High aspect ratio nanomaterials pose an asbestos-like hazard to the pleural mesothelium.

High aspect ratio nanomaterials (HARN) have a high ratio of length to width, are nanoscale in two dimensions and may be made from a wide range of elements and compounds. The increasing use and diverse applications of HARN in the nanotechnology industry has led to increased risk of exposure of workers during manufacturing processes. Their fibrous structure make HARN industrially useful materials however it is also the basis for their similarity to asbestos, raising concern that the pathogenic properties of asbestos may be mimicked. In particular the unique hazard posed to the pleural mesothelium by asbestos has made the development of mesothelioma in response to exposure to HARN a major concern.
Utilising a model of direct instillation into the pleural cavity of mice we assessed the acute and chronic inflammatory responses to a panel of HARN including carbon nanotubes (CNT), nickel nanowires (NiNW) and silver nanowires (AgNW) and compared the responses to long and short asbestos fibres and nanoparticulate controls. Results showed a length-dependent pathogenicity for all types of HARN tested, consistent with the asbestos controls. We further explored the likely mechanisms by which length-dependent pathogenicity might occur at this key site and identified the threshold length for fibre-induced pleural pathogenicity.
In order to streamline the risk assessment process, the EU funded project, GRACIOUS aims to generate a highly innovative science-based Framework to enable practical application of grouping, leading to read-across and classification of nanomaterials (NM). The results of these pleural studies may be incorporated into a hypothesis-driven intelligent testing strategy which will underpin the rationale for grouping of morphologically similar HARN. Application of the GRACIOUS Framework will allow movement away from the case-by-case risk assessment paradigm, thereby improving the efficiency of risk analysis and decision making for safer design of quality NM.