Acute toxicity of sodium chloride-based road salt formulations to juvenile aquatic invertebrates

Globally millions of tons of de-icing agents are applied each year, and about half of these salts enter surface water adjacent to sites of application. While numerous studies have demonstrated the potential impact de-icing agents such as NaCl have on freshwater invertebrates, many of these studies have used laboratory grade NaCl for evaluation, and less is known about the relative toxicity of formulations. The purpose of this study was to compare the 24 and 96 h LC50s of NaCl and two NaCl-based road salt formulations for three aquatic species: juvenile Hyalella azteca, Hexagenia rigida, and Chironomous dilutus. As expected, LC50 values were greater for 24 h exposures than 96 h exposures. However, the relative toxicity of the road salt formulations varied by exposure duration and species. Although the acute LC50 values found in this study were within environmental concentrations of chloride ions reported by existing literature, more research is needed to evaluate chronic or sublethal effects of road salt formulations on a range of freshwater macroinvertebrates.