Grantee Research Project Results
2008 Progress Report: The Bioavailability, Toxicity, and Trophic Transfer of Manufactured ZnO Nanoparticles: A View from the Bottom
EPA Grant Number: R832530Title: The Bioavailability, Toxicity, and Trophic Transfer of Manufactured ZnO Nanoparticles: A View from the Bottom
Investigators: Bertsch, Paul M. , Neal, Andrew , Jackson, Brian , Williams, Phillip , Glenn, Travis
Institution: University of Kentucky , University of Georgia , Dartmouth College , Savannah River Ecology Laboratory
Current Institution: Savannah River Ecology Laboratory , Dartmouth College , University of Georgia
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 2005 through September 30, 2008 (Extended to September 30, 2009)
Project Period Covered by this Report: January 1, 2007 through July 31,2009
Project Amount: $363,680
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Environmental and Human Health Effects of Manufactured Nanomaterials: A Joint Research Solicitation - EPA, NSF, NIOSH (2005) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
The overall objectives of our research are to evaluate 1) the bioavailability and toxicity of manufactured nanoparticles (ZnO-np) as a function of particle size to the model bacteria, Burkholderia vietnamiensis PR1301 and the model detritivore Caenorhabditis elegans as referenced against aqueous Zn2+, 2) the ability of manufactured ZnO nanoparticles to be transferred from one trophic level to the next as assessed in the simple food chain consisting of pre-exposed PR1 and C. elegans, and 3) the synergistic or antagonistic effects of manufactured ZnO nanoparticles on the toxicity of Cu2+ to PR1 and C. elegans. These three overall objectives will be approached in the context of the following four hypotheses:
Hypothesis 1: The bioavailability and toxicity of manufactured ZnO nanoparticles increases with decreasing particle size (i.e., 3 nm vs. 80 nm).
Hypothesis 2: The toxicity of ZnO nanoparticles to PR1 and C. elegans is lower than an equivalent concentration of dissolved Zn2+.
Hypothesis 3: The bioavailability and toxicity of ZnO nanoparticles introduced via trophic transfer differs from direct exposure.
Hypothesis 4: ZnO nanoparticles alter the bioavailability and toxicity of dissolved metals
Progress Summary:
Year 1: Tasks were successfully completed without major difficulties. Data obtained has addressed specific questions tied to the project hypotheses. It was found that the thorough characterization of the nanoparticles under a range of chemical conditions representative of exposure and environmental conditions is essential to the understanding environmental fate and toxicity of the nanoparticles. Characterization data obtained with a variety of techniques including transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and raman spectroscopies (FT-R) and high resolution thermogravimetric analysis (HR-TGA) found evidence for at least three acetate populations. This is important as acetate inhibits surface reactivity; removing acetate significantly increases surface reactivity.
The toxicity of ZnO-np to B. vietnamiensis and C. elegans was found not to be significantly different than an equivalent concentration of dissolved Zn2+ but that the underlying toxicity mechanisms are likely different. Following 24 hours of B. vietnamiensis cell growth, significant flocculation of primary particles was observed. Aggregates could result from acetate degradation and/or exopolymer secretion. In ZnO-np and ZnCl2 exposed C.elegans, Zn distribution showed similar patterns with the areas of maximum intensity being more widely distributed through the nematode tissues as exposure concentration increases. The maximum intensities in ZnCl2 exposed nematode are approximately twice as high as in ZnO-np exposed nematode, which may suggest their different bioavailability.
While the overall aim of the project did not change, the trophic transfer research on pre-exposed B. vietnamiensis consumed by C. elegans was analytically challenging and experiments were expanded to include an addtional detritivore, the model earthworm Eisenia fetida. Also, based on initial results on the importance of acetate, a constitutive acetate utilizing metal sensitive bacteria Cupriavidus necator was included starting year 2.
Year 2 and partial year 3: The second year research activities focused on: 1) characterization of both the smaller (3 nm- sZnO-np) and larger (80 nm-lZnO-np) size ZnO-np 2) understanding the bioavailability and toxicity of lZnO-np to C. elegans, 3) deciphering differences in toxicity mechanisms of sZnO-np and aqueous zinc acetate to C. necator using proteomics techniques, 4) the effects of sZnO-np and ZnCl2 on Cu toxicity, and 5) the bioavailability and toxicity of sZnO-np introduced via trophic transfer as opposed to direct exposure. The major findings were as follows. In terms of characterization, it was found that: (1) size determination and surface chemistry are critical issues; (2) transmission electron microscopy may be problematic as a method for size determination of small metal oxide nanomaterials resulting from e-beam interactions and induced crystal growth; (3) acetate controls smaller ZnO-np reactivity and passivates surface sites, but this is not the case for larger particles; and (4) removal of acetate leads to flocculation/aggregation of small ZnO-np primary particles but promotes surface reactivity. Results from bacterial exposure experiments showed that: (1) there is no significant difference in the growth rate of C. necator and B. vietnamiensis following exposure to ZnO-np and aqueous zinc; (2) C. necator displays higher acetate utilization rates with aqueous zinc compared to ZnO-np, indicating a possible difference in bioavailability; and (3) there is greater compromised cells membranes associated with ZnO-np than with the free Zn ion. Experiments with nematodes indicated that: (1) mortality is not significantly different between aqueous zinc and ZnO-np; and (2) at higher zinc concentrations (> 100 mg.L-1), ZnO-np decreases copper toxicity compared to aqueous zinc. Finally, there was no evidence for significant trophic transfer in the bacterial-nematode model however, this may be more related to experimental challenges, and ZnO-np is bioavailable from soils as demonstrated in earthworm exposures.
Future Activities:
These results obtained during the second and third year of the project almost completes the planned research activities. We anticipate the remaining tasks to be completed by September 30, 09 to be :1) Finish all experiments described above, 2)Submit results to refereed journals; and 3)Complete final report due to EPA.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 24 publications | 3 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Ma H, Bertsch PM, Glenn TC, Kabengi NJ, Williams PL. Toxicity of manufactured zinc oxide nanoparticles in the nematode Caenorhabditis elegans. Environmental Toxicology and Chemistry 2009;28(6):1324-1330. |
R832530 (2008) R832530 (Final) |
Exit |
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Ma H, Kabengi NJ, Bertsch PM, Unrine JM, Glenn TC, Williams PL. Comparative phototoxicity of nanoparticulate and bulk ZnO to a free-living nematode Caenorhabditis elegans: the importance of illumination mode and primary particle size. Environmental Pollution 2011;159(6):1473-1480. |
R832530 (2008) R832530 (Final) |
Exit Exit |
Supplemental Keywords:
nanotechnology, metal oxides, nanoparticles, adsorption, absorption, exposure, ecological effects, bioavailability, trophic transfer, organism, cellular, population, enzymes, metals, nanoparticles, Environmental chemistry, analytical, Ecosystem Protection/Environmental Exposure & Risk, RFA, Ecological Effects-Environmental Exposure & Risk, ecological Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, Ecosystem protection, Ecosystem/Assessment/Indicators, Environmental Microbiology, Risk Assessment, exploratory research environmental biology, ecological assessment, ecological impacts, ecosystem assessment, environmental fate, Health, Scientific Discipline, Water, Environmental Chemistry, Health Risk Assessment, Risk Assessments, Biochemistry, Engineering, Chemistry, & Physics, fate and transport, food chain, trophic transfer, nanotechnology, carbon fullerene, bioavailability, particle exposure, environmental contaminants, nanomaterials, ambient particle health effects, human exposure, engineered nanomaterials, biochemical researchProgress 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.