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Environmental Transformations of Engineered Nanomaterials and Impacts on ToxicityEnvironmental Transformations of Engineered Nanomaterials and Impacts on ToxicityJoel A. Pedersen, Kevin M. Metz, Paige N. Wiecinski, Robert J. Hamers, Warren Heideman and Richard E. Peterson
Nanoscale Science and Engineering Center, Molecular and Environmental Toxicology Center, Environmental Chemistry and Technology Program, Department of Chemistry, School of Pharmacy and Department of Soil Science, University of Wisconsin, Madison WI 53706
After release into the environment, engineered nanoparticles may be transformed by microbially mediated oxidative and reductive processes, potentially altering their interactions with living systems. As a first step toward understanding such transformations, we are developing in vitro chemical models to simulate important microbial redox processes. Here, we report the transformation of PEGylated CdSecore/ZnSshell quantum dots (QDs) in a biomimetic assay modeled after the extracellular chemistry of lignolytic fungi. The transformed QDs exhibit altered toxicity to developing zebrafish (Danio rerio) embryos. While QDs are used to illustrate the utility of the assay, the method can in principle be applied to nearly any nanomaterial of interest, making this and similar assays useful tools for investigating the transformation of nanomaterials in the environment.
Nanomaterials Under Investigation
Quantum DotsEvident Technologies, NY, http://www.evidenttech.com
CdSecore/ZnSshell quantum dots (2.5 nm core diameter)
Au nanospheres (2, 20 nm diameters)
Ag nanospheres (20 nm diameters)
Pd nanoparticles (5-30 nm diameters)
Gloeophyllum trabeumCourtesy of Prof. K. E. Hammel
Pathways for reactive oxygen special production in the environment
Reductant-driven Fenton’s reaction:
H2O2 + Fe+2 + MHQ HO˙ + OH- + Fe+3 + MHQ+
Nanomaterials are exposed to assay in batch reactors.
[Fe+2]:[methoxyhydroquinone (MHQ)]: [H2O2] = 20:20:200 μM
pH 4, dark, under Ar
[nanoparticles] = 2 nM to 2 μM
Biological Basis of Oxidative Assay:Extracellular Chemistry of Lignolytic Fungi
Toxicity of Exposed Quantum Dots
Adult Zebrafish (Danio rerio)
www.depauw.edu
blake.monteclair.edu
www.cas.vanderbilt.edu
Developmental toxicity of exposed quantum dots was assessed using an embryonic
zebrafish assay
Oxidative degradation increases lethality of PEGylated QDs, as shown by a shift in LC50 values
MHQ-Fenton’s Exposed PEG350
MHQ-Fenton’s Exposed PEG5K
Sublethal Toxicity of Oxidatively Degraded Quantum Dots
Dose-Response
0102030405060708090
100
0 0.2 2 20 200 400 800 1600
Concentration (uM Cd Equivalence)
MHQ-Fenton’s Exposed PEG350 QD
PEG350 QD
CdCl2
LC50 341 μM
LC50 39.5 μM
(29.3-51.6)
% M
ort
ali
ty @
12
0 h
pf
PEG350-QD
0102030405060708090
100
0 0.2 2 20 200 400 800 1600
Concentration (uM Cd equivalents)
MHQ-Fenton’s Exposed PEG5000 QD
PEG5000 QD
CdCl2
LC5014.2 μM (9.3-21.6)
LC50 42 μM
LC50 341 μM
% M
ort
ali
ty @
12
0 h
pf
PEG5000-QD
• MHQ-Fenton’s exposure substantially increases sublethal toxicity shown by PEG350-QDs
• Sublethal toxicities include edema (pericardial, periocular ect), curvature of the spine, uninflated swim bladder
Transformation of QDs Under Simulated Environmental Oxidative Conditions
UV-Visible absorption spectroscopy is used to monitor changes to the QDs.
Core Diameter
Number Concentration
UV-Visible spectroscopy characterization of quantum dots exposed to assay
• Classic Fenton’s reaction has little effect relative to H2O2 exposure
• Exposure to MHQ-driven Fenton’s reaction leads to loss of first exciton peak, erosion of Zn shell and release of Cd from core
Acknowledgements: Jackie Bastyr-Copper for assistance with ICP data.
National Science Foundation award DMR-0425880
Concentrations of Cd and Zn from QD-PEG5000 exposed to H2O2 and (reductant-driven) Fenton’s reagent, then separated through a centrifugal concentrator.
Effect of Excess Ligands on Stability
QD-PEG5000 Classic Fenton reaction
QD-PEG350 with excess ligand QD-PEG350 without excess ligand
Excess ligand in solution protect the QDs from degradation by the assay.
QD-PEG5000 reductant-driven Fenton reaction
AA=Ascorbic Acid, MHQ=Methoxyhydroquinone