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46th International Conference on Environmental Systems ICES-2016-416
10-14 July 2016, Vienna, Austria
Chemical Characterization and Identification of
Organosilicon Contaminants in ISS Potable Water
John E. Straub II
1
, Debrah K. Plumlee
2
and William T. Wallace
3
Wyle Science, Technology and Engineering Group, Houston, Texas, 77058
and
Daniel B. Gazda
4
NASA Johnson Space Center, Houston, Texas, 77058
2015 marked the 15th anniversary of continuous human presence on board the International Space Station.
During the past year crewmembers from Expeditions 42-46, including two participating in a 1-year mission,
continued to rely on reclaimed water as their primary source of potable water. This paper presents and
discusses results from chemical analyses performed on ISS water samples returned in 2015. Since the U.S.
water processor assembly (WPA) became operational in 2008, there have been 5 instances of organic
contaminants breaking through the treatment process. On each occasion, the breakthrough was signaled by an
increase in the total organic carbon (TOC) concentration in the product water measured by the onboard TOC
analyzer (TOCA). Although the fifth and most recent TOC rise in 2015 was not unexpected, it was the first
time where dimethylsilanediol (DMSD) was not the primary compound responsible for the increase. Results
from ground analysis of a product water sample collected in June of 2015 and returned on Soyuz 41 showed
that DMSD only accounted for <10% of the measured TOC. After considerable laboratory investigation, the
compound responsible for the majority of the TOC was identified as monomethysilanetriol (MMST). MMST
is a low-toxicity compound that is structurally similar to DMSD.
Nomenclature
CE Capillary Electrophoresis
DAI Direct Aqueous Injection
DMSD Dimethylsilanediol
EDV Russian Portable Water Tank (22 liters)
EPA Environmental Protection Agency
GC/MS Gas Chromatography/Mass Spectrometry
HX Heat Exchanger
IC Ion Chromatography
ICP/MS Inductively Coupled Plasma/Mass Spectrometry
ISS International Space Station
JSC Johnson Space Center
LC Liquid Chromatography
LC/MS Liquid Chromatography/Mass Spectrometry
LCV Leuco Crystal Violet
MCL Maximum Contaminant Level
MMST Monomethylsilanediol
MORD Medical Operations Requirements Document
N/A Not Applicable
NA Not Analyzed
NASA National Aeronautics and Space Administration
NTU Nephelometric Turbidity Unit
PFU Protoflight unit
1
Senior Engineer, Wyle Science, Technology and Engineering Group, Mail Stop: Wyle/HEF/37A.
2
Senior Scientist, Wyle Science, Technology and Engineering Group, Mail Stop: Wyle/HEF/37A.
3
Senior Scientist, Wyle Science, Technology and Engineering Group, Mail Stop: Wyle/HEF/37A.
4
Environmental Chemistry Laboratory Technical Monitor, NASA Johnson Space Center, Mail Stop: SK4.
International Conference on Environmental Systems
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PWD Potable-Water Dispenser
RL Reporting Limit
RI Refractive Index
SRV-K System for Regeneration of Condensate Water
SVO-ZV System for Water Storage and Dispensing
SWEG Spacecraft Water Exposure Guideline
TEC Toxicology and Environmental Chemistry
THM Trihalomethanes
TOCA Total Organic Carbon Analyzer
U.S. United States
UV-VIS Ultraviolet-Visible
WPA Water Processor Assembly
I. Introduction
Analytical results from characterization of chemical contaminants in archival-water samples returned in 2015
from the International Space Station (ISS) Expeditions 42-45 are presented and discussed herein. These results have
been evaluated for compliance with the potable-water quality requirements for Russian Segment water supplies in the
ISS Medical Operations Requirement Document (MORD)1 and for U.S. Segment water supplies in the System
Specification for the ISS document2. Spacecraft specific limits have also been defined as Spacecraft Water Exposure
Guidelines (SWEGs)3 for some contaminants of interest to NASA and have been used when available. Analytical data
for archival-water samples returned from Expeditions 1-41 have previously been published and presented at the
International Conference on Environmental Systems4-16.
Table 1 summarizes the details for the archival samples that were collected and returned in 2015. All water
samples returned on Russian Soyuz vehicles were transported to the United States in the same NASA aircraft as the
returning U.S. crewmembers. A representative of the NASA Johnson Space Center (JSC) Toxicology and
Environmental Chemistry (TEC) laboratory took possession of these samples upon their arrival in Houston, Texas,
then delivered them directly to the laboratory for processing and analysis.
Sample allocation was determined based upon the volume of each return water sample. Samples with
sufficient volume received full chemical characterization while those with insufficient volume required reductions in
allocated volumes and/or elimination of some analyses. A list of the analytical methods used for sample analysis is
provided in Table 2.
Expedition
Flight No.
