Technical BRIEF
INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
Transport of Persistent Chemical Warfare Agents HD and VX
into Porous Materials and Permeable Layers
Practical data for remediation of contaminated building materials
Purpose
The Organisation for the Prohibition of Chemicai
Weapons (OPCW) continues to investigate the alleged
use of chemical weapons around the world. The use of
chemical warfare agents (CWAs) on the battlefield has
a long history. More recent (since 2012) use has
occurred in Syria, Malaysia, the United Kingdom, and
Russia [1-4]. Two CWAs, the nerve agent VX and blister
agent sulfur mustard (HD), are of great concern due to
their high toxicity and high persistence in the
environment. This brief compiles data from several
recent U.S. Environmental Protection Agency (EPA)
bench-scale studies [5-10] that assessed the fate and
transport of these two chemicals, each studied
separately, into porous and/or permeable materials.
This summary provides decision-makers with practical
information on the expected degree of
absorption/permeation of VX or l-ID (VX/HD) into
several types of materials following a chemical incident
resulting in the release of the CWA to the environment.
This practical information will inform the remediation
strategy for the reopening of contaminated buildings
or infrastructure.
Background
EPA's Homeland Security Research Program conducts
research to help on-scene coordinators and decision-
makers minimize human health effects and
environmental impacts following the release of a CWA.
A release of a persistent CWA inside a building would
result in its deposition onto a large variety of materials
ranging from nonporous, impermeable materials to
those with varying degrees of porosity leading to
permeation of the agent into and potentially through
the material.
Definitions and Descriptions
Permeation can occur in two main ways. First, a
material may be porous, meaning that it contains void
spaces (spaces not occupied by the atomic/molecular
framework that make up the structure). Bulk VX/HD
liquid can enter these pores by capillary action, just like
a paper towel absorbs water. Second, for some
materials like certain polymers, the large polymer
molecules are close enough together that they do not
form pores, but VX/HD molecules can move through
them via forces of diffusion, i.e., to move from a place
of high concentration to a place of low concentration,
because the VX/HD are essentially soluble in the
polymers. It is like a drop of food coloring as it
dissolves in and spreads through a glass of water.
Permeation of VX/HD into building materials can occur
as a combination of these two processes, depending on
the building material. For example, liquid VX/HD can
enter the pore structure and move some depth into the
material, all the while adsorbing onto the surface of the
material and diffusing through it.
To simplify resulting complexities, for purposes of
discussion, designing experiments, and practically
applying the resulting data, it is useful to group
materials via common characteristics. Figure 1
illustrates such a grouping, including common materials
falling into groups that need to be considered in a
remediation strategy following a CWA incident. A brief
description of each material group follows.
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July 2021

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I. Nonporous, impermeable II. Nonporous, permeable
•	Glass
•	Metals
•	Glazed ceramic tiles
Painted/sealed materials
Vinyl, laminate
Rubber, silicone
Materials

