Road salt - or deicer - is used to melt ice and snow from paved roadways in the winter. In North America it is used regularly in northern states and provinces, and on high elevation roads. Road salt improves tire adherence to the pavement, greatly increasing vehicle safety, but it has effects on the environment beyond the road surface.
What Is Road Salt?
Road salt is not necessarily table salt, or sodium chloride. A wide variety of products exists on the market to melt snow and ice, including sodium chloride, calcium chloride, even beet juice. Sometimes salt is spread as a highly concentrated brine instead of in solid form. Most deicers fundamentally work the same way, lowering the freezing point of water by adding ions, which are charged particles. In the case of table salt for example, each NaCl molecule yields a positive sodium ion and a negative chloride ion. In large enough concentrations, the different ions released by road salt have detrimental effects on the environment.
Road salt is applied before and during ice and snow events, at rates that vary according to the local conditions. A planning tool from the Salt Institute estimates that transportation authorities need to plan for hundreds of pounds of salt per mile of two-lane road, per storm. Approximately 2.5 million tons of road salt are applied annually to roadways in the Chesapeake Bay watershed alone.
The salt does not evaporate or otherwise disappear; it disperses away from the road in one of two ways. Dissolved in melt water, salt enters streams, ponds, and groundwater, contributing to water pollution. Secondly, aerial dispersion comes from dry salt getting kicked up by tires and as salty melt water is turned into airborne droplets by passing vehicles and sprayed away from the road. Substantial amounts of road salt can be found 100 m (330 feet) away from roads, and measurable amounts are still observed beyond 200 m (660 ft).
Road Salt Effects
- On groundwater. Salt seeps into groundwater where it can reside for long periods of time, in turn affecting human, animal, and vegetation health. Contaminated wells have to be abandoned. Over a 20-year period, the New Hampshire Department of Transportation replaced 424 private wells due to road salt contamination, at a cost of $3.2 million.
- On vegetation. Leaf damage and dieback is commonly observed along roads, but these effects can extend some distance away. Salt-tolerant invasive species, for example Japanese knotweed, take over road sides.
- On aquatic life. Salt in ponds and lakes create a salt water layer at the bottom, imprisoning nutrients away from aquatic plants and animals. In addition, elevated concentrations of salt in freshwater has detrimental effects on the growth, reproduction, and survival of a large range of invertebrates, fish, and amphibians.
- On mammals and birds. Drinking of salt water can lead to salt toxicity. Small birds confuse salt crystals with grit, and the ingestion of small amounts leads to acute toxicity and death.
- On wildlife collisions. Large mammals like deer and moose are attracted to the salt along roadways, habituating them to traffic and increasing risks of dangerous collisions.
Ultimately, human lives are saved by the use of road salt in winter. Research into safe alternatives to road salt is important: active research is ongoing with beet juice, cheese brine, and other agricultural byproducts.
What Can I Do?
- Encourage your municipality to use road salt smartly. The twin cities in Minnesota have reduced their salt application significantly simply by adopting optimal application strategies. And it saves money, too.
- Reduce your own salt application. Shovel well and shovel often. Removing snow before it is walked on or driven upon prevents the formation of a hard-packed, slippery snow layer.
- Choose safer alternatives for your walkway and driveway. Although they are not entirely problem free, products like calcium magnesium acetate (CMA) and sand are reasonable alternatives.
Illinois DOT. Accessed January 21, 2014. Atmospheric Dispersion Study of Deicing Salt Applied to Roads
New Hampshire Department of Environmental Services. Accessed January 21, 2014. Environmental, health, and economic impacts of road salt.
The Salt Institute. Accessed January 21, 2014. The Snowfighter's Handbook: a Practical Guide for Snow and Ice Control.