1. Phytoremediation: A sustainable alternative to traditional
brownfield remediation methodology
Dennis P. Poole
A Thesis
Submitted in Partial Fulfillment of the
Requirements for the Degree of
Master of Arts in Biological Sciences: Global Sustainability
Department of Biology
Central Connecticut State University
New Britain, Connecticut
December, 2014
Thesis Advisor
Dr. Clayton Penniman
Department of Biology

2. i
Abstract
The growing brownfield epidemic has to be addressed in such a way as to not further
promote or produce secondary problems in the future. Conventional remediation methods
can prove to be extremely costly due to their dependency on labor and heavy machinery.
Secondly, many of these methods can pose serious health and environmental risks at any
point during extraction, transportation or disposal. Due to the risk factors and the
unpleasant aesthetics associated with the conditions of these sites during remediation
along with the presence of heavy machinery, conventional remediation methods are also
lacking in public support. Due to compounded environmental, economic and
socioeconomic issues surrounding brownfields and conventional remediation, a more
sustainable approach is critical. In response to this, extensive research is being directed
into how plants break down or store an impressive array of toxic substances. Known as
phytoremediation, this alternative method is gaining considerable support due to
competitively lower cost and greater community support. In this paper I have outlined the
benefits and detriments of the most commonly used conventional remediation methods
and compared them with phytoremediation practices in terms of sustainability. Based on
review articles and case studies, phytoremediation methods are convincingly the more
sustainable choice due to a variety reasons. Despite this, phytoremediation methods
represent only a small fraction of the projects currently under way. Critics point to factors
such as prolonged time tables for growth, geographic applicability, and climatic effects as
the pitfalls of phytoremediation. However, research into enhancing phytoremediation
through the use of chelators and genetic engineering can greatly improve results.

3. ii
Table of Contents
Title page
Abstract i
Table of Contents ii
Introduction 1
Chapter 1: How did we get here 6
and what are we doing about it?
Chapter 2: The factors of sustainable 11
brownfield redevelopment
Chapter 3: Conventional remediation methods: 16
A solution to the problem or a problem with the solution?
Chapter 4: Phytoremediation methods: 27
Digging deeper for a more holistic approach.
Chapter 5: How do phytoremediation and conventional 48
remediation methods fit into a sustainable framework?
Chapter 6: Discussion and conclusions: 52
Is there a right answer?
Acknowledgements 55
Bibliography 56
Appendices 64

4. 1
Introduction
Within the last thirty years, rapid innovations in industry and technology have increased
humanity's ability to extract and process natural resources. Simultaneously, newer
technologies render previous technologies and their facilities obsolete. As a result of their
obsolescence many owners of the properties and their respective businesses become
destitute resulting in business foreclosure or bankruptcy. In many cases these facilities
may house potentially hazardous or toxic chemicals. Over time, inadequate storage may
be compromised resulting in further spread and dilution of onsite contaminants. These
conditions result in high remediation cost and increased liabilities in the form of removal,
transportation and disposal of the contaminated material for those who own the facilities
or the prospective buyers who wish to reuse them. Due to these preexisting conditions,
many potential investors of these properties seek out undeveloped land also known as
greenfields, which may in time result in similar outcomes, thus furthering the problem.
The EPA refers to developed sites as brownfields and defines them as real property, the
expansion, redevelopment, or reuse of which may be complicated by the presence or
potential presence of a hazardous substance, pollutant, or contaminant (USEPA, 2013).
In the United States there are an estimated 425,000 sites constituting approximately 5
million acres, an area equivalent to the space being used today by 60 of our most
populated cities (USHUD, 2013). A similar report released by the European
Environmental Agency surveyed over 1.8 million brownfields in Europe (Karachaliou
and Kaliampakos, 2011). With the United States and Europe representing less than
twenty-five percent of the inhabited land on earth, this easily places global estimates of

5. 2
contaminated sites into the millions. However, this estimate could increase drastically in
the near future if developing nations throughout Asia, Africa and South America continue
to follow the industrialized path pioneered by the United States and Europe.
The threat these sites pose to the overall quality of life are complex. Onsite contaminants
can be found anywhere and can be comprised of any combination of organic and
inorganic contaminants. Most commonly when we think of brownfields the terrestrial
landscape comes to mind. However, there are many situations in which contaminants do
not restrict themselves to any one substrate. Many contaminants may mobilize, change
state or even restructure their chemical makeup to affect the air as well as ground and
surface waters. Where and how onsite contaminants concentrate themselves can also
present a challenge both within abiotic processes and within biotic food webs. Once
mobilized, these chemicals may spread out and be diluted. They may then be consumed
and biomagnified within food webs (Juwarkar et al., 2010). While the majority of us are
aware of the hazards these sites pose to the environment and human health, many
communities surrounding brownfields fall victim to secondary economic degradation,
which can further result in tertiary impacts upon the quality of social well-being with
these communities. An article by Litt et al. (2002) published in the journal Environmental
Health Perspectives, showed strong correlations in South Baltimore pertaining to
brownfield proximity and density to a host of economic, social and public health
problems (Appendix A). Economic disparities among households where brownfields
were present showed decreased family incomes, property values and home ownership
along with increased percentages of poverty. Relationships between social inequality and

6. 3
brownfield proximity included increased high school dropout rates, greater percentages
of minority households living closer to brownfield properties and more working class
citizens. The wide spectrum of correlations pertaining to detrimental public health effects
to those living closer proximity to brownfields were extensive, with increased rates of
cancers, respiratory illnesses, influenza, heart disease, strokes, diabetes and chronic
obstructive pulmonary disease (COPD) (Litt et al., 2002).
The total list of organic and inorganic contaminants potentially responsible for these
effects is extensive. Some sites may contain radioactive substances or heavy metals while
others may be contaminated with excessive pesticides, nutrients or petroleum-based
hydrocarbons. The totality of contaminants may be too long to list, however, the EPA has
categorized them
(Figure 1). In many
cases there is usually
more than one
contaminant present;
making the process of
remediation even more
complicated. Traditional
remediation of brownfields usually involves the use of heavy machinery and/or chemicals
to either immobilize, neutralize, or remove the contaminated material from the property
with the soil where it can be further processed or disposed. However, these methods
usually come at a high cost for site developers and investors in the form of extensive

7. 4
labor, machinery and liabilities (Witters et al., 2012). As a result of these factors there
has been an increased impetus for developing more sustainable land remediation,
redevelopment and management practices. Among them, phytoremediation is emerging
as a promising alternative due to its ability to remediate a wide variety of contaminants at
relatively lower cost and lower liability when compared to the traditional normative of
current remediation practices (Lee, 2013).
Still, many researchers, critics and analysts point out that this technology is still in its
infancy and further development to bring phytoremediation to the scale of other
technologies will require much time (Mench et al., 2010; Oh et al., 2013; Schwitzguébel,
2002). As the EPA's 2000 report of innovative remediation technologies points out
(USEPA, 2000),
phytoremediation
field-scale
demonstrations
represented less than
three percent of the
total technologies
being implemented
(Figure 2). Due to the exponential growth and development of humanity over the last
hundred and fifty years, resource availability is becoming a greater issue.
As we are coming to terms with this fact, the question of how we are going to sustain
ourselves with the various ecosystems we depend on is unavoidable. As a result of this

8. 5
awareness, the idea of sustainability as an underlying practice in both business and
resource management is growing. In 1987 the United Nations defined sustainability in
terms of development that meets the needs of the present without compromising the
ability of future generations to meet their own needs (World Commission on
Environment and Development, 1987). Sustainable remediation and redevelopment work
with a three pillared system that addresses the needs of the environment, the economy
and that of social equity as well as the interdependent relationships. Given the complexity
and magnitude of the brownfield epidemic more sustainable land management and
remediation practices need to be developed and employed in order to adequately address
these issues.
In the following chapters of this paper I will quantify and compare the benefits and short
comings of conventional remediation and phytoremediation from the stand point of
sustainability. Unlike traditional business practices which are meant to serve an economic
bottom line to the sites investors and developers, sustainable remediation practices also
address factors pertaining to the quality of environment as well as issues which protect
the social equity of the surrounding communities. The purpose of this literature review is
to compare phytoremediation and conventional remediation practices and determine how
they fit within the constraints of sustainability's three pillar system. Secondly, this paper
will further serve to help define the boundaries of present day sustainable development.

