Impacts of Microbial Growth on the Air Quality of the International Space Station

Abstract

An understanding of the various sources of non-methane volatile organic compounds (NMVOCs) is one facet to ensuring the habitability of crewed spacecraft. Even though the International Space Station (ISS) atmosphere is relatively well characterized in terms of what is in the atmosphere and approximately how much, linking the majority of these trace contaminants detected to their source is virtually impossible. Albeit a few of can be associated to a single source, the majority of these trace contaminants have their origins from multiple sources. On crewed spacecraft such as ISS, trace contaminants are broadly categorized as either coming from equipment, which includes systems and payloads, or from the metabolic processes of the crew members. Such widely encompassing categories clearly illustrate the difficulty in linking air contaminants to their source(s). It is well known that microbial growth in ISS can flourish if left unchecked. Although processes are in place to limit microbial growth, in reality, microbial growth has pervaded the habitable environment of ISS. This is simply a consequence of having crewed spacecraft, as humans are the largest contributor to the bioload. As with crew members, microbes also have metabolic processes which, in many ways, are comparable to human metabolism. As such, it can be expected that microbial growth can lead to the release of volatile organic compounds into the ISS atmosphere. Given a large enough microbial population, the impact to the air quality of ISS can be potentially large. A survey of the microbiology found in ISS will be presented as well as the possible types of volatile organic compounds that can result from such organisms. This will be correlated to the observations provided by ground-based analysis of ISS atmosphere samples

Factors affecting flavor perception in space: Does the spacecraft environment influence food intake by astronauts?

“…Further, the composition of ambient air on the ISS is routinely sampled and returned to Earth for laboratory analyses, typically via gas chromatography-mass spectrometry(GC-MS) (Limero & Wallace, 2017). Such analyses show the overall composition of gas-phase compounds (Figure 11), with methane being the largest contributor (making up 63%) F I G U R E 1 1 Composition of volatiles in a sample of ISSrecycled air, returned to Earth for detailed analysis (Macatangay & Bruce, 2010). Percentages are on a volume basis and the group of nonmethane hydrocarbons (NMHCs) second (22%) (Macatangay & Bruce, 2010).…”

“…Such analyses show the overall composition of gas-phase compounds (Figure 11), with methane being the largest contributor (making up 63%) F I G U R E 1 1 Composition of volatiles in a sample of ISSrecycled air, returned to Earth for detailed analysis (Macatangay & Bruce, 2010). Percentages are on a volume basis and the group of nonmethane hydrocarbons (NMHCs) second (22%) (Macatangay & Bruce, 2010). Within the NMHCs, alcohols contribute 76%; aldehydes, ketones, and halocarbons each account for 6%; and the remaining trace compounds comprise aromatics and esters, making up 4% and 2%, respectively.…”

“…Most of these compounds are at levels below the mean odor thresholds of humans (Nagata, 2003), thus the crew are unlikely to perceive them, with the notable exception of the aldehydes, as well as n-butanol. Calculating the DoT values based on the reported concentrations (Macatangay & Bruce, 2010) and their associated odor thresholds (as reported in Nagata, 2003), the DoTs range from 2 for acrolein to 117 for acetaldehyde (spanning propanal, butanal, pentanal, hexanal, and heptanal); by comparison, the derived DoT value for n-butanol is 1.5, that is, with a concentration only slightly above the odor threshold. In this context, two important aspects should be noted: first that odor threshold values reported in the literature vary widely (see, e.g., Leonardos, Kendall, & Barnard, 1969) whereby taking alternative literature values delivers DoT values below 1; and second, odor thresholds are not equivalent to perception thresholds, that is, the threshold at which an odor can be perceived (identified), which can be several factors higher.…”

“…Further, the composition of ambient air on the ISS is routinely sampled and returned to Earth for laboratory analyses, typically via gas chromatography–mass spectrometry(GC–MS) (Limero & Wallace, 2017). Such analyses show the overall composition of gas‐phase compounds (Figure 11), with methane being the largest contributor (making up 63%) and the group of nonmethane hydrocarbons (NMHCs) second (22%) (Macatangay & Bruce, 2010). Within the NMHCs, alcohols contribute 76%; aldehydes, ketones, and halocarbons each account for 6%; and the remaining trace compounds comprise aromatics and esters, making up 4% and 2%, respectively.…”

“…Composition of volatiles in a sample of ISS‐recycled air, returned to Earth for detailed analysis (Macatangay & Bruce, 2010). Percentages are on a volume basis…”