When winter events create icy roads, salt helps your travel but research shows that it's finding its way to lakes rivers and wetlands in higher concentrations, causing some environmental concerns.
Since 1992, use of road salt in the US has increased by over 15 million tons per year, mainly due to an increasing amount of roadways to cover and increasing safety expectations. You can see short term effects on plant growth near the sides of consistently salted roads but long term, that sodium stays in the soil and is carried via melting ice or spring rains into aquatic ecosystems.
"You can get some acute toxicity which is basically, things are starting to die," said UW-La Crosse's interim Dean of the College of Science and Health Roger Haro.
The higher concentrations of sodium chloride kills zooplankton, an important baseline food resource for many ecosystems.
"We use a particular critter called the water flea - which is daphnea - as a test organism," Haro said. "They are sort of a key intermediary in the food webs of aquatic ecosystems."
Highway departments across the country have a balancing act between remaining effective for both safety and cost.
"I've been in this line of work since 1992," said County Highway Commissioner Ron Chamberlain. "And in the course of those years the expectations of the motoring public have done nothing but increase."
Use of preventative brines and salt-sand mixtures can help reduce the sheer numbers of sodium chloride, but those come with their own issues. Alternatives using organic additives like brines made from salt mixed with sugar beets take a toll because of how it fertilizes undesirable algae.
"You're trading one problem for another," Haro said. "When that organic material gets in the water, bacteria respond to that and they chew it up […] Oxygen is stripped out of the water."
Some researchers characterized it as "throwing compost into the lake".