10
Total Organic Carbon

John T. James, Ph.D. NASA-Johnson Space Center Habitability and Environmental Factors Office Houston, Texas

GOALS OF A TOTAL ORGANIC CARBON STANDARD

Because NASA probably will not have the real-time capability to quantify all individual organics that might break through the water recovery system (WRS), a spacecraft water exposure guideline (SWEG) for total organic carbon (TOC) will have to serve as a first-line screening parameter for water quality. For this screening purpose, an upper limit SWEG for TOC is proposed rather than guidelines for different exposure periods, so the approach taken to estimating the SWEG is different than for individual chemicals. That approach and the assumptions made are detailed below.

Compliance with the SWEG for total organic carbon will accomplish the primary goal of ensuring, with a high degree of confidence, that the crew is not exposed to potentially harmful chemicals as they consume processed water over a period of time up to 100 days (d). TOC is the total measured mass of carbon per unit volume in a water sample minus the carbon present from carbon dioxide and bicarbonate. Secondarily, the standard may ensure that the water is readily palatable; although, the standard will not guarantee that the water will have no taste or odor. If the crew discovers that the water is not readily palatable, they can mix in flavoring or recycle it through the water recovery system. The crew should not have their water consumption discouraged by water that is not readily palatable.

We will assume that any reactions between organic carbon compounds and other components of the processed water will be limited to concentrations that do not pose an indirect health concern. For example, organic carbon may act as a substrate for microbial growth, indirectly



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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 10 Total Organic Carbon John T. James, Ph.D. NASA-Johnson Space Center Habitability and Environmental Factors Office Houston, Texas GOALS OF A TOTAL ORGANIC CARBON STANDARD Because NASA probably will not have the real-time capability to quantify all individual organics that might break through the water recovery system (WRS), a spacecraft water exposure guideline (SWEG) for total organic carbon (TOC) will have to serve as a first-line screening parameter for water quality. For this screening purpose, an upper limit SWEG for TOC is proposed rather than guidelines for different exposure periods, so the approach taken to estimating the SWEG is different than for individual chemicals. That approach and the assumptions made are detailed below. Compliance with the SWEG for total organic carbon will accomplish the primary goal of ensuring, with a high degree of confidence, that the crew is not exposed to potentially harmful chemicals as they consume processed water over a period of time up to 100 days (d). TOC is the total measured mass of carbon per unit volume in a water sample minus the carbon present from carbon dioxide and bicarbonate. Secondarily, the standard may ensure that the water is readily palatable; although, the standard will not guarantee that the water will have no taste or odor. If the crew discovers that the water is not readily palatable, they can mix in flavoring or recycle it through the water recovery system. The crew should not have their water consumption discouraged by water that is not readily palatable. We will assume that any reactions between organic carbon compounds and other components of the processed water will be limited to concentrations that do not pose an indirect health concern. For example, organic carbon may act as a substrate for microbial growth, indirectly

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 threatening crew health; conversely, the presence of disinfectants such as chlorine, and possibly iodine, can form toxic compounds in the presence of organic carbon (Miettinen et al. 1996). These considerations are mitigated by the fact that TOC will be measured in situ soon after the sample is acquired. Hence, there will be insufficient time for these secondary reactions to occur before the measurement is taken. Thus, in creating a standard, we will not attempt to compensate for microbial growth due to the presence of organic carbon, nor will we be concerned with chemical reactions that could increase the toxicity of the water. ASSUMPTIONS To meet the primary goal stated above, the WRS must be bounded, or known, in a number of ways. The input water, which can come from humidity condensate, urine, or makeup sources (e.g., water brought up from the ground or obtained through fuel cells), must be reasonably well characterized so that, knowing the elements of the processing system, one can predict the most likely organic components to break through to the product water. We will assume that the WRS will be taken offline under conditions where the load may knowingly exceed capacity or might damage the processor’s capability. For example, the WRS would not process humidity condensate immediately after a serious fire or after leakage of certain air pollutants such as ammonia from the U.S. Laboratory Module of the International Space Station (ISS). We will assume that microbial control is accomplished with iodine or silver and that there will be no mixing of the product water with other water that may have an organic residue from a biocide. Specifically, we will assume that none of the water for analysis has originated from an ethanol tincture of iodine. We will further assume that any other treatment of the post-process water will not involve an addition of organically contaminated water. For example, we will assume that the process of adding minerals does not involve the use of an organic counter ion such as formate. We will assume that any mixing in of ground-supplied water will not provide contamination from unusual pollutants (for example, pesticides and chloroform). Such additions to the product water totally confound the interpretation of the TOC measurement. Alternatively, quantification of the confounding compounds would enable the calculation of a TOC measurement that could be compared to the standard.

