Fate and biological effects of titanium dioxide nanoparticles in the aquatic environment
Year: 2017
Type: dissertation
Abstract: The increasing use of titanium dioxide nanoparticles (TiO2 NPs) and their consequent release into the environment, make it important to understand the behaviour, fate and potential adverse effects that TiO2 NPs may have upon organisms. After being introduced into the aquatic environment, TiO2 NPs will undergo transformation processes, which will affect their properties, including, chemical composition, size, surface charge and coating, and these may also have substantial implications on the fate and toxicity of the NPs. This highlights the importance of physiochemical characterization of the NPs in conjunction with a toxicological assessment. The transformation processes are dependent both on the physicochemical properties of the NPs and on the physicochemical properties of the ambient environment. However, these properties have been seldom studied in complex natural waters. Therefore, the research done for this PhD dissertation aimed to investigate the behaviour of TiO2 NPs in natural waters, and to associate the NPs colloidal stability with various water properties. The toxicity tests of TiO2 NPs were performed on two aquatic organisms each of which represent different trophic levels: Lemna minor (L. minor) and Daphnia magna (D. magna) according to ISO 20079 and OECD test 202, respectively. The specific aim was to assess the possible toxic effects of TiO2 NPs with maintained colloidal stability in an optimized ecotoxicological test medium. Given the potential of TiO2 NPs to carry other pollutants, the mixture toxicity of TiO2 NPs with cadmium (Cd) and lead (Pb) on D. magna were also investigated. TiO2 NPs exhibited different colloidal stability, which depend on the physicochemical properties of the natural waters. Total phosphorus, total nitrogen, alkalinity, pH, electrical conductivity and turbidity were shown by experimental and linear regression analysis to be the main water properties that negatively influence NPs stability among 14 water properties that were compared. All six of these physicochemical properties of water had positive correlations on the deposition of TiO2 NPs in lake waters. TiO2 NPs showed low colloidal stability in standard ecotoxicological test media, but modification of the current standard medium enabled the steady exposure of L. minor and D. magna. TiO2 NPs showed no adverse effect on the growth rate or chlorophyll a content of L. minor, or immobility of D. magna. However, TiO2 NPs were found to become attached to the cell wall of L. minor and to the body surface of D. magna, both of which may cause the potential transfer of TiO2 NPs into the aquatic food chains. Such a transfer would lead to an exposure of other organisms and contribute to the environmental fate of NPs. The presence of TiO2 NPs also influenced the bioaccumulation and toxicity of Cd and Pb in D. magna. TiO2 NPs increased the bioaccumulation and toxicity of Cd in daphnia, whereas it reduced the toxicity of Pb regardless of the 3- to 4-fold increase of bioaccumulation found. Surface attached TiO2 NPs combined with adsorbed heavy metals, caused adverse effects on D. magna swimming and moulting behaviour, which was assumed to lead to chronic toxicity. The research findings presented in this thesis elucidate the water physicochemical properties that control the aggregation and deposition of TiO2 NPs in complex natural waters, and offer an insight into their biological effects and accumulation potential upon aquatic organisms.
Source: Työväentutkimus Vuosikirja
Author: Ling Li
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2612089040