Samples
Received
Sample Type
Sample Collection Date
Sample Receipt
Date
Soyuz 40
1
PWD Ambient
2/2/2015
1
PWD Hot
3/4/2015
1
SRV-K Hot
3/4/2015
1
SVO-ZV
3/4/2015
Total:
4
SpaceX-6
1
PWD Ambient
3/31/2015
1
PWD Hot
5/4/2015
1
SRV-K Warm
5/4/2015
1
SVO-ZV
5/4/2015
Soyuz 41
1
PWD Aux
6/10/2015
6/12/2015
Total:
5
Soyuz 42
1
PWD Aux
9/10/2015
9/19/2015
Total:
1
Soyuz 43
1
PWD Hot
11/10/2015
1
PWD Ambient
12/1/2015
1
SRV-K Warm
12/1/2015
1
SVO-ZV
12/1/2015
Total:
4
Table 1. Archival Potable Water Samples Returned during Expeditions 42 through 45
42
43
5/26/2015
12/14/2015
45
44
3/13/2015
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Table 2. TEC Laboratory Methods for Water Analysis
Parameter
Analytical Method
pH and conductivity
Potentiometric
Total Solids
Gravimetric
Turbidity
Nephelometric
Iodine and iodide
Leuco crystal violet (LCV)
Metals/Minerals
Inductively coupled plasma/mass spectrometry (ICP/MS)
Inorganic anions & cations
Ion chromatography (IC)
Total organic carbon (TOC)
Ultraviolet or heated persulfate oxidation
Alcohols and glycols
Direct aqueous injection gas chromatography/mass spectrometry (DAI/GC/MS)
Volatile organics
GC/MS with a purge and trap concentrator
Semivolatile organics
GC/MS after liquid/liquid extraction
Organic acids and amines
Capillary electrophoresis (CE) and IC
Urea/Caprolactam
Liquid chromatography with ultraviolet-visible detector (LC/UV-VIS)
Formaldehyde
GC/MS after derivatization and extraction
Dimethylsilanediol,
Monomethylsilanetriol
Liquid chromatography with refractive index detector (LC/RI)
II. Background
The onboard potable water supplies available for use by the ISS Expeditions 42-45 crews included reclaimed
water from the U.S. Segment and both regenerated and stored potable water from the Russian Segment.
U.S. Potable Water System
The U.S. Segment water processor assembly (WPA) and total organic carbon analyzer (TOCA) both arrived
at the ISS in late 2008. The WPA processes a combined wastewater feed (humidity condensate and urine distillate)
using a combination of treatment processes including multifiltration beds, high-temperature catalytic oxidation
reactor, and ion exchange bed (Figure 1).4 Iodine biocide is added as part of the final ion exchange process to maintain
Figure 1 - U.S. Segment Water Processor Assembly (WPA)1.
microbial control in the product water. The U.S potable water dispenser (PWD) provides the ISS crews access to WPA
product water. Deiodinated potable water is provided via the ambient and hot ports and iodinated product water is
available via the auxiliary (Aux) port. The TOCA provides the capability to measure total organic carbon (TOC)
concentrations in WPA product either directly via hose (weekly) or indirectly via bag filled from the PWD (monthly).
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Russian Segment Water Systems
The Russian Segment regenerated potable water system (SRV-K) removes contaminants from humidity
condensate using multiple processes, including catalytic oxidation, phase separation, and multifiltration. Silver biocide
and minerals are added to the product water before storage. In the SRV-K galley dispenser the product water is
pasteurized for microbial control then made available to the ISS crews from either hot or warm ports (Figure 2). The
Russian Segment stored water system (SVO-ZV) provides the crews with access to ground-supplied potable water
that has been delivered on Russian Progress vehicles and transferred to an EDV bladder tank. The SVO-ZV provides
water at ambient temperature from a dispenser port (Figure 3). Both the SRV-K and SVO-ZV water systems have
been previously described in detail.4
Figure 2 - SRV-K galley.
Collection of archival sample from SRV-K by Donald Pettit
(NASA/JSC Photo #ISS006E08616)
Figure 3 - SVO-ZV water dispenser.
Collection of water sample from SVO-ZV by Donald Pettit
(NASA/JSC Photo #ISS006E08628)
III. Discussion of Analytical Results
The ISS water samples returned from Expeditions 42-45 were analyzed in the TEC laboratory at JSC. The
results from chemical analyses are presented in tabular format in Appendix 1 for SRV-K (regenerated) water,
Appendix 2 for SVO-ZV (stored) water, and Appendix 3 for WPA reclaimed water. ISS potability limits have been
included in each table for easy comparison to analytical results and a discussion of these results by expedition follows.
EXPEDITION 42
Four archival potable-water samples were collected during Expedition 42 of 2015 from the PWD ambient,
PWD hot, SRV-K hot, and SVO-ZV ports (see Table 1). After their return on the Soyuz 40 vehicle, these samples
were received in the TEC laboratory for chemical analysis on March 13, 2015. All samples were analyzed for pH,
conductivity, anions, cations, metals, total silicon, minerals, TOC, carboxylates, amines, alcohols, glycols,
dimethylsilanediol (DMSD), and formaldehyde, as well as volatile, semivolatile, and nonvolatile organics. Iodine was
also analyzed on the PWD samples, dissolved silver on the SVO-ZV and SRV-K samples, and turbidity on the SVO-
ZV sample. Total solids were not measured on any of the samples due to limited sample volume.
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ISS U.S. Segment
PWD Potable-Water Samples
For the PWD ambient and hot water samples collected on February 2 and March 4, 2015, all chemical
parameters measured met the ISS potability limits for the U.S. Segment in the System Specification for the
International Space Station, SSP 410002. Total iodine was not detected (<0.05 mg/L) in either sample, thereby meeting
the ISS potability limit at the point of consumption of <0.2 mg/L. An updated historical plot of iodine levels in WPA
archival-water samples is shown in Figure 4. Total organic carbon (TOC) levels for both samples were below the
method reporting limit of <0.1 mg/L and well below the ISS potability limit of 3.0 mg/L. An updated historical plot
of TOC levels in WPA archival-water samples is shown in Figure 5. These results are also consistent with TOC
concentrations measured in flight using the TOCA as shown in Table 3. No individual target organic constituents were
detected in either sample.
Table 3. Comparison of Expedition 42 Archive Samples to In-flight TOCA Results
In-flight TOCA Results
Archive Results
Date
Location
TOC (mg/L)
Date
Location
TOC (mg/L)
2/02/15
PWD ambient
<0.285
2/02/15
PWD ambient
<0.10
3/02/15
WPA*
<0.285
3/04/15
PWD hot
<0.10
*TOCA PWD analysis scheduled for 3/04/15 was cancelled due to crew time limitations.
