Natural Attenuation of Persistent Chemical Warfare Agent VX on Selected Interior Building Surfaces


EPA
EPA/600/R-16/110 I October 2016
www.epa.gov/homeland-security-research
United States
Environmental Protection
Agency
Natural Attenuation of Persistent
Chemical Warfare Agent VX on
Selected Interior Building Surfaces
Office of Research and Development
Homeland Security Research Program

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EPA/600/R-16/110
October 2016
Natural Attenuation of Persistent Chemical
Warfare Agent VX on Selected Interior
Building Surfaces
U.S. Environmental Protection Agency
Office of Research and Development
National Homeland Security Research Center
Research Triangle Park, NC 27711

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Disclaimer
The U.S. Environmental Protection Agency, through its Office of Research and Development,
funded and managed the research described here under contract EP-C-11-038, Task Order 23
with Battelle. It has been subjected to the Agency's review and has been approved for
publication. Note that approval does not signify that the contents necessarily reflect the views of
the Agency. Mention of trade names, products, or services does not convey official EPA
approval, endorsement, or recommendation.
Questions concerning this document or its application should be addressed to:
Lukas Oudejans, Ph.D.
National Homeland Security Research Center
Office of Research and Development
U.S. Environmental Protection Agency (MD-E343-06)
109 T.W. Alexander Drive
Research Triangle Park, NC 27711
Phone: 919-541-2973
Fax: 919-541-0496
E-mail: Oudeians.Lukas@epa.gov
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Acknowledgments
This effort was initiated following discussions with the U.S. Environmental Protection Agency's
(EPA's) Office of Solid Waste and Emergency Response (OSWER)'s Office of Emergency
Management (OEM) on high-priority research needs to support response and recovery following
incidents involving chemical, biological, or radiological (CBR) agents or materials. This work
was managed by the principal investigator from Office of Research and Development (ORD)'s
National Homeland Research Center (NHSRC) with input from US EPA project team members:
Lukas Oudejans, Ph.D. (Principal Investigator), ORD/NHSRC
Paul Lemieux. Ph.D., ORD/NHSRC
Lawrence Kaelin, OSWER/OEM/Consequence Management Advisory Division (CMAD)
Catherine Young, EPA Region 1
Charlie Fitzsimmons, EPA Region 3
Brian Englert, EPA Region 4
This effort was completed under U.S. EPA contract EP-C-11-038, Task Order 23, with Battelle;
their efforts are greatly appreciated.
The authors would like to thank Joan Bursey for her technical editing; QA reviewers Ramona
Sherman and Eletha Brady-Roberts; and Matthew Magnuson (ORD/NHSRC), Shannon Serre
(OSWER/OEM), and Dave Mickunas (OSWER/Emergency Response Team (ERT)) for their
review contributions to this report.
ii

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Executive Summary
The U.S. Environmental Protection Agency (EPA) Office of Research and Development's
(ORD's) Homeland Security Research Program (HSRP) strives to protect human health and the
environment from adverse impacts resulting from, among others, acts of intentional
contamination (including terrorist incidents) by investigating the effectiveness and applicability
of technologies for environmental response. Within the HRSP, EPA's National Homeland
Security Research Center (NHSRC) conducts research necessary to identify methods and
equipment that can be used for decontamination of surfaces contaminated with chemical warfare
agents (CWAs). Previous research has indicated that natural attenuation might be an effective
option for CWAs, especially given the relatively high volatility of some of these agents.
For more persistent and less volatile CWAs such as O-ethyl S-(2-[diisopropylamino]ethyl)
methylphosphonothioate (VX), further study is needed to determine the applicability of using
natural attenuation for surface decontamination. This project evaluated factors potentially
affecting the natural attenuation of VX, including surface material, temperature, relative
humidity (RH), and air exchange. In addition, the transfer of evaporated VX to adjacent
materials, including more absorptive materials and the surrounding air, was investigated.
More specifically, the project objectives included:
• Investigating the natural attenuation of VX on various materials under different
environmental conditions.
• Investigating the redistribution of evaporated VX vapor onto various uncontaminated
materials after being placed inside a chamber next to silanized glass spiked with VX.
The longest weathering period (up to 35 days) was dependent on the environmental condition
and was based on a fixed number of time points at the onset of each test. An iterative approach
was used to establish the longer weathering periods based on observed VX amounts recovered
and expected attenuation.
The mean VX recovery from the spike controls (2 microliters [|iL] of VX added directly to
hexane) during the natural attenuation testing was 2187 micrograms (|ig) of VX. The initial
average surface concentration of VX on the coupon surfaces was thus estimated to be 2.187
grams per square meter, although VX was applied as a single droplet and not evenly distributed
over the entire coupon surface. After weathering periods (ranging from 30 minutes [min] to 35
days), VX was extracted from the coupons using hexane and quantified via gas
chromatography/mass spectrometry (GC/MS). The VX attenuations (estimated by: 100% - mean
%VX recovery relative to spike controls) by environmental condition, material, and weathering
period are shown in Figure ES-1. The x-axis is not to chronological scale.
iii

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Concrete (25C, 40% RH, no air exchange)
Glass (25C, 40% RH, no air exchange)
Metal (25C, 40% RH, no air exchange)
Tape (25C, 40% RH, no air exchange)
Tile (25C, 40% RH, no air exchange)
>	Concrete (25C, 40% RH, 1 air exchange/hr)
>	Glass (25C, 40% RH, 1 air exchange/hr)
Metal (25C, 40% RH, 1 air exchange/hr)
Tape (25C, 40% RH, 1 air exchange/hr)
Tile (25C, 40% RH, 1 air exchange/hr)
»Concrete (IOC, 40% RH, 1 air exchange/hr)
• Glass (IOC, 40% RH, 1 air exchange/hr)
Metal (IOC, 40% RH, 1 air exchange/hr)
Tape (IOC, 40% RH, 1 air exchange/hr)
Tile (IOC, 40% RH, 1 air exchange/hr)
>	Concrete (35C, 40% RH, 1 air exchange/hr)
>	Glass (35C, 40% RH, 1 air exchange/hr)
Metal (35C, 40% RH, 1 air exchange/hr)
Tape (35C, 40% RH, 1 air exchange/hr)
Tile (35C, 40% RH, 1 air exchange/hr)
30min 4 hr 7 hr lday 2 days 4 days 7 days 10 days 14 days 21 days 35 days
Extraction Time (Weathering Period)
Figure ES-1. Percent of VX attenuated over time by material and environmental condition.
IV

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Figure ES-1 shows that natural attenuation of VX occurred for all five materials under all four
environmental conditions. Natural attenuation occurred fastest at Environmental Condition 4 (35
°C, 40% RH, with one chamber volume of air exchanged per hour) as VX attenuations were
>98% and > 99.8% for all materials after 4 or 10 days, respectively. After 10 days under
Environmental Condition 4, VX was still present on all painted dry wall coupons; one of the
sealed concrete and silanized glass coupons while no VX was detected on galvanized ductwork
and glazed ceramic tile. A non-detect in this study is defined as below the quantification limit,
defined here as the lowest standard to establish the calibration curve and above, but near the
GC/MS instrument detection limit. The slowest natural attenuation was observed at
Environmental Condition 3 (10 °C, 40% RH, with one chamber volume of air exchanged per
hour) as VX attenuations ranged from 93.5% to 99.6% after 35 days. The VX attenuation was
>98% from all materials after 10 days of weathering for Environmental Condition 1 (25 °C, 40%
RH, without air exchanged) and after 14 days for Environmental Condition 2 (25 °C, 40% RH,
with one chamber volume of air exchanged per hour). Higher temperatures clearly reduce the
time (order of days across tested environmental conditions) to remove VX from materials.
The VX natural attenuations were high (>93%) for all materials at the longest weathering period
for each environmental condition. In fact, at the longest test durations, 16 of 20 tests
(material/environmental condition combinations) were estimated to have >99% natural
attenuation. However, galvanized metal (at Environmental Conditions 1, 2, and 4) and glazed
ceramic tile (at Environmental Conditions 1 and 4) were the only occasions where VX was not
detected at the longest weathering period.
VX attenuation appeared to occur most rapidly on sealed concrete. It seems unlikely that VX is
volatilizing from this material faster than the other materials tested. VX recoveries for this sealed
concrete ranged from approximately 25 to 50%, depending on the environmental conditions,
after just 30 min of weathering. The VX attenuation associated with sealed concrete may actually
be a reflection of the inherently poor extraction efficiency from this sealant and/or underlying
(porous) material. VX may either be reacting with the sealant or becoming strongly absorbed
within the concrete or concrete's sealant making VX difficult to extract or no longer present
(decomposed). VX appeared to attenuate at a similar rate from the remaining materials, although
some significant differences among materials was detected by analysis of variance (ANOVA) at
a significance level of p <0.0001, and some differences among materials were noted at a p
<0.005 level in pairwise comparison.
The redistribution investigation demonstrated limited transfer of VX to surrounding materials.
For this investigation, the mean VX recovery from the spike controls was 2225 |ig. The mean
VX recoveries from the spiked and unspiked coupons after seven days of weathering are shown
in Table ES-1. The spiked silanized glass coupons had a mean VX recovery of 49 |ig. Although
unspiked, VX was also recovered from leather upholstery, HDPE, and cubicle divider cloth
(mean VX recoveries were <4.1 |ig). VX was not recovered from painted metal or desktop
laminate. Air samples collected from the chamber prior to coupon removal were negative for VX
(<0.11 milligram per cubic meter). Wipe samples of interior chamber surfaces, collected after
coupon removal, were also negative for VX (<0.03 |ig per square cm). It should be noted that
only 35% of the spiked VX was accounted for based on detected VX amounts on various
materials. Considering detection limits, chamber wall sizes, gas volumes sampled, and actual
sizes of materials present in the chamber, the VX amount that may have gone unaccounted for
v

