“Road salt” is a generic term for deicing agents that contain sodium chloride and other chloride salts. These salts lower the freezing temperature of water, which helps to keep roads free from ice and snow. While there's no question that deicing pavements is necessary to prevent accidents and save lives, the massive volume of sodium chloride applied annually to U.S. roads poses a serious threat to soil, vegetation, water bodies and the many species that rely on them. For this reason, the U.S. Environmental Protection Agency recommends minimizing the application of road salts containing sodium chloride and using alternative deicers where possible.
Primary Ingredients of Road Salt
Sodium chloride is the most common deicing agent due to its low cost. According to the EPA, approximately 15 million tons of sodium chloride are used annually on U.S. roads. Calcium chloride, magnesium chloride and potassium chloride are costlier salts that work at lower temperatures than sodium chloride and are generally safer for the environment; some road salts contain a mixture of these compounds. Road salt mixtures may also contain sand, which acts as an abrasive while improving vehicle traction. Newer, environmentally preferable road salts contain sugar derived from beets or molasses, and this ingredient reduces salt content and improves the deicer’s adhesion to icy surfaces. In addition, many road salts contain sodium ferrocyanide or ferric ferrocyanide as an anticaking additive.
Road salt can pollute soil at every stage of the deicing process. Improper sitting and inadequate maintenance of salt piles are important preventable causes of soil and water contamination. Roadside soil and vegetation can also become saturated with road salt as a result of application, plowing, meltwater runoff, wind transport and spray from passing vehicles. In its official assessment of road salt pollution, Health Canada notes that potentially harmful levels of chloride have been detected in soil approximately 218 yards from treated roadways. However, a 2007 report by the U.S. Transportation Research Board indicates that most contamination occurs within roughly 30 feet of the pavement edge.
Effects on Soil and Vegetation
Many roadside plants can’t tolerate salty soil because elevated levels of sodium and chloride ions inhibit their uptake of water and nutrients. Furthermore, high soil salinity can inhibit the germination of roadside grass and wildflower seeds. In some regions, road salt pollution has caused salt-tolerant coastal plants to replace native inland species. Sodium chloride can also displace mineral ions and harm bacteria that maintain soil stability, leading to an increased risk of erosion; this may contribute to the pollution of rivers, lakes and groundwater. High levels of sodium may result in soil crusting and clogging, which not only prevents air and water from penetrating the soil but also impedes the growth of new plant shoots.
Calcium magnesium acetate is a biodegradable, chloride-free deicer that is comparatively safe for soil and plants. Unlike sodium chloride, CMA decomposes in two to four weeks and can improve soil stability. Unfortunately, it's less effective than sodium chloride at temperatures below 23 degrees Fahrenheit. Potassium acetate works at much lower temperatures, but it's more toxic than CMA and doesn't have a positive effect on soil stability. Although acetate-based deicers are more expensive than rock salt, their smaller environmental impact may make them a bargain, particularly in environmentally sensitive areas.
- Environment Canada: Risk Management Strategy for Road Salts
- Environmental Protection Agency: Source Water Protection Practices Bulletin: Managing Highway Deicing to Prevent Contamination of Drinking Water
- Environmental Protection Agency: What You Should Know About Safe Winter Roads and the Environment
- Environmental Health Perspectives: De-icers Add Sweet to Salt
- Wisconsin Department of Transportation: Anti-caking Admixtures to Road Salt
- New York State Department of Transportation: Environmental Impacts of Winter Road Management at the Cascade Lakes and Chapel Pond
- Transportation Research Board: Guidelines for the Selection of Snow and Ice Control Materials to Mitigate Environmental Impacts
- New Hampshire Department of Environmental Services: Environmental, Health and Economic Impacts of Road Salt
- Norwegian Public Roads Administration: Salt SMART: Environmental Damages Caused by Road Salt -- A Literature Review
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