Imagine a long line of upright dominos. A single flick to the first block can knock over hundreds of other dominos. Similarly, a single environmental input—even one that can seem somewhat mundane—to an aquatic system may have broad, cascading impacts. Road salt might not be the first thing you think of when you think of water pollution, but for waterways near places that apply deicers to roads year after year, salt is a contaminant of growing concern with surprising reach.
The first domino to fall is the application of salt. In the US, this practice started in 1938, when New Hampshire began experimenting with salt as a deicer. It caught on fast—by the winter of 1941/42, about 5,000 tons of salt were applied to roads throughout the country. It works as a relatively simple chemical process. Road salt is usually made up of the same compound as table salt—sodium chloride (NaCl)—although there are some other deicing salts where sodium is replaced by magnesium, calcium, or potassium, as well as other additives to salts.
When salt in its typical NaCl form dissolves, the sodium and chloride separate into ions. “Those ions act kind of like referees in a hockey game” says Kris Stepenuck, Associate Director and Extension Program Leader for Lake Champlain Sea Grant. “The water molecules are trying to bond together to form an ice crystal, but the sodium and chloride get in-between the water molecules and they prevent those bonds from happening.” This lowers the freezing point of water and stops the formation of ice—though notably, the freezing point is lowered to 15 degrees F., making road salt effective only in conditions above that temperature. Salt’s ability to block the formation of ice in the right conditions is why it is applied annually on many roads, sidewalks, and parking lots, and why Lake Champlain and other waterways in cold regions around the world are getting saltier.
The next domino is where the salt ions go after they do their work as deicers. Roadside ecosystems are the first casualty of salt’s entry into the environment. Fan favorite tree species of northern hardwood forests such as sugar maple, beech, and white pine are sensitive to salinity and cannot thrive in salty environments. Native species that pervade roadsides throughout the Lake Champlain basin, such as cottonwood, staghorn sumac, and chokecherry, are fortunately quite salt-tolerant; however, adaptable invasives such as common buckthorn and honeysuckle are similarly capable of withstanding saltier water.
Salt then either seeps into groundwater or flows into surface water, making drinking water saltier. This can be a concern for individuals monitoring sodium intake. The salt itself isn’t the only issue. The next domino in the line of human health is the mobilization of other harmful substances into water supplies, such as mercury leached from contaminated sediments and radium from contaminated groundwater. Water high in chloride from salt increases the thinning of pipe walls and the release of lead. While the deeper causes of the water crisis in Flint, Michigan are rooted in systemic racism, it was salt-contaminated freshwater that leached lead from the city’s old water pipes.
Road salt contamination disrupts aquatic ecosystems in a cascade of falling dominos. Salt affects the growth of organisms adapted for freshwater, particularly in frogs, salamanders, and salmon. It can have an even greater impact on organisms not visible to the human eye: a study published in 2022 concluded that current thresholds for chloride (a measure of salinity) set by the Environmental Protection Agency (230 mg/L) are not sufficient to protect lake food webs at their base levels. Salinity levels within the recommended threshold still killed off more than half of the zooplankton populations in most of the lakes they studied. This decrease in zooplankton corresponded to an increase in phytoplankton such as cyanobacteria, establishing potential link between rising salinity and cyanobacteria blooms—an issue that is all too familiar for Lake Champlain. The echoes of salt’s impact on the species at the base of aquatic food webs are heard all the way up—one domino cannot fall without knocking over others. This research serves as a call to action on road salt regulation.
The trend of salinization in freshwater is alarming to say the least, but what can we do about it? On an individual level, if you choose to salt your driveway or sidewalk there are ways to do so strategically. Salt before snowfall, use a 23% saltwater solution (brine) rather than rock salt, shovel before applying, use only as much as needed, and sweep up excess for re-use. Do not apply salt on concrete, gravel, or dirt because salt is even more harmful for the environment and can cause dangerous conditions for driving if applied to an unpaved surface (with the exception of calcium chloride on dirt roads in the summer to keep down the dust). Regardless of surface type, no salt should be applied anywhere when temperatures are below 16 degrees F. It is important for each of us to cut back on our own salt usage, but in the grand scheme of salt contamination, these actions need to be supplemented by change at a larger scale.
