In recent years, production of both silver nanoparticles (AgNPs) and zinc oxide nanoparticles (ZnONPs) increased exponentially, which may pose potential risks to aquatic ecosystems. There are few studies on the toxicity caused by co-exposure of nanomaterials in aquatics. The aim of this study was to determine the toxicity of AgNPs in the presence of ZnONPs on zebrafish (Danio rerio) as a model aquatic organism. This study was conducted according to the OECD 203. Juvenile zebrafish were exposed to different concentrations of AgNPs in the presence of 0, 1, 10, and 100 mg.L-1 ZnONPs, and their mortality was evaluated during 96 hours. Data were analyzed using the EPA Probit analysis program. The 96h LC50s of AgNPs in the presence of 0, 1, 10, and 100 mg.L-1 ZnONPs were 0.030, 0.037, 0.104, 0.166 mg.L-1 respectively. Accordingly, the toxicity of AgNPs decreased in the presence of ZnONPs. Based on visual observations, ZnONPs caused precipitation of AgNPs, which probably reduced the availability of AgNPs for fish. This study showed that the combination of AgNPs and ZnONPs can result in an antagonistic effect on the toxicity to zebrafish. This could probably be because when ZnONPs are present in the freshwater, they can bind to AgNPs and form a complex that is less bioavailable to fish. Another hypothesis could be that zinc as an essential nutrient for many aquatic organisms, can also help to mitigate any negative effects of AgNPs exposure by providing additional nutrients.
