Assessing exposure to airborne nanomaterials: Current abilities and future requirements

For over half a century, health-related aerosol exposure measurements have been characterized in terms of the mass of material present per unit volume of air. Yet recent research has challenged the applicability of this paradigm to airborne nanometer-scale particles (nanoparticles) and nanometer-structured particles (nanostructured particles). By classifying engineered nanoparticles into categories based on physical/chemical structure, and relating these categories to health impact-relevant attributes, we have explored the applicability of different physical exposure metrics to a range of particle class/attribute combinations. Using this approach, it is clear that no single method for monitoring nanoaerosol exposure will suit all nanomaterials. Rather, there will be occasions where particle number, surface area and even mass concentration measurements will play an important role in evaluating potential impact. Correspondingly, currently available techniques to measure exposure against these three metrics are reviewed. While current methods enable aerosol concentration to be evaluated against all three metrics, most techniques are inappropriate for making routine personal exposure measurements on a regular basis. We therefore explore the idea of a universal aerosol monitor, which would enable personal exposure measurements to be collected for all three metrics simultaneously, while being inexpensive enough to encourage widespread use. Such a device would provide an economical and adaptable solution to monitoring exposure to nanostructured aerosols, as both the materials and information on the potential risks they present are developed.