Porous, low adsorption IV. Porous, high adsorption
Figure 1. Generic grouping of commonly used building materials based on
their interaction with VX/HD,
I.	Nonporous, impermeable materials
VX/HD present on materials such as glass and various
metals are expected to remain on the nonporous,
impermeable surface from which they (slowly)
evaporate or possibly degrade via natural attenuation.
II.	Nonporous, permeable materials
Painted and/or sealed surfaces fall in the category of
nonporous materials. Such paints and sealants are
intended to prevent water absorption into the porous
material behind or below it (e.g., painted drywall or
sealed concrete, wood). However, VX/HD, being oily
substances, may behave differently than water
because paint or sealant layers are permeable to
VX/HD [5] via diffusion. Painted surfaces account for
60% to 70% of exposed surfaces in residences [11].
Once this occurs, VX/HD can slowly evaporate from
these (painted) materials, remain in the permeable
paint/sealant layers, or diffuse into the underlying
porous and even more absorptive material. Organic
materials such as rubber, silicone, vinyl or laminate
also fall into this category, as VX/HD can diffuse into
these materials, too. If these organic materials are
thick enough and the VX/HD have permeated far
enough into the material, it may take a very long time
for them to diffuse back out. Then, these materials
become reservoirs for VX/HD, potentially presenting
long-term remediation challenges.
U.S. Environmental Protection Agency
III.	Porous, low adsorption materials
Liquid HD/VX can penetrate quickly (seconds, minutes)
into porous materials such as unsealed concrete or
limestone. The penetration depth into a porous
material, movement across the substrate, and possible
chemical degradation reactions with the surrounding
matrix will impact the remediation strategy. In the
absence of degradation processes, VX/HD may reside
within a porous material for periods of time that can
exceed the time they would be present on a nonporous
surface. Hence, the materials become reservoirs of
VX/HD, with associated remediation challenges. For
materials in this category, the VX/HD are not expected
to adsorb and diffuse through the material but remain
on the interior surface of the pores, meaning that they
potentially can be physically dislodged from the pores.
IV.	Porous, high adsorption materials
Materials in this category may be the most difficult to
remediate and may be candidates for disposal Namely,
the VX/HD not only penetrates the porous structure
but then diffuses into the material. Thus, remediation
techniques must overcome both mechanisms, which
can be technically complex or uneconomical. Many of
the materials in this category are polymeric materials
manufactured in a manner that they are also porous.
For example, carpets and clothes can be composed of
natural or synthetic polymer fibers, which are

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processed to have desirable touch-and-feel properties,
which coiricidentally can increase porosity of these
materials. The fate and transport of VX/HD for this
group of materials will be part of future studies.
Experimental Methods
EPA studied the transport of VX/HD when applied to
several porous and to painted and sealed materials. VX
(O-ethyl S-[2-(diisopropylamino)ethyl] methyl-
phosphonothioate) is highly persistent [12] with a
vapor pressure of 7 x 1CT4 mm Hg at 20 °C and oily
appearance. HD [bis(2-ch!oroethyl)su!fide] is less
persistent with a vapor pressure of 0.072 mm Hg at 25
°C [13], The experimental designs of the EPA studies
are described briefly here. Contamination occurred in
each study by application of a single droplet of
chemical agent (typically 1 or 2 (iL volume across these
studies) onto these materials.
Study A [5] investigated the permeation of VX/HD into
three different paint types and two types of sealants.
This included measurement of the partitioning of the
chemical into the permeable paints/sealants and
underlying simulated porous material as function of
time (up to 48 h for HD and 72 h for VX) (Figure 2).
whether the amount of VX remained on the surface or
whether it permeated or absorbed into the material.
Instead, it provided information how much of VX
remained with the coupon (the extracted sample of the
material being tested) after specific time.
Study E [10] was a decontamination study and was not
designed to focus on the fate and transport of VX/HD.
However, the positive controls that were part of this
study provided insight in the fate and transport by
measurement of the remaining VX/HD mass on the
surface (surface wipe sample) and mass held by the
porous or permeable material (extraction of the full
material after the surface wipe sampling).
Results
Table 1 summarizes the expected percent of VX/HD
that can be detected on the surface (as determined via
surface wipe sampling) 24 h (unless noted otherwise)
after the contamination occurs. Also noted, where
applicable, is how much of the VX/HD migrated into
the material (full material extraction) and how much
was recovered from the underlying material (Studies A
and E) or within the first 0.25-inch depth (Study B) or
held by the material itself (Studies C and D). Table 2
provides additional information associated with the
paints and sealants in Table 1. Prior to the fate and
transport studies, surface wipe sampling methods and
material extraction methods were verified, as
applicable, on their high efficiency to sample VX/HD
from all materials.
Figure 2. Setup with paint layer and solid phase
extraction disk below the layer.
Study B [6] assessed the level of VX permeation into
limestone as a porous inorganic material and into
sealed concrete as a nonporous organic barrier to a
porous inorganic material.
Studies C [7] and D [8] (as summarized in [9])
addressed the persistence of VX as function of
temperature and material. This study did not measure
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Table 1. Surfaces, Materials, Function, Properties, and Percent Recoveries for VX and for Sulfur Mustard (HD) after 24 h.
„ „ , Water Oil VX percent on surface and HD percent on surface „ „
Subsurface Study ID
Surface Function Permeability Permeability in other layers or material and in other layers or Ref.
3 ena Top Layer Top Layer after 24 h material after 24 h 3 6
1. Nonporous, impermeable materials
Glass
Same

