Cation Composition Influences the Toxicity of Salinity to Freshwater Biota

The effects of salinization on freshwater ecosystems have been estimated by testing sodium chloride (NaCl) since it is the most widely used salt as a deicing agent and Na⁺ and Cl^- ions are the most representative in seawater composition. However, calcium, magnesium, and/or potassium are starting to be proposed as potential surrogates for NaCl, but for which ecotoxicological effects are less explored. This study aimed to identify (i) the less toxic salt to freshwater biota to be suggested as a safer alternative deicer and (ii) to contribute to the lower tiers of salinity risk assessment frameworks by identifying a more suitable surrogate salt than NaCl. The battery of ecotoxicity assays with five key trophic level species showed that among the tested salts (MgCl₂, CaCl₂, and KCl), KCl and CaCl₂ seemed to induce the highest and lowest toxicity, respectively, compared with NaCl. CaCl₂ is suggested as a safer alternative for use as a deicer and KCl as a surrogate for the risk assessment of seawater intrusion in coastal regions. These results enrich the salt toxicity database aiming to identify and propose more suitable surrogate salts to predict the effects of salinization to a broader extent.