2011 Progress Report: Environmental Behavior And Bioavailability Of Ag And Ceo2 Nanoparticles: The Role Of Surface Functionalization and its Interaction with Natural Organic Substances and Iron Oxohydroxides

EPA Grant Number: R834857
Title: Environmental Behavior And Bioavailability Of Ag And Ceo2 Nanoparticles: The Role Of Surface Functionalization and its Interaction with Natural Organic Substances and Iron Oxohydroxides
Investigators: Unrine, Jason M. , Bertsch, Paul M. , Graham, Ursula M. , Tsyusko, Olga V. , Butterfield, Allan
Institution: University of Kentucky
EPA Project Officer: Klieforth, Barbara I
Project Period: August 1, 2010 through July 31, 2014
Project Period Covered by this Report: August 1, 2010 through July 31,2011
Project Amount: $599,840
RFA: Increasing Scientific Data on the Fate, Transport and Behavior of Engineered Nanomaterials in Selected Environmental and Biological Matrices (2010) RFA Text |  Recipients Lists
Research Category: Chemical Safety for Sustainability

Objective:

The objective of this project is to investigate the role of nanoparticle surface chemistry and environmental modifications of nanoparticle surfaces in determining their aggregation, deposition and dissolution in environmental matrices, as well as bioavailability and toxicity, including phototoxicity, to a model organism (Caenorhabditis elegans). This objective will be met by testing the following hypotheses:

Hypothesis 1: Surface chemistry of engineered nanomaterials controls environmental surface modification with natural organic matter and iron oxohydroxides.

Hypothesis 2: Aggregation and dissolution of nanomaterials is heavily influenced by interactions with natural organic matter and iron oxohydroxides.

Hypothesis 3: Bioavailability and toxicity of nanomaterials in soil invertebrates are modified by interaction with natural organic matter and iron oxohydroxides.

Hypothesis 4: Surface modification of nanomaterials with natural organic matter and iron oxohydroxides can alter the response of molecular biomarkers of exposure as well as the nature and extent of damage to biomolecules.

Progress Summary:

We developed a method to synthesize ~4 nm CeO2 particles using dextran as a coating (Fig 1). Dextran (dex) is a non-ionic coating and thus has no charge. We then developed techniques to conjugate these particles to convert the coatings to either carboxymethyl-dextran (CM- dex), which has a negative charge over a wide pH range, and diethylaminoethyl-dextran (DEAE-dex), which has a permanent positive charge. The particles display auto-catalytic redox behavior. For example, they can be oxidized by H2O2, causing a color change from yellow to bright orange. Over 24-48 hours, the absorbed oxygen is released in the form of O2 gas, and the color shifts back to yellow. The change in oxidation state is being confirmed with X-ray photoelectron spectroscopy. In the future, we anticipate that we also will be able to manipulate the molecular weight of these coatings. Thus, we will have created a library of particles with identical CeO2 cores where we can manipulate the charge and molecular weight of the coatings.


Experiments comparing the interaction of natural organic matter (Suwannee River humic and fulvic acids) with the dextran-CeO2 and DEAE-dextran-CeO2 in either DI water or moderately hard reconstituted water have yielded interesting results (data not shown). The moderately hard water itself shifts the pH of zero net charge (PZC) from about 7.2 to around 6.0. Experiments with individual components demonstrated that this was due to sulfate, likely due to formation of an inner-sphere complex with the ceria surface (data not shown). Organic matter had a more profound effect, shifting the PZC to around pH 4. On the other hand, the DEAE-dex CeO2 had PZC of around 12-13 and the NOM only shifted the PZC slightly to around pH 11. We had anticipated that interaction with organic matter would dominate the surface chemistry; however, even at a 1:1 ratio of organic matter to particles, the effect of the manufactured coating on the PZC was still apparent with the DEAE-dex coated particles.


