Road salt may be hurting aquatic life

National report supports U research that links road salt to increasing chloride levels in metro-area rivers and streams.

By BOB VON STERNBERG, Star Tribune

Last update: September 16, 2009 - 8:38 PM

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Rivers and streams in the Twin Cities metro area have become so salty that the region's aquatic life is imperiled, according to a new government study.

The culprit: road salt that is scattered across icy streets, roads and freeways every winter, the U.S. Geological Survey reported Wednesday.

Metro-area waterways contain levels of chloride, a major component of salt, that exceed federal standards set to protect aquatic life. Such heavy chloride loads can interfere with plant growth, reduce the diversity of organisms in rivers and impair reproduction, the study found.

Chloride levels spike during the winter and have steadily increased between 1991 and 2004, it concluded.

The new study supports a University of Minnesota study published last winter that estimated that 70 percent of the deicing salt used on metro-area roadways gushes into area wetlands and lakes and seeps into groundwater.

That study also found that the chloride load in the metro area is increasing each year, with about 30 percent going into the Mississippi River.

In the Geological Survey study, scientists examined about 100 streams in parts of 20 northern states and found that more than 40 percent of the waterways exceeded the federal chloride standard.

Levels were highest in the Twin Cities and several other metro areas, including Chicago, Milwaukee, Detroit, New York and Boston.

In addition to salt used to deice roads and parking lots, other sources of chloride contamination include wastewater treatment, septic systems and farming operations, the report found.

Noting that road salt is a major contributor to motorist safety, Geological Survey official Matthew C. Larsen said transportation officials nationwide are trying to find alternatives to using salt.

"These findings are not surprising, but rather remind us of the unintended consequences that salt use for deicing may have on our waters," he said in a prepared statement.

Minnesota Department of Transportation officials have said the agency has made steady improvements in reducing the amount of road salt needed to keep the state's roads clear. Crews apply anti-icing chemicals in many areas before a snow and ice storm as an alternative to salt, they say.

The new study found that chloride levels were substantially higher in cities than in farmlands and forests. Urban streams carried 88 tons of chloride per square mile of drainage area, while woodland streams carried about 6 tons of chloride per square mile.

Only 4 percent of the streams in agricultural areas had chloride levels that exceeded federal standards, compared with more than 40 percent of urban streams.

The study, which sampled 1,329 wells, found that only 2 percent of the wells used for drinking water had chloride levels greater than federal standards set for human consumption.

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