Soon the snow will fly. And chances are good that you will find yourself behind a truck spreading salt on the roads in an attempt to deice them. Chances are also good that you may try a little salt on your own front porch. Annually we spread about 20 million tons of road salt in the U.S., and we’ve been doing it since the late 1930s.
We all know the effects of salt on cars and bridges. It seems that soon after your last car payment, those tell-tale bulges appear around the wheel-well—a harbinger of full-fledged rust holes a few months later. And, local communities spend an extraordinary amount of money repainting the steel girders of bridges that receive salt spray and runoff.
More quietly salt has health impacts on humans and wildlife. Salt is certainly not a toxic substance; indeed, its components, sodium and chloride are both essential elements for life. Too little dietary salt can be a problem in desert environments, where people sweat a lot. But, too much salt can be bad for you, especially in its role in causing hypertension (high blood pressure).
When salt is applied to roads, it melts snow and the runoff carries saline waters to local streams. Salty waters can percolate down to the water-table contaminating sources of drinking water. In one community where I lived for a few years, nearly half of the household wells had sodium concentrations above EPA recommended standard, and the waters of a local creek routinely carried more than 20 milligrams of sodium per liter—about three times what they carried 30 years ago.
Roadside trees, especially sugar maple and white pine, show branch dieback and mortality as a result of excessive salt spray. Salt that reaches wetlands has direct impacts on the amphibians and other wildlife that live there. Both the number of eggs and the survival of young are reduced at high salinities. As a result of their high density, salty waters can prevent the spring mixing of lakes that is essential to the supply of oxygen for deep-water fishes, such as lake trout.
It’s not likely that we will stop using road salt anytime soon. It is important for highway safety and the passage of emergency vehicles in wintertime conditions. But, we can use road salt more judiciously, and alternatives to traditional salt are available. One community in eastern New York State found it could save $14 per ton of salt by equipping highway trucks with devices that regulated the amount of applied based on local road conditions. Salt can be mixed with sand and pre-wet to reduce the amount applied to roads and increase its efficiency in melting ice.
Available alternatives such as calcium chloride, calcium acetate, and urea are more expensive than traditional salt, but less harmful to wetlands. Potassium acetate is not corrosive and more effective at temperatures below the efficacy of sodium chloride. For landscapes with many wetlands, these alternatives to sodium chloride should be considered.
At the very least, think twice about using salt on your own walks and driveways. Sand is a good friend. And, driving slowly in winter has no enemies.
References
Bubeck, R.C., W.H. Diment, B.L. Deck, A.L. Baldwin and S.D. Lipton, 1973. Runoff of deicing salt: effect on Irondequoit Bay, Rochester, New York. Science 172: 1128-1132.
Findlay, S.E.G. and V.R. Kelly 2011. Emerging indirect and long-term road salt effects on ecosystems. Annals of the New York Academy of Sciences – The Year in Ecology and Conservation Biology 1223: 58-68.
Karraker, N.E., J.P. Gibbs, and J.R. Vonesh. 2008. Impacts of road deicing salt on the demography of vernal pool-breeding amphibians. Ecological Applications 18: 724-734.
Kaushal, S.S., P.M. Groffman, G.E. Likens, K.T. Belt, W.P. Stack, V.R. Kelly, L.E. Band and G.T. Fisher. 2005. Increased salinization of fresh water in the northeastern United States. Proceedings of the National Academy of Sciences 102: 13517-13520.
Kelly, V.R. et al., 2008. Long-term sodium chloride retention in a rural watershed: Legacy effects of road salt on stream water concentrations. Environmental Science and Technology 42: 410-415.
Likens, G. E. and D. C. Buso. 2010. Salinization of Mirror Lake by road salt. Water Air and Soil Pollution 205:205-214.