebrates and vertebrates” (Ecological Significance, 2002). Also, mature amphibians prey on pests. When food webs are stressed ecological imbalance occurs affecting all species in the web. Wildlife is negatively affected by the use of NaCl. Birds often mistake road salt crystals for seeds. A minute amount of NaCl can produce a diseased condition in birds from poisoning, which can result in a decline in bird populations (New Hampshire Department of Environmental Services, 2006).


Wildlife drink out of waterways to relieve thirst, and when these watering holes are polluted by road salts it causes salt toxicity. This often leads to dehydration accompanied by confusion and weakness. Studies conducted by the New Hampshire Department of Environmental Service revealed that deer as well as moose‘s ingestion of road salts lead to a higher rate of motorist accidents and “wildlife kills.” Importantly, when investigating the impact that road salt have on wildlife, individuals need to keep in mind the effect of NaCl on vegetation, too because its role in food webs is essential to sustaining life. Road salt has a substantial influence over wildlife habitat. For instance, high concentrations of NaCl are known to destroy food resources. Also, the ecological imbalance disrupts nesting and breeding areas, and due to the change in environment non-native invasive species can become a problem. According to USA Today author, Larry Copeland’s article, “Communities seek a substitute for road salt,” studies published in the Annals of The New York Academy of Sciences and Environmental Science and Technology have uncovered “chronic salt concentrations.” This can harm algae, which are eaten by insects, which are then consumed by fish and amphibians.

Furthermore, adjacent road populations of amphibians will be affected by the long-term use of road salt. Land transformation has profound negative effects on ecological stability. A studied conducted by Steven Brady from the School of Forestry & Environmental Studies at Yale University explains that adjacent habitats are damaged by fragmentation. When this occurs the chance of specie isolation is elevated, which often results in inbreeding. Inbreeding strains populations of amphibians sometimes causing disease (Ecological significance, 2002). The consequences of these actions may serve as “…novel agents of selection, setting the stage for contemporary evolutionary changes in local populations” (Brady, 2012). However, studies on the extent of ecological change that may take place remain largely unknown due to a lack of research.

Armed with the knowledge that road salt creates an ecological imbalance and even possible extinction for some species, the question must be reiterated: Is there any doubt about whether salting the roads during the winter season is beneficial to humans, or not? Perhaps, a better question may be whether or not alternatives to road salt exist? If there are alternatives, why do the United States and European countries continue to utilize NaCl as a deicer? Answering the first question requires a bit of research; however, the answer is there are better alternatives to road salt.

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Alternatives To Road Salt

Alfalfa meal is an organic fertilizer that provides traction while melting snow and ice. Importantly, Alfalfa meal does not degrade the environment (Joyce, 2012). Another chemical compound that could be used is Urea. Urea is commonly utilized as a deicing agent at airports; however, it will cause algae blooms if used near rivers, which is not good (Joyce, 2012). Additionally, places such as, Anoka County, Minnesota, used sugarcane molasses this past winter, Des Plaines, Illinois used beet juice, and in Wisconsin cheese brine was used on the roads. These substitutes did cut down the on the amount of road salt used, but did not eliminate the use of NaCl (Copeland, 2013). Individually, motorist should have their vehicles fitted for winter tires when the winter season arrives. Also, when removing snow a shovel is the most environmentally friendly method one could use.

While these may seem like small steps to ensure the ecological balance of many food webs, if individuals as well as departments of transportation chose an alternative to road salt it would reduce the amount of chloride that makes its way into local waterways often killing aquatic life and negatively affecting other species of wildlife, too. Moreover, road salt should not be used near wetlands, streams, lakes or ponds.

There is no question that road salt is harmful to amphibians, wildlife, aquatic species and vegetation. Alternatives to salt and / or practicing mixing NaCl with products such as sugarcane molasses, beet juice or cheese brine reduces the need to use large amounts of road salt. Unfortunately, substitutes are not always considered. Perhaps, that can change as scientists continue to link the degradation of a variety of different habitats to the utilization of road salt as a deicer.


Barlow, Jim. (2004). Out-of-balance ecosystems play role in demise of amphibian populations.

Brady, Steven. (2012). Road to evolution? Local adaptation to road adjacency in an amphibian (Ambystoma maculatum).

Copeland, Larry. (2013). Communities seek a substitute for road salt.

Ecological significance. (2002)

Environment Canada (EC). (2007). Priority Substances List Assessment Report: Road Salts.

Joyce, Shawn. (2012). SUSTAINABLE LIVING: Road salt alternatives.


Konkel, Lindsey. (2009). Death by Rubber: Global amphibian declines have scientists and volunteers scrambling to preserve backyard biodiversity.

New Hampshire Department of Environmental Services. (2006). Environmental, Health and Economic Impacts of Road Salt.

Siegel, Lori. (2007). Hazard Identification for Human and Ecological Effects of Sodium Chloride Road Salt.

Rader, Andrew. (2012). AMPHIBIANS - SLIMY IS GOOD.

© 2014 Suzanl


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