Biological and physical characterization of aerosols generated in showers
Although drinking water treatment facilities treat raw water sources to remove and inactivate microorganisms, some microorganisms will survive treatment and enter the distribution system. Regrowth and infiltration in distribution systems leads to the presence of diverse microbial communities in drinking water at residential taps. In the shower environment, these microorganisms might be present in the bulk water, within biofilms in the plumbing or on shower surfaces. Shower microbial communities are important to investigate because this environment might subject the occupant to microbial exposure risks through inhalation, ingestion, and skin contact. The goal of this research was to investigate the biological and physical characteristics of aerosols generated during shower operation. Specifically, this research sought to (1) identify potentially pathogenic and allergenic microbial species in residential showers, (2) determine the contribution of tap water to shower bioaerosols, and (3) determine the effects of air exchange rate and shower water temperature on shower bioaerosols, particulate concentrations, relative humidity, and ambient temperature. This study yielded several key findings. The allergenic fungal species Alternaria alternata was detected in shower aerosols in a residential shower in Austin, TX, and in a residential shower in San Antonio, TX, but it was not found in water or shower surface biofilms from these two showers. In addition, Mycobacteria was found in the Austin, TX, residential shower. However, quantitative real-time polymerase chain reaction (qPCR) indicated that the opportunistic human pathogens that make up the Mycobaterium avium complex were not present at this residence to the detection limit of 29 gene copies/µL. Experiments run in a recirculating experimental shower indicate that tap water is more diverse and contains substantially different communities than do shower bioaerosols. However, it was not evident from the experiments conducted whether tap water significantly impacted the composition of the bioaerosol communities present during shower operation. Nevertheless, particle concentration monitoring suggests that shower occupants are exposed to a 10× increase in inhalable particulate concentrations during shower operation as compared to before shower operation. Additionally, the concentration of particles in air during shower operation increases with decreasing air exchange rate. Finally, it was determined that increasing shower water temperature from 25 to 40˚C increased the relative humidity in the shower unit by over 10% and ambient temperature by ~5˚C during shower operation. The work reported in this thesis adds to our understanding of the shower microbiome and provides suggestions for further research on the topics presented.