United States
Environmental Protection
Agency
Office of Solid Waste and
Emergency Response
(5102G)
EPA542-R-01-006
July 2001
www.brownfieldstsc.org
www.epa.gov/TIO
&EPA
Brownfields Technology Primer:
Selecting and Using Phytoremediation
for Site Cleanup
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Brownfields Technology Primer:
Selecting and Using Phytoremediation
for Site Cleanup
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Technology Innovation Office
Washington, DC 20460
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
Notice
This document has been funded by the United States Environmental Protection Agency (EPA)
under Contracts 68-W-99-003 and 68-W-99-020 to Tetra Tech EM Inc. The document was
subjected to the Agency's administrative and expert review and was approved for publication as
an EPA document. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
Acknowledgments
The Technology Innovation Office would like to acknowledge and thank the individuals who
reviewed and provided comments on draft documents, and provided current information on the
application of phytoremediation at various sites across the country.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
CONTENTS
Section Page
1.0 INTRODUCTION 1
1.1 Purpose 1
1.2 Background 2
1.3 Approach 2
2.0 WHAT IS PHYTOREMEDIATION? 4
2.1 Types of Sites and Contaminants Treated by Phytoremediation 5
2.2 Plants Species Used for Phytoremediation 5
2.3 Phytoremediation Processes 7
3.0 APPLICATION OF PHYTOREMEDIATION FOR THE CLEANUP OF SOIL, SEDIMENT,
SURFACE WATER, AND GROUNDWATER 9
3.1 Advantages to the Selection of Phytoremediation at Brownfields Sites 9
3.2 Related Uses of Plants at Brownfields Sites 11
3.3 Discussions with Regulators 11
3.4 Community Involvement 11
4.0 PRACTICAL CONSIDERATIONS AND LIMITATIONS 12
5.0 SELECTION AND DESIGN OF A PHYTOREMEDIATION SYSTEM 14
5.1 Technical Factors 14
5.2 Strategies for Contaminant Control 16
5.3 Innovative Technology Treatment Trains 16
5.4 Design Team 17
6.0 OPERATION AND MAINTENANCE 18
6.1 Operation and Maintenance 18
6.2 Disposal 18
6.3 Performance Evaluation and Monitoring 19
7.0 COST OF PHYTOREMEDIATION 20
7.1 Cost Savings Based on Actual Cost Estimates 20
7.2 Sample Phytoremediation Costs 20
8.0 SUPPORTING RESOURCES 22
Tables
1 Selected Phytoremediation Projects 6
2 Types of Plants, Contaminants, and Media 8
3 Estimated Cost Savings Through the Use of Phytoremediation Rather Than
Conventional Treatment 21
4 References by Topic 25
Appendices
1 LIST OF ACRONYMS AND GLOSSARY OF KEY TERMS
2 THE PROCESSES OF PHYTOREMEDIATION
3 PHYTOREMEDIATION DECISION TREE MODELS
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
1.0 INTRODUCTION
1.1 Purpose
The Brownfields Technology Support Center
(BTSC) (see box) has developed this
document to provide an educational tool for
site owners, project managers, and regulators
to help evaluate the applicability of the
phytoremediation process at brownfields sites.
Cleanup technologies that reduce costs,
decrease time frames, or positively affect
other decision considerations (for example,
community acceptance) can have a significant
effect on the redevelopment potential of
brownfields sites. Increased attention to
brownfields sites and the manner in which
they are redeveloped places greater
importance on the selection of cleanup
technologies.
Phytoremediation represents a group of
innovative technologies that use plants and
natural processes to remediate or stabilize
hazardous wastes in soil, sediments,
surface water, or groundwater. Because it
is based on natural processes,
phytoremediation may be easily adaptable
to many redevelopment plans for
brownfields sites. Phytoremediation is
being evaluated at a variety of sites and on
myriad contaminants to determine the
conditions under which phytoremediation
systems are effective in reducing
contamination. The primer presents some
of the advantages and technical limitations
of phytoremediation that the evaluations
indicate. The primer illustrates the
potential of phytoremediation to serve as:
> An interim approach for stabilizing sites
while other cleanup strategies are being
evaluated
> An approach that augments the overall
effectiveness of other cleanup
technologies
> A stand-alone approach for providing
cost-effective, long-term cleanup
solutions
The primer also illustrates the potential
limitations of phytoremediation and how such
factors as levels of contaminants and
properties of the soil, as well as concerns
about potential risk of exposure may affect the
use of phytoremediation at brownfields sites.
Because phytoremediation is more than
simply planting vegetation, brownfields
decision makers must: (1) select the correct
plants, (2) work effectively with regulators and
the local community, (3) understand
maintenance and monitoring requirements,
and (4) compare the costs of
phytoremediation with the costs of other
technology options.
Until phytoremediation is a more proven and
established technology, advocates for its use
may find it necessary to demonstrate its
potential applicability and efficacy on a site-
specific basis. To do so may require an up-
Brownfields Technology Support Center
EPA recently established the
Brownfields Technology Support Center
to ensure that brownfields decision
makers are aware of the full range of
technologies available for conducting
site assessments and cleanup, and can
make informed decisions about their
sites. The center can help decision
makers evaluate strategies to
streamline the site assessment and
cleanup process, identify and review
information about complex technology
options, evaluate contractor capabilities
and recommendations, explain complex
technologies to communities, and plan
technology demonstrations. The center
is coordinated through EPA's TIO and
works through the laboratories of EPA's
Office of Research and Development.
Localities can submit requests for
assistance directly through their EPA
Regional Brownfields Coordinators;
online at ; or
by calling 1-877-838-7220 (toll free).
For more information about the
program, the point of contact is Dan
Powell of EPA TIO at 703-603-7196 or
.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
front commitment of time and resources to
demonstrate that the performance of
phytoremediation is comparable to the
performance of traditionally accepted
technology options. Such an investment
ultimately could save site owners significant
amounts of money when they clean up their
properties for redevelopment.
1.2 Background
The U.S. Environmental Protection Agency
(EPA) has defined brownfields sites as
"abandoned, idled or under-used industrial
and commercial facilities where expansion or
redevelopment is complicated by real or
perceived environmental contamination."
Numerous technology options are available to
assist those involved in the cleanup of
brownfields sites. EPA's Technology
Innovation Office (TIO) encourages the use of
innovative, cost-effective technologies to
characterize and clean up contaminated sites.
An innovative technology is a technology that
has been field-tested and applied to a
hazardous waste problem at a site, but that
lacks a long history of full-scale use.
Although readily available information about
its cost and how well it works may be
insufficient to encourage use under a wide
variety of operating conditions, an innovative
technology has the potential to significantly
reduce the cost and time required to
redevelop brownfields sites.
Historically, fear of contamination and its
associated liability has hampered
redevelopment of brownfields sites.
Phytoremediation offers a unique advantage
over other remediation technologies. It
provides ecosystem restoration and "green
areas" that may be desired by the local
community.
The process of redeveloping brownfields sites
provides an excellent framework for using
innovative technologies because: (1) state
and federal regulators tend to be flexible in
approving cleanup plans for brownfields sites,
particularly those sites for which voluntary
cleanup plans have been submitted; (2) most
of the current brownfields sites are not
encumbered by a history of litigation or
enforcement actions for which traditional
technologies already may have been
specified; and (3) redevelopment plans have
been prepared for many brownfields sites and
are used to establish site-specific cleanup
targets and the time frames for cleanup - that
information provides an excellent basis for
tailoring innovative approaches to the
investigation and cleanup of individual sites.
1.3 Approach
This primer will assist brownfields decision
makers in considering phytoremediation as an
innovative treatment technology option for
cleanup at brownfields sites. The document
discusses the factors important in the
selection of phytoremediation, such as
regional climate and local growing conditions,
location and type of contaminants to be
treated, and site-specific redevelopment
objectives. The primer illustrates how those
factors can be potential advantages (or
limitations) in the selection of
phytoremediation at a brownfields site;
presents examples that illustrate the field
applications of phytoremediation at
brownfields sites; and identifies additional
resources to assist brownfields decision
makers in evaluating phytoremediation as an
option for their sites.
In addition, this document provides the
following information in appendices:
> A list of acronyms
> A glossary that explains technical
terms related to phytoremediation
* A description of the processes of
phytoremediation;
> Decision tree diagrams developed by the
Phytoremediation Work Group of the
Interstate Technology and Regulatory
Cooperation Work Group. The decision
tree diagrams provides guidelines for
determining the applicability of
phytoremediation at a brownfields site
after site characterization has been
completed.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
This primer is not an authoritative or original
source of research on phytoremediation.
Instead, it is intended to briefly describe the
phytoremediation process and its potential
applicability in a brownfields setting in a tone
appropriate for audiences who have only a
limited technical background.
It is important to note that this primer cannot
be used as the sole basis for determining this
technology's applicability to a specific site.
That decision is based on many factors and
must be made on a case-by-case basis.
Technology expertise must be applied and
treatability studies conducted to support a
final remedy decision. For a more technical
and thorough treatment of the topic and of
issues described in this primer, consult EPA's
Introduction to Phytoremediation (EPA/600/R-
99/107, February 2000). Ordering information
is provided in the Supporting Resources
section of this primer.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
2.0 WHAT IS PHYTOREMEDIATION?
Physical Effects -
Transpiration ofvolatiles
and hydraulic control of
dissolved plume
Enhanced
rhizosphere
biodegradation
Phytoremediation is the direct
use of living green plants for in
situ (in-place or on-site) risk
reduction for contaminated soil,
sludges, sediments, and
groundwater, through removal,
degradation, or containment of
the contaminant (synonyms:
green remediation and botano-
remediation). Figure 1
illustrates the mechanisms
involved in the
phytoremediation process.
Phytoremediation warrants
consideration for cleaning up
brownfields sites at which there
are relatively low
concentrations of contaminants
(that is, organics, nutrients, or
metals) over a large cleanup area and at
shallow depths. Another potential application
for phytoremediation is at sites that currently
are "mothballed" and may be redeveloped in
the future. Phytoremediation can be a cost-
effective alternative approach for reducing
the leaching of contaminatnts through soil or
groundwater, reducing the run-off of
contaminated stormwater, beginning an initial
level of cleanup, and improving the aesthetic
condition of a site. Phytoremediation
warrants consideration for use in conjunction
with other technologies when the
redevelopment and land use plans for the
site include the use of vegetation.