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was 31% or higher of the spiked VX amount, depending on the extraction efficiencies. The
redistribution investigation did not address whether VX can be successfully extracted from these
more permeable materials. Therefore, actual VX amounts transferred to these (unspiked)
materials may therefore be higher.
Table ES-1. Redistribution: Mean VX Recovered by Material (Seven-day Weathering
Period)
Silanized glass
Leather upholstery
HDPE
Painted metal
Desktop
Cubicle divider
(spiked), fig
(unspiked), fig
(unspiked), fig
(unspiked), fig
laminate
cloth (unspiked),
(FOD)
(FOD)
(FOD)
(FOD)
(unspiked), fig
Hg (FOD)




(FOD)

49 (15/15)
2.8 (3/3)
<2.5 (2/3)
<2.5 (0/3)
<2.5 (1/3)
4.1 (3/3)
< = all replicate results were less than the quantitation limit (2.5 |ig).
FOD = frequency of detection (number of samples above quantification limit / total number of samples.
Impact of the Study:
Based on the results obtained from this investigation, natural attenuation of persistent CWAs
such as VX may occur, given sufficient time (days to weeks) and favorable temperatures. Natural
attenuation was found to be faster at warmer temperatures (i.e., 35 °C and 25 °C) than cooler
temperatures (i.e., 10 °C). Attenuation of VX was material dependent with a general trend of
faster to slower attenuation in the order ceramic tile - galvanized metal - silanized glass - painted
drywall. Trace amounts of VX may still be present weeks to months after a contamination event.
These surface concentrations should be put into context with surface clean up levels for VX
which have not been established or endorsed by US EPA. Such cleanup levels are expected to be
site specific and at or below the detection limit for VX in this study. Therefore, detectable
amounts of VX on the investigated materials as observed in this study, even after weeks of
natural attenuation, would require surface or volumetric decontamination / neutralization to reach
the expected cleanup level for VX.
Sealed concrete appears to absorb VX on a very short time scale (more than 50% within 30 min)
and should be considered as a separate permeable entity as VX may have become trapped under
the sealant. This would require long term monitoring to ascertain whether VX may resurface by
diffusion through this sealant, creating a long term contact and inhalation hazard.
A limited redistribution of VX (mean recoveries <5 |ig for unspiked material) to unspiked
materials was observed over a period of seven days. These amounts may be biased low and
should be considered semi quantitative as extraction efficiencies for VX from the unspiked
materials were not established.
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Table of Contents
Disclaimer	i
Acknowledgments	ii
Executive Summary	iii
Table of Contents	vii
List of Figures	ix
List of Tables	x
Acronyms and Abbreviations	xi
1.0	Introduction	1
1.1	Purpose	1
1.2	Proj ect Obj ectives	1
1.3	Test Facility Description	2
2.0	Experimental Methods	3
2.1	General Experimental Design	3
2.2	Test Matrices	4
2.2.1	Natural Attenuation Investigation	4
2.2.2	Redistribution Investigation	6
2.3	Test Chamber	8
2.4	Test Materials	9
2.4.1	Natural Attenuation Investigation	9
2.4.2	Redistribution Investigation	10
2.5	Chemical Agent and Spiking Coupons	11
2.6	Extraction of VX from Coupons, Wipe Samples, and Solid Sorbent Tubes	12
2.7	Recovery Efficiency	12
2.8	Analytical Methods for VX	13
2.9	Extraction Efficiency	14
2.10	Analysis of Variance to Test Hypotheses	15
3.0	Test Results	19
3.1	Recovery Efficiency Results	19
3.2	Natural Attenuation Results	19
3.2.1	Environmental Condition 1	19
3.2.2	Environmental Condition 2	22
3.2.3	Environmental Condition 3	26
3.2.4	Environmental Condition 4	29
3.3	Analysis of Variance Results	32
3.4	Redistribution Results	34
4.0	Quality Assurance/Quality Control	36
4.1	Control of Monitoring and Measuring Devices	36
vii

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4.2	Equipment Calibrations	37
4.3	Technical Systems Audit	39
4.4	Performance Evaluation Audits	39
4.5	Data Quality Audit	40
5.0 Summary	41
6.0 References	47
Appendix A	48
viii

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List of Figures
Figure ES-1. Percent of VX attenuated overtime by material and environmental condition	vi
Figure 1. Schematic drawing of test chamber showing wipe sample locations and solid sorbent tube ports.
	9
Figure 2. Temperature during Environmental Condition 1 testing	20
Figure 3. Relative humidity during Environmental Condition 1 testing	20
Figure 4. VX recovery at Environmental Condition 1	22
Figure 5. Temperature during Environmental Condition 2 testing	23
Figure 6. Relative humidity during Environmental Condition 2 testing	23
Figure 7. VX recovery at Environmental Condition 2	26
Figure 8. Temperature during Environmental Condition 3 testing	27
Figure 9. Relative humidity during Environmental Condition 3 testing	27
Figure 10. VX recovery at Environmental Condition 3	29
Figure 11. Temperature during Environmental Condition 4 testing	30
Figure 12. Relative humidity at Environmental Condition 4 testing	30
Figure 13. VX recovery at Environmental Condition 4	32
Figure 14. VX recovered from the natural attenuation investigation. The x-axis is not to scale
chronologically	44
Figure 15. VX recovered from the redistribution investigation	46
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List of Tables
Table ES-1. Redistribution: Mean VX Recovered by Material (Seven-day Weathering Period)	viii
Table 1. Natural Attenuation Test Matrix and Coupons Used for Each Material Type	5
Table 2. Redistribution Test Matrix and Coupons Used for Each Material Type	8
Table 3. Description of Materials Used for the Natural Attenuation Investigation	10
Table 4. Description of Materials Used for the Redistribution Investigation	11
Table 5. Gas Chromatography/Mass Spectrometry Conditions	13
Table 6. Summary of Recovery Efficiency Testing	19
Table 7. VX Recovery at Environmental Condition 1	21
Table 8. Relative Humidity during Environmental Condition 2 Testing	24
Table 9. VX Recovery at Environmental Condition 2	25
Table 10. VX Recovery at Environmental Condition 3	28
Table 11. VX Recovery at Environmental Condition 4	31
Table 12. VX Recovery from the Redistribution Investigation	35
Table 13. Arrangement of Individual Coupons on Shelf within Test Chamber during the Redistribution
Investigation and Associated VX Recovery	35
Table 14. Quality Control Requirements and Results	36
Table 15. Equipment Calibration Schedule	37
Table 16. Gas Chromatography Performance Parameters and Acceptance Criteria	39
Table 17. Technical Systems Audit Results	39
Table 18. Performance Evaluation Results	40
Table 19. Percent VX Attenuated over Time by Environmental Condition	42
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Acronyms and Abbreviations
%R	percent recovery
%RSD	percent relative standard deviation
°C	degrees Celsius
ANOVA	analysis of variance
CBR	chemical, biological, radiological
CCV	continuing calibration verification
CMAD	Consequence Management Advisory Division
cm	centimeter(s)
cm2	square centimeter(s)
CWA	chemical warfare agent
DoD	U.S. Department of Defense
EPA	U.S. Environmental Protection Agency
ERT	Emergency Response Team
FID	flame ionization detector
FOD	frequency of detection
GC	gas chromatography
GLM	General Linear Model
HDPE	high density polyethylene
HMRC	Hazardous Materials Research Center
h	hour(s)
HS	Homeland Security
HSRP	Homeland Security Research Program
IS	internal standard
kHz	kilohertz
LC	liquid chromatography
LED	light-emitting diode
|ig	microgram(s)
|iL	microliter(s)
|im	micrometer(s)
min	minute(s)
mL	milliliter(s)
mm	millimeter(s)
MS	mass spectrometry
NHSRC	National Homeland Security Research Center
NIST	National Institute of Standards and Technology
OEM	Office of Emergency Management
ORD	Office of Research and Development
xi

