Technology Profile Phytotechnology


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Technology
Profile -
Phytotechnology

EPA/600/R-25/137 | May 2025 | www.epa.gov/research

Office of Research and Development

Center for Environmental Solutions
and Emergency Response

v»EPA

United States
Environmental Protection
Agency

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SEPA

Phytotechnology

United States
Environmental Protection
Agency

Technology Profile

Technology
Phytotechnology

David Gwisdalla, Commander, U.S. Public Health Service
Director, Engineering Technical Support Center (ETSC)
U.S. EPA Office of Research & Development (ORD)

Center for Environmental Solutions & Emergency Response (CESER)
Technical Support Coordination Division (TSCD)

Cincinnati, Ohio 45268

Michele Mahoney
U.S. EPA Office of Land and Emergency Management (OLEM)
Technology Innovation and Field Services Division (TIFSD)
Technology Assessment Branch (TAB)

Washington, District of Columbia 204600

by

Kendra Waltermire
Environmental Engineer
Jacobs Engineering
Dallas, Texas 21044

Katherine Bronstein
Environmental Engineer
RTI International
Research Triangle Park, North Carolina 27709

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Phytotechnology Technology Profile

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Notice/Disclaimer

The U.S. Environmental Protection Agency (U.S. EPA), through its Office of Research and Development, funded
and conducted the research described herein. It has been subjected to the Agency's peer and administrative
review and approved for publication as a U.S. EPA document. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.

Foreword

The U.S. EPA is charged by Congress with protecting the nation's land, air, and water resources. Under a
mandate of national environmental laws, the Agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural systems to support and nurture life. To
meet this mandate, U.S. EPA's research program is providing data and technical support for solving
environmental problems today and building the scientific knowledge base necessary to manage our ecological
resources wisely, understand how pollutants affect our health, and prevent or reduce environmental risks in the
future. The Center for Environmental Solutions and Emergency Response (CESER) within the Office of Research
and Development (ORD) conducts applied, stakeholder-driven research and provides responsive technical
support to help solve the nation's environmental challenges. The Center's research focuses on innovative
approaches to address environmental challenges associated with the built environment. We develop
technologies and decision-support tools to help safeguard public water systems and groundwater, guide
sustainable materials management, remediate sites from traditional contamination sources and emerging
environmental stressors, and address potential threats from terrorism and natural disasters. CESER collaborates
with both public and private sector partners to foster technologies that improve effectiveness and reduce the
cost of compliance, while anticipating emerging problems. We provide technical support to U.S. EPA regions and
programs, states, tribal nations, and federal partners, and serve as the interagency liaison for U.S. EPA in
homeland security research and technology. The Center is a leader in providing scientific solutions to protect
human health and the environment.

Gregory Sayles, Director

Center for Environmental Solutions and Emergency Response

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Phytotechnology Technology Profile

Acknowledgments

This Technology Profile was prepared for the U.S. EPA Office of Research and Development (ORD), Center for
Environmental Solutions and Emergency Response (CESER), Technical Support Coordination Division's
Engineering Technical Support Center (ETSC) by RTI International under Contract No. 68HERC21D0004, Task
Order 008. David Gwisdalla served as the EPA Alternate Task Order Manager and Technical Co-Lead. Michele
Mahone from the Office of Land and Emergency Management (OLEM) served as a technical co-lead. Katherine
Bronstein (RTI International) managed this work and provided technical content. Kendra Waltermire of Jacobs
Engineering was the primary author.

We also would like to recognize those who conducted both technical and peer reviews of this document.
Technical reviews were conducted by Emmie McCleary a Remedial Project Manager (RPM) from EPA Region 5,
Christian Bako, an Environmental Engineer from the Great Lakes National Program Office (GLNPO), and Felicia
Barnett, the Director of ORD's Site Characterization and Monitoring Technical Support Center (SCMTSC). Peer
reviews were conducted by Reid Simmer, Research Scientist in the Hydroscience & Engineering Department of
the College of Engineering at the University of Ohio; and Dr. Valentine A. Nzengung, Professor of Environmental
Geochemistry in the Department of Geology of the University of Georgia.

This document is intended as an overview of phytotechnologies for EPA staff, regional program offices, remedial
program managers, and state governmental environmental staff. Interested parties should further consult the
body of literature and experience that constitutes the state-of-the-science. Web links are provided for readers
interested in additional information; these weblinks, while accurate at the time of publication, are subject to
change.

As of the date of this publication, questions may be addressed to:

David Gwisdalla, Director

Engineering Technical Support Center (ETSC)

Technical Support Coordination Division (TSCD)

Center for Environmental Solutions and Emergency Response (CESER)

U.S. EPA Office of Research and Development (ORD)

26 W. Martin Luther King Drive, Mail-Stop 445

Cincinnati, Ohio 45268

513-569-7011

gwisdalla.david(a)epa.gov

Michele Mahoney, Soil Scientist

Technology Assessment Branch (TAB)

Technology Innovation and Field Services Division (TIFSD)

Office of Superfund Remediation and Technology Innovation (OSRTI)

U.S. EPA Office of Land and Emergency Management (OLEM)

1301 Constitution Ave NW

Washington, District of Columbia 20460

202-566-0874

mahonev.michele(a)epa.gov

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Phytotechnology Technology Profile

Contents

Notice/Disclaimer	v

Foreword	v

Acknowledgments	vi

Contents	vii

Figures	ix

Tables	ix

About this technology profile	10

What are phytotechnologies and how do they work?	10

How is phytotechnology effectiveness evaluated in scientific literature?	11

Advancements in phytotechnologies	13

Borings	13

Tree poles	13

Plant varieties—hybrid poplars, hybrid willows, and native species	14

Hybrid poplars	14

Hybrid willows	14

Natives	14

Endophytes, bioaugmentation, and biostimulation	15

Phytoforensics	16

What contaminants are suited for phytotechnologies?	17

VOCs, CVOCs, and SVOCs	17

1,4-Dioxane	17

Dioxins and furans	17

Explosives	18

Per- and polyfluoroalkyl substances (PFAS)	19

Heavy metals	21

What kinds of plants can be used?	21

Advantages and disadvantages of phytoremediation	23

How long does it take to work?	25

Selected case studies	29

What do I need to do after planting?	31

Operations and maintenance	31

Biomass and wildlife considerations	32

Biomass waste disposal	32

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Resilience considerations	33

Long-term monitoring	33

Lessons learned from field applications	34

Sustainability and co-benefits	35

Sustainability	35

Ecosystem benefits	35

Carbon sequestration	36

Is phytotechnology right for my site?	36

For more information	39

Acronyms and abbreviations	40

References	42

Quality Assurance Statement	50

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Figures

Figure 1. Visualization of phytotechnology mechanisms	10

Figure 2. Young tree poles with endophyte inoculant (above) and tree pole cuttings placed in a borehole

(below)	13

Figure 3. Illustration of bioaugmentation with endophytes	15

Figure 4. Vadose zone, capillary fringe, and saturated zone	16

Figure 5. Tree core sample	16

Figure 6. A tree sampler being placed inside a trunk borehole	16

Figure 7. General timeline for a phytoremediation project, from installing plants to meeting remedial goals	26

Figure 8. Plant hardiness zones in the United States	28

Figure 9. Rooting depth and spread of roots for commonly used plants	29

Figure 10. Potential end-uses of phytoremediated sites	35

Table 1. Definitions of different phytotechnologies	11

Table 2. Dioxin and furan removal range, by plant type	18

Table 3. Plants known to be effective at remediating contaminants	22

Table 4. Advantages and disadvantages of phytoremediation	24

Table 5. General range of time required to observe significant remediation of selected contaminants	26

Table 6. Selected case studies of phytotechnology applications at Superfund sites	30

Table 7. Checklist for determining whether phytotechnologies are suitable	37

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Phytotechnology Technology Profile

About this technology profile

This guide provides key information to help environmental cleanup professionals and others understand the
mechanisms of phytotechnologies and assess their applicability to remediate or control contaminants in various
media. Also included are case study examples and useful information for planning a phytotechnology application
(e.g., successful plant-contaminant combinations, operation and maintenance (O&M), and long-term
monitoring).

What are phytotechnologies and how do they work?

Phytotechnologies are a suite of technologies that
broadly refer to the use of living plants for in situ
remediation of certain contaminants in soil, ground
water, surface water, or sediments (Interstate Technology
Regulatory Council [ITRC], 2009). Phytotechnologies have
been successfully demonstrated on a variety of
contaminants, including organics, such as volatile organic
compounds (VOCs), polycyclic aromatic hydrocarbons
(PAHs),1 petroleum hydrocarbons, and munitions
constituents; some metals; radionuclides; and emerging
contaminants such as perfluoroalkyl substances (PFAS).

The terms phytotechnology and phytoremediation are
often used interchangeably. In this fact sheet,
phytoremediation collectively refers to the suite of
phytotechnologies, while phytotechnology refers to a
specific mechanism or application. Figure 1 identifies
several phytotechnologies and areas where the
mechanisms to control select contaminants may occur.

0 Contaminant
^ Volatile form

^ Organic contaminant
W Degradation product

Phytostabilization

reduction of bioavailability of
contaminants

Many types of plants—including grasses, shrubs, and
trees—can be used for phytotechnology applications
(Raskin et al,, 1997; Wenzel et a!., 1999). In general,
plants can remediate low to moderate and high levels of
contaminants over large areas in addition to source	Figure 1. Visualization of phytotechnology

zones. Plantings can also function as a final "polishing"

step to treat trace residual contamination, act as a buffer Source: R' I International with Getty Images, 2023.
against potential waste releases, decrease a plume's

spread, and accelerate ecological restoration, which enhances rates of monitored natural attenuation
(McCutcheon & Schnoor, 2003).

Phytoextraction

concentration of contaminants
from soil to plant tissues

Phytovolatilization

volatilization of pollutants

Phytodegradation

degradation of organic
contaminants

Contaminant remediation or control using phytotechnology works through different mechanisms depending on
the plant or tree species used. For example, the contaminant type(s), their concentration(s), and site conditions

1 PAHs are a class of chemicals that occur naturally in coal, crude oil, and gasoline.

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(e.g., soil type, climate) all play a role in selecting an appropriate phytotechnology. If possible, a pilot study
should be conducted to identify the most suitable plant type, species, size, depth, and other variables to be
optimized such that a phytotechnology is selected that best achieves site-specific cleanup goals.

Table 1 defines each phytotechnology and identifies the plant component where contaminants primarily
remain, even though contaminants can be found in all parts of the plant.

