Culture medium mediated aggregation and re-crystallization of silver nanoparticles reduce their toxicity

Due to their wide uses in both domestic and industrial applications it is important to consider possible releases of silver nanoparticles (AgNPs) into the environment and the possible consequences. Thus, the potential toxicity of AgNPs to aquatic organisms has been intensively studied recently. However, culture media composition and stability of AgNPs seriously affect dose-response relationship. In present study the chronic toxicity of AgNPs to Daphnia magna in undiluted and 2-fold diluted media was examined. Both gelatin-stabilized and non-stabilized AgNPs were synthesized and their stability was assessed by transmission electron microscopy and UV/Visible spectroscopy. The half maximal effective concentrations (EC50 values) for D. magna reproduction of non-stabilized AgNPs in undiluted medium, non-stabilized AgNPs in 2-fold diluted medium and AgNPs stabilized with 0.0001% (w/v) gelatin in 2-fold diluted medium were found to be 0.96, 0.32 and 0.16 mg/L, respectively. AgNPs stabilized with 0.005% gelatin did not aggregate and marked toxicity was observed across the AgNP concentration range from 0.001 to 1 mg/L. On the contrary, AgNPs with low stability in media were subjected to aggregation and re-crystallization towards large particles, which reduced their toxicity. Thus, the results demonstrate the importance of rigorous characterization of media composition for robust assessment of AgNPs' toxicological effects. (C) 2018 Elsevier Ltd. All rights reserved.