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 Finally, we will assume that the measurement of TOC is performed within a short period of time after the sample collection, so that there is no question about the decay of TOC as the sample is retained. For example, microbial metabolism could alter the concentration of TOC if the sample is not kept cold or treated with a biocide. The U.S. Environmental Protection Agency (EPA) requires analysis of a water sample for TOC immediately, or within 28 d if the sample is refrigerated and acidified to a pH < 2 (Clesceri et al. 1998). COMPOSITION OF ORGANIC CARBON IN RECOVERED WATER Ground-Based Testing High-fidelity, ground-based testing of a WRS can be helpful when predicting the organic components of processed water. Far more data can be obtained from these tests than from ones performed in space; the input load to the processor can be controlled, and supporting data can be taken at various points within the WRS. In addition, ground-based data can be acquired quickly before chemical concentrations such as TOC are changed by the presence of microorganisms. One such test lasted for 128 d at the Marshall Spaceflight Center and involved input from many sources, including humidity condensate, urine, and personal hygiene (Carter 1997). During the test, the nominal concentration of TOC in processed water was between 0.2 and 0.5 milligrams per liter (mg/L); however, an excursion to 1.6 mg/L was observed on day 7 when a software anomaly allowed intermediate processor water to be mixed into the product water tank. A smaller anomaly of 0.6 mg/L was noted on day 9 of the test. The average concentration of TOC during the test was 0.30 mg/L, and the TOC component averages were as follows: 2-propanol, 0.14 mg/L; acetone, 0.12 mg/L; ethanol, 0.16 mg/L; and methanol, 0.21 mg/L, accounting for 100% of the TOC concentration. The concentrations of each of these components in the water were well below concentrations that would pose a health risk. In another series of tests conducted at Johnson Space Center, humans were placed in a closed environment for up to 91 d, and water was recovered from all available sources, including condensate, urine, hygiene water, and wash water. The first phase used tap water, the second phase used physiochemical recovery, and the third phase used physio-

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 TABLE 10-1 TOC in Recovered Water Test Duration (d) Lowest TOC (mg/L) Highest TOC (mg/L) No. of Samples Taken Comments Phase I 15 0.24 0.43 2 Public water supply Phase II 30 0.10 0.24 7 Humidity condensate and reprocessed urine Phase IIa 60 0.14 0.53 51 Was most like ISS processor Phase III 91 0.06 0.29 45 Biologic recovery system added Abbreviations: ISS, International Space Station; No., number. Source: Data from Pierre et al. 2002. chemical and biologic recovery systems (Pierre et al. 2002). The TOC ranges were as shown in Table 10-1. The TOC was managed to prevent the crew from drinking water in which the concentration of TOC was above 0.5 mg/L, which was the standard at that time. Eleven times during Phase IIa, the recovered water was reprocessed because the TOC concentration exceeded 0.5 mg/L (Pierre et al. 2002). The most consistently found organic compounds during the recovery tests (Phases II, IIa, and III) were acetone, toluene, and formaldehyde. Typically, they were found at about 10 micrograms (µg) per liter or less in the samples. The percentage of identified components in the TOC concentration was very low. Other low-molecular-weight compounds found occasionally in processed water and their maximum concentrations were as follows: 2-propanol, 175 µg/L; methanol, 274 µg/L; bis-2 ethylhexyl phthalate, 28 µg/L; methyl sulfone, 54 µg/L; oxalate, 410 µg/L; lactate, 1,100 µg/L; urea, 300 µg/L; 4-methyl-2-pentanone, 47 µg/L; and 2-methyl-2,4-pentanediol, 34 µg/L. Mir During the late 1990s, the National Aeronautics and Space Administration (NASA) participated in a cooperative program with Russia in the operation of their space station Mir. As part of that program, seven samples of hot, regenerated water from the Mir WRS during missions Mir 18 and Mir 19 were tested in ground-based laboratories for TOC and or-

