Investigation on the durability of man-made vitreous fibers in rat lungs

Two types of sized stonewool with median lengths of 6.7 and 10.1 um and median diameters of 0-63 and 0.85 um, and crocidolite with fibers of median length of 4.8 um and median diameter of 0.18 um were instilled intratracheally into female Wistar rats. A single dose of 2 mg in 0.3 ml saline was used for the stonewool samples and 0.1 mg in 0.3 ml saline for crocidolite. The evenness of distribution of fibers in the lung was checked by scanning electron microscopy (SEM). Five animals per group were sacrificed after 2 days, 1, 3, 6, and 12 months. After low-temperature ashing of the lungs about 200 fibers per animal were analyzed by SEM for length and diameter. The number and mass of fibers in the total lung were calculated. For the stonewool samples the decrease in the number of fibers in the lung ash followed approximately first order kinetics resulting in half times of 90 and 120 days. (Abstract truncated)