The effect of fibre size on the in vitro biological activity of three types of amphibole asbestos.

Three standard (UICC) samples of amphibole asbestos were subjected to ball-milling; the main effect of this procedure was to reduce the length of the fibres present in each sample. The numbers of fibres in unit masses, and the distribution of fibre sizes in all the samples, both parent and milled, were estimated from electron micrographs. The ability of all the samples to reduce the plating efficiency of V79-4 cells is compared, on the basis of mass, fibre number and fibre number number above various length thresholds. This biological activity of all the samples correlated best with the number of fibres above a threshold length of 6.5 micron. This is compared with the sizes of fibre previously reported to induce mesotheliomata when implanted into the pleural cavities of rats.