Rock Salt–A Danger Hiding In Plain Sight and Underfoot

New York City experiences winter with a capital W every year. From the months of December to March, the city endures ice-coated streets and an average of 25.3 inches of snow. If left untouched, the concrete maze of city streets would morph into a slippery danger zone of ice and snow with no way to get kids to school and adults to work. 

So what magical cure comes to the rescue when the city is faced with winter’s onslaught? Rock salt. Rock salt melts the snow on our streets, saving the day when the rain puddles freeze and the blizzards pile on drifts of white fluff. But this crystallized antidote can also cause great harm to New York’s roads, plant life, watershed—and dog paws. 

Every winter, the city opens up its 31 permanent salt storage sites and 11 seasonal ones. “We start the snow season with more than 300,000 tons of salt on hand, and can reorder more throughout the season, as needed,” explains the Department of Sanitation’s Belinda Mager in an email. That’s a lot of salt. But New York is also a city that cannot afford to be shut down by snowfall and icy roads. So, the Department of Sanitation takes preparedness to the highest level. Rock salt’s effects, however, are not limited to melting snow. 

Rock salt can corrode electrical units beneath manholes on the roads. When rock salt melts snow, the watery solution of the sodium chloride and the melted snow seeps through the manholes. The wet salt then corrodes the insulation of the electrical cables and can create sparks on the electrical cables. Such sparking can escalate to a fire that might cause the manhole to explode from the combustion of gasses. 

This happened on February 3, 2015, in Park Slope, Brooklyn. At 4 a.m. that day, then-10-year-old resident Nora Loftus awoke to a firefighter repeatedly ringing her doorbell. When Loftus and her family stumbled out of bed and made it to the door, the firefighter told them to evacuate their building. 

“We put on jackets and were just in our pajamas as we walked outside and saw a big fire in the street,” she recalls. According to a 2019 New York Times article, the increased frequency of these explosions prompted the city to respond by adding vents to manhole covers to reveal any smoke from underground fires. However, these old generation covers are not entirely phased out as manhole explosions have occurred as recently as 2021. 

Rock salt also has substantial effects on waterways and ecosystems in New York state. When the salt melts with the snow, much of it runs off into waterways. According to a 2014 Smithsonian article by Joseph Stromberg, 91 percent of sodium chloride levels in Southeastern New York’s watershed can be attributed to rock salt. Fortunately, the affected waterways are not the ones used to source our drinking water, but 40 percent of urban streams have chloride levels deemed too high to keep aquatic life safe.

In Brooklyn, the highly polluted Gowanus Canal is subjected to combined sewage overflows, or CSOs, in which excessive rainwater or snowmelt runs into the same pipe that holds sewage, causing the pipe to overflow into the waterway. When a large snowmelt occurs, the combined runoff and sewer water deposits into the canal. Rock salt runoff can change the chemistry of the canal water and impact its wildlife. Despite this effect, the Gowanus Canal Conservancy (GCC) does not flag rock salt as a major pollutant. 

According to Amy Motzny, watershed senior planner of the GCC, the canal faces worse pollutants including toxins and sewage. The necessity of rock salt in the city, she says, means the GCC addresses rock salt as “an existing constraint that’s going to be present in an urban environment.” To lessen rock salt’s impact on the canal, the GCC has identified and cultivated “salt-tolerant” plant species in rain gardens, small gardens designed to collect and absorb rainwater, Motzny explains. 

Rock salt is not only corrosive and polluting—it is also sharp. For dogs who walk bare-pawed on the sidewalk, rock salt can puncture and burn their paw pads. Many dog owners try to protect their dogs’ paws by putting “booties” on them. But, as many dog owners can attest, it is often a struggle to wrangle these booties onto dogs—because who wouldn’t hate having tight rubber balloons on their feet? 

Malaya Goldberg, a Millennium Brooklyn High School junior, says that her dog, Ponzu, resists wearing booties. As Goldberg says, when she manages to get them on, Ponzu “hates them and kicks them off.” Not all dogs are like Ponzu, though, so be ready to see dogs with booties trotting through the city this season!

Despite issues of runoff, corrosion, and irritation to dogs’ paws, the general safety of the city would be jeopardized if no salt was deployed. According to an article in a 2015 article from Vox by Ben Plumer, a 1992 study found that spreading salt can reduce car accidents by 87 percent during and after a snowstorm. Such is the reason why salt trucks have been vigilantly salting and plowing roads during snowfall days. 

Is there a way to compromise between icy danger and salt corrosion? Does the city cut down on usage or do researchers hunt for alternatives? For now, rock salt does the job, but we need to find a better way.