UC Davis

The air pollution of the California Central Valley is composed of a complex mixture of gases and particles arising from a diverse number of sources. Exposure to air pollution is especially prevalent in the agricultural professions in Fresno County, California with the exposure of workers to dust and other airborne particles, which can cause pneumoconiosis and fibrosis. This thesis includes a literature review predominantly from publications coming from the Pinkerton laboratory, as well as an observational research project that expands on the research previously completed on coroner cases from the Fresno Medical Examiner’s office and in collaboration with students in the Forensic Science Graduate Program at the University of California, Davis. The literature review follows four articles specifically related to the Fresno, CA coroner cases that explore the relationship between particles and the evolution of lung pathology. Furthermore, a fifth article shows how particle size and density affect deposition in different airway generations with an emphasis on first generation respiratory bronchioles using a mathematical model. The research shows a strong correlation between fibrotic severity and the relative score of particles present. All other correlations examined demonstrated no statistically significant differences. The research for this study was limited due to a relatively small sample size of 30 cases for histological assessment, thus reducing statistical power. Nevertheless, prior studies demonstrated strong implications for the effects of black and birefringent particles on the severity of fibrosis. The objective of the present study was to explore the potential differences in particle retention and fibrotic severity between the upper and lower lung lobes as a means to better determine the importance of particle retention and lung tissue remodeling and fibrosis.The literature review of the Fresno coroner cases studied, formed the basis for this thesis research, which explores the pathological differences between the upper and lower lung lobes and its relationship to tissue particle retention. An pulmonary pathologist with extensive expertise graded the lung tissue samples using a semi-quantitative scale between 0 and 3. The pathologist graded 107 cases based on black particle retention, birefringent particle retention, and fibrotic severity. A student t-test revealed that the upper lung lobe had a significantly higher average for severity in all three variables, compared to the lower lung lobe. After comparing the upper and lower lung lobes, the cases with the highest severity were selected for analysis in the same fashion to determine if the trend was still present for high severity cases (n=30). The results of this analysis demonstrated the trend to also be present for these samples of greater particle retention and fibrosis. These findings demonstrate a statistically significant difference in particle retention and the degree of fibrosis between the upper and lower lobes of the human lung following chronic occupational and environmental particulate exposure.