Aquatic Transformations And Ecotoxicological Effects Of Four Types Of Manufactured Nanoparticles

With the increasing use of various nanostructured materials, manufacuted nanoparticles (MNPs) are inevitablily discharged into the environment. Thereby MNPs could become potential pollutants, and pose a potential health risk to human and ecological species. Once released into the environment, MNPs can undergo many transport and transformation processes affecting their ecotoxicity. How to assess and predict aquantic behavior (particular for the interaction of MNPs with dissolved organic matter (DOM) and their effects on agglomeration of MNPs colloids) and toxicological effects to aquatic organisms is the frontier research in the field of nanoecotoxicology. In this thesis, interactions of fullerene (C6o) with dissolved organic matters (DOM) were investigated by the means of molecular modelling, and the mechanism by which DOM influence dissolution and agglomeration behavior of C6o was elucidated. In addition, toxicological effects of nano-titanium dioxide (nTiO2), nano-cerium dioxide (nCeO2) and nano-silver (nAg) colloids on aquatic organisms were observed and mechanisms of action for their aquatic toxicity were illustrated. Main contents and results are as follows:(1) The interaction of fullerene C60with DOM analogues is computationally simulated by molecular mechanics and density functional theory. The calculated interaction energies displayed that the DOM could stablize C60, and the stability between C60and the soil DOM analogues is greater than that between C60and the DOM analogues from fresh water or coal. The computed electrostatic potential indicates that DOM analogues are electron acceptors in the C60-DOM complexes. The presence of DOM increases the apparent water solubility of C60-It is also observed that the C60apparent water solubility decreases with the increase of the energy gaps of frontier molecular orbitals (ELUMO-EHOMO) for each C60-DOM complex.(2) The effects of nTiO2and nCeO2colloids on cell membrane permeability and cell membrane potential of a green alga (Scenedesmus obliquus) were investigated by the fluorescent probe technique. The stability of nanoparticle colloids was evaluated by the DLVO theory. The results show that the magnitude of the peak value in the potential energy profiles of the nTiO2colloids is4.2times that of the nCeO2colloids, indicating that nTiO2colloids displayed more stable than the nCeO2colloids. The nTiO2colloids inhibited the cell membrane permeability of Scenedesmus obliquus, conversely, the nCeO2colloids induced an enhancement of the cell membrane permeability of Scenedesmus obliquus. The two nanoparticle colloids induced an increase of the cell membrane potential of Scenedesmus ohliquus, and the nTiO2colloids showed stronger effects than the nCcO2colloids. These findings suggest that disturbing the functions of the cell membrane is a possible mechanism of toxicity of MNPs to algae. Compared with the nCeO2colloids, the nTiO2colloids with high stability displayed high toxicity to the cell membrane system in Scenedesmus obliquus, suggesting that the colloid stability of MNPs is an important factor governing their ecotoxcitity.(3) The relative contribution of ionic silver (Ag+) or particles in nano-silver (nAg) colloids to the toxicity to three aquatic organisms of different trophic levels, i.e. an alga species (Raphidocelis subcapitata), a cladoceran species (Chydorus sphaericus) and a freshwater fish larva (Dainio rerio), was quantitatively evaluated by a response addition model. A bare and a polyvinylpyrrolidone (PVP)-coated nAg, as well as a monodispersed nAg with a dispersant (DIS-nAg) were examined. The toxicity of the nAg in the form of colloids decreases in the order DIS-nAg> PVP-nAg> Bare-nAg for all the three trophic aquatic organisms (in terms of median effect concentration). The DIS-nAg had the highest free Ag+concentration. and the Bare-nAg the lowest concentration of free Ag+, implying that the free Ag+cannot be neglected in explaining the toxicity of the nAg colloids. Furthermore, it was found that the contribution of free Ag+to the toxicity of nAg colloids for Raphidocelis subcapitata is the highest, but for Danio rerio the lowest, implying that the organisms tested have different accumulation ability for Ag+or nAg particles.(4) The effects of DOM on the ecotoxicity of nAg colloids were investigated. A commercial DOM model compound (HS) and PVP-coated nAg with primary size of20nm were selected as test materials. Raphidocelis subcapitata, Chydorus sphaericus, and Danio rerio, representing different trophic organisms, were exposed to the nAg colloids in the presence and absence of HS. The results show that the presence of HS alleviates the aquatic toxicity of the nAg colloids to all the organisms in a concentration dependent manner. A particle size distribution shifts to lower values of the nAg colloidal particles due to the presence of HS, implying that the decrease in toxicity of the nAg colloids is not related to the variation of agglomerated size. Surface charge of nAg agglomerates only displayed more negative in the presence of HS with high concentration, suggesting that the surface charge is not a decisive factor for the decrease in the toxicity of the nAg colloids. The presence of HS inhibited Ag’release from the nAg particles, and the inhibition degree depended on the HS concentrations. In addition, a concentration-response relationship was observed clearly for the toxicity effects expressed as free Ag+in the colloids. This finding indicates that the HS controlling Ag’release is a crucial mechanism, which contributes to the detoxification of nAg released to the environment.