9. 6
Chapter 1: How did we get here and what are we doing about it?
The legacy of the industrial age
Within the past two-hundred years continuous discoveries have been made in the areas of
agriculture, manufacturing and technology. Advancements in agriculture pertaining to
fertilizers, pesticides, antibiotics, genetic engineering and more sophisticated machinery
have enabled farms to produce far more food than ever before. Our rapid development
over these broad areas however has not come without serious consequences. The practice
of factory farming along with the excessive use of pesticide and fertilizer amendments for
crops has come to dominate the agricultural landscape (Wang et al., 2012; Xing et al.,
2012). Improper over-irrigation of these crops mobilizes the amendments due to runoff
and ground water penetration, enabling hypoxia and eutrophication while simultaneously
raising soil salinity, eventually rendering the soils incapable of supporting plant growth.
Over-irrigation can also result in acidifying soils, which has been observed to mobilize
many metals such as aluminum which is also toxic to most plant growth (Li et al., 2014).
Along with these metals the acidic media can also mobilize pesticides which can persist
in soils long after their initial application and bind to soil particles (Castillo et al., 2011).
If not remediated these pesticides build up and can be transported throughout the food
chain (Castillo et al., 2011).
Many other pollutants, both organic and inorganic, can affect almost any part of the
ecosystem where they reside, possibly damaging the ability of that ecosystem and its
resident organisms to maintain their natural functions (Juwarkar et al., 2010).

10. 7
Fortunately, within the last four decades many highly developed economies are beginning
to scale back their industrialization practices. Where vacant brownfields were seen as
development problems, they are now being recognized for their potential to enrich the
quality of the communities that host them (Adams et al., 2010). There are numerous
published articles that have pointed to the potential benefits these sites could have to their
surrounding communities (Hula and Bromley-Trujillo, 2010). Some of the potential
benefits of restoring these sites besides the overall improvement to neighborhoods
include: increased property values, reduced urban sprawl, new jobs and pathways to
sustainable development (Hula and Bromley-Trujillo, 2010).
Government action and initiatives
Regardless of the method of remediation, contaminated sites are rarely, if ever,
remediated without some sort of government assistance. Legislation focused towards
liability, maintenance and incentives for brownfield redevelopment occur at every level
of government in the United States. Most notable was the federal government's institution
of the Superfund or the Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) and the National Priorities List (NPL) in 1980. This legislation
raised over 1.5 billion dollars in taxes from chemical and petroleum industries used to
further remediate deserted brownfield properties (Sedman et al., 1992). However
CERCLA also drew significant criticism due to its heavy focus on liability (Alberini et
al., 2002).

11. 8
Solitare and Greenberg (2011) stated that due to CERCLA's heavy focus on liability most
redevelopment of these sites came to a halt due to economic penalties and legal concerns.
Due to these trends the legislation was amended with the Superfund Amendments and
Reauthorization Act (SARA) in 1986. Part of this initiative involved later eliminating
sites from the Comprehensive Environmental Response Compensation and Liability
Information System (CERCLIS) in 1997 which enabled site developers, investors and
insurance agencies to redevelop sites by reducing the cost associated with liability. Sites
that were associated with CERCLIS could easily be moved to Superfund or the National
Priority List where the likelihood of lengthy and expensive court battles could ensue
indefinitely (Solitare and Greenberg, 2011). This was also accompanied by the
Brownfields Assessment Demonstration Pilot program initiated in 1995 which helped to
fund select projects for nearly all aspects of redevelopment except the clean-up itself.
In terms of sustainability, the present and future effects of this program and its
development address every pillar of sustainability. While not only acknowledging the
economic pitfalls associated with cost of assessment, insurance and the remediation itself,
the pilot program adjusted the priority of funding to applicable communities by order of
social justice. To this effect, it awarded funding to projects based on locations where
certain socio-economic factors needed to be most significantly addressed, such as:
increased poverty, unemployment, per capita income, education and home ownership
(Greenberg and Hollander, 2006). From initiation of CERCLA in 1980 to the reformation
of the pilot program in the 1990s the federal government has been consciously and
actively taking a sustainable stance against the brownfield sprawl.

12. 9
By addressing the social, economic and environmental factors of the brownfield epidemic
the federal government influences developers to be more conscience and innovative
while simultaneously enabling them to employ more effective and efficient
redevelopment strategies through economic and educational programs. In 1994 the
Brownfield Tax Incentive further encouraged redevelopment of these sites by enabling
financial deductions within the same year of a remediation. In doing so, the federal
government effectively offered a four to one return for private investment. This occurred
in the form of incentives accumulating to 1.5 billion dollars enabling the private sector to
invest an estimated six billion dollars which would facilitate the cleanup of
approximately 14,000 eligible brownfield sites (USEPA, 1997a). Later in 2002, this was
accompanied by the Brownfield Revitalization and Environmental Restoration Act which
provided a buffer against fines incurred under CERCLA through liability while offering
financial support for initial steps prior to remediation such as assessment, characterization
and planning (Solitare and Greenberg, 2011).
As well as the federal government, there are various policies implemented at the state
level which have addressed this issue in terms of both necessity and sustainability. Much
like at the federal level, state policies also go through a continuous gauntlet of mixed
criticisms that shape the direction and effectiveness of brownfield remediation. As an
example, a case study in the State of Michigan identifies the steps taken at the state level.
The State of Michigan has instituted many changes through state legislation and
executive orders noting qualitative declines in most sites but noteworthy progress at
others (Hula and Bromley-Trujillo, 2010).

13. 10
When focusing upon individual communities these authors make the case that the single
most important factor towards community renewal begins with brownfield remediation
programs. However, regardless of the decreased value of these properties, reconstruction
of these sites is still avoided due to legal constraints and the overall cost of the
remediation itself (Hula and Bromley-Trujillo, 2010). They further point out that it is
fundamental for urban communities in Michigan to have brownfield redevelopment
programs in place in order to facilitate private investment. Some of the factors that
contribute to the efficiency in which private companies can work with these properties
include the restructuring of remediation laws, tax credits and lowered interest on loans for
redevelopment. While ideally state and federal programs should work together in order to
maximize the efficiency and effectiveness of remediation, Solitare (2005) finds that the
federal government's stance on brownfields as an environmental issue, effectively turns
communities away from taking part in the redevelopment of these sites. Hula and
Bromley-Trujillo (2010) state that a significant amount of research indicates that focusing
upon individual sites may be the wrong direction and that examining the infrastructure of
entire districts may lead to more significant changes in areas where large numbers of
brownfields are located.
In 2000, Michigan broadened its definition of brownfields to include "functionally
obsolete" structures so that assistance may be applicable to properties where toxic or
harmful substances may or may not be present (Hula and Bromley-Trujillo, 2010).
Secondly, the state enabled exemption from liability for new owners by creating and
mandating a form known as a Baseline Environmental Assessment (BEA) which new

14. 11
owners file with the Michigan Department of Environmental Quality (MDEQ). This
guaranteed that the new owners of a site would not be held liable for preexisting
conditions on a site while still enforcing legal action towards previous site owners
responsible for the original contamination (Hula and Bromley-Trujillo, 2010). The
assumption behind this legislation is that by decreasing the necessity of public assistance,
developers would seek out private investors. It is highly suspect that these efforts were in
direct response to the previous federal regulatory efforts (Hula and Bromley-Trujillo,
2010).
Chapter 2: The factors of sustainable brownfield remediation
Before getting into the application of sustainability to remediation, it is important to
identify the steps of the remediation process itself. As Juwarkar et al. (2010) explains, it
is fundamental to identify onsite conditions before implementing a remediation method.
The authors further explain that there are three main steps to the remediation process.
First is identifying the contamination on-site; is it one source or many? Is the
contamination organic, inorganic or both? Second is identifying the nature of the
contamination. What are the conditions of containment on the site? Is the contamination
inert, volatile or mobilized? Is it a threat to the surrounding community or ecosystem?
How long has the contamination been present? It is from these initial assessments that
the third step, the method(s) of remediation can be chosen.

15. 12
Traditionally, brownfield remediation projects were viewed predominantly as
environmental problems. However, in order for brownfield redevelopment to be
considered sustainable it has to address the requirements of many different parties in the
areas of economics, social justice and environmental concerns (Appendix B).
Another important quality of sustainable brownfield remediation is that its effects are
present over the long term and that it does not provide only a quick fix that deteriorates
over time making problems worse for future site owners or their surrounding
communities. Therefore, based on the three-pillared system of sustainability an ideal
sustainable remediation method would have the following characteristics:
1. It would promote or enable the site to be biologically productive (Mandelbaum et
al., 1995).
2. It would not leave any secondary contaminants (e.g., detergents or solvents)
(Ward, 2003).
3. It would be aesthetically acceptable to the surrounding community (Doick et al.,
2009).
4. It would not pose a danger or threaten the surrounding community by exposing
them to on-site contaminants (Schädler et al., 2011).
5. It should be affordable (Grommen and Verstraete, 2002).
6. It would offer or be applicable for economic incentives to developers and
investors (Doick et al., 2009).
Inversely, unsustainable remediation methods would include such qualities as:
1. Sterilizing or rendering the site as biologically unproductive.
2. Leaving onsite contamination that may incur future financial cost to site
developers and prolong environmental hazards to the surrounding community.
3. Aesthetically displeasing site conditions.
4. Factors that put the surrounding community at risk of exposure to contaminants.
5. High labor and equipment expenses.
6. Increased liability.

