# Scientific, Technical, Research, Engineering, and Modeling Support

(STREAMS)



# Sampling and Analysis of Nanomaterials

in the Environment: A State

- Of

- The

Science Review [ Final Report ]

Prepared for:



## U.S. Environmental Protection Agency

National Exposure Research Laboratory
Environmental Sciences Division

944 E. Harmon Ave. Las Vegas, NV 89119

Prepared by:



### Eastern Research Group, Inc.

10200 Alliance Road

Suite 190 Cincinnati, OH 45242

29 August 2008

EPA Contract No. EP

- C

- 05

- 059

Task Order # 66ii 

### Table of Contents

Executive Summary

................................ ................................ ................................ ............ 1 List of Acronyms

................................ ................................ ................................ ................ 2

1.0 Introduction and Scope of Review

................................ ................................ .......... 3

2.0 Information Search Strategy

................................ ................................ ................... 4

2.1 Dialog® Search Strategy and Results

................................ ................................ . 4

2.1.1 Dialog® Search Parameters

................................ ................................ ........ 5

2. 1.2 Dialog® Search Procedure and Results

................................ ...................... 5

2.2 Targeted Search of Sources

................................ ................................ ................ 9

2.2.1 Nano

- specific Journals

................................ ................................ ................ 9

2.2. 2 Conference Proceedings

................................ ................................ ............ 12

2.2.3 Databases of Nanotechnology Research

................................ ................... 13

2.2.4 Grant Databases

................................ ................................ ........................ 13

2.3 List of Contacted Researchers

................................ ................................ .......... 14

2.4 Results of Literature Search and Potential Future Reviews

.............................. 15

3.0 Background

................................ ................................ ................................ ........... 23

3.1 Overview of Nanomaterials

................................ ................................ .............. 23

3.1.1 Natural Nanomaterials

................................ ................................ .............. 23

3.1. 2 Anthropogenic Nanomaterials

................................ ................................ .. 24

3.2 Overview of Environmental Transport

................................ ............................. 27

3.2.1 Surface Water Transport

................................ ................................ ........... 27

3. 2.2 Soil Transport

................................ ................................ ............................ 29

3.2.3 Groundwater Transport

................................ ................................ ............. 30

4.0 Sampling Techniques

................................ ................................ ............................ 31

4.1 Sampling Techniques Suited for Surface Waters

................................ ............. 32

4.2 Sampling Techniques Suited for Sediments

................................ ..................... 32

4.3 Sampling Techniques Suited for Soil

................................ ............................... 33

4.4 Sampling Techniques Suited for Groundwater

................................ ................. 34

4.5 Comparison of Sampling Techniques

................................ ............................... 34

5.0 Analytical Techniques

................................ ................................ .......................... 34

5.1 Analytical Techniques for Size Fractionation

................................ ................... 36

5.2 Analytical Techniques for Size Distribution

................................ ..................... 39

5.3 Analytical Techniques for Surface Area

................................ ........................... 42

5.4 Analytical Techniques for Direct Visualization

................................ ............... 43

5.5 Analytical Techniques for Phase and Structure

................................ ................ 44

5.6 Analytical Techniques for Chemical Analysis

................................ ................. 46

5.7 Comparison of Analytical Techniques

................................ .............................. 51

6.0 Differentiation of Anthropogenic Nanomaterials

................................ ................. 55

7.0 Summary

................................ ................................ ................................ ............... 55

8.0 References

................................ ................................ ................................ ............. 57

Appendix A DIALOG® SEARCH OUTPUTE XECUTIVE S UMMARY

This state

- of

- the

- science review was undertaken to identify and assess currently available sampling and analysis methods to identify and quantify the occurrence of

nanomateri als in the environment

. The environmental and human he alth risks associated with nanomaterials are largely unknown, and methods needed to monitor the

environmental occurrence of nanomaterials ar e very limited or nonexistent. Because this research is current and ongoing, much of the applicable information is found in gray literature (e.g., conference proceeding, communications with research scientists and other experts).

The approach to this review included three separate strategies:

 C ollection of available published literature u s ing Dialog® ;

 R eview of information from targeted sources, such as nano

specific journals, conference proceedings, grants databases, and

researc h databases ; and

 C ontacts with industry and academic experts.

This report summarizes the key characteristics that must be considered when collecting and analyzing samples in various environmental media. Based on results of the literature review, and personal communication with researchers, typical analytical methods and techniques that are currently used for na nomaterials are identified and briefly discussed.

The review also identifie s several sources that provided information on analytical techniques and equipment for nanomaterials. However, l ittle information was obtained for sampling techniques that are s pecific for analysis of nanomaterials. Information

obtained indicated that nanomaterial

- specific sampling techniques have not yet been developed. Another area for which the search results provided little information is for differentiating anthropogenic ( man

- made) nanomaterials from natural nanomaterials. A number of potential sources that may provide additional information upon a more in

depth review were identified. As this report provides a current st ate

- of

- the

- science review of active research topics at the time of writing , this report may require

modifications as additional research is conducted.2

L IST OF A CRONYMS

Acronym Definition

AAS Atomic Absorption Spectrometry

AEM Analytical Electron Microscopy

AES Atomic Emission Spectrometry

AFM Atomic Force Microscopy

BET Brunauer

- Emmett

- Teller method

CBED Convergent Beam Electron Diffraction

CCD C harged C oupled D evice

CE Capillary Electrophoresis

DLS Dynamic Light Scattering

EDS Energy Dispersive Spectroscopy

EDX Energy

- Dispersive X

- ray Spectroscopy

EELS Electron Energy Loss Spectroscopy

EFTEM Energy

- Filtered Transmission Electron Microscopy

ESEM Environmental Scanning Electron Microscopy

ETEM Environmental Transmission Electron Microscopy

FFF Field

- Flow Fractionation

FLD Fluorescence Detector

FlFFF Flow Field

- Flow Fractionation

GF Graphite Furnace

HAADF High

- Angle Annular Dark Field

HPLC High

- Performance Liquid Chromatography

HR High Resolution

ICP Inductively

- Coupled Plasma

LIBD Laser

- Induced Breakdown Detection

LC Liquid Chromatography

MALLS Multi

- Angle Laser Light Scattering

MS Mass Spectrometry

NMR Nuclear Magnetic Resonance

RTM R esonant T unneling M odel

SAED Selected

- Area Electron Diffraction

SAXS Small

- Angle X

- ray Scattering

SEC Size Exclusion Chromatography

SEM Scanning Electron Microscopy

SIMS Secondary Ion Mass Spectrometry

SPM Scanning Probe Microscopy

STEM Scanning Transmission Electron Microscopy

STM Scanning Tunneling Microscopy

TEM Transmission Electron Microscopy

TFF Tangential

- Flow (cross

- flow) Ultrafiltration

UV Ultraviolet radiation

XAS X

- ray Absorption Spectroscopy

XEDS X

- ray Energy

- Dispersive Spectroscopy3

XPS X

- ray Photoelectron Spectroscopy

XRD X

- ray Diffraction

WAXS Wide

- Angle X

- ray Scattering

1.0 I NTRODUCTION AND S COPE OF R EVIEW

The rapidly advancing field of nanotechnology offers potential benefits to almost all industries and products. According to the Woodrow Wilson International Center for Scholars’ Project on Emerging Nanotechnology’s Nanote chnology Consumer Product Inventory

, nanomaterials are currently being used in over 500 consumer products. However, the environmental and human health risks associated with these materials are largely unknown. Before the environmental and general populat ion risk of these materials can be measured or monitored, methods will be needed to collect, separate, detect, identify, and quantify the occurrence of nanomaterials in the environment over time. The rate of product development has outpaced the rate of me thods development,

and

, unfortunately, the methods needed to monitor the environmental occurrence of nanomaterials are very limited or nonexistent. Only l imited research has been conducted, in part due to the immense challenges of sampling nanomaterials i n the environment (e.g., distinguishing between naturally

- occurring nanoparticles and engineered nanoparticles). While EPA’s Office of Research and Development ( ORD ) may eventually sponsor research to develop remote, in situ, and continuous monitoring devices to detect engineered nanomaterials at very low concentrations, the purpose of this

initial effort is to identify and assess currently

- available sampling and analysis methods

. Th is report focuses on soil, sediment, and groundwater environmental sampling

. A companion research effort is focusing on air sampling and analytical techniques.

Due to the limited data available and the rapid advancements that are being made,

a tradition al literature search (i.e., using an abstract database to search peer

- reviewed journals) is not expected to effectively capture the cutting

- edge information on environmental sampling and analysis methods for nanomaterials, particularly those under developm ent and those that have not been fully peer

- reviewed. Because this research is current and ongoing, much of the applicable information is found in gray literature (e.g., conference proceeding, communications with research scientists and other experts).

A dditionally, many of the techniques for environmental sampling and analysis of nanomaterials may need to be adapted from trace sampling methods and methods used in quality assurance or characterization of manufactured nanomaterials; therefore, peripheral l iterature has also been identified and reviewed. Section 2.0 presents the technical approach that was used to conduct the information search for t his report.

As this report provides a current state

- of

- the

- science review of active research topics at the time of writing, this report may require modifications as additional research

is conducted

.4

2.0 I NFORMATION S EARCH S TRATEGY

A detailed information search to support EPA’s review of sampling and analysis procedures for detecting and monitoring nanomaterials in complex environmental

matrices was conducted . The approach to this search included three separate , but parallel, strategies described in the fo llowing subsections:

 Section 2.1 describes the collection of available published literature using Dialog® (Search Strategy #1);

 Section 2.2 describes the review of information from targeted sources, such as nano

- specific journals, conference proceedings, grants databases, and research databases (Search Strategy #2); and

 Section 2.3 describes contacts with industry and academic experts (Search Strategy #3).

The approach general ly included the following steps:

1. Conduct an initial review focused on targeted sources;

2. Evaluate information collected during initial review and identify topic areas that require additional information; and

3. Review additional sources to identify articles , presentations, or research that could provide the needed information.

Initial efforts focused on reviewing a targeted list of journal articles under Search Strategy #2 and contacting industry experts under Search Strategy #3. Additional

resources were also identified using the Dialog® search results, a list of nano

- specific journals, conference proceedings, grants databases, and research databases.

2.1 Dialog® Search Strategy and Results

The Dialog® search produced two lists of titles of potentially

- releva nt articles:

 Fifty

- eight titles pertaining to characterization and sampling to

detect nanomaterial s in the environment (Appendix A

- 1); and

 Sixty

- one titles pertaining to the use of nanomaterials for environmental remediation ( Appendix A

- 2).

This subsection describes the parameters that were specified for the Dialog® search, the search procedure and results, and next steps.5

2.1.1 Dialog® Search Parameters

The parameters that were specified for the DIALOG search include keywords, publication date, languages, and the list of databases included in the search.

Keywords : Keywords were searched in the “title

, ” “abstract

, ” and “descriptor”

fields.

 Primary Keyword: “nano*”

This was identified as a keyword, assuming it would capture the following word s of interest: nanomaterial, nanoparticle, nanoscale

.

 Secondary Keywords:

 “soil” or “air” or “water” or “sediment” or “environment*” or “ground*” or “expos*”

<AND>

 “analy*” or “sampl*” or “remediat*” or “contamina*” or

“characteriz*” or “anthropogenic*” or “manufactur*” or “fate” or “transport” or “separat*” or “detect*” or “monitor*”

Words of interest these secondary keywords were expected to encompass include: samples, sampling, analysis, analytical, soil, air, water, sediment,

remedia tion, contaminants, contamination, anthropogenic, environment, environmental, characterize, characterization, ground, groundwater, manufactured, manufacturing, fate, transport, separate, separation, detect, detection, monitor, monitoring, exposure, expose

.

Publication Dates : The Dialog® search included all articles published in the year

2000 and later.

Language : Only article s published in English were evaluated.

Databases : Thirty databases were included in the search (see Table 2

- 1 for the list) . These were identified by evaluating the Dialog® subject guide in “Science

- Energy & Environment” and “Science

- Engineeri ng & Technology

. ”

2.1.2 Dialog® Search Procedure and R esults

Figure 2

- 1 shows a decision

- making flowchart for the Dialog® literature search.

This flowch art describes the search procedure and the results of each step:6 1. Dialog® was run using the specified paramete rs described in the previous section. The Dialog® output produced approximately 585 unique records.

2. The search was then modified by removing the keywords

“remediat*

, ” “air

, ” and “manufactur*

. ” However, the Dialog® output continued to produce more than 400 records.

3. It was determined that the list of 585 records could be reviewed manually within a reasonable timeframe; therefore, a list of titles to identify those pertaining to characterization and sampling for nanomaterials in the environment was prepared. This initial

review identified a list of 58 potentially

- rele vant titles

.

4. A bstracts and citations for the 5 8 potentially

- relevant titles (see

Table A

- 1 of Appendix A) were obtained . Based on informatio n provided in the abstract, unrelated articles and a rticles of interest

were identified . This review identified 1 4 articles of interest (identified in Table A

- 1) , which were obtained and evaluat ed for this report. Articles that are cited in this report are presented in

Tab le 2

- 6 at the end of this section

.

5. In addition, it was determined that a list of titles pertaining to the use of nanomaterials for environmental remediation may be useful (if not for this project, then potentially for future efforts). The use

of nanomaterials for e nvironmental remediation may be of interest to EPA because it is a mechanism by which nanomaterials enter

the environment. Table A

- 2 of Appendix A list s 61 titles that were

identified as potentially pertaining to the use of nanomaterials for

environmental remediation.

