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Effekte von Titandioxidnanopartikeln auf den Nematoden Caenorhabditis elegans unter besonderer Berücksichtigung von UV-Strahlung
Citation Link: https://doi.org/10.15480/882.1129
Other Titles
Effects of titanium dioxide nanoparticles on the nematode Caenorhabditis elegans
Publikationstyp
Doctoral Thesis
Publikationsdatum
2013
Sprache
German
Author
Advisor
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2013-08-30
Engineered nanoparticles (ENPs) are increasingly used in a variety of industrial and consumer products and will inevitably enter the aquatic environment. Modelling environmental emissions of nanoscale titanium dioxide (nTiO2) resulted in predicted sediments accumulation rates up to 1.4 mg/kg*year. Potential effects of ENPs on human health and the environment are still poorly understood.
In comparison to their bulk scale counterparts, nanoparticles pose a higher risk to the environment for several reasons. First, their small size (< 100 nm) enables them to penetrate organisms and cells, where they can interfere with cellular processes. Also, due to their large surface area, nanoparticles have the potential to affect bioavailability and toxicity of co-existing contaminants like heavy metals or PAHs by acting as a carrier. For TiO2-particles, photocatalytic activity increases with increasing surface area, as this property depends strongly on the accessibility of the particles’ surface to the environment.
In order to assess the nanoscale specific effects and the potential impacts of varying environmental conditions, this study addresses the following questions:
1) Does particle size affect the toxicity of TiO2 particles?
2) How does sunlight impact the toxicity of photocatalytically active nanoparticles?
3) Does nTiO2 interact with phenanthren as a common co-contaminant in sediments?
4) How does nTiO2 impact phenanthren as co-contaminant exposed to sunlight?
The nematode Caenorhabditis elegans was used to determine the chronic toxicity of two different TiO2-materials: A 21 nm, nanoscale TiO2 (P25) and a 90 to 230 nm, bulkscale TiO2 (bTiO2: NM100). While agglomerating to a comparable secondary particle size of 300 to 1500 nm, only nTiO2 inhibited reproduction of C. elegans significantly with a LOEC of 10 mg/l and an EC50 > 100 mg/l, while no effects were observed for bTiO2. Results of Microscopy and ‘Energy Dispersive X-Ray-analysis’ indicate that both materials are taken up by the intestinal tract of C. elegans. Further examination of the agglomeration of TiO2-particles in the gut of C. elegans showed that both materials caused a dysfunction of the defecation process by inhibiting feeding efficiency.
Exposition to simulated solar radiation increased toxicity of nTiO2 to an EC50 of 53 mg/l, while no phototoxicity has been observed for bTiO2. Since nTiO2 produces more reactive oxygen species (ROS) than bTiO2, when measured as photo-degradation of methylene blue, the observed photoactivated effects of nTiO2 are likely due to oxidative stress. To test for a corresponding genetic response, expression of sod-3 was analyzed on mRNA and enzymatic level by using real-time PCR and a sod-3:gfp transgenic strain, respectively. Independent of the applied light conditions, nTiO2 did not impact sod-3 expression, suggesting that no ROS-production occurred within C. elegans cells. Therefore it was concluded that the nano-particles did not enter the cells and the observed phototoxicity was evoked by oxidative damage at the outer apical membrane of the intestinal cells, due to modes of action such as lipid and protein peroxidation.
nTiO2 was not found to have a significant effect on the toxicity or bioavailability of phenanthrene, when measured as gene expression of cyp-35C1. In combined exposure with radiation, nTiO2 appears to block the impact of UV-light on the photo-sensitive PAH and decreases photo-toxicity.
