The production prospects of silver nanoparticles (AgNPs) are contingent upon guaranteeing their safety, as they are present in numerous consumer goods. The potential impact of AgNPs aging during storage on the anticipated toxicity of nanoparticles must be taken into consideration. The present study aimed to assess the impact of AgNPs aging on their toxicity in adult zebrafish (Danio rerio). Specifically, the toxicity of recently synthesized AgNPs was compared to those that had been stored for a period of 180 days. All toxicity experiments were conducted in accordance with the protocols specified in OECD 203. Mortality data were analyzed using Probit software. The results showed that long-term storage of AgNPs reduces their toxicity in zebrafish, so that LC50 values increase from 0.029 ± 0.004 mg/L for pristine (unaged) to 0.046 ± 0.006 mg/L for six-month aged AgNPs. The observed variations in the toxicity of aged/unaged AgNPs could be attributed to various mechanisms, including aggregation, agglomeration, dissolution, oxidation, degradation of capping agents, and the attachment of Ag+ ions to the walls of containers. Consequently, the phenomenon of NPs 'aging' can significantly contribute to the conflicting toxicity outcomes reported in the scientific literature for identical NPs. Therefore, it is crucial to evaluate NP aging concurrently with toxicity assessment in order to gain a comprehensive understanding of their potential adverse effects.
