Abstract No:
1678
Abstract Type:
Student Poster
Authors:
M Saylor1, T Peters1
Institutions:
1University of Iowa, Iowa City, IA
Presenter:
Matthew Saylor
University of Iowa
Faculty Advisor:
Thomas Peters
University of Iowa
Description:
Developing a microscopic method to quantify crystalline silica content in bulk dust samples and compare results to standard analytical methods.
Situation/Problem:
Over 2 million Americans are exposed to crystalline silica at work. Crystalline silica is incredibly hazardous and carcinogenic. Occupational exposure assessments for silica typically rely on air sampling, but bulk analysis can help identify potential hazards and air sampling strategies. Current analytical methods to measure the percentage of crystalline silica in bulk dust requires costly instruments and lengthy sample preparation. There is a need for a rapid, inexpensive method capable of quantifying crystalline silica in the field.
Methods:
This study developed and evaluated a polarized light microscopy (PLM) method to quantify crystalline silica in bulk dust. Particles were imaged under single and cross-polarized light. ImageJ was used to obtain particle metrics (area, circularity, mean RGB) from these images; and a custom Python script was used to match RGB to relative retardation, then calculated particle size, birefringence, and estimated silica and non-silica mass. Percent crystalline silica was calculated using the ratio of crystalline silica particle mass to total particle mass. The calculations require key assumptions, including constant particle density, spherical particle shape, and averaged RGB values. Spatial calibration was conducted with a stage micrometer. Retardation was adjusted with a polymer retarder. Mass percent silica from the new PLM method was compared with established analytical techniques (gravimetric bulk mixing, X-ray diffraction (XRD), and Fourier-transform infrared spectrometry (FTIR)) for four bulk dusts (talc, feldspar, amorphous silica, and Arizona Road Dust). Talc, feldspar, and amorphous silica were mixed 50:50 by mass with quartz to generate known percent silica content. The ARD was analyzed as received. Five samples of each dust were analyzed by each method (20 samples per method). The XRD and FTIR samples were analyzed by accredited laboratories. Method comparison included paired t-tests of percent silica between PLM analysis and bulk composition estimates. A two-way ANOVA assessed differences in percent crystalline silica across analytical method and dust type, and statistically significant results were evaluated using Tukey's HSD to identify differences.
Results / Conclusions:
Percent crystalline silica by mass determined with the PLM method most closely aligned with expected values from gravimetric mixing. We found statistically significant difference in percent crystalline silica between the PLM method and gravimetric bulk mixtures for each dust without stratification by method. The two-way ANOVA also confirmed differences between percent silica, by method and dust mixture. However, the Tukey test revealed that percent silica estimates across all methods differed significantly from one another, except silica identified from PLM method and that from the gravimetric bulk estimates, indicating alignment of PLM method and gravimetric mixing. Moreover, the PLM method performed more consistently with the computed gravimetric bulk mixture than XRD or FTIR. These findings demonstrate the potential for PLM to be a reliable method to quantify crystalline silica in bulk samples, making it suitable for future field technique using low-cost compact microscopes or smartphone-based PLM attachments.
Core Competencies:
Chemical Sampling and Instrumental Analysis
Secondary Core Competencies:
Risk Assessment
Choose at least one (1), and up to five, (5) keywords from the following list. These selections will optimize your presentation's search results for attendees.
Asbestos, lead, and dust
Labs – Health & Safety, Testing
Based on the information that will be presented during your proposed session, please indicate the targeted audience practice level: (select one)
Professional: Professional is a job title given to persons who have obtained a baccalaureate or graduate degree in IH/OH, public health, safety, environmental sciences, biology, chemistry, physics, or engineering or who have a degree in another area that meets the standards set forth in the next section, Knowledge and Skill Sets of IH/OH Practice Levels, and has had 4 or more years of practice. One significant way of demonstrating professional competence is to achieve certification by a 3rd party whose certification scheme is recognized by the International Occupational Hygiene Association (IOHA) such as the Board of Global EHS Credentialing (BGC).
Was this session organized by an AIHA Technical Committee, Special Interest Group, Working Group, Advisory Group or other AIHA project Team?
No
Are worker exposure data and/or results of worker exposure data analysis presented?
No
How will this help advance the science of IH/OH?
This method we have developed may be a reliable way to quantify crystalline silica with a rapid, low-cost procedure. The method, combined with other research, could potentially be used in a field analysis of crystalline silica with compact mobile forms of microscopy. This could provide a way to conduct rapid exposure assessment in the field without waiting for laboratory analysis or paying for the high costs.
Have you presented this information before?
No
I have read and agree to these guidelines.
Yes