16. 13
Environmental standards and biological productivity
Adequately addressing the environmental pillar is actually more complicated than simply
removing contaminants or rendering them inert. It is important to note that the three pillar
system of sustainability is more hierarchical. That is to say that while social and
economic issues are dependent upon the quality of the surrounding environment and the
resources it has to offer, it does not necessarily work in the reverse order, simply put the
rest of the Earth is not dependent upon the continued existence of the economy or people.
Therefore, defining how brownfield remediation can be environmentally sustainable from
an anthropocentric perspective is complicated, especially when attempting to give
somewhat equal weight to the economic and social factors involved.
The most obvious question is, does the form of remediation neutralize, remove or render
inert the resident contamination? From this point, the next concern is the state of the
abiotic resources on and around the site in question. After remediation, are the soil, water
and air in and around the property still biologically productive? This is very important
because some techniques may remove or destroy contaminants along with soil nutrients
essentially eliminating biological productivity of plants, fungi and other organisms. This
renders redeveloped sites biologically unproductive, creating further problems in the
future.

17. 14
Economically feasible guidelines for site developers
From an economic standpoint the remediation and redevelopment of a property has to be
financially feasible for investors, site developers, property holders as well as state and
federal government organizations where public assistance is required. Adams et al.
(2010) explains that in order for there to be any substantial ground work in brownfield
development these sites have to go beyond feasibly affordable to lucrative investments
for the private sector, a point which he further concludes can be accomplished through
thoughtfully calculated public policies. Other factors that increase the potential
profitability of these sites for investors involve the state of transportation in around the
area as well as enhancements to the surrounding community (Meyer and Lyons, 2000).
Hula and Bromley-Trujillo (2010) combined these factors and found that the probability
of redevelopment of these sites increased with efficient transportation around the site and
cooperation among private businesses and governmental agencies.
The most significant factor to financing of the remediation process pertains to the type of
contamination. While organic contaminants may be broken down or altered, toxic heavy
metals and metalloids cannot (Juwarkar et al., 2010). Conventional remediation strategies
for the removal of inorganic contaminants such as excavation or land filling can be
exceptionally expensive and cause site developers to seek alternative methods of
contamination removal (Juwarkar et al., 2010). Another significant common factor
among many brownfield sites is that they are situated in densely built up locations
(Juwarkar et al., 2010). In cases where conventional excavation may need to be

18. 15
employed, cement and asphalt can increase the workload on heavy equipment which
increases the overall cost. These costs can also be compounded by contamination that has
seeped into the subsoil or ground water to the point where excavation is no longer an
option due to the increased cost of transporting vast amounts of substrate and treating it
off site (Juwarkar et al., 2010). As a result of the financial setbacks associated with
recurring complications, extensive research has been conducted towards the improvement
of every stage of the remediation process, from the accuracy of the initial assessment to
the reuse and recycling of the substrate.
Social equity through process transparency
Issues encompassing social equity are inseparable from the remediation process and have
historically shaped the process through liability, community support and subsequent
regulation. One of the key issues concerning the remediation process involves
transparency (O'Reilly and Brink, 2006). The communities encompassing brownfields
need to be involved and aware of the risk as well as the potential benefits. Many sites
have their contamination trapped within deeper soils making excavation increasingly
difficult. Once reached the contaminated media surrounding the communities can expose
people to health hazards, deterring further development through lack of public support
(Juwarkar et al., 2010). In order for a remediation technique to be considered socially
sustainable it has to be accepted by the surrounding community and put them at as little
risk as possible. Additionally, the process should not hinder the efforts of any future or
potential owners.

19. 16
Chapter 3: Conventional remediation methods: A solution to the problem or a
problem with the solution?
The benefits and detriments of conventional remediation methods and technologies
Up until the late 1990s traditional remediation techniques mostly involved excavation
and land filling. Since then, numerous conventional and non-conventional methods of
remediation have been researched and employed. A majority of the remediation
techniques used today involve conventional technologies for some part of the remediation
process (US EPA, 2000). Conventional remediation methods involve the use of heavy
machinery and/or chemical amendments and require a significant amount of labor.
Within the last thirty years conventional remediation strategies and technologies have
grown significantly. The methods explained in this chapter are excavating, soil washing,
solidification/stabilization, thermal desorption, in situ oxidation, soil vapor extraction,
capping, landfilling, and incinerating.
Excavation
Almost all brownfield sites require excavation to some extent. This involves the removal
of the contaminated soil, where afterwards it can be treated using other remediation
techniques or placed in a regulated landfill where the soil is left to natural attenuation.
The benefit of this option is that it provides a quick and simple solution that fits within

20. 17
the time frame of most development projects. In the case of inorganic metals that cannot
be broken down, in situ excavation may be the only initial option.
However, the excavation method of contamination removal can be extremely costly due
to the high cost accrued from labor and equipment. This is especially true in densely
populated urbanized areas where physical barriers such as concrete can complicate the
excavation process or where the contaminated material is deep within the soil (Juwarkar
et al., 2010). A publication from the EPA in 2000 showing the comparative cost of
phytoremediation vs. conventional methods to clean up an abandoned magic marker
factory estimated a 50-80% difference when comparing final cost (Table 1).
This method also entails significant health and environmental risks to those in charge of
removing and transporting the contaminated material once it is exposed to open air
conditions (Juwarkar et al., 2010). Communities that reside near the point of extraction as
well as those where the contaminated material must be transported through are also at
risk, which incurs insurance and liability costs for site developers. Depending upon the
extent of contamination there is also the biological productivity of the soil to consider.
Once the soils of a site are disturbed or removed on a large scale, microbial and
invertebrate activity that contribute to soil nutrition and oxygenation may also be

21. 18
detrimentally affected. Another recurring concern of communities towards excavation is
the aesthetics of these projects once they are under way. Many people complain about the
noise, appearance and diesel fumes of the equipment.
Capping
This method of
remediation is used in
order to prevent
precipitation from
percolating into soils
and further mobilizing
contaminants within
subsurface soils and is
used in situ and in
many land fill projects.
In doing so, these
systems can reduce the probability of contamination entering ground water (USDA,
2014). In the case of many organic substances, caps also allow contamination to break
down through biological processes associated with natural degradation by various
microbial and fungal organisms (Hartley et al., 2012). Usually caps are composed of
multiple layers that vary in composition depending upon the conditions on site (USDA,
2014). On average caps are composed of a vegetative layer to provide stabilization for the

22. 19
surface, and a layer to facilitate drainage and one or more low permeability layers to
prevent further percolation into the contaminated area (Figure 3) and a layer for venting
gas to compensate for gas buildup during decomposition. Presently, many capping
projects use geotextiles as their permeable layer since they are able to allow drainage
while simultaneously filtering out contamination (USDA, 2014). Some of the other
benefits of this method include the reduced probability of burrowing organisms
transporting contaminants to the surface. Capping also effectively reduces exposure in
contrast to excavating or dredging due to the reduced factors of handling, treatment and
disposal of contaminated material (USDA, 2014). The two major concerns of whether or
not developers would choose to use a cap as part of the remediating process are the cost
and availability of capping material and the projected rates of ground water flow (USDA,
2014). Another significant concern is whether or not the reduced long-term risk of the
project compensates for the habitat disruption during installation.
Ex situ landfilling and incineration methods
If contaminants cannot be broken down in situ then they must be disposed of or
processed ex situ in such a way that does not pose a threat or cause further harm to
communities or the environment. Landfills are most likely one of the oldest and most
commonly used method of disposal and ex situ remediation (Jones et al., 2006). While
this does provide an alternative location for the contaminated material it does not resolve
the problem in cases where the contamination cannot be broken down through natural
attenuation. If these sites are unregulated or irresponsibly maintained the impacts to

