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Short-term toxicity of photocatalytic titanium dioxide tobacteria under ambient conditions

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  1. Tez No: 569990
  2. Yazar: AYÇA ERDEM
  3. Danışmanlar: Prof. CHIN-PAO HUANG
  4. Tez Türü: Doktora
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2008
  8. Dil: İngilizce
  9. Üniversite: University of Delaware
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 204

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Özet (Çeviri)

Nanotechnology deals with materials and systems whose structures and components exhibit novel and significantly improved physical, chemical and biological properties, phenomena and processes due to their nanoscale size, which is in the range of 0.1 to 100 nm. Nanotechnology is actively being pursued in many technical fields including aerospace, information science, engineering and medicine, and it represents one of the fastest growing areas of research and development. The nanoparticles have been used in many industrial applications and water/wastewater treatment systems for the last decades. The excessive usage of the nanoparticles has brought a new issue that how the environment has been affected. The earliest toxicological studies showed that the UV light has an adverse effect on the bacteria. As far as the toxicity of fine particles are concerned, TiO2 is the most studied. This is because TiO2 has been used as antibacterial agent. However, only the commercial TiO2 P25, which has an article size of 35 nm, is evaluated. There is no study on the effect of particle size on the toxicity effect of TiO2. The early findings of photocatalytic inactivation of bacteria have prompted the attention of many researchers, however, the mechanism of semiconductor catalyzed degradation of bacteria in aqueous media, and properties of the nanoparticles and mechanism controlling nanotoxicity are still unclear. There is a lack of studies on the eco-toxicity of manufactured nanoparticles. What are the fundamental effects of nanoparticles on the growth and survival of bacteria and other microorganisms? What are the synergistic or anti-synergistic effects of nanoparticles? In order to address above questions, the toxicity of nanoparticles to bacteria was studied. The toxicity of different sizes and concentrations of TiO2 toward bacteria exemplified by E. coli and B. subtilis under dark and different light conditions were discussed. Six endpoints were used to determine the effects of TiO2 on bacteria: (1) The numbers of viable cells in cell suspensions were determined by plating serially diluted suspensions onto LB-agar plates. (2) Confocal, and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging were facilitated to give a better understanding of the morphological changes happened in the cell structure. (3) Lipid peroxidation of the bacterial cell membrane was measured by measuring the malondialdehyde (MDA) production. (4) Cellular respiration was determined by the reduction of 2,3,5-triphenyltetrazolium chloride (TTC) to its reduced product, 2,3,5- triphenyltetrazolium formazan (TTF). (5) The enzymatic response was measured in terms of the expression of Glutathione S'Transferase (GST). (6) The in vitro response and the quantification of DNA damage was done by ethanol precipitation method explained in standard protocols. The results showed that nanoparticles have adverse effect on the growth of bacteria under both dark and light conditions. The observed bacteria inactivation in dark indicates that undetermined mechanisms additional to photocatalytic reactions were responsible for toxicity. The photocatalytic bacteria inactivation rate was dependent on several parameters such as: physiological state and initial concentration of bacteria, nanoparticle concentration and size, and the intensity of the light source. The die-off of bacteria takes in two stages; fast die-off and slow die-off. The higher particle concentrations and smaller primary particle sizes (16 to 20 nm) appear to be more damaging to the bacteria in absence of light. The bacterial die-off increases as a function of light intensity, whatever the photocatalytic conditions (different TiO2 concentrations and sizes) were applied. TiO2 nanoparticles have been shown to exhibit strong cytotoxicity when exposed to UV and solar irradiation. Membrane (lipid peroxidation and respiration) and enzymatic responses, and oxidative DNA damage were detected. In presence of light, higher levels of lipid peroxidation and DNA damage were detected as a function of time and nanoparticle treatment. The lipid peroxidation and the simultaneous losses of both membrane-dependent respiratory activity showed that survival of the bacteria depends on the presence of both light and TiO2. Additionally, the microscopy images showed that when bacteria were treated with TiO2 nanoparticles, the morphology of the cell structure changed. The results from this study highlights the need for caution during the use and disposal of such manufactured nanomaterials to prevent unintended environmental impacts, as well as the importance of further research on the mechanisms and factors that increase toxicity to enhance risk management.

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