December 2, 2005
External Review Draft
U.S. Environmental Protection Agency
EXTERNAL REVIEW DRAFT
Nanotechnology White Paper
Prepared for the U.S. Environmental Protection Agency
by members of the Nanotechnology Workgroup,
a group of EPA's Science Policy Council
Science Policy Council
U.S. Environmental Protection Agency
Washington, DC 20460
lt)0
NOTICE
This document is an external review draft. It has not been formally released by the U.S.
Environmental Protection Agency and should not at this stage be construed to represent
Agency position.
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Draft Nanotechnology White Paper - External Review Draft
DISCLAIMER
Mention of trade names or commercial products does not constitute endorsement of
recommendation for use.
Note: This is an external review draft, and is not approved for final publication.
11
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Draft Nanotechnology White Paper - External Review Draft
Nanotechnology White Paper
Workgroup Co-Chairs
Jeff Morris Jim Willis
Office of Research and Development Office of Prevention, Pesticides and
Toxic Substances
Science Policy Council Staff
Kathryn Gallagher
Office of the Science Advisor
Subgroup Co-Chairs
External Coordination
Steve Lingle, ORD
Dennis Utterback, ORD
Ecological Effects
Anne Fairbrother, ORD
Vince Nabholz, OPPTS
Risk Management
Flora Chow, OPPT
EPA Research Strategy
Barbara Kam, ORD
Human Exposures
Scott Prothero, OPPT
Converging Technologies
Nora Savage, ORD
Risk Assessment
Phil Sayre, OPPTS
Environmental Fate
John Scaiera, OEI
Bob Boethling, OPPTS
Pollution Prevention
Walter Schoepf, Region 2
Physical-Chemical
Properties
Tracy Williamson, OPPTS
Environmental Detection
and Analysis
John Scaiera, OEI
Richard Zepp, ORD
Sustainability and Society
Michael Brody, OCFO
Diana Bauer, ORD
Health Effects
Kevin Dreher, ORD
Deborah Burgin, OPEI
Statutes, Regulations, and
Policies
Jim Alwood, OPPT
Public Communications
and Outreach
Anita Street, ORD
in
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Draft Nanotechnology White Paper - External Review Draft
Workgroup Members
Suzanne Ackerman, OPA
Kent Anapolle, OPPTS
Fred Arnold, OPPTS
Ayaad Assaad, OPPTS
Dan Axelrad, OPEI
John Bartlett, OPPTS
Diana Bauer, ORD
Sarah Bauer, ORD
John Blouin, OPPT
Jim Blough, Region 5
Pat Bonner, OPEI
William Boyes, ORD
Gordon Cash, OPPTS
Gilbert Castellanos, OIA
Tai-Ming Chang, Region 3
Teri Conner, ORD
Paul Cough, OIA
Lynn Delpire, OPPTS
John Diamante, OIA
Christine Dibble, OPA
Thomas Forbes, OEI
Conrad Flessner, OPPTS
Jack Fowle, ORD
Sarah Furtak, OW
Hend Galal-Gorchev, OW
David Giamporcaro, OPPTS
Michael Gill, ORD liaison for Region 9
Tala Henry, OW
Collette Modes, OPPTS
Gene Jablonowski, Region 5
Joe Jarvis, ORD
Y'vonne Jones-Brown, OPPTS
Edna Kapust, OPPTS
Nagu Keshava, ORD
David Lai, OPPTS
Skip Laitner, OAR
Warren Layne, Region 5
Do Young Lee, OPPTS
Virginia Lee, OPPTS
Monique Lester, OARM on detail OIA
Michael Lewandowski, ORD
Laurence Libelo, OPPTS
Bill Linak, ORD
David Lynch, OPPTS
Tanya Maslak, OSA intern
Paul Matthai, OPPT
Carl Mazza, OAR
Nhan Nguyen, OPPTS
Carlos Nunez, ORD
Onyemaechi Nweke, OPEI
Marti Otto, OSWER
Manisha Patel, OGC
Steve Potts, OW
Mary Reiley, OW
Mary Ross, OAR
Bill Russo, ORD
Mavis Sanders, OEI
Bernie Schorle, Region 5
Paul Solomon, ORD
Maggie Theroux-Fieldsteel, Region 1
Stephanie Thornton, OW
Alan Van Arsdale, Region 1
William Wallace, ORD
Barb Walton, ORD
IV
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6.7 SUMMARY OF RECOMMENDATIONS 82
7.0 REFERENCES 83
APPENDIX A: GLOSSARY OF NANOTECHNOLOGY TERMS '. 98
APPENDIX B: PRINCIPLES OF ENVIRONMENTAL STEWARDSHIP BEHAVIOR 101
APPENDIX C: ADDITIONAL DETAILED RISK ASSESSMENT INFORMATION 103
Cl ENVIRONMENTAL FATE OF NANOMATERIALS 103
C2 THE ENVIRONMENTAL DETECTION AND ANALYSIS OF NANOMATERIALS no
C3 HUMAN HEALTH EFFECTS ASSESSMENT '. 120
C4 ECOLOGICAL EFFECTS 121
VI
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Table of Contents
FOREWORD : VII
ACKNOWLEDGMENTS VIII
ACRONYMS IX
EXECUTIVE SUMMARY 1
1.0 INTRODUCTION 3
1.1 PURPOSE 3
1.2 NANOTECHNOLOGY DEFINED 4
1.3 WHY NANOTECHNOLOGY Is IMPORTANT TO EPA 9
1.4 WHAT EPA is DOING WITH RESPECT TO NANOTECHNOLOGY 10
1.5 CONTEXT FOR EPA's ENVIRONMENTAL SCIENCE ROLES 10
1.6 COMMUNICATION AND OUTREACH 15
1.7 OPPORTUNITIES AND CHALLENGES 15
ZO ENVIRONMENTAL BENEFITS OF NANOTECHNOLOGY 17
2.1 INTRODUCTION 17
2.2 BENEFITS THROUGH ENVIRONMENTAL TECHNOLOGY APPLICATIONS 17
2.3 BENEFITS THROUGH OTHER APPLICATIONS THAT SUPPORT SUSTAIN ABILITY 19
3.0 RISK MANAGEMENT AND STATUTES 24
3.1 RISK. MANAGEMENT 24
3.2 STATUTES : 26
4.0 RISK ASSESSMENT OF NANOMATERIALS 33
4.1 INTRODUCTION ; 33
4.2 CHEMICAL IDENTIFICATION AND CHARACTERIZATION OF NANOMATERIALS 34
4.3 ENVIRONMENTAL FATE OF NANOMATERIALS 35
4.4 ENVIRONMENTAL DETECTION AND ANALYSIS OF NANOMATERIALS 42
4.6 HUMAN HEALTH EFFECTS OF NANOMATERIALS 52
4.7 ECOLOGICAL EFFECTS OF NANOMATERIALS 57
5.0 EPA'S RESEARCH NEEDS FOR NANOMATERIALS 62
5.1 INTRODUCTION 62
5.2 RESEARCH NEEDS FOR ENVIRONMENTAL APPLICATIONS 62
5.3 CHEMICAL IDENTIFICATION AND CHARACTERIZATION 64
5.4 ENVIRONMENTAL FATE RESEARCH NEEDS 64
5.5 ENVIRONMENTAL DETECTION AND ANALYSIS RESEARCH NEEDS 67
5.6 RELEASES AND HUMAN EXPOSURES 67
5.7 HUMAN HEALTH EFFECTS ASSESSMENT RESEARCH NEEDS 68
5.8 ECOLOGICAL EFFECTS RESEARCH NEEDS 70
5.9 RISK ASSESSMENT RESEARCH NEEDS 72
6.0 RECOMMENDATIONS 73
6.1 POLLUTION PREVENTION AND ENVIRONMENTAL STEWARDSHIP RECOMMENDATIONS 73
6.2 RESEARCH RECOMMENDATIONS 74
6.3 RECOMMENDATIONS TO ADDRESS OVERARCHING RISK ASSESSMENT NEEDS 80
6.4 RECOMMENDATIONS FOR COLLABORATIONS 80
6.5 RECOMMENDATION TO CONVENE ACROSS-AGENCY WORKGROUP 81
6.6 RECOMMENDATION FOR TRAINING 81
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FOREWORD
Nanotechnology presents opportunities to create new and better products. It also has the
potential to improve assessment, management, and prevention of environmental risks. However,
there are unanswered questions about the impacts of nanomaterials and nanoproducts on human
health and the environment.
In December 2004, EPA's Science Policy- Council (SPC) formed a cross-Agency
Nanotechnology Workgroup to develop a white paper examining potential environmental
implications and applications of nanotechnology. This document describes the issues that EPA
must address to ensure that society benefits from advances in environmental protection that
nanotechnology may offer, and to understand any potential risks from environmental exposure to
nanomaterials. Nanotechnology will have an impact across EPA. Agency managers and staff
are working together to develop an approach to nanotechnology that is forward thinking and
informs the risk assessment and risk management activities in our program and regional offices.
This document is intended to support that cross-Agency effort.
We would like to acknowledge and thank the Nanotechnology Workgroup subgroup co-
chairs and members and for their work in developing this document. We would especially like
to acknowledge the Workgroup co-chairs Jim Willis and Jeff Morris for leading the workgroup
and document development. We also thank SPC staff task lead Kathryn Gallagher, as well as
Jim Alwood and Dennis Utterback, for their efforts in assembling and refining the document.
It is with pleasure that we present the EPA Nanotechnology White Paper.
William H. Farland, Ph.D.
Acting Chair, Science Policy Council
Charles M. Auer
Director, Office of Pollution, Prevention
and Toxics
Vll
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ACKNOWLEDGMENTS
The Nanotechnology Workgroup would like to acknowledge the Science Policy Council
and its Steering Committee for their recommendations and contributions to this document. We
thank Paul Leslie of TSI Incorporated, and Laura Morlacci, Tom Webb and Peter McClure of
Syracuse Research Corporation for their support in developing background information for the
document. We also thank the external peer reviewers for their comments and suggestions.
Finally, the workgroup would like to thank Bill Farland (ORD) and Charlie Auer (OPPT) for
their leadership and vision with respect to nanotechnology.
Vlll
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ACRONYMS
ADME Absorption, Distribution, Metabolism, Elimination
ANSI American National Standards Institute
ASTM American Society for Testing and Materials
CAA Clean Air Act
CAAA Clean Air Act Amendments
CAS Chemical Abstracts Service
CDC Centers for Disease Control and Prevention
CERCLA Comprehensive Environmental Response, Compensation and Liability Act
CFCs Chlorofluorocarbons
ChemSTEER Chemical Screening Tool for Exposures and Environmental Releases
CNT Carbon nanotubes
CPSC Consumer Products Safety Commission
CWA . Clean Water Act
DfE Design for Environment
DHHS Department of Health and Human Services
DHS Department of Homeland Security
DNA Deoxyribonucleic Acid
DOC • Department of Commerce
DOE Department of Energy *
DOI Department of Interior
DOJ Department of Justice
DOS Department of State
DOT Department of Transportation
DOTreas Department of the Treasury
E-FAST Exposure and Fate Assessment Screening Tool
EPA Environmental Protection Agency
EPCRA Emergency Planning and Community Right-to-Know Act
FDA Food and Drug Administration
FIFRA Federal Insecticide, Fungicide and Rodenticide Act
GI Gastrointestinal
GSH Glutathione-S-Transferase
HAPEM Hazardous Air Pollutant Exposure Model
HAPs Hazardous Air Pollutants
HEPA High Efficiency Paniculate Air
HPV High Production Volume
IAC Innovation Action Council
ISO International Organization for Standardization
ITIC Intelligence Technology Information Center
Kow Octanol-Water Partition Coefficient
LCA Life Cycle Assessment
LEDs Light Emitting Diodes
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MCLGs Maximum Contaminant Level Goals
MCLs Maximum Contaminant Levels
MFA Material Flow Analysis
MW Molecular Weight
NAAQS National Ambient Air Quality Standards
NASA National Aeronautics and Space Administration
NCEI National Center for Environmental Innovation
NCER National Center for Environmental Research
NEHI Nanotechnology Environmental and Health Implications (NNI work group)
NERL National Exposure Research Laboratory
NHEERL National Health and Environmental Effects Research Laboratory
NHEXAS National Human Exposure Assessment Survey
NIH National Institutes of Health
NIOSH National Institute for Occupational Safety and Health
NNAP National Nanotechnology Advisory Panel
NNCO National Nanotechnology Coordinating Office
NNI National Nanotechnology Initiative
NOx Nitrogen oxides
NRC National Research Council
NRML National Risk Management laboratory
NSET NSTC Committee on Technology, Subcommittee on Nanoscale Science,
Engineering and Technology
NSF t National Science Foundation
NSTC National Science and Technology Council
NTP National Toxicology Program (DHHS)
OAR Office of Air and Radiation
OCFO Office of the Chief Financial Officer
OECD Organization for Economic Cooperation and Development
OEM Original Equipment Manufacturers
OEI Office of Environmental Information
OLEDs . Organic Light Emitting Diodes
OPEI Office of Policy, Economics and Innovation
OPPT Office of Pollution Prevention and Toxics
OPPTS Office of Prevention, Pesticides and Toxic Substances
ORD Office of Research and Development
OSA Office of the Science Advisor
OSHA Occupational Safety and Health Administration
OSTP Office of Science and Technology Policy (Executive Office of the President)
OSWER Office of Solid Waste and Emergency Response
OW Office of Water
PC AST President's Council of Advisors on Science and Technology
PCBs Polychlorinated Biphenyls
PM Paniculate Matter
PMN Premanufacture Notice
PPE Personal Protective Equipment
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QSAR Quantitative Structure Activity Relationship
RCRA Resource Conservation and Recovery Act
SAMMS Self-Assembled Monolayers on Mesoporous Supports
SAR Structure Activity Relationship
SDWA Safe Drinking Water Act
SDWIS Safe Drinking Water Information System
SEM Scanning electron microscopy
SFA Substance Flow Analysis
SPC Science Policy Council
STAR Science To Achieve Results
STM Scanning Tunneling Microscope
SWCNT Single-Walled C arbon Nanotubes
TOC Total Organic Carbon
TRI Toxics Release Inventory
TSCA Toxic Substances Control Act
USDA US Department of Agriculture
USPTO US Patent and Trade Office
ZVI Zero Valent Iron
XI
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i EXECUTIVE SUMMARY
2
3 Nanotechnology has the potential to change and improve many sectors of American
4 industry, from consumer products to health care to transportation, energy and agriculture. In
5 addition to these societal benefits, nanotechnology presents new opportunities to improve how
6 we measure, monitor, manage, and minimize contaminants in the environment, and the U.S.
7 Environmental Protection Agency (EPA, or "the Agency") will continue to support and
8 advance these opportunities. However, as the applications of nanotechnology continue to
9 expand, EPA also has the obligation and mandate to protect human health and safeguard the
10 environment by better understanding and addressing potential risks from exposure to
11 materials containing nano-scale particles (commonly known as "nanomaterials").
12
13 For the past five years, EPA has played a leading role in funding research and setting
14 research directions to develop environmental applications for, and understand the potential
15 human health and environmental implications of, nanotechnology. That research has already
16 borne fruit, particularly in the use of nanomaterials for environmental clean-up and in
17 understanding the disposition of nanomaterials in biological systems. Some environmental
18 technologies using nanotechnology have progressed beyond the research stage. Also, a
19 number of specific nanomaterials have come to the Agency' s attention, whether as novel
20 products intended to promote the reduction or remediation of pollution or because they have
21 entered one of EPA's regulatory review processes. For EPA, nanotechnology has evolved
22 from a futuristic idea to watch, to a current issue to address.
23
24 In December 2004, EPA's Science Policy Council created a cross-Agency workgroup
25 charged with describing the issues EPA must address to ensure that society accrues the
26 important benefits to environmental protection that nanotechnology may offer, as well as to
27 better understand any potential risks from exposure to nanomaterials in the environment. This
28 paper is the product of that workgroup.
29
30 The paper begins with an introduction that describes what nanotechnology is, why
31 EPA is interested in it, and what opportunities and challenges exist regarding nanotechnology
32 and the environment. It then moves to a discussion of the potential environmental benefits of
33 nanotechnology, 'describing environmental technologies as well as other applications that can
34 foster sustainable use of resources. Following is a brief section on risk management and the
35 Agency's statutory mandates, which sets the stage for a discussion of risk assessment issues
36 specific to nanotechnology. The paper then provides an extensive review of research needs
37 for both environmental applications and implications of nanotechnology. To help EPA focus
38 on priorities for the near term, the paper concludes with recommendations on next steps for
39 addressing science policy issues and research needs. Supplemental information is provided in
40 a number of appendices.
41
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2 Key recommendations include:
3 • Pollution Prevention, Stewardship, and Sustainability. The Agency should engage
4 resources and expertise to encourage, support, and develop approaches that promote
5 pollution prevention, sustainable resource use, and good product stewardship in the
6 production and use of nanomaterials. Additionally, the Agency should draw on new,
7 "next generation" nanotechnologies to identify ways to support environmentally
8 beneficial approaches such as green energy and green manufacturing.
9
10 * Research. The Agency should undertake, collaborate on, and catalyze research to
11 belter understand and apply information regarding nanomaterials':
12 o chemical identification and characterization,
.13 o environmental fate,
14 o environmental detection and analysis,
15 o potential releases and human exposures,
16- o human health effects assessment,
17 o ecological effects assessment, and
18 o environmental technology applications.
19 • ' •
20 • Risk Assessment. The Agency should conduct case studies on several engineered or
21 manufactured nanomaterials. Such case studies would be useful in identifying unique
22 considerations for conducting risk assessments on nanomaterials. The case studies
23 would also aid in identifying information gaps, which would help map areas of
24 research to inform the risk assessment process.
25
26 * Collaboration and Leadership. The Agency should continue and expand its
27 collaborations regarding nanomaterial applications and potential human health and
28 environmental implications.
29
30 • Cross-Agency Workgroup. The Agency should convene a standing cross-Agency
31 group to foster information sharing on nanotechnology science and policy issues.
32
33 • Training. The Agency should continue and expand its nanotechnology training
34 activities for scientists and managers.
35
36 Nanotechnology has emerged as a growing and rapidly changing field. New
37 generations of nanomaterials will evolve, and with them new and possibly unforeseen
38 environmental issues. It will be crucial that the Agency's approaches to leveraging the
39 benefits and assessing the impacts of nanomaterials continue to evolve in parallel with the
40 expansion of and advances in these new technologies.
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i 1.0 Introduction
2 1.1 Purpose
3 Nanotechnology presents new opportunities to create better materials and products.
4 Already, nanomaterial containing products are available in U.S. markets including coatings,
5 computers, clothing, cosmetics, sports equipment and medical devices. A survey by EmTech
6 Research of companies working in the field of nanotechnology has identified approximately
7 80 consumer products, and over 600 raw materials, intermediate components and industrial
8 equipment items that are used by manufacturers. Our economy will be increasingly affected
9 by nanotechnology as more products containing nanomaterials move from research and
10 development into production and commerce.
11
12 Nanotechnology also has the potential to improve the environment, both through
13 direct applications of nanomaterials to detect, prevent, and remove pollutants, as well as
14 indirectly by vising nanotechnology to design cleaner industrial processes and create
15 environmentally friendly products. However, there are unanswered questions about the
16 impacts of nanomaterials and nanoproducts on human health and the environment, and the US
17 Environmental Protection Agency (EPA or "the Agency") has the obligation to ensure that
18 potential risks are adequately understood to protect human health and the environment. As
19 products made from nanomaterials become more numerous and therefore more prevalent in
20 the environment, EPA is thus considering how to best leverage advances in nanotechnology to
21 enhance environmental protection, as well as how the introduction of nanomaterials into the
22 environment will impact the Agency's environmental programs, policies, research needs, and
23 approaches to decision making.
24
25 In December 2004, the Agency's Science Policy Council convened a cross-Agency
26 Nanotechnology Workgroup and charged the group with developing a white paper to examine
27 the implications and applications of nanotechnology. This document describes the issues
28 EPA must.address to ensure that society accrues the important benefits to environmental
29 protection that nanotechnology may offer, and to make sure that we understand any potential
30 risks from environmental exposure to nanomaterials.
31
32 The paper begins with an introduction that describes what nanotechnology is, why
33 EPA is interested in it, and what opportunities and challenges exist regarding nanotechnology
34 and the environment. It then moves to a discussion of the potential environmental benefits of
35 nanotechnology, describing environmental technologies as well as other applications that can
36 foster sustainable use of resources. Following is a brief section on risk management and the
37 Agency's statutory mandates, which sets the stage for a discussion of risk assessment issues
38 specific to nanotechnology. The paper then provides an extensive review of research needs
39 for both environmental applications and implications of nanotechnology. To help EPA focus
40 on priorities for the near term, the paper concludes with recommendations on next steps for
41 addressing science policy issues and research needs. Supplemental information is provided in
42 a number of appendices.
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Draft Nanotechnology White Paper - External Review Draft
1
2 A discussion of an entire technological process or series of processes, as is
3 nanotechnology, could be wide ranging. However, because EPA operates through specific
4 programmatic activities and mandates, this document confines its discussion of
5 nanotechnology science policy issues within the bounds of EPA's statutory responsibilities
6 and authorities. In particular, the paper discusses what scientific information EPA will need,
7 and how it will use that information, to address nanotechnology in environmental decision
8 making.
9 1.2 Nanotechnology Defined
10 A nanometer is one billionth of a meter (10"9 m)—about one ten-thousandth the
11 diameter of a human hair, a thousand times smaller than a red blood cell, or about half the size
12 of the diameter of DNA. Figure 1 illustrates the scale of obj ects in the nanometer range. For
13 the purpose of this document, nanotechnology is defined as: research and technology
14 development at the atomic, molecular, or macromolecular levels using a length scale of
15 approximately one to one hundred nanometers in any dimension; the creation and use of
16 structures, devices and systems that have novel properties and functions because of their small
17 size; and the ability to control or manipulate matter on an atomic scale.
18 '
19 Nanotechnology manipulates matter for particular applications, and includes the
20 deliberate engineering of particles by certain chemical and/or physical processes (referred to
21 as "bottom-up" production) to create materials with specific properties not displayed in their
22 macro-scale counterparts, as well as the use of such manufacturing processes as milling or
23 grinding ("top-down" production) to produce nano-sized particles that may or may not have
24 properties different from those of the bulk material from which they are developed. For the
25 remainder of this document such engineered or manufactured nanomaterials will be referred
26 to as "intentionally produced nanomaterials," or simply "nanomaterials." The definition of
27 nanotechnology does not include unintentionally produced nanomaterials, nano-sized particles
28 or materials that occur naturally in the environment, such as viruses or volcanic ash, and
29 nanoparticle byproducts of human activity, such as diesel exhaust particulates or other friction
30 or airborne combustion byproducts. Where information from natural or incidentally formed
31 nano-sized materials (such as ultrafme particulate matter or combustion products) may aid in
32 the understanding of intentionally produced nanomaterials, this information will be discussed,
33 but the focus of this document is not on these other materials.
34
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Draft Nanotechnology White Paper - External Review Draft
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Figure 1. Diagram indicating relative scale of nano-sized objects. From NNI website, courtesy Office of Basic Energy Sciences,
Office of Science, U.S. Department of Energy
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1 There are many types of intentionally produced nanomaterials. For the purpose of this
2 document, nanomaterials are organized into four types:
3
4 (1) Carbon-based materials. These nanoparticles are composed entirely of carbon taking the
5 form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are sometimes called
6 buckyballs, while cylindrical fullerenes are called nanotubes. These particles have many
7 potential applications, including improved films and coatings, and stronger and lighter
8 materials.
9 (2) Metal-based materials such as quantum dots, nanogold, nanosilver and reactive metal
10 oxides like titanium dioxide. A quantum dot is a closely packed semiconductor crystal
11 comprised of hundreds or thousands of atoms, and whose size is on the order of a few
12 nanometers to a few hundred nanometers. Quantum dots can be manipulated to change their
13 physical properties, particularly their optical properties. The small size also means that,
14 typically, over 70 percent of the atoms are at surface sites, so that chemical changes at these
15 sites allow tuning of the light-emitting properties of the dots, permitting the emission of
16 multiple colors from a single dot.
17 3) Dendrimers, which are nano-sized polymers built from branched units. The surface of a
18 dendrimer as numerous chain ends, which can be tailored to perform specific chemical
19 functions. This property could also be useful for catalysis. Also, because three-dimensional
20 dendrimers contain interior cavities into which other molecules could be placed, they may be
21 useful for drug delivery.
22
23 (4) Composites, which combine nanoparticles with other nanoparticles or with larger, bulk-
24 type materials. Already, nanoparticles, such as nano-sized clays, are being added to products
25 ranging from auto parts to packaging materials, to enhance mechanical, thermal, barrier, and
26 flame-retardant properties.
27
28 The unique properties of these various types of intentionally produced nanomaterials
29 give them novel electrical, catalytic, magnetic, mechanical, thermal, or imaging features that
30 are highly desirable for applications in commercial, medical, military, and environmental
31 sectors. As we identify new uses for materials with these special properties, the number of
32 products containing such nanomaterials and their possible applications continues to grow.
33 Table 1 lists some examples of nanotechnology products. There are estimates that global
34 ' sales of nanomaterials could exceed $1 trillion by 2015 (M.C. Roco, presentation to the NRC,
35 23 March 2005).
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Draft Nanotechnology White Paper - External Review Draft
1
2
Table 1. Examples of nanotechnology products.
find Us*r
Applications
Tennis balls
and rackets
Clothing,
Cameras,
Respirators,
Razor blades,
Cosmetics,
Sunscreens,
Beer bottles
Therapeutic
Systems
Drugs,
Sprays,
Burn
dressings,
Medical
equipment
components
Components
Transistors,
Fillers,
Catalytic
converters,
Fenders,
Mirror
housings,
Fuel Cells,
Step assists,
Polarizers/
Wave plates,
Display s-
OLEDs
Software
Modeling,
Controllers for
microscopes,
Computer Aid
Design
navigation
Capital
Equipment
Positioners,
Cantilevers,
Coaters,
Probers/Manip
ulators,
Lithography
masks, Resists
Imaging
Microscopes,
Electron
Beams,
X-ray
4 1.2.1 Converging Technologies
5 In the long-term, nanotechnology increasingly will likely be discussed within the
6 context of the convergence, integration, and synergy of nanotechnology, biotechnology,
7 information technology, and cognitive technology. Convergence involves the development of
8 novel products with enhanced capabilities that incorporate bottom-up assembly of miniature
9 components with accompanying biological, computational and cognitive capabilities. The
10 convergence of nanotechnology and biotechnology, already rapidly progressing, will result in
11 the production of novel nanoscale materials. The convergence of nanotechnology and
12 biotechnology with information technology and cognitive science is expected to rapidly
13 accelerate in the coming decades. The increased understanding of biological systems will
14 provide valuable information towards the development of efficient and versatile biomimetic
15 tools, systems, and architecture.
16
17 Generally, biotechnology involves the use of microorganisms, or bacterial factories,
18 which contain inherent "blueprints" encoded in the DNA, and a manufacturing process to
19 produce molecules such as amino acids. Within these bacterial factories, the organization and
20 self-assembly of complex molecules occurs routinely. Many "finished" complex cellular
21 products are < 100 nanometers. For this reason, bacterial factories may serve as models for
22 the organization, assembly and transformation for other nanoscale materials production.
23
24 Bacterial factory blueprints are also flexible. They can be modified to produce novel
25 nanobiotechnology products that have specific desired physical-chemical (performance)
26 characteristics. Using this production method could be a more material and energy efficient
27 way to make new and existing products, in addition to using more benign starting materials.
28 In this way, the convergence of nano- and biotechnologies could improve environmental
29 protection. As an example, researchers have extracted photosynthetic proteins from spinach
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1 chloroplasts and coated them with nanofilms that convert sunlight to electrical current, which
2 one day may lead to energy generating films and coatings (Das et al., 2004). The addition of
3 information and cognitive capabilities will provide additional features including
4 programmability, miniaturization, increased power capacities, adaptability, and reactive, self-
5 correcting capacities
6
7 Another example of converging technologies is the development of nanometer-sized
8 biological sensor devices that can detect specific compounds within the natural environment;
9 store, tabulate, and process the accumulated data; and determine the import of the data;
10 providing a specific response for the resolved conditions would enable rapid and effective
11 human health and environmental protection. Responses' could range from the release of a
12 certain amount of biological or chemical compound, to the removal or transformation of a
13 compound.
14
15 The convergence of nanotechnology with biotechnology and with information and
16 cognitive technologies may provide such dramatically different technology products that the
17 manufacture, use and recycling/disposal of these novel products, as well as the development
18 of policies and regulations to protect human health and the environment, may prove to be a
19 daunting task.
20
21 The Agency is committed to keeping abreast of emerging issues within the
22 environmental arena, and continues to support critical research, formulate new policies, and
23 adapt existing policies as needed to achieve its mission. However, the convergence of these
24 technologies will demand a flexible, rapid and highly adaptable approach within EPA. As
25 these technologies progress and as novel products emerge, increasingly the Agency will find
26 that meeting constantly changing demands will require proactive actions and planning.
27
28 We are currently nearing the end of basic research and development on the first
29 generation of materials resulting from nanotechnolpgies that include coatings, polymers, more
30 reactive catalysts, etc. (Figure 2). The second generation, which we are beginning to enter,
31 involves targeted drug delivery systems, adaptive structures and actuators, and has already
32 provided some interesting examples. The third generation, anticipated within the next 10-15
33 years, will bring novel robotic devices, three-dimensional networks and guided assemblies.
34 The fourth stage will result in molecule-by-molecule design and self-assembly capabilities.
35 Although it is not likely to happen for some time, this integration of these fourth-generation
36 nanotechnologies with information, biological, and cognitive technologies will lead to
37 products we can only now vaguely imagine. The Agency need not develop the ability to
38 predict the future, it only needs to prepare for it. Towards that aim, understanding the unique
39 challenges and opportunities afforded by converging technologies before they occur will
40 provide the Agency with the essential tools required for the effective and appropriate handling
41 of emerging technology and s cience.
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Technological Complexity
increasing
Stages of Nanotechnology Development
First Generation ~Z001: Passive nanostructures
Nano-structured coatings, nanoparticles, ncnostructured metals, polymers, ceramics,
Catalysts, composites, displays
Second generation ~Now: Active nanostructures
Transistors, amplifiers, targeted drugs and chemicals, actuators, adaptive
structures, sensors, diagnostic assays, fuel cells, solar cells, high performance
nanocomposites, ceramics, metals
Third Generation ~ 2010: 3-D nanosystems and systems of nanosystems
Various assembly techniques, networking at the nanoscale and new architectures,
Biomimetic materials, novel therapeutics/targeted drug delivery
Fourth Generation ~2015 Molecular Nanosystems
Molecular devices "by design", atomic design, emerging functions
Figure 2. The stages of nanotechnology development
3 1.3 Why Nanotechnology Is Important to EPA
4 Nanotechnology holds great promise for creating new materials with enhanced
5 properties and attributes. These properties, such as greater catalytic efficiency, increased
6 electrical conductivity, and improved hardness and strength, are a result of nanomaterials'
7 larger surface area per unit of volume and quantum effects that occur at the nanometer scale
8 ("nanoscale"). Nanomaterials are already being used or tested in a wide range of products
9 such as sunscreens, composites, medical and electronic devices, and chemical catalysts.
10 Similar to nanotechnology's success in consumer products and other sectors, nanomaterials
11 have promising environmental applications. For example, nano-sized cerium oxide has been
12 developed to decrease diesel emissions, and iron nanoparticles can remove contaminants from
13 soil and ground water. Nano-sized sensors hold promise for improved detection and tracking
14 of contaminants. In these and other ways, nanotechnology presents an opportunity to improve
15 how we measure, monitor, manage, and reduce contaminants in the environment.
16
17 Some of the same special properties that make nanomaterials useful are also properties
18 that may cause some nanomaterials to pose hazards to humans and the environment, under
19 specific conditions. Some nanomaterials that enter animal tissues may be able to pass through
20 cell membranes or cross the blood-brain barrier. This may be a beneficial characteristic for
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1 such uses as targeted drug delivery and other disease treatments, but could result in
2 unintended impacts in other uses or applications. Inhaled nanoparticles may become lodged
3 in the lung, and the high durability and reactivity of some nanomaterials raises issues of their
4 fate in the environment. It may be that in most cases nanomaterials will not be of human
5 health or ecological concern. However, at this point not enough information exists to assess
6 environmental exposure for most engineered nanomaterials. This information is important,
7 because EPA needs a sound scientific basis for assessing and managing any unforeseen future
8 impacts resulting from the introduction of nanoparticles and nanomaterials into the
9 environment.