Table 1. Definitions of different phytotechnologies

Rhizodegradation - A plant's ability to form a symbiotic relationship with soil microbes that live in the root zone and
adjacent soil (rhizosphere) to break down contaminants. Plant root secretions (exudates) feed microorganisms and soil
microbes (e.g., archaea, bacteria, fungi) to enhance contaminant biodegradation in the soil by stimulating their
necessary catabolic enzymes. Plant root exudates include organic acids, sugars, amino acids, and secondary
metabolites. Plant roots also physically open pore space, promoting aerobic conditions and benefiting soil microbe
populations to enhance contaminant biodegradation.

Phytodegradation - A plant's ability to uptake and break down complex organic molecules into simpler organic
molecules within the plant tissues and metabolize and/or assimilate them to form less toxic substances. The process
can also occur within the plant tissue or in the rhizosphere (the area around the plant's roots; referred to as

rhizodegradation).

Rhizostabilization - A plant's ability to adsorb, absorb, or accumulate contaminants in the root zone. Minimizes
contaminant migration below the ground surface by intercepting contaminant plumes and physically stabilizing the
soil. Rhizofiltration and phytostabilization as illustrated in Figure 1 refer to these combined root zone processes.

Phytosequestration - A plant's ability to sequester or accumulate contaminants in its roots, or to precipitate/
immobilize contaminants in the root zone.

Phytoextraction or phytoaccumulation - Ability of plants to uptake contaminants through the roots (extraction) and
sequester the contaminants in the plant tissue. Organic contaminants with log K0w values of 1.5-4 are generally
suitable for plant uptake and translocation (Burken & Schnoor, 1998; Simmer & Schnoor, 2022). Most published
studies involving trees were conducted with saplings or young trees versus mature trees. Studies have shown that
contaminants are sequestered predominantly in the roots (e.g., Mleczek et al., 2017).

Phytovolatilization - Ability of plants to uptake VOCs from soil; transform the less volatile contaminants into more
volatile forms; and subsequently emit, or volatilize, those contaminants into the atmosphere. Some compounds can
directly volatilize from the stem and leaves, while others can directly volatilize from the root-soil interaction (Kafle et
al., 2022).

Hydraulic control - Use of plant roots and their water consumption (i.e., transpiration) to mitigate the contaminated
groundwater from migrating off-site.

How is phytotechnology effectiveness evaluated in scientific literature?

Thousands of peer and non-peer reviewed studies on phytotechnologies have been published, spanning a
variety of plant species, contaminants, durations, locations (both geographical, and greenhouse- or bench-scale
versus field- or pilot-scale), and other factors. Phytotechnology applications at Superfund, Resource
Conservation and Recovery Act (RCRA), and brownfield sites will have remedial objectives defined in terms of
lowering contaminant levels for the agreed-upon end use. Phytotechnology effectiveness is generally measured
by a decrease in the targeted contaminant(s) in the environmental media, which may be soil, groundwater,
surface water, sediment, or stormwater; and in terms of how well the defined remedial objectives have been
met.

Many researchers use the terms translocation factor (TF) or translocation index, bioconcentration factor (BCF),
or bioaccumulation factor (BAF) to define the efficiency with which plants uptake and accumulate a

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contaminant. All three metrics are a ratio of the contaminant of interest in a plant to the same contaminant in
the substrate (i.e., environmental media of interest). BCF and BAF are often used interchangeably. TF is often
used to portray the measure of the phyto extract ion capacity of a plant. The terms can be further explained as
follows:

• TF = Contaminant (plant shoot or leaves) / Contaminant (plant root); explains the ability of a plant to
translocate a contaminant from roots to the shoots and leaves of the plant (Mashau et al., 2018)

• BCF = Contaminant concentration in plant / Contaminant concentration in media (U.S. EPA, 2024)

• BAF = Contaminant concentration in organism / Contaminant concentration in media to which the

organism is exposed through all routes, including the food chain (U.S. EPA, 2024).

Remediation practitioners may encounter these terms when determining whether certain phytotechnologies
are effective for a chosen site. All three terms are used to assess a plant's potential for phytoremediation
purposes. These terms (TF, most often) may also refer to how efficiently contaminant(s) move from a substrate
to specific plant parts, such as the roots, shoots, and/or foliage (e.g., a plant's roots may have a higher TF than
its shoots).

BAF is often used to reference how aquatic organisms uptake pollutants from water but some researchers use it
in reference to plants. The TF, BCF, and BAF are not constants; they are variables that depend on the
environmental and biological conditions of the plant and contaminant properties. For example, they vary based
on plant genotype, growing season, contaminant equilibrium concentrations in specific plants (Kc values),
contaminant hydrophilicity, irrigation requirements, and root lipid content (Hussain et al., 2022). Some studies
referenced within this document use the term BCF to determine whether a plant can be considered a
hyperaccumulator species.

Soil properties also affect plant contaminant uptake. These properties include soil organic matter, soil type (i.e.,
sand, clay, loam), pH value, heterogeneity, and aerobic or anaerobic conditions. Rhizospheric microbial activities
can also influence contaminant uptake. For example, compounds released into the soil by rhizospheric microbes
can increase or decrease plant bioavailability of metals (Wenzel, 2009), as well as the bioavailability of
hydrophobic organic contaminants such as PAHs. Finally, other mechanisms that may decrease plant
contaminant concentrations include volatilization, metabolized degradation, and photodegradation. BCF values
greater than 1 indicate a potential hyperaccumulator species (i.e., there is a higher contaminant concentration
in the plant than in the substrate). Generally, plants tend to be capable of hyperaccumulating smaller, inorganic
metals—such as nickel—rather than larger, organic compounds—such as polychlorinated biphenyl compounds
(PCBs) or PAHs. Hyperaccumulators are plants that can accumulate relatively large amounts of contaminants
without exhibiting phytotoxic symptoms when exposed to elevated concentrations (such as heavy metals;
Suman et al., 2018). Plants are classified as hyperaccumulators based on their tissue's dry weight concentration
of a specific accumulated contaminant. For example, the dry weight concentration for cadmium is at least 1,000
mg/kg (0.1%) and for manganese, at least 10,000 mg/kg (0.1%) (Mclntyre, 2003; Nwaichi & Dhankher, 2016; Van
der Ent et al., 2012).

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Advancements in phytotechnologies

Historically, phytotechnologies have been effectively implemented on sites having shallow contamination with
low-level concentrations of contaminants. New advancements, however, have opened the door to
implementing phytotechnologies at a broader range of sites and improving the reliability of the plants. This
section includes a discussion of examples of these advancements.

Borings

Predrilling or auguring a borehole into the subsurface before
installing a plant has been shown to increase rooting depth, which
in turn can improve the chances of the plant reaching maturity
and remediation of subsurface contamination. The boring
produces a vertical, homogenous conduit that provides increased
pore space, soil moisture, and nutrients. Borings are advanced to
the depth of contamination (i.e., subsurface soil location or
capillary fringe) and can be lined with plastic sleeves to limit
access to shallow soil water, thereby forcing roots vertically
downward to optimize growth and uptake of deep contaminated
ground water. Boreholes can also be backfilled with soil
amendments such as organic material, mycorrhiza (rhizosphere-
dwelling fungi), and other nutrient enrichments.

Tree poles

A tree pole is a young stem removed of its branches and roots. It
quickly produces new roots and sprouts when planted in the
ground. Planting dormant tree pole cuttings is a successful
propagation technique for quickly establishing a phytotechnology
system. Planting a tree pole instead of a seedling gives a "head
start" because of the advantage of increased height and rooting
depth. The height and size of the new canopy also can increase
resilience from damage by foraging animals. Further, tree poles
can produce roots at depths up to 10 feet below the ground
surface, which expedites the remediation timeline if contact with
subsurface-contaminated soil or groundwater is required.

Most tree poles used in phytotechnology applications are willow
(Salix spp.) and poplar (Populus spp.) species due to their ability
to re-root and re-branch quickly. Figure 2 provides an example of
tree poles before being planted, above- and below-ground in a
borehole. If tree poles are to be planted in a borehole, workers
can fill the borehole to the desired depth of rooting, place the
tree pole into the boring, and follow with additional backfill.

Figure 2. Young tree poles with
endophyte inoculant (above) and tree
pole cuttings placed in a borehole
(below)

Photo credits: Kendra Waltermire, Jacobs
Engineering

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Plant varieties—hybrid poplars, hybrid willows, and native species

Hybrid poplars

Although different plants are used for phytotechnology systems, most sites and research use hybrid poplar trees
(Populus spp.) because they tend to be fast-growing and effective due to their deep, dense root systems, high
transpiration rates, and general resiliency. Advantages of using poplars include their ability to reach mature
growth quickly and their adaptability to varying climates, contaminants, and locations. Poplar trees are
extremely fast-growing, at a rate of 5 to 8 feet (ft) per year. Poplars can flourish geographically from boreal
midcontinental regions to subtropical zones. They transpire water at a rate of up to 100 gallons per mature tree
each day (when water is readily available). Poplars can withstand flooded conditions for short periods, but their
roots need to remain aerobic. This process is facilitated by aerenchyma, gas passages through the vascular
structure, which allows poplars to transport oxygen downward to maintain root systems and the rhizosphere.
Thousands of hybrid poplar cultivars are commercially available throughout the world, mostly developed by
traditional plant breeding techniques (Simmer & Schnoor, 2022). Hybrid poplar cultivars are also all male clones,
which prevents the spread of poplar as an invasive species.

Poplar trees are widely used to facilitate phytoremediation of a variety of contaminants. They are hardy and can
improve poor-quality soils by adding carbon and nitrogen from root turnover, thus providing a healthier habitat
for native species. Poplars also tolerate higher concentrations of contaminants compared to most other plant
species.

Hybrid willows

Hybrid willow trees (Salix spp.) are widely used in phytoremediation applications to address soil and water
pollution due to their fast growth rate, extensive root systems, and high tolerance to contaminants. Hybrid
willows are much better suited for saturated conditions (high water table and low oxygen) than hybrid poplars.
These characteristics enable willows to absorb, store, and in some cases detoxify pollutants such as heavy
metals, organic compounds, and excess nutrients from soils and wastewater. Studies show that willows can
accumulate and stabilize metals like cadmium (Cd), lead (Pb), and zinc (Zn), while also effectively removing
nitrates and phosphates, which can otherwise lead to eutrophication in nearby water bodies (Pulford & Watson,
2003; Ruttens et al., 2011). In addition to metal uptake, willow roots release organic acids and other compounds
that can immobilize certain pollutants (e.g., the trace elements Cd, chromium (Cr), copper (Cu), nickel (Ni), and
Zn and organic compounds [as summarized in Faubert et al., 2021]; mineral oil, PAHs [Vervaeke et al., 2003],
reducing their bioavailability and mitigating the environmental impact of contaminated sites (Robinson et al.,
2000). Due to these attributes, hybrid willows are increasingly employed in engineered wetlands, riparian buffer
zones, and contaminated soil sites, proving to be a sustainable and cost-effective solution for ecological
remediation (Dickinson & Pulford, 2005; Volk et al., 2006; Ferro et al., 2013; McCutcheon & Schnoor, 2003).

