Road Salt Does More than Make Roadways Safe
Countries around the world experience extended periods of snow and ice. In order to combat the icy road conditions crews spread road salt on sidewalks and roadways. Salt was first used in the United States on an experimental basis in New Hampshire in 1938. By the winter of 1941-1942, 5,000 tons of salt was spread on highways nationwide. Today, road salts may include sodium chloride, calcium chloride, potassium chloride, magnesium chloride, and ferrocyanide salts. More than 20 million tons of these various salt mixtures are used yearly.
Salt is a natural mineral that lowers the freezing/melting point of water. Salt is made of two components, sodium and chloride. When dry salt is spread onto a paved surface, it will dissolve and form a solution called brine. It is the brine that melts the snow and ice by reducing the temperature at which water will freeze. At 32o water will turn to ice and above that point ice will melt. A 10 % salt solution will freeze at 20o and a 20 % solution freezes at 2o, so the colder it gets, the more salt is needed. While it may sound relatively simple, it is actually quite complicated and scientific.
Salt not only damages metal and concrete, it contaminates drinking water, kills vegetation, and accumulates in streams, lakes, reservoirs, and groundwater, harming aquatic plants and animals. It is only the beginning of February, Wisconsin hasn’t seen very much snowfall, yet our roadways are white from the dried brine. As much as 70% of salt spread on roadways stays within the watershed.
Salt also causes soil alongside roads and sidewalks to become more acidic and reduces its ability to retain water which increases its susceptibility to erosion. It also affects the soils ability to transfer nutrients to plants resulting in the extra nutrients being leached into the ground water. The salt also damages trees and vegetation; it dehydrates the cells creating a drought like effect when absorbed.
In high concentrations sodium chloride can be harmful to aquatic organisms. While most waterways have not reached a status that is considered lethal, the high concentrations the excess salinity due to the salt concentrations impedes the survival of spotted salamanders and wood frogs. Changes in the salinity of a pond or lake can also affect the way the water mixes as the seasons change, leading to the formation of salty pockets near the bottom and biological dead zones.
Sodium is essential to life and good health at recommended levels. Since the body doesn’t produce sodium or chloride it is necessary to obtain the mineral in both food and beverage. Road salt does have a negative impact on human health. High concentrations of sodium in groundwater increase the amount of the mineral into the body, leading to hypertension, increasing the chance of heart attacks, and strokes. Too much salt can also irritate the stomach lining and may trigger stomach cancer. Some states monitor their drinking water for sodium, but there are no federal regulatory standards for sodium concentrations in drinking water in the United States.
So why do we keep using road salt if it is harmful to humans, aquatic organisms and the environment? Well, it is not only effective, but it is cheap compared to other forms of de-icing that are available. Alternative chemicals are expensive and often require municipalities to invest in new spreading equipment. Calcium chloride, for example, is quite effective for extremely cold temperatures, but costs five times more than road salt and is much more corrosive. Road salt it a necessary evil in some parts of the world. Its use prevents accidents and loss of productivity due to impassable roads. The only win-win is to use road salt in the most efficient manner to decrease the amount of salt needed to keep people safe.