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11 A challenge for environmental protection is to allow full realization of the societal
12 benefits of nanotechnology, while identifying and minimizing any adverse impacts to humans
13 or ecosystems from exposure to nanomaterials. In addition, we need to understand how to
14 best apply nanotechnology for pollution prevention in current manufacturing processes and in
15 the manufacture of new nanomaterials and nanoproducts, as well as in environmental
16 detection, monitoring, and clean-up. This understanding will come from scientific
17 information generated by environmental research and development activities within
18 government agencies, academia, and the private sector. How we prioritize, develop, and use
19 this scientific information will determine how well we succeed at ensuring safe and
20 sustainable development of nanotechnology.
21 1.4 What EPA is Doing with Respect to Nanotechnology
22 EPA is actively participating in nanotechnology development and evaluation. Some
23 of the activities EPA has undertaken include: 1) actively participating in the National
24 Nanotechnology Initiative, which coordinates nanotechnology research and development
25 across the federal government, 2) funding nanotechnology research through EPA's Science
26 To Achieve Results (STAR) grant program and Small Business Innovative Research (SBIR)
27 program, 3) collaborating with scientists internationally in order to share the growing body of
28 information on nanotechnology, 4) initiating the development of a voluntary pilot program for
29 the evaluation of nanomaterials and reviewing of nanomaterial new chemical submissions in
30 the Office of Pollution Prevention and Toxics ; and 5) reviewing nanomaterial registration
31 applications in the Office of Air and Radiation/Office of Transportation and Air Quality.
32 1.5 Context for EPA's Environmental Science Roles
33 EPA's role in nanotechnology exists within a larger framework of activities that have
34 been ongoing for several years. Many sectors—including US federal and state agencies,
35 academia, the private sector, other national governments, and international bodies—are
36 considering potential environmental applications and implications of nanotechnology. This
37 section describes some of the major players in this arena, for two principal reasons: to
38 describe EPA's role regarding nanotechnology and the environment, and to identify
39 opportunities for collaborative and complementary efforts.
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1 1.5.1 Federal Agencies - The National Nanotechnology Initiative
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The National Nanotechnology Initiative (NNI) was launched in 2001 to coordinate
nanotechnology research and development across the federal government. Investments into
federally funded nanotechnology-related activities, coordinated through the NNI, have grown
from $464 million in 2001 to approximately $1 billion in 2005.
The NNI supports a broad range of research and development including fundamental
research on the unique phenomena and processes that occur at the nano scale, the design and
discovery of new nanoscale materials, and the development of nanotechnology-based devices
and systems. The NNI also supports research on instrumentation, metrology, standards, and
nanoscale manufacturing, Most important to EPA, the NNI has made responsible
development of this new technology a priority by supporting research on environmental
health and safety implications.
Twenty-four federal agencies currently participate in the NNI, eleven of which have
budgets dedicated to nanotechnology research and development. The other thirteen agencies
have made nanotechnology relevant to their missions or regulatory roles. Only a small part of
this federal investment aims at researching the social and environmental implications of
nanotechnology including its effects on human health, the environment, and society. Nine
federal agencies are investing in implications research including the National Science
Foundation, the National Institutes of Health, the National Institute of Occupational Health
and Safety, and the Environmental Protection Agency, These agencies coordinate their
efforts through the NNI's Nanoscale Science, Engineering, and Technology Subcommittee
(NSET) and its Nanotechnology Environmental Health Implications workgroup (NEHI)
(Figure 3). The President's Council of Advisors on Science and Technology (PCAST) serves
as an advisory body to the NNI.
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Council
NNAP (PCAST) ]
Non-governmental '
Organizations
State^ and ioeai
Nanotechnolagy fniti-ati
industry Sectors
Figure 3. NNINSET subcommittee structure
1.5.2 Efforts of Other Stakeholders
About $2 billion in annual research and development investment are being spent by
non-federal US sectors such as states, academia, and private industry. State governments
collectively spend an estimated $400 million on facilities and research aimed at the
development of local nanotechnology industries.
Although the industry is relatively new, US nanotechnology trade associations have
emerged. A directory of nanotechnology industry-related organizations can be found at
http;//www.nanovip. com. The American Chemistry Council also has a committee devoted to
nanotechnology and is encouraging research into the environmental health and safety of
nanomaterials.
Environmental nongovernmental organizations (NGOs) such as Environmental
Defense, Greenpeace UK, and the Natural Resources Defense Council are engaged in
nanotechnology issues. Also,'scientific organizations such as the National Academy of
Sciences, the Royal Society of the United Kingdom, and the International Life Sciences "
Institute are providing important advice on issues related to nanotechnology and the
environment. . *
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1 1.5.3 International Activities
2 Fully understanding the environmental applications and implications of
3 nanotechnology will require the concerted efforts of scientists and policy makers across the
4 globe. Europe and Asia match or exceed the US federal nanotechnology research budget.
5 Globally, nanotechnology research and development spending is estimated at around $9
6 billion (Lux Research, 2005). Thus, a great opportunity exists for internationally coordinated
7 and integrated efforts toward environmental research. International organizations such as the
8 Asian-Pacific Economic Cooperation, the British Standards Institute, the National Institute of
9 Standards and Technology, the American National Standards Institute, and the American
10 Society of Testing Materials are involved in nanotechnology issues. The Organization for
11 Economic Cooperation and Development (OECD) is currently engaging the topic of the
12 implications of engineered nanomaterials among its members under the auspices of the Joint
13 Meeting of the Chemicals Committee and Working Party on Chemicals, Pesticides and
14 Biotechnology (Chemicals Committee). The OECD Chemicals Committee has identified this
15 international forum for ensuring global cooperation, coordination, and communication
16 between member countries, nonmembers, industry, and NGOs on nanotechnology issues. As
17 a member of the Chemicals Committee., EPA will participate in this effort.
18
19 Additionally, the United States and European Union Initiative (June 2005) addresses
20 both regulatory and research areas in nanotechnology. Specifically, the document states that
21 the United States and the European Union will work together to, among other things, "support
22 an international dialogue and cooperative activities for the responsible development and use
23 of the emerging field of nanotechnology." EPA is currently working with the US State
24 Department, the NNI, and the EU to bring about research partnerships in nanotechnology.
25 Furthermore, in the context of environmental science, the EPA has worked with foreign
26 research institutes and agencies (e.g., UK and Taiwan) to help inform nanotechnology-and .
27 related environmental research programs.
28
29 By continuing to actively participate in international scientific fora, EPA will be well
30 positioned to inform both domestic and international environmental policy. This will provide
31 essential support for US policy makers who work to negotiate international treaties and trade
32 regimes. As products made from nanomaterials become more common in the domestic and
33 international channels of trade, policy makers will then be able to rely on EPA for the high
34 quality science necessary to make effective decisions that could have a significant impact,
35 both domestically and internationally, on human and environmental health, and economic
36 well-being.
37 1.5.4 EPA's Nanotechnology Research Activities
38 Since 2001, EPA's Office of Research and Development (ORD) STAR grants
39 program has funded 39 research grants for more than $11 million in the applications of
40 nanotechnology to protect the environment, including the development of: 1) low-cost, rapid,
41 and simplified methods of removing toxic contaminants from surface water, 2) new sensors
42 mat are more sensitive for measuring pollutants, 3) green manufacturing of nanomaterials;
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and 4) more efficient, selective catalysts. Additional applications projects have been funded
through the Small Business Innovative Research (SBIR) program.
In addition, 14 recent STAR program projects focus on studying the possible harmful
effects, or implications, of engineered nanomaterials. EPA has awarded or selected 32 grants
to date in this area, totaling $10 million. The most-recent research solicitations include
partnerships with the National Science Foundation, the National Institute for Occupational
Safety and Health, and the National Institute for Environmental Health Sciences. Research
areas of interest for this proposal include the toxicology, fate, transport and transformation,
bioavailability, human exposure, and life cycle assessment of nanomaterials.
EPA's own scientists have done research in areas related to nanotechnology, such as
on the toxicity of ultrafine particulate matter. In addition, EPA scientists have begun to gather
information on various environmental applications currently under development. However,
EPA has not yet initiated an in-house research program for nanotechnology.
16 1.5.5 Regional Nanotechnology Research Activities for Remediation
17 A pilot study is planned at an EPA Region 5 National Priorities List site in Ohio. The
18 pilot study will inject zero valent iron nanoparticles into the groundwater to test its
19 effectiveness in removing the pesticide Mirex. The study includes smaller pre-pilot studies
20 and an investigation of the ecological effects of the treatment method. Information on the pilot
21 can be found at http;//www.epa.gov/regioii5/sites/index.htai#ne.as.e.
22 1.5.6 Office of Pollution Prevention and Toxics Voluntary Pilot Program for Nanoscale
23 Materials
24 EPA's Office of Pollution Prevention and Toxics (OPPT) convened a public meeting
25 in June 2005 regarding a potential voluntary pilot program for nanoscale materials and the
26 information needed to adequately inform the conduct of the pilot program. ("Nanoscale
27 Materials; Notice of Public Meeting," 70 Fed. Reg. 24574, May 10, 2005). At the meeting
28 EPA received comment from a broad spectrum of stakeholders concerning all aspects of the
29 voluntary pilot program. On September 29 and October 12, 2005, OPPT's National Pollution
30 Prevention and Toxics Advisory Committee held public meetings of its Interim Ad Hoc Work
31 Group on Nanoscale Materials. The purpose of the meetings was to further discuss and
32 receive additional public input on issues pertaining to the voluntary pilot program for
33 nanoscale materials. The Interim Ad Hoc Work Group on Nanoscale Materials developed
34 overview documents proposing.the general parameters of a voluntary pilot program, which
35 EPA is considering in its development and implementation of the final pilot program. OPPT
36 is also simultaneously considering development and implementation of regulatory approaches
37 for nanomaterials. OPPT is already reviewing new chemical submissions for nanomaterials
38 under the Toxics Substances Control Act (TSCA).
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1 1.5.7 Office of Air and Radiation/Office of Transportation and Air Quality-
2 Nanomaterials Registration Applications
3 EPA's Office of Air and Radiation/Office of Transportation and Air Quality has
4 received and is reviewing an application for registration a diesel additive containing cerium
5 oxide. Nano-cerium oxide particles are being employed in Europe as on- and off-road diesel
6 fuel additives to decrease emissions and some manufacturers are claiming fuel economy
7 benefits.
8 1.6 Communication and Outreach
9 Gaining and maintaining public trust and support is important to fully realize the
10 societal benefits and clearly communicate the impacts of nanotechnology. Responsible
11 development of nanotechnology should involve and encourage an open dialogue with all
12 concerned parties about potential risks and benefits. EPA is committed to keeping the public
13 informed of the potential environmental impacts associated with nanomaterial development
14 and applications. As an initial step, EPA has developed a dedicated web site,
15 www.epa.gov/nano. to provide comprehensive information and enable transparent dialogue
16 concerning nanotechnology. In addition, EPA has been conducting outreach by organizing
17 and sponsoring sessions at professional society meetings, speaking at industry, state, and
18 international nanotechnology meetings.
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20 . EPA already has taken steps to obtain public feedback on issues, alternative
21 approaches, and decisions. For example, the previously noted OPPT public meetings were
22 designed to discuss and receive public input. EPA will continue to work collaboratively with
23 all stakeholders, including industry, other governmental entities, public interest groups, and
24 the general public, to identify and assess potential environmental hazards and exposures
25 resulting from nanotechnology, and to discuss EPA's roles in addressing issues of concern.
26 EPA's goal is to earn and retain the public's trust by providing information that is objective,
27 balanced, accurate and timely in its presentation, and by using transparent public involvement
28 processes.
29 1.7 Opportunities and Challenges
30 For EPA, the rapid development of nanotechnology and the increasing production of
31 nanomaterials and nanoproducts present both opportunities and challenges. Using
32 nanomaterials in applications that advance green chemistry and engineering, and lead to the
33 development of new environmental sensors and remediation technologies, may provide us
34 with new tools for preventing, identifying, and solving environmental problems. In addition,
35 at this early juncture in nanotechnology' s development, we have the opportunity to develop
36 approaches that will allow us to produce, use, recycle, and eventually dispose of
37 nanomaterials in ways that protect human health and safeguard the natural environment. The
38 integration and synergy of nanotechnology, biotechnology, information technology, and
39 cognitive technology will present opportunities as well as challenges to EPA and other
40 regulatory agencies. To take advantage of these opportunities and to meet the challenge of
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ensuring the environmentally safe and sustainable development of nanotechnology, EPA must
understand both the potential benefits and .the potential impacts of nanornaterials and
nanoproducts. Hie following chapters of this document discuss the science issues
surrounding how EPA will gain and apply such understanding.
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i 2.0 Environmental Benefits of Nanotechnology
2 2.1 Introduction
3 As applications of nanotechnology develop over time, they have the potential to help
4 shrink the human footprint on the environment. This is important, because over the next 50
5 years the world's population is expected to grow 50%, global economic activity is expected to
6 grow 500%, and global energy and materials use is expected to grow 300% (World Resources
7 Institute, 2000). So far, increased levels of production and consumption have offset our gains
8 in cleaner and more-efficient technologies. This has been true for municipal waste
9 generation, as well as for environmental impacts associated with vehicle travel, groundwater
10 pollution, and agricultural runoff (OECD, 2001). This chapter will describe how
11 nanotechnology can create materials and products that will not only directly advance our
12 ability to detect, monitor, and clean-up environmental contaminants, but also help us avoid
13 creating pollution in the first place. By more effectively using atoms and energy throughout a
14 product lifecycle, nanotechnology may contribute to reducing pollution or energy intensity
15 per unit of economic output, reducing the "volume effect" described by the OECD.
16
17 2.2 Benefits Through Environmental Technology Applications
IS 2.2.1 Remediation/Treatment
19 Environmental remediation includes the degradation, sequestration, or other related
20 approaches that result in reduced risks to human and environmental receptors posed by
21 chemical and radiological contaminants such as those found at Comprehensive Environmental
22 Response, Compensation and Liability Act (CERCLA), Resource Conservation and Recovery
23 Act (RCRA), or other state and local hazardous waste sites. The benefits from use of
24 nanomaterials for remediation could include more rapid or cost-effective cleanup of wastes
25 relative to current conventional approaches. Such benefits may derive from the enhanced
26 reactivity, surface area, subsurface transport, and/or sequestration characteristics of
27 nanomaterials.
28
29 Chloro-organics are a major class of contaminants at U.S. waste sites, and several
30 nanomaterials have been applied to aid in their remediation. Zero-valent iron has been used
31 successfully in the past to remediate groundwater by construction of a permeable reactive
32 barrier (iron wall) of zero-valent iron to intercept and dechlorinate chlorinated hydrocarbons
33 such as trichloroethylene in groundwater plumes. Laboratory studies indicate that a wider
34 range of chlorinated hydrocarbons may be dechlorinated using various nanoscale iron
35 particles (principally by abiotic means, with zero-valent iron serving as the bulk reducing
36 agent), including chlorinated methanes, ethanes, benzenes, and polychlorinated biphenyls
37 (Elliot and Zhang, 2001). Nanoscale zero-valent iron may not only treat aqueous dissolved
38 chlorinated solvents in situ, but also may remediate the dense nonaqueous phase liquid
39 (DNAPL) sources of these contaminants within aquifers (Quinn, et al, 2005).
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2 In addition to zero-valent iron, other nano-sized materials such as
3 methalloporphyrinogens have been tested for degradation of tetrachlorethylene,
4 trichloroethylene, and carbon tetrachloride under anaerobic conditions (Dror, 2005). Titanium
5 oxide based nanomaterials have also been developed for potential use in the photocatalytic
6 degradation of various chlorinated compounds (Chen 2005).
7
8 Metal remediation has also been proposed, using zero-valent iron and other classes of
9 nanomaterials. Nanoparticles such as poly(amidoamine) dendrimers can serve as chelating
10 agents, and can be further enhanced for ultrafiltration of a variety of metal ions (Cu (II),
11 Ag(I), Fe(III), etc.) by attaching functional groups such as primary amines, carboxylates, and
12 hydroxymates (Diallo, 2005). Other materials such as silica-titania nanocomposites can be
13 used for elemental mercury removal from vapors such as those coming from combustion
14 sources, with silica serving in enhanced adsorption and titania used to photocatalytically
15 oxidize elemental mercury to the less volatile mercuric oxide (Pitoniak, 2005). Other research
16 indicates that arsenite and arsenate may be precipitated in the subsurface using zero-valent
17 iron, making arsenic less mobile (Kanel, 2005). Finally, self-assembled monolayers on
18 mesoporous supports (S AMMS) are nanoporous ceramic materials that have been developed
19 to remove mercury or radionuclides from wastewater (Mattigod, 2003).
20
21 Enhanced retention, as noted above, or solubilization of a contaminant may be helpful
22 in a remediation setting. Nanomaterials may be useful in decreasing sequestration of
23 hydrophobic contaminants, such as poly cyclic aromatic hydrocarbons (PAHs), bound to soils
24 and sediments. The release of these contaminants from sediments and soils could make them
25 more accessible to in situ biodegradation. For example, nanomaterials made from
26 poly(ethylene) glycol modified urethane acrylate have been used to enhance the
27 bioavailability of phenanthrene (Tungittiplakom, 2005).
28 2.2.2 Sensors
29 Sensor development and application based on nanoscale science and technology is
30 growing rapidly due in part to the advancements in the microelectronics industry and the
31 increasing availability of nanoscale processing and manufacturing technologies. In general,
32 nanosensors can be classified in two main categories: (1) sensors that are used to measure
33 nanoscale properties (this category comprises most of the current market) and (2) sensors mat
34 are themselves nanoscale or have nanoscale components. The second category can eventually
35 result in lower material cost as well as reduced weight and power consumption of sensors,
36 leading to greater applicability.
37
38 One of the near-term research products of nanotechnology for environmental
39 applications is the development of new and enhanced sensors to detect biological and
40 chemical contaminants. Nanotechnology offers the potential to improve exposure assessment
41 by facilitating collection of large numbers of measurements at a lower cost and improved
42 specificity. It soon will be possible to develop micro- and nanoscale sensor arrays that can
43 detect specific sets of harmful agents in the environment at very low concentrations. Provided
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adequate informatics support, these sensors could be used to monitor agents in real time, and
the resulting data can be accessed remotely. The potential also exists to extend these small-
scale monitoring systems to the individual level to detect personal exposures and in vivo
distributions of toxicants.
In the environmental applications field, nanosensor research and development is a
relatively uncharted territory. Much of the new generation nanoscale sensor development is
driven by defense and biomedical fields. These areas possess high-need applications and the
resources required to support exploratory sensor research. On the other hand, the
environmental.measurement field is a cost sensitive arena with less available resources for
leading-edge development. Therefore, environmental nanosensor technology likely will
evolve by leveraging the investment in nanosensor research by related fields.
14 2.3 Benefits through Other Applications that Support Sustainability
15 Nanotechnology may be able to advance environmental protection by addressing the
16 long-term sustainability of resources and resource systems Listed in Table 1 are examples
17 describing actual and potential applications relating to water, energy, and materials. Some
18 applications bridge between several resource outcomes. For example, green manufacturing
19 using nanotechnology (both top down and bottom up) can improve the manufacturing process
20 by increasing materials and energy efficiency, reducing the need for solvents, and drastically
21 reducing waste products.
22
23 Table 1. Outcomes for Sustainable Use of Major Resources and Resource Systems*
Water sustain water resources of quality and availability for desired uses
Energy generate clean energy and use it efficiently
Materials use material carefully and shift to environmentally preferable materials
Ecosystems protect and restore ecosystem functions, goods, and services
Land support ecologically sensitive land management and development
Air sustain clean and healthy air
*EPA Innovation Action Council, 2005
26 Many of the following applications can and should be supported by other agencies.
27 However, EPA has an interest in helping to guide the work in these areas.
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1 2.3.1 Water
2 Nanotechnology has the potential to contribute to long-term water quality, availability,
3 and viability of water resources, such as through advanced filtration that enables more water
4 re-use, recycling, and desalinization. For example, nanotechnology-based flow-through
5 capacitors (FTC) have been designed that desalt seawater using one-tenth the energy of state-
6 of-the art reverse osmosis and one-hundredth of the energy of distillation systems. The
7 projected capital and operation costs of FTC-based systems are expected to be one-third less
8 than conventional osmosis systems (NNI, 2000).
9 Applications potentially extend even more broadly to ecological health. One long-
10 term challenge to water quality in the Gulf of Mexico, the Chesapeake Bay, and elsewhere is
11 the build up of nutrients and toxic substances due to runoff from agriculture, lawns, and
12 gardens. In general with current practices, about 150% of nitrogen required for plant uptake
13 is applied as fertilizer (Frink et. al., 1996). More-targeted fertilizers and pesticides that result
14 in less agricultural and lawn/garden runoff of nitrogen, phosphorous, and toxic substances is
15 potentially an important emerging application for nanotechnology that can contribute to
16 sustainability. These potential applications are still in the early research stage (USDA, 2003).
17 2.3.2 Energy
18 There is potential for nanotechnology to contribute to reductions in energy demand
19 through lighter materials for vehicles, materials and geometries that contribute to more
20 effective temperature control, technologies that improve manufacturing process efficiency,
21 and materials that reduce electrical losses in electrical components. Table 2 illustrates some
22 potential nanotechnology contributions to energy efficiency in transportation and electricity
23 (adapted from Brown, 2005). Some estimates are that the eight technologies could result in
24 national energy savings of about 14.6 quadrillion BTU's (British thermal units, a standard unit
25 of energy) per year, which is about 14.6% of total US energy consumption per year.
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Table 2: Potential US Energy Savings from 8 Nanotechnology Applications
(Adapted from Brown, 2005)
Nanotechnology Application
Estimated Percent
Reduction in Total
Annual US Energy
Consumption**
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Strong, lightweight materials in transportation
Solid state lighting (such as white light LED's)
Self-optimizing motor systems
Smart roofs (temperature-dependent reflectivity)
Novel energy-efficient separation membranes
Energy efficient distillation through supercomputing
Molecular-level control of industrial catalysis
Transmission line conductance
Total
6.2*
3.5
2.0
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* Assuming a 5.15 Million BTU/ Barrel conversion (corresponding to reformulated gasoline -
from EIA monthly energy review, October 2005, Appendix A)
** Based on US annual energy consumption from 2004 (99.74 Quadrillion Btu/year) from the
Energy Information Administration Annual Energy Review 2004
The items in Table 2 represent many different technology applications. For instance,
one of many examples of molecular-level control of industrial catalysis is a nanostructured
catalytic converter that is built from nanotubes and has been developed for the chemical
process of styrol synthesis. This process revealed a potential of saving 50% of the energy at
this process level. Estimated energy savings over the product life cycle for styrol were 8-9%
(Steinfeldt et al., 2004).
Current average overall energy loss in transmission lines is 7%. Power transmission
could be improved by using carbon nanotubes that provide better conduction of large
quantities of high voltage electricity than copper wire, at one-sixth the weight.
There are additional emerging innovative approaches to energy management that
could potentially reduce energy consumption. For example, nanomaterials arranged in
superlattices could allow the generation of electricity from waste heat in consumer appliances,
automobiles, and industrial processes. These thermoelectric materials could, for example,
further extend the efficiencies of hybrid cars and power generation technologies (Ball, 2005).
In addition to increasing energy efficiency, nanotechnology also has the potential to
contribute to alternative energy technologies that are environmentally cleaner. For example,
nanotechnology is forming the basis of a new type of highly efficient photovoltaic cell that
consists of quantum dots connected by carbon nanotubes (NREL, 2005). Also, gases flowing
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1 over carbon nanotubes have been shown to convert to an electrical current, a discovery with
2 implications for novel distributed wind power (Ball, 2004).
3
4 Nanotechnology may also contribute to a hydrogen economy. Multi-walled nanotubes
5 may increase the performance of hydrogen fuel cells; nanomaterials might safely store
6 hydrogen for hydrogen transportation infrastructure; and nariocatalysts may efficiently create
7 hydrogen from water using solar energy, and achieve the DOE goal of 10% efficiency for
8 commercial viability.
9 23.3 Materials
10 Nanotechnology may also lead to more efficient and effective use of materials. For
11 example, nanotechnology may improve the functionality of catalytic converters and reduce by
12 up to 95% the mass of platinum group metals required. Because platinum group metals occur
13 in low concentration in ore, this reduction in use may reduce ecological impacts from mining
14 (Lloyd et. al., 2005).
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16 Nanostructured catalysts can also increase yield (and therefore reduce materials use) at
17 the process level. For example, the petroleum industry now uses nanotechnology in zeolite
18 catalysts to crack hydrocarbons at a significantly improved process yield (NNI, 2000).
19
20 With nanomaterials' increased material functionality, it may be possible in some cases
21 to replace toxic materials and still achieve the desired functionality (in terms of electrical
22 conductivity, material strength, heat transfer, etc.), often with other life-cycle benefits in terms
23 of material and energy use. One example is lead-free conductive adhesives formed from self-
24 assembled monolayers based on nanotechnology, which could eventually substitute for leaded
25 solder. Leaded solder is used broadly in the electronics industry; about 3900 tons lead
26 use/year in the United States alone. In addition to the benefits of reduced lead use, conductive
27 adhesives could simplify electronics manufacture by eliminating several processing steps,
28 including the need for acid flux and cleaning with detergent and water (Georgia Tech, 2005).
29
30 Nanotechnology is also used for Organic Light Emitting Diodes (OLEDs). OLEDs
31 are a display technology substitute for Cathode Ray Tubes, which contain lead. OLEDs also
32 do not require mercury, which is used in conventional Flat Panel Displays (Frazer, 2003).
33 The OLED displays have additional benefits of reduced energy use and overall material use
34 through the lifecycle (Masciangioli and Wang, 2003).
35 2.3.4 Fuel Additives
36 Nanomaterials also show potential as fuel additives and automotive catalysts. For
37 example, nano-cerium oxide particles, are being employed in the United Kingdom as on- and
38 off-road diesel fuel additives to decrease emissions. These manufacturers also claim a more
39 than 5% decrease in fuel consumption with an associated decrease in vehicle emissions. Such
40 a reduction in fuel consumption and decrease in emissions would result in obvious
41 environmental benefits. Limited published research and modeling have indicated that the
42 addition of cerium oxide to fuels may increase levels of specific organic chemicals in exhaust,
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and result in emission of cerium oxide (Health Effects Institute, 2001); the health impacts
associated with such alterations in diesel exhaust were not examined. As noted above in
section 1.5.7, a manufacturer of a diesel additive containing cerium oxide has applied to
Office of Air and Radiation/Office of Transportation and Air Quality for registration of this
fuel additive. Nanocatalysts can also be used to increase energy efficiency in utility boilers
and other energy-producing facilities.
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i 3.0 Risk Management and Statutes
2 3.1 Risk Management
3 EPA makes risk management decisions within the statutory framework laid out in this
4 chapter. Risk management options and how risks are characterized vary based on the
5 program area (air, water, toxic substances etc.) and also the specific statute involved (for
6 example, Clean Air Act, Clean Water Act, Toxic Substances Control Act). Risk management
7 decisions at EPA are informed by an understanding of the risk from exposure to potential
8 hazard. Section 4 of this paper discusses the risk assessment process and the types of
9 information that EPA will need to inform its decisions. An understanding the toxicity of
10 nanomaterials, dose metrics, probable exposure pathways, and environmental fate is needed to
11 provide sound scientific information that informs the risk management process.
12 3.1.1 Risk Management and Nanoscale Materials
13 Nanomaterials may present risk management issues that are not easily characterized
14 because of the breadth of categories of such substances. Some nanoscale materials are
15 produced under established industrial hygiene practices based on their history of
16 manufacturing processes and use. Human and environmental exposure information for these
17 particular substances likely would already be available to inform risk management decisions.'
18 For some other nanoscale materials, there is less certainty of expected exposure and potential
19 hazard. The uncertainty may be greater where new industrial methods are employed.
20
21 EPA realizes the potential benefits of nanomaterials. To fully realize that potential,
22 the responsible development of such products is in the interest of EPA, producers and users of
23 nanotechnology, as well as society as a whole. EPA believes that a proactive approach is
24 appropriate in risk management, and using the principles of pollution prevention is an
25 important first step. To that end, EPA expects producers and users of nanotechnology to
26 develop stewardship programs and workplace practices based on pollution prevention
27 principles. Additionally, EPA believes that partnerships with industrial sectors will ensure
28 that proactive risk management approaches are part of initial decision making. Working in
29 partnership with producers and users of nanotechnology to develop best practices and
30 standards in the workplace, as well as other environmental programs, would help ensure that
31 the production and use of nanomaterials results in minimal risk to human and environmental
32 health.
33 .
34 EPA will review nanotechnology products and processes as they are introduced. This
35 would occur under EPA's product review authorities under TSCA, FIFRA, and the Clean Air
36 Act. EPA will work with producers arid users of nanotechnology to prescribe protocols and
37 approaches that limit exposure and address any potential risks. As knowledge becomes
38 incrementally available, a refinement of risk management approaches may be needed. In
39 addition, EPA will use its other statutory authorities, where appropriate, as the technology
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1 develops in the marketplace. This would allow EPA to address any risks not identified by
2 pollution prevention principles or product review statutes.
3 3.1.2 Environmental Stewardship
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Nanotechnology provides an opportunity for EPA to lead discussions with industry
and other stakeholders on best practices for acting first to prevent pollution at its source, using
less toxic and more environmentally benign materials, and conserving natural resources
whenever possible. Environmental stewards incorporate this approach voluntarily, to any and
all stakeholders that might be affected by their actions, as part of their overall strategy for
producing and using goods and services. These are the fundamental characteristics of
environmental stewardship; Appendix B contains a fuller discussion of stewardship
principles. At EPA, there are a number of programs already in place that are based upon
environmental stewardship principles.
EPA has a number of programs that address processes, including inputs; waste
streams; and the design, use, disposal, and stewardship of products consistent with the goal of
pollution prevention. Information on nanotechnologies and materials could be supplied
through existing information networks, and EPA could pursue additional voluntary initiatives
or integrate nanotechnology and nanomaterials into already existing voluntary programs. For
example, the National Pollution Prevention Resource Exchange National Networks have topic
hubs that provide overviews on common operations and typical waste streams, as well as what
pollution prevention opportunities exist and where specialized expertise can be found. Also,
the Green Engineering Program is working on a number of industrial sectors (e.g., pulp and
paper) to apply green engineering concepts and tools in evaluating and improving
environmental performance of processes and products. These efforts could be targeted at the
facility level and their operations, sectors, as well as supply chains.
EPA also could continue to expand its own work within the areas of Life Cycle
Analysis (LCA) to targeted nanomaterials and products. EPA's Design for Environment
(DfE) program already uses LCAs to examine the environmental impact of products over their
entire life cycle from materials acquisition, through use, to disposal. LCAs can evaluate
impacts on human health, atmospheric deposition/air quality, soil, sediment, water quality,
and natural resource consumption. LCA also focuses the assessment on the product life stage
of greatest environmental impact so that preventive measures can be taken. Material flow
analysis also gives information about the environmental impacts throughout the product life
cycle.
Another role for EPA is to supply information so that others can act as environmental
stewards. EPA can provision directly new information appropriate to nanotechnology and
nanomaterial producers, users and consumers, and can also work with state technology
assistance organizations and other tech transfer groups to integrate an environmental
stewardship orientation into their ongoing assistance efforts. For example, at the state level,
the Office of Technical Assistance (OTA) conducts site visits to manufacturers in
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1 Massachusetts to help them assess their processes and identify opportunities to reduce or
2 eliminate the use of toxic chemicals, and to conserve water.
3 3.2 Statutes
4 EPA administers a wide range of environmental statutes. Some of these statutes will
5 apply to nanomaterials depending on their specific media of application or release. Other
6 statutes will apply to certain nanomaterials depending on their specific uses, applications, and
7 processes and will require EPA to evaluate the nanomaterials before they enter into
8 commerce. Some risk management activities carried out under these statutes could also
9 utilize nanomaterials or products for environmental remediation or pollution prevention
10 technologies.
11
12 The framework of environmental statutes outlined below is a starting point for
13 evaluating and managing risks and benefits from products of nanotechnology. Some current
14 EPA policies and regulations may require modifications to address this new technology. For
15 example, some nanomaterials are not currently well characterized by existing nomenclature
16 conventions. Until adequate nomenclature conventions are developed, it will be difficult to
17 determine in some instances if reporting to EPA is required because the nanomaterials are not
18 contained on the TSCA Inventory, or if use of a nanoscale material results in a change to a
19 pesticide product already registered under FIFRA.
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21 Nanoscale materials will present other novel risk assessment/management challenges.
22 Standards that will need to be developed include not only terminology/nomenclature, but also
23 physical standards such as dimensions and behaviors, testing procedures, and instrumentation.
