Scores of compounds are found in the International Space Station (ISS) atmospheric samples that are returned to the Johnson Space Center Toxicology Laboratory for analysis. Spacecraft Maximum Allowable Concentrations (SMACs) are set with the view that each compound is present as if there were no other compounds present. In order to apply SMACs to the interpretation of the analytical data, the toxicologist must employ some method of combining the potential effects of the aggregate of compounds found in the atmospheric samples. The simplest approach is to assume that each quantifiable compound has the potential for some effect in proportion to the applicable SMAC, and then add all the proportions. This simple paradigm disregards the fact that most compounds have potential to adversely affect only a few physiological systems, and their effects would be independent rather than additive. An improved approach to dealing with exposure to mixtures is to add the proportions only for compounds that adversely affect the same physiological system. For example, toxicants that cause respiratory irritation are separated from those that cause neurotoxicity or cardiotoxicity. Herein we analyze ISS air quality data according to toxicological groups with a view that this could be used for understanding any crew symptoms occurring at the time of the sample acquisition or when an on-board air quality monitor indicates high pollution. In addition, this approach could be useful in post-flight longitudinal surveys in which the flight surgeon may need to identify post-flight, follow-up medical studies because of on-orbit exposures that target specific physiological systems.
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