CLUSTERING OF ASBESTOS FIBERS IN CELL-DAMAGE - A PERCOLATIONAL PERSPECTIVE

In vitro researches on rat cells exposed to several types of thin asbe stos fibres show a saturation in cytotoxicity as one increases the fib re concentration n on the cell surface. For given average fibre length s, the saturation occurs at values that are 2-3 times the critical con centration n(c) for a percolative arrangement of randomly thrown stick s on a surface. Measurements of the threshold for genotoxic damage giv e concentrations that are about O.1n(c). One expects that, somewhere b etween these concentrations, large scale ''critical fluctuations'' wil l be observed in the data. These fluctuations are indeed seen in chrys otile treated rat pleural mesothelial cells, exhibiting DNA damage and chromosomal-number aberrations. We hypothesize that at such concentra tions that fibre-clustering occurs, the fibres lock together and are h indered from traversing the cell membranes and internalizing. Some dam age processes are thereby impeded. The kinetics of internalization is worked out with models involving continuum percolation. Pieces of evid ence from in vivo results that support the theory are noted.