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OSWER
Office of Solid Waste and Emergency Response
PE
performance evaluation
QA
quality assurance
QAPP
quality assurance project plan
r2
coefficient of determination
RH
relative humidity
SD
standard deviation
SOP
standard operating procedure
SST
solid sorbent tube
TSA
technical systems audit
VX
O-ethyl S-(2-[diisopropylamino]ethyl) methylphosphonothioate
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1.0 Introduction
The U.S. Environmental Protection Agency's (EPA's) Homeland Security Research Program
(HSRP) is helping to protect human health and the environment from adverse impacts resulting
from the release of chemical, biological, or radiological (CBR) agents. The HSRP is functioning
to develop tools and information that will help detect and quantify the intentional release of CBR
contaminants in buildings, water systems, or the outdoor environment; contain these
contaminants; decontaminate buildings, water systems or the outdoor environment; and facilitate
the treatment and disposal of hazardous materials resulting from remediation/cleanup activities.
As part of the HSRP, EPA investigates the effectiveness and applicability of technologies and/or
approaches for homeland security (HS)-related applications by developing test plans that are
responsive to the needs of the HSRP's EPA Program Office and Regional partners, conducting
tests, collecting and analyzing data, and preparing peer-reviewed reports. EPA provides high-
quality information that is useful to decision makers in responding to incidents and implementing
appropriate technologies to mitigate consequences to the public resulting from CBR incidents.
U.S. EPA is responsible for planning for and responding to releases of toxic chemicals into the
environment, including the deliberate release of chemical warfare agents (CWAs). Natural
attenuation of volatile chemical agents might be an effective option for some CWAs that have
high volatility. Natural attenuation might provide a low cost and low impact approach for
decontaminating surfaces and may also be a desirable option for structures that do not require
immediate reopening/reoccupation.
For more persistent and less volatile CWAs such as O-ethyl S-(2-[diisopropylamino]ethyl)
methylphosphonothioate (VX), further study is needed to determine the applicability of using
natural attenuation for decontamination of surfaces. This project evaluated factors potentially
affecting the natural attenuation of VX after VX was applied as a liquid onto presumably
impermeable surfaces: temperature, relative humidity (RH), and air exchange. In addition, the
transfer of evaporated VX to adjacent materials, including more absorptive materials and the
surrounding air, was evaluated.
1.1 Purpose
The purpose of this project was to generate natural attenuation and redistribution data following
the application of VX onto various materials under different environmental conditions to better
inform potential decontamination options for less volatile CWAs such as VX from impermeable
materials.
1.2 Project Objectives
The project objectives included:
• Investigating the natural attenuation, for up to 35 days, of VX on materials under
different environmental conditions.
• Investigating the redistribution of evaporated VX vapor onto uncontaminated materials
after being placed inside a chamber next to silanized glass spiked with VX.
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1.3 Test Facility Description
All testing was performed at the Battelle Hazardous Materials Research Center (HMRC), West
Jefferson, Ohio. The HMRC is certified to work with chemical surety material through its
Bailment Agreement W911SR-10-H-0001 with the U.S. Department of the Army.
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2.0 Experimental Methods
As a general overview, coupons (small representative pieces) of various materials were spiked
with VX for the natural attenuation investigation. The coupons were placed in a test chamber
under controlled temperature, RH, and air exchange conditions. At designated times, the coupons
were removed from the chamber, extracted, and analyzed for VX. For the redistribution
investigation, VX was spiked onto silanized glass coupons and placed in the chamber with other
unspiked materials. After a designated time sufficiently long enough to volatilize VX, the
unspiked coupons, chamber air, and chamber surfaces were sampled and analyzed for VX. The
redistribution investigation was intended to investigate whether VX spiked onto an impermeable
material could contaminate other materials in the test chamber, presumably via evaporation and
deposition, absorption or adsorption. More specific experimental methods are provided in
Sections 2.1 through 2.8.
2.1 General Experimental Design
A multiple group time-series experimental design was used, as represented below:
Xi
Oio
On
012
Ol3
Ol4
Ol5
016
Ol7
X2
O20
On
022
023
024
025
026
O21
X3
O30
031
032
033
034
035
036
037
X4
O40
041
042
043
044
045
046
047
For this experimental design, time passes from left to right. The Xn represents the experimental
treatment (X) at a given environmental condition (n). Coupons were randomly assigned to
groups that were extracted and analyzed for VX after up to eight time durations (t). The mean
masses of VX recovered from coupons for a given material after a given time (t) under a given
environmental condition (n) were the experimental results/observations (Ont).
Three hypotheses were tested:
Test #1:
• Null hypothesis: No decline occurs in mean recovered VX over time.
• Alternative hypothesis: Mean recovered VX declines over time.
Test #2:
• Null hypothesis: The mean rate of VX loss does not change among different
temperatures and air exchange rates.
• Alternative hypothesis: The mean rate of VX loss differs among temperatures and air
exchange rates.
Test #3:
• Null hypothesis: The mean rate of VX loss does not vary among different materials.
• Alternative hypothesis: The mean rate of VX loss does vary among different materials.
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Each test was addressed in an analysis of variance (ANOVA) performed on the natural log-
transformed residual masses of VX with an exponential decay. The ANOVA model included
effects for the duration of time from spiking occurrence (i.e., eight distinct time points, treated as
continuous time measurements), material type, environmental condition, and interactions
between these terms (as they are deemed statistically significant at the 0.05 level). Each
hypothesis test is associated with a test for a specific parameter in the ANOVA model:
• Test #1: Test for whether the slope parameter associated with time from initial spiking is
significantly less than 0 (i.e., results in a decline in the mass measurement with increasing
time).
• Test #2: Test for whether the fixed effects of environmental condition differ significantly
from 0 (i.e., mean mass measurement differs among environmental conditions).
• Test #3: Test for whether the fixed effects of material type differ significantly from 0
(i.e., mean mass measurement differs among environmental conditions).
For a specific test within the analysis of variance, the null hypothesis was rejected for the
alternative hypothesis if the p-value for the F-test performed on the given model parameter was
no higher than 0.05.
2.2 Test Matrices
2.2.1 Natural Attenuation Investigation
The test matrix for VX natural attenuation is shown in Table 1. Between attenuation tests, the
test chamber and work area were cleaned, and contaminated test items and waste were disposed.
Attenuation was evaluated at controlled temperature (10 to 35 degrees Celsius [°C] range), RH,
and air exchange rates in a custom-built test chamber. Briefly, the natural attenuation
investigation was conducted as follows:
• Five materials were used for the attenuation investigation: sealed concrete, silanized
glass, galvanized metal ductwork, painted drywall tape, and glazed ceramic tile.
• Four environmental conditions were each run as a separate test in the chamber.
• Environmental conditions in the chamber (with coupons present) were stabilized at
specified experimental conditions for at least one hour prior to spiking coupons.
• On each day of testing, 40 coupons of each material type were spiked with 2 microliters
(|iL) of VX as described in Section 2.5. Coupons were spiked in the test chamber. In
addition, 2 |iL of VX was spiked directly into hexane (five replicates) at time zero to
serve as spike controls. The spike controls were spiked as follows:
o One at the beginning, prior to spiking any coupons
o One after 25% of the coupons had been spiked
o One after 50% of the coupons had been spiked
o One after 75% of the coupons had been spiked
o The last after all coupons had been spiked.
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Five coupons of each material type were extracted at 30 minutes (min) after spiking plus
seven additional time points after spiking, as shown in Table 1.
•	In addition to the five test coupons, one procedural blank coupon (a coupon inside the test
chamber that was not spiked with VX) of each material type and one laboratory blank
coupon (a coupon kept outside the agent hood and test chamber that was not spiked with
VX) of each material type were extracted and analyzed along with the test coupons at
each time point.
•	An adaptive management approach was used during the natural attenuation tests in which
data from one condition were used to derive time points for the next test condition
Table 1. Natural Attenuation Test Matrix and Coupons Used for Each Material Type
Environmental
Conditions
Material
Initial Analyses
(Coupons per
Each Material)
Seven Additional Time Points
(Coupons per Each Material)
Condition 1:
25 °C, 40% RH,
without air
exchanged
sealed concrete,
silanized glass,
galvanized metal ductwork,
painted drywall tape,
glazed ceramic tile
5 spike controls
(no coupon),
5 test coupons
(30 min after spike)
5 test coupons
1 procedural blank
1 laboratory blank
(Time points: 4 hours [h]; 1, 4,
7, 10, 14, and 21 days)
Condition 2:
25 °C, 40% RH,
with one chamber
volume of air
exchanged per
hour
sealed concrete,
silanized glass,
galvanized metal ductwork,
painted drywall tape,
glazed ceramic tile
5 spike controls
(no coupon),
5 test coupons
(30 min after spike)
5 test coupons
1 procedural blank
1 laboratory blank
(Time points: 4 and 7 h; 1, 2, 4,
7, and 14 days)
Condition 3:
10 °C, 40% RH,
with one chamber
volume of air
exchanged per
hour
sealed concrete,
silanized glass,
galvanized metal ductwork,
painted drywall tape,
glazed ceramic tile
5 spike controls
(no coupon),
5 test coupons
(30 min after spike)
5 test coupons
1 procedural blank
1 laboratory blank
(Time points: 7 h; 1, 4, 7, 14,
21, and 35 days)
Condition 4:
35 °C, 40% RH,
with one chamber
volume of air
exchanged per
hour
sealed concrete,
silanized glass,
galvanized metal ductwork,
painted drywall tape,
glazed ceramic tile
5 spike controls
(no coupon),
5 test coupons
(30 min after spike)
5 test coupons
1 procedural blank
1 laboratory blank
laboratory blank
(Time points: 4 and 7 h; 1, 2, 4,
7, and 10 days)
Materials were selected based on their presumed impermeable characteristics and perceptible
presence in indoor facilities; time points for Condition 1 were based on existing persistence data
[Columbus et al. (2012)] while time points for other conditions were derived from results
obtained for Condition 1.
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2.2.2 Redistribution Investigation
To assess whether redistribution of evaporated VX vapor was occurring, coupons (not spiked) of
five selected materials typically present in an office space were placed into the test chamber with
silanized glass coupons spiked with VX. The unspiked coupons were maintained with the VX-
spiked silanized glass coupons inside the test chamber at a specific controlled temperature and
RH conditions for a weathering period of seven days to allow for adequate volatilization of the
liquid VX. Following the weathering period, all coupons were extracted with hexane solvent and
the extracts were analyzed via gas chromatography (GC)/mass spectrometry (MS). Briefly, the
redistribution investigation was conducted as follows:
• The test chamber and work area were cleaned, and contaminated test items and waste
from prior testing were disposed in accordance with the SOP for chemical agent
decontamination and collection and disposal of waste.
• Materials tested during the redistribution investigation were likely permeable office
materials leather upholstery, HDPE, painted metal, desktop laminate, and cubical divider
cloth.
• Three coupons of each material type were used during testing.
• Silanized glass coupons were spiked with VX and distributed uniformly in the
environmentally-controlled test chamber among the unspiked coupons of various
materials.
• Two [j,L of VX was applied to the silanized glass coupons as described in Section 2.5.
• Three spike controls were prepared by directly injecting 2 [xL of VX into hexane.
• Coupons were maintained at the specified temperature and RH conditions in the test
chamber (Table 2).
• Air inside the test chamber was not exchanged during the test. Mixing fans ensured
adequate mixing of the air inside the test chamber.
• After a single weathering period of seven days, all coupons were removed from the test
chamber, extracted as described in Section 2.6, and analyzed as described in Section 2.8.
• Prior to the removal of coupons from the chamber, solid sorbent tubes (SSTs) were used
to sample the air inside the chamber. The SSTs (T060302, CAMSCO, Houston, TX)
consisted of a polytetrafluoroethylene tube packed with Chromosorb 106 sorbent material
(60/80 mesh, single 1.5 inch (3.8 centimeters [cm]) deep bed [-180 milligrams of media],
0.25 inch (0.6 cm) outside diameter x 2 inch (5 cm) length polytetrafluoroethylene
housing). Air was drawn through the SSTs at a rate of 300 milliliters (mL)/min for 15
min (4.5 liters total air volume sampled). The sorbent material was then removed from
the tube, extracted with hexane, and extracts analyzed for VX by GC/MS.
• After the removal of coupons from the test chamber, selected interior surfaces of the test
chamber were wipe-sampled using lint-free 2 inch (5 cm) x 2 inch (5 cm) four-ply
rayon/polyester blend sponges (Part # 22-037-921, Fisher Scientific, Pittsburgh, PA). The
sponges were wetted with hexane prior to use consistent with EPA (2007). Internal
chamber surfaces, each approximately 100 square centimeters (cm2), were wiped using
an established pattern (four horizontal and four vertical strokes). Wipes were solvent
extracted and extracts analyzed for VX by GC/MS.
6