Natives

Using native plants is encouraged in phytoremediation design because they are well adapted to site-specific
conditions and less likely to attract nuisance animals or pests. Typically, native plants require fewer fertilizers
and pesticides to grow and thrive than non-native alternatives. Native plants can promote higher biodiversity,
shelter, and food for wildlife. Natives are also adapted to the site's regular climate and rainfall conditions, which
increases their survival rate and resiliency to drought. Although native species can be relatively slow growing,
they tend to be more resilient in their environment compared to faster growing non-native species. Native
species can also act as "nurse" plants by providing ground coverage to prevent weeds and the exchange of
chemicals within the subsurface to other plants.

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Another factor to consider with respect to native and non-native species is the use of plants referred to as
phreatophytes. A phreatophyte is a plant with a deep root system that draws its water supply from close to the
water table (phreatic zone). Native species tend to outlive other fast-growing species, providing the next
generation of plant cover after the shorter life cycle of phreatophytes. Common phreatophytes in the Midwest,
for example, are cottonwood and poplar (Populus spp.), mulberry (Morus spp.), and willow (Salix spp.) trees.
Phreatophytes—whether they are native to a given area or not—have a strong, competitive advantage over
shallow-root plants at arid sites because their roots can reach groundwater more easily. When interplanted with
phreatophytes, native plants are unlikely to outcompete neighboring plants. Many times, the native and
phreatophyte plants will work together by providing varying canopy coverage (i.e., not competing for canopy
space).

Endophytes, bioaugmentation, arid biostimulation
Changing the plant microbiome through bioaugmentation with
endophytes or contaminant-degrading microorganisms has been
proven to increase efficiency in phytoremediation systems (Simmer
and Schnoor, 2022).

Bioaugmentation is the process of adding microorganisms into the
subsurface to enhance the degradation of specific contaminants.

Biostimulation focuses on increasing or stimulating the ability of
native microorganisms within soil and groundwater by adding
nutrients to promote their natural degradation capabilities.

Bioaugmentation introduces new microbes while biostimulation
boosts the activity of already present microbes. Researchers have
demonstrated enhanced treatment of contaminants, including PCBs,
hydrocarbons, and heavy metals, when bioaugmentation or
biostimulation are paired with phytoremediation (Basu et a!., 2015;

Liang et a!., 2014; Tiwari et al., 2023; Wojtowicz et al., 2023).

Endophytes are microorganisms that live in and establish a
symbiotic relationship with living plant cells. Endophytes receive
carbohydrates (food) from plants. In return, the plants enhance their
catabolic metabolism of contaminants and benefit from improved
stress tolerance to salinity and drought (Rodriguez et al., 2004).

Endophytes are also known to increase biomass and vitality within
plants (Doty et al., 2017). Figure 3 illustrates this process.

Strains of endophytes can be separated from plants through microbial isolation. Specific endophytes isolated
from plants thriving in contaminated environments can be bioaugmented into other plants to increase their
tolerance, transpiration rate, and contaminant degradation capabilities. Various tree, grass, and plant-bacterial
endophytic strains have been isolated to target PAHs, benzene, toluene, ethylbenzene, and xylenes (BTEX),2
chlorinated solvents, fluorinated compounds, PCBs, phenanthrene, trinitrotoluene (TNT), and RDX3 (Doty et al.,

2 BTEX refers to a group of compounds—benzene, toluene, ethylbenzene, and total xylenes—that are naturally
occurring components of petroleum and that end up in gasoline through the refining process.

3 RDX—or hexogen, among other names—is an explosive and organic compound with the formula (CH2N2Q2)3.

O Organic pollutants
Endophyte

Figure 3. illustration of
bioaugmentation with endophytes

Source: RTI International with Getty Images,
2023

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Capillary Fringe

(nearly saturated)

Saturated Zone

(spontaneous water movement)

Surface soil

(unsaturated)

VadoseZone

(unsaturated, no
spontaneous
water movement)

2017). Endophytes can be bioaugmerited into seeds and tree poles (described in the next section) by soaking the
seed or root zone in an inoculum. Mature trees can also be inoculated with light spraying of inoculum on
targeted zones on a plant.

Phytoforensics

Vegetation interacts with environmental
media, including air, water, and soil.

Contaminants are transported from the
vadose zone/vapor phase and the saturated
zone/aqueous phase into plant tissue
(Struckhoff et al., 2005). The vadose zone is
the depth just beneath the surface soil, as
illustrated in Figure 4. Analysis of tree cores
and tree samplers through phytoforensics
allows site managers to understand the
spatial density of contamination at a site.

These techniques can be useful in developed
or urban areas where several contamination
plumes may be intermixed or when the
public will not accept other relatively
invasive investigative solutions that disturb
the subsurface.

WaterTable

Figure 4. Vadose zone, capillary fringe, and saturated zone
Source: RTI International with Getty Images, 2023.

Sampling techniques like tree cores and solid-phase samplers allow researchers and practitioners to assess
phytoremediation effectiveness by identifying contaminants and their breakdown products within the plant
tissue. Tree cores are particularly useful for finding and tracking groundwater contamination. Figure 5 presents
an example of tree cores collected using an increment borer (a type of tree sampler), as shown in Figure 6. The
tree cores are then placed in a volatile organic analysis (VOA) vial (Figure 5).

Figure 5. Tree core sample
Photo credit: K. Waltermire

Figure 6. A tree sampler being placed inside a trunk borehole
Photo credit: K. Waltermire

The headspace in the vial can be analyzed using a gas chromatography instrument to determine contamination
within the wood biomass. This result can also be used to quantify the contamination in the subsurface soil,
and—in this example—for VOCs (Larsen et al., 2008; Vroblesky et al., 1999). Partitioning coefficients between

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air, water, and woody biomass have been investigated to provide quantifiable concentrations (Ma and Burken,
2002). A small borehole remains within the tree's trunk after a core is removed and samplers can be placed
inside. The samplers are removed after a set timeframe ranging from one to two hours for most sites. Solid-
phase microextraction (SPME) fibers and solid-phase samplers are two innovative sample preparation
technologies that obtain a greater uptake of VOCs, resulting in better resolution and decreased minimum
detection limits (Limmer et al., 2011; Limmer and Burken, 2015; Waltermire, 2009).

Sampling during periods of rapid growth or high transpiration (i.e., summer, tropical zones) will capture the
maximum availability of the contaminants in tree tissues and vascular systems. Additionally, the core or sampler
should be collected from the side of the tree suspected to be closest to the target contamination.

What contaminants are suited for phytotechnologies?

Hundreds of contaminants can be remediated using phytotechnologies, including VOCs and semivolatile organic
contaminants (SVOCs), PCBs, nutrients, pesticides, explosives, metals, and PFAS. Applying phytotechnology to
treat chlorinated solvents, petroleum products, and organic nutrients has become an industry-standard
technique. However, not all applicable contaminants are described in this section. Instead, this section focuses
on a discussion of chemicals for which exploratory investigations have been initiated to determine plant types,
species, and phytotechnology mechanisms that may be used to remediate specific emerging contaminants and
contaminant classes most effectively.

VOCs, CVOCs, and SVOCs

Common VOCs where phytotechnologies have been successfully demonstrated include trichloroethylene (TCE),
vinyl chloride, carbon tetrachloride, benzene, chloroform, and some PAHs, including BTEX and total petroleum
hydrocarbons (TPH). Poplars effectively remediate these compounds in contaminated soil (Doty et al., 2007) and
groundwater (Landmeyer et al., 2020; Limmer et al., 2018). Phytoremediation of VOCs, specifically BTEX in
indoor air, has also been demonstrated as summarized in a state-of-the-art review on indoor air
phytoremediation (Matheson etal., 2023).

1,4-Dioxane

Phytotechnologies can be highly effective at treating 1,4-dioxane. Due to the compound's high solubility and low
sorption, 1,4-dioxane is readily taken up by plants via the transpiration stream and is released to the
atmosphere via phytovolatilization (Aitchinson et al., 2000). In lab studies, hybrid poplar cuttings have been
demonstrated to remove dioxane from both aqueous solutions (up to 73% of the 1,4-dioxane mass in a 23 mg/L
solution over 9 days) and soil (approximately 11 to 27% after 15 days) (Aitchinson et. al, 2000). In the cited
study, approximately 76 to 83% of the dioxane taken up by poplar cuttings was released into the atmosphere
through transpiration from leaf surfaces. While 1,4-dioxane released into the atmosphere is broken down by
photo-oxidation (estimated half-life of 1 to 3 days), its release can be an inhalation hazard in populated areas
(ATSDR, 2012). To counter this, another study bioaugmented the tree rhizosphere with dioxane-metabolizing
bacteria to increase the fraction of 1,4-dioxane metabolized in the root zone, enhancing rhizodegradation, and
decreasing tree uptake by over 75% (Simmer et al., 2020). Nevertheless, the ITRC (2021) lists phytoremediation
as a fully validated in-situ treatment technology for both groundwater and the vadose zone.

Dioxins and furans

While field-scale data regarding the efficacy of phytoremediation on dioxins and furans is scarce, greenhouse
studies have indicated that plants can remove dioxins from soil at rates ranging from 24 to 98%, as summarized
in Table 2. Researchers have reported varying degrees of contaminant removal of dioxins from soil in other

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greenhouse studies. For example, Meglouli et al. (2019) reported that soil stimulated with amendments paired
with alfalfa removed approximately 23% of dioxins and furans over 6 months. Others found the highest
performance for the treatment of dioxins to range from 46 to 72% removal over 30 to 32 days (Hanano et al.,
2014; Inui et al., 2008).

The longest field study (Yanitch et al., 2020) was conducted in Quebec over four years. It involved four different
types of plants (purple willow [Salix purpurea], tall fescue [Festuca arudinacea], alfalfa [Medicago sativa], and
mustard greens [Brassica juncea]) grown in soil contaminated with dioxins and furans from use of wood
preservatives. Plant translocation and concentration of trace elements of heavy metals (Cu, Ni, Zn), dioxins, and
furans in above-ground plant tissue were observed. Results showed the most accumulation of Cu, Zn, and
pentachlorophenol (PCP), a dibenzo-furan, in the aerial plant parts, suggesting that these species could be
potential candidates for heavy metal and PCP remediation (Yanitch et al., 2020).

