With winter just around the corner, I thought Id run a few posts on road salt, something Ive been studying for a while. Take a look at this figure, which shows the amount of road salt purchased annually for the past 70 years or so:
(data from the Road Salt Institute)
As you can see, there’s been a dramatic increase in the amount of road salt used in the U.S. over that period. While sales have varied quite a bit in the last 15 years or so (a function of how snowy the winter is), the trend is still increasing.
Road salt, primarily halite (NaCl), is a very effective deicing agent, lowering the melting temperature of snow and ice from 32ºF down to the lower 20’s. It’s also very cheap. While prices have spiked in recent years to $50-60 per ton, it’s still much cheaper than alternatives.
One reason NaCl is such an effective deicing agent is its very high solubility. Unfortunately, that is also the main reason it has become a serious water quality problem in northern regions of North America and Europe; once it’s applied, it will invariably wind up in our water resources.
Here’s a graph showing chloride (Cl-) concentrations in Lake Michigan since the early 1980s:
(data from USEPA)
As you can see, there’s been a steady increase, although the concentration has only increased about 3 mg/L in 25 years. However, Lake Michigan is a Great Lake with a great deal of water, and this 3 mg/L increase is equivalent to about 660,000 tons of chloride being added annually to Lake Michigan. And that’s mainly due to road salt runoff.
This small increase in chloride (and sodium as well) is probably not affecting aquatic life in Lake Michigan. But we are observing much larger increases in streams, rivers, and inland lakes in the Chicago region, and this salinization is likely detrimental to many aquatic organisms. In future posts I’ll talk more about what we’re finding in surface waters and groundwater in the Chicago region.