Grantee Research Project Results
2009 Progress Report: Functionalized Metal Oxide Nanoparticles: Environmental Transformations and Ecotoxicity
EPA Grant Number: R833860Title: Functionalized Metal Oxide Nanoparticles: Environmental Transformations and Ecotoxicity
Investigators: Pedersen, Joel A. , Hamers, Robert J. , Peterson, Richard E. , Heideman, Warren
Current Investigators: Pedersen, Joel A. , Peterson, Richard E. , Hamers, Robert J. , Heideman, Warren
Institution: University of Wisconsin - Madison
EPA Project Officer: Aja, Hayley
Project Period: July 1, 2008 through June 30, 2011
Project Period Covered by this Report: July 1, 2008 through June 30,2009
Project Amount: $382,345
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Fate, Transport, Transformation, and Exposure of Engineered Nanomaterials: A Joint Research Solicitation - EPA, NSF, & DOE (2007) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
The main objectives of the project are to determine (1) the extent to which the surface chemistry of functionalized metal oxide nanoparticles is altered under simulated oxidative and reductive environmental conditions, and (2) the degree to which oxidative and reductive transformations alter metal oxide nanoparticle (photo-enhanced) toxicity.
Progress Summary:
Transition metal oxides comprise an important class of engineered nanoparticles with diverse applications and high current and projected production volumes. Existing and proposed applications include sunscreens, paints, UV shielding in plastics, biomedical imaging, drug delivery, photovoltaics, catalysis, data storage, and sensing. As production and use of engineered metal oxide nanoparticles rises, introduction into the environment becomes inevitable. Inadvertent release of engineered nanoscale metal oxides into the environment may occur at numerous points during a product’s life cycle including production, transport, manufacturing, consumer use, recycling, and disposal. In addition, some applications involve intentional introduction of metal oxide nanoparticles into the environment (e.g., remediation). Many applications of these nanoparticles require surface functionalization (i.e., surface coatings) to increase dispersibility, enhance biocompatibility, and modulate photocatalytic activity. Nanoparticle surface chemistry is expected to strongly influence uptake and toxicity, as well as interactions with environmental media. Evaluation of potential risks posed by engineered metal oxide nanoparticles in the environment therefore requires consideration of these materials with their surface coatings.
Microbially mediated redox processes have the potential to alter the surface chemistry of functionalized metal oxide nanoparticles, thereby impacting their toxicity and fate. Redox reactions are important in the degradation of many organic toxicants and in the speciation, dissolution and precipitation of inorganic contaminants. Transformation typically alters bioavailability or toxicity; in some cases, increased toxicity is observed. At present, fundamental information on changes in the surface chemistry of commercially important metal oxide nanoparticles under environmentally relevant oxidative and reductive conditions is lacking. Furthermore, the influence of surface coatings on the toxicity of metal oxide nanoparticles has not been thoroughly studied, and little information exists on the effects of environmentally induced changes in surface chemistry on toxicity.
Nanoparticle Synthesis and Characterization
During the first project year, our synthetic efforts have focused primarily on TiO2 nanoparticles. We adapted a published method to synthesize spherical anatase TiO2 nanoparticles with diameters of 6 ± 1 nm. The TiO2 nanoparticles were made suspendable in water by functionalizing with organic ligands via either carboxylate (citrate) or catechol (e.g., 3,4-dihydroxybenzaldehyde (DHBA), rutin) moieties. The aldehyde functionality of DHBA provides a ready means to further modify surface chemistry via Schiff base reaction between the aldehyde and primary amines. We have demonstrated this by coupling 1-kDa poly(ethylene glycol) amine to DHBA-functionalized TiO2 nanoparticles. These TiO2 nanoparticles have been thoroughly characterized by transmission electron microscopy (TEM; primary particle size), Raman spectroscopy (crystal phase), UV/Vis spectroscopy (band gap), x-ray photoelectron spectroscopy (XPS; functionalization density) and Fourier transform infrared spectroscopy (nature of ligands). Current efforts focus on functionalizing TiO2 nanoparticles with aminosuccinic acid and human immunoglobulin G (IgG). We have also used a solution-based method to synthesize quantum-confined ZnO nanoparticles and have functionalized them with citrate. Our collaborators at University of Puerto Rico Mayagüez have provided us 10-nm diameter Fe3 O4 (magnetite) and CoFe2 O4 (cobalt ferrihydrite) nanoparticles synthesized via thermodecomposition and functionalized with carboxymethyl dextran (CMDx).
We have characterized the suspension stability of the anatase nanoparticles functionalized with citrate and DHBA. Suspensions of nanoparticles functionalized with DHBA (Critical Coagulation Concentration, CCC > 1 M) are more stable than those functionalized with citrate (CCC ≈ 0.5 M). Suspensions of commercially available Degussa P25 TiO2 Aerosil nanoparticles (3:1 anatase-to-rutile ratio; mean primary particle diameter = 21 nm) were used in some of the toxicity studies described below. Suspensions of these nanoparticles are not stable in water. In exposure medium, these TiO2 particles form aggregates with Z-average hydrodynamic diameters of 370 ± 46 nm. Dissolved organic matter decreases the extent of aggregation (Z-average hydrodynamic diameters of 260 ± 28 nm).
We measured the production of reactive oxygen species by Degussa P25 and citrate-coated TiO2 nanoparticles under light in solution using 3′-(p-aminophenyl) fluorescein (APF), a fluorescent indicator specific for hydroxyl radicals. For citrate-coated TiO2 , we found that under UV illumination the ligands attached to these particles degraded.
