The wide uses of nanosilver (nAg) have resulted in concerns regarding ecotoxicity to aquatic organisms. Some previous studies have found that the toxicity of nAg is due to the nanoparticles themselves, while others have found that ionic silver (Ag(+) ) released by nAg particles plays an important role. In the present study, the authors quantitatively evaluated the relative contribution of nAg particles and Ag(+) to the toxicity to three aquatic organisms of different trophic levels, including an algal species (Raphidocelis subcapitata), a cladoceran species (Chydorus sphaericus), and a freshwater fish larva (Danio rerio). A bare and a polyvinylpyrrolidone (PVP)-coated nAg as well as a monodispersed nAg with a dispersant (DIS-nAg) were examined. The toxicity of the nAg in the form of colloids decreased in the order DIS-nAg > PVP-nAg > Bare-nAg for all three trophic aquatic organisms (in terms of median effect concentration). The DIS-nAg had the highest and Bare-nAg the lowest concentration of free Ag(+) , implying that free Ag(+) cannot be neglected in explaining the toxicity of nAg colloids. Furthermore, the contribution of free Ag(+) to the toxicity of nAg colloids for R. subcapitata was the highest but for D. rerio the lowest, implying that the organisms tested have different accumulation abilities for Ag(+) or nAg particles.
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