Table 2

- 1 list s databases that were included in the Dialog® search and the number of hits per database for the initial search

.7 Figure 2

- 1 . DIALOG® Literature Search Flow Chart8

Table 2

- 1 . List of Databases Included for DIALOG® Search and Results

Database

Number Database Name Number of Hits Pertaining to

Characterization and Sampling Number of

Hits Pertaining to

Environmental

Remediation

6 NTIS

- National Technical Information Service 0 0

9 Business & IndustryTM 0 0

19 Chemical Industry Notes (CIN) 2 0

31 World Surface Coatings AbstractsTM 1 0

32 METADEX® 0 0

34 SciSearch®

- a Cited Reference Science Database

- 1990 28 36

35 Dissertation Abstracts Online 5 8

36 MetalBase 0 0

40 Enviroline® 0 3

41 Pollution Abstracts 2 1

57 Electronics and Communications Abstracts 0 0

60 ANTE: Abstracts in New Technologies and Engineering 0 0

64 Environmental Engineering Abstracts 0 0

65 Inside Conferences 8 6

73 EMBASE® (1974

- present) 4 0

76 Environmental Sciences 3 1

95 TEME

- Technology and Management 1 0

99 Wilson Applied Science & Technology Abstracts 0 0

103 Energy Science and Technology 1 2

110 WasteInfo 0 0

245 WATERNETTM 1 0

293 Engineered Materials Abstracts® 0 1

315 Chemical Engineering and Biotechnology Abstracts 0 1

317 Chemical Safety Newsbase 2 1

322 Polymer Online 0 0

323 RAPRA: Rubber and Plastics 0 0

335 Ceramic Abstracts/World Ceramics Abstracts 0 0

369 New Scientist 0 0

370 Science 0 0

636 Gale Group Newsletter Database 0 1

Total 58 61

For more information on databases, see http://library.dialog.com/bluesheets/.9 Appendix A

- 3 list s approximately 470 titles that were not selected for further analysis based on their titles and expected content . Examples of common keywords and phrases that were found in the unrelated titles include the following:

"nanogram

, " "nanometer

, " "nanomolar

, " "nanofiltration

, " "nanofilm detectors

, "

"nanofiber filters

, " "nano composite membranes

, " "nanoemulsion

, " "growth/preparation/synthesis and characterization of nanomaterials

, " and "application of nanomaterials in environmental detection

. "

2.2 Targeted Search of Sources

This sub section describes the review of targeted source s (Search Strategy #2), which includes four groups of targeted sources:

 Nano

- specific journals;

 Conference proceedings;

 Databases of nanotechnology research; and

 Grant databases.

2.2.1 Nano

- specific J ournals

As a first step, 24 journal articles were acquired and reviewed that were recommended by industry and academia experts as good sources of information on sampling and analytical techniques for detecting and quantifying nanomaterials in the

environment

. Additional articles were added to this list from perso nal contacts with industry e xperts (described in Section 2.3 ) and from the Dialog ® literature search (described in Section 2.1 ).

Tab le 2

- 6

, at the end of this section, presents the entire list of articles reviewed for this repor t and notes the general topics covered by each.

Table 2

- 2 presents a preliminary list of targeted journals for this review. Articles reviewed for this report includ e 4 of the 16 targeted journals. The remaining 12 journals may provide a starting point for future research efforts.10

Table 2

- 2 . Preliminary List of Journals to Review for Search Strategy #2

Nano

- Specific Journals

Environmental Pollution* Nanorisk Newsletter Nanotechnology NanoNow

Journal of Nano Research Journal of Nanobiotechnology Particle and Fiber Toxicology Nanotoxicology

Journal of Environmental Monitoring* Journal of Nanoparticle

Research* Journal of Environmental Engineering International Journal of Nanoscience (IJN)

Environmental Monitoring and

Assessment Nano Letters (American Chemical Society)* Journal of Nanoscience and Nanotechnology Fullerenes, Nanotubes

and Carbon

Nanostructures

*Journal was includ ed in literature review

.

Table 2

- 3 lists the top 20 nanoscience and nanotechnology journals and the top 20

environmental sciences journals ranked by their 2006 impact factors. The impact factor is the ratio of the number of times journal articles published in the previous two years were cited during a particular year to the total number of citable items that the journal published in the two previous years; for example:

A = the number of times articles published in 2004 and

2005 were cited during 2006

B = the number of citable items published by the journal in

2004 and 2005

Impact Factor = A/B

The impact factor provides a measure of the importance of a journal to its field. This literature search has identified articles in the following journals listed in Table 2

- 3 :

 Nano Letters;

 Journal of Nanoparticle Research;

 Environmental Science and Technology; and

 Environmental Pollution.

Future research could focus search efforts on other journals with high impact factors.11

Table 2

- 3 . List of Top Nanotechnology and Environmental Sciences Journals by Impact Factor

Journal Title ISSN Total

Citations Impact

Factor Top Nanoscience and Nanotechnology Journals

Nano Letters 1530

- 6984 19,403 9.960

Small 1613

- 6810 1,240 6.024 Lab Chip 1473

- 0197 2,879 5.821

Biosensors Bioelectronics 0956

- 5663 7,198 4.132 Nanotechnology 0957

- 4484 6,798 3.037 Micropor. Mesopor. Mat. 1387

- 1811 6,264 2.796

Microfluid nanofluid 1613

- 4982 117 2.615

IEEE T. Nanobiosci. 1536

- 1241 316 2.592

Biomedical Microdevices 1387

- 2176 620 2.551 J. Micromech. Microeng. 0960

- 1317 3,839 2.321 Journal of Nanoscience and Nanotechnology 1533

- 4880 1,755 2.194 Scripta Materiala 1359

- 6462 8,571 2.161 J. Nanopart. Res. 1388

- 0764 870 2.156

Current Nanoscience 1573

- 4137 60 2.080

IEEE T. Nanotechnol. 1536

- 125X 713 1.909 Journal of Vacuum Science and Technology B 1071

- 1023 10,633 1.597 Material Science and Engineering, A Structural Materials 0921

- 5093 18,437 1.490

Microelectornic Engineering 0167

- 9317 3,817 1.398 Journal of Microlithography, Microfabrication, and Microsystems 1537

- 1646 304 1.243 Physical E. 1386

- 9477 2,854 1.084 Top Environmental Science Journals Environmental Health Perspectives 0091

- 6765 14,434 5.861 Frontiers in Ecology and the Environment 1540

- 9295 900 4.842 Global Change Biology 1354

- 1013 5,729 4.339 Environmental Science and Technology 0013

- 936X 44,915 4.040 Global Biogeochemical Cycles 0886

- 6236 5,597 3.796 Conservation Biology 0888

- 8892 11,192 3.762

Annual Review of Environment and Resources 1543

- 5938 190 3.080 Remote Sensing of Environment 0034

- 4257 8,817 3.064

J. Paleolimnol 0921

- 2728 1,925 3.016

J. Aerosol Science 0021

- 8502 4,040 2.952 J. Aerosol Science and Technology 0278

- 6826 3,112 2.905 Conservation Biology 0006

- 3207 8,759 2.854 Critical Reviews in Environmental Science and Technology 1064

- 3389 733 2.769

Environmental Pollution 0269

- 7491 8,569 2.769 Environmental and Molecular Mutagenesis 0893

- 6692 2,351 2.653 Applied Catalysis A: General 0926

- 860X 15,023 2.630 Atmospheric Environment 1352

- 2310 19,210 2.630

Environment International 0160

- 4120 2,762 2.626 Reviews of Environmental Contamination and Toxicology 0179

- 5953 701 2.619 International Journal of Hydrogen Energy 0360

- 3199 3,790 2.61212

2.2.2 Conference Proceedings

Table 2

- 4 presents a preliminary list of conferences to review for the targeted search. The DIALOG® search identified three additional conferences that may be sources of applicable papers/presentation s:

 The 4 th International Surface Engineering Congress & Exhibition, St. Paul, MN (August 2005);

 Institut fur Festkorperforschung (Institute of Solid State Research) IFF, Germany (March 2002);

 NSTI Nanotech

, the Nanotechnology conference and trade show, Anaheim, CA (May 2007);

 The 7 th International Symposium on Nanocomposites and Nanoporus materials (ISNAM7), Gyeongju, Korea (February 2006); and

 BioMEMS and nanotechnology, Perth, Australia (December 2003).

Table 2

- 4 . Preliminary List of Conferences to Review for Search Strategy #2

Nano

- Specific Conferences
International Symposium on Nanotechnology in Environmental Protection and Pollution. Hong Kong.

June 18

- 21, 2006 Experimental Analysis of Nano and Engineering Materials and Structures ICEM 13. Alexandroupolis, Greece. July 01

- 06, 2007 "Nanotechnology and Health: Evidence and Impact

, " Ann Arbor, MI. October 25

- 26, 2007 Nanoparticles for European Industry II. London, UK.

October 24

- 25 2007 11th International Conference Detection Technologies 2007. San Diego, CA. November 01

- 02, 2007 Material Characterization of Nanoscale Materials Peer

Consultation

. U

. S

. September 6

- 7, 2007 3rd International Symposium on Nanotechnology, Occupational and Environmental Health. Taipei,

Taiwan

, August 29

- September 1, 2007 International Conference on Nanotechnology Occupational and Environmental Health & Safety:

Research to Practice. December 03

- 08, 2006

Pollution Prevent ion through Nanotechnology , U.S. September 25

- 26, 2007 Nanotechnology

- Products and Processes for Environmental Benefit. London, UK

, May 15

- 16, 2007
Safer Nano 2006. Beaverton, Ore. March 06

- 07, 2006 Nanoforum 2007. Milan, Italy

, September 18

- 19 200 7 TMS 2007 Symposium: Towards Functional

Nanomaterials

– Synthesis, Characterization, and Applications. Orlando, F L. February 25

- March 1, 2007 3rd International Conference on Humanoid, Nanotechnology, Information Technology, Communication and Control, E nvironment, and Management. Manila. March 15

- 18, 2007

Aerosol and Particle Measurement Short Course. Minneapolis, MN. August 20

- 22, 2007 Nanotechnology and Toxicology in Environment and Health. Leipzig, Germany. March 27, 2007 OECD Working Party on Manufactured Nanomaterials. Berlin, Germany. April 25

- 27, 2007 Technology, Characterization and Fabrication at the Nanoscale. Atlanta, GA. July 24

- 25, 200713

T his state

- of

- the

- science review does not include information from the a bove list of

conferences. Conferences listed in Table 2

- 4 could provide a starting point for future

research.

2.2.3 Databases of Nanotechnology Research

T he following publicly

- available databases listing nanotechnology environmental

and human health research were identified:

 International Council on Nanotechnology (ICON)’s Environmental Health and Safety Database ( http:// icon.rice.edu/research.cfm );

 Project on Emerging Nanotechnologies’s Inventory of Current Nanotechnology Health and Environmental Implications Research ( http://www.nanotechproject.com/index.php );

 National Institute for Occupational Safety and Health (NIOSH) ’s Nanoparticle Information Library (NIL) ( http://www2a.cdc.gov /niosh

- nil/index.asp ) ; and

 Institute of Occupational Health’s (UK) SAFENANO Publication Database Search ( http://www.safenano.org/AdvancedSearch.aspx )

.

T his literature review does not include infor mation from the above list of nanoresearch databases. These databases could provide a starting point for future research.

2.2.4 Grant Databases

T he following is a list of potentially

- relevant research projects funded by EPA ’ s Science to Achi e ve Results (STAR) Grants in 2008:

 University of Delaware, Newark, D E

. - Develop an understanding of the fate of manmade nanoparticles released into subsurface environments. Project will evaluate mobility of nanomaterials in soil and groundwater in a laboratory setting u sing batch experiments. Testing methods include dynamic light scattering and confical microscopy experiments. Goal is to evaluate current conceptual models. Contacts: Yan Jin and John Xiao.

 University of Michigan, Ann Arbor, M I

- Provide fundamental information about the movement, fate and bioavailability of manmade, carbon nanotubes under different environmental

conditions.14  Purdue University, West Lafayette, I N

- Investigate how manmade nanomaterials change or transform under certain environmental

conditions.

 Arizona State University , AZ

- Evaluate biological treatment for removal of nanomaterials in wastewater treatment plants. The project will examine the fate of nanomaterials in wastewater treatment and drinking water treatment plants. The ASU researchers hope that this work will lead to methods for quantifying nanomaterials in water matrices and biosolids. Contact: Paul Westerhoff, Professor (Civil and Environment al Engineering). Paul Westerhoff was contacted under Search Strategy #3 (s ee S ection 2.3 ).

A dditional contacts may be identified from the above list of STAR grants for future

research efforts (see S ection 2.3 ). The following additional grant sources were also identified and may be reviewed to identify ongoing research in the field of sampling and analytical procedures for detecting nanomaterials:

 EPA’s Nationa l Center for Environmental Research (NCER) Nanotechnology Research Proj ect (complete list available at http://es.epa.gov/ncer/nano/research/index.html ); and

 National Nanotechnology Institute (NNI) Research Centers ( http://www.nano.gov/html/centers/nnicenters.html ).

2.3 List of Contacted Researchers

Table 2

- 5 lists the contacted researchers

.15 Table 2

- 5 . List of Researchers Contacted

Last Name First Name Title/Office/Department Organization

Denison Richard Senior Scientist Environmental Defense

Murashov Vladimir Special Assistant to the

Director National Institute for Occupational Safety and Health

Hochella Michael Professor, NanoBioEarth, Department of Geoscience Virginia Tech
Englert B rian C arl Environmental Scientist EPA Office of Water

Penn R

. L ee Professor, Department of Chemistry University of Minnesota

Diallo M amadou S

. Director of Molecular

Environmental Technology, Materials and Process Simulation Center,

Beckman Institute Caltech

Baer D on Environmental Molecular Science Laboratory Pacific Northwest National Laboratory

Erickson Larry E. Professor, Department of Chemical Engineering Kansas State University

Turco Ron ANE Project Coordinator Purdue University

Westerhoff Paul Professor, Department of

Civil and Environmental Engineering Arizona State University

2.4 Results of Literature Search and Potential Future Reviews

As a result of the information search strategy described in this section, the following information was obtained and evaluated for inclusion in this report:

 More than 500 titles identified by Dialog®; and

 Approximately 6 0 published articles.

