Multi-instrument assessment of fine and ultrafine titanium dioxide aerosols

ABSTRACT

The measurement of fine (diameter: 100 nanometers–2.5 micrometers) and ultrafine (UF: < 100 nanometers) titanium dioxide (TiO₂) particles is instrument dependent. Differences in measurements exist between toxicological and field investigations for the same exposure metric such as mass, number, or surface area because of variations in instruments used, operating parameters, or particle-size measurement ranges. Without appropriate comparison, instrument measurements create a disconnect between toxicological and field investigations for a given exposure metric. Our objective was to compare a variety of instruments including multiple metrics including mass, number, and surface area (SA) concentrations for assessing different concentrations of separately aerosolized fine and UF TiO₂ particles. The instruments studied were (1) DustTrak™ DRX, (2) personal DataRAMs™ (PDR), (3) GRIMM^TM, and (4) diffusion charger (DC). Two devices of each field-study instrument (DRX, PDR, GRIMM, and DC) were used to measure various metrics while adjusting for gravimetric mass concentrations of fine and UF TiO₂ particles in controlled chamber tests. An analysis of variance (ANOVA) was used to apportion the variance to inter-instrument (between different instrument-types), inter-device (within instrument), and intra-device components. Performance of each instrument-device was calculated using root mean squared error compared to reference methods: close-faced cassette and gravimetric analysis for mass and scanning mobility particle sizer (SMPS) real-time monitoring for number and SA concentrations. Generally, inter-instrument variability accounted for the greatest (62.6% or more) source of variance for mass, and SA-based concentrations of fine and UF TiO₂ particles. However, higher intra-device variability (53.7%) was observed for number concentrations measurements with fine particles compared to inter-instrument variability (40.8%). Inter-device variance range(0.5–5.5%) was similar for all exposure metrics. DRX performed better in measuring mass closer to gravimetric than PDRs for fine and UF TiO₂. Number concentrations measured by GRIMMs and SA measurements by DCs were considerably (40.8–86.9%) different from the reference (SMPS) method for comparable size ranges of fine and UF TiO₂. This information may serve to aid in interpreting assessments in risk models, epidemiologic studies, and development of occupational exposure limits, relating to health effect endpoints identified in toxicological studies considering similar instruments evaluated in this study.

Graphical abstract

KEYWORDS:

• Real-time instruments
• aerosol mass concentration
• aerosol number concentration
• aerosol surface area concentration
• particle morphology

Acknowledgments

The authors would like to thank Christopher Coffey and Matthew Duling for reviewing this manuscript.

Disclosure statement

The findings and conclusions in this report are those of the author(s) and do not necessarily represent the official position of the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention (CDC). Mention of any company or product does not constitute endorsement by NIOSH, CDC. In addition, citations to websites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of these websites. All web addresses referenced in this document were accessible as of the publication date.

Data availability statement

Data inquiries can be directed to Anand Ranpara, [email protected].

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15287394.2022.2150730

Additional information

Funding

This work was supported by internal funding from the National Institute for Occupational Safety and Health (NIOSH) and external funding from the National Institutes for Health (NIH).