ISS Russian Segment
SRV-K Potable-Water Sample
All chemical parameters measured in the SRV-K hot water sample collected on March 4, 2015 met the ISS
potability limits for the Russian Segment listed in the ISS Medical Operations Requirements Document (MORD)1.
The total silver concentration of 33 µg/L was below the desired minimum biocidal level of 100 µg/L, which may
increase the risk of microbial growth in the system. An updated historical plot of organic carbon levels in SRV-K
archival-water samples is shown in Figure 6. The TOC level in the SRV-K sample from Expedition 42 was 0.69 mg/L
and well below the ISS limit (Figure 6). The only specific target organic constituent detected in the sample was acetone
at 14 µg/L.
SVO-ZV Potable-Water Sample
All chemical parameters measured in the SVO-ZV water sample collected on March 4, 2015 met the ISS
potability limits for the Russian Segment listed in the ISS MORD1 with the exception of manganese. An updated
historical plot of manganese in SVO-ZV archival-water samples is shown in Figure 7. The manganese level of 75
µg/L in the SVO-ZV sample from Expedition 42 was slightly above the ISS limit of 50 µg/L (Figure 7) but well below
the SWEG of 300 µg/L3. The total silver concentration of 52 µg/L was below the desired minimum biocidal level of
100 µg/L, which may increase the risk of microbial growth in the system. The TOC concentration in the sample was
0.9 mg/L well below the ISS limit. No individual target organic constituents were detected.
EXPEDITION 43
Five archival water samples were collected during Expedition 43 of 2015 from the PWD ambient, PWD hot,
SRV-K warm, SVO-ZV, and PWD Aux ports (see Table 1). After their return on the SpaceX-6 and Soyuz 41 vehicles,
these samples were received in the TEC laboratory for chemical analysis on May 26 and June 12, 2015, respectively.
The four potable water samples that returned on SpaceX-6 were analyzed for pH, conductivity, anions, cations, metals,
total silicon, minerals, TOC, carboxylates, amines, alcohols, glycols, DMSD, and formaldehyde, as well as volatile,
semivolatile, and nonvolatile organics. Iodine was also analyzed on the PWD potable water samples as well as
turbidity and dissolved silver on the SRV-K and SVO-ZV samples. Total solids were not measured on any of the
potable samples due to limited sample volume. The product water sample returned on Soyuz 41 was analyzed for
cations, metals, total silicon, reactive silica, minerals, TOC, carboxylates, amines, alcohols, glycols, DMSD,
formaldehyde, volatile organics, and nonvolatile organics, based on limited sample volume.
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Figure 4 - Total I & iodine levels in WPA archival-water samples from ISS ULF2 to Soyuz 43 4-10.
2015 data is from Expeditions 42-45
Figure 5 - TOC levels in WPA archival-water samples from ISS ULF2 to Soyuz 43 4-10.
Note the 4 previous TOC rises in 2010, 2012, 2013, and 2014 from dimethylsilanediol breakthrough,
2015 data is from Expeditions 42-45
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Figure 6 - Total, formate, and nonformate organic carbon levels in SRV-K water samples
from ISS Flights 4A to Soyuz 43 4-16.
2015 data is from Expeditions 42-45
Figure 7 - Manganese levels in SVO-ZV water samples from ISS Flights 5A to Soyuz 43 4-16.
2015 data is from Expeditions 42-45
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ISS U.S. Segment
PWD Potable-Water Samples
For the PWD ambient and hot water samples collected on March 31 and May 4, 2015, all chemical parameters
measured met the ISS potability limits in SSP 410002. Total organic carbon (TOC) levels were <0.1 mg/L and 0.18
mg/L, respectively, and well below the potability limit of 3.0 mg/L as shown in Figure 5. These results are also
consistent with TOC concentrations measured in flight using the TOCA as shown in Table 4. The only individual
target organic constituents identified in the samples were methyl sulfone at 86 and 71 µg/L and diethylphthalate at 14
µg/L (PWD hot only). Total iodine was not detected (<0.05 mg/L) in either sample as shown in Figure 4.
Table 4. Comparison of Expedition 43 Archive Samples to In-flight TOCA Results
In-flight TOCA Results
Archive Results
Date
Location
TOC (mg/L)
Date
Location
TOC (mg/L)
3/31/15
PWD ambient
<0.285
3/31/15
PWD ambient
<0.10
5/4/15
PWD hot
<0.285
5/4/15
PWD hot
0.180
Product Water Sample (PWD Aux)
A contingency sample was collected from the PWD Aux port during Expedition 43 on June 10, 2015 in
response to a rapid increase in the TOC concentration in the WPA product water as measured by the in-flight TOCA.
The measured TOC of 2.44 mg/L in the PWD Aux sample was much higher than that found in the May 4 PWD hot
sample (0.18 mg/L), but remained below the TOC potability limit of 3.0 mg/L (Figure 5). Since the U.S. water
processor assembly (WPA) became operational in 2008, there have been 5 previous instances of organic contaminants
breaking through the WPA treatment process. On each occasion, the breakthrough was signaled by an increase in the
TOC concentration in the product water as measured by the in-flight TOCA. For all of the previous TOC increases,
dimethylsilanediol (DMSD) was determined to be the primary source.4-9 Although DMSD was measured at a
concentration of 0.85 mg/L in the June PWD Aux sample, that level was only sufficient to account for 9% of the
measured TOC. Therefore DMSD was not the primary compound responsible for the elevated TOC and no other
individual target organic constituents were detected in the sample. The total silicon concentration in the sample of 4.3
mg/L was much higher than typically found in WPA water when DMSD is not present, so analysis for reactive silica
(inorganic silicon) was performed in the Advanced Water Recovery Lab at JSC. Results from that analysis showed
2.0 mg/L SiO2 (or 0.94 mg/L total silicon equivalent), which suggested that organosilicon compounds other than
DMSD must be present but unidentified in the sample. After considerable laboratory investigation the unknown
compound was determined to be monomethysilanetriol (MMST), an organosilicon compound structurally similar to
DMSD. After reviewing the available toxicologic data on MMST an interim SWEG was set at 110 mg/L, which is
much higher than the concentration that could potentially have been present in the June PWD Aux sample.