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 ganic components. In five of the samples, the range of TOC concentrations was 1.5-5.4 mg/L (Pierre et al. 1996). The components that exceeded 0.01 mg/L in any of the samples were as follows: acetone, 3/5; chloroform, 1/5; benzothiazole, 2/5; 2-methylthiobenzothiazole, 2/5; N-phenyl-2-naphthylamine, 1/5; and formaldehyde, 3/5. Acetone and formaldehyde were the most prevalent of these individual components. The percentage of the identified individual components composing the TOC was very low in these samples, typically only 3-6%. The samples were not evaluated for potential changes in components from the date of sampling until analysis in the laboratory. In the final report of the Mir Phase 1 project, the potable water pollutants were provided in order of decreasing average concentrations (Pierre et al. 1999). It is essential to note that the potable water consisted of reprocessed water supplemented with water obtained from municipal ground sources and on-orbit sources that had magnesium and calcium formate salts added, as well as an iodine tincture containing ethanol. In decreasing order, the 10 highest averages in the potable water were as follows: formate, ethylene glycol, ethanol, acetate, acetone, chloroform, methanol, di-n-butyl phthalate, benzothiazole, and formaldehyde. Ethylene glycol broke through the processor once at a concentration of 46 mg/L because of its overwhelming concentration in the humidity condensate. This resulted in a TOC concentration of 25 mg/L. The addition of a catalytic reactor to the processing system after this problem much reduced the ethylene glycol concentrations in potable water. Chloroform was believed to originate from ground-supplied water. ISS Two types of TOC measurements have been taken in water processed for consumption aboard the ISS. An on-board analyzer has been sporadically available to take measurements from freshly obtained samples, and an archival method has been used to sample product water and take ground-based measurements from those samples, which can be several months old by the time they reach the lab. Refrigerator space is not available aboard the ISS, so these samples remain at ambient temperature during the storage period. Although no formal health or epidemiologic studies have been conducted, major adverse health effects have not been reported during mission debriefings after flights in which the TOC concentrations in ISS water were as high as 30 mg/L (Plumlee et al. 2002). The current standard

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 for ISS is 20 mg/L (MORD 2000). Much of the TOC comes from the deliberate addition of formate and, to a lesser extent, residual ethanol in shuttle-derived water. If these contributions are subtracted from the total, then the “corrected” TOC concentrations have ranged from 0.1 to 1.2 mg/L through August 25, 2003, except for a sample obtained in a unique sampler (Straub et al. 2004). ORGANIC COMPOUNDS AT RISK FOR BREAKTHROUGH Russian WRS A scaled-down, ground-based test conducted in Russian laboratories involved injecting actual humidity condensate recovered from shuttle flights STS-89 and STS-91 while docked to the Mir into a model of the Mir WRS (Mudgett et al. 1999). The system was operated until organic carbon compounds began to break through. The initial breakthrough came from methanol, ethanol, acetic acid, ethylene glycol, and propylene glycol. The TOC increased from 1 part per million (ppm), at a cumulative throughput of 100 L, to 25 ppm after a cumulative throughput of 590 L. Planned U.S. WRSs Although the U.S. WRS will recover potable water from urine, the Russian and U.S. WRSs are similar. Thus, the breakthrough products would be expected to be similar. On the basis of a personal communication (L. Carter, Marshall Space Flight Center, Huntsville, AL, 2002) predicted that ethanol or methanol would be the most likely to get through the processor, because they are in the humidity condensate and are structurally similar to water. Acetaldehyde and formaldehyde are also possible breakthrough products. Acetone could break through if combustion products enter the humidity condensate, and acetic acid also is a possible early contaminant in the recovered water. Because ethylene glycol is not used in the thermal loops of the ISS, the concerns over its possible leakage into the air, capture in the condensate, and breakthrough of the water purification system are negligible when compared with the situation aboard Mir. The thermal control system of the Russian segment of ISS currently uses a solution of glycerol for heat exchange.