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7

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Table 2. Redistribution Test Matrix and Coupons Used for Each Material Type
Environmental
Conditions
Material
Initial
Analyses
Final Analyses
(Spiked [Silanized
Glass] Coupons)
Final Analyses
(Coupons Per
Unspiked Material)
25 °C, 40% RH,
without air
exchanged
silanized glass (spiked),
leather upholstery (unspiked),
HDPE (unspiked),
painted metal (unspiked),
desktop laminate (unspiked),
cubicle divider cloth (unspiked)
3 spike controls
(no coupons)
15 test coupons
1 procedural blank
1 laboratory blank
(Time point: 7 days)
3 test coupons
1 laboratory blank
(Time point: 7 days)
2.3 Test Chamber
A custom-fabricated acrylic test chamber that enabled monitoring, recording, and control of
temperature, RH, and chamber air exchange was used for testing. The test chamber was held
within a chemical fume hood for secondary containment.
Temperature within the test chamber was adjusted with a radiator/heat exchanger (Part #
3525K25, McMaster-Carr, Aurora, OH) installed at the top of the chamber. The heat exchanger
was fed by a refrigerated/heated bath circulator filled with propylene glycol heat transfer fluid
(-28 °C to 150 °C operating range, ±0.1 °C temperature stability, 500 Watt cooling capacity, 1
kilowatt heating capacity). Humidity was added to the chamber air using a Nafion®
humidification tube (Model #FC100-80, Perma Pure LLC, Toms River, NJ). In the air exchange
configuration, house air was fed through the Nafion® tube to achieve the desired RH and then
supplied to the chamber. The supplied house air was directed through a series of particulate
filters (rated as low as 0.01 micrometers [|im]) and desiccant dryers to clean and dry the air prior
to delivery to the laboratory. A redundant carbon filter and moisture trap were installed at the test
chamber supply air inlet (upstream of the Nafion® tube) to further clean and dry the air. Chamber
supply air exchange was controlled using a calibrated mass flow controller to achieve one air
exchange per hour. In the static configuration, chamber air was recirculated, as necessary,
through a closed loop incorporating the Nafion® tube to replenish water vapor in the air as it
passively depleted.
Process controllers were used to monitor, record, and control temperature, RH, and the chamber
air exchange rate. Temperature and RH input was provided to the controllers from a calibrated
temperature/RH probe (HMT338, Vaisala Oyj, Helsinki, Finland) installed in the test chamber.
In addition, shelf-specific temperature and RH monitoring was conducted with HOBO data
loggers (Onset Computer Corporation, Bourne, MA). A double-door controlled access port
(airlock) in the test chamber allowed for the addition or removal of coupons and supplies with
minimal disturbance to the controlled environmental conditions within. A 2-inch (5 cm) thick
closed-cell foam insulation was also used to prevent chamber heat loss/gain. To minimize the
exposure of the coupons to ultraviolet light, lights in the fume hood and laboratory were turned
off when not needed. Light-emitting diode (LED) bulbs with little to no ultraviolet light were
used inside the test chamber, and black Kraft paper (Part # 883458, Staples, Columbus, OH) was
used to block light at the hood face when no work was being performed. Glove ports allowed the
chamber to remain sealed while operators manipulated coupons and supplies within the chamber.
Circulation fans inside the chamber helped ensure uniformity of the environmental parameters.
8

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Fans were oriented so that air flow was not directed at the coupons. Ports on the test chamber
enabled air to be sampled with SSTs for analysis of VX in the chamber atmosphere.
Figure 1 shows a schematic drawing of the test chamber, including wipe sampling locations
(numbered 1-5) and the three SST ports (numbered 1-3) used during the redistribution
investigation. Mixing fans were present to provide mixing of the air inside the test chamber.
Sample tray placed on left
side shelf, near bottom
(not on bottom shelf)
Top wall, toward left side
(over top of tray)
Front wall, center
SST 3
Chamber floor, right front
corner
SST 2
Chamber floor, near center
Chamber floor, left front
corner
SST 1
Figure 1. Schematic drawing of test chamber showing wipe sample locations and solid
sorbent tube ports.
2.4 Test Materials
2.4.1 Natural Attenuation Investigation
The natural attenuation investigation was conducted using the following types of material
coupons: sealed concrete, silanized glass, galvanized metal ductwork, painted drywall tape, and
glazed ceramic tile. Table 3 presents information about the building materials and preparation
approaches that were used. Coupons were cut to uniform length and width (4.0 cm x 2.5 cm)
from a large piece of material except for concrete. Concrete coupons were poured into a 4.0 cm x
2.5 cm mold and, after curing, coated with a weather sealer (Siloxane PD, PROSOCO,
Lawrence, KS) designed for both exterior and interior applications. Edges and damaged areas
were avoided in cutting test coupons. Glass coupons were silanized following a modification of
the method of Labit et al. (2008).
9

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Table 3. Description of Materials Used for the Natural Attenuation Investigation
Material
Description
Manufacturer/
Supplier Name
Coupon Size
Length (cm) x
Width (cm)
Preparation
Sealed
concrete (all
sides)
Weather sealer (Siloxane PD,
PROSOCO, Lawrence, KS) sealed
concrete (5 parts sand; 2 parts
cement [Buzzi UnicemUSA,
Greencastle Plant, Greencastle,
IN]); custom preparation.
Wysong Concrete
Cincinnati, OH
4.0 x 2.5
Cleaned with dry air
to remove loose dust
Silanized glass
Window glass
(initially uncoated)
Brooks Brothers,
West Jefferson OH
4.0 x 2.5
Silanized*
Galvanized
metal
ductwork
Industry heating, ventilation and air
conditioning standard; 24 gauge
galvanized steel; thickness 0.7
millimeter (mm) (Adept
Manufacturing)
Adept
Products, Inc.
West Jefferson, OH
4.0 x 2.5
Cleaned with
acetone to remove
oil from the surface
Painted
dry wall tape
(one side)
White joint tape, Sheetrock® brand,
item number 15335, model number
380041;
KILZ® latex primer, item number
45548, model number 20902
Lowe's
Hilliard, OH
4.0 x 2.5
1.	Applied one coat
of latex primer;
2.	Allowed to dry;
3.	Applied one coat
Belir® Premium Plus Interior Flat
White Latex Paint, item number
923827
Home Depot
Columbus, OH

of paint;
4. Allowed to dry.
Glazed
ceramic tile
Caribbean slate matte ceramic floor
tile, item number 16286, model
number L301123
Lowe's
Hilliard, OH
4.0 x 2.5
Cleaned with dry air
to remove loose dust
* The process used to silanized the glass is according to Labit et al. (2008).
2.4.2 Redistribution Investigation
The redistribution investigation was conducted using the following types of office material
coupons: silanized glass (from Table 3, which was spiked with VX) and the following unspiked
materials: leather upholstery, HDPE, painted metal, desktop laminate, and cubicle divider cloth.
Table 4 describes the coupon materials and preparation approaches (if any) in detail. Coupons
were cut to uniform length and width (4.0 cm x 2.5 cm) from a larger piece of material. Edges
and damaged areas were avoided in cutting the coupons.
10

