Length-dependent retention of fibres in the pleural space

Introduction When considering the potential risks to human health associated with the use of carbon nanotubes (CNT) and indeed other forms of high-aspect-ratio nanoparticles (HARN), the comparison has been drawn to asbestos (1, 2) and the pandemic of disease its use has caused across the globe. Therefore, when considering the potential health effects of exposure to carbon nanotubes, it would seem sensible to look at the health effects caused by exposure to asbestos. The most common diseases associated with asbestos exposure involve the lung or the surrounding serosal tissues of the pleural and peritoneal cavities. Within the lung, the most common of these effects include lung fibrosis, or asbestosis, and lung cancer whilst within the pleural space these are mesothelioma, pleural plaques and pleural effusions. The formation of lung disease such as asbestosis after respiratory exposure to a toxic material is readily explicable, as the dose is presented to the lung and this leads to an adverse effect. However, disease of the pleura after respiratory exposure to pathogenic fibres is interesting as it suggests an interaction between the inhaled material and the pleurae. There are indeed causes of the pathologies mentioned above other than fibre exposure, such as trauma (pleural plaques (3)), tuberculosis (pleural plaques (3), effusions (4)) and heart failure (pleural effusions (5)). However, mesothelioma is a rare tumour of the pleura/peritoneal space which has seen a rise in its incidence in countries where asbestos mining/use has been substantial (6). This link between exposure to pathogenic fibres such as asbestos and the fibrous zeolite mineral erionite and the development of mesothelioma is now well established (7). This raises the question of what is driving the generation of such disease pathologies and, based on the simple idea of cause and effect, one would assume that an interaction between pathogenic fibres, or some intermediate, and the pleural environment is likely. This shall be the basis for this chapter.