(Wang 1997)
Emerging Nanotechnologies for Site
Remediation and Wastewater Treatment
August 2005
Prepared by
Katherine Watlington
National Network for Environmental Management Studies Fellow
North Carolina State University
for
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Office of Superfund Remediation and Technology Innovation
Technology Innovation and Field Services Division
Washington, DC
www.epa.gov
www.clu-in.org
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
NOTICE
This document was prepared by a National Network of Environmental Management studies
grantee under a fellowship from the U.S. Environmental Protection Agency. This report was not
subject to EPA peer review or technical review. The EPA makes no warranties, expressed or
implied, including without limitation, warranty for completeness, accuracy, or usefulness of the
information, warranties as to the merchantability, or fitness for a particular purpose. Moreover,
the listing of any technology, corporation, company, person, or facility in this report does not
constitute endorsement, approval, or recommendation by the EPA.
The report contains information attained from a wide variety of currently available sources,
including project documents, reports, periodicals, Internet websites, and personal communication
with both academically and commercially employed sources. No attempts were made to
independently confirm the resources used. It has been reproduced to help provide federal
agencies, states, consulting engineering firms, private industries, and technology developers with
information on the current status of this project.
About the National Network for Environmental Management Studies
The National Network for Environmental Management Studies (NNEMS) is a comprehensive
fellowship program managed by the Environmental Education Division of EPA. The purpose of
the NNEMS Program is to provide students with practical research opportunities and
experiences.
Each participating headquarters or regional office develops and sponsors projects for student
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Students must meet certain eligibility criteria.
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
ABSTRACT
The impacts of nanotechnology are increasingly evident in all areas of science and technology,
including the field of environmental studies and treatment. Experts anticipate the development
and implementation of environmentally beneficial nanotechnologies in the categories of sensing
and detecting, pollution prevention, and treatment and remediation. Of the three, the category of
treatment and remediation has seemingly experienced the most growth in recent years. In terms
of site remediation, the development and deployment of nanotechnology for contaminant
destruction has already taken place. Nanoscale iron particles and the subsequent derivatives
(bimetallic iron particles and emulsified iron) represent a viable commercially available
nanotechnology for remediation. Currently, over 15 academic and commercial field scale tests
involving nano-iron particles are underway or have reached completion. Many more sites have
scheduled field studies and consequently the number of vendors supplying this product continues
to grow. In addition, a multitude of nanotechnology applications for site remediation and
wastewater treatment are currently in the research and development stages. From dendritic
polymers to functionalized ceramics, the technologies poised to impact the treatment field are
considerably diverse.
ACKNOWLEGEMENTS
I would like to acknowledge and thank the various individuals and groups who contributed to
this report as reviewers and as contributors. Most importantly, I would like to thank everyone in
the Technology Innovation and Field Services Division of the Office of Superfund Remediation
and Technology Innovation. Specifically, I would like to thank my mentor, Marti Otto, for her
continued guidance. I would also like to thank all of the people both in the academic and
commercial field who contributed information to this report. Please note their names in the
reference section.
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
TABLE OF CONTENTS
1. FORWARD 1
2. PURPOSE 2
3. INTRODUCTION TO NANOTECHNOLOGY 3
4. COMMERCIAL USES OF NANOTECHNOLOGY FOR SITE REMEDIATION: NANO
IRON AND ITS DERIVATIVES 5
4.1. Background 5
4.2. Technology Overview 6
4.3. Remedial Applications 8
4.4. Vendors 10
4.5. Case Studies 11
4.5.1. Edison New Jersey Industrial Site 14
4.5.2. GlaxoSmithKline, Research Triangle Park, NC 14
4.5.3. Naval Air Station, Jacksonville, Florida 15
4.5.4. Launch Complex 34 at Cape Canaveral Air Force Station, Florida 17
4.6. Toxicity and Safety Concerns 18
5. BIMETALLIC PARTICLES AND OTHER METALS 18
5.1. Technology Overview 18
5.2. Remedial Applications 19
5.3. Toxicity and Safety Concerns 20
6. FERRITIN 20
6.1. Technology Overview 20
6.2. Remedial Applications 21
6.3. Toxicity and Safety Concerns 22
7. NANOSCALE SEMICONDUCTOR PHOTOCATALYSTS 22
7.1. Technology Overview 22
7.2. Remedial Applications 23
7.3. Toxicity and Safety Concerns 24
8. SELF ASSEMBLED MONOLAYER ON MESOPOROUS SUPPORTS- SAMMS 25
8.1 Technology Overview 25
8.2 Remedial Applications 26
8.3 Toxicity and Safety Concerns 27
9. DENDRIMERS 27
9.1. Technology Overview 27
9.2. Remedial Applications 27
9.3. Toxicity and Safety Concerns 29
in
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
10. POLYMERIC NANOPARTICLES 29
10.1. Technology Overview 29
10.2. Remedial Applications 30
10.3. Toxicity and Safety Concerns 31
11. SINGLE-ENZYME NANOP ARTICLES 31
11.1. Technology Overview 31
11.2. Remedial Applications 32
11.3. Toxicity and Safety Concerns 33
12. TUNABLE BIOPOLYMERS 33
12.1. Technology Overview 33
12.2. Remedial Applications 33
12.3 Toxicity and Safety Concerns 34
13. NANOCRYSTALLINE ZEOLITES 34
13.1. Technology Overview 34
13.2. Remedial Applications 35
13.3. Toxicity and Safety And Concerns 35
14. OVERALL TOXICITY AND SAFETY CONCERNS 35
15. REGULATORY NEEDS 37
16. CONCLUDING REMARKS: THE FUTURE OF NANOTECHNOLOGY FOR
ENVIRONMENTAL REMEDIATION 38
17. REFERENCES 40
IV
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TABLE OF FIGURES
Figure 1. Division of sites still in need of remediation based on regulatory responsibility
(USEPA2004) 1
Figure 2. Diagram of EZVI droplet (Quinn 2005) 8
Figure 3. Diagram of SAMMS structure (Fryxell 2005) 25
Figure 4. Different dendritic polymers: dendrimer, core-shell tecto(dendrimer), dendrigraft
polymer, hyperbranched polymer (Diallo 2005) 27
Figure 5. Diagram of Dendrimer Enhanced Ultrafiltration Unit (Diallo 2005) 28
Figure 6. Structure of polyurethane acrylate anionomer (UAA) and poly(ethylene glycol)-
modified urethane acrylate (PMUA) derived nanoparticles (Tungittiplakorn 2004) 30
Figure 7. Diagram of the modification process (a), and chemical reactions in the process (b) of
creating SENs (Kim 2003) 32
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
TABLE OF TABLES
Table 1. Contaminants remediated by nanoscale iron (Zhang 2003) 9
Table 2. Field studies where nZVI, RNIP, EZVI, or BNIP injections have occurred 12
Table 3. Sites where nZVI, RNIP, EZVI, or BNIP injections have been proposed 13
VI
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
LIST OF ABBREVIATIONS
ANSI American National Standards Institute
BNIP Bimetallic Nanoscale Iron Particles
BTEX Benzene, Toluene, Ethylbenzene, and Xylene
CA Chloroethane
cDCE cis-l,2-dichloroethene
COC Chlorinated Organic Contaminant
CVOC Chlorinated Volatile Organic Contaminant
Cr(III) Trivalent Chromium
Cr(VI) Hexavalent Chromium
DCA Dichloroethane
DCE Dichloroethene
DNAPL Dense Non-Aqueous Phase Liquids
DOD Department of Defense
DOE Department of Energy
EZVI Emulsified Zero-Valent Iron
MTBE Methyl-fert-butyl ether
NNI National Nanotechnology Initiative
NPL National Priority List
nZVI Nanoscale Zero-Valent Iron
PAMAM Poly(amidoamine)
PCB Polychlorinated Biphenyl
PCE Tetrachloroethene
PRB Permeable Reactive Barrier
RCRA Resource Recovery Conservation and Recovery Act
RNIP Reactive Nanoscale Iron Product
SAMMS Self Assembled Monolayers on Mesoporous Silica
SEN Single Enzyme Nanoparticle
TCA Trichloroethane
TCE Trichloroethene
TSCA Toxic Substances Control Act
UST Underground Storage Tank
VC Vinyl Chloride
ZVI Zero-Valent Iron
vn
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
1. FORWARD
For the next few decades, at the very least, our country will be faced with serious issues
regarding the cleanup of contaminated sites across the country. Despite a significant effort over
the past 25 years, the job remains far from complete and as of yet, many sites remain
inadequately characterized. A number of contaminated areas await remedial action, and many
still await identification. Adhering to the current regulatory standards, an estimated 294,000
sites (range 235,000-355,000) require some form of remediation; this does not include sites with
completed or ongoing remediation projects. Contaminated sites can be divided into seven groups
based around regulatory and decontamination responsibility: Superfund, Resource Conservation
and Recovery Act (RCRA) Corrective Action, Underground Storage Tanks (USTs), Department
of Defense (DOD), Department of Energy (DOE), Civilian Federal Agencies, and States
(USEPA 2004). Figure 1 shows the breakdown of the 294,000 sites remaining for the various
segments (USEPA 2004).
Division of Sites Requiring Remediation
• Superfund (736 sites)
n RCRA (3,800 sites)
• Underground Storage Tanks (USTs) (125,000 sites)
nDOD (6,400 sites)
n DOE (5,000 sites)
• Civilian Federal Agencies (>3,000)
n States (150,000 sites)
Figure 1. Division of sites still in need of remediation based on regulatory responsibility (USEPA 2004)
The majority of these sites, which are both large and complex, will require the collaboration of
multiple stakeholders for successful cleanup as well as the development and implementation of
innovative remedial solutions. The drive for novel remediation processes is in high demand.
Expedited and efficient processes often reduce costs, thus saving the responsible parties a great
deal of money. Successful remediation also allows for the ability to reuse land. Another driver
for innovation originated from the 1986 reauthorization of the Superfund law, which added a
new emphasis to "permanence and treatment," (USEPA 2004). While the law only encompasses
the National Priority List (NPL)/Superfund sites that comprise a relatively small fraction of the
total list of contaminated sites, the Superfund program has greatly influenced the entire field of
remediation. The idea of permanence and treatment has largely been adopted by all site
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
divisions. In addition, many new and better remediation technologies implemented at Superfund
sites have spread to other sectors due to the interchangeability of innovative technologies across
the various segments. The remedial compatibility across site divisions, in turn, has created an
extremely large market and, thus, a substantial demand for these new technologies (USEPA
2004).
In the past ten years, emerging technologies such as phytoremediation, bioremediation, and
permeable reactive barriers have become popular new tools. These novel treatments have begun
to compete with more established technologies such as solidification/ stabilization, soil vapor
extraction, and thermal desorption for soil, and pump and treat systems for groundwater (USEPA
2004).
At the very forefront of these emerging technologies lies the development of nanotechnology for
site remediation. Nanotechnology represents an extremely broad field, which encompasses a
number of materials and technologies spanning multiple disciplines. Currently a wide variety of
potential remedial tools employing nanotechnology are being examined at the bench-scale for
use in waste water and soil remediation. One emerging nanotechnology, nanosized zero valent
iron and its derivatives, has reached the commercial market for field-scale remediation and
studies.
2. PURPOSE
While nanotechnology is considered the new buzzword by many in the scientific community,
information regarding the subject remains largely dispersed and fragmented due to the relative
novelty of the technology. This fact holds true for the specific developments in the field of
hazardous waste remediation. While one specific nanotechnology and its derivatives have
reached the commercialization process, a majority of the current studies involving
nanotechnologies for remedial applications remain on the bench scale. Recent journals and
books, such as the Environmental Science and Technology'?, Special Issue on Nanotechnology
and the ACS Symposium Series, Nanotechnology and the Environment, provide a more
comprehensive view of the recent advances. However both of these publications present the
majority of information as a compilation of peer-reviewed articles. These types of publications
often detail the science behind the technology, leaving the overall relevance and connections to
field scale applications vague. In general, a lack of assembled information exists on how these
individual nanotechnologies might eventually be implemented, the type of sites where they
would be appropriate, and the general feasibility for scale-up.
In evaluating the status of this emerging field while also looking ahead to the future, it becomes
important to examine both the science behind these nanotechnologies as well as their current and
potential applications. This paper seeks to provide a more holistic view of the state of the
science. Both the commercialized nanotechnology products and many of the technologies being
researched in academia are discussed. Attention is given both to the research itself as well as the
remedial capabilities. The toxicity and safety concerns of the individual technologies are also
briefly outlined as are the overall toxicity concerns related more generally to the field of
nanotechnology. Finally the current state of regulation is addressed.
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
3. INTRODUCTION TO NANOTECHNOLOGY
"If I were asked for an area of science and engineering (S&E) that will most likely produce the
breakthroughs of tomorrow, I would point to nanoscale science and engineering. "
~ Neal Lane, testifying before Congress in 1998
In 1959, Richard Feynman, a professor at Cal Tech, introduced the world to the expansive
concept of nanotechnology in his lecture, "Plenty of Room at the Bottom," (Feynman 1959). A
revolutionary theory at the time, Feynman envisioned a world where scientists like him could,
"arrange atoms the way we want, the very atoms, all the way down!" (Feynman 1959). While
his lecture incited a great deal of interest in the scientific community, it was the 1980s before
Feynman's radical vision became feasible.
