My association with Canadian winter is complicated by the road salt that is used to keep us safe. Having slipped on ice a couple of times during my first winter in Toronto, I started appreciating the salt sprinkled on sidewalks, but when I looked at the trees planted on those sidewalks it upset me to think of all the salt their roots are exposed to every winter. I also wondered at their survival rates and life expectancy. I learned that often street tree selection is based on their salt tolerance capacity, but how much salt can they possibly tolerate?
Municipalities and highway authorities get into action using mechanical methods of snow removal and applying de-icing salt on our roads and highways to ensure safe transit mobility. And on one level this dependence on road salt makes sense…
As soon as the weather forecast mentions snowfall, we find people spreading de-icing salt on the pathways in front of their houses and businesses to prevent accidents and injuries. Municipalities and highway authorities get into action using mechanical methods of snow removal and applying de-icing salt on our roads and highways to ensure safe transit mobility. And on one level this dependence on road salt makes sense; for instance, one accident analysis study found that use of road salt reduced crashes by 88%, injuries by 85% and accident costs by 85% (Kuemmel and Rashad, 1992).
What started as an experiment in de-icing highways in New Hampshire, USA in 1938, is set to become a global phenomenon with countries like Canada, Europe, Japan, China, and even South America now joining this predominantly US phenomenon. Overall North America and Europe lead in rock salt consumption followed by Asia and South America at much lower levels (Breining, 2017).
In the US, Detroit was the first city to officially use 5,000 tons of rock salt to de-ice its roads in 1940. By 1941-42 more cities adopted the practice. It is estimated that every year approximately 60 million tons of road salt is used around the world with the US leading at over 20 million tonnes. Winter road maintenance in the US alone costs over $2.3 billion. Image 2 below shows road salt use across the United States. Compared to the US, Canada uses approximately five million tons of rock salt with Toronto using anywhere between 130,000 – 150,000 tons, and Montreal using 130,000 tons per year (Shillington, 2019). But what does the use of this salt mean for human and ecological health? What is the economic impact of road salt on our environment?
Environmental, Health, and Economic Impacts
There is a correlation between economics, urbanisation, mobility, and the use of road salts. Scientists warn that increasing the use of road salts due to increasing road infrastructure threatens freshwater availability (Kaushal et al, 2005). Since it dissolves in water, road salt can travel large distances through surface or ground water into rivers, streams, ponds, and lakes, affecting our watersheds and the quality of our drinking water supplies. It is detrimental to animal and plant life on land and water as it affects their behaviour and lifecycles due to bioaccumulation where it can reach toxic levels. Human health, too, is impacted by road salt bioaccumulation in the form of cardiovascular, kidney, and liver diseases. Our pets can suffer seizures, coma, and even death caused by licking the salt off their paws in winter (Soleimanifar, 2019). Salt travels through air as well in the form of salt sprays created by vehicular traffic (NRC, 1991). It causes erosion, damages buildings, bridges and paved surfaces, and corrodes cars leading to high economic costs.
It causes erosion, damages buildings, bridges and paved surfaces, and corrodes cars leading to high economic costs.
Winter Road Maintenance in South Asia
While working on this article, I remembered one week, long ago, when my family and I were stranded in Srinagar, India due to unseasonal snowfall. The main tunnel connecting the Srinagar valley to the rest of India was blocked and it took the Indian army and Border Roads Organisation a while to get it cleared. I wondered if things have changed with time.
Roads in the upper reaches of the Himalayas in Pakistan, India, and Nepal need to be cleared of snow. I wanted to find out whether they too use road salt to keep traffic moving, and if yes, then how much? As an environmentalist, I was pleased to note that road salt application in these countries is minimal and often done manually. These countries depend heavily on manpower and machines like JCB snow plows, snow cutters, bulldozers, tippers, and loaders for snow removal. Often highways get blocked due to unexpected snow events, lack of machines, and skilled manpower and people resort to manually shoveling the snow (See these images). Early in 2022, a blizzard in Pakistan’s city of Muree left tourists stranded in the cold on the highway, and local residents went without essential supplies for several days (See this image). Similar stories can be heard from locals and tourists visiting cities like Srinagar, Shimla, and Darjeeling in India and the Trans-Himalayan districts in Nepal.
However, economics and geopolitics in the region is leading to ambitious road construction projects in the Himalayas. Trade and commerce between nation states like China, Nepal, Pakistan, and Bhutan are likely to increase with improved increased road networks, as will recreational and religious tourism. Unfortunately, as road construction work in these areas increases, it is likely that these countries too will adopt road salts to allow for year long flow of traffic.
Alternatives to Road Salt
Due to the high economic and ecological costs of road salt use, cities are looking to find alternatives. One common recommendation is to reduce the total amount of salt applied per snow event. Another possible alternative is to replace the use of sodium chloride with calcium chloride, which is effective at temperatures as low as -32°C and covers three times the surface area as rock salt. It effectively suppresses ice and dust formation and absorbs excess moisture as it is also a desiccant, but it is still harmful to certain species of plants and animals. Other alternatives that are being tested use carbohydrates, which are a form of sugar that reduces freezing point. These include brine solutions made from beet juice, cheese and pickle brine, molasses, corn, and soyabean oil. Sand mixed with salt and grit is also an alternative being used that can be re-used for 3-4 applications. Are there really any alternatives that can ensure the safety of people, plants and animals and our economic-driven lifestyles and still not be an economic and ecological burden?
Are there really any alternatives that can ensure the safety of people, plants and animals and our economic-driven lifestyles and still not be an economic and ecological burden?
Our current global economic systems demand that we maintain the same level of mobility year-round, no matter the seasonal weather conditions. Maybe, we need to learn to slow down our limitless economic growth model, our car speeds, and our lifestyles.
Alternatively, we could raise public awareness about excessive road salt use and its impact on the health of our watersheds, as well as its impact on our health and economics. We can involve students and the public in various nature walks, workshops, and citizen science programmes at the local watershed level to study the impact of road salt on plant and animal health. Lastly, we need to create research and advocacy groups to study the economic, environmental, and social cost of road salt use, remedial action, and alternatives to work with different levels of government, to hold them accountable for the loss of our natural world to salt. Our greenspaces and watersheds provide us with health and wellbeing benefits free of cost. We can raise our voice for their health, just as we need to rise in action to steward them.
Feature Image: “Road Salt” by b_ungar is licensed under CC BY-NC-ND 2.0.
Kuemmel, David and Hanbali, Rashad, “Accident Analysis of Ice Control Operations – Abstract” (1992). Transportation Research Center: Accident Analysis of Ice Control Operations. 1. https://epublications.marquette.edu/transportation_trc-ice/1
National Research Council (US). Committee on the Comparative Costs of Rock Salt, & Calcium Magnesium Acetate (CMA) for Highway Deicing. (1991). Highway deicing: comparing salt and calcium magnesium acetate (Vol. 235). Transportation Research Board.
Soleimanifar, P. (2019). Effects of Road Salt Applications on Human and Ecological Health: A Risk Assessment and Risk Management for Prospective Policy Options. https://beta.nsf.gov/news/road-salts-are-threatening-worlds-freshwater
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