Meeting Summary Report

Material Characterization of Nanoscale Materials

(September 6 and 7, 2007

Peer Consultation Meeting)

Prepared for:

**U.S. Environmental Protection Agency**

Office of Prevention, Pesticides and Toxic Substances

1200 Pennsylvania Avenue, NW

Washington, D.C. 20460

Prepared by:

**Eastern Research Group, Inc.**

14555 Avion Parkway

Suite 200

Chantilly, VA 20151-1102

October 15, 2007

EPA Contract No. EP-W-05-014

Work Assignment 3-06

**TABLE OF CONTENTS**

Page

[[1.0]{.smallcaps} [Introduction 1-1]{.smallcaps}](#introduction)

[1.1 Panel Members 1-1](#panel-members)

[1.2 Meeting Background and Purpose
1-2](#meeting-background-and-purpose)

[2.0 Day One Summary (September 6, 2007)
2-1](#day-one-summary-september-6-2007)

[2.1 Introductions 2-1](#introductions)

[2.2 General Discussion 2-3](#general-discussion)

[2.3 Session 1: Discussion -- Types of Nanoscale Materials &\
Their Structure and Chemical Composition
2-4](#session-1-discussion-types-of-nanoscale-materials-their-structure-and-chemical-composition)

[2.3.1 Question 1: Are there any other significant categories, based on
structure and chemical composition, that should be included in this
discussion because they are substantially different from the categories
mentioned (e.g., hybrids, self- assembly devices, others)?
2-4](#question-1-are-there-any-other-significant-categories-based-on-structure-and-chemical-composition-that-should-be-included-in-this-discussion-because-they-are-substantially-different-from-the-categories-mentioned-e.g.-hybrids-self--assembly-devices-others)

[2.3.2 Question 2: For the different categories of nanoscale materials,
what is the current state of knowledge about structure and\
chemical composition?
2-7](#question-2-for-the-different-categories-of-nanoscale-materials-what-is-the-current-state-of-knowledge-about-structure-and-chemical-composition)

[2.3.3 Question 3: Can structures and chemical composition be correlated
to specific properties and is this correlation\
quantifiable? Chemical Identification Elements (e.g.,\
which ones? for which substances? test methods?)
2-9](#question-3-can-structures-and-chemical-composition-be-correlated-to-specific-properties-and-is-this-correlation-quantifiable-chemical-identification-elements-e.g.-which-ones-for-which-substances-test-methods)

[2.3.4 Question 12: How important are impurity identity and\
impurity levels to the understanding and characterization of nanoscale
materials?
2-10](#question-12-how-important-are-impurity-identity-and-impurity-levels-to-the-understanding-and-characterization-of-nanoscale-materials)

[2.3.5 Question 13: Are there routine purification procedures that can
effectively control or remove impurities, when desirable, for certain
classes of nanoscale materials?
2-11](#question-13-are-there-routine-purification-procedures-that-can-effectively-control-or-remove-impurities-when-desirable-for-certain-classes-of-nanoscale-materials)

[2.4 Session 2- Discussion: Physical Chemical Properties
2-11](#session-2--discussion-physical-chemical-properties)

[2.4.1 Question 4: Which physical-chemical properties are\
relevant to nanoscale materials and how? Which are\
known or reasonably ascertainable and which have\
data gaps?
2-11](#question-4-which-physical-chemical-properties-are-relevant-to-nanoscale-materials-and-how-which-are-known-or-reasonably-ascertainable-and-which-have-data-gaps)

[2.4.2 Question 5: Are there properties that would have little or no
relevance under the NMSP?
2-13](#question-5-are-there-properties-that-would-have-little-or-no-relevance-under-the-nmsp)

[2.4.3 Question 6: Which properties are associated with\
aggregated or agglomerated nanoscale materials, as opposed to properties
that are inherent to the material regardless of\
physical form?
2-14](#question-6-which-properties-are-associated-with-aggregated-or-agglomerated-nanoscale-materials-as-opposed-to-properties-that-are-inherent-to-the-material-regardless-of-physical-form)

[2.4.4 Question 7: Are there routine manipulations of nanoscale
materials that result in physical-chemical properties changes or other
defining characteristics (e.g., surface modifications of nanotubes to
enhance solvent dispersibility)?
2-14](#question-7-are-there-routine-manipulations-of-nanoscale-materials-that-result-in-physical-chemical-properties-changes-or-other-defining-characteristics-e.g.-surface-modifications-of-nanotubes-to-enhance-solvent-dispersibility)

[3.0 Day two Summary (September 7, 2007)
3-1](#day-two-summary-september-7-2007)

[3.1 Session 2 - Discussion: Physical Chemical Properties (Continued)
3-1](#session-2--discussion-physical-chemical-properties-continued)

[3.1.1 Question 8: How should physical-chemical property data be
prioritized for the NMSP? Based on availability, effect\
(toxicity or exposure criteria), or other factors?
3-1](#question-8-how-should-physical-chemical-property-data-be-prioritized-for-the-nmsp-based-on-availability-effect-toxicity-or-exposure-criteria-or-other-factors)

[3.2 Session 3 - Discussion: Nanoscale Manufacture and Processing
3-2](#session-3---discussion-nanoscale-manufacture-and-processing)

[3.2.1 Question 9: What are the common processes used to\
manufacture nanoscale materials?
3-2](#question-9-what-are-the-common-processes-used-to-manufacture-nanoscale-materials)

[3.2.2 Question 10: How are processes used to produce specific
characteristics or properties?
3-3](#question-10-how-are-processes-used-to-produce-specific-characteristics-or-properties)

[3.2.3 Question 11: Which methods reduce particle size but do\
not result in property changes? Which methods reduce\
particle size and result in property changes?
3-3](#question-11-which-methods-reduce-particle-size-but-do-not-result-in-property-changes-which-methods-reduce-particle-size-and-result-in-property-changes)

[3.3 Session 4 - Discussion: Methodologies for Characterizing\
Nanoscale Materials Analytical Methods
3-4](#session-4---discussion-methodologies-for-characterizing-nanoscale-materials-analytical-methods)

[3.3.1 Question 14: Are validated methods available for the\
different categories of nanoscale materials?
3-4](#question-14-are-validated-methods-available-for-the-different-categories-of-nanoscale-materials)

[3.3.2 Question 15: Are there techniques that can be\
universally applied?
3-4](#question-15-are-there-techniques-that-can-be-universally-applied)

[3.3.3 Question 16: For small quantities of materials, are there\
sampling, handling, and collection techniques as well as\
sample integrity, accuracy and precision QA/QC\
methodologies available?
3-5](#question-16-for-small-quantities-of-materials-are-there-sampling-handling-and-collection-techniques-as-well-as-sample-integrity-accuracy-and-precision-qaqc-methodologies-available)

[3.3.4 Question 17: What is the status of standardization efforts?\
Are these efforts focused on broadly applicable\
characterization methods or category-specific methods?
3-5](#question-17-what-is-the-status-of-standardization-efforts-are-these-efforts-focused-on-broadly-applicable-characterization-methods-or-category-specific-methods)

[3.3.5 Question 18: What alternative or innovative methods or
technologies can be applied to nanomaterial analysis?
3-6](#question-18-what-alternative-or-innovative-methods-or-technologies-can-be-applied-to-nanomaterial-analysis)

[3.3.6 Question 19: Are there models that are currently used to\
obtain property data for nanoscale materials? For which\
properties and which nanoscale materials?
3-6](#question-19-are-there-models-that-are-currently-used-to-obtain-property-data-for-nanoscale-materials-for-which-properties-and-which-nanoscale-materials)

[3.3.7 Question 20: Has any validation work been conducted that compares
predicted values with measured data? For which properties and which
nanoscale materials?
3-7](#question-20-has-any-validation-work-been-conducted-that-compares-predicted-values-with-measured-data-for-which-properties-and-which-nanoscale-materials)

[3.3.8 Question 21: Are there current significant characterization\
needs for which the NMSP should investigate model\
development?
3-7](#question-21-are-there-current-significant-characterization-needs-for-which-the-nmsp-should-investigate-model-development)

[3.4 Session 5 - Discussion: Prioritization of Data Gaps
3-8](#session-5---discussion-prioritization-of-data-gaps)

[3.5 Closing Remarks 3-9](#closing-remarks)

Appendix A: MEETING AGENDA

Appendix B: DISCUSSION PAPER

Appendix C: PRELIMINARY PANEL COMMENTS ON DISCUSSION PAPER

# Introduction

This report summarizes the Panel discussions and public comments during
the Peer Consultation Public Meeting on The Material Characterization of
Nanoscale Materials organized by the U.S. Environmental Protection
Agency (EPA). The meeting took place in Arlington, VA, on September 6
and 7, 2007. Eastern Research Group, Inc. (ERG), a contractor to EPA,
organized the logistics, provided facilitation support, and prepared
this summary report. Meeting minutes were not prepared and a transcript
was not recorded. The intent of this report is to provide an overview of
the discussion that occurred. No attempt has been made to analyze or
evaluate any portion of the discussions. The discussion and comments
presented in this summary reflect individual opinions of the commenters
and should not be considered to be the opinion or belief of EPA.

## Panel Members

-   Dr. Joseph BelBruno, Professor, Department of Chemistry, Dartmouth
    College.

-   Dr. Ahmed Busnaina, William Lincoln Smith Professor and Director,
    NSF Nanoscale Science and Engineering Center for High-rate
    Nanomanufactruing and the NSF IURC Center for Microcontamination
    Control, Northesastern University.

-   Dr. Richard Canady, DABT, Office of the Commissioner, Food and Drug
    Administration.

-   Dr. Alan Cassell, Project Scientist/Task Manager, Ames Research
    Center, National Aeronautics and Space Association.

-   Dr. Vicki Colvin, Director, Center for Biological and Environmental
    Nanotechnology (CBEN), Rice University (participated on Day 2,
    September 7^th^ only).

-   Dr. Joerg Lahann, Professor, Department of Chemical Engineering,
    University of Michigan (participated on Day 1, September 6^th^
    only).

-   Dr. Vladimir Murashov, Special Assistant to the Director, National
    Institute for Occupational Safety and Health (NIOSH).

-   Dr. James Murday, Associate Director for Physical Sciences, Office
    of Research Advancement, University of Sourthern California.

-   Dr. John Small, Group Leader, Center for Nanoscale Science and
    Technology, National Institutre of Standards and Technology (NIST).

-   Dr. David Warheit, DuPont Haskell Laboratory.

## Meeting Background and Purpose

As part of EPA's initiative to address growing interest in the potential
health and safety issues of engineered nanoscale materials (NMs), EPA is
developing the voluntary Nanoscale Materials Stewardship Program (NMSP).
This program is being designed to encourage responsible commercial
development of NMs. The NMSP will enable EPA, the relevant industry, and
interested stakeholders to better assess potential risks to human health
and the environment from NMs and to identify risk management practices
which may reduce such potential risks.

[]{.mark}

The NMSP is intended to include but is not limited to engineered NMs
manufactured or imported for commercial purposes as defined in 40 CFR
720.3 (r). The NMSP is envisioned to have two parts: 1) a basic
reporting program and 2) an in-depth program. This public peer
consultation meeting is intended to support the NMSP by identifying
material characterization data that participants could submit under the
Basic Program if they are known or are reasonably ascertainable as
defined in 40 CFR 720.3 (p). The data and experience generated by the
basic reporting phase will help to inform the types of in-depth data to
be developed.

[]{.mark}

The Scientific Peer Consultation Public Meeting on The Material
Characterization of Nanoscale Materials was organized to help clarify
which data and elements should be included in the NMSP basic and/or
in-depth program (see Appendix A for the meeting agenda). The goal was
to have an applied discussion that considers 1) the current
understanding of material characterization as it relates to NMs and 2)
how this understanding can be used to guide the Agency's thinking
regarding the material characterization data elements that would be most
useful and important to include in the NMSP

Prior to the meeting, EPA developed a paper to facilitate discussion on
topics related to material characterization (Appendix B). EPA then
convened a Panel to review the discussion paper. The Panelists reviewed
the discussion paper and submitted comments prior to the meeting, which
were summarized and circulated for review to aid the meeting discussions
(Appendix C). The requested approach for the Panel during the meeting
was to discuss what data are known or reasonably ascertainable to
characterize NMs. This was then to be followed by a discussion on the
methodology used to obtain and use characterization endpoints of
interest. There was no attempt prior to, or during the meeting, to
arrive at joint decisions, reach consensus, or provide majority advice.

The meeting was organized into a series of sequential sessions over a
two-day period. After initial introductions from EPA, an open,
facilitated discussion occurred regarding the questions posed to the
Panel in the topical areas per the discussion paper. After Panelists
concluded their discussion, meeting observers were asked to provide
comment. As time permitted, the Panel then responded or continued
discussion based on the public comments.

Additional information pertaining to the specific charge to the Panel, a
summary of their written responses prior to the meeting, and the meeting
agenda can be found in the public docket and appendices of this report

# Day One Summary (September 6, 2007)

## Introductions

**Opening Remarks and Background**

*Jim Alwood (EPA, Office of Pollution Prevention and Toxics (OPPT),
Chemical Control Division)*. Mr. Alwood greeted Panelists and members of
the public. Mr. Alwood stated that the purpose of the meeting was to
solicit input from individual Panelists and the public. EPA would then
consider all input, but there would be no specific attempt during the
meeting to come to consensus on any discussion topics.

*Greg Fritz (EPA, OPPT, Economics, Exposure, and Technology Division
(EETD))*. Dr. Fritz addressed the group and summarized the scope of the
meeting. He stated that the Panelists had been asked to review a
document titled, "*Peer Consultation Public Meeting on The Material
Characterization of Nanoscale Materials: Discussion Topics, August 7,
2007*" prior to the meeting and consider the corresponding series of
questions. Dr. Fritz stated that the Panel discussions surrounding the
questions during the meeting would help inform EPA as the Nanoscale
Materials Stewardship Program (NMSP) is structured, specifically
regarding the data elements that may be requested for participation in
the basic and in-depth programs.

Dr. Fritz then summarized the content of the discussion paper and the
specific questions that EPA asked the Panelists.

**Nanoscale Materials Stewardship Program Overview and Status**

*Jim Willis (EPA, Office of Pollution Prevention and Toxics; Director,
Chemical Control Division).* Mr. Willis provided additional remarks to
set the stage for the meeting, including a background and history on
EPA's effort to develop the NMSP and how material characterization fits
into the program.

He stated EPA's intent is to develop and implement the NMSP in an open
and transparent manner. The meeting is the third in a series of public
meetings held to solicit input on various components of The Program. The
first was held on October 19^th^ and 20^th^, 2006 regarding Risk
Management Practices; and the second was held August 2^nd^, 2007 to
discuss EPA's, "Concept Paper for the Nanoscale Materials Stewardship
Program under TSCA" and the "TSCA Inventory Status of Nanoscale
Substances - General Approach".

Mr. Willis also discussed the overall status of the NMSP. EPA is
currently in the "design phase" of the program. The current meeting is
intended to help finalize the structure and design. After completion of
this first phase, the NMSP will be implemented such that participants
will submit information to EPA. After the "implementation phase" has
been functional for a time period (still to be determined), an
"evaluation phase" will begin. During the evaluation, EPA will review
data submitted, modify the program as appropriate, and provide a summary
to the public.

**Facilitated Introductions and Charge to Panelists**

*Jan Connery (ERG)* facilitated the meeting. The Panelists were first
asked to briefly introduce themselves. After introductions, Ms. Connery
stressed to all participants and observers that there would be no
attempt to reach consensus during the discussion. Rather, the intent of
the meeting is to provide EPA with input from a broad, scientific
stakeholder community on the various discussion topics. All comments and
suggestions were to be recorded as individual opinions for EPA to
consider while proceeding with development of the NMSP. However, to aid
EPA's evaluation, the meeting summary document would note instances when
multiple Panelists concurred on any topic.

Ms. Connery then noted six general topical areas that were not intended
for discussion during the meeting.

-   EPA Policy

-   Classification and Nomenclature

-   Environmental Fate or Transport

-   Risk Management or Hazard Assessment

-   Solutions to Perceived Data Gaps

-   Assessment of the NMSP or other EPA programs

*Dr. Canady* asked for clarification regarding the topic of
nomenclature.

*Tracy Williamson (EPA, OPPT, EETD; Chief, Industrial Chemistry Branch)*
provided a response. Dr. Williamson agreed that a standardized
classification scheme and standardized nomenclature are important and
relevant. However, she noted that there are ongoing efforts to discuss
these topics in great detail. Therefore, EPA desired not to devote
significant portions of the Material Characterization meeting to address
nomenclature, recognizing that there may be some topics that require
some discussion.

#### Public Comment and Q/A Session {#public-comment-and-qa-session .unnumbered}

*Public Comment #1: Scott Sweeney (Safer Nanomaterials and
Nanomanufacturing Initiative, SNNI)* provided a prepared statement that
included three primary points, briefly summarized below.

1.  He noted his organization has developed a library with information
    pertaining to nanomaterials and suggested this type of repository
    may be very useful.

2.  He noted that the purity of nanomaterials is important and
    applicable to environmental assessments. He also provided examples
    of test data that may show purity has a considerable toxicological
    impact.

3.  His organization has access to "rapid characterization methods" to
    evaluate purity, noting that electron microscopy has been used
    historically; but it is not useful data in many circumstances. Mr.
    Sweeney suggested the use of other techniques such as nuclear
    magnetic resonance spectroscopy (NMR), Thermogravimetric Analysis
    (TGA), and X-ray photoelectron spectroscopy (XPS).

Mr. Sweeney's statements resulted in extensive dialogue from Panelists
regarding the test data and SNNI's characterization methods. Mr. Sweeney
stated SNNI is developing a data base that could be made available upon
request. Mr. Sweeney was asked to provide written comments to EPA.

*Public Comment #2: Shekhar Subramoney (DuPont Company)* asked EPA to
clarify the rationale for excluding discussions regarding hazard
assessment from this meeting.

*Dr. Williamson* noted that NPPTAC recommended a public meeting
specifically devoted to material characterization, which she
acknowledged helps inform risk management and hazard assessments. Dr.
Williamson also reminded the audience of a previous meeting (held
October 19^th^ and 20^th^, 2006) that was focused on the Risk Management
of Nanomaterials. Portions of that meeting were specifically devoted to
discussing hazard assessments.

Dr. Williamson also clarified that EPA was interested in all media
(e.g., dry state, air, water) regarding material characterization.

*Public Comment #3: Shaun Clancy (American Chemistry Council, ACC))*
requested that EPA clearly state the test methods that will be required
of NMSP participants to provide appropriate data when the NMSP is
ultimately developed.

## General Discussion

*Ms. Connery* asked each Panelist to provide their general thoughts and
comments on the discussion paper and issues surrounding material
characterization of nanomaterials before delving into the detailed
session topics.

*Dr. Warheit* commented that the questions posed in the discussion paper
were generally appropriate. He also noted that from a toxicological
view, many people have attempted to generate lists of appropriate tests
for characterizing nanomaterials. His view is that this exercise
typically results in an extensive list that is too long because a great
number of tests will provide potentially-useful information. One reason
is the nearly infinite number of potential nanomaterials and a
corresponding infinite number of uses. He suggested developing a
smaller, prioritized list of required information and the tests that are
needed to provide that information. Dr. Warheit provided a suggested
list in his pre-meeting comments.

