Occupational Medicine Implications of Exposure To

Engineered Nanoscale Particulate Matter

Rick Kelly, MS, CIH Lawrence Berkeley National Laboratory

American Chemical Society Meeting

Safety in Nanotechnology Research

THE MOLECULAR FOUNDRY

Nanoscale Science Research Center and User Facility

Free Engineered Nanoscale Particulate Matter–“Nanoparticles”

•  Not firmly attached to a surface

•  Not part of a bigger item (e.g., microchip, cell wall)

• Can result in exposure via inhalation, skin absorption or ingestion (or other nanospecific routes of exposure!)

Primarily Talking About Inorganic Nanoparticles

Bucky Ball (C60) Nanoflowers Single Wall Carbon Nanotube

Silica Whiskers Rods, Wires, Shapes Quantum Nanodots

Goals of Occupational Medicine

1.  Prevent injury and illness — Workplace (exposure) monitoring

•  Comparison to safe exposure limits —  Engineered, administrative and personal

protective controls •  Ventilation, respirators, gloves, training etc.

2.  Detect early signs & symptoms of injury or illness — Medical surveillance

3.  Intervene in disease process —  Removal from exposure —  Treatment

Why Are We Concerned?

Potential for Novel Toxicity

•  Properties of nanoscale materials may be fundamentally different from bulk materials of same composition

•  Among the new properties of nanoscale materials may be: — New toxicological properties not seen

in bulk material

Particle Size Dependent Occupational Toxicity

•  Free crystalline silica — Most toxic when <10 µm

•  Alveolar deposition •  Probably surface area

effect as well

http://www4.umdnj.edu/cswaweb/rad_teach/silicosis.html

Nanoparticles Have Been Produced Commercially for Decades

• Carbon black

• Fumed silica

• Iron oxide

• Titanium dioxide

• Aluminum oxide

• Zirconium oxide

• Asbestos

Ambient Ultrafines Are Associated With Worsening of Disease

•  Ambient fines and ultrafines are associated with increased cardiovascular and respiratory events, including death, in susceptible populations

Particulate Air Pollution and Risk of ST-Segment Depression During Repeated Submaximal Exercise Tests Among Subjects With Coronary Heart Disease

Juha Pekkanen et al 2002

Reflects myocardial ischemia

Nanoparticle Surface Area is Huge!

•  1/2 the size = 2x the surface area and 23 = 8x the number or particles

•  Approaches 100% of atoms on the surface

• www.gly.uga.edu/railsback/1121WeatheringArea.jpeg

8 1

64 512

Surface Area May Be Critical Metric

•  Toxicity of ultrafine TiO2 appears much higher than fine TiO2 per unit mass

•  Toxicity is equivalent when surface area is the exposure metric

Measured polymorphonuclear neutrophils in lung lavage fluid, an index of inflammation

Oberdorster, Int Arch Occup Environ Health. 2001 Jan;74(1):1-8.

Nanotubes Look A Lot Like Chrysotile Asbestos

www.gly.uga.edu/schroeder/geol6550/CM07.html

Two similar appearing nanofibers

•  Chrysotile asbestos (left)

•  Multiwall carbon nanotube (above)

Similar toxicity?

Asbestos and macrophage

Fiber Toxicology: Dose, Dimension & Durability

• Key factors contributing to toxicity: • Diameter < 1000 nm

• Length >5,000 nm:

• High biopersistance

• Poor pulmonary clearance

•  Carbon nanotubes can fall into this size range

•  80% of raw CNTs retained in lung at 60 days

Distribution Across Anatomical Barriers

•  Nanoparticles may go where other particles can not! — Through intact skin — Through the GI

epithelium — Through the respiratory

tract epithelium — Through the bloodstream — Up along nerve axons

from the nose to brain — Across the placenta — Through the blood-brain

barrier?

Sally Tinkle, NIEHS

Cardiovascular Toxicity of CNTs Instilled In The Respiratory Tract

•  Li Zheng of NIOSH, March 2007 - Intrapharyngeal

dosing of SWCNT in mice resulted in oxidative stress in aorta and heart tissue and damaged mtDNA in aorta

- Accelerated atherosclerosis

The Devil Is In The Details!

• Factors shown to influence CNT toxicity • Dose

• SWCNT vs. MWCNT

• Length/aspect ratio

• Manufacturing method (CVD, HIPCO, laser ablation, carbon arc)

• Catalyst residue (Ni, Y, Co, Fe)

• Degree of aggregation and methods of dispersion

• Oxidation

• Functionalization (increase or decrease toxicity)

• Species, dosing method, cell type

• CNTs may disrupt a number of standard assays of cell viability, stress and function, giving false positive or negative results

Pulmonary Toxicity: All Published Instillation/Aspiration Studies

Year Author Species Granuloma Inflamm Diffuse Fibrosis

2001 Huczko Guinea pig – No – 2004 Warheit Rat Yesa Yesb No 2004 Lam Rat Yes Yes – 2005 Muller Rat Yes Yes Yes 2005 Huczko

(Grubek-Jaworska)

Guinea pig Yes Yes Yes

2005 Shvedova Mouse Yes Yesb Yesd 2006 Mangum Rats Yes No Yes 2006 Carrero

Sanchez Mice Yes Yes –

2007 Shvedova Mice Yes Yes Yes

A = non-uniform, b = transient, c = by choking, d = progressive

Inhalation Studies

• No good published CNT inhalation studies to date!

• NIOSH has completed an inhalation study but has not released the results, pending publication

What is the Real Occupational Exposure Potential?

Raw single walled carbon nanotube material HiPCO Process

Air sampling when handling raw carbon nanotubes

Maynard, 2004

CNT Clumps In Air Sample

Raw nanotubes consist mostly of clumps and bundles of nanotubes on the micro scale, very few free nanoscale structures

Nanotube Exposure Summary

Nanotube mass concentration estimated from metals analysis is relatively low

So what is an appropriate exposure limit for CNTs?

Highest

Are CNTs Just Graphite Toxicologically?

• Actual MSDS for CNTs (May, 2007)

• Quoted PEL is for graphite!

Redacted!

Anna Shvedova from NIOSH, 2005

“…if workers are exposed to respirable SWCNT particles at the current PEL (for graphite particles) they may be at risk of developing some lung lesions.”

• Granulomatous lesion resulting from exposure to CNTs at a level ~ 20 days of inhalation at the permissible exposure limit for graphite.

Where Do We Stand for Nanoparticles?

1.  Prevent injury and illness —  Workplace (exposure) monitoring

•  No widely accepted methods, tools and analysis expensive and experimental, high background level

•  No accepted workplace exposure limits —  Engineered, administrative and personal protective controls

•  Ventilation systems, HEPA filters, respirators, gloves all work 2.  Early detection of signs or symptoms of injury or illness

—  Medical surveillance •  No accepted protocols specific to nanoparticles •  Technical basis limited

3.  Intervene in disease process —  Removal from exposure

•  Might be helpful —  Treatment

•  Unknown

Prudent Approach 1.  Prevent injury and illness

—  Workplace (exposure) monitoring •  Use simple screening tools, control banding approach

—  Engineered, administrative and personal protective controls •  Treat all engineered nanoparticles as toxic, use prudent

practices to control exposure 2.  Early detection of signs or symptoms of injury or illness

—  Medical surveillance •  Implement optional general health awareness exams •  Register and track employees with significant exposure •  Stay abreast of new toxicological findings, implement specific

health screening protocols as appropriate, perhaps on an experimental basis

3.  Intervene in disease process —  Removal from exposure

•  Very sensitive as it impacts employability —  Treatment

•  Unknown