Nanotechnology for Site Remediation
Fact Sheet
INTRODUCTION
This fact sheet presents a snapshot of
nanotechnology and its current uses in
remediation. It presents information to help site
project managers understand the potential
applications of this group of technologies at their
sites. The fact sheet also identifies contacts,
such as vendors or project managers with field
experience, to facilitate networking.
Nanotechnology is still relatively in its infancy
but it is rapidly evolving. It holds promise in
remediating sites cost effectively and addressing
challenging site conditions, such as the
presence of dense nonaqueous phase liquids
(DNAPL). For example, nanoscale iron is in use
in full-scale projects with encouraging success.
Ongoing research at the bench- and pilot-scale
is investigating particles such as self-assembled
monolayers on mesoporous supports
(SAMMS™), dendrimers, carbon nanotubes,
and metalloporphyrinogens to determine how to
apply their unique chemical and physical
properties for full-scale remediation. There are
many unanswered questions regarding
nanotechnology. Further research is needed to
understand the fate and transport of free
nanoparticles in the environment, whether they
are persistent, and whether they have
toxicological effects on various biological
systems.
This fact sheet includes information on sites
where nanoscale iron has been tested for site
remediation. Because many of the remediation
projects using nanoparticles are just beginning
or are ongoing, there are limited cost and
performance data at this point. In addition, due
to proprietary concerns, information about cost
is often not made publicly available. However,
as the technology is applied at an increasing
number of sites with varying geologies, more
data will become available on performance and
cost, providing site managers and other
stakeholders additional information to determine
whether the technology might be applicable to
their sites.
The following topics are covered in this fact
sheet:
Background
Description of Nanoparticles Used in
Site Remediation
Description of Nanomaterials with
Potential Remediation Applications
Chemistry of Selected Nanoparticles
In situ Application of Nanoparticles
Limitations
Fate, Transport, and Toxicity Questions
Performance and Monitoring
Cost
List of Identified Vendors for
Nanotechnology
Selected Sites Using or Testing
Nanoparticles for Remediation
Other potential environmental applications of
nanotechnology are not addressed in this fact
sheet.
BACKGROUND
The definition of nanotechnology is multifaceted.
For the purposes of this fact sheet, it is defined
as technology at the scale of one to one
hundred nanometers (nm) in any dimension; the
creation and use of structures, devices, and
systems with novel properties and functions due
to their size in this range; and the ability to
control or manipulate matter on an atomic scale
(NNI, 2008). Figure 1 shows a micrograph of a
nanowire compared to a human hair. Nano-
Preparation of this fact sheet has been funded by the U.S. Environmental Protection Agency (EPA) under Contract Number 68-W-
07-078. Information in the fact sheet is derived from numerous sources (including personal communications with experts in the
field), some of which have not been peer-reviewed. The fact sheet has undergone EPA and external review by subject-matter
experts. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5203P)
EPA 542-F-08-009
October 2008
www.epa.gov
http://cluin.org
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sized particles have large surface areas relative
to their volumes and may have enhanced
chemical and biological reactivity (U.S. EPA,
2007). They can be manipulated for specific
applications to create novel properties not
commonly displayed by particles of the same
material at macroscale. Nanoparticles may be
produced via a "top down" approach, such as
milling or grinding of macroscale material, or,
most commonly, via a "bottom up" approach,
such as the chloride synthesis method, which
creates nanoparticles from component atoms or
molecules (Lien, 2006; U.S. EPA, 2007).
Figure 1. Micrograph of a looped nanowire
against the backdrop of a human hair (Mazur
Group, Harvard University, 2008)
An increasing variety of nanomaterials with
environmental applications have been
developed over the past several years. For
example, NanoScale Corporation is marketing
its product, FAST-ACT, as a chemical
containment and neutralization system that first
responders can use to clean up toxic chemical
releases of industrial chemicals or chemical
warfare agents (NanoScale, 2008). A group of
researchers at the Massachusetts Institute for
Technology (MIT) have developed a "paper
towel" for oil spills that is comprised of a
membrane or mat of potassium manganese
nanowires. According to the researchers, the
nanowire membrane selectively absorbs oil with
high efficiency. The oil can be recovered by
heating the mat, which can then be reused. The
membrane, which appears to be impervious to
water, may have additional uses in water
filtration (Thomson, 2008).
Nanomaterials have also been used to
remediate contaminated groundwater and
subsurface source areas of contamination at
hazardous waste sites. Early treatment
remedies for groundwater contamination were
primarily pump-and-treat operations. Because
of the relatively high cost and often lengthy
operating periods for these remedies, the use of
in situ treatment technologies is increasing.
Since the early 1990s, site project managers
have taken advantage of the properties of
metallic substances such as elemental iron to
degrade chlorinated solvent plumes in
groundwater. One example of an in situ
treatment technology for chlorinated solvent
plumes is the installation of a trench filled with
macroscale zero-valent iron to form a permeable
reactive barrier (PRB) (ITRC, 2005).
