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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