Dr. Warheit also stated his belief that purity of the nanomaterial being
evaluated is very important.

Finally, Dr. Warheit discussed his view that exposure assessments of
nanomaterials are highly dependent on:

-   Whether the material is in a wet or dry state;

-   The composition of the matrix being evaluated; and,

-   Whether assessments are conducted on the core or the shell of the
    nanomaterial

*Dr. Canady* asked for clarification from EPA regarding the rationale
for establishing the categories that were posed as starting points for
grouping nanomaterials in the discussion paper.

*Dr. Williamson* responded that the categories were established to
facilitate discussion and that they could be altered if appropriate.
After additional discussion, Dr. Williamson acknowledged that the Toxic
Substances Control Act (TSCA) does not include categories of chemicals
on the TSCA Inventory. She noted, however, that categorizing chemicals
sometimes aids EPA's internal review process when determining how to
assess and evaluate chemicals. Therefore, it may be useful to establish
categories.

*Dr. Busnaina* noted that he would have suggested different categories
because the existing categories were developed for macro materials based
on the distinguishing characteristics of their properties. He stated
that these characteristics are not appropriate for distinguishing
between different nanomaterials. Dr. Busnaina suggested developing
categories based on: chemicals with inert surfaces, active surfaces, and
functionalized surfaces.

Dr. Busnaina also stated that EPA should recognize qualifying
terminology such as "simple structures" may not be appropriate. As an
example, he noted that even discussing nanoscale titanium dioxide can be
very complex.

*Dr. Murday* initiated a clarifying discussion regarding composites that
include a macromaterial core and a nanomaterial attached to the surface.

*Dr. Williamson* stated the group may not want to exclude these
materials, but she suggested the discussion should focus on
free-standing nanomaterials.

## Session 1: Discussion -- Types of Nanoscale Materials & Their Structure and Chemical Composition

*Ms. Connery* opened this session by stating that there were five
related questions in EPA's discussion paper that would be discussed
(questions 1, 2, 3, 12, and 13). She reviewed each question and then
asked Panelists to discuss their responses. The questions and subsequent
discussions are presented below.

### Question 1: Are there any other significant categories, based on structure and chemical composition, that should be included in this discussion because they are substantially different from the categories mentioned (e.g., hybrids, self- assembly devices, others)?

*Dr. Murday* suggested that using the term "molecule" when discussing
nanomaterials may not be appropriate. He commented that this term
implies uniformity, whereas many nanomaterials are not uniform and are
not based on a specific chemical formula (for example, the number of
atoms in a gold nanomaterial is flexible). Dr. Murday agreed with the
comments provided by Dr. Murashov in his pre-meeting comments.

*Dr. Murashov* reiterated the statements made in his pre-meeting
comments. He noted a particular concern regarding "purity". He noted
that if a nanomaterial were defined based on a chemical structure, EPA
would need to determine an acceptable "level of purity". For example,
EPA would need to specify a range regarding the number of atoms for
various nanomaterials.

Dr. Murashov also suggested that EPA should consider the difference in
chemical composition between the core and the surface of the
nanomaterial (and the associated purity of these two different regions
of the nanomaterial). He noted that this is important because the
effects based on the content of the core are different than those based
on the surface. The surface chemistry may result in more immediate
concerns related to exposure; however, the potential hazards associated
with the core are also important because the surface may eventually
degrade.

Dr. Murashov suggested that if EPA must develop categories and
corresponding characterization, the Agency could group nanomaterials
based on the structure of the core, recognizing surface chemistry and
function will have effects.

Dr. Murashov pointed out inconsistencies in the proposed grouping into
categories of nanomaterials described as "organic" and "inorganic". He
suggested "carbonaceous" is a more suitable category to describe
carbon-based nanomaterials, noting that pure carbon is not "organic".

*Dr. Canady* reviewed his written, pre-meeting comments. He then
expanded on a few topics. First, Dr. Canady recognized the need to
develop categories. However, he proposed that EPA recognize that the
categories could be modified in the future as more information is
acquired (possibly modifying the definition of existing categories, or
adding and deleting categories).

Dr. Canady suggested EPA consider nanomaterials that may exist as
"combinations" of the existing categories (he suggested some could fall
into multiple categories as they are written).

Dr. Canady also suggested a separate category for emulsions, vesicles,
and micelles. He stated they are omitted from the categories in EPA's
discussion paper; however, there are drug applications that may
eventually be utilized in industry.

*Dr. Joerg Lahann* agreed with Dr. Canady's comments regarding
emulsions, vesicles, and micelles. He also agreed with the comment
regarding the potential for "combinations", and suggested development of
a "hybrid" category (or categories, if appropriate).

*Dr. Lahann* stated that the effects of nanomaterials are often
dependent upon functionality; not their specific size, structure, or
composition.

*Dr. BelBruno* commented that it is appropriate to develop initial
categories based on the chemical structure; however, functionality is
very important and should be considered for future categorization.

*Dr. Cassell* stated that organometallic materials should be a separate
category. This initiated a discussion regarding the potential effects
from a metal atom that is surrounded by various functional groups.
*Various Panelists* noted potential concerns depending on the specific
metal and the functional groups.

*Dr. Canady* suggested that organometallic materials could be a
sub-category or could be a "hybrid" as previously discussed.

*Dr. Murday* suggested the following categories and subcategories:

-   Free-Standing nanomaterials

    -   Materials whose core is always capped

    -   Materials whose core consists of a uniform shell (e.g., quantum
        dots)

    -   Hybrid materials

        -   those with multiple shells

        -   those with multiple nanostructures linked together

-   Nanomaterials embedded in a composite material

-   Thin-film nanostructures (e.g., those used in electronic devices)

Dr. Murday suggested this categorization would allow analysis in a
hierarchy from simple to more complex.

*Dr. Lahann* agreed with Dr. Murday's proposed categories.

*Dr. Murashov* also agreed.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session .unnumbered}

*Public Comment #1: Dan Ewart (NanoProducts Corp.)* noted that TSCA is
based on chemical structures. Therefore, he commented the EPA may need
to consider implications of grouping nanomaterials in categories that
are not based on chemical formulae.

*Dr. Williamson* reiterated her previous remarks that categories of
chemical are not included on the TSCA inventory, but EPA utilizes
categories (based on structure) to assist internal review.

She also presented a brief overview of EPA's current vision for the
NMSP. This vision includes the need to understand how to characterize
nanomaterials based on chemical identification information and
physical-chemical properties and the test methods needed to acquire the
characterization data. Dr. Williamson recognized that the list of
properties and tests may be lengthy; therefore, EPA is hoping to receive
input on how to prioritize the most important, needed information.

*Public Comment #2: Mark Herwig (General Electric)* asked if other
organizations had already developed categories for nanomaterials. This
question resulted in significant discussion regarding other
categorization attempts.

*Mr. Willis* specifically discussed current activities of the
Organization of Economic Cooperation and Development (OECD) Working
Party on Manufactured Nanomaterials and of the International
Organization for Standardization (ISO) Technical Committee (TC) that
promotes international standardization in nanotechnology (TC229).

*Dr. Canady* reiterated his view that it is appropriate to establish
categories for initial discussion and evaluation. However, EPA should
allow for category modification as more information becomes available.

### Question 2: For the different categories of nanoscale materials, what is the current state of knowledge about structure and chemical composition? 

*Dr. Small* indicated that the structure and composition of some
nanomaterials is known and can be measured "very accurately." However, a
problem occurs when nanomaterials are purchased from manufacturers. He
noted that the actual composition, core, and sometimes functional groups
vary from batch to batch; even when product specifications are
well-defined.

*Other Panelists* agreed and brought up this as an issue during several
discussions throughout the remainder of the meeting.

*Dr. Warheit* commented that from a toxicological perspective the
structure and composition is well understood for specific
nanomaterial-types that have been studied; however, this is not
necessarily true for nanomaterials as a whole.

*Dr. BelBruno* agreed with and expanded upon Dr. Small's assertion that
there are differences between batches of the same material. He noted
that given a sample, laboratories can conduct tests to characterize the
nanomaterial. However, the results may only apply to that particular
batch.

*Dr. Murashov* stated that there are only two examples of nanomaterials
he feels are well-characterized (fullerenes and dendrimers). He noted
that even titanium dioxide has multiple states and is not completely
characterized.

*Dr. Busnaina* commented that it may not be possible to acquire all the
information needed to fully characterize each nanomaterial from a
particular supplier. He questioned whether the suggested categories are
appropriate. Dr. Busnaina then suggested selecting a few properties to
prioritize the characterization (such as surface activity) then conduct
follow-up evaluations with secondary properties (such as oxidation
potential).

*Dr. Murday* commented that nanomaterials are very complex; therefore,
the proposed properties for characterization may not apply. For example,
he noted that the core is often very different in its chemistry and
functionality than the surface. Therefore, he suggested it may be more
appropriate to consider properties of concern rather than the actual
chemical structure.

*Dr. Murashov* agreed with Dr. Murday's previous comment. He also agreed
with Dr. Small's comment about variability between batches.

*Dr. Lahann* suggested that although there may be variability between
batches, there may be appropriate ways to characterize the purity based
on statistical analyses. He commented on current methods of
characterizing uncertainty when evaluating the purity of polymers.

*Dr. Canady* observed that based on other Panelist's comments regarding
this question it seemed there is some level of knowledge regarding
certain specific nanomaterials; however, it is not appropriate to state
there is significant knowledge for nanomaterials in general and there is
no knowledge for most.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-1 .unnumbered}

*Dr. Williamson* provided comments on the Panel discussions. She stated
the discussion was very informative and asked Panelists and observers to
provide additional information regarding the variability between
batches. Dr. Williamson also asked Panelists to elaborate on the
specific characteristics being studied (e.g. for metal oxides). Finally,
she asked if there are certain characteristics that are more important
than others for characterization. The following summary of discussions
ensued.

*Dr. Murashov* indicated that X-Ray crystallography is commonly
conducted on metal oxides.

*Dr. Warheit* agreed with Dr. Murashov, but noted that this was
typically done to evaluate the core. He noted there are different grades
of TiO2 for which his laboratory had tested (and published information).
His work considered different formulations for first time (as far as he
was aware). He also stated there are different degrees of surface
coatings, which may not be common knowledge.

*Dr. Murashov* addressed another question from Dr. Williamson by stating
he felt primary data needs to include a measurement of the distribution
of material in the sample, the nanomaterial's size, and its shape.

*Dr. Fritz* asked Panelists to elaborate on their experience with
variability between samples.

*Dr. Busnaina* confirmed this was a significant issue, elaborating on
his specific experiences. For example, he observed considerable
variability when purchasing nanomaterials with the same product
specifications from the same supplier. He specifically noted that
processing steps that a manufacturer believes are routine can change
certain properties and chemical characteristics of nanomaterials.

*Dr Murashov* then initiated a discussion regarding "surface activity".
He commented that although surface activity is an important
consideration, it was not clear how to define or measure this
characteristic (e.g., redox potential or something else?).

*Dr. Fritz* asked Panelists to elaborate on potential differences or
concerns regarding tests conducted on dry nanomaterials vs. emulsions.

*Dr. Warheit* initiated an extended discussion among multiple Panelists
and EPA representatives on the importance in recognizing differences in
nanomaterials in dry vs. wet matrices. Differences will include the
toxicological and environmental effects as well as the most important
characteristics to measure the effects and the corresponding measurement
techniques.

*Public Comment #1: Shekhar Subramoney (DuPont Company)* commented that
his experience is that analytical tools are available to identify the
structure and composition of nanomaterials. He agreed there is
variability between batches, but disagreed with most Panelists'
assertion that this is a primary concern.

### Question 3: Can structures and chemical composition be correlated to specific properties and is this correlation quantifiable? Chemical Identification Elements (e.g., which ones? for which substances? test methods?)

*Dr. Warheit* referenced a paper that was recently published on the lung
toxicity of pristine and fully hydroxylated fullerenes. The original *in
vitro* study showed increases in toxicity of at least three orders of
magnitude between the pristine (more toxic) and the fully hydroxylated
fullerene samples. However, in the *in vivo* pulmonary toxicity study,
few toxicity differences were measured between the two samples. The
different results between the two studies indicate that the structure
and chemistry and other *in vitro* analyses may not be predictive of the
inherent toxicity of the nanomaterial and that each sample has to be
evaluated on a case-by-case basis.

*Dr. Murday* felt there is a correlation between structures and chemical
composition, and properties. He also felt computer modeling based on
structure and composition could be developed to predict properties. Dr.
Murday also suggested that EPA contact industry stakeholders that
produce catalysts regarding their work on this topic. Finally, Dr.
Murday noted that we still do not fully understand everything that
impacts a living system, whether or not the material is nanoscale. This
may affect correlations.

*Dr. Murashov* referred to his pre-meeting comments, reiterating them
and stating he felt there were correlations.

*Dr. Lahann* also agreed it is possible to develop models and
correlations once data are obtained. However, he noted there are still
many unknowns.

Additional discussion between Panelists followed these specific remarks.
*Multiple Panelists* stated that theoretical modeling could be
conducted; however, the model goals would need to be clearly defined.
Further, *Panelists* acknowledged modeling results would need to be
validated and tested for scale-up to production levels.

### Question 12: How important are impurity identity and impurity levels to the understanding and characterization of nanoscale materials? 

*Dr. Cassell* replied that the effects of impurities are extremely
important. However, he noted examples where the impurities result in
more risk than the nanomaterial itself (e.g., when heavy metals are used
as catalysts). Dr. Cassell also stated that the term "impurity" must be
defined when referring to nanomaterials (referencing previous
discussions on this topic). He suggested that small changes in
structure, aspect ratio, and location of ligands may not result in
different chemical formulae, but will result in very different
characteristics. These could be considered impurities.

*Dr. Murashov* agreed with these comments. He noted that it is important
to agree on what is considered the "pure material" before an evaluation
of impurities can be conducted. Further, Dr. Murashov suggested
establishing an acceptable range for a material to be considered "pure".

*Dr. Small* noted that measuring purity may be difficult (depending on
the characteristic that is selected to define purity). He also noted
that tests must be designed to distinguish between the bulk material and
the catalysts within it.

Dr. Small's comment regarding catalysts resulted in an extended
discussion about what other chemicals in the commercial nanomaterial
product should be evaluated (besides the nanomaterial itself).
*Panelists* noted examples where specific catalysts are expected to
remain with the nanomaterial and other examples where contamination of
unknown chemicals results from processing operations. *Panelists*
suggested this is of primary concern during full-scale production
opposed to Research & Development where samples are typically tested and
monitored more closely. *Multiple Panelists* suggested the focus should
be on characteristics that can impact environmental health and safety.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-2 .unnumbered}

*Dr. Williamson* asked the Panelists and observers if EPA should ask for
more information on impurities for the NMSP.

*Public Comment #1: Shaun Clancy (ACC)* stated that the issue of
impurities may be very important in context of the NMSP. He recognized
that EPA may request data on specific chemical impurities in the
commercial mixture. He also recognized the potential for multiple NMSP
participants to submit data on the same nanomaterial. Test results may
be affected by impurities; therefore, concentration data and data
regarding the specific impurities will be needed to compare the results.

*Public Comment #2: Donald Ewert (NanoProducts Corp.)* commented that
his customers require information regarding impurities. Therefore, he
believes this is an important topic. He further stated that his company
routinely characterizes their products and the corresponding impurities,
believing that measurement techniques are available to acquire
appropriate information.

### Question 13: Are there routine purification procedures that can effectively control or remove impurities, when desirable, for certain classes of nanoscale materials?

*Dr. Canady* responded that these procedures are available. However,
they vary depending on the specific nanomaterial. There is not one
procedure that is universally suitable.

*Dr. Cassell* referred to his pre-meeting comments for more detail. He
also specifically noted that the methods currently used for
nanomaterials are the same as those used for macromaterials.

Each Panelist was asked for input and all concurred with the statements
made by Dr. Canady and Dr. Cassell.

## Session 2- Discussion: Physical Chemical Properties

*Ms. Connery* opened this session by stating that there were five
related questions in EPA's discussion paper that would be discussed
(questions 4 through 8). She reviewed each question and then asked
Panelists to discuss their responses. The questions and subsequent
discussions are presented below.

### Question 4: Which physical-chemical properties are relevant to nanoscale materials and how? Which are known or reasonably ascertainable and which have data gaps?

Prior to the discussion on this topic, *Dr. Williamson* clarified that
relevant properties include those that may impact the function of the
material in its intended use, or those that may impact the material's
effects.

*Dr. Murday* commented that virtually all properties are relevant to
some degree; however, he suggested some have a more dramatic influence.
Dr. Murday referred to his pre-meeting comments for a list of those he
believes are most significant.

*Dr. Murashov* agreed with Dr. Murday's list but suggested a few
additions, referenced in his pre-meeting comments for a list of the most
relevant properties.

*Dr Warheit* reminded the group of the earlier discussion that the
biological matrix from which the nanoparticle is dispersed can
significantly affect characteristics (e.g., wet (water, culture media)
or dry).

*Dr. Lahann* commented that EPA should try to identify properties that
are unique to nanomaterials; however, he did not suggest what those
properties may be.

*Dr. Canady* noted that there are differences in observed properties,
and the corresponding characteristics, when the nanomaterial is
aggregated.

*Dr. Busnaina* agreed with the lists that were provided by Dr. Murday
and Dr. Murashov, and with the discussion regarding aggregates. He added
that surface energy is also an important property (recognizing it is not
easy to measure).

*Dr. BelBruno* agreed with the lists discussed above.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-3 .unnumbered}

*Dr. Fritz* asked Panelists to expand on comments regarding
agglomeration, specifically asking whether surface energy was a factor
in agglomeration.

*Various Panelists* commented that surface energy (or perhaps
"interfacial energy") does affect the agglomeration potential, but the
degree is case-by-case. Also, *some Panelists* noted that nanomaterials
can be coated to prevent agglomeration. This is desirable in some
situations and can be done to reduce the hazard. However, *other
Panelists* noted that coatings do not fully mitigate concerns.

*Public Comment #1: An observer* asked the group if there are concerns
related to silver in the nanoscale that are different from those in the
macroscale. Panelists did not provide a response.

*Public Comment #2: Shaun Clancy (ACC)* suggested that EPA should revise
their investigation on this topic to only include an analysis of
properties that are important to specified toxicological end points.

Mr. Clancy also urged EPA to develop the required elements for the NMSP
based on information that will help fill data needs (information that
will inform a risk assessment opposed to general data gaps).

*Public Comment #3: Steve Hayes (Gobbell Hays Partners, Inc.)* suggested
that EPA should revise their investigation on this topic to focus on
properties that are relevant:

-   Compared to materials in the bulk form

-   Performance

-   For toxicological effects

-   For fate & transport analyses

-   Persistence (because it relates to considerations during cleanup)

He also suggested that EPA consider topics that may affect clean up of
unintended releases (e.g., spills).

*Public Comment #4: Tanya Spellman (Washington Council of Government)*
commented that EPA should consider the ultimate fate of nanomaterials;
specifically noting that they may be transferred to Publicly--Owned
Treatment Works and these facilities will need to understand appropriate
handling and cleanup procedures. Ms. Spellman also concurred with Mr.
Clancy's remarks that EPA should only request information that will help
inform a risk assessment.

