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.农业颗粒物污染对从业者及周边居民而言是一项全球性健康风险。此类颗粒物包含多种化学与生物组分（生物气溶胶，bioaerosols），其空气动力学直径符合可吸入颗粒物的粒径范围。受限于采样与分析技术瓶颈，学界对10~100μm大粒径颗粒物的相对贡献及其与呼吸系统疾病的生理关联仍存在显著认知空白。本研究采用新型大容量级联撞击器，对奶牛场可吸入颗粒物（inhalable particulate matter, IPM）的完整粒径分布进行表征，将空气中的粉尘划分为4个空气动力学粒径分级：>30μm、10~30μm、3~10μm及<3μm。本研究采用包括高通量DNA测序在内的多种化学与生物学分析方法，对上述分级颗粒物进行检测，以深入解析生物气溶胶的异质性，具体包括：(1) 细菌群落组成；(2) 机会致病菌；(3) 炎症潜能。基于颗粒物质量浓度，本研究观测到双峰粒径分布：一个峰值位于3μm以下，另一个峰值位于30μm以上。可吸入颗粒物与细菌化学标志物之间的相关性具有统计学显著性，这表明在暴露评估中必须纳入大粒径颗粒物的考量，否则大部分的暴露情况（及对应的健康结局）可能被忽视。此外，生物气溶胶中的细菌主要来自动物源，但其他值得关注的来源还包括鸟类、水体、土壤与人类。研究鉴定出葡萄球菌属（*Staphylococcus*）、假单胞菌属（*Pseudomonas*）及链球菌属（*Streptococcus*）等分类群，这些菌群与肺部及鼻腔微生物组相关的感染性疾病具有重要关联。本研究是首个针对农业奶牛养殖场所排放的空气颗粒物完整粒径分布进行系统表征的工作。本研究中可吸入颗粒物的粒径、组成及形态特征表明，大、小粒径颗粒物均需引起重视，未来需开展更多研究以深入解析其对上呼吸道系统（包括鼻咽区域）的健康影响。