A recent U.S. Geological Survey (USGS) study claims that road salt, used to deice roads during winter storms, permeates urban streams. Steven Corsi, et al., “A Fresh Look at Road Salt: Aquatic Toxicity and Water-Quality Impacts on Local, Regional, and National Scales,” Environmental Science & Technology, September 1, 2010. The Wisconsinbased researchers monitored chloride concentrations in local creeks and streams at 13 sites throughout the Milwaukee area during winter 2007. More than one-half of the local streams had chloride levels that exceeded EPA’s recommended threshold.  

The study also found that the chloride-laced water samples were toxic to two endemic species—the fathead minnow and a water flea. The researchers examined historical USGS data for 13 northern and four southern metropolitan areas. This data revealed that chloride concentrations exceeded EPA waterquality criteria at 55 percent (chronic) and 25 percent (acute) of 168 monitoring locations in northern metropolitan areas from November to April. Only 16 percent (chronic) and 1 percent (acute) exceeded criteria from May to October. At southern sites, very few samples exceeded water-quality criteria.