Phytoremediation is distinct from Monitored
Natural Attenuation (MNA), that is, a
controlled and monitored site cleanup
approach that relies on natural attenuation
processes to achieve remediation objectives
within time frames that are reasonable
vis-a-vis more active methods. Though both
processes involve some similar elements
such as biodegradation, sorption,
volatilization, stabilization, phytoremediation
technologies represent active processes that
are designed and implemented to control and
eliminate contamination. MNA and
Phytodegradation - The breakdown of contaminants taken up by
the plant through metabolic processes within the plant, or the
breakdown of contaminants external to the plant through the
effect of compounds (such as enzymes) produced by the plant
Accumulation in roots
translocated to shoots
and leaves
Figure 1: Examples of Mechanisms Involved in Phytoremediation
phytoremediation also are similar in that both
might be considered significant components
of a treatment-train approach to hazardous
waste cleanup at brownfield sites. For more
information on EPA's directives regarding the
the use of MNA refer to .
Successful Reduction of Lead Contamination
Phytoextraction was demonstrated at a site in
Trenton New Jersey that had been used for the
manufacture of lead acid batteries. Phytoextraction
using Indian mustard (Brassicajuncea)and
ethylenediaminetetraacetic acid (EDTA) soil
amendment reduced the average surface lead
concentration by 13 percent in one growing season.
The target soil concentration of 400 milligrams per
kilogram (mg/kg) was achieved in approximately 72
percent of a 4,500 square-foot area. (Some of the
reduction may be attributed to dilution as a result of
tilling and spreading contaminants deeper into the
soil column.) For more information, contact Larry
D'Andrea of EPA at (202) 673-4314 or
D'Andrea. Larry @epa,gov.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
2.1 Types of Sites and Contaminants
Treated by Phytoremediation
There is potential to use phytoremediation
beneficially under a wide variety of site
conditions. Types of sites at which
phytoremediation has been applied or
evaluated include: pipelines; industrial and
municipal landfills; agricultural fields; wood
treating sites; military bases; fuel storage
tank farms; gas stations; army ammunition
plants; sewage treatment plants; and mining
sites.
Phytoremediation is being tested and
evaluated for its effectiveness in containing
and treating a wide array of contaminants
found at brownfields sites. While much more
testing is needed, current results indicate that
plants have the potential to enhance
remediation of the following types of
contaminants:
Petroleum hydrocarbons
Benzene, toluene, ethylbenzene, and
xylene (BTEX)
Polycyclic aromatic hydrocarbons (PAH)
Polychlorinated biphenyls (PCB)
Trichloroethene (TCE) and other
chlorinated solvents
Ammunition wastes and explosives
Heavy metals
Pesticide waste
Radionuclides
Nutrient wastes (such as phosphates and
nitrates)
One of the more optimal applications of
phytoremediation is as a containment
technology. Since many brownfields sites
are characterized by wide-spread
contamination at low concentrations that are
close to target cleanup levels,
phytoremediation is a good containment
alternative if geology and rainfall amounts are
favorable.
Table 1 lists types of sites at which
phytoremediation has been employed with
some level of success in cleaning up the
sites. The table provides only a
representative sample of sites and
contaminants.
2.2 Plants Species Used for
Phytoremediation
Plants species are selected for use according
to their ability to treat the contaminants of
concern and achieve the remedial objectives
for redevelopment (for example, time frame
and risk management), and for their
adaptability to other site-specific factors such
as adaptation to local climates, depth of the
plant's root structure, and the ability of the
species to flourish in the type of soil present.
Often the preferred vegetation characteristics
include: an ability to extract or degrade the
contaminants of concern to nontoxic or less
toxic products, fast growth rate, adaptability
to local conditions, ease of planting and
maintenance, and the uptake of large
quantitities of water by evapotranspiration
(see the glossary of terms in Appendix 1 for
definitions of technical terms). The selection
and use of plant species must be conducted
with care to prevent the introduction of non-
native species into areas where those
species are not already present. Plant
species that are benign under most
circumstances may become a problem when
introduced into a new area. For example,
water hyacinth is considered a noxious
aquatic weed that should be used only in
isolated bodies of water from which there are
no risks of unintentional transport (for
example, by flood).
Maintenance requirements should be
considered when selecting plant species for
use at brownfields sites; those requirements
may include the frequency with which the
plant must be mowed; the need for fertilizer;
and the need for replanting, pruning,
harvesting, and monitoring programs.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
Table 1
Selected Phytoremediation Projects
Contaminants )/
Purpose of Project
Chlorinated solvents/
Control groundwater
migration at an urban
brownfields site and
remove TCE and
derivatives from
groundwater
Chlorinated solvents/
Biologically (pump
and treat)
contaminated
groundwater
Chlorinated solvents/
Control groundwater
migration and remove
solvents from
groundwater
Heavy metals/
Reduce lead
concentration in soil
BTEX compounds/
Treat petroleum and
organic contaminants;
prevent contaminated
groundwater from
migrating
PAH's/Control
groundwater and
surface water
migration, stabilize
soil, and degrade
contaminants
Explosives and
fertilizers/
Contain and treat
toxic solvents
Wood preservatives/
Treat PAHs and
DNAPLs
Media/
Mechanism
Groundwater/
Phytoextraction,
phytovolatilization,
rhizodegradation
Soil/
Rhizodegradation,
phytovolatilization
Groundwater/
Phytovolatilization,
rhizosphere
biodegradation,
phytodegradation
Phytoextraction
Soil and
groundwater/
Hydraulic control,
Phytoextraction,
phytovolatilization,
rhizodegradation
Soil and
groundwater/
Hydraulic control,
rhizodegradation
Soil and
groundwater/
Phytodegradation,
phytovolatilization
Soil and
groundwater/
Rhizodegradation,
hydraulic control
Plant
Species
Hybrid poplar
and willow
Hybrid poplar,
white willow,
native species
Eastern
cottonwood
Indian
mustard
Hybrid poplar
Grasses,
hybrid poplar
Hybrid poplar
Herbaceous
species and
hybrid poplar
Location
(Scale*)
Findlay, OH
(Full scale)
Solvents
Recovery
Systems of New
England,
Southington, CT
(Full scale)
Carswell AFB, TX
(Pilot)
Trenton, NJ
Brownfields Site
(Pilot)
Ashland
Chemical Co,
Milwaukee, Wl
(Full scale)
Oneida, TN (Full
scale)
Aberdeen
Proving Ground,
MD (Pilot)
Laramie, WY
(Full scale)
Point of
Contact
Steve Synder, Ohio
Environmental Protection
Agency (OEPA)
(419)352-8461
Ed Gatliff, Applied Natural
Sciences, Inc. (ANS)
(513)942-6061
Steve Rock, U.S. EPA
(513)569-7149
Ari Ferro, Phytokinetics
(801)750-0950
Steve Hitt, U.S. EPA
(214)665-6736
Greg Harvey, USAF
(937)255-7716
Larry D'Andrea, U.S. EPA
(212)637-4314
Dr. Michael Blaylock,
Edenspace (703)961-8700
Scott Ferguson, Wisconsin
Department of Natural
Resources (WDNR)
(414)263-8685
Dr. Louis Licht, Ecolotree
(319)358-9753
Dr. John Novak, VATech
(540)231-6132
Dr. Louis Licht, Ecolotree
(319)358-9753
Harry Compton, U.S. EPA
(732)321-6751
Steve Hirsh, U.S. EPA
(215)814-3352
Marisa Latady, Wyoming
Department of Environmental
Quality, (307) 777-7752
Jennifer Uhland, CH2M Hill
(303^ 771-0900
Source: Various research documents, internet web sites, and discussions with points of contact.
Notes:
* Full scale = Phytoremediation is part of the final remedy for site cleanup
Pilot scale = Phytoremediation is being evaluated as a potential treatment technology for the site.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
Several types of plants and sample species
frequently used for phytoremediation are
listed below:
Hybrid poplars, willow, and cottonwood
trees
Grasses (rye, Bermuda grass, sorghum,
and fescue)
Legumes (clover, alfalfa, and cowpeas)
Aquatic and wetland plants (water
hyacinth, reed, bullrush, and parrot
feather)
Hyperaccumulators for metals (such as
alpine pennycress for zinc or alyssum for
nickel)
Herbaceous species, such as mustard,
alfalfa, and grasses, can be used in the
remediation of contaminants in surface soil.
Hybrid poplars, willows, cottonwood, and
other woody species that have rapid growth
rates, deep roots, and high transpiration rates
(resulting in uptake of abundant quantities of
water), can be in the remediation of
contaminants in groundwater or can be used
to provide hydraulic control.
Phytoremediation Selected for
RCRA Corrective Action
An Ashland Chemical Company tank farm in
Milwaukee, Wisconsin shows the potential for the
use of phytoremediation at active industrial sites, as
well as the adaptability of the technology for
brownfields sites. Under the Resource Conservation
and Recovery Act (RCRA), the facility was required
to remediate contamination with petroleum products
and organic solvents that resulted from years of fuel
and solvent handling at the facility. Hybrid poplar
trees have been arrayed to prevent contaminated
groundwater from discharging into an adjacent river
while remediating concentrations of contaminants in
soil and groundwater. An extensive monitoring
program, consisting of several monitoring wells
transects and frequent groundwater and soil
sampling, assesses the project's impact on
groundwater migration, concentrations of
contaminants, and growth conditions for the trees.
Despite that rigorous program, the project was
considerably less expensive than excavating and
landfilling contaminated soil and pumping and
treating contaminated groundwater. For more
information, contact Scott Ferguson of the
Wisconsin Department of Natural Resources at
(414)263-8685.
Constructed wetlands also are being used to
remediate contaminated sites. There are two
broad categories of wetland plants -
emergent and submerged species.
Emergent plants, those rooted in shallow
water with most of the plant exposed above
the water's surface, transpire water and can
be easier to harvest, if necessary.
Submerged species, which lie entirely
beneath the water's surface, do not transpire
water but provide more biomass (increased
vegetative growth and density) for the uptake
and sorption of contaminants. (See the
glossary). Plant species that have a
relatively high biomass generally improve the
overall effectiveness of phytoremediation.
(See the Selection and Design of a
Phytoremediation System section of this
primer for a more detailed discussion of the
role biomass plays in phytoremediation).