None
None
65% (coupon)
Not included in test

7
Galvanized metal
Same
HVAC ductwork


48% (coupon)
Not included in test

7
Glazed Ceramic Tile

Wall, floors


18% (coupon)
Not included in test

7
Glass




73% (coupon)
Not included in test

8
Glazed Ceramic Tile

Wall, floors


74%
120% [5 h], <0.5% [76 h]

9
Glass
Same



94%
61% [5 h], <0.5% [76 h]

9
Stainless Steel
Same



79%
57%
89%
Not included in test
40%, 0.12% [48 h]
31%, 0.01% [48 h]

6
5
5
II. Nonporous, permeable materials
Paint - Latex Flat [i]
Paint - Latex Semi-Gloss
[ii]
Paint - Oil-Based [iii]
Steel
Surrogate for
nonporous
material
Low-Medium
Low
42%; 15% in latex flat
17%; 30% in latex semi-
gloss
26%; 8% in oil-based layer
4%; 76% in latex flat
3%; 89% in latex semi-
gloss
8%; 40% in oil-based layer
A1
5
Paint - Latex Flat [i]
SPE disk
Surrogate for
porous material
30%; 25%; 8% on surface;
in paint; and in SPE
0.7%; 33%; 61% on
surface; in paint; and in
SPE
A2
5
Paint -Latex Semi-Gloss
[ii]
SPE disk
Surrogate for
porous material
18%; 40%; 4% on surface;
in paint; and in SPE
0.5%; 27%; 67% on
surface; in paint; and in
SPE
A3
5
Paint - Oil Based [iii]
SPE disk
Surrogate for
porous material
15%; 18%; 2% on surface;
in paint; and in SPE
0.3%; 27%; 48% on
surface; in paint; and in
SPE
A4
5
Paint - Primer & Oil-
Based
Steel
Building material
58% (surface)
Not included in test
B1
6
Paint - Primer & Oil-
Based
Hardwood
Building material
42% (surface)
Not included in test
B2
6
Paint - Primer & Latex
Flat
Dry wall
Wall material
NA; 69% (coupon)
Not included in test
CI
7
Sealant - Epoxy
Sealant - Polyurethane
Steel
Surrogate for
nonporous
material
None Low
23%; 37% in epoxy
16%; 35% in polyurethane
9%; 13% in epoxy
7%; 57% in polyurethane
A5
5
Sealant - Epoxy
SPE disk
Surrogate for
porous material

58%; 22%; 0% on surface;
in sealant; and in SPE
1%; 14%;21% on surface;
in sealant; and in SPE
A6
5
II
U.S. Environmental Protection Agency

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_ , , Water
Subsurface
Surface Function Permeability
IVIaLcilal
Top Layer
Oil VX percent on surface and HD percent on surface „ „
Study ID
Permeability in other layers or material and in other layers or Ref.
Top Layer after 24 h material after 24 h 3 6
Sealant - Polyurethane
SPE disk
Surrogate for
porous material
Low
Low-Medium
11%; 57%; 10% on surface;
in sealant; and in SPE
0.2%; 26%; 73% on
surface; in sealant; and in
SPE
A7
5
Sealant- Silane/Siloxane
Concrete
Protective flooring
material
0.3-0.8%; 8-14% in top 1/4"
Not included in test
B3
6
Sealant- Silane/Siloxane
Concrete
Protective flooring
material
NA; 6% (coupon)
Not included in test
C2
7
Sealant- Silane/Siloxane
Sandstone
Used as surrogate
for porous
material
NA; 29% (coupon)
27% (coupon 5 h),
2.2% (coupon 76 h),
El
10
Rubber
Same
Escalator handrail,
wall base molding
56% (coupon)
Not included in test