Tab le 2

- 6 presents the articles that were selected and reviewed in detail for this report and the general to pic areas covered by each article

. This list of articles includes articles that

were identif

ied by Dialog® and articles that were identified by the search of targeted literature sources and personal contacts. As shown in the table, little to no information

was found for sediment, soil, and groundwater sampling and for differentiating16

anthropogen ic nanomaterials from natural nanomaterials

. As a state

- of

- the

- science review, this document is a “living” document and may benefit from additional research.

Additional areas for future work include:

 Research additional currently

- identified journal arti cles;

 Research identified journals for additional articles;

 Research identified conference proceedings;

 Contact additional researchers; and

 Focus areas of research on those in which the current review did not find

substantial information.Tab le 2

- 6 . Article s Review ed for Literature Search

Article Citation Overview Transport Sampling Analysis

Natural Engineered Surface Water
Soil Groundwater Surface Water Sediment Soil Groundwater Other

Size Fractionation Size Distribution/Surface Area Direct Visualization Mineral Phase/Internal Structure Chemical Analysis Differentiati on of Anthropogenic Nanomaterials

Baer, D.R. et al. Characterization Challenges for Nanomaterials. Surface and Interface Analysis

. 2008 , 40: 529

- 537 X X X X

Baalousha, M.; et al . Size

- Based Speciation of Natural Colloidal Particles by Flow Field Flow Fractionation, Inductively Coupled

Plasma

- Mass Spectrometry, and Transmission Electron Microscopy/X

- ray Energy Dispersive Spectroscopy: Colloids

Trace Element Interaction. Environmental Science & Technology 2006, 40 , 2156

- 2162. X X X X X X
Benoit, G.; Rozan, T. F. The influence of size distribution on the particle concentration effect and trace metal partitioning in rivers.

Geochimica et Cosmochimica Acta 1999, 63 , 113

- 127. X X X X X

Bundshuh et al. Quantification of Aquatic Nano Particles after Different Steps of Bodensee Water Purification with Laser

induced Breakdown Detection (LIBD). Acta hydrochimica et hydrobiologica 2001, 29 (1), 7

- 15. X XTable 2

- 6. (Continued)

18 Article Citation Overview Transport Sampling Analysis

Natural Engineered Surface Water
Soil Groundwater Surface Water Sediment Soil Groundwater Other

Size Fractionation Size Distribution/Surface Area Direct Visualization Mineral Phase/Internal Structure Chemical Analysis Differentiati on of Anthropogenic Nanomaterials

Burleson, D. J. et al. On the characterization of environmental nanoparticles. Journal of Environmental Science and Health Part

A

- Toxic/Hazardous Substances & Environmental Engineering 2004, 39 (10), 2707

- 2753. X X X X X X
Chen, Zhou et al. . Quantification of C60 Fullerene Concentrations

in Water. Environmental Toxicology and Chemistry

. 2008, DOI:

10.1897/07

- 560.1 X X X Eggleston, C. M et al. The structure of hematite ([alpha]

- Fe2O3) (001) surfaces in a queous media: scanning tunneling microscopy and resonant tunneling calculations of coexisting O and Fe

terminations. Geochimica et Cosmochimica Acta 2003, 67 (5),

985

- 1000. X X X X Essington, M. E. Soil and Water Chemistry: An Integrative Approach; CRC Press: Boca Raton, FL, 2004. X
Fortner, J. D. et al. C60 in Water: Nanocrystal Formation and Microbial Response. Environmental Science & Technology 2005,

39 (11), 4307

- 4316. X X X X X

Gil bert, B.et al . Stable cluster formation in aqueous suspensions of iron oxyhydro xide nanoparticles. Journal of Colloid and Interface Science 2007, 313 , 152

- 159. X X X X X X

Gimbert, L. J.et al

. Partitioning and stability of engineered ZnO nanoparticles in soil suspensions using flow field

- flow X X X X XTable 2

- 6. (Continued)

19 Article Citation Overview Transport Sampling Analysis

Natural Engineered Surface Water
Soil Groundwater Surface Water Sediment Soil Groundwater Other

Size Fractionation Size Distribution/Surface Area Direct Visualization Mineral Phase/Internal Structure Chemical Analysis Differentiati on of Anthropogenic Nanomaterials

fractionation. Environmental Chemistry 2007, 4 (1), 8

- 10.

Herr mann, A. M.e al.

. Nano

- scale secondary ion mass

spectrometry

- A new analytical tool in biogeochemistry and soil ecology: A review article. Soil Biology & Biochemistry 2007, 39 (8), 1835

- 1850. X Heymann, D.et al . Determination of C60 and C70 fullerenes in geologic materials by high

- performance liquid chromatography. Journal of Chromatography A 1995, 689 (1), 157

- 163. X X X
Hochella, M. F.; Madden, A. S. Earth's nano

- compartm ent for

toxic metals. Elements 2005, 1 (4), 199

- 203. X X Hwang, W. et al. Separation of Nanoparticles in Different Sizes and Compositions by Capillary Electrophoresis. Bulletin of the Korean Chemical Society 2003, 24 (5), 684

- 686. X

Lead, J. R.et al. Trace metal sorption by natural particles and

coarse colloids. Geochimica et Cosmochimica Acta 1999, 63

, 1661

- 1670. X X X X X Li, X. Q. et al . Zero

- valent iron nanoparticles for abatement of environmental pollutants: Materials and engineering aspects.

Critical Reviews in Solid State and Materials Sciences 2006, 31 (4), 111

- 122. X XTable 2

- 6. (Continued)

20 Article Citation Overview Transport Sampling Analysis

Natural Engineered Surface Water
Soil Groundwater Surface Water Sediment Soil Groundwater Other

Size Fractionation Size Distribution/Surface Area Direct Visualization Mineral Phase/Internal Structure Chemical Analysis Differentiati on of Anthropogenic Nanomaterials

Lienemann, C. et al. Optimal preparation of water samples for the examination of colloidal material by transmission electron microscopy. Aquatic Microbial Ecology 1998, 14 , 205

- 213. X X X X Lyven, B. et al. Competition between iron

- and carbon

- based colloidal carriers for trace metals in a freshwater assessed using

flow field

- flow fractionation coupled to ICPMS. Geochimica et

Cosmochimica Acta 2003, 67 , 3791

- 3802. X X X X X Madden, A. S.; Hochella, M. F. A test of geochemical reactivity as a function of mineral size: Manganese oxidation promoted by hematite nanoparticles. Geochimica et Cosmochimica Acta 2005,

69 , 389

- 398. X X X X X

Novak, J. P. et al. Pur ification of Molecularly Bridged Metal Nanoparticle Arrays by Centrifugation and Size Exclusion Chromatography. Analytical Chemistry 2001

, 73 (23), 5758

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Novikov, A. et al. Colloid Transport of Plutonium in the Far

Field of the Mayak Production Association, Russia. Science 2006,

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Saleh, N. et al . Adsorbed Triblock Copolymers Deliver Reactive Iron Nanoparticles to the Oil/Water Interface. Nano Letters 2005,

5 (12), 2489

- 2494. X XTable 2

- 6. (Continued)

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Natural Engineered Surface Water
Soil Groundwater Surface Water Sediment Soil Groundwater Other

Size Fractionation Size Distribution/Surface Area Direct Visualization Mineral Phase/Internal Structure Chemical Analysis Differentiati on of Anthropogenic Nanomaterials

Stolpe, B et al. High resolution ICPMS as an on

- line detector for

flow field

- flow fractionation; multi

- element determination of colloidal size distributions in a natural water sample. Analytica

Chimica Acta 2005, 535 , 109

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Tarassov, M. et al. Chemical composition and vibrational spectra of tungsten

- bearing goethite and hematite from western rhodopes, Bulgaria. European Journal of Mineralogy 2002, 14 , 977

- 986. X

USEPA U.S. Environmental Protection Agency Nanotechnology White Paper ;EPA 100/B

- 071/100; EPA Science Policy Council: Feb 1, 07. X Waychunas, G. et al. Nanoparticulate oxide minerals in soils and sediments: unique properties and contaminant scavenging

mechanisms. Journal of Nanoparticle Research 2005, 7 , 409

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Wigginton, N. S.; Haus, K. L.; Hochella, M. F. Aquatic environmental nanoparticles. Journal of Environmental Monitoring 2007, 9 (12), 1306

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Yuan, G. Environmental Nanomaterials: Occurrence, Syntheses, Characterization, Health Effect, and Potential Applications. Journal of Environmental Science and Health Part A

- Toxic/Hazardous Substances & Environmental Engineering 2004,

A39 (10), 2545

- 2548. X XTable 2

- 6. (Continued)

22 Article Citation Overview Transport Sampling Analysis

Natural Engineered Surface Water
Soil Groundwater Surface Water Sediment Soil Groundwater Other

Size Fractionation Size Distribution/Surface Area Direct Visualization Mineral Phase/Internal Structure Chemical Analysis Differentiati on of Anthropogenic Nanomaterials

Zhang, Y . et al . Stability and Removal of Water Soluble CdTe Quantum Dots in Water. Environ. Sci. Technol. 2008, 42 (1), 321

- 325. X X

Total 1 7 8 7 1 4 6 1 0 1 0 10 15 13 6 16 023

3.0 B ACKGROUND

This sect ion describes natural and anthropogenic nanomaterials that may be present in the environment and the factors that affect their transport in various environmental media including surface water, groundwater, and soil. An analysis of nanomaterials in air is outside the scope or t his review.

3.1 Overview of Nanomaterials

The U.S. National Nanotechnology Initiative defines nanomaterials as materials

that measure 1 to 100 nanometers in at least one dimension. Nanomaterials exist naturally in the environment and also are intentionally a nd unintentionally produced from

human activities. Section 3.1.1 presents an overview of the nanomaterials that may exist naturally in the environment , and Section 3.1.2 describes anthropogenic nanomaterials, both intentional and incidental, that are commonly produced.

3.1.1 Natural Nanomate rials

Several types of nanomaterials exist naturally and are produced by natural events such as chemical and physical weathering of rocks and minerals, combustion, volcanic eruptions, biomineralization, and precipitation reactions. 1 For example, volcanic ash

soils contain a nanodimensional aluminosilicate mine ral, called imogolite, that has a hollow tubular particle morphology 2

. Natural inorganic nanoparticles, found in soils and geologic systems, can have atmospheric, geogenic or biogenic origin. 3 Table 3

- 1 presents examples of naturally occurring nanomaterials and the mechanism of formation

, and Table 3

- 2 list s minerals discussed in this report.

Table 3

- 1 . Examples of Formation Processes for Natural Nanomaterials

Formation Process Type of Nanom aterial Examples

Carbon

- Containing Nanomaterials Biogenic Organic colloids Humic, Fulvic acids Organisms Viruses Geogenic Soot Fullerenes Atmospheric Aerosols Organic acids Pyrogenic Soot Carbon nanotubes, fullerenes Inorganic Nanomaterials Biogenic Oxides Magnetite

Metals Silver, Gold Geogenic Oxides Iron oxide Clays Allophane Atmospheric Aerosols Sea salt

Source: No wack et al. 324

Table 3

- 2 . List of M inerals U sed in J ournal A rticles R eferenced in this R eport 4

Mineral Name Molecular Formula Description

Hematite 

- Fe 2 O 3 Iron oxide

Goethite 

- FeOOH Iron oxyhydroxide
Ferrihydrite Fe 5 HO 8 •4H 2 O Iron hydrous oxide

3.1.2 Anthropogenic Nanomaterials

Anthropogenic nanomaterials are nanomaterials that are produced from human activity. They include both intentionally and unintentionally produced nanomaterials. Examples of unintentionally produced nanomaterials include diesel engine exhaus t products and combustion process byproducts. The remainder of this sub section describes intentionally produced nanomaterials, including their applications and manufacturing

processes.

Nanotechnology entails manipulat ing matter through chemical and/or physical processes to create materi als with specific properties for use in particular applications

. Size

- dependant properties , such as catalytic, electrochemical, melting, magnetic, and optical propertie s, change when mater ials are reduced to the nanoscale. These unique characteristics make nanomaterials highly valuable for applications in commercial, medical, military, and env ironmental sectors

. 5

Nanomater ials in their unprocessed form are not marketable to consumers. The nanotechnology value chain is often describe d with three levels of nano

- based products :

1. Nanomaterials: The first level includes the unprocessed nanomaterials, which serve as the building blocks for other products.

2. Nanointermediates: The second level includes intermediate products,

called “nanointermediates” th at incorporate nanomaterials or that have

bee n designed with nanoscale features. Examples of nanointermediates include coatings, fabrics, catalysts, and computer chips.

3. Nano

- enabled products: The third level includes nano

- enabled products, which are finished goods that use nanomaterials or nanointermediates. Examples of nano

- enabled products include clothing, sporting goods, pharmaceuticals, and medical devices.

As described previously, nanomaterials are materials that are nano

- sized in at

least one dimension. One

- dimensional nanomaterial s include thin films and surfaces and coatings, two

- dimensional nanomaterials include nanotubes, nanowires, and nanofibers,

and three

- dimensional nanomaterials include fullerenes, quantum dots, and dendrimers.25

3.1.2.1 Manufacturing Processes

Manufacturing process es to produce nanomaterials fall into o ne of two major categories:

 “Bottom

- up” processes

– These processes build nanoscale materials from individual atoms or molecules; and

 “Top

- down” processes

– These processes create nanoscale materials from

their macr o counterparts.

The bottom

- up process, also called “molecular nanotechnology

, ” uses forces of

nature to assemble nanomaterials atom by atom or molecule by molecule . The process can use chemical synthesis, self

- assembly, or positional assembly. In general, bottom

- up processes are less expensive than top

- down processes.

The top

- down process starts with a bulk material, and uses micro

- or nano

lithography and etching to cut the bulk material into nanoscale structures. Processes include photolithogra phy, electron beam lithography, and dip

- pen lithography. The top

down proc esses are the dominant and most well

- established manufacturing methods.

3.1.2.2 Nanomaterial Examples and Applications

N anomaterial products are often characterized into four major categor ies :

 Carbon

- based materials including carbon nanotubes and fullerenes;

 Metal

- based materials including quantum dots, nanogold, nanosilver, and metal oxides;

 Dendrimers; and

 Composites.

