Grantee Research Project Results
2009 Progress Report: Effects of Quantum Dot on Microbial Communities
EPA Grant Number: R833858Title: Effects of Quantum Dot on Microbial Communities
Investigators: Alvarez, Pedro J. , Colvin, Vicki L. , Mahendra, Shaily
Institution: Rice University
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 2008 through September 30, 2011
Project Period Covered by this Report: October 1, 2008 through October 1,2009
Project Amount: $399,889
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:
Introduction and Objectives
Quantum dots (QDs) are being increasingly used in a wide variety of commercial products and applications such as biomedical imaging, targeted gene and drug delivery, solid state lighting, and solar cells. QDs are reported to be safe for their intended use, but they contain hazardous constituents that could be released as they weather in the environment, and their behavior and potential impact to human and ecosystem health as are not yet known. This project is characterizing the weathering of QDs and its effects on indigenous bacteria, which serve as models of cell toxicity and indicators of ecosystem health. Specific tasks include:
(1) quantification of the heavy metal release (rate and extent) during weathering of QDs,
(2) characterization of QD-bacterial interactions,
(3) evaluation of the impact of QDs on the composition and selected environmental services of microbial communities.
(4) investigation of QDs’ affect on microbial gene expression and metabolisms
The relevance of this work to the EPA mission is related to the fact that microorganisms are the foundation of all ecosystems and are often the basis for food chains and the main agents of biogeochemical cycles. Thus, understanding their interactions with QDs is important to ensure that nanotechnology improves material and social conditions without exceeding the ecological capabilities that support them. At the conclusion of this project, we will have an improved understanding of the chemical and physical factors that control nanoparticle mobility and bioavailability, and their impacts on microbial activities, diversity and community structure. This will also benefit risk assessment and management efforts.
Progress Summary:
Heavy metal ions release from QDs.
CdSe/ZnS-containing QDs were bioconjugated with three different coatings including polymaleic anhydride-alt-1-octadecene (PMAO), polyethylene imine (PEI), and uncoated QDs. These QDs were “weathered” by adjusting the pH to 2, 4, 7, 10, and 12 for 24 hours at room temperature. Several different processes could be initiated under extreme acidic or alkaline conditions, including core/shell leaching, QD aggregation, and precipitation of metal oxides. Low pH was expected to readily solubilize core/shell metals while high pH could be relevant for Cd or Zn speciation, precipitation, and bioavailability. Polymer coatings themselves are unlikely to be stable at very acidic (pH < 3) or very basic conditions (pH > 10) due to hydrolysis of the ether bonds (PMAO) or decrease in the number of amine linkages (PEI). QDs containing intact surface coatings were associated with supernatant concentrations of 8-23 µg/L cadmium, 2-10 µg/L selenium, and nondetectable to 5 µg/L zinc. QD exposure to various pH conditions resulted in rapid releases of large concentrations of cadmium, as well as some selenium and zinc into the supernatant. The total concentrations of cadmium with QDs capped with NH2PEG, PMAO, or PEI ranged from 138 to 186 µg/L at pH values other than 7. The uncoated QDs released 67-78 µg/L cadmium initially, and 70-80 µg/L after exposure to various pH conditions.
Antibacterial activity of QDs and their weathered products
QDs were evaluated for their effects on bacterial pure cultures, which serve as models of cell toxicity and indicators of potential impact to ecosystem health. QDs with intact surface coatings decreased growth rates of Gram positive Bacillus subtilis and Gram negative Escherichia coli but were not bactericidal. In contrast, weathering of various types of QDs under acidic (pH ≤ 4) or alkaline (pH ≥ 10) conditions significantly increased bactericidal activity due to the rapid (<1 min) release of cadmium and selenite ions following QD destabilization upon loss of the organic coating. Toxicity was mitigated by humic acids, proteins, and other organic ligands that reduced metal bioavailability. The best available science, which is limited, suggests that QDs are potentially safe materials when used in their intended applications at near-neutral pH. These results forewarn us that even moderately acidic or alkaline conditions could lead to significant and localized organism effects due to toxic exposure to dissolved heavy metals. Thus, biocompatibility and ecotoxicity tests for QDs should consider in vivo and/or in situ transformations to fully characterize the potential risks to environmental health.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
| Other project views: | All 8 publications | 2 publications in selected types | All 2 journal articles |
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Kashiwada S, Ariza ME, Kawaguchi T, Nakagame Y, Jayasinghe BS, Gartner K, Nakamura H, Kagami Y, Sabo-Attwood T, Ferguson PL, Chandler GT. Silver nanocolloids disrupt medaka embryogenesis through vital gene expressions. Environmental Science & Technology 2012;46(11):6278-6287. |
R833858 (2009) R833859 (Final) |
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Mahendra S, Zhu H, Colvin VL, Alvarez PJ. Quantum dot weathering results in microbial toxicity. Environmental Science & Technology 2008;42(24):9424-9430. |
R833858 (2009) |
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Supplemental Keywords:
Health, Scientific Discipline, Health Risk Assessment, Risk Assessments, Environmental Microbiology, Biochemistry, Environmental Monitoring, bioavailability, nanomaterials, carcinogenic, human exposure, aquatic ecosystem, biological pathways, CNT, nanoparticle toxicity, nanotechnology, human health risk, toxicologic assessmentProgress 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.