Nanotechnology

Strategic Plan for NIOSH Nanotechnology Research: Filling the Knowledge Gaps

Appendix G. Summary of Capabilities and Gaps for Nanotechnology Measurement Methods at NIOSH

Measurement Methods is a critical topic area in the NIOSH Nanotechnology Research Center (NTRC) Strategic Plan. This reflects the fact that effective and scientifically justified measurement methods are essential to understanding, predicting, and quantifying the chemical and physical properties and the behavior and toxicity of nanomaterials. The overarching Measurement Methods goals identified in the NTRC Strategic Plan are:

1. Extend existing measurement methods. Evaluate current methods for measuring airborne mass concentrations of respirable particles in the workplace and determine whether these mass-based methods can be used as an interim approach for measuring nanomaterials in the workplace and to maintain continuity with historical methods.
   
   
2. Develop new measurement methods. Expand the currently available instrumentation by devel-oping and field testing methods that can accurately measure workplace airborne exposure concen-trations of nanomaterials using metrics associated with toxicity (e.g., particle surface area).
   
   
3. Validation of measurement methods. Develop testing and evaluation systems for compari-son and validation of sampling instruments and methods.

Meeting these goals supports success in the other nine critical topic areas of the NTRC Strategic Plan: Toxicity and Internal Dose, Risk Assessment, Epidemiology and Surveillance, Engineering Controls and Personal Protective Equipment, Exposure Assessment, Fire and Explosion Safety, Recommendations and Guidance, Communication and Education, and Applications.

In addition, the key components of the NTRC Strategic research plan have been incorporated into the five critical Environmental, Health and Safety (EHS) research areas identified by the Nanotechnology Environmental and Health Implications (NEHI) Working Group: Instrumentation, Metrology, and Analytical Methods; Nanomaterials and Human Health; Nanomaterials and the Environment; Health and Environmental Exposure Assessment; and Risk Management Methods.

Similar to NIOSH goals in the NTRC Strategic Plan, the NEHI goals in the research category of “Instrumentation, Metrology, and Analytical Methods” are:

1. Develop methods to detect nanomaterials in biological matrices, the environment, and the workplace.
   
   
2. Understand how chemical and physical modifications affect the properties of nanomaterials.
   
   
3. Develop methods for standardizing assessment of particle size, size distribution, shape, struc-ture, and surface area.
   
   
4. Develop certified reference materials for chemical and physical characterization of nanomate-rials.
   
   
5. Develop methods to characterize a nanomaterial's spatio-chemical composition, purity, and heterogeneity.

Success in the Measurement Methods activities at NIOSH will foster success in overall national program. The following sections summarize NIOSH capabilities and critical gaps in Measurement Methods as they apply to the ten NTRC critical topic areas:

Toxicity and Internal Dose: NIOSH has developed and is using a suite of biological measurement techniques to assess mechanisms of damage and health endpoints such as oxidative stress, inflammation, and fibrosis (See attached Table G-1). The ability to relate those endpoints to physical and chemical properties of the administered nanoparticles cannot rely on simple measures such as particle mass. The recent purchase and installation of a field-emission electron microscope to the NIOSH HELD facility in Morgantown has improved the capability to image nanoparticles such as gold-labeled carbon nanotubes in biological tissues. I addition, this instrument is being used to determine the size of nanoparticles sampled from an aerosol or a suspension. Evaluations of the capabilities of the new microscope are underway, including examination of reference materials obtained in collaboration with NIST. NIOSH/HELD is also determining the size of nanoparticles in suspension using a Dynamic Light Scattering Analyzer. The NIOSH field team needs similar improvements their microscopy capabilities to characterize workplace aerosols. Completion of the purchase and delivery of a new TEM/STEM to the NIOSH DART laboratories in Cincinnati will provide an improve linkage between measurement studies for toxicity and measurement studies for field team and exposure assessment studies.

Development of a graded suite of nano-reference materials is needed to support improved understanding of the mechanisms of toxicity of mixed materials. NIOSH/HELD is studing well characterized SWCNT (NASA), MWCNT (Mitsui), SnO2 and TiO2 nanospheres and nanowires (WVU), and silicon nanowires (IBM). They are also working with NIST to obtain other nanoparticles types. Recent in vitro toxicity testing at NIOSH of a raw single-walled carbon nanotube material obtained from NIST has demonstrated the uncertainties associated with assessing toxicity of a “real-world” complex mixture material. The joint NIOSH-NIST-DOE certified reference material for 200-nm diameter primary particle size beryllium oxide will be issued in early 2008.

