Late winter is a dirty time of year in Canada. The snow is dirty, the roads are dirty and winter coats, boots and especially cars have a white film on them from the road salt.
We have used a lot of it this winter to keep us safe while driving and walking, however, eventually much of the salt we have been dumping on the roads and sidewalks will be washed into waterways. Other salt that is entrained in snowbanks will end up in soil by the sides of roads.
Salt in surface water can cause toxic effects to spawning or hatching fish, and can cause metals to become dissolved in water, which can have further toxic effects. Drinking water quality, whether from surface water or groundwater, can also be impacted. Salt washed into soil doesn’t go anywhere and accumulates year after year, destroying soil structure and causing fewer plants to grow in this soil and erosion to increase.
Salt by the side of roads lures animals to these “salt licks,” which increases the likelihood that these animals will be hit by a car.
Now don’t get us wrong, de-icing is necessary. A city can shut down for the odd severe snowstorm, but all activities cannot cease when we get a few centimetres of snow. There are, however, de-icing alternatives that should be considered for our roads.
The most commonly used road salt is rock salt, or sodium chloride, which is also the chemical that forms table salt. Alternatives to sodium chloride include magnesium chloride and calcium magnesium acetate. Magnesium chloride could cause less vegetation damage and less solubilization of metals in water than sodium chloride. It works at lower temperatures than rock salt and is commonly used in combination with rock salt when it gets very cold. It is, however, about seven times more expensive than rock salt.
Calcium magnesium acetate has far fewer toxic effects than rock salt and is, to some extent, biodegradable. The calcium and magnesium would remain in soil but the acetate would degrade. Using this alternative would avoid toxicity caused by chloride ions. It could be spread in much the same way as rock salt although because of its particle size, it may be more likely to blow around. It does, however, take longer to melt ice than rock salt does and is roughly 20 times more expensive.
Various de-icing techniques can also reduce salt use. Anti-icing, or the pre-emptive spreading of salt before a snowfall, can result in the requirement for less salt per unit of road surface. Pre-wetting the salt, i.e., spraying on the roads as a solution rather than as a powder also results in the use of less salt. Sanding is another option, although it comes with its own set of environmental issues, and probably can’t be used as the sole de-icer without a severe impact to the way we travel in the winter.
When it comes to keeping our roads safe in the winter without doing further harm to the environment the truth must be faced.
We are going to need to pay more for de-icing. The use of cheap rock salt is going to have to be drastically reduced and one or more of these more expensive alternatives is going to have to be phased in. We cannot keep trading short-term cost for long-term cost.
– Sophia Dore is an environmental scientist with Conestoga-Rovers & Associates. Andrew Laursen is an assistant professor at Ryerson University.