Salty runoff can hurt nearby plants.
Snowy roads and icy bridges are the bane of drivers in the winter. Driving in those conditions is a perilous undertaking. Cities have fought this problem by de-icing roads so that most cars can move along freely. However, de-icers can have negative environmental effects. A common de-icer is sodium chloride, or salt.
Sodium Chloride
Salt is a cheap, effective material for melting ice and snow on roadways, working in temperatures near 0 degrees F. Lower temperatures require combining the salt with calcium chloride or magnesium chloride, although according to the USDA, magnesium chloride can be corrosive to metal such as that in lampposts, resulting in fires if the wiring is affected. According to Discovery.com, the United States uses over 22 million tons of salt each year in an effort to keep roads clear.
Environmental Effects
Runoff as the snow and ice melt carries the salt into reservoirs and other water systems. Melted snow left on the side of the road can increase soil sodium content to a point that interferes with soil structure and plant growth. William Wegner and Marc Yaggi write in the Journal for Surface Water Quality Professionals that the resulting plant destruction can erode the "buffer areas" that prevent road pollutants from entering water sources.
Animal Risks
Road salt can harm not only water supplies and vegetation, but animals as well. Immediate risks include the animals eating the salted snow (effectively using it as a salt lick, according to a February 2010 Washington Post article by Nina Shen Rastogi) and increasing their risk of being hit by cars. Wegner and Yaggi report that "moose drinking salty water lose their fear of vehicles and humans." They also note that birds can confuse salt and grit, leading to "salt toxicosis." There is also a risk to freshwater fish living in water that is contaminated by the salty runoff.
Chemical Alternatives
Non-salt chemical de-icers exist but are typically more expensive, and they can be a problem as well, as with magnesium chloride's corrosion. Potassium acetate is one alternative, but expensive; calcium magnesium acetate is also under investigation, but according to Theresa J. Lins of Wisconsin Natural Resources, it may affect oxygen availability in water.
Other Avenues
Cities have tried other tactics to keep roads safe while minimizing harm to the environment. The Seattle Times reported in December 2008 that the city of Seattle tried hard-packing snow and covering it with a layer of sand, to turn it into a drivable surface for cars with four-wheel drive or tire chains. However, sand has its own environmental issues and is not as effective; the article noted that police were responding to calls partially on foot and not driving on hills, despite having tire chains. Discovery.com reported in February 2010 that a town in Minnesota was considering using a type of pavement that is permeable and allows water to sink in instead of run off.
Tags: magnesium chloride, Cities have, February 2010, keep roads, tire chains