Airborne nanostructured particles and occupational ... - Wilson Center

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Journal of Nanoparticle Research (2005) 7: 587–614 DOI 10.1007/s11051-005-6770-9

 Springer 2005

Perspectives

Airborne nanostructured particles and occupational health

Andrew D. Maynard*, and Eileen D. Kuempel Project on Emerging Nanotechnologies, Woodrow Wilson International Center for Scholars, Woodrow Wilson Plaza, 1300 Pennsylvania Ave., N.W., Washington, D.C. 2004-3027; *Author for correspondence (E-mail: [email protected]) Received 15 February 2005; accepted in revised form 25 April 2005

Key words: aerosol, ultrafine, nanoparticle, nanotechnology, nanostructured particle, health, risk, inhalation, exposure, exposure control, exposure measurement, environment

Abstract Nanotechnology is leading to the development in many field, of new materials and devices in many fields that demonstrate nanostructure-dependent properties. However, concern has been expressed that these same properties may present unique challenges to addressing potential health impact. Airborne particles associated with engineered nanomaterials are of particular concern, as they can readily enter the body through inhalation. Research into the potential occupational health risks associated with inhaling engineered nanostructured particles is just beginning. However, there is a large body of data on occupational and environmental aerosols, which is applicable to developing an initial assessment of potential risk and risk reduction strategies. Epidemiological and pathological studies of occupational and environmental exposures to airborne particles and fibers provide information on the aerosol-related lung diseases and conditions that have been observed in humans. Toxicological studies provide information on the specific disease mechanisms, dose–response relationships, and the particle characteristics that influence toxicity, including the size, surface area, chemistry or reactivity, solubility, and shape. Potential health risk will depend on the magnitude and nature of exposures to airborne nanostructured particles, and on the release, dispersion, transformation and control of materials in the workplace. Aerosol control methods have not been well-characterized for nanometer diameter particles, although theory and limited experimental data indicate that conventional ventilation, engineering control and filtration approaches should be applicable in many situations. Current information supports the development of preliminary guiding principles on working with engineered nanomaterials. However critical research questions remain to be answered before the potential health risk of airborne nanostructured particles in the workplace can be fully addressed. Disclaimer The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health

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Introduction Airborne particles are ubiquitous in the air we breathe, and have been an integral component of the earth’s atmosphere for as long as generation mechanisms such as fires, volcanic emissions, sea spray and dust re-suspension have been in existence. Natural aerosol sources are estimated as accounting for between 65% and 95% of the global aerosol mass burden of all particle sizes (Baltensperger and Nyeki, 1998). Naturally occurring processes lead to particles being generated in the nanometer size range, including gasto-particle conversion from volcanic emissions and aerosol emissions associated with trees and other plants (e.g., particle formation from terpenes). Anthropogenic sources, primarily involving combustion of fossil fuels, account for a significant proportion of nanometer–diameter aerosols in urban areas (e.g. Cass et al., 2000; Harrison et al., 2000), and many industrial processes, including welding, smelting and the use of diesel engines, lead to the production of airborne particles in the nanometer size range. In response to the continual presence of airborne particles, human lungs have developed biological mechanisms for dealing with inhaled particles of all sizes (Parent, 1992; McClellan, 2000). However, these lung clearance and defense mechanisms have limits, and airborne particles from natural and anthropogenic sources have long been recognized as a potential health risk at sufficiently high concentrations and durations of exposure. The occupational health literature is replete with examples of respiratory hazards and studies of lung diseases associated with aerosol exposures in the workplace, and modern occupational health research on airborne particles and fibers dates back many decades. Recent years have seen an increasing emphasis on the health impact of particles in the submicrometer and even nanometer size ranges in both the environment and the workplace. Events such as the London Smog episode of 1952 (Ministry of Health, 1954) have demonstrated the potentially severe health impact of inhaling fine aerosol particles and underpin recent epidemiology showing increased morbidity and mortality with exposure to particulate matter (PM) smaller than 10 lm (PM10) and 2.5 lm (PM2.5) in

diameter (Dockery et al., 1993; Schwartz and Morris, 1995; Seaton et al., 1995; Wichmann and Peters, 2000; Pope et al., 2002). At the same time, research since the 1980s has been challenging our understanding of how nanometer–diameter particles impact the respiratory system and beyond (Donaldson et al., 2000; Oberdo¨rster, 2000; Kreyling et al., 2002; Oberdo¨rster et al., 2004). The significance of this research was initially seen in the context of occupational exposures to nanometer–diameter particles formed as by-products during processes such as welding, smelting and combustion. Although never formally defined, the term ‘ultrafine particle’ found increasing use as a descriptor of airborne particles smaller than 100 nm (Brown et al., 2003). Research into the impact of occupational and environmental ‘‘ultrafine’’ particles has gained considerable attention in recent years due to the rapid development of nanotechnology – as predicted more than a decade ago: ‘‘Although at present ultrafine particles may not be of major importance at the workplace, this may change with increasing future applications and use of new-technology compounds’’ (Oberdo¨rster et al., 1992). In the 13 years since this was written, nanotechnology has more than fulfilled this prediction, with significant government, public and industry interest in the potential health and environmental impact of engineered nanomaterials being demonstrated (ETC Group, 2003; Hood, 2004; NSET, 2004; The Royal Society and The Royal Academy of Engineering, 2004). Nanotechnology is a generic term encompassing the manipulation of matter at atomic and nearatomic length scales to produce new materials, structures and devices. Nanostructured materials, including nanometer–diameter particles or nanoparticles, are defined as having at least one dimension 200 lm) (24 h following intratracheal instillation), and that proportion increased with increasing particle dose (as mass or surface area) (Oberdo¨rster et al., 1992). Much greater inflammation (measured by neutrophil cells and protein in lavage fluid) was observed for the ultrafine particles compared to the larger respirable particles. Similar results have been observed for other metals, including aluminum oxide (Al2O3) (Ferin et al., 1991), gallium oxide (Ga2O3) (Webb et al., 1986; Wolff et al., 1988), cobalt (Zhang et al., 2000), and nickel (Zhang et al., 2003). The size of nanometer–diameter particles may also allow them to more readily enter cells and cellular organelles. In a study of concentrated particles from air pollution, in human bronchial epithelial cells and mouse alveolar macrophages, the ultrafine fraction (