Particle size-dependent effects of silver nanoparticles on swim bladder damage in zebrafish larvae.

Particle size-dependent biological effects of silver nanoparticles (AgNPs) are of great interest; however, the mechanism of action of silver ions (Ag) released from AgNPs concerning AgNP particle size remains unclear. Thus, we evaluated the influence of particle size (20, 40, 60, and 80 nm) on the acute 96-h bioaccumulation and toxicity (swim bladder damage) of AgNPs in zebrafish (Danio rerio) larvae, with a focus on the mechanism of action of Ag released from differently sized AgNPs. The 40- and 60-nm AgNPs were more toxic than the 20- and 80-nm versions in terms of inflammation and oxidative damage to the swim bladder, as indicated by inhibition of type 2 iodothyroxine deiodinase enzyme activity, mitochondrial injury, and reduced 30-50% adenosine triphosphate content. Furthermore, up-regulation and down-regulation of swim bladder development-related gene expression was not observed for pbx1a and anxa5, but up-regulation expression of shha and ihha was observed with no statistical significance. That 20-nm AgNPs were less toxic was attributed to their rapid elimination from larvae in comparison with the elimination of 40-, 60-, and 80-nm AgNPs; thus, less Ag was released in 20-nm AgNP-exposed larvae. Failed inflation of swim bladders was affected by released Ag rather than AgNPs themselves. Overall, we reveal the toxicity contribution of Ag underlying the observed size-dependent effects of AgNPs and provide a scientific basis for comprehensively assessing the ecological risk and biosafety of AgNPs.