Salle 2, Site Marcelin Berthelot
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Silicon dioxide SiO2 is the most abundant mineral on earth. It exists mainly as crystals (quartz, cristobalite), glasses and amorphous artificial silicas. Silicon oxides are used in a wide range of applications, covering five main industrial fields: electronics and jewelry (resonators, oscillators, sensors, semi-precious stones), cosmetics and food (release of oils and perfumes, antibacterial, toothpaste, sun protection...), specialty chemicals (additions for building materials, encapsulation and release of compounds, mineral fillers in polymers and tires...), health (delivery of poorly soluble active ingredients, components of dressings and wound-healers). In their many applications, silicon dioxides can be produced or used in the form of powders with micron, submicron or even nano-sized grains. These powdered forms can also be generated by abrasion during the performance of certain trades (construction and insulation, quarry work, miners, porcelain workers, prosthetists, etc.). We therefore felt it important to take stock of current knowledge on the toxicity of SiO2 silicon dioxides. Crystalline silica powders (quartz, cristobalite) and those derived from industrial glass cause inflammation of the respiratory tract (fibrosis, oedema, lung cancer) and are cytotoxic. This cytotoxicity is due to the fact that the grinding of these crystalline silicas can create very high concentrations of surface radicals (ROS for Radical Oxygen Species), which generate strong oxidative stress. Moreover, this toxicity can be heightened by the fact that some quartz or cristobalite can be contaminated with iron, the presence of which leads to Fenton-type reactions, a further source of hydroxyl free radical formation. Amorphous silicas are often used as nanostructured powders in applications such as mineral fillers to improve rheological control and mechanical behavior, catalysts, desiccants, toothpastes and cosmetic or therapeutic vectors. These amorphous silicas are produced in large quantities (world production of amorphous silica nanoparticles was estimated at 1.3 tonnes per year in 2000), making them the most abundant synthetic nanoparticles on earth.