As February continues to plunge Concord into a frigid winter, snow is not the only thing you will see lining the streets. The sight of crunchy, white snow is often accompanied by the light-blue tint of sodium chloride, more commonly known as road salt. On a day like January 29, when Concord’s streets and paths were clogged with over a foot of snow, road salt plays a key role in melting the snow so that cars can drive safely. But, how exactly does this essential chemical work to assist in keeping us safe?
When road salt is applied to snow or ice, it combines with trace amounts of liquid water on the surface to form a mixture called brine. Brine has a lower freezing temperature than water, so once it forms, it remains unfrozen. The exception is if outside temperatures are lower than the freezing point of brine, -6 ºF, when ice will form on the road once again. The brine formed from road salt spreads deeper into the layers of snow, eventually reaching the ground where it separates the sticky snow from the pavement, allowing it to be removed more easily. In essence, road salt works by lowering the freezing point of snow.
This works so well, in fact, that the US uses approximately 10-20 million tons of road salt every winter. Although this number is quite colossal, its usage is not superfluous. Road salt can reduce the number of car accidents by around 90 percent in icy conditions. Only costing around $90 per ton, it is an irresistible solution against the dangers of driving on icy infrastructure.
However, despite its benefits, road salt comes with numerous hidden costs, both financial and environmental. To start, road salt has a corrosive effect on most metals. It tends to ionize metallic elements, causing oxidation and therefore corrosion. This affects not only vehicles but also water pipes, allowing salt to seep into water supplies. Additionally, road salt strips calcium from concrete, which weakens roads and bridges. It is estimated that the US spends an additional $5 billion every winter to repair the damage caused by road salt.
Still, the largest downside of road salt is environmental. All of that leftover salt has to go somewhere, and naturally it flows downward until it reaches either groundwater or rivers and lakes. This causes disastrous effects on aquatic wildlife as many freshwater organisms such as trout and zooplankton are highly sensitive to even small changes in the salinity of their environment. Amphibious creatures such as frogs and salamanders who take in water directly through their skin are unable to do so anymore because of increased salinity. Even moose and deer are affected: As animals who need salt to survive, they are now attracted to road salt instead of natural salt deposits. This increases the likelihood of crashes that are dangerous to both the animal and the driver.
Despite these harms, an immediate stoppage of road salt usage would be disastrous for the US, causing thousands of cars to be trapped in dangerous conditions. This is why there have been attempts to gradually reduce its usage and mitigate its consequences. One solution is to build roads with porous pavement, allowing melted snow and salt to seep into the road instead of causing damage elsewhere. Road salt can also be replaced with pre-mixed brine, which remains effective even in smaller quantities. Better yet, spraying brine on roads before snow starts to fall can reduce salt usage by 40-75 percent.
The numerous drawbacks of road salt show us that safe streets and pathways are not to be taken for granted. While being thankful for the efforts of our hardworking staff to keep us safe, it is necessary to be conscious of road salt’s role as a pollutant. We must continuously seek a more economical and sustainable alternative, or else our solution will become yet another problem.