Impact of potassium ion concentration on the aquatic ecological risk of monovalent thallium leached from lithium slag

Lithium smelting slag, the solid waste generated from the extraction of lithium from ores, contains the hazardous element thallium, which can be mobilized into adjacent aquatic systems through rainwater leaching. Assessing the aquatic ecological risk of monovalent thallium (Tl+) is essential for informing the safe disposal of this residue. Potassium ions (K+), which are ubiquitously present in natural freshwaters, are known to antagonize the toxicity of Tl+. Nevertheless, prevailing aquatic ecological risk assessments for Tl+ often neglect the influence of ambient K+ concentrations. This study evaluates the effects of varying aqueous K+ levels on the aquatic ecological risk of Tl+, by analyzing toxicity data from 17 freshwater species utilizing the species sensitivity distribution (SSD) approach. The findings were further corroborated by the zebrafish embryo-larval acute toxicity test. When waterborne K+ concentrations were 0.25, 0.5, 1, 2, 4, 6, 8, and 10 mg/L, the derived acute ecological risk thresholds for aquatic organisms (AERT) for Tl+ were 1.9, 5.1, 13.9, 37.8, 102.9, 184.8, 279.8, and 386.2 μg/L, respectively, while the chronic ecological risk thresholds for aquatic organisms (CERT) were 0.1, 0.3, 0.7, 1.9, 5.2, 9.2, 13.9, and 19.0 μg/L, respectively. These results provide a scientific basis for refining the safety standards that govern thallium-containing solid wastes from the burgeoning new energy sector.