An assessment of the fibrogenic potential of very short 4T30 chrysotile by intratracheal instillation in rats.

Three groups of five rats each received, respectively, a single intratracheal instillation of saline (control), 5 mg of UICC chrysotile B asbestos, and 5 mg of a preparation of very short chrysotile fibers (4T30, 100% less than 8 micron) isolated by a sedimentation procedure. At various intervals after the treatment (1 to 60 days), assessment of lung morphology was performed on each animal. Although the two types of chrysotile fibers have similar chemical composition, structure, and surface charge, the lung tissue reaction differed considerably. Lungs of animals exposed to UICC chrysotile B showed significant pathological alterations as early as 7 days following treatment. The lesions were localized in and around terminal bronchioles and consisted of inflammatory cells, fibroblasts and collagen deposition which distorted and obstructed small airways. Reaction to very short 4T30 chrysotile fibers was quite distinct. Seven days after treatment, lungs of these animals showed alveolar and interstitial accumulation of inflammatory cells. The alveolitis persisted 60 days after treatment and no fibrosis was apparent. It appears that very short 4T30 chrysotile fibers are much less fibrogenic than UICC chrysotile B and that intratracheal instillations in rats may represent a useful mean of rapidly assessing the fibrogenic potential of various dusts. These observations support the concept that fiber length is an important factor for fibrogenicity of asbestos.