24 There is also a need to review conventional hazard, exposure, and risk assessment tools for
25 their applicability to nanomaterials, as weir as development of risk mitigation options that are
26 tailored to nanoscale materials (e.g., use of personal protective equipment). These issues are
27 discussed in detail throughout the paper.
j
28 3.2.1 Toxic Substances
29 Under the Toxic Substances Control Act (TSCA) section 5(a), Premanufacture
30 Notices (PMNs) must be submitted to EPA by a person intending to manufacture or import
31 chemical substances not on the TSCA Inventory of Chemical Substances. Nanoscale
32 materials that are chemical substances under TSCA and which are not on the TSCA Inventory
33 must be reported to EPA. The premanufacture review process serves as a gatekeeper to
34 identify concerns and exercise appropriate regulatory oversight. For example, use
35 restrictions, occupational exposure limits/controls, limits on releases to the environment and
36 limits on manufacture may be required until toxicity and fate data are developed to better
37 inform a risk assessment of the chemical. Section 5(a)(2) of TSCA authorizes EPA to
3 8 determine that a use of a chemical substance is a "significant new use." EPA must make this
39 determination by rule after considering all relevant factors, including a series of risk-related
40 factors that are listed in section 5(a)(2) of TSCA. Once EPA promulgates a rule specifying
41 that a use of a chemical substance is a significant new use, section 5(a)(l )(B) of TSCA
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1 requires persons to submit a notice to EPA at least 90 days before they manufacture, import,
2 or process the substance for that use (40 CFR 721.5).
3
4 Under TSCA section 6, EPA has the authority to, by rule, prohibit or limit the
5 manufacture, import, processing, distribution in commerce, use, or disposal of a chemical
6 substance if there is a reasonable basis to conclude that the chemical "presents or will present
7 an unreasonable risk" of injury to health or the environment Section 8(e) of TSCA requires
8 that chemical manufacturers, processors, and distributors notify EPA of information that
9 "reasonably supports the conclusion that a chemical substance or mixture presents a
10 substantial risk of injury to human health or the environment." Under section 8(a) of TSCA
11 EPA may collect information associated with chemical substances. Some of the types of
12 information that can be required include categories of use, production volume, byproducts, an
13 estimate of the number of individuals exposed, and duration of such exposures. EPA may
14 require manufacturers of chemical substances to submit unpublished health and safety studies
15 under section 8(d) of TSCA. EPA also engages in voluntary programs such as the High
16 Production Volume Challenge program to gather information on chemical substances.
17 Nanomaterials that are chemical substances under TSCA could be subject to all these
18 provisions and programs.
19
20 Voluntary and regulatory measures for evaluating nanomaterials are being developed
21 and implemented by OPPT under TSCA, as noted in the introduction. OPPT is already
22 reviewing new chemical submissions for nanomaterials under TSCA.
23 3.2.2 Pesticides
24 Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), EPA is
25 responsible for registering pesticide products for use in the United States. An application for
26 registration under FIFRA must disclose the specific chemicals in the pesticide formulation.
27 Pesticide registration decisions are based on a detailed assessment of the potential effects of a
28 product on human health and the environment, when used according to label directions.
29 These approved labels have the force of law, and any use that is not in accordance with the
30 label directions and precautions may be subject to civil and/or criminal penalties. FIFRA also
31 requires that EPA reevaluate older pesticides to ensure that they meet more recent safety
32 standards. FIFRA requires EPA and states to establish programs to protect workers, and
33 provide training and certification for applicators. It is expected that pesticide products
34 containing nanomaterials will come under FIFRA review and registration.
35 3.2.2.1 Registration
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Under FIFRA sections 3 and 12, EPA must approve all new pesticide products, as well
as new uses and changes in the composition of existing pesticide products, before the products
may be sold or distributed in commerce. EPA issues its approvals in the form of registrations
or amended registrations. In order to evaluate an,application for registration, EPA requires the
applicant to provide a complete characterization of the composition of the product, proposed
labeling which describes the intended use of the product, and the results of extensive health
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1 and safety testing. Using this information, EPA determines whether the product may "cause
2 unreasonable adverse effects on the environment." FIFRA defines "unreasonable adverse
3 effects on the environment" as any "unreasonable risk to man or the environment taking into
4 account the economic, social, and environmental costs and benefits of the use of any
5 pesticide..." EPA may refuse to approve an application unless the applicant agrees to modify
6 the composition or labeling of the product to reduce its risks to acceptable levels.
7 3.2.3 Clean Air Act
8 The Clean Air Act (most recently amended in 1990) has provided the primary legal
9 framework for protecting public health and welfare from the harmful effects of air pollution.
10 The Act has a number of provisions that need to be considered in determining its applicability
11 to nanotechnology. These provisions are summarized below.
12 3.2.3.1 Criteria Air Pollutants
13 Two sections of the Clean Air Act (CAA) govern the establishment, review and
14 revision of national ambient air quality standards (NAAQS). Section 108 of the Act (42
15 U.S.C. 7408) directs the Administrator to identify certain pollutants which "may reasonably
16 be anticipated to endanger public health and welfare" and to issue air quality criteria for them.
17 These criteria air pollutants could result from use or manufacture of nanomaterials. These air
18 quality criteria are to "accurately reflect the latest scientific knowledge useful in indicating the
19 kind and extent of all identifiable effects on public health or welfare which may be expected
20 from the presence of [a] pollutant in the ambient air... ". Section 109 of the Act (42 U.S.C.
21 7409) directs the Administrator to propose and promulgate "primary" and "secondary"
22 NAAQS for pollutants identified under section 108 of the Act. Section 109(b)(l) of the Act
23 defines a primary standard as one "the attainment and maintenance of which in the judgment
24 of the Administrator, based on [the] criteria and allowing an adequate margin of safety, are
25 requisite to protect the public health."
26 3.2.3.2 Air Toxics (Hazardous Air Pollutants (HAPs^
27 Title III if the 1990 CAA Amendments (CAAA) significantly changed the pre-existing
28 system for control of hazardous air pollutants (HAPs) which required the Agency to both
29 identify and develop health-based emission standards for each pollutant. The HAPs could
30 result from use or manufacture of nanomaterials. Under the CAA Amendments, 189 Air
31 Toxics (hazardous air pollutants) are identified for regulation. The law directs EPA to
32 identify the sources of the 189 pollutants and establishes a ten year time period for EPA to
33 issue technology-based emissions standards for each source category. Section 112(r) of the
34 CAA also contains requirements that address accidental releases of hazardous substances
35 from stationary sources that potentially can have serious adverse effects to human health or
36 the environment.
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1 3.2.3.3 Registration of Fuels and Fuel Additives
2 Section 211 of the Clean Air Act (CAA) provides EPA with the authority to designate
3 any mobile source fuel or additive for registration. Section 211 (b) requires, for the purpose of
4 registration, that the manufacturer provide certain compositional and related information, and
5 available health-effects data. Section 21 l(b) also provides EPA with the authority to require
6 health-effects testing. EPA promulgated health effects testing requirements for fuels and fuel
7 additives on June 21,1994 in Part II 40 CFR Part 79. Gasoline and diesel fuels and their
8 additives (regardless of claims categorizing an additive as nanotechnology) are subject to the
9 regulations promulgated by EPA in 1994. These fuels and additives for use in on-road
10 applications may not be introduced into commerce until it has been registered by EPA. •
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12 EP A's Office of Air and Radiation/Office of Transportation and Air Quality has
13 received and is reviewing an application for registration of a diesel additive containing cerium
14 oxide. Nano-cerium oxide particles are being employed in Europe as on and off-road diesel
15 fuel additives to decrease emissions and some manufacturers are claiming fuel economy
16 benefits.
17 3.2.4 Pollution Prevention
18 3.2A.I Legislation
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20 The Pollution Prevention Act of 1990 (Public Law 101-508) was enacted in November
21 1990 and amended through Public Law 107-377 in December 2002. The Act was-considered
22 a turning point in how the nation looks at the control of pollution. Instead of focusing on
23 waste management and pollution control, Congress declared a national policy for the United
24 States to address pollution based on "source reduction." The policy established a hierarchy of
25 measures to protect human health and the environment, where multi-media approaches would
26 be anticipated: (1) pollution should be prevented or reduced at the source, (2) pollution that
27 cannot be prevented should be recycled in an environmentally safe manner, (3) pollution that
28 cannot be prevented or recycled should be treated in an environmentally safe manner; and (4)
29 disposal or other release into the environment should be employed only as a last resort and
30 should be conducted in an environmentally safe manner.
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32 The first tier of the hierarchy is the preferred strategy for addressing potential
33 environmental issues, and is referred to as "source reduction." Source reduction is defined in
34 the Act as: "Any practice which: (1) reduces the amount of any hazardous substance,
35 pollutant, or contaminant entering any waste stream or otherwise released into the
36 environment (including fugitive emissions) prior to recycling, treatment, or disposal; and (2)
37 reduces the hazards to public health and the environment associated with the release of such
38 substances, pollutants, or contaminants."
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1 3.2.4.2 Implementation of the Pollution Prevention Act.
2 The Act required EPA to establish an office to carry out the functions of the Act. In
3 1990, EPA formally established the Office of Pollution Prevention and Toxics (OPPT).
4 Within this office were initiated two programs, with two different approaches, to meet the
5 spirit of the new national policy: the Design for the Environment (DfE) Program and the
6 Green Chemistry Program. Under DfE, EPA works in partnership with industry sectors to
7 improve performance of commercial processes while reducing risks to human health and the
8 environment. The Green Chemistry Program promotes research to design chemical products
9 and processes that reduce or eliminate the use and generation of toxic chemical substances. In
10 1998, EPA complimented these two programs with the Green Engineering Program, which
11 applies approaches and tools for evaluating and reducing the environmental impacts of
12 processes and products (see http://www.epa. gov/oppt/green engineermg/textbook.htmn. As
13 described in the environmental stewardship discussion above, nanotechnology offers an
14 opportunity to implement pollution prevention principles into the design of a new technology.
15
16 3.2.5 Clean Water Act
17 If a wastewater stream of nanomaterials is produced, it will be subj ect to effluent
18 guidelines of the Clean Water Act. Depending on the nature of the wastewater stream other
19 water quality guidelines or standards could apply. Nanomaterials have been proposed for use
20 as bactericides.
21 3.2.6 Safe Drinking Water Act
22 The Safe Drinking Water Act (SDWA), as amended in 1996, is the main federal law
23 that protects public health by regulating hazardous contaminants in drinking water. SDWA
24 authorizes the Agency to establish non-enforceable health-based Maximum Contaminant
25 Level Goals (MCLGs) and enforceable Maximum Contaminant Levels (MCLs) or required
26 treatment techniques, as close as feasible to the MCLGs, taking into consideration costs and
27 available analytical and treatment technology. Nanotechnology has the potential to influence
28 the setting of MCLs through improvements in analytical methodology or treatment
29 techniques, or by nanomaterials themselves potentially qualifying for regulation as drinking
30 water contaminants based on health risks and occurrence in drinking water.
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32 Nanotechnology has the potential to contribute to better and cost-effective removal of
33 drinking water contaminants, such metals (e.g. arsenic or chromium), toxic halogenated
34 organic chemicals, suspended participate matter and pathogenic microorganisms.
35 Nanotechnology-based sensors are being developed that result in vastly improved sensitivity
36 for measuring contaminants in drinking water. Improved, cost-effective treatment technology
37 and analytical techniques have the potential to lead to maximum contaminant levels (MCL)
38 closer to the public health-based MCL Goals and therefore, to better public health protection.
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40 If nanoparticles enter drinking water, such as through their use in water treatment, then
41 exposure to nanomaterials may occur through drinking water ingestion or inhalation (e.g.
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1 from showering). The magnitudes of exposure and toxicity of nanomaterials in drinking
2 water are unknown at present. However, the possibility exists that, based on their toxicity and
3 occurrence in drinking water supplies, nanomaterials would need to be regulated under the
4 SDWA.
5 3.2.7 CERCLA
6 The Comprehensive Environmental Response Compensation and Liability Act
7 (CERCLA) addresses problems associated with closed and abandoned waste sites. CERCLA
8 gives EPA the authority to respond to actual or threatened releases of hazardous substances to
9 the environment or to actual or threatened releases to the environment of pollutants or
10 contaminants that may present an imminent and substantial danger to the public health or
11 welfare. Nanomaterials that meet these criteria would be subject to this authority.
12
13 If a compound is comprised of a chemical or chemicals that are listed as hazardous
14 substances under the Clean Water Act, the Clean Air Act, RCRA, or TSCA, or under section
15 102 of CERCLA, then the compound is considered a hazardous substance under CERCLA. If
16 a compound is not listed as a hazardous substance under CERCLA, then EPA may still
17 address an actual or threatened release to the environment of that substance under CERCLA if
18 the substance is a pollutant or contaminant that may present an imminent and substantial
19 danger to the public health or welfare.
20 3.2.8 RCRA
21 The Resource Conservation and Recovery Act (RCRA), which amended the Solid
22 Waste Disposal Act, regulates the transportation, treatment, disposal (other than to surface
23 water), and cleanup of hazardous wastes being generated by businesses, industries, and
24 government agencies. RCRA transportation, treatment, and disposal requirements apply to
25 RCRA hazardous wastes; RCRA groundwater monitoring and corrective action requirements
26 apply to releases of RCRA hazardous wastes and RCRA hazardous constituents.
27 Nanomaterials that meet the definition of RCRA hazardous wastes would be subject to these
28 regulations.
29 3.2.8.1 RCRA Hazardous Wastes
30 A waste is a RCRA hazardous waste only if it is a solid waste and is either listed or
31 exhibits a hazardous characteristic. A solid waste may be solid, liquid, or gas, must be
32 discarded (abandoned, released to the environment); and, excludes domestic sewage,
33 industrial wastewater to publicly owned treatment works, nuclear wastes, and certain mining
34 materials. A solid waste is a RCRA hazardous waste if it is listed in the Code of Federal
35 Regulations (CFR), or if it exhibits a hazardous characteristic. RCRA hazardous constituents
36 are listed in 40 CFR Part 261 Appendix VIII. Appendix VIII has no independent regulatory
37 status, but this list is referenced by groundwater monitoring, corrective action, and delisting
38 regulations.
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1 3.2.9 Toxics Release Inventory Program
2 Some producers of nanomaterials containing materials listed on the Toxic Release
3 Inventory (TRI) may be subject to reporting under the TRI Program (www.epa.gQV/tri/). In
4 1986 when Congress passed the Emergency Planning and Community Right to Know Act
5 (EPCRA) the TRI was established. The TRI is a publicly available database containing
6 information on toxic chemical releases and other waste management activities that are
7 reported annually by manufacturing facilities and facilities in certain other sectors, as well as
8 federal facilities. Facilities required to report TRI chemical releases and other waste
9 management quantities are those that met or exceeded the minimum criteria of number of
10 employees and total mass of chemical manufactured, processed, or otherwise used in a
11 calendar year. Of the nearly 650 toxic chemicals and chemical compounds on the TRI,
12 several are metallic elements and the compounds composed of these metals. The TRI
13 includes compounds containing cadmium, chromium, copper, cobalt and antimony. Some of
14 these metals are a part of the composition of nanomaterials like quantum dots.
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4.0 Risk Assessment of Nanomaterials
2 4.1 Introduction
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EPA's mission and mandates require an understanding of the health and
environmental implications of intentionally produced nanomaterials. A challenge in
evaluating risk associated with the manufacture and use of nanomaterials is the diversity and
complexity of the types of materials available and under development as well as the
seemingly limitless potential uses of these materials. A risk assessment is the evaluation of
scientific information on the hazardous properties of environmental agents, the dose-response
relationship, and the extent of exposure of humans or environmental receptors to those agents.
The product of the risk assessment is a statement regarding the probability that humans
(populations or individuals) or other environmental receptors so exposed will be harmed and
to what degree (risk characterization). EPA generally follows the risk assessment paradigm
described by the National Academy of Sciences (NAS) (NAS/NRC, 1983 1994).
The overall risk assessment approach used by EPA for conventional chemicals is
thought to be generally applicable to nanomaterials. It is important to note that nanomaterials
have large surface areas per unit of volume, and novel electrical and magnetic properties
relative to conventional chemicals. Some of the special properties that make nanomaterials
useful are also properties that may cause some nanomaterials to pose hazards to humans and
the environment, under specific conditions, as noted below. It will be necessary to consider
these unique properties and their potential impacts on fate, exposure, and toxicity in
developing risk assessments for nanomaterials. At this point in time, we assume that the NAS
paradigm is appropriate for the assessment of nanomaterials. However, we note that
modifications of the NAS risk assessment approach for other stressors such as biotechnology
products and paniculate matter research have been proposed (Committee on Environment and
Natural Resources, 2002).
Occupational and environmental exposures to engineered nanomaterials have been
reported (Baron et al., 2004). Uncertainties in health, ecology, and the environment effects
associated with exposure to engineered nanomaterials raise questions about potential risks
from such exposures (Dreher, 2004; Swiss Report Reinsurance Company, 2004; UK Royal
Society Report, 2004; European Commission Report, 2004; European NanoSafe Report 2004;
Hearth and Safety Executive, 2004).
The purpose of this chapter is to briefly review the state of knowledge regarding the
components needed to conduct a risk assessment on nanomaterials. The following key
aspects of risk assessment are addressed as they relate to nanomaterials: chemical
identification and characterization, environmental fate, environmental detection and analysis,
human exposure, human health effects, and ecological effects. Each of these aspects is
discussed by providing a synopsis of key existing information on each topic. Additional
technical discussion and details on specific studies for several topics are provided in
Appendix C.
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1 4.2 Chemical Identification and Characterization of Nanomaterials
2 The identification and characterization of chemical substances and materials is an
3 important first step in assessing their risk. Understanding the physical and chemical
4 properties in particular is necessary in the evaluation of hazard (both toxicological and
5 ecological) and exposure (all routes). Chemical properties that are important in the
6 characterization of discrete chemical substances include, but are not limited to, molecular
7 weight, melting point, boiling point, vapor pressure, octanot-water partition coefficient, water
8 solubility, reactivity, and stability. In addition, information on a substance's manufacture and
9 formulation is important in understanding purity, product variability, performance, and use.
10
11 The diversity and complexity of nanomaterials makes chemical identification and
12 characterization not only more important but also more difficult. A broader spectrum of
13 ' properties will be needed to sufficiently characterize a given nanomaterial for the purposes of
14 evaluating hazard and assessing risk. Chemical properties such as those listed above may be
15 important for some nanomaterials, but other properties such as particle size and distribution,
16 surface/volume ratio, magnetic properties, coatings, and conductivity are expected to be more .
17 important for the majority of nanoparticles. '
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19 A given nanomaterial can be produced in many cases by several different processes
20 yielding several derivatives of the same material. For example, single-walled carbon
21 nanotubes can be produced by four different processes that can generate products with
22 different physical-chemical properties (e.g., size, shape, composition) and potentially different
23 ecological and toxicological properties. It is not clear whether existing physical-chemical
24 property test methods are adequate for sufficiently characterizing various nanomaterials in
25 order to evaluate their hazard and exposure and assess their risk. It is clear that chemical
26 properties such as boiling point and vapor pressure are insufficient. Alternative methods for
27 measuring properties of nanomaterials may need to be developed both quickly and cost
28 effectively.
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30 Because of the current state of development of chemical identification and
31 characterization, current chemical representation and nomenclature conventions may not be
32 adequate for some nanomaterials. Nomenclature conventions are important to eliminate
33 ambiguity when communicating differences between nanomaterials and bulk materials and in
34 reporting for regulatory purposes. EPA's OPPT is participating in new and ongoing
35 workgroup/panel deliberations with the American National Standards Institute (ANSI), the
36 American Society for Testing and Materials (ASTM), and the International Organization for
37 Standards (ISO) concerning the development of terminology and chemical nomenclature for
38 nano-sized substances, and will also continue with its own nomenclature discussions with the
39 Chemical Abstracts Service (CAS).
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1 4.3 Environmental Fate of Nanomaterials
2 4.3.1 Introduction
3 Potential nanomaterials release sources include direct and/or indirect releases to the
4 environment from the manufacture and processing of nanomaterials, releases from oil refining
5 processes, chemical and material manufacturing processes, chemical clean up activities
6 including the remediation of soil-contaminated sites, releases of nanomaterials incorporated
7 into materials used to fabricate products for consumer use including pharmaceutical products,
8 and releases resulting from disposal of consumer products containing nanoscale materials
9 (e.g., disposal of screen monitors, computer boards, automobile tires, clothing and cosmetics).
10 The fundamental properties concerning the environmental fate of nanomaterials are not well
11 understood (European Commission, 2004), as there are few available studies on the
12 environmental fate of nanomaterials. The following sections summarize what is known or
13 can be inferred about the fate of nanomaterials in the atmosphere, in soils, and in water. These
14 summaries are followed by sections discussing: 1) biodegradation, bioavailability, and
15 bioaccumulation of nanomaterials; 2) the potential for transformation of nanomaterials to
16 more toxic metabolites; 3) possible interactions between nanomaterials and other
17 environmental contaminants; and 4) the applicability of current environmental fate and
18 transport models to nanomaterials. Appendix C contains additional details on the
19 environmental fate of nanomaterials.
20 4.3.2 Fate of Nanomaterials in Air
21 Several processes influence the fate of airborne nanomaterials in addition to their
22 initial dimensional and chemical characteristics: the length of time the particles remain
23 airborne, the nature of their interaction with other airborne particles or molecules, and the
24 distance that they may travel prior to deposition. The processes important to understanding
25 the potential atmospheric transport of nano-sized particles are diffusion, agglomeration, wet
26 and dry deposition, and gravitational settling.
27
28 With respect to the length of time particles remain airborne, particles with
29 aerodynamic diameters in the nanoscale range (<100 nm) follow the laws of gaseous diffusion
30 when released to air. The rate of diffusion is inversely proportional to particle diameter, while
31 the rate of gravitational settling is proportional to particle diameter (Aitken et al., 2004).
32 Airborne particles can be classified by size and behavior into three general groups: Small
33 particles (diameters <80 nm) are described as being in the agglomeration mode; they are
34 short-lived because they rapidly agglomerate to form larger particles. Large particles (>2000
35 nm) are described as being in the coarse mode and are subject to gravitational settling.
36 Intermediate-sized particles (>80 nm and < 2000 nm) are described as being in the
37 accumulation mode and can remain suspended in air for the longest time, days to weeks, and
38 can be removed from air via dry or wet deposition (Bidleman, 1988; Preining, 1998; Spumy,
39 1998; Atkinson, 2000; Royal Society, 2004; Dennenkamp et al., 2002). Note that these
40 generalizations apply to environmental conditions and do not preclude the possibility that
41 humans and other organisms may be exposed to large as well as smaller particles by
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1 inhalation. Additionally, intentionally produced nanomaterials may or may not behave in
2 similar fashion to the ultrafine particles described in the above citations.
3
4 Deposited nanoparticles are typically not easily resuspended in the air or re-
5 aerosolized (Colvin 2003; Aitken et al. 2004). Because physical particle size is a critical
6 property of nanomaterials., maintaining particle size during the handing and use of
7 nanomaterials is a priority. Current research is underway to produce carbon nanotubes that do
8 not form clumps either by functionaiizing the tubes themselves, or by treatment with a coating
9 or dispersing agent (Royal Society; 2004; Colvin, 2003), so future materials may be more
10 easily dispersed.
11
12 Many nano-sized particles are reported to be photoactive (Colvin, 2003), but their
13 susceptibility to photodegradation in the atmosphere has not been studied. Nanomaterials are
14 also known to readily adsorb a variety of materials, and many act as catalysts. However, no
15 studies are currently available that examine the interaction of nano-sized adsorbants and
16 chemicals sorbed to them, and how this interaction might influence their respective
17 atmospheric chemistries.
18 4.3.3 Fate of Nanomaterials in Soil
19 The fate of nanomaterials released to soil is likely to vary depending upon the physical
, 20 and chemical characteristics of the nanomaterial. Nanomaterials released to soil can be
21 strongly sorbed to soil due to their high surface areas and therefore be immobile. On the other
22 hand, nanomaterials are small enough to fit into smaller spaces between soil particles, and
23 might therefore travel farther than larger particles before becoming trapped in the soil matrix.
24 The strength of the sorption of any intentionally produced nanoparticle to soil will be
25 dependent on its size, chemistry, applied particle surface treatment, and the conditions under
26 which it is applied. Studies have demonstrated the differences in mobility of a variety of
27 insoluble nano-sized materials in a porous medium. (Zhang, 2003; Lecoanet and Wiesner,
28 2004; Lecoanet et al., 2004).
29
30 Additionally, the properties of the soil and environment can affect nanomaterial
31 mobility. For example, the mobility of mineral colloids in soils and sediments is strongly
32 affected by charge. Surface photoreactions provide a pathway for nanomaterial
33 transformation on soil surfaces. Humic substances, common constituents of natural particles,
34 are known to photosensitize a variety of organic photoreactions on soil and other natural
35 surfaces that are exposed to sunlight. Studies of nanomaterial transformations in field
36 situations are further complicated by the presence of naturally occurring nanomaterials of
37 similar molecular structures and size ranges. Iron oxides are one example.
3 8 4.3.4 Fate of Nanomaterials in Water
39 Fate of nanomaterials in aqueous environments is controlled by aqueous solubility or
40 dispersability, interactions between the nanomaterial and natural and anthropogenic chemicals
41 in the system, and biological and abiotic processes. There are limited data on the fate and
42 transport of nanoparticles, but existing data show that their behavior can be very different
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1 from much larger particles of the same materials. Nanoparticles generally will be retained in
2 the water column due to diffusion and dispersion. Waterbome nanoparticles generally settle
3 more slowly than larger particles of the same material but can be removed from water by
4 agglomeration or sorption and sedimentation. Dispersed insoluble nanoparticles can be
5 stabilized in water by interactions with naturally-occurring humic substances or other species.
6 Biodegradation or association with biological materials may remove nanomaterials.
7 Photocatalyzed reactions may alter the physical and chemical properties of nanomaterials and
8 so alter their behavior in water. Processes that control transport and removal of nanoparticles
9 in water and wastewater are being studied to understand nanoparticle fate. Nanoparticle
10 photochemistry is being studied with respect to its possible application in water treatment.
11
12 Dispersed insoluble nanoparticles can be stabilized by naturally-occurring colloids
13 made up of humic acids and other organics, which would also delay settling from the water
14 column. Insoluble materials may also form stable colloidal suspensions in water. For
15 example, researchers at Rice University have reported that although Ceo fullerene is initially
16 insoluble in water, it spontaneously forms aqueous colloids containing nanocrystalline
17 aggregates. The concentration of nanomaterials in the suspensions can be as high as 100 parts
18 per million (ppm), but is more typically in the range of 10-50 ppm. The stability of the
19 particles and suspensions is sensitive to pH and ionic strength.
20
21 Due to their high surface-area-to-mass ratios, nano-sized particles have the potential to
22 sorb to suspended soil and sediment particles (Oberdorster et al., 2005). However, there are
23 not yet any published studies on sorption of nanomaterials to particles in the water column. In
24 the case of abiotic processes, both chemical and photoactivated reactions in particle/water
25 systems are likely involved in nanomaterial transformations.
26
27 Certain organic and metallic nanomaterials may possibly be transformed under
28 anaerobic conditions, such as in aquatic (benthic) sediments. From past studies, it is known
29 that several types of organic compounds are generally susceptible to reduction under such
30 conditions. Complexation by natural organic materials such as humic colloids can facilitate
31 reactions that transform metals in anaerobic sediments (see Nurmi et al., 2005 and references
32 therein).
33
34 Particles in the upper layers of aquatic environments, on soil surfaces, and in water
35 droplets in the atmosphere are exposed to sunlight. Light-induced photoreactions often are
36 important in determining environmental fate of chemical substances. Heterogeneous
37 photoreactions on metal oxide surfaces are increasingly being used as a method for drinking
38 water, wastewater and groundwater treatment. Semiconductors such as titanium dioxide and
39 zinc oxide as nanomaterials have been shown to effectively catalyze both the reduction of
40 halogenated chemicals and oxidation of various other pollutants, and heterogeneous
41 photocatalysis has been used for water purification in treatment systems.
42
43 The fate of nano-sized particles in wastewater treatment plants is not well
44 characterized. Wastewater may be subj ected to many different types of treatment, including
45 physical, chemical and biological processes, depending on the characteristics of the
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1 wastewater, whether the plant is a publicly owned treatment work (POTW) or onsite
2 industrial facility, etc. Broadly speaking, nano-sized particles are most likely to be affected
3 by sorption processes (for example in primary clarifiers) and chemical reaction. The ability of
4 either of these processes to immobilize or destroy the particles will depend on the chemical
5 and physical nature of the particle and the residence times in relevant compartments of the
6 treatment plant. As noted above, sorption, agglomeration and mobility of mineral colloids are
7 strongly affected by pH; thus pH is another variable that may affect sorption and settling of
8 nanomaterials. Current research in this area includes the production of microbial granules
9 that are claimed to remove nanoparticles from simulated wastewater (Ivanov et al., 2004).
10 Nanomaterials that escape sorption in primary treatment may be removed from wastewater
11 after biological treatment via settling in the secondary clarifier. Normally the rate of
12 gravitational settling of particles such as nanomaterials in water is dependent on particle
13 diameter, and smaller particles settle more slowly. However, settling of nanomaterials could
14 be enhanced by entrapment in the much larger sludge floes, removal of which is the objective
15 of secondary clarifiers.
16 4.3.5 Biodegradation of Nanomaterials
17 Biodegradation of nanoparticles may result in their breakdown as typically seen in
18 biodegradation of organic molecules, or may result in changes in the physical structure or
19 surface characteristics of the material. The potential for and possible mechanisms of
20 biodegradation of nano-sized particles have just begun to be investigated. As is the case for
21 other fate processes, the potential for biodegradation will depend strongly on the chemical and
22 physical nature of the particle. Many of the nanomaterials in current use are composed of
23 inherently nonbiodegradable inorganic chemicals, such as ceramics, metals and metal oxides,
24 and are not expected to biodegrade. However, a recent preliminary study found that Ceo and
25 C?o fullerenes were taken up by wood decay fungi after 12 weeks, suggesting that the
26 fullerene carbon had been metabolized (Filley et al., 2005). For other nanomaterials
27 biodegradability may be integral to the material's design and function. This is the case for
28 some biodegradable polymers being investigated for use in drug transport (Madan et al., 1997;
29 Brzoska et al., 2004), for which biodegradability is mostly a function of chemical structure
30 and not particle size.
31
32 Biodegradability in waste treatment and the environment may be influenced by a
33 variety of factors. Recent laboratory studies on Ceo fullerenes have indicated the development
34 of stable colloid structures in water that demonstrate toxicity to bacteria under aerobic and
35 anaerobic conditions (CBEN, 2005; Former et al., 2005). Further studies are needed to
36 determine whether fullerenes may be toxic to microorganisms under environmental
37 conditions. One must also consider the potential of photoreactions and other abiotic processes
38 to alter the bioavailability and thus biodegradation rates of nanomaterials. In summary, not
39 enough is known to enable meaningful predictions on the biodegradation of nanomaterials in
40 the environment and much further testing and research are needed.
41
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1 4.3.6 Bioavailability and Bioaccumulation of Nanomaterials
2 Bacteria and living cells can take up nano-sized particles, providing the basis for
3 potential bioaccumulation in the food chain (Biswass and Wu, 2005). Aquatic and marine
4 filter feeders near the base of the food chain feed on nano-sized and larger particles. The
5 bioavailability of specific nanomaterials in the environment will depend in part on the
6 particle. Environmental fate processes may be too slow for effective removal of persistent
7 nanomaterials before they can be taken up by an organism. In the previous section, it was
8 noted that some physical removal processes, such as gravitational settling, are slower for
9 nano-sized particles than for microparticles. This would lead to an increased potential for
10 inhalation exposure to terrestrial organisms and for increased exposure of aquatic organisms
11 to aqueous colloids. Not enough information has been generated on rates of deposition of
12 nanomaterials from the atmosphere and surface water, or of sorption to suspended soils and
13 sediments in the water column, to determine whether these processes could effectively
14 sequester specific nanoparticles before they are taken up by organisms.
15
16 Complexation of metallic nanomaterials may have important interactive effects on
17 biological availability and photochemical reactivity. For example, the biological availability
18 of iron depends on its free ion concentrations in water and the free ion concentrations are
19 affected by complexation. Complexation reduces biological availability by reducing free
20 metal ion concentrations and dissolved iron is quantitatively complexed by organic ligands.
21 Solar UV radiation can interact with these processes through photoreactions of the complexes.
22 . Further, iron and iron oxides can participate in enzymatic redox reactions that change the
23 oxidation state, physical chemical properties and bioavailability of the metal (Reguera et al.
24 2005).
25 4.3.7 Potential for Toxic Transformation Products from Nanomaterials
26 Certain nanomaterials are being designed for release as reactants in the environment,
27 and therefore are expected to undergo chemical transformation. One example of this is iron
28 (Fe°) nanoparticles employed as reactants for the dechlorination of organic pollutants (Zhang,
29 2003). As the reaction progresses, the iron is oxidized to iron oxide. Other metal particles are
30 also converted to oxides in the presence of air and water. Whether the oxides are more or less
31 toxic than the free metals depends on the metal. Under the right conditions, certain metal
32 compounds could be converted to more mobile compounds. In these cases, small particle size
33 would most likely enhance this inherent reactivity. Degradation products from carbon
34 nanomaterials (fullerenes and nanotubes) have not yet been reported.
