Compatibility of engineered stone materials with tetrahydrofuran processing for crystalline silica analysis by XRD

This study investigated the compatibility of Tetrahydrofuran (THF) dissolution, following the procedures outlined in NIOSH Method 7500 and the similar OSHA ID-142 method, as a sample preparation technique for respirable crystalline silica (RCS) analysis in engineered stone materials compared to the muffle furnace (MF) ashing method. Our results revealed considerable variability in RCS content across different batches of engineered stone tested, underscoring the inherent material heterogeneity in engineered stone products. A statistically significant underestimation of RCS concentrations was observed when using THF dissolution for Stone A (polyester-based) samples collected on 47 mm polyvinyl chloride (PVC) filters, particularly at lower analyte loadings. In contrast, no statistically significant differences in RCS measurement were found between THF dissolution and MF ashing for the other 3 stone types, including one laboratory-synthetic material. The observed discrepancy in Stone A is likely attributed to the interaction of THF with its polyester resin binder, leading to swelling of the filter matrix and forming a non-volatile residue. This residue may physically entrap silica particles, hindering their complete recovery and subsequent quantification by X-ray diffraction (XRD). The suitability of THF processing as a sample preparation method is therefore highly dependent on the specific composition of the engineered stone. Based on these findings, MF ashing is recommended as the more reliable and universally applicable sample preparation method for engineered stone samples, especially those containing polyester resin binders. Caution should be exercised when considering THF dissolution for RCS analysis in engineered stones due to the potential for significant underestimation of actual RCS values, which could have implications for exposure assessments and regulatory compliance.