Preparing for winter: Weighing the environmental cost of road salt
It’s that time of year again when towns and cities, like those in Ohio, that experience snow and ice prepare for the upcoming winter by purchasing tons of salt to help melt accumulating ice on the roads.
Road salt — or rock salt — is halite, which is the mineral form of sodium chloride. Road salt lowers the freezing point of water and is the most popular method for de-icing in the winter.
Brad McKay, central maintenance facilities manager for the city of Kent, said the city always tries to enter winter with a stockpile of salt to avoid being caught off guard without enough when it’s needed. He said there’s a barn in Kent with a 4,500 to 5,000 pound capacity that is stocked over the summer depending on salt prices.
McKay said prices have fluctuated over the last five years and right now, under Kent’s contract with distributor Cargill, it’s $79.26 per ton of road salt. The amount of salt used each winter depends on the amount of snowfall, but McKay said there have been winters where Kent used 2,000 tons and winters when they used 5,000 tons.
“Price is a factor,” he said. “But we — as a city employee — there are a few things we could do that aggravates the general public more than not [having] enough salt to put on the road.”
But despite the convenience of clear roads in the winter, road salt has been found to have negative effects on the environment from contaminating waterways to damaging surrounding ecosystems.
Anne Jefferson, an associate geology professor at Kent State, said road salt, just like table salt, is sodium chloride, which makes melting ice easier. But, as the ice melts and mixes with salt it can runoff the roads into surrounding soils, streams and wetlands.
“Our water is freshwater in Northeastern Ohio, so it doesn’t naturally have high concentrations of salt in it,” Jefferson said. “So the ecosystems that are in place did not evolve in the presence of salt, so there are a lot of species that are not salt tolerant. And to make matters worse, chloride in high concentrations is actually what we call ecotoxic.”
If a substance is ecotoxic, that means it is toxic to the environment. Jefferson said the level of concentration that is deemed toxic varies depending on the species affected, but each species has some concentration of salt above which it is unable to complete its life cycle.
“We apply so much salt to our roads that many of the streams in the Northern and Northeastern United States, including in Northeastern Ohio, are exceeding those ecotoxic concentrations multiple times in a winter or even for a months at a time,” she said.
There are two different types of ecotoxicity effects, acute and chronic ecotoxicity. Acute ecotoxicity, in regard to road salt, occurs when there is a high dose of chloride for a short period of time.
Photo courtesy of Kent State University.
“In streams I’ve studied in Northeast Ohio, we can exceed that a dozen times a winter, basically with almost every salt event,” Jefferson said.
Jefferson said chronic ecotoxicity occurs between winter storms when there is still enough salt in the water, or it’s coming into the water from groundwater that has been exposed, causing streams and other water sources to stay above chronic ecotoxicity levels for months at a time.
“So what happens is the most salt sensitive species leave the stream,” she said. “So [they] either die out or if they can migrate, they migrate and get replaced by more salt tolerant species, which are usually invasive species — not ones that are native to the area, not ones that people would consider desirable.”
Sodium from road salt can get stuck in roadside soils, which then gets absorbed by plants. Jefferson said a small amount of sodium is OK, but large amounts can be toxic because that means the plants are getting more sodium than the nutrients they actually need. Because this salt gets stuck in waterways and soil, it doesn’t get flushed out enough and has lasting effects even after the winter months.
“Over the years, the concentrations are building up more and more,” Jefferson said. “So, even if we were hypothetically to stop salting, the problems we have with the chloride toxicity in the streams, for example, might take years to completely resolve because of this buildup in our groundwater in urban areas.”
Salt doesn’t appear to have as much of a negative impact on humans as it does the environment, because people are able to swim in oceans without a problem. But, Jefferson said there is a potential human health effect of having salty rivers and streams that are used as sources for drinking water. The high salt concentrations increase water pipe corrosion, particularly where lead pipes are being used like in Flint, Michigan.
“The city of Flint used to get its drinking water from Lake Michigan, which has low salt concentrations, but when the state took over they made the city switch to pulling water from the Flint river, which had higher salt concentrations,” she said. “And then they weren’t adequately treating the water to prevent the corrosion of the lead pipes, so the lead pipes were corroding and that’s why people were drinking lead tainted water.”
Considering the negative environmental impacts of road salt, some states have considered more environmentally friendly options like sand or a sand and salt mixture. McKay said salt is the method of choice because right now people aren’t aware of any other options to melt ice on the road below 32 degrees the way salt does.
Jefferson said the best option to use instead of using the solid granules of salt would be to use a salt water mixture, or brine.
“What cities can do is go out just as the rain and snow is starting, or a little bit before, and take a salt water mixture and spray it on the streets,” she said. “That brine solution then keeps the ice from adhering to the pavement. And even though we’re still applying salt, the overall amount of salt in the brine applied to the streets ends up being much less than applying the solid salt. So it greatly reduces the overall concentrations of salt used.”
Anthony Chenault, media coordinator for the Northeast, Central and Southeast districts of Ohio’s Environmental Protection Agency, said “Dilution is the best way to reduce the impact of chloride in waterways.”
As for the salt buildup in groundwater and soil, Jefferson said there is no easy fix other than continuing to reduce salt use and hope to eventually get to a place where far less of it is being added to the system in any given year, relative to the amount of freshwater coming in and flushing it out.
Jefferson said this is one of the few places where she thinks climate change has an interesting and not necessarily negative effect.
“As communities and regions warm up and we get less snow events or ice events, eventually if it’s just raining in the winter we won’t be salting,” she said. “But on the other hand, other communities, like say the one I grew up in in Minnesota where it was too cold to salt in the winter growing up, now they salt the roads. Because now they’re in that temperature range where salt is actually effective.”
In science, the situation with road salt is referred to as a “wicked problem” because there are no good solutions, Jefferson said.
“Obviously we want to keep people safe,” she said. “And helping with safety does tend to mean some level of salt application, but it does lead to this environmental conundrum.”