A new study examining the rising use of road salt over the last 50 years points out how it has impacted water quality and wildlife in streams.

Road salt running off pavement and into waterways has long been recognized as a downside of attempting to make wintertime driving safer. A new study by the U.S. Geological Survey documents how big that downside has become.

Agency officials looked back at road salt records from 30 sites, including Milwaukee, suburban Chicago and warmer locations, going back as far as 1960 and found a substantial increase in road salt usage.

Middleton-based hydrologist Steve Corsi said in some regions studied, there was more snow and ice, but he also said in some cases, people are just applying more salt to the same area.

"You know in one driveway for instance, maybe someone applied more salt than they did back in the '90s," he said. "Nowadays ... because they want it to be a cleaner surface."

Much of the salt is finding its way into streams and rivers. The USGS report shows that 29 percent of the sites studied exceeded U.S. Environmental Protection Agency water toxicity standards for chloride by an average of more than 100 days per year from 2006 to 2011.

Corsi said some of the highest salt concentrations happen when stream flows are low and road crews dump a lot of salt on relatively little snow and ice.

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"So, the concentration is higher than when a lot of rainfall comes in to dilute the salt," he said.

Corsi said high salt concentrations are usually bad news for creatures in the water.

'That indicates there's a strong possibility of some degree of toxicity to aquatic organisms in the stream, and that can mean insects or fish or a variety of organisms," he said.

Corsi also said that in nearly half the streams studied, chloride concentrations were also up during the summer. He added that's partly because some salt first went into nearby groundwater and then eventually flowed to the banks of the streams.

Corsi said his study emphasizes the need to consider de-icing efforts that minimize use of road salt and yet keep drivers safe.

The study is published in the journal Science of the Total Environment.