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.