Size, Composition, and Source Profiles of Inhalable Bioaerosols from Colorado Dairies

Agricultural particulate pollution is a global health risk among workers and nearby residents. This particulate matter contains a wide range of chemical and biological constituents (bioaerosols) with aerodynamic diameters consistent with the inhalable fraction. Due to sampling and analytical limitations, major gaps exist in understanding the relative contribution of large particles (i.e., 10-100 µm) and their physiological relevance in respiratory disease. We evaluated the full distribution of dairy inhalable particulate matter (IPM) using a novel high-volume cascade impactor that segregated airborne dust into four aerodynamic size fractions: &gt;30, 10-30, 3-10, and &lt;3 μm. We analyzed these size-fractionated particles using multiple chemical and biological methods, including high-throughput DNA sequencing, to better understand the heterogeneity of bioaerosols, in particular: (1) bacterial communities, (2) opportunistic pathogens, and (3) inflammatory potential. Based on particulate mass, a bimodal size distrubution was observed with one mode under 3 µm and a second mode above 30 µm. Correlations between inhalable particulate matter and bacterial chemical markers were statistically signficant indicating that large particles need to be considered during assessements otherwise a large proportion of exposure (and health outcomes) may go unnoticed. Further, bacteria in bioaerosols were derived predominantly from animal sources, but other noteworthy sources included birds, water, soil, and humans. Taxa such as <i>Staphlyococcus</i>,<i> Pseudomonas</i>, and <i>Streptococcus</i> were identified, which have important implications in infectious disease in the context of the lung and nasal microbiome. This is the first study to characterize the full size distribution of airborne particles emitted by agricultural dairy operations. The size, composition, and speciation of IPM in this study suggest that both small and large particles are of concern and more research is needed to better understand health effects in the upper respiratory system, including the nasopharyngeal region.