Table 2. Dioxin and furan removal range, by plant type

Plant type

Plant name in order of contaminant removal efficacy

Approximate removal
range (%)a

Perennial shrub
(tropical)

Elderberry (Sambucus nigra "Gerda")

46-50

Tree

Gold rush (Metasequoia spp.)

60-62

Flowering plant

Spinach (Spinacia oleracea) < thale cress (Arabidopsis thaliana)

36-72

Vegetable/herb

Alfalfa (Medicago sativa) < cucumber (Cucumis satifus) < bok choy
(Brassica rapa spp.) < zucchini (Cucurbita pepo) < pumpkin (Cucurbita
pepo)

23-79

Grass

Rice (Oryza sativa)

90-98

Sources: Hanano et al., 2014; Inui et al., 2008; Meglouli et al., 2019; Nhung et al., 2022.

3 The minimum range corresponds to the first plant name in the middle column, while the high-end of the range corresponds to the last plant name in
the middle column. Most study durations for phytoremediation are for a short timeline (less than one year) partly due to the life cycle and harvesting
of the subject plants.

Explosives

Explosives, including TNT and RDX, are commonly used in military, mining, and construction activities. Their use
may release nitroaromatics and heavy metals into the soil and potentially groundwater. Remediating a site
contaminated by explosives adds a layer of complexity compared to other heavy metal contaminated sites due
to the potential presence of unexploded ordinance, decomposition products from energetic explosives, and the
emergence of new types of explosives (e.g., 2,4-Dinitroanisole [DNAN], nitrotriazolone [NTO], high melting
explosive [HMX]) with compositions that are difficult to define (Mystrioti & Papassiopi, 2024). Another issue
specific to phytotechnologies is the toxicity of explosives, including TNT and RDX, to certain plants, bacteria, and
other microorganisms. Understanding the site contamination and toxicity of the explosives at the site is
important. RDX, for example, is generally less toxic than TNT (Rylott & Bruce, 2019 and 2009).

Using phytotechnologies to remediate explosives is best suited for larger-scale areas and/or where longer clean
up times are acceptable (Rylott & Bruce, 2019). Phytotechnologies are typically considered long-term options,
typically lasting more than 3 years and sometimes decades. Landfilling, incineration, chemical reduction, or
advanced oxidation are best suited to small-scale, highly polluted areas where the target clean up time is less
than 3 years. The most suitable species for effective remediation of explosives tend to be quick growing,

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phreatophytic species with relatively high biomass production rates and low maintenance (Rylott & Bruce,
2019). Low-growing species are recommended for active military sites and sites with high potential for wildfire.
Access may also be restricted at sites with unexploded ordinance, requiring additional emphasis on suitable
plant selection for the climate, the need for irrigation, mowing and pruning, and plant maintenance needs.

Rylott & Bruce (2019) recommend using seed balls with a robust matrix of rhizospheric and endophytic bacteria
previously isolated from the contaminated site, nutrients, and an improved water holding capacity to help
establish seedlings. They also recommend genetically modifying the endophytic bacteria to contain explosive-
detoxifying genes, and using soil amendments (e.g., compost, biochar, and molasses) to aid in microbial
degradation.

Few studies documenting field trials for explosives are available in the peer-reviewed literature. Of those
reviewed, plants suitable for explosive-contaminated sites include perennial grass species such as switchgrass
(Panicum virgatum); miscanthus {Miscanthus x giganteus); vetiver (Vetiveria zizaniodes); and hybrid poplar
(Populus sp.) and willow (Salix sp.) trees (Rylott & Bruce, 2019; Kiiskila et al., 2015). Vetiver has been shown to
effectively remove explosives from wastewater effluents from an industrial munition facility, with RDX, HMX,
and DNAN transformation products detected in root and aerial tissues (Panja et al., 2018). The cool season
orchard grass (Dactylis glomerata; Duringer et al. 2010), and species native to the Caribbean (Correa-
Torres et al., 2012) are also effective.

Per- and polyfluoroalkyl substances (PFAS)

While the science is still emerging, several researchers have investigated PFAS uptake in plants (as summarized
in Adu et al., 2023; Gobelius et al., 2017; Hilliard et al., 2023; Wiirth et al., 2023; Huff et al., 2020; and Wang et
al., 2020). Gobelius et al. (2017) and Huff et al. (2020) investigated trees and forest ground cover plants at field
and greenhouse scale, respectively, to understand plant uptake and accumulation of PFAS from soil and
groundwater. Hilliard et al. (2023) investigated how plant type affects PFAS removal from stormwater.

Research suggests that phytotechnology applications composed of short-lived herbaceous plants with long-lived
tree species could be developed and refined to maximize remedial efficiency of PFAS in different media. PFAS
chain length is the most dominant factor affecting their accumulation in plants. Short-chain PFAS (four to six
carbon atoms) have been shown to demonstrate a higher accumulation potential in plants compared to longer-
chain PFAS (six or more carbon atoms). Short-chain PFAS typically have higher water solubility and smaller
molecular size, which facilitates their penetration through plant root layers into the plant tissue during water
transpiration (Adu et al., 2023; Hilliard et al., 2023; Wang et al., 2020).

In a field-scale study, Gobelius et al. (2017) investigated 26 PFAS in ground cover plants and trees at a fire
training site in Sweden in 2016. The BCFs were highest in foliage, while the total tree accumulation of 26 PFAS
per tree was reported to be up to 11 mg for birch (Betula spp.) and 1.8 mg for spruce (Picea spp.). This study did
not include other proven plants for phytoremediation, including common reed grass (Phragmites australis),
willows (Salix spp.), and poplars (Populus spp.). The researchers noted that it may be feasible to remove 1.4 g of
PFAS per year per hectare from heavily contaminated sites using a mixed stand of silver birch (Betula pendula)
and spruce (Picea spp.) with an understory of ground elder (Aegopodium podagraria) (Gobelius et al., 2017).

The study by Huff et al. (2020) demonstrated the potential use of phytoremediation for PFAS-contaminated
sites. The authors showed at greenhouse scale that six PFAS compounds (PFPeA, PFHxA, PFOA, PFBS, PFHxS, and
PFOS) accumulated in above-ground portions of herbaceous plants and trees. Hyperaccumulation was defined in
this study as the ratio of tissue to soil concentrations more than 10 to 1 and was observed for all six PFAS
compounds in at least one plant species (Huff et al., 2020). There were species-specific differences in observed

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tissue concentrations for individual PFAS and
accumulation pattern. In general, individual PFAS
tissue concentrations (ng/g) from greatest to least
were PFPeA, PFHxA, PFBS, PFOA, PFHxS, and PFOS,
with some variation by plant species. The highest plant
uptakes were observed with the five-chain PFPeA
compound and the lowest were observed with the
eight-chain PFOS compound. Four herbaceous and
three tree species were identified as
hyperaccumulators for at least one of the six PFAS
compounds. Red fescue (Festuca rubra), tall fescue
{Schedonorus arundinaceus), amaranth (Amaranatus
tricolor), horsetail (Equisetum hyemale), black willow
(Salix nigra), river birch (Betula nigra), and tulip poplar
(Lirodendron tulipfera) were hyperaccumulators of
PFHxA. Red fescue, tall fescue, and tulip poplar were
hyperaccumulators of PFBS, and river birch was a
hyperaccumulator of PFOS.

Hilliard et al. (2023) evaluated how effectively 10
indigenous Pacific Northwest plant species planted in
bioswales removed 16 artificially introduced PFAS
compounds from stormwater. Bioswales are channels
designed to concentrate and convey stormwater
runoff while removing pollutants. A general increase in
PFAS accumulation was observed in the plant roots
while a general decrease in PFAS accumulation was
observed in the stems and leaves as the PFAS C-F
chain length increased. On average, plant groups with
the greatest to least PFAS accumulation (by average
BCF across all PFAS) were as follows: herbaceous
dicots (perennials with nonwoody stems) more than
grasses more than sedges more than woody dicots
(plants with woody stems) more than rushes. Herbaceous dicots (yarrow [Achillea millefolium] and
checkermallow [Sidalcea spp.]) hyperaccumulated four PFAS (PFBA, PFNA, PFBS, and PFPeS), while grasses and
sedges hyperaccumulated three PFAS (grasses: PFPeA, PFBS, and PFPeS; sedges: PFBA, PFBS, and PFPeS). The
woody dicots (salal [Gaultheria shallon] and Oregon grape [Mahonia repens]) hyperaccumulated two PFAS (PFBS
and PFPeS), while rushes hyperaccumulated only PFBS.

Wiirth et al. (2023) conducted a comprehensive field study to investigate the applicability of phytoscreening
using three tree species - black alder (Alnus glutinosa L.), black poplar (Populus nigra L.), and white willow (Salix
alba L.) - at a PFAS-contaminated site in Germany. Phytoscreening is a laboratory-based process that uses plants
to identify and map environmental pollutants in soil, groundwater, and pore water. Tree samples were collected
from up to 22 trees at three time intervals (October 2020, July 2021, and October 20201) to evaluate seasonal
and annual variations in PFAS concentrations. The results demonstrated the highest PFAS sum concentrations in

Plant Uptake and Accumulation of PFAS

Research to date has largely been conducted at
greenhouse scale. Most studies have focused on
PFOA and/or PFOS uptake by agricultural crops.

PFAS compounds analyzed by researchers have
varied:

•	Gobelius et al. (2017) investigated plant uptake of
26 PFAS from soil and groundwater: 13 PFCAs
(including PFOA), 4 PFSAs (including PFOS), 3
FOSAs, 2 FOSEs, 3 FOSAAs, and FTSA.

•	Huff et al. (2020) included 6 PFAS in soil: PFPeA,
PFHxA, PFOA, PFBS, PFHxS, and PFOS.

•	Hilliard et al. (2023) looked at 14 PFAS in
stormwater: PFBA, PFPeA, PFHxA, PFHpA, PFOA,
PFNA, PFDA, PFBS, PFPeS, PFHxS, PFOS, PFDS,
FHxSA, FOSA.

•	Wiirth et al. (2023) investigated 23 PFAS, including
short-chain and long-chain PFCAs, PFSAs, and
FTSAs in three different tree species at a field site
with contaminated soil and groundwater.

Short-chain PFAS are more likely to be absorbed by
plants than longer chain PFAS.

Other factors that may affect plant uptake include
PFAS molar volume, the soil organic carbon-water
partition coefficient (log Koc) values, protein and lipid
content, pH, temperature, soil organic carbon, and
plant transpiration rates (as reviewed in Adu et al.,
2023; Hilliard et al., 2023).

Section 5.6 of the PFAS Technical and Regulatory
Guidance Document (ITRC, 2023) summarizes
additional findings related to plant uptake of PFAS.