35 4.3.8 Interactions Between Nanomaterials and Organic or Inorganic Contaminants:
36 Effects and the Potential for Practical Applications
37 The examples cited in this section illustrate how nanomaterials have been
38 demonstrated to alter the partitioning behavior of chemicals between environmental
39 compartments and between the environment and living organisms. Furthermore, several
40 nanomaterials are reactive toward chemicals in the environment, generate reactive species, or
41 catalyze reactions of other chemicals. These properties are currently under study for use in
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1 waste remediation operations. It should be noted that the potential also exists for
2 nanomaterials to effect unforseen changes if released to the environment in large quantities.
3
4 Two types of effects under study for possible exploitation are sorption and reaction.
5 The high surface area of nano-sized particles provides enhanced ability to sorb both organic
6 and inorganic chemicals from environmental matrices compared to conventional forms of the
7 same materials. This property potentially can be utilized to bind pollutants to enhance
8 environmental remediation. Many examples of immobilized nanomaterials for use in
9 pollution control or environmental remediation have been described in the literature. These
10 include nanosponges or nanoporous ceramics, large particulate or bead materials with nano-
11 sized pores or crevasses (Christen, 2004), and solid support materials with coatings of
12 nanoparticles (for example, see Comparelli et al., 2004). This section will instead focus on
13 releases of free nanoparticles and the effects they have had on chemicals in the environment.
14 The remainder of this section will be organized into known changes in the mobility of
15 chemicals caused by their sorption to nanoparticles, and known instances of reactivity and
16 catalytic activity toward chemicals mediated by nanoparticles.
17
18 No single overall effect can be described for the sorption of chemicals to
19 nanomaterials based on their size or chemical makeup alone. In air, aerosolized
20 nanoparticles can adsorb gaseous or parti dilate pollutants. In soil or sediments, nanomaterials
21 might increase the bioavailability of pollutants, thereby increasing the pollutant's availability
22 for biodegradation (U.K. Royal Society, 2004). Depending on the conditions, nano-sized
23 carbon such as Ceo or nanotubes could either enhance or inhibit the mobility of organic
24 pollutants. (Cheng et al., 2004). Stable colloids of hydrophobic nanomaterials in an aqueous
25 environment could provide a hydrophobic microenvironment that suspends hydrophobic
26 contaminants and retards their rate of deposition onto soils and sediments. Similar effects are
27 known to happen with naturally occurring colloids made up of humic acids and suspended
28 sediment particles (Schwarzenbach et al., 1993). Nanoparticles can be altered to optimize
29 their affinities for particular pollutants by modifying the chemical identity of the polymer.
30
31 Several studies investigating the sorption of organic pollutants and metals in air, soil,
32 and water to nano-sized materials have recently been reported in the literature. The sorption
33 of naphthalene to Ceo from aqueous solution was compared to sorption to activated carbon
34 (Cheng et al., 2004). The investigators observed a correlation between the surface area of the
35 particles and the amount of naphthalene adsorbed from solution. In other studies,
36 nanoparticles made of an amphiphilic polymer have been shown to mobilize phenanthrolene
37 from contaminated sandy soil and increase its bioavailability (Tungittiplakorn et al.,
38 2004,2005). .It has been reported that magnetite crystals adsorb arsenic and chromium (CrVI)
39 from water (CBEN 2005; Hu et al. 2004), suggesting potential purification techniques for
40 metal-laden drinking water (CBEN,' 2005). The adsorption and desorption of volatile organic
41 compounds from ambient air by fullerenes has been investigated (Chen et al., 2000).
42 Inhalation exposures of benzo(a)pyrene sorbed to ultrafme aerosols of GaiOs (Sun et al, 1982)
43 and diesel exhaust (140 nm) (Sun et al., 1984) were studied in rats. The studies showed that
44 when compared to inhalation of pure benzo(a)pyrene aerosols, material sorbed to the gallium
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1 oxide had increased retention in the respiratory tract, and increased exposure to the stomach,
2 liver, and kidney.
3
4 Nanoscale materials are typically more reactive than larger particles of the same
5 material. This is true especially for metals and certain metal oxides. In the environment,
6 nanomaterials have the potential to react with a variety of chemicals; their increased or novel
7 reactivity coupled with their sorptive properties allows for accelerated removal of chemicals
8 from the environment. Many groups are currently investigating the use of nanomaterials for
9 the destruction of persistent pollutants in the environment.
10
11 Nanoscale iron particles have been demonstrated to be effective in the in situ
12 remediation of soil contaminated with tetrachloroethylene. A wide variety of additional
13 pollutants are claimed to be transformed by iron nanoparticles in laboratory, experiments,
14 including halogenated (Cl, Br) methanes, chlorinated benzenes, certain pesticides, chlorinated
15 ethanes, polychlorinated hydrocarbons, TNT, dyes, and inorganic anions such as nitrate,
16 perchlorate, dichromate, and arsenate. Further investigations are underway with bimetallic
17 nanoparticles (iron nanoparticles with Pt, Pd, Ag, Ni, Co, or Cu deposits) and metals
18 deposited on nanoscale support materials such as nanoscale carbon platelets and nanoscale
19 poly aery lie acid (Zhang, 2003). Nanosized clusters of Ceo have been shown to generate
20 reactive oxygen species in water under UV and polychromatic light. Similar colloids have
21 been reported to degrade organic contaminants and act as bacteriocides (Boyd et al., 2005).
22 Fullerol (Ceo(OH)24) has also been demonstrated to produce reactive oxygen species under
23 similar conditions (Pickering and Wiesner, 2005).
24 43.9 Applicability of Current Environmental Fate and Transport Models to
25 Nanomaterials
26 When performing exposure assessments on materials for which there are no
27 experimental data, models are often used to generate estimated data, which can provide a
28 basis for making regulatory decisions. It would be advantageous if such models could be
29 applied to provide estimated properties for nanomaterials, since there is very little
30 experimental data available for these materials. The models used by EPA's Office of
31 Pollution Prevention and Toxics (OPPT) to assess environmental fate and exposure, are, for
32 the most part, designed to provide estimates for organic molecules with defined and discrete
33 structures. These models are not designed for use on inorganic materials; therefore, they
34 cannot be applied to inorganic nanomaterials. Many models derive their estimates from
35 structural information and require that a precise structure of the material of interest be
36 provided. Since many of the nanomaterials in current use, such as quantum dots, ceramics
37 and metals, are solids without discrete molecular structures, it is not possible to provide the
38 precise chemical structures that these models need. While it is usually possible to determine
39 distinct structures for fullerenes, the models cannot accept the complex fused-ring structures
40 of the fullerenes. Also, the training sets of chemicals with which the quantitative
41 structure-activity relationships (QSAR) in the models were developed do not include
42 fullerene-type materials. Fullerenes are unique materials with unusual properties, and they
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1 cannot be reliably modeled by QSARs developed for other substantially different types of
2 materials.
3
4 In general, models used to assess the environmental fate and exposure to chemicals are
5 not applicable to intentionally produced nanomaterials. Depending on the relevance of the
6 chemical property or transformation process, new models may have to be developed to
7 provide estimations for these materials; however, models cannot be developed without the
8 experimental data needed to design and validate them. Before the environmental fate,
9 transport and multimedia partitioning of nanomaterials can be effectively modeled, reliable
10 experimental data must be acquired for a variety of intentionally produced nanomaterials.
11
12 However, models are also used-which focus on the fate and distribution of particulate
13 matter (air models) and/or colloidal materials (soil; water; landfill leachates; ground water),
14 rather than discrete organics. For example, fate of atmospheric particulate matter (e.g. PMio)
15 has been the subject of substantial research interest and is a principal regulatory focus of
16 EP A's Office of Air and Radiation. Since intentionally produced nanomaterials are expected
17 to be released to and exist in the environment as particles in most cases, it is wise to
18 investigate applicability of these other models. In fact it can be reasoned that the most useful
19 modeling tools for exposure assessment of nanomaterials are likely to be found not in the area
20 of environmental fate of specific organic compounds (more precisely, prediction of their
21 transport and transformation), rather in fields in which the focus is on media-oriented
22 pollution issues: air pollution, water quality, ground water contamination, etc. A survey of
23 such tools should be made and their potential utility for nanomaterials assessed.
24 4.4 Environmental Detection and Analysis of Nanomaterials
25 The challenge in detecting nanomaterials in the environment is compounded not only
26 by the extremely small size of particles of 100 nanometers or less, but also by their unique
27 physical structure and chemical characteristics. The varying of physical and chemical
28 properties can significantly impact the extraction and analytical techniques that can be used
29 for the analysis of a specific nanomaterial. As noted above, the chemical properties of
30 particles at'the nanometer size can significantly differ from the chemical properties of larger
31 particles consisting of the same chemical composition. Independent of the challenges brought
32 on by the intrinsic chemical and physical characteristics of nanomaterials,- the interactions of
33 nanomaterials with the environment also provide significant analytical challenges. Some
34 nanomaterials are being developed with chemical surface treatments that maintain
35 nanoparticle properties in various environments. These surface treatments can also
36 complicate the detection and analysis of nanomaterials.
37
38 In characterizing an environmental sample for intentionally produced nanomaterials,
39 one must be able to distinguish between.the nanoparticles of interest and other ultra-fine
40 particles, such as nanoscale particles in the atmosphere generated from coal combustion or
41 forest fires, or nanoscale particles in aquatic environments derived from soil runoff, sewage
42 treatment, or sediment resuspension. Information used to help characterize nanomaterials
43 includes particle size, morphology, surface area and chemical composition. Other
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1 information taken into consideration in identifying the source of nanomaterials includes
2 observed particle concentrations mapped over an area along with transport conditions (e.g.
3 meteorology, currents) at the time of sampling. For nanomaterials with unique chemical
4 composition as found in some quantum dots containing heavy metals, chemical
5 characterization can play an important role in their detection and source identification.
6
7 The level of effort (and in turn costs) needed to perform analysis for nanomaterials
8 will depend on which environmental compartment samples are being taken from, as well as
9 the type of desired analytical information. The analysis of nanomaterials from an air matrix
10 requires significantly less (if any) "sample" preparation than samples taken from a soil matrix
11 where it is necessary to employ greater efforts for sample extraction and/or particle isolation.
12 Analytical costs also depend on the degree of information being acquired. Analyzing
13 samples for number concentration—/. z. the number and size distribution of nanoparticles per
14 unit volume—requires significantly less effort than broadening such analyses to include
15 characterization of particle types (fullerenes, quantum dots, nanowires, etc.). The level of
16 effort also increases for elemental composition analyses.
17
18 Although significant advancements in particle measurement technology have been
19 made over the past two decades in response to National Ambient Air Quality Standards
20 (USEPA, 2004), many of these technologies were designed to effectively function on micron
21 sized particles, particles hundreds to a thousand times larger than nanoparticles. Many of
22 these technologies are not effective in die separation or analysis of particles at the nanometer
23 scale. However, some of these technologies can be applied for the separation and collection
24 of fine particulates that may be composed of an agglomeration of nanoparticles or contain
25 nanoparticles that have attached to larger particulates by way of weak molecular forces. The
26 fine particulates collected using these methodologies would need to undergo test methods
27 capable of analyzing for the nanoparticles of interest
28
29 The information available from the bulk analysis of nanomaterials from environmental
30 samples has limitations when one is trying to identify a specific nanomaterial. As stated
31 previously, nanoscale particles generated by natural and other anthropogenic sources cannot
32 be separated from nanomaterials of interest using sampling methodologies based upon particle
33 size. During analysis, detected signals generated by nanoscale particles that are not of interest
34 can mask or augment the signals of nanomaterials of interest, resulting in inadequate or
35 erroneous data. Where procedures are available for the selective extraction of nanomaterials
36 of interest, one can avoid interfering signals from other nanoscale particles obtained during
37 sampling. In the case of inseparable mixtures of natural and engineered/manufactured
38 nanomaterials, the use of single particle analysis methodologies such as scanning electron
39 microscopy may be necessary to provide definitive analysis for the engineered/manufactured
40 nanomaterials.
41
42 Even given all the challenges presented in analyzing for specific nanomaterials of
43 interest, methods and technologies are available that have demonstrated success. Scanning
44 Mobility Particle Sizers can isolate aerosol nanoparticle fractions down to a few nanometers
45 and provide the concentration of that fraction in the sample taken. Commercial samplers are
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1 available that use electrostatic precipitation to collect aerosol nanoparticle fractions for future
2 analysis using technologies like Transmission Electron Microscopy (TEM). TEM can
3 provide both morphological and chemical composition information. Atomic Force
4 Microscopy, a relatively new technology, can also provide morphological and compositional
5 information on single nanoparticles in both liquid and gas media Appendix C provides more
6 information on these and other methods and technologies available for the detection and
7 analysis of nanomaterials in the environment.
8
9 4.5 Human Exposures and Their Measurement and Control
10 4.5.1 Introduction
11 As the use of nanomaterials in society increases, it is reasonable to assume that their
12 presence in environmental media will increase proportionately, with consequences for human
13 and environmental exposure. Potential human exposures to nanomaterials, or mixtures of
14 nanomaterials, include workers exposed during the production and use of nanomaterials,
15 general population exposure from releases to the environment during the production or use in
16 the workplace, and direct general population exposure during the use of commercially
17 available products containing nanomaterials. This section identifies potential sources,
18 pathways, and routes of exposure, discusses potential means for mitigating or minimizing
19 worker'exposure, describes potential tools and models that may be used to estimate exposures,
20 and identifies potential data sources for these models.
21 4.5.2 Exposure to Nanomaterials
22 The exposure paradigm accounts for a series of events beginning from when external
23 mechanisms (e.g., releases or handling of chemicals) make a chemical available for
24 absorption or other mode of entry at the outer body boundary to when the chemical or its
25 metabolite is delivered to the target organ. Between outer body contact with the chemical and
26 delivery to the target organ, a chemical is absorbed and distributed. Depending on the nature
27 of the chemical and the route of exposure, the chemical may be metabolized. For the
28 purposes of this section, we will limit the discussion to the types of resources that are needed
29 (and available) to assess exposure up to the point where it is distributed to the target organ.
30 4.5.3 Sources and Pathways of Exposure
31 The.potential for intentionally produced nanomaterials to be released into the
32 environment or used in quantities that raise human exposure concerns are numerous given
33 their predicted widespread applications in products. This section discusses some of the
34 potential sources and pathways by which humans may ,be exposed to nanomaterials.
35
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1 4.5;3.1 Occupational Exposure
2
3
4
5
6
7
8
Table 3 presents the potential sources of occupational exposure during the common,
methods fornanoscale material synthesis: gas phase synthesis, vapor deposition, colloidal,
and attrition methods. . .
Table 3. Potential Sources of Occupational Exposure for Various Synthesis Methods
(adapted from Aitken, 2004)
Synthesis
Process
Gas Phase
Vapor Deposition
Colloidal
Attrition
Particle
Formation
in air
on substrate
liquid
suspension
liquid
suspension
Exposure Source or Worker Activity
Direct leakage from reactor, especially if the reactor
is operated at positive pressure.
Product recovery from bag filters in reactors.
Processing and packaging of dry powder.
Equipment cleaning/maintenance (including reactor
evacuation and spent filters).
Product recovery from reactor / dry contamination
of workplace.
Processing and packaging of dry powder.
Equipment cleaning/maintenance (including reactor
evacuation).
If liquid suspension is processed into a powder,
potential exposure during spray drying to create a
powder, and the processing and packaging of the dry '
powder. *
Equipment cleaning/maintenance.
If liquid suspension is processed into a powder,
potential exposure during spray drying to create a
powder, and the processing and packaging of the dry
powder.
Equipment cleaning/maintenance ._ •
Primary Exposure Haute
Inhalation
Inhalation / Dermal
Inhalation / Dermal
Dermal (and Inhalation during
reactor evacuation)
Inhalation
Inhalation / Dermal
Dermal (and Inhalation during
reactor evacuation)
Inhalation / Dermal
Dermal
Inhalation / Dermal
Dermal
9 Note: Digestion would be a secondary route of exposure from all sources/activities from deposition of
10 nanomaterials on food or mucous that is subsequently swallowed (primary exposure route inhalation) and
11 from hand-to-mouth contact (primary exposure route dermal).
12
13 While there are several potential exposure routes for each manufacturing process,
14 packaging and transfer operations may provide the greatest potential for occupational
15 exposure. "The risk of particle release during production seems to be low, because most
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1
2
3
4
5
6
7
8
9
10
11
12
production processes take place in closed systems with appropriate filtering systems.
Contamination and exposure to workers is more likely to happen during handling and bagging
of the material and also during cleaning operations." (Luther, 2004).
During the formulation of the nanomaterials into products (e.g., coatings and
composite materials), releases and exposures may occur during transfer/unloading operations;
however, once the nanomaterial is incorporated into the formulation, the nanoparticles are
typically linked into the matrix. For some of these products, release and exposures of nano-
sized material after incorporation into the product are expected to be low (Luther, 2004). The
most notable exceptions would include consumer exposures to nanomaterials incorporated
into cosmetics, sunscreens, and other lotions.
13 4.5.3.2 Release and General Population Exposure
14 General population exposure may occur from environmental releases from the
15 production and use of nanomaterials and direct use of products containing nanomaterials.
16 During the production of nanomaterials, there are several potential sources for environmental
17 releases including the evacuation of production chambers, filter residues, losses during spray
18 drying, and wastes from equipment cleaning and product handling. No data have been
19 identified quantifying the releases of nanomaterials from industrial processes or of the fate of
20 nanomaterials after release into the environment. However, due to the small size of
21 nanomaterials, they will likely stay airborne for a substantially longer time than other types of
22 particulate. The most likely pathway for general population exposure from releases from
23 industrial processes is direct inhalation of materials released into the air during manufacturing
24 (U.K. Royal Society, 2004). Releases from industrial accidents, natural disasters, or
25 malevolent activity such as a terrorist attack may also lead to exposure of workers or the
26 general public.
27
28 Nanoscale materials have potential applications in many consumer products resulting
29 in potential general population exposure. Electronics, medicine, cosmetics, chemistry, and
30 catalysis are potential beneficiaries of nanotechnology. Widespread exposure via direct
31 contact with these products is expected. Table 4 presents several examples of potential
32 sources of general population and consumer exposure associates with the use of such
33 products.
34
35 Table 4. Examples of Potential Sources of General Population and / or Consumer
36 Exposure for Several Product Types
iiJfroawrf'iEy^^ir
Sunscreen
containing
nanoscale
material
ilMIJSip^wlTO^l'^E^siMf^jiSS'ffifiSfeo^i
Product application by consumer to skin
Release by consumer (e.g., washing with
soap and water) to water supply
Disposal of sunscreen container (with
residual sunscreen) after use (to landfill or
incineration)
iJJxpfiJseifiilFiJiwifliiTOJiis;
Consumer
General Population
General Population
fil&^$it&xi^]^;fQ^i^
Dermal
Ingestion
Ingestion or Inhalation
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Product Type
Metal catalysts in
gasoline for
reducing vehicle
exhaust*
' Release andfer Exposure Source
Release from vehicle exhaust to air (then
deposition to surface water)
Exposed Population
General Population
Potential Exposure Route
Inhalation or Ingestion
1
2
3
4
5
6
Note: Ingestion would be a secondary route of exposure from some sources from deposition of
nanomaterials on food or mucous that is subsequently swallowed (primary exposure route inhalation)
and from hand-to-mouth contact (primary exposure route dermal).
* Metal catalysts are not currently being used in gasoline in the U.S. Nano-cerium oxide particles are
being employed in Europe as on and off-road diesel fuel additives.
7 4.5.4 Exposure Routes
8 Much remains to be scientifically demonstrated about the mechanisms by which
9 human exposure to nanomaterials can occur. Intentionally produced nanomaterials share a
10 number of characteristics, such as size and dimensions, with other substances (e.g., ultrafine
11 particles) for which significant information exists on how they access the human body to
12 cause toxicity. The data from these other substances focus primarily on inhalation as the
13 route of exposure. However, as the range of applications of nanomaterials expands, other
14 routes of exposure, such as dermal and oral, may also be found to be significant in humans.
15
16 4.5.4.1 Inhalation Exposure
17 A UK Health and Safety Executive reference suggests that aerosol science would be
18 applicable to airborne nanoparticle behavior. Aerosol behavior is primarily affected by
19 particle size and the forces of inertia, gravity, and diffusion. Other factors affecting
20 nanoparticle airborne concentrations are agglomeration, deposition, and re-suspension.
21 (Health and Safety Executive, 2004) All of these issues, which are discussed in more detail in
22 the reference, are relevant for understanding, predicting, and controlling airborne
23 concentrations of nanomaterials.
24
25 One reference study was found to have investigated issues involved with aerosol
26 release of a single-walled carbon nanotube (SWCNT) material. This study noted that while
27 laboratory studies indicate that sufficient agitation can release fine particles into the air,
28 aerosol concentrations of SWCNT generated while handling unrefined material in the field at
29 the work loads and rates observed were very low (Maynard et al, 2004). The study suggests
30 that more research will be needed in this area.
31 4.5.4.2 Ingestion Exposure
32 Information on exposure to nanoscale environmental particles via oral exposure is
33 lacking. In addition to traditional ingestion of food, food additives, dust and soil (particularly
34 in the case of children), ingestion of inhaled particles can also occur (such as through the
35 activities of the mucocilliary escalator). However, the quantity ingested is anticipated to be
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1 relatively small in terms of mass, though not much can be concluded at this time about
2 toxicity based on the mass ingested.
3 4.5.4.3 Dermal Exposure
4 Dermal exposure to nanomaterials has received much attention, perhaps due to
5 concerns with occupational exposure and the introduction of nanomaterials such as nano-sized
6 titanium dioxide into cosmetic and drug products. One reference study was found to have
7 investigated issues involved with potential dermal exposure to a single-walled carbon
8 nanotube (SWCNT) material. The study suggests that more research will be needed in this
9 area. This study noted that larger-than-respirable airborne particles of SWCNT may
10 contribute to potential dermal exposure along with surface deposits due to material handling.
11 Surface deposits on gloves were estimated to be between 0.2 mg and 6 mg per hand.
12 (Maynard et al, 2004)
13
14 Hart (2004) highlights physiological characteristics of the skin that may permit the
15 absorption of nano-sized materials. In particular the review highlights a conceivable route for
16 the absorption of nanoparticles as being through interstices formed by stacking and layering
17 of the calloused cells of the top layer of skin (Hart, 2004). Movement through these
18 interstices will subsequently lead to the skin beneath, from.which substances can be absorbed
19 into the blood stream. Nanomaterials also have a greater risk of being absorbed through the
20 skin than macro-sized particles. Reports of toxicity to human epidermal keratinocytes in
21 culture following exposure to carbon nanotubes have been made (Shvedova et al., 2003;
22 Monteiro-Riviere et al, 2005)
23 4.5.5 Personal Protective Equipment (PPE)
24 Properly fitted respirators with a high efficiency particulate air (HEPA) filter may be
25 effective at removing nanomaterials. Contrary to intuition, fibrous filters trap smaller and
26 larger particles more effectively than mid-sized particles. Small particles (<100 nm) tend to
27 make random Brownian motions due to their interaction with gas molecules. The increased
28 motion causes the particle to "zig-zag around" and have a greater chance of hitting and
29 sticking to the fiber filter (Luther, 2004). As noted in the fate section above, small particles
30 (diameters <80 nm) are short-lived because they rapidly coagulate to form larger particles.
31 Large particles (>2000 nm) are subject to gravitational settling. Intermediate-sized particles
32 (>80 nm and < 2000 nm) can remain suspended in air for the longest time. (Bidleman, 1988;
33 Preining, 1998; Spumy, 1998; Atkinson, 2000; Royal Society, 2004; Dennenkamp et al.,
34 2002)
35
36 Particle filter efficiencies are typically measured at 300 nm because they are the most
37 likely to penetrate the filters and represent a worst case. However, as with all respirators, the
38 greatest factor in determining their effectiveness is not penetration through the filter, but
39 rather the face-seal leakage bypassing the device. Due to size and mobility of nanomaterials
40 in the air, leakage may be more prevalent although no more than expected for a gas (Aitken,
41 2004). No available data on face-seal leakage has been identified.
42
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1 PPE may not be as effective at mitigating occupational dermal exposure. PPE is likely
2 to be less effective against dermal exposure to nanomaterials than macro-sized particles from
3 both human causes (e.g., touching face with contaminated fingers) and PPE penetration
4 (Aitken, 2004). However, no studies were identified that discuss the efficiency of PPE at
5 preventing direct penetration of nanomaterials through PPE or from failure due to human
6 causes.
7 4.5.6 Quantifying Exposure to Nanomaterials
8 A potential issue when quantifying exposure is that mass dose (most commonly used
9 by the Agency) may not be an appropriate metric to characterize exposure to nanomaterials.
10 Many studies have indicated that toxicity increases with decreased particle size and that
11 particle surface area is a better metric for measuring exposures (Aitken, 2004). This is of
12 particular concern for nanomaterials, which typically have very high surface-area-to-mass
13 ratios. Additionally, there currently are no convenient methods for monitoring the surface
14 area of particles in a worker's breathing zone or ambient air. While there could be a
15 correlation between mass and surface area (i.e., mass / weight of each particle x surface area
16 of each particle), there are typically large variations between particle weight and surface area
17 within a given batch. The average particle weight and average particle surface area of the
18 nanomaterials being assessed would also be required for any assessments based on surface
19 area
20 4.5.7 Tools for Exposure Assessment
21 Several tools exist for performing exposure assessments including monitoring data,
22 exposure models, and the use of analogous data from existing chemicals. The following
23 sections discuss these tools and their potential usefulness in assessing exposure to nanoscale
24 materials.
25 4.5.7.1 Monitoring Data
26 Types of monitoring data that can be used in exposure assessment include biological
27 monitoring, personal sampling, and ambient air monitoring. Although monitoring and
28 measurement are discussed earlier in section 4.4, the discussion below includes coverage of
29 some issues directly pertinent to exposure.
30 Biological Monitoring
31 Biomonitoring data, when permitted and applied correctly, provides the best
32 information on the dose and levels of a chemical in the human body. Examples of bio-
33 monitoring include the Centers for Disease Control and Prevention (CDC) national
34 monitoring program and smaller surveys such as the EPA's National Human Exposure
35 Assessment Survey (NHEXAS). Biomonitoring can be the best tool for understanding the
36 degree and spread of exposure, information that cannot be captured through monitoring
37 concentrations in ambient media. Biomonitoring, however, is potentially limited in its
38 application to nanotechnology because it is a science that is much dependent on knowledge of
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1 biomarkers, and its benefits are highest when there is background knowledge on what
2 nanomaterials should be monitored. Given the current limited knowledge on nanoscale
3 materials in commerce, their uses, and their fate in the environment and in the human body, it
4 is difficult to identify or prioritize nanomaterials for biomonitoring. Should biomonitoring
5 become more feasible in the future, it presents an opportunity to assess the spatial and
6 temporal distribution of nanomaterials in the population.
7 Personal Sampling
8 Personal sampling data provide an estimate of the exposure experienced by an
9 individual. It is limited in that it does not account for changes to the dose administered to the
10 target organ after the biological processes of absorption, distribution, metabolism and
11 excretion. Generally, for cost and feasibility reasons, personal and biomonitoring data are not
12 available for all chemicals on a scale that is meaningful to policymakers. Also, the
13 applicability of personal sampling to nanomaterials is dependent on the development of tools
14 for accurately detecting and measuring such materials in ambient media.
15 Ambient Monitoring
16 Ambient media monitoring measures concentrations in larger spaces such as in homes
17 or in the general environment. Ambient data are used as assumed exposure concentrations of
18 chemicals in populations when it is not feasible or practical to conduct personal sampling for
19 individuals in the populations. Typically, these data are used in models in addition to other
20 assumptions regarding exposure parameters, including population activities and demographics
21 such as age.
22 4.5.7.2 Exposure Modeling
23 A recent use of ambient monitoring data to estimate the exposure of a population is the
24 cumulative exposure project for air toxics recently completed for hazardous air toxics using
25 the Hazardous Air Pollutant Exposure Model (HAPEM), This model predicts inhalation
26 exposure concentrations of air toxics from all outdoor sources, based on ambient
27 concentrations from modeling or monitor data for specific air toxics at the census tract level.
28 As with personal sampling, the immediate applicability of ambient media monitoring to
29 nanomaterials is unclear.
30
31 Other EPA screening level models include the Chemical Screening Tool for Exposures
32 and Environmental Releases (ChemSTEER) and the Exposure and Fate Assessment
33 Screening Tool (E-FAST). ChemSTEER estimates potential dose rates for workers and
34 environmental releases from workplaces. E-FAST uses the workplace releases to estimate
35 potential dose rates for the general population. E-FAST also estimates potential dose rates for
36 consumers in the general public. However, whether ChemSTEER and E-FAST will be useful
37 for assessments of nanoscale materials is not clear because of the significantly different
38 chemical and physical properties of nanomaterials.
39 Challenges of Using Models with Nanoscale Materials
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1
2 There are several models that span multiple levels of complexity and are designed to
3 estimate exposure at several points in the exposure paradigm. The effectiveness of these
4 models at predicting human exposure will depend on the parameters and assumptions of each
5 model. For models that are based on assumptions specific to the chemical such as the
6 physical and chemical properties, and interactions in humans and the environment based on
7 these properties, much substance-specific data may be required.
8 Data Sets for Modeling
9 Clearly, critical to modeling exposure using ambient data is the availability of such
10 data. There are a number of res ources within EPA for this type of data. In some cases such as
11 for pesticides, the exposure can be anticipated based on the quantity of the substance that is
12 proposed to be applied and the anticipated residue on a food item as an example. Sometimes
13 there are data collected under statutory obligations, such as data collected for the Toxics
14 Release Inventory (TRI) under the Environmental Community Right to Know Act (EPCRA).
15 For contaminants in drinking water, the data may be reported to the Safe Drinking Water
16 .Information System (SDWIS). Generating data for nanomaterials necessitates the
17 identification of nanomaterials as separate and different from other chemicals of identical
18 nomenclature, and their classification as toxic substances, or in a manner that adds
19 nanomaterials to the list of reportable releases/contaminants. For reporting that is dependent
20 on quantity thresholds (e.g., TRI), there is also the need for understanding whether these
21 thresholds apply to nanoscale materials. For intentionally produced nanomaterials, quantity
22 thresholds might prove to be cumbersome given that their toxicity and reactivity do not seem
23 to be directly proportional to quantity and size. It is also worthwhile to note that reporting
24 systems dependent on a quantity threshold may not be directly applicable to intentionally
25 produced nanomaterials because of the smaller quantities of nanomaterials that are required to
26 achieve the same or better functions as their identical larger-size chemical analogues. Should
27 this prove correct, the Agency will have to adapt in ways that permit the collection of
28 meaningful data on nano-sized materials.
29
30 Though not fully representative of population exposure, workplace data have
31 frequently provided the foundation for understanding exposure and toxicity for many
32 chemicals in industrial production. A recent study in the United States, in which ambient air
33 concentrations and glove deposit levels were measured, identified a concern for exposure
34 during handling of nanotubes (Maynard et al., 2004). In the work environment, data on
35 workplace exposure is frequently collected under the purview of Occupational Safety and
36 Health Administration (OSHA)-mandated programs to assess worker exposure and assure
37 compliance with workplace regulations and worker protection. Employers, however, are not
38 required to report these data. In addition, OSHA standards are typically airborne exposure
39 levels that are based on health or economic criteria or both, and typically only defined
40 exceedences of these standards are documented. To understand nanotechnology risks in the
41 workplace, the National Institute of Occupational Safety and Health (NIOSH) is advancing
42 initiatives to investigate amongst other issues, nanoparticle exposure and ways of controlling
43 exposure in the workplace (NIOSH, 2004).
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2 4.6 Human Health Effects of Nanomaterials
3 4.6.1 Introduction
4 There is a significant gap in our knowledge of the environmental, health, and
5 ecological implications associated with nanotechnology (Dreher, 2004; Swiss Report 2004;
6 UK Royal Society, 2004; European NanoSafe, 2004; Health and Safety Executive, 2004).
7 This section provides an overview of currently available information on the toxicity of
8 nanoparticles; much of the information is for natural or incidentally formed nano-sized
9 materials, and is presented to aid in the understanding of intentionally produced
10 nanomaterials.
