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EC number: 231-130-8 | CAS number: 7440-21-3
In a subchronic inhalation study of Johnston et al. (2000), rats were exposed 6h/d, 5 d/wk to 50 mg SiO2/m3of hydrophilic pyrogenic silica (Aerosil® 200, MMAD 0.81 µm) or cristobalite (MMAD 1.3 μm) 3 mg/m3 for up to 13 weeks. The lung burden was measured after 6.5 and 13 weeks of exposure and after 3 and 8 months of recovery. Lung burden after 6.5 and 13 weeks exposure was 759 and 883 μg SiO2/lung for amorphous silica, respectively, and 336 and 819 μg SiO2/lung for crystalline silica. The lower increasement between 6.5 and 13 weeks of exposure suggests a phase in which retention and elimination are in equilibrium. Lung burden of amorphous silica reduced rapidly after the exposure: three months after exposure, the lung burden was 165 μg SiO2/lung (81% reduction) and after 8 months it had decreased further to 93 μg SiO2/lung, which represents a 90% reduction. The burden of crystalline silica burden remained relatively unchanged post exposure being 658 and 743 μg SiO2/lung after 12 and 32 weeks, respectively. The authors explained the rapid clearance of amorphous silica by its better solubility
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