Rat lung reactivity to natural and man-made fibrous silicates following short-term exposure

The inflammatory and fibrogenic potential of three naturally occurring and two man-made industrial minerals were compared. Groups of five rats each received respectively a single intratracheal instillation of saline (control), UICC chrysotile B asbestos, short chrysotile 4T30, attapulgite, xonotlite (a calcium silicate), and Fiberfrax (an aluminum silicate) at doses of 1, 5, and 10 mg. One month after the treatment, assessment of lung morphology and bronchoalveolar lavage were performed on each animal. Under these conditions, UICC chrysotile B at all doses tested (1, 5, and 10 mg) induced fibrotic lesions in bronchiolar tissues while short chrysotile 4T30 (1, 5, and 10 mg) caused focal accumulation of inflammatory cells in the alveolar structures but no apparent fibrosis. Compared to these positive reactions with different fibrogenicity, xonotlite caused minimal inflammatory reactions detectable only at high dose (10 mg) and by bronchoalveolar analysis. By contrast, the rat lung reacted more significantly to attapulgite and Fiberfrax although the tissue reaction differed considerably for these two materials. While attapulgite, at doses up to 10 mg caused minimal reactions characterized by mononuclear cell infiltration mainly in the alveolar structures, Fiberfrax at 1 mg and higher caused significant granulomatous reactions and the appearance of early fibrosis. Overall the order of lung biological reactivity observed for the various silicates was xonotlite much less than attapulgite less than short chrysotile 4T30 less than Fiberfrax less than UICC chrysotile B. These observations indicate that Fiberfrax, attapulgite, and, to a lesser extent, xonotlite are biologically active within the time span studied and potentially deleterious for lung tissue.