Winter Road Salt Keeps Drivers Safe, But Can Also Jeopardize Drinking Water

Each year, cities, states and individuals spread millions of tons of road salt, which can leach into nearby freshwater ecosystems.

Earlier in January, a polar vortex brought frigid temperatures and record amounts of snow to much of the United States. Many states carpeted roads with crunchy salt to battle icy conditions. 

While this strategy may help keep drivers safe, it causes widespread damage to the environment, research shows. The U.S. uses about 25 million tons of salt on roads each year, according to one estimate. Much of this runs off into freshwater ecosystems, increasing salinity to levels that can be toxic to humans and wildlife alike. 

That’s one of the ways that humans are increasingly disrupting Earth’s natural “salt cycle,” which describes how the mineral moves through the environment. Experts are urging governments and individuals to decrease their road salt usage—a movement that is picking up steam but still faces barriers as regions adapt to unpredictable weather. 

Salty Species: First off, happy Winter Salt Awareness Week! If you are anything like me, you may also be learning about this multi-state initiative for the first time—and wondering why it even exists. I mean, how bad can the road salt issue really be?  

Turns out, it’s pretty bad. Between 2013 and 2017, around 44 percent of the salt used in the U.S. was for de-icing the roads. Massachusetts alone uses nearly half a million tons of salt each year for winter road maintenance, according to the U.S. Environmental Protection Agency. 

“We’re a salty species,” Sujay Kaushal, a geologist at the University of Maryland, told me. “We have all this salt that we’re using for different things, [like] de-icing roads, we use it in household products where we have detergents and things like that that have salt, and we have wastewater that’s enriched in salts that we release back into streams and rivers and lakes.” 

Kaushal has been studying for years how humans are ramping up the amount of salt in the natural environment—what he referred to as an “anthropogenic salt cycle.” In fact, he spoke with me while he was on his way to sample the saltiness of a nearby stream in Maryland after a recent snow event. 

In 2021, Kaushal and a team of researchers published a study that found introducing salt into the environment, whether from de-icing roads or fertilizing farmland, releases toxic chemical cocktails and decreases our availability of freshwater resources, which is already dwindling due to climate change. If salinity levels are too high, drinking salty water can cause dehydration, or exacerbate certain medical conditions like high blood pressure and chronic kidney disease, studies show.  

But it’s not just humans at risk. A growing body of research shows that saltwater contamination from road maintenance is drying out some plant species and harming animals such as frogs, insects and fish. Veterinarians say that road salt can even hurt your pet dog’s paws, causing dryness, burning and irritation.

Kaushal adds that salt can also encourage the growth of certain invasive plants such as Phragmites grasses, which are more salt tolerant and can outcompete native plants for resources. In some cases, salty roads may even add some risk to driving. Road salt can cause corrosive damage to vehicles in the long term or increase the risk of wildlife-vehicle collisions by attracting deer and moose (which like to lick the brine), according to the EPA. 

Balancing Act: These salty consequences are playing out worldwide. Since 2019, the nonprofit Ottawa Riverkeeper in Canada has been working with citizen scientists to collect about 500 water samples from 45 locations at streams in populated areas. Only about 10 percent of the samples collected over the five-year study period had safe levels of chloride, one of the main molecules in salt, according to a new report released by the organization on Monday. Many of the freshwater sites they sampled had a chloride concentration over 120 milligrams per liter for an extended period of time, indicating “chronic toxicity,” said Larissa Holman, Ottawa Riverkeeper’s director of science and policy. 

“The biggest surprise to us was just how awful it was. Like, the levels are just consistently terrible and the reason why this is so bad is because it’s something that we are doing to our environment,” Holman told me. She added that they also identified high levels of salinity in certain areas during the summer months, likely due to the road salt being trapped in sediment. 

Experts agree that de-icing salt is necessary to help people stay safe on the roads. But they also agree that we are using entirely too much of it. 

Officials say that just a coffee mug’s worth of salt—around 12 ounces—is enough to treat a 20-foot driveway. Many people and communities use far more than this. 

In recent years, there have been state- and community-led pushes in some areas to minimize road salt use. For example, a coalition of nonprofits and government groups in Wisconsin—dubbed Wisconsin Salt Wise—has been training people on the appropriate use of road salt during winter. There are similar initiatives in other states across the Northeast and Midwest, and in Canada. In some cases, states are offering training to applicators to ensure they are calibrating their salt use accurately based on the weather and proximity to ecologically sensitive areas or drinking water, Grist reports. 

“We need to balance safety with our use,” Kaushal said. “The real way to treat the problem is to figure out ways to reduce the amount of salt that we use.” 

Cover photo:  Boston, MA - February 4: Salt trucks deposits salt onto the road in Massachusetts to help prevent unsafe conditions. Credit: Erin Clark/The Boston Globe via Getty Images