The aerodynamic behaviour and pulmonary deposition of carbon nanotubes

Introduction Rapid developments in the nanotechnology field have led to concerns about the possible effects on health of exposure to carbon nanotubes (CNT). It has been demonstrated that CNT have some toxicological properties in common with asbestos fibres and concerns have been voiced that exposure may lead to some of the diseases associated with exposure to asbestos. It is known that asbestos fibres are efficiently deposited in the gas exchange zone of the lung and that they can translocate to the pleural space by penetrating the visceral pleura. Recent work has suggested that such fibres are not efficiently cleared from the pleural space: they may fail to enter the stomata of the parietal pleura and this might lead to frustrated phagocytosis by macrophages moving on the surface of the parietal pleura. These ideas remain speculative, but they suggest that we should be concerned about deposition of CNT particles in the gas exchange zone of the lung. Whether aerosolised CNT particles behave in the same way as asbestos fibres in the air streams of the airways of the lung remains unknown. In this chapter we explore some of the factors that may affect their deposition. It should be noted that very little experimental work has been done in this area and that modelling the deposition of nanotubes in all the various forms in which they appear from first principles is likely to be difficult. However, the results of new work are likely to accumulate rapidly in the next few years. The ideas put forward here may provide a guide to the research that is needed; we note that these should be considered as speculative and will no doubt be refined as data accumulate. Particles, including fibres, are deposited in the lung as a result of their leaving the air streams within the pulmonary airways and coming into contact with the walls of those airways. The main physical processes governing particle behaviour are generally understood and over the past few decades a number of theoretical models have been developed to describe the transport and deposition behaviour of particles in the respiratory tract. In this chapter the application of these models to CNT is explored. Relevant experimental data are also considered. A key issue in relation to the deposition behaviour of carbon nanotubes is particle morphology, and this is where we start.