Abstract:The ecotoxicity of nanoscale TiO2, ZnO and Al2O3 water suspensions was examined using a method developed based on the standard OECD Guidelines for the Testing of Chemicals (i.e. OECD 201,202). The green algae (Scenedesmus obliquus) and the water-flea (Daphnia magna) were used as the testing organisms. The results showed that different nanoparticles exhibited different toxicities to the testing organisms. The 96 h EC50 of nZnO, nTiO2 and nAl2O3 on the growth of Scenedesmus obliquus were 1.049, 15.262 mg?L-1 and >1000 mg?L-1, respectively. The 48 h immobilization EC50 of nZnO, nTiO2 and nAl2O3 on Daphnia magna were 0.622, 35.306 mg?L-1 and 114.357 mg?L-1, respectively. Based on the results, their toxicity rank as nZnO > nTiO2 > nAl2O3. The toxicity results indicate that such nanoparticles might pose potential environmental impact. Further research on the ecotoxicological mechanisms of such nanoparticles is warranted in order to minimize the adverse ecological effects and human health risk of nanotechnology development.