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Table 4. Description of Materials Used for the Redistribution Investigation
- , ,	Coupon Size
. . . . Manutacturer/ „
Material	Description	Length (cm) x	Preparation
Supplier N ame	width (cm)
Leather
upholstery, e.g.,
office chairs
Fine Leather Accessories
8.5 inch (21.6 cm) x 11 inch
(27.9 cm) Pad Cover;
Country Lux Black;
Item number
WYF078275927070
Dr. Koffer / Staples
Columbus, OH
4.0 x 2.5
None
HDPE
26-inch (66 cm) x 20-inch
(52 cm) HDPE Small Black
All Purpose Tub; item
number 19251
MacCourt / Lowe's
Columbus, OH
4.0 x 2.5
Cleaned with dry air
to remove loose dust
Painted metal,
i.e., filing
cabinets
Vertical File Cabinet
(Graphite), item number
490199
Office Designs /
Staples Columbus,
OH
4.0 x 2.5
Cleaned with dry air
to remove loose dust
Desktop
laminate
Laminate 30-inch (76 cm) x
96-inch (244 cm) Folkstone-
Matte Postform Laminate
Kitchen Countertop Sheet;
item number 239114
Formica®/Lowe' s
Columbus, OH
4.0 x 2.5
Cleaned with dry air
to remove loose dust
Cubicle divider
cloth
Fabric Standard Modular
Panel, product number
302609
Best-Rite/Staples
Columbus, OH
4.0 x 2.5
None
2.5 Chemical Agent and Spiking Coupons
VX used for this study was obtained from EPA-owned agents, purchased from the U.S.
Department of Defense (DoD) and stored by Battelle at the HMRC. The VX was in a sealed
ampoule and had a -94% purity when sealed, and the purity was expected to remain high during
storage. The VX purity was measured six times during this project by GC/flame ionization
detector (FID). The preparation dates and associated purity were:
•	December 3, 2014	95.8%
•	January 5, 2015	95.4%
•	February 2, 2015	94.9%
•	March 26, 2015	92.8%
•	April 20, 2015	88.4% (redistribution test)
The coupons were inspected visually prior to spiking with the neat VX; coupons with surface
anomalies (scratches, pivits, etc.) were not used. Neat VX (concentrations corrected for percent
purity) was dispensed using a Hamilton repeating dispenser (#PB600-1, Hamilton, Reno, NV)
and 100 |iL Hamilton syringe (#81085, Hamilton, Reno, NV, or equivalent). All test coupons
were spiked with a single 2 |iL droplet of neat VX. The coupons were open to the atmosphere
within the test chamber. After being under the environmental conditions for a given experiment
11

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and specified time, a batch of coupons was transferred from the test chamber for solvent
extraction of residual agent. This process was repeated for each time point in the test matrix.
2.6	Extraction of VX from Coupons, Wipe Samples, and Solid Sorbent Tubes
The VX extraction procedure included placing each coupon (including blanks) into a separate 60
mL glass bottle (05-719-257, Fisher Scientific, Pittsburgh, PA) containing 25 mL of hexane and
internal standard (IS; 10 micrograms (|ig)/mL naphthalene-d8 [AC 17496-0010, Fisher Scientific,
Pittsburgh, PA]). Coupons (4 cm x 2.5 cm) fit lying flat within the inside diameter of the bottles.
The 25 mL of liquid reaches a height of approximately 1.3 cm, higher when the liquid was
displaced by coupons. This approach was sufficient to submerge all coupon types fully. The
bottles were swirled by hand for approximately five to ten seconds, and then placed into a
sonicator. Extraction bottles were sonicated at 40 to 60 kilohertz (kHz) for ten min. Within 30
min of completing this process, approximately 1 mL from each extraction bottle was transferred
to an individual GC vial (vial P/N 21140, cap P/N 24670, Fisher Scientific [Restek Corporation],
Hanover Park, IL) and sealed. Samples not analyzed the same day as extraction were stored at <-
20 °C. Wipe samples generated during the redistribution test were extracted in the same manner.
Following sampling, SSTs were extracted according to the below procedure:
•	The SST tube housing was cut at one end near the sorbent bed.
•	A vial, labeled with the unique sample identification of the SST, was placed at the base of
a modified press.
•	The SST was placed with the cut end facing downward into the clamp of the modified
press (while ensuring the cut end of the SST was inside the vial).
•	The press was actuated to eject the sorbent material from the SST into the vial.
•	The press clamp was released, allowing the SST to fall into the vial.
•	The vial was filled with 5.0 mL of hexane with IS, and the vial was securely capped
(capped with PTFE-lined lid).
•	The vial was mixed via vortex mixer for 30 seconds.
•	Following mixing, the vial remained undisturbed for one hour to complete extraction and
allow the sorbent material to settle.
•	Following the hour, an aliquot of the hexane extract was transferred to a labeled GC vial
for analysis via GC/MS.
2.7	Recovery Efficiency
VX recovery efficiency following extraction immediately after spiking was demonstrated for
sealed concrete, silanized glass, painted drywall tape, and glazed ceramic tile as they were novel
coupons/CWA combinations not used previously. High (81%) recovery of VX from galvanized
metal had been observed in a previous study (EPA 2010).
Recovery efficiency with hexane was evaluated as follows:
12

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• Tests were performed in triplicate. Three coupons of each material type (silanized glass,
glazed ceramic tile, painted drywall tape, and sealed concrete) were spiked: three spike
controls (a spike of equal amount of VX directly into the extraction solvent) and a single
laboratory blank for each of the four materials. The laboratory blank coupons were
extracted the same way as the other coupons; however, the laboratory blank coupons
were not exposed to VX (the laboratory blank was never placed inside the agent hood).
• Coupons were spiked as described in Section 2.5 and extracted as described in Section
2.6, except that the extraction occurred immediately after spiking, rather than after a
specified weathering period.
• To be acceptable, recoveries of VX for each of the materials had to be 70% to 120% of
the mean of the spike control recoveries with <30% coefficient of variance between
samples.
2.8 Analytical Methods for VX
The sample extracts were analyzed to quantify the amount of VX remaining on each coupon
using GC/MS (6890 gas chromatograph and 5973 mass selective detector, Agilent Technologies,
Santa Clara, CA) operated in the full-scan mode for compounds ranging from 40 to 500 atomic
mass units. VX was detected with ions 114, 72, 127, and 79. The GC/MS parameters that were
used are shown in Table 5.
The lowest standard used to establish the calibration curve (quantitation limit) was above, but
near, the GC/MS instrument detection limit. Samples with results below the lower calibration
level (i.e., 0.10 |ig/mL) were reported as less than the quantitation limit. The quantitation limit
corresponds to 2.5 |ig of VX on the coupon based on the 25 mL extraction solvent volume.
Table 5. Gas Chromatography/Mass Spectrometry Conditions
Parameter
Description
Instrument
Hewlett Packard Model HP 6890 Gas Chromatograph equipped with HP 5973 A
Mass Selective Detector and Model 7683 Automatic Sampler
Column
30 meters x 0.25 mL inside diameter Rtx-5 (cross-linked methylsilicone), fused
silica capillary column, 0.25 |im film thickness (Restek Catalog Number 05223)
Carrier gas flow rate
1.2 mL/min helium (constant flow)
Column temperature
40 °C initial temperature, hold 1 min 30 °C/minto 280 °C, hold 0 min
Injection volume/type
1 |iL splitless injection (4 mm inside diameter single gooseneck quartz insert) with
0.5 min purge activation time. Split vent flow rate at 80 mL/min
Injection temperature
250 °C
MS quad temperature
150 °C
MS source
temperature
230 °C
Solvent delay
3 min
13

