Silver Ion Release Accelerated in the Gastrovascular Cavity of Hydra vulgaris Increases the Toxicity of Silver Sulfide Nanoparticles

Abstract

Silver nanoparticles (Ag-NPs) streamed into aquatic environments are chemically transformed into various forms, and one of the predominant forms is silver sulfide NPs (Ag 2 S-NPs). Because of the lower dissolution rate of silver ions (Ag + ), the toxicity of Ag 2 S-NPs could be lower than that of Ag-NPs. However, the toxicity of Ag 2 S-NPs has been observed to be restored under oxidative or acidic conditions. In the present study, 4 aquatic organisms, Pseudokirchneriella subcapitata (algae), Daphnia magna (crustacean), Danio rerio (fish), and Hydra vulgaris (cnidarian), were exposed to Ag 2 S-NPs transformed from Ag-NPs using Na 2 S under anoxic conditions; and acute toxicity was evaluated. The acute toxicity of Ag 2 S-NPs was rarely observed in algae, crustaceans, and fish, whereas it was significantly restored in cnidarians. Although the dissolution rate was low in the medium exposed to Ag 2 S-NPs, high Ag + was detected in H. vulgaris. To understand the mechanisms of Ag 2 S-NP toxicity in cnidarians, transcriptional profiles of H. vulgaris exposed to Ag-NPs, Ag 2 S-NPs, and AgNO 3 were analyzed. As a result, most of the genes that were significantly changed in the Ag 2 S-NPs group were also found to be significantly changed in the AgNO 3 group, indicating that the toxicity of Ag 2 S-NPs was caused by Ag + dissolved by the acidic condition in the gastrovascular cavity of H. vulgaris. This finding is the first in an aquatic organism and suggests the need to reconsider the stability and safety of Ag 2 S-NPs in the aquatic environment.

Effect of Fluoride Content of Mouthwashes on the Metallic Ion Release in Different Orthodontics Archwires

“…The release of ions goes to the physiological environment, and different studies have observed that they can be stored in different organs. The threshold concentrations that can cause toxicity in humans are not known, and at the moment, the quantities of ions are compared to those we ingest in our daily diet [56][57][58].…”

Gut-microbial adaptation and transformation of silver nanoparticles mediated the detoxification of Daphnia magna and their offspring

“…In complex microcosms, nearly 100% of Ag was bound to sulfur, which decreased the bioavailability and toxicity of Ag + and AgNPs 77 . Another study also showed that Ag Hydra vulgaris (cnidarian) was detected 79 . Our studies demonstrated the possibility that the anaerobic gut environment of D. magna provided an ideal condition for the gut-microbial transformation of Ag + and AgNPs through sulfidation with enriched sulfate and sulfate reducing bacteria 80 , since low oxygen is one of the requirements for microbial sulfate reduction 81 .…”

Sensitivity of Hydra vulgaris to Nanosilver for Environmental Applications

“…The low release of Ag ions in Hydra medium, as shown by ICP-MS data, surely played a significant role in the observed reduced ecotoxicity, also based on the morphological effects observed upon exposure to AgNO 3 , confirming the sensitivity of Hydra to Ag. However, Kang and Park [30] measured high levels of Ag inside Hydra specimens exposed to sulfide-coated AgNPs (Ag 2 S-NPs), even if the nominal dissolution of AgNPs in the medium was as low as non-detectable (LOD not reported). This was associated with toxicity, both at the morphological and regeneration levels (with EC 50 of 0.65 and 0.09 mg/L, respectively).…”

“…This was associated with toxicity, both at the morphological and regeneration levels (with EC 50 of 0.65 and 0.09 mg/L, respectively). The authors hypothesized the ingestion of Ag 2 S-NPs followed by dissolution, triggered by the acidic environment of the gastrovascular cavity [30].…”