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Spacecraft Water Exposure Guidelines for Selected Contaminants: Volume 3
it is removed into the humidity condensate or recondenses on cool surfaces only to revolatilize later when the surface warms up. Estimates made with detector tubes showed airborne concentrations up to 75 milligrams per cubic meter (mg/m3) in the Mir space station, and ground-based analyses of water samples from Mir showed concentrations up to 440 mg/liter (L) in the humidity condensate and 46 mg/L in the recycled water (Lizanna Pierre, Wyle Laboratories, personal commun., 1999). Even though EG is not used in coolant loops in the International Space Station, it has been found in the U.S. laboratory humidity condensate at concentrations up to 11 mg/L; however, it has not been detected in the potable water (John R. Schultz, Wyle Laboratories, unpublished report, January 9, 2002).
PHARMACOKINETICS AND METABOLISM
The behavior of EG after it has been ingested into the body has been generally understood for many years, but new discoveries have been reported in the past few years. The understanding of the behavior of EG has important implications for treating acute poisonings and for understanding the metabolic pathways that lead to detoxification or to production of more toxic metabolites. There are likely to be significant interindividual differences in the metabolism of EG because of genetic variations in the catalytic activity of key enzymes in the major metabolic pathway.
Fasted rats given gavage doses of EG at 6 or 9 milliliters per kilogram (mL/kg) of body weight rapidly absorbed it into the body, where it reached peak blood concentrations in 1 to 4 h (Winek et al. 1978). At lower gavage doses of about 1 g/kg, serum concentrations of EG peaked in fasted rats and dogs 2 h after the dose was administered (Hewlett et al. 1989). Likewise, at an oral dose of 0.9 g/kg, female monkeys had peak plasma concentrations of EG of about 120 milligrams per deciliter (mg/dL) 2 h after dosing (McChesney et al. 1971). Rats and mice exposed orally at up to 1,000 mg/kg rapidly and completely absorbed the dose (Frantz et al. 1996).
Evidence from clinical cases of EG poisoning suggests that its volume of distribution is about 0.5 L/kg (Jacobsen et al. 1988), which indicates distribution into the total body water. The tissue distribution of 14C from [1,2- 14C]EG given orally was similar in female Sprague-Dawley rats and in CD-1 mice when the