The vision of nanotechnology expanded in 1981, when researchers at IBM developed the
scanning tunneling microscope (STM), which allowed scientists to "see" atoms and molecules.
By 1985, with the aid of the STM, IBM scientists "wrote" the letters IBM using 35 individual
xenon atoms (Lane 2005). These developments helped scientists realize the possibilities, thus
paving the way for the expansion of nanotechnology research and development (R&D).
Despite a growing interest in the subject, a fixed definition of what constitutes "nanotechnology"
remains undeniably elusive. Generally, nanotechnology covers objects on the "nano" scale, or in
other words, objects measuring between 1 and 100 nm (NNI 2005). However, basing
categorization simply on size does not give an adequate definition of the technology. Many
nanosized structures, such as weathered minerals, exist in the environment naturally
(Masciangioili 2003). While classified on the nanoscale, these materials do not fall into the
category of nanotechnology. The remaining requirements for categorization as nanotechnology
include the concept that compounds must possess unique physical, chemical, and/or biological
properties, different from those found in the same material on a large scale (NNI 2005).
Compounds also must be created on the principle of atomic scale control of the assembly and
structure. The National Nanotechnology Initiative (NNI) similarly breaks down the definition
into three requirements, of which any "nanotechnology" must involve all three: "1.) Research
and technology development at the atomic, molecular, or macromolecular levels, in the length
scale of approximately 1-100 nanometers, 2.) Creating and using structures, devices, and
systems that have novel properties and functions because of their small and/or intermediate sizes,
and 3.) Ability to be controlled or manipulated on the atomic scale." (NNI 2005).
A significant number of technologies today already fit the definition for "nano" as defined by the
NNI. Nanotechnology has contributed to the development of materials used in electronic,
magnetic and optoelectronic, biomedical, pharmaceutical, cosmetic, energy, catalytic, and
materials applications. In the manufacturing community, initially, the most profitable avenues
for nanoscale particles and materials have been in the areas of sunscreen, magnetic recording
tape, automotive catalyst supports, biolabeling, chemical-mechanical polishing,
electroconductive coatings, and optical fibers (NNI 2005).
With the many hi-tech functions of nanotechnology, environmental remediation would
seemingly prove an unlikely place to find many applications of nanotechnology. However, the
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
emergence of nanotechnology presents a number of potential environmental benefits, both
directly and indirectly. In a recent review, Masciangioli et al. divided the potential impact areas
for nanotechnology into three categories: treatment and remediation, sensing and detection, and
pollution prevention. Of the three environmental categories, treatment and remediation have felt
the earliest impacts of the nanotechnology revolution. A variety of nanomaterials are in various
stages of research and development, each possessing unique functionalities for treatment. Some
nanoparticles destroy contaminants, for instance, while others sequester them (Masciangioli
2003). The specific nanotechnologies discussed hereafter solely focus on site remediation and
some waste water treatment. In addition to remedial applications for soil, groundwater, and
wastewater, a number of technologies for air remediation are also in development. Carbon
nanotubes, for example, have been recognized for their ability to adsorb dioxin much more
strongly than traditional activated carbon (Long 2001).
Within the category of sensing and detection, nanotechnology anticipates the capability to
provide more sensitive and cost effective technologies for detecting pollution in the ground,
water, and air. Smaller particle size enables the development of smaller sensors, which can be
deployed more easily into remote locations (Masciangioli 2003). The high surface area to mass
ratio, characteristic of nanoparticles, amplifies changes in electrical conductivity and mechanical
resonance that occur when pollutants bind to the particle surface. This feature translates into
sensing systems able to detect very small amounts of pollutants (Rose-Pehrsson 2004). Array
sensors, capable of detecting various pollutants discriminately, also benefit from
nanotechnology. Their ability to manipulate the surface chemistry of particles allows a new
level of selectivity control (Rose-Pehrsson 2004). Single-wall nanotubes (SWNTs) are
exemplary of the potential developments in this field. The unique chemical and electronic
features of SWNTs enable them to act as sensors of electrical resistance changes in the presence
of a targeted pollutant, such as nitrogen dioxide. Zinc oxide also is being researched as a
potential dual-function sensor and remediator (Kamat 2002).
The ability of nanotechnology to abate pollution production is just beginning to be explored and
could potentially catalyze the most revolutionary changes in the environmental field
(Masciangioli 2003, Karn 2004). From the birth of manufacturing onward, production has been
achieved through a top-down approach. In many ways, top-down production parallels stone
sculpture, where an artist begins with a huge block of stone, chiseling, grinding, and sanding to
reach a finished product. Not only does this approach produce waste, but it requires large energy
expenditures (Karn 2004). The "1.7 kg microchip" has recently been adopted as the new
spokesmodel for the scientific community when discussing the problems of top-down
manufacturing (Masciangioili 2003). A study published in 2002 by Williams et al. determined
that the production of a single 2-gram, 32-megabyte chip requires the use of 32 kg of water and
1.7 kg of fossil fuels and chemicals (Williams 2002 and Masciangioli 2003). Nanotechnology
claims the ability to revolutionize manufacturing through a bottom-up assembly approach, where
products self-assemble from molecular building blocks similar to the biological assembly of
proteins (Karn 2004). The idea of molecular manufacturing, however, largely remains
theoretical and most likely will for the coming years. Many nanotechnologies on the market
today do exhibit a level of self-assembly, just not on the same scale required in manufacturing.
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
With any new technology, however, come concerns over its misuse and possible negative effects.
The great excitement for nanotechnology and its potential applications already has been met by
apprehensions over environmental and health effects induced by the unintentional release of
nanoparticles into the environment. Because nanotechnology produces substances with such
unique properties and functionalities, worker exposure and accidental release pose serious
potential threats. Similarly, because of the broadness of the field, regulation of nanoparticles
will be difficult. At the moment it is unclear whether current regulations are adequate for these
emerging technologies.
4. COMMERCIAL USES OF NANOTECHNOLOGY FOR SITE
REMEDIATION: NANO IRON AND ITS DERIVATIVES
4.1. Background
Over the years, the field of remediation has grown and evolved, continually developing and
adopting new technologies in attempts to improve the remediation process. One of the most
established systems is that termed "pump-and-treat" (USEPA 1998b). Pump-and-treat systems
operate on the basis of removing contaminated groundwater from the ground, downstream of the
contamination site, and then treating it before returning it to the ground. With this technology "it
takes a long time to achieve cleanup goals, it has been demonstrated to spread contamination in
some cases, and it is expensive to operate and maintain," requiring continual energy input
(USEPA 2004, 1998b). "A 2001 EPA study found that the average annual operations and
management (O&M) costs of pump-and-treat systems at 79 fund-financed sites are
approximately $570,000, and the median is $350,000... The periods of operation of these systems
as well as the costs vary widely from site to site. The average pump-and-treat system in the EPA
study operated for 18 years, for an average cost of $10 million. Pump-and-treat systems at some
sites with dense non-aqueous phase liquids (DNAPLs) may need to operate for considerably
longer periods." (USEPA 2004). Despite the number of limitations exhibited by these systems,
pump-and-treat remedies still account for 67% of the ground water remedies proposed or in
progress atNPL sites (USEPA 2004, 1998b).
In the early 1990s, the reducing capabilities of metallic substances, such as zero-valent iron
(ZVI), began to be examined for their ability to treat a wide range of contaminants in hazardous
waste/water (Zhang 2003). The most common deployment of ZVI has been in the form of
permeable reactive barriers (PRBs) designed to intercept plumes in the subsurface and
subsequently remediate them (USEPA 1998b). PRBs, first installed at the field-scale in 1994,
offer a substitute for the more established pump-and-treat systems (USEPA 1998b). [The first
full-scale commercial PRB was approved for use in the State of California by the San Francisco
Regional Water Quality Control Board (RWQCB) in 1994. USEPA1998b]. This passive
treatment system has been used to treat pollutants, including chlorinated hydrocarbons, nitro
aromatics, polychlorinated biphenyls (PCBS), pesticides and even chromate. The reducing
capabilities of ZVI can dechlorinate chemicals such as trichloroethene (TCE) and
polychlorinated biphenyls (PCBs) (Lien 2001). ZVI can reduce hexavalent chromium (Cr(VI))
to trivalent chromium (Cr(III)), as well, precipitating it out of solution, thus immobilizing it as Cr
(III) hydroxides or chromium-iron hydroxide solid solutions (USEPA 1997, 1998b).
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
While PRBs can potentially replace pump-and-treat systems as better remedial solutions, the
technology itself is not without drawbacks. As compared to pump-and-treat systems, installation
costs for PRBs are relatively high and the effective "time to replacement" is often uncertain
(USEPA 2004). The installation capabilities only allow PRBs to be inserted up to about 50 ft,
which restricts the technology to shallow plumes only. To prevent contaminants from
circumventing the PRB, plumes must be carefully characterized and delineated (USEPA 1997).
Problems occur from a decrease in iron reactivity caused by the precipitation of metal hydroxides
and metal carbonates onto the surface of the iron (Wang 1997). The low reactivity of ZVI
toward lightly chlorinated compounds allows the formation and perseverance of hazardous
byproducts. Compounds such as cis-l,2-dichloroethane (cDCE) and vinyl chloride often can be
observed as products from the reduction of tetrachloroethene (PCE) and trichloroethane (TCE)
(Wang 1997).
Just as PRBs were designed to provide a better alternative to pump-and-treat, new technologies
are now available to compete with PRBs. As detailed below, nanoscale iron particles and their
derivatives offer a potentially more effective and economical alternative to many remedial
technologies (Zhang 2003). The small particle size of the nano iron (1-100 nm) facilitates a high
level of remedial versatility. This allows a much greater diversity in applications as compared to
the traditional ZVI employed in PRBs. The elevated surface area to mass ratio, a common
characteristic of nanoparticles, also enhances the reactivity of the iron, making it a promising
emerging technology.
4.2. Technology Overview
Nanoscale Zero Valent Iron (nZVI) and Reactive Nanoscale Iron Product (RNIP) comprise the
most basic form of the nano iron technology (Zhang 2003, Okinaka 2004). Particles of nZVI,
typically about 100 to 200 nm in diameter, consist solely of zero valent iron (Fe°). The most
common route to nZVI synthesis employs sodium borohydride as the key reductant (Zhang
2003). In 1997, Wang et al. first produced the nanoscale iron particles in the laboratory using the
method of sodium borohydride reduction. By mixing sodium borohydride (NaBFLi) with
FeCl3'6H2O, Fe3+ is reduced according to the reaction scheme below:
Fe(H2O)63+ + 3BH4" + 3H2O -» Fe° + 3B(OH)3 + 10.5H2 (Wang 1997)
In laboratory scale production of nZVI, Wang et al. achieved a particle size distribution of less
than 100 nm for 90% of the particles produced. The BET surface area for the particles was
determined to be 33.5 m2/g (Wang 1997). Following the reaction, the reduced particles of iron
(Fe°) created could be directly used for contaminant destruction. The stoichiometry of the
reduction of trichloroethene (TCE) to ethane, a typical decontamination reaction, would proceed
as follow:
C2HC13 + 4Fe° + 5H+ -» C2H6 + 4Fe2+ + 3d' (Elliott 2001)
RNIP particles vary slightly from nZVI particles, in that RNIP particles consist of approximately
a 50/50 wt% mixture of iron and magnetite (FesO/t). The core of the particles consists of the
elemental iron (a-Fe), while the FesC^ surrounds the Fe, forming an outer shell (Okinaka 2004).
In a study by Okinaka et al., particle sizes for RNIP were averaged at about 70 nm and mean
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
BET surface areas were determined to be 28.8 m2/g (Okinaka 2004). The synthesis method for
RNIP particles has been patented and detailed, with ferrous sulfate listed as the starting material.
The use of ferrous sulfate as a raw material contributes to a small (-5,000 mg/kg) sulfur content
present in the RNIP particles.
A recent study by Liu et al. compared the efficiency and degradation capabilities of nZVI
synthesized using sodium borohydride reduction and the RNIP particles produced from ferrous
sulfate. The study found that nZVI demonstrated a higher initial surface area and Fe° content. It
was concluded, though, that the presence of boron and the shell thickness were the most likely
explanations for observed differences in reactivity. The nZVI particles demonstrated rapid
dechlorination of TCE and no deactivation; however rapid H2 evolution was observed. This
behavior could cause the particles to "burn out" before they could reach the treatment zone.
Conversely, RNIP particles showed much slower degradation rates of TCE and a lower
accessibility of Fe° due to the FesC^ shell. The shell, however, also protected the particles from
reacting with water, thus preventing the "burn out" observed with the nZVI particles (Liu 2005).
Other methods of producing nanosized iron particles also have been developed. Ball milling
represents another technique. In this process, micron-size iron powder is reduced to the
nanoscale through an attrition or abrasion process using a ball mill (Liles 2004). A vacuum/gas
condensation process also has been used to produce nanosized iron and other metals (Canano
Technologies 2005).
The production of Bimetallic Nonsocial Iron Particles (BNIP) represents an enhancement of the
nZVI technology described above. Grittini et al. reported in 1995 that a bimetallic system of
palladium and iron could rapidly degrade PCBs (Grittini 1995). While Grittini used microscale
iron particles in his experiments, the discovery of palladium's ability to enhance reductive
capabilities proved significant. In 1997, Wang et al. created the first nZVI particles. In the same
experiment, they also coated the nZVI particles with palladium. Later Zhang et al. determined
that the nanoscale palladium-coated ZVI degraded chlorinated compounds at rates 10 to 100
times faster than microscale particles.