23. 20
public health and the environment can be considerable. Many instances in recent history
have been documented where leachate from landfill sites has entered aquifers and other
sources of drinking water (Beeman and Suflita, 1987). The two primary issues that
surround improperly maintained landfills are the buildup of potentially explosive gasses
and seepage of liquid leachate (Jones et al., 2006). These sites are host to a plethora of
contaminants both in the air and as underground ground water plumes. Some of the
potentially hazardous outputs of landfills include of NH4
+
, BOD, COD, Na+
, and Cl-
(Jones et al., 2006). If left unchecked landfills can produce and release these
contaminants for decades, manifesting unforeseeable problems to the environment and
the communities in which they reside (Jones et al., 2006). Probably the most famous
incident of this type occurred at the Love Canal in upstate New York during the 1960s
and 1970s. Here the City of Niagara Falls bought land which was known to be a land fill
site for chemical waste from the Hooker Electrochemical Company. In the years
following the purchase, high incidents of birth defects, nervous disorders and other
physical abnormalities were documented along with random environmental incidents
such as sink holes opening to expose drums of waste and reportedly strange-colored
fluids with noxious odors bubbling up from the ground, sometimes in basements of
people's homes (Hernan, 2010). It is due to historical accounts like these problems that
many view landfills with hostility. Secondary to the possible environmental impacts of
these sites are the aesthetics (Juwarkar et al., 2010). Recent innovations to landfills have
incorporated geotextiles to capture toxins and prevent leaching into surface and ground
water. While these sites present problems to the surrounding soil and groundwater they
also affect the surrounding air quality. In the United States 40% of total methane

24. 21
emissions come from landfill sites (US EPA, 2013). Also, innovations in active gas and
leachate collection have not only significantly reduced this output, but have managed to
recover 300 billion cubic feet of land fill gas, approximately half of which is estimated to
consist of methane and is converted to reusable energy in excess of over 900 megawatts
per year which is
enough to power
approximately
750,000 homes
(Figure 4) (US EPA,
2013).
The other ex situ
option is
incineration. While
historically this
method of disposal
produced vast
amounts of air-borne pollution, trends in air quality regulation are transforming
incineration methods into more environmentally compliant means of disposal (Freed et
al., 2004). With new filtering technologies many of the harmful toxins can be captured
while the combustion process itself can be used for energy. However, in many
developing countries where air quality regulation is loosely regulated or nonexistent and
the technology is still unavailable or economically unfeasible air pollution resulting from
incineration is still a significant problem (Juwarkar et al., 2010). It is also important to

25. 22
point out that recent research into these ex situ methods of remediation are also being
combined with phytoremediation methods (Oh et al., 2013). In laboratory experiments,
Indian mustard (Brassica juncea) and sunflowers (Helianthus annuus) have demonstrated
the ability to tolerate and store large quantities of toxic heavy and radioactive metals (Oh
et al., 2013). These metals were then separated and recollected through an incineration
process so they could then be sold or reused for further profit (Pilon-Smits, 2005; Raskin
et al., 1997).
In situ soil washing, solidification and stabilization
The EPA defines soil washing
as using liquids and a
mechanical process to scrub
soils (Figure 5) (US EPA,
1996). Prior to scrubbing,
filters are used to separate
variously sized particles from
fine clays to larger coarse
gravels. Due to the fact that
most contaminants tend to bind to smaller particles this effectively concentrates the
contamination into a smaller portion of the substrate where they then can be removed and
either disposed of in a landfill or incinerated (US EPA, 1996). The most important factor
in this process is that it reduces the amount of contaminated material that needs to be

26. 23
transported off site. This significantly reduces costs related to transportation. However,
this process can also run into problems when soils consist of relatively similar grain size,
so this process not applicable to many sites. Like many other physical and mechanical
methods, soil washing also greatly disturbs the soils and unavoidably destroys any
biological activity still in the soil that could naturally attenuate contamination within the
soil (Dickinson, 2000).
There are many situations where remediation or removal may not be an option.
Depending upon the type of contamination or the site's location, sometimes containing
the contaminants may be a temporary, intermediate step. This method incorporates the
use of reactive chemical amendments in order to bind the contamination to the soil. In
doing so the contamination is prevented from further spreading off site and by doing so
reduces exposure and bioavailability (Hartley et al., 2009).
Thermal desorption
This method involves
the use of low levels of
heat to volatize and
mobilize contaminants
in soils so that they
may be consolidated
through a filter

27. 24
(Woolfenden, 2001). After consolidation the contaminants are collected and destroyed
through incineration depending upon the constituents (Figure 6). The process can be
accomplished in situ or ex situ subsequently after excavation. There are also many factors
that influence the time and efficiency of this process such as the depth and concentration
of the contamination, the degree of sorting and the capacity of the sorting equipment,
these factors make thermal desorption projects range from weeks to years (US EPA,
2012). While thermal desorption can be utilized for most forms of organic
contamination, it proves to be generally ineffective towards heavy metals with an
exception of mercury. This process also likely destroys any biological activity left in soil
(Dazy et al., 2009).
In situ chemical oxidation
This method of
remediation
makes use of
powerful
oxidizing
agents to create
aerobic
conditions in
the
contaminated,

28. 25
unsaturated soils (Figure 7). This facilitates a more effective and efficient microbial break
down of the contamination than would occur in anaerobic reducing soils (Wang et al.,
2014). This method of remediation has been shown to break down volatile solvents such
as trichloroethylene (TCE), ethanol and toluene (Mahmoodlu et al., 2013). Previous
laboratory experiments also demonstrated considerable success in removing polycyclic
aromatic hydrocarbons (PAHs) such as diesel and phenanthrene in contaminated soils
where after six hours of ozone injection over three quarters of the contamination was
removed from the substrate (Choi et al., 2002). However more recent innovations in this
technology using a combination of sodium persulphate and hydrogen peroxide removed
over 96% of total petroleum hydrocarbons (TPHs) (Wang et al., 2013).
While recent developments in this technology have demonstrated impressive results,
there are still potential hazards regarding the relationship between the type of
contamination and the composition of the soil. Unlike organic solvents and hydrocarbons,
metals cannot be broken down. Once oxidized some metals become more soluble and
mobilize more easily, which can complicate containment.
Soil vapor extraction
Another method of in situ remediation, also known as soil venting or vacuum extraction,
converts solid and liquid contaminants into gaseous volatile organic compounds (VOCs)
in the unsaturated area between surface soils and the groundwater in what is known as the
vadose zone (Figure 8). The gas is then collected on the surface using extraction wells

29. 26
and vacuums and
treated on site,
usually with a
highly absorbent
granular activated
carbon (Oostrom et
al., 2014). One of
the major
advantages of this
technology over
other forms of conventional remediation is that it has a much greater ability to remediate
larger sites at much lower cost (US EPA, 1997b). However, while proven to be effective
in removing less dense organic petroleum products and solvents, this method is less
effective at remediating less volatile, heavy petroleum products such as diesel, heating
oils, and kerosene (US EPA, 1997b). As is the case with most other forms of remediation
this method is also ineffective in removing metals.
Summary of conventional remediation factors
Conventional remediation methods offer site developers comprehensive means of
cleaning up brownfields within variable time constraints. However, these technologies
usually come at a high financial cost and increased risks in terms of contamination
exposure and liability. While excavation and incineration provide the quickest solutions
to the problems on site, they completely destroy the abiotic and biotic processes within

30. 27
the soil and can be prohibitively expensive depending upon the circumstances. Many
communities disapprove of these methods due to concerns regarding exposure from
improper handling and disposal of contamination, while others complain about the
problems associated with the noise and odors. In situ chemical oxidation, soil vapor
extraction and thermal desorption are less detrimental to environmental productivity and
can be performed on site but can be time consuming. Landfills and capping also provide
developers with an opportunity to dispose of contaminants rather quickly but are
ineffective for metal contamination and have been historically unpopular from adjacent
communities despite current innovative technologies.
Chapter 4: Phytoremediation methods: Digging deeper for a more holistic approach.
Phytoremediation is the process by which we can utilize the abilities of plants to take up,
break down or immobilize contamination in soil and groundwater in a way that is
interpreted as environmentally safe and sustainable (Terry et al., 2003). Phytoremediation
methods have demonstrated the ability to break down or store a wide range of harmful
substances such as heavy metals, radionuclides, polynuclear aromatic hydrocarbons,
polychlorinated bisphenols as well as other xenobiotics such as pesticides and excess
nutrients from fertilizers (Ali et al., 2013).

