Applying rock salt to roads in the winter to melt ice and snow seems as commonplace as getting in your car to drive to the grocery store. However, according to National Geographic, rock salt wasn’t applied to any roads until 1940 in Detroit, Michigan, thanks to the city’s extensive salt mine beneath its footprint. Since 1940, rock salt has been used by municipalities across the United States every winter. The question remains though, how harmful is that much salt—millions of tons, nation-wide—to the ecosystems surrounding our roads?
Deicing salt, it turns out, is one of the major stormwater issues facing municipalities these days. One study by the US Geological Survey reports that since 1960, chloride levels in streams have substantially increased in 30 monitored streams, and that road deicing appears to have directly contributed to the hazardously toxic increase. Twenty-nine percent of the monitored streams registered chloride levels above “the U.S. Environmental Protection Agency’s chronic water-quality criteria (230 milligrams per liter) by an average of more than 100 days per year from 2006 through 2011, which was almost double the amount of days from 1990 through 1994.” Additionally, watersheds with little urban land use and little winter precipitation experienced smaller fluctuations in chloride levels.
Some alternatives like beet juice and cheese brine are being explored by municipalities in order to cut down on rock salt dependency (both for financial reasons–rock salt mining is increasingly expensive as well as unreliable–and environmental ones), but these alternatives are still fairly experimental. As of last year, though, over 175 municipalities were using Beet Heet, the sugar beet molasses-based deicer, and Wisconsin is continuing its cheese brine supplement to traditional road salt.
Given the detrimental effects of increased chloride via stormwater runoff into watersheds (amphibians, fish, and native tree species are in greatest danger of dying due to high chloride concentrations), it’s important for research into rock salt alternatives to continue. Beet juice or cheese by-products may not be the answer for every community, but neither is rock salt when watersheds are considered.