### Question 5: Are there properties that would have little or no relevance under the NMSP?

*Multiple Panelists* discussed their view that virtually all properties
have some importance. *Some Panelists* commented that because there is a
lack of information regarding potential effects associated with exposure
to nanomaterials, EPA should attempt to acquire as much information as
possible rather than limiting the effort to investigate certain
properties. *Other Panelists* acknowledged that all properties could
potentially result in an impact; however, they felt it would be more
appropriate to prioritize efforts and focus on properties that are most
likely to result in an impact. They acknowledged that the costs
associated with testing may have an impact on which tests should be
performed, if only limited useful information would be produced.

*Multiple Panelists* suggested specific properties that may not be
relevant for certain aspects of a risk evaluation. These are briefly
summarized below.

*Dr. Murashov* referred to his pre-meeting comments for specific
suggestions. During the discussion he suggested that refraction may not
be relevant.

*Dr. Lahann* commented that elastic properties may affect cell uptake of
nanomaterials; therefore, they could be relevant.

*Dr. Murday* agreed with Dr. Murashov's list in general but stated that
optical properties can sometimes be important.

*Dr. Warheit* reiterated his previous statement that virtually all
properties have some relevance.

Thermal properties and superconductivity were also specifically
mentioned as properties that may not be relevant.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-4 .unnumbered}

There were no public comments or questions.

### Question 6: Which properties are associated with aggregated or agglomerated nanoscale materials, as opposed to properties that are inherent to the material regardless of physical form?

*Dr. Murashov* reviewed his pre-meeting comments. He stressed that
biological activity can be affected by agglomeration.

*Dr. Small* stated that agglomeration affects the fate and transport of
nanomaterials in the environment.

*Other Panelists* agreed with Dr. Murashov's initial comments and the
subsequent discussion that ensued during his review. It was noted that
larger aggregated particles are easier to remove from a sample by
filtration.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-5 .unnumbered}

There were no public comments or questions.

### Question 7: Are there routine manipulations of nanoscale materials that result in physical-chemical properties changes or other defining characteristics (e.g., surface modifications of nanotubes to enhance solvent dispersibility)?

EPA added a clarifying example: Coatings can be applied to minimize
agglomeration. How are these applied?

*Multiple Panelists* indicated there are many processes that industry
uses, but each is developed and implemented case-by-case, depending upon
the specific situation. *Multiple Panelists* indicated there is not a
"routine" process. However, Panelists offered the specific examples
presented below.

*Dr. Warheit* stated that sonication can reduce agglomeration.

*Dr. Murday* stated that the surface of many nanomaterials must be
"capped" during production. Depending on the complexity of the material
and the end use, the cap may include a ligand that imparts new
functionality.

*Dr. Cassell* stated there are many processes that manufacturers use to
package materials for transport to customers. These include annealing
and application of coatings. He referred to his pre-meeting comments for
additional information.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-6 .unnumbered}

*Public Comment #1: Mark Herwig (GE)* stated that routine manipulations
include applying coatings to alter the functionality of the
nanomaterial. However, the type of coating and desired functionality
affects the specific processes.

# Day two Summary (September 7, 2007)

## Session 2- Discussion: Physical Chemical Properties (Continued)

The meeting was reconvened on September 7^th^, with *Ms. Connery*
reminding Panelists and observers that Day One concluded with a
discussion pertaining to Question 7 from the discussion paper. Ms.
Connery then asked Panelists to continue their efforts beginning with
Question 8.

### Question 8: How should physical-chemical property data be prioritized for the NMSP? Based on availability, effect (toxicity or exposure criteria), or other factors?

*Dr. Warheit* stated that there is a very long list of physical-chemical
data that may be useful. However, he provided a list of "minimal
essential criteria" in his pre-meeting comments. *All Panelists* agreed
in general with Dr. Warheit's list (with some specific comments as
listed below).

Dr. Warheit then provided some additional points for EPA to consider
when finalizing the list:

-   Particle size

-   Wet vs. dry state

-   Differences in the core vs. the shell (the surface is often where
    most activity occurs)

Dr. Warheit also referred EPA to five studies that indicate the surface
activity is often more important than the particle size (see his
pre-meeting comments).

*Dr. Canady* agreed with Dr. Warheit's list and comments. However, he
noted that the list focuses on data to inform a hazard assessment.
Additional data may help inform other environmental effects that have
delayed or indirect effects on humans or ecosystems, for example, as are
recognized in the ozone depletion and global warming issues. He also
noted that the current Panel did not include an expert on ecotoxicity.
Additional items may be important from an ecotoxicity perspective.

*Dr. Colvin* concurred with Dr. Warheit's list; however, she suggested
acquiring all data and information would be useful (rather than limiting
the effort to a prioritized list). *Other Panelists* agreed that it may
not be appropriate to "eliminate" certain data elements and that
acquiring as much information as possible may be appropriate.

*Multiple Panelists* agreed that surface reactivity is very important.
An extended discussion regarding surface reactivity, the type of
information needed to appropriately define it, and the corresponding
tests that would be required ensued without specific resolution. The
types of chemical reactions associated with the surface were discussed.
In addition, surface reactivity was related to hazard and biological
activity. *One Panelist* encouraged EPA to consult NIH on this topic.

*Dr. Busnaina* commented that EPA should recognize that Confidential
Business Information (CBI) concerns may make it difficult to acquire
this information.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-7 .unnumbered}

*Public Comment #1: Andy Atkinson (Environment Canada)* initiated a
discussion by asking if agglomeration impacts the proposed list of
primary properties to consider. *Multiple Panelists* stated
agglomeration would affect the properties (particularly surface
reactivity). Follow-up discussions resulted in a suggestion to add a
study of persistence because agglomeration affects persistence in the
environment (and there is the potential for agglomerated nanomaterials
to disagglomerate over time).

## Session 3 - Discussion: Nanoscale Manufacture and Processing

*Ms. Connery* opened this session by stating that there were three
related questions in EPA's discussion paper that would be discussed
(questions 9, 10, and 11). She reviewed each question and then asked
Panelists to discuss their responses. The questions and subsequent
discussions are presented below.

### Question 9: What are the common processes used to manufacture nanoscale materials?

*Dr. Colvin* referred to a recent workshop devoted to this specific
topic. She stated the summary will be available soon. In general,
participants developed three primary methods for each of which there are
many specific processes:

1.  Gas phase processes

2.  Liquid phase processes

3.  Top-down manufacturing

Dr. Colvin noted agglomeration concerns are relevant to methods (1) and
(2) and that coatings are applied to prevent agglomeration for type (2).

*Dr. Murashov* suggested that biological processes leading to the
production of nanomaterials, such as nanoscale metal oxide particles,
could be identified as a major distinct method. This method can produce
nanomaterials with unique compositions, properties, and impurities and
therefore can be characterized by very unique hazard properties.

*Dr. Murday* commented that the above discussion refers to
chemical-based processes. He noted that physical-based processes such as
crushing and grinding are also commonly used.

*Dr. Cassell* suggested the following processes:

-   Chemical vapor deposition

-   Laser ablation

-   Thin film deposition

-   Self assembly (there could be "hundreds" of specific techniques

*Dr. Murday* indicted that various metallurgical processes using
mechanical deformation are used.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-8 .unnumbered}

*Comment #1: Shekhar Subramoney (DuPont Company)* stated he is aware of
a large-scale production process (thousands of pounds per year) using
mechanical/chemical exfoliation.

### Question 10: How are processes used to produce specific characteristics or properties?

*Dr. Cassell* commented that chemical vapor deposition can be used to
form one dimensional linear materials where the reaction time can be set
to control length. Also, self-assembly techniques (with micelle-based
approaches) can be used to control diameter. Finally, annealing can be
used to modify the surface area and porosity.

*Dr. BelBruno* indicated that "normal chemical methods" are used for
liquid synthesis.

Dr. *Murday* stated that there are different processes used for the
following three steps:

1.  Manufacture the core

2.  Cap the core

3.  Add a functionalized shell

This statement resulted in a discussion as to whether these general
steps are typical. *Multiple Panelists* indicated these are typical and
presented some examples.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-9 .unnumbered}

There were no comments relevant to this topic.

### Question 11: Which methods reduce particle size but do not result in property changes? Which methods reduce particle size and result in property changes?

*Multiple Panelists* asked for clarification from EPA. During the
resulting discussion the Panelists and EPA agreed that the question was
answered to EPA's satisfaction during discussions of previous questions.

## Session 4 - Discussion: Methodologies for Characterizing Nanoscale Materials Analytical Methods

*Ms. Connery* opened this session by stating that there were eight
related questions in EPA's discussion paper that would be discussed
(questions 14 through 21). She reviewed each question and then asked
Panelists to discuss their responses. The questions and subsequent
discussions are presented below.

### Question 14: Are validated methods available for the different categories of nanoscale materials?

*Dr. Colvin* stated that 10 methods are currently being validated and
another 15 are in the pre-validation phase. She referred to her
pre-meeting comments for additional information.

*Dr. Small* stated that NIST is developing standards. He also noted that
it is difficult to develop Standard Reference Materials.

*Dr. Murashov* commented that ISO is in the process of developing
standards. He also noted that there are no current industrial hygiene
methods to assess nanomateials and suggested that some bulk-phase
methods may be applicable (recognizing that further validation would be
required).

*Dr. Murday* commented that equipment and tools are available and are
used to measure and characterize nanomaterials on a regular basis;
however, their use is not "validated". He also noted that certain
analytical methodology (NMR & surface analytical tools) require "care"
in interpreting data.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-10 .unnumbered}

There were no public comments or questions.

### Question 15: Are there techniques that can be universally applied?

*All Panelists* agreed that there are no techniques that can be
universally applied. However, *several Panelists* provided specific
examples of techniques that can be used in various situations. These
examples are summarized below.

*Dr. Murashov* suggested that electron microscopy is widely used and
accepted. *Multiple Panelists* agreed but noted some limitations. For
example, *Dr. Small* commented that this technique works well to
characterize the core, but not the shell of nanomaterials. Also, *Dr.
Canady* noted that it does not provide statistical information (he
referred to the previous discussions regarding the analysis of
impurities).

*Dr. Colvin* provided EPA with citations for studies involving
measurements of aerosols and indicated she would provide references.

*Dr. Murday* commented that there are other techniques that are
available; however, many are cost-prohibitive.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-11 .unnumbered}

There were no public comments or questions.

### Question 16: For small quantities of materials, are there sampling, handling, and collection techniques as well as sample integrity, accuracy and precision QA/QC methodologies available?

*Dr. Colvin* referred to her pre-meeting comments for specific
information. In addition, Dr. Colvin commented that she does not believe
there is a need for nano-specific guidelines on this topic. She noted
that temperature control is important (particularly when measuring and
handling samples that may aggregate). She also stated that sonication
can alter surface coatings and should be used appropriately.

*Dr. Busnaina* agreed with Dr. Colvin's comments, particularly regarding
temperature control. He initiated a discussion between multiple
Panelists where examples of problems when samples were shipped occurred
due to extreme changes in temperature during flights to or from hot and
cold geographic locations.

*Multiple Panelists* noted that best management practices for ultrafine
materials may be appropriate for nanomaterials.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-12 .unnumbered}

No comments on additional topics were provided.

### Question 17: What is the status of standardization efforts? Are these efforts focused on broadly applicable characterization methods or category-specific methods?

*Dr.* *Small* commented that individual researchers develop and use
their own standards (referring to standard reference materials). He also
noted an upcoming NIST workshop that will be focused on developing a
prioritized list of standard reference materials for NIST to develop.

*Dr. Canady* stated that OECD is also investigating this issue and may
be developing a work group.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-13 .unnumbered}

*Public Comment #1: An observer* asked for clarification regarding the
phrase "NIST Certified" that he had observed on raw materials he had
received from suppliers.

*Dr. Small* responded that, in general, this means that the specific
sample can be traced to show it was compared to a NIST Standard
Reference Material.

### Question 18: What alternative or innovative methods or technologies can be applied to nanomaterial analysis?

*Dr. Colvin* suggested that a combination of mass spectroscopy and
electro ionization could be appropriate.

*Dr. Small* indicated that helium ion microscopes may be appropriate to
characterize materials greater than 10 nm.

*Dr. Murday* suggested that Atomic Force Microscopy (AFM) probes can be
used to analyze individual particles.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-14 .unnumbered}

*Public Comment #1: Shekhar Subramoney (DuPont Company)* stated that
X-Ray absorption spectroscopy allows for analysis down to the
atom-to-atom interactions. However, the equipment may be cost
prohibitive.

### Question 19: Are there models that are currently used to obtain property data for nanoscale materials? For which properties and which nanoscale materials?

*Dr. Murashov* referred to his pre-meeting comments for specific
examples.

*Dr. Cassell* stated models exist to predict mechanical and electrical
properties of carbon-based nanomaterial systems.

*Multiple Panelists* mentioned that models can be developed; however,
they need to be specific for every situation. Therefore, there are no
standard or general models. *Other Panelists* agreed they would have a
concern regarding model output because it would be difficult to verify
the results. Still, *some Panelists* agreed that appropriate models have
been (or could be) developed for specific nanomaterials.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-15 .unnumbered}

No comments on additional topics were provided.

### Question 20: Has any validation work been conducted that compares predicted values with measured data? For which properties and which nanoscale materials?

*Dr. Murday* stated that some modeling had been conducted and verified
but only for "simple" molecules; he was not aware of modeling for more
"complex" molecules.

*No other Panelists* were aware of existing models that had been
formally validated. However, *multiple Panelists* indicated there are
efforts in academia to develop models. *Panelists* noted that these
models may not be published because many scientific journals require
validation and there are no accepted validation methods. *Dr. Cassell*
stated one example is modeling of the thermoconductivity of carbon
nanotubes that has been developed at the University of California at
Berkeley.

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-16 .unnumbered}

No comments on additional topics were provided.

### Question 21: Are there current significant characterization needs for which the NMSP should investigate model development?

*Dr. Murashov* reviewed his pre-meeting comments.

*Dr. Warheit* agreed with Dr. Murashov and added that accurate models
generally cannot be developed until more information is acquired via
data generation. *Dr. Busnaina* agreed.

*Dr. Murday* suggested that EPA coordinate with other organizations for
development of specific types of models:

-   Reactivity (consult industry's catalyst manufacturers)

-   Toxicology (consult with NIH)

#### EPA Response, Public Comment, and Q/A Session {#epa-response-public-comment-and-qa-session-17 .unnumbered}

No comments on additional topics were provided.

## Session 5 - Discussion: Prioritization of Data Gaps

*Ms. Connery* asked each Panelist to reflect upon the discussions that
occurred during the meeting on each specific question and general topic,
then identify the most important data gaps from their perspective. A
summary list of Panelist responses is provided below.

*Dr. Canady*:

1.  What materials will be developed in the future (5, 10, and 15 years
    from now)?

2.  Specifically what needs to be validated?

3.  What are the priorities for modeling?

*Dr. Warheit*:

1.  How can surface reactivity be measured?

2.  What would be the disparity between measuring in the wet and dry
    states for each particle type in each category?

*Dr. Murday*:

1.  What parameters associated with health effects are most important?

2.  What is the ability to get "reliable" validated measurements?

3.  How can we determine the composition and structure of the shell of
    nanomaterials?

*Dr. Busnaina*:

1.  There is a lack of data regarding surface reactivity (from a
    toxicological perspective).

2.  There is a lack of data on functionalization (and effects from a
    toxicological perspective) specifically for commercial products.

3.  What are the effects of impurities and the correlation to toxicity
    and properties (and at what concentration are they important)?

*Dr. BelBruno*:

1.  There is a lack of information regarding the morphology (differences
    between the core, shell and crystal structures).

2.  There is a lack of information regarding surface reactivity and
    correlated with #1 above.

3.  There is a lack of information regarding impurities:

    a.  How can consistency between batches be ensured?

    b.  How are impurities defined?

*Dr. Small*:

1.  How can surface reactivity be defined and measured?

2.  There is a need to correlate data from wet vs. dry tests.

3.  There is a data gap regarding the use of standards.

4.  Determining criteria for categories.

*Dr. Cassell*:

1.  Standardization.

2.  Validation of characterization methods.

3.  There is a need for a publicly-available information repository.

4.  Surface reactivity.

5.  Relationship between size and other properties.

*Dr. Colvin*:

1.  There is a lack of understanding regarding wet nanoparticles and
    their interaction in the environment (micelles and complexation).

2.  A mechanism for data mining and sharing of information is lacking.

3.  Fully understanding the classification of commercial products

*Dr. Murashov*:

1.  There is a need to harmonize and standardize:

    a.  Common definitions (e.g., what does "impurity" mean?)

    b.  A list of physical-chemical properties that are critical for a
        risk assessment.

    c.  Protocol for collecting data.

## Closing Remarks

After *Ms. Connery* confirmed that all Panelists had provided
appropriate closing comments, EPA thanked the Panel and observers and
the meeting was adjourned.

