Derivation of ecotoxicologically acceptable Cu concentrations in the Han River basin, Korea with emphasis on Ca concentration and instantaneously changing water characteristics

Abstract

The biotic ligand model (BLM) was applied to derive ecotoxicologically acceptable Cu concentrations at 12 monitoring stations in the Han River Basin, South Korea, considering temporal variations in water characteristics. During the monitoring period, pH, dissolved organic carbon (DOC), and water temperature varied instantaneously, resulting in spatiotemporal variations in the half-maximal effective concentrations (EC50[Cu]T) of Daphnia magna. The effect of dissolved Ca2+ concentration was evaluated to determinate EC50[Cu]T using the Visual MINTEQ 3.1 speciation model. Dissolved Ca2+ concentration was directly proportional to EC50[Cu]T values, indicating that a higher Ca2+ in the solution will result in the lesser toxic effects on D. magna due to the competition between Ca2+ and Cu2+ ions. The Ca2+ concentration was set at 0.4 mM while deriving EC50[Cu]T, which is the geometric mean concentration in the Han River Basin. The lower confidence limit (LCL) of EC50[Cu]T was 28.7–67.8 μg/L in the monitoring stations. Among the water characteristics, DOC was more strongly positively correlated with EC50[Cu]T than that with pH and temperature. DOC concentration was significantly related to Cu2+ activity, pH was less explicitly related to EC50[Cu]T than to DOC, and water temperature had the weakest correlation coefficient. Compared to the 5% hazardous concentration (HC5) derived from the toxicity data for 171 aquatic species and Cu criteria in different countries, the computed LCL concentrations had similar orders of magnitude. With more information on actual Ca2+ concentrations at monitoring sites, a more accurate Cu concentration that reflects spatiotemporal variations of water characteristics can be obtained. © 2022