Below is a more detailed descri ption of these categories.

Carbon

- based nanomaterials

Carbon

- based nanomaterials include cylindrical shaped carbon nanotubes and spherical fullerenes. Carbon nanotubes are essentially graphite sheets that are rolled up into a tubular form. Nanotubes may be single

- walled or multi

- walled. An important property of carbon nanotubes is their high strength

- to

- weight ratio ; c arbon nanotubes are 100 times the strength of steel at a fraction of the weight. Carbon nanotubes also have unique electrical properties that allow them to be used for displays. Other applications of carbon nanotubes include computer chips, nanotools, and energy applications. For26

example, carbon nanotubes can be attached to the tips of atomic force microscopes (AFM). Research shows that this practice can enhance the resolution for AFM and prevent damage to the sample surface and probe. In addition, carbon nanotubes may be used as safe hydrogen storage for hydrogen fuel cells.

Fullerenes are spherical cages of carbon atoms. One of the most well known is a fullerene comp osed of 60 carbon atoms, known as C 60 fullere ne or “buckyball”. Fullerenes have applications in drug delivery and in medical imaging as a contrast agent for MRIs. In addition, fullerenes have enhanced antioxidant properties that make them

u seful for antiaging cosmetics and pharmaceuticals. Similar to carbon nanotubes, fullerenes have unique electrical properties that can be used for power supplies, data storage devices, and solar cells. Researchers have also considered us ing fullerenes for hydrogen storage for hydrogen fuel cells.

Metal

- based nanomaterials

Quantum dots are an example of metal

- based nanomaterials. Quantum dots are closely packed semiconductor crystals composed of hundreds of thousands of atoms.

These nanomaterials have u nique optical properties that allow them to be used in applications such as biomedical imaging. Quantum dots adsorb light energy, which causes the energy levels of the electrons in the crystal structure to increase and release energy in the form of light. Unique to fluorescent light, quantum dots can emit light at different wavelengths depending on the size of the particle.

Materials for manufacturing quantum dots include semiconductors such as cadmium selenide, cadmium sulfide, cadmium telluride, lead s ulfide, and lead telluride ; metals such as gold, silver, nickel, and cobalt; and hybrid structures. The two primary manufacturing methods for quantum dots include a lithogr aph ic process that uses pressure to break down a thin semiconductor film into dots and a colloidal synthesis process. Quantum dots manufactured using the lithographic process have applications in telecommunications, logic circuits, and quantum computing. In the colloidal synthes is process, materials are dissolved in a polymer solvent. Chemical reaction causes the quantum dots to precipitate from solution . Manufacturers can control the size of the quantum dot s by varying the reaction time. Quantum dots manufactured using the colloidal synthesis process can be used for biological and o ptics applications, such as light emitting d iodes (LEDs) and tunable lasers.

Den d rimers

Dendrimers are three

- dimensional nano

- sized polyme rs composed of an inner

core and branched units. Manufacturers use two methods to produce dendrimers:27  Divergent approach: This approach begins with the inner core and builds

outward.

 Convergent approach: This approach begins with the outer branches and

assembles them around the core.

Several modifications can be made to the dendrimer structure to alter its propert ies for specific applications. Modifications include filling the inner voids, modifying the dendrimer core, and modifying the dendrimer surface. Surface modifications can alter the particle’ s charge and s olubility, its ability to react with or bind to ta rget entities, and its ability to pass through cell boundaries. The primary application of dendrimers is in drug delivery. However, because of their spherical shape, viscosity characteristics, and catalytic properties, dendrimers also have applications i n coatings, additives, and inks.

Composites

Composites combine nanomater i als (such as nano clays) with other nanoparticles

or bulk

- type materials. Nanocomposites can enhance mechanical, thermal, barrier, and flame retardant properties for a wide range o f products including auto parts and packaging materials.

3.2 Overview of Environmental Transport

T he transport of nanoparticles in the environment requires extensive additional

research because the transport mechanisms can depend on the environmental media, various environmental parameters, and various nanoparticle parameters. Nanoparticle parameters to consider can include particle size and charge , chemical or elemental composition, and surfac e modifications. Environmental media parameters to consider can include pH, ionic strength, flow rate, composition, and presence of naturally occurring (such as dissolved organic carbon) as well as anthropogenic contaminants and

their interaction with nan oparticles. The following subsections summarize information collected that describes the transport of nanoparticles in surface water, soil, and groundwater. Each subsection identifies additional questions that are not addressed by

the information reviewe d to date.

3.2.1 Surface Water Transport

The colloidal stability and extent of aggregation of nanoparticles in water will greatly impact the transport p otential of the nanoparticles. The colloidal stability can be a function of the pH and ionic strength of the water and the particular nanoparticle of

interest.

With water samp les, the dissolved fraction of the water has typically been operationally define d using filters. These operational definitions would define any material that can pass through the filter ( e.g., a 0.2

-  m filter (particles less than 200 nm)28

or a 0.45

- 

m filter (particles less than 450 nm ) ) as the dissolved fraction

, and material that does not pass through as the particulate fraction . However, the growing research on nanoparticles has shown t hat this notion will not always hold true 3

, 6

, 7

. T he definition of a colloid as dispersed particles in the size range of 1 nm to 1  m 3

, 8 and suspended particles as particles greater than 1  m in size can help demonstrat e the role of nanoparticles in aquatic chemistry 8

. Observ ations of colloidal material in aquatic systems demonstrate how nanoparticles may exist as nondissolved particles in water, thereby completely changing their transport potential.

Chemical and physical alterations can be applied to nanomaterials to increas e their water solubility. For example, derivatization of hydrophobic C 60 fullerenes with hydrophilic functional groups increases the solubility of the C 60 nanomaterials. Sonicating C 60 in organic solvents and water can form stable aqueous suspensions of fullerene aggregates denoted as nC 60

. C 60 also has applications in personal care products that contain organic ligands. These ligands can affect the aquatic transport of C 60 9

.

Molecular solubility alone does not necessarily determine the water

- based availability of a nanomaterial. Fortner et al. 10 show that C 60 may form negatively charged

water

- stable colloidal aggregates with diameters from 50 to 500 nm. These colloids can

have concentration s up to 100 mg/L (100 ppm) , which is approximately 11 orders of magnitude greater than the estimated molecular solubility of C 60

. Fortner et al. 10 produce these aqueous colloidal suspensions by first producing a saturated solution of C 60 in tetrahydrofuran (THF). The authors then add water to the THF solution under mixing and then evaporate the THF to form the aqueous C 60 colloidal suspension. The authors note that adding an organic solvent, such as toluene, to the aqueous suspension results in low partitioning of nano

- C 60 from the water phase to the organic phase. However, the

addition of an oxidant drives the nano

- C 60 to partition from the water phase to the organic phase. Therefore, the process of forming the aqueous suspension changes the properties

of the C 60

. Fortner et al. 10 note that the water

- stable nano

- C 60 aggregates are crystalline in nature, and the aggregates’ particle sizes are functions of mixing rate, pH

, and ionic strength. The authors observe that lower mixing rates increase the particle size. Higher pH values produce smaller particles, while low er pH values produce larger particles. Higher ionic

- strength solutions give rise to larger particles, and i onic strengths similar to that of seawater (~0.7 I

) can cause particles to precipitate. On the other hand, lower ionic strengths, such as those similar to groundwater (~0.01 I ), can lead to stable particles that

can remain at concentrations of up to 100 p pm for at least 15 weeks. The researchers acknowledge that these fundamental laboratory experiments do not exactly predict what

will occur if C 60 is released into seawater or groundwater, as these experiments do not account for additional materials presen t in natural systems, such as proteins, humic acids, organic matter, and soils. This resear ch does demonstrate, however, that import ant water properties can affect the extent of particle aggregation and lead to stable colloids or unstable precipitates, wh ich can alter the transport of a nanomaterial.

Researchers at Arizona State University (ASU) 11 are currently studying the fate of nanomaterials in wastewater treatment plants. The researchers have sampled at eight wastewater treatment plants and performed simulations of sequence batch reactors in a29

laboratory setting to determine the portion of nanomaterials that partit ion to biomass. Unpublished findings of this research show that the partitioning of nanomaterials from water to biosolids ranges from 50 to 90 percent. ASU expects to publish its findings in May 2008 11

.

Additional Questions

How do materials present in the natural environment, such as proteins, humic acids, organic matter, charged clay particles, and soils, impact the transport of nanomaterials in groundwater and seawater?

3.2.2 Soil Transport

Understanding the transport of nanoparticles in soil requires knowledge of the nanoparticles ’ partitioning between the solid (soil) and liquid (water) phases. In general, the tendency for substances to partition from water to soil or sediment depends upon the hydrophobic characteristics of the substance and the properties of the solid media to

which it will adsorb. In addition, partitioning can occur via covale nt and ionic bond formation as well as through electrostatic adsorption. Surfactants, which are commonly used with engineered nanoparticles to aid in dispersions, might also affect the partitioning; therefore, the presence of a surfac tant should be noted in a study to help fully inform the reader. For example, natural organic carbon (NOC) can act as a natural surfactant and researchers have found some evidence that NOC coatings can help stabilize some aqueous nanomaterial dispersions.

Gimbert et al. 7 stud ied the partitioning of engineered ZnO nanoparticles in aqueous soil suspensions in the presence of sodium dodecyl sulfate (SDS) surfactant.

The authors use d SDS to ensure the ZnO nanoparticles disperse d in an aqueous solution as bare ZnO nanoparticles resist ed dispersion in water. The authors first produce d aqueous dispersions of ZnO in the presence of SDS and then use d this dispersion to spike soil samples to target a final concentration of 1.2 percent mass Zn in soil. This high

concen tration of Zn (as ZnO) in soil was required to simulate a significant environmental exposure. They then incubate d the soil samples at 60 percent moisture for 0, 7 , and 14 days before analysis. The authors fou nd that thi s ZnO dispersion quickly equilibrated between the solid and liquid phases and r emained relatively stable for the 14

- day period.

The authors f

ou nd little dissolution or increase in solid

- phase partitioning during the 14

- day period, indicating that the ZnO nanoparticles would pers ist in the environment. It

should be note d that these results occurred in the presence of a surfactant.

Wang et al. 12 studied the retention of nano

- C 60 aggregates in water

- saturated porous media. The authors produce aqueous suspensions of C 60 according to the methods

discussed in Fortner at al. 10 and summarized in Section 3.2.1 above : the authors begin

with a saturated THF solution of C 60 , add water under mixing, and then remove the THF to form the aqueous suspensions of nano

- C 60

. Wang et al. 12 study the retention of the

nano

- C 60 aggregates in columns packed with either glass beads or Ottawa sand. The authors conduct the retention experiments with aqueous C 60 suspensions prepared in30

deionized water containing 1.0 mM CaCl 2 buffered to a pH value of seven with 0.065

mM NaHCO 3 and also with C 60 suspensions prepared in deionized water alone. The authors find that, when using C 60 suspensions with CaCl 2 and NaHCO 3 ( 

- potential of approximately

- 23.9 mV and ionic strength of approximately 3 mM), the glass beads retained from eight to 49 percent of the introduced mass of nano

- C 60 , while the Ottawa sand retained up to 77 percent of the introduced mass of nano

- C 60

. Additionally, the

authors note that the retention of C 60 was irreversible as the introduction of nano

- C 60 - free

deionized water did not elute the retained mass from the column. The Ottawa sand

column had uniform nano

- C 60 retention, while the glass bead column had a nano

- C 60 retention that decreased with distance from the column inlet. This trend suggests that the

nano

- C 60 retention in the Ottawa sand approached a limiting capacity. The authors note that using aqueous C 60 suspensions prepared in deionized water alone (z

- potential of approximately

- 64 mV and ionic strength of zero mM ) showed no retention in either column packing. This observation demonstrates the importance of electrostatic

interactions on the transport and retention of nano

- C 60 aggregates in both glass beads and

Ottawa sand.

Additional Questions

Question 1:

How read ily do nanomaterials partition from liquid to solid phases in the absence of a surfactant or added surface functionality?

Question 2: How do soil properties affect transport of nanoparticles?

3.2.3 Groundwater Transport

The transport potential of nanoparticles in subsurface environments can depend upon several parameters, such as particle size, solution pH, ionic strength, soil composition, and groundwater flow velocity 13

. Groundwater typically has a higher ionic strength than rainfall but may have lower ionic strength than marine and many freshwater bodies. Higher ionic strengths can reduce the electrostatic repulsion among nanoparticles and increase aggregation. However, research has shown that surface modifications of nanoparticles can greatly alter their transport potential in environmental media. For example, many researchers are designing supports for zero

- valent iron nanoparticles for the purpose of groundwater remediation. These supports create negatively charged and hydrophilic surfaces to aid electrostatic repulsion among nanoparticles and aquifer materials and reduce nanopa rticle aggregation and aquifer mater ial filtration 13

.

Saleh et al. 14 design a zero

- valent iron nanoparticle core with a protective, nonreactive magnetite shell (Fe 3 O 4 ) to help remediat e trichloroethylene from groundw ater. They find that these nanoparticles rapidly flocculate and settle from

solution in water. The authors show that modif ying the nanoparticle with a novel triblock copolymer increase s the electrophoretic mobility and suspension stability of the nanoparticle

. The hydrophilic block of the triblock copolymer promotes electrostati c31

repulsion from negatively charged surfaces (such as Fe and Mn oxides and natural organic matter) that naturally occur in near

- neutral pH subsurfaces. Additionall y, the triblock copolymer drives the adsorption of the nanoparticle to the nonaqueous phase liquid

- water (NAPL

- water) interface. This example shows how surface modifications of nanoparticles can greatly alter their transport potential in environmental med ia.

Additional Questions

Question 1: How readily do bare nanomaterials partition from liquid to solid phases in the absence of a surfactant or added surface functionality?

Question 2: How effective are aquifer materials at filtering bare nanomaterials in the absence of an added surface functionality?

