Acute toxicity of Ag and CuO nanoparticle suspensions against Daphnia magna: The importance of their dissolved fraction varying with preparation methods

► Toxicity of Ag and CuO nanoparticles is highly dependent upon preparation methods. ► Preparation methods cause differences in dissolved concentrations of nanoparticles. ► Dissolved fractions of Ag and CuO nanoparticles govern their toxicity.