Recent research indicates that nanoscale zero-
valent iron (nZVI) may prove more effective and
less costly than macroscale ZVI under similar
environmental conditions. For example, in
laboratory and field-scale studies, nZVI particles
have been shown to degrade trichloroethene
(TCE), a common contaminant at Superfund
sites, more rapidly and completely than larger
ZVI particles. Also, nZVI can be injected directly
into a contaminated aquifer, eliminating the need
to dig a trench and install a PRB. Research
indicates that injecting nZVI particles into areas
within aquifers that are sources of chlorinated
hydrocarbon contamination may result in faster,
more effective groundwater cleanups than
traditional pump-and-treat methods or PRBs.
Research indicates that nanoparticles such as
nZVI, bi-metallic nanoscale particle (BNPs), and
emulsified zero-valent iron (eZVI) may
chemically reduce the following contaminants
effectively: perchloroethylene (PCE), TCE, cis-
1, 2-dichloroethylene (c-DCE), vinyl chloride
(VC), and 1-1-1-tetrachloroethane (TCA), along
with, polychlorinated biphenyls (PCBs),
halogenated aromatics, nitroaromatics, and
metals such as arsenic or chromium. There are
two common degradation pathways for
chlorinated solvents: beta elimination and
microbial reductive dechlorination. Beta
elimination, which occurs most frequently when
the contaminant comes into direct contact with
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the iron, follows the pathway of TCE + Fe — >
HC Products + CI" + Fe2+/Fe3+ (U.S. EPA, 2008).
Microbial reductive chlorination, which occurs
under the reducing conditions fostered by nZVI
in groundwater, follows the pathway of PCE — »
DCE^- VC^- ethene (Elliot, 2006).
Nanoparticles can be highly reactive due to their
large surface area to volume ratio and the
presence of a greater number of reactive sites.
This allows for increased contact with
contaminants, thereby resulting in rapid
reduction of contaminant concentrations.
Because of their minute size, nanoparticles may
pervade very small spaces in the subsurface
and remain suspended in groundwater, which
would allow the particles to travel farther than
macro-sized particles and achieve wider
distribution. However, as discussed in the
'Limitations' section, bare iron nanoparticles may
not travel very far from the injection point.
It is important to note that there is variability
among iron nanoparticles, even if they have the
same chemical composition (Liu, 2005). The
properties of particles such as reactivity,
mobility, and shelf-life can vary depending on
the manufacturing process or the vendor
providing the particle (Miehr, 2004).
DESCRIPTION OF NANOPARTICLES USED
IN SITE REMEDIATION
Most of the bench-scale research and field
application of nanoparticles for remediation at
full-scale have focused on nZVI and related
products, according to information obtained for
this fact sheet. Particles of nZVI may range
from 10 to 100 nanometers in diameter or
slightly larger. Figure 2 shows transmission
electron microscope (TEM) images of nZVI.
An example of a site where nanotechnology
showed positive results at full scale is a former
fill area in Hamilton Township, New Jersey,
which was treated with a nanoiron water slurry
(NanoFe Plus™). The groundwater at the site
was contaminated with TCE and associated
daughter products, with an initial maximum
volatile organic compound (VOC) concentration
of 1,600 micrograms per liter (ug/L). The nZVI
was injected in two phases over a total of 30
days. It was reported that post injection
monitoring indicated a decrease in the
concentration of chlorinated contaminants of up
to 90 percent. The site is now in the monitoring
phase (Varadhi, 2005).
Figure 2. Transmission electron microscope (TEM) images of iron nanoparticles (Zhang, 2006b)
Note: The scale bars in the figure are 200 nm.
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Information on other sites using nZVI can be
found in the 'Performance and Monitoring' and
'Selected Sites Using or Testing Nanoparticles
for Remediation' sections at the end of this fact
sheet.
Nanoscale iron particles can be modified to
include catalysts such as palladium (Pd),
coatings such as polyelectrolyte ortriblock
polymers (Saleh, 2007), or can be encased in
emulsified vegetable oil micelles (Hydutsky,
2007; He, 2007). Some nanoparticles are made
with catalysts that enhance the intrinsic reactivity
of the surface sites (Tratnyek, 2006). BNPs
have been used for the remediation of
contaminants in soil and groundwater. BNPs
consist of particles of elemental iron or other
metals in conjunction with a metal catalyst, such
as platinum (Pt), gold (Au), nickel (Ni), and
palladium. The combination of metals increases
the kinetics of the oxidation-reduction (redox)
reaction, thereby catalyzing the reaction.
Palladium and iron BNPs are commercially
available and currently the most common.
In bench-scale tests, BNPs of iron combined
with palladium showed contaminant degradation
two orders of magnitude greater than microscale
iron particles alone (Zhang, 2006b). These
particles were 99.9 percent iron and less than
0.1 percent palladium. Palladium can catalyze
the direct reduction of TCE to ethane without
producing other intermediate by-products such
as vinyl chloride (Nutt, 2005). Research is
ongoing using gold and palladium BNPs to
degrade TCE and other chlorinated compounds
(Nutt, 2005); however, unlike nanoiron, these
nanoparticles require a source of reductant such
as dissolved hydrogen. They may be used in
conjunction with nZVI to supply hydrogen, or an
external source of reductant must be applied.
