The Toxicity Effect Of Two Nanomaterials On Two Ciliates

With the increasing development of nanotechnology,various nanomaterial products are also appearing in people’s daily lives.However,some heavy metal nanomaterials have attracted widespread attention due to their biological toxicity.In this paper,two species of ciliates,marine Diophrys oligothrix and freshwater Stylonychia lemnaeits are used as experimental materials,by the used of microscopic observation,scanning electron microscopy（SEM）,EDS energy spectrum analysis,transmission electron microscopy（TEM）and electron microscopic enzyme cytochemistry technology to explore the toxicities of nano-silver and nano-zinc oxide on the two kinds of protozoa.The internal structures of the two ciliate cells treated with different nanomaterials were compared,and the effects of nanomaterials on cellular functions and possible mechanisms were elaborated.In order to provide a biological basis for the evaluation of the biological risk of nanomaterials,and to provide reference for the mechanism of nanomaterials acting on cells at the cellular level.The specific results are as follows.1.Effects of nano-silver and nano-zinc oxide on the acute toxicity and cell microstructure of Diophrys oligothrix and Stylonychia lemnaeits:Nano-silver particles of 30 nm treated Diophrys oligothrix and Stylonychia lemnaeits,the semi lethal concentration was 15.533 mg·L^-1 and 10.507 mg·L^-1,respectively;the lowest effect concentration was 12.280 mg·L^-1 and 3.565 mg·L^-1,respectively.Nano-zinc oxide particles treated Diophrys oligothrix and Stylonychia lemnaeits,the semi lethal concentration were 25.670 mg·L^-1 and 18.621 mg·L^-1,respectively;the lowest effect concentration were 6.481 mg·L^-1 and 3.773 mg·L^-1,respectively.The results of the analysis can be obtained as follows:（1）nano-silver particles are more toxic to ciliates than nano-zinc oxide particles;（2）the sensitivity of the Stylonychia lemnaeits to the nanomaterials is stronger than that of the Diophrys oligothrix.At the same time,the lowest effective concentrations measured by the two nanomaterials treated by ciliates were higher than the highest concentrations of the two nanomaterials in the environment by 0.1 mg·L^-1,indicating that the concentrations of the two nanomaterials in the environment will not cause these two Ciliate cell death.Both ciliates under the stress of the two nanomaterials undergo a morphologically tending to a spherical change and the vacuole gradually increased,finally breaking the process of death.However,it also has certain differences.The cilia of the marine Diophrys oligothrix was significantly constricted,the cell volume became larger,and the cytoplasm is gradually sparse;For freshwater species of the Stylonychia lemnaeits,its spherical surface was surrounded by cilia,and the volume gradually shrank,and the cytoplasm became denser.It is speculated that the changes in behavior,morphology and related structures of two ciliates after stimulation by nanomaterials are not only related to the osmotic pressure of their living environment,but also to the structure of ciliate cells themselves.2.Effect of nano-silver and nano-Zn O particles on the submicroscopic structure of the Diophrys oligothrix and Stylonychia lemnaeitsObserved by light microscopy,after treatment with nano-silver and nano-zinc oxide particles,both ciliates produced vacuoles in vivo.Further observation by transmission electron microscopy revealed that the large vacuoles in the cells were gradually fused by small vacuoles.The phenomenon of vacuolar membrane structure blurring during the fusion process can be used as a signal for judging whether the vacuoles are fused or not.The ultrastructural observation of the cells of Diophrys oligothrix and Stylonychia lemnaeits also showed that the treatment of both nanomaterials resulted in damage to the cell structure,but the intracellular changes in the two nanomaterials were different.Mitochondrial swelling and sacral ligament rupture were observed in both cells,but mitochondrial swelling and sacral breaks degree were higher in the nano-zinc oxide particle-treated group than in the nano-silver particle-treated group.However,the labeling of mitochondrial succinate dehydrogenase in the control and experimental groups of Stylonychia lemnaeits shows that the nanomaterial can reduce the activity of succinate dehydrogenase.Nanomaterials caused damage to organelles and induced autophagic vacuoles in cells.In the nano-zinc oxide-treated group,autophagic vacuoles were more in the cells than in the nanosilver-treated group,and autophagy degree was also higher.The above results indicate that although both nanomaterials all have toxic effects on the cells of Diophrys oligothrix and Stylonychia lemnaeits,the two nanomaterials may have different methods of action.After the nanomaterials enter cells,the mitochondrial function was gradually weakened along with the changes of mitochondrial structure（such as sacral break）and the activity of related enzymes（such as succinate dehydrogenase）,and the level of cellular energy metabolism was also gradually reduced.