To synthesize the particles, after obtaining Fe° as described above, Wang et al. saturated the iron
with an ethanol solution of [Pd(C2H3)2]3 leading to the deposition of palladium on the iron
surface through the reaction:
Pd2+ + Fe° -» Pd° + Fe2+ (Wang 1997)
Initial experiments performed by Wang et al. determined that while nZVI particles dechlorinated
TCE and PCB compounds at a higher rate than iron powders, palladium-coated BNIP proved the
most reactive and thus the destructive to the chlorinated organic contaminants (COCs) (Wang
1997). Scientists have experimented using other noble metal catalysts, such as plutonium, gold,
and nickel; however palladium/iron BNIPs are the only particles commercially available (See
section on Bimetallic Particles).
As with the addition of metal catalysts to nZVI particles, the formation of emulsified zero valent
iron (EZVI) also represents an enhancement to the existing nZVI technology. Emulsion droplets
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
can be created using a food grade surfactant, biodegradable vegetable oil, water, and nZVI,
where a surfactant-stabilized oil-liquid membrane forms around the iron particles in water
(Quinn 2005). Figure 2 shows a diagram of an EZVI droplet. Specifically, in a study performed
by Quinn et al., Sunlight-brand corn oil, sorbitan triolate (a nonionic surfactant) and RNIP
particles from Toda were used to make EZVI. Both nano and microscale iron can be used;
however the studies and information described in recent studies involve only nZVI. Emulsions
typically have a diameter of about 40 um and a specific gravity of approximately 1.1 (Quinn
2005, O'Hara 2004).
Figure 2. Diagram of EZVI droplet (Quinn 2005)
4.3. Remedial Applications
As mentioned previously, the small particle size and high surface area to mass ratio make iron
nanoparticles highly reactive and extremely versatile. The high surface area and surface
reactivity compared with granular forms enable the nanoparticles to remediate more material at a
higher rate and with a lower generation of hazardous byproducts (Zhang 2003). The ability of
the nanoparticles to act as strong reducers also enables the remediation of an extremely wide
range of contaminants. Table 1 lists many of the pollutants potentially remediated by nano iron.
Based on the documented case studies detailed below, the majority of field applications have
utilized nano iron to remediate chlorinated organics compounds, such as TCE. A growing
number of sites, though, contain metal ions such as chromium (Zhang 2003).
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
Carbon tetrachloride
Chloroform
Di chl oromethane
Chloromethane
Hexachlorobenzene
Pentachl orob enzene
Tetrachlorobenzenes
Tri chl orob enzenes
Di chl orob enzenes
Chlorobenzene
DDT
Lindane
Orange II
Chrysoidine
Tropaeolin
Acid Orange
Acid Red
Mercury
Nickel
Silver
Cadmium
Bromoform
Dibromochl oromethane
Dichlorobromomethane
Tetrachl oroethene
Trichloroethene
cis-Di chl oroethene
trans-Di chl oroethene
1 , 1 -Di chl oroethene
Vinyl Chloride
PCBs
Dioxins
Pentachl orophenol
NDMA
TNT
Dichr ornate
Arsenic
Perchlorate
Nitrate
Table 1. Contaminants remediated by nanoscale iron (Zhang 2003)
In conjunction with nano iron's diverse group of target contaminants, the field scale deployment
of the particles can be achieved in a variety of ways. Nanoparticles can be mixed with water to
form a slurry that can be injected using pressure or gravity into a contaminated plume (Zhang
2003). Once injected, the particles remain in suspension, forming a treatment zone. Particles of
iron also can be used in ex situ slurry reactors to treat soil, sediment, and solid waste. In cases of
water and/or wastewater treatment, anchoring nanoparticles onto a solid matrix, such as activated
carbon, can prove extremely effective (Zhang 2003).
The injection of nano iron into the ground represents the most common deployment of this
technology thus far. Overall the process provides a number of remedial benefits. In comparison
with PRBs, nanoparticle injection allows remediation at greater depths and in areas unreachable
by PRBs (i.e. land covered by a building). Most importantly, this technique facilitates source
zone remediation, a clear benefit for site cleanup. The hydrophilic surface of the nano iron
particles only permits the remediation of aqueous phases, which excludes DNAPL remediation.
However nano iron injections into the source still provide benefits unachievable by downgradient
technologies. Remediation at the point of dissolution eliminates the migration distance required
for PRBs and pump-and-treat systems. It also has been speculated that the presence of nZVI in
the source zone amplifies the concentration gradient between the aqueous phase and DNAPL,
which in turn increases the mass transfer of contaminants from DNAPL to the dissolved phase.
To address the significant number of sites across the country contaminated with chlorinated
VOCs in the form of DNAPL, researchers developed EZVI. As mentioned previously, NIP
injections only work for aqueous phase source zone treatment and while they can enhance
DNAPL dissolution, NIP injections cannot directly treat DNAPL. EZVI offers a solution to this
problem in the form of an external oil membrane (Quinn 2005, O'Hara 2004). The EZVI,
exhibiting a specific gravity of 1.1, can be considered in some ways a DNAPL itself.
Similarities between the exterior membrane and DNAPL allow the EZVI to be miscible with the
DNAPL (O'Hara 2004). As a result of this miscibility, when EZVI droplets come in contact
with pure phase contaminants, the DNAPL dissolves through the exterior oil membrane. Once
the DNAPL passes through the oil membrane, the contaminants become trapped. The
confinement of the DNAPL to the emulsion facilitates the degradation by the NIPs. This
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
capability thus can potentially allow source zone remediation of chlorinated DNAPLs (Quinn
2005).
4.4. Vendors
In the past five years, a variety of vendors for nZVI and RNIP have appeared. Polyflon
Company manufactures a nZVI product called Polymetallix, which is then distributed by
Nanitech LLC. PARS Environmental, Inc., manufactures and distributes NanoFe. Wei-xiang
Zhang of Lehigh University supplies nZVI particles to many field sites although he does not
manufacture his product on a commercial scale. OnMaterials represents the most recent market
edition with their product Z-loy. Toda Kogyo Corporation manufactures RNIP, and is the sole
producers of this patented technology.
Polymetallix, NanoFe, and Zhang's particles are all prepared in the same manner, using sodium
borohydride to reduce Fe3+ to nZVI (Zhang 2003, Bilvey Conversation 2005, PARS 2005).
While Zhang achieved particle sizes of less than 100 nm in the lab, for large-scale projects, all
three distributors advertise particle sizes of between 100 and 200 nm. The approximate surface
area of the nZVI particles is advertised as 37.0-58.0 mA2/g by Polymetallix manufacturers.
However, Zhang et al. determined the average surface area of their particles to be approximately
33 mA2/g (Zhang 2003).
OnMaterials employs the second technology outlined above for the manufacture of their product
Z-loy. The company website describes the mean particle size as 250 nm and the median particle
size as 200 nm, with particle surface areas ranging from 1-30 m2/g (OnMaterials 2005). As
described above, Toda's RNIP particles represent a mixture of Fe and Fe304, with an average
size of 70 nm and an average surface area of 28.8 mA2/g (Okinaka 2004).
Prices for nZVI and RNIP vary between vendors. Nanitech LLC has quoted the cost of
Polymetallix at $77 per pound for orders of 300 Ibs, and $72 per pound for orders of 400 Ibs
including delivery. PARS prices orders exceeding 1,000 pounds at $45 per pound for polymer-
supported particles and $31 per pound for unsupported material. OnMaterials quotes pilot scale
quantities of the Zloy product at $20 per pound with a shipping charge of $3 per pound. Toda
estimates the cost of RNIP from $26 to $34 per pound based on the order amount, where the
range is 10,000 Ibs to 100 Ibs respectively (Gavaskar 2005).
Many of the same vendors that manufacture pure nZVI also offer palladium-coated BNIP as
well. PARS Environmental, Inc., manufactures NanoFe Plus. OnMaterials advertises the ability
to customize orders of Zloy through choosing the ratio of iron to palladium. Wei-xiang Zang also
produces BNIP in his lab in addition to nZVI, with the majority of field tests and treatments
using BNIP.
In terms of cost, coating with a catalyst often adds significant expense to an order. PARS quotes
polymer supported nZVI at $45 a pound, while an order of palladium-coated (and supported)
BNIP costs $66 per pound. The near 50% cost increase accompanying palladium coating must
be thus factored into the cost-benefit (Gavaskar 2005).
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
Currently no vendors exist for EZVI. Case studies and experiments involving the technology
have used EZVI prepared on site. As previously noted, nZVI and RNIP particles act as bases
when forming EZVI.
4.5. Case Studies
The application of nano iron and its derivatives for site remediation has quickly gained
popularity as an option in the field. A number of projects involving some form of nano-iron
have been reported, and it appears that these sites represent a variety of the regulatory categories.
The following case studies attempt to provide an overview of the field applications. Table 2
provides a more comprehensive list of locations where field studies have been completed, are
currently underway, or are in planning.
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Site
Name/Description
Naval Air Engineering
Station, Lake hurst,
NJ
Naval Air Station,
Jacksonville, FL
Northeastern USA
(ARCADIS)
Defense contractor
site, Documented
Field Studies,
California
GlaxoSmith Kline
Pharmaceutical
Facility
Edison New Jersey
Industrial Site
Trane Co. Site
NASA Launch
Complex 34
Public Service
Electric and Gas
Company (PSE&G),
Klockner Road Site,
New Jersey
Classification
NPL (DOD)
NPL(DOD)
Private
RCRA
Private
Private
Private
DOD
Private
Region
2
4
9
4
2
2
4
2
Contaminant(s)
PCE, TCE, TCA,
DCE, VC
TCE, DCE, VC
PCE-Source
Zone and
DNAPL
Perchlorate,
NDMA, TCE,
DCE
TCE
TCA, TCE, DCA,
DCE, CA, VC
TCE
TCE
TCE, TCA, DCE,
DCA
Site
Characterization
Groundwater in
shallow aquifer
Fractured rock
aquifer, low
permeability siltstone
and shale, water
table to 100ftbgs
Fractured bedrock
aquifer
Fractured bedrock
Downgradient plume,
surficial aquifer
Surficial aquifer
containing sand,
DNAPL present
Groundwater
contamination in
"perched water zone
and upper table
aquifer"
Status
Field-scale test
complete
Field-scale test
complete
Small field test
complete; full-scale
test in planning
Pilot test completed;
full-scale test in
process
Field-scale test
Field-scale test
completed; larger-
scale treatment in
progress
Field test completed
Field test completed
Field test completed
Remediation Scheme
SNIP injection
SNIP injection into
source zone
nZVI in conjunction with
molasses
nZVI injection, Wei-xian
Zhang's particles
nZVI injection, Wei-xian
Zhang's particles
Injection of
OnMaterial's Z-loy, an
emulsified vegetable oil
amendment
SNIP injection
EZVI injection
SNIP injection with
PARS's NanoFe into
source zone
References
Gavaskar
2005
Gavaskar
2005
Horst 2004
Durant
2004
Glazier
2003
Chu 2005
Elliot 2001
Quinn 2005
Varadhi
2005
Table 2. Field studies where nZVI, RNIP, EZVI, or BNIP injections have occurred.
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Sit
in
o
D
CO
a>
03
o
CO
•o
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
4.5.1. Edison New Jersey Industrial Site
The Edison New Jersey location is the site of a retired adhesives manufacturing plant, which
operated from 1967 to 2002. Until 1990, the manufacturing process employed trichloroethane
(TCA). No major spills or releases were recorded during the operational period. However,
contamination has been attributed to small spills incurred during routine transfer of TCA from
tanker rail cars to aboveground storage tanks. A number of chlorinated volatile organic
contaminants have been detected in the groundwater at the site in high concentrations, primarily
TCA and TCE. Degradation products including DCA, DCE, CA, and vinyl chloride also have
been identified (Chu 2005).
The contamination area fell under the classification of fractured bedrock, specifically Brunswick
Shale. A thin layer (4-6 ft) of soil comprised mainly of silt and clay covered the bedrock. Both a
primary source area and secondary release area were identified. Concentrations as high as
37,000 mg/L of TCA indicated the possible presence of DNAPL in the primary source area. A
pump and treat system was installed in July 2001 and was operational up to the point of the study
(Chu 2005).
The Secondary Source Area served as the location for the pilot study. The contamination in the
area was considered relatively localized, and the area was located away from the buildings and
utilities on site. Z-loy, produced by OnMaterials, and emulsified vegetable oil were used
concurrently to provide an abiotic/biotic remedy. Concentrated iron product and vegetable oil
were mixed together on site; a total of 300 pounds of nZVI and 1,500 gallons of emulsified
vegetable oil comprised the mixture. Injection took place in two locations. One injection well
was converted from a groundwater extraction well, and the other injection point was converted
from a shallow bedrock monitoring well. The solution was injected into both wells in
approximately equal amounts and at pressures between 25 and 50 pounds psi (Chu 2005).