11 4.6.2 Adequacy of Current lexicological Database
12 The Agency's databases on the health effects of particulate matter (PM), asbestos,
13 silica, or other toxicological databases of similar or larger sized particles of identical chemical
14 composition (US EPA, 2004; US EPA, 1986; US EPA 1996) should be evaluated for their
15 potential use in conducting toxicological assessments of intentionally produced
16 nanomaterials. The toxicology chapter of the recent Air Quality Criteria for Particulate
17 Matter document cites hundreds of references describing the health effects of ambient air
18 particulate matter including ultrafine ambient air (PMo.i), silica, carbon, and titanium dioxide
19 particles (US EPA 2004). However, it is important to note that ambient air ultrafine particles
20 are distinct from intentionally produced nanomaterials since they are not purposely
21 engineered and represent a physicochemical and dynamic complex mixture of particles
22 derived from a variety of natural and combustion sources. In addition, only approximately
23 five percent of the references cited in the current Air Quality Criteria for Particulate Matter
24 document describe the toxicity of chemically defined ultrafine particles, recently reviewed by
25 Oberdorster et al. (2005).
26
27 A search of the literature on particle toxicity studies published up to 2005 confirms the
28 paucity of data describing the toxicity of chemically defined ultrafine particles and to an even
29 greater extent that of intentionally produced nanomaterials (Figure 3). The ability to assess
30 the toxicity of intentionally produced nanomaterials by extrapolating from the current particle
31 toxicological database was examined by Lam et al. (2004) and Warheit et al. (2004). Their
32 findings demonstrate that graphite is not an appropriate safety reference standard for carbon
33 nanotubes, since carbon nanotubes displayed very different mass-based dose-response
34 relationships and lung histopathology when directly compared with graphite.
35
36 These initial findings indicate a high degree of uncertainty in the ability of current
37 particle toxicological databases to assess or predict the toxicity of intentionally produced
38 carbon-based nanomaterials displaying novel physicochemical properties. Additional
39 comparative toxicological studies are required to assess the utility of the current particle
40 toxicological databases in assessing the toxicity of other classes or types of intentionally
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produced nanomaterials, as well as to relate their health effects to natural or anthropogenic
ultrafine particles.
Figure 3. Particle Toxicology Citations. Results depict the number of toxicological
publications for each type of particle obtained from a PubMed search of the literature up to
2005 using the indicated descriptors. Uf denotes ultrafine size (O.lnm) particles.
2
3
4
5
6
7
8
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40 4.6.3 Toxicity and Hazard Identification of Engineered/Manufactured Nanomaterials
41 Studies assessing the role of particle size on toxicity have generally found that
42 ultrafine or nanosize range (<100nm) particles are more toxic on a mass-based exposure
43 metric when compared to larger particles of identical chemical composition (Oberdorster et
44 al., 1994; Li et al., 1999; Hohr et al., 2002). Studies conducted by Lam et al. (2004) and
45 Warheit et al. (2004) examining the pulmonary toxicity of carbon nanotubes, have provided
46 evidence that intentionally produced nanomaterials can display unique toxicity that cannot be
47 explained by differences in particle size alone. For example, Lam reported single walled
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1 carbon nanotubes displayed greater pulmonary toxicity than carbon black nanoparticles.
2 Similar results have been obtained from comparative in vitro cytotoxicity studies (Jia et al.}
3 2005). Muller et al. (2005) reported multi-walled carbon nanotubes to be more
4 proinflammatory and profibrogenic when compared to ultrafine carbon black particles on an
5 equivalent mass dose metric. Shvedova et al. (2005) reported unusual inflammatory and
6 fibrogenic pulmonary responses to specific nanomaterials, suggesting lhat they may injure the
7 lung by new mechanisms. Exposure of human epidermal keratinocyte cells in culture to
8 single-walled carbon nanotubes was reported to cause dermal toxicity, including oxidative
9 stress and loss of cell viability (Shvedova et al., 2003). Several studies have demonstrated that
10 nanoparticle toxicity is extremely complex and multi-factorial, potentially being regulated by
11 a variety of physicochemical properties such as size and shape, as well as surface properties
12 such as charge, area, and reactivity (Sayes et al., 2004; Cai et al., 1992; Sclafani and
13 Herrmann 1996, Nemmar et al., 2003; Derfus et al., 2005).
14
15 lexicological assessment of intentionally produced nanomaterials will require
16 information on the route (inhalation, oral, dermal) that carries the greatest risk for exposure to
17 these materials, as well as comprehensive physicochemical characterization of them in order
18 to provide information on size, shape, as well as surface properties such as charge, area, and
19 reactivity. Establishment of dose-response relationships linking physicochemical properties
20 of intentionally produced nanomaterials to their toxicities will identify the appropriate
21 exposure metrics that best correlates with adverse health effects.
22
23 One of the most striking findings regarding particle health effects is the ability of
24 particles to generate local toxic effects at the site of initial deposition as well as very '
25 significant systemic toxic responses (US EPA, 2004). Pulmonary deposition of polystyrene
26 nanoparticles was found to not only elicit pulmonary inflammation but also to induce vascular
27 thrombosis (Nemmar et al., 2003). Pulmonary deposition of carbon black nanoparticles was
28 found to decrease heart rate variability in rats and prolonged cardiac repolarization in young
29 healthy individuals in recent toxicological and clinical studies (Holker et al., 2005; Frampton
30 et al., 2004). Submicron particles have been shown to penetrate the stratum corneum of
31 human skin following dermal application, suggesting a potential route by which the immune
32 system may be affected by dermal exposure to nanoparticles (Tinkle et al., 2003). It is clear
33 that toxicological assessment of intentionally produced nanomaterials will require
34 consideration of both local and systemic toxic responses (e.g., immune, cardiovascular,
35 neurological toxicities) in order to ensure that that we identify the health effects of concern
36 from these materials.
37 4.6.4 Capabilities of Current Test Methodologies
38 A challenge facing the toxicological assessment of intentionally produced
39 nanomaterials is the wide diversity and complexity of the types of materials that are available
40 commercially or are under development. In many cases, the same type of nanomaterial can be
41 produced by several different processes, giving rise to a number of versions of the same type
42 of nanomaterial. For example, single-walled carbon nanotubes can be mass produced by four
43 different processes, each of which generates products of different size, shape, composition,
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1 and potentially different lexicological properties (Bekyarova, 2005). It is not known whether
2 the toxicological assessment of one type and source of nanomaterial will be sufficient to
3 assess the toxicity of the same class/type of nanomaterial produced by a different process.
4 Manufactured materials may also be treated with coatings, or other surface modifications, in
5 order to generate mono-dispersed suspensions that extend and enhance their unique
6 properties. The extent to which surface modifications of intentionally produced
7 nanomaterials affect their toxicity is not known. Test methods that determine the toxicity and
8 hazardous physiochemical properties of intentionally produced nanomaterials in an accepted,
9 timely and cost effective manner are needed in order provide health risk assessment
10 information for the diversity of such nanomaterials that are currently available (ILS1 2005).
11 4.6.5 Dosimetry and Fate of Intentionally Produced Nanomaterials
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Much of what is known regarding particle dosimetry and fate has been derived from
pulmonary exposure studies using ultrafine metal oxide and carbon black studies (US EPA
2004; Oberdorster,1996; Oberdorster etal., 2005; Oberdorster et al., 2004; Kreyling et al.
2003). Ultrafine carbon black and metal oxide particles display differential deposition
patterns within the lung when compared to larger sized particles of identical chemical
composition. For example, 1 nm particles are preferentially deposited in the nasopharyngeal
region while 5nm particles are deposited throughout the lung and 20 nm particles are
preferentially deposited in the distal lung within the alveolar gas exchange region
(Oberdorster et al., 2005). Host susceptibility factor's such as pre-existing lung disease
significantly affect the amount and location of particles deposited within the lung. For
example, individuals with chronic obstructive pulmonary disease have 4-fold higher levels of
particles deposited in their upper bronchioles when compared to health individuals exposed to
the same concentration of particles (US EPA, 2004). Also, pulmonary deposited ultrafine
particles can evade the normal pulmonary clearance mechanisms and translocate by a variety
of pathways to distal organs (Oberdorster et al., 2005; Oberdorster et al., 2004; Kreyling et al.
2003; Renwick et al., 2001).
The deposition and fate of the class of nanomaterials called dendrimers have been
examined to some degree due to their potential drug delivery applications (Malik et al 2000;
Nigavekar et al. 2004.). Both studies demonstrated the critical role which surface charge and
chemistry play in regulating the deposition and clearance of dendrimers in rodents.
A significant amount of intradermally injected nanoscale quantum dots were found to
disperse into the surrounding viable subcutis and to draining lymph nodes via subcutaneous
lymphatics (Roberts et al., 2005). Other studies (Tinkle et al., 2003) have shown enhanced
penetration of submicron fluorospheres into the stratum comeum of human skin following
dermal application and mechanical stimulation. Drug delivery studies using model wax
nanoparticles have provided evidence that nanoparticle surface charge alters blood-brain
barrier integrity and permeability (Lockman et al., 2004). Toxicological studies have
demonstrated the direct cellular uptake of multi-walled carbon nanotubes by human epidermal
keratinocytes (Monteiro-Riviere et al., 2005).
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1 Very little is known regarding the deposition and fate (metabolism, dissolution,
2 clearance., translocation) of other types or classes of intentionally produced nanomaterials
3 following either inhalation, ingestion, or dermal exposures. Knowledge of tissue and cell
4 specific deposition, fate and persistence of engineered or manufactured nanomaterials, as well
5 as factors such as host susceptibility and nanoparticle physicochemical properties regulating
6 their deposition and fate, is needed to determine exposure-dose-response relationships
7 associated with various routes of exposures. Information on the fate of nanomaterials is
8 needed to assess their persistence in biological systems, a property that regulates
9 accumulation of these particles to levels that may produce adverse health effects following
10 long-term exposures to low concentrations of these particles.
11
12 At a 2004 nanotoxicology workshop at the University of Florida, concerns were
13 expressed about the ability of existing technologies to detect and quantify intentionally
14 produced nanomaterials in biological systems. New detection methods or approaches, such as
15 the use of labeled or tagged nanomaterials, may have to be developed in order to analyze and
16 quantify nanomaterials within biological systems.
17 4.6.6 Susceptible Subpopulations
18 Particle toxicology research has shown that not all individuals in the population
19 respond to particle exposures in the same way or to the same degree (US EPA, 2004). Host
20 susceptibility factors that influence the toxicity, deposition, fate and persistence of
21 intentionally produced nanomaterials are unknown. This information is critically needed to
22 understand the exposure-dose-response relationships of intentionally produced nanomaterials
23 in order to recommend safe exposure levels that protect the most susceptible Subpopulations.
24 4.6.7 Health Effects of Environmental Technologies That Use Nanomaterials
25 The potential for adverse health effects may arise from direct exposure to
26 intentionally-produced nanomaterials and/or byproducts associated with their applications.
27 Nanotechnology is being employed to develop pollution control and remediation applications,
28 Reactive zero-valent iron nanoparticles are being used to treat soil and aquifers contaminated
29 with halogenated hydrocarbons, such as TCE (trichloroethylene) or DCE (dichloroethylene),
30 and heavy metals (wwvv.bioxtech.com). However, the production of biphenyl and benzene
31 associated with nanoscale zero-valent iron degradation of more complex poly chlorinated
32 hydrocarbons has been recently reported (Elliott et al., 2005).
33
34 Photocatalytic nano-titanium dioxide (nano-TiCh) particles are being incorporated into
35 building materials such as cement and surface coatings in order to reduce ambient air nitrogen
36 oxides (NOx) levels. The European Union Photocatalytic Innovative Coverings Applications
37 for Depollution Assessment has evaluated the effectiveness of photocatalytic nano-TiC>2 to
38 decrease ambient air NOx levels and has concluded that this technology represents a viable
39 approach to attain 21 ppb ambient air NOx levels in Europe by 2010 (www.picada-
40 projeclcorri). However, the extent to which nano-Ti02 reacts with other ambient air co-
41 pollutants and alters their corresponding health effects is not known. •
42
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1 Nano-cerium oxide particles are being employed in the United Kingdom as on- and
2 off-road diesel fuel additives to decrease emissions and some manufacturers are claiming fuel
3 economy benefits. However, one study employing a cerium additive with a particulate trap
4 has shown cerium to significantly alter the physicochemistry of diesel exhaust emissions
5 resulting in increased levels of air toxic chemicals such as benzene, 1,3-butadiene, and
6 acetaldehyde. Modeling estimates have predicted that use of a cerium additive in diesel fuel
7 would significantly increase the ambient air levels of cerium (Health Effects Institute, 2001).
8 The health impacts associated with these alterations in diesel exhaust have not been examined
9 and are currently not known.
10
11 Environmental technologies using nanotechnology lead to direct interactions of
12 reactive, intentionally produced nanomaterials with chemically complex mixtures present
13 within a variety environmental media such as soil, water, ambient air, and combustion
14 emissions. The health effects associated with these interactions are unknown. Research will
15 be needed to assess the health and environmental risks associated with environmental
16 applications of nanotechnology.
17
18 4.7 Ecological Effects of Nanomaterials
19 4.7.1 Introduction
20 Nanomaterials may affect aquatic or terrestrial organisms differently than larger
21 particles of the same materials. As noted above, assessing nanomaterial toxicity is extremely
22 complex and multi-factorial, and is potentially influenced by a variety of physicochemical
23 properties such as size and shape, and surface properties such as charge, area, and reactivity.
24 Furthermore, use of nanomaterials in the environment may result in novel byproducts or
25 degradates that also may pose risks. The following section summarizes available information
26 and considerations regarding the potential ecological effects of nanomaterials; Appendix C
27 contains additional detailed analyses of existing information.
28 4.7.2 Uptake and Accumulation of Nanomaterials
29 Based on analogy to physical-chemical properties of larger molecules of the same
30 material, it may be possible to estimate the tendency of nanomaterials to cross cell membranes
31 and bioaccumulate. However, current studies have been limited to a very small number of
32 nanomaterials and target organisms. Similarly, existing knowledge could lead us to predict a
33 mitigating effect of natural materials in the environment (e.g., organic carbon); however, this
34 last concept would need to be tested for a wide range of intentionally produced nanomaterials.
35
36 Molecular weight (MW) and effective cross-sectional diameter are important factors
37 in uptake of materials across the gill membranes of aquatic organisms or the Gl tract of both
38 aquatic and terrestrial organisms. Uptake via passive diffusion of neutral particles is low, but
39 still measurable within a range of small molecular weights (600-900) (Zitko, 1981;
40 Opperhuizen et al, 1985; Niimi and Oliver, 1988; McKim et al., 1985). The molecular
41 weight of some nanomaterials falls within this range. For example, the MW of n-Ceo
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1 fullerene is about 720, although the MW of a Cg4 carbon nanotube is greater than 1000.
2 Passive diffusion through gill membranes or the GI tract also depends on the cross sectional
3 diameter of particles (Opperhuizen et al., 1985; Zitko, 1981; OPPT data). Existing evidence
4 indicates that the absolute limit for passive diffusion through gills is in the nanometer range
5 (between 0. 95 and 1.5 nm), which suggests that passive diffusion may be possible for
6 nanomaterials within this range, but not for nanomaterials with larger effective cross-sectional
7 diameters.
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9 Charge is also an important characteristic to consider for nanomateria! uptake and
10 distribution. For example, as noted above, drug delivery studies using model wax
11 nanoparticles have provided evidence that nanoparticle surface charge alters blood-brain
12 barrier integrity and permeability in mammals (Lockman et al., 2004).
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14 Other chemical and biotic characteristics may need to be considered when predicting
15 accumulation and toxicity of nanoparticles in aquatic systems. For example, the Office of
16 Water uses several specific characteristics, including water chemistry (e.g., dissolved organic
17 carbon and particulate organic carbon) and biotic (lipid content and trophic level)
18 characteristics, when calculating national bioaccumulation factors for highly hydrophobic
19 neutral organic compounds (U.S.EPA, 2003).
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21 Because the properties of some nanomaterials are likely to result in uptake and
22 distribution phenomena different from many conventional chemicals, it is critically important
23 to conduct studies that will provide a solid understanding of these phenomena with a range of
24 nanomaterials and species. Studies related to human health effects assessment will provide an
25 important foundation for understanding mammalian exposures and some cross-species
26 processes (e.g., ability to penetrate endothelium and move out of the gut and into the
27 organism). However, other physiology differs among animal classes, most notably
28 respiratory physiology (e.g., gills in aquatic organisms and air sacs and unidirectional air flow
29 in birds), while plants and invertebrates (terrestrial and aquatic) have even greater
30 physiological differences. Because of their size, the uptake and distribution of nanomaterials
31 may follow pathways not normally considered in the context of conventional materials (e.g.,
32 pinocytosis, facilitated uptake, and phagocytosis).
33 4.7.3 Aquatic Ecosystem Effects
34 . To date, very few ecotoxicity studies with nanomaterials have been conducted.
35 Studies have been conductedtpn a limited number of nanoscale materials, and in a limited
36 number of aquatic species. There have been no chronic or full life-cycle studies reported.
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38 For example, Oberdorster (2004b) studied effects of fullerenes in the brain of juvenile
39 largemouth bass and concluded that Ceo fullerenes induce oxidative stress, based on their
40 observations that (a) there was a trend for reduced lipid peroxidation in the liver and gill, (b)
41 significant lipid peroxidation was found in brains, and (c) the metabolic enzyme glutathione-
42 S-transferease (GST) was marginally depleted in the gill. However, no concentration-
43 response relationship was evident as effects observed at a low dose were not observed at the
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1 single higher dose and no changes in fish behavior were observed; effects could have been
2 due to random variation in individual fish. Oberdorster et al. (2005) and Oberdorster (2004)
3 tested un-coated, water soluble, colloidal fullerenes (nCgo) and estimated a daphnid 48-h LCso
4 at 800 ppb, using standard EPA protocols. Lovem et al. (in press) tested titanium dioxide
5 (TiCb) and uncoated Ceo fullerenes in a standard forty-eight hour acute toxicity test These
6 authors found that both nanomaterials were somewhat toxic to the Daphnia magna with
7 toxicities in the low ppm range and fullerenes exhibiting a slightly greater toxicity than TiC«2.
8 However, the way the particles were prepared impacted toxicity, with filtering of the water to
9 remove larger particles enhancing apparent toxicity. Large particles of titanium dioxide (the
10 kind found in sunblock, paint, and toothpaste) did not cause toxicity. Additionally, in
11 behavior tests with filtered fullerenes, Daphnia exhibited behavioral responses, with juveniles
12 showing an apparent inability to swim down from the surface and adults demonstrating
13 sporadic swimming and disorientation. Further research on ecological species is clearly
14 needed.
15 Toxicity studies and structure-activity relationship predictions for carbon black and
16 suspended clay particles suggest that some suspended natural nano-sized particles in the
17 aquatic environment will have low toxicity to aquatic organisms, with effects thresholds
18 ranging from tens to thousands of parts per million (see Appendix C). Limited preliminary
19 work with engineered/manufactured nanomaterials seems to substantiate this conclusion. For
20 example, Cheng and Cheng (2005) reported that aggregates of single-walled carbon
21 nanotubes (SWNT) added to zebraflsh embryos reduced hatching rate at 72 hrs, but by 77 hrs
22 post fertilization all embryos in the treated group had hatched. However, when evaluating a
23 limited data set of nanoscale materials (i.e., carbon black and clay only), available information
24 on differences in toxicity observed between natural and engineered or manufactured
25 nanomaterials should be considered. For example, as noted previously, SWNTs displayed
26 greater pulmonary toxicity than carbon black nanoparticles (Lam et al 2004). Shvedova et al.
27 (2005) reported unusual inflammatory responses to specific nanomaterials in mammals,
28 suggesting that some nanomaterials may injure organs by novel mechanisms.
29 Recent reports suggest that nanomaterials may be effective bactericidal agents against
30 both gram positive and negative bacteria in growth media. The ability of these "nano-Ceo"
31 aggregates to inhibit the growth and respiration of microbes needs to be demonstrated under
32 more realistic conditions. For example, effects on microbes in sewage sludge effluent and
33 natural communities of bacteria in natural waters should be examined.
34 4.7.4 Terrestrial Ecosystem Effects
*?;
35 To date, very few studies have successfully been conducted to assess potential toxicity
36 of nanomaterials to ecological terrestrial test species (plants, wildlife, soil invertebrates, or
37 soil microorganisms).
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39 For terrestrial mammals, toxicity test data on rats.and mice obtained for human health
40 risk assessments should be considered. For example, studies described above indicate that
41 ultrafine or nanosize range particles are more toxic on a mass-based exposure metric when
42 compared to larger particles of identical chemical composition in studies of lung toxicity
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1 (Oberdorster et al. 1994; Li et al. 1999; Hohr et al. 2002), and some nanomaterials can display
2 unique toxicity that cannot be explained by differences in particle size alone (Lam et al. 2004;
3 Warheit et al. 2004). Toxicity to mammalian epidermal cell in culture has also been reported
4 (Shvedova et al. 2003).
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6 The same properties of nanomaterials that regulate uptake in aquatic organisms may
7 limit uptake of nanoparticles by plant roots (i.e., reducing passive transport at lower MW or
8 size) or transport through plant leaves and stomata. Additionally, because many
9 nanomaterials are designed to have strongly reactive surfaces, it is quite possible that
10 significant pathways for toxicity may exist without uptake (e. g., disruption of respiratory
11 epithelium structure/function or other surface cell structure/function). In a recent study of
12 nanomaterial effects on plants, Yang and Watts (2005), reported that alumina nanoparticles
13 (13 nm) slowed root growth in a soil-free exposure medium. Species tested included
14 commercially important species used in ecological risk assessments of pesticides: com (Zea
15 mays), cucumber (Cucumis sativus), soybean (Glycine max), cabbage (Brassica oleracea),
16 and carrot (Daucus corota). The authors reported that coating the alumina nanoparticles with
17 an organic compound (phenanthrene), reduced the nanomaterial's effect of root elongation
18 inhibition. Larger alumina particles (200-300 nm) did not slow root growth, indicating that
19 the alumina itself was not causing the toxicity. The authors hypothesized that the surface
20 charge on the alumina nanoparticles may have played a role in the decreased plant root
21 growth. These studies were conducted in Petri dishes without soil, so environmental
22 relevance is uncertain.
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24 Fundamentally, our ability to extrapolate toxicity information from conventional
25 substances to nanomaterials will require knowledge about uptake, distribution, and excretion
26 rates as well as modes of toxic action, and may be based on existing structure-activity
27 relationships (SARs), such as SARs for polycationic polymers, published in Boethling and
28 Nabholz (1997). Synthesis of radio-labeled nanomaterials (e.g., carbon-14 labeled nanotubes)
29 may be a useful tool, along with advanced microscopy (e.g., comparable to techniques used
30 for asbestos quantification) for developing information on sites of toxic action and metabolic
31 distribution.
32 4.7.5 Ecological Testing Requirements
33 Because nanomaterials are often engineered to have very specific properties, it seems
34 reasonable to presume that they may end up having unusual toxicological effects. Experiences
35 with conventional chemicals suggestihat in these cases, chronic effects of exposure are often
36 a more important component of understanding ecological risk than acute lethality (e.g.,
37 compare effects of pesticides with general narcotic chemicals). As such, initial studies should
38 include longer-term exposures measuring multiple, sub-lethal endpoints. They should be
39 conducted (using appropriate forms and routes of exposure) in a manner that will elucidate
40 key taxonomic groups (i.e., highly sensitive organisms that may become indicator species)
41 and endpoints that may be of greatest importance to determining ecological risk. These
42 studies must also include careful tracking of uptake and disposition to understand toxicity as a
43 function of dose at the site of action.
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A number of existing test procedures that assess long-term survival, growth,
development, and reproductive endpoints (both whole organism and physiological or
biochemical) for invertebrates, fish, amphibians, birds, and plants (including algae, rooted
macrophytes, and terrestrial plants) should be adaptable to nanomaterials. These tests are able
to examine a wide range of species and endpoints to help pinpoint the types of effects most
significant to the evaluation of nanomaterials, and have a strong foundation relative to
projecting likely ecological effects. Both pilot toxicity testing protocols and definitive
protocols should be evaluated with respect to their applicability to nanomaterials. In addition,
field studies or mesocosm studies might be conducted in systems known to be exposed to
nanomaterials to screen for food chain bioaccumulation and unanticipated effects or
endpoints.
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i 5.0 EPA's Research Needs for Nanomaterials
2 5.1 Introduction
3 Research is needed to inform EPA's actions related to the benefits and impacts of
4 nanomaterials. However, there are significant challenges to addressing research needs for
5 nanotechnology and the environment. The sheer variety of nanomaterials and nanoproducts
6 adds to the difficulty of developing research needs. Since we don't have a complete
7 understanding of how nanoparticles behave, each stage in their lifecycle, from extraction to
8 manufacturing to use and then to ultimate disposal, will present separate research challenges.
9 Nanomaterials also present a particular research challenge over their macro forms in that we
10 lack a complete understanding of nanoparticles' scientific properties. Research should be
11 designed from the beginning to identify beneficial applications and to inform risk assessment,
12 pollution prevention, and potential risk management methods. Such research will come from
13 many sources, including academia, industry, EPA, and other agencies and organizations.
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15 An overarching, guiding principle for all testing, both human health and ecological, is
16 to determine which nanomaterials are most used and/or have potential to be released to, and
17 interact with, the environment. These nanomaterials should be selected from each of the
18 broader classes of nanomaterials (carbon-based, metal-based, dendrimers, or composites) to
19 serve as representative particles for testing/evaluation purposes.
20 5.2 Research Needs for Environmental Applications
21 5.2.1 Green Manufacturing Research Need s
22 Nanotechnology offers the possibility of changing manufacturing processes in at least
23 two ways: (1) by using less materials and (2) using nanomaterials for catalysts and separations
24 to increase efficiency in current manufacturing processes. Nanomaterial and nanoproduct
25 manufacturing offers the opportunity to employ the principles of green chemistry and
26 engineering to prevent pollution from currently known harmful chemicals. Research enabling
27 this bottom-up manufacturing of chemicals and materials is one of the most important areas in
28 pollution prevention in the long term. Research questions regarding green manufacturing
29 include:
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31 • How can nanotechnology be used to reduce waste products during manufacturing?
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33 • How can nanomaterials be made using benign starting materials?
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35 • How can nanotechnology be used to reduce the resources needed for manufacturing
36 (both materials and energy)?
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38 • What is the life cycle of various types of nanomaterials and nanoproducts under a
39 variety of manufacturing and environmental conditions?
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5.2.2 Green Energy Research Needs
Developing green energy approaches will involve research in many areas, including
solar energy, hydrogen, power transmission, diesel, pollution control devices, and lighting.
These areas have either direct or indirect impacts on environmental protection. In solar
energy, nanomaterials may make solar cells more efficient and more affordable. In addition,
nanocatalysts may efficiently create hydrogen from water using solar energy. Research
questions for green energy include:
• What research is needed for incentives to encourage nanotechnology to enable green
energy?
• How can nanotechnology assist "green" energy production, distribution, and use?
5.2.3 Environmental Remediation/Treatment Research Needs
The research questions in this area revolve around the effectiveness and risk
parameters of nanomaterials to be used in site remediation, Materials such as zero-valent iron
are expected to be useful in replacing current pump-and-treat or off site treatment methods.
In addition, other nanoremediation approaches can involve the methods of coating biological
particles, determining the effect on the particles (enzyme or bacteriophage) following coating,
and application technologies. This is an area that has not been examined in any great detail.
Therefore, research is needed to develop technologies using nanocoated biological particles
for environmental decontamination or prophylactic treatment to prevent contamination.
The products of this research would be technologies utilizing innocuous biological entities
treated with nanoparticles to decontaminate or prevent bacterial growth. In an age of
antibiotic resistance and aversion to chemical decontamination, enzyme and bacteriophage
technologies offer an attractive option. Remediation and treatment research questions
include:
* Which nanomaterials are most effective for remediation and treatment?
• What are the fate and effects of nanomaterials used in remediation applications?
• How can we improve methods for detecting and monitoring nanomaterials used in
remediation and treatment?
• To what extent are these materials and their byproducts persistent, bioaccumulative,
and toxic and what organisms are affected?
• If toxic byproducts are produced, how can they be reduced?
• What is needed to enhance the efficiency and cost-effectiveness of remediation and
treatment technology? •*'.'
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1 5.3 Chemical Identification and Characterization
2 Research that can be replicated requires agreement on the identification and
3 characterization of nanomaterials. In addition, understanding the physical and chemical
4 properties in particular is necessary in the evaluation of hazard (both human and ecological)
5 and exposure (all routes). It is not clear whether existing physical-chemical property test
6 methods are adequate for sufficiently characterizing various nanomaterials. Alternative
7 methods may be needed. Research questions include:
8
9 • What are the unique chemical and physical characteristics of nanomaterials? How do
10 these characteristics vary among different types of particles (e.g., nanotubes,
11 fullerenes)?
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13 • How do these properties affect the material's reactivity, toxicity and other attributes?
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15 • Should research be tailored to each type of particle and how they are used?
16
17 • Are there adequate measurement methods/technology available to distinguish between
18 intentionally produced nanomaterials and ultrafine particles or naturally occurring
19 nano-sized particles, and among different types of nanomaterials?
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21 • Are current test methods adequate to evaluate hazard and exposure?
22
23 • Do nanomaterial characteristics vary from their pure form in the laboratory to their
24 occurrence in the environment as components of products?
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26 • What intentionally produced nanomaterials are now on the market and what new types
27 of materials can be expected to be developed?
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29 • How will manufacturing processes alter the characteristics of nanomaterials?
30 5.4 Environmental Fate Research Needs
31 EPA needs to ascertain the fate of nanomaterials in the environment to understand the
32 availability of these materials for humans and other life forms. Research on the transport and
33 potential transformation of nanomaterials in soil, subsurface, surface waters, wastewater,
34 drinking water, and the atmosphere is essential as nanomaterials are used increasingly in
35 products. To support these investigations, existing methods should be evaluated and if
36 necessary, they should be modified or new methods should be developed. Research is needed
37 to address the following high-priority questions.
38 5.4.1 Transport Research Questions
39 • What are the physicochemical factors that influence the transport and deposition of
40 intentionally produced nanomaterials in the environment? How do nanomaterials
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move through these media? Do novel materials, such as fullerenes without
corresponding bulk materials, differ in their mobility from the bulk materials? Can
existing information on soil colloidal fate and transport and atmospheric ultrafine
particulate fate and transport inform our thinking?
• How are nanomaterials transported in the atmosphere? What nanomaterial properties
and atmospheric conditions control the atmospheric fate of nanomaterials?
• To what extent are nanomaterials mobile in soils and in groundwater? What is the
potential for these materials, if released to soil or landfills, to migrate to groundwater
and within aquifers, with potential exposure to general populations via groundwater
ingestion?
• What is the potential for these materials to be transported bound to particulate matter,
sediments, or sludge in surface waters?
• How do the aggregation, sorption and agglomeration of nanoparticles affect their
transport?
• How do nanomaterials bioaccumulate? Do their unique characteristics affect their
bioavailability? Do nanomaterials bioaccumulate to a greater or lesser extent than
macro-scale or bulk materials?
23 5.4.2 Transformation Research Questions
• How do nanoparticles react differently in the environment than their bulk
counterparts?
• What are the physicochemical factors that affect the persistence of intentionally
produced nanomaterials in the environment?
• Do particular nanomaterials persist in the environment, or undergo degradation via
biotic or abiotic processes? If they degrade, what are the byproducts and their
characteristics? Is the nanomaterial likely to be in the environment, and thus be
available for bioaccumulation/biomagnification?
• How are the physicochemical and biological properties of nanomaterials altered in
complex environmental media such as air, water, and soil? How do redox processes
influence environmental transformation of nanomaterials? To what extent are
nanomaterials photoreactive in the atmosphere, in water, or on environmental
surfaces?
• How do the aggregation, sorption and agglomeration of nanoparticles affect
transformation?
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1 '5.4.3. Chemical Interaction Research Questions
2 • How do nano-sized adsorbants and chemicals sorbed to them influence their respective
3 environmental interactions? Can these materials alter the mobility of other substances
4 in the environment? Can these materials alter the reactivity of other substances in the
5 environment?
6 5.4.4. Treatment Research Questions
7 • What is the potential for these materials to bind to soil, subsurface materials, sediment
8 or sludge in wastewater treatment plants?
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10 * Are these materials effectively removed from wastewater using conventional
11 wastewater treatment methods and, if so, by what mechanism?
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13 • Do these materials have an impact on the treatability of other substances in
14 wastewater, or on treatment plant performance?
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16 • Are these materials effectively removed in drinking water treatment and, if so, by what
17 mechanism?
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19 • Do these materials have an impact on the removal of other substances during drinking
20 water treatment, or on drinking water treatment plant performance?
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22 • When nanomaterials are placed in groundwater treatment, how do they behave over
23 time? Do they move in groundwater? What is their potential for migrating to drinking
24 water wells?
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26 • How effective are existing treatment methods such as carbon adsorption, filtration, and
27 coagulation and settling for treating nanomaterials?
28 5.4.5. Assessment Approaches and Tools Questions
29 • Can existing information on soil colloidal fate and transport, as well as atmospheric
30 ultrafine particulate fate and transport, inform our thinking? Do the current databases
31 of ultrafines/fibers shed light on any of these questions?
