Abstract
Due the rapid expansion of frac sand production, local residents, community leaders, and state regulatory authorities have expressed concerns regarding the lack of ambient respirable crystalline silica concentration data for areas near to these facilities. Long-term average data are needed to compare the fence line concentrations against chronic reference exposure guidelines such as the one adopted by the California Office of Environmental Health Hazard Assessment (OEHHA). This paper provides comprehensive sets of 24 h respirable crystalline silica concentration measurements compiled during multi-year sampling programs at the fence lines of four Wisconsin facilities—three frac sand mines and one frac sand processing plant. The authors adapted Environmental Protection Agency (EPA) reference method PM2.5 filter-based samplers to provide respirable (PM4) filter samples. Crystalline silica content of the PM4 particulate matter samples was measured using National Institute of Occupational Safety and Health (NIOSH) Method 7500 X-ray diffraction. The respirable crystalline silica limit of quantification was 0.31 µg/m3. The geometric mean (GM) respirable crystalline silica concentrations at the fence lines of the frac sand-producing facilities were less than 10% of the 3.0 µg/m3 California OEHHA chronic exposure level and were consistent with background concentrations throughout the upper Midwest of the U.S.
Highlights
OEHHA has adopted a 70-year chronic reference exposure level (REL) for ambient respirable (PM4) crystalline silica [1]
To help compile data for direct comparison to the OEHHA REL, Richards and Brozell [2] developed an ambient PM4 crystalline silica sampling method that combined the high volume sampling capability of PM2.5 reference method samplers meeting the requirements of 40 Code of Federal Regulations (CFR) Part 50, Appendix L [3] with the sensitive crystalline silica analytical capabilities provided by the X-ray diffraction (XRD) analysis procedures in National Institute of Occupational Safety and Health (NIOSH)
The primary focus in this study was on the comparison of long-term average respirable crystalline silica concentrations at the fence lines of frac-sand producing facilities and the OEHHA chronic exposure REL
Summary
OEHHA has adopted a 70-year chronic reference exposure level (REL) for ambient respirable (PM4) crystalline silica [1]. OEHHA defined the REL as an ambient concentration below which adverse, non-cancer health effects are not anticipated. In 2005, when OEHHA published the ambient respirable crystalline silica REL, no technique for direct measurement was available. To help compile data for direct comparison to the OEHHA REL, Richards and Brozell [2] developed an ambient PM4 crystalline silica sampling method that combined the high volume sampling capability of PM2.5 reference method samplers meeting the requirements of 40 CFR Part 50, Appendix L [3] with the sensitive crystalline silica analytical capabilities provided by the X-ray diffraction (XRD) analysis procedures in NIOSH
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