Impacts of Road Deicing Application on Sodium and Chloride Concentrations in Philadelphia Region Drinking Water

Historical application of roadway deicing agents (e.g., road salt and brines) has led to an increase in sodium and chloride concentrations in surface water over time. Numerous studies have explored the impacts of road salt on freshwater aquatic organisms such as amphibians and benthic macroinvertebrates; however, the public health risk associated with consuming drinking water with elevated sodium has been largely unexplored in the literature. Yet, sodium ingestion, primarily through diet, has been linked to adverse human health conditions, such as hypertension. This study documents weekly sodium and chloride concentrations in municipal tap water from three municipalities within the Philadelphia metropolitan area during winter 2018-2019 (November through March). A late winter peak in sodium and chloride concentrations was observed for all three municipalities immediately following successive snow events coupled with daily high temperatures above 0 degrees C. Among municipalities, mean and peak sodium and chloride concentrations were associated with relatively higher development in upstream areas. Observed sodium concentrations ranged from 1 to 6.4x the USEPA recommended guideline of 20 mg/L for individuals restricted to a total sodium intake of 500 mg/day. Additionally, the contribution of sodium ingestion from water consumption to the recommended daily sodium intake limits for adults ranged from 3.5% to 18.8% for non-restricted and 4.2%-33.3% for "low salt" (i.e., <1,500 mg/day) diets, respectively. The study results coupled with a records review for 40 U.S. municipalities in snow affected regions indicate the need for real-time communication between water utilities and the general public regarding sodium exposure risk during winter months. Plain Language Summary Each year, over 20 million metric tons of road salt (e.g., sodium chloride) are applied to U.S. roadways as a de-icing agent. Much of this salt makes its way into rivers and streams that serve as a source of drinking water by downstream municipalities. This study evaluated the relative change in the amount of sodium and chloride in Philadelphia region tap water during the 2018-2019 winter; Philadelphia represents an area that relies primarily on rivers for its drinking water. We found that peak sodium and chloride levels coincided with a late season period of snowmelt. This contribution of tap water sodium to the recommended daily sodium intake limits ingested by adults on "low salt" diets (<1,500 mg/day) ranged from 4.2% to 33.3%. Additionally, almost all tap water samples collected were above the USEPA recommended guideline of 20 mg/L. This represents a problem for individuals whose total sodium intake is restricted to 500 mg/day. The study results point to the need for real-time communication between water utilities and the general public regarding sodium exposure risk during winter months.