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: >30, 10-30, 3-10, and <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 Staphlyococcus, Pseudomonas, and Streptococcus
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.