Pulmonary clearance of fibrous and angular SiC particulates in the sheep model of pneumoconiosis.

Both angular and fibrous SiC (carborundum) particulates can be emitted by SiC production operations. Carborundum pneumoconiosis is now recognized as an occupational lung disease with specific pathological features. These were previously reproduced in the sheep model of pneumoconiosis with fibrous SiC but not with angular SiC. To further document this question, the pulmonary retention in the sheep of the two morphological types was studied. Animals were injected in the tracheal lobe with equal mass (100 mg) of particulates prepared from SiC materials taken in the field. Particles were measured by analytical transmission electron microscopy in samples of bronchoalveolar lavage fluids (BAL) obtained at months 2, 4, 6 and 8 after the injection. They were also measured in samples of lung parenchyma obtained at month 8. Measurements in BAL and in lung samples both indicated a much lower retention for fibrous than for angular SiC. The retention rate in lung parenchyma at month 8 was 30 times lower for fibrous SiC. The half-life of decrease of concentrations was 3.4 times shorter for fibrous SiC. Other data in the literature support the notion that fine fibres are cleared more effectively than coarser angular particles.