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The reaction of iodine, a potential disinfectant for use in the treatment of recycled water during long-duration manned space missions, and several organic substrates that are expected chemical constituents in a closed-loop recycle water system, yields iodinated disinfection by-products. The reactions were studied using procedures analagous to those developed by the U. S. Environmental Protection Agency for evaluation of chlorinated disinfection by-products in water. The iodinated products formed in these studies were identified using gas chromatography with both electron capture and mass spectrometric detection. Aqueous solutions of acetic acid and of dextran produce iodinated alkyl-compounds when treated with iodine, as triiodide ion, at neutral pH. Similar treatment of phenol yields iodine-substituted phenols at appreciable concentrations.

Until now, NASA's space water reuse research program has not considered the transport of water borne infectious enteric viruses; however, viral diseases probably are a significant concern in long duration space missions. To simplify monitoring and prediction of pathogen distribution, model indicator strains historically have been used. In this research, the male specific RNA coliphage MS-2 is used as a model of enteric viruses due to their similar size and biochemical composition. Inactivation of some water borne enteric viruses by iodine has previously been characterized. In this paper, iodine inactivation of the model coliphage MS-2 in buffered water is compared with earlier bench-scale disinfection survival data and with survival in iodinated simulated shower water used in a test water recycling system.

Iodine is being considered for disinfection of recycled hygiene and potable water in Space Station Freedom. Like chlorine, the halogen iodine can form disinfection by-products (DBPs) when used as a disinfectant in waters with dissolved or colloidal organic compounds. Recycled shower and laundry wastewater, urine and condensate from the space cabin atmosphere all have large amounts of dissolved and colloidal organic compounds and may generate iodinated DBP's which can be toxic to humans. We have investigated the formation of iodinated DBP's (IDP's) in model compounds typical of shower wastewater and condensate. The selection of these model compounds and flask experiments to test for IDP formation have been described. Methods for reaction, extraction and analysis for IDP's also have been developed. We have tentatively identified likely organic precursors from recycled water and several iodinated organic compounds formed during the reaction with iodine.

Investigations of iodine species distribution of various aqueous solutions of iodine disinfectants and water from equilibrated suspensions of triiodide and pentaiodide resins were done at the University of Colorado for the Center for Space Environmental Health during 1992 and 1993. Direct measurements of three individual iodine species: I-, I2 and I3-, were made. In addition three measures of total titratable iodine species were used. It has been found that I2 and I3- solutions produce a significant fraction of the non-disinfecting species iodide (I-), ranging from 50 to 80% of added iodine, respectively, at pH values of approximately 5. Correspondingly, I2 solutions produce more than twice the concentration of disinfecting iodine species per mass iodine dose than I3- solutions. Both I- and I2 species were found in aqueous extracts of pentaiodide resin, although no soluble species were detected with triiodide resin.

Water reuse is essential for long duration space missions. However, water recycle systems also provide a habitat for microorganisms and allow accumulation of chemical compounds which may be acutely or chronically toxic to mission crew members. Contaminant fate and accumulation in closed-loop water recycle systems is being investigated at the University of Colorado and Martin Marietta as part of the activities of the Center for Space Environmental Health (CSEH), a NASA Specialized Center of Research and Training (NSCORT). The water contaminant distribution research uses a scaled-down physical model of a water (shower, laundry, urine and/or condensate) recycle system to analyze for and model four “indicator” contaminants: viruses and bacteria, nitrogen species, and selected organic and inorganic compounds. The water recycle test bed is comprised of five or more individual water treatment processes linked in a closed loop, and spiked with chemical and biological contaminants.