Accordingly, the presence of MMST at levels well below the SWEG was not expected to pose a significant crew
health risk, so a waiver was put in place. This allowed the ISS crews to temporarily continue consumption of WPA
water until replacement ion exchange and multifiltration beds arrived on the HTV-5 resupply vehicle. The replacement
beds were installed in early October to remediate the TOC rise.
ISS Russian Segment
SRV-K Potable-Water Sample
All chemical parameters measured in the SRV-K warm water sample collected on May 4, 2015 met the ISS
MORD potability limits with the exceptions of manganese and turbidity. The manganese concentration of 95 µg/L
was above the MORD limit of 50 µg/L but well below the SWEG of 300 µg/L. The measured turbidity of 1.6 NTU
was only slightly above the MORD limit of 1.5 NTU, but turbidity is an aesthetic parameter for which a slight elevation
is not considered to pose a risk to crew health. The total silver concentration of 61 µg/L was below the desired
minimum biocidal level of 100 µg/L, which may increase the risk of microbial growth in the system. The TOC level
in the sample of 9.7 mg/L was below the ISS MORD limit (Figure 6). Organic compounds detected near or above 1
mg/L consisted of ethanol (11.2 mg/L), acetate (4.8 mg/L) and methanol (0.9 mg/L). Trace levels of acetone,
acetaldehyde and bis-(2-ethylhexyl)phthalate were also measured.
SVO-ZV Potable-Water Sample
All chemical parameters measured in the SVO-ZV water sample collected on May 4, 2015 met the ISS
MORD potability limits with the exception of manganese. The manganese level of 98 µg/L in the sample was slightly
above the ISS limit of 50 µg/L (Figure 7) but well below the SWEG of 300 µg/L15. The total silver concentration of
108 µg/L was above the desired minimum biocidal level of 100 µg/L. The TOC concentration in the sample was
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0.89 mg/L and well below the ISS MORD limit. Trace levels of bis-(2-ethylhexyl) adipate, bis-(2-ethylhexyl)
phthalate, and monomethyl phthalate were the only specific target organic constituents detected.
EXPEDITION 44
Again, in response to the 2015 TOC rise, a WPA product water sample was collected from the PWD Aux
port on September 10, 2015 during Expedition 44 (see Table 1). After returning on the Soyuz 42 vehicle, the sample
was received in the TEC laboratory for chemical analyses on September 19, 2015. The sample was analyzed for pH,
conductivity, anions, cations, metals, total silicon, reactive silica, minerals, TOC, carboxylates, amines, alcohols,
glycols, DMSD, MMST, formaldehyde, volatile organics, and nonvolatile organics. Total solids and semivolatile
organics were not analyzed due to limited sample volume.
Product Water Sample (PWD Aux)
The measured TOC of 2.50 mg/L in the September PWD Aux sample was slightly higher than that found in
the June PWD Aux sample (2.44 mg/L), but remained below the TOC potability limit of 3.0 mg/L (Figure 5). The
individual target organic constituents detected in the sample were DMSD at 5.5 mg/L, MMST at 3.8 mg/L, and
trimethylamine at 0.289 mg/L, accounting for about 83% of the measured TOC. DMSD accounted for the majority of
the TOC (57%) in the September sample, whereas MMST was estimated to be the primary source of TOC in the June
sample. The total silicon concentration was 16.5 mg/L in the September sample, which was the highest level ever
measured for WPA product water samples. Because this value was much higher than the silicon that could be
accounted for by DMSD and MMST (~2.8 mg/L), an aliquot of the sample was analyzed for reactive silica in the
Advanced Water Recovery Lab at JSC. The result of this analysis was 35 mg/L of SiO2 (or 16 mg/L total silicon
equivalent) confirming that inorganic silicon accounted for a significant portion of the total silicon in the sample.
Iodine was present at a concentration of 1.42 mg/L, which fell within the required biocidal range of 1.0 to 4.0 mg/L.
EXPEDITION 45
Four archival potable-water samples were collected during Expedition 45 of 2015 from the PWD ambient,
PWD hot, SRV-K warm, and SVO-ZV ports (see Table 1). After their return on the Soyuz 43 vehicle, these samples
were received in the TEC laboratory for chemical analyses on December 14, 2015. All samples were analyzed for pH,
conductivity, iodine, anions, cations, metals, total silicon, minerals, TOC, carboxylates, amines, alcohols, glycols,
DMSD, MMST, and formaldehyde, as well as volatile, semivolatile, and nonvolatile organics. Dissolved silver was
analyzed on the SRV-K and SVO-ZV samples. Turbidity was also analyzed on the PWD hot and SRV-K warm
samples. Total solids were not measured on any of the samples due to limited sample volume.
ISS U.S. Segment
PWD Potable-Water Samples
For the PWD water samples collected on November 10 and December 1, 2015, all chemical parameters
measured met the ISS potability limits in SSP 410002. The TOC levels for both samples were below the method
reporting limit of <0.1 mg/L and well below the ISS potability limit of 3.0 mg/L (see Figure 5). These results were
also consistent with TOC concentrations measured in flight using the TOCA as shown in Table 5. These results
together confirmed that the replacement of the ion exchange and multifiltration beds on October 2, 2105 had resulted
in a return to nominal TOC levels in the WPA product water. The only individual target organic constituents detected
were methyl sulfone at 115 µg/L in PWD ambient and diethylphthalate at 13 µg/L in PWD hot. Total iodine was not
detected (<0.05 mg/L) in either sample, thereby meeting the ISS potability limit at the point of consumption of <0.2
mg/L (Figure 4).
