The Preliminary Study Of Nano-silicon Dioxide And Normal Sized Silicon Dioxide On Aquatic Ecotoxicology

Nanotechnology is in a stage of rapid development, which has been widely used in many fields, such as industrial manufacture, medical equipment, bio-pharmaceuticals, cosmetics and the integrated control of environmental pollution, and brought a huge influence on our society. But as a result of negligence during the process of production and usage of nanomaterials, they may get into atmosphere, water and soil and cause great potential safety hazard on the environment and human health. Nano-silicon dioxide (Nano-SiO2, SiO2 NPs) has already shown great application in the field of fungicide, paint additives, electronic materials, lubricants, and biological medicine. With the large number of uses, Nano-SiO2 could be discharged into the environment directly or indirectly. Some studies have shown that Nano-SiO2 can cause the toxicity on lung, cardiovascular system, immune system and other part of body. However, the studies of the ecotoxicology of Nano-SiO2 have limited. This study uses two kinds of model species, Daphnia magna (D. magna) and Zebrafish (D. rerio), to evaluate the ecological toxicity of Nano-SiO2, especially the aquatic ecotoxicology, and provide experimental support for the safe application of Nano-SiO2.The first part of the study was about the acute toxicity through the morphological observe and the immobilization (24h-EC50) and mortality (24h-LCso) of D. magna after nano-silicon dioxide and normal sized silicon dioxide (Nor-SiO2) 24 hour exposure. The results showed that in the SiO2 NPs exposure groups, the nanoparticles were distributed in the most organs in the body of D. magna, especially the gut tract and gill. The rupture of guts and the broken bodies could be observed in 400 mg/L Nano-SiO2 group. The observation of exposure duration showed a dose-response feature, and the immobilization and death increased as the increasing of the exposure concentrations. According to the results, the program calculated that the24-h EC50 and LC50 were 148.871 mg/L and 660.943 mg/L, respectively. In Nor-SiO2 group, no particle got into the bodies and only some of the surfaces of D. magna were covered by the Nor-SiO2, in addition to the highest dose group. There was no obvious increase trend in both the immobilization and death, and showed no dose-response feature.The second part of the study was under the exposure of Nano-SiO2 and Nor-SiO2 on Zebrafish eggs respectively. The development of the zebrafish embryos and larvae was observed at specified time points (t=12,24,36,48,60,72,84 and 96 hpf), then recorded the survival embryo/larvae, embryo hatching rate, developmental defects and LC50 of 84 hpf. At the conclusion of the oxidative damage, malondialdehyde (MDA) was determined to assess oxidative stress and damage at 108 hpf. The results showed that multiple developmental defects could be observed with microscope in the SiO2 NPs exposure groups, especially hatch in advance. With the increasing concentrations of SiO2 NPs, the cumulative hatching rate of embryos were notable lower than that of control group (p<0.05) at the concentrations of 150-300 mg/L, while the cumulative mortality rate was significantly increased with SiO2 NPs exposed concentration in addition to 50 mg/L and 100 mg/L at 84 hpf. According to the results, the program calculated that 84 h LC50 of these SiO2 NPs was 240 mg/L. In Nor-SiO2 group, no developmental defects were found during the exposures time. Both the cumulative hatching rate and mortality rate showed no significant increasing.The study shows that both SiO2 NPs and Nor-SiO2 can be taken in D. magna but only nano-sized materials will cause the acute toxicity. The reason why zebrafish do not move even die is about the damage caused by oxidative stress. During the development of zebrafish embryos, SiO2 NPs not only can lead to hatch in advance, but also have toxicity on zebrafish larvae, and cause high mortality rate and serious oxidative damage. This has already showed developmental toxicity on the zebrafish embryos. But Nor-SiO2 has not showed the toxicity on the development of zebrafish.