Thesis
A method to determine percent crystalline silica by mass of bulk dust using polarized light microscopy
University of Iowa
Master of Science (MS), University of Iowa
Spring 2026
DOI: 10.25820/etd.008290
Abstract
Crystalline silica is a Group 1 human carcinogen that causes silicosis, lung cancer, and other chronic diseases in workers across mining, construction, and foundry industries. Current standard methods for quantifying crystalline silica in bulk dust include X-ray powder diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR). The methods are accurate but require expensive instrumentation, extensive sample preparation, and laboratory settings that limit accessibility in field or low-resource settings.
This study developed and compared a polarized light microscopy (PLM) method as a rapid, low-cost alternative for quantifying crystalline silica mass percentage in bulk dust samples. The method uses PLM imaging paired with ImageJ and a custom Python script to extract particle area, circularity, and RGB values, which were used to calculate equivalent-volume diameter, birefringence, and estimated particle mass. Particles with birefringence within ±0.0016 of 0.004 as concluded by a sensitivity analysis, were classified as crystalline silica, and their mass fraction of total particle mass was reported as percent crystalline silica. The method was evaluated against four bulk dusts: talc, feldspar, amorphous silica, and Arizona Road Dust. The talc, feldspar, and amorphous silica were mixed at known ratios with Min-U-Sil® 5 quartz.
PLM results were compared to the gravimetric bulk mixes and to XRD and FTIR analyses. A paired t-test showed PLM and gravimetric values agreed for two of the four dust mixtures. Two-way ANOVA and Tukey post-hoc testing revealed significant differences among all method pairs except PLM versus gravimetric. When stratified, PLM agrees with the gravimetric mixes more than the other analytical methods. The PLM method can offer a promising alternative that is inexpensive, rapid, and accurate. Future research can adapt to filter-based respirable samples, implement with a mobile microscopy method, and generally improve the equipment for improved accuracy and precision.
Details
- Title: Subtitle
- A method to determine percent crystalline silica by mass of bulk dust using polarized light microscopy
- Creators
- Matthew Saylor
- Contributors
- Thomas Peters (Advisor)Patrick O'Shaughnessy (Committee Member)Jin Pan (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Occupational and Environmental Health
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008290
- Publisher
- University of Iowa
- Number of pages
- x, 64 pages
- Copyright
- Copyright 2026 Matthew Saylor
- Language
- English
- Date submitted
- 04/28/2026
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 35-40).
- Public Abstract (ETD)
- Crystalline silica is a natural mineral found in rock, sand, and soil. Workers in industries like mining, construction, and manufacturing are regularly exposed to silica dust when they cut, drill, or disturb these materials. Breathing in small silica particles can cause serious and permanent lung diseases, including silicosis and lung cancer. Because these diseases develop slowly over years, it is important to monitor silica exposure in workplaces before harm occurs. Currently, the best tools for measuring how much crystalline silica is in a dust sample require expensive laboratory equipment and highly trained staff. This makes regular monitoring difficult for smaller worksites or resource-limited settings. This study developed a new, low-cost method to measure crystalline silica in bulk dust samples using a polarized light microscope, an instrument that causes crystalline silica particles to glow with distinctive colors under special lighting conditions. A camera attached to the microscope captures images of the particles, and custom software identifies which particles are crystalline silica based on how they interact with light. The software then estimates the mass of those particles to calculate the percentage of crystalline silica in the sample. The entire process takes about 30 minutes and costs roughly $10 per sample. Standard methods typically take longer and are much more expensive to analyze. The new method was tested against established laboratory techniques and performed favorably. When compared between standard methods, the new method was the only one not statistically different from the pre-measured amounts of crystalline silica. While further improvements are needed before it can replace standard methods, results suggest it could serve vi as a practical screening tool. Future work aims to adapt the method for field use with compact, low-cost microscopes, expanding access to silica monitoring for workers across many industries.
- Academic Unit
- Occupational and Environmental Health
- Record Identifier
- 9985177073202771
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