Crystalline silica content of natural, engineered, and synthetic stone products and their relation to silicosis policy development

Crystalline silica minerals – quartz, cristobalite, and tridymite – are hazardous when inhaled. They are at least an order of magnitude more toxic than crystalline silica-free inert mineral dusts. Workplace exposure to hazardous levels of crystalline silica is entirely preventable, yet accelerated silicosis is emerging in developed countries, from the fabrication of crystalline silica-rich natural and synthetic stone materials (including engineered stone). The Australian government responded to this crisis through legislation to first limit, and then later ban crystalline silica in engineered stone, while other governments have focused their efforts on workplace monitoring and enforcing safety regulations. To approach this issue sensibly, policymakers must know the range of crystalline silica in natural rocks, engineered stone and other synthetic stone products such as porcelain – since these materials typically contain >1 vol.% crystalline silica and are commonly fabricated by stonemasons. Workers in other industries, such as mining, tunnelling, and construction are also routinely exposed to dust containing crystalline silica from natural rocks and concrete. Here, we review and compare the crystalline silica contents of natural rocks and synthetic stone products to demonstrate the efficacy of limits on the amount of crystalline silica in products (“thresholds”) relative to other dust control measures. We review molecular-scale determinants of silica toxicity and suggest that the fabrication of alternative, and newer generations of engineered stone products may also pose a significant health risk.