Attapulgite is a fibrous
mineral industrially consumed at the rate of over a million tons per year but the
biological activity of the material is not fully known. To evaluate the in vivo toxicity of the fibrous material, we exposed the tracheal lobe of 16 sheep to a single exposure of either 100 ml saline, 100 mg UICC
asbestos fibers in 100 ml saline, 100 mg short
asbestos fibers in 100 ml saline, or 100 mg
attapulgite in 100 ml saline. The animals were studied by bronchoalveolar lavage (BAL) at Days 2, 12, 24, 40, and 60 and by autopsy at Day 60. In the saline-exposed sheep, BAL and lung histology did not change. In the UICC
asbestos-exposed animals, we reproduced the BAL changes previously reported (R. Bégin, M. Rola-Pleszczynski, S. Massé, Y. Berthiaume, and G. Drapeau, 1985, Environ. Res. 36, 389-404). In the short
asbestos-exposed sheep, there were no significant BAL changes. In the
attapulgite sheep, we found significant and sustained increases in total BAL cells (X2, P less than 0.05), macrophages (X2, P less than 0.05), neutrophils (X5, P less than 0.01),
fibronectin (X2-3, P less than 0.05),
lactate dehydrogenase (X2, P less than 0.05),
beta-glucuronidase (X2, P less than 0.05), but BAL cellularity returned to control levels by Day 60 whereas in the UICC
asbestos-exposed sheep, it remained significantly above control. Lung histology demonstrated the characteristic peribronchiolar
fibrosing alveolitis in the UICC
asbestos-exposed sheep, whereas macrophagic alveolitis with minimal airway distortion was seen in the short
asbestos-exposed sheep and in all of the
attapulgite-exposed sheep but three which had typical peribronchiolar alveolitis quite similar to that observed in UICC-exposed sheep, but of lower intensity. In conclusion, the study documents that
attapulgite is not an inert material for lung tissue; it does produce a macrophagic and neutrophilic alveolitis in the early inflammatory phase of lung reaction with peribronchiolar involvement in some sheep. Whether or not this initial
attapulgite induced alveolitis leads to lung
fibrosis remains to be evaluated in a longer follow-up study of
attapulgite-exposed animals.