Investigation of TiO 2 Toxicity using the Zebrafish Embryo. Evaluation of the developmental toxicity of nanomaterials requires the identification of toxicological endpoints in dose-response and time course studies. Zebrafish (Danio rerio) embryos and larvae are well suited for this purp ose and have emerged as a model for investigating developmental toxicity of environmental contaminants, including engineered nanoparticles. During the first project year, we have examined the toxicity of commercially available TiO2 nanoparticles, as well as those synthesized by our team. Waterborne exposures were conducted in the absence and presence of simulated sunlight. We hypothesized that TiO2 nanoparticle toxicity would be substantially enhanced by simultaneous exposure to light energy equal to or higher than the band gap.
We have demonstrated that the toxicity induced by Degussa P25 TiO2 nanoparticles is enhanced under simulated sunlight. In the absence of light, symptoms of toxicity were observed only at relatively high concentrations (≥ 1000 mg ⋅ L -1 ). We hypothesized that the mechanism by which these TiO2 nanoparticles become toxic in sunlight is oxidative stress. Absorption of light energy larger or equal to the band gap of titanium dioxide nanoparticles results in electron-hole separation. When these separated electrons and holes do not recombine and instead react with water or molecular oxygen, reactive oxygen species are formed. Under oxidative conditions within the fish, reactive oxygen species are present in higher concentrations than are antioxidant compounds, a situation that results in indiscriminate damage to macromolecules and can lead to cellular death. To further investigate oxidative stress as a mechanism of photoactivated toxicity of TiO2 nanoparticles, we constructed a transgenic zebrafish that “reports” induction of oxidative stress by expressing enhanced green fluorescent protein, and have conducted several experiments showing that photo-activation leads to reactive oxygen species formation and increased DNA damage in embryos exposed to photo-activated particles. Furthermore, we have evidence that the particles are taken up and physically associated with the embryos. Overall, our data support the idea that photo-activated titanium dioxide nanoparticles lead to oxidative stress and toxicity. Our findings suggest that the photo-enhanced toxicity of semiconductor nanoparticles warrants consideration in assessing the potential risks posed by these materials.
We have conducted preliminary experiments to investigate the effect of dissolved organic matter on TiO2 nanoparticle (photo-enhanced) toxicity. For the Degussa P25 TiO2 nanoparticles, relatively high concentrations of dissolved organic matter appear to decrease TiO2 nanoparticle-induced mortality to zebrafish embryos/larvae in the dark but not under simulated sunlight.
For the functionalized anatase nanoparticles, mortality to zebrafish embryos/larvae increases in the order citrate < rutin < DHBA. Preliminary experiments indicate that simultaneous exposure to simulated sunlight increased the toxicity of citrate- and rutin-functionalized nanoparticles.
Chemical Models of Environmental Redox Processes
During the first project year, we have adapted a juglone-sulfide system for use with engineered nanoparticles. This chemical model simulates reductive and some ligand exchange processes mediated by natural organic matter under anoxic conditions. Sulfide serves as the bulk reductant and juglone is an analog for electron shuttles present in natural organic matter. We have exposed silver nanoparticles functionalized with citrate, polyvinylpyrrolidone and gum Arabic to the juglone-sulfide system and each individual assay component. Silver nanoparticle transformation has been investigated by UV-Vis spectroscopy, dynamic light scattering, electrophoretic light scattering, inductively coupled plasma-optical emission spectroscopy, XPS and TEM. Treatments containing sulfide show a dramatic effect in the UV-Vis and XPS spectra, and some aggregation is apparent in treatments containing both sulfide and juglone. Further characterization of reaction products is underway. The juglone-sulfide system will be useful for screening nanomaterials for transformations possible in anoxic sediments. The experiments with silver nanoparticles will provide insight into possible transformations of these nanoparticles under anoxic conditions.
We have exposed citrate-coated TiO 2 nanoparticles to a methoxyhdyroquinone-Fenton system we developed to simulate the extracellular chemistry of lignolytic fungi (Metz et al., Environ. Sci. Technol. 2009). Preliminary data suggest that the citrate-TiO2 nanoparticles are not altered by this treatment.
Future Activities:
Future Activities include expanding the range of functionalizations for TiO2, ZnO and Fe3O4 nanoparticles; determining of the effect of TiO2 surface chemistry on life stage-dependent uptake by zebrafish; evaluating oxidative stress markers; rescuing toxicity by upregulating antioxidant genes; examining (photo-enhanced) toxicity of functionalized ZnO, Fe3O4 and CoFe2O4 nanoparticles; investigating alterations to metal oxide nanoparticles induced by exposure to simulated oxidative and reductive environments and any concomitant changes in toxicity.icles will provide insight into possible transformations of these nanoparticles under anoxic conditions.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 41 publications | 6 publications in selected types | All 6 journal articles |
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Type | Citation | ||
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Wiecinski PN, King Heiden TC, Metz KM, Mangham AN, Hamers RJ, Heideman W, Peterson RE, Pedersen JA. Developmental toxicity of oxidatively degraded quantum dots. Geochimica et Cosmochimica Acta Supplement. 2009;73:A1437. |
R833860 (2009) |
not available |
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Mangham AN, Louis KM, Bramson AM, Metz KM, Pedersen JA, Hamers RJ. Ligand effects on the oxidative stability of CdSe nanoparticles. Geochimica et Cosmochimica Acta Supplement. 2009;73(13):A827 |
R833860 (2009) |
not available |
Supplemental Keywords:
Water, exposure, bioavailability, metals, environmental chemistry, Health, Scientific Discipline, Risk Assessments, Biochemistry, biological pathways, CNT, bioavailability, nanotechnology, carbon fullerene, human exposure, nanomaterials, toxicologic assessment, nanoparticle toxicityProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.