By Sam Wasson
Updated Oct 12, 2022
Driveway salt — or what is commercially known as road salt — is a commonly used commodity come wintertime. It helps keep your driveway and sidewalks free from ice and snow while providing traction to prevent slipping. Cities and towns also use salt to keep the roadways free of snow and to prevent ice, ensuring the winter roads and byways are safe and drivable. However, while extremely effective and necessary, salt comes with a heavy, often unseen price. It’s absorbed into the soil, groundwater, and drinking water sources via runoff and is hazardous to plant, animal, and human health. Even worse, it’s not biodegradable, contaminating soil for up to seven years or until water drains it away. When exposed to bodies of water, road salt can contaminate them, affecting them for decades or until it’s mechanically removed or diluted.
In this guide, we’ll go over driveway salt’s history and environmental impact. We’ll also list some handy alternatives and DIY methods for deicing.
Several types of driveway salt exist, but sodium chloride (NaCl) is the most common. Sodium chloride is the primary mineral in many products, including table salt or rock salt, but when used as a deicer is unpurified and filled with many impurities, giving it a gray or flecked color. It has been used as a deicer since 1938 when New Hampshire used it to remove ice and snow from roads. It proved extremely effective, and in less than a decade, the entire nation had adopted sodium chloride as the deicer of choice for roads and highways. Today, 40% of all dry salt in the U.S. goes to deicing roads, and overall, we use an estimated 20 million tons of salt on our roads each year.
Sodium chloride is an ionic compound (an alkaline) that, when added to water as a solute (something that is dissolved in a solution), makes it harder for water to freeze. It does this by a process called “freezing point depression,” which functionally lowers the freezing point of water, making it impossible to freeze at 32°F. As salt is added to water, it breaks down into its basic components, sodium and chloride ions. When these ions interact with water, they get between water molecules, disrupting them and making it harder for them to form the rigid structures of ice.
Unfortunately, while salt is a necessary tool for cities in winter, it’s incredibly bad for the environment. There is no natural way to break down sodium chloride, so when it gets into soil or groundwater, it tends to stick around. It damages plant life by absorbing moisture from the soil and any part of a plant it touches. When introduced to bodies of water, sodium chloride can make it hazardous to beneficial bacteria, microorganisms, fish, insects, and amphibians.
The damage salt causes goes beyond the environment, as it harms humane-made structures and objects. Roads, sidewalks, cars, fabrics, and leather can all be damaged by road and driveway salt. According to the Environmental Protection Agency (EPA), we spend an estimated $5 billion yearly on maintenance and repairs for roads, streets, and other public facilities damaged by road salt.
The largest ecological threat presented by road salt is its impact on water supplies, groundwater, and surface water. When salt makes its way into local bodies of water, like lakes, ponds, or reservoirs, it settles on the bottom, slowly turning the water saltier over time (a process called salination). Water with high salinity is toxic to freshwater life, like amphibians, bacteria, and aquatic plants.
Salt-laden water is denser than freshwater, and if introduced to a freshwater source through runoff, it will sink to the bottom. Once there, it will disrupt the transfer of oxygen from one layer to another, making it difficult for aquatic life to breathe. According to a study published in 2014, 84% of urban streams have increasing chloride levels, with 29% exceeding the EPA’s safety guidelines.
Salt negatively impacts the soil and surrounding plant life when water with high chloride concentrations is splashed outward from nearby roads. As the salt-laden water seeps into the soil, several things happen. First, the salt will absorb water within the soil, drying it out and creating conditions similar to drought, making it harder for plant roots to absorb water. Next, sodium ions will begin to displace potassium and phosphorus in the soil, and over time, this will lead to denser soil with less aeration. Finally, if exposed to high enough concentrations, sodium ions can be absorbed into plants via the roots, damaging the plant.
Salt may also harm plant life when exposed directly to the plant’s body or leaves. The sodium will begin to absorb moisture from the plant, resulting in leaf burn. This damage can harm the plant’s growth or outright kill sections if the sodium concentration is high enough.
Salt is a highly corrosive chemical that, when exposed to concrete, both directly and indirectly damages it. As the sodium interacts with the calcium hydroxide inside the surface of the concrete, it creates calcium oxychloride, more commonly known as bleaching powder. This compound forms as small crystals in the surface layers of the concrete, which expand and create small cracks, causing damage. These cracks then fill with water and, thanks to the freeze-thaw cycle, expand and create pits, larger cracks, and potholes.
Salt affects concrete indirectly by expanding the freeze-thaw cycle of water that makes contact with concrete. As the salt interacts with the snow, ice, and slush coating roads and sidewalks, it will lower its freezing point, causing it to melt prematurely. This water then filters into the small cracks, like those made from snow plows. As the salt is washed away or temperatures drop low enough to refreeze, the water will turn to ice and expand. This expansion widens the cracks and holes, causing increased damage. Through this process, salt artificially alters the natural freeze-thaw cycle of ice and snow. Since it causes the snow to melt early and refreeze again as more snow falls, you have more cycles than normal, increasing the damage to concrete and asphalt roads.
Beyond roads and sidewalks, salt will corrode, dye, or stain other objects, including the following:
Several alternatives to rock salt exist as an effective deicer. Deicers containing magnesium chloride or calcium chloride are technically less damaging than road salt but also have their own problems. These chemical alternatives are typically much more expensive than road salt, so we recommend avoiding them.
Here are some of the least damaging, more economically viable options we could find:
Ultimately, we need large-scale deicers to keep roads functional in the wintertime. Unfortunately, the use of road salt is the most economically viable solution for just about any city at this time. While other options exist, most are either too expensive or not feasible for wide application. Thankfully, many groups are working on solutions, like using beet juice as a pretreatment to reduce the amount of salt needed for a season.
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