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 BASIS FOR THE SWEG FOR TOC Background on Suggested Water Quality Values for TOC The limit currently used in ISS operations is 20 mg/L (with formate already subtracted) based on the experience of Russian experts (MORD 2000). This is slightly less than the 25 mg/L limit used in the Mir Phase 1 program. In the past, a standard of 10 mg/L has been proposed for spacecraft for “relatively short crew exposures” (Macler and Cantwell 1993). For the U.S. water processor slated for the U.S. segment of the ISS, the water quality goal has been 0.5 mg/L; however, the origin of that goal cannot be traced to a scientific debate about what the value ought to be. The thinking at the time was that 0.5 mg/L was achievable and would protect against any toxic compounds not removed during urine processing. The value first appeared in a conference report in which it is stated that “if 0.5 mg/L is the maximum allowable TOC, then up to 0.1 mg/L of the organic chemicals present in the final potable water after several recyclings could remain uncharacterized” (Willis 1987). Our approach to setting a TOC concentration limit includes two facets. The first will be a typical standard defining an upper guideline for taking action if analyses indicate that the guideline has been exceeded. It will be based on the potential breakthrough compounds suggested in Table 10-2. Our second task will be to create a statistically based qualitycontrol guideline that establishes when, if a TOC measurement has unaccountedly risen above the TOC concentrations that preceded it, a response is required. This implies a one-sided test for deviations from the norm. ESTIMATION OF AN UPPER-LIMIT SWEG FOR TOC Basically, the task of the WRS is to reduce contaminants in influent water from a TOC concentration of a few hundred mg/L to one that is safe for human consumption. The weight of evidence is that any organic compound that initially breaks through the purification beds and increases the TOC concentration is unlikely to pose an immediate threat to crew health. NASA probably will not have the real-time capability to quantify individual pollutants that might break through the WRS, so the TOC measurement will have to serve as a first-line screening parameter for water quality.

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 TABLE 10-2 Pollutants in Potable Water from Space Vehicles and Test Bedsa,b Pollutant MSFC Ground Testc (average concentration) JSC Ground Test Phases II, IIa, IIId,e Mir Phase 1 Programd,f ISS Expeditions 1-7d,g Exposure Standard: 100-d SWEG (mg/L) Oral RfD (mg/kg/d) (EPA 2004) Methanol 0.21 0.27 0.49 0.31 — — Ethanol 0.16 — 2.4 16.1 — — 2-Propanol 0.14 0.18 — — — — Ethylene glycol — — 45.5 — [23]h 2 Acetone 0.12 0.03 0.13 0.17 [ 150 ] 0.9 Formaldehyde — 0.02 0.06 0.01 [12] 0.2 Acetaldehyde — — 0.05 — — — Caprolactam — — 0.03 2.15 [100] 0.5 Lactate — 1.1 — 0.24 — — Oxalate — 0.41 — — — — Urea — 0.30 — — — — Acetate — 0.6 1.5 0.14 — — Propionate — — — 0.15 — — Methyl sulfone — 0.05 — 0.11 — — Phenyl sulfone — — 0.08 — — — Dibutyl phthalate — — 0.30 — 80 0.1 Di(ethylhexyl) phthalate — 0.03 0.03 0.05 30 0.02

