sate. The typical concentrations of ammonia found in humidity condensate and processed water from space habitats are shown in Table 2-2.

The U.S. Laboratory Module of the International Space Station (ISS) uses anhydrous ammonia in the external loop of the heat exchanger, and there is a remote chance that some of this ammonia could enter the internal heat-exchange loop containing water and then reach the inhabited portion of the module. Because there are many liters of anhydrous ammonia in the external loop, such a series of leaks could result in a catastrophe. If such a leak were suspected, the water-recovery systems would be stopped until the atmospheric ammonia concentration returned to nominal levels. In addition, some payload proponents want to use ammonia in the cooling of their hardware.

Ingested ammonia, like endogenously produced ammonia, is readily absorbed from the gastrointestinal (GI) tract, metabolized to urea primarily in the liver, and then excreted (as urea) mostly by the kidney. A healthy person has a high capacity for metabolizing ingested ammonia.

Bacteria in the digestive tract produce ammonium ions (NH₄⁺) from the metabolism of nitrogen-containing compounds that come from in-