Figure 3 shows a schematic of gold and
palladium BNPs from a study where the
amounts of palladium were varied to optimize
the contaminant degradation rate by maximizing
the percentage of surface cover. In that study,
the TCE reaction rate was maximized at 12.7
percent palladium content. Using palladium in
BNPs may improve the reaction kinetics and
more effectively distribute the injected slurry or
mixture.
BNPs can be injected by gravity or by pressure
feed (Gill, 2006). BNPs were used in an
application at the Naval Air Engineering Station
in Lakehurst, New Jersey, where the soil and
groundwater were contaminated with PCE, TCE,
and other daughter products. Data indicate that
the BNP treatment resulted in a decrease in the
average total VOC concentration by 74 percent
within six months (NAVFAC, 2005).
Figure 3. Schematic of Pd/Au BNPs idealized as clusters, with a 4-nm Au core and variable Pd
surface coverage from 0 to 100 percent (with corresponding Pd content). (Nutt, 2006)
Surface
coverage
Pd content
(wt%)
0%
10%
25%
50%
75%
90%
0% 2.4% 5.8% 10.9% 15.5% 18.1%
100%
19.7%
Another product, eZVI, is also commercially
available and has been used for the remediation
of chlorinated solvents. The product consists of
ZVI surrounded by an oil-liquid membrane that
facilitates the treatment of chlorinated
hydrocarbons. eZVI is made from food-grade
surfactant, biodegradable oil, water, and either
nanoscale or microscale iron to form emulsion
droplets. Figure 4 illustrates the structure of an
eZVI particle. The exterior oil membrane of the
emulsion is hydrophobic, as are DNAPL
contaminants such as TCE. The emulsion is
therefore miscible with the DNAPL, allowing
increased contact between the TCE DNAPL and
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the ZVI within the droplet. When the emulsion
droplets combine with the TCE, it is believed
that the contaminant dissolves and diffuses into
the droplet where it comes into contact with the
ZVI and is degraded. A concentration gradient
is established from the migration of the TCE
molecules into the aqueous emulsion droplet
and by the migration of the by-products out of
the particles and into the surrounding water
phase, further driving the degradation reactions
(O'Hara, 2006). While both nZVI and eZVI have
been shown to reduce TCE DNAPL, according
to one researcher, eZVI appears to be more
effective in treatment, lowering TCE
concentrations to a greater extent than nZVI.
The vegetable oil also enhances biological
activity, which contributes to the destruction of
the contaminant (Quinn et al, 2005).
Figure 4. Structure of an eZVI particle
(modified from O'Hara, 2006)
Like other iron nanoparticles, the size of eZVI
particles can reach the microscale range (larger
than 100 nm). This could make the emulsion
more difficult to emplace. Because microscale
particles are less costly to produce than
nanoscale eZVI, using a mixture of nano and
microscale particles provides cost savings while
maintaining the benefits of nanoscale iron. eZVI
has been used to clean up TCE-contaminated
soil and groundwater at an industrial site on
Patrick Air Force Base in Florida. The particles
were introduced via high-pressure pneumatic
injection. While initial TCE concentrations were
as high as 150,000 ug/L, the highest
concentration measured after treatment was
3,580 ug/L. The remediation project was still in
operation at the time this fact sheet was
prepared. More information on eZVI
applications can be found at the Web site link
provided in the 'Selected Sites Using or Testing
Nanoparticles for Remediation' section at the
end of this fact sheet.
DESCRIPTION OF NANOMATERIALS WITH
POTENTIAL REMEDIATION APPLICATIONS
Researchers are developing a variety of
nanomaterials for potential use to adsorb or
destroy contaminants as part of either in situ or
ex situ processes. These particles include
SAMMS™, ferritin, dendrimers, and
metalloporphyrinogens. The stage of
development ranges from bench to pilot scale.
Some materials can be made with surface
functional groups to serve as adsorbents to
scavenge specific contaminants from waste
streams. SAMMS™ particles consist of a
nanoporous ceramic substrate coated with a
monolayer of functional groups tailored to
preferentially bind to the target contaminant.
The functional molecules covalently bond to the
silica surface, leaving the other end group
available to bind to a variety of contaminants.
According to researchers, SAMMS™ particles
maintain good chemical and thermal stability
and can be readily reused or restored (Fryxell,
2007). Figure 5 shows a schematic of a
functionalized nano-sized pore within a
SAMMS™ particle. The particle has a large
surface area to allow for quick sorption kinetics.
Contaminants successfully sorbed to SAMMS™
particles include radionuclides, mercury,
chromate, arsenate, pertechnetate, and selenite
(Mattigod, 2003; Tratnyek, 2006). According to
the SAMMS™ Adsorbents Web site
(http://sammsadsprbents.com/paqe/resource-
center), SAMMSIM has shown positive results in
pilot scale tests in the remediation of mercury in
well water with a high concentration of dissolved
solids, aqueous mercury in low concentrations,
highly radioactive mercuric waste, and gaseous
elemental mercury.
