11 Raman Spectroscopy to Monitor Short-Term and Transient RCS Aerosol Exposure

Abstract Exposure to respirable crystalline silica (RCS) at concentrations at or below the OSHA permissible exposure limit (PEL) of 50 µg/m3 are challenging to monitor with the current industry standard methods X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). In particular, the assessment of short-term or transient exposure to RCS concentration calls for more sensitive analytical methods that are able to quantify RCS from low dust amounts within the desired uncertainty limits. Here, we present results from a verification study of a Raman spectroscopy-based Identifier system including dedicated respirable air samplers (badges) for the collection of airborne RCS. The air sampling badges concentrate the analyte onto dedicated 1 mm2 collection membranes suitable for direct-on-filter (DOF) Raman analysis. The sampling efficiency of the badges was assessed experimentally and shown to closely adapt the respirable sampling convention according to ISO 7708, with a low sampler bias of < 10%. Using a fully automated Raman-based bench-top reader, the limit of detection (LOD) and limit of quantification (LOQ) were determined empirically with 0.1 and 0.3 µg, respectively. The limits are approx. an order of magnitude lower than for the current industry standards and enable the relevant monitoring of short-term or transient exposure of workers to RCS, as they typically occur in construction or mining environments. The optimized workflow of the Identifier system makes it an attractive alternative to the industry standards XRD and FTIR, with the opportunity to monitor exposure down to the action level.