Following the injections, both injection well and two downgradient monitoring wells were
monitored for 13 months. Results indicated that the nZVI produced rapid abiotic degradation in
the injection wells while the vegetable oil encouraged a more lasting biological process
downstream in the monitoring wells. This was inferred from data collected over the monitoring
period. Injection Well 1 experienced a sharp drop in TCA concentration from 10,000 ug/L to a
level below the minimum detection limit. DCA concentrations experienced an initial increase
due to the degradation of TCA, however levels quickly began to decline. CA, the product of
DCA degradation, increased for a longer period of time before finally beginning to decrease.
DCE concentrations also decreased with no accumulation of VC or ethene, indicating complete
degradation to ethane. Overall ethane concentrations for Injection Well 1 steadily increased.
Also of note, alkanes/alkenes and molecular hydrogen were observed in the injection well up to
month 7, indicating ZVI activity throughout that time period (Chu 2005).
4.5.2. GlaxoSmithKline, Research Triangle Park, NC
The site detailed in this particular case study was located in Research Triangle Park, NC, and
owned by GlaxoSmithKline (GSK). While GSK was supervising the cleanup of the RCRA-
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
regulated site, contamination could be attributed to industrial activities carried out by the former
property owners. A waste disposal area was previously located on site but was cleared out prior
to the study by waste excavation. Despite the waste removal, residual contaminants remained.
While multiple chlorinated volatile organic (CVOCs) were detected at the site, TCE was the
primary contaminant of concern. The groundwater concentration of CVOCs reached 14,000
ug/L in the injection well prior to the study. Concentrations in the immediate vicinity of the
former waste disposal area most likely exceeded this value (Zhang 2003).
The site was located in the Durham subbasin, an area composed of Triassic age sedimentary
bedrock. Groundwater was located approximately 30 feet bgs within the interbedded siltstone
and sandstone. The injection site for the case study was located about 125 feet downgradient
from the former waste disposal site mentioned previously. Two downgradient monitoring wells
were installed approximately 22 and 43 feet from the injection site (Zhang 2003, Glazier 2003).
BNIPs and chemical oxidation were both considered for remediation; however BNIPs were
ultimately chosen for the job. Part of the reasoning behind that decision was that the anaerobic
bacteria, Dehalococcoides ethenogenes, had been detected at the site in early characterization.
As mentioned earlier, the lowering of the groundwater ORP has been shown to stimulate the
degradation of CVOC by bacteria (Glazier 2003).
The BNIPs used in the study consisted of iron with a palladium coating and were prepared by
researchers at Lehigh University. A slurry was mixed on site with a BNIP concentration of 1.9
g/L. The total slurry volume was 6,056 L or 1,600 gallons, which translated to a total of 11.2 kg
of iron to be injected. The injection was carried out over a span of three days at an injection rate
of 0.6 gallons per minute (gpm) (Zhang 2003).
Following the injection period, the treatment accomplished over a 90% reduction in the total
concentration of CVOCs in the injection well. This change occurred within several days of the
treatment. A similar reduction in contamination occurred downgradient in the monitoring wells;
however the decontamination process took longer (about 40 days to level out). Individual PCE,
TCE, and DCE concentrations reached groundwater quality standards within six weeks of
remediation and no significant amounts of hazardous daughter products were detected (Zhang
2003, Glazier 2003).
4.5.3. Naval Air Station, Jacksonville, Florida
The Naval Air Station (NAS) located in Jacksonville, Florida, has been operational since 1940.
The site of interest for this case study, H1K, was positioned near the center of the NAS. The
source of contamination for the site was two underground storage tanks (USTs), Tank A and
Tank B. While they were excavated and capped in 1994 along with the associated pipelines,
they were expected to be the source of contamination in the area. Prior to removal, two USTs
stored waste solvents in addition to other substances received from a wash rack, manhole, and
various other operations. Following removal, soil samples taken in 1995 confirmed that the
removal of tanks and pipelines accomplished clean closure for unsaturated soil. The main
groundwater contaminants detected, TCE and TCA, had accumulated around the former location
of Tank A (Gavaskar 2005).
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
From 2000 to 2001 a chemical oxidation method was used to treat the source area. Rebound of
the dissolved phase concentration occurred after each treatment. In 2002, the recharacterization
of the site took place to reassess the level of contamination. Maximum soil concentrations of
25,300 ug/kg, 4,369 ug/kg, and 60,100 ug/kg were detected for TCA, PCE, and TCE,
respectively. Groundwater maximums reached 173 ug/L, 5,520 ug/L, and 1,350 ug/L for PCE,
TCE, and DCE respectively. The concentrations indicated the potential presence of DNAPL,
which would lead to the rebound experienced (Gavaskar 2005).
Groundwater was present in a shallow aquifer located approximately 7 to 24 feet bgs.
Characterization of the unsaturated zone at the site indicated a fairly uniform composition of
medium grained sand and sandy fill. Directly below the water table, between 6 and 12 feet bgs,
a thin layer of clayey and/or silty sand rested on a fine to medium silty sand layer positioned 10
to 17 feet bgs. Between 20 to 24 feet bgs, the composition shifts to a larger amount of silt and
clay, and then at 24 feet becomes mostly clay to a depth of 54 bgs (Gavaskar 2005).
PARS Environmental's product, NanoFe Plus, was chosen for use. The BNIPs consisted of
99.9% iron and 0.1% palladium by weight. The BNIPs were distributed throughout the site
using both direct injection into known "hot spots" and closed loop recirculation. Direct-push
technology (DPT) was used for the injections, where a suspension of BNIPs at 10 g/L was
pumped directly into the DPT boor holes and allowed to discharge via gravity flow. Four
injection and three extraction wells were used for the recirculation system. A BNIP
concentration of 2 g/L was implemented initially in the recirculation process and then increased
to 4.5 g/L (Gavaskar 2005).
Results of the remedial process varied widely from well to well. The recirculation process
appeared to enhance desorption of contaminants into the dissolved phase. Many wells achieved
over a 65% decrease in concentrations of parent VOCs within a short period of five weeks. All
wells showed the present of "daughter" products, such as DCE, where in some cases the
concentration of daughter products rose rapidly after injection and then decreased over time. An
increase in ethane and ethane concentrations accompanied decreases in daughter products,
indicating complete conversion (Gavaskar 2005).
Some source zone wells however, experienced a rise in both TCE and DCE concentrations after
injection. This likely stems from poor distribution of the BNIP slurry and possible displacement
of dissolved TCE. Of additional note, while the presence of ethane/ethane and C4-hydrocarbons,
such as acetylene, indicate some abiotic degradation, the predominance of anaerobic reductive
products such as 1,2-DCE suggests that much of the "parent" degradation occurred through
microbial action. However, a well 20 feet downgradient of the source zone reported almost a
99% reduction in contamination, signifying that a significant amount of BNIPs potentially
migrated out of the treatment zone (Gavaskar 2005).
Overall, the treatment provided some benefit to the site. In the end though, it was unclear how
much of the decontamination that occurred could be attributed to abiotic degradation. nZVI and
BNIPs have been identified as microbial enhancers and it is likely that a significant amount of
the VOC destruction occurred through microbial pathways. It was speculated that some of the
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
BNIPs might have become passivated before injection and also that the concentration of BNIPs
in the slurry was not high enough (Gavaskar 2005).
4.5.4. Launch Complex 34 at Cape Canaveral Air Force Station, Florida
From 1960 to 1968, Launch Complex 34 (LC34) served as a launch site for Saturn Rockets.
Ground contamination most likely occurred during that period and can be attributed to the rocket
cleaning methods employed. Documented evidence indicates that rockets were cleaned with
solvents including TCE directly on the launch pad. At the time of cleaning, excess solvents were
allowed to evaporate, penetrate the subsurface directly, or migrate to surface drainage pits as
runoff material. Following the cessation of the rocket launching program at LC34 in 1968, the
site was abandoned and became overrun with plant life. The contamination that occurred during
the operational period resulted in the presence of DNAPL at the site prior to the study. TCE
represented the main component of DNAPL contamination. However, cis-l,2,-dichloroethene
(cDCE) and vinyl chloride, both products of the natural biodegradation process of TCE, were
also detected in the groundwater. (Quinn 2005).
The study itself was conducted on a small plot of land near the Engineering Support Building, a
site of known DNAPL presence. The site contained a surficial aquifer and a semi-confined
aquifer, where the groundwater TCE concentrations approached solubility (of TCE). The
surficial aquifer, covered by a clay unit, started at the water table, which began at a range of 3-7
feet bgs. Three layers comprised the surficial aquifer, an upper sand unit, a middle fine-grained
unit, and a lower sand unit. The upper sand unit extended from the ground surface to between 18
and 25 feet bgs and contained a mixture of medium to coarse-grained sand and crushed shells.
At the bottom of the upper sand unit, the middle fine-grained unit began, extending to about 30
feet bgs and comprised of "gray, fine-grained silty/clayey sand," (Quinn 2005). The lower sand
unit extended from the middle fine-grained unit to about 45 feet bgs. The injection of EZVI was
planned for the upper sand unit (Quinn 2005).
Both soil and ground water samples were collected before the start of the injection to assess
contamination levels. Six soil cores were obtained and samples from 21 monitoring wells were
taken to provide pre-injection data. In an effort to maintain hydraulic control of the groundwater
within the site area, a groundwater control system was installed. The system also served to
assess the flux of DNAPL to groundwater during treatment. The EZVI, consisting of 44.3%
water, 37.2% oil, 1.5% surfactant, and 17.0% nZVI by weight, was prepared on site. A total of
about 670 gallons were injected across the entire pilot test area, which contained eight separate
injection wells. The injection volumes across the eight wells were adjusted based on
contamination concentration (Quinn 2005).
Based on the soil samples from the upper sand unit, significant reductions of TCE concentrations
upwards of 80% were achieved at most of the soil boring locations. Problems in remediation
were encountered at two wells, where it appeared that following injections, the EZVI migrated
upwards, thus not reaching the contamination zone. It was suggested that the injection technique
used, pressure pulse technology, contributed to the upward migration. Linear interpolation and
kriging, a "statistical interpolation method for analyzing spatially variable data," also were used
to estimate the overall success of DNAPL removal. Linear analysis estimated an initial total
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
mass of 17.8 g of TCE with 3.8 g of DNAPL. This method then approximated an 85% reduction
in TCE and TCE DNAPL mass. Kriging produced a value of 28 g of TCE for the initial mass
and an average reduction of 58%. It was also observed that the total mass of TCE present below
the upper sand unit, in the middle fine-grain unit, also decreased. An increase in "daughter"
products however, points to possible biotic degradation in the lower soil unit (Quinn 2005).
Groundwater samples were also measured in the experiment and showed a marked reduction in
contamination. A variance of contaminant destruction between 57 and 100% was observed in
TCE concentrations between the various observation wells. Samples also displayed considerable
increases in cDCE, VC, and ethane. The presence of cDCE and VC in the groundwater indicated
the occurrence of biotic degradation. Combining the observation of daughter products in the soil
and groundwater implied that biodegradation was responsible for a significant portion of TCE
destruction (Quinn 2005).
Overall the case study reported successful results for the remediation of TCE in both soil and
groundwater. The study, however, reported inconclusive evidence on the actual mechanism of
the TCE degradation and was unable to account for the amount of TCE degraded by the EZ VI
versus biotic degradation (Quinn 2005).
4.6. Toxicity and Safety Concerns
Generally, concerns regarding the toxicity of this technology have been mild. The confidence in
safety is largely due to the fact that iron oxides formed during remediation are already present in
the ground as rust, coupled with the fact that nano iron particles do not exhibit radically new
properties. No studies reporting the safety and toxicity of iron nanoparticles or bimetallic
particles have been published. However a study is due out within the next few months. The
preliminary studies in daphnids found that nano-iron exhibited a similar toxicity level to that of
the bulk form (Oberdorster conversation 2005). These findings are significant in that they
support the previous theories of toxicity. In a recent review, Oberdorster et al. advised that
studies not just concern toxicity as related to wildlife and human, but also focus on benthic and
soil flora and fauna, "the basis of many food chains, which could be dramatically affected by
nanoparticle injections." (Oberdorster 2005).
5. BIMETALLIC PARTICLES AND OTHER METALS
5.1. Technology Overview
While scientists and contractors have developed and tested nZVI and palladium-coated nZVI
particles on a large scale, many other metals and bimetallic combinations that can serve as
substitutions exist. Metals such as zinc and tin possess similar reduction capabilities of iron
(Boronina 1995). Like iron, these metals are converted to metal oxides in the decontamination
process. Other metals have been combined with iron as well to produce similar results. Both
iron-nickel and iron-copper bimetallic particles have been demonstrated to degrade
trichloroethane and trichloroethene (Lien 2001, Schrick 2002). Another example is iron-
platinum particles, which possess similar capabilities in degrading chlorinated benzenes (Lien
2001).
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
In producing bimetallic nanoparticles, inert base metals, such gold and aluminum, also have been
used. Unlike iron, aluminum and gold particles are non-reactive or inert. Subsequently, they can
only serve as base metals used in conjunction with a catalyst coating. Despite the lack of
reactivity, base metals have been shown to increase the catalytic rates of the coating metal (Nutt
2005 and PARS 2005). In terms of metal catalysts able to be applied as coatings, many
substitutions exist for palladium. Platinum, silver, cobalt, copper, and nickel represent
alternatives tested in the lab (Nutt 2005, Zhang 2003). While these catalysts possess the ability
to work alone, coupling with other particles can enhance degradation and catalytic rates. It then
follows that the various base metals can be fused with different noble metals to form a multitude
of combinations. It should be distinguished that when metal catalysts are coupled with reactive
metals such as iron, they serve to enhance the reactive properties of the iron. In contrast, when
metal catalysts are coupled with non reactive metals such as gold, they act as the catalysts
themselves.