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Figure 5. Schematic of functionalized nano-
sized pore within a SAMMS™ particle
(modified from Mattigod, 2004)
Nanotubes are engineered molecules most
frequently made from carbon. They are
electrically insulating, highly electronegative and
easily polymerized. Nanotubes have also been
made from titanium dioxide (see Figure 6) and
have demonstrated potential for use as a
photocatalytic degrader of chlorinated
compounds (Chen, 2005). Bench-scale
research has shown titanium dioxide nanotubes
to be particularly effective at high temperature,
capable of reducing contaminant chemicals by
greater than 50 percent in three hours
(Xu, 2005).
Figure 6. Scanning electron microscope
image of titanium dioxide nanotubes
(Chen, 2005)
Bench-scale tests using ferritin, an iron storage
protein, have indicated that it can reduce the
toxicity of contaminants such as chromium and
technetium in surface water and groundwaterto
facilitate remediation (Temple University, 2004).
Like titanium dioxide, ferritin is photocatalytic; in
one bench-scale project, the addition of visible
light caused ferritin to reduce toxic, water-
soluble hexavalent chromium to the less toxic
trivalent chromium, which is not water soluble
and precipitates out of solution.
Dendrimers are hyper-branched, well-organized
polymer molecules made up of three
components: core, branches, and end groups.
Dendrimer surfaces terminate in several
functional groups that can be modified to
enhance specific chemical activity. Fe°/FeS
nanocomposites, synthesized using dendrimers
as templates, could be used to construct
permeable reactive barriers for the remediation
of contaminated groundwater. Bench-scale
research has indicated that dendrimers have
flexible delivery options (Diallo, 2006).
Metalloporphyrinogens are complexes of metals
with naturally occurring, organic porphyrin
molecules. Examples of biological
metalloporphyrinogens are hemoglobin and
vitamin B12. Batch-reactor experiments have
shown that metalloporphyrins are capable of
reducing chlorinated hydrocarbons such as
TCE, PCE, and carbon tetrachloride under
anoxic conditions to remediate contaminated soil
and groundwater, with some structures showing
a reduction of TCE and PCE by greater than 990
percent from the original concentration
(Dror, 2005).
Researchers are also using nanotechnology to
develop membranes for water treatment,
desalination, and water reclamation. These
membranes incorporate a wide variety of
nanomaterials, including nanoparticles made of
alumina, zero-valent iron, and gold (Theron,
2008). Carbon nanotubes can be aligned to
form membranes with nanoscale pores to filter
organic contaminants from groundwater
(Mauter, 2008; Meridian Institute, 2006).
These and other types of nanoscale materials
are chemical substances as defined under the
Toxic Substances Control Act (TSCA). Pursuant
to TSCA section 5(a)(1), any person
manufacturing (including importing) a new
chemical substance must file with EPA a
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premanufacture notice (PMN) at least 90 days
prior to manufacture, unless the substance is
exempt from PMN reporting.
CHEMISTRY OF SELECTED
NANOPARTICLES
Zero-valent, or elemental, iron is a reducing
reagent that can react with both dissolved
oxygen (DO) and water (Zhang, 2003). In the
presence of an oxidizing agent, Fe° becomes
oxidized to ferrous ions (Fe2+), and the two
released electrons become available to reduce
other compounds. In aerobic conditions, Fe°
reacts with dissolved oxygen to form ferrous
ions and water. Fe° can also reduce water to
form ferrous ions, hydrogen, and hydroxide ions.
These reactions are shown below:
2Fe°+4H+ + 02 -
(Matheson, 1994)
2Fe°+2H20 -» 2Fe
(Matheson, 1994)
2+
'+ + 2H20
H2 + 20H"
In addition to the above reactions, ZVI can also
react with contaminants. Figure 7 illustrates a
reaction that shows the reducing ability of
elemental iron with a chlorinated hydrocarbon.
In this example, the Fe° (in the form of a BMP)
transforms TCE to ethane, releasing Fe
and chloride ions.
2+
ions
Figure 7. Reaction of iron in a bimetallic
nanoscale particle with TCE (image courtesy
of Wei-Xian Zhang, Lehigh University)
CLHC1
C2H6+3C1-
The reductive capacity of Fe when it comes into
contact with chromium contamination in soil and
groundwater can be seen in the following
equation, where iron is oxidized to its ferrous
form and chromium is reduced from chromium
(VI) to the less toxic chromium (III) (Cao, 2006):
3Fe° + 2Cr2+ -» 3Fe2+ + 2Cr3+
Nanosized titanium dioxide has been shown to
mineralize a variety of herbicides, insecticides,
and pesticides via photocatalysis and can
convert other contaminants to less toxic
compounds (Konstantinou, 2003). When
aqueous titanium dioxide suspensions are
irradiated with light energy greater than 3.2 eV,
electrons are generated according to the
equation below:
TiO2 + hv -> e" + h+
The electrons are capable of reducing specific
contaminants directly. The electrons may also
react with dissolved oxygen or the oxygen
adsorbed on the surface of the titanium dioxide,
reducing it to a superoxide radical anion that can
oxidize specific contaminants.
