•SER& technical BRIEF
www.epa.RoV'Tesearcl
Fate and Transport of Cesium ROD Contamination -
Implications for Cleanup Operations
INTRODUCTION
A radiological dispersal device (ROD) is used to spread radiological contamination to do harm. A
dirty bomb is an ROD that uses a conventional explosive device for dispersal. The EPA would likely
be involved with remediation of areas contaminated after an ROD incident. In support of its
customers, the EPA's Homeland Security Research Program (HSRP) is assessing strategies and
methodologies for remediation of areas contaminated due to RDDs. Initial research efforts have
focused on cesium (Cs), an extremely mobile and difficult to ^^^^^^^^^^^^^^^^^^
clean up radionuclide. To inform cleanup and sampling
strategies, EPA's National Homeland Security Research Center
has conducted a series of studies focused on assessing how
cesium travels into and adheres to urban materials as a function
of relative humidity and precipitation.
CESIUM INTERACTIONS WITH URBAN SURFACES
UNDER TYPICAL AMBIENT CONDITIONS
Cesium chloride (CsCI), even if it is deposited as a dry particle,
will eventually become aqueous when exposed to relative
humidities (RH) above 67% or to rain. Cs containing aqueous
droplets can easily be transported through the pores of porous
materials or through surface cracks. Once Cs ions (Cs
hereafter) have migrated into these materials, Cs can be difficult
to efficiently extract without removal of the affected surface. The
adsorption of the Cs to the porous materials also hampers its
ability to be extracted using existing chemically based
decontamination technologies.
The ability to remove Cs from surfaces depends on the ability to
reach the contamination. This ability is partially governed by the
penetration depth. To experimentally assess the migration of Cs
in its aqueous form into urban materials, water solutions of Cs
were aerosolized onto the surfaces of five study materials:
asphalt, brick, concrete, limestone, and granite.
The migration was determined by measuring Cs penetration
depths as a function of high and low RH. Results from the 87%
RH experiments are shown in the table.
Summary Points
Study Materials: asphalt, brick,
concrete, limestone, and granite
Cs penetrates 0.2 to 3.5 mm in
28 days depending on material
type and RH.
Of the study materials, it
penetrates furthest in granite
and concrete.
For concrete, limestone and
brick the maximum degree of
sorption was seen after 24
hours of interaction, while for
asphalt and granite it occurred
after 6 days.
Weathering, as simulated rain,
was observed to remove Cs
from the materials.
The overall removal was
dependent upon the material
type with the highest percent
removed observed for asphalt.
From these studies, it was concluded that the Cs penetration depth profile primarily depends on
the type of building material and heterogeneity of the sample surface. These studies also
demonstrate that the penetration depth was not strongly affected by the contaminant-surface
interaction time for up to 28 days; operationally this would be the time between contamination and
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Contaminant-
Surface
Interaction
Time (days)
Penetration Depth* (mm) 87% Relative
Asphalt Limestone Granite Cor
0.2
0.4
0.4
0.6
0.7
1.7
1.3
1.4
2.0
0.2
3.5
2.3
0.5
0.8
0.7
0.8
0.5
0.7
cleanup. The ability
to remove Cs from
these surfaces also
depends on the
ability to desorb the
Cs from the material
or to extract the Cs
before it develops
strong binding to
the material. This
ability is partially
governed by the Cs
adsorption. The Cs
sorption
characteristics were
determined by
spiking water solutions of Cs onto the urban surfaces. These studies showed that sorption of Cs
increased with time (from 1 to 28 days) for the five study materials studied. The maximum degree
of sorption was seen after 24 hours of interaction for concrete, limestone and brick, while for
asphalt and granite it occurred after 6 days. These sorption test results also suggested that asphalt
is the material with the highest sorption capability. Lastly, to assess the properties to desorb the
Cs, the ability to extract Cs with competing ions was tested. This extraction ability increased in the
following order: brick > granite > limestone > concrete > asphalt.
2.6
1.1
Data extracted from Gusarov et al.i and Maslova et al.ii.
*Penetration depths (mm) indicate where 90 % of the cesium was found
EFFECT OF WEATHERING ON CS CONTAMINATED SURFACES
Figure 1: Percent of initial Cs contamination removed from study materials
after simulated rainfall (2 cm/hr)'".
50
40
30
20
It is known that
weathering can reduce
the contamination on
surfaces. To assess the
impacts of weathering
process on Cs
contamination, the
amount of Cs removed
from urban surfaces
(asphalt, brick,
concrete, limestone,
and granite) and the
amount of Cs
penetrated into the
building materials after
a simulated rain event
(average 2 cm per hour
for 30 min) was
determined. The
coupons were
contaminated by spiking them with water solutions of Cs. The percent of Cs removed is shown in
Figure 1 iii. The penetration depth of Cs into the building materials was in the following order:
limestone > brick > concrete = asphalt = granite. These results suggest that that it would be more
difficult to remove Cs from some materials such as brick, concrete, and limestone after a rain event
than prior to the event due to greater subsurface penetration
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asphalt granite brick concrete limgstone
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CONTACT INFORMATION
For more information, visit the EPA Web site at www.epa.gov/nhsrc.
Technical Contact: Sang Don Lee (lee.sangdon@epa.gov)
General Feedback/Questions: Kathy Nickel (nickel.kathv@epa.gov)
REFERENCES
i A. Gusarov, N. N'icheva, A. Konoplev, S.D. Lee, K. Maslova, V. Popov and I. Stepina. Fate and
Transport of radiocesium in urban building materials. International Conference on Radioecology &
Environmental Radioactivity: Environment & Nuclear Renaissance. 2011, 46(6): S265-S269.
ii Maslova, K., et al., Fate and transport of radiocesium, radiostrontium and radiocobalt on urban
building materials, Journal of Environmental Radioactivity. 2013, 125: 74-80.
http://dx.doi.0rg/10.1016/i.ienvrad.2013.01.013.
iii U.S. Environmental Protection Agency. Fate of Radiological Dispersal Device (ROD) Material on
Urban Surfaces: Impact of Rain on Removal of Cesium, EPA/600/R-12/569, 2012.
U.S. EPA's Homeland Security Research Program (HSRP) develops products based on
scientific research and technology evaluations. Our products and expertise are widely used in
preventing, preparing for, and recovering from public health and environmental emergencies that
arise from terrorist attacks or natural disasters. Our research and products address biological,
radiological, or chemical contaminants that could affect indoor areas, outdoor areas, or water
infrastructure. HSRP provides these products, technical assistance, and expertise to support EPA's
roles and responsibilities under the National Response Framework, statutory requirements, and
Homeland Security Presidential Directives.
August 2014
EPA/600/R-14/250
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