Toxic Effects Of Single And Combined Systems Of Multi-walled Carbon Nanotubes And Nano-copper Oxide On Tetradesmus Obliquus

Multi-walled carbon nanotubes(MWCNTs)and nano-copper oxides(CuO NPs)are the most widely used nanoparticles,they inevitably enter the aquatic environment during the life cycle of production,transportation,and use,causing certain potential dangers to aquatic organisms.As the most common primary producer in aquatic ecosystems,algae are often used as model organisms for toxicity testing of aquatic organisms as they reproduce rapidly and are sensitive to poisons.Therefore,studying the toxic effects of nanomaterials on algae is of great environmental significance.The single toxicity of nanoparticles and the combined toxicity of nanoparticles and heavy metals or organic pollutants have been extensively studied,but the coexistence of different types of nanoparticles has rarely been studied.When two types of NP exist in the same environment,the presence of one type of NP may affect the characteristics and biological effects of the other type of NP.Therefore,this study selected MWCNTs and CuO NPs as the two experimental particles and studied the single toxic effect and the combined toxic effect of the two NPs,in order to explore the impact of the two NPs on aquatic organisms.This paper studied the single toxicity and combined toxicity of MWCNTs(0,0.01,0.1,1,10,100 mg/L)and CuO NPs(0,0.1,1,10,100,200 mg/L)on Tetradesmus obliquus.The results showed that both MWCNTs and CuO NPs had toxic effects on Scenedesmus obliquus,and the toxic effects of MWCNTs were significantly stronger than CuO NPs.The 96h-EC50 of MWCNTs and CuO NPs on algae were 33.8 mg/L and 169.2 mg/L,respectively.Oxidative stress and cell membrane damage were the main reasons for the toxicity of two NPs to algae.The integrity of the cell membrane was concentration dependent.The presence of CuO NPs in certain groups can reduce cell membrane damage caused by MWCNTs.This may be due to the formation of heteroaggregation between CuO NPs and MWCNTs,thereby reducing the contact between nanoparticles and cell membranes then reducing the physical damage caused by nanoparticles.The SEM and TEM results also showed heteroaggregation of MWCNTs-CuO NPs,the obvious internalization of nanoparticles,and the damage and incompleteness of the cell membrane caused by NPs.At the same time,in terms of oxidative stress,in some groups,the presence of CuO NPs significantly reduced the ROS levels induced by MWCNTs.For the highest concentration group,the ROS levels were much higher than the sum of the two NPs single treatment groups and this may be due to the stress caused by nanoparticles to algae at high concentrations.By observing the distribution of Cu in the system,it was found that MWCNTs can promote the internalization of CuO NP.This paper proved that MWCNTs and CuO NPs will influence and interact with each other when they coexist.This will provide a certain foundation for the subsequent study of the biological effects of multiple NPs coexisting on organisms in the environment and help to take effective measures to reduce the ecological risks caused by the composite pollution of multiple NPs to the aquatic environment.