IN SITU APPLICATION OF NANOPARTICLES
The method of application for nanoparticles is
usually site-specific and is dependent on the
type of geology found in the treatment zone and
the form in which the nanoparticles will be
injected. The most direct route of injection
utilizes existing monitoring wells, piezometers,
or injection wells. Recirculation is a technique
that involves injecting nanoparticles in
upgradient wells while downgradient wells
extract groundwater. The extracted
groundwater is mixed with additional
nanoparticles and reinjected in the injection well.
The wells keep the water in the aquifer in
contact with the nZVI, and also prevent the
larger agglomerated iron particles from settling
out, allowing continuous contact with the
contaminant.
Additional methods and processes to inject the
nanomaterials include direct push, pressure-
pulse technology, liquid atomization injection,
pneumatic fracturing, and hydraulic fracturing.
The direct push method involves driving direct-
push rods, similar to small drilling augers,
progressively deeper into the ground. This
method allows materials to be injected without
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having to install permanent monitoring wells
(Butler, 2000). Pressure pulse technology
utilizes large-amplitude pulses of pressure to
insert the nZVI slurry into porous media at the
water table; the pressure then excites the media
and increases fluid level and flow (OCETA,
2003). Liquid atomization injection is a
technology that is proprietary to ARS
Technologies, a company that specializes in
pneumatic fracturing and injection field services.
It introduces an nZVI-fluid mixture into the
subsurface using a carrier gas. The nZVI liquid-
gas combination aerosolizes, allowing for more
effective distribution; this method can be used in
geologic formations with lower permeability
(NAVFAC, 2008). Fracturing injection
(pneumatic or hydraulic) is a high pressure
injection technique using compressed air
(pneumatic) or a water-based, highly viscous
slurry containing sand (hydraulic) that fractures
rock and allows liquids and vapors to be
transported quickly through the channels
created. Pneumatic fracturing uses air to create
a fracture network of preferential flow paths in
rock around the injection point to allow liquids
and vapors to be transported quickly through
fractured rock. This method of injection
improves access to contaminants and allows
liquids to flow freely (Pneumatic Fracturing Inc.,
2008; Zhang, 2003).
Research is ongoing into methods of injection
that will allow nanoparticles to better maintain
their reactivity and increase their access to
recalcitrant contaminants by achieving wider
distribution in the subsurface. Creating nZVI on
site reduces the amount of oxidation the iron
undergoes, thereby reducing loss in reactivity.
Researchers in green chemistry have
successfully created nZVI in soil columns using
a wide range of plant phenols, which, according
to the researchers, allows greater access to the
contaminant and creates less hazardous waste
in the manufacturing process (Varma, 2008).
Figure 8 illustrates the basic principles of two
methods of remediating contaminated
groundwater using nanoscale iron. The image
at the top shows treatment of DNAPL
contamination by injection of nanoparticles. In
the second image, a reactive treatment zone is
formed by sequential injections of nZVI. This
creates overlapping zones of particles that
adsorb to the native aquifer material.
Post-injection observations of the subsurface
indicate an increase in pH (due to the formation
of hydroxyl ions) and a decrease in the
oxidation-reduction potential (ORP) (due to the
reducing conditions that are created). A lower
ORP would most likely favor anaerobic bacteria
growth, which in turn may promote increased
degradation. Other chemicals formed when
using particles such as nZVI may include
hydrogen gas and Fe2+ ions, which would further
promote microbial growth. After an nZVI
injection, the ORP tends to decrease sharply
before becoming stable (Zhang, 2003).
LIMITATIONS
Site-specific conditions such as the site location
and layout, geologic conditions, concentration of
contaminants, and types of contaminants may
limit the effectiveness of nanoparticles. For
example, the research conducted for this fact
sheet documents only two sites that have used
nanoparticles in fractured bedrock, although
several pilot studies have been undertaken
(Mace, 2006). Prior to injection of nanoparticles,
geologic, hydrogeologic, and subsurface
conditions should be evaluated to determine
whether injected particles would have adequate
subsurface infiltration. Factors that affect
subsurface mobility include composition of the
soil matrix, ionic strength of the groundwater,
hydraulic properties of the aquifer, depth to the
water table, and geochemical properties
(including pH, dissolved oxygen, ORP,
concentration of nitrate, nitrite, and sulfate),
among others. Performance will be site specific
and depend on the presence of competing
oxidants such as DO and NO3" (nitrate ion),
contaminant concentration, and soil/groundwater
pH (Liu, 2006; Liu, 2007).
Studies have shown that nanoparticles may not
achieve widespread distribution in the
subsurface due to agglomeration prior to
complete dispersion within the soil or
groundwater matrix, limiting the radius of
influence. Nanoscale zero-valent iron particles
are attracted to one another, which can cause
them to agglomerate into larger micron-sized
particles (greater than 100 nm) (Tratnyek, 2006;
Phenrat 2007). Agglomeration also reduces the
exposed reactive surface area of the particles.
