The Toxicity Of Nano Cerium Dioxide And Cadmium Sulfide Quantum Dots To Two Aquatic Organisms

Nano materials often exert particular characteristics which are different from the normal materials and this makes the nano materials widely used in daily life. However, the nano particles can be unavoidablely enter the ecosystem, especially the water environment system which may cause environment pollutions. In order to avoid such a situation, it is necessary to study the toxicity of the mostly wide used nano materials.Nano cerium dioxide and cadmium sulfide quantum dots were chosen in this study because of their wide range in application. The toxicity of these chemicals was tested with the common aquatic organisms-Scenedesmus obliqnus and Daphnia Magana. The main conslusions were summarized as following:Nanoparticulate CeO2concentrations of5and10mg/L caused a significant increase in growth, while50mg/L of nanoparticles started to inhibit the growth and high concentrations of100and200mg/L significantly inhibited the growth. As the concentration increased, the stimulative effect was reduced and the inhibition effect was enhanced. The influence on the chlorophyll and SOD contents was consistent with that of cell growth, while the influence on the MDA contents was opposite with that of SOD indicating that varying degrees of lipid peroxidation occurred in the cell membrane. Optical microscopy images and changes in the diameter of the S.obliquus cells illustrated that with the increase of the concentration of the Cerium (IV) oxide nanoparticles, there was a tendency of miniaturization of the cells.CdS QDs concentrations of0.2-1.0mg/L caused a significant inhibitive effect to the growth. The microscopy images demonstrated that when CdS QDs concentration is increased, the cells tend to turn pallor, indicating that it might inhibit the synthesis of chlorophylls whose content varied with cell density. The influences on the MDA and SOD contents were opposite which indicate varying degrees of membrane lipid peroxidation.In48h, compared to the control group, different concentrations of nano cerium dioxide (500,1000,2000mg/L) did not show any obvious inhibit effects to Daphnia magana which indicate the little toxicity of nano cerium dioxide to Daphnia magana in short period of time.The48h EC50of CdS QDs, CdCl2(cation control) and Na2S (anion control) to Daphnia Magana were0.23mg/L,0.40mg/L,1.00mg/L respectively. CdS QDs and CdCl2are highly toxic while the Na2S is toxic according to the acute toxic class method.