8
77% (coupon)
130% (coupon 5 h),
130% (coupon 76 h)*

10
HDPE Plastic
Same
Water pipes, liner
Low
Low
92% (coupon)
Not included in test

8
III. Porous, low adsorption materials
Limestone
Same
Building material
High
Medium-High
Medium-High
Medium-High
0.41% (surface)
0.2-0.4%; 11-43% in top
1/4"
Not included in test

6
Unsealed Concrete
Same
Walls, floors
0.8% (surface)
13% (coupon)
Not included in test

6
8
Plywood
Same
Subfloor material
62% (coupon)
Not included in test

8
IV. Porous, high adsorption materials
Ceiling Tile
Same
Dropped ceiling
High
Medium-High
81% (coupon)
Not included in test

8
*: Recoveries biased high due to significant interferences in ion chromatograms
coupon: the extracted sample of the material being tested, HDPE: high-density polyethylene, SPE: solid phase extraction
m
U.S. Environmental Protection Agency

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Table 2. Additional Data for Paints and Sealants.
Study ID Reference Top Surface Specifics Product Information Notes
A1
5
Painted Steel
Latex Flat
Latex Semi-Gloss
Paint - Oil-Based
See info for specific paints below (A2, A3, and A4)

A2
5
Paint Layer
Latex Flat
Behr® Premium Plus Ultra-Pure White Flat Zero VOC Interior
Paint
Free standing paint layer
A3
5
Paint Layer
Latex Semi-Gloss
Behr® Premium Plus Ultra-Pure White Semi-Gloss Zero VOC
Interior Paint
Free standing paint layer
A4
5
Paint Layer
Paint - Oil-Based
Rust-Oleum® Professional High Performance White Gloss Oil-
Based Enamel Interior/Exterior Paint
Free standing paint layer
A5
5
Sealed Steel
Epoxy-based
Polyurethane-based
See info for specific sealants below (A6, A7)

A6
5
Sealant Layer
Epoxy-based
Rust-Oleum® 5300 System Water-Based Epoxy in White,
Gloss Finish with Activator
Free standing sealant
layer
A7
5
Sealant Layer
Polyurethane-based
Rust-Oleum® 6711 System Water-Based Polyurethane, Clear
Free standing sealant
layer
B1
6
Painted steel
Primer + Oil-based
metal paint
Latex White Interior/Exterior Multi-Surface Primer, Sealer,
and Stain Blocker + High Performance Protective Enamel
Gloss White Oil-Based Interior/Exterior Metal Paint

B2
6
Painted
hardwood
Primer + Oil-based
metal paint
Latex White Interior/Exterior Multi-Surface Primer, Sealer,
and Stain Blocker + High Performance Protective Enamel
Gloss White Oil-Based Interior/Exterior Metal Paint
Same paint was used for
consistency with study ID
B1
B3
6
Sealed concrete
Siloxane Sealant
Sure Klean® Weather Seal Siloxane PD (predilute)

CI
7
Painted dry wall
Latex primer + Latex
Flat
KILZ® latex primer + Behr® Premium Plus Interior Flat White
Latex Paint