**Appendix A**

**MEETING AGENDA**

![](media/image1.png){width="1.4993055555555554in" height="0.5in"}

United States

Environmental Protection Agency

**Peer Consultation on the Material Characterization of**

**Nanoscale Materials - Agenda**

Holiday Inn Rosslyn at Key Bridge, Arlington, Virginia

September 6-7, 2007

**Day One: Thursday, September 6**

8:30 a.m. Registration

9:00 a.m. **EPA Opening Remarks and Background** *EPA*

-   Meeting Purpose and Objectives

9:30 a.m. **Nanoscale Materials Stewardship Program (NMSP) Overview and
Status** *EPA*

-   Summary of EPA's Concept for the NMSP

-   NMSP Relationship to OPPT TSCA Programs

10:00 a.m. BREAK

10:15 a.m. **Introductions, Meeting Agenda, Format and Charge** *ERG*

> 10:45 a.m. **Public Comment Period** *ERG*

11:45 a.m. LUNCH

> 1:00 p.m. **Discussion: Types of Nanoscale Materials & Their Structure
> and Chemical Composition**

-   *Question 1:* *Are there any other significant categories, based on
    structure and chemical composition, that should be included in this
    discussion because they are substantially different from the
    categories mentioned (e.g., hybrids, self- assembly devices,
    others)?*

-   *Question 2:* *For the different categories of nanoscale materials,
    what is the current state of knowledge about structure and chemical
    composition?*

-   *Question 3: Can structures and chemical composition be correlated
    to specific properties and is this correlation quantifiable?
    Chemical Identification Elements (e.g., which ones? for which
    substances? test methods?)*

-   *Question 12: How important are impurity identity and impurity
    levels to the understanding and characterization of nanoscale
    materials?*

-   *Question 13: Are there routine purification procedures that can
    effectively control or remove impurities, when desirable, for
    certain classes of nanoscale materials?*

4:30 p.m. Wrap-up and Prepare for Day Two

5:00 p.m. ADJOURN

**Day Two: Friday, September 7**

> 8:30 a.m. **Discussion: Physical-Chemical Properties**

-   *Question 4: Which physical-chemical properties are relevant to
    nanoscale materials and how? Which are known or reasonably
    ascertainable and which have data gaps?*

-   *Question 5: Are there properties that would have little or no
    relevance under the NMSP?*

-   *Question 6: Which properties are associated with aggregated or
    agglomerated nanoscale materials, as opposed to properties that are
    inherent to the material regardless of physical form?*

-   *Question 7: Are there routine manipulations of nanoscale materials
    that result in physical-chemical properties changes or other
    defining characteristics (e.g., surface modifications of nanotubes
    to enhance solvent dispersibility)?*

-   *Question 8: How should physical-chemical property data be
    prioritized for the NMSP? Based on availability, effect (toxicity or
    exposure criteria), or other factors?*

**Discussion: Nanoscale Manufacture and Processing** Methodologies for
Characterizing Nanoscale Materials

-   *Question 9: What are the common processes used to manufacture
    nanoscale materials?*

-   *Question 10: How are processes used to produce specific
    characteristics or properties?*

-   *Question 11: Which methods reduce particle size but do not result
    in property changes? Which methods reduce particle size and result
    in property changes?*

Noon LUNCH

1:15 p.m. **Discussion: Methodologies for Characterizing Nanoscale
Materials**

> Analytical Methods:

-   *Question 14: Are validated methods available for the different
    categories of nanoscale materials?*

-   *Question 15: Are there techniques that can be universally applied?*

-   *Question 16: For small quantities of materials, are there sampling,
    handling, and collection techniques as well as sample integrity,
    accuracy and precision QA/QC methodologies available?*

-   *Question 17: What is the status of standardization efforts? Are
    these efforts focused on broadly applicable characterization methods
    or category-specific methods?*

-   *Question 18: What alternative or innovative methods or technologies
    can be applied to nanomaterial analysis?*

> Models:

-   *Question 19: Are there models that are currently used to obtain
    property data for nanoscale materials? For which properties and
    which nanoscale materials?*

-   *Question 20: Has any validation work been conducted that compares
    predicted values with measured data? For which properties and which
    nanoscale materials?*

-   *Question 21: Are there current significant characterization needs
    for which the NMSP should investigate model development?*

> **Discussion: Prioritization of Data Gaps**

2:30 p.m. BREAK

2:45 pm Public Comments

3:15 p.m. Panelist Closing Remarks

3:45 p.m. Next Steps and EPA Closing Remarks

4:00 p.m. ADJOURN

**Appendix B**

**DISCUSSION PAPER**

![](media/image2.png){width="1.0in" height="1.0in"}

**Peer Consultation Public Meeting on**

**The Material Characterization of Nanoscale Materials**

***Discussion Topics***

**August 7, 2007**

**Peer Consultation Public Meeting on**

**The Material Characterization of Nanoscale Materials**

***Discussion Topics***

**[Meeting Background and Purpose]{.underline}**

EPA is convening a public scientific peer consultation meeting on
material characterization for nanoscale chemical substances ("nanoscale
materials") to inform the development of its Nanoscale Materials
Stewardship Program (NMSP) under the Toxic Substances Control Act
(TSCA). The peer consultation is one of several actions EPA is taking to
better understand the potential risks and benefits of nanotechnology.

On October, 18, 2006, EPA invited the public, industry, environmental
groups, other federal agencies and other stakeholders to participate in
the design, development and implementation of a stewardship program for
nanoscale materials. On July 12, 2007, EPA announced the availability of
a NMSP concept paper and related documents and a public meeting on
August 2, 2007 to discuss and receive comments on these materials
(http://www.epa.gov/oppt/nano/nmspfr.htm).

The NMSP will complement and support the Agency\'s new and existing
chemical programs under TSCA and will help provide a firmer scientific
foundation for regulatory decisions by encouraging the development of
key scientific information and appropriate risk management practices for
new and existing chemical nanoscale materials. The NMSP is intended to
include but not limited to engineered nanoscale materials manufactured
or imported for commercial purposes as defined in 40 CFR 720.3 (r). The
NMSP is envisioned to have two parts: 1) a Basic Reporting Program and
2) an In-depth Program. This discussion paper and the public peer
consultation meeting are intended to support the NMSP by identifying
material characterization data that participants could submit under the
Basic Program if they are in the participant's possession or are
reasonably ascertainable as defined in 40 CFR 720.3 (p). The data and
experience generated by the basic reporting phase will help to inform
the types of in-depth data to be developed. In-depth data development
could begin at any time and would entail, among other types of data,
development of material characterization data in a greater amount of
detail. In-depth data development could also include additional types of
material characterization data if they are identified.

EPA received input in November, 2005 from the National Pollution
Prevention and Toxics Advisory Committee (NPPTAC) regarding a voluntary
stewardship program for nanoscale materials. A NPPTAC ad-hoc work group
on nanoscale materials developed an overview paper that stated that a
voluntary stewardship program should:

1.  Give EPA, and the public to the extent possible recognizing
    legitimate CBI issues, a better understanding of the types of
    engineered nanoscale materials; the physical, chemical, hazard and
    exposure characteristics of such substances; the volume of such
    substances; and the uses of such substances;

2.  Help EPA develop capacity and a process to identify and assess risks
    of engineered nanoscale materials;

3.  Help EPA determine what information it needs about engineered
    nanoscale materials and articulate those information needs to
    industry and other stakeholder groups;

4.  Help EPA understand what risk management practices are being used at
    production, processing, use and disposal stages, and what additional
    risk management practices need to be implemented;

5.  Prompt or reinforce the implementation of risk management practices;
    and

6.  Provide the information and experience needed to develop an overall
    approach to the treatment of nanoscale chemical substances under
    TSCA that builds public trust in nanoscale materials while enabling
    innovation and responsible development.

EPA will utilize all public input, including that from NPPTAC, other
stakeholders, public meetings and peer consultations to further inform
the development of its Nanomaterials Stewardship Program and TSCA
program for nanoscale materials.

**[Meeting Objectives]{.underline}**

The EPA public peer consultation meeting on material characterization
needs for nanoscale materials will help clarify which data and elements
should be included in the NMSP Basic Program and/or In-depth Program.
The goal is to have an applied discussion that considers 1) the
currently available understanding of material characterization as it
relates to nanoscale materials and 2) how this understanding can be used
to guide the Agency's thinking regarding the material characterization
data elements that would be most useful and important to include in the
NMSP. The specific objectives of the public peer consultation meeting
are as follows:

1.  To inform industry and the public of EPA's level of understanding of
    the material characterization needs for nanoscale materials in
    general and for the NMSP;

2.  To further develop EPA's understanding of how nanoscale materials
    are engineered or manufactured to achieve specific properties and
    characteristics;

3.  To further develop EPA's understanding of which chemical
    identification elements and physical-chemical property data are
    generally relevant in characterizing nanoscale materials and which
    identification elements and property data are most important in
    characterizing specific classes of nanoscale materials;

4.  To discuss what analytical procedures and test methods are available
    for acquiring these material characterization data, and where
    procedure and method validation or development is needed;

5.  To discuss how these material characterization data needs should be
    prioritized for the NMSP Basic and/or In-depth Program; and

6.  To discuss potential nomenclature needs for specific classes of
    nanoscale materials based on material characterization outcomes.

**[Discussion Overview]{.underline}**

Despite the rapid advancement of nanotechnology, the breadth of
nanoscale material types coupled with the limited hazard data available
for many of these materials pose a challenge in understanding and
measuring their benefits and risks. Numerous efforts are underway to
begin to address these challenges. The International Life Sciences
Institute (ILSI) Research Foundation/Risk Science Institute, for
example, convened an expert working group to develop a strategy for
identifying hazards associated with engineered nanoscale materials.
Focusing on the limited data available, the working group developed a
screening strategy for hazard identification (rather than a detailed
testing protocol) that includes a broad data gathering effort.[^1]

The ILSI report describes the characterization of nanoscale materials,
in addition to in vitro and in vivo screening, as a key third aspect of
an overall screening strategy due to the likely dependence of the
biological activity of nanoscale materials on physical-chemical
properties not often considered in toxicity screening studies.
Additionally, given the difficulties associated with characterizing many
nanoscale materials, nanoscale material characterization is a subject
appropriate for detailed investigation and discussion.

Numerous national and international standards organizations, including
the American National Standards Institute (ANSI)[^2] and the
International Organization for Standardization (ISO)[^3], have also
convened committees to begin to address many of these same challenges
and in particular the need for methods standardization. Several of these
committees have indicated that, given the breadth of nanotechnology and
its data issues, the initial products the committees develop may be in
the form of best practices rather than actual test protocols.

The remainder of this paper discusses a proposed approach for the EPA
scientific peer consultation meeting on nanoscale material
characterization. EPA recognizes that the different chemical classes of
nanoscale materials would make universal application of any particular
characterization endpoint or methodology impossible. The premise of the
Basic Reporting phase of the NMSP is that some information is known or
reasonably ascertainable. The approach for this Panel is therefore to
discuss what data are known or reasonably ascertainable to characterize
nanoscale materials. This will be followed by a discussion on the
methodology used to obtain and use characterization endpoints of
interest.

**[Discussion Topics]{.underline}**

I.  Characterization of Nanoscale Materials

> 1\. Description of nanoscale materials

a.  Types/categories of nanoscale materials

> 2\. Physical-chemical properties of potential interest

a.  Particle size and distribution

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a.  Particle shape and dimensions

b.  Agglomeration and aggregation

c.  Surface area

d.  Surface charge

e.  Surface chemistry

f.  Chemical composition

g.  Crystal structure

h.  Impurity identification and levels

> 3\. Design to achieve unique properties

a.  Manufacturing and processing methodologies

b.  Chemical transformations

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```
II. Methodologies for Characterizing Nanoscale Materials

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1.  Obtaining characterization data for nanoscale materials

    a.  Analytical methods for detecting and quantifying nanoscale
        materials

    b.  Analytical methods measuring physical-chemical properties
        (measurement techniques and testing protocols)

    c.  Models to predict properties and effects

2.  Metrology

    a.  Methods validation

    b.  Standards and harmonization

3.  Prioritization of characterization data and data gaps

4.  Miscellaneous -- Do Panelists have additional topics to discuss?

**[Discussion]{.underline}**

This section provides additional information on specific technical
issues to facilitate discussion at the meeting. The information will
include literature findings as well as questions on the specific
discussion topics.

**Types of Nanoscale Materials & Their Structures and Chemical
Compositions**

Based on structure and chemical composition, EPA has grouped
nanomaterials into 4 distinct categories for purposes of this
discussion: 1) simple organic molecules; 2) simple inorganic molecules;
3) polymeric substance (including dendrimeric substances); and 4)
composites. A fifth category, biological compounds will not be addressed
in the peer consultation. While all of these categories can be divided
further, only the organic category will be divided further into
molecules based predominantly on carbon (e.g., fullerenes, nanotubes)
and all other organic substances (e.g., salts of carboxylic acids). This
grouping is similar to the American National Standards Institute
Nanotechnology Standards Panel approach presented at the September 2004
meeting at the National Institute of Standards and Technology in
Gaithersburg Maryland[^4].

[Question 1]{.underline}: Are there any other significant categories,
based on structure and chemical composition, that should be included in
this discussion because they are substantially different from the
categories mentioned (e.g., hybrids, self- assembly devices, others)?

[Question 2]{.underline}: For the different categories of nanoscale
materials, what is the current state of knowledge about structure and
chemical composition?

[Question 3]{.underline}: Can structures and chemical composition be
correlated to specific properties and is this correlation quantifiable?

**Physical-Chemical Properties**

The importance of nanoscale materials is due to their potential for
unique or greatly enhanced properties. EPA routinely uses a base set of
physical-chemical property data (e.g., melting point, boiling point,
vapor pressure, water solubility) for a variety of programs (e.g., High
Production Volume Challenge, New Chemicals) and decision-making. As
mentioned previously, certain material properties are of significant
importance in characterizing nanoscale materials. Recent research
suggests that particle size, surface area, and surface chemistry (or
surface activity) are initially some of the most important properties to
measure.

As expected for most chemicals, class 1[^5] substances having specific
molecular structures and formulas may be more readily studied and
characterized at the nanoscale than the polymer and composite
categories. For example, carbon-based nanoscale materials as well as
metal oxide nanoscale chemicals are often well characterized. Structural
and physical-chemical property data therefore are likely to be well
documented for these types of materials.

[Question 4]{.underline}: Which physical-chemical properties are
relevant to nanoscale materials and how? Which are known or reasonably
ascertainable and which have data gaps?

[Question 5]{.underline}: Are there properties that would have little or
no relevance under the NMSP?

[Question 6]{.underline}: Which properties are associated with
aggregated or agglomerated nanoscale materials, as opposed to properties
that are inherent to the material regardless of physical form?

[Question 7]{.underline}: Are there routine manipulations of nanoscale
materials that result in physical-chemical properties changes or other
defining characteristics (e.g., surface modifications of nanotubes to
enhance solvent dispersibility)?

[Question 8]{.underline}: How should physical-chemical property data be
prioritized for the NMSP? Based on availability, effect (toxicity or
exposure criteria), or other factors?

**Nanoscale manufacturing and processing**

The number of manufacturing and processing methods for generating
nanoscale material continues to grow and become more sophisticated. The
two primary areas for this discussion include physical reduction methods
(milling) and engineering methods (e.g., particle stabilization, vapor
deposition, self assembly).

[Question 9]{.underline}: What are the common processes used to
manufacture nanoscale materials?

[Question 10]{.underline}: How are processes used to produce specific
characteristics or properties?

[Question 11]{.underline}: Which methods reduce particle size but do not
result in property changes? Which methods reduce particle size and
result in property changes?

**Impurities**

Impurity content is a growing area of interest in nanotechnology due to
improved performance observed in some cases (e.g., solar cells and
semiconductors) and deleterious effects observed in others (e.g.,
quantum dot quantum computers). The confounding effects that impurities
have with respect to toxicological endpoints are also being studied
(National Nanotechnology Initiative 2006 Environmental Health and Safety
research report[^6]).

[Question 12]{.underline}: How important are impurity identity and
impurity levels to the understanding and characterization of nanoscale
materials?

[Question 13]{.underline}: Are there routine purification procedures
that can effectively control or remove impurities, when desirable, for
certain classes of nanoscale materials?

**Obtaining characterization data**

Determining identity, quantifying the nanoscale particle range, and
measuring physical-chemical properties for that identity and particle
range are essential to the characterization of nanoscale materials.
Because of the challenges associated with size, shape, surface
characteristics, and possibly other aspects of nanoscale materials, an
evaluation of existing measurement techniques is critical to nanoscale
material characterization. The National Nanotechnology Initiative report
stated that "\...Accurate and useful measurement techniques are also
important because agglomerated nano materials may either retain or lose
their emergent properties - or take on new properties - thus affecting
the potential biological response."

[Question 14]{.underline}: Are validated methods available for the
different categories of nanoscale materials?

[Question 15]{.underline}: Are there techniques that can be universally
applied?

[Question 16]{.underline}: For small quantities of materials, are there
sampling, handling, and collection techniques as well as sample
integrity, accuracy and precision QA/QC methodologies available?

[Question 17]{.underline}: What is the status of standardization
efforts? Are these efforts focused on broadly applicable
characterization methods or category-specific methods?

[Question 18]{.underline}: What alternative or innovative methods or
technologies can be applied to nanomaterial analysis?

**Modeling**

Empirical modeling can be a useful approach to predict physical-chemical
properties when experimental data are not known or ascertainable. The
initial problem with modeling is that, to accurately predict property
endpoints for a given category of substances, there must be some
experimental data available in the tool's database for at least some
representative substances in that category. For newly discovered or
studied materials, the minimum but necessary quantity and type of
experimental data often is not available to sufficiently populate a
tool's database and allow accurate prediction by the tool. Some
estimation methods have been developed for specific property endpoints,
but many others are lacking.

[Question 19]{.underline}: Are there models that are currently used to
obtain property data for nanoscale materials? For which properties and
which nanoscale materials?

[Question 20]{.underline}: Has any validation work been conducted that
compares predicted values with measured data? For which properties and
which nanoscale materials?

[Question 21]{.underline}: Are there current significant
characterization needs for which the NMSP should investigate model
development?

**Appendix C**

**PRELIMINARY PANEL COMMENTS ON DISCUSSION PAPER**

**Comment Compilation of Panelists' Preliminary Responses to Panel
Discussion Questions Posed in the Discussion Paper for the Public
Meeting on Material Characterization of Nanoscale Materials**

***Draft Compilation as of August 31, 2007***

A compilation of Panelists' preliminary comments received in response to
"Panel Discussion Questions" contained in the Discussion Paper for the
Public Meeting on Material Characterization of Nanoscale Materials is
provided below. This compilation is organized as follows:

a)  General Observations

b)  Discussion Category Responses

    a.  Types of Nanoscale Materials and their Structures and Chemical
        Compositions

    b.  Physical-Chemical Properties

    c.  Nanoscale Manufacturing and Processing

    d.  Impurities

    e.  Obtaining Characterization Data

    f.  Modeling

c)  Supporting Figures

d)  Supporting References

**[General Observations]{.underline}**

[Dr. Warheit:]{.underline}

Thank you for giving me the opportunity to provide some preliminary
comments on the Discussion Topics for EPA's Peer Consultation Public
Meeting on the Material Characterization of Nanoscale Materials. The
forthcoming meeting should provide useful information, both for EPA and
for stakeholders/outside participants. I would caution EPA, that in my
opinion, many of the answers to the questions contained in the
"Discussion Topics" document are case-by-case and/or nanoparticle-type
specific (e.g. those pertaining to metal oxides vs. carbon structures)
and a universal response cannot be given (e.g. questions 9 and 10 --
"What are the common processes used to manufacture nanoscale materials?
And "How are processes used to produce specific characteristics or
properties"). Indeed the various subsets of nanoparticle-types are
likely to require different answers to the same questions.

**[Discussion Category Responses]{.underline}**

**Types of Nanoscale Materials & Their Structures and Chemical
Compositions**

Based on structure and chemical composition, EPA has grouped
nanomaterials into 4 distinct categories for purposes of this
discussion: 1) simple organic molecules; 2) simple inorganic molecules;
3) polymeric substance (including dendrimeric substances); and 4)
composites. A fifth category, biological compounds will not be addressed
in the peer consultation. While all of these categories can be divided
further, only the organic category will be divided further into
molecules based predominantly on carbon (e.g., fullerenes, nanotubes)
and all other organic substances (e.g., salts of carboxylic acids). This
grouping is similar to the American National Standards Institute
Nanotechnology Standards Panel approach presented at the September 2004
meeting at the National Institute of Standards and Technology in
Gaithersburg Maryland[^7].

[Question 1]{.underline}: *Are there any other significant categories,
based on structure and chemical composition, that should be included in
this discussion because they are substantially different from the
categories mentioned (e.g., hybrids, self- assembly devices, others)?*

[Dr. BelBruno:]{.underline}

The classification scheme presented seems to be the most practical. To
do otherwise, would overwhelm the issue at a time when we are trying to
get a basic set of data together. Most other nanoparticles are
combinations or composites of the classes already listed, for example,
polymer coated iron nanoparticles for imaging. While the combined
material will need to (eventually) be examined for its own possible
unique properties, the components need to be understood first.

Self-assembled and hybrid materials, cited in the topic description,
fall into the same composite or "combination" category as the imaging
particles noted above.

