Silver Ion Release Accelerated in the Gastrovascular Cavity of Hydra vulgaris Increases the Toxicity of Silver Sulfide Nanoparticles (Ag 2 S-NPs).

Silver nanoparticles (Ag-NPs) streamed into aquatic environments are chemically transformed into various forms, and one of the predominant forms is silver sulfide nanoparticles (Ag2 S-NPs). Due to the lower dissolution rate of silver ions (Ag+ ), the toxicity of Ag2 S-NPs could be lower than that of Ag-NPs. However, the toxicity of Ag2 S-NPs has been observed to be restored under oxidative or acidic conditions. Here, four aquatic organisms, Pseudokirchneriella subcapitata (algae), Daphnia magna (crustacean), Danio rerio (fish), and Hydra vulgaris (cnidarian), were exposed to Ag2 S-NPs transformed from Ag-NPs using Na2 S under anoxic conditions, and acute toxicity was evaluated. The acute toxicity of Ag2 S-NPs was rarely observed in algae, crustaceans, and fish while it was significantly restored in cnidarians. Although the dissolution rate was low in the medium exposed to Ag2 S-NPs, the high Ag+ was detected in H. vulgaris. To understand the mechanisms of Ag2 S-NP toxicity in cnidarians, transcriptional profiles of H. vulgaris exposed to Ag-NPs, Ag2 S-NPs and AgNO3 were analyzed, respectively. As a result, most of the genes that were significantly changed in the Ag2 S-NPs group were also found to be significantly changed in the AgNO3 group, indicating that the toxicity of Ag2 S-NPs was caused by Ag+ dissolved due to acidic condition in the gastrovascular cavity of H. vulgaris. This finding is the first report in aquatic organism and suggests that the need to reconsider the stability and safety of Ag2 S-NPs in the aquatic environment. This article is protected by copyright. All rights reserved.