The potential of road salt alternatives is a mixed bag. Beet juice, molasses, and cheese brine could all be substituted for salt. These alternatives, while initially touted as “eco-friendly,” have been found to be too tasty for their own good as each also has the potential to impact freshwater ecosystems. “Beet juice, molasses, and cheese brine that runoff into waterways will serve as a super yummy treat for small microorganisms that live in the water,” says Stepenuck. “They’ll eat the product that has entered the waterway as it’s essentially made up of sugars, or carbohydrates, which they can use as a food source. The process of all these microorganisms feasting on those sugars will use up oxygen in the water.” She adds that when they eventually run out of food and die, their mass decomposition would use up more oxygen on top of that. This all can result in hypoxic (or anoxic) conditions, which means that water is not carrying enough oxygen to support life (or lacks oxygen entirely). Another alternative, brine, is a saltwater solution that acts as an “anti-icer” before snowfall by preventing ice from forming, rather than a post-treatment “deicer” like rock salt. It is a promising option for reduction because of its efficiency—while it is usually just dissolved rock salt, it is only about 23% salt solution, so ice can be prevented with much less salt application.
States are starting to take action to address the salt problem on a broader scale. New York’s Road Salt Reduction Act passed in 2020 and created a multi-year pilot program to implement salt reduction tactics across municipalities, many of which are in the Lake Champlain Basin. Indeed, the Adirondacks have stepped up in the past few years with community-wide efforts to cut back on salt. Towns including Hague, North Elba, Lake George Village, and Lake Placid Village, among other Adirondack towns who have signed a pledge from the non-profit AdkAction to reduce salt use, have started managing road salt with water quality in mind. For example, Hague, NY reduced road salt from 1,600 tons in 2016/17 to just over 500 tons in 2020/21—a nearly 70% reduction in just five years. They did this by using brine and investing in new technology such as live-edge plows, which hug the contours of the road. Other technology such as surface temperature sensors and live calibration tools allow drivers to track the output of salt so they know how much goes onto the roads. South Burlington, VT does this as well, and has been able to reduce salt through tracking and setting output to lower rates accordingly. Free online resources such as Lake Champlain Sea Grant’s deicing calculator help salt applicators decide the best amount of deicer to use given surface type and temperature. All of these tools help plow drivers salt more efficiently.
The Lake Champlain Committee is currently advocating for a measure in the Vermont Legislature that will establish the Chloride Contamination Reduction Program at the Agency of Natural Resources (ANR). This program has the goal of, as the name suggests, reducing chloride in surface and groundwater across the state. It will require ANR to collaborate with the Vermont Agency of Transportation to establish a program to reduce salt application from municipal and private salt applicators modeled after the state program. This expanded training and certification program for salt applicators will emphasize reduction by establishing standards for when salt should be used and sharing techniques for efficiency. Additionally, water quality monitoring will identify baseline levels of salt contamination and priority areas with high salinity. Further, all salt and sand storage facilities, which can be major contributors to salt contamination, will be required to be covered to prevent leaks by 2030.
In New York, preliminary data suggest that their work to reduce salt use is already paying off: Hague Brook, which feeds Lake George, goes against the common trend of rising salt in freshwater and has shown an annual decrease in chloride concentrations since 2016. Mirror Lake’s salt levels have also been trending downward since 2019 when best management practices were first embraced. Community action works, and if the Chloride Contamination Reduction Program passes in Vermont, results will follow. This gives hope to an otherwise bleak subject: with a shift in priorities, salt contamination can be avoided, and the dominos can be picked up.
Lake Look is a monthly natural history column produced by the Lake Champlain Committee (LCC). Formed in 1963, LCC is a bi-state nonprofit that uses science-based advocacy, education, and collaborative action to protect and restore water quality, safeguard natural habitats, foster stewardship, and ensure recreational access. You can join, renew your membership, make a special donation, or volunteer to further our work.