Toxicological Effects Of Three Oxidized Nanomaterials On Tetrahymena Thermophila

Nanomaterials are widely used in various fields such as industry and medical care.With the use of nanomaterials,it is inevitable that nanomaterials will enter directly or indirectly into the ecosystem.Nanomaterials have larger specific surface area and surface activity than traditional materials,which may lead to increased bioavailability and toxicity.Tetrahymena thermophila is an aquatic single-cell eukaryote.Because of its ultra-high sensitivity for environmental change,it is as a model organism in toxicological risk research to aquatic environment.In the study,we investigated the effects of three common oxidized nanomaterials,nano-TiO2,nano-SiO2,and nano-ZnO for T.thermophila.1.The effect concentration of n-TiO₂,n-SiO₂ and n-ZnO nanomaterials on T.thermophila is 10 ?g/mL,100 ?g/mL and 50 ?g/mL respectively.When the dose exceeds the effect concentration,it will exert biotic stress on cell viability,proliferation,superoxide dismutase activity and catalase activity in a dose-effect relationship.The semi-inhibitory concentration of T.thermophila on n-SiO₂ at 24 h is 1.74 times that of n-TiO₂,which is 5.83 times that of n-ZnO.At the same dose,the toxicity of nanomaterials was n-ZnO>n-TiO₂>n-SiO₂ after 24 h treatment.Among them,n-ZnO exhibits the dual toxicity of ionic toxicity of Zn2+ dissolution and bulk toxicity of n-ZnO particles in a water environment.2.The combined effects of n-TiO₂,n-SiO₂ and n-ZnO nanomaterials inhibit the proliferation of T.thermophila.The combination of n-TiO₂ and n-SiO₂,n-TiO₂ and n-SiO₂ has a dose-and time-dependent relationship.The inhibition rate of T.thermophila is positively correlated with the total dose of nanomaterials and the increase of exposure time.At 24 h,n-TiO₂ and n-ZnO reduced the inhibition rate of 2.04%-10.81% of T.thermophila at 10 ?g/mL,which had antagonistic effect on the toxicity of n-ZnO.As the concentration of n-TiO₂ increased,the toxicity of n-ZnO was superimposed at concentrations of 50 and 100 ?g/mL,with dose-dependent relationship.n-TiO₂ and n-ZnO showed antagonism at 36 h,and n-TiO₂ reduced n-ZnO toxicity.n-TiO₂ can reduce the Zn2+ concentration in water by 14.3%¹9.4% by adsorbing Zn2+ produced by n-ZnO dissolution,thus reducing the toxicity to T.thermophila.At the same time,the combined action of nanomaterials also enhances the oxidative stress of cells,and the activity of superoxide dismutase and catalase increases.3.The expression level of ATP2 was down-regulated under 100 ?g/mL concentration of n-TiO₂,n-SiO₂ and n-ZnO nanomaterials stress in T.thermophila.The expression level was 0.39 times,0.8 times,and 0.26 times after 24 h stress,respectively.The expression level was 0.55 times?0.57 times,and 0.16 times after 36 h stress,respectively.However,expression levels of stress response-related genes HSP70,SOD2 and CAT were up-regulated.The expression levels of the three genes upregulated 1.31 times,1.88 times,and 2.67 times under n-TiO₂ stress,respectively.The expression levels of the three genes upregulated 1.41 times,1.88 times,and 2.67 times under n-SiO₂ stress.Taken together,misuse of nanomaterials n-TiO₂,n-SiO₂ and n-ZnO decreased cellelar viability and activated cellular stress response.This study provided important data for evalutaion of the using risk of nanomaterials and for exploring T.thermophila as a toxic biosensor.