2.3 Phytoremediation Processes
Phytoremediation is the broad term for the
use of plant systems to remediate
contamination. Phytoremediation can be
classified further on the basis of the physical
and biological processes involved. Those
processes include:
Hydraulic control: The use of plants to
rapidly uptake large volumes of water to
contain or control the migration of subsurface
water (synonym: phytohydraulics).
Phytodegradation: The breakdown of
contaminants taken up by the plant through
metabolic processes within the plant, or the
breakdown of contaminants external to the
plant through the effect of compounds (such
as enzymes) produced by the plant
(synonym: phytotransformation).
Phytoextraction: The uptake of a
contaminant by plant roots and the
translocation of that contaminant into the
aboveground portion of the plants; the
contaminant generally is removed by
harvesting the plants. This technology is
applied most often to soil or water
contaminated with metals.
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
Phytostabilization: The immobilization of a
contaminant through absorption and
accumulation by roots, adsorption onto roots,
or precipitation within the root zone of plants.
Phytovolatilization: The uptake and
transpiration of a contaminant by a plant, with
release of the contaminant or a modified form
of the contaminant to the atmosphere from
the plant.
Rhizodegradation: The breakdown of a
contaminant in soil through microbial activity
that is enhanced by the presence of the root
zone (synonyms: plant-assisted degradation,
plant-assisted bioremediation, plant-aided in
situ biodegradation, and enhanced
rhizosphere biodegradation).
Rhizofiltration: The adsorption or
precipitation onto plant roots or the
absorption into the roots of contaminants that
are in solution in the root zone.
Appendix 2 to this document provides a brief
explanation of the mechanisms of
phytoremediation. For more technical
information about the various processes of
phytoremediation, refer to EPA's Introduction
to Phytoremediation (EPA/600/R-99/107,
February 2000). Table 2 shows the types of
contaminants and media that can be treated
by commonly used plants. The table also
includes the type(s) of phytoremediation
process that occur in each situation
identified.
Table 2
Types of Plants, Contaminants, and Media
Type of
Contaminant
Organic
Inorganic
Medium
Soil
Sediment
Groundwater
Soil
Sediment
Groundwater
Type of Plant
a
A
PV
A
PV
fi
1
<
A
PE
A
PE
1
2
ffl
A
PD
RD
A
PD
RD
A
PD
&
3
o
M
%
ffl
A
PV
A
PV
a
0
i
a
o
A
HC
A
HC
1
6
A
RD
A
RD
A
PS
A
PS
«
1
8
M
A
PD
RD
A
PD
RD
A
HC
PD
A
PE
PS
PV
A
PE
PS
PV
A
HC
P
1
1
A
PE
PS
PV
A
PE
PS
PV
A
RF
E/3
E/5
H
P-i
A
PE
A
PE
3
%
rt
A
RD
A
RD
tJ
u
a
00
A
PD
A
PD
A
PD
1
O
50
A
PE
A
PE
A
RF
fl
d
1
1
A
RF
a
§:
A
PD
RD
A
PD
RD
A
HC
PD
A
HC
A Plant is effective for the type of
contamination and medium shown.
HC Hydraulic control
PD Phytodegradation
PE Phytoextraction
PS Phytostabilization
PV Phytovolatilization
RD Rhizodegradation
RF Rhizofiltration
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BROWNFIELDS TECHNOLOGY PRIMER:
SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP
3.0 APPLICATION OF PHYTOREMEDIATION
FOR THE CLEANUP OF SOIL, SEDIMENT,
SURFACE WATER, AND GROUNDWATER
Other
Treatment
Technologies
Phytoremediation has been attempted on a
full- or demonstration-scale basis at more
than 200 sites nationwide. Although
phytoremediation is a naturally-occurring
process, discovery of its effectiveness and
advances in its application as an innovative
treatment technology at waste sites, including
brownfields sites, have been recent. The
technology first was tested actively at waste
sites in the early 1990s, and use of the
approach has been increasing. As the
number of successful demonstration projects
grows and new information about the
application of phytoremediation becomes
available, the use of phytoremediation as a
treatment technology is increasing because
the technology has been proven an efficient
and effective approach at brownfields sites.
3.1 Advantages to the Selection of
Phytoremediation at Brownfields
Sites
When deciding on the applicability of
phytoremediation at a brownfields site,
decision makers should compare the
potential effectiveness and efficiency of
phytoremediation technology with other
treatment technologies that might be
appropriate for the site. The comparison
should address any specific needs of and
conditions at the site. Several
characteristics that are common to
brownfields sites should be considered during
the decision-making process. Those
characteristics include the need to enhance
the redevelopment potential and economic
value of the affected properties; the desire to
avoid indirect impacts on the community
(such as hauling large quantities of excavated
soil through neighborhoods); sensitive public
relations issues; and the fact that, sometimes,
the problem at a brownfields site is a
"perceived" one, rather than actual
contamination. Some advantages
phytoremediation offers in a brownfields
redevelopment setting are listed below.
> Potentially treats a wide variety of
contaminants. Relevance: Brownfields
sites often are made up of a collection of
former manufacturing facilities or
manufacturing processes that have left
behind a legacy of contaminants.
Research has shown that plant species
used in remediation can potentially treat a
wide variety of contaminants or families of
contaminants (for example, treating both
organics and metals).
> Provides in situ treatment. Relevance:
Stakeholders' concern about potential
health risk at brownfields sites can play a
significant role in the selection of a
treatment remedy. If a site is located in a
populated area, as is often the case, or
near sensitive receptors, such as school
children or residents, phytoremediation
offers a solution through which soil remains
in place during treatment and is usable
after treatment. Phytoremediation does not
require excavation of soil, and its
application may require only minimum
materials handling. Further,
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phytoremediation can have a positive
effect on the aesthetic character of a site.
> Offers a permanent solution.
Relevance: In some cases,
phytoremediation can destroy most or all
the pollutants, leaving little or no residual
contamination. Permanent mitigation of
potential risks can broaden the appeal of a
site to a potential developer. In addition,
future redevelopment may be encouraged
if the developer is not required to place
such institutional controls as deed
restrictions because there are no residual
contaminants of concern.
> Serves as an interim solution.
Relevance: In addition to offering a
permanent solution, in some cases
phytoremediation can act as a stop-gap
measure to contain the spread of
contaminants and begin the treatment
process. Although phytoremediation may
not be the selected final technology, the
benefits of a well designed and capably
managed phytoremediation system may be
preferable to the risks that might be posed
should a brownfields site be left completely
untreated during preparation of the final
redevelopment plan and selection of a final
remedy.
> Installation and operating and
maintenance costs can be low.
Relevance: Phytoremediation systems are
installed and maintained by traditional
agricultural or landscaping equipment,
materials, and practices. Those
techniques typically are less expensive in
up-front and long-term costs than
technology-intensive alternatives that may
require the use of sophisticated
equipment.
> Can be integrated into the natural
environment and landscaping plans.
Relevance: Phytoremediation can be
designed to be unobtrusive and
aesthetically pleasing in a variety of site
layout conditions. Wetlands, forests, or
grasslands are examples of natural areas
Using Poplars to "Pump and Treat" Groundwater
A system consisting of a dense stand of hybrid poplar,
white willow, and six native tree species was installed at
the Solvents Recovery Systems of New England
(SRSNE) Superfund Site in Southington, Connecticut.
The overall objective of the project was to biologically
"pump and treat" contaminated ground water, reducing
the amount and toxicity of contaminated groundwater
that reaches the traditional mechanical extraction wells
and ultraviolet-oxidation system. Initial greenhouse
studies found that the concentration of total volatile
organic compounds (VOC) at the site did not limit the
growth of the trees. Sap flow measurements reported
as field results indicate that the stand of trees is
accomplishing both its goals, pumping contaminated
groundwater and removing some pollutants in the
process. For more information, contact Steve Rock of
EPA at (513) 569-7149 or rock.steven@epa.gov.
that can be used in phytoremediation
design to enhance or restore the physical
appearance of a brownfields site. Other
treatment technologies that may employ
heavy construction equipment, large
pumps or wells, or other equipment (for
example, an incinerator) may have less
visual appeal and may be objectionable to
certain stakeholder groups.
> Can be an effective element of a unified
treatment-train remediation approach.
Relevance: From a cost savings and
treatment effectiveness point of view, it is
often advisable to combine, spatially and/or
over time, different treatment technologies
into a unified cleanup strategy. Treatment
trains are implemented in cases where no
single technology is capable of treating all
of the contaminants in a particular medium
or where one technology might be used to
render a medium more easily treatable by a
subsequent technology. Phytoremediation
is a technology that can provide benefit
when used in concert with more intensive
and therefore more expensive
technologies. It thus reduces overall
project costs, while achieving cleanup
goals.
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3.2 Related Uses of Plants at
Brownfields Sites
Aside from landscaping applications, plants
with potential use for phytoremediation also
have other potential applications for
protecting the environment at brownfields
sites. Installing vegetated areas, called
riparian buffers, next to surface water
resources can provide protection from non-
point source pollution, while at the same time
stabilize the banks of the water bodies and
provide a habitat area for wildlife. Vegetation
is often a crucial component in the abatement
of soil erosion in riparian zones, as well as
any area in which soil erosion could occur if
the soil is not protected. Hybrid poplars and
other trees are being tested as an alternative
to grassy clay caps, which often are used at
landfills to direct rainwater away and help
minimize the volume of leachate from those
landfills. The mechanism is a similar to that
involved in using plants to control site
hydrology. Species of trees, such as hybrid
poplars, quickly take up large quantities of
water and can be used to reduce plumes of
groundwater.
3.3 Discussions with Regulators
Many regulators have been receptive to the
use of phytoremediation at brownfields sites
because of the increasing number of positive
results demonstrated. However, as in the
selection of any innovative treatment
technology, it is important to consider site-
specific conditions and develop a level of
certainty that phytoremediation is applicable
for the site. Stakeholders that wish to use
phytoremediation should be prepared to
demonstrate that the performance of the
system would compare favorably with that of
other traditional and innovative technology
options and that phytoremediation is the
preferred option for the site. In addition,
regulatory requirements may vary by state or
region; federal, state, and local regulatory
agencies should be consulted to determine
those requirements. Consulting with the
regulatory agencies will provide access to
members of those agencies' staff who may
have expertise in and experience with
phytoremediation at similar sites.
