Fate, Transport, and Toxicity of Nanoparticles in the...

Fate, Transport, and Toxicity of Nanoparticles in the Environment, JSEM May 24, 2007

Fate, Transport, and Toxicity of Nanoparticles in the Environment

Steven J. OIdenburg, Thomas K. DarlingtonnanoComposix, Inc., San Diego, CA

Tonya Savage and Mitch BogleAFOSR, Eglin AFB, FL


Talk Outline

Nanotechnology and Nanotoxicology

Challenges of Nanotoxicology Research

Nanoparticles for Environmental Studies

Transport of Benchmark Nanoparticles

Transport of Aluminum Nanoparticles


Nanotechnology

Research and technology development at the atomic, molecular, or macromolecular

levels using a length scale of 1-100 nanometers in any dimension.

EPA Nanotechnology White PaperFebruary 2007


Risks Associated with Nanotechnology

Nanotechnology has emerged as a growing and rapidly changing field. New generations of nanomaterialswill evolve, and with them new and possibly unforeseen environmental issues.

EPA White Paper on NanotechnologyFebruary 2007


Environmental Nanotoxicology

• Determine the impact of manufactured nanomaterialson the environment

• Monitor the fate and transport of nanoparticles in soil, water, and the atmosphere

• Understand the effect of nanoparticles on plants, micro-organisms, and aquatic species

• Once hazards have been identified, propose remediation techniques that will minimize environmental impact


Challenges

#1: Size, Shape and Surface Dependent Properties

“Nanostructures of zinc oxide” Wang ZL, Materials Today, June 2004 p.27-33


Challenges

#2: Size Dependent Toxicity

20 nm diameter TiO2 particles have a much greater pulmonary toxicity than pigment-grade TiO2 particles (>10X larger) with the same composition (Bermudez, E., et al., Toxicol. Sci. (2004) 77, 347)

Individual 26 nm diameter polytetrafluoroethene (PTFE) particles are toxic to rats as individual but not as agglomerated particles. (Oberdörster, G., et al., Inhal. Toxicol. (1995) 7, 111)

Multi-walled carbon nanotubes are more proinflammatory when compared to ultrafine carbon black particles on an equivalent mass dose metric. (Shvedova et al. Am. J. Physiol. Lung Cell Mol. Physiol. (2005) 289, L698)


Challenges

#3: Aggregation Dependent Properties

2000 nanoparticles dispersed(diameter = 10 nm)

2000 nanoparticles aggregated (aggregate size = 100 nm)


Initial Study Goals

• Understand transport of aluminum nanoparticles in sand and soil.

• Study nanoparticle benchmark particles with monodisperse sizes and well defined surface chemistry.

• Compare benchmark particle transport to aluminum nanoparticle transport (aggregated nanoparticles with a dynamic surface chemistry).

• Measure nanoparticle induced toxicity in plants and aquatic species


Gold and silver nanoparticle benchmark materials

• Well controlled size and shape

• Colorimetric aggregation signature

• Surface chemistry can be easily modified

• ICP can trace to PPB level

• Gold is non-toxic, silver is toxic


The optical properties of gold and silver change dramatically when the dimensions of the material are reduced below 100 nm.

From Kelly et. al, J. Phys. Chem B, 107, 668.

Nanoparticle Characterization:Dark Field Microscopy & Plasmon Resonance


Nanoparticle Characterization:Dark Field Microscopy

80 nm Gold Colloid 60 nm Silver Colloid


Nanoparticle Characterization:Dark Field Microscopy

Dark field images of (a) 80 nm diameter gold particles (b) soil sample (c) gold nanoparticles and soil samples mixed.


Soil Analysis After Transport

40 nm Gold nanoparticles interact with specific soil components


Nanoparticle Transport Experimental Setup

• Syringe pump delivery of particles and precise flow rate• Glass column to hold transport matrix• In line flow cell detection with HP8453 UV-Vis


Transport of 19 nm Gold in Sand

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Nanoparticle flow through a 7 cm sand (60 mesh) column loaded with 3.9 g of sand at a rate of 0.05 mL / minute.


Transport of Gold Particles in Sand

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4 nm Gold (THPC)

19 nm (Citrate)

43 nm (KCarbonate)

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Nanoparticle flow through a 7 cm sand (60 mesh) column loaded with 3.9 g of sand at a rate of 0.05 mL / minute.


Transport of Gold Particles in Soil

19 nm citrate stabilized gold nanoparticles flowing through a 7 cm soil column (Eglin AFB soil sample).

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Transport of Gold Nanoparticles in Sand

• Low affinity of gold particles for sand: consistent with negative surface charge of both sand and gold

• No effect of size on particle mobility in the range tested (4-190 nm)

• Surface properties determine transport characteristics

• Gold nanoparticles interact with soil components.


Bulk Aluminum Toxicity

Aluminum in bulk form is generally regarded as safe:

• Oral – little toxicity – on the order of grams• Dermal – minimal• Inhalation – on the order of nuisance dust• Systemic – suggested link with Alzheimer's Disease


Nanoaluminum Toxicity

Toxicity of nanoaluminum is under investigation:

• Nanoaluminum readily internalized into cell lysosomes• Evidence that unreacted nanoaluminum is more toxic

than aluminum oxide (in-vitro model – A549 cells)• Possible mechanism is the release of heat or H2 gas

during oxidation once the nanoparticles are inside the cells.

• Flake shaped nanomaterials more toxic than spherical. Comparable toxicity to that of quartz


Aluminum Nanoparticle Characteristics

• 50 nm aluminum particles from Nanotechnologies, Inc. (NT50 Austin, TX).

• Supplied as dried gray powder

• Average Grain Size (TEM): 44 ± 18 nm

• DLS: Hydrodynamic Radius = 340 ± 210 nm

• Zeta Potential: +44 mV

• Solution prepared using probe sonication and degassed 18.2 MΩ water. 100 ppm solution


DLS vs TEM: Aluminum Nanoparticles

TEM of aluminum nanoparticles:Grain Size: 44 ± 18 nm

DLS of aqueous suspension of aluminum nanoparticles:

340 ± 210 nm


Transport of Aluminum in Sand

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Nanoparticle flow through a 7 cm sand (60 mesh) column at a rate of 0.05 mL / minute.


Transport of Aluminum in Soil

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Nanoparticle flow through a 7 cm soil column at a rate of 0.05 mL / minute.


Transport of Gold Nanoparticles in Sand

• Aluminum nanoparticles bind strongly to sand until sand is saturated

• Even higher retention rates are demonstrated when looking at transport in soil

• Rate dependent transport effects are observed• Transport is complicated by oxidation of aluminum

nanoparticles in water


Conclusions and Future Directions

• Further studies will use precisely fabricated nanoparticles where a single variable is changed for each run (size, shape, surface chemistry, etc.)

• Transport dependence on flow rates, pH, TOC, conductivity, and particle loading levels will be investigated

• Develop models to link nanoparticle characteristics to transport dynamics.


Acknowledgements

Eglin AFB:

Tonya SavageMitch Bogle

AF SBIR Phase II Contract: FA8651-06-C0136

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