31. 28
There are three ways plants facilitate the tasks of remediation; through direct uptake into
the plants biomass, immobilization within the soil through the release of enzymes directly
onto the contaminants or through uptake and degradation in the rhizosphere (Juwarkar et
al., 2010). The four primary phytoremediation methods that utilize these processes for
soils and groundwater are phytodegradation, phytostabilization, phytoextraction and
phytovolatilization (Figure 9).
Some of the advantages of phytoremediation pertaining to sustainability include: its
negligible environmental impact, its acceptance by surrounding communities, its relative
cost in comparison to conventional technologies (50 to 80% less), and in the case of
heavy metals, the potential for their recovery and reuse (Lee, 2013). The use of plants as
an intermediate step
in remediation or
reforestation, after the
remediation process,
is becoming more
accepted. This use
can make many
projects economically
and environmental
feasible (French et
al., 2006).

32. 29
Frequently, phytoremediation has demonstrated the ability to increase fertility and
productivity of soils through inputs of organic matter (Ali et al., 2013). Certain plants
such as willow and poplar can also be used for energy production after the remediation
process, increasing the economic incentive that would otherwise not be available through
the use of chemical amendments or heavy equipment (Ali et al., 2013). This is especially
true when using perennial warm-season grasses to remove excess phosphorous (Silveira
et al., 2013). Due to their high dry matter yields and intricate rooting structures, grasses
efficiently absorb excess nutrients and reduce soil erosion runoff while providing an
economic incentive by reusing the harvested biomass as a renewable energy source
(Silveira et al., 2013). While the evidence indicates certain advantages to site owners and
developers, research also indicates some unavoidable short comings and possible hazards
(Bert et al., 2009). Some of the factors limiting the applicability of phytoremediation
include the conditions of season and climate as well as the soil conditions and available
nutrients (Juwarkar et al.,
2010; Lee, 2013). There is
also the possibility of the
plants used being ingested
by various fauna and passed
unpredictably into the food
web (Lee, 2013). Two
significant factors that limit
plants’ effectiveness are
their root depth (less than 5

33. 30
meters) and the time involved in plant growth and uptake (Figure 10) (Juwarkar et al.,
2010; Lee, 2013).
There are some unavoidable financial costs associated with phytoremediation that deter
developers from these methods such as, the cost of disposal of the harvested biomass, as
well as the cost of establishing, maintaining and producing the crops (Silveira et al.,
2013). Lastly, there are limitations as to the severity of contamination in which any plant
species can grow which eliminates the option of phytoremediation entirely (Lee, 2013).
The history of phytoremediation and current applications
More than a hundred years ago, botanists observed that certain plants could store high
levels of metals that would normally be toxic to most other organisms (Baker et al.,
1994). However, research and development of what is known today as phytoremediation
has only been pursued for the last three decades, resulting in relatively few commercial
examples when compared to conventional technologies currently in use (Juwarkar et al.,
2010). While phytoremediation technologies may be relatively new, their development
has grown into a 35 million dollar industry here in the U.S. and has a combined global
market value of over 18 billion dollars (Krämer and Chardonnens, 2001). These
technologies have shown considerable success in remediating an extensive variety of
organic and inorganic contaminants (Terry et al., 2003).

34. 31
Some of this technology's possible applications include, remediation of heavy metals,
2,4,6-trinitrotoluene (TNT) and other organic contaminants such as polychlorinated
biphenyls (PCBs) and even certain radioactive substances such as cesium and strontium
(Lee, 2013). Other applications include remediation of chlorinated solvents, BTEX
compounds, excess nutrients and ammunition and petroleum-based waste (Schnoor et al.,
1995). Even though conventional remediation practices still represent the vast majority of
active projects, cumulative research into the refinement of phytoremediation has created
some compelling socioeconomic advantages that are being recognized by the
international community (Juwarkar et al., 2010).
Research over the last two decades has incorporated transgenic plants, both natural and
engineered, to increase qualities that would make plants optimally effective in
remediation and other commercial applications (Lee, 2013). In the case of metals and
metalloids that cannot be broken down or transformed, researchers are constantly
discovering more efficient hyperaccumulators that can store 50 to 100 times more than
naturally occurring plants, in some of the most extreme cases the stored metals can reach
upwards of 5% of the total dried biomass of the harvest (Lee, 2013). In 2003 genetic
research discovered that over-expressing enzymes that contribute to assimilating sulphate
and synthesizing phytochelatin also increased the plant's capacity to tolerate and store
significant quantities of toxic selenium and cadmium (Terry et al., 2003). Partially due to
these pressures, research into increasing growth rate and increasing biomass production
has been at the forefront of developing hyperaccumulators (Watanabe, 1997). Research
has also discovered that the growth of many plants can also be accelerated in the presence
of certain symbiotic arbuscular mycorrizal fungi (AMF) (Corradi and Charest, 2011).

35. 32
As with all living organisms, increases in the amount of toxic substances absorbed by
plants will increase the likelihood of compromising their immune systems (Zhang et al.,
2006). This is probably why another essential characteristic in hyperaccumulator
development is the plants’ ability to resist disease and pests (Watanabe, 1997). Other
research into improving phytoremediation includes using assemblages of species to
increase bioavailability for situations where a complex array of contaminants may be
present (Pulford and Watson, 2003). Some of the best results facilitating plants’ ability to
take up contaminants makes use of chelating soil amendments such as
ethylenediaminetetraacetic acid (EDTA), for lead, ethyleneglycoltetraacetic acid (EGTA)
for cadmium, and citrate for uranium (Salt et al., 1998). In other cases phytoremediation
can be used with other remediation techniques such as landfill caps, buffer zones for
agriculture and to facilitate the treatment of industrial waste water (Juwarkar et al., 2010).
The benefits and detriments of currently available phytoremediation technologies
Phytodegradation
This form of in situ phytoremediation utilizes plant enzymes (dehalogenases, oxygenases
and reductases, in most cases) to break down organic contaminants within the plant tissue
(Figure 11) (Newman and Reynolds, 2004). Some of the applications where this method
has proven effective include sites where ammunition waste, chlorinated solvents and
herbicides were present (Black 1995).

36. 33
This may also include the use of the microorganisms surrounding the rhizosphere that
enable many plants to break down contaminants in the soil (Lee, 2013). There are,
however, many plant species that do not require rhizospheric microorganisms for the
breakdown process (Ali et al., 2013; Mench et al., 2010). The primary goal of
phytodegradation is to mineralize the target contaminant into a less harmful or non-
harmful byproduct such as carbon dioxide, nitrate, chlorine or ammonia (Mench et al.,
2010). While a significant amount of research on this method began in Europe with the
help of nationalized economic support, the push in the United States for more sustainable
remediation practices has influenced developers to investigate and utilize
phytodegradation due to the potential economic and environmental benefits
(Schwitzguébel et al., 2002). Research into the effectiveness of phytodegradation has
shown very impressive results, in some cases completely eliminating soil and
groundwater contamination. Phytodegradation has been implemented in sites to
successfully break down contaminants such as chlorinated solvents, ammunition waste
and even herbicides which were designed originally to eradicate many plant species

37. 34
(Juwarkar et al., 2010). This form of remediation has also shown considerable success
when targeting PCBs, PAHs, TNT and TCE (Mench et al., 2010).
In 1992, the Remediation Technologies Development Forum (RTDF) was established by
the EPA in an effort to bring together government, industry and academia to address and
develop economically sound solutions for hazardous waste treatment technologies (Beck
et al., 2005). Research reported by the RTDF in 2005 explained how a wide variety of
enzymes produced by hybrid poplar, oak, castor beans and saw palmetto are capable of
breaking down PCE and TCE (Beck et al., 2005). One study had shown that poplar trees
were capable of eliminating 99% of TCE contamination from groundwater in less than
two years (Beck et al., 2005). While 9% of the TCE removed in this study was shown to
be transpired into the air, further testing continuing into the third year yielded a complete
elimination of air transpired chlorinated compounds (Beck et al., 2005). Phytoworks,
Inc., a company from Gladwyne, Pennsylvania, is currently using this method in sites
where TNT, PCP, PAHs, PCBs as well as TCE are present (Suresh and Ravishankar,
2004). This form of remediation has proven to breakdown 97 to 99 percent of some
organic contaminants such as phenol within a wide range of soil pH contaminated from
industrial runoff waste-water (Klibanov et al., 1983). The success of this remediation
method is dependent on the properties of the contamination at the site. If the
contamination is exceedingly hydrophilic then it will not permeate through the cell
membranes. Inversely, if the contamination is excessively hydrophobic it will adhere to
the rooting surface and be unable to enter the plant for metabolization (Lee, 2013). For
many xenobiotics there are two properties that can inhibit uptake, strong lipophilic