Demonstrating the technical results and
success stories of implementation of
phytoremediation at similar sites can help tip
the scales toward regulatory acceptance. Up-
front efforts to evaluate the advantages of
using phytoremediation will pay off in
increased overall support of the process of
remedy selection and expedited approval of
the redevelopment plans by regulatory
agencies.
3.4 Community Involvement
Acceptance of a redevelopment plan that
involves the use of any cleanup technology
can be a sensitive community issue. It is
important to promote acceptance of the
redevelopment plan and the cleanup
alternatives by involving the community early
in the decision-making process through
community meetings, newsletters, or other
outreach activities. An advantage of
phytoremediation is that it is an easily
understood approach. Phytoremediation is
more intuitive than many other treatment
technologies and therefore may gain greater
acceptance in the community. For an
individual site, the community should be
aware of how use of the technology may
affect redevelopment plans and the adjacent
neighborhood. For example, there may be
aesthetic or visual improvements that result
from the planting of trees or the creation of a
wetland; there may be site-security issues or
long-term maintenance issues which may
affect site access; or there may be risk
factors that must be conveyed to the
community and may require the preparation
of a risk-management plan.
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4.0 PRACTICAL CONSIDERATIONS AND LIMITATIONS
As is true of any cleanup alternative,
phytoremediation offers a number of
advantages, as described in the preceding
section. However, it also has technical
limitations related to the types and levels of
contaminants present, soil properties,
acceptable exposure risks, and other site-
specific considerations. Discussed in this
section are a number of factors that decision
makers may find necessary to consider when
evaluating phytoremediation as a cleanup
option for their site. A more comprehensive
discussion of potential limitations to the
implementation of phytoremediation can be
found in the documents listed in the
Supporting Resources section of
this primer.
The total length of time required to
clean up a site through
phytoremediation may be too long
to be acceptable for some
redevelopment objectives.
Phytoremediation is limited by the
natural growth rate of plants and
the length of the growing season.
Several growing seasons may be
required before phytoremediation
systems become effective, while
traditional methods may require a
few weeks to a few months.
Therefore, low removal rates may
prohibit the use of
phytoremediation in cases in which
the time period available for cleanup is limited
and is a key criterion in selecting a
technology.
The growth rate of a plant species will have a
direct effect on the potential for use at a
particular site. For example, fast-growing
grasses will begin treating soil contamination
more quickly than a tree, which must
establish deeper roots to treat target
contaminants. As plants, particularly trees
used in phytoremediation, mature their root
structures deepen and their capacity to treat
deeper levels of contamination improves.
Phytoremediation can provide a number of
benefits during the course of vegetation
maturation. Plantings during initial stages
can provide a cover that minimizes water
infiltration. As the tree roots mature,
phytodegradation, rhizodegradation, and/or
phytovolatilization processes can take place
to treat contaminants at increasing depths
below the surface. In fully mature stages,
phytoremediation cover can develop a
hydraulic control, hydrostatic barrier function.
Figure 2 illustrates the progressive
development stages for phytoremediation to
YearO
Trees planted
Year!
Tree roots penetrate
waste - Remediation
Tree continues to mature -
Soil created -
Water balance established
Figure 2. Phytoremediation Developmental Stages
Source: EPA. 2000. Introduction to Phytoremediation (E.PAIQOOIR-99IW7).
National Risk Management Research Laboratory. February.
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support capping to reduce infiltration,
degradation, and then hydraulic control.
While this developmental process can be
beneficial, consideration also must be given
to whether phytoremediation is a safe and
protective remedy during the time it takes for
the plants to establish themselves to a point
at which they are treating the contaminants
effectively.
It must be determined whether
phytoremediation can be effective for the
site-specific conditions and contaminants.
For example, phytoremediation works better
in shallow soils and groundwater, unless
deep-rooted plants are suitable for the site.
In addition, phytoremediation works best on
certain types of contaminants or mixed waste
and may be less effective when used on
other combinations of waste. For example,
phytoremediation may not be the most
effective treatment option if levels of
contamination are so high that concentrations
of contaminants are toxic to plants
(phytotoxic).
In some cases, phytoremediation might not
provide adequate protection, from an eco-
receptor perspective. For example,
contamination that is below ground can be
transferred into the leaves and stems of
plants that are a food source. Further, in
some cases, contaminants are not destroyed
in the phytoremediation process; instead,
they are transferred from the soil onto the
plants and then are transpired in to the air.
Phytoremediation could also increase the
rates of bioaccummulation of contaminants
than might otherwise occur.
Potential costs associated with monitoring
and maintaining the phytoremediation
process at the site also must be factored into
the selection process. Maintenance costs
often are lower with phytoremediation than
with conventional treatment technologies.
On the other hand, monitoring costs could be
higher, especially if the cleanup rates are
slower and monitoring of the site continues
longer than monitoring for conventional
treatment technologies. An activity that will
increase the cost of long-term maintenance is
the harvesting and proper disposal of plant
materials that contain contaminants.
The state of phytoremediation technology is
emerging, and more information from
treatability studies and long-term applications
are needed to support its consideration as a
viable technology. Until that information is
available, the diversity of opinions about the
conditions and contaminants for which
phytoremediation may be a well-suited
cleanup technology will continue.
Consulting with technical experts to
determine the applicability of
phytoremediation on a site-by-site basis is
advised. Further, in many cases, it will be
important to identify a contingency plan for
cleaning up the site in the event that
phytoremediation will not meet cleanup
objectives in an effective and timely manner.
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5.0 SELECTION AND DESIGN OF A PHYTOREMEDIATION SYSTEM
The design of a phytoremediation system
varies according to the contaminants, the
conditions at the site, the level of cleanup
required, and the plants used. As previously
noted, contaminants and site conditions are
perhaps the most important factors in the
design and success of a phytoremediation
system. Other factors that influence the
selection and design of a phytoremediation
system are discussed below.
5.1 Technical Factors
Because phytoremediation is an agronomic
process, it is highly dependent on climate
and site-specific characteristics. Soil
properties determine the ability of a plant
species not only to become established in the
soil, but also to maximize biomass and,
therefore, removal of contaminants. Soil
parameters typically analyzed to determine
whether phytoremediation is applicable
include texture; pH; moisture content; organic
matter content; lime content; cation exchange
capacity; and content of nutrients, such as
calcium, magnesium, potassium, phosphate,
and sulfate.
As with most treatment technologies,
innovative or not, a treatability study should
be conducted before a final remediation
technology can be selected for use at a site
to demonstrate that the technology will work
at that specific site. Information to assess
the effectiveness of phytoremediation also
may be available in existing literature. For
example, research may reveal phytotoxicity
levels or regional agronomic practices for the
simple application of phytoremediation, given
adequate site characterization and
monitoring.
Where treatability studies are necessary, site
characterization and bench-scale tests may
be used to determine system performance in
the field and evaluate whether the design will
meet the desired level of cleanup in the
specified time period. For phytoremediation,
it may be necessary to conduct treatability
studies under laboratory conditions (for
example, in an artificial hydroponic system) to
simulate site conditions and obtain an initial
result that proves the effectiveness of the
design. Acceleration of the process can be
expedited by typical approaches, including
artificial light, water, and temperature
conditions. The advantage of such
laboratory studies is that the process can be
accelerated to provide early results and
reduce implementation time.
Local climatic conditions, particularly the
length of the growing season, govern the
type and number of crops that can be planted
each year and therefore the annual rate of
removal of contaminants. Climatic
conditions, such as rainfall and temperatures,
also influence irrigation strategies and the
selection of plant species. Plant species that
grow well in the Pacific Northwest may not
survive in the arid Southwest.
Hydrologic models allow the calculation of the
flow of water and how that flow might be
affected by the application of
phytoremediation. Irrigation flows can have
an impact on groundwater conditions and
ultimately on the movement of the
contaminants to be treated. Although
irrigation of plants may be necessary to
ensure a robust start for a phytoremediation
system, even in drought conditions, careful
modeling may be necessary to predict with
any certainty the effects of phytoremediation
at a site.
Agronomic techniques include the addition of
nutrients necessary for vigorous growth in
vegetation. To maximize the efficiency of the
phytoremediation treatment system, the soil
type first must be determined. Analysis will
help determine the need for amendments,
such as nitrogen, potassium, phosphorous,
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manure, sewage sludge compost, straw,
or mulch, which are added as required to
improve the performance of the plant.
For example, maintenance of the
phytoremediation system may require
the addition of chemicals to stabilize
metals in the soil or the addition of
chelates to ensure that plants take up
the contaminants. A close working
relationship with regulators is especially
important in such a situation to quickly
determine any rules, regulations, or
prohibitions related to the addition of
amendments to the subsurface. Any
changes made in the soil through the
application of soil amendments,
however, should be evaluated and
monitored for their effects on the site
conditions.
Biomass is the amount of living or
organic matter produced by plants.
Increased biomass results in higher
levels of treatment and containment
because more materials available to the
plant (including contaminants) are used
to support growth. Phytoremediation
designs commonly involve higher
Source: EPA. 2000. Introduction to Phytoremediation (EPAIGOQIR-99nQ7).
National Risk Management Research Laboratory. February.
Remediating Wood Preservatives and Residual DNAPLs
Phytoremediation is being tested as an approach to
addressing both wood preservatives and dense non-
aqueous phase liquids (DNAPL) at a RCRA site in Laramie,
Wyoming. The active Union Pacific Railroad (UPRR) facility
became contaminated with polycyclic aromatic
hydrocarbons (PAH) during almost 100 years of treating
railroad ties with creosote. UPRR installed a bentonite-filled
trench to contain contaminated groundwater but had no
means of addressing residual PAHs in soil and groundwater
because of the perceived technical infeasibility of cleaning
up to the relatively low maximum contaminant levels (MCL).
The Wyoming Department of Environmental Quality
(WDEQ) approved a phytoremediation demonstration that
will serve as a research project for the WDEQ as well as the
facility and therefore includes rigorous requirements for
monitoring. More than 10,000 plants are being installed at a
50-acre site, including test plots in highly contaminated "hot
spots" at which the technique's ability to address high levels
of contamination will be assessed. Particular attention has
been paid to selecting native species that will be tolerant of
Laramie's harsh climate, and seed and plant stock for the
plantings have been harvested from the Laramie area. The
public has been included in planning for the project, as well,
and the phytoremediation plot has been integrated into
Laramie's greenspace plan and bicycle trail system. A bike
trail to the site was completed in early 2001, and a 1.5-mile
bike loop through the phytoremediation plot is being
planned. For more information, contact Marisa Latady of
WDEQ at (377) 777-7752.
planting densities than standard
agronomic rates for various species
to overcome decreased
germination because of
contaminated soils and to maximize
overall production of biomass for
the area. Consulting with an
experienced agronomist is essential
to designing a healthy and
productive phytoremediation
system.