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33 • Do the different nanomaterials act similarly enough to be able to create classes of like
34 compounds? Can these classes be used to predict structure-activity relationships for
35 future materials? .
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37 • Should current fate and transport models need to be modified to incorporate the unique
38 characteristics of nanomaterials?
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1 5.5 Environmental Detection and Analysis Research Needs
2 A variety of methods currently exist to detect nanoparticles, including sampling
3 methods, methods used to measure nanoparticle mass/mass concentrations, surface area,
4 particle count concentration, size, physical structure (morphology), and chemical
5 composition. Research is needed to address the following high-priority questions:
6 5.5.1 Existing Methods and Technologies Research Questions
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• Are existing methods and technologies capable of detecting, characterizing, and
quantifying intentionally produced nanomaterials by measuring particle number, size,
shape, surface properties (e.g., reactivity, charge, and area), etc.? Can they distinguish
between intentionally produced nanomaterials of interest and other ultrafine particles?
Can they distinguish between individual particles of interest and particles that may
have agglomerated or attached to larger particles?
• Are standard procedures available for both sample preparation and analysis?
• Are quality assurance and control reference materials and procedures available?
17 5.5.2. New Methods and Technologies Research Needs
What low-cost, portable, and easy-to-use technologies can detect, characterize, and
quantify nanomaterials of interest in environmental media and for personal exposure
monitoring.
21 5.6 Releases and Human Exposures
22 Potential sources of human exposure to nanomaterials include workers exposed during
23 the production and use of nanomaterials, general population exposure from releases to the
24 environment during the production or use in the workplace, and direct general population
25 exposure during the use of commercially available products containing nanoscale materials.
26 Releases from industrial accidents, natural disasters, or malevolent activity such as a terrorist
27 attack should also be considered. Research is needed to identify potential sources, pathways,
28 and routes of exposure, potential tools and models that may be used to estimate exposures,
29 and potential data sources for these models. Research is needed to address the following
30 high-priority questions.
31 5.6.1. Risk and Exposure Assessment Research Questions
Is the current exposure assessment process adequate for assessing exposures to
nanomaterials? Is mass dose an effective metric for measuring exposure? What
alternative metric (e.g., particle count, surface area) should be used to measure
exposure? Are sensitive populations' (e.g., endangered species, children, asthmatics,
etc.) exposure patterns included?
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1 • How do physical and chemical properties of nanomaterials affect releases and
2 exposures?
3 5.6.2. Release and Exposure Quantification Research Questions
4 • What information is-available about unique release and exposure patterns of
5 nanomaterials? What additional information is needed?
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7 • What tools/resources currently exist for assessing releases and exposures within EPA
8 (chemical release information/ monitoring systems (e.g., TRI), measurement tools,
9 models, etc)? Are these tools/resources adequate to measure, estimate, and assess
10 releases and exposures to nanomaterials? Is degradation of nanomaterials accounted
11 for?
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13 • What research is needed to develop sensors that can detect nanomaterials, including
14 personal exposure monitoring?
15 5.6.3. Release and Exposure Reduction and Mitigation Research Questions
16 • What tools/resources exist for limiting release and/or exposure during manufacture,
17 use or following release via waste streams? Are these tools/resources adequate for
18 nanomaterials?
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20 • Are current respirators, filters, gloves, and other PPE capable of reducing or
21 eliminating exposure from nanomaterials?
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26 • Are technologies and procedures for controlling spills during manufacture and use
27 . adequate for nanomaterials? Can current conventional technologies (i.e. for non-
28 nanomaterials) be adapted to control nanomaterial spills?
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30 • Do existing methods using vacuum cleaners with HEPA filters work to clean up a spill
31 of solid nanomaterials? If not, would a wet vacuum sy stem work?
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33 • What PPEs would be suitable for use by operators during spill mitigation?
34
Are current engineering controls and pollution prevention devices capable of
minimizing releases and exposures to nanomaterials?
35 5.7 Human Health Effects Assessment Research Needs
36 Adverse health effects of intentionally produced nanomaterials may result from either
37 direct exposure resulting from inadvertent release of these novel materials or unintentional
38 byproducts produced by their intentional release into the environment. Very little data exist
39 on the toxicity, hazardous properties, deposition and fate, as well as susceptibility associated
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with exposure to intentionally produced nanomaterials, their application byproducts, or
production waste streams. Finally, it is uncertain whether standard test methods will be
capable of identifying toxicities associated with the unique physical chemical properties of
intentionally produced nanomaterials.
It will be important for nanomaterial health effects risk assessment research to also
establish whether current particle and fiber toxicological databases have the ability to predict
or assess the toxi city of intentionally produced nanomaterials displaying unique
physicochemical properties. The limited studies conducted to date indicate that the
toxicological assessment of specific intentionally produced nanomaterials will be difficult to
extrapolate from existing databases. The toxic effects of nanoscale materials have not been
fully characterized, but it is generally believed that nanoparticles can have toxicological
properties that differ from their bulk material. A number of studies have demonstrated that
nanoparticle toxicity is complex and multifactorial, potentially being regulated by a variety of
physiochemical properties such as size, chemical composition, and shape, as well as surface
properties such as charge, area and reactivity. As the size of particles decreases, a resulting
larger surface-to-volume ratio per unit weight for nanoparticles correlates with increased
toxicity as compared with bulk material toxicity. Also as a result of their smaller size,
nanoparticles may pass into cells directly through cell membranes or penetrate the skin and
distribute throughout the body once translocated to the circulatory system. While the effects
of shape on toxicity of nanoparticles appears unclear, the results of a recent in vitro
cytotoxicity study appear to suggest that single-wall carbon nanotubes are more toxic than
multi-wall carbon nanotubes. Therefore, with respect to nanoparticles, there is concern for
systemic effects (e.g., target organs, cardiovascular, and neurological toxicities) in addition to
portal-of-entry (e.g. lung, skin, intestine) toxicity.
Initially, it will be important to be specific with respect to the nature of the surface
material/coating, the application for which the material is used, the likely route of exposure,
the presence of other exposures which may affect toxicity (e.g., UV radiation) and not rely on
information derived from a study conducted under one set of conditions to predict outcomes
that may occur under another set of conditions. However, past experience with conventional
chemicals suggests that toxicology research on nanomaterials should be designed from the
beginning with an eye towards developing hypothesis-based predictive testing.
Research is also needed to examine health impacts of highly dispersive
nanotechnologies that are employed for site remediation, monitoring, and pollution control
strategies. It will be necessary to determine both the impacts these types of nanotechnologies
have on regulated pollutants in air, soil, or water, as well as their corresponding potential
health effects. Research should be conducted in the following areas:
A. Determining the adequacy of current testing schemes, hazard protocols, and dose
metrics.
B. Identifying the properties of nanomaterials that are most predictive of toxicity to
receptors and their sensitive subpopulations.
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1 C. Identifying those nanomaterials with high commercial potential with dispersive
2 applications, and their most probable exposure pathways.
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4 These areas lead to the following research questions:
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6 • What are the health effects (local and systemic; acute and chronic) from either direct
7 exposure to nanomaterials, or to their byproducts, associated with dispersive
8 nanotechnology applications? (Addresses area C, above)
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10 • Are there specific toxicological endpoints that are of higher concern for nanomaterials,
11 such as neurological, cardiovascular, respiratory, or immunological effects, etc.?
12 (Addresses area C, above)
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14 • Are current testing methods (organisms, exposure regimes, media, analytical methods,
15 testing schemes) applicable to testing nanomaterials in standardized agency toxicity
16 tests (hLtp://www.epa.gov/opptsfrs/OPPTS_Harmoni?:ed/)? (Addresses area A, above)
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18 • Are current test methods, for example OECD and EPA harmonized test guidelines,
19 capable of determining the toxicity of the wide variety of intentionally produced
20 nanomaterials and byproducts associated with their production and applications?
21 (Addresses area A, above)
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23 • Are current analytical methods capable of analyzing and quantifying intentionally
24 produced nanomaterials to generate dose-response relationships? (Addresses area A,
25 above)
26 . .
27 • What physicochemical properties regulate nanomaterial adsorption, distribution,
28 • metabolism, and excretion (ADME)? (Addresses area A, above)
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30 • What physicochemical properties and dose metrics best correlate with the toxicity
31 (local and systemic; acute and chronic) of intentionally produced nanomaterials
32 following various routes of exposure? (Addresses area A, above)
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34 • Are there subpopulations that may be at increased risk of adverse health effects
35 associated with exposure to intentionally produced nanomaterials? (Addresses area B,
36 above).
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38 • What are the best approaches to build effective predictive models of toxicity (SAR,
39 PBPK, "omics", etc.)? (Addresses areas A and B, above)
40 5.8 Ecological Effects Research Needs
41 Ecosystems may be affected through inadvertent or intentional releases of
42 intentionally produced nanomaterials. Drug and gene delivery systems, for example, are not
43 likely to be used directly in the environment but may contaminate soils or surface waters
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through waste water treatment plants (from human use) or more directly as runoff from
concentrated animal feeding operations (CAFOs) or from aquaculture. Direct applications
may include nanoscale monitoring systems, control or clean-up systems for conventional
pollutants, and desalination or other chemical modifications of soil or water. Nanoscale
particles may affect aquatic or terrestrial organisms differently than larger particles due to
their extreme hydrophobicity, their ability to cross and/or damage cell membranes, and
differences in electrostatic charge. Furthermore, use of nanomaterials in the environment may
result in novel byproducts or degradates that also may pose significant risks.
Important considerations for prioritizing and defining the scope of the research needs
include determining which nanomaterials are most used (volume), are likely to be used in the
near future (imminence of use), and/or have most potential to be released into the
environment (dispersive applications). Another consideration is the need to test
representative materials from each of the four classes of nanomaterials (carbon-based, metal-
based, dendrimers, composites).
The same general research areas used for prioritizing human health effects research
needs were used to prioritize ecological research needs. Using these areas as a guide, the
following research questions were identified:
• Are current testing schemes and methods (organisms, endpoints, exposure regimes,
media, analytical methods) applicable to testing nanomaterials in standardized toxicity
tests? Bom pilot testing protocols and definitive protocols should be evaluated with
respect to their applicability to nanomaterials.
• What is the distribution of nanomaterials in ecosystems? Research on model
ecosystems studies (micro, mesocosms) is needed to assist in determining the
distribution of nanomaterials in ecosystems and potentially affected compartments and
species.
• What are the effects (local and systemic; acute and chronic) resulting from either
direct exposure to nanomaterials, or to their byproducts, associated with dispersive
nanotechnology applications and other uses?
* What are the absorption, distribution, metabolism, elimination (ADME) parameters
for various nanomaterials for ecological receptors? This topic addresses the uptake,
transport, bioaccumulation relevant to a range of species (fish, inverts, birds,
amphibians, reptiles, plants, microbes).
• What research is needed to examine the interaction of nanomaterials with microbes in
sewage treatment plants, in sewage effluent, and in natural communities of microbes
in natural soil and natural water?
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1 • What research is needed to develop structure activity relationships (SARs) for
2 nanomaterials for aquatic organisms?
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4 • What are the modes of action (MOA) for various nanomaterials for ecological
5 species? Are the MOAs different or similar across ecological species?
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7 5.9 Risk Assessment Research Needs
8 The overall risk assessment approach used by EPA for conventional chemicals is
9 thought to be generally applicable to nanomaterials. It will be necessary to consider
10 nanomaterials' special properties and their potential impacts on fate, exposure, and toxicity in
11 developing risk assessments for nanomaterials. It may be useful to consider a tiered-testing
12 scheme in the development of testing and risk assessment approaches to nanomaterials.
13
14 Case studies could be conducted based on publicly available information on several
15 intentionally produced nanomaterials. Such case studies would be useful in further
16 identifying unique considerations that should be focused in conducting risk assessments for
17 various 'types of nanomaterials. From such cas e studies and other information, information
18 gaps may be identified, which can then be used to map areas of research that are directly
19 affiliated with the risk assessment process and the use of standard EPA tools such as tiered
20 testing schemes. EPA frequently uses tiered testing schemes for specific risk assessment
21 applications. A series of workshops involving a substantial number of experts from relevant
22 disciplines could be held to use case studies and other information for the identification of any
23 unique considerations for nanomaterials not previously identified, testing schemes, and
24 associated research needs that will have to be met to carry out exposure, hazard and risk
25 assessments.
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i 6.0 Recommendations
2 This section provides recommendations for Agency actions related to nanotechnology.
3 These recommendations are based on the discussion of nanotechnology environmental
4 applications and implications discussed in this paper, and are presented to the Agency as
5 proposals for EPA near- and long-term actions for science and regulatory policy, research and
6 development, collaboration and communication, and other Agency initiatives.
7 6.1 Pollution Prevention and Environmental Stewardship
8 Recommendations
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Pollution prevention is a critical area to engage EPA resources and expertise as
nanotechnology industries form and develop. It is critical that EPA apply the principles
developed for green chemistry, green engineering, and environmentally benign manufacturing
in EPA's approach to nanotechnology. EPA has the opportunity to work with stakeholders to
apply approaches of pollution prevention and product stewardship to nanotechnology
development, so that emissions and risks are reduced as productivity and the economy grow.
The following is the primary recommendation for pollution prevention and environmental
stewardship:
• OPPT should take Agency leadership to incorporate product stewardship, design for
the environment, green engineering and green chemistry principles and approaches to
nanomaterials and nanoproducts.
Other recommendations for pollution prevention and environmental stewardship:
• NCEI and OECA should take the lead to identify nanotechnology sectors, supply
chains, analytical and design tools, and applications. OECA should take the lead to
work with other Agency programs, such as OPPT's Green Supply Chain Network to
identify nanotechnology sectors, supply chains, analytical and design tools, and
applications.
• OCIR and OCFO should work with organizations such as the Ecological Council of
the States (ECOS), state technology assistance organizations, and other tech transfer
groups to integrate an environmental stewardship orientation for nanotechnology into
their ongoing assistance efforts.
j
• OPEI and ORD should expand research on economic&ncentives for environmental
stewardship behavior associated with nanomaterials and nanoproducts.
• EPA should create policy, program and research designs that encourage an
environmental stewardship ethic and behaviors throughout the complete life cycle of
nanomaterials and products.
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1 6.2 Research Recommendations
2 The following are recommendations for research that EPA should conduct or
3 otherwise fund to address the Agency's decision-making needs. Where possible, relative
4 priorities have been given to these needs. Clearly, the ability of EPA to fund such research
5 will depend on available resources and competing priorities. These recommendations should
6 be seen as a point of departure for further Agency discussion and the possible development of
7 an EPA research strategy for nanotechnology.
8 6.2.1 Research Recommendations for Environmental Applications
9 • ORD should take the lead in supporting studies to improve pollutant capture or
10 destruction by exploiting novel nanoscale structure-property relations for
11 nanomaterials used in environmental control and remediation applications.
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13 • ORD should work with the other parts of the Agency to examine the implications
14 (risks) of the applications of nanotechnology. For example, to determine the impact of
15 certain airborne particles on the physicochemistry and health effects of diesel
16 emissions and the health effects associated with interactions with complex ambient air
17 aerosol mixtures. What is the nature of metal species being emitted including
18 potentially hazardous complex nanoparticles, and the change in other emissions
19 (including elemental carbon and organic species) as a result of the catalyst addition?
20
21 • ORD should take the lead in developing nanotechnology-enabled devices for
22 measuring and monitoring conventional chemical and biological contaminants.
23 ,
24 • ORD should take the lead in improving the methods for detecting and monitoring
25 nanomaterials in the environment. ORD's laboratories should engage in collaborative
26 research and development agreements to move fundamental research from the
27 laboratory to the field, (e.g., sensors, treatment technologies).
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29 • ORD should work with industrial partners to verify the performance of nanomaterials
30 and nanoproducts used for environmental applications.
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32 • ORD should continue to support research to develop non-polluting manufacture of
33 nanomaterials and nanoproducts (e.g., using alternative solvents, lower energy
34 processes, fewer processing steps, non-toxic starting materials. Further, the research
35 should promote environmentally beneficial applications of nanomaterials (e.g.,
36 nanocatalysts, nanomembranes and reactors, efficient lighting, etc.).
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38 * ORD should develop rapid screening methods that keep pace with rapid technological
39 change for nanomaterials and nanoproducts building on existing Life Cycle Analysis
40 methods. OPPTS, OW and OAR should collaborate with stakeholders developing
41 rapid screening methods.
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6.2.2 Research Recommendations for Environmental Implications
A multidisciplinary approach is needed that involves physics, biology, and chemistry
to understand nanomaterials at basic level and how they interact with the environment. This
requires a cross-media approach and one that involves collaboration with other federal
agencies, and the private and non-profit sectors.
6.2.2.1 Research Recommendations for Fate. Treatment. Detection. Release, and Exposure
8 The following are recommendations, in numbered order of priority, in support of the
9 fate, treatment, detection and release research needs identified as priorities in Chapter 5.
Fate and Treatment
1. OSWER and ORD should take the lead on research to assess the fate of nanomaterials
such as zero valence iron used in the remediation of chemically contaminated soil
sites. These offices should collaborate with state environmental programs and
academia on this research. Based upon available field activities where nanomaterials
are being used for site remediation, this research could be conducted within the next
one to two years.
2. ORD and OAR should take the lead on research on the stability of various types of
nanoparticles in the atmosphere. This effort should involve both theoretically derived
information as well as some laboratory testing.
3. ORD, OSWER and OW should lead research on the biotic and abiotic degradation of
nanomaterials in soils and aqueous solutions that are relevant to environmental
conditions.
4. ORD should develop a report on how the physical and chemical properties of
nanomaterials impact their environmental fate.
5. ORD, OSW and OW should collaboratively lead research wastewater treatment
process, including the specific types of nanomaterials that would end up in large
quantities in sewage treatment plants, the efficiency of removing nanoparticles from
the effluent, as well as the impact nanomaterials may have on the removal or
degradation of substances in sewage during the treatment process. EPA should
collaborate with municipal sewage treatment facilities and academia on this research.
6. ORD, OPPT and OW should share the lead on research on the fate of nanomaterials
used in the purification of drinking water. Research would be based on actual field
and/or laboratory findings and recommendations would be provided on how to
improve the nanomaterial removal process where human health issues are a concern.
This research should also evaluate individual processes; i.e., whether methods such as
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1 carbon adsorption, filtration, and coagulation and settling are effective for treating
2 nanomaterials.
3 Environmental Detection and Analyst^
4 Where applicable, the initial focus of environmental detection and analysis related
5 research should be on nanomaterials or types of nanomaterials that have demonstrated
6 potential human or ecological toxicity. The following is a prioritized list of research needs for
7 environmental detection and analysis.
8
9 1. ORD should lead the development of a report on the assessment of available
10 environmental detection methods and technologies for nanomaterials in environmental
11 media and for personal exposure monitoring. ORD could collaborate with NIOSH,
12 DOD, industry and academia in developing this report.
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14 2. ORD should collaborate with NIST, NIOSH, DOD, nanomaterial manufacturers and
15 government and private sector organizations in the development of quality control
16 reference materials for analytical methods for nanomaterials.
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18 3. ORD should lead development of a set of standard methods for the sampling and
19 analysis for nanomaterials of interest in various environmental media ORD should
20 collaborate with NIOSH, DOD, industry, academia, the American Society for Testing
21 Materials (ASTM) and the American National Standards Institute (ANSI) in
22 developing these methods.
23 Release and Exposure
24 1. OPPT should conduct a literature search to evaluate the effects of nanomaterial
25 physical/chemical properties on releases and exposures.
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27 2. OPPT should conduct an evaluation of sources of information for assessing chemical
28 releases and exposures for their applicability to nanomaterials. These sources,
29 including release and exposure tools and models, would be evaluated for whether they
30 would be applicable to assessing releases and exposures to nanomaterials. If found
31 applicable, the sources would be evaluated to determine whether additional data or
32 methods would be needed for assessing nanomaterials. Issues such as degradation
33 would be considered also.
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35 3. OPPT should lead the development of guidance to define risk assessment needs for
36 various types of nanomaterials. This guidance should be developed by OPPT in
37 consultation with other stakeholders.
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39 4. OPPT should lead development of guidance for performing exposure assessments for
40 nanomaterials for human and environmental species, including sensitive populations
41 (e.g., endangered species, children, asthmatics, etc.). This guidance should be
42 developed by OPPT in consultation with other stakeholders: A prerequisite for this
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guidance development is the completion of above noted guidance for performing risk
assessments for nanomaterials.
Some parts of the remaining exposure and release research initiatives below are
contingent upon completion of the risk and exposure assessment guidance documents
noted in the two paragraphs above. Until this contingency is met, many of the remaining
research needs cannot be fully completed.
5. OPPT should lead the development of exposure and release scenarios for
nanomaterials in manufacturing and use operations. This effort should be conducted
by OPPT with possible consultation with industry, NIOSH, and ORD
6. OPPT and ORD should collaborate to evaluate and test of equipment for controlling
and reducing chemical releases and exposures for their applicability to nanomaterials.
7. OPPT should lead the evaluation and testing of personal protective equipment for
controlling and reducing chemical exposures for their applicability to nanomaterials,
in collaboration with NIOSH and other external groups.
8. ORD should lead the development of sensors for monitoring personal exposures to
nanoparticles
6.2.2.2 Human Health Effects Assessment Research Recommendations
The following is a prioritized list of health effects research needs:
Test Methods
1. ORD should collaborate with OPPTS on research to determine whether current testing
methods (organisms, exposure regimes, media, analytical methods, testing schemes)
(http://www.epa.gov/opptsfrs/home/testmeth.htm) are applicable to testing nanoparticles
in standardized agency toxicity tests. These offices should consider whether OECD and
EPA harmonized test guidelines are capable of determining the toxicity of the wide
variety of intentionally produced nanomaterials and waste byproducts associated with
their production. In this effort ORD should lead research evaluating whether current
analytical methods are capable of analyzing and quantifying intentionally produced
nanomaterials to generate dose-response relationships. This is an immediate research
need.
Nanotoxicolosv
2. ORD should collaborate with other EPA offices on research to determine the health
effects (local and systemic; acute and chronic) resulting from either direct exposure to
nanomaterials, or to their byproducts, associated with dispersive nanotechnology
applications such as remediation, pesticides, and air pollution control technologies.
Research should determine whether there are specific toxicological endpoints that are of
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1 high concern for nanoparticles, such as neurological, cardiovascular, respiratory, or
2 immunological effects, etc. Research in this area should also provide information as to
3 the adequacy of existing toxicological databases to predict or extrapolate the toxicity of
4 intentionally produced nanomaterials. This is an immediate research need. The Agency
5 should also collaborate with stakeholders in catalyzing this research.
. >
6 Hazard Identification andDosimetry & Fate
7 3. ORD should lead research to determine what physicochemical properties and dose
8 metrics best correlate with the toxicity (local and systemic; acute and chronic) of
9 intentionally produced nanomaterials. This is an immediate research need.
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11 4. ORD should lead research on the adsorption, distribution, metabolism, and excretion
12 (ADME) of intentionally produced nanomaterials following various routes of exposure.
13 This research must also include determining what physicochemical properties regulate
14 intentionally produced nanomaterial ADME. This is an immediate research need. ORD
15 should collaborate with OPPTS on this research.
16 Susceptibility
17 5. ORD should take the lead on research to identify subpopulations that may be at
18 increased risk for adverse health effects associated with exposure to intentionally
19 produced nanomaterials. This is an intermediate need that cannot be established until
20 information from earlier research needs have been collected.
21 Computational Ncmotoxicology
22 6. ORD should take the lead on research to determine what approaches are most effective
23 to build predictive toxicity assessment models (SAR, PBPK, "omics", etc.). While
24 extremely useful, this is a long-term research need.
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26 Research into the human health effects assessment of intentionally produced
27 nanomaterials will be extremely challenging and the ability to interact with other federal,
28 international, academic, and private activities in this area would be most beneficial. A
29 number of organizations are engaged in health effects research. Collaboration with NASA,
30 NIOSH, FDA, NCI, NTP, DOD/MURI, NIST, NEHI, DOE, the European Union, EPA
31 grantees, academic institutions, and others will leverage resources in gaining knowledge on
32 the potential health effects of nanomaterials.
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34 6.2.2.3 Ecological Exposure and Effects
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36 It is critical that research be focused specifically upon the fate, and subsequent
37 exposure and effects, of nanomaterials on invertebrates, fish, and wildlife associated with
38 ecosystems. What is the behavior of nano materials in aquatic and terrestrial environments?
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How can environmental exposures be simulated in the laboratory? What are the acute and
chronic toxic effects? There is a need for development and validation of analytical
methodologies for measuring nanoscale substances (both parent materials and
metabolites/complexes) in environmental matrices, including tissues of organisms. In terms
of toxicity, a critical challenge in the area of ecosystem effects lies in determining the impacts
of materials whose cumulative toxicity is likely to be a manifestation of both physical and
chemical interactions with biological systems. The following is a prioritized list of ecological
research needs:
Test Methods
1. ORD should collaborate with other EPA offices in research on the applicability of
current testing schemes and methods (organisms, endpoints, exposure regimes, media,
analytical methods) for testing nanomaterials in standardized toxicity tests. Both pilot
testing protocols and definitive protocols should be evaluated with respect to their
applicability to nanomaterials. This is a near-term research need.
Environmental Fate/Distribution of Nanomaterials in Ecosystems
2. ORD should take the lead on research on the distribution of nanomaterials in
ecosystems. This is a near-term research need.
Nanotoxicologv andDosimetrv
3. ORD should collaborate with program offices to determine the effects of direct
exposure to nanomaterials or their byproducts, associated with dispersive
nanotechnology uses, on a range of ecological species (fish, inverts, birds, amphibians,
reptiles, plants, microbes). This research should be focused on organisms residing in
ecological compartments that the nanomaterials in question preferentially distribute to,
if any, as identified in 2 above. This research should include evaluation of the uptake,
transport, and bioaccumulation of these materials. This was also identified as a near-
term need.
4. ORD should collaborate with OW and OPPT on research regarding the interaction of
nanomaterials with microbes in sewage treatment plants in sewage effluent and natural
communities of microbes in natural soil and natural water. This is a mid-term need.
5. ORD should take the lead on research aimed at developing structure-activity
relationships (SARs) for nanomaterials for aquatic organisms. This is a mid- to longer-
term need.
6. ORD should take the lead on research on the modes of action for various
nanomaterials for a range of ecological species. This is a long-term research need.
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1 6.3 Recommendations to Address Overarching Risk Assessment Needs
2 One way to examine how a nanomaterial assessment would fit within EPA's overall
3 risk assessment paradigm is to conduct a case study based on publicly available information
4 on one or several intentionally produced nanomaterials. In the past, such case studies have
5 proven useful to the Agency in adjusting the chemical risk assessment process for stressors
6 such as bacteria. For example, assessments of recombinant bacteria need to account for
7 reproduction, and other factors not considered with chemical risk assessments. From such
8 case studies and other information, information gaps may be identified, which can then be
9 used to map areas of research that are directly affiliated with the risk assessment process.
10 This has been done in the past with research on airborne paniculate matter.
11
12 Additionally, a series of workshops involving a substantial number of experts from
13 several disciplines should be held to use available information and principles in identifying
14 data gaps and research needs that will have to be met to carry out exposure, hazard and risk
15 assessments.
16 6.4 Recommendations for Collaborations
17 In addition to the Agency's current collaborations on nanotechnology issues and our
18 ongoing communication activities (see www. epa. gov/nano). we recommend the following
19 additional actions.
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21 • EPA should collaborate with other countries (e.g., through the OECD) on burden-
22 sharing and harmonized approaches for generating data and assessing nanomaterials.
23
24 • OIA should consider potential human health and environmental impacts of
25 nanotechnology, as appropriate within the context of environmental review of trade
26 agreements, as EPA develops its research capacity and regulatory authority in this
27 area.
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29 • ORD's laboratories should put a special emphasis on establishing Cooperative
30 Research and Development Agreements (CRADAs) to leverage non-federal resources
31 to develop environmental applications of nanotechnology (CRADAs are established
32 between the EPA and research partners to leverage personnel, equipment, services,
33 and expertise for a specific research project.)
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35 • OCIR should lead efforts to investigate the possibilities for collaboration with and
36 through state and local government economic development, environmental and public
37 health officials and organizations.
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39 • OP A and program offices, as appropriate, should lead an Agency effort to implement
40 the communication strategy for nanotechnology described at www.epa.gov/nano.
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OPEI (SBO) should lead efforts to engage in information exchange with small
businesses, which comprise a large percentage of U.S. nanomaterial producers.
3 6.5 Recommendation to Convene a Cross-Agency Workgroup
4 The Agency should convene a standing cross-Agency group to foster information
5 sharing regarding risk assessment or regulatory activities regarding nanomaterials across
6 program offices and regions.
7 6.6 Recommendation for Training
8 EPA has begun educating itself about nanotechnology through seminars in the
9 program and regional offices, an internal cross-Agency workgroup (NanoMeeters) with an
10 extensive database, and a Millenium lecture series covering both the administrative and
11 technical aspects of nanotechnology. The SPC Nanotechnology Workgroup also held a
12 "primer" session on nanotechnology to help inform its members during the early stages of
13 development of this paper. While this white paper also provides information for Agency
14 managers and scientists, mere should be ongoing education and training for EPA managers
15 and staff to assist in the understanding of nanotechnology, its potential applications,
16 regulatory and environmental implications, as well as unique considerations when conducting
17 risk assessments on nanomaterials relative to macro-sized materials.
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2 6.7 Summary of Recommendations
3 EPA should begin taking steps to help ensure both that society accrues the important
4 benefits to environmental protection that nanotechnology may offer and that the Agency
5 understands potential risks from environmental exposure to nanomaterials. The Table 7
6 summarizes the recommendations identified above.
7
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Table 7, Summary of Workgroup Recommendations Regarding Nanomaterials
6.1 Pollution Prevention, Stewardship and Sustainability. EPA should engage resources
and expertise as nanotechnology industries form and develop to encourage, develop and
support nanomaterial pollution prevention at its source and an approach of stewardship.
Detailed pollution prevention recommendations are identified in the text. Additionally, the
Agency should draw on the "next generation" nanotechnologies for applications that support
environmental stewardship and sustainability, such as green energy and green manufacturing.
6.2 Research. EPA should undertake, collaborate on, and catalyze research on the various
types of nanomaterials to better understand and apply information regarding their:
i) chemical identification and characterization,
ii) environmental fate,
iii) environmental detection and analysis,
iv) potential releases and human exposures,
v) human health effects assessment, and
vi) ecological effects assessment, and
vii) environmental technology applications.
Specific research recommendations for each area are identified in the text.
6.3 Risk Assessment. EPA should conduct case studies based on publicly available
information on several intentionally produced nanomaterials. Such case studies would be
useful in further identifying unique considerations that should be focused in conducting risk
assessments for the various types of nanomaterials. The case studies would also aid in further
identifying information gaps which can then be used to map areas of research which are
directly affiliated with the risk assessment process.
6.4 Collaboration. EPA should continue and expand its collaborations regarding
nanomaterial applications and potential human and environmental health implications.
6.5 Cross-Agency Workgroup. EPA should convene a standing cross-Agency group to
foster information sharing regarding risk assessment or regulatory activities for nanomaterials
across program offices and regions.
6.6 Training. EPA should continue and expand its activities aimed at training Agency
scientists and managers regarding potential environmental applications and environmental
implications of nanotechnology.
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7.0 References
Aitken, R.J., Creely, K.S., Iran, C.L. 2004. Nanoparticles: An Occupational Hygiene Review.
Research Report 274. Prepared by the Institute of Occupational Medicine for the Health and
Safely Executive, North Riccarton, Edinburgh, England.
Atkinson, R. 2000. Atmospheric Oxidation (Chapter 14), in Boethling, R.S.; Mackay, D.
(eds.), Handbook of Property Estimation Methods for Chemicals, Environmental and Health
Sciences, Lewis Publishers, CRC Press, Boca Raton, FL.
Australia Department of Defence. 2004. The Risk Management Process - Application of
AS/NZS 4360:1999. http://www.defence.gov.aii/cfo/privfin/manual/07.htm
Ball, P. 2005. Nanomaterials Draw Electricity from Heat. Nature Materials Update. 24 March
2005.
Ball, P. 2004. Nanotubes Show the Way to Wind Power. Nature Materials Update. 2
September 2004.
Baron et al., 2004. Exposure to Carbon Nanotube Material: Aerosol Release During Handling
of Unrefined Single Walled Carbon Nanotube Material. J. Toxicol. Environ. Health, Part A,
67:87-107.
Baron, P. A., Maynard, A.D., Foley, M. 2003. Evaluation of Aerosol Release During the
Handling of Unrefined Single Walled Carbon Nanotube Material. NIOSH-DART-02-191
Rev. 1.1, April 2003.
Bekyarova E. et al., 2005. Applications of Carbon Nanotubes in Biotechnology and
Biomedicine. J. Biomedical Nanotechnology 1:3-17.
