Assessing the Solubility of Silicon Dioxide Particles Using Simulated Lung Fluid

Occupational exposure to respirable crystalline silica has the ability to cause silicosis. Silica is also suspected of being associated with an increased risk of lung cancer, kidney disease, rheumatoid arthritis, and other diseases. The specific mechanism(s) of pathogenesis for silicosis and these other potential health concerns remains unclear. This investigation measured dissolution rates of silicon dioxide (SiO 2 ) particles in simulated lung fluid to determine the residence times of such particles within the intracellular or extracellular spaces. Silicon dioxide dissolution rates were determined as a function of fluid pH, particle size, and SiO 2 concentration and mass. Gamble's solution was used to simulate intracellular and extracellular lung fluids at pH 6.0, pH 6.5, and pH 7.5. Test samples were paired by pH, particle size, and SiO 2 concentration/mass. Sample aliquots of filtered solution were collected over a 28-day test period. Results revealed SiO 2 became soluble and the dissolution rate increased with increasing pH and decreasing particle size. SiO 2 concentration and mass also appeared to have some effect on the rate of dissolution. These solubility characteristics appear likely to impact the residence times of particles within biological systems, suggesting a model for exposure and subsequent pathogenesis for systemic silica-related diseases.