Because various plant species
have different root structures,
careful consideration must be given
to selecting the most appropriate
species to address contaminants at
individual sites. Figure 3 illustrates
typical root depths of four plants
commonly used in
phytoremediation and
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demonstrates the depth to which each of the
species may be most effective. The figure
illustrates the potential limitation of
phytoremediation to shallow soils.
5.2 Strategies for Contaminant Control
Phytoremediation can support a variety of
cleanup strategies. One such strategy is to
plant the contaminated area with a specific
species known to extract the targeted
contaminant, subsequently harvest the
resulting biomass, and then reduce the
harvested material by composting or burning.
The resulting pile then becomes a
concentration of the extracted chemical that
can be treated as hazardous waste or, if the
contaminant is a metal, recycled. Another
strategy, which focuses on containment, is to
surround an underground plume of
contaminants with a selected species of
plants to prevent further movement of the
plume through the establishment of a
hydrostatic barrier of tree roots, that is, the
groundwater is taken up by the tree roots and
therefore does not migrate beyond the roots.
Hybrid poplars have achieved successes in
such approaches.
A common interim approach for brownfields
sites has been capping or paving over a site
to minimize infiltration of water. Several
experiments have been conducted to create
"phytocaps" as improvements of asphalt
coverings. A phytocap is a combination of
trees and other vegetation capable of
absorbing and transpiring most of the
infiltration water, thereby reducing the risk
that contaminants will spread. A phytocap
must be planted densely so that the rate at
which the evaporative processes of the plants
take place matches the rate of infiltration of
water. The approach thereby eliminates the
need to construct an impermeable surface.
Treatment or capture of contaminated
groundwater under a site may require a
certain minimum surface area and
configuration of trees, depending on
groundwater flow rates and considerations
related to the contaminant. Surface water
buffers and corridors, groundwater
interceptor strips, and vegetative covers are
examples of applications of phytoremediation
that can be integrated into redevelopment
landscaping plans on both large and small
sites.
5.3 Innovative Technology Treatment
Trains
Phytoremediation can be an effective
component of treatment train approaches
that combine innovative technologies with
traditional remediation technologies. The
purpose of combining technologies can be to
reduce the volume of material that requires
further treatment, to prevent emission of
volatile contaminants during excavation and
mixing, or to treat several contaminants in a
single medium.
An example might be to use
phytoremediation as part of a treatment train
involving soil vapor extraction and/or air
sparging. If the volatized compounds are
passed through a properly designed plant
rhizoshere zone before being extracted or
discharged to the atmosphere, there can be
enhanced degradation of hazardous
compounds.
Hybrid poplars or other deep-rooted species
with high groundwater uptake rates could
serve in a treatment wall capacity when
installed in a way that intercepts migrating
contaminated groundwater plumes. The
groundwater that flows through the plant
treatment wall would in many cases become
adequately treated such that MNA could be
implemented as the final stage of the train.
In shallow aquifer situations phytoremediation
could replace more costly and intensive
technologies such as pumping and treating.
Anaerobic, reducing conditions are required
for effective degradation of chlorinated
solvents and other organic compounds. A
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process whereby chemicals secreted from
tree roots lead to anaerobic degradation of
chlorinated solvents currently is receiving
research attention. This research has
examined the process in naturally occurring
trees, therefore in the context of MNA. For
additional information see the International
Journal of Phytoremediation, Vol. 2 (3), 2000.
5.4 Design Team
It is important that the development and
evaluation of a particular phytoremediation
design and long-term performance strategy
at a brownfields site be performed by an
experienced multidisciplinary team. The
design team can help the decision makers
weigh the advantages and limitations of
phytoremediation and select and design a
system that best addresses the factors
discussed in this section. The team might
include experts in the following disciplines or
fields:
Design Team Disciplines
Soil Science or Agronomy
Hydrology
Plant Biology
Environmental Engineering
Regulatory Analysis
Cost Engineering and Evaluation
Risk Assessment and Toxicology
Landscape Architecture
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6.0 OPERATION AND MAINTENANCE
A phytoremediation
treatment system must
be monitored and
evaluated periodically to
measure the
effectiveness of
operations and progress
toward attainment of the
remedial objectives for
brownfields
redevelopment.
Monitoring can help
determine the most
effective course for
continued operation and maintenance. This
section describes responsibilities for
operation and maintenance at a
phytoremediation site.
6.1 Operation and Maintenance
Maintenance is required to obtain a healthy
stand (or growth of plants). Weed control
and irrigation probably are the two most
important practices. Because of the
proliferation of specific weeds, predators, and
diseases that can cause significant
reductions in yields, it may be necessary to
rotate crops to maintain increased biomass
production. Weeds also can be controlled by
employing mechanical (cultivation) or
chemical (herbicides) methods. Irrigation
water should compensate for normal losses
to evaporation and transpiration. The
method of irrigation also must be considered
carefully. Drip irrigation tends to minimize
evaporation of water, improve efficiency, and
reduce costs. The long-term maintenance
needs of wetland systems typically are
minimal and may consist of monitoring the
distribution and level of water, removing
vegetation and contaminants, and other
predominantly land-management activities,
such as control of access and maintenance
of berms.
6.2 Disposal
In phytoextraction
systems, plant material
must be harvested and
disposed of. Plants that
accumulate
contaminants may pose
a risk of spreading
contamination into the
food chain if they are
consumed by insects or
other animals.
Consideration should be
given to addressing the need to avoid
consumption of contaminated plants by
wildlife or livestock before plants are
harvested. At brownfields sites, the end uses
under a redevelopment plan can be a
determining factor in the potential risk to
human and environmental receptors that
accumulated contaminants may pose. The
brownfields site redevelopment plan
therefore can affect the need for disposal.
It is important to monitor the system and test
whether the plants contain any hazardous
substances. If there are no hazardous
substances present, the material could be
composted or worked into the soil on site. If
that is not possible, off-site disposal will be
required. The harvest of contaminated
biomass and possible disposal of the material
as hazardous waste would be subject to
applicable regulations, such as those
established under the Resource
Conservation and Recovery Act (RCRA).
One option is disposal of contaminated
material in a regulated landfill. Disposal
under RCRA can add costs to a
phytoremediation project. However, the
removal and disposal of plant material used
in phytoremediation generally involves the
transporting and handling of materials that
are of far less volume and that probably are
less hazardous than materials generated by
operations that involve soil excavation or
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other innovative or traditional remediation
technologies. Therefore, phytoremediation
can be a strategy for decreasing the costs of
handling, processing, and possibly landfilling
the materials.
6.3 Performance Evaluation and
Monitoring
To evaluate the short-term performance and
effectiveness of phytoremediation, the
concentrations of contaminants and
degradation products should be measured.
Monitoring should be conducted for soil,
groundwater, plant root and mass, and
evapotranspiration vapor. Rigorous
performance evaluation will help demonstrate
the system's ability to meet cleanup goals
and objectives. Because phytoremediation is
an emerging technology, standard
performance criteria for phytoremediation
systems have not yet been established, and
performance must be determined on a site-
by-site basis.
Long-term monitoring typically is necessary
for phytoremediation systems that require
long time horizons to demonstrate their
continued effectiveness. Monitoring may be
continued after short-term cleanup goals
have been met to determine the impact of the
phytoremediation system on the ecosystem.
A monitoring plan should be developed to
guide both short- and long-term monitoring.
The plan should discuss the following
elements: constituents or other parameters
to be monitored; the frequency and duration
of monitoring; monitoring and sampling
methods; analytical methods; monitoring
locations; and quality assurance and quality
control (QA/QC) requirements.
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7.0 COST OF PHYTOREMEDIATION
Phytoremediation is an emerging technology;
standard cost information still is being
developed on the basis of experiences in
implementing phytoremediation projects.
This section provides information that
compares costs associated with the use of
phytoremediation to costs associated with the
use of conventional treatment technologies
based on actual cost estimates for three
sites, as well as other sample costs based on
laboratory and pilot scale work and field
information.
Many of those costs associated with
phytoremediation are not unique to
phytoremediation, but are common to
remediation technologies. The major cost
components for the implementation of
phytoremediation include the costs of:
> Site characterization
> Treatability studies
> Full-scale design (costs will vary according
to the contaminants, the site
characteristics, and the variety and amount
of vegetation needed)
> Construction costs (includes direct capital
costs for site preparation, plant material,
and irrigation and monitoring equipment
and indirect costs, such as those for
permitting during construction, contingency
design, and startup)
> Operation and maintenance and
monitoring costs (includes the cost of
labor, materials, chemicals, utilities,
laboratory analysis, disposal, and
monitoring)
As discussed in other sections of this primer,
startup and maintenance costs often are less
with phytoremediation than with conventional
treatment technologies because: (1)
phytoremediation is a natural process using
solar energy; (2) phytoremediation is in situ
and requires no digging or hauling of
contaminated soil; and (3) little or no
mechanical equipment is required to operate
the phytoremediation process. On the other
hand, monitoring costs could be higher than
with conventional treatment technologies
because monitoring typically is required for a
longer period of time at sites where
phytoremediation is used.
In comparing the potential costs to use
phytoremediation with the potential cost to use
conventional treatment technologies at a site,
care must be taken to compare the costs of
the entire system for the entire life cycle.
Under phytoextraction, the cost of processing
and ultimate disposal of biomass generated is
likely to account for a major percentage of
overall costs.
7.1 Cost Savings Based on Actual Cost
Estimates
Table 3 provides site-specific estimates that
have been reported of the cost savings
realized by using phytoremediation rather than
conventional treatment technologies
7.2 Sample Phytoremediation Costs
The estimated 30-year costs (1998 dollars) for
remediating a 12-acre lead site were
$12,000,000 for excavation and disposal,
$6,300,000 for soil washing, $600,000 for a
soil cap, and $200,000 for phytoextraction
(Cunningham 1996 in Introduction to
Phytoremediation (EPA/600/R-99/107)). The
costs of cleanup of various heavy metals at
the Twin Cities Army Ammunition Plant,
Minneapolis-St. Paul, MN Project were
reported in the Federal Remediation
Technologies Roundtable (see Supporting
Resources) to be $153 per cubic yard of soil
over the life of the project.
