The Toxic Mechanism Of CuO Nanoparticles To Microcystis Aeruginosa As Affected By Dissolved Organic Matter

As the rapid development and versatile applications of nanotechnology, lots of products based on the nanotechnology have been widely applicated recently in various fields. However, engineered nanoparticles (ENPs) are difficult to escape from coming into environment during their production, application and treatment process. Finally, ENPs would enter aquatic system through pathways such as sewage and industrial wastewater discharge, rainfall and surface runoff. Due to the novel physicochemical properties of tiny size, large specific surface area and abundant reactive sites on the surface, ENPs may pose a potential hazard to organisms to the whole ecosystem if they are exposed to environment. The aquatic behavior of ENPs is very complicated and the aquatic chemical conditions like dissolved organic matter (DOM), pH and ionic strength would influence the fate, behavior and bioavailability of ENPs. In this study, the typical alga Microcystis aeruginosa was chosen as test organism. The aim was to investigate the impact of ENPs to alga and the toxic mechanism affected by DOM. The results were present as follows:The toxic effect of CuO ENPs to M. aeruginosa in the presence and absence of DOM was compared. Result suggested the inhibition effect of CuO ENPs to M. aeruginosa in pond water medium (TOC, 26 mg C L^-1) was remarkably higher than that in distilled water medium. To simulate the DOM condition of natural water, 20 mg L^-1 Suwannee river fulvic acid (SRFA) was added into distilled water. The 72 h median effective concentration (EC50) value of CuO ENPs in the SRFA environment was significantly reduced. And the CuO ENPs-SRFA was more toxic than CuO ENPs alone treatment. Aggravating CuO ENPs in the presence of SRFA was attributed to: (1) promoting more Cu²⁺ dissolved from CuO ENPs; (2) enhancing the suspension stability of CuO ENPs, reducing their aggregation, increasing the opportunity that ENPs interacted with algal cell and internalized into cells.The aggregation with high electronic density in the algal cell was analysed by high resolution transmission electron microscope (HRTEM), suggesting that CuO ENPs smaller than 5 nm could permeate the cell wall through the pore on it and reach the plasmamembrane. The main transmembrane pathway of CuO ENPs was endocytosis, and Cu₂O ENPs were in major. The intracellular reductive environment and reductase may lead to Cu₂O ENPs formation. CuO ENPs after transmembrane would aggregate gradually at some location. Reactive oxygen species (ROS) generation and DNA damage were also monitored dynamically. Results indicated the accumulation of ROS caused DNA damage and plasmamembrane function failed. Consequently, the oxidative damage, which was caused by intracellular excess ROS resulted from internalization of ENPs, was an important mechanism of toxicity.