For nearly 70 percent of Americans, the winter months come with nasty weather. Snow and ice storms may look beautiful, but they can make for treacherous roads and walkways. The most commonly used item for managing ice is road salt, or sodium chloride. While this salt does melt ice, when overused or mismanaged, it can become a serious environmental pollutant.
According to the Cary Institute of Ecosystem Studies, between 10 to 20 million tons of salt is applied to America’s roads each year. Sodium chloride-based salts are the most popular deicers. They are inexpensive, readily available, and effective at temperatures above 15 degrees F. Other deicers, such as beet juice or cheese brine, can also be used, either in addition to, or in place of road salt.
In general, deicers work by lowering the freezing point of water. When dissolved, these materials form a solution, or liquid containing dissolved materials. Road salt, for example, becomes a solution of water molecules, sodium cations (positively charged), and chloride anions (negatively charged). Ice cannot form at 32 degrees F (its freezing point) in the presence of dissolved solids, as they prevent water molecules from aligning to form crystals. Any ice in contact with a solution will continue to melt until the solution becomes too dilute, or until the ground temperature drops below the solution’s freezing point.
Road salt is meant for streets and sidewalks, but it can easily bounce or blow to nearby soils. Salt can also be transported to soil via water from storms and ice melt. Once deposited, components of salts, particularly sodium ions, can wreak havoc on soil systems. They do this by reducing soils’ ability to retain plant nutrients and water, and maintain soil structure.
Most soils contain clays and organic materials that have negatively charged surfaces, otherwise known as “cation exchange sites.” These sites on the soil particles are essential for plant growth. They attract and hold positively charged nutrients that plants need, like calcium and magnesium. Soils that contain too much sodium are unable to effectively retain important plant nutrients, as their exchange sites are hogged by sodium cations. Sodium in soils can also reduce plant-available water, and is even toxic to many plant species. (Just think of how many people need to have low-sodium diets; the same is true for plants!)
The negative charges of clay particles and organic matter also hold soil particles together in clumps, known as aggregates. Aggregation is an important feature of healthy soils, as it creates empty spaces called pores that transport water and oxygen, and give animals and plant roots a place to grow. Sodium contamination, leads to the breakdown of soil aggregates, as it reduces the attractive properties of organic matter and clay particles.
The destruction of soil structure has serious consequences on water infiltration and soil aeration. As soil aggregates break apart, fine organic matter and sediments plug up pores. In turn, water and air cannot move as easily through the soil. This process makes for a harsh environment for plants. It also has water quality ramifications, as surface soils erode far more readily when water cannot easily penetrate the soil surface.
Once sodium salts are present in soils, it can take years for them to wash away. Just think, the salt you put down this year might affect plant growth this spring, and for many more to come! The time it takes to remove salts depends on several factors, including soil texture and precipitation patterns. Salt can leave sandy soils relatively quickly, as water and sodium easily move through their profiles. Soils high in clay, on the other hand, retain sodium for much longer. Regardless of texture, soils are at the mercy of the weather. Clearly, without adequate rainfall, sodium can never be fully removed from a soil.
If you are concerned about the health of your soil and nearby water resources, consider reducing your dependence on road salts and other chemical deicers. The first tip to minimizing usage is to be proactive. Shoveling soon after snow or sleet has fallen is a sure way to reduce the amount of ice that forms on your driveways, stairs, and sidewalks. This, in turn, will decrease your need for deicers.
Another tip is to use only the smallest amount of salt required to clear ice from desired areas. Wetting down deicers before application can increase their efficiency and prevent them from bouncing or blowing onto soil. This is similar to cities that are using a brine-solution before storms to reduce their use of deicers.1 Clay-based kitty litter and/or sand can also be used instead of, or in addition to salts, as they add traction to otherwise slippery surfaces. Lastly, consider only managing areas that get the most foot traffic. This can help you save money while reducing your overall use of road salts.
The weather outside may be frightful. So too is the impact of salts on soil and water quality. But rest assured; you have the power to reduce your environmental impact this winter. Make a change today!
By Mary Tiedeman, Florida International University