Bidleman, T.F. 1988. Atmospheric Processes, Wet and Dry Deposition of Organic
Compounds are Controlled by their Vapor-Particle Partitioning. Environ. Sci. Technol. 22(4),
361-367.
Biswas P, Chang-Yu W. 2005 Nanoparticles and the Environment. J. Air & Waste Manage.
Assoc. 55:708-746.
Boethling, R.S., Nabholz, J.V. 1997. Environmental Assessment of Polymers Under the U.S.
Toxic Substances Control Act, Chapter 10. pp. 187-234. in Hamilton, J. D. and R. Sutcliffe
(eds.), Ecological Assessment of Polymers: Strategies for Product Stewardship and
Regulatory Programs. Van Nostrand Reinhold, New York. 345 p.
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Borm, P.J.A., Hreyling, W. 2004. A Need for Integrated Testing of Products in
Nanotechnology, in Nanotechnologies: A Preliminary Risk Analysis on the Basis of a
Workshop, Organized in Brussels on 1-2 March 2004 by the Health and Consumer Protection
Directorate General of the European Commission.
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24 ityfiB&asjx
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1
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Conversation with Hongda Chen. May, 2005. Dr. Chen expressed great interest in nano-
fertilizers, and asked to be kept abreast of any work in this area, though he is not funding it.
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i Appendix A: Glossary of Nanotechnology Terms
2 Aerosol: A cloud of solid or liquid particles in a gas.
3 Array: An arrangement of sensing elements in repeating or non-repeating units that are
4 arranged for increased sensitivity or selectivity.
5 Biomimetic: Imitating nature and applying those techniques to technology.
6 Buckyballs: see fuUerengs
7 Catalyst: A substance, usually used in small amounts relative to the reactants, that modifies
8 and increases the rate of a reaction without being consumed or changed in the process..
9 Dendrimers: artificially engineered or manufactured molecules built up from branched units
10 called monomers. Technically, a dendrimer is a branched polymer, which is a large molecule
11 comprised of many smaller ones linked together.
12 Diamondoid: Nanometer-sizes structures derived from the diamond crystal structure.
13 Electron beam lithography: Lithographic patterning using an electron beam, usually to
14 induce a change in solubility in polymer films. The resulting patterns can be subsequently
15 transferred to other metallic, semiconductor, or insulating films.
16 Engineered/manufactured nanoparticles: Engineered/manufactured refers to those
17 nanoparticles that do not occur naturally but are purposefully made. These are in contrast to
18 incidental particles such as combustion ultrafine particles or occupational fumes like
19 beryllium or welding fumes.
20 Exposure assessment: The determination or estimation (qualitative or quantitative) of the
21 magnitude, frequency, duration, route, and extent (number of people) of exposure to a
22 chemical, material, or microorganism.
23 Fullerenes/Ceo: Pure carbon molecules composed of at least 60 atoms of carbon. Because a
24 fullerene takes a shape similar to a soccer ball or a geodesic dome, it is sometimes referred to
25 as a buckyball after the inventor of the geodesic dome, Buckminster Fuller, for whom the
26 fullerene is more formally named.
27 Intentionally produced nanomaterials: Nanomaterials that do not occur naturally but are
28 purposefully made. These include both deliberate engineering of particles by certain chemical
29 and/or physical processes-(referred to as "bottom-up" production) to create materials with
30 specific properties not displayed in their macro-scale counterparts, as well as the use of such
31 manufacturing processes as milling or grinding ("top-down" production) to produce nano-
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1 sized particles that may or may. These are in contrast to incidental particles such as
2 combustion ultrafme particles or occupational fumes like beryllium or welding fumes.
3 Manufacturing processes: General term used to identify the variety of processes used in the
4 production of the part. Processes may include plastic injection molding, vacuum forming,
5 milling, stamping, casting, extruding, die-cutting, sewing, printing, packaging, polishing,
6 grinding, metal spinning, welding, and so forth.
7 Metallocenes: a compound consisting of a group of atoms bound to a metal, where the group
8 includes two pairs of carbon atoms.
9 Nano-: a prefix meaning one billionth.
10 Nanometer: one billionth of a meter.
11 Nanobiology: A field of study combining biology and physics which looks at how nature
12 works on the nanometer scale, particularly how transport takes place in biological systems.
13 The interaction between the body and nanodevices are studied, for example, to develop
14 processes for the body to regenerate bone, skin, and other damaged tissues.
15 Nanochemistry: A discipline focusing on the unique properties associated with the assembly
16 of atoms or molecules on a nanometer scale. Chemistry dealing with individual molecules
17 where quantum effects can be significant, and new methods of carrying out chemical
18 reactions are possible.
19 Nanodevice: Functional nanoscale components.
20 Nanoelectronics: Electronics on a nanometer scale, whether by current techniques or
21 nanotechnology; includes both molecular electronics and nanoscale devices resembling
22 today's semiconductor devices.
23 Nanomaterial: Materials with basic structure of the nanometer size.
24 Nanometer: one billionth of a meter.
25 Nanoparticle: Free standing nanostructured material, consisting of between a few hundred to
26 hundreds of atoms.
27 Nanoscale: having dimensions measured in nanometers.
28 Nanoscience: the interdisciplinary field of science devoted to the advancement of
29 nanotechnology. ,
30 Nanostructures: structures at the nanoscale; that is, structures of an intermediate size
31 between molecular and microscopic (micrometer-sized) structures.
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1 Nanotechnology: Research and technology development at the atomic, molecular or
2 macromolecular levels, in the length scale of approximately 1-100 nanometer range; creating
3 and using structures, devices and systems that have novel properties and functions because of
4 their small and/or intermediate size; and the ability to control or manipulate on the atomic
5 scale.
6 Nanotube: Tubular structure, carbon and non-carbon based, with dimensions in nanometer
7 regime.
8 Nanowire: High aspect structures with nanometer diameters that can be filled (nanorods) or
9 hollow (nanotubes) and can be made from conducting or semiconducting materials.
10 PMo.i: Paniculate matter less than 0.1 micrometers in diameter
11 PMis: Particulate matter less than 2.5 micrometers in diameter
12 PMio) Particulate Matter less than 10 micrometers in diameter
13 Quantum dot: Semiconductor materials that have typical dimensions between nanometers
14 and a few microns and emit varying colors of light depending on their size and composition.
15 Self-Assembled Monolayers on Mesoporous Supports (SAMMS): nanoporous ceramic
16 materials that have been developed to remove contaminants from environmental media.
17 Self-assembly: The ability of objects to assemble themselves into an orderly structure.
18 Routinely seen in living cells, this is a property that nanotechnology may extend to inanimate
19 matter.
20 Self-replication: The ability of an entity such as a living cell to make a copy of itself.
21 Superlattice: nanomaterials composed of thin crystal layers. The properties (thickness,
22 composition) of these layers repeat periodically.
23
24 Unintentionally produced nanomaterials: Nario-sized particles that occur naturally in the
25 environment, such as viruses or volcanic ash, and nanoparticle byproducts of human activity
26 such as diesel exhaust particulates, occupational fumes like beryllium or welding fumes, or
27 other friction or airborne combustion byproducts.
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i Appendix B: Principles of Environmental Stewardship Behavior
2 What does a good environmental steward do?
3 (based on statements by environmental stewards and others)
4
5 Exceeds required compliance. An environmental steward views environmental regulations
6 only as a floor, not a target.
7
8 Protects natural systems and uses natural resources effectively and efficiently. An
9 environmental steward considers and reduces the household, community, farm or company's
10 entire environmental footprint. A steward safeguards and restores nature at home and
1 i elsewhere. A steward follows the pollution prevention hierarchy of acting first to prevent
12 pollution at its source. A steward uses less toxic, more environmentally benign materials,
13 uses local resources and conserves natural resources whenever possible. A steward reuses
14 and recycles materials and wastes and seeks sustainability.
15
16 Makes environment a key part of internal priorities, values and ethics, and leads bv example.
17 Environmental stewards make decisions through their own volition that will prevent or
18 minimize environmental harm. They anticipate, plan for, and take responsibility for
19 economic, environmental and social consequences of actions. A steward approaches business
20 strategies, policy planning, and life as an integrated dynamic with the environment. A
21 steward acts in innovative ways, using all available tools and creating or adding value. A
22 steward adopts holistic, systems approaches.
23
24 Holds oneself accountable. An environmental steward measures the effects of behavior on
25 the environment and seeks progress. A steward applies an understanding of carrying capacity
26 to measure progress and update objectives to achieve continuous improvement, often using
27 indicators, environmental assessments, and environmental management systems.
28
29 Believes in shared responsibility. An environmental steward recognizes obligations and
30 connections to all stakeholders- shareholders, customers, communities at home and elsewhere.
31 For a company, this means being concerned with the full life cycle of products and services,
32 beyond company boundaries, up and down the supply chain (including consumers and end-of-
33 life). For a community, this means to protect the environment for all members and takes
34 responsibility for effects on downstream air pollution, and effects of wastes disposed
35 elsewhere. A steward operates with transparency. They encourage others to be collaborative
36 stewards.
37
38 Invests in the future. An environmental steward anticipates the needs of future generations
39 while serving the needs of the present generation. Their actions reflect possible changes in
40 population, the economy and technology. A steward guides the development of technology to
41 minimize negative environmental implications and maximize potential environmental
42 stewardship applications. A steward values and protects natural and social capital. They seek
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1 preventative and long-term solutions in community development, business strategy,
2 agricultural strategy, and household plans.
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i Appendix C: Additional Detailed Risk Assessment Information
2
3 Cl Environmental Fate of Nanomaterials - Additional Details on Information
4 Currently Available
5 Cl.l Fate of Nanomaterials in Air
6 Although most nanomaterials do not demonstrate high vapor pressures indicative of
7 volatile chemicals, when released to the atmosphere nanomaterials behave like a gas or vapor
8 demonstrating Brownian motion. Several processes influence the fate of airborne
9 nanomaterials in addition to their initial dimensional and chemical characteristics: the length
10 of time the particles remain airborne, the nature of their interaction with other airborne
11 particles or molecules, and the distance that they may travel prior to removal. The processes
12 important to understanding the potential atmospheric transport of nanosized particles are
13 diffusion, agglomeration, wet and dry deposition, and gravitational settling.
14
15 Particles with aerodynamic diameters in the nanoscale range (<100 nm) follow the
16 basic laws of gaseous diffusion when released to air. The rate of diffusion is inversely
17 proportional to particle diameter, while the rate of gravitational settling is proportional to
18 particle diameter (Aitken et al., 2004).
19
20 Airborne particles are classified by size and behavior into three groups or modes: the
21 coagulation mode (diameters <80 nm), the accumulation mode (diameters >80 nm and <2
22 urn), and the coarse mode (diameters >2 um) (Bidleman, 1988; Preining, 1998; Spumy,
23 1998). Particles in the coagulation mode are short-lived because they rapidly coagulate to
24 form larger particles. Particles in the coarse mode are subject to gravitational settling.
25
26 Particles in the accumulation mode remain suspended in air for the longest time. Their
27 main modes of physical removal from the air are wet and dry deposition. Dry deposition
28 velocities, and in turn particle deposition rates, are at a minimum for particles with diameters
29 of 300-500 nm; larger particles deposit faster due to increased gravitational attraction, and
30 smaller particles deposit faster due to increased Brownian diffusion (Atkinson, 2000;
31 Bidleman, 1988). For example, nanoparticles form naturally from the condensation of gases
32 from combustion (as in forest fires or vulcanism). The initial particles, which are about 10
33 nm in diameter, rapidly coalesce to form aggregates of about 100 nm, which can remain
34 suspended in the air for days or weeks (Royal Society, 2004; Dennenkamp et al., 2002). Wet
35 deposition of particles is dependent on that particle's washout ratio, the ratio of the chemical's
36 concentration in the aqueous phase to its concentration in air. Values of W typical for
37 particle-associated chemicals have been correlated to residence times of about 20 days in air
38 based on a constant precipitation rate of 1 meter per year (Atkinson, 2000).
39
40 Deposited nanoparticles are typically not easily resuspended in the air or re-
41 aerosolized because of the action of van der Waals and other weak forces (Colvin, 2003;
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1 Aitken et al., 2004). For example, in an experiment to test the ready suspension of carbon
2 nanotubes., samples of single-walled carbon nanotubes and samples of fumed alumina were
3 agitated at a variety of speeds and the particle sizes of the resultant aerosol were measured. It
4 was found that the bulk of the nanotubes was aerosolized as clumps greater than 1 |im, and
5 the fraction of suspended particles <0.5 ^m decreased rapidly over time (within 15 minutes).
6 Significant amounts of particles with sizes <100 nm were generated only under vigorous
7 agitation, but the particles were not characterized. For comparison, the fumed alumina was
8 aerosolized at concentrations about 100 times that of the carbon nanotubes (Baron et al.,
9 2003). Carbon nanotubes are known to clump together due to the action of van der Waals
10 forces along the length of the tubes. Because physical particle size is a critical factor affecting
11 the properties of nanomaterials, maintaining particle size during the handling and use of
12 nanomaterials is a priority. Current research is underway to produce carbon nanotubes that do
13 not form clumps either via functionalizing the tubes themselves, or by treatment with a
14 coating or dispersing agent (Royal Society, 2004; Colvin, 2003), so future materials may be
15 more easily dispersed.
16
17 The atmospheric chemistry of nanomaterials has not been described in the literature.
18 Many nanosized particles are reported to be photoactive (Colvin, 2003), but their
19 susceptibility to photodegradation in the atmosphere has not been studied. It is generally
20 assumed (though not always true) that organic compounds are unreactive with respect to
21 oxidants such as hydroxyl radicals when bound to particles in the atmosphere; however no
22 studies have examined the reactivity of the particle itself. Reactivity to atmospheric oxidants
23 such as ozone or photochetnically produced hydroxy radicals will depend on the chemical
24 nature of the nanoparticle, and general statements are not possible at this time. Although not
25 volatile as vapors, nanosized particles can be suspended in the atmosphere long enough for
26 photooxidation to be possible. Nanomaterials are known to readily adsorb a variety of
27 materials, and many act as catalysts. No studies are currently available mat examine how
28 nanosized adsorbants and chemicals sorbed to them might influence their respective
29 atmospheric chemistries.
30 C1.2 Fate of Nanomaterials in Soil
31 The fate of nanomaterials released to soil will vary depending upon the physical and
32 chemical characteristics of the nanomaterial. Nanomaterials released to soil can be strongly
33 sorbed to soil due to their high surface areas, and therefore be immobile. On the other hand,
34 nanomaterials are small enough to fit into smaller spaces between soil particles, and might
35 therefore travel farther than larger particles before becoming trapped in the soil matrix.
36
37 The strength of the sorption of any engineered/manufactured nanoparticle to soil will
38 be dependent on its size, chemistry and the conditions under which it is applied. For example,
39 iron (Fe°) colloids tend to agglomerate and adhere to soil surfaces. Other studies have
40 demonstrated the differences in mobility of a variety of insoluble nanosized materials in a
41 porous medium. Based on their adherence to the model medium, their mobilities were
42 estimated for a sandy soil aquifer. Mobilities (as distance for C/C»nt = 0.1%, where C;nt is the
43 initial aqueous concentration and C is the aqueous concentration at a particular distance from
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1 the initial point) ranged from 14 meters for fullerol to 0.1 meter for Ceo aggregate, anatase and
2 ferroxane. Some interesting contrasts were observed: single walled carbon nanotubes (0.07-
3 1.1 x 80-200 nm) were about 100 times more mobile than Ceo aggregates (aggregate size 160
4 nm); the Ceo aggregates showed the same mobility as anatase (TiC>2, 198 nm) and ferroxane
5 (303 nm); finally, smaller particles of silica (57 nm) were about 10 times more mobile than
6 larger silica particles (135 nm) (Lecoanet et al., 2004). The mobility of the materials
7 investigated in these studies does not appear to be dependent on the velocity of the aqueous
8 solution through the sorbant medium. (Zhang, 2003; Lecoanet and Wiesner, 2004).
9
10 The properties of the soil environment can affect nanomaterial mobility. For example,
11 the mobility of mineral colloids in soils and sediments is strongly affected by zero point of
12 charge (ZPC). Most mineral colloids have a surface charge that depends on pH of the
13 environment. Above ZPC surface is negatively charged, below ZPC it is positive.
14
15 Surface photoreactions provide pathway for nanomaterial transformation on soil
16 surfaces. Humic substances, common constituents of natural particles, are known to
17 photosensitize a variety of organic photoreactions, including those mediated by singlet
18 oxygen, a reactive, excited form of dioxygen. Singlet oxygen photo production occurs on soil
19 and other natural surfaces that are exposed to sunlight. Studies of nanomaterial
20 transformations in field situations are complicated by the presence of naturally occurring
21 nanomaterials of similar molecular structures and size ranges. Iron oxides are one obvious
22 example. Also titanium oxide concentrates in soils from rock form quantitatively, so
23 dependably so .that the titanium concentration ratios in soil to rock often are used to infer how
24 many feet of rock are needed to form each foot of soil.
25
26 More research is needed to assess the mobility of nanomaterials in soils. A side-by -
27 side comparison of nanomaterials with micron-sized or bulk material of the same composition
28 would be useful to assess how the size of the material influences its mobility. Basic research
29 is also needed to determine the mobilities of novel materials that have no corresponding bulk
30 material. An example of this would be fullerenes and nanotubes. Although some
31 comparisons to soot, carbon black, or graphite are possible, fullerenes and nanotubes exhibit
32 novel properties, and it is not well understood how these properties may affect soil adsorption
33 and desorption.
34 C1.3 Fate of Nanomaterials in Water
35 The aqueous solubility/dispersability of nanomaterials will vary depending upon the
36 nanomaterial in question. At nanoscale dimensions, the distinction between a dissolved solute
37 and a suspended colloid is not readily defined. Some functionalized carbon nanostractures,
38 such as fullerols, are claimed to be water soluble, and nanosized particles of water-soluble
39 polymers are being investigated for a variety of uses. Insoluble particles will be subject to
40 diffusion, dispersion, agglomeration, and settling in water. As is the case for airborne
41 particles, waterborne nanoparticles are expected to settle more slowly than larger particles of
42 the same material.
43
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1 Dispersed insoluble nanoparticles can be stabilized in hydrophobic microenvironments
2 provided by naturally-occurring colloids made up of humic acids and other organics, which
3 would also delay settling from the water column. Insoluble materials may also form stable
4 colloidal suspensions in water. For example, researchers at Rice University have reported that
5 although Ceo is insoluble in water, it spontaneously forms aqueous colloids containing
6 nanocrystalline aggregates. Dubbed nano-Ceo or n-Ceo, these aggregates have diameters of
7 about 50 nm and carry a negative charge on their outer surfaces. The size of the aggregates
8 depends on the pH-of the water and the speed of mixing when C«o is introduced to water. The
9 concentration of the suspensions can be as high as 100 ppm, but are more typically in the
10 range of 10-50 ppm. The stability of the particles and suspensions are sensitive to salts
11 content. At salt concentrations typical of groundwater, n-Ceo suspensions are stable for
12 months. In simulated seawater, they sink to the bottom within hours. (CBEN, 2005; Fortner
13 et al., 2005). The researchers also observed that while Ceo will not partition from an organic
14 solution (toluene) into water, n-Ceo does not readily partition from water into toluene. n-Ceo
15 can also become resuspended in water after the original aqueous suspension has been
16 evaporated; however, the conditions (such as the presence of soil) for this experiment were
17 not reported (European Commission, 2004). ^
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19 No studies have been published investigating the sorption of nanomaterials to soil and
20 sediment particles in the water column. One report states that nanosized particles tend to sorb
21 to sediment and soil particles and are immobilized due to their high surface area to mass ratio
22 (Oberdorster et al., 2005). However, the source cited in that paper (Lecoanet and Wiesner,
23 2004) illustrates that the rate of sorption to porous media from aqueous solution depends on '
24 the nature of the particles. The Lecoanet and Wiesner study used artificial mediate mimic soil
25 and sediment environments. Due to their high surface area to mass ratios, nanosized particles
26 have the potential to sorb to suspended soil and sediment particles as described in the
27 Oberdorster paper. Although the rate of removal of engineered/manufactured nanomaterials
28 by sorption has not been investigated, it is likely that various heterogeneous processes on
29 environmental surfaces are important in the fate of nanomaterials. In the case of abiotic
30 processes, both thermal and photochemical reactions in particle/water systems are likely
31 involved in nanomaterial transformations. • As used here, the term "abiotic" refers to
32 processes that do not involve direct participation of metabolically active organisms. By this
33 definition, abiotic processes include reactions involving chemicals of biological origin, such
34 as extracellular enzymes or iron porphyrins.
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36 Certain organic and metallic nanomaterials likely will be reduced in anaerobic
37 sediments. From past studies, it is known that several types of organic compounds are
38 generally susceptible to reduction in anaerobic sediments: chlorinated hydrocarbons,
39 nitroaromatic compounds, N- and O-alkylated organic compounds, azo compounds, and
40 quinones, among others. Complexation by natural organic ligands such as humic colloids can
41 facilitate redox reactions that transform metals in anaerobic sediments, e.g., the reduction of
42 iron oxides in anaerobic sediments. Functional groups in the humic substances such as
43 quinones facilitate reduction by acting as an electron shuttle from reducing substances in the
44 bulk water (see Nurmi et al. 2005 and references therein).
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1 Particles in the upper layers of aquatic environments, on soil surfaces, and in water
2 droplets in the atmosphere are exposed to sunlight. Light-induced photoreactions often are an
3 important fate in such environments. Research has demonstrated environmentally significant
4 abiotic photoreactions involving particle surfaces (Helz et al. 1994). Also, heterogeneous
5 photoreactions on metal oxide surfaces are increasingly being used as a method for drinking
6 water, wastewater and groundwater treatment. Past research has focused on heterogeneous
7 photoreactions of iron oxides that apparently involve direct photolysis of inner sphere surface
8 complexes of iron with various ligands. These photoreactions initially involve the reduction
9 of iron (III) to iron (II). In addition, iron complexes can be reduced by superoxide ions that
10 are produced by photochemical processes in sunlit environments.
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12 Indirect photoreactions involving particles have also received considerable attention
13 during the past few years. Most of this research can be subdivided into two broad areas:
14 reactions involving reactive intermediates produced by surface photolysis, such as
15 semiconductor-type mechanisms, and reactions involving electronically excited surface
16 species. Heterogeneous organic photocatalysis involving particles with semiconducting
17 properties has received considerable attention recently. Semiconductors such as titanium
18 dioxide and zinc oxide have been shown to effectively catalyze both the reductions of
19 halogenated chemicals and oxidation of various other pollutants and heterogeneous photo-
20 catalysis has been used for water purification in treatment systems.
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22 The fate of nanosized particles in wastewater treatment plants is not well characterized
23 in the literature. Wastewater is subjected to multistep processes in treatment plants, including
24 screening to remove debris, gravitational removal of large particulates, combination, and
25 agitation with and digestion by activated sludge, settling, filtration, and chemical treatment
26 (Cla and SOi) to destroy pathogens. Chemicals in a wastewater treatment plant are removed
27 from the effluent via volatilization, sorption to sludge, biodegradation, and in some cases,
28 chemical reaction. The most likely processes to affect nanosized particles are sorption and
29 chemical reaction. The ability of either of these to immobilize or destroy the particles will
30 depend on the chemical nature of the particle and the residence times in each of the
31 compartments of the treatment plant. As noted earlier in the section on soils, the ZPC and
32 thus sorption, coagulation and mobility of mineral colloids is strongly affected by pH. It has
33 been demonstrated that the sorption of different nanomaterials to model soils from aqueous
34 solution can vary considerably (Lecoanet et al., 2004), It is therefore impossible to say that
35 all nanomaterials will be captured by sorption to sludge in wastewater treatment. Current
36 research in this area includes the production of microbial granules that are claimed to remove
37 nanoparticles (fluorescent microspheres, 100 nm) from simulated wastewater (Ivanov et al.,
38 2004). Further research is needed to determine the ability of various nanosized particles to
39 adsorb to activated sludge in order to characterize the fate of nanomaterials in wastewater
40 treatment plants. Nanomaterials that escape sorption may be removed from the effluent via
41 settling. As discussed earlier, the rate of gravitational settling of nanomaterials in fluids,
42 whether the fluid is air or water, will be dependent on particle diameter, and the smaller
43 particles will settle more slowly.
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1 C1.4 Unavailability and Bioaccumulation of Nanomaterials
2 The bioavailability of specific nanomaterials in the environment will depend in part on
3 the particle. Complexation of metallic nanomaterials may have important interactive effects
4 on biological availability and photochemical reactivity. For example, the biological
5 availability of iron, is dependent on its free iron concentrations in water, and the free iron
6 concentrations are affected by complexation or, in the case of metal oxides, by redox
7 transformations. Complexation reduces biological availability by reducing free metal ion
8 concentrations and dissolved iron is quantitatively complexed by organic ligands. Solar UV
9 radiation can interact with these processes by inducing direct photoreactions of the
10 complexes, by enhancing redox reactions between the ligands and metal oxides, or by indirect
11 photoreactions in which photochemically-produced reactive oxygen species react with the
12 complexes.
13 C1.5 Potential for Interactions Between Nanomaterials and Other Organic or Inorganic
14 Contaminants .
15 Engineered/manufactured nanomaterials are being created and studied because their
16 small sizes, high surface areas, and novel electrical properties affect their interactions with
17 other chemicals and with cells, tissues, and organisms. Two of the types of.effects under
18 study for possible exploitation are sorption and reaction.
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20 Cl .5.1 Sorption research- Detailed description of current information
21 Several studies investigating the sorption of pollutants to nanosized materials have
22 recently been reported in the literature.
23 .
24 1. The sorption of naphthalene to Ceo from aqueous solution was compared to activated
25 carbon (Cheng et al., 2004). Not surprisingly, the investigators observed a correlation
26 between the surface area of the particles and the amount of naphthalene adsorbed from
27 solution. Activated carbon with a surface area of about 1000 m2/g had the highest measured
28 solid-water distribution constant of 105'17 mL/g. Large aggregates of C6o (20-50 urn) had a
29 surface area of 0.07-0.17 m2/g, and a distribution constant of 1O2'39 mL/g. Small aggregates of
30 Ceo (1-3 um) were reported to have a surface area >10 times that of the large aggregates, and
31 had a measured distribution constant of 104'28 mL/g. The authors apparently did not
32 investigate "nano-Ceo", crystalline aggregates on the order of 50 nm in diameter.
33
34 2. Nanoparticles made of an amphiphilic PEG-modified polyurethane-acrylate polymer (80 ±
35 15 nm) have been shown to mobilize phenanthrolene (PHEN) from contaminated sandy soil
36 (Tungittiplakom et al., 2004). The particles have the ability to enhance PHEN desorption and
37 transport it in a manner similar to that of surfactant micelles, but unlike surfactants, the
38 nanoparticles do not sorb to the soil surface. In order to be effective, surfactants must be
39 present at concentrations at or above the critical micelle concentration. Sorption to soil
40 reduces the effective aqueous concentration of surfactants and disrupts the formation of
41 micelles. However, the activity of the nanoparticles is not dependent on maintaining a
42 particular concentration, and therefore provides a more stable environment for the
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solubilization of PHEN from soils. In addition, the nanoparticles can be altered to optimize
their affinities for particular pollutants by modifying the chemical identity of the polymer. In
a followup study, the rate of PHEN biodegradation was measured in aqueous media in the
presence and absence of both the nanoparticles and a sandy aquifer soil (Tungittiplakom et
al.s 2005). The presence of the nanoparticles increased the initial rate of mineralization of
radiolabeled PHEN (measured as 14CC>2), both with and without the soil. These studies show
that these nanoparticles not only enhance the mobility of PHEN, but also increase its
bioavailability.
3. Preliminary results report that arsenic irreversibly adsorbs to 15-20 nm magnetite crystals
dispersed in water. The arsenic can then be removed from the water by magnetic attraction of
the magnetite. This system is being investigated as a purification technique for arsenic-laden
drinking water (CBEN, 2005). Another investigator reports that 10 nm magnetite crystals
adsorbs Cr(VI) from wastewater (Hu et al., 2004).
4. The adsorption and desorption of volatile organic compounds (VOCs) from ambient air by
fullerenes has been investigated. In this study, 9 VOCs were adsorbed to fullerene tubes and
later desorbed and recovered with little loss of the adsorbed gas (Chen et al., 2000).
5. Inhalation exposures of benzo(a)pyrene sorbed to ultrafine aerosols of GaaOs (Sun et al,
1982) and diesel exhaust (140 nm) (Sun et al:, 1984) were studied in rats. The studies showed
that when compared to inhalation of pure benzo(a)pyrene aerosols, material sorbed to the
gallium oxide had increased retention in the respiratory tract, and increased exposure to the
stomach, liver, and kidney.
Cl.5.2 Research involving reaction of nanomaterials with environmental contaminants-
Detailed description of current information
Many groups are currently investigating the use of nanomaterials for the destruction of
persistent pollutants in the environment. Some examples are listed below.
Iron (Fe°) is a mild reducing agent, and has been used to dechlorinate halogenated
solvents, such as tetrachloroethylene, in the environment. Nanoscale iron particles have been
demonstrated to be effective in the in situ remediation of soil contaminated with
tetrachloroethylene. The nanosized iron particles were able to flow with the groundwater and
remained active for 4-8 weeks. Reaction times were rapid, with 99% reduction of
tetrachloroethylene occurring in a few days. A wide variety of additional pollutants are
claimed to be transformed by iron nanoparticles in laboratory experiments, including
halogenated (Cl, Br) methanes, chlorinated benzenes, certain pesticides, chlorinated ethanes,
polychlorinated hydrocarbons, TNT, dyes, and inorganic anions such as nitrate, perchlorate,
dichromate, and arsenate. Further investigations are underway with bimetallic nanoparticles
(iron nanoparticles with Pt, Pd, Ag, Ni, Co, or Cu deposits) and metals deposited on nanoscale
support materials such as nanoscale carbon platelets and nanoscale polyacrylic acid (Zhang,
2003).
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1 2. Nanosized clusters of Ceo were shown to generate reactive oxygen species in water under
2 UV and polychromatic light. Clusters with a mean diameter of 100 nm were more active than
3 clusters with a larger diameter of 300 nm (Pickering et al., 2005). Similar colloids have been
4 reported to degrade organic contaminants and act as bacteriocides (Boyd et al., 2005).
5 Fullerol (Ceo(OH)24) has also been demonstrated to produce reactive oxygen species under
6 similar conditions (Pickering and Wiesner, 2005).
7
8 The examples cited in this section illustrate how nanomaterials have been
9 demonstrated to alter the partitioning behavior of chemicals between environmental
10 compartments and between the environment and living organisms. Furthermore, several
11 nanoscale materials are reactive toward chemicals in the environment, generate reactive
12 species, or catalyze reactions of other chemicals. These properties are currently under study
13 for use in waste remediation operations. However, the potential also exists for nanomaterials
14 to affect unforseen changes if released to the environment in large quantities.
15 C2 The Environmental Detection and Analysis of Nanomaterials
16 C2.1 Overview
17 The challenge in detecting nanomaterials in the environment is compounded not only
18 by the extremely small size of the particles of 100 nanometers or less but also by their unique
19 physical structure and chemical characteristics
20
21 Particle analytical techniques can generally be classified as ensemble or single-particle
22 techniques. With ensemble techniques, a signal from an individual particle cannot be
23 isolated. Instead, ensemble techniques receive signals from multiple particles simultaneously.
24 Laser light diffraction is a commonly employed ensemble technique. In contrast with
25 ensemble techniques, single-particle techniques isolate and identify signals from individual
26 particles. Statistical information for groups of particles can be obtained by processing data
27 from many different individual particles. A common example of a single-particle technique is
28 optical imaging combined with image processing to measure and analyze particles. In general,
29 morphological information, such as shape and aspect ratio, as well as surface information,
30 such as texture and roughness parameters, cannot be obtained using ensemble techniques.
31 Only single-particle techniques that look at individual particles can supply such information.
32 Physical parameters for each particle in a set of particles are recorded to generate a statistical
33 distribution for the entire set of particles.
34
35 The following sections describe some of the technologies/methods available for the
36 analysis of nanoscale particles in the environment. The review is subdivided into several
37 sections starting with sampling methods and followed by methods used to measure
38 nanoparticle mass/mass concentrations, surface area, particle count concentration, size,
39 physical structure (morphology), and chemical composition.
