Toxicity of colloidal nano-silver to zebrafish, Danio rerio: ions, nanoparticles, or both?

Increasing production and utilization of silver nanoparticles can lead to their release into aquatic ecosystems and tend to toxic effects on aquatics. It is not yet clearly specified whether observed toxic effect following exposure of aquatic organisms to colloidal nano-silver is caused by silver nanoparticles contained in the colloid, by free silver ions, or by a combination of both. In this study, acute toxicity of "nanosilver colloid" (containing free ionic silver and silver nanoparticles) compared to the toxicity of "silver nanoparticles" separated from colloidal nanosilver (without free Ag ions) were investigated in zebra fish, Danio rerio. Acute toxicity tests were planned and performed according to standards of Organization for Economic Cooperation and Development. The results showed that No Observed Effect Concentrations (NOECs), Lowest Observed Effect Concentrations (LOECs), Maximum Acceptable Toxicant Concentrations (MATCs), and Median Lethal Concentrations (LC50s) of "nano-silver colloid" were 250, 240, 248.90, and 300.64 times less than those of "silver nanoparticles", respectively. Therefore, toxicity of colloidal nanosilver is mostly due to the free silver ions (Ag) rather than silver nanoparticles present in it. In general "nano-silver colloid" and "silver nanoparticles" are respectively classified as "highly toxic" and "toxic” chemicals for aquatics and the release of these substances into the environment should be prevented.