4.0 S AMPLING T ECHNIQUES

This section describes five research projects that involved collecting environmental samples for analysis of nanomaterials, including:

 One water sampling project;

 Three sediment sampl ing projects; and

 One soil sampling project.

Based on the information obtained , sampling techniques for nanomaterials in

environmental media currently do not differ from established techniques for sampling

environmental media.

Some issues regarding sampling remain whether one is sampling for nanomaterials or larger

- sized materials. Sample representation is always a concern when sampling environmental media . One research scientist interviewed for this report stated

that o ne should approach the issue of sample representation by visually inspecting a location for heterogeneity within the media. One should scale down the inspection from large to small spatial scales to identify areas of heterogeneity where sampling may be important 15

.

Another important concern with sampling is the risk of contamination. Although contamination is a concern for all types of sampling, nanomaterials may be more

sensitive to contamination as they are likely to be present in very small quantities within

the environmental media 15

.

One should also consider sample preservation and h olding time as research shows

that the structure and reactivity of nanomaterials can be time

- dependant and change when exposed to different environments

. Researchers of the Pacific Northwest National32

Laboratory observe that the reactivity of nanomaterials in aqueous solutions changes dramatically over the course of one day 16

. Baer et al. 17 describe two case studies that demonstrate the effects of time and environment on nanomaterials. In one study, the

authors demonstrate the infl uence of particle environments on the nano particle chemistry by measuring differences in UV

- visible transmission results for ceria nanoparticles before

and after adding an oxidizing agent to the aqueous solution

. In the second study, the

authors demonstrate the time

- dependent properties of iron nanoparticles by examining iron nanoparticles using transmission electron microscopy (TEM) before and after exposing the nanoparti cles to dei onized water for 24 hours. After 24 hours of exposure to

deioniz ed water, the oxide shell of the nanoparticle had thickened and was more porous and less ordered. 17

Researchers acknowledge that a need exists for nanomaterial

- specific sampling techniques. However, to date, develop ing sampling techniques has not been a high priority for nanomaterials research projects. Current priorities include determining how nanomaterials behave in the environment, identifying constituents of environmental concern, and developing analytical techniques 11

.

4.1 Sampling Techniques Suited for Surface Waters

One project was identified that involved sampling wastewater for nanomaterials.

As described in S ection 3.2.1

, researchers at ASU and the United States Geologic Survey (USGS) collected samples at eight wastewater treatment facilities in August 2007

. Sampling points included the final effluent from treatment and biosolids. The researchers analyzed the samples for fullerenes (C 60 ) and micro

- sized titanium dioxide (TiO 2 )

. The researchers hope that the approaches used for detecting micro

- sized titanium dioxide c an later be developed for nano

- sizes. For analysis of fullerenes, aqueous samples underwent

a solid

- phase extraction, were concentrated into methanol, and were analyzed using liquid chromatography coupled with mass spectrometry (LC

- MS)

. The biosolid samples were extracted into toluene, concentrated, and analyzed using LC

- MS. The detection limit for fullerenes analysis was 500 ng/L. The extraction methods for aqueous and biosolids samples were validated using matrix spikes. For analysi s of titanium dioxide, researchers used digression methods to show that TiO 2 was present and used SEM to identify the microparticles 11

.

The researchers noted that the samplers in this work did not use any special protocols that were specific for nanoma terials. D evelop ing sampling techniques is still in the early stages and was not the main focus of the project. Resea rc hers are currently evaluating the need for certain protocols, such as “clean hands” sampling, and future sampling activities may implement these protocols 11

.

4.2 Sampling Techniques Suited for Sediments

Three projects were identified that involved sampling sediments for nanomaterials. These projects did not use sampling techniques or protocols that were33

developed specif

ically for nanomaterials. The following discussion summarizes the sample collection and preparation techniques described for the three sediment sampling projects.

Hochella et al. 18 demonstrate samp ling riverbanks and riverbeds for further analysis of natural ly occurring nanomaterials. The authors obtain samples by digging into the side of a riverbank and collecting riverbed mud from beneath a layer of sediment

un der the shallow stream edge.

To prepare samples for TEM analysis , the authors perform the following steps

. The y first air dry their sediment samples before storage. They then lightly grind the dry samples to make them more friable, which reduces the la rger grain sizes and disperses the sample. The authors then use multiple stages of dry sieves at a cut

- off size of 65  m and

then wet sieve in ethanol at 25  m. They perform a final light grinding before preparing

the TEM ultramicrotomed thin sections.

Hochella et al. 19 sample bed sediment from the entrance of a mine for furt her analysis of natural nanoscale particles. The authors obtain the bed sediment from a small water channel and a small, shallow pond near the entrances of two mines. The authors sieve the wet sediment samples with 63

-  m sieves using ambient water to pre vent chemical changes from occurring. The authors note that sieving in this case helps to remove detrital material and allows for a uniform comparison between studies. The authors bottle and ice pack the samples for transport to the laboratory, where the y centrifuge and dry the sediment samples. They gently mash the sediment samples to separate clots and note the importance of avoiding high

- temperature drying to prevent mineralogical changes.

Heymann et al. 20 obtain samples of geologic materials from the Cretaceous

Tertiary (K

- T) boundary in New Zealand for further analysis of fullerenes. The authors crush and powder the samples and demineralize a portion of their samples using HCl and

HF treatments. The y then slurry the prepared solid samples with toluene and sonicate for

several hours to extract fullerenes from the solid materials. The authors recover the toluene extraction for analysis of fullerenes.

4.3 Sampling Techniques Suited for Soil

One project was identified that involves the sampling s oil for nanomaterials.

Gimbert et al. 7 obtain topsoil samples, which they air dry and sieve to 2 mm for performing nanomaterial transport studies. The authors did not describe any sampling techniques that were applied specifically for nanomateri als.

Additional Questions

Information found to date has been limited in this area. Additional research should be

conducted in this area.34

4.4 Sampling Techniques Suited for Groundwater

Information found to date has been limited in this area. Additional research should be

conducted in this area.

4.5 Comparison of Sampling Techniques

Information regarding techniques for sampling nanomaterials found to date has

been limited. The current literature search has not revealed well

- defined sampling

tec hniques specific to nanomaterials with outlined advantages and disadvantages.

Additional research should be conducted in this area.

5.0 A NALYTICAL T ECHNIQUES

This section identifies analytical techniques suited for characterizing naturally occurring nanomate rials and anthropogenic nanomaterials in natural media. Wigginton et

al. 21 identify the following characterization parameters applicable to characterizing

nanomaterials in natural media :

 Size distribution ;

 Surface area ;

 Direct visualization ;

 Phase and structure ; and

 Chemical composition

.

No single analytical technique provides information to address all five characterization parameters. Therefore, it is necessary to use combinations of analytical techniques to

characterize nanomaterials. Ad ditionally, nanomaterials in natural media may require

size

- fractionation techniques to separate the nanoparticles from larger particles. This section presents analytical techniques suited for fractionating and characterizing the five parameters of nanoma terials in natural media.

The ASTM Committee E

- 42 on Surface Analysis guides users of surface analytical instruments to produce more reliable results. The scope of the committee is to review and coordinate development of standards for all methods of surface analysis by photon, electron, and ion emissions or reflection methods, such as x

- ray spectroscopy and secondary ion mass spectrometry (SIMS). A member of the ASTM Committee E

- 42 on Surface Analysis emphasizes the importance of proper sample handli ng and use of analytical instruments for analy zing nanomaterials. Because analytical instrumentation for characterizing nanomaterials are highly sensitive, a greater potential for error exists 16

.

Burleson et al. 1 provide a technical review and description of many of the analytical techniques listed in S ection 5.0 . Section 5.7 includes general descriptions and35

comparisons of many of the analytical techniques listed below. Below are b rief descriptions of the major analytical techniques presented in th is section.

Transmission Electron Microscopy (TEM)

TEM utilizes an electron beam to probe a sample and images the electrons that pass through the sample. TEM can provide a high

- resolution direct image of the nanoparticles, typically greater than 0.1 nm of spatial resolution . Many TEMs can be operated in scanning transmission electron microscopy (STEM) mode 1

.

Scanning Electron Microscopy (SEM)

Like TEM, SEM also utilizes an electron beam to probe a sample. However, SEM primarily measures the secondary electrons (SE) emitted from the sample to produce topog raphical contrast maps. SEM does not provide the same high resolution as TEM: its resolution is limited to approximately 1 nm to 1  m 1

.

Energy

- Dispersive Spectroscopy (EDS)

X

- ray spectroscopy, commonly referred to as energy

- dispersive spectroscopy (EDS), X

- ray energy

- dispersive spectroscopy (XEDS), or energy

- dispersive X

- ray spectroscopy (EDX), measures secondary signals from characteristic X

- rays produced during TEM, STEM, or SEM imaging for detecting and quantifying elements present in the sample 1

.

Electron Energy Loss Spectroscopy (EELS)

EELS measure s primary signals from scattered electrons produced du ring TEM or STEM imaging for detecting and quantifying elements present in the sample 1

.

Atomic Force Microscopy (AFM)

AFM, a type of scanning probe microscopy (SPM), measures the forces between a sharp tip and a sample to determine topographic images at a spatial resolution of approximately 0.1 nm and provide s electrical and mechanical properties of the sample 1

.

Scanning Tunneling Microscopy (STM)

STM

, a type of scanning probe microscopy (SPM), measures a tunneling current between a conductive tip and a conductive or semiconductive sample to determine topographic images at a spatial resolution of approximately 0. 1 nm and is sensitive to the chemical identity of surface atoms and molecules 1

.36

X

- ray Diffraction (XRD)

XRD measures the diffraction of X

- ray beams to identify crystalline phases. XRD can measure structural properties of crystalline phases and probe atomic arrangements of amorphous phases 1

.

Dynamic Light Scattering (DLS)

DLS shines a light source on a suspensi on of particles and uses a photoelectric detector to measure the intensity of the scattered light. The constant Brownian motion of the particles causes time

- dependant fluctuations, which are directly related to the diffusion coefficients of the particles. The diffusion coefficients allow the estimation of the hydrodynamic radius of the particles 1

.

Laser

- Induced Breakdown Detection (LIBD)

LIBD uses an intense, pulsed laser beam to generate plasmas on nanoparticles. The generated plasmas emit light that is detected by the tool. The number of light

emissions per number of laser pulses provides information on the concentration and si zes of particles in the sample 22

.

X

- ray Absorption Spectroscopy (XA S)

XAS irradiates a sample with X

- rays and measures the amount of X

- ray energy the sample absorbs. X

- ray energies that meet the electron

- ejection threshold are absorbed and eject an electron. The ejected electrons are backscattered and produce interferences

with the X

- rays, which provide information on the average identity, number, and arrangement of the nearest neighboring atoms to the absorbing atom. T his information

allows researchers to identify the structure of the atoms in the sample 1

.

5.1 Analytical Techniques for Size Fractionation

Several fractionation tec hniques have the potential to separate particle samples

into vario us nanoparticle fractions:

 C entrifugation

– Centrifugation is a mechanical method that separates particles in a solution based on weight by applying a centrifugal force. Heavier particles sink outward ly while lighter particles rise towards the

center of the vortex.

 U ltrafiltration

– Ultrafiltration is a method that separates particles in solution based on molecular weight using a membrane barrier. Lower molecular weight particles permeate through the membrane while higher molecular weight particles remain in the retentate. The separation can be achieved by either direct

- flow (perpendicular to the membrane)

ultrafiltration or tangential

- flow (cross

- f low) ultrafiltration (TFF) . Th e37 benef it of TFF is the solution flows parallel to the membrane , which prevents bui l dup of particles at the membrane surface.

 F ield

- flow fractionation (FFF)

– FFF separates particles by applying a perpendicular gradient or cross flow to a sample solution that is flowing through a narrow channel . The perpendicular gradient drives particles of

different sizes toward the channel wall at different velocities.

 C apillary electrophoresis (CE)

– CE separates particles based on their size to charge ratios. In th is method, a buffer solution carries particles through a capillary typically from the anode to the cathode. When an electric charge is applied to the sample solution, the positively charged particles are attracted to the cathode while negatively charged p articles are attracted

to the anode. In addition to the particle charge, the particle’s size and shape determine the frictional forces that affect the particle’s transport through the buffer solution 23

.

 S ize exclusion chromatography (SEC)

– SEC separates particles based on size using the principle that particles of different sizes elute through a stationary phase at different velocities. A typical apparatus cons ists of a column packed with po rous polymer beads. As the sample solution passes through the column, smaller particles will enter the pores. Therefore larger particles wi ll elute faster.

These methods can apply for both aquatic colloids 3 and particles extracted from soil and sediment samples 7

, 19

. All methods require nanoparticles to be in solution. Therefore

, samples must be extracted into a solvent prior to analysis.

Aquatic Colloids

A t ypical and w idely used method for fractionating colloids is TFF 3

, 24 . Benoit

and Rozan 25 use TFF to fractionate colloidal particles from river water samples using

hollow

- fiber filters with a 3,000 molecular weight cutoff. They note that th e choice of a 3,000 molecular weight cutoff is arbitrary and, hence, their “colloidal” and “truly

dissolved” materi als are operationally defined. Lyven et al. 24 note that natural aquatic

colloids may exist in a dynamic state with respect to dissolved phase and particulate phase partitioning. Therefore, it is imperative that the fractionation technique involve mild and rapid pretreatment. They, therefore, re commend FFF as an appropriate

fractionat ion technique for aquatic colloids. They recommend flow FFF (FlFFF) for smaller colloidal particles in the size range of 1 to 50 nm. FlFFF is a type of FFF that utilizes a cross flow to provide the perpendicular gradient used in the separation 24

. Researchers commonly use FlFFF with on

- line detectors to measur e particle concentrations. These techniques are typically spectral methods such as UV absorbance

detectors 24

, 26

, 27 , fluorescence detectors (FLD) 26 , and multi

- angle laser light scattering (MALLS) 26

.38 FlFFF also allows the ease of coupling an on

- line detector for chemical analysis

, such as ICP

- MS 24

, 26

, 27

. Stolpe et al. 27 note that FlFFF and ICP

- MS match well for coupling concerning operating flow rates an d liquid phases. Additionally, band broadening from ICP

- MS is not a significant issue as FlFFF peaks are already comparatively broad. Stolpe et al. 27 also note that preconcentrat ing the sample may be necessary due to low elemental concentrati ons in natural waters and due to the large dilution of the sample during the FlFFF run. They note that preconcentration may

introduce artifacts and use an on

- channel preconcentration technique for their FlFFF

runs 27

. Both TFF and FFF necessit ate pretreatment to remove larger particles to prevent steric interferences and filter overloading 24

, 25

.

