Developmental toxicity of Japanese medaka embryos by silver nanoparticles and released ions in the presence of humic acid

The final destination point of nanoparticles is the environment, where they remain a long period; therefore, a deep understanding of the relationship between nanoparticles and the environmental factors is required. Japanese medaka embryos were exposed to two differently prepared AgNPs: freshly prepared AgNPs and aged AgNPs. With these two AgNP preparations, we studied the impacts of humic acid in terms of embryonic toxicity, as well as the behavior of AgNPs. Aged AgNPs exhibited a lower lethal concentration (LC50) value (1.44 mg/L) compared to fresh AgNPs (3.53 mg/L) through 96 h acute toxicity tests, due to the release of silver ions, as confirmed by kinetic analysis. The presence of humic acids considerably reduced the toxicity of aged AgNPs due to complexation with silver ions. Agglomeration, induced by interactions with humic acid, might reduce the bioavailability of AgNPs to Japanese medaka embryos. This study demonstrates that aged AgNPs releasing more silver ions are more toxic than fresh AgNPs, and humic acids play a role in reducing the toxicity of aged AgNPs.

Highlight
► Toxicity and kinetics of two AgNPs (e.g., aged and freshly prepared) were compared.
► Aged AgNPs showed greater toxicity compared to freshly prepared AgNPs in LC50.
► The role of humic acid coating AgNPs and bridging between AgNPs was observed.
► HA resulted in considerably reduced acute and developmental toxicity of aged AgNPs.