We also found that while the dex-CeO2 was essentially non-toxic in C. elegans, significantly greater toxicity was observed for the DEAE-dex-CeO2 (Fig 2). This indicates that coating charge is a primary determinant of toxicity for CeO2 particles. Using synchrotron X-ray imaging and X-ray absorption near edge structure spectroscopy, we confirmed the uptake of the particles and demonstrated that the positively charged DEAE-dex-CeO2 are more bioavailable than the neutral dex-CeO2 (Fig 3). In suspension in the exposure media, the CeO2 particles were mostly in the +IV redox state, but when they came into contact with the C. elegans, they were reduced and contained up to 75% Ce in the +III redox state (Fig 4). This suggests a possible mechanism of toxicity, where CeO2 is reduced and biomolecules within the C. elegans are oxidized. We will be performing redox specific proteomics studies to identify proteins that are oxidized during exposure.


We also have performed experiments in collaboration with CEINT demonstrating that Ag NPs with polyvinylpyrrolidone (PVP) coatings are not oxidized by exudates from aquatic plants, while particles with gum arabic coatings are oxidized, resulting in dissolution. The plant organic matter actually stabilized the PVP coated AgNPs, preventing their aggregation. The Ag NPs themselves stimulated the aquatic plants to release the exudates. The results have important implications because they suggest that manufactured particle coatings influence the biotic and abiotic modifications of Ag NPs. We demonstrated that these OM modifications also decrease the toxicity of the particles. These results are in press in Unrine, et al. (2012). Additional results from this experiment are in review in Bone, et al. (2012). 

Overall, our data demonstrate that manufactured coatings not only have important effects on the properties and toxicity of manufactured CeO2 and Ag NPs, but they also can influence the nature and rate of modifications in the environment by natural organic matter. We currently are conducting more detailed experiments with the set of CeO2 particles, investigating the influence of charge on organic matter interactions with particles and also will begin manipulating the molar mass of the coatings. We are investigating the redox couples that can occur between particles and different kinds of biomolecules, and how coatings influence these interactions. We also are ready to begin performing redox proteomics and gene expression studies to look at effects of coatings and modification of coatings on mechanisms of toxicity.

Future Activities:

We have developed a method to synthesize ultra-small CeO2 particles that exhibit reversible transitions in redox state (between the +III and +IV valence states). The particles are synthesized with a dextran coating. We have developed techniques to manipulate the charge of this coating (positive, negative and neutral) and will be experimenting with manipulating the molar mass of the coating. This has enabled us to begin testing hypotheses about the role of coating charge and molar mass on toxicity in C. elegans. We also have begun experiments that examine how these coatings with different charges influence interactions between the particles and natural organic matter. The next step will be to see how the organic matter changes the toxicity of the particles with different coatings.

We will continue the more detailed experiments with the set of CeO2 particles, investigating the influence of charge on organic matter interactions with particles and will begin manipulating the molar mass of the coatings. The investigation of the redox couples that can occur between particles and different kinds of biomolecules, and how coatings influence these interactions, will continue. We also are ready to begin performing redox proteomics and gene expression studies to look at effects of coatings and modification of coatings on mechanisms of toxicity.


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 11 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article Bone AJ, Colman BP, Gondikas AP, Newton KM, Harrold KH, Cory RM, Unrine JM, Klaine SJ, Matson CW, DiGiulio RT. Biotic and abiotic interactions in aquatic microcosms determine fate and toxicity of Ag nanoparticles: Part 2--toxicity and Ag speciation. Environmental Science & Technology 2012;46(13):6925-6933.
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R834857 (2011)
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  • Journal Article Unrine JM, Colman BP, Bone AJ, Gondikas AP, Matson CW. Biotic and abiotic interactions in aquatic microcosms determine fate and toxicity of Ag nanoparticles. Part 1. Aggregation and dissolution. Environmental Science & Technology 2012;46(13):6915-6924.
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    R834857 (2011)
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  • Journal Article von der Kammer F, Ferguson PL, Holden PA, Masion A, Rogers KR, Klaine SJ, Koelmans AA, Horne N, Unrine JM. Analysis of engineered nanomaterials in complex matrices (environment and biota): general considerations and conceptual case studies. Environmental Toxicology and Chemistry 2012;31(1):32-49.
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    R834857 (2011)
    R834857 (2012)
    R833859 (Final)
    R834574 (2011)
    R834574 (2012)
    R834574 (Final)
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