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1 C2.2 Sampling
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Aerosol nanomaterials can be collected by sampling technologies that isolate particles
based upon aerodynamic mobility or electrical mobility. The aerodynamic mobility of a
particle is dependent upon the shape, density and size of the particle. For larger size
nanoparticle fractions of 50 to 100 nm, cascade impactors have been use to isolate and collect
nanoparticles based upon aerodynamic mobility. Cascade impactors consist of a collective
series of inertia-based impactors and are limited to fractionating nanometer particles in size
ranges of no less than approximately 50 nanometers (McMurry, 2000). With decreasing
particle size, the lack of mass and inherent diffusion properties of nanoparticles inhibits the
use of inertia-based collection technologies like impactors and cyclones for sample separation
and collection (McMurry, 2000). Studies by Cabada et. al.(2004) and Hughes, et. al. (1998)
employed the use of a cascade impactor (referred to as a micro-oriface uniform deposit
impactor (MOUDI)) to collect nanoparticles in a size range of 56 to 100 nm onto filters for
mass and chemical analyses. The sizes of nanoparticles fractions isolated based upon
aerodynamic properties are referred to as "the aerodynamic diameter." However, in general,
the use of inertia-based sample collection technology for aerosol sampling does not collect
sufficient nanomaterial mass to perform gravimetric analysis or many chemical analysis
methods (like atomic absorption spectroscopy).
Differential mobility analyzers (DMAs) based upon particle electrical mobility are
used to separate and collect aerosol nanometer fractions ranging from 2 to 100 nanometers.
Before entering the DMA chamber, the sub-micron particles from an aerosol sample obtain an
equilibrium-charge distribution resulting in a known ratio of positives, negative and zero
charged particles (Fuch's equilibrium charge distribution). In the DMA the aerosol sample
flows around a negatively charged inner cylinder. The electrical mobility of nanoparticles is
dependent upon particle shape and size. Negatively charged particles are repelled by the inner
cylinder to the outer walls of the DMA. Neutral particles are exited with the excess air.
Positively charged particles are attracted to the negative inner cylinder. The electrical
mobility of the positively charged particles is inversely related to size. Only positively
charged particles within a narrow range of electric mobility have the correct trajectory to exit
the DMA through an open slit. Specific nanoparticle size fractions are separated and exited
out of the DMA by altering the voltage on the negatively charged inner cylinder. The size of
nanoparticles fraction isolated based upon electrical mobility is referred to as the "electrical
diameter." 'Commercial samplers are available that use electrostatic precipitation to collect
particle fractions exiting a DMA directly onto a substrate that can be used for electron
microscopic analyses (TSI, 2005A).
The material composition of the filter/substrate used to collect the nanometer fraction
varies depending upon the type of physical and chemical analyses to be conducted.
Composition materials include nylon, Teflon, quartz fibers and aluminum (USEPA, 2004;
Turpin, 2000). Where trace metals analyses are involved as in the assessment for quantum
dot nanoparticles, high purity filters must be used in order to avoid sample contamination
during trace metal analyses.
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1 For the analysis of soil, water and sediment samples, ultrafiltration (Wu et al., 2001;
2 Wiesner, 2003) and ultracentrifugation (Colfen, 2004) have been used to isolate nanoparticle
3 fractions. In the case of soil, sediment, and turbid water samples, a series of filtrations with
4 progressively smaller filter or membrane sizes can be helpful. However, the effective pore
5 size of the filter can be decreased during filtration by the accumulation of particles, i.e., by a
6 "clogging" effect. This effect depends on the volume of samples as well as the nature and
7 concentration of the particles.
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9 The many challenges of sampling for nanoparticles include the agglomeration of
10 nanoparticles with nanoparticles and other paniculate matter forming agglomerates far greater
11 in size than 100 nanometers. In the case of atmospheric particles, the surface absorption of
12 water and volatile chemicals can affect size separation efforts, as can the loss of semi-volatile
13 nanomaterials due to volatilization during sample collection and/or analysis and the loss of
14 nanomaterials during sampling and analysis due to the development of static charges on the
15 particles.
16 C2.3 Mass Analysis of Atmospheric Particles
17 As stated previously, bulk sampling and mass analysis of aerosol particle between 1
18 and 100 nm is challenging due to the lack of mass and diffusion properties. Success has been
19 noted by Cabada et. al. (2004) who employed the use of an inertia-based impactor to collect
20 nanoparticles between 56 nm and 100 nm onto Teflon filters for analysis using a high-
21 precision microbalance. The actual time of collection required to obtain a sample with
22 sufficient mass for accurate gravimetric measurement (sensitivity of ± 1 ug (McMurry, 2000)
23 will vary depending upon the concentration of nanoparticles in the atmospheric environment
24 being sampled. The accuracy of nanoparticle gravimetric analyses can also be significantly
25 impacted by the amount of moisture occluded to particles and the surface absorption of semi-
26 volatile organic compounds. It must also be noted that in cases where the nanomaterials of
27 interest include chemical complexes that are semivolatile, mass loss can be experienced due
28 to particle volatilization resulting from elevated sample inlet temperatures used to drive off
29 sample moisture and extreme pressure gradients created during collection using impactor-
30 based systems.
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32 Real-time aerosol particle mass concentration analysis instruments have been
33 developed in support of the EPA Air Quality Program (US EPA, 2004 ). These technologies
34 were designed for the'real-time mass analysis of particles in sizes ranging up to 10 microns.
35 These instruments include the TEOM (Tapered Element Oscillating Microbalance, Rupprecht
36 and Patashnick, 2005) and the Continuous Ambient Mass Monitor (CAMM). The detection
37 technologies employed in particle mass analysis instruments include Beta gauges,
38 piezoelectric crystals and harmonic oscillating elements (McMurry, 2000). An assessment of
39 these mass concentration analysis instruments needs to be made as to their applicability to
40 analyzing the mass concentration of nanometer-sized particles. Descriptions of these
41 technologies are available from the 2004 EPA Air Quality Criteria for Particulate Matter
42 (USEPA, 2004).
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1 An approximate sample mass concentration for nanoparticles can be calculated by
2 isolating the desired nanoparticle size fraction of interest, obtaining a particle count
3 concentration, and multiplying by a known or approximate particle density. Available
4 technologies for nanoparticle size fractioning and particle counting are described in the
5 following.
6 C2.4 Size Separation, Number Concentrations, Surface Area and Physical Structure
7 Air particulate analysis technologies have evolved and are capable of analyzing
8 aerosol samples for nano-sized particle concentrations in real time or near real time. These
9 technologies are designed for field use and require minimal or no attention once they are in
10 operation.
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12 Aerosol grab samples are taken through a size-selective inlet where an impactor or a
13 cyclone removes unwanted larger particles based upon inertia properties (Koropchak, J.A. et
14 al., 1999; McMurry, 2000). Particles exiting the particle separation chamber are
15 electrostatically charged. The particles are then passed though a bipolar ion neutralizer that
16 brings the charge level to the aerosol particles to a Fuch's equilibrium charge distribution. At
17 this point only a fraction of the particles retains a positive or negative charge. As explained in
18 section A2.2 on sampling, DMA technology is capable of separating nanoparticle fractions in
19 the 2 to 100 nm range by exploiting the different electrical mobility of various size fractions
20 of nanoparticles.
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22 In order to obtain particle concentration data, the output of the DMA must proceed to
23 a particle-counting instrument One of the most widely used type of instruments for particle
24 counting is the condensation particle counter (CPC), an instrument capable of detecting
25 particles as small as 3 nanometers (Koropchak, J.A. et al., 1999; McMurry, 2000).
26 Condensation particle counters are also referred to as condensation nuclei counters (CNCs) or
27 Aitken Nuclei Counters (ANCs). CPCs operate by supersaturating a vapor (water, isopropyl
28 alcohol, or butyl alcohol) about the particles from an incoming sample stream. This results in
29 the formation of a droplet some 100 to 1000 times larger than the initial particle size. The
30 formed condensate droplets are then passed through an optical detector where the light
31 attenuation is measured, results being reported as a concentration. Hand-held battery -
32 powered CPCs are commercially available at relatively low costs. The supersaturation
33 required to activate particles increases with decreasing particle size. Particles at
34 approximately 3 nanometers in size require supersaturation levels of several hundred percent.
35 At these high supersaturation levels, vapors can undergo self-nucleation resulting in particle
36 counting errors (McMurry, 2000). Another technology used for particle counting is a cloud
37 condensation counter (CCN). In contrast to CPCs, cloud condensation counters use only
38 water as the vapor generation fluid and are operated at supersaturation levels much lower than
39 CCN. CCN techniques are capable of detecting particles down to 40 nanometers (McMurry,,
40 2000).
41 More sophisticated instruments are commercially available that combine DMA with
42 particle counting technology into one instrument. These instruments, which are referred to as
43 scanning mobility particle size analyzers (SMPS), not only provide particle-counting data but
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1 also measure aerosol particle size distribution from 10 nm to several hundred nanometers.
2 Figure Al provides a general schematic of the basic components of an SMPS. As stated
3 previously, only particles within a narrow electrical mobility range and in turn size, are
4 focused by the DMA onto an open slit exiting the DMA. From the exit slit, the particles flow
5 - into the CPC where they are counted. The approximate time for one scan (DMA set at a single
6 negative potential) is a few minutes. This is the time needed to provide a count for the total
7 number of particles at a certain particle size (as defined by electrical mobility). Additional
8 particle size fractions can be quantified on a fraction-by-fraction basis by changing the
9 electrical potential of the DMA thereby focusing the traj ectory of another particle size onto
10 the open slit leading to the CPC.
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12 A fast mobility particle sizer spectrometer (FMPS) (TSI, 2005B) has the ability to
13 measure the size distribution and concentration of nanoparticles in real time. Where the •
14 SMPS is limited to a single scan every three minutes at one electrical potential, the FMPS, by
15 using an array of electrometers as charged particle detectors, can simultaneously assess the
16 concentration of nanoparticles in multiple size ranges within seconds.
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18 Optical particle counters (OPCs) using lasers as light sources can detect nanoparticles
19 down to approximately 50 nanometers (McMurry,2000). These technologies use a
20 photodetector to measure the amount of scattered light by individual particles. The
21 photodetector produces a voltage pulse based upon the scattered light that is proportional to
22 particle size. The relationship between voltage pulse and particle size is dependent upon
23 appropriate calibration curves. Accuracy of these techniques is challenging if the OPC is not
24 calibrated using particles of similar physical properties (shape, refractive index and
25 morphology). '
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27 Aerosol time of flight mass spectrometers (ATOFMS) can provide aerodynamic
28 particle size characterization in near real time for particles as small as 10 nm (Chow 2002).
29 In some designs, a two laser system is employed to access particle velocity which in turn is
30 correlated to particle size (TSI, 2005C).
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32 Another technology for assessment of the size of particles in an aerosol stream
33 involves the use of diffusion batteries. They are simple and rugged in design and can be used
34 in hostile environments such as in-stack sampling (McMurry, 2000). Diffusion batteries are
35 designed on the principal that as nanoparticle sizes decrease, the rate at which they deposit on
36 nearby surfaces increases. With diffusion batteries, aerosol flows through a series of fine
37 capillaries or fine wire-mesh screens where fine particulates are deposited on the surfaces.
38 Based upon the rate of decay in aerosol concentration observed through the series of
39 capillaries or screens, a particle size distribution can be calculated.
40
41 ' For water samples, particle size analysis of nanoparticles can be performed in situ by
42 Dynamic Light Scattering (DLS) or Photon Correlation Spectroscopy (PCS). DLS uses
43 scattered light to measure the diffusion rate of particles. Particle size is deduced from
44 observed particle diffusion rates.
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1 The technologies described above, although sensitive to the detection of particles only
2 a few nanometers in size, are limited by their inability to distinguish single nanoparticles from
3 a particle that consists of an agglomeration of smaller particles. In addition, there is a great
4 deal of interest in the correlation of human toxicity and exposure to nanoparticle surface area
5 versus nanoparticle number concentration and mass concentrations. Technology is available
6 that provides data relative to total nanoparticle surface area The Epiphaniometer is a device
7 that may be applicable in assessing accurate particle sizes at the nanometer level (Aitken et.
8 al., 2004). The Epiphaniometer passes aerosol samples through a charging chamber where
9 lead isotopes created from the decay of actinium attach to particle surfaces. The particles are
10 then passed through a capillary and onto a collecting filter. The amount of radioactivity
11 measured in the collected sample is proportional to the amount of surface area allowing for an
12 assessment of particle size. For a set mass, the smaller the particle size, the greater the
13 surface area. More recently, the development by TSI of a nanoparticle surface area monitor
14 based upon the diffusion charging of particles followed by electrometer detection provides
15 data that correlates with the deposition of airborne nanoparticles in human respiratory systems
16 (TSI, 2005D). These real time analyses are capable of assessing particles in the 10 nm to 1000
17 nm range.
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19 For air, water, sediment or soil samples collected onto a filter "or substrate, the physical
20 characterization of nanoparticles on a particle-by-particle basis can be obtained through the
21 use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM)
22 techniques (Kocum;et al, 2000; Lin et al., 2002; Nurmi et al., 2005) These methods can
23 provide detailed particle size, shape and structure, information that can be used to identify the
24 type of nanoparticles in question (i.e. fullerenes, quantum dots, nanowires, etc.,). Samples.are
25 collected directly onto or re-deposited onto substrates supported by the SEM or TEM
26 instrumentation. Sample particle loading must be controlled in order for effective analysis.
27 In contrast to automated particle size aerosol characterization technologies like SMPS and
28 FMPS, electron microscopic analyses are expensive, require sample collection and
29 preparation and do not provide real-time data. However, in contrast to automated particle
30 characterization technologies, both SEM and TEM provide definitive information concerning
31 the physical characterization of nanoparticles. Physical structure and size characterization of
32 single-particles can also be accomplished using a relatively new technology, atomic force
33 microscopy (AFM) (Sgro, L. A., 2003). AFM uses the interaction of van der Waals forces
34 between a microscopic probe tip and the nanoparticles in question lying on a substrate. AFM
35 information includes the height and topology of the nanoparticle. Fluorescence techniques
36 also can be used to characterize nanomaterials. Naturally-occurring organic colloids can be
37 characterized by excitation-emission matrix (EEM) fluorescence spectroscopy (Zepp et al.,
38 2004). Moreover, the fluorescence techniques have been used to characterize nanoparticles of
39 cadmium sulfide (Wang et al., 2002).
40 C2.5 Chemical Composition
41 Instruments have been developed by academia and commercial entities that along with
42 particle size, provide chemical profiles of nanometer aerosol particles in near real time
43 (Chow, 2002). Samples are taken directly from the atmosphere and analyzed for particle size
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v
1 and particle composition with no additional sample preparation by the analyst. Aerosol time
• 2 of flight mass spectrometers (ATOFMS) are capable of analyzing single particles with sizes
3 as low as 10 nanometers (Chow, 2002, TSI2005 C). In some designs, a two laser system is
4 employed to access particle velocity which in turn is correlated to particle size. Lasers are
5 also used to ionize the particles. The ionized particles then travel to a mass spectrometer for
6 ion characterization. Some instruments employ a bipolar ion detector where both positive and
7 negative ion mass spectra are obtained to characterize the chemical composition of the
8 particle based on detected inorganic and organic chemical fragments from the particle.
9 Portable ATOFMS instruments are commercially available for indoor-air quality monitoring
10 (TSI,2005C).
11
12 For off-line single-particle chemical analysis of collected samples', laser microprobe
13 mass spectrometry (LAMMS) can provide chemical composition information including trace
14 metals and organics analyses. Electron microscopy techniques like scanning TEM with
15 energy dispersive x-ray diffraction (TEM EDX) are also capable of providing single particle
16 chemical profiles on collected samples. An advancement in scanning TEM technology called
17 high angle annular dark field (HAADF) TEM EDX has proven to be an excellent tool for the
18 detection and analysis of nanoparticles containing metals, metals characteristic of quantum
19 dots (Utsunomiya, Swing 2003).
20
21 As stated previously, the information available from the bulk analysis of
22 nanomaterials from environmental samples has limitations when one is trying to identity for a
23 specific nanomaterial. For ensemble techniques signals generated by nanoscale materials that
24 are not of interest can mask or augment the signals of nanomaterials of interest resulting in
25 inadequate or erroneous data. Also, because of the lack of mass and diffusion properties of
26 nanomaterials, depending on the specific nanoparticle size fraction being analyzed, particle
27 concentration, and where applicable, sampling time, the available mass collected of the
28 nanoparticle of interest may not be sufficient to use the technologies described below.
29
30 For the bulk analysis of metals from particulate samples collected from air, water, soil
31 and sediment matrices, an array of analytical techniques are available. For samples in the
32 solid state, chemical profiles can be obtained using energy dispersive X-ray fluorescence
33 (EDXRF), proton induced X-ray emission spectroscopy (PIXE), and total X-ray reflection
34 fluorescence (TRXRF) (Wilson 2002). Metal concentrations in water samples or acid-
35 digested filters/substrates used to collect nanoparticles can be measured using graphite
36 furnace atomic absorption spectrophotometry (GFAA) or, when higher concentrations are
37 present, by inductively-coupled plasma-atomic emission spectrophotometry (ICP-AES) or
38 inductively-coupled plasma mass spectrometry. High-resolution differential surface plasmon
39 resonance (SPR) sensors have also been developed for analysis of heavy metals such as gold,
40 copper and nickel (Forzani et. al. 2005). Less expensive techniques are available for
41 measuring certain metals at low concentrations. A chemiluminescent technique can measure
42 iron concentrations at the nanomolar level, for example (King et al 1995).
43
44 In the analysis for carbon-based nanoparticles like fullerenes, the distinction of
45 carbon-based nanoparticles as "organic" (OC) versus "elemental" (EC) is important as a part
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1 of the chemical characterization process. The general distinction of organic carbon versus
2 elemental as well as carbonate nanomaterials can help support the identification of
3 nanomaterials of concern. Bulk carbon-type analytical techniques applicable to collected,
4 nanoparticle samples are available. These methods include both wet chemistry techniques
5 involving the acidification to convert carbonates to carbon dioxide and automated thermal
6 analysis techniques to help distinguish organic versus elemental carbon (Wilson 2002).
7 As described above, real time analysis of single-particles for organic composition (like
8 fullerenes) can be done using an aerosol time of flight mass spectrometer (ATOFMS). Laser
9 microprobe mass spectrpmetry (LAMMS) is capable of providing single particle off-line
10 organic analysis.
11
1 2 For the analysis of organic nanomaterials in samples of water, sediment or soil, a
13 procedure similar to the following can be used. Methods for trace organic analyses are
14 available from EPA (USEPA 2005a) and other sources. Samples are analyzed directly
15 (usually not possible) or are extracted. Sometimes an appropriate internal standard is added to
16 the sample before it is extracted. Extraction procedures are:
17 '
18 (a) Water- In the case of water, the techniques of liquid/liquid extraction (water extracted by
19 some organic solvent that is immiscible with water) or a form of solid phase extraction are
20 typically used. Solid phase extraction is the presentation of an adsorbent such as polystyrene
21 divinylbenzene in a convenient vehicle for the extraction of analytes from water. The water
22 sample flows through the adsorbent where the analyte of interest absorbs to the solid phase
23 absorption bed. A solvent is required to flush the analytes from the adsorption bed.
24
25 (b) Sediments or soils - The most widely used extraction tool for sediments or soil is 1he
26 Soxhlet system. In this technique a solvent mixture is boiled to produce a vapor that is then
27 condensed on a condenser and dripped onto an extraction thimble filled with sample. Once the
28 thimble is filled with solvent, the solvent flushes over into the boiling region and the process
29 repeats. This extraction process may involve procedures designed to speed it up or render it
30 more efficient, e.g. accelerated solvent extraction, temperature-pressure-assisted solvent
31 extraction, supercritical fluid extraction, SoxTec extraction, sonication extraction, and
32 shakeout extraction.
33
34 Once the trace organic has been extracted into an organic solvent, it usually is cleaned
35 up (e.g., by gel permeation chromatography and silica gel) to remove substances that can
36 interfere with the analysis. Sometimes an appropriate internal standard and calibration curves
37 are used. Then the extract usually is analyzed using a technique that separates the organic
3 8 compound of interest from other interfering substances that may be included in the extract.
39 Many separation techniques work similarly by having the mixture start at the beginning of a
40 column of separating material and components of the mixture exit the column one at a time as
41 some flowing material (liquid or gas) helps to move them through the column. Commonly
42 used separation techniques are Gas Chromatography (GC), High Performance Liquid
43 Chromatography (HPLC), and Capillary Electrophoresis (CE). The analysis also requires
44 detection of the trace organic substance after separation. Mass Spectrometry (MS) is. a widely
45 used detection system, and Mass Spectrometry/Mass Spectrometry (MS/MS), and High
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1 Resolution Mass Spectrometry (HRMS) also are now being widely used. Other less
2 expensive (but less specific) detectors for gas chromatography include electron capture,
3 flame, flame photometric, and limited-mass-range-scan detectors and HPLC can be coupled
4 with ultraviolet-visible, diode array and fluorescence detectors. Detector responses depend on
5 the nature of the organic analyte. Fullerenes are one common class of organic nanomateriais
6 that can be measured using mass spectral techniques (Kozlovski et al. 2004). Matrix-assisted
7 laser desorption/ionization mass spectral analysis is currently considered to be among the
8 most sensitive techniques.
9 C2.6 Analytical Technology Needs
10 As described in the proceeding sections, technologies do exist capable of detecting
11 nanomateriais in environmental samples. However, there are analysis related areas in need of
12 significant research and development. Reference materials need to be developed along with
13 application methodologies for nanoparticle that may pose significant health and
14 environmental risks. These reference materials will allow one to access the accuracy of the
15 analyses being conducted for nanomateriais. Surrogate materials must be made available to
16 access matrix effects like sequestration during sample preparation. Surrogates are also needed
17 to access degrees of particle agglomeration and the loss of semi-volatile nanoparticle fractions
18 during particle separation and analysis processes due to volatilization as well as adhesion to
19 vessel walls due to static and or other molecular forces. Standards methods of analysis need
20 to be developed for both sample analysis and sample preparation techniques. In particular,
21 sample preparation techniques need to be developed for bulk and single-particle analyses
22 (qualitative and quantitative) of nanomateriais in water, sediment and soil matrices. These
23 methods include the development of solid-phase column extraction techniques specific to the
24 extraction of the nanoparticle of interest The techniques presented for definitive single
25 particle characterization like TEM EDX are labor intensive and require expensive
26 instrumentation. A future alternative may well be the development of what is termed by
27 BASF as chemical force microscopy or CFM (Iden, 2002). CFM utilizes cantilever probes
28 that can be specifically designed to detect for the nanoparticles of interest. This technology
29 could possibly provide real-time qualitative and quantitative detection of rianoparticles of
30 interest for all matrices at a fraction of the cost of the technologies currently available.
31 Perhaps nanotechnology is an answer unto itself when it comes to the rapid and accurate
32 detection and analysis of nanomateriais in the environment.
33
34 Table Cl. Partial list of techniques available for the analysis of nanoparticles
TECHNIQUES
Aerosol Time of Flight Mass
Spectrometer (ATOFMS)
CHARACTERISTICS
Ensemble technique
Near real time aerosol analysis
Analysis of particles down to 1 0 nm in size
Potential inorganic and organic analysis
Potential particle size analysis
Single particle technique
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TECHNIQUES
Atomic Force Microscopy (AFM)
Cloud Condensation Nuclei Counter
(CNC)
Condensation Particle Counter (CPC)
Also referred to as condensation
nucleus counter (CNC) or Aitken
Nuclei Counter (ANC).
Differential Mobility Analysis (DMA)
Dynamic Light Scattering (DLS)
Energy Dispersive X-ray Fluorescence
(EDXRF)
Laser Microprobe Mass
Specttometry (LAMMS)
Scanning Electron Microscopy (SEM)
Scanning Mobility Particle Sizer (SMPS)
CHARACTERISTICS
Compositional and crystallographic information
can also be obtained
Can be performed in liquid or gas media
Typical range: Inm to 8mm
Ensemble technique
Measures concentration of particles converted to
cloud droplets
Detects particles as small as 40 nm
Uses supersaturated atmospheres consisting of
water
Ensemble technique
Measures total particulatele counts
Detects particles as small as 3nm
Uses supersaturated atmospheres consisting of
water or isopropanol or butanol
Ensemble technique
DMA creates monodisperse stream of particle;
relies on mass-based charge to isolate particles
within a specified size range
Applicable to particles down to 2 nm
• Ensemble Technique
• Commonly used in chemical and
pharmaceutical industries
• Relies of Brownian motion of particles in a
liquid medium to determine particle size
• Typical range 1 nm to 5 um
Ensemble technique
Provides qualitative and quantitative analysis for a
series of heavier elements (metals)
Analysis of sample on a collected substrate.
Single particle technique
Compositional inorganic and organic information
Performed on nanoparticles collected on a
substrate
Single particle technique
Compositional information can be obtained
Requires high-vacuum conditions
Typical range: 50nm to 1cm
• Combines DMA with particle counting technology
• Relies on mass-based charge to isolate particles
within a specified size range
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1
2
3
4
5
TECHNIQUES
Transmission Electron Microscopy
(TEM)
CHARACTERISTICS
• Typical range: >10nm
• Single particle technique
• Compositional and crystallographic information
can also be obtained.
• Requires high-vacuum conditions
• Typical range: 5nm to 500um
C3 Human Health Effects Assessment - Additional Details on Studies Currently
Available
6 C3.1 Toxicity and Hazard Identification of Engineered/manufactured Nanomaterials
7 Studies assessing the role of particle size on toxicity have generally found that
8 ultrafine or nanosize range (<1 OOnm) particles are more toxic on a mass-based exposure
9 metric when compared to larger particles of identical chemical composition (Oberdorster et al.
10 1994; Li et al. 1999; Hohr et al. 2002). However, studies conducted by Lam et al. (2004) and
11 Warheit et al.(2004) examining the pulmonary toxicity of carbon nanotubes, have provided
12 evidence that engineered/manufactured nanomaterials can display unique toxicity that cannot
13 be explained by differences in particle size alone. For example, Lam reported single walled
14 carbon nanotubes (SWCNTs) displayed greater pulmonary toxicity than carbon black
15 nanoparticles. Similar results have been obtained from comparative in vitro cytotoxicity
16 studies which have reported the hierarchy of toxicity of engineered/manufactured carbon-
17 based nanomaterials to be: SWCNT>MWCNT10>C60 fullerene based on an equal mass dose
18 metric (Jia et al., 2005). Shvedova et al. (2005) reported unusual inflammatory and fibrogenic
19 pulmonary responses to SWCNT suggesting that SWCNTs may injure the lung by new
20 mechanisms. The investigators of these studies speculated that nanoparticle surface area,
21 surface reactivity, or shape may regulate the toxicity of carbon nanomaterials. Sayes et al.
22 (2004) has shown that surface hydroxylation of fullerenes dramatically decreased their in
23 vitro cytotoxicity. In contrast, surface hydroxyl groups of nano-TiCh are responsible for
24 their photoelectronic and photocatalytic properties and may also be responsible for their in.
25 vitro photocatalytic cytotoxicity (Cai et al., 1992; Sclafani and Herrmann 1996). Nemmar et
26 al. (2003) demonstrated that surface charge was responsible for the pulmonary inflammatory
27 and vascular thromobotic effects of polystyrene nanoparticles.. In vitro toxicological studies
28 performed on quantum dots demonstrated that photoactivation and surface oxidation produced
29 alterations in the surface chemistry of these nanomaterials leading to the release of Cd and
30 subsequent hepatic cytotoxicity (Derfus et al. 2005). These studies demonstrate that
31 nanoparticle toxicity is extremely complex and multi-factorial potentially being regulated by a
32 variety of physicochemical properties such as size, shape, as well as surface properties such as
33 charge, area, and reactivity.
34
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1 C4 Ecological Effects - Additional Analyses
2 C4.1 Additional detailed analyses regarding the potential uptake and accumulation of
3 nanomaterials in aquatic ecosystems
4 For consideration of potential effects in aquatic systems, it may be useful to sort
5 nanosized particles into four classes, by their charge: neutral, anionic (negatively charged),
6 cationic (positively charged), or amphoteric (having characteristics of both and acid and a
7 base).
8
9 Based on general chemical behavior, it is expected that neutral nanosized particles
1 0 based on carbon or silicon will have very high octanol-water partition coefficients (log K<,w
1 1 values) and very low water solubilities, and will have great affinity for organic matter in the
12 environment. These neutral nanoparticles may preferentially bind to organic matter rather
13 than to gills because organic matter has a much larger surface area and is more prevalent in
14 the environment than are aquatic organisms. Research verifying this hypothesis for the
15 variety of nanomaterials is needed.
16
1 7 Anionic nanoparticles would be expected to be poorly absorbed by gill and
1 8 gastrointestinal (GI) tract membranes since they would be repelled by the anionic charges
19 commonly associated with these surfaces. Research verifying this hypothesis for a range of .
20 nanomaterials is needed.
21
22 Cationic and amphoteric particles may bind to membranes because of their cationic
23 charge and to damage these membranes. However, this would be only be expected occur after
24 the total organic carbon (TOC) in the environment was bound and neutralized. This
25 mitigating effect of TOC in natural water can be significant for conventional chemicals and
26 may be important for the effects of nanomaterials in aquatic ecosystems. For example, for
27 specific non-nano-sized chemicals, 10 mg TOC/L decreases fish toxicity 100-fold over
28 similar exposures at 2 mg TOC/L. The median TOC concentration in US surface waters is
29 6.8 mg TOC/L based on the Office of Water STORET database (Boethling and Nabholz,
30 1997). Therefore, mere is likely to be significant attenuation of toxicity from cationic and
31 amphoteric nanoparticles to aquatic organisms exposed in natural waters. Any laboratory-
32 based toxicity studies need to accommodate the potential impact of TOC on nanoparticle
33 toxicity. Based on the expected effects of TOC in the aquatic environment, effects values
34 may require a TOC adjustment factor when implemented for regulatory purposes (Boethling
35 and Nabholz, 1997). As noted above, research verifying the mitigating effects of TOC on
36 nanomaterials is needed for a range of nanomaterials.
37
38 Science Daily Magazine (March 2005) reported that nanosized cationic dendrimers
39 punch nanoscale holes in cell membranes in a manner analogous to polycationic polymers,
40 while neutral polymers did not damage membranes. Engineering the dendrimer surface to
41 make the dendrimers neutral may prevent or reduce this damage. Constituents of natural
42 waters, such as TOC, may possibly also mitigate this effect
43
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1 It is likely that nanomaterials can accumulate and biomagnify in aquatic organisms.
2 As an example of a conventional chemical in the nanometer size-range, 1,2,5,6,9,10-
3 hexabromo-cyclododecane (molecular weight 642, cross-sectional diameter 1.08 nm, log Kow
4 7.8 (Cash and Nabholz, 2002)) has a measured log bioconcentration factor in rainbow trout-
5 whole body of 13,085 from a mean water concentration of 0.18 ng/L (OPPTS data, note this
6 bioconcentration factor was not measured at steady state). However, this chemical is not an
7 engineered or manufactured nanomaterial; the behavior of these nanomaterials may or may
8 not be the same. Studies are needed to develop predictive relationships for different classes of
9 nanoparticles.
10 C4.2 Aquatic ecosystem effects
11 Toxicity studies for carbon black and suspended clay particles suggest that some
12 suspended nanosized particles in the aquatic environment will have low toxicity to aquatic
13" organisms (Table C2). Predictions are based on SARs for polynonionic polymers, SARs for
14 neutral organic chemicals, SAR-nearest analog analysis for fullerenes, carbon black, and
15 suspended clay particles.
16 Table C2 , .
17 Predicted (P) and measured (M) toxicity values in mg/L (ppm) either in terms of soluble
18 material or suspended particles
19
20
21
22
23
24
25
26
27
28
Organism End point
Zebra fish 96-hLC50 > 800
Fish 96-hLC50 > 1000
Daphnid 24-hLC50 > 4500
Daphnid 48-hLC50 > 1000
Algae 72-hEC50 > 8000
Algae 96-hEC50c. > 1000
sewage microbes 3-hEC50 > 640
Fish ChV > 80
Fish . ChV > 100
Daphnid ChV > 100
Daphnid ChV 500
Algae ChV > 8000
Algae ChV° > 300
Sewage microbes ChV > 640
ACR = acute-to-chronic ratio
P/M
M
M
M
M
M
M
MS,N
P
P
P
P
M
M
MS,N
Material
carbon black
clay
carbon black
clay
carbon black
clay
carbon black
carbon black
clay
clay
carbon black
carbon black
clay
carbon black
ChV = chronic value = geometric mean of lowest-observed-effect concentration (LOEC)
concentration (NOEC)
C = based on inhibition of biomass by cells/mL
M = measured toxicity value
N = nominal concentration
source
Rl
Rl
Rl
Rl
ZF/ACR10
F96/ACR10
D48/ACR10
Rl
O2
GAEC50/4
Rl
and no-observed-effect
O2 = inhibition of oxygen consumption or inhibition of respiration
P = predicted toxicity value using SAR
SAR = structure-activity relationship
S = static method
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3
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5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Predictions: SAR chemical class = polymer-nonionic->C84 nanotube; MW>10 000; log Kow» 8 (P); solid
with melting point link but S « 0.001 mg/L at 25 C (P) but particles can be suspended in water > 100.0 mg/L
(P);pH7.
Effective concentrations (EC) are based on 100% active ingredients and nominal concentrations, water hardness
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