An ultrastructural study of acute and long-term lung response to commercial diatomaceous earth

The acute pulmonary effects of intratracheally instilled particles of calcined diatomaceous earth were found to include a pronounced neutrophil invasion of the bronchioles by 4 h after exposure which remained well developed through 1 day post-exposure. The number of macrophages and neutrophils in the alveoli continued to increase through 1 day post-exposure and remained above control values through 7 days post-exposure. The number of macrophages, many of which contained diatomaceous earth, remained elevated for the duration of the experiment. Most phagocytosis of the particles was carried out by macrophages, with minor participation by neutrophils. Many of the reactive macrophages in the groups with post-exposure periods longer than 2 h showed various types of pathological alterations. A few particles were found in type I epithelial cells. Oedematous changes were observed in some type I epithelial cells and proliferation of type II epithelial cells was evident in some alveoli, particularly those near the respiratory bronchioles. Mild diffuse fibrosis was first observed at 6 months and was still present at 15 months but remained confined to the areas containing the diatomaceous earth.