Mesothelioma: the aetiological role of ultrathin fibres and repercussions on prevention and medical legal evaluation
The most important knowledge that must today be taken as certain is the fact that mesothelioma is not caused, as is the case for asbestosis, by all the fibres that are inhaled, but only by the ultra-thin fraction of these fibres, having diameter of 0.2 microm and length of only a few microm. Only fibres of this class of size can cross the pulmonary-pleural barrier and are, therefore, the causal agent of mesothelioma and other benign pleural manifestations (plaques).[This] means that any assumption of the disease being avoidable must be discarded, at least up to the second half of the 1980s because until then this class of fibres, which today must be considered as the true causal agent of the neoplasm, was not visible under the optical microscope, nor could such fibres be measured or eliminated from the atmosphere of working environments. The filter materials available both for fixed ventilation systems and for individual protective masks were not able to block the ultrathin fibres and were therefore only efficacious for the prevention of asbestosis and probably pulmonary carcinoma. It was only with the use of highly efficient HEPA filters and "absolute" filters towards the end of the 1980s that efficacious protection against all size classes of respirable fibres became possible in industrial plants.