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After several decades of human spaceflight, the community of space-faring nations has accumulated a diverse and sometimes harrowing history of toxicological events that have plagued human space endeavors almost from the very beginning. Some lessons have been learned in ground-based test beds and others were discovered the hard way - when human lives were at stake in space. From such lessons one can build a risk-management framework for toxicological events to minimize the probability of a harmful exposure, while recognizing that we cannot predict all possible events. Space toxicologists have learned that relatively harmless compounds can be converted by air revitalization systems into compounds that cause serious harm to the crew.

Airborne dust, suspended inside a space vehicle or in future celestial habitats, can present a serious threat to crew health if it is not controlled. During some Apollo missions to the moon, lunar dust brought inside the capsule caused eye irritation and breathing difficulty to the crew when they launched from the moon and reacquired “microgravity.” During Shuttle flights reactive and toxic dusts such as lithium hydroxide have created a risk to crew health, and fine particles from combustion events can be especially worrisome. Under nominal spaceflight conditions, airborne dusts and particles tend to be larger than on earth because of the absence of gravity settling. Aboard the ISS, dusts are effectively managed by high efficiency filters, although floating dust in newly-arrived modules can be a nuisance.

Environmental monitoring of microbial contaminants is important for crew health and assessing functionality of engineering systems. Routine monitoring of air and surfaces on the International Space Station found Staphylococcus spp. to be the most common bacterial species whereas Aspergillus spp. were the most common fungi. The levels of microbial contaminants in the air and surfaces were typically low and within the acceptability limits. Bacterial levels in the potable water from the hot water port were uniformly low. Levels in water from the warm port and the SVO-ZV water distribution system exceeded acceptability limits on occasion. Methylobacterium spp. And Ralstonia spp. were the bacteria most commonly isolated from the potable water systems. The space environment, stress, and other factors may also diminish the host immune system. The status of antimicrobial functions of neutrophils and monocytes was determined by flow cytometry.

To mitigate risk to crew health, the microbial surveillance of the quality of potable water sources of the International Space Station (ISS) has been ongoing since before the arrival of the first permanent crew. These water sources have included stored ground-supplied water, water produced by the Shuttle fuel cells during flight, and ISS humidity condensate that is reclaimed and processed. In-flight monitoring was accomplished using a self-contained filtering system designed to allow bacterial growth and enumeration during flight. Upon return to Earth, microbial isolates were identified using 16S ribosomal gene sequencing. While the predominant isolates were common Gram negative bacteria including Ralstonia eutropha, Methylobacterium fujisawaense, and Sphingomonas paucimobilis, opportunistic pathogens such as Stenotrophomonas maltophilia and Pseudomonas aeruginosa were also isolated.

A combustion products analyzer (CPA) was built for use on the Shuttle in response to several thermodegradation incidents during early flights. When the Toxicology Laboratory at Johnson Space Center (JSC) began to assess the air quality monitoring needs for the International Space Station (ISS), the CPA was the starting point for the design of a thermodegradation event monitor. The final product was significantly different from the CPA and was named the “compound specific analyzer-combustion products” (CSA-CP). One major change from the CPA was the replacement of the hydrogen fluoride sensor with an oxygen sensor. The focus of this paper will be the CSA-CP oxygen sensor’s ground testing, performance on ISS, and reduced pressure testing in response to a need on ISS.

The active control of problematic microbial populations aboard spacecraft, and within future lunar and planetary habitats is a fundamental Advanced Life Support (ALS) requirement to ensure the long-term protection of crewmembers from infectious disease, and to shield materials and equipment from biofouling and biodegradation. The development of effective antimicrobial coatings and materials is an important first step towards achieving this goal and was the focus of our research. A variety of materials were coated with antibacterial and antifungal agents using covalent linkages. Substrates included both granular media and materials of construction. Granular media may be employed to reduce the number of viable microorganisms within flowing aqueous streams, to inhibit the colonization and formation of biofilms within piping, tubing and instrumentation, and to amplify the biocidal activity of low aqueous iodine concentrations.

For long duration space flights, wastewater from humidity condensate, urine, and used hygiene water will be recycled to provide an adequate supply of potable quality water for the crew. Due to the diverse nature and multiple sources of contaminants entering the recycling system, it is a challenge to maintain the quality of product water such that no adverse health effects occur. NASA Johnson Space Center in cooperation with the Committee on Toxicology of the National Research Council (NRCCOT) has developed a science-based approach, taking into consideration space flight induced factors, to derive Spacecraft Water Exposure Guidelines (SWEG) for 1, 10, 100, 1000 days of consumption. This paper will discuss the ongoing process of setting SWEGs, how candidate chemicals were chosen for risk assessment, and how various toxicological data are collected and interpreted. Our goal is to help environmental engineers understand how the SWEGs they use for hardware design are developed.