The results of this study highlight the importance of primary particle size and environmental parameters on the toxicity of TiO2 materials. Even though bTiO2 and nTiO2 agglomerate to the same secondary particle size in the test system, only nano-TiO2 is toxic to C. elegans. Missing evidence for cell internal effects of the photocatalytically active nTiO2 suggests that nanoparticles act extracellular by inducing oxidative damage of the epithelial membranes in the gut. Potential enhancement of nano-TiO2 toxicity by physico-chemical parameters stresses the necessity of further investigations into their ecotoxicological effects under different environmental conditions.
In comparison to their bulk scale counterparts, nanoparticles pose a higher risk to the environment for several reasons. First, their small size (< 100 nm) enables them to penetrate organisms and cells, where they can interfere with cellular processes. Also, due to their large surface area, nanoparticles have the potential to affect bioavailability and toxicity of co-existing contaminants like heavy metals or PAHs by acting as a carrier. For TiO2-particles, photocatalytic activity increases with increasing surface area, as this property depends strongly on the accessibility of the particles’ surface to the environment.
In order to assess the nanoscale specific effects and the potential impacts of varying environmental conditions, this study addresses the following questions:
1) Does particle size affect the toxicity of TiO2 particles?
2) How does sunlight impact the toxicity of photocatalytically active nanoparticles?
3) Does nTiO2 interact with phenanthren as a common co-contaminant in sediments?
4) How does nTiO2 impact phenanthren as co-contaminant exposed to sunlight?
The nematode Caenorhabditis elegans was used to determine the chronic toxicity of two different TiO2-materials: A 21 nm, nanoscale TiO2 (P25) and a 90 to 230 nm, bulkscale TiO2 (bTiO2: NM100). While agglomerating to a comparable secondary particle size of 300 to 1500 nm, only nTiO2 inhibited reproduction of C. elegans significantly with a LOEC of 10 mg/l and an EC50 > 100 mg/l, while no effects were observed for bTiO2. Results of Microscopy and ‘Energy Dispersive X-Ray-analysis’ indicate that both materials are taken up by the intestinal tract of C. elegans. Further examination of the agglomeration of TiO2-particles in the gut of C. elegans showed that both materials caused a dysfunction of the defecation process by inhibiting feeding efficiency.
Exposition to simulated solar radiation increased toxicity of nTiO2 to an EC50 of 53 mg/l, while no phototoxicity has been observed for bTiO2. Since nTiO2 produces more reactive oxygen species (ROS) than bTiO2, when measured as photo-degradation of methylene blue, the observed photoactivated effects of nTiO2 are likely due to oxidative stress. To test for a corresponding genetic response, expression of sod-3 was analyzed on mRNA and enzymatic level by using real-time PCR and a sod-3:gfp transgenic strain, respectively. Independent of the applied light conditions, nTiO2 did not impact sod-3 expression, suggesting that no ROS-production occurred within C. elegans cells. Therefore it was concluded that the nano-particles did not enter the cells and the observed phototoxicity was evoked by oxidative damage at the outer apical membrane of the intestinal cells, due to modes of action such as lipid and protein peroxidation.
nTiO2 was not found to have a significant effect on the toxicity or bioavailability of phenanthrene, when measured as gene expression of cyp-35C1. In combined exposure with radiation, nTiO2 appears to block the impact of UV-light on the photo-sensitive PAH and decreases photo-toxicity.
The results of this study highlight the importance of primary particle size and environmental parameters on the toxicity of TiO2 materials. Even though bTiO2 and nTiO2 agglomerate to the same secondary particle size in the test system, only nano-TiO2 is toxic to C. elegans. Missing evidence for cell internal effects of the photocatalytically active nTiO2 suggests that nanoparticles act extracellular by inducing oxidative damage of the epithelial membranes in the gut. Potential enhancement of nano-TiO2 toxicity by physico-chemical parameters stresses the necessity of further investigations into their ecotoxicological effects under different environmental conditions.
Schlagworte
Titandioxidnanopartikel
Caenorhabditis elegans
Phototoxizität
Co-Kontamination
Titanium dioxid nanoparticles
caenorhabditis elegans
phototoxicity
co-contamination
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