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 N-Butylbenzene sulfonamide — — — 0.11 — — Dichloromethane — — 0.09i — 40 0.06 Chloroform — — 0.18i — 18 0.01 3-t-Butyl phenol — — 0.11 — — — Cyclododecane — — 0.15 — — — aCompounds found one or more times at a concentration at or above 0.05. Measurements in mg/L. bA dash signifies that the compound was not measured or detected in water or that no standard has been adopted. cCarter 1997. dMaximum concentration found during test series. ePierre et al. 2002. fPierre et al. 1999, Table 4. gPlumlee et al. 2002, 2003; Straub et al. 2004. hBrackets indicate pending SWEGs. iSource was water brought to Mir from the ground. Abbreviations: ISS, International Space Station; JSC, Johnson Space Center; MSFC, Marshall Space Flight Center; RfD, reference dose.

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 The probable breakthrough compounds are small alcohols, aldehydes, and acetone. Of these, formaldehyde is the most toxic with a drinking water exposure level (DWEL) of 7 mg/L (EPA 2004). Ingestion of water contaminated with formaldehyde at a concentration of 7 mg/L for several hundred days appears to pose minimal risk to crew health. The organic carbon derived from this exposure would be 12/30 × 7 mg/L = 2.8 mg/L. A second approach can be to start with the 100-d and 1,000-d SWEGs for formaldehyde of 12 mg/L (see Chapter 7). This is equivalent to 5 mg/L of organic carbon. We rounded up the lower of these numbers to 3 mg/L. Inspection of Table 10-2 suggests that formaldehyde-contaminated water is the worst-case scenario for elevation of TOC concentration. The chlorine-containing carbon compounds originate from ground sources, and the phthalates come from the holding of the water in plastic pipes. These compounds are extremely unlikely to break through the regeneration system in large quantities. Furthermore, according to SWEG values, formaldehyde is more toxic (potent) than the chlorocarbons or the phthalates. It is possible that the TOC safe concentration limits could change if final values in Table 10-2 differ significantly from those proposed or if new technology comes into use in the space program. As a comparison to EPA requirements for municipal water supplies, EPA form 5115 is instructive. The final acceptable TOC concentrations are determined in terms of the starting TOC concentrations. Using averages from the starting ranges, the required clean up of water is as follows: a source at 3 mg/L requires a 25% cleanup, a source at 6 mg/L requires a 35% cleanup, and a source at 9 mg/L requires a 40% cleanup. Thus, the product water’s TOC concentration would be below 2.25, 3.90, and 5.4 mg/L, respectively. Although the nature of the compounds comprising the TOC will be markedly different in space WRSs, these target values suggest that our TOC safe concentration limit of 3 mg/L is reasonable. ESTIMATION OF A LIMIT BASED ON CHANGES IN TOC There clearly are conditions in which the TOC limit is insufficient as an indicator of safe drinking water and in which breakthrough by organic compounds is not impending. For example, if the TOC concentration has been 0.5 ± 0.3 (standard deviation) mg/L, and it suddenly increases to 2.5 mg/L, that could be cause for action. The increase is not necessarily a direct crew health concern; however, it is a condition that if