Table 5. Comparison of Expedition 45 Archive Samples to In-flight TOCA Results
In-flight TOCA Results
Archive Results
Date
Location
TOC(mg/L)
Date
Location
TOC (mg/L)
11/10/15
PWD hot
<0.285
11/10/15
PWD hot
<0.10
12/1/15
PWD ambient
<0.285
12/1/15
PWD ambient
<0.10
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ISS Russian Segment
SRV-K Potable-Water Sample
All chemical parameters measured in the SRV-K warm water sample collected on December 1, 2015 met the
ISS MORD potability limits with the exceptions of manganese and turbidity. Although the manganese level of 59
µg/L was just slightly above the MORD limit of 50 µg/L, it was well below the SWEG of 300 µg/L. The measured
turbidity of 2.4 NTU was above the MORD limit of 1.5 NTU; however, slightly elevated turbidity alone is not
considered to pose a significant increase in risk to crew health. The total silver concentration of 77 µg/L was below
the desired minimum biocidal level of 100 µg/L, which may increase the risk of microbial growth in the system. The
TOC level in the sample of 0.78 mg/L was well below the ISS MORD limit (Figure 6). No individual target organic
compounds were detected in the sample.
SVO-ZV Potable-Water Sample
All chemical parameters measured in the SVO-ZV water sample collected on December 1, 2015 met the ISS
MORD potability limits with the exception of manganese. The manganese level of 67 µg/L in the sample was slightly
above the ISS limit of 50 µg/L but well below the SWEG of 300 µg/L3 (see Figure 7). The total silver concentration
of 102 µg/L was above the desired minimum biocidal level of 100 µg/L. The TOC concentration in the sample was
1.12 mg/L, which is well below the ISS MORD limit. No individual target organic compounds were detected in the
sample. IV. Conclusions and Recommendations
Despite the fifth and latest TOC rise, the WPA potable water available during ISS Expeditions 42-45 was
determined to be chemically acceptable for consumption based upon the analytical data from archival-water samples
returned in 2015. There have been 5 instances of organic contamination breaking through the treatment processes of
the WPA since it became operational in 2008. Each time that breakthrough occurred, it was signaled by an increase
in the TOC concentration of WPA product water as measured by the in-flight TOCA. Although the most recent TOC
rise in 2015 was not unexpected, it was the first time that DMSD was not the primary organic constituent contributing
to the increase. After considerable laboratory investigation the unknown compound was eventually identified as
monomethysilanetriol (MMST), a low-toxicity organosilicon compound that is structurally similar to DMSD. The
2015 TOC rise in WPA product water was anticipated based upon experience and lessons learned from previous TOC
rises, but the need for identification and subsequent confirmation of the presence of MMST was unique. Even though
the timing of DMSD breakthrough of the WPA treatment processes is considered predictable based upon historical
experience, the root cause for the presence of MMST in WPA product water needs to be further investigated.
Russian Segment potable water supplies (regenerated and stored) were chemically acceptable for crew
consumption during Expeditions 42-45 of 2015 based upon the analytical results for archival-water samples collected
and returned from the SRV-K and SVO-ZV ports. Although manganese levels in all 3 of the SVO-ZV samples and in
2 of 3 SRV-K samples slightly exceeded the ISS MORD limit of 50 μg/L, all levels were well below the 300 μg/L
SWEG limit. Silver biocide levels in all three SRV-K samples and one SVO-ZV sample were below the minimum
acceptable biocide level of 100 μg/L, which may increase the risk of microbial growth in the systems. These results
suggest that heating of the water by the pasteurization unit serves as the primary means of microbial control in the
SRV-K galley. Accordingly, it is recommended to continue collecting archive-samples for ground analysis of
manganese and silver biocide levels in both the SRV-K and SVO-ZV water supplies.
Appendices
Chemical analysis results summarizing the analytes detected in archival potable-water samples returned
during Expeditions 42-45 of 2015 for Russian Segment SRV-K (regenerated water) and SVO-ZV (stored water)
systems are provided in Appendix 1 and Appendix 2, respectively. Results for analytes detected in U.S. Segment
archival-water samples collected from the PWD hot, ambient, and auxiliary ports and returned in 2015 during those
same expeditions, are provided in Appendix 3.
Acknowledgments
Analytical work described herein was performed at the NASA Johnson Space Center TEC laboratory under
NASA contracts NAS9-02078 and NNJ15HK11B. The authors wish to acknowledge the ISS Expeditions 42-45 crews
for collecting and storing archival-water samples returned in 2015, as well as TEC laboratory chemists Jim Alverson,
Mickie Benoit, Robert Gillispie, David Hunter, Mike Kuo, and Jeff Rutz for performing chemical analyses of the
returned samples.
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References
1ISS Medical Operations Requirements Document, SSP 50260, Revision C, NASA Johnson Space Center, February 2006, Section
7.2 and Appendix D, Table D-1.
2System Specification for the International Space Station, SSP 41000 BY, National Aeronautics and Space Administration,
September 21, 2012, Table LXX.
3Spacecraft Water Exposure Guidelines (SWEGS), JSC-63414, NASA Johnson Space Center, November 2008.
4Straub, J.E., Plumlee, D.K., and Mudgett, P.D., “2014 ISS Potable Water Characterization and Continuation of the
Dimethylsilanediol Chronicle”, ICES-2015-038, Proceedings of the 2015 International Conference on Environmental Systems,
2015.
5Straub, J.E., Plumlee, D. K., Schultz, J. R., and Mudgett, P.D., “International Space Station Potable Water Characterization for
2013”, ICES-2014-190, Proceedings of the 2014 International Conference on Environmental Systems, 2014.