According to the latest information, palladium-coated gold nanoparticles have emerged as the
one of the most promising alternatives to nZVI and palladium-coated nZVI. As mentioned
previously, palladium-coated gold nanoparticles differ from palladium-coated nZVI in that,
palladium-gold particles act as catalysts instead of reactants. The gold particles, which serve as
the base metal, do not actually react with organic compounds, nor do they act as catalysts. Gold
does, however, augment the catalytic ability of palladium. The enhancing ability of gold, while
not yet clearly understood, has been proven by the fact that Pd-on-Au particles generate
increased rate constants over 100 times greater than those for palladium alone (Nutt 2005).
In a recent study, Nutt et al. created Pd-on-Au nanoparticles and tested their ability to
hydrodechlorinate trichloroethene in water (Nutt 2005). Because the Pd-Au particles catalyze
the "hydro"dechlorination of TCE, hydrogen gas is necessary for the reaction to proceed. While
scientists have studied gold and palladium particles as catalysts for a variety of other reactions,
Nutt et al. appear to be the first in applying the catalytic abilities to remediation. Nutt et al.
synthesized the catalysts by first creating gold nanoparticles. Using the citrate reduction method,
scientists produced an aqueous fluid containing gold nanoparticle suspensions (Au Sol). To form
the bimetallic particles, Nutt et al. added palladium salt in conjunction with a reducing agent to
the Au sol (Nutt 2005).
The experiment compared the catalytic ability of palladium nanoparticles, gold nanoparticles,
palladium-coated gold nanoparticles, palladium-alumina catalysts, and palladium-gold catalysts
on alumina. Within the category of the Pd-on-Au particles, Nutt et al. also compared the effect
of palladium coverage on activity. Results concluded that a sub-monolayer of palladium on gold
produced the highest catalytic rates. An increase in Pd loading resulted in decreased rate
constants, leading to the conclusion that once palladium coverage reached or surpassed one
monolayer, the particles behaved as regular palladium particles (Nutt 2005).
5.2. Remedial Applications
At this point in time, the potential remedial applications of palladium-coated gold nanoparticles
have been tested only in the lab for the capability to hydrodechlorinate trichloroethene and other
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
chlorinated organic compounds in water. Due to the catalytic nature of the Pd-Au particles, they
are not consumed in the reaction, and thus can be reused multiple times (Nutt 2005). This fact
differentiates them from nZVI and Pd-nZVI particles, which are oxidized by contaminants such
as COCs and subsequently passivated.
The ability to reuse Pd-Au particles multiple times, coupled with the product cost, greatly
impacts the potential remedial applications of the particles. In a pound for pound comparison,
nZVI particles cost much less than Pd-Au nanoparticles based on the price of the raw materials,
but by capitalizing on the reusability of the Pd-Au, a smaller amount of particles can used in
comparison to nZVI. Thus, in situ treatments involving slurry injections, where particles
dissipate into the ground, work well for nZVI and BNIPs because particle recovery is not
necessary. However, these applications would not be cost-effective for Pd-Au particles (Wong
Conversation 2005).
Presently, development of remedial applications is focusing on two different innovations. The
first technology involves mounting the nanoparticles onto membranes, allowing contaminated
ground water or waste water to be pushed through the membranes for remediation. The second
technology entails binding the nanoparticles to a powder. This technique enables particle
recovery from solution by filtration, a process unachievable with individual nanoparticles (Wong
Conversation 2005). Field simulation studies designed to test the ability of Pd-Au particles to
remediate groundwater contaminated with TCE are underway at Rice University (Wong
Conversation 2005). Plans to expand the study to include other contaminants are also in
development. The list of potential contaminants includes other chlorinated compounds,
fluorinated compounds, PCBs, nitrates, and potentially inorganic compounds such as arsenic
(Wong Conversation 2005, Morello 2005).
5.3. Toxicity and Safety Concerns
Similarly to the cases of nZVI particles and BNIPs, no toxicity studies have yet been published
on other bimetallic particles. Conversely, though, it is not apparent that there are any studies in
progress. It could be speculated that because of the similarities between particles that they would
exhibit similar toxicity levels. None of the bimetallic particles created exhibit radically different
properties, and they are created from materials that are non-toxic in the bulk form. However, the
persistence of catalytic materials such as the gold-palladium particles needs to be further
explored for environmental interactions.
6. FERRITIN
6.1. Technology Overview
In recent years biological systems, namely proteins, have elicited much attention from research
and development for their ability to control the formation of mineral structures (Kim 2002).
Cage-like protein composites can often function as controlled environments for the assembly
and/ or encapsulation of nanosized materials. Synthetic developments of this natural process
offer potential applications in drug delivery as well as catalysis (Douglas 1998). A prime
example of this occurrence is ferritin, an iron storage protein. Ferritin can be found throughout
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the animal, plant, and microbial kingdom and plays an integral role in the sequestration and
storage of iron. The formation of ferritin occurs when the 24 similarly structured polypeptide
subunits comprising the molecule self-assemble into a cage-like protein structure (Douglas
1998). The diameter of the assembled apoferritin (iron-free) is about 12 nm, and the inside
cavity is approximately 8 nm. After assembly, iron molecules can diffuse into the cavity through
channels in the protein shell, where mineralization converts the molecules into a nanoparticle of
ferrihydrite, a ferric oxyhydroxide. The reaction volume of the cage and the .5 nm channel size
spatially constrain the iron oxide nanoparticles formed. In vivo, the protein cavity can hold up to
4,500 iron atoms (Chasteen 1999). In vitro, scientists have control over the number of iron
molecules entering the shell, producing loadings between 500 and 4,500 molecules. This
translates to 5 nm to 7.5 nm iron oxide particles respectively (Kim 2002).
6.2. Remedial Applications
Ferritin offers potential benefits to the field of remediation in multiple areas, the most promising
being that of photoreduction of contaminants (Kim 2002). Research has centered on the ability
of ferritin to remediate toxic metals and possibly chlorocarbons in the presence of visible light or
solar radiation (Moretz 2004). Iron oxides in general have received a significant amount of
attention for their potential remedial abilities. While able to carry out significant photochemical
processes, however, Fe (III) bearing iron oxide quickly undergoes photoreduction to Fe (II).
This transformation renders the catalyst inactive (Strongin 2002). Ferritin naturally converts Fe
(II) to Fe(III), thus the encapsulation of iron oxide prevents photoreduction. Despite providing
stability, the ferritin cage does not inhibit the photoreduction of environmental contaminants.
This factor gives ferritin a significant advantage over the traditional freestanding particles.
Research on this technology is in the early stages. Specifically, scientists at Temple University
have demonstrated the ability of ferritin to reduce hexavalent chromium (Cr(VI)) to the trivalent
form (Cr(III)) (Kim 2002). Cr(VI), an EPA priority pollutant and a common byproduct of
industrial processes, can be toxic to humans and has been identified as a carcinogen. It is
regulated by the EPA under a variety of acts, including CERCLA and RCRA (EPA). Cr(III), in
contrast, occurs naturally, is less toxic, and is insoluble in water (Moretz 2004). Reducing
Cr(VI) to Cr(III) thus reduces the toxicity as well as the mobility, allowing for easier filtration
and removal (Kim 2002). Ferritin molecules with loading factors of 100, 500, 1,000, and 3,000
iron molecules have been tested for their ability to reduce Cr(VI). All experiments have been
performed on a relatively small scale, of the milliliter order of magnitude. Reactions carried out
in the presence of light demonstrated a significant ability to reduce Cr(VI). The results were
compared against reactions carried out in no light, as well as reactions with apoferritin (Kim
2002).
This research offers multiple dimensions of expansion. The most immediate area of
development includes the testing of ferritin on other toxic metals. Technetium-7, a metal
contaminant present at a nuclear waste site in Washington constitutes one such potential metal.
If proven applicable, this technology could be used to remediate groundwater that has been
contaminated from the slow leakage of the storage canisters containing nuclear waste (Moretz
2004). Besides testing other metals, this technology offers potential remedial capabilities for
aromatics and chlorocarbons.
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In addition to iron hydroxide, past research has demonstrated that the apoferritin protein cage
supports the synthesis of the other metal hydroxides, such as Mn(O)OH, Fe(O)OH, and
Co(O)OH (Kim 2002). Exploiting these capabilities could potentially expand this technology,
thereby increasing remediation speed and effectiveness as well as expanding the list of
contaminants that could be addressed.
Outside of using ferritin to remediate contaminants, this technology also offers a new route to
nanoparticle synthesis. A variety of techniques, including laser vaporization, electron beam
lithography, and a number of colloidal techniques, currently are being used to produce
nanoparticles (Hosein 2004). Despite these technologies, the manufacture of "uniform
nanosized, monodispersed transition metal based particles still represents a significant challenge"
(Hosein 2004). It has been demonstrated that ferretin could be employed in the production of
both metallic and metal hydroxide particles. Scientists recently have developed a fairly
straightforward synthesis route for both iron and cobalt metallic- and oxide-based nanoparticles.
Using this method, ferritin assembles the particles in solution. Following assembly, the ferritin is
dried on a solid support and cleaned with ozone to remove the protein cage. This leaves well-
dispersed nanooxide particles. Further exposure of the particles to hydrogen and high
temperature can be used to convert the metal oxides to metallic particles. This method allows a
relatively high degree of control for particle size between 2 and 8 nm as well (Hosein 2004).
6.3. Toxicity and Safety Concerns
There are no specific toxicity studies concerning the use of ferritin as a remedial tool. However,
the natural occurrence of ferritin in the environment points to its lack of toxicity in living
animals, plants, and microbes. Concerns about ferritin should be focused on the ecological
effects of its deployment in the environment.
7. NANOSCALE SEMICONDUCTOR PHOTOCATALYSTS
7.1. Technology Overview
Semiconductor photocatalysts act much in the same manner as traditional catalysts; however,
they obtain their energy from the absorption of light. A number of materials, such as titanium
dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), and tungsten oxide (WO3), act as
photocatalysts (Nagaveni 2004). Due to their light absorbing capabilities, they are employed in a
variety of applications. Both titanium dioxide and zinc oxide can be used as pigments to provide
whiteness for substances, such as paint and paper. The ability of photocatalysts to absorb
ultraviolet light makes them useful in sunscreen as well as cosmetics to provide opaqueness to
the creams or lotions. These properties also can be exploited for antimicrobial coatings; the
photocatalytic properties allow thin coatings to be self cleaning and to have disinfecting
properties after exposure to UV radiation. More importantly for this paper, photocatalysts have
the ability to oxidize organic pollutants into nontoxic materials. Traditionally, TiC>2 has been
used in advanced photochemical oxidation (APO) processes for environmental remediation
because of its low toxicity, high photoconductivity, high photostability, availability, and low cost
(USEPA 1998a, Nagaveni 2004).
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Semiconductors oxidize a variety of organic molecules using light energy. Exposure to light
illumination levels with energy greater than the band gap energy level of the photcatalyst result
in a charge transfer process. In the charge transfer process, an excited electron moves from the
valence band to the conduction band (USEPA 1998a). This process then results in the oxidation
of surrounding organic substances. TiO2, for example, exhibits photoconductivity when
illuminated by light with an energy level exceeding 3.2 eV, the band gap for TiO2 (Nagaveni
2004, USEPA1998a). This energy level translates to light with a wavelength shorter than 387.5
nm, which falls into the category of UV light (USEPA 1998a).
Nanotechnology has enabled the expansion of the field of semiconductor photocatalysis in a
number of ways. A greater variety of compounds can be achieved, with increased reactivity and
specificity. As with other nanoparticles, increases in surface area enhance reactivity. The ability
to form surface modified particles, films, and nanotubes with semiconductor photocatalysts also
plays a role in the increased specificity and selectivity of nanoparticles (Chen 2005, Kamat 2002,
Nagaveni 2004, NATO 1998).
7.2. Remedial Applications
Conventional semiconductor photocatalysts have been used and tested for a variety of remedial
applications. In 1995, a TiC>2 system was tested under the USEPA's SITE program at a
Department of Energy (DOE) facility in Oak Ridge. The TiO2 effectively remediated the
groundwater contaminated with 1,1-DCA, 1,1-TCA, xylenes, toluene, cis-l,2-DCE, and 1,1-
DCE (NATO 1998). Field and pilot scale applications also have demonstrated the ability of
TiO2 to remediate fuel-contaminated groundwater containing benzene, toluene, ethylbenzene,
and xylene (BTEX) compounds. In addition, TCE, Methyl-fert-butyl ether (MTBE), chloroform,
ethylbenzene, and nitrobenzene can be destroyed by semiconductor photocatalysis (NATO 1998,
EPA 1998a).