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 left unaddressed, could lead to further degradation in the WRS and, secondarily, to crew health effects. Statistical process control is an often-used technique to monitor and control technical processes. Basically, periodic samples of the product in question are obtained and analyzed, in this case, for TOC. The TOC values are found to fall within a range that can be defined by statistical properties. By some predetermined criteria, those values can be said to be within the expected random variation inherent in the system and monitoring technology. When a value or values exceed a predetermined criterion, then the system is said to be “out of control,” and an investigation of the cause ensues. The committee recommends that some form of statistical process control be implemented for monitoring TOC concentrations to ensure effective operation of the WRS. CONCLUSIONS The upper limit of the standard for a TOC concentration was set at 3 mg/L, assuming that the TOC comes entirely from formaldehyde, which is the most toxic component found at concentrations above 0.05 mg/L in the TOC of potable water. The DWEL for formaldehyde is 7 mg/L, which would contribute 2.8 mg/L to the TOC, and the 100- and 1,000-d SWEGs are 12 mg/L for a contribution of 5 mg/L to the TOC; therefore, taking the lowest of these two numbers, the TOC concentration becomes 3 mg/L (rounded) for ingestions of 100 d. Also it is recommended that a statistical-process control plan be developed to ascertain system performance from TOC measurements. REFERENCES Carter, D.L. 1997. Phase III integrated water recovery testing at MSFC: ISS recipient mode test results and lessons learned. SAE Technical Paper Series 972375. Clesceri, L.S., A.E. Greenberg, and A.D. Eaton, eds. 1998. Standard Methods for the Examination of Water and Waste Water. Washington, DC: American Public Health Association. EPA (U.S. Environmental Protection Agency). 2004. Drinking Water Standards and Health Advisories. U.S. Environmental Protection Agency, Washington, DC. Macler, B.A., and E.R. Cantwell. 1993. Risk analysis for setting drinking water

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Spacecraft Water Exposure Guidelines: For Selected Contaminants, Volume 2 standards for long-term space missions. SAE Technical Paper Series 932094. Miettinen, I.T., T. Vartiainen, and P.J. Martikainen. 1996. Contamination of drinking water. Nature 381:654-655. MORD (Medical Operations Requirements Document). 2000. ISS Medical Operations Requirements Document, Revision A. NASA Johnson Space Center, SSP document 50260. Mudgett, P.D., J.E. Straub, J.R. Schultz, R.L. Sauer, L.S. Bobe, P.O. Andreichuk, N.N. Protasov, and Y.E. Sinyak. 1999. Chemical analysis and water recovery testing of shuttle-Mir humidity condensate. SAE Techmical Paper Series 1999-01-2029. Pierre, L.M., J.R. Schultz, S.E. Carr, and R.L. Sauer. 2002. Water chemistry monitoring. Chapter 4.2 in Isolation: NASA Experiments in Closed-Environment Living, H.W. Lane, R.L. Sauer, and D.L. Feeback, eds. San Diego, CA: American Astronautical Society. Pierre, L.M., J.R. Schultz, S.M. Johnson, R.L. Sauer, Y.E. Sinyak, V.M. Skuratov, and N.N. Protasov. 1996. Collection and chemical analysis of reclaimed water and condensate from the Mir space station. SAE Technical Paper Series 961569. Pierre, L.M., J.R. Schultz, S.M. Johnson, R.L. Sauer, Y.E. Sinyak, V.M. Skuratov, N.N. Protasov, and L.S. Bobe. 1999. Chemical analysis of potable water and humidity condensate: Phase one final results and lessons learned. SAE Technical Paper Series 99-01-2028. Plumlee, D.K., P.D. Mudgett, and J.R. Schultz. 2002. ISS potable water sampling and chemical analysis: Expeditions 1-3. SAE Technical Paper Series 2002-01-2537. Plumlee, D.K., P.D. Mudgett, and J.R. Schultz. 2003. ISS potable water sampling and chemical analysis: Expeditions 4 & 5. SAE Technical Paper Series 2003-01-2401. Straub, J.E., D.K. Plumlee, and J.R. Schultz. 2004. ISS potable water sampling and chemical analysis: Expeditions 6 & 7. SAE Technical Paper Series 2004-01-pending. Willis, C.E. 1987. Space Station Water Quality Report. NASA Johnson Space Center, Biomedical Laboratories Branch, Medical Sciences Division, Contract NAS9-17720.