Salt harming watersheds - Ontario OUT of DOORS

Much effort is put into keeping our roads, sidewalks, and parking lots safe when winter storms bring snow and ice. We obviously need to limit vehicle collisions and slips and falls. The downside is that road salt entering our rivers and lakes ultimately harms flora and fauna.

Sodium chloride (NaCl) is the predominant de-icer, making up 97% of total usage due to its cost, abundance, and effectiveness. Calcium chloride, magnesium chloride, and potassium chloride make up the remaining salts. Road salt acts by lowering the freezing point of water, creating ice melt below water’s normal freezing point of 0˚C. Sodium chloride salt is not effective below -100˚C.

Road salt is soluble and dissolves in run-off water adjacent to roads, parking lots, and sidewalks. This water with elevated levels of chloride enters storm drains, ditches, and culverts, and flows onto the earth as soil water or penetrates deeper as groundwater. Water also flows overland into streams, ponds, and lakes. Based on the yearly addition of chloride, these salinity levels increase annually.

Assessing the damage

A 2020 University of Toronto Study by Jackson and Lawson measured chloride concentration at more than 200 sites on the Humber and Don rivers and Mimico and Etobicoke creeks. Almost 90% of the samples exceeded federal guidelines for long-term chronic exposure for aquatic life.

These samples taken during the summer indicate the slow transfer of groundwater carrying winter soluble chlorides. The study shows road salt is a year-round threat to watersheds. The results also show that one-third of the sites had levels that would be lethal to two-thirds of aquatic species.

An international research study co-led by Dr. Shelley Arnott of Queens University in Kingston examined human-induced salt pollution in lakes.

Study sites throughout Europe and North America, including the Lake Ontario watershed, showed that widespread salinity had created loss of zooplankton, which in turn led to unwanted increases in algae formation and subsequent lake oxygen depletion. Major damage is being done to freshwater lakes by salt concentrations at salt levels much below that of guideline levels established by government agencies, the study concluded.

The Lake Simcoe Region Concentration Authority (LSRCA) has also been monitoring chloride levels for years. The actual chloride level of Lake Simcoe has been increasing steadily at a rate of .7 milligrams per litre annually.

LSCRA researchers found that in nearby streams and rivers, particularly in urban areas, salinity levels regularly exceeded short- and long-term guidelines established by the Canadian government.

Monitoring of road salts

In 1995, the federal government recognized the harms being done by road salt and initiated an assessment report culminating in the 2004 Code of Practice for Environmental Management of Road Salts. A second review of the code was completed in 2022.

The assessment confirmed increased chloride levels were responsible for harmful adverse effects on aquatic species, terrestrial vegetation, wildlife mortality, and soil chemistry. Recommendations included management of storage facilities, roadway application, and snow disposal, with a focus on maximizing human safety while minimizing potential harm to the environment.

All road authorities in Ontario are encouraged to implement salt management plans and identify actions they will take to improve practices related to storage and application. Whereas road authorities both provincial and municipal need to follow regulations regarding maintenance procedures this is not the case for independent contractors working on private and commercial properties.

An area of concern for contractors is the possibility of litigation if there ever is an accident. Overuse of salt is the normal reaction. Excess use of road salt on private property is estimated to make up more than 50% of total salinity concentration in watersheds of the Great Lakes.

Zooplankton impact key

Of particular concern is that research shows road salt has a toxic effect on zooplankton, key members of the food web. Not only is zooplankton food for fish, it keeps algae levels somewhat under control. An increase in algae levels creates a corresponding reduction in oxygen levels of lakes. A decrease in zooplankton levels reduces growth rates of various fish species and will inhibit optimal reproductive success.

There is no disputing the evidence that the status quo of road salt application is not acceptable.

Each year our freshwater rivers and lakes are being progressively contaminated. If we as stakeholders ignore the immediacy of the problem, it could be too late to save our freshwater ecosystems.

What can be done

There’s no simple solution. For the time being, there is a salt dependency based on the need for safety. Actions we can take include:

• Continued research and scientific studies to identify areas of salt contamination in Great Lakes watersheds
• Experimental use of alternative de-icers. Some municipalities in Ontario have used beet juice and other products, with mixed results. Use of a sand/rock salt mix has not been encouraging. More experimentation is in progress
• Support for organizations such as the Smart About Salt Council which offers training and certification for private contractors
• Pre-wetting roadways with brine can help salt stick and not create excess waste on shoulders
• Commercial property guidelines which substantially reduce the rate of salt application
• Use embedded roadway sensors to provide information on air and pavement temperatures to help decide when salting is needed
• Calibrate spreader controls on salting equipment and keep accurate records of dispersal
• Property owners should apply salt on sidewalks and driveways at a minimal rate and consider using a mix with sand.

Other reasons why salt sucks:

• Infrastructure including steel foundations of buildings and bridges suffer corrosion and rust. The Gardiner Expressway in Toronto is an example.
• Not great for vehicles.
• Plants and animals in freshwater can tolerate fluctuations in salinity but reproduction, growth rates, reduced food sources, and habitat impairment can be issues.
• Salt concentration in soil can cause flushing, reducing nutrients needed by vegetation.
• Invasive saltwater species have an easier entry into Ontario’s waterways and adapt faster.
• In areas with groundwater-fed drinking wells, increased chloride could be dangerous for individuals on a sodium-reduced diet.

Approximately five million tonnes of road salt are applied in Canada each year, according to the federal government.