38. 35
properties and a contaminant’s ability to covalently bond to soil particles (Schwitzuébel,
2002). However, for many other plants, organic contaminants can be broken down into
inorganic compounds such as H2O and CO2 (Lee, 2013). These byproducts can then be
used by other organisms such as bacteria and fungi to facilitate the overall biological
productivity of the soils (Lee, 2013). A couple of fairly common contaminants where this
has been observed are polychlorinated biphenyls (PCBs) and polycyclic aromatic
hydrocarbons (PAHs) (Salt et al., 1998). One of the main uses for phytodegradation is for
soils contaminated with hydrocarbons (Mench et al., 2010). In many cases this method is
complicated by the presence of trace elements which reduce the ability of symbiotic
microorganisms near the rhizosphere to degrade hydrocarbon contamination (Mench et
al., 2010). In order to improve the process research using NPK fertilizers and compost
has been found to enhance this method (Mench et al., 2010). Another means by which
researchers have been improving this method is through the use of genetic modification
(Ali et al., 2013). Unfortunately, in situ remediation methods of this sort are inapplicable
to inorganic metals due to the fact that they cannot be broken down or transformed.
Phytostabilization
In contrast to other forms of phytoremediation, phytostabilization does not involve the
uptake of contaminants into the plant itself, but rather this technique effectively absorbs
the contamination to the soils around the rooting zone (Figure 12) (Lee, 2013). In doing
so, bioavailability via leaching and runoff into ground and surface waters as well as
volatilization into the air are significantly reduced (Morikawa and Erkin, 2003).

39. 36
Prior to its establishment as a remediation method, it was speculated that large woody
trees may have the ability to resolve contamination issues through extraction into their
biomass or by immobilization (French et al., 2006). There are several factors regarding
onsite conditions that can render the option of contamination removal impractical or even
impossible. In these situations phytostabilization provides developers with a secondary
option of immobilizing or stabilizing harmful contamination (Ali et al., 2013).
Phytostabilization has shown considerable success immobilizing metals in subsurface
soils in areas such as
mines, dumps and
quarries where lead,
manganese and other
metalliferous waste
byproducts are
prevalent by using a
combination of
legumes and deep
rooting trees (Juwarkar et al., 2010). Plants accomplish this task through a variety of
means such as root sorption, precipitation, complexation or reducing the valence within
the rhizosphere (Barcelo and Poschenrieder, 2003). As an evolutionary characteristic
many plants are capable of releasing special redox enzymes in response to the variable
valences of toxic metals within the proximity of their roots (Wu et al., 2010). In doing so,

40. 37
these plants transform the target molecules into a less toxic and less mobile byproduct
(Wu et al., 2010).
One of the key drawbacks of phytostabilization is that by itself it is not a permanent
solution. As with any remediation strategy, the end goal is to eliminate, neutralize or
remove the contamination in order to make the property environmentally healthy and
biologically productive. This is why phytostabilization is often used as an intermediary
stage in the process and is usually paired with phytoextraction or conventional
remediation methods (Vangronsveld et al., 2009). However, identifying and
implementing an effective sequence of plant species for stabilization and subsequent
extraction can be very complicated, especially when multiple metal and metalloids are
present. The difficulty is due to the variable mobility and adhesive properties of different
metals which is dependent upon the acidity of the soil, which also affects the ability of
uptake for extraction (Moreno-Jiménez et al., 2011). This creates a secondary hurdle for
site developers, which is that many plants do not do well in highly acidic soils. A
research study in Spain using four native Mediterranean shrub species demonstrated the
variability of adaptation, stabilization and uptake resulting from varying pH (Moreno-
Jiménez et al., 2011). The target contaminants were zinc, copper, cadmium, aluminum
and arsenic. Of the four species planted only one of the species had a survival rate as high
as 30% (Moreno-Jiménez et al., 2011). While that species demonstrated some resistance
to acidic and toxic soil conditions it was discovered that in order for the plant to take up
arsenic fixed to soil particles proximal to the rooting zone, the soil would have to be
raised to a pH above 5. Due to the complexity of the situation some question the

41. 38
sustainability of this method given the rates of plant mortality in relation to success
(Moreno-Jiménez et al., 2011).
Phytoextraction
This form of remediation utilizes the abilities of some plants to store toxic heavy or
radioactive metals as well as other trace elements within the plant tissue (Figure 13). The
process by which this is accomplished is actually part of the plants’ normal function in
that there are particular metals such as iron, manganese, copper, magnesium and nickel
that are vital and beneficial to plants (Lee, 2013). The primary goal of phytoextraction is
to accumulate as much of the target contaminant as possible in the above-ground tissues
so the crop can be
harvested with the
contaminant and
leave the soil
untouched (Krämer
and Chardonnens,
2001).
In comparison to
chemical treatments and excavation this method saves site developers significant cost due
to the lack of equipment and personnel required (Adams et al., 2013; Mench et al., 2010).
The harvested biomass is also significantly less expensive to transport due to much
lighter mass and saves developers from having to import soil from elsewhere (Krämer

42. 39
and Chardonnens, 2001). In some cases phytoextraction by crops can occur, and they can
be safely harvested in months or even weeks if properly and carefully cultured (Mench et
al., 2010). When particular attention to detail is performed in this process, time windows
for remediation performed by phytoextraction may compete with some conventional
methods. Interestingly, other plants have developed resistance and the ability to absorb
certain metals that have no known benefit such as cadmium, chromium, lead, cobalt and
silver (Salt et al., 1995).
When applicable this form of remediation is especially beneficial due to the fact that
metals within the plant tissue can be reclaimed and reused while the remaining biomass is
used in waste energy plants (Juwarkar et al., 2010; Krämer and Chardonnens, 2001).
Hyperaccumulators are ideal for this method of remediation due to the fact they save time
due to their fast growth and high biomass yields. Hyperaccumulators also help to save
developers considerable money in the form of labor, equipment use and fuel by
consolidating the number of harvests (Ali et al., 2013).
Besides the economic advantages of hyperaccumulators there are also ecological benefits
to reducing the number of necessary harvests. By reducing the time and frequency of the
harvest the soils retain more fertility enabling healthier, more productive subsequent
growth which will have greater resistance to disease and pests (Mench et al., 2010). In
order for a hyperaccumulator to be considered for a phytoextraction project it must meet
three prerequisites: it must be able to build up significant amounts of several trace
elements in its shoots, it must have a high rate of growth to support greater biomass, and

43. 40
it must develop an extensive root system capable of rapid and efficient uptake (Krämer
and Chardonnens, 2001). Other qualities that are important in order to maximize the
effectiveness of the process are: the ability to efficiently translocate metals from roots to
shoots, a strong tolerance to the toxic effects of metal storage and a strong tolerance to
pests and pathogens (Ali et al., 2013). Some studies suggest that although extensive root
systems facilitate the process by accelerating uptake, they still may require some top soil
excavation due to the
amount of
contamination still
present in the below-
ground biomass (Mench
et al., 2010). Presently,
there are more than 400
known species of flora
capable of
hyperaccumulating
metals (Juwarkar et al.,
2010). Some of which
can be found in Table 2.
Of the species
researched for this paper, none performed more remarkably than those that were capable
of taking up and storing radionuclides (Nehnevajova et al., 2007). For most organisms,

44. 41
prolonged exposure to these elements would result in radiation poisoning or cellular
tissue damage. While there are examples where radioactive contamination was the result
of nature, most situations arise from human activities such as weapon testing and nuclear
power plants (Lee, 2013). A well-known accident occurred in Ukraine in 1986 when the
Chernobyl Nuclear Power Plant had a meltdown. Eight years later, the Chernobyl
sunflower project began using the sunflower species (Helianthus annuus) and Indian
mustard (Brassica juncea) to take up and store radioactive elements leaked from the
failed reactors (Salt et al., 1995). Concurrently the sunflowers and Indian mustard
absorbed cesium in their roots and strontium in their shoots (Lee, 2013). Sunflowers have
also been shown to efficiently accumulate modest amounts of other trace elements.
However the ability to generate high biomass has primarily led research to focus on their
application to metals such as lead and cadmium as well as radionucleotides (Lee, 2013).
After the Fukushima accident in 2011, research for similar applications includes using the
giant milk weed (Caltropis gigantean) and the common reed species (Phragmites
australis) for uranium-contaminated soils in Japan (Lee, 2013). This research also led to
further investigation into remediating waste from mining operations where radioactive
isotopes, like cesium and cobalt, could be reabsorbed using water hyacinth (Eichhornia
crassipes) (Saleh, 2012). Other research focused towards community forestry
demonstrated that certain tree species such as Alnus, Populus and Salix could potentially
diminish contamination in higher risk areas where highly mobile elements such as
cadmium and zinc have been present for 25 to 30 years (French et al., 2006). This study
suggested that these species may have further applications with regards to excess zinc