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October for white willow (0-1800 ng/kg), followed by black poplar (6.7-32 ng/kg) and black alder (0-13 ng/kg).
Highly mobile PFCAs were primarily found in the leaves. Long-chain PFCAs, PFOA, and PDFA were predominantly
found in the soil indicating lower mobility. The PFAS composition in the groundwater was similar to that
observed in the leaves. Spatial interpolations of PFAS in groundwater and foliage correspond well and
demonstrate the successful application of phytoscreening to detect and delineate the impact of the studied
PFAS on groundwater (Wiirth et al., 2023).

Heavy metals

Several plant species can accumulate or hyperaccumulate heavy metals using phytoextraction (also known as
phytoaccumulation) and phytovolatilization. The plants absorb the metals into the roots and then translocate
them via the xylem to the plant's aerial parts for eventual storage. Examples of these plants for selected metals,
as summarized in Skuza et al. (2022), include the following:

•	Ni: yellow tuft (Alyssum murale), berkheya (Berkheya coddii), pennycress (Thlaspi goesingense)

•	Se: mustard plants (Brassica juncea), milkvetch (Astragalus bisulcatus, Astragalus racemosus), hairy
bittercress (Cardamine hirsute)

•	Zn: black poplar (Populus nigra), gray poplar (Populus canescens)

•	Pb, Cd, Cu, Ni, Zn, Cr: alpine pennycress (Thlaspi caerulescens), mustard plants (Brassica juncea), Chinese
brake fern (Pteris vittate), rockcress (Arabis paniculate), ryegrass (Lolium italicum), sweet alyssum
(Alyssum heldreichii).

When selecting a plant species for phytoremediation applications, it is important to note that larger plant
species not classified as hyperaccumulators can potentially remove more contaminants from soil by mass than
smaller hyperaccumulators because they have more total biomass (i.e., they may not be as efficient at removing
contaminants on a concentration basis but have "more room" to store contaminants removed from the soil).

Plants with dense root systems are the best for rhizodegradation (or rhizostabilization) and have been found to
absorb metals such as Pb, Cd, Zn, arsenic (As), Cu, Cr, selenium (Se), and uranium (Ur) most easily. Plants
reported to be successful metal hyperaccumulators include rice millet (Piptatherum miliaceum), spurge
(Euphorbia spp.), and big saltbush (Atriplex lentiformis).

What kinds of plants can be used?

Plant species should be selected for phytoremediation based on their ability to grow in the regional climate,
their rooting structure (depth and spread), and the nature of the contamination. Other factors that affect plant
species selection are demonstrated performance, literature providing evidence to support remediation
objectives, remediation mechanisms applicable to contaminants at the site, water usage, and growth rate.

Plants commonly used in phytoremediation applications are listed in Table 3. Research and field studies
continue to identify new plants that effectively remediate or control contaminants beyond the common plants
discussed in this fact sheet. Thousands of studies are available in the literature, many of them research-based,
short-term, and/or at bench-scale. Phytoremediation scientists and practitioners should also disseminate their
results (e.g., submissions to ITRC, conference proceedings, white papers, peer-reviewed articles) from field-scale
phytoremediation applications to provide guidance and data that others can leverage to support decision-
making for their own sites.

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Table 3. Plants known to be effective at remediating contaminants

Plant name

Plant type

Estimated
rooting
depth
(feet)

VOCs

SVOCs

Metals

Petroleum

PCBs

1,4-dioxane

Metals and other
contaminants

References

Brassica juncea
Brown or Indian
mustard

Flowering
plant

3-4;
taproot to 6





V

V





Cd, Cr, Cu, Mn, Ni,
Pb, Zn,

Pesticides, cesium

Bennett et al., 2003;
Mashau et al., 2018;
McCutcheon &
Schnoor, 2003;

Tong et al., 2014;
Yadav et al., 2022

Cannabis sativa
Hemp

Flowering
plant

1.5-3;
taproot 6-7





V







PFAS

Nason et al., 2021;
Nason et al., 2024

Carex spp.
Sedges

Wetland
plant

6

V



V







Pb

Ghosh, 2010

Chrysopogon

zizanioides

Vetiver

Grass

10-12

V



V







Cu, Fe, Mn, Pb, Zn

Suelee et al., 2017

Cortaderia
selloana
Pampas grass

Grass

10-12







V





Sulfates, herbicides,
tetracycline, dyes,
acid mine drainage,
3-nitro-l,2,4-triazol-
5-one (explosive)

Mirzaee et al., 2022

Cynodon
dactylon
Bermuda grass

Grass

6 in to 6





V

V





Cd, Cr, Pb, Zn

Mishra et al., 2020;
Song et al., 2022;
Yang et al., 1997

Festuca spp.
Tall fescue

Grass

1-5





V

V





Species dependent:
Cd, Cu, Fe, Hg, Mn,
Ni, Pb, Zn,
polybrominated
diphenyl ethers
(PBDEs)

Khashij et al., 2018

Helianthus

annuus

Sunflower

Flowering
plant

4





V







Cd, Cr, Ni, Zn,
radioactive isotopes,
TNT and metabolites
(explosives)

McCutcheon &
Schnoor, 2003;
Turgut et al., 2004

Horde um

vulgare

Barley

Ground
cover

5-6

V



V







Al

McCutcheon &
Schnoor, 2003

Juncus spp.
Rush spp.

Wetland
plant

5-6



V

V

V





As

Alam et al., 2022

Medicago sativa
Alfalfa

Ground
cover

3-6;
taproot to
20

V



V

V

V



Cr

Kirk et al., 1998;
McCutcheon &
Schnoor, 2003

Miscanthus x

giganteus

Giant

miscanthus

Grass

1-1.5





V

V





As, An, As, Cd

Zgorelec et al., 2020

(continued on next page)

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Table 3 (continued). Plants known to be effective at remediating contaminants

Plant name

Plant type

Estimated
rooting
depth
(feet)

VOCs

SVOCs

Metals

Petroleum

PCBs

1,4-dioxane

Metals and other
contaminants

References

Panicum
virgatum
Switchgrass

Grass







V

V

V



Cd, Cr, Pb, Zn

Aken et al., 2010;
Cary et al., 2021;
Hart et al., 2022;
Phouthavong-
Murphy et al., 2020

Pinus spp.
Pine spp.

Tree

5-9

V



V

V

V



Cd, Pb, Zn,
particulate matter,
radioactive isotopes

Placek et al., 2016

Populus spp.
Poplar spp.

Tree

6; large
lateral root
spread

V

V

V

V

V

V

Cd, Cu, Pb, Zn

Huang et al., 2011;
Nematian &
Kazemeini, 2013;
Liu et al., 2008;
Meggo et al., 2013;
Ruttens et al., 2011

Pteris vittata
Chinese brake
fern

Fern

1





V







As, Cd, Cr, Cu, Ni, Zn
fluoride,

diphenylarinic acid
(neurotoxin)

Ma et al., 2001; Tu
& Ma, 2005; Yadav
et al., 2022; Zhang
et al., 2004

Poaceae spp.
Grasses (cereal
grasses,
bamboos, lawn
and pasture
grasses)

Grass

Annual: 1.3;
perennial:
3-4





V

V





Species dependent:
As, Cd, Cu, Cr, Ni, Pb,
Zn, halogenated
flame-retardants,
uranium (radioactive
isotope)

AN et al., 2012;
Malik etal., 2010;
Patra et al., 2021

Salix spp.
Willow spp.

Tree

3; large
lateral root
spread

V

V

V

V

V

V

Ag, Cd, Cu, Hg, Pb,
Se, Zn, tritium
(radioactive isotope)

Ferro et al., 2013;
McCutcheon &
Schnoor, 2003;
Pulford &

Watson, 2003;
Ruttens et al., 2011;
Volk et al., 2006

Triticum

aestivum

Wheatgrass

Grass

1



V

V

V





Pb

Fiegl et al., 2011;
Kwok & Chan, 2022

Typha spp.
Cattail

Wetland
plant

1





V







As, Cd, Cu, Cr, Ni, Pb,
Zn

Patra et al., 2021

spp. = multiple species for the listed genus.

Advantages and disadvantages of phytoremediation

Phytoremediation has several key advantages over more traditional remediation technologies.
Phytoremediation is environmentally and economically sustainable because it uses plants and other renewable
resources (e.g., air, water, sunlight) to treat contamination. This method is less expensive than most other
remediation techniques because it is conducted in situ, which saves on contaminated material excavation,
transportation, off-site processing, and disposal costs (Schnoor, 1997). In addition, phytoremediation improves
ecosystem services within the project area, which can mitigate climate-related impacts from flooding; improve
soil stability, organic carbon, carbon sequestration when enhanced with biochar, and nutrient cycling; and

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provide habitat for fauna (Simmer & Schnoor, 2022). Another significant advantage of phytoremediation is its
public acceptability; it is aesthetically pleasing and seen as a "greener" approach to achieving cleanup objectives
because it takes advantage of natural plant processes and saves money by requiring less equipment and direct
labor than traditional remediation techniques.

Disadvantages are mainly associated with the time it takes to reach target concentrations and longer-term
O&M, monitoring, and reporting requirements. Many of these disadvantages can be mitigated by enhancing
root zone mechanisms with nutrient- and microbial-impregnated biochar, a soil amendment. Moreover,
processes depend highly on local climatology and must be designed with local considerations in mind. These and
other advantages and disadvantages are summarized in Table 4.

Table 4. Advantages and disadvantages of phytoremediation

Category

Advantages

Disadvantages

O&M

The remedy is low maintenance, requiring
limited annual site work and scheduled long-
term maintenance.

Unforeseen site work may need to occur after
initial installation, based on unknown site
conditions such as severe weather or animal,
insect, or fungal damage. Seasonal plant removal
and disposal may also need to be considered for
perennial plants at the end of a growing season.

Public
acceptance

Public acceptance tends to be high because it is a
"green," low-tech, visually natural aesthetic
option.

The public may want a remedy that can reach
goals quickly.

Site

characteristics

Plants minimize erosion. Soil structure and
health are improved after vegetation
establishment. The remedy is not limited to
remote access areas.

Locations with high elevations may not be
suitable for plant growth. Poor soil conditions
require amendments or deeper plantings to
overcome unsuitable initial conditions.

Timeline

Timelines for remediation are like pump-and-
treat systems due to the spatial distribution of
plantings to interact with groundwater
throughout the site. Depending on the
contamination and site conditions, the timelines
for phytoremediation may range from 2 to 30
years or more after the vegetative cover is
established. Establishing vegetative cover in new
plantings typically takes one year for perennial
plants and shrubs and two or more years for
trees.