6Straub, J.E., Plumlee, D. K., Schultz, J. R., and McCoy, J.T., “Potable-Water Quality for International Space Station Expeditions
30-33”, AIAA-2013-3310, AIAA Proceedings of the 2013 International Conference on Environmental Systems, 2013.
7Straub, J.E., Plumlee, D. K., Schultz, J. R., and McCoy, J.T., “International Space Station Potable Water Quality for Expeditions
26 through 29”, AIAA-2012-3413, AIAA Proceedings of the 2012 International Conference on Environmental Systems, 2012.
8Straub, J. E., Plumlee, D. K., Schultz, J. R., and McCoy, J.T, “Chemical Analysis Results for Potable Water for ISS Expeditio ns
21-25”, AIAA-2011-5152, AIAA Proceedings of the 2011 International Conference on Environmental Systems, 2011.
9Straub, J. E., Plumlee, D. K., and Schultz, J. R., “ISS Expeditions 16 thru 20: Chemical Analysis Results for Potable Water”,
AIAA-2010-6042, AIAA Proceedings of the 2010 International Conference on Environmental Systems, 2010.
10Straub, J. E., Plumlee, D. K., and Schultz, J. R., “Chemical Analysis Results for Potable Water Returned from ISS Expeditions
14 and 15”, SAE International Journal of Aerospace. 1(1): 556-577, 2008.
11Straub, J. E., Plumlee, D. K., and Schultz, J. R., “Sampling and Chemical Analysis of Potable Water for ISS Expeditions 12 and
13”, SAE International Journal of Aerospace, 2007.
12Straub, J. E., Plumlee, D. K., and Schultz, J. R., “ISS Expeditions 10 & 11 Potable Water Sampling and Chemical Analysis
Results”, SAE International Journal of Aerospace, 2006.
13Straub, J. E., Plumlee, D. K., and Schultz, J. R., “Chemical Analysis of ISS Potable Water from Expeditions 8 and 9”, SAE
International Journal of Aerospace, 2005.
14Straub, J. E., Plumlee, D. K., and Schultz, J. R., “ISS Potable Water Sampling and Chemical Analysis: Expeditions 6 & 7”, SAE
International Journal of Aerospace, 2004.
15Plumlee, D. K. and Schultz, J. R., “ISS Potable Water Sampling and Chemical Analysis: Expeditions 4 & 5”, SAE International
Journal of Aerospace, 2003.
16Plumlee, D. K. and Schultz, J. R., “Chemical Sampling and Analysis of ISS Potable Water: Expeditions 1-3”, SAE International
Journal of Aerospace, 2002.
International Conference on Environmental Systems
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Appendix 1. ISS SRV-K Potable Water (Regenerated)
Summary of Analytes Detected in Samples Returned from Expeditions 42 through 45
Miss ion Soyuz 40/Exp. 42 SpaceX-6/Exp. 43 Soyuz 43/Exp. 45
Sample Loc ation Pota ble Wate r SRV-K Hot SRV-K Warm SRV-K Warm
Sample D esc ription
Max imum
Contaminant
Max imum
Contaminant
Potable Water Potable Water Potable Water
Sample D ate Leve l Leve l 3/4/2015 5/4/2015 12/1/2015
Analysis /Sample I D Units (MCL) Source 20150313004 20150526010 20151214004
Physica l Characteris tics
pH pH units 5.5-9.0 MORD 7.56 7.80 7.92
Conductivity µS/cm 154 296 260
Turbidity NTU 1.5 MORD NA 1.6 2.4
Chloride mg/L 250 MORD 4.4 9.8 8.8
Fluoride mg/L 1.5/4 MORD/EPA <0.1 0.1 0.2
Sulfate mg/L 250 MORD 18.5 27.2 14.8
Calcium mg/L 100 MORD 20.7 36.4 29.9
Magnesium mg/L 50 MORD 4.34 8.49 8.59
Potassium mg/L 0.70 1.83 1.70
Sodium mg/L 3.28 8.29 7.89
Calcium mg/L 100 MORD 22.0 38.6 32.7
Magnesium mg/L 50 MORD 4.26 9.15 8.52
Potassium mg/L 0.62 2.00 1.68
Sodium mg/L 3.24 8.77 7.88
Aluminum µg/L 32 47 90
Barium µg/L 1,000/10,000 MORD/SWEG 11 27 53
Copper µg/L 1,000/1,300 MORD/EPA 426
Iron µg/L 300 MORD 15 <5 18
Manganese µg/L 50/300 MORD/SWEG 37 95 59
Nickel µg/L 100/300 MORD/SWEG 332
Silver µg/L 500/400 MORD/SWEG 33 61 77
Silver, Dissolved µg/L 2 5 10
Zinc µg/L 5,000/2,000 MORD/SWEG 49 63 35
Silic on (ICP/ MS)
Silicon (ICP/MS) µg/L 558 1340 2290
Inorganic Carbon mg/L 14.2 24.3 25.0
Organic Carbon mg/L 20 MORD 0.69 9.70 0.78
Vo latile Org anics (GC/ MS) - 2 o f 84 targe t analyte s above RL
Acetone µg/L 15,000 SWEG 14 52 <5
Acetaldehyde µg/L not found 99 not found
Se mi-volatile s (GC/ MS) - 0 of 9 targ et ana lyte s abov e RL
Ac id Extra ctable s (GC/ MS) -E PA 62 5 List - 0 of 15 t arget analy tes a bove RL
Bas e/N eutral Ext ractables (GC/M S)- EP A 625 List - 1 of 45 ta rget a nalyte s above RL
