Toxicity And Its Mechanisms Of MgO Nanoparticles To Scenedesmus Obliquus

With the rapid development of nanotechnology,nanoparticles?NPs?have extensive and potential influence on the ecological environment by entering human body via the food chain because of its so many unique physical and chemical properties as a sort of important emerging contaminants.As a new type of nanomaterials,the application fields of MgO nanoparticles?nano-MgO?is becoming more and more widespread,which increase the possibility of nano-MgO get into the aquatic,terrestrial and atmospheric environment,the biological safety problems of nanomaterials including nano-MgO have attracted high attention from the whole world.To reveal the toxicity effects and the toxic mechanism of nano-MgO on microalgae,the response of growth,chlorophyll concentration,the total amount of protein and polysaccharide,superoxide dismutase?SOD?and peroxidase?POD?activities of Scenedesmus obliquus?S.obliquus?exposed to different concentrations of nano-MgO were analyzed.The results showed that nano-MgO(concentration>0.8 mg·L^-1)inhibited the growth of S.obliquus and was positively correlated with the concentration of nano-MgO.High concentration of nano-MgO contributed to oxidative stress on algae cell and lastly leading to cell deformation so as to inhibit the growth of algae mainly by releasing a large number of ROS?Reactive Oxygen Species?;In addition,nano-MgO tended to aggregate and adhere to the surface of the algal cell.The aggregates of nano-MgO entrapped the flagella of S.obliquus,resulting in limitation of cell mobility and reduction in absorption of solar energy and nutrition by algal cells.The results were showed as follows:1.The scanning electron micrograph?SEM?showing that nano-MgO tend to aggregate and the attachment of the aggregated NPs onto the cell wall of S.obliquus after the interaction.The reunion of nano-MgO easily wrapped up the algae flagella and contributes to the union of algae cells,which further the case of adsorption of the aggregated NPs onto the surface.Decreased light availability?shading effect?owing to surface adsorption of the particles on the algal cell wall was one of the factors behind observed growth inhibitory effects.In this paper,the transmission electron micrograph?TEM?confirming no nano-MgO can entering into the interior of algae cell due to the block of algae cell wall.2.Nano-MgO(concentration>0.8 mg·L^-1)inhibited the growth of algae and the synthesis of chlorophyll in S.obliquus.The inhibitory effect was positively correlated with the addition of nano-MgO concentration;High concentrations of nano-MgO contributed to significantly inhibition of algae growth.The scanning electron micrograph?SEM?revealed that the deformation of algae cells significantly which indicated that nano-MgO has toxic effect on S.Obliquus obviously.3.Methylene blue?MB?test showed that reactive oxygen species?ROS?increased by the addition of nano-MgO in the cultivation system,which lead to the increasing of POD activity.But under the exposure of high concentration of nano-MgO,the POD activity induced by different concentrations of nano-MgO had no significant difference.SOD activity increased first and then decreased with the addition of nano-MgO,which indicated the oxidative damage on algae cell induced by nano-MgO.4.In this paper,it was observed that nano-MgO in the culture system can release Mg²⁺,which was positively related with the concentration of nano-MgO.100 mg·L^-1 nano-MgO dissociated 2.14 mg·L^-1 of Mg²⁺.The dissociation of Mg²⁺ had no effect on the growth of microalgae but decreased the synthesis of chlorophyll,and induced the increasing of POD activity.