45. 42
contamination in more urbanized environments and agricultural areas contaminated with
sewage sludge (French et al., 2006).
Phytoextraction in comparison with all other methods of remediation mentioned in this
paper may be the most economical and environmentally friendly. However many authors
have pointed out some of the potential hazards and short comings of phytoextraction. As
with all other phytoremediation methods the possibility of crop consumption by wildlife
and subsequent toxic metal dispersal throughout food webs is a problem (Pulford and
Watson, 2003). Another problem which many authors discuss pertains to the exposure to
other metals such as nickel and copper and the lack of mobility of other elements such as
lead and arsenic for uptake (French et al., 2006). Other research suggests that seeding
woody biomass promotes metal transformation and may not prevent mobility into the
environment for at least three years (French et al., 2006). Other authors also discussed
concerns regarding biomass combustion, which could release particulate matter rich in
targeted metals into the atmosphere (Dickinson et al., 2002; Pulford and Watson, 2003).
Some research suggests that phytoextraction methods may require further development
before they can compete with currently available conventional technologies. Two areas of
such development are by further increasing yields of biomass by hyperaccumulators or
the improvement of metal accumulation in non-accumulator species (Krämer and
Chardonnens, 2001). Two means which are widely discussed throughout the literature on
this topic are the use of genetically engineered plants or transgenic plants and the use of
chelators. One of the main reasons for genetic augmentation is that in order for
phytoextraction to be considered a viable method for remediation it has to be able to

46. 43
accumulate the targeted contaminant without a loss of growth (Maxted et al., 2007).
Researchers argue that by improving the plants’ resistance to the toxic effects of metal
uptake their rate of growth would be higher resulting in fewer cropping cycles required
for successful remediation (Maxted et al., 2007).
An area of major concern for both researchers and site developers is what to do with the
harvested biomass after it has been removed. Depending upon the constituents of the
contamination that were taken up there are a wide variety of options. In some cases the
harvested biomass can be designated as hazardous waste where it can be disposed of in a
landfill or incinerated (Mench et al., 2010). This end result however puts added cost onto
site developers. Research into how to make this process more lucrative for developers as
well as to viably compete with other conventional technologies has yielded impressive
results.
One means to a profitable end for the harvested biomass involves using specially
designated areas for composting (Mench et al., 2010). Depending upon the identity and
concentration of the absorbed contaminants the composting process can break down the
harmful contaminants which can eventually be sold, resulting in profitable material for
the developer while promoting biological activity elsewhere (Mench et al., 2010). Other
research has demonstrated that the biomass can be processed into oils and essential oils as
well as biofuels or syngases such as methane, carbon monoxide or hydrogen through
supercritical gasification or liquefaction (Mench et al., 2010). Two species that have
demonstrated the greatest financial returns during remediation are oilseeds and willows

47. 44
(Mench et al., 2010). Species that have also shown considerable tolerance to moderate
levels of contamination while producing high biomass are Brassica juncea (Indian
mustard), Brassica rapa (field mustard) and Brassica napus (rapeseed) (Van Ginneken et
al., 2007).
Other case studies have demonstrated that the remaining biomass from the
phytoextraction process can be combined with biofuel production in sites to produce
more sustainable energy sources (Vangronsveld et al., 2009). Some of the most prevalent
and financially lucrative outcomes for this research in the last two decades however have
been focused on extracting and recycling the remediated contaminants for reuse,
particularly in the cases of trace elements and metals (Mench et al., 2010). While these
options do present significant economic incentives, like all other remediation methods
they do not come without their own concerns and liabilities. This is often the case when
there is the option of extracting oils and essential oils from remediated biomass while still
leaving the question of how to dispose of the remaining product (Mench et al., 2010).
Trace element extraction and consolidation for reuse is also more difficult without the use
of secondary chemical or biological mobilizing agents such as EDTA which may have an
impact on ecological productivity of the soil (Maxted et al., 2007). EDTA is not only
toxic to most plants and wildlife at high concentrations, but due to its high rate of
mobility is not easily controlled and has a moderate chance to seep into groundwater if
not properly applied (Ali et al., 2013). As an alternative to toxic chelators other research
has led to the discovery of citric acid as a mobilizing agent (Smolinska and Krol, 2012).
Citric acid not only mildly lowers the pH facilitating the mobilization of most metals but

48. 45
is also nontoxic and relatively easy for most plants to break down without hindering
growth, making it an excellent alternative to highly toxic chemical chelators (Ali et al.,
2013).
Within the last decade, awareness of the profitability of the phytoextraction process has
also led to pioneering of what is known as phytomining. The process by which certain
plants can target certain metals for uptake has been known for quite a while; however, the
ability to focus and enhance that process has recently been given a boost by the
advancement of genetic engineering technologies (Siddiqui et al., 2009). One extractable
metal that has shown considerable profit-making potential with phytomining is nickel
(Chaney et al., 2007). One case study shows that by simultaneously growing Alyssum
murale and Alyssum corsicum in soils that are rich in nickel the yield could be over 400
kg/ha of the target metal. Given that the value of nickel in 2006 was approximately
$40/kg, the estimated value of that particular crop would be $16,000/ha (Chaney et al.,
2007; Siddiqui et al., 2009).
Phytovolatization
A more controversial method of phytoremediation, phytovolatization involves the use of
plants to take up and transform contaminants in the soil into less toxic, volatile states that
are then dispersed into the atmosphere (Figure 14) (Juwarkar et al., 2010; Krämer and
Chardonnens, 2001).

49. 46
This process occurs through methylation, as plants take up the contamination along with
water. Certain trace elements such as arsenic and selenium as well as toxic metals such as
mercury and tin can be
methylated into volatile
compounds (Juwarkar et al.,
2010). Normally the target
contaminant(s) would be
stored either within the plant
tissue or immobilized within
the proximity of the rooting
zone. The reason why this
method of remediation is
viewed favorably by some
developers is that by
methylating the contaminant(s) the general growth and productivity of the plant continues
unhindered, which equates to little to no harvesting, faster remediation times, and no need
for ex situ secondary processes (i.e. incineration or landfilling) for remediation (Krämer
and Chardonnens, 2001). Once volatized, some of these molecules might break down
further in the atmosphere or remain as air pollutants (Ali et al., 2013; Salt et al., 1998). It
is because of the ambiguity of the end result of this method that further in-depth risk
assessments need to be conducted in order to ascertain support from both the respective
governments and the communities where this is an option (Lee, 2013). Another criticism
of this method is that it may not fully be able to remediate a site due to the fact that it

50. 47
releases the transformed contamination into the atmosphere where it can eventually be
redeposited at a new site (Ali et al., 2013).
Summary of phytoremediation methods
Phytoremediation methods offer a number of incentives to developers that simply are not
available through the most widely used conventional methods. The economic incentives
of receiving additional revenue for crops by selling them for use as biofuels or recycling
and reselling targeted metal contaminants puts money back into the developer’s pockets.
Secondly, the reduction of physical labor means less handling of contaminated media
which reduces a variety of costs associated with liability. Phytoremediation techniques
also require significantly less heavy equipment which saves developers more money and
is generally viewed with greater acceptance from surrounding communities due to better
aesthetics. While there are many benefits to these methods there are also some negative
qualities and concerns regarding their applicability and overall success. Many
governmental and academic institutions have developed tools in order to help land
owners and developers decide whether or not phytoremediation is the right choice
(Appendix C). Limiting factors such as geographic location, general climate, soil type
and amount of contamination can limit or prohibit plant growth, eliminating
phytoremediation all together. Other research identifies the potential to promote the
transfer of onsite contaminants through herbivory of the remediating crops. However, in
response to these concerns significant research into improving uptake and biomass of
remediating plants through the use of chelators and genetic engineering has greatly

51. 48
improved plant remediating performance while addressing many of these ecological
issues.
Chapter 5: How do phytoremediation and conventional remediation methods fit into a
sustainable framework?
As humanity's numbers continue to increase, so do the resources we consume. As a
result, the awareness of Earth's limited resources has compelled many industries and
businesses to rethink how they develop and further expand. Besides the issues of cost and
liability to the site developers themselves, any company deciding to acquire brownfield
land is going to encounter a host of issues from both the government and the surrounding
community. While any form of remediation for a brownfield would likely be better for
the environment and its surrounding community, not every form of remediation is
applicable, affordable, or accepted by the community. In many cases the simple
aesthetics of a particular type of remediation process may be enough to deter a
community from supporting brownfield restoration. This is why the concept and question
of sustainability should be applied to the remediation process. In recent years the idea of
sustainability has developed into a discipline that addresses the environmental, economic
and social issues that are involved in everything we do and brownfield remediation is
certainly no exception.
In almost every case no one remediation method can single handedly clean up a site
completely. Most sites require multiple remediation techniques to work together, in some
cases combining conventional remediation methods with phytoremediation and other

