Exposure Characterization of Metal Oxide Nanoparticles in the Workplace

Abstract

This study presents exposure data for various metal oxides in facilities that produce or use nanoscale metal oxides. Exposure assessment surveys were conducted at seven facilities encompassing small, medium, and large manufacturers and end users of nanoscale (particles <0.1 μm diameter) metal oxides, including the oxides of titanium, magnesium, yttrium, aluminum, calcium, and iron. Half- and full-shift sampling consisting of various direct-reading and mass-based area and personal aerosol sampling was employed to measure exposure for various tasks. Workers in large facilities performing handling tasks had the highest mass concentrations for all analytes. However, higher mass concentrations occurred in medium facilities and during production for all analytes in area samples. Medium-sized facilities had higher particle number concentrations in the air, followed by small facilities for all particle sizes measured. Production processes generally had the highest particle number concentrations, particularly for the smaller particles. Similar to particle number, the medium-sized facilities and production process had the highest particle surface area concentration. TEM analysis confirmed the presence of the specific metal oxides particles of interest, and the majority of the particles were agglomerated, with the predominant particle size being between 0.1 and 1 μm. The greatest potential for exposure to workers occurred during the handling process. However, the exposure is occurring at levels that are well below established and proposed limits.

Keywords:

• exposure
• metal oxide
• nanoparticles
• ultrafine particles
• workplace

ACKNOWLEDGMENTS

The authors would like to thank the many people involved in providing technical and administrative support for this study. Special thanks go to Kevin L. Dunn and Donnie Booher (NIOSH) for their help with equipment preparation, logistics, and sample collection, and to Shawna Watts (NIOSH) for travel preparation and logistics. The authors are indebted to Donna Olsen (IHI Environmental) for her tireless efforts in company recruitment.

Notes

^A Maximum likelihood estimates for the GM and GSD were obtained using the LIFEREG procedure due to values below the LOD.

^B Levels with the same letter are not significantly different with a level of significance of .05.

^A Levels with the same letter are not significantly different in a Tukey multiple comparison procedure with a level of significance of 0.05.

^B Calculated by subtracting the summed OPC values in 0.3 μm to 1.0 μm range from the CPC values that record particle number concentration in the 0.01μm to 1 μm range.

^A Levels with the same letter are not significantly different in a Tukey multiple comparison procedure with a level of significance of 0.05.