Investigation of the critical amounts of inhaled particles in rat lung as a cause of fibrosis

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The adverse health effect of respirable particles in working environment is thought to depend on the amounts and biopersistence of particles in lung. From the results of our rodent research, fiber amounts in lung over the critical amount (about 1 mg per lung) caused the prolongation of the biopersistence and fibrotic change.For the clarification of the critical amounts of fiber in lung, the quantitative relationship between particle amount in lung and biopersistence and pathological change were investigated using potassium octatitanate whisker by intratracheal instillation method and inhalation method. In intratracheal instillation method, 0.5, 1.0, 2.0, 5.0 mg of whisker were instilled to rat lungs. The biopersistence became longer and the pathological change became severe as the dose in lung increased. However the discrepancy between instillation results and inhalation results in the quantitative relation was observed. Then inhalation research in high concentration during 4 week was performed. The amount in lung was 1.5 mg which is almost critical amount in previous research but the prolongation in bioresistence was not observed. In order to clarify the critical amount, we need to conduct more inhalation experiments using fibers which have different physicochemical properties when the deposited amount is around 1 or 2 mg.furthermore the effect of particle shape on the adverse health effect was investigated. 2 mg of potassium octatitanate particle was instilled to rat lung and compared with the results of whisker. Particle was cleared faster and smaller pathological change than whisker. This results suggest that the particle shape is important index for adverse health effect.