Toxicity Effect Of Titanium Dioxide Engineered Nanoparticles In Chlorella Pyrenoidosa Effected By Ocean Acidification

With the rapid development of nanotechnology, nanomaterials are widely used in various aspects. Engineered nanoparticles will transfer to ocean inevitable. Because of nanomaterials’ special size, it’s has many physical and chemical properties which will produce a potential threat to marine organism. The marine environment effect of nanometer particles gradually become a hot point of attention at home and abroad. At the same time, ocean acidification caused by human activities to release excess CO₂ has been the attention of people. Marine microalgae is the main primary producers in marine ecosystem and it is important to keep balance and stability of marine ecosystem. At present,we study NPs in natural pH seawater, but the toxicity mechanism of NPs to Marine microalgae under the condition of ocean acidification isn’t clear. So we choose Chlorella Pyrenoidosa as experimental organism, titanium dioxide engineered nanoparticles as experiment material, we study characterization and environmental behavior of TiO₂ NPs in natural seawater and acidulated seawater. Meanwhile,the impact on the growth of chlorella by acidification and NPs was researched through optical microscope. TiO₂ NPs interaction with algae was also researched through by TEM and SEM. The ROS, antioxidant enzymes system and the influence of lipid peroxidation were researched under acidulated seawater and NPs in order to explore toxic effects mechanism of marine micro algae under acidulated seawater and TiO₂ NPs.The main research results summarized as follows:（1） The dispersity of TiO₂ NPs at pH=7.47 is better than at pH=8.20 by transmission electron microscopy（TEM）. The diameter of nanoparticles reduced obviously in acidulated seawater through laser particle size distribution analyzer and ultraviolet spectrophotometer. It illustrates that acidification can inhibit aggregation of nanoparticles. The suspension of nanoparticles increased because of acidification, and then the whole of nanoparticles in seawater also increased.（2） In this paper, the Chlorella pyrenoidosa growth-inhibition test showed that the TiO₂ NPs can inhibit the growth of algal cells with obvious dose-effect relationship. The concentration of TiO₂ NPs below 5 mg/L will produce promoted effect on the growth of chlorella at lower pH. However, the concentration of TiO₂ NPs exceed 5 mg/L will produce inhibited effect on the growth of chlorella at lower pH.（3） The shape of algae cell were determined by scanning electron microscope（SEM）, we found the cell wall collapsed, a large number of large particles of TiO₂ NPs were found at cell wall. The same situation have been found in acidic conditions. However, the TiO₂ NPs is small. It is also illustrated that the dispersity of TiO₂ NPs in acidulated seawater is better than at natural seawater.（4） We found that the cell wall collapsed and TiO₂ NPs adsorbed on cell wall under natural seawater by transmission electron microscopy（TEM）. However, the algae cell put up kinds of phenomenon such as plasmolysis, cell wall collapsed, chloroplast photosynthetic lamellar structure is not clear, TiO₂ NPs were found in vacuole. Nanoparticles can be through the cell swallowing function into the cells. The results show that the acidification of the seawater will enhance toxic effect of TiO₂ NPs to chlorella.（5） The Ti content in cells which were acidulated significantly（p < 0.05） higher than in natural seawater using ICP-MS analysis test, there was no significant difference between two acidic groups. It is suggested that ocean acidification promoted the TiO₂ NPs into algal cells and then increasing the TiO₂ NPs biological effectiveness.（6） Algal cells in the ROS, antioxidant enzymes activity and lipid peroxidation did not have a significant impact under acidizing treatment.TiO₂ NPs can stimulate algal cells to produce excess ROS under the condition of acidification and inhibit algal cell antioxidant enzyme activity of antioxidant enzyme system. At last, accumulation of ROS can cause cell membrane damage and cause lipid peroxidation then a large number of MDA will be found.