Asbestiform fibers and cleavage Fragments: Conceptual approaches for differentiation in laboratory practice and data analysis.

The respirable fractions from 46 different crushed amphibole samples were separated by water elutriation. The dimensions of approximately 200 elongate mineral particles (EMPs) longer than 5 μm in each of these fractions were measured by transmission electron microscopy (TEM). The data were used to address three questions: 1. Can amphiboles be classified on a scale that represents the level of inhalation hazard they present? 2. Can prismatic amphibole be discriminated from amphibole asbestos on the basis of EMP size distributions and concentration measurements? 3. How do different exposure indices (Phase Contrast Microscopy Equivalent (PCME), Berman & Crump protocol fibers, Chatfield extra-criteria EMPs) compare when applied to these amphibole samples? For each sample, the number of respirable EMPs longer than 5 μm per gram of respirable dust and the number of extra-criteria EMPs per gram of respirable dust were calculated. The number of respirable EMPs longer than 5 μm per gram of respirable dust and the proportion of those with dimensions associated with mesothelioma in animal studies were considered to be contributors to the inhalation hazard presented by amphibole dust. In addition to these concentration measurements, the median EMP width, median aspect ratio and the aspect ratio geometric standard deviation (GSD) were considered to be relevant parameters in discriminating prismatic amphibole from asbestiform amphibole. A plot of the aspect ratio GSD against either the concentration of respirable EMPs per gram of respirable dust, the median aspect ratio or the median width allowed discrimination. The data showed a close correspondence between exposures in terms of Chatfield extra-criteria EMPs and Berman and Crump protocol structures for all of the amphibole samples. However, although for commercial asbestos varieties exposures in terms of PCME fibers were comparable to those of the other two metrics, they greatly exceeded those for non-asbestiform amphiboles.