Effect on Water and Natural Environment

When weighed against the need to maintain sidewalks, steps, entryways, driveways and parking lots in safe condition, the practical question is not which deicer is least harmful, but rather, which deicer can be used most effectively with a minimum of impact on the environment.

The effect of deicer runoff on surface water and groundwater has been the focus of a great deal of research by government agencies and academics. Collectively, the research agrees that no deicer can claim to be completely harmless to the environment. As a starting point, comparisons of the potential environmental impacts of deicers published by the National Cooperative Highway Research Program show that all of the commonly employed deicer chemistries have environmental drawbacks.¹

Generalized Potential Environmental Impairment Related to Common Snow and Ice Control Chemicals¹

Mechanical removal and coordinated control – To minimize environmental impacts, many researchers and government agencies emphasize the importance of using smaller quantities of deicers to increase the efficiency of mechanical ice removal instead of melting ice completely in place and producing high volumes of deicer saturated run off. One publication by the United States Environmental Protection Agency, “Storm Water Management Fact Sheet – Minimizing Effects from Highway Deicing”², recommends a coordinated approach incorporating effective stockpile containment, careful calibration of spreading equipment, pretreatment of surfaces when possible, and mechanical removal as effective means to minimize the impact of deicers. Calcium chloride’s high ice melting efficiency and excellent penetrating characteristics can effectively support coordinated ice control programs focused on mechanical removal. See: The Case for Calcium Chloride.

How Ice Melters Affect the Environment

Much of the concern related to the environmental impact of ice melters is in regard to chloride contamination of water and soil. Before discussion of the issue, it is important to recognize that chloride occurs naturally in the environment. For example, the seawater that covers 70% of planet earth has about 2% chloride content. Sodium chloride is also the primary ingredient in the ordinary table salt we consume every day. Chloride also occurs naturally in foods that are widely considered healthy, including seaweed, rye, tomatoes, lettuce, celery and olives. The National Academy of Sciences, Food and Nutrition Board publishes Recommended Dietary Allowances (RDA) for chloride, identifying age group- and gender-specific goals for daily consumption aimed at maintaining good health. Physicians say too much chloride (or salt) in our diets is not healthy. But the RDA recommendations suggest consuming small amounts of chloride daily is not a health threat. The same can be said for chloride in the lakes, streams and soil around us.

Concern about ice melter impact largely surrounds the introduction of excessive amounts of chloride into soil and water near areas where ice melters are applied. Although chlorides are already present in the natural environment, application of ice melting materials can result in local spikes in chloride concentrations in nearby bodies of water and soil. While there are many different viewpoints about the short- and longer-term impacts of specific deicer materials, there is general agreement that chloride, sodium, calcium and other components of ice melter products accumulate and can be readily measured in surface water, groundwater and soil near roadways and parking lots where deicers are used. Since sodium chloride, or rock salt, is the most widely used deicer, most research has focused on this deicer, which is not naturally present at high concentrations in fresh water and soils.

Impact on lakes and streams – Researchers have found that the presence of chlorides in surface water is often seasonal and tied to winter use of deicing materials. In a study conducted by the United States Geological Survey (USGS) and the Wisconsin State Laboratory of Hygiene of seasonal chloride levels in streams in the Milwaukee, Wisconsin area, a correlation was found between increased chloride levels and reduced survival and reproductive health of Ceriodaphnia dubia (a species of freshwater water flea) and Pimephales promelas (fathead minnow). The same researchers reviewed USGS chloride monitoring data from 1969 through 2008 for major urban areas in both the northern and southern United States and found that during winter months, northern urban areas experienced significantly more frequent spikes in chloride levels in surface waters above both chronic (230 mg/L) and acute (860mg/L) levels.³

Another urban study underscores the importance of minimizing deicer runoff in areas draining into inland lakes. In a study sponsored by the Minnesota Department of Transportation, researchers from the University of Minnesota documented seasonal as well as longer-term increases in chloride concentrations in lakes in the Twin Cities Metropolitan Area. Their report also documents the potential for a saline water layer to form in the bottom strata of lakes, which can interfere with vertical mixing during spring and fall, depriving the lake bottom of oxygen.⁴

A major study⁵ of deicer impact in lakes in the Adirondack region of New York included a review of the scientific literature on the environmental impacts of deicers. The study reports that the toxicity of chloride-based ice melters varies. They rank from highest to lowest toxicity as follows: 1. Potassium Chloride, 2. Magnesium Chloride, 3. Calcium Chloride, 4. Sodium Chloride.⁵

The study further reports that algae such as Phytoplankton and Periphyton found in water are more affected by chloride levels than larger, more complex organisms. Zooplankton, tiny invertebrate organisms that float freely in bodies of water, are more sensitive than fish to deicer contamination, but generally, deicer levels in typical water bodies are below toxic levels for zooplankton.⁵

Macroinvertebrates such as insects, snails and worms are more sensitive than fish to deicer contamination, but generally, deicer levels in typical water bodies are below toxic levels for these organisms as well. Among aquatic insects, Ephemeroptera (mayflies) are among the most sensitive to chloride contamination and can serve as indicator species for those monitoring the impact of deicers in local surface water ⁵

Most freshwater fish species are tolerant of higher salinity levels than are typically found as a result of deicer runoff. Less is known about the sensitivity of amphibians, but the studies that have been conducted appear to indicate they have a higher sensitivity than fish.⁵

The best way to protect the natural environment from excessive chloride contamination is to limit the amount of ice melter you introduce into the environment. See: Proper Ice Melter Application.

¹ Guidelines for the Selection of Snow and Ice Control Materials to Mitigate Environmental Impacts, National Cooperative Highway Research Program, Report 577, Transportation Research Board of the National Academies, 2007.

²U.S. EPA, Storm Water Management Fact Sheet – Minimizing Effects from Highway Deicing, Office of Water, EPA 832-F-99-016, 1999.

³A Fresh Look at Road Salt: Aquatic Toxicity and Water-Quality Impacts on Local, Regional, and National Scales; S.Corsi, S. Graczyk, S.Geis, N. Booth, K. Richards, Environmental Science and Technology, 2010.

⁴Study of Environmental Effects of De-Icing Salt on Water Quality in the Twin Cities Metropolitan Area, Minnesota; University of Minnesota, Department of Civil Engineering and Minnesota Department of Transportation; H. Stefan, E. Novotny, A. Sander, and O.Hohseni, 2008.

⁵Environmental Impacts of Winter Road Management at the Cascade Lakes and Chapel Pond, Clarkson Center for the Environment Report #1, Funded by the New York State Department of Transportation; T. Langen, M. Twiss, T. Young, K. Janoyan, J. Stager, J. Osso, H. Prutzman and B. Green, 2006.