[Asbestos fibres and reference values].

Biological RV for asbestos implies several problems, due to the difficult interpretation of values obtained from various biological samples (sputum, BALF, lung tissue). Therefore, it seems it advisable to refer to environmental concentrations (ERC), which are not avoidable, since asbestos is an ubiquitous contaminant. On the basis of the available studies the 1 f/L value is usually reported as the most representative, although more recent and reliable studies would indicate lower values, at least for outdoor concentrations, as determined by SEM. However, further studies are needed: standardized methods based on SEM (author's opinion) should be adopted; the accuracy of such technique is sufficient for air concentrations from 0.05-0.1 f L-1 upwards, with the advantage of lower costs and time as compared to TEM.