52. 49
forms of bioremediation. Another important issue when comparing remediation methods
is that while many conventional methods are already widely used, the use of
phytoremediation methods on a commercial scale are disproportionally insignificant
(Witters et al., 2012). Most peer-reviewed journals site case studies where
phytoremediation is being implemented as part of research with "projected" related cost
to conventional methods. Therefore, when comparing phytoremediation to conventional
remediation methods an accurate evaluation is difficult to estimate. There are however
quantifiable aspects that can be applied in terms of sustainability. In fact many academic
and governmental institutions have created support tools designed specifically for
sustainable remediation. In order to ascertain the applicability of remediation methods to
sustainability, certain criteria must be met in accordance with what it means to be
"sustainable" and more importantly, what it is to be defined as a sustainable remediation
method.
The first condition for a sustainable form of remediation is that it should provide an
economic incentive to the developer. This equates to lower cost in terms of labor and
equipment. In some cases this also means the possibility of recycling and reusing
contaminants such as heavy metals. The second condition is that the process needs to
acquire and maintain public support. Of all the sources covered in this paper the most
important factor in obtaining community support was that it did not put the surrounding
community at risk. Another common concern amongst communities that was mentioned
frequently involved the aesthetics of the removal process. In certain cases issues
pertaining to the sight and sound of heavy machinery along with the smells associated

53. 50
with diesel equipment were not viewed favorably. Juwarkar et al. (2010) made it a
secondary point also including the aesthetics of the contaminated media itself and how
the projected public's reaction towards it could influence the method that developers
choose regarding remediation.
The third factor for sustainable remediation is that by the definition of sustainability, the
process must leave the site biologically productive for the future. This means that not
only should the remediation process remove the contamination from the site, but that it
should also not leave any secondary contamination. Ideally, this would enable or promote
further biological productivity in the soils for plants, fungi, invertebrates and other
microbial life. By doing so, the form of remediation meets the three-pillared system while
simultaneously addressing the requirement of not negatively impacting future
generations.
In terms of sustainability there are many that argue in support of phytoremediation over
the more commonly used conventional technologies (Salt et al., 1995). One of the
significant factors supporting this methodology concerns soils contaminated with heavy
metals. In most cases conventional brownfield reclamation projects involve steps that
require the disposal of contaminated soils and the import of new soils, which is expensive
and environmentally disruptive (Dickinson et al., 2002). Of all the conventional methods
none of them could remove heavy metal contamination without either reducing or
eliminating the biological productivity of the soil. Where physical and chemical
techniques decrease or eliminate the biological productivity in the soil, phytoextraction
projects have been shown to promote and increase soil productivity (Moreno-Jiménez et

54. 51
al., 2011). This was successfully demonstrated in one study where various species of
Salix, Populus and Alnus were used for trace element uptake in dredged sediments
(Hartley et al., 2012). By performing a before and after evaluation of soil biological
quality it was found that populations of earthworms had increased from 5 to 24/0.25 m2
and microarthropod groups had increased from 70 to 88/0.25 m2
(Hartley et al., 2012).
This combined with the extensive cost of excavation with ex situ incineration and land
filling as well environmental repercussions of leaching and chemical fixation rendered
most conventional methods comparatively unsustainable (Juwarkar et al., 2010).
Phytoextraction, however, was the only viable method that would successfully take up
and store these metals where they could later be harvested. This method of remediation is
also rapidly increasing in its overall effect with the use of naturally occurring native
hyperaccumulators (Zhang et al., 2006). In comparison with most other methods of
inorganic contaminant removal, phytoextraction is more economically feasible,
environmentally sound and often wins public support (Zhang et al., 2006). The
incorporation of genetics into the development of hyperaccumulators is also growing in
popularity amongst many researchers who are highly in favor of more government
support for this application (Zhang et al., 2006). For more than thirty years geneticists
have identified a number of genes that influence metal uptake as well as resistance to
these metals (Zhang et al., 2006). What is also important is that depending upon the
stored contaminant in harvested biomass, it could be used for biofuel or the metals could
be extracted off site and recycled for further use, both providing an economic incentive
for site developers. However there are concerns regarding the use phytoremediation
technologies as well. One reoccurring issue pertained to the increased bioavailability of

55. 52
contaminants once in the plants prior to harvest. One author suggested using plants that
store contaminants in their roots and not their shoots, stems or leaves (Zhang et al.,
2006).
For any phytoremediation method there are a few characteristics that should be met in
order for the industry to compete with conventional technologies and remain sustainable.
First, the plants should be fast growing and achieve a high biomass in the shortest amount
of time possible (Zhang et al., 2006). However, as the same author points out there are
very few naturally occurring plants capable of these two qualities simultaneously while
capable of being easily harvested. One of the many factors that conflict with conventional
remediation methods’ applicability to sustainability is the lack of public support. Ex situ
methods such as incineration and landfilling are frequently looked upon unfavorably by
the surrounding community (Juwarkar et al., 2010).
Chapter 6: Discussion and conclusions: Is there a right answer?
Within the last two centuries humanity's exponential population growth and geographic
expansion have put unprecedented pressures on Earth's resources and the organisms
which we share it with. Historically, our ability to be responsible stewards of our
environment has been deplorable. However, as our awareness is inevitably drawn to the
issues regarding our increasingly limited resources, governments, businesses and
communities are beginning to work together in order to clean up and restore what damage
has already been done. The use of green space is becoming less an option as native
habitat is being consumed. Many credit this trend towards what is being called the sixth

56. 53
great extinction. That is why if we are to maintain or hope to improve the quality of
ecosystems and the global environment as a whole we have look back to where we
started. We cannot ignore contaminated properties because of the financial cost to clean
them up, especially when the environmental and healthcare impacts to future generations
are likely to be exponentially greater.
Current trends show increasing support for phytoremediation due to the lower cost and
decreased environmental impact when compared to conventional methods (Lee, 2013).
While phytoremediation methods appear to be more sustainable than conventional means,
they are not without practical limitations. It is due to these limitations that many
institutions such as the USEPA have generated decision making trees in order choose the
best course of action for remediating processes (Appendix D). Restrictions regarding soil
type and climate conditions as well as the soil depth and the severity of contamination
can render phytotechnology impractical or even impossible. Secondly, time constraints
put significant pressures on development projects that make the appearance of
phytoremediation seem unreasonable in comparison with the mechanical means and
chemical amendments of conventional remediation methods. Although conventional
remediation methods are more time efficient this comes at a significant financial cost in
terms of labor and equipment. Most of these methods also have detrimental effects on the
productivity of soils by either chemically sterilizing them or physically with use of
machinery or incineration. While the results regarding the research with
hyperaccumulators are promising, research into the genes responsible for fast growth,
high biomass and increased contaminant resistance is proving to be difficult. More

57. 54
specifically, although the genes responsible for these individual characteristics are being
identified, the genes’ interactions with each other are still less understood and phenotypic
development of hyperaccumulating flora with all of these qualities is still in the
developmental phase (Zhang et al., 2006). Of all the phytoremediation methods discussed
however the applicability of phytovolatization as a sustainable remediation method is
questionable. This is because there are many contaminants that once airborne have
unknown interactions in the atmosphere. Regardless, phytoremediation methods have
demonstrated that they have strong potential to clean up a vast array of contaminants.
Where applicable the investments into this technology undoubtedly have strong potential
to decrease cost by reducing the dependence on heavy machinery and labor while
significantly reducing liability and increasing public support.

58. 55
Acknowledgments
I would like to thank Dr. Clayton Penniman and the rest of the biology department at
Central Connecticut State University for giving me the confidence to accomplish my
academic and professional goals. Without your guidance and patience I would not be able
to interpret and reflect upon the world as critically and creatively as I do now, thank you.
I would also like to thank my wife, as there were many moments where I thought I would
not be able to meet the challenges of academia. I would also like to thank my mom and
sister. Without their support and acknowledgement of all my hard work over the last
eight years none of this would even be possible. Lastly, I would like to thank my father
for sparking my interest in nature as a child. Even though he could not be here to read my
work or see my accomplishments it is because of him that I work towards helping
improve humanity's relationship and coexistence with nature.

59. 56
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