Winter De-icing Makes for Toxic Streams

First posted on 09-02-2010

A new study by the U.S. Geological Survey shows that de-icing salts used on winter roadways can cause urban streams to become toxic to aquatic life.

The study was conducted in eastern Wisconsin and Milwaukee, but Steve Corsi of the USGS Wisconsin Water Science Center was quick to point out that “it’s not just a Milwaukee problem.” Corsi noted that stream contamination was an issue nationally.

The survey showed that half the streams in Milwaukee became toxic during periods of de-icing. All streams in more rural areas in the eastern and southern parts of the state had potentially toxic levels of chloride in winter. Some streams even remained at toxic levels into spring and summer. Nationwide, streams flowing through 13 northern cities were examined and results showed 55 percent had samples that demonstrated poor water quality.

“We expected to see elevated chloride levels in streams near northern cities during the winter months,” Corsi added. “The surprise was the number of streams exceeding toxic levels and how high the concentrations were.” Corsi was the study’s leader.

Salt used to clean roadways is only one source of stream pollution. Public and private organizations use salt to clear parking lots and sidewalks while individual homeowners also put down salt to keep driveways clear.

Although certainly not needed in as heavy a dosage as northern cities, the Ozarks still puts down tons of salt during our milder winters. In addition, farming operations, septic systems and water treatment facilities all contribute to elevated chloride levels in streams.

“While winter driving and walking safety are the priority in treating pavements, this study suggests the need for advancements that will reduce salt loads to surface waters without compromising safety,” said Matthew C. Larsen, USGS Associate Director for Water.

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