Risk Assessment: Because occupational exposure limits have not been, and are not soon expected to be developed for nanoscale particles and nanoparticle-containing materials, NIOSH is developing proactive guidance for risk assessment and risk management that incorporates successful pharmaceutical industry approaches to the use of performance-based occupational exposure limits. Current measurement gaps to bringing together the key risk assessment factors of risk identification, exposure assessment, dose-response relationships, and human dosimetry are two-fold: lack of real-time instruments that can discriminate nanomaterials of interest and lack of actual field measurements of actual workplace conditions. Progress is unlikely on the real-time discrimination front, but there is promise in NIOSH work on an improved method to discriminate between types of carbon materials. As noted in the toxicity section, evaluation of nanomaterial properties is likely to require retrospective analyses such as microscopy. In the risk assessment area, as well as for all critical areas in the NTRC strategic plan, the opportunity to develop and validate improved measurement methods will be ongoing.

Epidemiology and Surveillance: “Who is exposed to what” is the key measurement question for epidemiology and surveillance that may be filled in part by the NIOSH study of industrial exposures to nano-metal-oxides. Based on available technologies for measuring airborne nanoparticles, the metrics of exposure are currently limited to particle number concentration, and particle size distributions based on total particle mass or number, or retrospective analysis of collected material. This gap is not soon likely to be filled. Collecting and archiving airborne total and size-selected dust samples from representative workplaces may provide a resource for future analysis.

Engineering Controls and Personal Protective Equipment: Recent experimental confirmation at NIOSH and at other research centers that nanoparticles are efficiently collected on filter media by diffusion has filled a critical gap in the understanding area of respiratory protection. These studies were enabled by aerosol generation and measurement methods for nanoscale aerosols including silver and sodium chloride. Measurement methods are being developed to assess penetration of nanoparticles through protective clothing.

Exposure Assessment: The NIOSH nanotechnology field team protocol for baseline exposure assessment involves condensation particle counting, optical particle counting, and electron microscope for particles collected on 37-mm diameter filter cassettes (See Table G-2). This protocol is currently the state of the art. The expanded field team assessment protocol involves research-grade instruments that are larger in size, heavier in weight, more susceptible to damage, more expensive, and more labor-intensive. These include scanning mobility particle sizing, lung-deposited surface area sampling, and electrical and low-pressure cascade impaction. A challenging gap to be addressed my instrument manufacturers is to improve the portability of research grade instruments. A key gap that NIOSH can address is to determine the extent to which basic measurements and research measurements can be related.

Fire and Explosion Safety: The essential measurement methods gap for fire explosion safety is the need to assemble the currently available body of information about the state of the art for assessing fire and explosion safety, both for conventional materials and for nanomaterials. NIOSH can provide a valuable contribution by bringing this information together and making it accessible to the industrial hygiene community.

Recommendations and Guidance: The key measurement methods gaps for providing recommendations and guidance are the lack of validated tools to conduct a comprehensive set of risk assessment and risk management steps. The best that can currently be done is to establish an approach that can function with limited information, and grow with improved measurement methods in the future. The draft approach under development involves a combination of proactive qualitative risk assessment and control, performance-based occupational exposure limits, and verification of the efficacy of control.

Communication and Information: An alternate way to view measurement methods goes beyond measuring properties of nanomaterials and focuses on measuring the need for an effectiveness of communication and education for nanotechnology health and safety. One view of measuring effectiveness is that it can best be done in conjunction with existing safety initiatives that begin with the similarities of concerns for nanomaterials as a subset of chemical hazards in the workplace.

Applications: Although a number of nanotechnology-enabled improvements of occupational safety and health practice have been proposed, a critical gap is that few have been catalogued and critically evaluated. An example question is whether nanosilver impregnated filters actually involve nanoparticles, and whether such filters are actually more efficacious for collection and neutralization of bioaerosols than conventional filter media.

Strategic Plan for NIOSH Nanotechnology Research:
Appendix F	Figures
Page last modified: March 4, 2008 Page last reviewed: March 4, 2008 Content Source: National Institute for Occupational Safety and Health (NIOSH)