Several different authors filter their samples thr ough a 0.45

-  m filter before

fractionation 24

- 27 , although settling is also an option 24

.

Lead et al. 8 demonstrate the use of flow

- through centrifugation of colloidal and suspended particulates from river water samples. They achieve three nominal size

fraction s of greater than 1.0  m, 0.5 to 1.0 

m, and 0.05 to 0.5 

m. Their nominal size

fractions are b ased on Stoke’s law and assume a particle density of 2.5 g/cm 3

. They note that these fractions represent lower limits due to organic matter entrained in the fractions

and from applying Stoke’s law to generally nonspherical particles.

Lienemann et al. 28 describe a method for using ultracentrifugation to deposit aquatic colloidal particles directly onto TEM grids for further analysis.

Soils and Sediments

Hochella et al. 19 demonstrate the use of centrifugation to remove interstitial water

f rom wet sediment samples. After centrifugation, they pour off the supernatant liquid leaving the solid sediment behind.

Gimbert et al. 7 demonstrate a method of fractionating the sub

- 1.0

-  m fraction of soil suspensions spiked w ith engineered ZnO nanoparticles using FlFFF. They couple

FlFFF with a UV absorbance detector to characteriz e the partic les and obtain fractograms. They find FlFFF to be successful in measuring the particle size distributions

of the 180

- nm nominally size d ZnO nanoparticles.

Engineered Nanoparticle Systems

Additional techniques used to separate engineered nanoparticles within an engineered system may prove applicable to separating nanoparticles within

environmental media.

Hwang et al. 23 use capillary electrophoresis (CE) to separate mixtures of gold and polystyrene nanoparticles of varying sizes. The authors first demonstrate the application of CE in separating gold nanoparticles of varying sizes and then in separating polystyrene nanoparticles of varying sizes. Lastly, the authors demonstrate the application of CE in39

separating a mixture of gold and polystyrene nanoparticles of equal size. The authors use

a UV

- visible light absorbance detector to detect the separated particles and plot electropherograms. The electroph erograms show the successful separation of the nanoparticles, and the authors note the potential application of CE to mixtures of other nanoparticles.

Novak et al. 29 demonstrate us ing centrifugation and size exclusion chromatography to purify molecularly bridged gold nanoparticle arrays. The authors

wish to separate dimers and trimers of the molecularly

- bridged gold nanoparticles.

The authors note that centrifugation has the following drawbacks: 1) the nanoparticles may aggregate upon concentration, and 2) the nanoparticles may become unstable if combined with high ionic strength or nonaqueous solvents. The authors overcome aggregation by replacing one of the bridging ligands with anot her that would not cause particle aggregation. The authors perform stepwise g

- force density centrifugation and collect highly viscous slurries of their modified molecularly

- bridged gold nanoparticles 29

.

Novak et al. 29 note that SEC has similar drawbacks as centrifugation. Additionally, SEC may also lead to the irreversible adsorption of the analytes to the

stat ionary phase. The authors overcome this additional drawback by using an aqueous mobile phase containing sodium dodecyl sulfate (SDS) buffer. The authors couple SEC

with a UV

- visible light absorbance detector to detect the nanoparticles as a function of

t heir column retention time and develop chromatograms. The authors note a high resolution of separation when separating pure gold nanoparticles of varying sizes but lower resolutions of separation when separating the dimer and trimer molecularly

- bridged

go ld nanoparticles. The authors conclude that centrifugation is simpler and less expensive than SEC, but SEC has the potential for postcolumn analysis of optical and electrochemical properties of the analyzed nanoparticles.

5.2 Analytical Techniques for Size D istribution

Several analytical techniques are suitable for measuring size distribution of nanoparticles. The microscopy methods discussed in this section either use point count techniques that measure the sizes of individual particles or bulk analyses tha t measure the average and range of particle sizes in a sample, and include the following:

 Transmission Electron Microscopy ( TEM )

– TEM measures the size of individual particles by produc ing a high resolution ( 0. 1 nm) two

dimensional image of the nanomaterial.

 Scanning Electron Microscopy ( SEM )

– SEM measures the size of individual particles by produc ing a topographical three

- dimension image

of the nanomateria l at resolutions ranging from 1 nm to 1  m.40  Scanning Probe Microscopy (SPM)

– SPM techni ques determine the size of individual particles and include a tomic f orce m icroscopy ( AFM ) , which measures forces between a sharp tip and a sample to determi ne the topography of the sample, and scanning tunneling microscopy (STM), which measures a tunneling current between a conductive tip and a conductive or semiconductive sample to determine the topography of the sample.

 Dynamic Light S cattering (DLS)

– DLS is a bulk analysis that measures the average particle size of dispersions or suspensions.

 Laser

- In duced Breakdown Detection (LIBD)

– LIBD is a bulk analysis

that measures the average particle size and concentration of particles in the sample.

 Small

- and Wide

- Angle X

- ray S cattering (SAXS/WAXS)

– SAXS/WAXS is a bulk analysis that determines particle sizes and populations.

TEM

Many works cited in this report use TEM or a variation of it to obtain size distributions of nanoparticles along with shape and dimensional information 10

, 18

, 19

, 30

- 33

. Variations of TEM can include high

- resolution (HR) TEM 32

, 33 and cryogenic (cryo)

TEM 10

.

Madden and Hochella 30 and Madden et al. 31 use TEM images, along with AFM images, to determine diam eters and heights of synthesized hematite nanoparticles. The authors assign the nanoparticles by diameter into histogram bins with each bin assigned an average height. This method obtains a size distribution suitable for calculating surface

area. See S ection 5.3 for additional discussion.

Hochella et al. 19 use TEM

- EDS and EFTEM

- EELS to characterize sediment samples. The authors are able to characterize 85

- 90 percent by volume of the TEM

sections as contain ing ferrihydrite particles between 10 and 100 nm in dia mete r. The

authors note that EFTEM

- EELS obtains spatially resolved elemental distributions better

than TEM

- EDS.

SEM

SEM images may also be used to measure nanoparticle size distributions 7

, 8

, 18

, 19

. Lead et al. 8 demonstrate the use of SEM to verify the discrete size fractionation of aquatic nanoparticles from centrifugation. The authors note that most particles sampled are less

than 1  m in size with some particles as large as 10  m or 100 

m in at least one

dimension.41 Hochella et al. 19 use SEM in conjunctio n with TEM to gain an additional perspective on the sediment samples. The authors note that SEM does not capture the complex n ature of the particles as well as TEM.

SP M

Madden and Hochella 30 and Madden et al. 31 use AFM images, along with TEM images, to determine diam eters and heights of synthesized hematite nanoparticles. The authors assign the nanoparticles by diameter into histogram bins with each bin assigned an average height. This method obtains a size distribution suitable for calculating surface

area. See S ection 5.3 for additional discussion.

E ggleston et al. 34 use STM image s of hematite nanoparticles in both air and aqueous media to obtain dimensional measurements . They additionally use the resonant tunneling model (RTM) to help interpret the STM images. They find RT M to qualitatively agree with many features of the STM images.

DLS

Waychunas et al. 32 , Gilbert et al. 33

, Fortner et al. 10 , and Zhang et al. 35 demonstrate the use of dynamic light scattering (DLS) to measure average size distributions of nanoparticle dispersions and suspensions of iron oxyhydroxide 32

, 33

, C 60 fullerene 10 , and CdTe quantum dots 35

. Further, Gilbert et al. 33 use DLS to measure average size

distributio ns as a function of pH, and Waychunas et al. 32 use DLS to measure average size distributions as function of suspension aging. Both of these works use DLS to help

characteriz e nanoparticle aggregation and understand the factors that can lead to aggregation.

LIBD

Bundschuh et al. 22 demonstrate the use of LIBD to quantif y colloids in the effluents of various treatment stages in a drinking water treatment plant. LIBD is a sensitive analytica l tool capable of quantifying low concentrations (< 1  g/L) nanoparticles smaller than 100nm. The method uses an intense, pulsed laser beam to generate plasmas on colloidal particles. The generation of plasmas is called a

“breakdown event

. ” The plasmas generated by the breakdown event emit light or generate shock waves that are detected by the tool. In general, solids require less energy

to break down than liquids or gases. LIBD is based on the difference in breakdown thresholds of liquid and solid mat ter. The laser beam energy is set to exceed the solid breakdown threshold but not the liquid threshold. The number of breakdown events per number of laser pulses depends on the concentration and size of the particle.

A charged coupled device (CCD) came ra detects the light emissions of single plasmas to det er mine the particle size. Detection of optical spatially resolved plasma light emissions results in a spatial distribution of breakdown events within the focal volume. Spatial distribution depends on the particle size. The authors compare the42

distribution to the distribution width of reference particles to determine the mean particle diameter. They then calculate the mean particle diameter and breakdown pr obability 22

.

SAXS/WAXS

Waychunas et al. 32 demonstrate the use of small

- and wide

- angle X

- ray scattering (SAXS/WAXS) to determine the size distribution and population of goethite nanoparticles as a function of time. The authors make in situ measurements and note that these particular nanoparticles aggregate in solution as they age . The authors additionally

use SAXS/WAXS to make ex situ measurements on samples they measured using other techniques. The authors present graphical proce ssed SAXS results that demonstrate the aging particle size distributions over time.

Gilbert et al. 33 use SAXS to study the colloidal stability of iron oxyhydroxide nanoparticles as a function of pH and ionic strength over time. The authors make in situ

measurements and note slight nanoparticle aggregation after 10 weeks but no macroscopic aggregation even after four months at pH values less than 6.6. The authors note a greater extent of aggregation at pH values greater than 6.6.

5.3 Analytical Techniques for Surface Area

The average surface area of nanoparticles is a useful characterization p arameter. Average surface area may be calculated in conjunction with size distribution or may be calculated directly using the Brunauer

- Emmett

- Teller method (BET). The BET method utilizes a gas, typically nitrogen, to adsorb to the accessible surface are a of a sample. The adsorbed gas forms a monolayer of molecules or atoms along the accessible surface area. One may then measure the volume of the adsorbed monolayer of gas and, with knowledge of the size of the gas molecules or atoms and the mass of the sample, calculate the surface area per mass of the sample 1

.

Madden and Hochella 30 and Madden et al. 31 discuss methods for calculating the

surface area of synthesized hematite nanoparticles using measurements from TEM and AFM and the particles’ nanocrystalline geometries. The authors use two

- dimensional TEM images to determine two

- dimensional length and width measurements and use AFM to determine height measurements. Madden and Hochella 30 note that , in this particular work, particle diameters measured from AFM are larger than diameters measured from TEM due to tip

- sample interaction, although heights measured from AFM are accurate. Therefore, they use TEM

- measured diameters and AFM

- measured heights. The particles are arran ged by diameter into histogram bins with each bin assigned an average AFM

- measured height. Knowing the nanocrystalline geometry of the particles,

the authors then calculate the average surface area of the individual particles for each bin

. The authors ca lculate the total surface area for all particles by converting the average surface are a per particle to surface area per mass for each bin and calculate the weighted

sum of all surface areas.43 I t is important to note that the above method for calculating surface area may not be applicable to nanomaterials that do not have a regular or pseudo

- regular geometry or have significant porosity.

Madden and Hochella 30

, Madden et al. 31

, Waychunas et al. 32

, and Gilbert et al. 33

use BET to directly measure the surface area of nanoparticles. Madden and Hochella 30

also note that surface area s for ultrafine particles, less than 15 nm in diameter, are typically lower from BET measurement s than those calculated from geometric models as described above

.

5.4 Analytical Techniques for Direct Visualization

Direct visualization can produce a direct visual representation or image of individual nanoparticles from a small sample. Visualization allows one to examine geometry and shape characteristics of the observed nanoparticles. Techniques f or direct

visualization include:

 E lectron microscopy techniques, such as transmission electron microscopy (TEM) and scan ning electron microscopy (SEM); and

,

 S canning probe microscopy (SPM), such as atomic force microscopy (AFM) and scanning tunneling microscopy (STM)

.

Electron Microscopy

A widely used electron microscopy technique is TEM , which is an indispensable

tool an d is often a staple for nanomaterial researchers 1

, 36

.

A number of cited papers in this report use TEM to obtain images of individual

nano particles 10

, 18

, 19

, 28

, 30

, 31 . Other variations of TEM include high

- resolution (HR)

TEM 1

, 32

, 33 and scanning transmission electron microscopy (STEM) 1

, 26

. Coupling TEM with EELS can produce energy

- filtered (EF) images with spatial resolutions on the order

of 0.5 nm 1 . Hochella et al. 19 find better spatially resolved information about elemental

distributions from EFTEM

- EELS images. Fortner et al. 10 even use cryogenic (cryo) TEM, which uses a cryogenic sample holder to allow the imaging of flash

- frozen samples. See S ection 5.7 for a discussion and comparison of these different variations of

TEM.

Additionally, HR TEM images may show morphological characteristics of nanoparticles. Waychunas et al. 32 use HRTEM images to determine morphological changes of goethite nanoparticles in suspension from initial oblong shapes to rod

- like

s hapes caused by oriented aggregation during aging. The images show rod

- shaped particles with dimensions of approximately 10 x 100 nm after 33 days of aging.