The pH of the subsurface may also limit the
effectiveness of nanoparticles because the
sorption strength, agglomeration, and mobility of
the particles are all affected by the pH of the
groundwater (U.S. EPA, 2007). The ionic
strength and types of cations in the
groundwater, as well as the chemical and
physical characteristics of the aquifer materials,
also affect the agglomeration and movement of
iron nanoparticles (Saleh, 2008).
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Figure 8. Schematic of two methods of groundwater remediation using nanoiron
(Tratnyek, 2006)
Tratnyek and Johnson (2006)
NanoToday 1(2): 44-48
. Low-Permeability Layer
TtMtnyek and Johnson (2006)
NanoToday 1(2): 44-48
Contaminated
Groundwater
Treated
Groundwater
Reactive Treatment Zone
Passivation is another factor that may limit the
effectiveness of iron nanoparticles. If nZVI is
being used, improper handling can result in the
iron becoming oxidized and passivated prior to
reacting with the contaminants. As a rule,
injection mechanisms should limit the volume of
water injected along with the iron, to limit
exposure to oxygen and other oxidants that
could passivate the iron before and during
injection. If using larger volumes, deoxygenated
water can minimize the iron passivation, but
other oxidants may still be present to react with
the iron (Gavaskar, 2005).
A challenge with evaluating the effectiveness of
nanoparticle injection is monitoring the
distribution of injected particles in the
subsurface. It is therefore important to identify
the appropriate parameters to measure
performance. Typically, geochemical measures
such as ORP are monitored as a surrogate.
Dissolved iron can also be monitored. Reaction
kinetics are difficult to monitor; however, post-
injection chemical concentrations are measured
using standard approaches. Additionally, the
kinetics and reactivity of nanoparticles in a
DNAPL source zone may vary from the kinetics
and reactivity in a dissolved plume (U.S. EPA,
2008; Liu, 2007).
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FATE, TRANSPORT, AND TOXICITY
QUESTIONS
While nZVI is the most widely used nanoparticle
in site remediation, knowledge is limited on the
fate and transport of iron nanoparticles in the
environment, and little research has been done
on the potential toxicological effects
nanomaterials might pose. There are
insufficient data on the potential for
bioaccumulation of nanoparticles in
environmentally-relevant species (Kreyling,
2006) and there have been few studies on the
effects of any nanoparticles on environmental
microbial communities (Klaine, 2008).
As described in the Limitations section,
agglomeration often affects transport of
nanoparticles in the subsurface. The particles
may become associated with the aquifer matrix
as oxidized iron particles after reacting with
contaminants. Under standard environmental
conditions (aerated water, pH 5 to 9), Fe2+ will
readily and spontaneously oxidize to Fe3+ and
precipitate out of the groundwater as insoluble
iron oxides and oxyhydroxides. Researchers
are working on methods to improve the mobility
of iron nanoparticles within aquifers and to
optimize contact between the nanoparticle and
contaminant. Ongoing studies are evaluating
surface coatings and other modifications that
would reduce agglomeration of nanoparticles
and maximize subsurface mobility (Phenrat,
2008). Preliminary research indicates that
polymers and surfactants stabilize nanoparticle
suspensions in aquifers, inhibiting their
agglomeration and allowing greater dispersal
without compromising the ability of the iron to
remediate contaminants (He, 2007). Soils high
in clay content have been shown to allow
greater dispersal of nZVI as well; anionic clay
particles appear to function as a natural
stabilizer, allowing for more effective transport
(Schrick, 2004, Hydutsky, 2007). While
increased mobility would allow more efficient
remediation, it could also result in the possibility
of the nanomaterials migrating beyond the
contaminated plume area, seeping into drinking
water aquifers or wells, or discharging to surface
water during the remediation process.
Studies are being conducted on the potential
toxicity of various types of manufactured
nanomaterials. The increased surface area and
larger number of reactive sites of nanomaterials
may equate to greater biological activity per unit
mass than micro- or macro-scale particles of the
same composition. Substances considered
nontoxic at macroscale may have negative
impacts on human health when nanoscale
particles are inhaled, absorbed through skin, or
ingested (Kreyling, 2006). Because of the
minute size of nanomaterials, the particles have
the potential to migrate to or accumulate in
places that larger particles cannot, such as the
alveoli in the lungs (Grassian, 2007), thereby
potentially increasing toxicity. Some
nanoparticles have demonstrated an ability to
increase bioavailability of certain hydrophobic
contaminants, for example, by increasing
mobility of contaminants bound to soil and
sediment surfaces (Tungittiplakorn, 2005).
Issues of toxicity and safety have limited the use
of nanotechnology for remediation by some
private sector companies. For example, DuPont
has ruled out the use of nZVI for site
remediation at any of its sites until issues
concerning fate and transport have been more
thoroughly researched. The company has cited
questions of post-remediation persistence and
potential human exposure to the particles as
areas of particular concern (DuPont, 2007). As
another example of a cautionary approach, the
Continental Western Group of insurance
companies announced that it will no longer
cover injury and/or damage arising from
nanotubes or nanotechnology, as used in
products or processes. See:
http://cwqins.com/mike/documents/CW3369060
8NanotubesExclusion.pdf.