The Toxicology Laboratory at Johnson Space Center (JSC) had provided the combustion products analyzer (CPA) since the early 1990s to monitor the spacecraft atmosphere in real time if a thermodegradation event occurred aboard the Shuttle. However, as the operation of the International Space Station (ISS) grew near, an improved CPA was sought that would include a carbon monoxide sensor that did not have a cross-sensitivity to hydrogen. The Compound Specific Analyzer-Combustion Products (CSA-CP) was developed for use on the International Space Station (ISS). The CSA-CP measures three hazardous gases, carbon monoxide, hydrogen cyanide, and hydrogen chloride, as well as oxygen. The levels of these compounds in the atmosphere following a thermodegradation event serve as markers to determine air quality. The first permanent ISS crew performed the CSA-CP checkout operations and collected baseline data shortly after arrival aboard the ISS in December 2000.

Experiences during the Shuttle and NASA/Mir programs illustrated the need for a real-time volatile organic analyzer (VOA) to assess the impact of air quality disruptions on the International Space Station (ISS). Toward this end, a joint development by the Toxicology Laboratory at Johnson Space Center and Graseby Dynamics (Watford, UK) produced a 1st generation VOA that has been delivered and is ready for the first 5 years of ISS operation. Criteria for the selection of the 1st generation VOA included minimizing the size, weight, and power consumption while maintaining analytical performance. Consequently, a VOA system based upon gas chromatography/ion mobility spectrometry (GC/IMS) was selected in the mid-90’s. A smaller, less resource-intensive device than the 1st generation VOA will be needed as NASA looks beyond ISS operations. During the past three years, efforts to reduce the size of ion mobility spectrometers have been pursued.

The monitoring of trace pollutants in spacecraft air is essential to protect the crew from harmful exposures. Monitoring requirements are focused on those sources of pollutants that pose the highest risk to crew health. Deciding which sources pose the greatest risk is done based on years of experience with the Space Shuttle, and more recently with the Russian Mir space station. Combustion of nonmetallic materials associated with electric circuits or heat-generating devices poses the greatest risk to crew health. Major leaks of fluids from systems or payloads also pose a significant risk. Other potential risks include accumulation of metabolites, entry of propellants, and excess offgassing, especially in modules that have been sealed for long periods.

The microgravity environment of space introduces a major new variable for consideration that will affect the design and operation of bioreactors. Adequate aeration for aerobic bioreactors will be a challenge as will gas/liquid separation, removal of carbon dioxide and other bacterial metabolic waste products, control algorithms, and overall performance assessment. These challenges must be addressed in order to fully assess the efficacy of biological approaches to the recovery of potable water from wastewater in microgravity. The first step in this process is to define the fermentation parameters of the organism or consortia that will be used in these space bioreactors. This study was designed to investigate the ability of bacteria to degrade the space station detergent IGEPON.

The Crew Health System (CHeCS) plays a pivotal role in monitoring the life-support activities that maintain space station environmental quality and crew safety. Sampling hardware will be used in specific protocols to monitor the microbial dynamics of the closed spacecraft environment. NASA flight experience, ground-based studies, consultations with clinical and environmental microbiologists, and panel discussions with experts in engineering, flight-crew operations, microbiology, toxicology, and water quality systems all have been integral to the revision of in-flight microbial standards. The new standards for air and internal surfaces differentiate between bacterial and fungal loads, unlike previous standards that relied on total microbial counts. Microorganisms that must not be present in air or water or on surfaces also are listed.

One of the proposed methods for monitoring the microbial quality of the water supply aboard the International Space Station is membrane filtration. We adapted this method for space flight by using an off-the-shelf filter unit developed by Millipore. This sealed unit allows liquid to be filtered through a 0.45 μm cellulose acetate filter that sits atop an absorbent pad to which growth medium is added. We combined a tetrazolium dye with R2A medium to allow microbial colonies to be seen easily, and modified the medium to remain stable over 70 weeks at 25°C. This hardware was assembled and tested in the laboratory and during parabolic flight; a modified version was then flown on STS-66. After the STS-66 mission, a back-up plastic syringe and an all-metal syringe pump were added to the kit, and the hardware was used successfully to evaluate water quality aboard the Russian Mir space station.

