COMPARATIVE INVESTIGATIONS OF THE BIODURABILITY OF MINERAL FIBERS IN THE RAT LUNG

The biodurability of various glass fibers, rockwool, and ceramic fiber s was examined in rat lungs and compared with natural mineral fibers. Experiments were based on studies that have shown that the biodurabili ty of fibers is one of the essential factors of the carcinogenic poten cy of these materials. Sized fractions of fibers were instilled intrat racheally into Wistar rats. The evenness of distribution of fibers in the lung was checked by scanning electron microscopy (SEM) or careful examination of tbe fiber suspension before treatment. After serial sac rifices up to 24 months after treatment, the fibers were analyzed by S EM following low temperature ashing of the lungs. Parameters measured included number of fibers, diameter, and length distribution at the va rious sacrifice dates, so that analyses could be made of the eliminati on kinetics of fibers from the lung in relation to fiber length (F-L). Size selective plots of the fiber elimination correlated with fiber d iameters enables the mechanism of the fiber elimination (dissolution, fiber breakage, physical clearance) to be interpreted. The half-time o f fiber elimination from the lung ranges from about 10 days for wollas tonite to more than 300 days for crocidolite. The biodurability of man -made vitreous fibers (MMVF) is between these Values and is dependent on the chemical composition of the fibers and the diameter and length distribution. Results indicate that the in vivo durability of glass fi bers is considerably longer than expected from extrapolation of publis hed data on their in vitro dissolution rates.