Quantification of respirable, thoracic, and inhalable quartz exposures by FT-IR in personal impactor samples from construction sites.

The classification of quartz as a group I human carcinogen by the International Agency for Research on Cancer (IARC) highlights the need to develop a method to assess quartz exposures in the thoracic and inhalable particle size fractions to supplement the current method for the respirable size fraction. Heavy and highway construction operations can produce high respirable quartz exposures, but inhalable and thoracic exposures have not previously been well characterized. These larger particle size fractions may well contribute to the elevated cancers of the buccal cavity, throat, and GI tract in occupational cohorts of construction workers. A description is provided of the application of FT-IR for quartz analysis of personal cascade impactor air samples collected from highway construction sites. Separate calibration curves were generated for each stage of the four-stage personal impactor by using the impactor to sample quartz dust (Min-U-Sil 5 and Min-U-Sil 30) in an aerosol-generating loop. In addition, three separate calibration curves were generated using filters spiked with bulk Min-U-Sil 5, Min-U-Sil 30, and SRM 1878a (a respirable standard from NIST). The results showed that bulk Min-U-Sil 5 and SRM 1878a calibrations were identical and accurately estimated the respirable quartz fraction. Bulk Min-U-Sil 30 underestimated quartz in stages 1, 2, and 3 by 46 percent, 38 percent, and 18 percent, respectively. Using a respirable standard (bulk Min-U-Sil 5 or SRM 1878a) to quantify the larger particle sizes underestimated quartz in stages 1, 2, and 3 by 73 percent, 72 percent, and 63 percent, respectively. Until a standard reference material for quartz is developed for the larger particle sizes, the method described here, with some modifications, can be used to provide estimates of these biologically relevant particle size fractions. The results of this study also reaffirmed the need to collect narrow ranges of particle size in order to minimize quantification errors, since the FT-IR and XRD instrumental response is particle size-dependent.