The Relative Toxicity of Road Salt Alternatives to Freshwater Mussels; Examining the Potential Risk of Eco-Friendly De-icing Products to Sensitive Aquatic Species

The negative impact of road salt on freshwater ecosystems has led to an interest in "eco-friendly" de-icing products. Biota, including freshwater mussels that have heightened salt sensitivity, would be expected to benefit from a transition to alternative de-icing products. However, it was unknown whether the alternatives themselves pose a risk. The toxicity of three road salt alternatives including a salt brine, a beet juice, and a brine–beet juice product were examined. Lampsilis fasciola glochidia (larvae) were exposed to dilutions (0–2%) of de-icing products. On a per volume basis, beet juice products were significantly more toxic than brine with 48 h EC50s (95% confidence intervals) as follows: brine, 0.42% (0.35–0.50%); beet juice, 0.020% (0.018–0.022%); and brine–beet juice, 0.034% (0.028–0.039%). Unlike brine, beet juice toxicity did not correspond with the concentration of chloride in the exposure. While elevated trace metals (Cu, Fe, Zn) and reduced water quality occurred in the 1% and 2% beet juice exposures, toxicity occurred at much lower dilutions (≤0.05%). The toxicity of beet juice products aligned with glochidia potassium EC50s. Based on toxicity and application rates, beet juice de-icing products pose more of a hazard to early life stage mussels than traditional products and could contribute substantial potassium to receiving environments.