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2.9 Extraction Efficiency
CWA concentrations in coupon, wipe, and SST extract samples and spike control samples were
calculated by the GC/MS instrument software and provided in units of |ig/mL. The GC/MS
analysis result for each extract sample was fitted to the calibration curve generated for the
specific GC used to analyze the sample. The CWA concentration was determined from the ratio
of the CWA peak area response to that of the IS peak area response. Use of an IS compensated
for potential variability in sample injection volumes as well as decreasing or increasing
instrument sensitivity. During the effort, VX exhibited a quadratic response over the
concentration range analyzed [0.1-125 |j,g/mL], and thus the ratio of VX concentration to IS
concentration could be plotted (x-axis) versus the ratio of VX area response to the IS area
response (y-axis). The quadratic VX calibration curve fit had the equation:
(As /Ais) = a x (Cs/ Cis)2 + b x (Cs / Cis) + c	(1)
where:
As = area response of the target analyte
Ais = area response of the internal standard
Cs = concentration of the target analyte
Cis = concentration of the internal standard
a, b, c = coefficients of quadratic curve fit.
GC concentration results (|ig/mL) were converted to total mass recovered by multiplying by
extract volume:
Mm=CxEv	(2)
where:
Mm= measured mass of chemical agent (|_ig)
C = GC concentration (ng/mL), see Equation 1
Ev = volume of extract (mL).
The primary assessment of attenuation and extraction efficiency relied upon comparing the total
mass of VX recovered from test coupons to mean mass measured in spike controls. Recovery in
percent was calculated as follows:
%R = [Mm / Msc] • 100%	(3)
where:
%R = percent recovery
Mm = calculated mass of CWA recovered from a test coupon (jig)
Msc = mean calculated mass of CWA recovered from spike controls (|ig).
A separate %R calculation was made for recovery of VX from each test coupon. For each type of
material, the mean and percent relative standard deviation (%RSD) of recovery results were
reported. Thus, the primary %R results from the weathering of coupons spiked with VX was a
14

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matrix table in which each entry shows the mean %R and %RSD over time from each type of
coupon material.
2.10 Analysis of Variance to Test Hypotheses
Three hypotheses were evaluated using the analysis of variance (ANOVA). The ANOVA model
took the following form:
where "In" denotes the natural logarithmic transformation and the following notation was used:
•	Yijkn is the residual mass measurement (|ig) of VX recovered from the nth replicate test
(coupon) extracted at the Kh time point within the ith attenuation, where the coupon is of
the/* material type (/ = 1, ...,4\j= 1, 5; k = 1, 8; n = 1, 5),
•	n is an overall constant value,
•	a.i is a constant value (added to u) associated with the ith attenuation,
•	Mj is a constant value (added to u) associated with the jth material type,
•	(oM)ij is a constant value (added to u) associated with the specific combination of the ith
attenuation and jth material,
•	Tk is the number of hours (from initial spiking) at which the coupon was extracted and
tested,
•	X is an overall constant slope value applied to the time point value Tk,
•	Pi is a constant value (added to the slope X) associated with the ith attenuation,
•	fj is a constant value (added to the slope /.) associated with the jth material type,
•	Sijkn is random error representing the difference between the observed and model-
predicted values of log(7yyte) (assumed to be normally distributed with mean 0 and
variance which is constant across all attenuations, material types, time points, and
coupons).
Only the terms Yijkn and Tk represent observed testing data; all other model terms are unknown
and must be estimated by fitting the model to the 4 x 5 x 8 x 5 = 800 observed data points. This
model is log-linear in nature, meaning the model on the untransformed residual mass
measurement is exponential and multiplicative:
This model represents exponential decay over time, with the rate of decay allowed to vary among
the attenuations and material types. The General Linear Model (GLM) procedure in SAS® 9.4
(SAS Institute Inc., Cary, NC, USA) was used to fit the log-linear model to the observed data.
Only data for the five material types were included in this analysis; data for the spike control
were excluded. In addition, any data reported as being below the lower calibration limit of 0.10
|ig/mL were included in the analysis as 2.5 |ig/coupon considering the 25 mL extraction solvent
volume.
) = jA 1- Ci i + .'¦fj. + l" Of.Vf 11 j -r ;ft-, i-
f: in"»
(4)
-r _	+Mj +iaM)ij + j P £ijkn
ijkn ~ ^	^	^
(5)
15

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The three sets of statistical hypothesis tests performed within this ANOVA to address study
objectives were the following. Recall that in statistical hypothesis testing, null and alternative
hypotheses are specified, and the null hypothesis is assumed to hold unless applying the
observed data to the statistical test procedure is sufficient to support rejecting the null hypothesis
for the alternative. All statistical tests were performed at a 0.05 significance level unless
otherwise noted, meaning that the likelihood of incorrectly rejecting the null hypothesis for the
alternative based on the observed data is no more than 5%.
Test #1:
• Null hypothesis: No decline occurs in average recovered VX over time.
• Alternative hypothesis: Average recovered VX declines over time.
For Test 1, a statistical test was performed to determine whether the average slope (2 + /? + y)
associated with the time factor was significantly less than 0 (i.e., an overall exponential decline
occurs in the mass measurement with increasing time), where and / represent the average of
the incremental amounts added to the slope that are specific to attenuation and material type,
respectively. In addition, statistical tests of whether the attenuation-specific slope (A + f + f3i.) or
the material-specific slope {A + p + y ) is significantly less than 0 were performed, to determine
whether observing a significant rate of decline was dependent on either the attenuation or
material type.
Test #2:
• Null hypothesis: The average rate of VX loss does not change among different
temperatures and air exchange rates.
• Alternative hypothesis: The average rate of VX loss differs among temperatures and air
exchange rates.
Because the four attenuations were distinguished by temperature and air exchange rate, this test
considered whether the attenuation effect was statistically significant on average across the time
points.
Test #2 addressed whether the attenuation-specific slopes (Z + y + /? ) differed significantly from
each other at a 0.05 level, indicating that the rate of decline in residual mass measurement of VX
over time differed between the four attenuations. If so, then pairwise differences in these slopes
(i.e., differences among the Pi values) were statistically compared at an overall 0.05 level (i.e.,
each test performed at a 0.05/6 = 0.00833 level) to determine which pairs of attenuations differed
significantly in their rates of decline.
In addition, statistical tests were performed as follows to determine whether significant
differences were present in the average values of (log-transformed) residual mass measurement
of VX across the four attenuations:
16

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1. The significance of the interaction term (aM)ij was first tested at a 0.05 level; this test
determined whether the significance of the attenuation effect was dependent on the
material type.
a. If this interaction term were significant, then statistical comparisons between pairs
of attenuations were done by material type, with the overall significance level
among all six pairs of the four attenuation types being no higher than 0.05 within
each material type (i.e., each test performed at a 0.05/6 = 0.00833 level). No
further tests were performed.
b. If the interaction term was not significant, then a test for significance of the main
attenuation rate term a, was performed at a 0.05 level.
i. If this test were significant, then at least one of the attenuation rates a,
differed significantly from 0. Therefore, this test was followed by pairwise
tests to determine which of the six possible pairs of attenuations differed
significantly at an overall 0.05 level (i.e., each test performed at a 0.05/6 =
0.00833 level).
ii. If this test were not significant, then on average across time points, the
four attenuations did not differ significantly overall or for any material
type.
Test #3:
• Null hypothesis: The mean rate of VX loss does not vary among different materials.
• Alternative hypothesis: The mean rate of VX loss does vary among different materials.
This test was performed in a manner similar to Test #2. First, statistical tests were performed to
determine whether the material-specific slopes (A + /? + y s) differed significantly from each
other at a 0.05 level, indicating that the rate of decline in residual mass measurement of VX over
time differed between the five material types. If so, then pairwise differences in these slopes (i.e.,
differences among the y, values) were statistically compared at an overall 0.05 level (i.e., each
test performed at a 0.05/10 = 0.005 level) to determine which of the ten pairs of material types
differed significantly in their rates of decline.
Then, statistical tests were performed as follows to determine whether significant differences
were present in the average values of (log-transformed) residual mass measurement of VX across
the five material types:
1. The significance of the interaction term (oM)tj was first tested at a 0.05 level; this test
determined whether the significance of the material type effect was dependent on the
attenuation. (This same test was performed as part of Test #2.)
a. If this interaction term were significant, then statistical comparisons between pairs
of material types were done by attenuation, with the overall significance level
among all 10 pairs of the five material types being no higher than 0.05 within
17

-------
each attenuation (i.e., each test performed at a 0.05/10 = 0.005 level). No further
tests were performed.
b. If the interaction term was not significant, then the test for significance of the
main material type effect Mj was performed at a 0.05 level.
i.	If this test were significant, then at least one of the material types Mj
differed significantly from 0. Therefore, this test was followed by pairwise
tests to determine which of the 10 possible pairs of material types differed
significantly at an overall 0.05 level (i.e., each test performed at a 0.05/10
= 0.005 level).
ii.	If this test were not significant, then on average across time points, the
five material types did not differ significantly overall or within any
attenuation.
18

