Culturable bioaerosols along an urban waterfront are primarily associated with coarse particles

Abstract

The source, characteristics and transport of viable microbial aerosols in urban centers are topics of significant environmental and public health concern. Recent studies have identified adjacent waterways, and especially polluted waterways, as an important source of microbial aerosols to urban air. The size of these aerosols influences how far they travel, their resistance to environmental stress, and their inhalation potential. In this study, we utilize a cascade impactor and aerosol particle monitor to characterize the size distribution of particles and culturable bacterial and fungal aerosols along the waterfront of a New York City embayment. We seek to address the potential contribution of bacterial aerosols from local sources and to determine how their number, size distribution, and taxonomic identity are affected by wind speed and wind direction (onshore vs. offshore). Total culturable microbial counts were higher under offshore winds (average of 778 CFU/m3 ± 67), with bacteria comprising the majority of colonies (58.5%), as compared to onshore winds (580 CFU/m3 ± 110) where fungi were dominant (87.7%). The majority of cultured bacteria and fungi sampled during both offshore winds (88%) and onshore winds (72%) were associated with coarse aerosols (>2.1 µm), indicative of production from local sources. There was a significant correlation (p < 0.05) of wind speed with both total and coarse culturable microbial aerosol concentrations. Taxonomic analysis, based on DNA sequencing, showed that Actinobacteria was the dominant phylum among aerosol isolates. In particular, Streptomyces and Bacillus, both spore forming genera that are often soil-associated, were abundant under both offshore and onshore wind conditions. Comparisons of bacterial communities present in the bioaerosol sequence libraries revealed that particle size played an important role in microbial aerosol taxonomy. Onshore and offshore coarse libraries were found to be most similar. This study demonstrates that the majority of culturable bacterial aerosols along a New York City waterfront were associated with coarse aerosol particles, highlighting the importance of local sources, and that the taxonomy of culturable aerosol bacteria differed by size fraction and wind direction.

Concentrations and Size Distributions of Bacteria-Containing Particles over Oceans from China to the Arctic Ocean

“…Prospero et al [19] found that NSBCP concentrations were 2-3 orders of magnitude lower in selectively sampled marine air than those sampled at an island only a short distance inland. Montero et al [11] reported that the offshore and onshore total culturable microbial counts were 778 CFU m −3 and 580 CFU m −3 , respectively. Because different sources can cause microbial composition to be different and marine bacteria grow selectively on saline growth media, these previous reports may not meaningfully account for bacteria from ocean waters.…”

“…At present, however, the concentrations and size distributions of airborne bacteria in different regions of the Earth are not well characterized [2]. Most studies on the concentrations of airborne bacteria have been carried out in continental areas, with a handful in coastal regions [6][7][8][9][10][11]. There are only a few studies measuring bacterial concentrations in marine air, and even fewer over polar waters [12,13].…”

Concentration and Size Distribution of Culturable Bacteria in Ambient Air during Spring and Winter in Gliwice: A Typical Urban Area

“…For example Montero et al [47] reported that during summer season wind speed and total coarse bioaerosols were significantly correlated. Wind velocity is clearly associated with the release and dispersal of spores, although its effect varies according to its intensity and the height at which it is recorded.…”

Onshore Wind Speed Modulates Microbial Aerosols along an Urban Waterfront

“…As found by Lighthart et al [65] and discussed by Montero et al [10], once a microbial aerosol is produced, a vertical downwind size fractionation should occur as larger particles settle out more quickly than smaller particles. Given the 3+ km fetch over Flushing Bay and NY Harbor waters, this should result in a decrease in urban terrestrial and background aerosol contributions in waterfront samples, and an increased representation of local aquatic bacteria.…”