The costs of removing radionuclides from
water with sunflowers has been estimated to
be $2 to $6 per thousand gallons of water
(Dushenkov et al. 1997 in Introduction to
Phytoremediation (EPA/600/R-99/107)). The
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costs of cleanup of explosives at the Milan
Army Ammunition Plant, Milan, TN were
reported in the Federal Remediation
Technologies Roundtable (see Supporting
Resources) to be $1.78 per thousand gallons
of water over the life of the project.
Estimated costs for hydraulic control of an
unspecified contaminant in a 20-foot-deep
aquifer at a 1-acre site were $660,000 for
conventional pump-and-treat and $250,000
for phytoremediation (Gatliff 1994 in
Introduction to Phytoremediation (EPA/600/R-
99/107)).
Cost estimates indicate savings for an
evapotranspiration cover compared to a
traditional cover design to be 20-50%,
depending on availability of suitable soil
(RTDF 1998 in Introduction to
Phytoremediation (EPA/600/R-99/107)).
Studies indicate that phytoremediation is
competitive with other treatment alternatives,
as costs are approximately 50 to 80 percent of
the costs associated with physical, chemical,
or thermal techniques at applicable sites.
Table 3
Estimated Cost Savings Through the Use of Phytoremediation
Rather Than Conventional Treatment
Contaminant
and Matrix
Lead in soil
(1 acre)3
Solvents in
groundwater
(2.5 acres)"
Total petroleum
hydrocarbons
in soil (1 acre)0
Phytoremediation
Application
Extraction, harvest,
and disposal
Degradation and
hydraulic control
In-situ degradation
Estimated Cost
$150,000 -$250,000
$200,000 for
installation and
initial maintenance
$50,000 -$100,000
Conventional Treatment
Application
Excavate and
landfill
Pump and
treat
Excavate and
landfill or
incinerate
Estimated Cost
$500,000
$700,000 annual
operating cost
$500,000
Projected
Savings
50-65 percent
50 percent cost
saving by third
year
80 percent
Source: Introduction to Phytoremediation. EPA/600/R-99/107. February 2000.
a Phytotech estimate for Magic Marker site
b Potentially responsible party estimate for SRS site
c PERF estimate
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8.0 SUPPORTING RESOURCES
This section identifies Internet sites and
documents that will help the user obtain
additional information about
phytoremediation. In addition, Table 4
presents a list of references used to prepare
this document and a guide to the subject
matter included in each reference.
> EPA. Office of Research and
Development (ORD) Internet web site
(http://www.epa.gov/ord). ORD is the
principal scientific and research arm of
EPA. ORD conducts research and
fosters the use of science and technology
in fulfilling EPA's mission. ORD is
organized as three national laboratories
and two national centers located in a
dozen facilities around the country and in
Washington, D.C. Several EPA
laboratories have work underway to
determine the fate of contaminants in
phytoremediation applications. Much of
this work is based at the EPA National
Risk Management Research Laboratory
(NRML). (Refer to the description below.)
ORD along with the Office of Solid Waste
and Emergency Response (OWSER)
supports the Remediation Technologies
Development Forum (RTDF) that also is
described in more detail below. In
addition within ORD, the EPA National
Exposure Research Laboratory (NERL)
http://www.epa.gov/NERU, is exploring
topics such as the degradation of TNT by
wetland plants and plant
enzyme-contaminant interactions. The
EPA-supported Hazardous Substance
Research Center at Kansas State
University engages in research on plant
and contaminant interactions. EPA
Region 10 continues to explore and
encourage innovative applications and
interactions between phytoremediation
and ecosystem restoration.
EPA. National Risk Management
Research Laboratory (NRMRL).
Introduction to Phytoremediation
(EPA/600/R-99/107). February 2000.
(Web site availability http://cluin.org/
techfocus). The National Risk
Management Research Laboratory,
(NRMRL), part of EPA's Office of
Research and Development, conduct
research into ways to prevent and reduce
risks from pollution that threaten human
health and the environment. The
laboratory has a broad program of
investigating methods and their cost-
effectiveness for prevention and control
of pollution including those relevant to
remediation of contaminated sites,
sediments and groundwater. NRMRL
collaborates with both public and private
sector partners to foster technologies that
reduce the cost of compliance and to
anticipate emerging problems. Its
Superfund Innovative Technology
Evaluation (SITE) Program encourages
the development and implementation of
innovative treatment technologies for
hazardous waste site remediation. The
phytoremediation document has been
developed to provide a tool for site
regulators, owners, neighbors, and
managers to evaluate the applicability of
phytoremediation to a site. Information
on the SITE program or individual
projects can be found at
http://www. epa. gov/ORD/SITE.
Federal Remediation Technologies
Roundtable (FRTR) Case Studies
http://www.frtr.gov/cost
The Federal Remediation Technologies
Roundtable (FRTR) case studies contain
detailed information about specific
remedial technology applications. FRTR
case studies are developed by the U.S.
Department of Defense (DoD), the U.S.
Army Corps of Engineers (USAGE), the
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U.S. Navy, the U.S. Air Force (USAF), the
U.S. Department of Energy (DOE), the
U.S. Department of the Interior (DOI),
and the U.S. Environmental Protection
Agency (EPA). As of September 1998,
FRTR published and made available on
its Internet site 140 cost and performance
case studies. The case studies focus on
full-scale and large field demonstration
projects and include background
information about the site, a description
of the technology, cost and performance
data for the technology application, and a
discussion of lessons learned. Both
innovative and conventional treatment
technologies for contaminated soil,
groundwater, and solid media are
included. A search function on the web
site allows a user to search the case
studies using key words for media,
contaminant, and primary and
supplemental technologies.
Interstate Technology and Regulatory
Cooperation Work Group (ITRC).
Phytoremediation Decision Tree.
November 1999 (Web site availability
http://www.itrcweb.org). ITRC is a
state-led national coalition dedicated to
achieving better environmental protection
through the use of innovative
technologies. ITRC helps regulatory
agencies and technology developers,
vendors, and users reduce the technical
and regulatory barriers to the deployment
of new environmental technologies. ITRC
products and services are building the
collective confidence of the environmental
community about using new technologies.
Phytoremediation is one such technology.
ITRC has provided a tool that can be
used to determine whether
Phytoremediation can be effective at a
given site. It allows the user to use basic
information about a specific site to
decide, through the use of a flow chart
layout, whether phytoremediation is
feasible at that site.
EPA. Phytoremediation Resource
Guide. June 1999 . (EPA 542-B-99-003)
(Web site availability http://cluin.org/
techfocus). The document identifies a
cross-section of information intended to
aid users in remedial decision-making,
including abstracts of field
demonstrations, research documents,
and information about ordering
publications.
EPA. A Citizen's Guide to
Phytoremediation. April 2001. (EPA
542-F-01-002) (Web site availability
http://cluin.org/techfocus). The
document is a technology fact sheet
developed to help communicate to citizen
stakeholders issues related to the use of
phytoremediation.
The Remediation Technologies
Development Forum (RTDF).
Internet web site (http://www.rtdf.org) -
EPA established the RTDF in 1992 by
determining what government and
industry can do together to develop and
improve the environmental technologies
needed to address their mutual cleanup
problems in the safest, most cost-
effective manner possible. The RTDF
fosters public- and private-sector
partnerships to undertake research,
development, demonstration, and
evaluation efforts focused on finding
innovative solutions to high-priority
problems. The RTDF has grown to
include partners from industry, several
federal and state government agencies,
and academia who voluntarily share
knowledge, experience, equipment,
facilities, and even proprietary technology
to achieve common cleanup goals. The
Phytoremediation of Organics Action
Team and the In-Place Inactivation and
Natural Ecological Restoration
Technologies (IINERT) Soil- Metals
Action Team are two of eight Action
Teams that foster collaboration between
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the public and private sectors in
developing innovative phytoremediation
solutions to hazardous waste problems.
The Action Teams include
representatives from industry,
government, and academia who share an
interest in further developing and
validating the of use of plants and trees to
remediate organic hazardous wastes in
soil and water.
Public Technologies, Inc.
Brownfieldstech Internet web site
(http://www.brownfieldstech.org) - The
site is a source of information about
characterization and remediation of
brownfields sites. The web site is
sponsored by EPA's TIO. It is hosted and
maintained by Public Technology, Inc.
(PTI), the technology development arm of
the National League of Cities, the
National Association of Counties, and the
International City/County Management
Association. The site focuses on the
demonstration, dissemination, and
promotion of innovative characterization
and remediation technologies for
brownfields. Its goal is to help local
governments increase efficiencies and
reduce costs associated with brownfields
redevelopment. See "Hot Technologies"
page for links to reports on projects
utilizing phytoremediation.
EPA. The Hazardous Waste Clean-Up
Information (Clu-ln) System
Internet web site (http://cluin.org/
techfocus) - EPA's Clu-ln provides
information about innovative treatment
technologies to the hazardous waste
remediation community. It describes
programs, organizations, publications,
and other tools for federal and state
personnel, consulting engineers,
technology developers and vendors,
remediation contractors, researchers,
community groups, and individual
citizens. The site is managed by EPA's
TIO and is intended as a forum for all
waste remediation stakeholders.
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Table 4
References by Topic
Reference
Rock, Steven. 1997. "Phytoremediation." The Standard Handbook of
Hazardous Waste Treatment and Disposal, Second Edition. Harry Freeman,
ed. McGraw Hill.
CERCLA Education Center. 2000. Innovative Treatment Technology Course,
Module on Phytoremediation.
Phytoremediation Work Team, Interstate Technology and Regulatory
Cooperation Work Group. 1999. Decision Tree Document. November.
EPA. 1998. A Citizen's Guide to Phytoremediation, Technology Fact Sheet
(EPA542-F-98-011). August.
Brownfieldstech.org Internet web site (particularly for case studies). 2000.
Rock, Steven and Philip Sayre. 1998. "Phytoremediation of Hazardous
Wastes: Potential Regulatory Acceptability." Vol. 8, No. 4.
Black, Harvey. 1999. "Phytoremediation: A Growing Field with Some
Concerns." The Scientist. Volume 13, Number 5. March.
Interstate Technology and Regulatory Cooperation Work Group. 1999.
Phytoremediation Technical and Regulatory Guidance.
