Combined Toxicity Study Of Mixed Metal Oxide Nanoparticles Against Freshwater Green Algae

With the mass production and wide application of engineering nanoparticles(ENPs),various ENPs are inevitably released into the environment,which has attracted the attention of scholars on the joint toxicological effects of multiple ENPs mixtures.In this dissertation,the joint toxicity of titanium dioxide nanospherical particles(TiO₂ NPs)and titanium dioxide nanotubes(TiO₂ NTs)/znic oxide nanospherical particles(ZnO NPs)to two kinds of freshwater green algae(Scenedesmus obliquus and Chlorella pyrenoidosa)was investigated,and the modes of toxic action and mechanism of the joint toxicity were elucidated,as well as the joint toxicity was quantitatively predicted.The main research results are as follows:(1)The joint toxicity of TiO₂ NPs and NTs to S.obliquus was between the single toxicity of TiO₂ NTs and NPs,while the joint toxicity to C.pyrenoidosa was higher than their single toxicity.Moreover,the toxicity of the binary mixtures to C.pyrenoidosa was higher than that to S.obliquus.The modes of joint toxic action of TiO₂ NPs and NTs were additive to the algae.The mechanism of the toxicity caused by the binary mixtures of TiO₂ NPs and NTs may be associated with the dispersion stability of the nanoparticles in aquatic media and the reactive oxygen species(ROS)-induced oxidative stress effects.The joint toxicity to S.obliquus and C.pyrenoidosa can be effectively predicted by the concentration addition(CA)model and the independent action(IA)model,respectively.(2)The growth inhibition toxicity of ZnO NPs to S.obliquus and C.pyrenoidosa was significantly higher than that of TiO₂ NPs at different exposure times.The modes of joint toxic action of ZnO NPs and TiO₂ NPs to S.obliquus was additive when their mixture concentration was less than 1 mg/L,and was antagonistic when their mixture concentration was greater than1 mg/L.The modes of joint toxic action of the binary mixtures to C.pyrenoidosa at 24 h was synergistic,while the joint toxicity at 48 h and 72 h was antagonistic.The mechanism of the joint toxicity of ZnO NPs and TiO₂ NPs to freshwater green algae is related to the toxic contribution of TiO₂ NPs interfering with the dissolved part of ZnO NPs and to the algal cellular oxidative stress effect induced by the binary mixtures.The predictive ability of the joint toxicity of the binary ZnO NPs and TiO₂ NPs mixtures by the IA model at different exposure times was stronger than that by the CA model.