Nick Redmond, MJLST Staffer
Winter is coming. Or—at least according to the 2017 Farmer’s Almanac—“winter is back” after an exceptionally mild 2015–2016 season, and with it comes all of the shoveling, the snow-blowing, and the white walkers de-icing of slippery roads that we missed last year. So what does the most overused Game of Thrones quote and everyone’s least favorite season have to do with Kool-Aid (actually, Flavor-Aid)? Just like the origins of the phrase “drinking the Kool-Aid,” this post has to do with cyanide. More specifically, the ferrocyanide compounds that we use to coat our road salt and that are potentially contaminating our groundwater.
De-icing chemicals are commonly regarded as the most efficient and effective means of keeping our roads safe and free from ice in the winter. De-icing compounds come in many forms, from solids to slurries to sticky beet juice- or cheese brine-based liquids. The most common de-icing chemical is salt, with cities like Minneapolis spending millions of dollars to purchase upwards of 15,000 tons of treated and untreated salt to spray on their roads. In order to keep the solid salt from clumping or “caking” and becoming unusable as it sits around it’s usually treated with chemicals to ensure that it can be spread evenly on roads. Ferrocyanide (a/k/a hexacyanoferrate(II)) and the compounds sodium ferrocyanide and potassium ferrocyanide are yellow chemicals commonly used as anti-caking additives for road salt in Minnesota and other parts of the country, and they can be found in varying concentrations depending on the product, from 0.0003 ppm to 0.33 ppm. To put those numbers in perspective, the CDC warns that cyanide starts to produce harmful effects on humans at 0.05 mg/dL, or 0.5 ppm.
But why are chemicals on our road salt troubling? Road salt keeps ice from forming a bond with the pavement by lowering the freezing point of snow as it falls on the ground. As the salt gets wet it dissolves; it and the chemicals that may be attached to it have to go somewhere, which may be our surface and ground waters or the air if the liquids evaporate. The introduction of these chemicals into groundwater is of particular concern for the 75% of Minnesotans and people like them who rely on groundwater sources for drinking water. The potential for harm arises when ferrocyanide compounds are exposed to light and rapidly decompose, yielding free cyanide (CN and HCN). Further, as waters contaminated with cyanide are chlorinated and introduced to acids they may produce the harmful compound cyanogen chloride, a highly toxic gas that was once considered for use in chemical warfare. Taking into account the enormous amount of salt used and stored each year, even small concentrations may add up over time. And although the EPA has placed cyanide on the Clean Water Act’s list of toxic substances, the fact that road salt is a non-point source means that it’s entirely up to states and municipalities to decide how they want to regulate it.
The good news is that ferrocyanides are among the least toxic cyanide salts, and tend not to release toxic free cyanide. What’s more, the concentrations of ferrocyanide on road salt are generally quite low, are spread out over large areas, and are even further diluted by precipitation, evaporation, and existing ground and surface water. In order to really affect drinking water the ferrocyanide has to (1) not evaporate into the air, (2) make its way through soil and into aquifers, and (3) in large enough concentrations to actually harm humans, something that can be difficult for a large molecule. Despite all of this, however, the fact that Minneapolis alone is dumping more than 15,000 tons of road salt each year, some of it laced with ferrocyanide, should give us pause. That’s the same weight as 15,000 polar bears being released in the city streets every year! Most importantly, these compounds seep into our garden soil, stick to our car tires and our boots, and soak the fur of our pets and wild animals. While cyanide on road salt certainly isn’t a significant public health risk right now, being a part of local conversations to explore and encourage alternatives (and there are a number of alternatives) to prevent future harm might be something to consider.
At the very least think twice about eating snow off the ground (if you weren’t already). Especially the yellow stuff.