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3.0 Test Results
3.1 Recovery Efficiency Results
As discussed in Section 2.7, recovery efficiency following extraction immediately after spiking
was demonstrated for silanized glass, glazed ceramic tile, painted drywall tape, and sealed
concrete prior to the natural attenuation investigation or the redistribution investigation. The
results of the recover efficiency tests are summarized in Table 6.
Table 6. Summary of Recovery Efficiency Testing.
Material
Mean Recovery (%)
Coefficient of Variation (%)
Test Date: 12/4/2014
Spike control
88 (versus theoretical, corrected for purity)
8
Silanized glass
117 (versus spike control)
5
Painted drywall tape
117 (versus spike control)
8
Glazed ceramic tile
114 (versus spike control)
2
Test Date: 1/12/2015
Spike control
115 (versus theoretical, corrected for purity)
7
Sealed concrete
79 (versus spike control)
20
The tests were conducted on two separate days, and a different spike control was used for
silanized glass, glazed ceramic tile, and painted drywall tape than was used for sealed concrete.
The recovery efficiency results were deemed acceptable for all three tested materials since the
mean recoveries were within 70% to 120% of the mean of the spike control recoveries with
<30% coefficient of variance (also known as the [percent relative standard deviation] %RSD)
between samples. All four laboratory blanks were non-detect for VX (<5.0 |ag/mL in the extracts
for silanized glass, glazed ceramic tile, and painted drywall tape and <0.10 jag/m L in the extract
for sealed concrete).
3.2 Natural Attenuation Results
3.2.1 Environmental Condition 1
The first environmental condition evaluated was 25 ± 3 °C, 40 ± 5% RH, without air exchanged.
The actual temperatures and RH measured during this test are presented in Figures 2 and 3,
respectively. As shown in these figures, the environmental conditions of temperature and RH
were attained within test specifications. The Vaisala measurement provided the overall
conditions in the test chamber. The HOBO measurement on individual shelves was used to
confirm that substantial differences in microenvironments did not exist between shelves.
19

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21
.V
•	Upper Limit
•	Lower Limit
Vaisala
—	Shelf 1 (21 day samples)
Shelf 8 (14 day samples)
Shelf 5 (10 day samples)
	Shelf 6 (7 day samples)
—	Shelf 4 (4 day samples)
	Shelf 3 (1 day samples)
	Shelf 2 (4 hr samples)
	Shelf 7 (30 min samples)
Date, Time
Figure 2. Temperature during Environmental Condition 1 testing.

46

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Date, Time
•	Upper Limit
•	Lower Limit
Vaisala
	Shelf 1 (21 day samples)
Shelf 8 (14 day samples)
Shelf 5 (10 day samples)
	Shelf 6(7 day samples)
	Shelf 4 (4 day samples)
	Shelf 3 (1 day samples)
	Shelf 2 (4 hr samples)
	Shelf 7 (30 min samples)
Figure 3. Relative humidity during Environmental Condition 1 testing.
20

-------
The amount of VX recovered over time is presented in Table 7 and Figure 4 (error bars equal
plus one SD). The spike control recovery for VX for Environmental Condition 1 was 2204 |ig.
After a 30-min weathering period, the mean VX recovery was >1980 |ig for all materials except
sealed concrete, which had a much lower mean VX recovery of 602 |ig. The decrease in
recovered VX was rather notable between days 1 and 4 (Figure 4). After a 10-day weathering
period, the mean VX recoveries were <50 |ig for all materials, and by day 21 all VX recoveries
were <5 |ig (i.e., >99.8% natural attenuation). In addition, VX was not detected from galvanized
metal ductwork or glazed ceramic tile after 21 days of weathering.
Table 7. VX Recovery at Environmental Condition 1
Material
Measure of VX
Recovered
30 min
4 h
Extraction Time (Weathering Period)
4
1 day 7 days 10 days 14 days
21 days

Mean (|ig)
602
346
311
18
4.9
24
5.4
3.0
Sealed
SD (|ig)
76
111
46
25
3.2
25
2.4
0.87
concrete
%RSD
13%
32%
15%
139%
66%
103%
44%
29%

FOD
5/5
5/5
5/5
3/5
4/5
3/5
4/5
2/5

Mean (|ig)
2196
1953
1789
142
81
25
19
3.7
Silanized
SD (|ig)
95
59
139
58
38
16
3.4
1.2
glass
%RSD
4%
3%
8%
41%
47%
61%
18%
33%

FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
3/5
Galvanized
metal
ductwork
Mean (|ig)
2196
1841
915
76
6.7
34
2.6
<2.5
SD (|ig)
122
215
670
95
8.7
70
0.23
0.00
%RSD
6%
12%
73%
124%
129%
207%
9%
0%
FOD
5/5
5/5
5/5
5/5
3/5
1/5
1/5
0/5
Painted
drywall
tape
Mean (|ig)
2153
2136
1935
254
111
45
18
4.5
SD (|ig)
156
299
160
61
22
5.6
4.3
1.2
%RSD
7%
14%
8%
24%
20%
13%
24%
26%
FOD
5/5
5/5
5/5
5/5*
5/5
5/5
5/5
5/5

Mean (|ig)
1980
1566
1449
71
40
27
12
<2.5
Glazed
SD (|ig)
202
518
519
82
24
21
7.7
0.00
ceramic tile
%RSD
10%
33%
36%
116%
60%
76%
65%
0%

FOD
5/5
5/5*
5/5
5/5
5/5
5/5
4/5
0/5
SD = standard deviation.
FOD = frequency of detection (number of coupons above the quantitation limit/total number of coupons).
< = all replicate results were less than the quantitation limit.
For results less than the quantitation limit, the quantitation limit (i.e., a 2.5 |ig residual mass) was used for the
calculation of summary statistics.
* A replicate coupon flipped over during coupon handling; some VX might have been lost.
21

-------
2600
2400
2200
Sealed concrete
Silanized glass
2000
bjo
— 1800
Galvanized metal ductwork
Painted drywall tape
Glazed ceramictile
1600
1400
1200
1000
800
600
400
200
0
30 min
4 hr
1 day
4 days
7 days
10 days 14 days 21 days
Extraction Time (Weathering Period)
Figure 4. VX recovery at Environmental Condition 1.
3.2.2 Environmental Condition 2
The second environmental condition evaluated was identical to Environmental Condition 1
except that the chamber air was exchanged during the test. Environmental Condition 2 was
specifically defined as: 25 ± 3 °C, 40 ± 5% RH, with one chamber volume of air exchanged per
hour. The actual temperatures and RH measured during this test are presented in Figures 5 and 6,
respectively. As shown in Figure 5, temperatures throughout the testing were within the targeted
test condition of 25 ± 3 °C. The RH level briefly dropped below the lower limit of 35% during
coupon spiking, and exceeded the upper limit of 45% RH by 2% - 3% at the shelf level during
the 4-, 7-, and 14-day tests (Figure 6). A summary of the RH levels measured during the
weathering period, as captured by the shelf-specific HOBO data loggers, is provided in Table 8.
The RH means (rounded to two significant figures) were within the target RH level, and the
majority of the weathering period times were spent exposed to RH within the target level (Table
8).
22

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Date, Time
•	Upper Limit
•	Lower Limit
Vaisala
	Shelf 4 (14 day samples)
—Shelf 2 (7 day samples)
Shelf 1 (4 day samples)
—Shelf 8 (2 day samples)
—Shelf 6 (1 day samples)
Shelf 3 (7 hr samples)
—Shelf 7 (4 hr samples)
	Shelf 5 (30 min samples)
Figure 5. Temperature during Environmental Condition 2 testing.
49
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Date, Time
•	Upper Limit
•	Lower Limit
Vaisala
	Shelf 4 (14 day samples)
	Shelf 2 (7 day samples)
Shelf 1 (4 day samples)
	Shelf 8 (2 day samples)
— Shelf 6 (1 day samples)
Shelf 3 (7 hr samples)
= Shelf 7 (4 hr samples)
	Shelf 5 (30 min samples)
Figure 6. Relative humidity during Environmental Condition 2 testing.
23

-------
Table 8. Relative Humidity during Environmental Condition 2 Testing
Measurement
30 min
4 h
Extraction Time (Weathering Period)
7 h 1 day 2 days 4 days
7 days
14 days
Mean RH (%)
34.8
39.9
40.0
41.6
41.2
43.2
43.8
44.0
Minimum RH (%)
33.1
32.8
33.0
32.9
32.5
33.4
33.3
34.4
Maximum RH (%)
36.7
43.5
43.9
44.2
43.3
45.5
46.2
47.9
Estimated Time
RH Outside of
Target Level
(40 ± 5%)
10 min
(lower)
25 min
(lower)
40 min
(lower)
25 min
(lower)
35 min
(lower)
1.6 h
(higher)
35.7 h
(higher)
95.8 h
(higher)
Note: Based on test/shelf-specific RH measured with HOBO data loggers during the weathering periods only. Lower
and higher designations are used to indicate the amount of time below or above the target RH level.
The amount of VX recovered over time is presented in Table 9 and Figure 7 (error bars equal
plus one SD). The spike control recovery for VX for Environmental Condition 2 was 2380 |ig.
After a 30-min weathering period, the mean VX recovery was >2162 |ig for all materials, except
sealed concrete, which had a lower mean VX recovery of 1129 |ig. For most materials, there was
a relatively steady decrease in recovered VX over the weathering period. After 14 days, the mean
VX recoveries were <50 |ig for all materials (i.e., >98.0% natural attenuation), and VX was not
detected from the galvanized metal ductwork. VX recoveries after 4 days were lower than after 7
days for the sealed concrete and glazed ceramic tile. This anomaly cannot be attributed to
deviations in environmental conditions as the VX recoveries from the other three materials after
4 days were consistently higher than those after 7 days. Further, coupons were spiked in random
order which excludes systematic errors from consideration. This anomaly remains unresolved.
Appendix A shows representative chromatograms (total ion current) for two weathering times of
VX, namely after 30 min and after 14 days.
24

