MINERAL DUST RETAINED IN LUNG TISSUE OF RESIDENTS REFLECTS AMBIENT PM10 MINERALOGY IN FRESNO, CALIFORNIA

Most of California has not attained state standards for particulate matter with an aerodynamic diameter ≤10 µm (PM₁₀), a combination of coarse and fine (PM_2.5) particles that can accumulate in the respiratory system associated with adverse health effects. Airborne soil particles are major components of summer and fall PM₁₀ in Fresno, located in California’s San Joaquin Valley Air Basin, where some of state's highest annual average concentrations of PM₁₀ and PM_2.5 have been measured. The purpose of this study was to examine the mineralogical composition and spatial distribution of retained inorganic dust in the lungs of deceased individuals who were not known to have pulmonary disease and had lived in Fresno, an area with elevated ambient PM.

We analyzed mineral particles in ashed lung samples from 30 subjects using SEM, energy-dispersive X-ray analysis (EDXA), X-ray diffractometry (XRD), and in situ dust in lung sections by polarized light microscopy (PLM) and electron probe microanalysis (EPMA). We identified dust particles in the lungs of all 30 subjects. Mineral groups confirmed by XRD were quartz, plagioclase feldspar, potassic feldspar, and biotite-like layer silicate. Layer silicates and quartz were each present in 27 of 30 cases, and feldspars were present in all cases. Accumulations of in situ dust were observed around blood vessels, in dust macules (accumulations of dust-laden macrophages), and in the transitional zone between conduction and gas exchange areas. Particles in macules were all ≤3 µm in one dimension, with variable mineralogy (i.e., quartz, feldspars, and layer silicates). Mineral composition of dust in lung tissue was similar to PM₁₀ sampled during field agricultural operations in Fresno County. This similarity may be due to insufficient clearance of inhaled particles from the lungs after repeated and prolonged exposures to elevated concentrations of PM from the environment.