C2
7
Sealed concrete
Siloxane Sealant
Sure Klean® Weather Seal Siloxane PD

El
10
Sealed
Sandstone
Siloxane Sealant
Sure Klean® Weather Seal Siloxane PD

m
U.S. Environmental Protection Agency

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Impact of VX/HD Transport into Materials
on Sampling, Decontamination and Waste
Management
The observed transport of VX/HD into porous and/or
permeable materials will impact the environmental
sampling of these agents during the consequence
management phase following an incident. The impact
described below on surface wipe sampling is derived
from bench-scale surface wipe sampling approaches,
which were effective in the experiments but are not
fully verified field sampling methods. Further, most of
the efficacious decontaminants that are capable to
degrade VX/HD are water based. Hence, it is likely that
any transport of decontaminants into a porous
material that would degrade the agent within the
material will differ significantly in magnitude and
mechanism in comparison to the transport of these oily
chemicals. Specific impacts on sampling,
decontamination, and waste management are
summarized here.
I.	Nonporous, impermeable materials
VX/HD present on materials in the nonporous,
impermeable group remain on the nonporous or
impermeable surface. Wear and tear over time may
make these materials porous. Cracks in glazed ceramic
tile are known to result in the transport of chemicals
into the clay material. The rate of evaporation will
determine the amount of agent remaining [see
reference 9 for VX],
Sampling: Wipe sampling methods can recover agent
on the surface. High surface wipe sampling efficiencies
can be achieved that will lead to more accurate level of
agent contamination characterization.
Decontamination and Waste Management: These
types of surfaces can be relatively straightforward to
clean/decontaminate. They are expected to remain in
place and would not enter the waste stream.
II.	Nonporous, permeable materials
The observed transfer of VX/HD into a paint or sealant
and into a potentially more porous material below or
behind it (like drywall behind paint) complicates
remediation of such material or such combination of
materials. The degree to which this permeation occurs
depends on the chemical and physical properties of
both agents and the paint/sealant type and sheen. The
rate of permeation may exceed the evaporation rate.
No data have been collected for rubber to determine
how much of the recovered agent in a coupon extract
can be attributed to the amount on the surface versus
the amount permeated into the material. High
recoveries after 24 h suggest that VX may have
substantially permeated the substrate.
Sampling: Surface wipe sampling of these type of
painted or sealed surfaces may not recover the actual
amount of agent present and may even lead to false
negatives on the presence of an agent. Surface wipe
sampling of materials such as rubber is expected to
recover the non-permeated agent remaining on the
surface, but not VX/HD that has diffused into the
material.
Decontamination and Waste Management: Full
decontamination of the permeable paint or sealant
layers is expected to be complex considering the
inability of water-based decontaminants to react with
the agents in the paint or sealant layer. Modifications
to decontamination approaches would be required to
be confident that the agent in the paint or sealant has
degraded. For bulk materials such as rubber, residual
VX/HD post-decontamination may diffuse back to the
surface from which it would volatilize and become an
airborne and contact hazard. Currently,
decontamination of these types of materials is difficult
and often cost prohibitive. In many cases, they may
become part of the waste stream.
III. Porous, low adsorption materials
Low recoveries of VX (no direct information for HD
available) demonstrate the penetration into porous
materials. Degradation (of VX) through interactions
with the material should not be excluded either,
especially for more materials known to be reactive
with VX, such as concrete.
Sampling: Surface wipe sampling of these surfaces may
detect low or minimal VX/HD on the surface. Most of
the VX/HD would not be accessible to a surface wipe.
The VX/HD would slowly diffuse back to the surface
and volatilize from the substrate.
Decontamination and Waste Management: Applied
decontaminants may not be able to reach deeper into
pores because the pores are occupied by the VX/HD
and will have limited efficacy. Physical removal of top
layers containing the agent may be possible without
loss in integrity of the material [10]. Currently,
decontamination of these materials is difficult and
U.S. Environmental Protection Agency

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often cost prohibitive. In many cases, they may
become part of the waste stream. Less waste would be
generated if only layers of materials (containing the
VX/HD) are removed.
IV. Porous, high adsorption materials
Transport studies for this group of materials have been
limited. Impacts on sampling, decontamination and
waste management are expected to be like those
porous, low adsorption materials described under III)
and are not repeated here.
Limitations of Studies
•	All transport studies were conducted with
representative, new, and clean surfaces and
materials. Soiling, degradation, hardening, cracking
or other deteriorations by wear and tear over time
would impact the transport and permeation of the
VX/HD into a material. For instance, deep cracks or
fissures that might occur during normal wear and
tear of originally less permeable surface (like a
glazed ceramic tile) could result in unexpected
transport of agent into the material.
•	Other paints or sealants are expected to behave
differently than described here, based on the large
variations between the limited numbers of these
products investigated in these studies.
•	Unsealed concrete is an example of a frequently
encountered porous and reactive material. The
transport and observed degradation of VX/HD
on/in unsealed concrete is complex and is not
discussed in detail in this brief. The provided
transport data for unsealed concrete complements
information already in the literature.
Contacts
Technical Contacts
•	Lukas Oudejans, oudeians.lukas(a)epa.gov
Communications Contact
•	Amelia McCall, mccall.amelia(5>epa.gov
Disclaimer: This document is for informational
purposes only. Any mention of or reference to
commercial products, processes, or services by trade
name, trademark, manufacturer, or otherwise does
not imply an endorsement by the U.S. Government
or the U.S. Environmental Protection Agency and
shall not be used for advertising or product
endorsement purposes. EPA does not endorse any
commercial products, services, or enterprises.
U.S. Environmental Protection Agency

