Silicon carbide

Endpoint summary

Description of key information

Inhalation is the only exposure route that is of concern in relation to the direct effects of SiC particles on human health. Absorption in the lung represents the main route of uptake for dust particles. Deposition of particles depends on physical and physiological factors, as well as on particle size. No specific data concern SiC non fibrous dust deposition. Once deposited in the lung, most particles are removed by various clearance mechanisms. Insoluble particles deposited on ciliated airways are generally cleared from the respiratory tract by mucociliary activity in 24-48 hours and will be swallowed in the mouth (ingestion). Clearance from the pulmonary region may occur through the action of alveolar macrophages or by alternative mechanisms. Migration through the intercellular spaces of the alveolar membrane to the lymphatic system of the lungs may occur. Clearance of insoluble particles deposited in the pulmonary region of the lung has half-times that are measured in months to years.

Additional information

The specific clearance patterns of fibrous and non-fibrous forms of silicon carbide have been examined in the sheep model (Dufresne et al., 1992; see chapter 7.1.1). Animals were exposed by slow infusion of a particulate suspension (100 ml saline containing 100 mg of particulates) in the tracheal lobe. Bronchoalveolar lavage was performed before the exposure, and 2, 4, 6 and 8 months post exposure. The lung parenchymal retention rate of exposed animals was 30 times less for fibrous than for angular silicon carbide particles, suggesting a higher reactivity of fibres. Similar observations were made by Bruch et al. (1993; see chapter 7.5.3) who compared pulmonary early retention and subsequent clearance of SiC (non-fibrous) and crystalline silica (quartz) after inhalation of 20 mg/m3 on five consecutive days during two weeks. The lowest initial retention of quartz was attributed to higher activity.