EPA's Office of Research and Development
(ORD) published a Draft Nanomaterial Research
Strategy (MRS) in January 2008. The initial
emphasis of the MRS will be to evaluate and
assess the extent to which nanomaterials and
products impact the environment and human
health. Results from this research will directly
inform future policy decisions regarding how to
address possible adverse implications
associated with the production, use, recycling, or
disposal of nanomaterials and nanoproducts
(that is, products containing nanomaterials).
Initially, a smaller portion of the proposed
research will focus on beneficial environmental
applications, such as more effective control
technologies and enhanced production
processes that reduce emissions and releases
of conventional pollutants. As the program
evolves overtime, ORD will augment its efforts
in this area.
10
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In the Draft MRS, ORD identified four key
research themes for investigating nanomaterials
for EPA:
• Sources, Fate, Transport, and Exposure
• Human Health and Ecological Research
to Inform Risk Assessment and Test
Methods
• Risk Assessment Methods and Case
Studies
• Preventing and Mitigating Risks
(USEPA 2008A).
PERFORMANCE AND MONITORING
As of September 2008, data exhibiting varying
degrees of comprehensiveness were obtained
for a total of 26 sites using or testing
nanoparticles for remediation. Details on these
selected sites are available at http://clu-
in.org/products/nanozvi, and will be updated
periodically as new information is received.
One site is located in Quebec, Canada; the
remaining 25 sites cover seven states in the
United States. Of these 25 sites, data for 16
were independently verified through peer-
reviewed sources or by government regulators.
Data for the other nine sites were not
independently verified. There are seven full-
scale remediation applications and 19 pilot-scale
projects represented. Thirteen remediation
projects used nZVI, eight used BNPs, four used
eZVI, and one used nanoscale calcium ions with
a noble metal catalyst. The most frequently
treated contaminants of concern were
chlorinated solvents, such as TCE, PCE, TCA,
and VC.
Of the seven full-scale projects, five indicated
that site-specific cleanup goals were met,
according to the points of contact. The other
two demonstrated decreasing trends in
contaminant concentrations. Of the 12 pilot-
scale projects, six indicated that cleanup goals
had been met. The other six either did not meet
cleanup goals or sufficient information on
cleanup goals was not provided to assess
performance.
Details for two projects in the list of sites are
provided below.
Use of nZVI at a former Manufacturing site in
Passaic, New Jersey. nZVI was applied at a
former manufacturing site in Passaic, New
Jersey, where chlorinated solvent contaminants
such as TCE had been found in groundwater. A
pilot scale test was conducted from September 9
to 13, 2005, to treat a shallow sand aquifer. The
technology design included the injection of 108
pounds of nZVI slurry and 1,200 pounds of
emulsified oil into 3 points within the silt unit.
Pneumatic fracturing injections were used at two
of the injection points and hydraulic injection
was used at the third. At the end of the pilot-
scale test, there was a 90 to 100 percent
reduction in TCE concentrations throughout the
contaminant plume. Monitoring occurred weekly
during the first month of the project and was
conducted monthly thereafter (Zhang, 2006a).
Use of nZVI at Fill Area in Hamilton Township,
New Jersey. Contaminants at the Klockner
Road Site in Hamilton Township, New Jersey
were treated using nZVI. The site was a former
fill area, where contaminants such as TCE, TCA,
DCE, and dichloroethane (DCA) were found in
the groundwater. A full-scale project was
implemented using nZVI (NanoFe Plus™).
NanoFe Plus™ is manufactured by PARS
Environmental Inc. and consists of nZVI with an
added catalyst to enhance the speed and
efficiency of remediation. The nanoscale iron
was injected in three phases. Phase I injection
contained 3,000 pounds of slurry and was
injected at the northern end of the site over a
period of 20 days. Phase II injection contained
1,500 pounds of slurry and was injected
throughout the northern half of the site over a
period of 10 days. Information on Phase III was
not available at the time this fact sheet was
prepared. The results of the full-scale injections
showed up to 90 percent reduction in the overall
contaminant concentrations. ORP, pH, and
groundwater elevations were monitored during
each phase of the injection. The first post-
injection monitoring event was conducted one
week after the first injection and the second
event was conducted two weeks after
completion of the Phase II injection. At
preparation of this fact sheet, monitoring
activities were ongoing and included collecting
groundwater samples to monitor trends in any
remaining groundwater contamination. Cost
information was not available in the materials
reviewed to prepare this fact sheet (Gill, 2006).
11
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COST
Three site-specific examples of project costs are
shown in Table 1 below. The first two sites
achieved their remedial objectives; information
on performance for the third site was not
available. The cost information that was
provided is limited; therefore, a comparison of
nanotechnology costs with the costs of
traditional technologies cannot be accurately
conducted at this time. Factors contributing to
the costs include site type, type of contaminants,
concentrations of contaminants, extent of the
plume, and any challenges that may have
occurred during remediation. The factors that
were included in the total cost for the Naval Air
Engineering Station in New Jersey included
monitoring well installation, sampling, nZVI
injection, post-injection sampling, and reporting.
