Separation of Asbestos Fibers by Length – Procedure for Obtaining Different-length Samples for Biological Experiments – [Translated]†

Abstract

A size-selective procedure has been developed in order to obtain samples of asbestos fibers of different lengths for use in biological experiments. Short chrysotile fibers less than 5 μm in length are widely suspected to be less carcinogenic than longer fibers. The bulk sample of U.I.C.C, standard asbestos (Chrysotile B) was aerosolized using a 2- component fluidized bed. It was then separated in a dry state by wire screens (200 mesh and 635 mesh) and a virtual impactor with a cut-off point of 2 μm. 0.1 g (sufficient weight for in-vitro tests) of a short-fiber fraction that passed through the wire screens and then onto the fine side of the virtual impactor, and 1.5 g of a medium fraction that passed through the 200 mesh screen but did not pass through the 635 mesh screen, were obtained from about 20 g of raw material. The length distribution of the short fiber fraction was 81% of fibers less than 5 μm long and 96 % of fibers less than 10 μm long. X-ray diffraction analysis revealed that the crystallinity of the separated chrysotile did not change markedly. The present dry and mild separation process that was developed thus successfully avoids any artificial change in the physicochemical properties of asbestos fibers.† This report was originally printed in J. Soc. Powder Technology, Japan. 27(12), 804-810 (1990) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.