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

Abstract

Particulate matter emissions from agricultural livestock operations contain both chemical and biological constituents that represent a potential human health hazard. The size and composition of these dusts, however, have not been well described. We evaluated the full size distribution (from 0 to 100 μm in aerodynamic diameter) and chemical/biological composition of inhalable dusts inside several Colorado dairy parlors. Four aerodynamic size fractions (<3, 3-10, 10-30, and >30 μm) were collected and analyzed using a combination of physiochemical techniques to understand the structure of bacterial communities and chemical constituents. Airborne particulate mass followed a bimodal size distribution (one mode at 3 μm and a second above 30 μm), which also correlated with the relative concentrations of the following microbiological markers: bacterial endotoxin, 3-hydroxy fatty acids, and muramic acid. Sequencing of the 16S-rRNA components of this aerosol revealed a microbiome derived predominantly from animal sources. Bacterial genera included Staphlyococcus, Pseudomonas, and Streptococcus, all of which have proinflammatory and pathogenic capacity. Our results suggest that the size distribution of bioaerosols emitted by dairy operations extends well above 10 μm in diameter and contains a diverse mixture of potentially hazardous constituents and opportunistic pathogens. These findings should inform the development of more effective emissions control strategies.

Figure 1.

Milking parlor configurations: (a) parallel and (b) rotary used at the dairy operations that participated in this study. Reprinted/adapted with permission from ref . Copyright 2013 Taylor & Francis.

Figure 2.

Average size distributions of inhalable particles and their microbial enrichment: (a) total PM mass by gravimetry; (b) muramic acid and (c) 3-hydroxy fatty acids by mass spectroscopy; (d) endotoxin by recombinant factor c assay. Error bars represent standard deviations taken across independent sampling days. The y-axis represents the mass.

Figure 3.

Type and source attribution of common bacterial aerosols from dairy milk parlors: (a) bacteria were traced largely to animal feces, as well as bird and human-associated sources; (b) relative bacterial abundance was comparable across different parlor types with Staphylococcus, Streptococcus, and Pseudomonas as the predominant genera; (c) heat map showing unique fingerprints of bacteria were identified by source including known pathogens with potential for antibiotic-resistance. The color key and histogram represent the distribution of the relative abundance (via counts) of the OUT at the genus level. Each square is proportional to the counts of operational taxonomic units (normalized to an even sequencing depth). The taxa shown in this plot were associated with varying degrees of counts. The color yellow represents low abundant taxa, while dominant taxa are shown in red.

Figure 4.

Heat map of the abundance of the top 25 OTUs differentiating bacterial enrichment by aerodynamic diameter of inhalable bioaerosols. For this analysis, one set of IESL v2 samples was analyzed to demonstrate that the bioaerosol microbiome spans the entire inhalable fraction. The color of each square is proportional to the counts of OTUs as stated in Figure 2.

Figure 5.

Magnesium (Mg), aluminum (Al), silicon (Si), and calcium (Ca) were identified by single-particle analysis using SEM-EDS. Elemental maps of single particles illustrate the presence of these chemical elements based on color density: (A) PM30–100; (B) PM10–30; and (C) PM03–10. An elemental map is not shown for particles smaller than 3 μm due to strong background signals of fluorine from the PTFE afterfilter.