Inhalation of amorphous silica: morphological and morphometric evaluation of lung associated lymph nodes in rats

Male Wistar rats inhaled amorphous silica (quartz glass VP 203-006) for 12 months. Animals were sacrificed after 4, 8, and 12 months of inhalation and after a post-inhalation period of additional 12 months. Morphological as well as morphometric changes of lung associated lymph nodes are studied in comparison with findings due to crystalline quartz (DQ-12) and with a control group without dust exposure. Qualitatively, the lymph node morphology of the dust exposed groups is the same. During the first months mainly small quartz-typical reaction areas occur. From 12 months severe fibroses are detectable. Relative organ weights and the total lymph node area (LNA) are increased in all dust exposed groups. After inhalation of the amorphous quarz glass, the changes seem to appear with a certain delay. But, at the end of the experiment, the morphometric parameters (quartz-typical areas (QTA) and QTA/LNA-ratio) are more enlarged after the amorphous quartz glass than after crystalline quartz DQ-12. The results show that amorphous as well as crystalline silica can lead to severe lymph node fibrosis. This indicates that occupational exposure limits for amorphous silica are generally justified.