[Dr. Canady:]{.underline}

Perhaps the categories, or EPA's thinking about "mechanisms to help
clarity of approach," should not be limited by structure AND
composition. A useful classification scheme (including cross-referenced
sub-classifications across categories) should probably be more amenable
to identifying attributes that are important to regulatory clarity by
being open to structure, composition, or combinations of structure and
composition. From asbestos and PM data it seems there may be
combinations of structure and composition that are important and there
may also be structures that are important independent (to a large
degree) of composition. Function (e.g., OP compounds, endocrine active
compounds) may also be a useful classification attribute. Classification
should be amenable to a matrix approach with composition, structure, and
function as dimensions of the matrix. It seems likely, as more and more
NMs are developed, that the very broad categories presented here by EPA
will begin having very little practical utility because we will be
discovering categories and classes within them that are more important
in understanding how to regulate, and that confuse the boundaries.

If EPA stays with large bins, here are some other categories to
consider:

**Combinations:** There are already intersections of
inorganic/organic/polymer/composite materials in the form of
specifically constructed nanoscale materials or particles that will
challenge any category-based approach to nomenclature or regulation. At
some point the combinations may comprise the bulk of the applications as
molecular assembly comes into full use.

**Emulsions, vesicles, liposomes, micelles:** This would be a structure
(or form) rather than composition category with either amphiphillic
molecules forming "filled balloons" or small collections of molecules
forming nanoscale particles in stasis in a liquid. These kinds of
particles are being developed for use in food and drug applications,
biocides, and, most likely, pesticides. Based on the utility of the
approach in drug delivery and nutrient stabilization in foods, it's not
hard to imagine that industrial uses would also be developed (for
chemical processes to control/specify reactions, solubilization of
insoluble intermediates, and transport/stabilization of compounds).

[Dr. Cassell:]{.underline}

I'm confused at this terminology defined in the introductory paragraph.
For instance, simple organic molecules would not be inclusive of
multiwalled carbon nanotubes (this is implied that it can be done this
way). I think there needs to be more thought put into classifying these
materials correctly.

Hybrid structures in particular need to be considered. For example,
there are emerging reports detailing the use of engineered nanomaterials
that could be placed into multiple categories (organic, inorganic and
polymeric). Filled carbon nanostructures (e.g. metal filled multiwalled
carbon nanotubes) are a class of materials that could be grouped in such
a way. Another common class of materials is hybrid inorganic/organic
polymers.

[Dr. Lahann:]{.underline}

In principle, the four categories are sufficient for broad
classification on a materials basis. However, hybrid materials have also
been observed increasingly in recent times and are distinct from
composites. For instance, a particle with an inorganic core and an
organic shell should be considered a hybrid material rather than a
composite. Thus, adding a 5^th^ category may be wise.

[Dr. Murashov:]{.underline}

The concept paper proposes the following grouping of nanomaterials: 1)
simple organic molecules; 2) simple inorganic molecules; 3) polymeric
substances (including dendrimeric substances); 4) composites; 5)
biological (nanomaterials assigned to the latter group are not
considered under the proposed stewardship program). The first category
is further subdivided into molecules based predominantly on carbon (e.g.
fullerenes and nanotubes) and all other organic substances (e.g. salts
of carboxylic acids).

This categorization suffers from inconsistency with the conventional
usage of chemical terms. Specifically:

a)  Carbonaceous materials including allotropes of carbon such as
    fullerenes and carbon nanotubes are considered inorganic materials.

b)  It is not clear why nanoscale formulations of simple organic
    molecules such as salts of carboxylic acid were made into a separate
    category of nanomaterials given their little significance as
    engineered nanomaterials at this point.

c)  Traditionally, "simple inorganic molecules" means molecules such as
    CO~2~, SO~2~, NO, H~2~O. It is not clear why nanoscale formulations
    of these materials would be made into a separate category of
    nanomaterials given their little significance as engineered
    nanomaterials at this point. Was this category meant to describe
    "simple inorganic compounds" to include solid materials with a high
    degree of ionic or metallic bonding such as TiO~2~ and Ag,
    respectively?

d)  It is not clear what is meant by "composite" category of
    nanomaterials. For example, would nanoparticles composed of cores
    and shells of different chemistries be considered composites? Would
    functionalized nanoparticles be considered composites?

An alternative classification of simple nanomaterials can be found, for
example, in the draft ISO TC229 Technical Report on "Health and Safety
Practices in Occupational Settings Relevant to Nanotechnologies" and
includes the following categories: 1) carbonaceous; 2) oxides; 3)
metals; 4) semiconductors; 5) organic polymeric; 6) bio-inspired. This
classification is better aligned with the chemistry of simple
nanomaterials and their hazard properties. More complex nanomaterials
could be categorized further along the lines of nomenclature tree being
developed by ISO TC229 which includes distinction between nano-objects
(includes nanoparticles) and nanostructured materials (includes
nanocrystals and complex assemblies of nano-objects).

[Dr. Murday:]{.underline}

a)  The presently identified categories apparently presume freestanding
    nanostructures (NS). These certainly pose a greater risk for
    pervasive dissemination. One might also think about NS embedded
    physically in a matrix (i.e. no chemical bonding), embedded
    chemically in a matrix (i.e. chemical bonding) and what might be
    called "thin film" where NS are etched out of deposited films (that
    are chemically bonded to the substrate).

b)  There is some danger in working from a molecular perspective of NS.
    Molecules are largely well defined entities -- one knows exactly
    what atoms are present and their first order bonding structure (some
    second order effects like chain folding, cis/trans folding might not
    be known). Nanostructures will almost never be that precisely known
    -- if for no other reason than the number of atoms can be too large
    for effective, specific nomenclature.

c)  There is benefit from utilizing a molecular perspective. There is
    policy/procedure in place to handle hazardous molecules. That
    policy/procedure should be adequate (albeit over constraining) to
    handle NS safely. NS are not some brand new form of matter that
    presents a [totally new]{.underline} set of problems.

[Dr. Small:]{.underline}

a)  EPA should probably include a category for "elemental"
    nanoparticles, i.e. Au, Ag, Cu, or are these considered simple
    inorganic molecules. To me they seem to be a separate class from say
    oxides like TiO2.

b)  Which category includes layered nanomaterials?

c)  Is EPA considering only those materials with 3 nanodimensions i.e.
    particles?

d)  Where do functionalized surfaces fit in this scheme?

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 2]{.underline}: *For the different categories of nanoscale
materials, what is the current state of knowledge about structure and
chemical composition?*

[Dr. BelBruno:]{.underline}

Pure materials (perhaps better defined as single component?) can be
well-defined. For example, pure carbon-based materials such as
fullerenes or nanotubes may be well-characterized by size, microscopy
and chemical functionality. Generally impurities consist of remnants of
metal catalysts, which can be detected and (usually) removed. Similarly,
inorganic materials such as TiO~2~ nanoparticles may be characterized by
size and structure using standard techniques (described elsewhere in
response to subsequent questions).

Polymer nanoparticles can present problems with respect to chemical
composition, but may be characterized by size distribution using
standard methods. Chemical composition is more difficult since, even for
macroscopic polymers, there are impurities and mixed compositions. This
problem can probably be solved, but requires more attention. Composite
materials fall into this same category.

[Dr. Canady:]{.underline}

I don't have this detailed knowledge but based on the breadth of the 4
categories, not sure the question is answerable. If the question were
about carbon nanotubes versus quantum dots or dendrimers you could start
forming a basis for the state of knowledge, but where do you start and
end in a description of the state of knowledge about particles of
inorganic materials?

[Dr. Cassell:]{.underline}

For newer nanomaterials systems, knowledge concerning structure and
composition varies widely. Some nanomaterials systems are very well
characterized whereas in other systems, I would say there is little if
any knowledge. The extent to which characterization is performed is
often determined by the particular study involved and whether the
researchers/users of the material required this additional
characterization for understanding their system.

[Dr. Lahann:]{.underline}

For categories 1 and 2, chemical particle compositions and often also
structures are in many cases well understood. Mostly, the role of
impurities is often hard to assess and their influence on structure
maybe underestimated in cases. How composition and structure relates to
function is however often unclear and more work will need to be done.
Nanomaterials in categories 3 and 4 are often less well characterized.
Synthetic polymers are associated with variations of their molecular
weight and structure, which equally holds for nanomaterials comprised of
polymers. The extent of this variability may change between different
polymer materials, but is always present at least to some extend. Again,
it may be important to assess the role of this variability with respect
to function. Similarly, composite materials can be associated with
substantial variability in chemical composition and structure.

[Dr. Murashov:]{.underline}

It is possible to characterize relatively well almost any nanoscale
material. The main challenge is that this characterization is time
consuming, expensive and limited to only a small sample. At the present
state of the development, many nanomaterials have wide distributions of
chemistries and structures within the same product batch. This
heterogeneity of chemical composition and structure results in a range
of properties which are not fully characterized by conventional
measurements.

[Dr. Murday:]{.underline}

a)  Presumably NMSP is presently focusing on free standing
    nanostructures.

b)  In the chemistry/physics research laboratories, where there is
    generally careful attention to the identity of the NS being
    measured, the state of knowledge is okay. But there remain
    limitations to the analytical tools available for full
    characterization of NS (as is true generally for all materials).

c)  There is generally poor knowledge from the standpoint of large scale
    NS batches where separation/purification problems are more
    difficult/expensive to handle. This problem is clearly illustrated
    in carbon nanotubes. A couple of years ago one researcher purchased
    CNT from two vendors and multiple batches. He carefully analyzed the
    procured material. See Figure A. The worst batch had only 40% carbon
    in it -- and not all of that carbon was likely to be CNT.

d)  NS will frequently (usually) have "surface treatments" or "shells"
    to make them compatible with exposure to their intended environment.
    In the case of medical/health applications, the shell will likely
    impart recognition/transport functions. Those same two functions
    clearly have environmental implications.

e)  Another level of challenge is the role of "interphase" -- roughly
    speaking a layer of material enveloping/separating the NS.

[Dr. Small:]{.underline}

Simple organic molecules: The structure and chemical composition of the
fullerenes and C nanotubes are well known for the specific
nanomaterials. However when these materials are sold as a product the
product can be very inhomogeneous and the purity of the commercial
material (structure and chemical composition) is often unknown.

Simple inorganic molecules: The structure and chemical composition of
simple inorganic molecules like salts and metal oxides are for the most
part well known. The purity of the commercial product is more
homogeneous that commercial nanotubes but can still be an issue
depending on how the nanoproduct is made.

Polymeric materials: For materials like dendrimers, lipids the
theoretical structures are known to the degree this structure applies to
what is sold is unknown i.e. particularly for functionalized systems %
coverage. For polymeric materials that "contain" specific compounds
there is very little validation of structure.

Composites: For more complex materials multifunctional, layered, phase
separated etc. the current state of structure and chemical composition
is much less well known if at all. Several initial studies of complex
nanomaterials indicate that there is significant variation with respect
to structure and composition.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 3]{.underline}: *Can structures and chemical composition be
correlated to specific properties and is this correlation quantifiable?*

[Dr. BelBruno:]{.underline}

As a general rule, we are not at the point where we can correlate
physical properties to chemical structure/composition. The properties
have the potential to be size-dependent and until theory can provide a
rigorous method to describe the change in properties with size, this
desirable goal cannot be claimed. For example, silver nanoparticles, in
a select size range, may have antibacterial activity (C. N, Lok, et al,
*Journal of Biological Inorganic Chemistry* (2007), **12**, 527), but
this is not a prior, predictable. Magnetic properties of nanoparticles
also show a size and structure dependence (S Kar, et al, *Journal of
Nanoscience and Nanotechnology* (2006), **6**, 771; Y.T. Jeon, et al,
*International Journal of Modern Physics B* (2006), **20**, 4390).

[Dr. Canady:]{.underline}

Yes and yes. Why is this considered even potentially uncertain?

[Dr. Cassell:]{.underline}

Yes to a certain extent. For instance, we know that surface area of
nanoscale materials increases as diameter of the material decreases.
However, direct correlation between chemical composition and reactivity
for instance is not as well understood for nanoscale systems. I do think
it is quantifiable in a qualitative sense, but perhaps not in a
quantitative sense.

[Dr. Lahann:]{.underline}

Structure and chemical composition are critical aspects of every
nanomaterial, and as such contribute to the specific properties of a
material. In some cases, there is a direct correlation to a specific
property, which then is quantifiable. In other cases, structure and
composition influence specific properties through secondary mechanisms.
For instance, nanomaterials of category 3 may be water-soluble and as
such highly resorbable, unless the polymer chains are further
crosslinked. The extent of crosslinking may directly correlate with the
solubility of a material and its resorption. Similarly, molecular weight
or chirality of polymers can influence resorption and degradation
kinetics significantly.

[Dr. Murashov:]{.underline}

Yes. Structure and chemical composition can be quantifiably correlated
to specific risk-related properties. Examples are:

a)  Aerodynamic properties as a function of particle aerodynamic
    diameter (Lee and Liu, 1982);

b)  Surface area as a dose metric for low solubility low toxicity
    particulate matter (Maynard and Kuempel, 2005);

c)  Biological response as a function of surface charge (e. g. for
    dendrimers see Jevprasesphant et al, 2003; Mecke et al, 2004);

d)  Biological response and pharmacokinetics as a function of surface
    chemistry (e. g. for functionalized fullerenes and carbon nanotubes
    see Sayes, 2004; Singh et al, 2006).

Once nanomaterial's structure approaches atomic-level consistency
(nano-molecular materials?), it should be straightforward to develop and
reliably employ Quantitative Structure Activity Relationship - like
models. Presently, we have very limited number of nanomaterials which
have such an atomic-level consistency. An example of nanomaterials where
we do have such atomic level control over chemical structure is
dendrimers.

[Dr. Murday:]{.underline}

a)  As an academic question, the answer is definitively yes --
    composition/ structure will define the chemical/physical properties
    -- on NS as well as any other form of material. As a practical
    question the correlation is difficult because samples are generally
    not the same level of purity as we expect for chemical reagents.

b)  I have included a preliminary table that identifies selected
    properties and "critical scale lengths," i.e., properties that will
    likely vary significantly from predictions of the solid state
    (larger scale) / chemical (smaller scale) models we presently use.
    See Figure B. There could be real value for EPA to sanction a
    careful examination of "critical scale lengths" to identify when
    problems would be more likely to occur.

c)  One area that is very important is chemical reactivity -- clearly an
    environmental issue. Surface science has developed reasonable
    understanding of reactions on atomically flat surfaces, and some
    understanding of vicinal surfaces (where atomic scale "roughness" is
    higher). But NS have surfaces more complex than these. The research
    on catalysis does address some of that complexity, but the
    understanding - because of the difficulty in preparing well defined
    samples, characterizing them, and modeling the higher level of
    complexity -- is not as good.

[Dr. Small:]{.underline}

For some properties the answer is yes, for example the color or
absorption of light by specific sized Au particles. The correlation for
most properties related to risk assessment and EHS is not well known.
Efforts to understand these types of correlation are hindered by lack of
validated "standards" and methods.

[Dr. Warheit:]{.underline}

No specific comments provided.

**Physical-Chemical Properties**

The importance of nanoscale materials is due to their potential for
unique or greatly enhanced properties. EPA routinely uses a base set of
physical-chemical property data (e.g., melting point, boiling point,
vapor pressure, water solubility) for a variety of programs (e.g., High
Production Volume Challenge, New Chemicals) and decision-making. As
mentioned previously, certain material properties are of significant
importance in characterizing nanoscale materials. Recent research
suggests that particle size, surface area, and surface chemistry (or
surface activity) are initially some of the most important properties to
measure.

As expected for most chemicals, class 1[^8] substances having specific
molecular structures and formulas may be more readily studied and
characterized at the nanoscale than the polymer and composite
categories. For example, carbon-based nanoscale materials as well as
metal oxide nanoscale chemicals are often well characterized. Structural
and physical-chemical property data therefore are likely to be well
documented for these types of materials.

[Question 4]{.underline}: *Which physical-chemical properties are
relevant to nanoscale materials and how? Which are known or reasonably
ascertainable and which have data gaps?*

[Dr. BelBruno:]{.underline}

The prelude to the questions really has it all there. The important
properties (aside from chemical structure/composition) are particle
size, surface area and reactivity. Size, surface area and structure are
measurable and standard procedures are possible, but reactivity is more
difficult to quantify and often particle specific. Techniques such as
dynamic light scattering, BET procedure and x-ray diffraction,
respectively, are routinely employed.

[Dr. Canady:]{.underline}

It seems you have to first express the decisions that need to be made
about the materials and then what is minimally sufficient for decisions
and therefore relevant. I am afraid I am not familiar enough with TSCA
to begin this process.

There is a risk here of developing lists of what we can do or can think
of and then letting them stand forever as requirements. The list of
relevant properties should flow from the decision needs. For example,
some recent reviews focus on surface area because of the thought that it
may correlate better with toxicity than mass does. However, other
measures may be enough to capture the listing decision needs or even
reportable quantity determinations without the need to measure surface
area in any specific way.

Basing property needs on a minimally sufficient set to make decisions
could more easily consider both cost and utility so that unnecessary
costs can be avoided.

On the other hand, at least initially and until we get a better sense of
what is useful for decisions, the response to this question could be
rather long for the general case of all nanoscale material so that we
can begin to sort through the utility functions.

There are likely to be properties relevant to decisions about specific
classes of materials but not others.

[Dr. Cassell:]{.underline}

The most relevant physical-chemical properties are crystallinity,
surface properties (charge, roughness, and area), and solubility state
of agglomeration because these properties directly influence the direct
assessment of toxicological risk. I think that most new materials the
crystallinity has been characterized well but the state of agglomeration
is probably not as well understood.

[Dr. Lahann:]{.underline}

As for all other materials, nanoscale materials have specific sets of
properties that can be used for characterization. In addition, these
materials often have specific properties due to the nanoscale
information encoded in their structure. This information may be
transient and alter with temperature. For instance, for a given CdSe
nanoparticle material, its optical properties are -- within a certain
range -- a function of the particle diameters. Another example is the
magnetic properties of iron oxide particles, which alter with diameter.
In general, properties that are associated with the nanoscale structure
of a material are better suited for characterization of nanomaterials.
Often, the characterization of individual nanoobjects on the basis of
size and size distribution, shape and shape distribution, chemical
composition, structure, etc., may be more insightful than "bulk
characterization".

[Dr. Murashov:]{.underline}

All listed physical-chemical properties in the discussion paper are
relevant to risk potential of nanomaterials:

a)  Particle size and distribution

b)  Particle shape and dimensions

c)  Agglomeration and aggregation

d)  Surface area

e)  Surface charge

f)  Surface chemistry

g)  Chemical composition

h)  Crystal structure

i)  Impurity identification and levels

In addition, the following are important parameters for characterization
(see also draft ISO TC229 TR "Guidance on physico-chemical
characterization of engineered nanoscale materials for toxicologic
assessment"):

1.  Solubility;

2.  Porosity;

3.  Stability under different experimental conditions (biopersistence,
    durability and dispersibility).

In particular, since interactions between biological species and
nanomaterials occur primarily at the nanomaterial surface, it is
critical to characterize not just the chemistry of nanomaterial core,
but also chemical species represented on the surface of nanomaterials.
For example, if one considers titania nanoparticles coated with silica
and made to reflect UV light, the commercially important active
ingredient is titania. However, since silica is on the surface, the
biological response is expected to be to silica at least initially until
silica coating is dissolved or otherwise altered.