Controlling microbial growth and biofilm formation in spacecraft water-distribution systems is necessary to protect the health of the crew. Methods to decontaminate the water system in flight may be needed to support long-term missions. We evaluated the ability of iodine and ozone to kill attached bacteria and remove biofilms formed on stainless steel coupons. The biofilms were developed by placing the coupons in a manifold attached to the effluent line of a simulated spacecraft water-distribution system. After biofilms were established, the coupons were removed and placed in a treatment manifold in a separate water treatment system where they were exposed to the chemical treatments for various periods. Disinfection efficiency over time was measured by counting the bacteria that could be recovered from the coupons using a sonication and plate count technique. Scanning electron microscopy was also used to determine whether the treatments actually removed the biofilm.

Clinical-microbiological investigations are an important aspect of the crew health stabilization program. To ensure that space crews have neither active nor latent infections, clinical specimens, including throat and nasal swabs and urine samples, are collected at 10 days (L-10) and 2 days (L-2) before launch, and immediately after landing (L+0). All samples are examined for the presence of bacteria and fungi. In addition, fecal samples are collected at L-10 and examined for bacteria, fungi and parasites. This paper describes clinical-microbiological findings from 144 astronauts participating in 25 Space Shuttle missions spanning STS-26 to STS-50. The spectrum of microbiological findings from the specimens included 25 bacterial and 11 fungal species. Among the bacteria isolated most frequently were Staphylococcus aureus, Enterobacter aerogenes, Enterococcus faecalis, Escherichia coli, Proteus mirabilis and Streptococcus agalactiae.

We evaluated the ability of a 3% (8800 μM) solution of hydrogen peroxide to kill 12 strains of bacteria and 12 strains of fungi. A 1:4 dilution of 3% H2O2, equivalent to 1100 μM, was lethal to all the tested strains. If the situation calls for a nonaggressive disinfectant without residue or toxic aftereffects, 3% H2O2 seems an ideal choice.

Space flight and related factors such as stress appear to have an adverse effect on astronauts' immune systems. The presence of potentially pathogenic microbes including several genera of fungi reported from spacecraft environment may be a cause of concern in such situations. In order to study the role of such organisms in causing opportunistic or allergic diseases in crewmembers, we have tried to develop an animal model. BALB/c mice were suspended upside down for varying periods of time to induce stress, and their lymphocyte functions were evaluated. These studies indicate that the stress resulted in lowered mitogen induced lymphocyte stimulation as represented by 3H-thymidine uptake. We have also studied the ability of these animals to respond to Aspergillus fumigatus spores. The results of the study clearly demonstrate a definite down-regulation in T-cell proliferation and a higher incidence of infection with A. fumigatus.

Reference cultures of 16 microorganisms obtained from the American Type Culture Collection and four clinical isolates were used in standardized solutions to inoculate 60 cards for each test strain. A set of three ID and three susceptibility cards was processed in the Vitek AutoMicrobic System (AMS) immediately after inoculation. The remaining cards were refrigerated at 4°C, and sets of six cards were removed and processed periodically for up to 17 days. The preinoculated AMS cards were evaluated for microorganism identification, percent probability of correct identification, length of time required for final result, individual substrate reactions, and antibiotic minimal inhibitory concentration (MIC) values. Results indicate that 11 of the 20 microbes tested withstood refrigerated storage up to 17 days without detectable changes in delineating characteristics. MIC results appear variable, but certain antibiotics proved to be more stable than others.

Two simulated spacecraft water systems are being used to evaluate the effectiveness of iodine for controlling microbial contamination within such systems. An iodine concentration of about 2.0 mg/L is maintained in one system by passing ultrapure water through an iodinated ion exchange resin. Stainless steel coupons with electropolished and mechanically-polished sides are being used to monitor biofilm formation. Results after three years of operation show a single episode of significant bacterial growth in the iodinated system when the iodine level dropped to 1.9 mg/L. This growth was apparently controlled by replacing the iodinated ion exchange resin, thereby increasing the iodine level. The second batch of resin has remained effective in controlling microbial growth down to an iodine level of 1.0 mg/L. Scanning electron microscopy indicates that the iodine has impeded but may have not completely eliminated the formation of biofilm.

With the restructure and funding changes for Space Station Freedom, the Environmental Health System (EHS)/Microbiology Subsystem revised its scheduling and operational requirements for component hardware. The function of the Microbiology Subsystem is to monitor the environmental quality of air, water, and internal surfaces and, in part, crew health on board Space Station. Its critical role shall be the identification of microbial contaminants in the environment that may cause system degradation, produce unsanitary or pathogenic conditions, or reduce crew and mission effectiveness. EHS/Microbiology operations and equipment shall be introduced in concert with a phased assembly sequence, from Man Tended Capability (MTC) through Permanently Manned Capability (PMC). Effective Microbiology operations and subsystem components will assure a safe, habitable, and useful spacecraft environment for life sciences research and long-term manned exploration.