www. epa. gov/researc h
technical BRIEF
INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
Summary of the Transport of Cesium in the Environment
Introduction
The U.S. Environmental Protection Agency's (EPA's) Homeland Security Research Program (HSRP) is
assessing strategies and methodologies for remediation of areas contaminated with radionuclides.
Most of EPA's research efforts have focused on Cesium (Cs), an extremely mobile and difficult to clean
up radionuclide, with the 137Cs and 134Cs being the predominant isotopes. Cs is a likely contaminant
that would result from its use (probably in the form of cesium chloride [CsCI]) either in a radiological
dispersal device, from its release or generation through decay processes from nuclear power plant
accidents, or from its release from an improvised nuclear device. The EPA would likely be involved with
remediation of areas contaminated after one of these types of radiological incidents. The resulting
contamination could be potentially widespread, involving many square miles urban, agricultural, and
forested areas.
Because of its initial mobility right after deposition, knowledge of the transport of Cs in the
environment is crucial to inform cleanup and sampling strategies. EPA's Homeland Security Research
Program has conducted a series of experimental studies and has acquired field data from the
Fukushima and Chernobyl accidents focused on assessing how Cs moves within the environment
following an intentional or accidental release. This information on the mobility of Cs (see Figure 1) falls
into several areas, all of which are important to simultaneously consider following a radiological
incident, including:
•	Cs interaction with urban surfaces under ambient conditions
•	Effect of weathering on Cs-contaminated surfaces
•	Cs movement within soil
•	Cs movement in bodies of surface water
•	Cs uptake into vegetation
•	Cs movement within water and wastewater infrastructure
•	Cs movement due to wildfires in contaminated forest land
•	Cs movement due to precipitation events.
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U.S. Environmental Protection Agency
Office of Research and Development
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Figure 2: Percent of initial Cs contamination removed from study materials after simulated rainfall (2
cm/hour) (U.S. EPA, 2012).
Cs Movement within Soil
In Fukushima, Japan, it was found that most of deposited radioactive Cs (more than 90%) remained
within 2 inches (5 cm) of the ground soil surface at most sites (Matsuda et al., 2015). After the
Fukushima incident, Cs was deposited in vegetative surfaces and the Cs was transported to the litter
layer due to natural activities such as wind, precipitation, plant shedding, etc. The recent study in
Fukushima suggested that Cs was rapidly leached from the forest-floor litter layer to soil layer. Then Cs
was immobilized in the upper (0-5 cm) mineral soil layer through its interaction with clay minerals
(Koarashi et al., 2016). Another Japanese study suggested that the transfer rate of Cs in litter layer to
soil surface depended on the litter layer decomposition rate, which is a function of activity and
biomass of microorganisms in the soil (Kurihara et al., 2018). The Cs-soil penetration depth and time
may vary depending on various factors including soil clay content, litter decomposition rate, weather,
precipitation, etc. However, based on the observations in Fukushima, the soil penetration depth will be
less than 4 inches (10 cm) and the time to transfer the initial Cs on vegetation to the soil layer will take
a few months to a year depending on the region.
Cs Movement in Bodies of Surface Water
Runoff from contamination sources to surface waters is an important pathway for aiding in the
transport of contaminants (Comans et al., 1989). The migration of contaminants is typically facilitated
by decontamination efforts (i.e., wash water) and precipitation events. Although groundwater
contamination resulting from the migration of radiological contaminants is still a concern, the
spreading of contaminants at the surface level increases the odds of exposure through various routes,
including direct exposure, ingestion (both direct and indirect) and possibly inhalation.
Once introduced to aquatic environments, radionuclides begin accumulating in bottom sediments and
organic matter (Thiessen et al., 1999). Factors influencing aquatic contamination levels include ground-
surface contamination levels, volumetric flow rate, and time since initial deposition (Monte et al.,
2006). These levels are known to drop relatively quickly by means of flushing, burying, and radioactive
decay. This process is accelerated in oceans, rivers, and lakes that are supplied by tributaries.