All properties can be measured at a research level. However, presently
atomic-level description is limited to individual nanoscale features
such as individual nanoparticles. There is a lack of standardized
methods and techniques to conduct characterization of representative
nanomaterial samples routinely that is cost- and time-effective.

[Dr. Murday:]{.underline}

a)  All physical/chemical properties are relevant to NS. Perhaps the
    more important question is which of those properties might vary
    significantly at the nanoscale and are those properties of
    environmental concern.

b)  For the NS itself one can address this question by examining
    property vice critical scale length -- two generic specific issues
    to watch for are quantization (size) and correlation (many atoms)
    effects.

c)  Many, if not most NS, will have a core/shell(s) structure -- i.e.,
    they will not be a monolithic entity. The shell(s) will impart
    different/additional physical and chemical properties. As we move
    more to "smart" structures -- those that sense and respond - the
    complexity of those added properties will grow.

d)  In addition, NS can have an "interphase." This will be a tougher
    problem since the "interphase" may be generally even more complex
    and hard to characterize.

[Dr. Small:]{.underline}

I think it will be important to define relevance to what. In general,
properties such as size, surface area, chemical structure, surface
characteristics, functionalization, and charge are relevant to the
properties of most nanoscale materials. Different materials will have a
different set of properties that are relevant to its use or hazard
evaluation. Most methods for the determination of physical-chemical
properties of nanomaterials have large gaps. Critical to minimizing
these gaps is to provide information that is consistent and reproducible
from one lab to the next. Accuracy may well be a secondary
consideration.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 5]{.underline}: *Are there properties that would have little
or no relevance under the NMSP?*

[Dr. BelBruno:]{.underline}

At this point, it is not at all clear which, if any, properties have
little relevance. I do not believe that any measurements should be
ignored or discouraged by the standards that might be set.

[Dr. Canady:]{.underline}

There is probably a list of things that are not relevant from the
chemical realm, which EPA might have included in a list of what to ask
for out of habit. For example, volatility measures that you might
require for chemicals may be valueless.

I can't think of a case for a categorical exclusion on a property other
than things like volatility (i.e., property measures that just come up
blank because they don't apply to particles). We probably don't know
what will have little or no relevance in all cases. There would need to
be a theoretical basis to "prove a negative" and this may be
particularly difficult while we are in the middle of discovering
behaviors and uses as a result of manipulating properties.

Perhaps when SAR or other methods of relating properties to function
evolve to a point of understanding null points in chemical and
biological interaction we can begin to develop maps of where there are
not effects. Seems likely they would be multivariate likelihood
statements rather than "this property never interacts" with biology.

[Dr. Cassell:]{.underline}

I think all of the information is useful. In certain contexts, optical
properties (photoelectric properties for instance) would not be relevant
to NMSP. All of the well-accepted physical chemical properties should be
relevant to NMSP however.

[Dr. Lahann:]{.underline}

See response to question 4.

[Dr. Murashov:]{.underline}

At this point, it appears that the following properties have little
direct relevance to the risk potential of nanomaterials:

a)  thermal properties such as thermal conductivity, heat capacity and
    thermal diffusivity;

b)  optical properties such as refractive index, optical rotation,
    luminescence;

c)  elastic properties such as Young modulus and elastic constants.

[Dr. Murday:]{.underline}

a)  Presumably the emphasis is on impacting living systems. There is not
    enough NS volume to worry about unsightly/unwieldy waste piles.

b)  Some likely properties with little/no relevance from an
    environmental protection perspective - thermal conductivity,
    plasmonics, superconductivity.

[Dr. Small:]{.underline}

It is reasonable to assume that so little is known regarding the
relationship between properties and impacts that most properties have to
be considered relevant until definitive studies are conducted to show
they are not relevant. That said, I would think the determination of
mass alone will not be relevant to NMSP.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 6]{.underline}: *Which properties are associated with
aggregated or agglomerated nanoscale materials, as opposed to properties
that are inherent to the material regardless of physical form?*

[Dr. BelBruno:]{.underline}

If we are dealing with aggregates or agglomerated materials, we need to
measure those properties cited above, size, surface area, reactivity)
for both the components and the aggregates. Essentially, we need "core
and aggregate" measurements. Obviously, the chemical
composition/structure issue arises in these cases as well. This issue of
properties and agglomeration affecting dosage rates for *in vitro*
studies was covered in a recent review paper: J.C Teeguarden, et al,
*Toxicological Sciences*, (2007) **95** 300.

[Dr. Canady:]{.underline}

I don't know.

[Dr. Cassell:]{.underline}

Surface charge, surface area, surface chemistry, geometry, and
solubility are properties that come to mind for aggregates and
agglomerates.

[Dr. Lahann:]{.underline}

Most properties are depending on the dispersion state of the
nanoobjects. Some times, individual nanoobjects can self-assemble into
well-defined structures leading to novel functions and properties.

[Dr. Murashov:]{.underline}

**Transport properties** will depend greatly on the state of
aggregation/ agglomeration. Specific examples are

a)  diffusion coefficient;

b)  precipitation rate;

c)  surface deposition rate (lungs, skin);

d)  rate of penetration of filters, membranes, fabrics;

e)  translocation rates *in vivo*.

Effect of aggregation/agglomeration on **biological activity** will be
determined by the mechanism of biological activity. For example, for
poorly soluble low toxicity nanomaterials if aggregation/agglomeration
results in changes in the total surface area available for interaction
with biological species, then the biological activity of such materials
is expected to change. For example, pulmonary exposure of rats to a well
dispersed a sample of ultrafine carbon black was more toxic and
inflammatory than an equal dose of a less dispersed sample (Shvedova et
al., 2007).

[Dr. Murday:]{.underline}

a)  Buoyancy (size/weight); capillarity; Ostwald ripening; grain growth;
    pore size distribution; hybrid structures -- link a variety of
    different NP each with different properties (nano Au color in
    solution as an example); electrical/thermal transport in compact;
    mechanical behavior of compact; supported catalysis.

[Dr. Small:]{.underline}

Agglomeration may affect size distributions from indirect methods such
as DLS and surface area measurements. In addition agglomeration will
also affect properties such as respirability, movement in environment
and possible uptake.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 7]{.underline}: *Are there routine manipulations of nanoscale
materials that result in physical-chemical properties changes or other
defining characteristics (e.g., surface modifications of nanotubes to
enhance solvent dispersibility)?*

[Dr. BelBruno:]{.underline}

Obviously, the cited case of surface modification is the main issue
here. As may be inferred from responses to previous queries, such
modification necessitates re-evaluation of the nanoparticle properties.
Surface modifications include functional groups directed towards other
applications, for example, to stealthly transport materials in
biological systems. Usenko, et al, in an attempt to establish a rapid
screening assay, have shown that C~60~(OH)~24~ was "significantly" less
toxic than C~60~. (*Carbon*, (2007) **45** 1891)

[Dr. Canady:]{.underline}

I don't have specific knowledge of this but there are surely lots of
data being developed and discarded in development of materials now that
would speak to this. There is probably not a finite set or a small list
of key manipulations, and the manipulations that result in relevant
change will vary based on the material and the matrix or setting it is
used in.

[Dr. Cassell:]{.underline}

Yes, there are a number of physical and chemical treatments that can
alter the defining characteristics of nanoscale materials. Vacuum
treatment, thermal annealing, drying can all drastically influence the
defining characteristics of nanoscale materials.

[Dr. Lahann:]{.underline}

Fundamentally, dispersion requires the offset of interparticulate
interactions with solvent/particle interactions. Changing the surface
chemistry is an effective way of changing the surface energy of the
particle and can therefore be used to tune the balance between these
competing interactions. Similarly, change the solvent system can have
similar effects. Finally, the application of electrical or magnetic
fields may be used to tune dispersibility.

[Dr. Murashov:]{.underline}

My understanding is that depending on application some nanomaterials are
routinely modified to

a)  improve biocompatibility (e. g. surface functionalization of medical
    nanoapplications with polyethylene glycole);

b)  protect from dissolution and improve photoluminescence by surface
    passivation (e. g. coating of quantum dots with ZnS in CdSe/ZnS
    and/or organic ligands);

c)  improve dispersibility and reduce agglomeration (e.g. use of
    surfactants to disperse carbon nanotubes).

[Dr. Murday:]{.underline}

b)  "Routine" varies depending on NS and application, i.e., it is not
    clear that the word "routine" is valid in this context.

c)  It is likely that most NS will require a "shell" to make them
    compatible with their intended application(s). The creation of that
    shell can happen by many variants of either gas (including low
    pressure -- vacuum) or liquid deposition. Since the environment
    interacts directly with the outermost shell, it should receive
    careful attention.

[Dr. Small:]{.underline}

Materials may be modified in the purification process i.e. CNT can be
acid washed to remove catalyst which may functionalize surface.
Chemicals may be added during production to modify surface
characteristic to prevent aggregation. Milling will change the surface
characteristics.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 8]{.underline}: *How should physical-chemical property data be
prioritized for the NMSP? Based on availability, effect (toxicity or
exposure criteria), or other factors?*

[Dr. BelBruno:]{.underline}

The preferred method should be toxicity. However, it is not at all clear
that such data would be available for each nanoparticle. The best
approach would be to begin with those nanomaterials for which we do have
data and construct what could be a prototype nanomaterial MSDS.
Obviously, the test cases would be "pure" materials such as carbon
nanotubes or TiO­~2~ or many of the quantum dot materials. However, we
must establish consistent (and meaningful) standards for *in vitro*
testing.

[Dr. Canady:]{.underline}

Not sure what is meant by priority in this case but there is probably a
set that is relevant to decisions and a broader set where the intention
is to build knowledge of what might be relevant to decisions. Variables
that would be informed by the data might include

a)  Classification for regulatory purposes like things that would change
    inventory status or inclusion in a SNUR,

b)  Fate and transport (and exposure or bioaccumulation or magnification
    or sequestration in odd places as a result), and

c)  Toxicity or environmental effect

The degree to which data inform decisions in consideration of these
variables would seem to be the main prioritization criteria.

[Dr. Cassell:]{.underline}

The NMSP should take a careful and comprehensive approach to
understanding nanoscale materials. Priortization of data should be made
based upon the detailed context of the question and the specific
situation. There are also many poor sources of information or
information that may not be valid.

[Dr. Lahann:]{.underline}

Based on effect.

[Dr. Murashov:]{.underline}

Nanoscale Materials Stewardship Program goal is to better understand the
potential risks and benefits of nanotechnology, therefore,
physical-chemical property data should be prioritized according to its
relevance to risk assessment and risk management of nanomaterials.
However, it is also important to collect all the available information
relevant to risk assessment (hazard and exposure) and risk management.

[Dr. Murday:]{.underline}

a)  Risk is roughly the product of exposure and harm.

b)  Free standing nanostructures can lead to exposure; embedded might be
    released if not covalently bonded, otherwise parts of matrix will
    likely be attached; "thin film" nanostructures likely will never be
    available for incorporation into living systems.

c)  Higher priority properties might be:

    a.  Chemical reactivity

    b.  Solubility/Partition (largely governed by surface properties and
        Hamaker constants)

[Dr. Small:]{.underline}

The prioritization of the physical-chemical property data to be relevant
needs to be based first on measurements that can be made in a
reproducible manner both intra - and inter - laboratory. Next once these
methods have been identified then their effect/application to risk
assessment, (toxicity, exposure etc.) needs to be applied to the
prioritization process.

[Dr. Warheit:]{.underline}

With regard to human health effects or ecotoxicity testing, there are
however, certain generalized points relating to material
characterization for all nanoparticle-types that should be emphasized.
These are the following:

Many scientific organizations or task forces have strongly recommended
that toxicologists adequately characterize physicochemical properties of
the nanoparticle-types that are being evaluated for hazard testing.
However, too often this recommendation becomes a "laundry list" of
physicochemical characteristics and does not have adequate
prioritization. As a consequence, in order to adequately describe the
physical characteristics of the nanoparticle-type being evaluated, I
would recommend that toxicologists characterize the following
(prioritized) physicochemical properties prior to conducting hazard
studies with nanoparticle-types:

a)  Particle size and size distribution (wet state) and surface area
    (dry state) in the relevant media being utilized -- depending upon
    the route of exposure;

b)  Crystal structure/crystallinity;

c)  Aggregation status in the relevant media;

d)  Composition/surface coatings;

e)  Surface reactivity;

f)  Method of nanomaterial synthesis and/or preparation including
    post-synthetic modifications (e.g., neutralization of ultrafine TiO2
    particle-types);

g)  Purity of sample;

This represents a focused approach concomitant with a minimum,
standardized assessment of physicochemical properties that should be
investigated prior to the development of toxicity testing with
nanoparticles.

Additional points to consider for material characterization:

a)  Depending upon the exposure scenario, it may be appropriate to
    conduct assessments of nanoparticle characteristics in both the wet
    state (in the relevant media) and the dry state. Therefore a BET
    surface area measurement may not suffice -- but should be carried
    out in parallel with different types of measurements such as cryo
    TEM (dry state) and DLS (dynamic light scattering - particle sizing
    in the wet phase).

b)  The chemical composition of the nanoparticle core vs. shell (hard or
    soft) should be evaluated.

c)  In this regard, the surface chemistry could be specific for each
    nanoparticle-type.

Below, I have listed 5 recently-published nanoparticle toxicity studies
from our Laboratory concomitant with the specific physicochemical
characteristics that were identified from each of the studies.
Accordingly, we have concluded that characteristics of nanoparticle
surface reactivity appeared to be the best predictors of in vivo
pulmonary toxicity in rats. However, it should be pointed out that
surface reactivity evaluations are particle-type specific (e.g. Vitamin
C assay for TiO2 particles; erythrocyte hemolysis for silica particles).
Therefore, the same tests for surface reactivity cannot be utilized for
each nanoparticle-type.

A Listing of Material Characterization Methods utilized in the 5 studies
listed below

1)  "Pulmonary Instillation Studies with Nanoscale TiO2 Rods and Dots in
    Rats: Toxicity is not dependent upon Particle Size and Surface
    Area". Warheit DB, Webb TR, Sayes CM, Colvin VL, and Reed KL. .
    Toxicol Sci. 91: 227-236, 2006

Material characterization employed in this study:

a)  synthesis method

b)  crystal structure

c)  particle size

d)  surface area

e)  composition/surface coating

f)  aggregation status

g)  cryo TEM

h)  crystallinity

i)  purity (TGA)

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2)  "Pulmonary bioassay studies with nanoscale and fine quartz particles
    in rats: Toxicity is not dependent upon particle size but on surface
    characteristics". Warheit DB, Webb TR, Colvin VL, Reed KL and
    Sayes CM. Toxicol Sci. 95:270-280, 2007;

Material characterization employed in this study:

a)  synthesis method

b)  crystal structure/crystallinity (XRD)

c)  median particle size - particle size (range)

d)  purity (% Fe content)-- ICP-AES

e)  surface area

f)  TEM

g)  aggregation status

h)  purity

i)  surface reactivity (erythrocyte hemolysis)

j)  reactive oxygen species (ESR)

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3)  "Pulmonary Toxicity Study in Rats with Three Forms of ultrafine-TiO2
    Particles: Differential Responses related to Surface Properties".
    Warheit DB, Webb TR, Reed KL, Frerichs S, and Sayes CM. Toxicology
    230:90-104, 2007;

Material characterization employed in this study:

a)  crystal phase

b)  median particle size and size distribution in water and PBS

c)  pH in water and PBS

d)  surface area (BET)

e)  TEM

f)  aggregation status

g)  chemical (surface) reactivity -- (Vitamin C assay)

h)  surface coatings/composition, purity

    4.  Assessing toxicity of fine and nanoparticles: Comparing in vitro
        measurements to in vivo pulmonary toxicity profiles Sayes CM,
        Reed KL, and Warheit DB. Toxicol Sci, 97:163-180, 2007.

Particle-types utilized in this study:

a)  Fine-sized carbonyl iron

b)  Fine-sized crystalline silica

c)  Fine-sized amorphous silica

d)  Nano ZnO

e)  Fine ZnO

Particle characterizations conducted both in the "dry state" and "wet
state"

Material characterization employed in this study:

Particle characterization in the dry state

a)  particle size

b)  surface area

c)  density

d)  calculated size in dry state (based on surface area determinations)

e)  crystallinity

f)  purity

Particle characterization in the wet state

a)  particle size in solutions -- PBS, culture media, water

b)  average aggregated size in solutions

c)  \% distribution

d)  surface charge

e)  aggregation status

Conversion and comparisons of in vitro and in vivo doses for dosimetric
comparisons

5)  Comparative Pulmonary Toxicity Assessments of C60 Water Suspensions
    in Rats: Few Differences in Fullerene Toxicity In Vivo in Contrast
    to In Vitro Profiles. Sayes CM, Marchione AA, Reed KL, and Warheit
    DB. Nano Lett. 2007 Aug;7(8):2399-2406.

Material characterization employed in this study:

a.  particle size and size distribution

b.  surface charge

c.  crystallinity

d.  TEM

e.  Composition

f.  oxidative radical activity (ESR measurements)

g.  surface reactivity (erythrocyte hemolytic potential)

**Nanoscale manufacturing and processing**

The number of manufacturing and processing methods for generating
nanoscale material continues to grow and become more sophisticated. The
two primary areas for this discussion include physical reduction methods
(milling) and engineering methods (e.g., particle stabilization, vapor
deposition, self assembly).

[Question 9]{.underline}: *What are the common processes used to
manufacture nanoscale materials?*

[Dr. BelBruno:]{.underline}

The list in the paragraph above covers the general "bottom up" and "top
down' methods.

[Dr. Canady:]{.underline}

A list was developed in the ICON workshop last year at NIH -- I don't
have the full list, but it is extensive.

[Dr. Cassell:]{.underline}

Solution based methods are quite common and include a number of
approaches (self-assembly, colloidal preparation), chemical vapor
deposition is also used extensively. All techniques conventionally used
in organic and inorganic synthesis are also adapted for nanoscale
materials manufacture.

[Dr. Lahann:]{.underline}

Organic materials: self-assembly

Inorganic materials: CVD

Polymers: staged synthesis, self-assembly, suspension polymerization,
grafting, electrified jetting

Composites: similar to polymers

[Dr. Murashov:]{.underline}

The draft ISO TC229 Technical Report on "Health and Safety Practices in
Occupational Settings Relevant to Nanotechnologies" lists the following
categories of major processes used to manufacture nanoscale materials:

a)  Gas phase processes such as flame pyrolysis, high temperature
    evaporation and plasma synthesis;

b)  Vapor deposition;

c)  Liquid phase methods: colloidal, self-assembly, sol-gel;

d)  Supercritical fluid;

e)  Electro-spinning for polymer nanofiber synthesis;

f)  Mechanical processes including grinding, milling and alloying;

g)  Bioreactors.

[Dr. Murday:]{.underline}

a)  Since NS, by definition, have large surface to volume ratios,
    quality manufacturing processes must utilize a controlled
    environment.

b)  For large scale bulk NS the processes are largely either a variant
    on colloid chemistry or gas phase nucleation and growth. Fumed
    silica and carbon black are examples of the latter -- both can be NS
    and have been made in volume for decades.