Emerging nanotechnologies and processes have recently enabled the production of a variety of
conventional photocatalytic derivatives. Doping particles or modifying the surfaces of the
photocatalysts with metal has become an increasingly popular enhancement. While dating back
to a pre-nanotech era, the doping of photocatalytic particles is currently being applied to
nanoparticles. Metals such as platinum, copper, silver, and gold have been tested for their ability
to improve decontamination rates of TiO2. Coupling with these metals also can induce a
sensitivity and subsequent response to visible light. This combats the remediation problems
faced by photocatalysts' requirement of UV light, which does not comprise a very large section
of solar light (Rajeshwar 2001).
In a study coupling TiO2 with copper for the remediation of Cr(VI), Rajeshwar et al. reported
that the combination produced a "synergistic photocatalytic effect." (Rajeshwar 2001). This
effect causes the acceleration of Cr(VI) reduction, as well as the reduction of Cu(II) ions,
catalyzed by the Cr(VI) (Rajeshwar 2001). Coupling of TiO2 with gold and silver produced
similar reductive capabilities to that of TiO2 and copper (Rajeshwar 2001). Scientists at
Clemson University are currently exploring the reverse of metal doping on TiO2 particles,
instead coating silver and gold particles with a TiO2 shell. This research also aims at achieving
enhanced photocatalytic activity and an increase in light absorbing capabilities (Kumbhar 2004).
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The development of TiO2 based nanotubes represents a separate area of photocatalytic
nanotechnology. Recently, Chen et al. reported the production of a TiO2-based p-n junction
nanotubes containing platinum on the inside and TiO2 on the outside. The nature of the p-n
junction allows the outside of the tube to act as an oxidizing surface, while the inside of the tube
acts as a reductive surface. Chen et al. tested the ability of the nanotubes to destroy toluene,
finding the p-n nanotube catalyst to have a much higher destruction rate than nonnanotube
structured material. While still in the very early stages of research, Chen et al. projected the
ability of this technology to be used in sensors, light emitting diodes, nanofiltration membranes
for air, and water treatments (Chen 2005).
As mentioned previously, characteristics of TiC>2, such as low cost, low toxicity and high
reactivity, make the compound more popular than other semiconductor photocatalysts. Recently,
however, ZnO has been proposed as a dual function photocatalytic material. In 2002, Kamat et
al. reported that ZnO possessed both sensing and remediating capabilities for organic
contaminants in water (Kamat 2002). By creating nanostructured ZnO films, Kamat et al. tested
the ability of ZnO to both detect and treat 4-chlorocatechol. The study concluded that the ZnO
films showed a high degree of sensitivity on the order of 1 ppm to aromatic compounds such as
chlorinated phenols. Under UV lighting, the films degraded the aromatic compounds. The
coupling of these two features also facilitated the monitoring of the degradation process, because
as decontamination occurred, a direct change in the emission intensity followed (Kamat 2002).
7.3. Toxicity and Safety Concerns
The toxicity and safety concerns related to semiconductor photocatalysts have been studied fairly
extensively, especially for titanium dioxide and zinc oxide. Because of their use in sunscreen
and other direct use human products, testing for these materials has likely exceeded that for all
other nanoparticles. Inhalation in the workplace presents a greater area of toxicity concern,
largely because photocatalyst nanoparticles already have been approved for use in dermal
applications, such as sunscreen.
In 2000, a study compared the respiratory effects of TiO2 particles 20 nm and 250 nm in size.
Rats and mice were used as test species. The study found that the smaller particles induced a
greater pulmonary-inflammatory neutrophil response as compared to the larger particles when
introduced to the rats and mice at the same mass doses. A second study comparing particle
surface area (instead of mass) to response, though, found the results to be similar for both
particle sizes (Oberdorster 2005). Other studies, however, have found that smaller photocatalyst
particle size does not necessarily indicate a greater level of toxicity. At the 2004 American
Chemical Society conference, a study was presented comparing the respiratory effects in rats of
micron-sized quartz to nano-sized quartz particles and the effects of fine titanium dioxide to
nano-sized TiO2 rods and dots. Preliminary data indicated no difference between the effects of
TiO2 nanodots and rods and fine-sized TiO2 particles. The preliminary data indicated that the
nano-sized quartz actually caused less of an inflammatory response compared to the micron-
sized quartz (Warheit 2004).
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8. SELF ASSEMBLED MONOLAYER ON MESOPOROUS SUPPORTS-
SAMMS
8.1 Technology Overview
As suggested by their name, Self Assembled Monolayers on Mesoporous Silica, or SAMMS, can
most simply be described as functionalized nanoporous ceramics or the "marriage of mesoporous
ceramics with self-assembled monolayer chemistry" (Mattigod 1999). The overall ceramic
structure resembles a hexagonal honeycomb, as seen in Figure 3. The monolayers, formed
within the porous surfaces actually adsorb or bind molecules. The nature of the SAMMS,
namely the ability to alter the exposed functional group of the monolayer, allows this class of
highly sorbent materials to potentially bind a broad range of molecules, and in the case of
environmental remediation, contaminants (Fryxell 2005, SAMMS Technical Summary 2005).
A. Seltasttmbled roonoliyirj
ooo ooooooooo
C. Self-assembled monotayers
on itiesoporous supports (SAMMS)
Figure 3. Diagram of SAMMS structure (Fryxell 2005)
Construction of both the ceramic and the monolayer include multiple steps, many reliant on the
method of molecular self-assembly. In the first step of production, the starting surfactant
molecules aggregate to form micelle templates of ordered liquid crystalline structures "such as
hexagonally ordered rodlike micelles" (Mattigod 1999). This aggregation represents the first
phase of self assembly (Fryxell 2005). Oxide materials are then precipitated onto the surface of
the micelles in the presence of solvents and under mild hydrothermal conditions (Mattigod
1999). The formation of the preliminary mesoporous backbone represents the second phase of
self-assembly (Fryxell 2005). The final step in creating the mesoporous ceramic requires the
calcination of the organic-oxide material to remove the surfactants. Functionalized silane
molecules are then mixed in excess with the mesoporous ceramics and self assemble in an
ordered monolayer on the pore surfaces of the ceramic (Fryxell 2005). The bifunctional silanes
used in the process can be engineered to have hydrophilic head groups that bind the target
materials and hydrophobic tail groups, which covalently bind to the ceramic substrate (Yantassee
2003).
Upon their creation, SAMMS can be mixed with aqueous solutions where they bind to the target
of interest. Following sequestration of the targeted molecules, SAMMS can be filtered from
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
solution and recycled. Acid stripping causes SAMMS to release bound compounds, at which
point they can be separated out of solution and reused.
8.2 Remedial Applications
As mentioned earlier, the ability to alter the exposed functional group of the SAMMS monolayer
enables the potential remediation of a very broad range of contaminants. A multitude of
different SAMSS classes have been developed at this point. The first and most widely studied
material is termed thiol-SAMMS. Designed mainly for the sequestration of mercury, thiol-
SAMMS can also bind other metallic cations, such as silver, cadmium, lead, and thallium
(Mattigod 1999). Anion-SAMMS or metal-capped ethylenediamine (EDA) SAMMS have been
developed to absorb anions, such as chromate and arsenate. Their derivative, chelate-SAMMS,
contain only the EDA functional group, and can bind metals, such as copper, nickel, cobalt, and
zinc (SAMMS Technical Summary). Cu-EDA-SAMMS (a type of anion-SAMMS) has been
further functionalized to bind cesium by incorporating ferrocyanide-forming Cu-Ferrocyanide-
SAMMS (Lin 2001). Finally, a variety of phosphonate and hydroxypyridone (HOPO)
functionalized SAMMS have been created and tested for the sequestration of actinides and
lanthanides (Fryxell 2004, Fryxell 2005, Lin 2005).
The majority of the SAMMS have only been tested on the bench-scale level, with the exception
of thiol-SAMMS. Both bench-scale and pilot-scale tests have been carried out to test the ability
of thiol-SAMMS to remediate mercury. Initial studies indicated thiol-SAMMS could remove
dissolved mercury from smelter condensate to meet the EPA regulatory standard of. 15 mg/L
(Mattigod: Bench-Scale2). Following bench-scale studies, a total volume of 160 L of smelter
waste containing mercury at a concentration 10.55 mg/L was used in a scaled-up pilot test. The
study concluded that three consecutive treatments with approximately 200g of thiol-SAMMS
each were required to meet regulatory standards (Mattigod: Pilot-Scale2). In this study,
SAMMS used in each consecutive treatment could be recycled and reused. While this is an
attractive feature in terms of cost, studies have also indicated that mercury-laden SAMMS are
bound tightly enough for landfilling. Mattigod et al. tested the stability of thiol-SAMMS and
mercury using the USEPA's Toxicity Characteristics Leaching Procedure (TCLP). The TCLP
test indicated that the concentration of mercury released into solution was in the range of 0.0002-
0.001 mg/L, an extremely low value. The EPA only requires less than .2 mg/L be released,
indicating that the stability of mercury loaded SAMMS allows for easy disposal (Mattigod: Pilot-
Scale2).
In addition to mercury removal from waste water, thiol-SAMMS have been shown to remediate
mercury-contaminated soil as well. A proprietary lixiviant system has been developed that
would allow the removal of mercury and potentially other metals, such as cadmium, silver, and
molybdenum from soils and sludges (SAMMS Technical Summary 2005).
Currently, scientists at Pacific Northwest National Laboratory are working with Perry Equipment
Corp. on the commercialization of thiol-SAMMS. The industrial development of this technology
aims to target ocean-based petroleum operations. The ocean drilling sometimes produces
mercury-contaminated sea water, which cannot be returned to the ocean without treatment.
Current procedures routinely require the shipment of contaminated water back to land for
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
remediation, which is a costly procedure. Thiol-SAMMS are being developed in an effort to
target this problem and permit remediation on-site (Fryxell Conversation 2005).
8.3 Toxicity and Safety Concerns
Because the actual ceramic supports that comprise SAMMS are not on the nano scale—rather the
functionalized pores are nanosized—they do not carry the same toxicity concerns of nanosized
particles (Fryxell Conversation 2005).
9. DENDRIMERS
9.1. Technology Overview
Dendrimers represent a novel class of three-dimensional, highly branched, globular
macromolecules, which fall into a broader category deemed dendritic polymers. This category
includes hyperbranched polymers, dendrigraft polymers, and dendrons. Three covalently bonded
components comprise dendrimers: a core, interior branch cells, and terminal branch cells (Diallo
2005). Both architecture and composition can be highly controlled in these monodisperse
polymers. Synthesis techniques allow molecular design parameters, including size, shape,
surface/interior chemistry, flexibility, and topology to be almost completely ordered (Cagin
2005). The size of dendrimers ranges between 2 and 20 nanometers; common shapes include
cones, spheres, and disc-like structures. Altering the surface and interior chemistry allows
functionalization, where, for example, particles can be designed to be soluble in certain media or
bind appropriate molecules (Diallo 2005).
Figure 4. Different dendritic polymers: dendrimer, core-shell tecto(dendrimer), dendrigraft polymer,
hyperbranched polymer (Diallo 2005)
9.2. Remedial Applications
Because dendrimers encompass such a broad technology, the potential remedial applications are
expansive. Currently, poly(amidoamine), or PAMAM, dendrimers have been developed for use
in the remediation of waste water and soil contaminated with a variety of transition metal ions
such as copper (Cu(II)). Diallo et al. first reported on the use of PAMAM dendrimers for copper
removal in 1999.
In general, PAMAM dendrimers represent an extremely broad class of materials, with a diversity
of applications. As mentioned above, dendrimers are comprised of a core, interior branch cells,
and terminal branch cells. The term PAMAM refers to the interior branch cells. In the case of
PAMAM dendrimers, that includes functional nitrogen and amide groups repeatedly attached in
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
radially branched layers (Diallo 2004). While the interior branch dictates the classification as
"PAMAM," dendrimers falling into this class can have a wide range of core compounds and
terminal functional groups. Dendritic Nanotechnologies, Inc., for example, offers over 40
variations of PAMAM dendrimers with varying cores and terminal groups. Diverse cores and
functional groups translate into broad applications. Beside remedial uses, dendrimers have been
commercialized for HIV prevention and anthrax detection (Dendritic Nanotechnologies, Inc.,
2005).
For the specific development of metal-remediating dendrimers, researchers have employed an
ethylenediamine (EDA) core. The high concentration of nitrogen ligands within the interior
branches makes PAMAM dendrimers useful as chelating agents for metal ions (Diallo 2004, Xu
2005). The ability to choose a multitude of functional groups as terminal cells also contributes to
functionality as metal chelators. Surface terminal groups, including primary amine, succinamic
acid, gycidol, hydroxyl and acetamide, have been tested (Diallo 2004, Xu 2005).
Expanding on initial research developing EDA core PAMAM dendrimers for copper
remediation, Diallo et al. devised a dendrimer-enhanced ultrafiltration (DEUF) method to
recover copper from aqueous solutions. DEUF is a variation of polymer-enhanced ultra filtration
(PEUF), a remedial tool that has emerged in the past 10 years as a promising technology for
metal ion removal from waste streams. PEUF and DEUF work on the same principles, where the
binding of metal ions to the polymers or dendrimers allows the removal of contaminants though
membrane filtration. In the first step of the process, either linear polymers or dendrimers are
mixed with contaminated waste water, where they subsequently bind to metal ions present. The
solution is then pushed through an ultra filtration (UF) membrane, which prevents the passage of
the polymer/dendrimer-metal ion complexes. The metal-laden polymers or dendrimers can then
be sent to a second location where the metal is detached from the polymers or dendrimers so that
they can be reused (Diallo 2005). Diallo et al.'s proposed process consisting of a clean water
recovery unit and a dendrimer recovery unit can be seen below in Figure 5. Diallo et al. are
currently working on the engineering development of this process with hopes of having pilot-
scale demonstration in the next four years (Diallo Conversation 2005).