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References
1.	Organisation for the Prohibition of Chemical Weapons (OPCW). "Syria and the OPCW." See
https://www.opcw.org/media-centre/news/2019/03/opcw-issues-fact-finding-mission-report-chemical-weapons-
use-allegation. Last accessed May 24, 2021.
2.	Organisation for the Prohibition of Chemical Weapons (OPCW). "Malaysia. Statement by the Delegation of
Malaysia at the eighty-sixth Session of the Executive Council." See
https://www.opcw.org/fileadmin/OPCW/EC/86/en/ec86natl2 e .pdf. Last accessed May 24, 2021.
3.	Organisation for the Prohibition of Chemical Weapons (OPCW). "Incident in Salisbury." See
https://www.opcw.org/media-centre/featured-topics/incident-salisbury. Last accessed May 24, 2021.
4.	Organisation for the Prohibition of Chemical Weapons (OPCW). "Case of Mr Alexei Navalny." See
https://www.opcw.org/media-centre/featured-topics/case-mr-alexei-navalny. Last accessed May 24, 2021.
5.	U.S. EPA. 2016. "Fate and Transport of Chemical Warfare Agents VX and HD across a Permeable Layer of Paint or
Sealant into Porous Subsurfaces." EPA/600/R-16/173, Research Triangle Park, NC: U.S. Environmental Protection
Agency.
6.	U.S. EPA. 2020. "Physical and Chemical Removal Options for Porous/Permeable Materials Contaminated with the
Persistent Chemical Warfare Agent VX." EPA/600/R-20/047, Research Triangle Park, NC: U.S. Environmental
Protection Agency.
7.	U.S. EPA. 2016. "Natural Attenuation of Persistent Chemical Warfare Agent VX on Selected Interior Building
Surfaces." EPA/600/R-16/110, Research Triangle Park, NC: U.S. Environmental Protection Agency.
8.	U.S. EPA. 2017. "Natural Attenuation of the Persistent Chemical Warfare Agent VX on Porous and Permeable
Surfaces." EPA/600/R-17/186, Research Triangle Park, NC: U.S. Environmental Protection Agency.
9.	U.S. EPA. 2019. "Technical Brief: Persistence of Chemical Warfare Agent VX on Building Material Surfaces."
EPA/600/S-19/074, Research Triangle Park, NC: U.S. Environmental Protection Agency.
10.	U.S. EPA 2017. "Remediation Options for Porous Materials Contaminated with Persistent Chemical Warfare
Agents VXand HD." EPA/660/R-17/348, Research Triangle Park, NC: U.S. Environmental Protection Agency.
11.	Manuja, A, J Ritchie, K Buch, Y Wu, CMA. Eichler, JC Little and LC Marr. 2019. Total surface area in indoor
environments. Environ. Sci.: Processes & Impacts 21: 1384-1392.
13	National Response Team Quick Reference Guide VX, January 2015 Update. Available at
https://nrt.Org/sites/2/files/NRT WMD CHEM UPDATE VX ORG FINAL 2015 01 22.pdf. Last accessed May 25, 2021.
14	National Response Team Quick Reference Guide HD, January 2015 Update. Available at
https://www.nrt.Org/sites/2/files/NRT WMD CHEM UPDATE Sulfur Mustard HD ORG FINAL 2015 01 22.pdf. Last
accessed May 25, 2021.
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