Occupational Exposure Assessments of Nanomaterials in the USA

Laura Hodson, MSPH, CIH

Nanotechnology Research CenterEducation and Information Division

National Institute for Occupational Safety and HealthThe findings and conclusions in this presentation have not been formally reviewed by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy.

Considerations

• Realm of possible measurements• Nanomaterials with an exposure limit• Nanomaterials without an exposure limit• “Newer” sampling devices• In-depth assessments• Challenges• Practical approach to all the options

Realm of possible measurements

What metric to use?Metric Qualification

Mass Standard (NIOSH CNT and TiO2 CIB)

Surface Area Advantage for low solubility particles

Surface Chemistry Toxicological studies

Particle Number Relevance

Particle Size Translocation

Particle Shape HAR versus spheres

Nanomaterials with an exposure limit

Assessing Worker Exposure:Nanomaterials with exposure limits

NIOSH Current Intelligence Bulletins • Recommended Exposure

Limits (RELs) are mass based:300 µg/m3 for nano TiO2 1 µg/m3 for CNT and CNF

• How and where to measure

6

Sampling for Titanium Dioxide

• NIOSH Method 0600 for Respirable Dust (pre-weighed PVC filter and cyclone)– This is weighed– If > 0.3 mg/m3 analyze same filter

by NIOSH Method 7300, Metals for Titanium by ICP

• Collect a duplicate open-face sample using MCE filter (for electron micrograph)

Sampling for CNT/CNF

• NIOSH Method 5040 for elemental carbon (EC). Collect the respirable fraction (25mm quartz fiber filters with a cyclone inlet)

• Collect a second open face MCE filter sample to be analyzed by electron microscopy

• Personal breathing zone, source and background samples

Sampling for CNT/CNF– Verify elemental carbon using electron

microscopy• SEM or TEM with energy dispersive X-ray

spectrometry (EDS)• Helpful for identification ( composite matrix bound

vs. free unbound elemental carbon)• No counting convention exists

– Particle counters have limitations with fiber structures

Sampling for nanomaterials without an exposure limit

History of the initialNanoparticle Emission Assessment Technique

(NEAT)

• NEAT was developed as an initial step to semi-quantitatively evaluate emissions in nanomaterial workplaces and consists of a combination of field portable, direct-reading instrumentation (DRI) and filter-based air sampling with subsequent laboratory analysis.

• No-cost field evaluations have been available from NIOSH since 2006. We have completed over 100 site visits!

NEAT – Lessons LearnedDirect-reading Instrumentation– Background concentrations fluctuate significantly• Averaging pre- and post-task does not adequately address

background influences• Data logging would better capture and account for

background variations• Documentation of critical events is essential

– Direct-Reading Instruments alone are insufficient to adequately evaluate a worksite

Filter-Based Sampling– Need both task-based and full-shift sampling– Need both open-face cassettes and respirable cyclone inlets

Highlights of the new

Nanomaterial Exposure Assessment Technique NEAT 2.0

Key Elements of NEAT 2.0

• Pre-assessment prioritization• Field measurements• Risk management• Routine monitoring (confirmation)

Comparison of US Risk Management Approach and ISO (EU) Tiered Approach

NEAT 2.0

• Pre-assessment prioritization

• Exposure sampling (particle counters, EM samples, mass samples in personal breathing zone and area. Sometimes expanded into additional aerosol samples

• Risk management summary• Confirmation

Tiered Approach

• Tier 1- Pre-assessment information gathering

• Tier 2- Basic exposure assessment (area particle counters and EM samples)

• Tier 3- Personal breathing zone samples, mass samples, additional aerosol samples

Pre-assessment Prioritization(Similar to Tier 1)

– Process description and flow– Number of employees and job description– Safety Data Sheets or other information– Walk about to look at process, identify

possible exposure potentials– Review occupational exposure limits and

health effects. – Identify and review pertinent literature.

Photo courtesy Adrienne Eastlake, NIOSH

Field Measurements• Filter-cassette based– Elements and Electron

Microscopy (EM)– PBZ, Source/ Area, Background– Full shift and task specific– With and without cyclones– Various filter media

• Data logging with DRI’s– Source/Area and Background

Photos courtesy Adrienne Eastlake, NIOSH

Note that red font corresponds to Tier 2

Filter Media and Methods

• NMAM 7402 (Transmission Electron Microscopy) open-face cassette with Mixed Cellulose Ester filter. Scanning Electron Microscopy collection on Polycarbonate or Teflon filter

• NMAM 5040 (Elemental Carbon) respirable fraction collection with Quartz Fiber filter

• NMAM 7300 (Elements by ICP) both open-face cassette and respirable with Mixed Cellulose Ester filter

Total dust, inhalable or respirable filter samples?

• Total dust: open-face cassettes. Tells the “whole story”. Good for electron microscopy and elemental analysis.

• Inhalable: collected with a 100 µm cut size cyclone

• Respirable- collected with a 4 µm cut size cyclone. Tells what is reaching the lungs. Corresponds to NIOSH RELs for Ti02 and CNT/CNF. GK 2.69 BGI, Inc.

Mention of a trade name does not constitute endorsement

Direct Reading Instruments (DRIs)

• TSI CPC 3007 (TSI Inc., Shoreview, MN)– Condensation Particle Counter– Measures particles between 10 nm and ~ 1 µm

• TSI OPS 3330 (TSI Inc., Shoreview, MN)– Optical Particle Counter with collection filter– 16 user defined bins– Measures particles between 300 nm -10 µm

• TSI DustTrak DRX (TSI Inc., Shoreview, MN)– Optical Particle Counter with collection filter– 4 pre-determined size bins (1, 2.5, 4.0, and 10 µm)

Mention of a trade name does not constitute endorsement

Interpretation of real-time data

In- depth assessments(Corresponds to Tier 3)

• Wipe sampling• Concentration mapping• Use of advanced aerosol sampling equipment

(SMPS, FMPS, ELPI, MOUDI, Surface Area)• Complete industrial hygiene sampling (VOCs, acids, IAQ, etc.)

“Newer” sampling devices and analyses being explored in US

• Collection directly onto a EM grid (thermophoretic or electrostatic sampling)

• Taping of EM grids to filters in cassettes • Analysis of filters by dark field hyperspectral

imaging microscopy

• Zefon Personal NRD (Nanoparticle Respiratory Deposition) sampler – 300 nm cut size, elemental analysis

• PENS: Personal nanoparticle sampler

Challenges to nanomaterial exposure assessments

Challenges

• Need for portability & cost effective evaluations• Variability of incidental background

nanoparticles• There is no prescribed counting convention for

microscopy (though many are offering suggestions)

We need to be practical

“of or concerned with the actual doing or use of something rather than with theory and ideas.”

NEAT 2.0 includes a set of filter based samples and data-logging real time particle counters

Elemental Analysis

Particle Counters and Size Analyzers

Electron microscopy

To assess workers’ exposures to nanomaterials, personal breathing zone, source and background samples are all necessary

Photo credits, Laura Hodson, Chris Sparks and Adrienne Eastlake, NIOSH

Photos courtesy A Eastlake and L Hodson, NIOSH

Thanks to the NIOSH Field Team

Photos courtesy Chris Sparks, Doug Evans, NIOSH

Thank you!lhodson@cdc.gov

www.cdc.gov/niosh/topics/nanotech/