Nanotechnology

Approaches to Safe Nanotechnology:
An Information Exchange with NIOSH

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Guideline for Working with Engineered Nanomaterials

Engineered nanomaterials are diverse in their physical, chemical, and biological nature. The processes used in research, material development, production, and use or introduction of nanomaterials have the potential to vary greatly. Until further information on the possible health risks and extent of occupational exposure to nanomaterials becomes available, interim precautionary measures should be developed and implemented. These measures should focus on the development of safe working practices tailored to the specific processes and materials where workers might be exposed. Hazard information that is available about common materials that are being manufactured in the nanometer range (for example, TiO2) should be considered as a starting point in developing appropriate work practices and controls.

The following guidelines are designed to aid in the assessment of hazard for engineered nanomaterials and for reducing exposures in the workplace. Using a hazard-based approach to evaluate exposures and for developing precautionary measures is consistent with good occupational safety and health practices, such as those recommended by the UK Royal Society and Royal Academy of Engineers [The Royal Society and The Royal Academy of Engineering 2004].

A. Potential for Occupational Exposure

Few workplace measurement data exist on airborne exposure to nanoparticles that are purposely produced and not incidental to an industrial process. In general, it is likely that processes generating nanomaterials in the gas phase, or using or producing nanomaterials as powders or slurries/suspensions/solutions (i.e. in liquid media) pose the greatest risk for releasing nanoparticles. In addition, maintenance on production systems (including cleaning and disposal of materials from dust collection systems) is likely to result in exposure to nanoparticles if it involves disturbing deposited nanomaterial. Exposures associated with waste streams containing nanomaterials may also occur.

 The magnitude of exposure to nanoparticles when working with nanopowders depends on the likelihood of particles being released from the powders during handling. Studies on exposure to SWCNTs have indicated that although the raw material may release visible particles into the air when handled, the particle size of the agglomerate can be a few millimeters in diameter and the release rate of inhalable and respirable particles relatively low (on a mass or number basis) compared with other nanopowders; however, providing energy to the bulk dust (vortexing) generated significant levels of respirable dust [Maynard et al. 2004]. Since data are generally lacking with regard to the generation of inhalable/respirable particles during the production and use of engineered nanomaterials, further research is required to determine exposures under various conditions.

Devices comprised of nanostructures, such as integrated circuits, pose a minimal risk of exposure to nanoparticles during handling. However, some of the processes used in their production may lead to exposure to nanoparticles (for example, exposure to commercial polishing compounds that contain nanoscale particles, or exposure to nanoscale particles that are inadvertently dispersed or created during the manufacturing and handling processes). Likewise, large-scale components formed from nanocomposites will most likely not present significant exposure potential. However, if such materials are used or handled in such a manner that can generate nanostructured particles (e.g., cutting, grinding), or undergo degradation processes that lead to the release of nanostructured material, then exposure may occur by the inhalation, ingestion, and/or dermal penetration of these particles.

B. Factors Affecting Exposure to Nanoparticles

Factors affecting exposure to engineered nanoparticles include the amount of material being used and whether the material can be easily dispersed (in the case of a powder) or form airborne sprays or droplets (in the case of suspensions). The degree of containment and duration of use will also influence exposure. In the case of airborne material, particle or droplet size will determine whether the material can enter the respiratory tract and where it is most likely to deposit. Inhaled particles smaller than 10 µm in diameter have some probability of penetrating to and being deposited in the gas exchange (alveolar) region of the lungs, but there is at least a 50% probability that particles smaller than 4 µm in diameter will reach the gas-exchange region [Lippmann 1977; ICRP 1994; ISO 1995]. Particles that are capable of being deposited in the gas exchange region of the lungs are considered respirable particles.  The mass deposition fraction of nanoparticles is greater in the human respiratory tract than that for larger respirable particles. Up to 50% of inhaled nanoparticles may deposit in the gas-exchange region [ICRP 1994]. For inhaled nanoparticles smaller than approximately 30 nm, an increasing mass fraction of particles is also predicted to deposit in the upper airways of the human respiratory tract [ICRP 1994].

At present there is insufficient information to predict all of the situations and workplace scenarios that are likely to lead to exposure to nanomaterials. However, there are some workplace factors that can increase the potential for exposure.  These include:

Approaches to Safe Nanotechnology:
Potential Safety Hazards	Exposure Assessment and Characterization