Preparation of fractured nanoquartz: surface features and cell membrane damage

Abstract

Occupational exposure to quartz dust is associated with fatal diseases. Quartz dusts generated by mechanical fracturing are characterized by a broad range of micrometric to nanometric particles. The contribution of this nanometric fraction to the overall toxicity of quartz is still largely unexplored, primarily because of the strong electrostatic adhesion forces that prevent isolation of the nano-fraction. Furthermore, fractured silica dust exhibits special surface features, namely Nearly Free Silanols (NFS), which impart membranolytic activity to quartz. Nanoquartz can be synthetized via bottom-up methods, but the surface chemistry of those crystals strongly differs from nanoparticles resulting from fracturing. We report here a top-down milling procedure to obtain a nanometric quartz that shares with fractured quartz the key surface properties relevant to toxicity. Ball milling was optimized by coupling dry and wet milling steps, using water as a dispersing agent, and varying milling times and rotational speeds. Nanoquartz with a strong tendency to form submicrometric agglomerates was obtained. Deagglomeration with surfactants or simulated body fluids was negligible. Partial lattice amorphization and bimodal crystallite domain size were observed. A moderate membranolytic activity, which correlated with the amount of NFS, signaled coherence with previous toxicological data. Membranolytic nanoquartz for toxicological investigations was obtained.