-------
Table 9. VX Recovery at Environmental Condition 2
Material
Measure of VX
Recovered
30 min
4 h
Extraction Time (Weathering Period)
7 h 1 day 2 days 4 days 7 days
14 days

Mean (|ig)
1129
490
295
143
101
8.2
84
46
Sealed
SD (|ig)
450
120
283
133
77
6.3
65
42
concrete
%RSD
40%
25%
96%
93%
76%
76%
78%
90%

FOD
5/5
5/5
5/5
5/5
5/5
5/5
4/5
5/5

Mean (|ig)
2162
1899
1839
1549
979
222
113
14
Silanized
SD (|ig)
37
50
145
326
269
39
42
9.1
glass
%RSD
2%
3%
8%
21%
27%
18%
37%
66%

FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
5/5

Mean (|ig)
2210
1831
1905
1153
633
268
215
<2.5
Galvanized
metal
ductwork
SD (|ig)
129
173
68
494
716
285
290
0.00
%RSD
6%
9%
4%
43%
113%
106%
135%
0%

FOD
5/5
5/5
5/5
5/5
5/5
5/5
3/5
0/5

Mean (|ig)
2332
2022
1930
1638
1380
268
96
13
Painted
drywall
tape
SD (|ig)
218
96
150
197
105
28
15
3.0
%RSD
9%
5%
8%
12%
8%
10%
15%
22%
FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
5/5

Mean (ng)
2199
1866
1329
425
231
31
38
8.6
Glazed
SD (|ig)
87
137
444
390
255
43
60
8.4
ceramic tile
%RSD
4%
7%
33%
92%
110%
141%
156%
97%

FOD
5/5
5/5
5/5
5/5
5/5
5/5
2/5
4/5
SD = standard deviation.
FOD = frequency of detection (number of coupons above the quantitation limit / total number of coupons).
< = all replicate results were less than the quantitation limit.
For results less than the quantitation limit, the quantitation limit (i.e., a 2.5 |ig residual mass) was used for the
calculation of summary statistics.
25

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i_
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>
o
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-------
14
13
12
S_ 11
10

7 •
• Upper Limit
• Lower Limit
Vaisala
Shelf 2 (35 day samples)
Shelf 7 (21 day samples)
Shelf 1 (14 day samples)
Shelf 8 (7 day samples)
-Shelf 6 (4 day samples)
Shelf 4 (1 day samples)
Shelf 3 (7 hr samples)
Shelf 5 (30 min samples)
^ ^ cP
J?' <$' J?' J?' J?'
/ / J3
V V S* ^ ^ ">X # of
Date, Time
Figure 8. Temperature during Environmental Condition 3 testing.
a:
5S
-------
The amount of VX recovered over time is presented in Table 10 and Figure 10 (error bars equal
plus one SD). The spike control recovery for VX for Environmental Condition 3 was 2272 |ig.
The 30-min VX recovery was >1914 |ig for all materials, except sealed concrete, which had a
lower mean VX recovery of 594 |ig. In general, more VX was recovered for a longer period of
time than under any other environmental conditions tested. For example, after 14 days, the mean
VX recoveries were 608 |ig for silanized glass and 987 |ig for painted drywall tape. The amount
of VX recovered decreased considerably for these materials on day 21, but the amount of VX
recovered between days 14 and 21 increased for the other materials (sealed concrete, galvanized
metal ductwork, and glazed ceramic tile). Relatively low amounts of VX were recovered (9.3 |ig
to 148 |ig) even after the 35-day weathering period. Natural attenuation ranged from 93.5% to
99.6% after the 35-day weathering period.
Table 10. VX Recovery at Environmental Condition 3
Material
Measure of VX
Recovered
30 min
7 h
Extraction Time (Weathering Perioi
1 day 4 days 7 days 14 days
)
21 days
35 days
Sealed
concrete
Mean (|ig)
594
500
418
209
89
38
117
24
SD (|ig)
202
213
165
106
27
24
38
23
%RSD
34%
43%
39%
51%
31%
62%
33%
99%
FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
5/5
Silanized
glass
Mean (|ig)
1918
2057
2168
1894
1172
608
191
138
SD (|xg)
54
133
95
40
192
96
23
16
%RSD
3%
6%
4%
2%
16%
16%
12%
12%
FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
5/5
Galvanized
metal
ductwork
Mean (|ig)
2015
2192
2105
1664
913
74
494
9.3
SD (|xg)
83
225
159
151
576
80
654
12
%RSD
4%
10%
8%
9%
63%
108%
132%
129%
FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
5/5
Painted
drywall
tape
Mean (|ig)
1962
2190
2028
1890
1377
987
272
148
SD (|xg)
145
110
37
87
58
162
59
20
%RSD
7%
5%
2%
5%
4%
16%
22%
14%
FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
5/5
Glazed
ceramic
tile
Mean (|ig)
1914
1873
1743
934
329
55
120
37
SD (|xg)
117
195
325
406
365
22
93
52
%RSD
6%
10%
19%
43%
111%
40%
77%
140%
FOD
5/5
5/5
5/5
5/5
5/5
5/5
5/5
5/5
SD = standard deviation.
FOD = frequency of detection (number of coupons above the quantitation limit / total number of coupons).
28
-------
2600
2400
2200
2000
"eg 1800
"g 1600
i-
g 1400
oc 1200
l/>
I 1000
> 800
S 600
§
400
200
0
Figure 10. VX recovery at Environmental Condition 3.
3.2.4 Environmental Condition 4
The fourth environmental condition evaluated was identical to Environmental Conditions 2 and 3
except the target temperature was increased to 35 °C. Specifically, Environmental Condition 4
was defined as: 35 ± 3 °C, 40 ± 5% RH, with one chamber volume of air exchanged per hour.
The actual temperatures and RH measured during this test are presented in Figures 11 and 12,
respectively. As shown in Figure 11, temperature was constantly held at the target level of 35 ± 3
°C. The RH decreased initially to approximately 26% (outside the target level) when spiking the
coupons (after three days of chamber conditioning). Four other minor (generally no lower than
34% RH) instances occurred when the RH was outside the target level. As shown on Figure 12,
the duration that the RH level was outside the target range was very brief.
Sealed concrete
Silanized glass
Galvanized metal ductwork
Painted drywall tape
Glazed ceramictile
30min 7 hr lday 4 days 7 days 14 days 21 days 35 days
Extraction Time (Weathering Period)
29
-------
u
Q
i_
3
n
at
Q.
E
38 <»
• Upper Limit
• Lower Limit
Vaisala
Shelf 1 (10 day samples)
Shelf 7 (7 day samples)
Shelf 5 (4 day samples)
-Shelf 3 (2 day samples)
Shelf 2 (1 day samples)
Shelf 8 (7 hr samples)
Shelf 6 (4 hr samples)
Shelf 4 (30 min samples)
1.Ov

, \v< ,"0' , *0' -o-
/ „/„/ /
&
.0'
.o1.
Date, Time

0
Silanized glass Leather
(spiked) upholstery
(unspiked)
HDPE Painted metal Desk laminate Cubicle divider
(unspiked) (unspiked) (unspiked) cloth
(unspiked)
Figure 15. VX recovered from the redistribution investigation.
46
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6.0 References
Columbus, I., D. Waysbort, I. Marcovitch, L. Yehezkel, andD.M. Mizrahi, 2012. VXFate on
Common Matrices: Evaporation versus Degradation. Environmental Science & Technology 46:
3921-3927.
EPA, 2007. A Literature Review of Wipe Sampling Methods for Chemical Warfare Agents and
Toxic Industrial Chemicals. EPA/600/R-11/079. U.S. Environmental Protection Agency, Office
of Research and Development, Washington, D.C.
EPA, 2010. Decontamination of Residual VX on Indoor Surfaces using Liquid Commercial
Cleaners. EPA/600/R-09/159. U.S. Environmental Protection Agency, Office of Research and
Development, Washington, D.C.
Labit, H., A. Goldar, G. Guilbaud, C. Douarche, O. Hyrien, and K. Marheineke, 2008. A Simple
and Optimized Method of Producing Silanized Surfaces for FISH and Replication Mapping on
Combed DNA Fibers. BioTechniques 45: 649-658.
Munro, N., S. Talmage, G. Griffin, L. Waters, A. Watson, J. King, and V. Hauschild. 1999. The
Sources, Fate, and Toxicity of Chemical Warfare Agent Degradation Products. Environmental
Health Perspectives 107(12): 933-974.
47
-------
Appendix A
Representative chromatograms (total ion current) for two weathering times for VX on silanized
glass. (A) After 30 min and (B) after 14 days. The retention times for the latter period are shorter
due to the clipping of the column length by approximately 6" as part of regular maintenance of
the GC system.
r liJAt'i •
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A
Weathering Time: 30 minutes
VX Retention Time: 5.42
IS Retention Time: 3.24
B
Weathering Time: 14 days
VX Retention Time: 4.82
IS Retention Time: 2.63
Environmental Condition 2: 25°C, 40% RH, 1 chamber vol. air exchange / hour
48
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vvEPA
United States
Environmental Protection
Agency
PRESORTED STANDARD
POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
Office of Research and Development (8101R)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
-------