Phytoremediation can take significantly longer
than other remedial technologies to achieve site
goals because the remedy relies on establishing
well-developed roots and biomass to be
effective. The amount of time to reach
establishment largely depends on the plant
species, its size when planting, and proper care
during the establishment period.

How long does it take to work?

Phytoremediation timelines depend upon several factors, such as contaminant type, contaminant
concentrations, remediation area size, climate, depth of plantings, depth of contamination, and remedial
objectives (Gerhardt et al., 2017; Chirakkara et al., 2016). The simplified timeline in Figure 7 presents major
milestones in the process, from initiating pre-planting activities to achieving full operation of the
phytoremediation system.

Activities prior to planting (pre-Year 0) may include a remedial investigation or site assessment and site
characterization (depending on whether the area is a Superfund site). Year 0 includes all preparatory steps to
get the site ready for planting, including applying soil amendments and installing irrigation systems, if needed.
The first two years are focused on establishing a robust root system for the plantings, after which significant top
cover growth should occur. The entire process may last 30 years or more, depending on the stringency of the
site-specific remedial objectives.

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Years 15-30+

Remedial goals are met for
the site.

Remediation timelines depend
on contaminant type,
concentration, size of area,
climate, and interaction of the
roots with the contaminant.

Continuous monitoring and reporting

i i

Years

Ground cover density is
established.

Observable remediation of
contamination for established sites.

Surface soil remediation
begins with establishment of
root growth.

Observable decreases in contaminant
concentration can be detected before 10
years on sites when the roots establish sooner
within or near the zone of contamination.

Figure 7. General timeline for a phytoremediation project, from installing plants to meeting remedial goals

Source: RTI International, 2023.

Table 5 presents timelines to see significant remediation by selected contaminant groups. Remediation may
take one or few decades to remediate contamination in the vadose zone (Trapp et al., 2014). The estimated time
required to achieve remedial goals from a phytotechnology and operating conditions applied at one site cannot
necessarily be extrapolated to other contaminated sites specifically for sites with a mixture of contaminant
groups (Chirakkara et al., 2016; Hyman and Dupont, 2001). Gerhardt et al. (2017) note that "phytoremediation
of [petroleum hydrocarbons] PHC via rhizodegradation, particularly using microbially-enhanced systems ...
provides the best return on investment and is the closest to full acceptance globally."

No studies documenting a specific timeline to remediate explosives, dioxins and furans, and PFAS were
identified in literature reviewed by the authors of this document. Additionally, the timelines presented in Table
5 do not explicitly factor in optimization through the use of amendments (e.g., endophytes, bacterial genes). For
example, explosives such as TNT and RDX are phytotoxic and cannot be effectively treated by using conventional
phytoremediation, but can be remediated by introducing bacterial genes involved in the metabolism of TNT and
RDX (Doty et al., 2007; Rylott et al., 2006; Hannink et al., 2001).

Table 5. General range of time required to observe significant remediation of selected contaminants

Type of Contaminant

Timeline to Remediate

References

Explosives

Years to decades

No specific timeline was
identified in literature reviewed.

Dioxins and furans

Years to decades

No specific timeline was
identified in literature reviewed.

Heavy metals

5-15 years (phytoextraction)
1-5 years (phytostabilization)

Yan et al. (2020)
Salt et al. (1998)

Petroleum hydrocarbons (PHCs)

1-5 years

Doty et al. (2017): Gerhardt et
al. (2017 and 2009); Wenzel
(2009)

PFAS

Years to decades

No specific timeline was
identified in literature reviewed.

Complete site
assessment and
characterization
and define
remedial goals.

Site preparation and plant
and seed installation.

Groundwater extraction sites
begin remediation at the start of
irrigation and establishment of
root growth.

Trees begin reaching maturity.

Plant density is established.

Native and evergreen trees will establish
later than fast-growing options like
hybrid poplar. It may take 6 to 15 years to
reach maturity. If needed, remove dead
plantings for proper disposal.

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Type of Contaminant

Timeline to Remediate

References

Polychlorinated biphenyls (PCBs)

3 to 10 or more years

(range depends on plant species and whether
microbial or bacterial inoculants were
applied)

Aken & Doty (2009); Alkorta &
Garbisu (2001)

Radioactive contaminants

5-10 years

Pilon-Smits (2005)

VOCs, CVOCs, and SVOCs

Up to 15 or more years

Trapp et al. (2014); Doty et al.
(2007); site field studies as
referenced in Van den Bos
(2002)

Table note: The references including in this table are not exhaustive. Results of many field studies are not published for public
consumption. The range of timelines to remediate the selected contaminants depend on the site conditions, contaminant concentrations,
and plant efficiency. Optimal plant growth conditions throughout the timeline are assumed.

Two considerations that will affect the timeline to establish the vegetative cover of a phytoremediation project
are the ability to procure enough plants of the correct species and synchronizing delivery with the ideal planting
season. Typically, trees and tree poles will need to be procured in temperate regions by early December of each
year to ensure that size, type, and quantities are available to plant the following year. Site managers should
make sure to build in time to acquire vendors for specific plant types and amount needed in the schedule.
Installation of many plants can be completed year-round, but installation of trees and tree poles should occur in
early spring or late fall.

Stress from extreme weather, pests, phytotoxicity, high salinity, drought, foraging animals, and/or poor site
operation will extend the remedial timeline. Reducing stress on plants through regular maintenance will
decrease the remedial timeline. Planting species recommended for a given hardiness zone will increase the
ability of large plants to reach maturity and operate most efficiently. Growing seasons, as indicated in the U.S.
Department of Agriculture's (USDA's) plant hardiness zone map (Figure 8), range from 126 days to 290 days in
the continental United States. Trees in areas with longer growing seasons (Zone 8 and 9) will establish maturity
years before those in colder climates with short growing seasons (Zones 3 and 4). Temporary measures may be
required to protect young plants from pests and foragers while they are establishing themselves.

Plant rooting habits determine the surface area of remediation and therefore affect the timeline of remediation
based on interaction with the contaminant. Planting density should be increased based on desired above-ground
coverage to prevent bare spots, exposure of contaminants on the surface, and the desired root coverage and
depth in the soil.

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Hawaii

*

USDA Agricultural Research Service

U.S. DEPARTMENT OF AGRICULTURE

2023 USDA Plant Hardiness Zone Map

Oregon State
University

Mapping by the
PRISM Climate Group
College of Engineering
Oregon State University

Average Annual Extreme
Minimum Temperature
1991-2020

Temp (F) Zone Temp (C)

-60 to -50

m

-51.1 to-45.6

-50 to -40

m

-45.6 to -40

-40 to -30

m

-40 to -34.4

-30 to -20

nn

-34.4 to -28.9

-20 to-10

rn

-28.9 to -23.3

-10to0

..

-23.3 to-17.8

Oto 10

i * i

-17.8 to-12.2

10 to 20

m

-12.2 to -6.7

20 to 30

m

-6.7 to -1.1

30 to 40

r- i

-1.1 to 4.4

40 to 50

~LI

4.4 to 10

50 to 60



10 to 15.6

60 to 70

¦

15.6 to 21.1

Figure 8. Plant hardiness zones in the United States

Source: Modified from USDA, 2023. The most recent USDA map provides further resolution through 26
zones versus the 13 zones shown here.

Figure 9 presents the root-to-depth ratio of common and successful plantings used in phytoremediation. The
common names of the plants, from left to right, are poplar {Populus spp.); maiden grass, Chinese silver grass,
Japanese silver grass, susuki grass, or eulalia grass (Miscanthus spp.); alfalfa (Medicago sativa); brown mustard
(Brassica juricea); and barley (Hordeum vulgare).

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Depths of Roots and Spread
of Roots for Each Plant

20 feet bgs

Figure 9. Rooting depth and spread of roots for commonly used plants
Source: RTI International with Getty Images, 2023.

Figure note: The roots shown in this figure are illustrative and not to scale.

Hordeum
vulagre

Ground Surface

2 feet bgs

4 feet bgs

6 feet bgs

8 feet bgs

Selected case studies

Phytoremediation for remedial action has been implemented by the U.S. EPA and state and tribal environmental
agencies at many Superfund, RCRA Corrective Action, and other contaminated sites across the United States to
address a wide variety of contaminants. Table 6 presents a sample of phytoremediation applications at selected
sites.

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Table 6. Selected case studies of phytotechnology applications at Superfund sites

Site name and
location

Contamination,
media and
depth of
contamination

Land
area
(acres)

Application

Timeline

Status/results

Aberdeen Proving
Ground,
Edgewood, MD
(Superfund)

•	VOCs

•	Soil,
groundwater

•	0-3 ft bgs

1-2

Hybrid poplar trees.

Over 200 trees (primarily
hybrid poplars).

1997-
present
(2023)
26 years

Successful in capturing the
groundwater plume
contaminants.

Combustion, Inc.,
Denham Spring, LA
(Superfund)

•	VOCs, semi-
VOCs

•	Groundwater

•	~250 ft bgs

~3.5

6 tree stands of bald
cypress or sweet gum
trees (2001) with
cottonwood added in
2008, 2009, and 2013
(using TreeWell system in
2013).

2001-
present
(2023)
22 years

Effectively treating
groundwater
contamination;
concentrations of
toluenediamine and
endocrine disrupting
chemical have decreased.

Festival Pier,
Pawtucket, Rl
(Brownfields)

•	Arsenic (heavy
metal), PAHs,
petroleum
products

•	Soil,
groundwater

•	No data
identified for
depth of
contamination

~5

Grasses and trees in park
setting.

The site now features a
waterfront pedestrian
plaza, lighting, new
parking areas,
landscaping, a canoe/
kayak launching area and
an accessible boat ramp.

2014-
2015
~ 2 years

Properties in the former
industrial area have been
redeveloped into riverfront
public event and green open
space (grasses, trees) for
recreation. Wildlife has
returned. Stormwater
runoff remains a concern
from fertilizer use.

La Salle Electric
Utilities,
La Salle, IL
(Superfund)

•	VOCs

•	Soil,
groundwater

•	4-12 ft bgs

1.1

Poplar, willow, and bald
cypress trees.

About 1,000 trees
between 2 plots.

2002-
present
(2023)
21 years

Continues to degrade
contaminants in the
tetrachloroethylene (PCE)-
contaminated area.

Ryeland Road
Arsenic Site,
Heidelberg
Township, PA
(Superfund)

•	Metals

•	Soil, sediment

•	Surface

~0.2

10 plots of Chinese brake
fern: 5,000 ferns in 2009;
7,200 ferns in 2010;
additional ferns in 2011-
2014.

