Study on dissolution behavior of CuO nanoparticles in various synthetic media and natural aqueous medium

Due to the wide applicability of copper-based nanoparticles (CBNPs), their long-term utilization could raise the toxicological concerns owing to their potential persistence, accumulation, and relatively low soluble nature. The present study is focused on the dissolution behavior of commercially procured CuO nanoparticles (NPs) in natural surface water system (pond water) and DI water at environmental concentration (1 mg/L) of CuO NPs. The dissolution of CuO NPs in DI water was higher than the pond water. Maximum dissolved Cu concentration in DI water and pond water was 0.054 and 0.035 mg/L, respectively. However, the dissolution kinetics followed reverse trend. High rate of dissolution (i.e., 0.049 h⁻¹) observed in pond water, whereas the dissolution rate was low in DI water (i.e., 0.034 h⁻¹). The trend of dissolution in presence of humic acid was 10 mg/L > 100 mg/L > 1 mg/L. Additionally, the dissolution of CuO NPs increased with increasing the IS (i.e., KH₂PO₄ > CaCl₂ > NaCl) and decreasing the pH (i.e., pH 9 < pH 7 < pH 5.7) of suspension. The speciation modelling using a Visual MINTEQ software showed the presence of various species of Cu in pond water such as Cu-DOC (80%), Cu²⁺ (4%), CuCO_{3 (aq)} (9%), CuOH⁺ (6%), and Cu(OH)_{2 (aq)} (1%). The experimental half-life of CuO NPs varied from 2.4 to 36 h in different mediums which confirms the persistence nature of CuO NPs in natural water system.