By Cate Twining-Ward

On early Tuesday morning, a swift moving Nor’Easter brought the most snow New Yorkers have seen in over two years. The hazardous forecast called for de-icing salt, and lots of it. 

In the United States we put salt on everything, including our streets. Every winter, more than 137 pounds of salt – per person – is scattered on American roads. While proven to dramatically reduce the frequency of traffic accidents and pedestrian injuries, equally strong evidence now suggests that this lifesaving substance may simultaneously poison our drinking water.

The salt used for de-icing is almost identical to what we sprinkle on our pasta water. It’s the same sodium chloride, NaCl, a chemical as cheap as it is accessible. When sodium chloride reacts with, and breaks apart, the water molecules making up ice, the melted runoff flows off our streets and out of our minds. But, not quite out of range.   The ions in sodium chloride trigger the release and transport of harmful chemicals, notably heavy metals, which reside in roadside soils and sediment. Picked up by the runoff, these chemicals can then flow into drinking water reservoirs and wells, threatening the health and safety of unsuspecting residents. Not to mention, the chloride in salt is superbly effective at corroding metal pipes. 

Mercury and lead, two metals with the highest degree of toxicity, are released and transported at a rate that is two to five times higher in the presence of de-icing salts. Road salt can also mobilize and increase concentrations of copper and cadmium, metals which pose neurological, reproductive, and cardiovascular health risks. More alarming still, when in contact, sodium ions in NaCl can trigger the release of dissolved radium, a chemical which emits radon gas. Radon gas is highly radioactive and carcinogenic. 

North American public water supplies were long considered as some of the best in the world. But in 2019, a national water study in Canada found unsafe lead levels in one third of homes. The same year, lead poisoning in Newark, New Jersey threatened hundreds of thousands of people. The United States Environmental Protection Agency now categorizes polluted runoff “as one of the greatest threats to clean water.”

Just ten years ago in Flint, Michigan, a devastating water crisis left nearly 100,000 residents exposed to harmful chemicals and 12 people dead. We were quick to blame old pipes and systemic racism—and rightly so. Yet, roadside, lay an inconspicuous relevant detail. The mystery culprit? Road salt. 

Switching the city’s water source to the local Flint River was, for many reasons, poor policy-making. First, chlorine levels in Flint’s River were reported to be eight times higher that of Detroit’s water. According to the American Chemical Society, the high chlorine in Flint’s River was linked to run-off produced from nearby icy highways, ones that had been treated with copious road salt.  

As a result, a chemical reaction occurred between the chloride ions and Flint’s antiquated water pipes, which were made from lead and iron. The chloride-concentrated water corroded and dissolved Flint’s pipes from the inside out, releasing toxic levels of lead into residential drinking water. 

Census data analyzed by the Detroit Free Press found that 8,657 children under the age of six were exposed to lead from Flint’s water—and the effects are still felt by residents today. A 2023 fact sheet published by the World Health Organization stated there is “no known safe blood lead concentration,” and that the adverse neurological and behavioral effects of lead are irreversible. 

In addition to posing threats to humans, it’s well established that de-icing runoff causes severe long-term environmental damage. According to the Environmental Protection Agency, excess salt endangers and kills wildlife in freshwater habitats, and high chloride levels are toxic to fish, bugs, and amphibians.  

Despite the overwhelming evidence that road salt poses profound threats to human and environmental health, the pervasive use of de-icing salts has more than tripled over the past 45 years. And not just in places like Flint, Michigan. New York State is now the largest consumer of road salt in North America. 

One solution to this dilemma may be the development of environmentally friendly anti-icing agents. Several non-toxic alternatives exist already. These substitutes blend salt brine with biobased materials such as beet juice, molasses, and corn; this reduces salt concentrations by 75 percent while keeping roads just as safe, according to the Cary Institute. The US Department of Transportation affirms that the deployment of commercial bio-based products has been hindered due to high cost, quality control issues, and concerns over their possible attraction to wildlife. 

It shouldn’t take another deadly water crisis for officials to act. The perils of roadside salt have long been made clear. There are effective alternatives. Now it is up to local governments to turn scientific knowledge into action by evaluating best practices, monitoring the rate and transport of applied salts, and collecting ample site-specific data. We must act now, to facilitate changes that will benefit all of us, including society’s most vulnerable groups. Our health depends on it. 

Cate Twining-Ward (MPA ‘24) studies Environmental Science and Policy at the Columbia School of International and Public Affairs. Previously she has worked at the United Nations, with NGOs conducting field work on endangered primates and indigenous land rights in west and east Africa, and as a senior correspondent for Planet Forward, an environmental journalism organization. Her work at Columbia has focused on addressing the climate crisis through the research and implementation of environmental justice programs, sustainable food systems, and system change.