Report stresses toxicity of road salting

    January, 2001
    Five million tonnes of road salts are used each winter in Canada. ES&E photo.

    The salt used to de-ice Canadian roads is toxic to the environment, according to a federal government study.

    A five year assessment by Environment Canada found that the five million tons of road salts used across the country every winter contaminate groundwater, surface water, poison wildlife and harm vegetation.

    Streams, small lake ecosystems and groundwater are particularly vulnerable to road salt, which should be added to the Canadian Environmental Protection Act’s toxic substances list, Environment Canada said in its report.

    That designation will not mean a ban on road salt but control measures. Under the Canadian Environmental Protection Act, Environment Canada has two years to develop such measures and a further 18 months to implement them.

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    Road salts are sodium chloride, calcium chloride, potassium chloride, magnesium chloride and ferrocyanide salts. The principal salt used on roads is the table salt used on food. The only irritation for humans from road salt is its adverse effect on the taste of contaminated roadside well waters, said the study.

    Environment Canada’s advisory panel, comprising scientists, environmentalists, health organizations, industry and other governments, decided to assess road salts’ effects on the environment, not humans.

    Road salts enter the environment from storage facilities, through their applications to roads, streets and sidewalks and through the disposal of waste snow. Runoff of meltwater from roads and releases from patrol yards where salts are stored have resulted in high concentrations of chloride in surface water, with concentrations greater than 1,000 milligrams per litre (mg/l).

    Rainbow trout die after a week’s exposure to concentrations of 1,000 mg/l, and 10 percent of aquatic species are harmed by prolonged exposure to chloride concentrations greater than 220 mg/l, Environment Canada estimates.

    Sensitive fishes are harmed not only by the salt, but by the ferrocyanide used as an anti-caking agent to keep the salt from clumping together. The assessment found that reducing salt use or reducing the content of ferrocyanides in road salt formulations could reduce the risks to sensitive aquatic vertebrates in areas of high use of road salts.

    High chloride concentrations in groundwater are of concern because the groundwater eventually surfaces at springs and contributes further to surface water contamination. Urban areas in Ontario, Quebec and the Maritime provinces of New Brunswick, Nova Scotia and Prince Edward Island where rock salt is used heavily during winter suffer most from contaminated ground and surface water.

    The assessment found 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 as far as 50 metres (162 feet) from roadways treated with road salts. Plant species sensitive to salt are disappearing along roadways.

    As plants die, wildlife is affected. The study found road salt has behavioural and toxic impacts on animals and birds. Salt increases the vulnerability of birds to car strikes and may poison the birds directly.

    Public consultation, recommendations

    The August 11 report was subject to a 60 day public comment period. It makes several recommendations on how road salts’ effects could be mitigated. Environment Canada recommends that patrol yards implement better storage of salt and abrasives to reduce losses through weathering. Management practices to reduce losses during transfers, and management of stormwater and equipment washwater to minimize releases should be started.

    When handling disposal of snow, measures should be considered to minimize percolation into soil and groundwater and direct release into water, Environment Canada suggests. In cases of release into surface water via storm sewer systems, the salted snow should be diluted before release.

    Environment Canada recommends reduction of chloride salts in areas such as southern Ontario, southern Quebec and the Maritime provinces, where salt use is highest. The selection of alternative products or of appropriate technology or practices to reduce salt use should be considered while ensuring maintenance of roadway safety.

    By adding a snow melter to its fleet, the city of Toronto has found a way to use less salt on its roads. Producers of road salts should consider reducing the rate of ferrocyanide added as an anti-caking agent, Environment Canada recommends.

    Before any recommendations can be adopted, road salt must officially be declared toxic by the Environment Minister David Anderson. His decision was expected by December, after the results of the 60 day public consultation had been reviewed.