Technically Speaking: Salts, Chlorides, and Deicers

By Jeff Swano, Executive Director of the Salt Creek Watershed Network
Reprinted by permission from their newsletter:
Confluence - People getting together to enhance Salt Creek

Salt is a chemical compound made up of sodium and chlorine. Its chemical compound name is sodium chloride (NaCl). Chemically, it is 39.337% sodium and 60.663% chlorine. Sodium chloride is by far the most popular of the deicers since it is inexpensive, effective, and easy to store and apply. It usually comes from mined rock salt that has been crushed, screened, and treated with an anti-caking agent.

Chlorides are salts resulting from the combination of the gas chlorine and various metal ions. Chlorine alone in the form of Cl2 is very toxic. In combination with a metal ion, such as sodium (Na+), and in small amounts, it becomes an essential element for normal cell function.

Road salt lowers the freezing temperature of water and prevents ice formation on the ground. In addition, when vehicles drive over the salt crystals, the weight of the vehicles applies forces onto the ice. These forces perse the snow and shatter the ice.

When melt water seeps into road cracks, it may refreeze again. The ice’s volume expands as it freezes and as the freeze-thaw cycle continues, the ice can break concrete apart. In addition, road salt causes metal corrosion to automobiles and infrastructures (food for thought: concrete and steel are the main ingredients in bridges). In the United States, it has been estimated that the annual road salt cost for motor vehicle and infrastructural damage is between $3.5 to $7 billion.

A University of Wisconsin-Madison study showed that extensive use of potassium chloride(KCL) has the potential of inducing plant damage through nutrient imbalances and/or excessive amounts of soluble salts. Other studies show that soils, vegitation, and water(fish and aquatic plants) are also adversely affected. Most soil and vegitation damage occurs within 60 feet of the road and is greatest close to the pavement.

Trees and shrubs planted along the roadside are hit with salt spray, which causes bud death, twig dieback, and disfiguration on broadleaf and evergreen trees and shrubs. The salt spray affects plants above ground as well as below because salt accumulates in the soil. Furthermore, deicing salts have contaminated groundwater aquifers in 11 northern states.

Salt dissolves into sodium and chloride ions, which enter Salt Creek through storm sewers. The ions will flow downstream and continue to accumulate from all urban surfaces draining into the area’s waterways. A city the size of Toronto applies 65,000 tons of salt each year. Chlorides can also enter surface waters from such sources as 1) rocks, 2) agricultural runoff, 3) industrial wastewater, 4) oil well wastes, and 5) wastewater treatment plant effluent.

Despite the beneficial impact on cell function, chlorides can contaminate fresh water streams and lakes. Fish and other aquatic life forms cannot survive when levels of chlorides are high, like right after a snow melt. For Salt Creek, the Illinois EPA has established the standard for chloride at 500 milligrams per liter(mg/L). For drinking water, the established chloride level is 250 parts per million (ppm).

(Note: Salt Creek is located in the various communities of Cook and DuPage Counties in northeastern Illinois).

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