[Dr. Small:]{.underline}

Common methods would include: lithography, vacuum and spray coating,
CVD, Vapor deposition, Plasma vaporization, laser ablation,
arc-discharge, gas-phase catalytic growth of CNT from carbon monoxide,
and Sol gel. There are of course many "variations" on these methods some
of which are proprietary. In the case of the more complex materials
these would probably start with one of the above and then have
proprietary additional steps.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 10]{.underline}: *How are processes used to produce specific
characteristics or properties?*

[Dr. BelBruno:]{.underline}

The size of synthesized particles can be controlled through the
chemistry, either by limiting reagents or by the specific conditions of
the chemistry (heat, solvent, reaction mechanism, etc). To the extent
that properties reflect size (and surface area), then the properties are
controlled by the chemistry. Of course, that relationship
(size-properties) is not yet well-defined. Similarly, self assembly can
be chemically controlled and the surface characteristics, therefore,
influenced by the process. Finally, chemistry can be used to modify or
functionalize the particles. We know that functionalized nanotubes, for
example, have different properties from the naked nanotubes.

[Dr. Canady:]{.underline}

I don't know.

[Dr. Cassell:]{.underline}

Self assembly for instance can be used to control nanoparticle diameter.
Polymerization techniques (stoichiometric control, temperature,
pressure, etc.) can be used to control engineered polymer systems.
Thermal/chemical treatment can be used to increase surface area or
surface chemistry. There are a wide variety of techniques borrowed from
conventional disciplines that are used in the manipulation of nanoscale
materials.

[Dr. Lahann:]{.underline}

By exactly controlling chemical composition and structure of
nanoparticles/nanoobjects, a specific characteristic or property can be
achieved. For instance, in the case of CdSe nanocrystals, the particle
diameter defines important optical properties and developing processes,
which can generate monodisperse particles with defined diameters, will
give a unique function.

[Dr. Murashov:]{.underline}

This depends on the process, materials and application.

[Dr. Murday:]{.underline}

a)  After the formation of most NS it will be necessary to tailor the
    surface to make the NS compatible with further processing. The
    tailored surfaces can be thought of as a shell. There may be several
    shells as we progress toward "smart" NS.

b)  As an example, the first shell of a semiconductor QD is designed to
    trap the electron-hole pair in the core, a second shell might have a
    therapeutic function and a third shell a recognition function.

c)  Processes used to produce the shells will likely vary considerably,
    but would again be mostly variants on colloid/gas phases processing.

[Dr. Small:]{.underline}

No specific comments provided.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 11]{.underline}: *Which methods reduce particle size but do
not result in property changes? Which methods reduce particle size and
result in property changes?*

[Dr. BelBruno:]{.underline}

See response to question 10.

[Dr. Canady:]{.underline}

First, the question should be about change not reduction. Size going up
from 50 to 200nm will cause different disposition effects in the body,
so increase in size in the nanoscale range is relevant as well.

But I don't understand this question. Size is a property that has
relevance in biology on its own. If "property" as a function of size
means lack of biological or environmental impact, then how could you
know that properties are not changed without testing? How could we know
the answer to this question unless the answer is that all methods to
change size will result in some unknown likelihood of a change in
biological or environmental response? This is a smaller set of the
question of whether you can assume that any modification will have no
effect (by limiting the modification to "size change" rather than "any
modification").

[Dr. Cassell:]{.underline}

This depends on the system under question. Cutting a carbon nanotube in
half reduces its particle size, but does not greatly effect other
properties. Reducing gold particle diameters dramatically alter melting
point for instance.

[Dr. Lahann:]{.underline}

If a material's change in particle size results in fundamental property
changes, the outcome is more a function of the material itself and less
of the method used to reduce the size. However, the process used to
reduce the size of a material may determine polydispersity and may still
be influencing properties.

[Dr. Murashov:]{.underline}

If the reduction in size results in changes in properties of interest,
then it does not matter how the reduction in size was achieved. If
properties of interest also depend on surface characteristics, then the
production method can affect these properties and additional steps such
as surface passivation might be required (see also answer to question
7).

[Dr. Murday:]{.underline}

a)  The question is not meaningful -- all methods may/may not change
    properties.

b)  Processes without a controlled environment are likely to lead to
    wider variation in surface composition and thereby different
    behaviors. For instance, the technique of ball milling larger
    particles into smaller frequently is inadequately controlled;
    compacted powder studies have suffered from inability to reproduce
    results.

c)  To control size, processes growing NS will need to have a nucleation
    event separate from the growth step. If nucleation and growth
    proceed in parallel, there is an inevitable distribution in NS size.

[Dr. Small:]{.underline}

Many of the production methods are bottom up so this question does not
apply to those. In general the property change results for the nanoscale
characteristics of the materials not on how they are produced. Not sure
what this question refers to.

[Dr. Warheit:]{.underline}

No specific comments provided.

**Impurities**

Impurity content is a growing area of interest in nanotechnology due to
improved performance observed in some cases (e.g., solar cells and
semiconductors) and deleterious effects observed in others (e.g.,
quantum dot quantum computers). The confounding effects that impurities
have with respect to toxicological endpoints are also being studied
(National Nanotechnology Initiative 2006 Environmental Health and Safety
research report[^9]).

[Question 12]{.underline}: *How important are impurity identity and
impurity levels to the understanding and characterization of nanoscale
materials?*

[Dr. BelBruno:]{.underline}

Impurity level and identity are important factors, since the impurities
are also nanometer scale and their own properties add to the difficulty
in assessing the impact of the target particles. Again using nanotubes
as an example, the catalytic metals that are sometimes incorporated in
the final product need to be identified, quantified and, often, removed.
This has been accomplished in a number of different ways. One example is
provided by Y. Wang, et al, *Chemical Physics Letters* (2006), **432**,
205.

[Dr. Canady:]{.underline}

Impurity identity is critical and not clear at this point. It could be
defined relative to the set of nanoscale properties of interest which
would also be the specification of the material, or of the nanoscale
particle. Something could be an impurity if it has slight topographic
variation from the optimal and conversely, something may not be an
impurity if it has dramatically differing composition but similar enough
structure so that the effect does not depend on composition.

Impurity could also be defined based on unwanted side effects of a
variation in nanoscale material even if the nanoscale material that is
"impure" (in the sense of its unwanted side effects) is "pure" with
respect to its intended effects.

Impurity could also just be a solvent or carryover from the
manufacturing in the typical sense, such as the PAHs in CNTs.

The need to measure impurity level is a function of effect and would be
case-dependent.

[Dr. Cassell:]{.underline}

Extremely important. I would say that impurities become more relevant as
you scale your system to smaller dimensions. Impurities could be even
more important in the context of toxicological effects.

[Dr. Lahann:]{.underline}

Depending on the application, the effects can either be hugely important
or can be neglected. However, impurities always introduce an additional
source for structural variability into a nanomaterial.

[Dr. Murashov:]{.underline}

There is a need to clarify what is meant by "impurity". Term "impurity"
when it is applied to nanomaterials is more similar to molecular
chemicals (e. g. organic polymers) than to macroscopic materials with a
high degree of ionic or metallic bonding (e.g. SiO~2~, Si, NaCl).
Specifically, target nanomaterials can be contaminated by other
nanomaterials and chemicals (example is a raw carbon nanotube material
composed of a mixture of carbon nanotubes and nanoscale metal catalyst
particles). Nanomaterials can be also "contaminated" by atomic/molecular
species covalently bonded to nanomaterials. If such a "defect" or
"contamination" results in significant changes of nanomaterial
properties, it could be considered a new nanomaterial rather than
"contaminated" or "defective", just as replacement of an atom in a
molecule for a different chemical element creates a new
molecule/chemical. Presently, in many instances nanomaterials are
produced as mixtures of nanoparticles with a range of particle sizes,
shapes and chemistries, which is, to some degree, similar to a mixture
of oligomers obtained during polymer synthesis.

The importance of "impurity" or "impurity" level (or the amount of other
molecules and nanomaterials in the mixture) for a particular application
will be strongly dependent on that application. The importance of
"impurity" or "impurity" level on risk of a target nanomaterial will be
strongly dependent on risk-related properties of the "impurity" and the
target nanomaterial.

[Dr. Murday:]{.underline}

a)  Impurity identify and level can be very important, i.e., doping of a
    semiconductor NS. The NS size is sufficiently small that a single
    dopant atom will have dramatic impact on its electrical properties.
    Doping at the nanoscale might be better accomplished by injecting
    charge through surface bond compensation.

b)  CNT manufacture provides an excellent case study in quality control
    (or lack thereof). Figure A shows the results of an analysis of
    eight different nominal CNT samples -- the worst has only 40% carbon
    (as a fraction of C, H, O; all other elements were excluded from the
    analysis), and that carbon might not be NT.

[Dr. Small:]{.underline}

This is a critical area when characterizing these materials. For
example, the catalyst in NT production is nanosized metal (Fe, Ni)
particles. Some studies indicate that these may be more toxic than the
NTs. The ability to determine the amount and the physical-chemical
character of the impurities contained in ENM relates directly to
understanding and evaluating exposure and risk.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 13]{.underline}: *Are there routine purification procedures
that can effectively control or remove impurities, when desirable, for
certain classes of nanoscale materials?*

[Dr. BelBruno:]{.underline}

For nanotubes, the response is yes (see Q12). Removing impurities from
inorganic materials is more difficult because procedures could also
affect the desired particles.

[Dr. Canady:]{.underline}

I don't know.

[Dr. Cassell:]{.underline}

Yes. There are many techniques that are borrowed from those known in a
number of disciplines (chemistry, materials science, biology) and used
in nanoscale materials manipulation. They are too numerous to list here,
but include techniques such as annealing, chemical treatment,
separation, chromatography, sedimentation, plasma treatment.

[Dr. Lahann:]{.underline}

Processes to remove impurities from nanoscale materials are often
available.

[Dr. Murashov:]{.underline}

The following broad classes of purification processes can be
distinguished:

a)  chemical modification to reduce heterogeneity;

b)  dissolution of ionic, molecular and particulate species from target
    nanomaterials (e.g. acid-washing has been reported as a means of
    removing metal catalytic particles from raw carbon nanotube
    material);

c)  mobility sizing using difference in mobility of nanomaterials of
    different sizes, masses, charges and shapes in gas and liquid
    phases, across membranes and subject to force-fields.

[Dr. Murday:]{.underline}

a)  Chemistry provides a rich source of purification processes that can
    be exploited for NS. One limitation could be difficulty in
    sustaining solubility/suspension in fluid media.

[Dr. Small:]{.underline}

Acid washing for CNT along with other steps has been used for
purification of CNTs. There are several lab-based methods these are not
routine.

[Dr. Warheit:]{.underline}

No specific comments provided.

**Obtaining characterization data**

Determining identity, quantifying the nanoscale particle range, and
measuring physical-chemical properties for that identity and particle
range are essential to the characterization of nanoscale materials.
Because of the challenges associated with size, shape, surface
characteristics, and possibly other aspects of nanoscale materials, an
evaluation of existing measurement techniques is critical to nanoscale
material characterization. The National Nanotechnology Initiative report
stated that "\...Accurate and useful measurement techniques are also
important because agglomerated nano materials may either retain or lose
their emergent properties - or take on new properties - thus affecting
the potential biological response."

[Question 14]{.underline}: *Are validated methods available for the
different categories of nanoscale materials?*

[Dr. BelBruno:]{.underline}

Particles are easily sized using commercially available equipment. This
measurement is a bit more difficult (larger uncertainty) for coated
nanoparticles. Force and electron microscopy may also be used to measure
the size of particles. These are essentially universal, but tedious,
methods. X-ray spectroscopic techniques can be used to identify metallic
impurities (in many electron microscopes). Surface area measurement is
also a well-developed technique. (see Q4)

[Dr. Canady:]{.underline}

No specific comments provided.

[Dr. Cassell:]{.underline}

I am unaware of validated methods for nanoscale materials in particular,
but there may be methods (e.g. ISO) that are inclusive of nanoscale
materials.

[Dr. Lahann:]{.underline}

Some validated methods are available, but further efforts are needed.

[Dr. Murashov:]{.underline}

There are no validated methods specific to engineered nanoparticles
(NIOSH 2006). There are validated methods for materials that exist in
the nanometer scale, such as welding fume, carbon black; but these
methods do not discriminate by size. There are some methods that have
been validated for the larger (bulk) form of nanomaterials that may be
applied to the nano form; for instance dust sampling with a cyclone
(ISO, 2007); sampling for a specific element with analysis by NIOSH 7300
(NIOSH, 1994); fiber sampling and analysis by Transmission Electron
Microscopy (TEM). These methods have not been validated for nanoscale
material, but there is potential for reapplication and they can provide
useful information for evaluating occupational exposures with respect to
particle size, mass, surface area, number concentration, composition,
and surface (NIOSH, 2006). The challenge is demonstrating that the data
generated by the measurement (the metric) was created by the engineered
nanoparticle rather than by incidental nanoparticles of similar chemical
composition. Variations of the sampling process for mixtures of
nanoscale and fine TiO~2~ are being tested (NIOSH, 2005). One of the
challenges of that method is collecting enough material for the first
mass-based step in the analysis. Often the electron microscopy analysis
is used to verify that the material collected has the expected elemental
composition and is in the nanometer size range though there is always
some degree of agglomeration.

[Dr. Murday:]{.underline}

a)  MS and light scattering are the closest to validated.

b)  NIST and NCL are working this issue -- EPA should partner.

[Dr. Small:]{.underline}

There are several methods under development be few in publication. One I
am aware of is IEEE P1650 standard test method of meas. of electrical
properties of CNTs adopted in 2005.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 15]{.underline}: *Are there techniques that can be universally
applied?*

[Dr. BelBruno:]{.underline}

See response to question 14.

[Dr. Canady:]{.underline}

No specific comments provided.

[Dr. Cassell:]{.underline}

I would think so, yes. Especially the more generic particle
characterization techniques (surface area, particle size determination,
etc.) that have been utilized in other materials characterization work.

[Dr. Lahann:]{.underline}

Particle size and shapes can be characterized using Transmission
electron microscopy, scanning electron microscopy and scanning probe
microscopy independent of the materials composition.

[Dr. Murashov:]{.underline}

The collection and analysis of an air sample by TEM is an example of a
universal technique which can be applied across several types of
nanomaterials.

[Dr. Murday:]{.underline}

a)  In a broad context, there are no techniques that provide all the
    necessary information, all the time. NS can be found in free form
    and embedded in matrices. The NS itself is likely to have
    composition/structure that varies with distance from its center.

b)  Light scattering is likely to be useful for size/shape measurement.
    It might be useful/important to extend the photon energy in the far
    UV to make the wavelength more comparable to the NS size (however,
    this may invoke a problem for the optics).

c)  Mass Spectrometry has been developed to handle very large molecules
    -- 100s of KDa. Fragmentation patterns can illuminate substructures.
    This technique could prove very useful in probing core/shell NS.

d)  MS and light scattering require multiple copies of a NS and yield
    ensemble averaged results. Techniques to probe individual NS
    properties are also very useful. Some variant on HRSEM with energy
    dispersive analysis for composition, coupled with AFM, is likely to
    be the most versatile.

e)  SERS might be developed with enough sensitivity to analyze one or a
    few NS for a vibrational approach to composition.

[Dr. Small:]{.underline}

Not that I am aware of. Perhaps some of the microscopy methods could be
used to characterize multiple classes.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 16]{.underline}: *For small quantities of materials, are there
sampling, handling, and collection techniques as well as sample
integrity, accuracy and precision QA/QC methodologies available?*

[Dr. BelBruno:]{.underline}

Many nanoparticles are available from commercial suppliers (quantum
dots, fullerenes, nanotubes, inorganic cluster molecules), with
specified purity levels and chemical composition. Clearly, commercial
suppliers can arrange QA procedures and we should look to these methods
as a means of introducing standards.

For example, from American Elements
(http://www.americanelements.com/fenp.html): "Iron (Fe) Nanoparticles,
nanodots or nanopowder are spherical or faceted high surface area metal
nanostructure particles. Nanoscale Iron Particles are typically 20-40
nanometers (nm) with specific surface area (SSA) in the 30 - 50 m^2^/g
range and also available in with an average particle size of 100 nm
range with a specific surface area of approximately 7 m^2^/g. Nano Iron
Particles are also available in Ultra high purity and high purity and
coated and dispersed forms."

[Dr. Canady:]{.underline}

No specific comments provided.

[Dr. Cassell:]{.underline}

I would say that there may be generic techniques published in the
technical literature, but these are probably not standardized by a
leading organization. Quality control procedures for nanoscale materials
are largely dependent upon the organization that handles the materials
and most of these are based upon the needs of that particular
organization.

[Dr. Lahann:]{.underline}

Some specialized procedures are available, but further efforts are
needed.

[Dr. Murashov:]{.underline}

At this point, the greatest QA/QC challenge is the lack of methods
specific for nanoscale particles and the lack of reference materials
that accurately represent the material being evaluated.

[Dr. Murday:]{.underline}

a)  The traditional handling of chemicals provides proven precedents.
    But they will have to be adapted to the broader range of
    size/properties incumbent in NS.

b)  Testing on NS shows (at least in some circumstances) that they can
    be collected effectively on filters -- van der Wall forces or
    surface charges attract to the filter material; NS are small enough
    that fluid drag forces are small and don't displace them from the
    filter.

[Dr. Small:]{.underline}

No. I think best-practices methods (handling of ultrafines) are used
although there are several efforts by government agencies and industry
to develop safe handling practices for ENMs that would apply to "small"
quantities.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 17]{.underline}: *What is the status of standardization
efforts? Are these efforts focused on broadly applicable
characterization methods or category-specific methods?*

[Dr. BelBruno:]{.underline}

Mostly category specific, as the response to Q19 indicates.

[Dr. Canady:]{.underline}

No specific comments provided.

[Dr. Cassell:]{.underline}

NIST is active in generating standards for single walled carbon
nanotubes see: <http://polymers.nist.gov/Nanotube3/Agenda.pdf>. There
are a variety of techniques described for characterizing single walled
carbon nanotubes.

[Dr. Lahann:]{.underline}

Depending on the field and material, standardization efforts vary and
further activities are needed.

[Dr. Murashov:]{.underline}

Standardization efforts are focused on both broadly applicable
characterization methods and category-specific methods. For example, the
ISO TC 229 (Nanotechnologies), Working Group 3 (Health, Safety and the
Environment) is working on five projects:

a)  Technical Report "Health and Safety Practices in Occupational
    Settings Relevant to Nanotechnologies" -- broadly applicable
    characterization methods;

b)  International Standard "Endotoxin test on nanomaterial samples for
    in vitro systems" -- broadly applicable;

c)  International Standard "Generation of silver nanoparticles for
    inhalation toxicity testing" -- specific to silver nanoparticles;

d)  International Standard "Monitoring silver nanoparticles in
    inhalation exposure chambers for inhalation toxicity testing" -
    specific to silver nanoparticles;

e)  Technical Report "Guidance on physico-chemical characterization of
    engineered nanoscale materials for toxicologic assessment" - broadly
    applicable.

The ISO TC 229 Working Group 2 (Metrology and Instrumentation) is
working on a number of standards for characterizing carbon nanotubes.

[Dr. Murday:]{.underline}

No specific comments provided.

