Canadian Government discovers widely-used road salts are toxic to the environment

The results from a five-year study by the government’s environment ministry, released on 11 August concluded that the salts used throughout Canada should be added to the government’ List of Toxic Substances because of increasing chloride levels in water to potentially lethal levels for wildlife.

The road salts: sodium chloride; calcium chloride; potassium chloride; magnesium chloride and ferrocyanide salts, which are used for de-icing roads during Canada’s long winters and for dust suppression in the summer, generally find their way into water systems by being carried in meltwater from streets and through disposal of waste snow and ice. Although by far the most common salt used, sodium chloride, is part of any human’s daily diet, its potential effects on the environment are grave.

Researchers discovered that chloride concentrations greater than 100 milligrams per litre (mg/l) were often common in affected areas. An exposure concentration of 1000 mg/l for one week is lethal to rainbow trout. It was estimated that 10% of aquatic species would be adversely affected by prolonged exposure to chloride concentrations greater than 220 mg/l. It was also discovered that high concentrations of chloride in lakes can increase the presence of metals in the waters and prevent the distribution of oxygen and nutrients. Laboratory and field data during the assessment found damage to vegetation approximately 50 meters from roadways treated with road salts, also affecting wildlife habitats. The salts were also found to have toxicological impacts for terrestrial animals and birds.

By law, the government now has two years to develop control measures for the salts and a further 18 months to implement them. While the government study recommended four areas where action is needed to reduce the exposure of road salts to the environment, it also stressed that road safety would “be fully taken into account when choosing risk management instruments”.

The report recommends action in the following areas:

• preventing salts from escaping within storage areas;
• minimising percolation into soil and groundwater and direct release into water when disposing of snow;
• reducing the spread of chloride salts in the most affected areas, which are the most built-up parts of Canada in southern Ontario and Quebec;
• reducing the use of especially harmful ferrocyanide salts.

The report says that the most effective way to reduce the use of salts by as much as 30% is by more accurately predicting weather conditions. This could be done by using weather and road data from automated weather reporting stations with special sensors embedded in the roadway. Salt could then be spread before snow falls, using much less salt to prevent icy conditions than to treat icy or snowy roads.