< Iran Wmc:
„ ,. .
Rctovrtv UaiS
Cfcln
Water
Dcaliittitt
Retxiverv Unit
Figure 5. Diagram of Dendrimer Enhanced Ultrafiltration Unit (Diallo 2005)
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
The ability of EDA-core PAMAM dendrimers to remove copper from soil also has been
examined. Laboratory-scale testing by Xu et al. revealed that dendrimers could achieve up to a
54% removal of copper from the soil. In comparison to other extracting agent such as EDTA,
the larger molecule size of dendrimers proves advantageous for separation (Xu 2005). Currently,
however the price of dendrimers restricts their usefulness as soil remediators (Diallo
Conversation 2005).
While the current status of dendrimer research for remediation only includes EDA core PAMAM
dendrimers for copper and other metal ion recovery, the technology possesses potential for
expansion. PAMAM dendrimers can be functionalized with redox active metal clusters of FeS.
These dendrimers could then be used for reductive decontamination of organic pollutants, such
as chlorinated compounds and poly(nitroaromatics) (Diallo Conversation 2005).
9.3. Toxicity and Safety Concerns
Toxicity concerns of the developed remedial dendrimers are currently being researched. In
general dendrimers encompass such a broad range of materials that a blanket statement about
their toxicity would be inappropriate. Some PAMAM dendrimers already are being used in
pharmaceutical applications as mentioned above, which would indicate that those dendrimers are
nontoxic. However, analysis must be performed on an individual basis.
10. POLYMERIC NANOPARTICLES
10.1. Technology Overview
Polymeric nanoparticles embody an extremely broad category of molecules or molecular
aggregates that can be used in a variety of applications, from drug delivery to sunscreen. Similar
to surfactant micelles, polymeric nanoparticles possess amphiphilic properties that originate from
the properties of each polymer present in the particle. Individual polymers contain a
hydrophobic as well as a hydrophilic section. In the presence of water, the molecules self-
assemble to form polymer vesicles with diameters in the nanometer range, where the
hydrophobic segments are oriented inwards, and the hydrophilic segments form the outer layer
(Goho 2004). Polymeric nanoparticles differ from surfactant micelles in synthesis. Cross-
linking of the particle precursor chains following aggregation enables the particles to maintain
stability regardless of precursor chain concentration (Tungittiplakorn 2004, 2005). Surfactant
micelles on the other hand, can only maintain their structure when the concentration of the
individual surfactant reaches or exceeds the critical micelle concentration (CMC)
(Tungittiplakorn 2004, 2005).
Amphiphilic polyurethane (APU) nanoparticles represent the specific molecular-type of particles
in development for remedial applications. Just in the beginning stages of research, scientists
have synthesized a number of particles using polyurethane acrylate anionomer (UAA) and
poly(ethylene glycol)-modified urethane acrylate (PMUA) as precursor chains (Tungittiplakorn
2004, 2005). The precursor chains influence the structure and properties of the particles. In the
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
case of UAA derivatives, the non-polar backbones remain in the interior of the particle and the
carboxylic side chains form the particle surface. On the other hand, the hydrophilic
poly(ethylene oxide) portions of the PMUA derived particles form pendant side chains on the
particle surface. These structures are seen in Figure 6. Further variation in the nanoparticles
structure and functionality can be achieved by altering the properties and synthesis techniques
for the precursor chains. For example, varying the size of poly(tetramethylene glycol) (PTMG),
a chemical used in synthesizing both UAA and PMUA chains, can alter the structure of the end
particle (Tungittiplakorn 2004).
tr -
,,i-*~E
Figure 6. Structure of polyurethane acrylate anionomer (UAA) and poly(ethylene glycol)-modified urethane
acrylate (PMUA) derived nanoparticles (Tungittiplakorn 2004)
10.2. Remedial Applications
For remedial techniques, polymeric nanoparticles offer a potential replacement for traditional
surfactants commonly used to enhance the remediation of hydrophobic organic contaminants
(HOCs) using pump-and-treat systems. Contaminants falling into this category often sorb
strongly to soils or form nonaqueous phase liquid (NAPL) (Yeom 1996). Their overall
persistence causes a large problem for successful pump-and-treat remediation where "low
recoveries can result from: (1) slow dissolution of NAPLs into the ground-water, (2) slow
diffusion of contaminants from low conductivity zones to high conductivity zones, (3) slow
desorption of sorbed contaminants, and (4) hydrodynamic isolation in dead-end zones," (Jafvert
1996, Yeom 1996) The implementation of surfactants largely has been used to combat the
inefficiencies of the pump-and-treat-systems (Yeom 1996). Surfactants can mobilize and
solubilize NAPL, as well as solubilize sorbed contaminants (Yeom 1996, Jafvert 1996). This
greatly increases the mass recovery rate of pump-and-treat remediation and, in cases of dual
remediation, can enhance biodegradation (Yeom 1996).
APU nanoparticles display very similar properties to those of surfactant micelles. Scientists have
demonstrated in laboratory-scale research that UAA- and PMUA-derived nanoparticles
potentially can be used to enhance pump-and-treat remediation of poly cyclic aromatic
hydrocarbons (PAHs). Specifically, scientists at Cornell have tested the ability of UAA and
PMUA nanoparticles to remove phenanthrene (PFtEN), a PAH found in coal tar, from a sandy
aquifer media (EST Science). Four different variations of nanoparticles were tested: UAA2K,
UAA1K-1, UAA1K-2, and PMUA (EST). The UAA-derivative particles averaged
approximately 40 nm in size, while the PMUA particle averaged 80 nm (Tungittiplakorn 2004).
Scientists tested each particle type for its affinity for PFLEN, the adsorption of the nanoparticles
on the sandy material, and the tendency of particles to aggregate (EST). The study concluded
that the particles would effectively compete with sand for the sorption of PHEN. It was also
determined that changes in functionality can be achieved through particle modifications.
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Increasing the length of the hydrophobic backbone can increase PHEN affinity, for example
(Tungittiplakorn 2004, 2005).
Currently, in the beginning of the research phase, the scale-up of this project is being examined.
Certain hurdles would still need to be crossed before larger tests could begin, such as
determining suitability of the particles for treating various soil types, and the development of a
recovery and recycling process for the particles. Researchers also plan to further examine the
bioavailability of contaminants in the nanoparticles and the potential dual treatment remediation
approach (Lion Conversation 2005).
10.3. Toxicity and Safety Concerns
Currently no toxicological studies of the polymeric nanoparticles designed for soil remediation
have taken place (Lion Conversation 2005). This represents another research need in the
progression to pilot-scale testing of this technology.
11. SINGLE-ENZYME NANOPARTICLES
11.1. Technology Overview
Enzymes offer vast capabilities in the areas of chemical conversions, biosensing, and
bioremediation. Their specificity and targeted effectiveness make them much more effective
than synthetic catalysts. However, the lack of stability and relatively short life of enzymes
inhibit their ability to provide cost effective options (Kim 2003, Kim 2004). Researchers have
experimented with methods, such as enzyme immobilization, enzyme modification, and genetic
modification, to improve the stability and subsequent persistence of enzymes.
Nanotechnology has recently provided a new method of enzyme stabilization in the form of
single enzyme nanoparticles (SENs). In laymen's terms, SENs can be described as armored
enzymes surrounded by a protective cage a few nanometers thick (PNL). The "cage" is actually
a silicate shell, linked with the surface of the enzyme. While it covers most of the enzyme, the
active site remains chemically accessible, maintaining the functionality of the enzyme (Kim
2003, Kim 2004).
Kim et al. assembled the first SENs in 2003, using chymotrypsin as a model enzyme. Synthesis
of SENs involves a three part process. The first step requires covalent modification of the
enzyme surface creating vinyl group functionality and solubilization of the enzyme in a non-
polar/hydrophobic solvent such as hexane. In the second step, silane monomers with both vinyl
and trimethoxysilane groups are mixed with the modified enzymes. Vinyl group polymerization
creates linear polymers with free trimethoxysilane groups attached to the enzyme surface. The
third and last step requires the hydrolysis of the trimethoxysilane groups and the subsequent
condensation of the silanols. This final step creates the cross-linked silicate shell resembling
armor (Kim 2003, Kim 2004). Figure 7 shows the various stages of formation and the chemistry
for synthesis.
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Emerging Nanotechnologies for Site Remediation and Wastewater Treatment
tSI-Ns)
(b)
Enz -
En* —
Enz— NH-
lMll E.'L
Armored, Single Enzyme Nanopartides
(SENs)
Figure 7. Diagram of the modification process (a), and chemical reactions in the process (b) of creating SENs
(Kim 2003)
11.2. Remedial Applications
The use of single enzymes offers potential decontamination methods for a range of compounds.
Compared to traditional microbial remediation, the use of individual enzymes offers a variety of
advantages. Single enzymes can be used to remediate recalcitrant compounds, for example.
They can withstand more extreme conditions, such as high/low pH, high contaminant
concentration, high salinity, and high/low temperature. Enzymes also do not require nutrients
and biomass acclimation. Metabolic intermediates and byproducts, as well as mass transfer
limitations due to cellular transport, are avoided as well. Generally, it is a much easier process to
control than whole cell degradation (Kim 2004).
The contaminant of interest dictates the type of enzyme employed for remediation. Peroxidases,
polyphenol oxidases such as laccase and tyrosinase, dehalogenases, and organophosphorous
hydrolases are examples of applicable enzymes. The plethora of enzymes to choose from allows
the potential remediation of an extremely broad class of organic contaminants. Phenols,
polyaromatics, dyes, chlorinated compounds, organophosphorous pesticides or nerve agents, and
explosives all can be degraded using enzymes (Kim 2004).
Despite the benefits achievable through enzymatic remediation, as mentioned above, enzyme
stability and lifetime proves a cost limiting factor for large-scale remedial purposes. While SEN
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research only has been conducted on the enzyme chymotrypsin, the technology is transferable
across all enzymes, thus potentially allowing enzymatic remediation to be cost effective.
11.3. Toxicity and Safety Concerns
No specific toxicity studies or safety concerns have been reported for SENs. Their enzymatic
basis would initially point to a lack of toxicity. However, their potential persistence in the
environment and/or in mammals if absorbed or ingested should be more clearly detailed.
12. TUNABLE BIOPOLYMERS
12.1. Technology Overview
Tunable biopolymers can be best described as artificial or synthetic protein polymers that exhibit
novel organization and control at the molecular level. Genetic engineering and recombinant
DNA techniques allow the design and production of nanoscale biopolymers through the creation
of a synthetic genetic template. The ability to design these genetic templates allows the
sequence, size, composition, and function of the biopolymers to be pre-determined.
Elastin-like polypeptides (ELP) are biopolymers that possess structurally similar characteristics
to the mammalian protein elastin (Kostal 2001). Their unique characteristics render them good
candidates for base formation of tunable biopolymers. Comprised of the repeating pentapeptide
VPGVG, they undergo a reversible phase transition from water soluble forms or polymer
solutions into aggregates with increases in temperature. The transition temperature of the ELP
can be tuned/controlled by altering the chain length and sequence (Kostal 2001, Kostal 2003). It
also fluctuates with changes in pH, ionic strength, pressure, and covalent modifications. ELP
can be produced in mass quantities through overexpression in E. coli. Purification to
homogeneity is readily achievable through exploitation of the temperature responsive trait of
ELP. This factor makes it an attractive candidate for biopolymer production. Fusion with other
peptides and/or proteins allows functionalization of the ELP, while still maintaining the
temperature responsive characteristic (Kostal 2001, Kostal 2003).
12.2. Remedial Applications
Tunable biopolymers have been synthesized on a laboratory scale to specifically bind to heavy
metals, making them useful for the removal of heavy metals from waste streams and soil.
Through the fusion of ELP with proteins that specifically target metals, such as cadmium,
mercury, arsenic and lead, biopolymers that target individual metals can be created. Currently,
tunable biopolymers that bind to cadmium and mercury have been developed (Kostal 2001,
Kostal 2003).
In 2001, Kostal et al. created a tunable biopolymer useful for the remediation of heavy metals
and tested its binding ability for cadmium. An ELP comprised of a repeating VPGVG was used.
A hexahistidine tail was also incorporated to serve as the metal binding moiety. The metal
binding capabilities of the biopolymer was tested in a buffer solution containing Cd2+. The
biopolymers were found to bind to cadmium at a 1:1 ratio. As mentioned above, upon addition
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of the biopolymers to solution, the nature of the ELP allows them to be precipitated out of
solution by increases in temperature or salt solution (Kostal 2001).
Besides testing the ability of ELPs with polyhistidine moieties to remediate waste water,
Prabhukumar et al. tested the capacity of the polypeptide to remediate cadmium contaminated
soil. Using mostly sandy soil soaked with cadmium nitrate, solution containing the biopolymers
was added and cadmium removal measured. The study concluded that cadmium removal
increased with the added concentration of biopolymers, and a modest maximum of 55%
cadmium removal was achieved. The study noted that other proteins with a stronger cadmium
affinity could be employed as replacements for the polyhistidine moiety to increase recovery
(Prabhukumar 2004).