[Dr. Small:]{.underline}

Physical standards: Standardization efforts are in the process of
ramping up both from an activity as well as a funding view point.
Government, industry, and academia, in the US as well as other areas
like Europe are in the process of defining and measuring candidate
materials. Efforts are focused on both category-specific i.e. CNT and on
broader definitions such as metal oxides or on schemes used for
classifications of materials like toxicity, commercial impact, and
environmental impact.

Documentary Standards (methods): As with the physical standards these
efforts are also increasing although development of "standard methods,
in most cases, requires the availability of well characterized physical
standards.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 18]{.underline}: *What alternative or innovative methods or
technologies can be applied to nanomaterial analysis?*

[Dr. BelBruno:]{.underline}

No specific comments provided.

[Dr. Canady:]{.underline}

No specific comments provided.

[Dr. Cassell:]{.underline}

Atomic force microscopy along with some of the latest scanning probe
microscopy techniques could be useful for nanomaterials analysis. I'm
unsure if standards for characterizing with these techniques have been
set.

[Dr. Lahann:]{.underline}

Transmission electron microscopy, scanning electron microscopy and
scanning probe microscopy, fluorescence microscopy, X-ray microscopy.

[Dr. Murashov:]{.underline}

Some examples of alternative or innovative methods or technologies that
could be applied to nanomaterial analysis as part of safety and health
assessments are:

a)  A number of instruments providing on-line size-resolved chemical
    speciation of aerosols, such as aerosol mass-spectrometry, have been
    developed. These techniques can provide compositional information on
    single particles or ensembles of size-selected particles in real
    time.

b)  Size distribution and number concentration of nanoparticles in
    liquid phase can be characterized using light scattering, laser
    diffraction, size exclusion chromatography, acoustic techniques and
    field flow fractionation (Powers et al, 2006), while space-resolved
    spectroscopic techniques can be useful in obtaining information
    about chemical composition and structure of nanoparticles.

[Dr. Murday:]{.underline}

a)  ASTM interlab standards not yet in place.

b)  Tip characterization for proximal probes is a major challenge.

c)  Absence of standard materials another factor.

d)  Lab on a chip and variants on microarrays might offer new approaches
    that could be readily adapted to field use.

e)  To the extent that NS impact on living systems is paramount, cell
    based microarrays (being developed for drug candidate screening)
    might provide a "canary on a chip."

[Dr. Small:]{.underline}

There are many novel technologies, e.g. microscopy-based, as well as
others, which are applicable to nanoscale regimes. Is the EPA looking
for methods that are likely to be widely used (cheap and fast) or for
very specific research areas? Many of these methods are currently
difficult and expensive to make and are confined to laboratory studies
some may eventually become routine others will not. Examples of some
techniques include: super-resolution optical, 3D chemical tomography,
TGA on chip, size-exclusion chromatography.

[Dr. Warheit:]{.underline}

No specific comments provided.

**Modeling**

Empirical modeling can be a useful approach to predict physical-chemical
properties when experimental data are not known or ascertainable. The
initial problem with modeling is that, to accurately predict property
endpoints for a given category of substances, there must be some
experimental data available in the tool's database for at least some
representative substances in that category. For newly discovered or
studied materials, the minimum but necessary quantity and type of
experimental data often is not available to sufficiently populate a
tool's database and allow accurate prediction by the tool. Some
estimation methods have been developed for specific property endpoints,
but many others are lacking.

[Question 19]{.underline}: *Are there models that are currently used to
obtain property data for nanoscale materials? For which properties and
which nanoscale materials?*

[Dr. BelBruno:]{.underline}

I believe that we need to have a long-term view for this. Simulations
provide agreement with already established data, but are not predictive.
Quantum mechanical calculations provide a basis for the emission in
quantum dots. However, structure function type relationships of the type
used in the pharmaceutical industry do not exist.

[Dr. Canady:]{.underline}

I don't know.

[Dr. Cassell:]{.underline}

There are some atomistic approaches that have been used to predict
properties of nanoscale materials and some of these models have been
extended to molecular dynamics and mesoscale modeling approaches. I am
not an expert in the field, but I am aware of these techniques. The
properties modeled are typically physical in nature such as mechanical,
thermal or electrical in nature. Primarily these approaches are utilized
to understand transport phenomena.

[Dr. Lahann:]{.underline}

A series of different approaches is currently under development
depending on specific materials categories.

[Dr. Murashov:]{.underline}

Only few risk-related models exist that are currently used to obtain
property data for nanoscale materials. Examples are:

a)  Several models currently used to obtain property data for nanoscale
    materials are models based on aerodynamic properties of
    nanoparticles such as penetration through filter media, coagulation
    and deposition in the lung (Lee and Liu, 1982; Maynard and Kuempel,
    2005; ICRP, 1994).

b)  Research data indicate that health hazard properties of poorly
    soluble, low-toxicity nanoparticles can be modeled using their total
    surface area (Maynard and Kuempel, 2005; Duffin et al., 2007).

[Dr. Murday:]{.underline}

a)  It is possible to extrapolate from smaller (atomistic) and larger
    (continuum) scale models, but caution must be exercised.

b)  First principle models of CNT were able to predict accurately many
    of their properties well before the experimental community could
    measure them (see Figure C). However, CNT is a special case of NS --
    CNT is all C, has only on type of bond, and has a high degree of
    symmetry.

[Dr. Small:]{.underline}

No specific comments provided.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 20]{.underline}: *Has any validation work been conducted that
compares predicted values with measured data? For which properties and
which nanoscale materials?*

[Dr. BelBruno:]{.underline}

See response to question 19.

[Dr. Canady:]{.underline}

NCL has published standard methods through ASTM for some assays that
have validation data.

[Dr. Cassell:]{.underline}

Individual carbon nanotube based thermal conductivity has been predicted
by theory and subsequently validated using experimental approach. Prof.
Arun Majumdar's group at UC Berkeley performed these elegant
experiments.

[Dr. Lahann:]{.underline}

Some of the models have been validated. A good example is the work of
Nick Kotov and Sharon Glotzer at University of Michigan that
experimentally validated the formation of nanoparticle sheets (Science
2006). More work is needed.

[Dr. Murashov:]{.underline}

Validation work has been conducted for data related to penetration of
filter media by nanoscale particles (see for example, Rengasamy et al.,
2007).

[Dr. Murday:]{.underline}

a)  CNT model predictions have been verified by experiment (see Figure
    C).

b)  QD model predictions have been verified by experiment.

c)  Fluid flow in nanopores has been examined by Navier Stokes
    (continuum) and molecular dynamics approaches to understand the
    modeling limitations. Results have been partially validated by
    experiment.

[Dr. Small:]{.underline}

No specific comments provided.

[Dr. Warheit:]{.underline}

No specific comments provided.

[Question 21]{.underline}: *Are there current significant
characterization needs for which the NMSP should investigate model
development?*

[Dr. BelBruno:]{.underline}

See response to question 19.

[Dr. Canady:]{.underline}

Yes -- but an entire workshop or similar effort should be devoted to
developing ideas and projects for modeling. The most immediate one may
be developing a modeling approach that allows updating of the
information needs relative to the decision needs. As more is learned
about the materials and the properties that are most relevant to
decisions there will need to be a process for adjusting the information
requirements.

[Dr. Cassell:]{.underline}

I'm not sure if there are aggregation/agglomeration models that could be
used for various types of nanomaterials, but I see this as being a
valuable method to augment characterization approaches. Any predictive
tool that is useful in a contextual setting as opposed to idealized
models would be extremely useful.

[Dr. Lahann:]{.underline}

Specifically in the area of correlation between nanoparticle properties,
such as size, shape, composition, and biological properties, such as
cell uptake or cytotoxicity, there would be a great potential for model
developments.

[Dr. Murashov:]{.underline}

Examples of current significant characterization needs for which the
NMSP should investigate model development are:

a)  Risk assessment models for nanoscale materials are needed.
    Specifically, models to extrapolate toxicity data from *in vitro* to
    *in vivo*; from *in vivo* to human; external exposure levels to
    internal dose should be further developed.

b)  There is a need to develop models correlating biomarkers of exposure
    with specific nanomaterials.

c)  There is also a need to determine if certain physico-chemical
    properties of nanoparticles are predictive of biological activity.

[Dr. Murday:]{.underline}

a)  Chemical reactivity -- partner with catalysis efforts.

b)  Toxicology -- partner with NIH, NIOSH, NIST, NCL.

c)  Fate and effect in soils -- a topic more closely aligned with EPA
    than other agencies.

[Dr. Small:]{.underline}

No specific comments provided.

[Dr. Warheit:]{.underline}

No specific comments provided.

**[Supporting Figures]{.underline}**

[Figures provided by Dr. Murday:]{.underline}

![](media/image3.wmf){width="4.988888888888889in"
height="3.7493055555555554in"}

**Figure A**

+--------------------+----------------------------------+---+---+--------+
| FIELD              | PROPERTY                         | S |   |        |
|                    |                                  | C |   |        |
|                    |                                  | A |   |        |
|                    |                                  | L |   |        |
|                    |                                  | E |   |        |
|                    |                                  | L |   |        |
|                    |                                  | E |   |        |
|                    |                                  | N |   |        |
|                    |                                  | G |   |        |
|                    |                                  | T |   |        |
|                    |                                  | H |   |        |
+--------------------+----------------------------------+---+---+--------+
| ELECTRONIC         | ELECTRON WAVELENGTH              | 1 | \ | 100nm  |
|                    |                                  | 0 | - |        |
|                    | INELASTIC MEAN FREE PATH         |   | - | 100nm  |
|                    |                                  | 1 |   |        |
|                    | TUNNELING                        |   | \ | 10nm   |
|                    |                                  | 1 | - |        |
|                    |                                  |   | - |        |
|                    |                                  |   |   |        |
|                    |                                  |   | \ |        |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| MAGNETIC           | DOMAIN WALL                      | 1 | \ | 100 nm |
|                    |                                  | 0 | - |        |
|                    | EXCHANGE ENERGY                  |   | - | 1nm    |
|                    |                                  | 0 |   |        |
|                    | SPIN-FLIP SCATTERING LENGTH      | . | \ | 100nm  |
|                    |                                  | 1 | - |        |
|                    |                                  |   | - |        |
|                    |                                  | 1 |   |        |
|                    |                                  |   | \ |        |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| OPTIC              | QUANTUM WELL                     | 1 | \ | 100nm  |
|                    |                                  |   | - |        |
|                    | EVANESCENT WAVE DECAY LENGTH     | 1 | - | 100nm  |
|                    |                                  | 0 |   |        |
|                    | METALLIC SKIN DEPTHS             |   | \ | 100nm  |
|                    |                                  | 1 | - |        |
|                    |                                  | 0 | - |        |
|                    |                                  |   |   |        |
|                    |                                  |   | \ |        |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| SUPERCONDUCTIVITY  | COOPER PAIR COHERENCE LENGTH     | 0 | \ | 100nm  |
|                    |                                  | . | - |        |
|                    | MEISSNER PENETRATION DEPTH       | 1 | - | 100nm  |
|                    |                                  |   |   |        |
|                    |                                  | 1 | \ |        |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| MECHANICS          | DISLOCATION INTERACTION          | 1 | \ | 1000nm |
|                    |                                  |   | - |        |
|                    | GRAIN BOUNDRIES                  | 1 | - | 10nm   |
|                    |                                  |   |   |        |
|                    |                                  |   | \ |        |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| NUCLEATION/        | DEFECT                           | 0 | \ | 10nm   |
|                    |                                  | . | - |        |
| GROWTH             | SURFACE CORRUGATION              | 1 | - | 10nm   |
|                    |                                  |   |   |        |
|                    |                                  | 1 | \ |        |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| CATALYSIS          | LOCALIZED BONDING ORBITALS       | 0 | \ | 0.1nm  |
|                    |                                  | . | - |        |
|                    | SURFACE TOPOLOGY                 | 0 | - | 10nm   |
|                    |                                  | 1 |   |        |
|                    |                                  |   | \ |        |
|                    |                                  | 1 | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| SUPRAMOLECULES     | PRIMARY STRUCTURE                | 0 | \ | 1nm    |
|                    |                                  | . | - |        |
|                    | SECONDARY STRUCTURE              | 1 | - | 10nm   |
|                    |                                  |   |   |        |
|                    | TERTIARY STRUCTURE               | 1 | \ | 1000nm |
|                    |                                  |   | - |        |
|                    |                                  | 1 | - |        |
|                    |                                  | 0 |   |        |
|                    |                                  |   | \ |        |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+
| IMMUNOLOGY         | MOLECULAR RECOGNITION            | 1 | \ | 10nm   |
|                    |                                  |   | - |        |
|                    |                                  |   | - |        |
+--------------------+----------------------------------+---+---+--------+

**Figure B: Characteristic Lengths in Solid State Science Models**

![](media/image4.wmf){width="4.988888888888889in"
height="3.7493055555555554in"}

**Figure C**

**[Supporting References]{.underline}**

[References provided by Dr. Murashov:]{.underline}

Duffin, R., Tran, L., Brown, D., Stone, V., and Donaldson, K. (2007).
Proinflammogenic effects of low-toxicity and metal nanoparticles in vivo
and in vitro: highlighting the Role of Particle Surface Area and Surface
Reactivity, Inhal. Tox. 19(10), 849-856.

ICRP, Human respiratory tract model for radiological protection, 1994,
ICRP publication 66.

ISO, Workplace Atmospheres -- Ultrafine, nanoparticle and
nano-structured aerosols -- Inhalation exposure characterization and
assessment, ISO/TR 27628:2007, 2007.

Jevprasesphant, R., Penny, J., Jalal, R., Attwood, D., MckEown, N. B.,
and D'Emanuele, A. (2003). The influence of surface modification on the
cytotoxicity of PAMAM dendrimers, Int. J. Pharm. 252, 263-266.

Lee, K. W. and Liu, B. Y. H. (1982). Theoretical study of aerosol
filtration by fibrous filters, Aerosol Sci. Technol. 1(2), 147-162.

Maynard, A. D. and Kuempel, E. D. (2005). Airborne nanostructured
particles and occupational health. J. Nanopart. Res. 7, 587-614.

Mecke, A., Uppuluri, S., Sassanella, T. M., Lee, D. K., Ramamoorthy, A.,
Baker, J. R., Jr., Orr, B. G., and Banaszak Holl, M. M. (2004). Direct
observation of lipid bilayer disruption by poly(amidoamine) dendrimers.
Chem. Phys. Lipids 132, 3-14.

NIOSH (1994). NIOSH Manual of Analytical Methods (NMAM®), 4th ed. DHHS
(NIOSH) Publication 94-113 (August, 1994), Schlecht, P.C. & O\'Connor,
P.F., Eds., 1994. Available on line at
[www.cdc.gov/niosh/nmam/chaps.html](http://www.cdc.gov/niosh/nmam/chaps.html).

NIOSH (2005). Evaluation of Health Hazard and Recommendations for
Occupational Exposure to Titanium Dioxide. Available on line at
[www.cdc.gov/niosh/review/public/TIo2/](../www.cdc.gov/niosh/review/public/TIo2/).

NIOSH (2006). Approaches to Safe Nanotechnology: An Information Exchange
with NIOSH. Available online at:
<http://www.cdc.gov/niosh/topics/nanotech/safenano/>.

Powers, K. W., Brown, S. C., Krishna, V. B., Wasdo, S. C., Moudgil, B.
M., and Roberts, S. M. (2006). Research Strategies for Safety Evaluation
of Nanomaterials. Part VI. Characterization of Nanoscale Particles for
Toxicological Evaluation. Tox. Sci. 90(2), 296-303.

Rengasamy, S., Verbofsky, R., King, W. P., and Shaffer, R. E. (2007).
Nanoparticle Penetration through NIOSH-approved N95 Filtering-facepiece
Respirators, J. Int. Soc. Resp. Protec. 24, 49-59.

Sayes, C. M., Fortner, J. D., Guo, W., Lyon, D., Boyd, A. M., Ausman, K.
D., Tao, Y. J., Sitharaman, B., Wilson, L. J., Hughes, J. B., West, J.
L., and Colvin, V. L. (2004). The differential cytotoxicity of
water-soluble fullerenes, Nano Lett. 4 (10), 1881-1887.

Shvedova, A.A., Sager, T., Murray, A.R., Kisin, E., Porter, D.W.,
Leonard, S., Schwegler-Berry, D., Robinson, V.A., and Castranova, V.
(2007). Critical issues in the evaluation of possible adverse pulmonary
effects resulting from airborne nanoparticles. In: Nanotoxicology --
Characterization, Dosing and Health Effects. N.A. Monteiro-Riviere and
C.L. Tran (eds), Informa Healthcare, NY, Chap14, pp 225-236.

Singh, R., Pantarotto, D., Lacerda, L., Pastorin, G., Klumpp, C., Prato,
M., Bianco, A., Kostarelos, K. (2006). Tissue biodistribution and blood
clearance rates of intravenously administered carbon nanotube
radiotracers, Proc. Nat. Acad. Sci. 103 (9), 3357-3362.

Wexler, A. S., and Johnston, M. V. (2001). Real-time single-particle
analysis. In Aerosol Measurement: Principles, Techniques and
Applications, Baron, P. A. and Willeke, K. eds., John Wiley & Sons, New
York, pp. 365-385.

[References provided by Dr. Warheit:]{.underline}

References for Nanoparticle Material Characterization Strategies for
Toxicity Studies

1)  International Life Sciences Institute -- Panel -- "Principles for
    characterizing the potential human health effects from exposure to
    nanomaterials: elements of a screening strategy" - Oberdorster G,
    Maynard A, Donaldson K, Castranova V, Fitzpatrick J, Ausman K,
    Carter J, Karn B, Kreyling W, Lai D, Olin S, Monteiro-Rivere N,
    Warheit DB, and Yang H. Particle and Fibre Toxicology 2005, 2:8.

"Physicochemical properties that may be important in understanding the
toxic effects of test materials include particle size and size
distribution, agglomeration state, shape, crystal structure, chemical
composition, surface area, surface chemistry, surface charge, and
porosity".

2)  Testing strategies to establish the safety of nanomaterials:
    Conclusions of an ECETOC workshop. Inhal. Toxicol., 19:
    631-643, 2007. Warheit DB, Borm PJA, Hennes C, and Lademann J.
    Inhal. Toxicol., 19: 631-643, 2007.

"In summary, it was concluded that nanoparticle composition,
dissolution, surface area and characteristics, size, size distribution,
and shape are parameters needed for any target organ toxicity
assessment. Depending on the type of toxicological study undertaken,
other physicochemical parameters would also be required

[^1]: http://www.particleand fibretoxicology.com/content/2/1/8

[^2]: http://www.ansi.org/standards_activities/standards_boards_panels/nsp/overview.aspx?menuid=3

[^3]: <http://www.iso.org/iso/en/stdsdevelopment/tc/tclist/TechnicalCommitteeDetailPage.TechnicalCommitteeDetail>?
    COMMID=5932

[^4]: <http://publicaa.ansi.org/sites/apdl/Documents/Forms/AllItems.aspx>

[^5]: Class 1 substances are distinct chemicals with known, non-variable
    molecular structures

[^6]: http://www.nano.gov/NNI_EHS_research_needs.pdf

[^7]: <http://publicaa.ansi.org/sites/apdl/Documents/Forms/AllItems.aspx>

[^8]: Class 1 substances are distinct chemicals with known, non-variable
    molecular structures

[^9]: http://www.nano.gov/NNI_EHS_research_needs.pdf