The National Institute for Occupational Safety and Health (NIOSH) is deeply engaged in scientific research and development activities pertinent to nanotechnolo-gies, and has been particularly proactive in identifying research needs and helping to fill them . NIOSH maintains an exceptionally well-designed website devoted exclusively to nanotechnology *
One of the most useful NIOSH initiatives is the issuance of an updated version of its October 2005 document entitled Approaches to Safe Nanotechnology: An Information Exchange with NIOSH. NIOSH intends the document to review what is currently known about nanoparticle toxicity and control but notes that it "is only a starting point ." According to NIOSH, the document serves as a request from NIOSH to occupational safety and health practitioners, researchers, product innovators and manufacturers, employers, workers, interest group members, and the general public "to exchange information that will ensure that no worker suffers material impairment of safety or health as nanotechnology develops . Opportunities to provide feedback and information are available throughout this document " The document is available on the Internet at http://www cdc gov/niosh/topics/nanotech/safenano/ pdfsZapproaches_to_safe_nanotechnology.pdf.
A summary of findings and key recommendations includes the following:
• Nanomaterials have the greatest potential to enter the body if they are in the form of nanoparticles, agglomerates of nanoparticles, and particles from nanostructured materials that become airborne or come into contact with the skin
• Based on results from human and animal studies, airborne nanomaterials can be inhaled and deposited in the respiratory tract; and based on animal studies, nanoparticles can enter the bloodstream, and translocate to other organs
• Experimental studies in rats have shown that equivalent mass doses of insoluble ultrafine particles (smaller than 100 nm) are more potent than large particles of similar composition in causing pulmonary inflammation and lung tumors in those laboratory animals Toxicity may be mitigated
* See http://www. cdc . niosh . gov/niosh/topics/nanotech .
by surface characteristics and other factors, however Results from in vitro cell culture studies with similar materials generally are supportive of the biological responses observed in animals
• Cytotoxicity and experimental animal studies have shown that changes in the chemical composition, structure of the molecules, or surface properties of certain nanomaterials can influence their potential toxicity.
• Studies in workers exposed to aerosols of manufactured microscopic (fine) and nanoscale (ultrafine) particles have reported lung function decrements and adverse respiratory symptoms; however, uncertainty exists about the role of ultrafine particles relative to other airborne contaminants (e g , chemicals, fine particles) in these work environments in causing adverse health effects
• Engineered nanoparticles whose physical and chemical characteristics are like those of ultrafine particles should be studied to determine if they pose health risks similar to those that have been associated with the ultrafine particles
• Although insufficient information exists to predict the fire and explosion risk associated with nanoscale powders, nanoscale combustible material could present a higher risk than coarser material with a similar mass concentration given its increased particle surface area and potentially unique properties due to the nanoscale
• Some nanomaterials may initiate catalytic reactions, depending on their composition and structure, that would not otherwise be anticipated from their chemical composition alone
Nanomaterial-enabled products such as nanocomposites and surface coatings, and materials comprised of nanostructures such as integrated circuits, are, according to NIOSH, unlikely to pose a risk of exposure during their handling and use . Some of the processes (formulating and applying nanoscale coatings) used in their production may lead to exposure to nanoparticles, however Processes generating nanomaterials in the gas phase, or using or producing nanomaterials as powders or slurries/suspensions/solutions pose the greatest risk for releasing nanoparticles 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
The following workplace tasks, according to NIOSH, may increase the risk of exposure to nanoparticles:
• Working with nanomaterials in liquid media without adequate protection (e g , gloves) will increase the risk of skin exposure
• Working with nanomaterials in liquid during pouring or mixing operations, or where a high degree of agitation is involved, will lead to an increased likelihood of the formation of inhalable and respirable droplets
• Generating nanoparticles in the gas phase in non-enclosed systems will increase the chances of aerosol release into the workplace
• Handling nanostructured powders will lead to the possibility of aerosolization .
• Maintenance on equipment and processes used to produce or fabricate nanomaterials or the clean-up of spills or waste material will pose a potential for exposure to workers performing these tasks .
• Cleaning of dust collection systems used to capture nanoparticles can pose a potential for both skin and inhalation exposure .
• Machining, sanding, drilling, or other mechanical disruptions of materials containing nanoparticles can potentially lead to aerosolization of nanomaterials
Until more information becomes available on the mechanisms underlying nanopar-ticle toxicity, NIOSH believes that it is uncertain as to what measurement technique should be used to monitor exposures in the workplace Current research indicates that mass and bulk chemistry may be less important than particle size and shape, surface area, and surface chemistry (or activity) for nanostructured materials Many of the sampling techniques available for measuring airborne nanoaerosols vary in complexity but can provide useful information for evaluating occupational exposures with respect to particle size, mass, surface area, number concentration, composition, and surface Unfortunately, presently relatively few of these techniques are readily applicable to routine exposure monitoring
Regardless of the metric or measurement method used for evaluating nano-aerosol exposures, NIOSH believes that it is critical that background nanoaerosol measurements be conducted before the production, processing, or handling of the nanomaterial/nanoparticle . When feasible, personal sampling is preferred to ensure an accurate representation of the worker's exposure, whereas area sampling (e.g ., size-fractionated aerosol samples) and real-time (direct reading) exposure measurements may be more useful for evaluating the need for improvement of engineering controls and work practices
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