The components contributing to the total cost at
the Naval Air Station in Jacksonville, Florida,
included mobilization, monitoring well
installation, nZVI injection, sampling and
analysis, and other miscellaneous costs
(Gavaskar, 2005). nZVI production is included
in the injection costs for both of these sites. The
final costs for the Patrick Air Force Base Site
include mobilization and site setup, monitoring
well installation, recirculation/ injection events,
surveying, disposal of demonstration derived
waste, and monitoring. Administrative costs
associated with project management, work plan
generation, and bench-scale treatability study
costs were not included.
Additional factors that may increase the total
cost of nanoparticle application may include
operational requirements connected with any
contamination found underneath a building, or
the need to treat or dispose extracted fluids
(Wilson, 2004).
Table 1. Costs for example projects using nanotechnology for site remediation
Site Name
Naval Air Engineering Station
Lakehurst, NJ1
Naval Air Station
Jacksonville, FL2
Patrick Air Force Base, FLJ
Cost Components
Remediation
Cost (Total)
$255,500
$260,000
$4,000,000
Capital
Costs
-
-
$2,000,000
O & M Costs
$213,000
$110,000
$70,000
Unit
Cost
-
$269/cy
$180/cy
1. O&M costs: Monitoring Well Installation $24,400, Sampling and Analysis $58,400, Reporting $18,100.
2. nZVI cost: $37,000. O&M costs: Monitoring Well Installation $52,000, Sampling and analysis $110,000.
967 cubic yards (cy) soil treated.
3. Capital costs: $1,000,000 for eZVI, $1,000,000 for pneumatic injection contractor. 22,222 cy soil treated.
LIST OF IDENTIFIED VENDORS FOR
NANOTECHNOLOGY
Several vendors supply nanomaterials for site
remediation. Some of the suppliers that were
identified and their products are shown in
Table 2. This list should not be considered to be
comprehensive or as an endorsement by EPA.
More information about the vendors and other
types of nanomaterials can be found at
http://www.nanovip.com.
SELECTED SITES USING OR TESTING
NANOPARTICLES FOR REMEDIATION
A list of sites using or testing nanoparticles for
remediation is available at http://clu-
in.org/products/nanozvi. This list will be updated
periodically as new information is received.
12
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Table 2. Identified nanomaterial vendors
Vendors*
Crane Polyflon
Lehigh University
Environmental Restoration
Services, LLC
OnMaterials LLC
PARS Environmental Inc.
Toda Kogyo Corporation
VeruTEK Technologies,
Inc.
Pacific Northwest National
Laboratory
Nanomaterial Produced
PolyMetallix
Fe/B
Nano-Ox
ZLoy
NanoFe™ and NanoFe
Plus™
RNIP
Green Chemistry and
Nanotechnoloy
SAMMS™
Web site
www.polymetallix.com
www.lehiqh.edu/nano/environmental.html
http://www.ersllccorp.com/index.html
www.onmaterials.com
www.parsenviro.com
www.toda.co.ip/enqlish/c02-02.html
www.verutek.com
http://samms.pnl.gov/
* Mention of product does not imply endorsement. Vendors that would like
submit their request in a comment to the Clu-in Web site at: http://www.clu
to be included in future iterations of this table should
-in.ora/gbook.cfm
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NOTICE
Preparation of this fact sheet has been funded
wholly or in part by the U.S. Environmental
Protection Agency under Contract Number EP-
W-07-078. For more information regarding this
fact sheet, please contact Martha Otto, EPA, at
(703) 603-8853 orotto.martha@epa.gov. This
fact sheet is available for viewing or
downloading from EPA's Hazardous Waste
Cleanup Information (CLU-IN) Web site at
http://cluin.org/542F08009. A limited number of
hard copies are available free of charge from:
EPA/National Service Center for Environmental
Publications
P.O. Box 42419
Cincinnati, OH 45242-2419
Phone: (800)490-9198
Fax: (301)604-3408
Web site: www.epa.gov/nscep
ACKNOWLEDGMENT
Special acknowledgment is given to the
following individuals for their review and
thoughtful suggestions to support the
preparation of this fact sheet: Glen E. Fryxell
(Pacific Northwest National Laboratory), Gregory
V. Lowry (Carnegie Mellon University), Paul
Tratnyek (Oregon Health and Science
University), Don Zhao (Auburn University),
Robert Ellis (ARCADIS), Florin Gheorghiu
(Colder Associates, Inc.), Heather Henry
(NIEHS), David A. Sheets (U.S. Army
Environmental Policy Institute), and EPA staff:
Joseph Freedman and Manisha Patel of the
Office of the General Counsel, Bernard Schorle
of U.S. EPA Region 5, Jim Alwood and Jed
Costanza of the Office of Pollution Prevention
and Toxics, Michael Gill, Jon Josephs, Nora
Savage, and Katrina Varner of the Office of
Research and Development, Elisabeth Freed of
the Office of Site Remediation Enforcement,
Catherine Davis of the Office of Solid Waste,
Matt Charsky of the Office of Superfund
Remediation and Technology Innovation, and
Hal White of the Office of Underground Storage
Tanks.
17
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