The fiber biopersistence is an important factor in estimating the carcinogenicity and fibrogenicity of fibers. In order to explore the biopersistence of Japanese glasswools in the lung, we examined the clearance of deposited fibers in fibers-exposed rat lungs. The tested fibers were glasswools of GFA10 and GFA20 used conventionally in Japan, and CM44 as the control. Values of KNB (Index of Solubility) of GFA10, GFA20 and CM44 were 28.4, 30.3 and 26.74 respectively. Rats were exposed to 2 mg of each fiber intratracheally and sacrificed at 1, 3 days, 2 and 4 weeks after the instillation. The whole lung from the rat was ashed by O2 plasma reactor. The number of recovered fibers longer than 20 μm in rat lungs was counted using scanning electric microscope (SEM) , and the clearance half-times of fibers were calculated by single exponential regression of the fibers. The clearance half-times of fibers with length > 20 μm for GFA10, GFA20 and CM44 from the lung were 9, 8, and 6 days, respectively. The half-times of all glasswools are shorter than 40 days of the clearance half-times in short term biopersistence test by intratracheal instillation regulated by Directive 97/69/EU. SEM microphotographs revealed that recovered fibers had a rough surface and some thin fibers were curled as fibers with high solubility. Taken together, we established the short term biopersistence test by intratracheal instillation, and these data suggested that 2 Japanese glasswools might be biosoluble fibers in the lung.