2009-
2014
5 years

Effectively remediated
arsenic in soil at or below
the 140 mg/kg cleanup goal
in half of the plots.

Sangamo Electric
Dump/Crab Orchard
National Wildlife
Refuge,

Carterville, IL
(Superfund)

•	VOCs

•	Soil,
Groundwater

•	0-3 ft bgs

2.2

Four plots with 2,675
plants/trees (150
sycamore whips, 700
cottonwood whips, 875
willow whips, and 700
poplar whips).

2010-
present
(2023)
13 years

Continues to remove
contaminant mass
(trichloroethylene [TCE],
other chlorinated VOCs,
PCBs).

(continued on the next page)

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Table 6 (continued). Selected case studies of phytotechnology applications at Superfund sites

Site name and
location

Contamination,
media and
depth of
contamination

Land
area
(acres)

Application

Timeline

Status/results

Ashland Inc.,
Milwaukee, Wl
(RCRA)

• VOCs, SVOCs

• Soil,
groundwater

• 10 ft bgs

0.4

485 hybrid poplars with
understory grasses.
Tree survival = 88%
initially, 99% after
replanting phytotoxic
areas.

2000-

present

(2023

although

results

data are

from

2004)

Trees have tripled in height
since planting. Roots
observed at 10 feet depth
during first growing season.
Subsurface aeration has
increased soil oxygen levels
from 5% to 15%.

Continues to remove
contaminant mass (BTEX,
TCE, gasoline, diesel fuel,
toluene).

Ensign-Bickford
Company, Simsbury,
CT

(Brownfields)

• Metals
(average lead
concentration
was 635
mg/kg)

• Soil

2.35

Soils were fertilized and
amended with dolomite
lime to adjust soil pH to
optimize plant growth
and metal uptake. Site
was mechanically seeded
with Indian mustard
(Brassica juncea).

1998

Plant growth was generally
good, although some areas
remained saturated and
thus exhibited poor plant
growth and lower biomass
yields. Lead uptake ranged
in Indian mustard from 342
mg/kg to 3,252 mg/kg
across three treatment
crops.

Loring Air Force Base
(AFB), Aroostook
County, Maine
(Tribal)

• Several PFAS

• PFOS is the
primary
contaminant
at 150 ppb

• Soil,
groundwater

n.d.

Fiber hemp plants in two
small-scale field tests.
Hard to scale up the
project because team
had to bring water to the
site for the plants;
available water on-site
was too contaminated to
use.

2019-
2020

(initial test
plots)

Field test
research is
ongoing

In 2019, several PFAS
accumulated in hemp
tissue; short-chain
compounds showed greater
bioaccumulation than long-
chain. In 2020, PFOS soil
concentrations decreased in
both plots.

Sources: Nason, Koelmel, et al., 2021; Nason, Stanley, et al., 2021; U.S. EPA, 2020.

What do I need to do after planting?

Operations and maintenance

A phytoremediation project does require periodic maintenance. An O&M plan should be developed based on
the contaminants being treated, site conditions, and the type of phytoremediation being used. During the initial
growing season, O&M should include increased site visits for watering, especially during times of high heat and
drought. O&M should also include an annual site visit completed by the phytoremediation and/or plant expert
to identify potential problems and/or to monitor ongoing issues. During the site visit, the plant's health and
growth should be evaluated and documented, along with corrective actions to be made during future visits.

Fertilizer, lime, and/or organic material may need to be applied to the site to maintain optimal soil conditions.
Inspection and repair offences and cages will prevent potential damage from animals and trespassers. Irrigation
monitoring, inspection, and repairs should be completed to ensure optimal delivery of water to the entire
system without clogging tubes and emitters (i.e., to avoid over- or underwatering). Pumps should be replaced if

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the pressure or flow rate do not meet design parameters. Mowing may be necessary to keep new plantings or
seedlings from being outcompeted by opportunistic native plants and weeds from the surrounding area. The site
should be retrofitted with additional plantings or seedings if mortality decreases vegetation density or the site is
not meeting remedial milestones.

Pruning large plants, shrubs, and trees is important to focus the plant's energy on healthy, growing portions.
Biomass waste disposal may be required when phytoextraction or phytostabilization is used. Phytoaccumulation
results in contaminated biomass and phytostabilization does not remove contaminants from the soil and may
result in a re-release of contaminants to the soil in the future (Onwubuya et al., 2009; Vangronsveld, et al.,

2009).

Biomass and wildlife considerations

While phytoremediation aims to clean up contaminated environments using plants, a potential negative impact
on wildlife (e.g., insects, birds, land mammals) can arise from contact with contaminated soil or their
consumption of plant parts (e.g., leaves, nuts, berries) that may hyperaccumulate contaminants (Gerhardt et al.,
2017; Jeyakumar et al., 2023). There may also be soil changes (e.g., pH changes, increases in organic acids)
during phytoremediation that can make contaminants more bioavailable to the food chain before they can be
remediated (Gerhardt et al., 2017). The potential impacts to wildlife in response to field-scale phytotechnology
applications have not been widely published, but should be considered when phytoextraction or
phytostabilization mechanisms are used, or if the contaminants are expected to accumulate in the plant parts to
levels that exceed critical threshold values for animals. An ecological risk assessment may be needed, and
extensive, long-term monitoring of the site may be required.

Biomass waste disposal

Biomass waste generated from pruning and other perennial die-off generally does not contain contaminant
concentrations requiring special waste disposal (e.g., as hazardous waste). However, select contaminants may
leach from fallen or pruned biomass (e.g., explosives [Das et al., 2015], PFAS) or may be re-released into the soil
when phytoextraction and phytostabilization processes are used (Hu et al., 2013; Mench et al., 2010). In these
cases, plant biomass produced from the process of phytoextraction may be classified as a RCRA hazardous waste
if it contains a listed hazardous waste or exhibits one or more hazardous waste characteristics (ignitability,
corrosivity, reactivity, or toxicity; 40 CFR 261). Pruned and fallen biomass may need to be collected or plants
removed, followed by proper handling and disposal, such as through incineration (Jeyakumar et al., 2023; Liu &
Tran, 2021). There are several suggestions in the literature for reuse or disposal of the contaminated plant tissue
(Kovacs & Szemmelveisz, 2017). Plants used to treat heavy metals will need to be tested and disposed through
standard practices (Kovacs & Szemmelveisz, 2017; Liu & Tran, 2001).

Incineration with proper ash disposal ensures that the contaminants in the plant biomass are not reintroduced
to the environment. If contaminants are not volatilized and remain in the ash, they must be further processed or
treated as hazardous waste, based on waste determination results (Gerhardt et al., 2017). If plants are
incinerated, it may be necessary to dispose of the ash in a hazardous waste landfill. The volume of ash from
incinerated plant biomass is less than 10% of the volume that would have been otherwise generated if the
contaminated soil itself were dug up for treatment and disposal (U.S. EPA, 1999).

Gerhardt et al. (2017) note that plant harvest should be done at or prior to the end of each growing season for
herbaceous plants in temperate and arctic regions. It may be several years before trees that accumulate high
concentrations of contaminants in bark or wood should be harvested (Gerhardt et al., 2017).

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The site managers must determine biomass risk levels and define biomass disposal practices before installation
based on known concentrations of contaminants, especially for sites where significant concentrations of certain
contaminants such as dioxins, furans, and PCBs occur, or when the remediation involves using hyperaccumulator
plants. Incineration as a solution for disposal of plant biomass may not be necessary if the contaminants of
concern are organic compounds that are phytodegraded in plant tissues.

Resilience considerations

Extreme weather events, such as floods and droughts, negatively impact many plants' establishment, growth,
and vitality. Designing with resiliency and using adaptive management will ensure a phytoremediation system's
success. Moreover, improving site soil in preparation for planting, before implementing O&M practices will
allow the soil to retain moisture under drought conditions. Emergent plants can be rooted in water to extend
above its surface, making them ideal for removing water contaminants in areas affected by rising water levels. In
areas with an increased risk of wildfire, mowing, removing vegetation, and establishing fire lines in the design
can minimize ignitable material and thus decrease the potential for damage in the event of a wildfire.
Incorporating native plants into phytoremediation design can increase resilience because the plants can more
easily adapt to the local changing weather patterns and climatic conditions, such as increased sun exposure,
increased winds, and increased/decreased rainfall. The introduction of mycorrhizal, plant growth-promoting,
contaminant-degrading, and/or endophytic bacteria has also been shown to increase plant resiliency. Finally,
reducing plant stress through regular maintenance like fertilizing, pruning, and adding ground cover (e.g., mulch,
clover and other low-growing vegetative cover) can increase their survival and success under stressful
conditions.

Long-term monitoring

Phytoremediation effectiveness depends on the type of contaminant, the plant species used, and the site
conditions. Monitoring is essential to ensure that phytoremediation is effective; however, the types of
monitoring needed on a phytoremediation site will vary. Common monitoring methods are listed below.

• Sampling soil and groundwater allows for the direct measurement of contaminant concentrations in the
matrix of concern.

• Analyzing plant tissue samples of contaminants or contaminant metabolites provides a line of evidence
of remediation. Plant tissues can be a collection of leaves, grass blades, and/or tree cores. Detection of
the contaminant or metabolites within plant tissues indicates that the plant interacts with and
translocates the contaminant from the target matrix.

• Examining root depth is another line of evidence indicating that the plants interact with the
contaminated matrix. Soil boring or potholing near the trunks of trees or within the plants of interest
visually verifies the depth of main and fine roots.

• Monitoring groundwater with lysimeters, for example, can help track changes in water levels and flow
rates. Decreased water levels or ground water flow rates indicate water uptake and usage by the plants.

• Probing to monitor soil moisture is used to determine irrigation schedules and infiltration rates.

• Using remote sensing techniques, such as aerial photography and satellite imagery, can help to monitor
the overall health of the phytoremediation site. Remote sensing can be used to track changes in plant
growth and soil conditions.

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• Sampling with microbial community samplers helps to identify additional remedial support from
microorganisms. Examples of microbial community samplers include the Bio-Trap Sampler (Microbial
Insights, 2013a), phospholipid fatty acids (PLFA) analysis (Microbial Insights, 2013b), and next-
generation sequencing. Microbial analyses, including quantifying contaminant-degrading organisms
and/or the functional genes encoding enzymes to catalyze biodegradation, can also provide evidence of
remediation or determine which amendments may enhance ongoing bioremediation (Taggart & Clark,
2021). Furthermore, identifying transformation products produced by microbes provides direct evidence
that bioremediation is occurring at the site. Additional information on microbial sampling methods can
be reviewed at ITRC's Environmental Molecular Diagnostics (EMD) Fact Sheets (ITRC, 2011).

