1. ` Environmental Transformations of Engineered Nanomaterials and Impacts on Toxicity Joel 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 CdSe core /ZnS shell 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 Dots Evident Technologies, NY, http://www.evidenttech.com CdSe core /ZnS shell 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 trabeum Courtesy of Prof. K. E. Hammel Pathways for reactive oxygen special production in the environment Reductant-driven Fenton’s reaction: H 2 O 2 + Fe +2 + MHQ HO˙ + OH - + Fe +3 + MHQ + Nanomaterials are exposed to assay in batch reactors. [Fe +2 ]:[methoxyhydroquinone (MHQ)]: [H 2 O 2 ] = 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.ed u 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 LC 50 values MHQ-Fenton’s Exposed PEG350 MHQ-Fenton’s Exposed PEG5K Sublethal Toxicity of Oxidatively Degraded Quantum Dots Dose-Response 0 10 20 30 40 50 60 70 80 90 100 00.22202004008001600 Concentration (uM Cd Equivalence) MHQ-Fenton’s Exposed PEG350 QD PEG350 QD CdCl2 LC 50 341 μM LC 50 39.5 μM (29.3-51.6) % Mortality @ 120 hpf PEG 350 -QD 0 10 20 30 40 50 60 70 80 90 100 00.22202004008001600 Concentration (uM Cd equivalents ) MHQ-Fenton’s Exposed PEG5000 QD PEG5000 QD CdCl2 LC 50 14.2 μM (9.3-21.6) LC 50 42 μM LC 50 341 μM % Mortality @ 120 hpf PEG 5000 -QD MHQ-Fenton’s exposure substantially increases sublethal toxicity shown by PEG 350 -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 H 2 O 2 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- PEG 5000 exposed to H 2 O 2 and (reductant- driven) Fenton’s reagent, then separated through a centrifugal concentrator. Effect of Excess Ligands on Stability QD-PEG 5000 Classic Fenton reaction QD-PEG 350 with excess ligandQD-PEG 350 without excess ligand Excess ligand in solution protect the QDs from degradation by the assay. QD-PEG 5000 reductant-driven Fenton reaction AA=Ascorbic Acid, MHQ=Methoxyhydroquinone