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Road Salt

In Canada, road salts are used as de-icing and anti-icing chemicals for winter road maintenance, with some used in summer as dust suppressants. Common types of road salts include:

• Sodium chloride
• Calcium chloride
• Potassium chloride
• Magnesium chloride

In Muskoka, sodium chloride is the most common form of salt used for winter maintenance. Pre-wetting agents are sometimes used in conjunction with road salt to help reduce the scatter and therefore the quantity of salt needed during application. Muskoka uses magnesium chloride as a prewetting agent because it is cost effective and less corrosive than other chemicals.

Some Area Municipalities use calcium chloride as a dust suppressant on gravel roads in the summer. Muskoka and the six Area Municipalities have road salt management plans and are in the process of implementing them.

The amount of road salt applied to our roadways depends on the length and severity of weather during the winter months. The Ministry of Transportation (MTO) estimates that 500,000 to 600,000 tonnes of salt are used in Canada each year. The MTO Winter Highway Maintenance section on their website includes the measures and precautions taken when managing for safer roadways while minimizing the impact on the surrounding environment.

Road salt is toxic

Environment and Climate Change Canada evaluates substances for toxicity to the environment and have performed an evaluation regarding Road Salts. This evaluation identifies Road Salts as toxic, which means that it requires careful management through a specific management plan.

In December 2001, Environment and Climate Change Canada released their final Assessment Report on Road Salts that evaluates inorganic chloride salts, including sodium chloride, calcium chloride, potassium chloride, magnesium chloride and ferrocyanide salts (salt of ferrocyanic acid usually obtained by a reaction of a cyanide with iron sulphate) and their impact on the environment. The report concluded that

"Road salts that contain inorganic chloride salts with or without ferrocyanide salts are "toxic" as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999)."

The report estimates that approximately 4,750,000 tonnes of sodium chloride were used as road salts in the winter of 1997-98 and that 110,000 tonnes of calcium chloride are used on roadways on an average year.

The highest annual uses of road salts are in Ontario and Quebec and the lowest uses of road salts are in the western provinces.

How road salt enters our environment

• Melt water from roadways
• Snow dumps
• Releases from patrol yards where salts are stored

All have resulted in unnaturally high concentrations of chloride from salts entering soil, groundwater and surface water.

It can also enter the environment at:

• Storage sites
• Through direct use and application
• Through disposal of snow removal
• Through spring runoff
• Through the air by spray from vehicles
• As a wind-borne powder

Chloride ions are conservative, moving with water without being held back or lost. Therefore, almost all chloride ions that enter the soil and groundwater can be expected to eventually reach groundwater or surface waterbodies.

Runoff from roadways and releases from storage yards and transfer stations have resulted in high concentrations of chloride in both surface and groundwater in some areas of Canada.

What are the adverse effects?

The use of road salts may increase salt content in ground and surface drinking water sources beyond extablished health standards. It is estimated that 10% of aquatic species will be adversely affected by prolonged exposure to chloride concentrations greater than 220 mg/L. The Ontario guideline for chlorides in drinking water is 250 mg/L.

High concentrations of chloride and sodium in the soil and air damage the foliage and roots of sensitive plants. They also reduce growth and flowering. This damage to vegetation also affects the wildlife that depend on these plants for food and shelter. Behavioral and toxicological impacts on mammals and birds have also been associated with exposure to road salts.

Learn more about reducing salt damage to trees. 

Road salt management in Muskoka

In 2010, the Muskoka Watershed Council released a report on the implementation of municipal salt management plans across Muskoka. Monitoring of Municipal Salt Management Plans in the District of Muskoka is a summary of the findings of a four-year survey undertaken by MWC volunteers documenting progress and highlighting areas that require ongoing action.

For more information about local salt management plans, check out local municipal websites:

• District Municipality of Muskoka - Muskoka Winter Control Operations
• Georgian Bay - Winter Control for Roads
• Huntsville - Snow Removal