U.S. Environmental Protection Agency
Office of Research and Development
EPA/600/S-18/289
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involving pine needles and peat doped with non-radioactive Cs. In this study, emissions of Cs were
measured as a function of aerodynamic particle size and compared to Cs content of the residual ash. In
these tests, only 1-2.5 % of the Cs on the pine needles burned was emitted as Cs in the airborne
particulate matter. Peat fires did not emit Cs into the air. Most of the Cs was concentrated on particle
sizes larger than 10 micrometers (pm). Additional work is ongoing to evaluate different forest fire
conditions and different types of biomass.
Cs Movement within Water and Wastewater Infrastructure
For Cs in water as a soluble ion, its movement through water and wastewater infrastructure primarily
follows the flow of the water, relentlessly spreading contamination wherever it goes ((U.S. EPA, 2013).
However, spread of Cs is also related to the ability of the Cs ion to interact with construction materials
and other substances found in the urban environment (Kaminski et al., 2015b), including water and
wastewater systems (U.S. EPA, 2014a). For many common construction materials (U.S. EPA, 2018),
such as iron, copper (see Figure 3), and plastic pipes, interaction in water and wastewater system is
minimal, occurs slowly, or is inhibited by other substances found in water and wastewater systems
(e.g., other naturally occurring ions that out-compete Cs ions for available adsorption sites) (U.S. EPA,
2Q14d). However, adsorption to cement-mortar pipes and concrete infrastructure components (like
channels, tanks, etc.) can occur under some conditions (Szabo and Minamyer, 2014), retarding
movement and increasing persistence of Cs as described above. In fact, several other urban surface
materials, like brick, are also used in construction of water and wastewater infrastructure (Kaminski et
al., 2016). Hence, they are subject to the same Cs persistence as described above.
Figure 3. Laboratory experiments to investigate the persistence of Cs on copper surfaces. The
different colors result from varying water quality parameters.
Cs strongly adsorbs to many clay and clay-containing substances (Jolin and Kaminski, 2016), such as
soils, which may be found in water systems as sediments. Such sediments may be found in both
drinking water and waste water systems. For instance, drinking water storage tanks can accumulate
sediments that can act as reservoirs of Cs (U.S. EPA, 2014c). Sometimes these sediments result from
fine particles arising from river/lake sediments containing clay that adsorb Cs. For waste water
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systems, examples include stormwater, which can wash clay/sediments/soils into collection systems,
changing the movement of Cs in several ways. Examples include: (1) transport of dissolved Cs into
receiving waters; (2) concentration of adsorbed Cs when solids are removed from storm water via
engineering controls; and (3) partitioning of Cs into wastewater collection and treatment plant
components, especially when the stormwater enters into a combined stormwater-sewer system (as
are found in many cities) (Kaminski et al., 2015a). In the wastewater collection system and plant, Cs can
adsorb to construction materials (such as concrete, clay tiles, and brick). It can also be concentrated by
unit operations designed to remove solids to which the Cs in coincidentally adsorbed (see Figure 4).
Figure 4, Close-up view of the collection trench in a drained aeration grit tanks showing potential for
Cs contaminated sediment accumulation and concentration.
Cs Movement Due to Precipitation Events
Contaminants can be remobilized due to precipitation and flooding (James et al., 2005; Ueda et al.,
2012). Contamination levels following these events have been closely correlated with increasing
volumetric flow rates. River banks and flood plains near large rivers are of particular concern. These
areas are known to collect high concentrations of Cs following significant precipitation events for many
years following initial deposition (Japan Atomic Energy Agency, 2015). The EPA's Homeland Security
Research Program is currently working to address the data gap associated with transport of
radionuclides into and out of surface water.
Contact Information
For more information, visit the EPA Web site at http://www2.epa.gov/homeland-security-research.
Technical Contact: Paul Lemieux (lemieux.paul@epa.gov)
General Feedback/Questions: Amelia McCall (mccall.amelia@epa.gov)
U.S. Environmental Protection Agency
Office of Research and Development
EPA/600/S-18/289
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