In a separate study, Kostal et al. created a tunable biopolymer with a specific affinity for
mercury. The protein MerR was used as the metal-binding moiety fused with an ELP. MerR is a
bacterial metalloregulatory protein that has a very high affinity and specificity for mercury, even
in the presence of other heavy metals, such as cadmium and zinc. The synthesized biopolymers
demonstrated the ability to remediate mercury in buffered solutions to ppb levels. Following
separation, the mercury could be removed and the biopolymers recycled. The study also tested
the ability of the biopolymers to remediate mercury-contaminated lake water (with a higher pH
and turbidity) and found that the efficiency was maintained (Kostal 2003).
12.3 Toxicity and Safety Concerns
No specific toxicity concerns have been reported for bioploymers. Their biological basis makes
the technology potentially less of a concern than other inorganic nanotechnologies. As
mentioned for other nanotechnologies, ecological interactions should be further examined.
13. NANOCRYSTALLINE ZEOLITES
13.1. Technology Overview
The term zeolite represents a very broad group of crystalline structures generally comprised of
silicon, aluminum, and oxygen (Song 2005a, Song 2005b). Offering a diversity of potential
applications in catalysis and separations, zeolites have become especially popular for use as
catalysts in petrochemical processing (Song 2005a, Alwy 2005). Properties of zeolites include
high cation exchange capacities, high specific surface areas, and high hydrothermal stability
(Song 2005a, Bowman 2002). The specific surface areas of zeolites can be attributed to their
porous crystalline structure. Conventional synthesis methods produce zeolites on the scale of
1,000 to 10,000 nm, or 1 to 10 um. However, because the pores fall into the molecular size
range (.4 to 1 nm), zeolites are considered nanomaterials.
Recently, researchers have begun to synthesize nanocrystalline zeolites as a way to explore a
new avenue relating zeolites and nanotechnology. Nanocrystalline zeolites are comprised of
"discrete, uniform crystals with dimensions of less than 100 nm" (Song 2005b). The nano-sized
particles often exhibit unique properties in comparison to the same micro-sized structures.
Advantages, such as greater external surface areas, smaller diffusion path lengths, and a greater
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aversion to coke formation make nanocrystalline zeolites superior to traditional micron-sized
zeolites (Song 2005a, Song 2005b). In addition, enhanced absorbency capacities of up to 50%
greater than those for micron-sized zeolites have been reported (Song 2005b). The ability to
assemble nanocrystalline zeolites into thin films and other nanostructures facilitates the potential
formation of separation membranes (Song 2005b, Alwy 2005).
13.2. Remedial Applications
It has been projected that the enhanced properties of nanocrystalline zeolites will lead to an
increase in the total number of applications for this technology (Song 2005a). Regular-sized
zeolites already have been tested for a variety of environmental applications. Zeolites have the
ability to remediate water containing cationic species, such as ammonium and heavy metals, as
well as chemicals, such as 137Cs and 90Sr. These radioactive species are found in nuclear plant
wastewater and polluted groundwater (Bowman 2002). MTBE, a contaminant used as a gasoline
additive, also has been reported as a potential target of zeolites. H-ZSM-5, a type of zeolite,
converts MTBE to biodegradable chemicals in aqueous solutions, for example (Centi 2002). In
addition, surfactant modified zeolites (SMZ) have been researched as potential remedial agents.
In 2003, Bowman reported the creation of an SMZ permeable barrier to adsorb the contaminants
PCE and chromate from groundwater. Bowman also evaluated the ability of the modified
zeolites to remove petroleum hydrocarbons such as BTEX from oilfield wastewater (Bowman
2002).
Currently, nanocrystalline zeolites are still in the research phase, and no specific soil or water
remediation processes have been proposed. However, as mentioned previously, the advantages
of nano-sized zeolites is compared to micron-sized, will likely lead to an increase in
technological applications. This will translate to a growth in environmental applications as well.
13.3. Toxicity and Safety And Concerns
No specific toxicity concerns involving nanocrystalline zeolites have been reported. Studies,
however, are currently underway.
14. OVERALL TOXICITY AND SAFETY CONCERNS
Human exposure to nanosized particles does not represent an emerging problem, necessarily.
Nanosized particles have been naturally present in the environment for millennia. Examples of
these particles include viruses, volcanic ash, forest fire ash, and naturally occurring ferritin.
Anthropogenic exposure to nanosized particles is also not a new concept. Since the start of the
Industrial Revolution, human contact with nanosized particles has increased dramatically.
Internal combustion engines, incinerators, metal fumes, and polymer fumes all represent sources
of nanoparticles. These particles, however, are produced unintentionally as byproducts to
reactions. The recent emergence of nanotechnology, though, has ushered humans into an era of
exposure to intentionally created nanosized particles. As seen throughout this report, these new
"manufactured" particles have unique properties, including shape, functionality, and reactivity.
While the term "manufactured" does not necessarily indicate toxicity, the increasing number of
particles in production increases routes and means of human exposure (Oberdorster 2005).
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Human exposure to nanoparticles can occur in a variety of different ways, including through
ingestion, inhalation, injection, and dermal exposure (Oberdorster 2005). Thus, the toxicology
of nanoparticles must be studied across a variety of exposure routes and test organisms.
Inhalation, however, is expected to be the most predominant route of human exposure,
particularly in the workplace (Hood 2004). Currently, a number of different laboratories and
researchers are conducting toxicity studies involving nanoparticles. A number of studies already
have been published, and significantly more data are being generated. In November 2003, the
EPA awarded 12 grants to various universities to investigate the potential health and
environmental impacts of nanomaterials. In addition, EPA, NSF, and NIOSH have jointly
funded an additional grant program this year for further toxicological studies.
The majority of the studies published thus far have centered on carbon nanotubes, fullerenes, and
photocatalytic particles. Carbon nanotubes represent a cause for concern due to their similarities
to asbestos. A number of studies have already demonstrated the negative impacts that nanotubes
have on the respiratory tracts of rats and mice. One study, completed by scientists at NASA
compared the effects of soot-like carbon particles to carbon nanotubes on the respiratory tracts of
mice. The mice exposed to the nanotubes sustained significant lung damage, while the mice
exposed to carbon soot did not show any negative effects. Mice exposed to the carbon nanotubes
also showed signs of granuloma formation, a common side effect to particulate exposure (Raloff
2005). These findings have been supported by other similar studies (Oberdorster 2005). While
these studies present cause for alarm, it should be noted that exposure levels influence toxicity in
humans, and safe handling of these materials can reduce exposure to allowable levels (Raloff
2005).
Outside of carbon nanotubes, carbon nanospheres, such as fullerenes, also have been studied.
Most notably, ecotoxicological studies with fullerenes have been conducted using the test
organism Daphnia magna, as well as largemouth bass. A median lethal concentration of 800
ppb was established for/), magna. Similarly, fullerene concentrations as low as 0.5 ppm have
been shown to cause glutathione depletion in the gills of largemouth bass, as well lipid
peroxidation in the brain over 48-hour exposure periods (Oberdorster 2005). Movement of
nanospheres from the lungs to the blood in inhalation studies also has been reported. Once in the
blood stream, nanoparticles can attach to red blood cell causing an increased susceptibility to
clotting (Raloff 2005).
While a number of studies involving various nanotechnologies already have been performed,
adequate risk assessments will ultimately require more studies. Many of the studies thus far have
focused on carbon-based nanotechnologies. And of these studies, a majority of them have
focused on inhalation as a means to exposure. In terms of understanding the environmental
impacts of nanotechnologies, an increasing number of studies will need to focus on the
ecological impacts of nanotechnologies used in product production as well as for remedial
purposes.
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15. REGULATORY NEEDS
"We recommend that the use of free (that is, not fixed in a matrix) manufactured nanoparticles
in environmental applications such as remediation be prohibited until appropriate research has
been undertaken and it can be demonstrated that the potential benefits outweigh the potential
risks. " -The Royal Society of the United Kingdom
Fearing that nanotechnology will suffer fates similar to those of genetically modified foods,
nuclear power, or asbestos, experts are currently scrambling to adequately address the regulatory
questions raised by nanotechnology. The sheer vastness of the various materials and
technologies encompassed in the term "nanotechnology" represent the main source of the
regulatory problem. Evident throughout this paper, the technologies currently available, as well
as those in development, possess unique characteristics and subsequently very individualized
toxicity capacities. In a recent editorial, Nature magazine reaffirmed this position, stating that
"nanotechnology is a diverse field united only by a factor of scale. So it is not even clear how
one would go about regulating nanotech in a manner unique to the discipline" (Nature 2003). As
with the regulation of any technology or process, regulating nanotechnology will require a
balancing act. Too much regulation could stifle progress and innovation, while too little could
create a number of consequences.
Currently, nanotechnology regulations in the US fall on the minimal side. European countries,
while also lacking specific regulations, have taken a much more preventative approach to
nanotechnology. For example, the Royal Society and the Royal Academy of Engineering has
advised the prohibition of nanoparticle deployment into the environment in the United Kingdom
until more conclusive safety data is generated (The Royal Society 2004).
The need for more explicit regulations in the US is increasing. The field of nanotechnology in
general is growing very rapidly across a number of disciplines. In the absence of greater
regulations, some scientists and policy makers fear that nanotechnology will become the next
"Frakenfood." Experts such as Julia Moore, a senior advisor in the NSF's Office of International
Science and Engineering, have expressed concern that the news of a single environmentally
detrimental nanotechnology could ignite public opposition to the entire field similar to that of
genetically modified foods (Service 2004). In reality, nanotechnology covers an imminently
broad group of technologies and products with widely varying safety concerns; however a
negative public perception of the term "nanotechnology" could hinder future progress across all
disciplines.
Calls for more stringent regulations are also appearing from the less obvious sectors. Industry
and industry consultants are increasingly pushing for a more defined regulatory strategy. On
June 29th, 2005, Matthew Nordan of Lux Research, Inc., testified at a hearing of the House
Science research subcommittee that "based on [Lux's] contact with individuals driving nanotech
initiatives at America's largest corporations, it's clear to us that ambiguity surrounding
environmental, health, and safety regulation of nanoparticles is hampering commercialization."
According to Nordan, companies are "reluctant to play a game whose rules may change at any
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time." (InsideEPA 2005). Lux Research, Inc., is a consulting firm focused on nanotechnology
industry.
At the moment, a number of steps have been taken by various federal agencies to begin the
process of generating concrete regulations and standards. In August 2004, the American
National Standards Institute (ANSI) formed the Nanotechnology Standards Panel (ANSI-NSP).
The primary focus of ANSI-NSP is "nomenclature and terminology" for nano-materials,
although later work may be extended to testing methodology and material properties (ANSI [No
Date]).
The USEPA stands to serve as the primary regulator of nanotechnology. Currently, however, the
USEPA is only asking nanomaterials producers to voluntarily provide information about the
types of materials they are making and at what volumes. While this information is helpful at a
preliminary level, requirements will need to be ramped up quickly to meet the growing
production of nanomaterials (Service 2005). The existing regulatory framework for chemicals
and now nanomaterials is the Toxic Substances Control Act (TSCA). It is unclear, however, that
TSCA has the ability to adequately regulate nanomaterials. TSCA gives EPA the authority to
regulate new chemicals. Unfortunately though, there are no provisions in TSCA to distinguish
between nanosized materials and their larger-scale counterparts. Because of the nature of
nanotechnology, even when chemical compositions remain the same, the functionality of the
material can change (Wardack 2003). Recently, EPA received a request for exemption from
submitting a full Pre-Manufacture Notice (PMN) for single-walled carbon nanotubes. The
request was for a Low-Volume Exemption (LVE). This request again raised the question of
whether or not a carbon-based particle can be considered a new chemical (InsideEPA 2005).
With numerous nanoparticles being manufactured, and nZVI injections already taking place, it is
clear that, at the moment, the regulations lag behind the technology. As applications and uses of
these technologies continue to arise, it will become increasingly important for voluntary
programs to become definitive about rules and regulations. With support from both regulatory
agencies and industry, alike, a clear incentive exists for establishing better regulations and
addressing the deficiencies in the current policies of TSCA.
16. CONCLUDING REMARKS: THE FUTURE OF NANOTECHNOLOGY
FOR ENVIRONMENTAL REMEDIATION
The United States, as well as the greater world, is faced with the serious problem of cleaning up
polluted lands and waters. With a growing population and growing land requirements, past
efforts to sequester contaminants are not adequate. Increasing importance is falling on
technologies that can treat pollution and decontaminate sites. With technologies such as
bioremediation and phytoremediation gaining popularity, nanotechnology offers a number of
emerging technologies that could work to treat contaminants. While one nanotechnology is
already commercially available for use in remediation, it is inevitable that other technologies
currently on the bench scale will gradually move into field-scale trials. These technologies will
hopefully open the door to more effective and less costly toxicant treatments. As can be seen,
though, the success of these technologies is reliant on a better understanding of their potential
health impacts. Success in the public eye is also dependent on maintaining a positive image for
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the entire field of nanotechnology. In the end, it likely will be the next few years that dictate the
direction of nanotechnologies for environmental remediation.
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