bis-(2-Ethylhexyl)phthalate µg/L 20,000/6 SWEG/EPA <20 60 <8
Ethanol µg/L <400 11,200 <400
Methanol µg/L 40,000 SWEG <400 886 <400
Silano ls (DM SD a nd MM ST by LC/RI ) - 0 of 2 targe t analyt es above RL
Acetate µg/L MI 4770 <500
Orga nic Carbon Re cov ery percent 1.30 84.98 0.00
Unacc ounted O rganic Ca rbon mg/L 0.68 1.46 0.78
EPA = Environmental Protection Agency; SWEG = Spacecraft Water Exposure Guideline, JSC 63414
Vo latile Org anics -Spe cial I ntere st Compounds (Semi-qua ntitative ) - 1 of 2 targe t analytes a bove RL
Iodine (LCV) - 0 of 1 target analyte above Reporting Limit (RL)
Anions/ Cations (I C) - 7 o f 11 ta rget a nalyte s above RL
Me tals (I CP/MS ) - 13 o f 23 ta rget a nalytes above RL
Alc ohols (DA I/G C/MS) - 2 of 14 t arget analy tes a bove RL
Glyc ols (D AI/ GC/MS ) - 0 o f 2 targ et analyte s above RL
Total O rganic Ca rbon (Hea ted pe rsulfate oxidation)
Carbox ylates (CE/I C) - 1 o f 11 ta rget a nalyte s above RL
Amine s (CE/ IC) - 0 of 4 ta rget a nalytes above RL
Alde hydes (GC/MS ) - 0 o f 1 targ et analy te abo ve RL
No n-volatile s (LC/U V-V IS) - 0 o f 2 targ et analy tes a bove RL
NOTES: NA=Not analyzed; MI=M atrix interference; MORD = M edical Operations Requirements Document, SSP 50260;
International Conference on Environmental Systems
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Appendix 2. ISS SVO-ZV Potable Water (Stored)
Summary of Analytes Detected in Samples Returned from Expeditions 42 through 45
Miss ion Soyuz 40/Exp. 42 SpaceX-6/Exp. 43 Soyuz 43/Exp. 45
Sample Loc ation Pota ble Wate r SVO-ZV SVO-ZV SVO-ZV
Sample D esc ription
Max imum
Contaminant
Max imum
Contaminant
Potable Water Potable Water Potable Water
Sample D ate Leve l Leve l 3/4/2015 5/4/2015 12/1/2015
Analysis /Sample I D Units (MCL) Source 20150313003 20150526009 20151214003
Physica l Characteristic s
pH pH units 5.5-9.0 MORD 7.82 7.88 7.91
Conductivity µS/cm 357 345 320
Turbidity NTU 1.5 MORD 0.4 1.3 NA
Chloride mg/L 250 MORD 10.5 10.9 11.7
Fluoride mg/L 1.5/4 MORD/EPA 0.1 0.1 0.3
Nitrate as Nitrogen (NO3-N) mg/L 10 MORD/EPA 0.2 <0.2 <0.2
Sulfate mg/L 250 MORD 35.2 28.0 21.1
Calcium mg/L 100 MORD 46.7 42.7 44.1
Magnesium mg/L 50 MORD 10.4 10.6 10.9
Potassium mg/L 2.13 2.18 2.27
Sodium mg/L 8.68 9.63 10.5
Calcium mg/L 100 MORD 47.9 45.5 42.4
Magnesium mg/L 50 MORD 10.2 11.6 10.4
Potassium mg/L 1.88 2.26 2.17
Sodium mg/L 8.74 9.67 10.1
Aluminum µg/L 138 83 232
Barium µg/L 1,000/10,000 MORD/SWEG 23 30 68
Copper µg/L 1,000/1,300 MORD/EPA 222
Iron µg/L 300 MORD <5 <5 16
Manganese µg/L 50/300 MORD/SWEG 75 98 67
Nickel µg/L 100/300 MORD/SWEG 4 1 3
Silver µg/L 500/400 MORD/SWEG 52 108 102
Silver, Dissolved µg/L 225 8
Zinc µg/L 5,000/2,000 MORD/SWEG 175 86 61
Silic on (ICP/ MS)
Silicon (ICP/MS) µg/L 1960 1990 2950
Inorganic Carbon mg/L 34.5 30.1 31.3
Organic Carbon mg/L 20 MORD 0.89 0.89 1.12
Vo latile Organic s (GC/ MS) - 0 o f 86 targe t analyte s above RL
Se mi-volatile s (GC/ MS) - 1 o f 9 targ et ana lyte s abov e RL
bis-(2-Ethylhexyl)adipate µg/L 400 EPA <20 90 <20
Ac id Extra ctable s (GC/ MS) -E PA 62 5 List - 0 of 15 t arget analy tes a bove RL
Bas e/N eutral Extrac tables (GC/M S)- EP A 625 List - 1 of 45 ta rget a nalytes above RL
bis-(2-Ethylhexyl)phthalate µg/L 20,000/6 SWEG/EPA <20 161 <20
Monomethyl phthalate µg/L not found 40 not found
Silano ls (DM SD a nd MMST by LC/RI ) - 0 of 2 targe t analyte s above RL
Orga nic Carbon Re cov ery percent 0.00 23.14 0.00
Unacc ounted Orga nic Carbon mg/L 0.89 0.69 1.12
Se mi-volatile s - S pecial Inte res t Compounds (S emi-quantita tive - 2 pt curv e) - 1 of 47 target analyte s above RL
Carbox ylates (CE/I C) - 0 o f 11 targe t analyte s above RL
Amine s (CE/ IC) - 0 of 4 ta rget a nalytes above RL
Alde hydes (GC/MS ) - 0 o f 1 targ et analyte above RL
No n-volatile s (LC/U V-V IS) - 0 o f 2 targ et analy tes above RL
NOTES: NA=Not analyzed; MORD = M edical Operations Requirements Document, SSP 50260;
EPA = Environmental Protection Agency; SWEG = Spacecraft Water Exposure Guideline, JSC 634 14