CH2MHNI. 1999. Guidance for Successful Phytoremediation. Prepared for
CWRT. March.
Lasat, Mitch. 2000. "Notes of a Plant Scientist."
EPA. 2000. Introduction to Phytoremediation (EPM600/R-99n07). February.
EPA. 1999. Phytoremediation Resource Guide (EPA 542-B-99-003). June.
EPA. 1 998. Electrokinetic and Phytoremediation In Situ Treatment of Metal-
Contaminated Soil: State-of-the-Practice.
What is
Phytoremediation
Examples of
Phytoremediation
Advantages and
Considerations in
Selecting
Phytoremediation
Significance of
Site
Characterization
Note: The table provides a list of references that were used to develop this primer.
25
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APPENDIX 1
LIST OF ACRONYMS AND GLOSSARY OF KEY TERMS
bgs Below ground surface
BTEX Benzene, toluene, ethylbenzene, and xylene
BTSC Brownfields Technology Support Center
cm Centimeter
EPA U.S. Environmental Protection Agency
ITRC Interstate Technology Regulatory Cooperation Work Group
NRMRL National Risk Management Research Laboratories
PAH Polycyclic aromatic hydrocarbons
PCB Polychlorinated biphenyl
PCP Pentachlorophenol
QA/QC Quality assurance and quality control
RCRA Resource Conservation and Recovery Act
TCA Trichloroethane
TCE Trichloroethylene
TIO Technology Innovation Office
TNT Trinitrotoluene
UPRR Union Pacific Railroad
VOC Volatile organic compound
APPENDIX 1 - List of Acronyms and Glossary of Key Terms
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Abiotic
Not biotic or living.
Absorption
The process of one
substance actually
penetrating into the structure
of another substance. The
process is different from
adsorption, in which one
substance adheres to the
surface of another substance.
Adsorption
The physical process that
occurs when liquids, gases,
or suspended matter adheres
to the surfaces of, or in the
pores of, an adsorbent
material. The process is
physical and occurs without a
chemical reaction.
Agronomic
The application of soil and
plant sciences to soil
management and crop
production; scientific
agriculture.
Bench-Scale
Testing phase conducted to
demonstrate effectiveness of
an emerging treatment
technology; usually a small-
scale version is tested under
laboratory conditions.
Bioaccumulation
The absorption and
concentration of
contaminants, such as heavy
metals, in plants and animals.
Bioconcentration is a
synonym for bioaccumulation.
Biomass
All the living matter present in
a given area; organic
structures produced by living
organisms. The generic term
for any living matter that can
be converted into usable
energy through biological or
chemical processes. Can be
expressed numerically as a
mass-density or as calories
per unit area.
Biotic
Related to life or specific life
conditions; living.
Brownfields
An abandoned, idled, or
under-used industrial or
commercial facility where
expansion or redevelopment
is complicated by real or
perceived environmental
contamination.
Cap
A barrier that covers
contaminated media and that
prevents rainwater from
percolating into the ground
and causing contaminants
under the cap to leach into
groundwater. Also may
prevent surface exposure to
covered contaminants.
Cation Exchange
A chemical process in which
positively charged ions of like
charge are exchanged
equally between a solid and a
solution (such as water).
Chelates
A compound in which a
metallic ion is attached by
covalent bonds to two or
more nonmetallic atoms in
the same molecule.
Chelating agents are used to
remove metals, particularly
lead, from insoluble soil
fractions and keep them in
solution.
Concentration
The amount of a specified
substance in a unit amount of
another substance; the
relative abundance of a
solute in a solution.
Degradation
Decomposition of a
compound by stages,
exhibiting well-defined
intermediate products.
Drip Irrigation
Irrigation whereby water is
slowly applied to the soil
surface through small
emitters that have a low rate
of discharge.
Emergent Plant
An herbacious plant standing
erect and rooted in shallow
water, with most of the plant
growing above the water's
surface.
APPENDIX 1 - List of Acronyms and Glossary of Key Terms
-------
Evapotranspiration
The loss of water from the
soil both by evaporation and
by transpiration from the
plants growing in the soil.
Evaporation involves the
change of state of water from
liquid to gas form as water
molecules escape from the
surface of a body into the
atmosphere. Transpiration is
the process by which water is
drawn from the soil by
osmotic pressure of the root
systems of vegetation and
moved through the leaves to
the surrounding atmosphere.
Extraction
Removal by chemical or
mechanical action.
Full-Scale Technology
An established technology for
which cost and performance
information is readily
available.
Groundwater
The supply of fresh water
found beneath the Earth's
surface, usually in aquifers,
that supplies wells and
springs.
Herbacious Plant
A plant with no persistent
woody stem above ground.
Hydrostatic Barrier
In phytoremediation, the use
of plants to control movement
of water, generally from an
area of higher levels of
contamination to an area of
lower levels of contamination.
Hyperaccumulators
Metallophytes that
accumulate an exceptionally
high level of a metal to a
specified concentration or to
a specified multiple of the
concentration found in
nonaccumulators. Alpine
pennycress is an example
(see metallophytes).
Immobilize
To make incapable of further
movement.
In Situ
In place, without excavation.
In situ soil technologies treat
contamination without digging
up or removing the
contaminants.
Indian Mustard (Brassica
juncea)
A potentially useful plant with
relatively high biomass that is
not a hyperaccumulator. The
plant has been frequently
used in toxic metal and
radionuclide phytoextraction.
Infiltration
To pass into or through a
substance (such as soil) by
penetrating its pores or
interstices; generally refers to
water entering a physical
area.
Innovative Treatment
Technologies
A technology that has been
field-tested and applied to a
hazardous waste problem at
a site, but lacks a long history
of full-scale use. Information
about its cost and how well it
works may be insufficient to
encourage use under a wide
variety of operating
conditions. Innovative
treatment technologies are
better analyzed on a site-by-
site basis.
Inorganic Chemical or
Compound
A chemical or compound that
generally does not contain
carbon atoms (carbonate and
bicarbonate compounds are
notable exceptions).
Examples of inorganic
compounds include various
acids and metals.
Leaching
A process through which a
liquid in contact with or
moving through a solid
mobilizes constituents from
the solid through the actions
of dissolution and physical
transport.
Lignification
Formation into wood through
the formation and deposit of
lignin (a polymer functioning
as a natural binder and
support for the cellulose fiber
of woody plants) in cell walls;
the process of making
something woody.
APPENDIX 1 - List of Acronyms and Glossary of Key Terms
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Mass Transfer
The conveyance of any
material like liquids, gases, or
solid materials from one
location to another location;
in phytoremediation, the term
might refer to the conveyance
of a contaminant from soil or
groundwater to a plant.
Metallophytes
Plants that preferentially
colonize in metal-rich soils.
Microorganisims
An organism too tiny to be
seen by the unaided eye.
Includes bacteria, algae,
fungi, and viruses.
Natural Attenuation
An approach to cleanup that
uses natural processes over
time to contain contamination
and reduce the
concentrations and amounts
of pollutants in contaminated
soil and groundwater. The
processes of natural
attenuation include dilution,
volatilization, biodegredation,
and adsorption.
Nutrients
Elements or compounds
essential for the growth and
development of an organism.
Nitrogen, phosphorous, and
potassium are examples of
essential plant nutrients.
Organic Chemical or
Compound
A chemical or compound
produced by animals or
plants that contains mainly
carbon, hydrogen, and
oxygen.
Phreatophyte
A deep-rooted plant that
obtains water from the water
table.
Phytocap (or Vegetative
Cap)
A long-term, self-sustaining
planted area growing in and
over materials that pose an
environmental risk. The
phytocap requires minimal
maintenance and is designed
to reduce the risk that the
contaminant will leach.
Phytoremediation
A technology that uses living
plants to remediate or
stabilize contaminants in soil,
sediment, surface water, or
groundwater.
Phytotoxic
Harmful to plants.
Pilot-Scale Testing
Testing stage of a treatment
technology, between bench-
and full-scale, that is
conducted in the field to
provide data on performance,
cost, and design objectives
for the treatment technology.
Plume
A visible or measurable
emission or discharge of a
contaminant from a given
point of origin into any
medium.
Poplar (Eastern
Cottonwood or Populus
deltoides)
A tree widely studied for its
potential for hydraulic control,
phytodegredation, and
phytovolatilization.
Rhizosphere
The zone of soil adjacent to
plant roots that exhibits
significantly higher microbial
numbers, species, and
activity than bulk soil.
Root Zone
Generally considered to be
the area surrounding the
underground part of a plant,
the functions of which include
absorption, aeration, and
storage for the plant.
Sorption
The action of soaking up or
attracting substancesa
general term used to
encompass the processes of
absorption and adsorption.
Submergent Species
Plant species that lie entirely
under water.
Transpiration
The plant-based process that
involves the uptake,
transport, and eventual
vaporization of water through
the plant's leaves.
Volatile Organic
Compounds (VOC)
Organic chemicals capable of
becoming vapor at relatively
low temperatures.
Volatilization
The transfer of a chemical
from the aqueous or liquid
phase to the gas phase.
Solubility, modular weight, the
vapor pressure of the liquid
and the nature of the gas-
liquid affect the rate of
volatilization.
APPENDIX 1 - List of Acronyms and Glossary of Key Terms
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APPENDIX 2
THE PROCESSES OF PHYTOREMEDIATION
Phytoremediation can be classified according to the biological processes involved. Those
processes are described below.
Hydraulic Control, also known as phytohydraulics, is designed to control groundwater
transport mechanisms through plant transpiration. The process uses plants that have a high
transpiration rate to take up large quantities of water, thereby achieving hydraulic control of the
site to contain contaminants and prevent their further migration. The transpiration rate depends
on the type of plant, leaf area, nutrients, soil moisture, temperature, wind conditions, and
relative humidity.
Phytodegradation, also known as phytotransformation, is the uptake of organic contaminants
from soil and groundwater, followed by their degradation in plant tissue. The extent of
degradation depends on the efficiency of contaminant uptake and the concentration of
contaminants in soil and groundwater. Uptake efficiency depends on the contaminant's
physical and chemical properties and the plant itself. After uptake, the plant either stores the
contaminants or volatizes or metabolizes the contaminants completely to carbon dioxide and
water. The process is an efficient removal mechanism at shallow depths for moderately
hydrophobic organic contaminants like benzene, toluene, ethylbenzene, and xylene (BTEX);
chlorinated solvents; and short-chain aliphatic hydrocarbons.