A number of cited papers in this report additionally use SEM to obtain images of individual nanoparticles 7

, 8

, 18

, 19

. Lead et al. 8 are even able to visually identify the presence of bacteria in their SEM images. Hochella et al. 18 additionally capture44

backscattered electron (BSE) images to locate grains of sediment samples containing heavy metals. Hochella et al. 19 use SEM in conjunction with TEM to gain an additional perspective on the sediment samples. The a uthors note that SEM does not capture the complex nature of the particles as well as TEM. See S ection 5.7 for a discussion and comparison of these different variations of SEM.

Scanning Probe Microscopy

A number of cited papers in this report use AFM to image individual nanoparticles 30

, 31

, 34

. Madden and Hochella 30 and Madden et al. 31 mainly use AFM to obtain heights of the sampled nan oparticles.

Additionally, Eggleston et al. 34 use STM to image hematite nanoparticles in both

air an d aqueous media. They additionally use the resonant tunneling model (RTM) to help interpret the STM images. They find RTM to qualitatively agree with ma ny features of the STM images.

5.5 Analytical Techni ques for Phase and Structure

The structure of nanoparticles may be crystalline or amorphous. Knowledge of the structure of naturally occurring crystalline nanoparticles along with chemical information may determine the identity of the mineral phase of the nanoparticle. Techniques that provide information on nanoparticle structure include electron diffraction, X

- ray absorption spectroscopy (XAS), X

- ray diffraction (XRD), and Raman

spectroscopy.

Electron Diffraction

When using TEM, one may measure the diffraction of e lectrons passing through the sample to obtain the crystal structure of crystalline materials. Hence, electron diffraction can differentiate between amorphous and crystalline materials. Additionally,

information from electron diffraction and TEM images ca n determine size and size distribution of crystalline nanoparticles. Variations of electron diffraction include

selected

- area electron diffraction (SAED) and convergent beam electron diffraction (CBED) 1

.

Madden and Hochella 30 use electron diffraction to confirm the identity of their synthesized hematite nanoparticles as judged by the mineral’s structure.

Fortner et al. 10 use SAED to confirm the crystalline structure of C 60 nanoparticles. The SAED diffraction patterns from a single particle show a simple hexagonal unit cell

structure.45

X

- ray Absorption Spectroscopy

XAS irradiates a sample with X

- rays and measures the amount of X

- ray energy the sample absorbs. X

- ray energies that meet the electron

- ejection threshold are absorbed and eject an electron. The ejected electrons are backscattered and produce interferences

with the X

- rays, which provide information on the average identity, number, and arrangement of the nearest neighboring atoms to the absorbing atom. From this information, the structure of the atoms in the sample may be obtained 1

.

Waychunas et al. 32 are able to use Extended X

- ray Absorption Fine Structure ( EXAFS ) measurements to determine that their goethite nanoparticles increase in structural ordering during the aging process of their studies.

X

- r ay Diffraction

XRD measures the diffraction of X

- ray beams to identify crystalline phases. When compared to a database of known diffraction patterns, it can quantitatively identify mineral composition. For example, Hochella et al. 18 use XRD with the computer program RockJock to quantitatively determine the mineralogical composition of riverbank and riverbed samples. RockJock compares the intensities of the diffraction

patterns to that of an internal standard: ZnO.

Hochella et al. 19 use XRD to determine the pre sence of mineral phases, such as quartz and jarosite, in their acid mine drainage samples.

Madden et al. 31 use XRD to confirm the structural characteristics of their synthesized nanoparticles are consistent with hematite.

Waychunas et al. 32 use XRD to confirm their synthesized iron oxyhydroxide nanoparticles are initially goethite and remain as such throughout the aging process of

thei r studies.

Gilbert et al. 33 use XRD to determine that the crystal phase of their synthesized iron oxyhydroxide nanoparticles is consistent with a nanoscale and highly disordered goethite phase.

Raman Spectroscopy

Tarassov et al. 37 use micro

- Raman spectroscopy to study the atomic arrangement

of hema tite and goethite microparticles sampled from the oxidation zone of the Grantcharitza scheelite deposit in Bulgaria. The authors compare the Raman spectra of their samples against spectra from reference particles. This analysis enables the authors

to det ermine that the local atomic structure of the sampled hematite particles deviate from reference hematite. The Raman spectra reveal that the sampled hematite has a disordered

structure.46

5.6 Analytical Techniques for Chemical Analysis

C hemical analytical techn iques either are suitable for a bulk analysis or capable of obtaining spatial resolutions. Bulk chemical analytical techniques do not directly identify the presence of nanoparticles, nor do they provide appropriate information to characterize

them . They do, however, directly identify and possibly quantify the presence of atoms, functional groups, or molecules. These c hemical analytical techniques allow one to identify the atomic or molecular components of nanoparticles. Chemical analytical techniques ca pable of obtaining spatial resolutions can identify and spatially map

elements. These chemical analytical techniques allow for greater surface characterization of the sample. This section presents information obtained on sample extraction techniques, bul k chemical analyses, and chemical analyses with spatial resolution.

An important step in bulk chemical analysis is sample extraction and preparation. Sample extraction techniques directly impact the method detection limit. Chen et al. 9
evaluate three techniques for extracting nC 60 fullerene from aqueous samples for HPLC/MS analysis:

 Technique 1

– Evaporation of aqueous phase followed by partitioning of dry fullerenes into tol uene

 Technique 2

– Liquid

- liquid extraction with addition of salts; and

 Technique 3

– Solid phase extraction (SPE) of aqueous sample using preconditioned SPE cartridges followed by toluene extraction to remove
fullerene s from the cartridge s

.

The addition of salts for Technique 2 improved recovery of C 60 compared to Technique 1. However, the authors found Technique 3 to be the most effective of the three methods

in C 60 extraction. The SPE method can be automated and can handle larger volumes of

s ample than Techniques 1 and 2, resulting in less time required for analysis , lower detection limits, and reduced potential for error. The authors conclude that SPE is applicable for extracting nanoparticles that exist in aqueous environments as discrete or aggregated forms, and can also be used for analysis of biological or soil samples. The sample extraction technique s directly impacted the method detection limit for the analysis

as shown in Table 5

- 1

.

Table 5

- 1

. Determination of Method Detection Limit for the Measurement of Stable

Aqueous C 60 Aggregates in Ultrapure Water 9

Technique MDL (  g/L) Technique 1

– Evaporation 2.78 Technique 2

– Liquid

- liquid extraction 3.33 Technique 3

– Solid phase extraction 0.3047

Bulk Chemical Analysis

General analytical techniques suitable for bulk chemical analysis include atomic absorption spectrometry (AAS) , atomic emission spectrometry (AES) , and mass

spectrometry (MS) . These methods are used to identify the elements present in a sample and can quantify the average elemental composition of a sample. Excitation sources include flame, graphite furnace (GF) and inductively

- coupled plasma (ICP). These bulk elemental analytical techniques h ave several advantages: 1) they are relatively easy to perform and relatively inexpensive, 2) they hav e relatively good detection limits, and 3) they provide an average composition of a sample of nanoparticles. These methods also

h ave several disadvantages: 1) they are destructive techniques ( i.e. one may not recover the sample after analysis ) , 2) sample preparat ion and matrix effects can introduce major

contaminants , and 3) they are limited to providing only an average composition of the sample of nanoparticles and cannot correlate chemical composition to spatial location 1

.

Benoit and Rozan 25 demonstrate a method of extracting particulates from river water samples for elemental analysis by GFAAS. They also chelate dissolved metals for elemental analysis by GFAAS. The authors use ICP

- AES for elements that were at higher concen trat ions. Zhang et al. 35 use GFAAS to measure the cadmium concentration

of water suspensions of CdTe quantum dots. The authors are able to derive the quantum

dot core concentrations from the cadmium concentrations.

Baalousha et al. 26

, Lyven et al. 24 , and Stolpe et al. 27 demonstrate coupl ing ICP

MS o n line with FlFFF. Stolpe et al. 27 note that FlFFF and ICP

- MS match well for coupling concerning operating flow rates an d liquid phases. Additionally, band broadening from ICP

- MS is not a significant issue as FlFFF peaks are already comparatively broad.

Stolpe et al. 27 additionally note that they choose to use high

- resolution ICP

- MS (HR

- ICP

- MS) over quadrupole ICP

- MS. The authors note that, when compared to quadrupole

- ICP

- MS, HR

- ICP

- MS offers a higher resolving power, higher sensitivity, and lower background noise; hence, it increase s the numbers of elements capable of detection

and lowers the detection limits . However, using a magnetic

- sector MS design to obtain high resolution images requires a longer time to change magnetic fields; thus, scanning large mass ranges of elements may increase the time for analysis 27

.

Table 5

- 2 presents results from Lyven et al. 24 demonstrating the detection limit

and actual measured concentration of various elements identified in their aquatic samples using ICP

- MS

.

Benoit and Rozan 25 and Lyven et al. 24 use high temperature catalytic oxidation to quantify organic carbon. Lyven et al. 24 note they could not reliably quantify the ICP

- MS carbon signal.

Fortner et al. 10 use 13 C

- NMR to analyze suspensions of nano

- C 60 in D 2 O. They

enrich the C 60 with 13 C at 25 percent.48 Heymann et al. 20 quantify the naturally occurring C 60 and C 70 fullerenes in various geologic samples. They demonstrate a method for using HP LC to separate C 60 and C 70 fullerenes from the organic material associated with the geologic samples coupled with

UV

- visible light absorption spectroscopy to quantify the fullerenes at their respective retention times. The authors discuss the importance o f sample preparation and prior knowledge of the nanomaterials sought after. They cite that fullerenes are vulnerable to ultraviolet radiation, heating in air, and exposure to ozone and, as such, avoid strong irradiation and heating above 60 o C of the samples. They note that HPLC is nondestructive, which allows the recovery of the sampled fullerenes.

Fortner et al. 10 also use HPLC with UV

- visible absorption spectroscopy to compare the retention time of C 60 fullerenes that were recov ered from an aqueous phase to an organic phase with C 60 fullerenes in an organic phase that did not contact an aqueous phase initially. Chen et al. 9 evaluate UV/vis spectroscop y for analyzing aqueous

nC 60 fullerenes. The authors established a linear relationship between UV absorbance

and the concentration of nC 60 in standard water samples. The authors determined that the detection limit of 0.3 mg/L was higher than expected env ironmental concentrations and concluded that UV spectrophotometry is not a selective or sensitive method to quantify

C 60 fullerene in aqueous environmental samples.49

Table 5

- 2 . ICP

- MS Detection Limits and Rat io of Measured Concentration to

Detection Limit from F reshwater Samples as P rovided by Lyven et al. 24

Element Isotope

(m/z) Detection

Limit (nmol/L) Ratio of Measured

Concentration to

Detection Limit

C 12 Not Quantified 144 a
Mg 26 7.7 21

Al 27 11 47

Ca 44 23 91

Mn 55 0.1 31

Fe 57 14 1000

Co 59 0.02 13

Ni 60 0.2 36

Cu 65 1.5 9

Zn 66 0.9 11

Sr 88 0.005 44

Y 89 10 66

Zr 90 1 3

Mo 95 0.1 7

Sb 121 0.1 5

Ba 137 0.3 28

La 139 0.06 111

Ce 140 0.2 41

Pr 141 0.06 34

Nd 147 0.07 18

Gd 157 0.04 17 Dy 162 0.04 23

Pb 208 0.05 52

Th 232 0.03 26

U 238 0.03 18

a Estimated using 10 times the standard deviation of the baseline and the fractionated creek sample.

Chemical Analysis with Spatial Resolution

X

- ray spectroscopy, commonly referred to as energy

- dispersive spectroscopy (EDS), X

- ray energy

- dispersive spectr oscopy (XEDS), or energy

- dispersive X

- ray spectroscopy (EDX), measures secondary signals from characteristic X

- rays produced during TEM, STEM, or SEM imaging for detecting and quantifying elements present in the sample. EDS is relatively easy to use in co njunction with TEM, STEM, or SEM and can obtain a spatial resolution on the order of 0.5 nm for elemental mapping 1

.

Electron Energy Loss Spectroscopy (EELS) measure primary signals from scattered electrons produced during TEM or STEM imaging for detecting and50

quantifying elements present in the sample. EELS h as an increased energy resolution over EDS, which allows it to obtain additional information on chemical bonding, oxidation state, and average bond distances. EELS also can achieve a greater spatial resolution for elemental mapping, although the resolutio n is still on the order of 0.5 nm 1

.

Hochella et al. 18 use TEM

- EDS and SEM

- EDS to analyze riverbank and riverbed samples. Hochella et al. 19 use TEM

- EDS and EFTEM

- EELS to characterize acid mine drainage sediment samples. The auth ors note that EFTEM

- EELS obtains spatially

resolved element al distributions better than TEM

- EDS. The authors additionally use

SEM

- EDS, which obtains a poorer spatia l resolution of elements than TEM

- EDS and

TEM

- EELS. Hochella et al. 19 note that TEM

- EDS and EFTEM

- EELS added significant details to the understanding of their acid mine drainage samples that SEM

- EDS and XRD

alone would not h ave revealed.

Baalousha et al. 26 use STEM

- EDS to determine surface elemental chemical maps of river colloidal particles. The authors use the surface elemental maps to verify the chemical compositions determined from FlFFF coupled with ICP

- MS. The authors note

their STEM

- EDS results are semiquantitative.

Nanoscale secondary ion mass spectrometry (NanoSIMS) is a high

- resolution microscopic technique capable of isotopic analysis. A primary ion beam, s uch as Cs + or O - , is rastered across the surface of the sample causing it to sputter and eject secondary ions from the sample. The ejected secondary ions are separated by their mass

- to

- charge ratios for detection and isotope identification. NanoSIMS may simultaneously identify

up to five to seven species, depending on the model. The raster

- scanning process can map the surface isotopes and may achieve a lateral resolution of 50 nm. In addition to surface information, NanoSIMS may also provide depth infor mation. Static NanoSIMS

can provid e information within the first nanometer of depth from the sample surface, while dynamic NanoSIMS may achieve depths within a few nanometers from the sample

surface. Herrmann et al. note that time

- of

- flight secondary ion mass spectrometry (ToF

SIMS) may also provide molecular and isotopic surface information, but not while simultaneously providing high mass resolution and high spatial resolution with adequate signal transmission. NanoSIMS can provid e high mass and spatia l resolutions with excellent signal transmission 38

.