• Evaluating for salinity, macro- and micronutrients, and organic matter is important to understand the
soil conditions. Healthy soil conditions will lower stress on the plant, improve vitality, and improve
growth. Soil samples can be collected and submitted to soil laboratories or local agricultural extension
programs.

• Measuring plant growth can provide a year-to-year evaluation of the plants' health. For grasses, ground
cover, and shrubs, growth may reach a maximum limit within a few years. For trees, growth in height is
expected over the first 5 to 10 years, with minimal girth increase. As trees mature, height is difficult to
measure, but tree trunk diameter will increase each year.

• Monitoring and inspecting vegetative cover density is important to ensure that exposure pathways to
contaminated soil are eliminated. Visual and quantitative measurements can determine whether
additional ground cover is needed.

Generally, monitoring is completed at least once a year for many parameters. More frequent monitoring may be
needed in some cases, such as when the site experiences excess rainfall or when there are concerns about
contaminants migrating off-site. The need for less frequent monitoring may also be evaluated during the high-
growth phase and before maturity of the phytoremediation system.

Lessons learned from field applications

Phytoremediation is a promising technology for cleaning up contaminated sites. Below are some challenges that
may need to be addressed at a given site before phytoremediation techniques are applied.

• Plants remove some contaminants more easily than others.

• Not all plants are equally effective at removing contaminants.

• Climatic, soil, and physiographic conditions can alter the effectiveness of phytoremediation.

• Phytoremediation can take a long time to be effective. Plants may take several years to fully establish
their root systems and remove significant amounts of contaminants from the soil.

• Careful monitoring, data management, and data analysis are critical to demonstrating progress toward
remedial objectives.

• Phytoremediation can be a cost-effective way to clean up contaminated sites. Still, the costs may vary
depending on the type of contaminant, the type of plant, and the climate and soil conditions.

• Forecasting future site conditions and usage is important to enhance the resiliency of the
phytoremediation design.

• Phytoremediation, especially using native plants, provides additional ecological benefits that need to be
considered and factored into cost-benefit analyses.

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Sustainability and co-benefits

Phytoremediation systems can provide benefits beyond remediation and ecosystem improvement. They can
beautify industrial and urban areas, restore previously disturbed areas, minimize erosion, provide shade,
increase stormwater infiltration, and combat climate change. Phytoremediation sites can also become public
access areas for dog parks, playgrounds, parks, sports and recreation areas, and community gardens after plants
are established (see Figure 10). With all of these possibilities, phytoremediation plots also have the potential to
mitigate environmental justice concerns such as unequal access to green space and nutritional produce, poor
stormwater management, poor air quality, and heat islands.

Education Learning Center

Dog Park

Trails

Playground

Nature Conservation Area

Community Garden

Sports and
Recreation Area

Public Park

Figure 10. Potential end-uses of phytoremediated sites
Source: RTi International with Getty images, 2023.

Sustainability

Phytotechnologies use natural processes to remove or decrease contaminants from the environment. Using
phytotechnologies is a more sustainable option than other remedial methods such as excavation and treatment.
In addition to tree plantings, system designs can incorporate other factors, including solar-power pumps for
irrigation; dense ground cover to choke out noxious weeds; biochar incorporation in the rootzone to optimize
rhizodegradation, sequestration of carbon, and overall plant health improvement; and rainwater capture to be
used for irrigation.

Ecosystem benefits

Phytoremediation can many provide ecosystem benefits, including:

Improved soil quality by adding organic matter, increasing water infiltration, and reducing erosion.
Increased biodiversity by attracting and supporting a variety of wildlife, including insects, birds, and
mammals.

Lower air pollution by absorbing pollutants from the atmosphere.

Increased stormwater infiltration and lower risk of flooding.

Decreased surface temperatures.

Decreased risk of vapor intrusion by intercepting gas within the soil.

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Carbon sequestration

At disturbed sites, the natural processes of soil and plant cycling, respiration, and terrestrial carbon
sequestration have significantly diminished if not ceased entirely (U.S. EPA, 2016). Established plants draw
carbon dioxide from the atmosphere during photosynthesis. Plants also cycle carbon dioxide through their roots
into the soil, using it for soil microbial respiration or storing it (i.e., sequestration). Incorporation of a soil
amendment, such as biochar into the design and application of phytoremediation not only enhances the
efficiency of phytoremediation but also increases the amount of carbon that is sequestered in soil. These
processes lead to lower greenhouse gas emissions into the atmosphere. There is also the additional benefit of
carbon emission avoidance from reusing organic materials that may have been destined for a landfill, where
their decomposition would emit carbon dioxide and methane. Tree systems that meet requirements set by state
and federal governments may also claim carbon offset credits at a typical rate of 10 tons of carbon per acre of
trees per year.

Is phytotechnology right for my site?

The primary considerations for determining whether a phytotechnology is a possible remedial alternative for a
site are:

• The type of contaminated media,

• The type and concentration of contaminants,

• The potential vegetation to grow at the site, and

• The vegetation's ability to achieve site-specific remedial objectives through at least one
phytotechnology mechanism identified in Table 1.

Table 7 presents key questions to help consider whether phytoremediation is appropriate. If all, or most (e.g.,
75%), of the questions can be answered with a "yes," then phytoremediation is likely feasible and should be
considered. All questions answered with a "no" or "unknown" should be further investigated. A comprehensive
decision-making process for evaluating whether phytoremediation is a viable option is included in Chapter 4 of
U.S. EPA's Introduction to Phytoremediation (2000).

Decision support tools, reviewed elsewhere (Cundy et al., 2015; Onwubuya et al., 2009), can be used to help
choose the most suitable remedial strategy for a site. Phytoremediation should be compared to other remedial
options in terms of effectiveness, cost, and time frame against the planned future site use. Additionally, a
feasibility study should be conducted to determine effective phytoremediation applications for the site.

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Table 7. Checklist for determining whether phytotechnologies are suitable

1

What contaminants have been identified for each medium at the site and at what concentrations? List each
contaminant here or on a separate sheet, along with the range of concentrations and the date the field data were
collected.

2

Has phytoremediation been proven to remediate the known contaminants?
If no, phytotechnologies may not be right for the site. Additional research and
conversations with experts about the specific contaminants and site conditions
may be needed. Continue to question 3 to document additional site conditions.

Yes

No

Unknown

2a

If yes, will the verified remediation plants grow with good vitality in the site's
climate?

Yes

No

Unknown

2b

If yes, does the site have concentrations that are below phytotoxic levels?

Yes

No

Unknown

3

Is the contamination within soil or water that is reachable by plant roots, or
within 0 to 8 feet below ground surface?

Yes

No

Unknown

3a

If no, can trees be installed in boreholes to meet deeper contamination?

Yes

No

Unknown

4

Will phytoremediation reach the desired remedial goal or closure requirements
within the timeline agreed upon by the client, regulatory agency, and/or
landowner?

Yes

No

Unknown

5

Does the site receive enough rainfall to sustain the healthy growth of plants?

Yes

No

Unknown

5a

If no, can irrigation be applied?
Comments:

Yes

No

Unknown

37

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For more information

ITRC Phytotechnology Technical arid Regulatory
Guidance and Decision Trees

EPA Clu-ln Phvtotechnologies



EPA Clu-ln EcoTools

EPA Clu-ln Phytotechnology Project Profiles

39

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Acronyms and abbreviations

AFB	Air Force base

Ag	silver

Al	aluminum

An	antimony

As	arsenic

BAF	bioaccumulation factor

BCF	bioconcentration factor

bgs	below ground surface

BTEX	benzene, toluene, ethylbenzene, and total xylenes

Cd	cadmium

CESER	Center for Environmental Solutions and Emergency Response

CVOC	chlorinated volatile organic compound

Cr	chromium

Cu	copper

DDT	dichlorodiphenyltrichloroethane

DNAN	2,4-dinitroanisole

EDTA	Ethylenediaminetetraacetic acid

EMD	Environmental Molecular Diagnostics

ETSC	Engineering Technical Support Center

EPA	United States Environmental Protection Agency

Fe	iron

ft	feet

GLNPO	Great Lakes National Program Office

Hg	mercury

HMX	high melting explosive

ITRC	Interstate Technology Resource Center

Kc	equilibrium concentration of contaminants

log Koc	the soil organic carbon-water partition coefficient

mg/kg	milligrams per kilogram

mg/L	milligrams per liter

Mn	manganese

Ni	nickel

ng/g	nanograms per gram

NTO	nitrotriazolone

OLEM	Office of Land and Emergency Management

O&M	operations and maintenance

ORD	Office of Research and Development

PAHs	polycyclic aromatic hydrocarbons

Pb	lead

PBDEs	polybrominated diphenyl ethers

PCBs	polychlorinated biphenyl compounds

PCE	tetrachloroethylene

PCP	pentachlorophenol

PFAS	perfluoroalkyl substances

PLFA	phospholipid fatty acids

RCRA	Resource Conservation and Recovery Act

RDX	an explosive organic compound with the formula (CH2N202)3

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Phytotechnology Technology Profile

RPM

Remedial Project Manager

SCMTSC

Site Characterization and Monitoring Technical Support Center

Se

selenium

SPME

Solid-phase microextraction

spp.

species

SVOC

semivolatile organic compound

TAB

Technology Assessment Branch

TIFSD

Technology Innovation and Field Services Division

TCE

trichloroethylene

TF

translocation factor

TNT

trinitrotoluene

TSCD

Technical Support Coordination Division

Ur

uranium

USDA

United States Department of Agriculture

VOA

volatile organic analysis

VOCs

volatile organic compounds

Zn

zinc

PFAS and Compounds

PFAS

per- and polyfluorinated substance(s)

FhxSA

perfluorohexane sulfonamide

FOSA

perfluorooctane sulfonamide

FOSAA

perfluorooctane sulfonamide acetic acid

FOSE

perfluorooctane sulfonamide ethanol

FTSA

fluorotelomer sulfonic acid

PFBA

perfluorobutanoic acid

PFBS

perfluorobutane sulfonate

PFCA

perfluoroalkyl carboxylic acid

PFDA

perfluorodecanoic acid

PFHpA

perfluoroheptanoic acid

PFHxA

perfluorohexanoic acid

PFHxS

perfluorohexane sulfonate

PFNA

perfluorononanoic acid

PFOA

perfluorooctanoic acid

PFOS

perfluorooctanesulfonic acid

PFDS

perfluorodecane sulfonic acid

PFHpA

perfluoroheptanoic acid

PFPeA

perfluoropentanoic acid

PFPeS

perfluoropentanesulfonic acid

PFSA

perfluoroalkane sulfonic acid

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This document was developed as literature review. The document's development followed the requirements
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