Phytoextraction uses plants to transport metals from the soil and concentrate them into roots
and aboveground shoots that can be harvested. Many types of plants can be used to remove
metals. Some grasses accumulate surprisingly high levels of metals in their shoots without
exhibiting toxic effects. However, their low biomass production results in a relatively low
extraction rate for metals. Genetic engineering or breeding of hyperaccumulating plants for
high biomass production could make the extraction process highly effective. Using crop plants
to extract metals from the soil seems practical because of their high biomass production and
relatively fast growth rate. Crop plants also are easy to cultivate and exhibit genetic stability.
However, using crop plants to accumulate metals is a potential threat to the food chain.
Phytostabilization uses plants to limit the mobility and bioavailability of metals in soil by
sorption, precipitation, complexation, or the reduction of metal valences. The process helps to
stabilize the soil matrix to minimize erosion and migration of sediment. To eliminate the
possibility that residues in harvested shoots might become hazardous wastes, phytostabilizing
plants should exhibit low levels of accumulation of metals in shoots. Phytostabilization
immobilizes metal contaminants in the soil through a combination of processes, including
reaction with soil amendments, adsorption or accumulation in the rhizosphere, and physical
stabilization of the soil. In addition, the process minimizes the generation of airborne
contaminants caused by wind erosion. Some researchers consider an interim measure to be
applied until extraction becomes fully developed. Other researches are developing
Phytostabilization as a standard protocol of metal remediation technology, especially at sites at
which removal of metals does not seem economically feasible.
APPENDIX 2- The Process of Phytoremediation
-------
Phytovolatilization uses plants to takeup volatile organic compounds (VOC) and the metabolic
products of the plant and transpire them into the atmosphere. Because VOCs are released into
the atmosphere through plant transpiration, air monitoring may be required. This form of
phytoremediation may not be as desirable as in situ degradation, but it may be preferable to
prolonged contamination of soil and groundwater contamination.
Rhizodegradation also known as phytostimulation, plant-assisted bioremediation, or enhanced
rhizosphere bioremediation, is root-stimulated microbial degradation of organic contaminants.
Rhizodegradation involves a root zone that provides a habitat for beneficial microbial growth
and fungi associated with plant roots that help in metabolizing organic contaminants. Root
turnover for trees like mulberry, osage orange, and apple release flavonoids and coumarin that
stimulate the degradation of polychlorinated biphenyls (PCB).
Rhizofiltration is the removal or concentration of metal contaminants from an aquatic
environment such as contaminated surface water and groundwater in the root zone. One
variation of rhizofiltration removes metals by sorption, which involves biochemical processes.
The roots absorb, concentrate, and precipitate metals from polluted effluent, which may include
leachate from soil. Another variation of rhizofiltration is the construction of wetlands or reed
beds for the treatment of contaminated water or leachate. The technology generally has been
found to be cost-effective for the treatment of large volumes of wastewater that contain low
concentrations of metals. Plant species used for rhizofiltration often are raised hydroponically
in greenhouses and transplanted to a floating system in which the roots are in contact with
contaminated water.
APPENDIX 2- The Process of Phytoremediation
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APPENDIX 3
PHYTOREMEDIATION DECISION TREE MODELS
The three decision tree charts on the following pages were developed by the Phytoremediation
Work Group of the Interstate Technology and Regulatory Cooperation Work Group (ITRC).
The Phytoremediation Work Team effort, as part of the broader ITRC effort, is funded primarily
by the U.S. Department of Energy. Additional funding and support is provided be the U.S.
Department of Defense and the U.S. Environmental Protection Agency.
These charts provide guidelines for determining the applicability of phytoremediation at a
brownfields site after site characterization for the treatment of soil, groundwater, or sediments
has been completed.
APPENDIX 3 - Phytoremediation Decision Tree Models
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Decision Tree for Phytoremediation
Soil
YES I Will the climate support the proposed plants? I NO
NO I Is time or space a constraint?! YES
37
YES I Is the contaminant physically within the range of the proposed plant (typically less than 1-2 feet bgs)? I NO
NO
Is the contaminant at phytotoxic concentrations
(this may require a greenhouse dose-response test)'
YES
Are there hotspots that can be
removed or treated?
YES
Will the rhizosphere microbes and plant-exuded enzymes degrade the target
contaminants in the rhizosphere and are the metabolic products acceptable?
NO
NO
Is the log Kow of the contaminant or metabolic
products between 1 and 3.5 (will uptake occur)?
YES
Will the plant degrade the
contaminant after uptake and are
the metabolic products acceptable?
NO
NO
lt~\ N0
Will the plants transpire the
contaminant or metabolic products?
YES
Is the quantity and rate of transpiration
acceptable for this site?
NO
Will the plant accumulate the contaminant
or metabolic products after uptake?
YES
Is the level of accumulation acceptable
for this site throughout the growth of the plant'
NO
YES
Can controls be put in place to prevent
the transfer of the contaminant or metabolic
products from a plant to humans/animals?
NO
^ YES I Can engineering controls make it acceptable?! NO
YES
Is the final disposition of the contaminant
or metabolic products acceptable?
NO
YES
Can the contaminant or metabolic product
be immobilized to acceptable levels?
NO
NO I Does the plant material constitute a waste if harvested?! YES
YES I Can the plant waste be economically disposed? I NO
Phytoremediation is NOT an option
at the site; consider other options
APPENDIX 3 - Phytoremediation Decision Tree Models
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Decision Tree for Phytoremediation
Groundwater
YES I Will the climate support the proposed plants? I NO
NO I Is time or space a constraint?! YES
YES
Is the contaminant physically within the range of the proposed plant
(typically less than 10-20 feet bgs for Sa/w species -willows, cottonwoods, poplars)?
NO
YES
Will the plants be used for hydraulic
control ONLY (prevent water from
REACHING the contaminated zone)?
NO
YES
Will the water be mechanically pumped and
applied to the phytoremediation system?
NO
YES
NO
Is the contaminant at phytotoxic concentrations
(this may require a greenhouse dose-response test)"?
Will state regulations allow
this type of phytoremediation?
YES
Will the rhizosphere microbes and plant-exuded enzymes degrade the target
contaminants in the rhizosphere and are the metabolic products acceptable?
NO
NO
Is the log Kowof the contaminant or metabolic
products between 1 and 3.5 (will uptake occur)?
YES
YES
Will the plant degrade the
contaminant after uptake and are
the metabolic products acceptable?
NO
NO
Will the plants transpire the
contaminant or metabolic products?
YES
YES
Is the quantity and rate of transpiration
acceptable for this site?
NO
NO
Will the plant accumulate the contaminant
or metabolic products after uptake?
YES
YES
Is the level of accumulation acceptable
for this site throughout the growth of the plant?
NO
YES
Can controls be put in place to prevent
the transfer of the contaminant or metabolic
products from a plant to humans/animals?
NO
YES I Can engineering controls make it acceptable?! NO
YES
Is the final disposition of the contaminant
or metabolic products acceptable?
YES
Can the contaminant or metabolic product
be immobilized to acceptable levels?
NO
^ NO I Does the plant material constitute a waste if harvested?! YES
YES I Can the plant waste be economically disposed? I NO
Phytoremediation has the potential
i be effective at the sits
Phytoremediation is NOT an option
at the site; consider other options
APPENDIX 3 - Phytoremediation Decision Tree Models
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Decision Tree for Phytoremediation
Sediments
| YES | Will the climate support the proposed plants? j NO
NO Its time or space a constraint?! YES
YES lean the sediments be treated in place (wetlands)? I NO
Are the sediments
to be dredged?
YES I Will the regulatory statutes allow the dredged sediments to be treated as a soil? I NO
YES I Is there strong public support to treat the sediment as a soil? I NO
| YES | Is the contaminant physically within the range of the proposed plant (typically less than 1 -2 feet bgs)? j NO
NO
Is the contaminant at phytotoxic concentrations
(this may require a greenhouse dose-response test)?
YbS
| YES
Are there hotspots that can be
removed or treated?
NO |
YES
Will the rhizosphere microbes and plant-exuded enzymes degrade the target
contaminants in the rhizosphere and are the metabolic products acceptable?
NO
NO
Is the log Kow of the contaminant or metabolic
products between 1 and 3,5 (will uptake occur)?
YES
YES
Will the plant degrade the
contaminant after uptake and are
the metabolic products acceptable?
NO
NO
Will the plants transpire the
contaminant or metabolic products?
YES
Is the quantity and rate of transpiration
acceptable for this site?
NO
NO
Will the plant accumulate the contaminant
or metabolic products after uptake?
YES
Is the level of accumulation acceptable
for this site throughout the growth of the plant'
NO
YES
Can controls be put in place to prevent
the transfer of the contaminant or metabolic
products from a plant to humans/animals?
NO
| YES | Can engineering controls make it acceptable?| NO
YES
Is the final disposition of the contaminant
or metabolic products acceptable?
NO
YES
Can the contaminant or metabolic product
be immobilized to acceptable levels?
NO
^ NO I Does the plant material constitute a waste if harvested?! YES
YES I Can the plant waste be economically disposed? I NO
-^.(^Phytoremediation has the potential
' > be effective at the sits
Phytoremediation is NOT an option |l-<-
at the site; consider other options J9
APPENDIX 3 - Phytoremediation Decision Tree Models
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For additional information, please see these other publications
issued by the Brownfields Technology Support Center:
Road Map to Understanding Innovative Technology Options for
Brownfields Investigation and Cleanup, Second Edition
EPA 542-B-99-009
Directory of Technology Support Services to Brownfields Localities
EPA 542-B-99-005
Assessing Contractor Capabilities for Streamlined
Site Investigations
EPA 542-R-00-001
Brownfields Technology Primer: Requesting and Evaluating
Proposals That Encourage Innovative Technologies for
Investigation and Cleanup
EPA 542-R-01-005
These publications are available online at:
http://www. brownfieldstsc. org
or can be ordered by contacting:
U.S. Environmental Protection Agency
National Service Center for Environmental Publications
(NSCEP)
P.O. Box42419
Cincinnati, OH 45242-2419
1 (800)490-9198
FAX (513) 489-8695
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E PA 542-R-01-006
July 2001
Brownfields Technology Primer:
Selecting and Using Phytoremediation for Site Cleanup
Visit the Brownfields Technology
Support Center Web Site at:
http://www.brownfieldstsc.org
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