Iodine (LCV) - 0 of 1 target analyte above Reporting Limit (RL)
Anions/ Cations (I C) - 8 o f 11 ta rget a nalyte s above RL
Me tals (I CP/MS ) - 13 of 2 3 targe t analytes above RL
Total O rganic Ca rbon (Heate d persulfa te ox idation)
Alc ohols (DA I/G C/MS) - 0 of 14 target analyte s above RL
Glyc ols (D AI/ GC/MS ) - 0 o f 2 targ et analyte s above RL
46th International Conference on Environmental Systems ICES-2016-416
10-14 July 2016, Vienna, Austria
Appendix 3. ISS WPA - PWD Ambient, Hot, and Aux Ports
Summary of Analytes Detected in Samples Returned from Expeditions 42 through 45
14
International Conference on Environmental Systems
Miss ion Soyuz 41/Exp. 43 Soyuz 42/Exp. 44
Sample Locat ion Potable Wate r WPA PWD Ambient WPA PWD Hot WPA PWD Ambient WPA PWD Hot WPA PWD Hot WPA PWD Ambient PWD Aux Port PWD Aux Port
Sample De scription
Maximum
Contaminant
Maximum
Contaminant
Potable Water Potable Water Potable Water Potable Water Potable Water Potable Water Product Water Product Water
Sample Date Le ve l Leve l 2/2/2015 3/4/2015 3/31/2015 5/4/2015 11/10/2015 12/1/2015 6/10/2015 9/10/2015
Analy sis/S ample I D Units (MCL) Sourc e 20150313001 20150313002 20150526007 20150526008 20151214001 20151214002 20150612003 20150919001
Physic al Charac teris tics
pH pH units 4.5-8.5 41000 6.25 5.65 6.17 6.58 5.59 5.46 NA 6.72
Conductivity µS/cm 2 3 1 1 2 2 NA 4
Turbidity NTU 1 41000 NA NA NA NA <0.4 NA NA NA
Iodine (LCV)
Total I mg/L 6/0.2
41000 (Total/at pt of
consumption)
<0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA 3.00
Iodine mg/L <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA 1.42
Iodide mg/L <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA 1.58
Calcium mg/L 30 41000 <0.01 <0.01 <0.01 0.01 <0.01 <0.01 0.04 0.10
Potassium mg/L 340 41000 <0.01 <0.01 <0.01 <0.01 0.01 <0.01 0.02 0.11
Sodium mg/L <0.01 <0.01 <0.01 <0.01 0.05 0.05 <0.02 0.05
Aluminum µg/L 2 1 <1 <1 5<1 <2 <2
Barium µg/L 10,000 SWEG&41000 <1 6<1 <1 <1 1<2 <2
Chromium µg/L 230 41000 <1 <1 <1 <1 <1 <1 <2 24
Iron µg/L 300 41000 49 <5 <5 <5 <5 <5 <10 <10
Nickel µg/L 300 SWEG&41000 4 7 7 6 8 2 96 101
Zinc µg/L 2,000 SWEG&41000 <1 <1 2 2 2 2 <2 4
Silic on (ICP/ MS)
Silicon (ICP/MS) µg/L 25 18 44 248 62 30 4,260 16,500
Inorganic Carbon mg/L 0.96 0.96 0.79 0.80 0.84 0.72 0.81 0.37
Organic Carbon mg/L 3 41000 <0.10 <0.10 <0.10 0.18 <0.10 <0.10 2.44 2.50
Vola tile Org anics ( GC/MS ) - 0 of 86 targ et ana lytes above Reporting Limit ( RL)
Se mi-volatile s (GC/ MS) - 1 of 9 t arget analyte s above RL
Methyl sulfone µg/L NA NA 86 71 <8 115 NA NA
Ac id Extrac tables (GC/M S) -E PA 625 List - 0 of 15 ta rget a nalytes above RL
Bas e/N eutral E xtrac tables (GC/MS )- EPA 625 Lis t - 1 of 46 targ et ana lytes above RL
Diethylphthalate µg/L <8 <8 <8 14 13 <16 NA NA
Silanols (DM SD and M MST by LC/ RI) - 2 of 2 ta rget a nalytes above RL
Dimethylsilanediol (DMSD) µg/L 35,000 SWEG <500 <500 <500 <500 <1000 <1000 850 5500
Monomethylsilanetriol (MMST) µg/L 110,000 SWEG NA NA NA NA <1000 <1000 NA 3800
Trimethylamine µg/L Trialkylamines 400 SWEG <500 <500 <250 <250 <250 <250 <250 289
Organic Carbon Re cove ry percent NA NA NA 15.11 NA NA 9.07 83.71
Unac counte d Organic Carbon mg/L NA NA NA 0.15 NA NA 2.22 0.41
NOTES: NA=Not analyzed; 41000 = Syst em Specification for ISS, SSP 41000; SWEG = Spacecraft Water Exposure Guideline, JSC 63414
Se mi-volatile s - S pecial I ntere st Compounds (Semi-qua ntitative - 2 pt c urve) - 0 of 4 7 targe t analyt es abo ve RL
Alc ohols (D AI/ GC/M S) - 0 of 14 ta rget a nalytes above RL
Glyc ols (D AI/ GC/MS ) - 0 of 2 targe t analy tes a bove RL
Carboxy lates (CE/I C) - 0 of 11 targ et ana lytes above RL
Amine s (CE/ IC) - 1 of 4 ta rget a nalytes above RL
Alde hydes ( GC/MS ) - 0 of 1 targe t analy te abov e RL
Non- volatile s (LC/U V-VI S) - 0 of 2 t arget analytes above RL
Soyuz 40/Exp. 42
SpaceX-6/Exp. 43
Soyuz 43/Exp. 45
Anions /Cations (IC) - 0 of 11 targe t analyte s abov e RL
Me tals (I CP/MS ) - 9 of 22 targ et analy tes a bove RL
Total Or ganic Car bon (Ultra violet pe rsulfate oxidat ion)
