Nanomaterials in the Aquatic Environment: Persistence, Transformations, and Bioavailability Heileen (Helen) Hsu-Kim Duke University Civil & Environmental Engineering
What are engineered nanomaterials? Materials manufactured to ~1-100 nm in size Exhibit unique properties due to their small size (relative to larger materials) Concerns for their safety and environmental impacts: Auffan et al., Nature Nano, 2009
Breaking the Cycle of Unintended Consequences Mercury amalgamation for precious metals mining Pesticides for control of disease Chloroflurocarbons (CFCs) 3
Environmental health and safety of nanomaterials Life cycle of a material: Raw materials, Fabrication Products use, Disposal unintended release Exposures and Effects?
Environmental exposure to nanomaterials: Key Questions: What are the main processes controlling exposures of nanomaterials to ecosystems? How do other water constituents alter nanomaterial surfaces, speciation, and persistence? Do nanomaterials naturally occur in these settings?
Presentation Outline 1. Exposure of metal-based nanomaterials in the aquatic environment 2. How other water constituents alter nanomaterial reactivity Example: Silver nanomaterials in public wastewater treatment systems 3. Naturally-occurring nanomaterials
Ag 0 NPs in commercial products Purpose: antimicrobial coating in household goods Ref: Project on Emerging Nanotechnologies
Release of silver nanomaterials into domestic wastewater Raw sewage with Ag nanomaterials End products: Treated Water Biosolids 8
Geochemistry and Toxicity of Trace Metal Pollutants The Conventional View: Biotic Ligand Model Weak metal complexes AgCl, AgCl 2 - Particles Ag 2 S (s), AgCl (s) free metal ion Ag + Biotic ligand bioavailable chelation by ligands strongly complexed metals Ag-humic not bioavailable
Ag 0 persistence and bioavailability Stable NP suspension dissolved silver Aggregated NPs What is the influence of other water constituents for nanoparticle reactivity?
Other constituents in natural waters Meters 10-10 10-9 10-8 10-7 10-6 10-5 10-4 1 nm 450 nm Dissolved organic matter Dissolved metal complexes Polynuclear cluster Nanoparticles Colloids Viruses Bacteria 10 kda filter 0.45 m filter Dissolved Colloidal Particulate 11
Other constituents in environmental media Dissolved Organic Matter Interactions with nanoparticles: Macromolecular surfactant Hydrophilic and hydrophobic moieties Potential to bind Ag + ions
Ag 0 persistence and bioavailability Stable NP suspension surfacemodified NPs Adsorption of ligands ligand-promoted or inhibited dissolution dissolved silver bioavailable Not bioavailable Aggregated NPs
Absorption (a.u.) Dissolved silver (μm) Absorption (a.u.) Nanomaterial reactivity in wastewater PVP-coated Ag nanoparticles Transformations after exposure to cysteine Surface modification (a) Ag(CYS) 2 20 nm Dissolution (b) Ag(CYS) 2 8 Ag-CIT Ag-PVP 6 4 (b) Total silver 400μM Cysteine 6.8% Ag(CYS) 400 μm Serine 2 ) No amino acid 24 h (94.6% Ag-CIT, 2 h (97.2% Ag-CIT, 3.7% Ag(CYS) 2 ) 24 h (91.0% Ag-PVP, 8.8% Ag(CYS) 2 ) 2 h (91.5% Ag-PVP, 8.6% Ag(CYS) 2 ) 2 0 0 20 40 60 Time (h) 3330 3350 3370 3390 3330 3350 3370 3390 Energy (ev) Energy (ev)
Aggregation Rate, nm/min Nanomaterial reactivity in wastewater Transformations after exposure to cysteine 100 10 (b) Aggregation Dissolution rate: 2.4 μmol m -2 h -1 1 0.1 0.01 400 μμ CYS 0 μμ CYS 0.001 0.01 0.1 1 Ionic Strength (M) Dissolution rate: 2.8 μmol m -2 h -1 15
Dissolved silver (μm) Dissolved silver (μm) Nanomaterial reactivity in wastewater Transformations induced by cysteine Citrate-coated Ag NPs PVP-coated Ag NPs 8 8 6 (a) Total silver 400μM Cysteine 400 μm Serine No amino acid 6 (b) Total silver 400μM Cysteine 400 μm Serine No amino acid 4 4 7.2 μmol m -2 h -1 2 2 2.8 μmol m -2 h -1 0 0 20 40 60 Time (h) 0 0 20 40 60 Time (h) 16
Survival of E. coli Nanomaterial reactivity in wastewater Reaction with sulfide Levard et al. 2011 Reinsch et al. 2012 Ag 2 S Ag 0 17
Ag 0 persistence and bioavailability Stable NP suspension surfacemodified NPs Adsorption of metal-binding ligands ligand-promoted or inhibited dissolution dissolved silver bioavailable Not bioavailable Aggregated NPs
Naturally-Occurring Nanomaterials Contaminated soil and sediments nano ZnS nano-fes/cus on sediment bacteria nano HgS Treated Sewage Effluent and Biosolids Oak Ridge, TN nano Ag 2 S Originally from silver nanomaterials? Kim et al. (2010)
Naturally-Occurring Nanomaterials New nanoparticles formed from silver objects Silver wire Silver nanoparticles 500 nm 50 nm Glover et al. ACS Nano (2011) Silver earring 20
Manufactured vs. Naturally-Occurring Nanomaterials Similarities Shared core composition: TiO 2 Metallic Ag 0, Au 0, Cu 0 SiO 2 ZnS, CuS, CdS ZnO CeO 2 Fullerenes (C 60 ) (?) carbon nanotubes (?) quantum dots (e.g. CdSe, CdTe ) Differences Surface coatings (synthetic vs. natural) Polydispersivity & Crystallinity Composites of nanomaterials
cluster formation in presence of DOM Summary and Challenges Increasing use of nanomaterials Increase of exposure Transformations in the environment (example: natural organic matter) Dissolution, Surface Chemistry, Aggregation Naturally-occurring nanomaterials: Can they provide lessons for engineered nanomaterials? Stable DOM-capped polynuclear clusters Heterogeneous amorphous nanoparticles ripening or aging Stable colloid and nanoparticle suspension sorption of DOM dissociation dissolved metal complexes ligand-promoted or inhibited dissolution bioavailable not bioavailable Aggregated colloids and nanoparticles