Release of Crystalline Silica Nanoparticles during\nEngineered Stone Fabrication

Inhalation\nexposure to respirable crystalline silica (RCS) during\nthe fabrication of engineered stone-based kitchen countertops has\nbeen on the rise in recent years and has become a significant occupational\nhealth problem in the United States and globally. Little is known\nabout the presence of nanocrystalline silica (NCS), i.e., particles\nbelow 100 nm. We present a methodology to quantify the crystalline\nsilica content in the sub-100 nm size fraction of the aerosol released\nduring engineered stone fabrication using X-ray diffraction (XRD)\nand Fourier transform infrared (FTIR) spectroscopy. Aerosol was generated\nin a test chamber designed per EN 1093-3 and sampled using cascade\nimpactors. XRD and FTIR analysis showed the presence of both α-quartz\n(15–60%) and cristobalite (10–50%) polymorphs in all\nsize fractions. With increasing particle size, the cristobalite content\nincreased. Seventy percent of the total aerosol mass in the sub-100\nnm fraction was found to be crystalline silica, qualitatively confirmed\nby electron diffraction and electron energy loss spectroscopy. The\npresence of other minerals was detected in all size fractions; no\npolymeric resin binder was detected in the sub-100 nm fraction. Although\nthe sub-100 nm fraction was about 1% of the aerosol mass, it accounted\nfor 4–24% of the aerosol surface area based on the total lung\ndeposition. If the surface area is a more relevant exposure metric,\nthe assessment of the efficacy of current engineering control systems\nusing mass as an exposure metric may not provide adequate protection.