1. mined both by intrinsic properties of fibers (5) it is very difficult to determine the
2. and extrinsic chemical modifications of degree of biopersistence necessary for fiber
3. fibers in the tissue milieu. Biological mask- carcinogenicity. Longer exposures will
4. ing of fibers by proteins and other biomol- increase the probability of a carcinogenic
5. ecules in vivo can inactivate even persistent response but very short exposures still may