Herrmann et al. 38 provide several considerations for using NanoSIMS. The analyzed sample should be dry, stable, conductive, and able to withstand the ultra

- high

vacuum of NanoSIMS. Soil samples should be flat and highly polished to avo id cha rging effects. Additionally, the use of a gold coating and an electron gu n may reduce charging

effects. Aqueous and in vivo samples may not be analyzed with NanoSIMS. Proper sample preparation is required. Freeze drying samples may cause ice crystal damage. Embedding the sample in an epoxy resin is a suitable sample preparation method. Sulphur embedding is also possible, a lthough it is limited to small samples and has a short time frame of consistency. Samples should be less than 4 mm thick to avoid outgassing issues. Analyzing soil samples may prove semiquantitative and the use of standards may prove difficult. NanoSIMS has a field of view ranging from 5 to 50  m.51

Precisely aligning the sample where the NanoSIMS analysis is to occur may prove challenging due to the restricted field of view. Optical microscopy may assist in navigating the sample. Additionally, because NanoSIMS is a destructive technique, one may not further analyze the same sample.

Novikov et al. 39 use NanoSIMS to analyze the elemental composition, particularly plutonium and uraniu m, of groundwater colloidal samples. NanoSIMS provides elemental maps of the colloidal particles.

5.7 Comparison of Analytical Techniques

This section describes the major analytical techniques presented and summarizes the advantages and disadvantages of each of the above described analytical techniques for each of the covered areas of characterization (e.g.

, size fractionation, size distri bution). Advantages and disadvantages of the analytical techniques may include ease of use, potential resolution, and data interpretation.

Spectroscopies for Electron Microscopy

X

- ray spectroscopy, commonly referred to as energy

- dispersive spectroscopy (EDS), X

- ray energy

- dispersive spectroscopy (XEDS), or energy

- dispersive X

- ray spectroscopy (EDX), measures second ary signals from characteristic X

- rays produced during TEM, STEM, or SEM imaging for detecting and quantifying elements present in the sample. EDS is relatively easy to use in conjunction with TEM, STEM, or SEM and can obtain a spatial resolution on the o rder of 0.5 nm for elemental mapping 1

.

Electron Energy Loss Spectroscopy (EELS) measure s primary signals from scattered electrons produced during TEM or STEM imaging for detecting and quantifying elements present in the sample. EELS has an increased energy resolution over EDS, which allows it to obtain additi onal information on chemical bonding, oxidation state, and average bond distances. EELS also can achieve a greater spatial resolution for elemental mapping, although the resolution is still on the order of 0.5 nm 1

.

Transmission Electron Microscopy (TEM)

TEM utilizes an electron beam to probe a sample and ima ges the electrons that pass through the sample. TEM offers several advantages for characterizing nanoparticles. TEM is typically coupled with EDS or EELS for chemical anal ysis. TEM can provide a high

- resolution direct image of the nanoparticles, typical ly greater than 0.1 nm of spatial resolution. TEM can also use electron diffraction, such as SAED or CBED, to distinguish between crystalline and amorphous phases. Additionally, TEM can determine the size and size distribution of crystalline nanoparticle s 1

.

However, TEM also carries several disadvantages. Only a small fraction of nanoparticles sampled are examined, which makes it difficul t to ensur e that a representative sample is examined 1 (10,000 images should be examined to ensure52

statistical validity 1 ). TEM produces a two

- dimensional image of a three

- dimensional object, which requires proper interpretation of th e image. TEM operates near vacuum, which requires an ex situ analyzing environment. Sample preparation can introduce substantial artifacts, such as aggregate fragmentation, precipitation of salts, or nanoparticle aggregation 1

.

Hochella et al. 19 note the difficulty in preparing heterogeneous precipitates, which might be sensitive to vacuum and beam exposure, while assuring an unbias ed sampling of particles. The authors choose a method of embedding the samples in epoxy resin and cutting cross

- sections using a diamond

- knife ultramicrotome. This method allows unbiased sampling and uses encapsulation t o stabilize delicate phases 19

.

TEM can be oper ated at high resolution (HR TEM), which is capable of spatial

r esolutions on the order of 0.1 nm. Energy

- f iltered TEM (EFTEM), coupled with EELS, may produce energy

- filtered images with spatial resolutions on the order of 0.5 nm. Many TEMs can be operated in scanning transmission electron microscopy ( STEM )

mode. ST EM provides superior resolution (<0.1 nm spatial resolution) and can still be coupled with EDS or EELS. It can also be coupled with high

- angle annular dark field ( HAADF ) to pr oduce “Z

- contrast” images. A Z

- contrast image directly relates image

contrast w ith atomic weight of the imaged atoms. Environmental TEM ( ETEM ) allows the characterization of nanoparticles in a controlled atmosphere up to several torr of pressure. It can even allow the characterization of nanoparticles while reacting with

gases to p rovide more of an in situ characterization 1

. Despite its disadvantages, TEM still remains a staple in characterizing environmental nanoparticles due to its many advantages 36

.

Scanning Electron Microscopy ( SEM )

Like TEM, SEM also utilizes an electron beam to probe a sample. However,

SEM primarily measures the secondary electrons (SE) emitted from the sample to produce topographical contrast maps

. SEM d oes not provide the same high resolution TEM provides: its resolution is limited to approximately 1 nm to 1  m

. Like TEM, SEM can also be coupled with EDS for chemical analysis. SEM requires less sample preparation than TEM, but SEM still maintains the concern for proper sample representation. Unlike TEM, S EM does provide reliable three

- dimensional topographic imaging. SEM can also reduce any hydrocarbons present in the sample, which can deposit a layer of carbonaceous material on the imaged area and reduce image contrast. The high

- vacuum environment can b e detrimental to samples with volatile components. Inadequately coated samples can lead to charging, which can lead to image distortion, artifacts, or sudden discharges. The electron beam itself can damage or alter samples 1

.

SEM offers the option of capturing backscattered electron (BSE) signals and

measurin g their diffraction through the sample to obtain crystallographic and texture

information. Additionally, BSE intensities can yield atomic number contrast maps. Environmental SEM ( ESEM ) allows the characterization of nanoparticles in a controlled53

atmosphe re in the range of 1 to 10 torr. However, ESEM can only provide a maximum spatial resolution o f three to four nanometers 1

.

Scanning Probe Microscopy (SPM)

Atomic Force Microscopy ( AFM ) , a type of scanning probe microscopy (SPM), measures the forces between a sharp tip and a sample to determine topographic images at a spatial resolution of approximately 0.1 nm and provide electrical and mechanical properties of the sample. Unlike electron microscopies, AFM offers in situ

characterization and characterizati on of nonconducting samples, can characterize surfaces undergoing reaction, provides sub

- nan ome ter spatial and vertical resolution, and

possesses an inherent surface sensitivity 1

.

Disadvantages of AFM include a lack of direct information on chemical composition, tip limitations, potential tip and sample damage, potential displace ment of nanoparti cles, and data interpretation 1

.

A nothe r type of SPM is scanning tunneling microscopy (STM), which measures a tunneling current between a conductive tip and a conductive or semiconductive sample. STM is capable of achieving molecular

- to atomic

- scale resolution. STM is also s ensitive

to the c hemical identit y of the surface atoms and molecules 1

.

X

- ray Diffraction ( XRD )

X

- ray diffraction (XRD) measures the diffraction of X

- ray beams to identify crystalline phases. XRD can measure structural properties of crystalline phases and probe atomic arrangements of amorphous phases. By comparison to a data base of known diffraction patterns and use of a computer program such as RockJock, XRD can quantitatively identify the mineralogical composition of samples such as quartz or feldspar 1

, 18

. XRD can determine average particle size of crystalline materials below approximately 50 nm. However, XRD cannot directly identify elements present in the sample 1

.

The advantages of XRD include the following : it allows for quick identification of crystalline materials, it distinguish es between crystalline and amorphous materials, it produces additive patterns, it is quick and relatively in expensive, it obtain s particle size and size distribution of crystalline particles, and it can analyze samples in controlled atmosphere cha mbers 1

.

The disadvantag es include the following : trace components (less than approximately one mass percent ) can be difficult to detect, the technology cannot directly identify elements, XRD patterns are an average over all particles in the sample, and peak shapes c an be difficult to interpret 1

.54

Dynamic Light Scattering (DLS)

Dynamic light scattering (DLS) shines a light source on a suspension of particles and uses a photoelectric detector to measure the intensity of the scattered light. The constant Brownian motion of the particles causes time

- dependant fluctuations, which are directly related to the diff usion coefficients of the particles. The diffusion coefficients allow the estimation of the hydrodynamic radius of the particles 1

.

DLS allows for in situ and real

- time analysis of particle size and aggregation of suspensions of nanoparticles. A particle suspension with a concentration that is too high

or to o low or with particles with strong interparticle interactions may lead to inaccurate particle size determinations 1

.

Laser

- Induced Breakdown Detection (LIBD)

Laser

- Induced Breakdown Detection (LIBD) uses an intense, pulsed laser beam to breakdown colloidal particles and generate s plasmas. The generated plas mas emit light back to the CCD camera. The CCD detects light emissions of single plasmas to determine particle size . In addition, detection of optical spatially resolved plasma light provides the spatial distribution of breakdown events within the focal volume. LIBD allows particles within a sample to be quantified. However, this method does not distinguish between or id entify individual compounds. The tool can detect colloids as

small as 2 nm in diameter and at concentrations as low as 1.6 ng/L.

The authors applied this technique in analy zing drinking water samples. The ability of this method to apply to environmental samples containing higher concentrations of suspended solids is not known based on information reviewed for this report. In

addition , the method application is specific to analysis of colloids and assumes that particle shape is spherical. LIBD uses reference particles to determine the sizes of the sample particles. Therefore the method assumes that the particles in the sample have

co mparable properties, adsorption coefficients, dielectric properties, and ionization energies to t he reference particles 22

.

X

- ray Absorption Spectroscopy (XAS)

X

- ray absorption spectroscopy (XAS) irradiates a sample with X

- rays and

measures the amount of X

- ray energy the sample absorbs. X

- ray energies that meet the

electron

- ejection threshold are absorbed and eject an electron. The ejected e lectrons are backscattered and produce interferences with the X

- rays, which provide information on the average identity, number, and arrangement of the nearest neighboring atoms to the absorbing atom. From this information, the structure of the atoms in t he sample may be

obtained 1

.

XAS can provide detailed st ructural information and may be useful for semicrystalline and amorphous nanoparticles . This utility of XAS is important when compared to XRD, which is suited for primarily for crystalline nanoparticles. XAS55

allows for the following advantages: in situ e xperimentation as high vacuum is not required, the possibility of distinguishing between surface and bulk chemical species, the identification of elements and their oxidation states, characteriz ation of the degree of order of the particles, and determinati on of atomic arrangement, measurements of surface sensitivity. However, XAS has the following disadvantages : the required use of synchrotron radiation, complicated data interpretation, and an overall average of all the particles for all results 1

.

6.0 D IFFERENTIATION OF A NTHROPOGENIC N ANOMATERIALS

A literature sea rch to date has not revealed peer

- reviewed documents concerning the differentiation of anthropogenic and natural nanomaterials. Conversations with researchers have revealed that differentiating anthropogenic and natural nanomaterials can prove difficult, especially when the anthropogenic nanomaterial is released in to
environmental media 15

. It is helpful to compare the sampled nanomaterial to a known sample of an engineered nanomaterial to look for similarities as a control

. However, it is

also important to note that an engineered nan omaterial may undergo changes upon entering in to the environment.

Some anthropogenic nanomaterials do not occur naturally. Therefore, a nalyzing the composition of a sampled nanomaterial from environmental media may provide information as to the origin of the nanomaterial. For example, CdSe does not occur naturally and, if discovered in the environment, one can assume its original source is most likely anthropogenic 15

.

The current difficulties with differentiating anthropogenic and natural nanomaterials have led to the idea of isotopic enrichm ent of engineered nanomaterials for ultimate tracking purposes . Isotopic enrichment could serve as a marker that would essentially barcode engineered nanomaterials to identify them with their specific source.

Researchers have indicated that c urrently thi s would prove to be e conomically infeasible; therefore, this technology is not being used 15

.

7.0 S UMMARY

This state

- of

- the

- science review was undertaken to identify and assess currently available sampling and analysis methods to identify and quantify the occurrence of

nanomateri als in the environment

. The environmental and human health risks associated

with n anomaterials are largely unknown, and methods needed to monitor the environmental occurrence of nanomaterials are very limited or nonexistent. Because this research is current and ongoing, much of the applicable information is found in gray literature (e. g., conference proceeding, communications with research scientists and other experts).

The approach to this review included three separate strategies:56  C ollection of available published literature us ing Dialog® ;

 R eview of information from targeted sour ces, such as nano

specific journals, conference proceedings, grants databases, and

researc h databases ; and

 C ontacts with industry and academic experts.

This report summarizes the key characteristics that must be considered when collecting and analyzing samples in various environmental media. Based on results of the literature review, and personal communication with researchers, typical analytical methods and techniques that are currently used for nanomaterials are identified and briefly discussed.

Th e review also identifies several sources that provided information on analytical techniques and equipment for nanomaterials. However, little information was obtained for sampling techniques that are specific for analysis of nanomaterials . Information

obt ained indicated that nanomaterial

- specific sampling techniques have not yet been developed. Another area for which the search results provided little information is for differentiating anthropogenic (man

- made) nanomaterials from natural nanomaterials. A

number of potential sources that may provide additional information upon a more in

depth review were identified. As this report provides a current state

- of

- the

- science review of active research topics at the time of writing, this report may require

modifi cations as additional research is conducted

.57

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