Nanotechnologies — Characterization of carbon nanotube and carbon nanofibre aerosols to be used in inhalation toxicity tests

This document reviews characterization of CNT and CNF aerosols for inhalation exposure studies. The document also provides useful information on appropriate characterization of CNT and CNF, which is required to evaluate and understand the inhalation toxicity of CNT and CNF aerosols. This document neither provides guidance on aerosol characterization for other carbon nanomaterials, nor provides guidance for characterization of carbon nanotube and nanofibre aerosols in the workplace or ambient air.

Nanotechnologies — Caractérisation des aérosols de nanotubes de carbone et de nanofibres de carbone à utiliser dans les tests de toxicité par inhalation

General Information

Status
Published
Publication Date
17-May-2022
Current Stage
Ref Project

Buy Standard

Technical report
ISO/TR 23463:2022 - Nanotechnologies — Characterization of carbon nanotube and carbon nanofibre aerosols to be used in inhalation toxicity tests Released:5/18/2022
English language
32 pages
sale 15% off
Preview
sale 15% off
Preview

Standards Content (sample)

TECHNICAL ISO/TR
REPORT 23463
First edition
2022-05
Nanotechnologies — Characterization
of carbon nanotube and carbon
nanofibre aerosols to be used in
inhalation toxicity tests
Nanotechnologies — Caractérisation des aérosols de nanotubes
de carbone et de nanofibres de carbone à utiliser dans les tests de
toxicité par inhalation
Reference number
ISO/TR 23463:2022(E)
© ISO 2022
---------------------- Page: 1 ----------------------
ISO/TR 23463:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TR 23463:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Abbreviated terms ............................................................................................................................................................................................. 8

5 Considerations in CNT and CNF inhalation studies ........................................................................................................ 8

5.1 General ........................................................................................................................................................................................................... 8

5.2 Workplace exposure scenario ................................................................................................................................................... 8

5.3 Existing inhalation toxicity testing guidelines .......................................................................................................... 9

6 Physicochemical parameters related to the toxicity of CNTs and CNFs ....................................................9

6.1 General ........................................................................................................................................................................................................... 9

6.2 Aerodynamic properties of aerosols for deposition of fibres ....................................................................... 9

6.3 Size and shape (including length, width, aspect ratio, state of aggregation/

agglomeration, and rigidity) ................................................................................................................................................... 10

6.4 Specific surface area ....................................................................................................................................................................... 11

6.5 Crystalline structure and defects....................................................................................................................................... 11

6.6 Surface chemistry, functionalization, surface charge, impurities, and radical

generation/scavenging potential ........................................................................................................................................ 11

6.7 Biodurability.......................................................................................................................................................................................... 12

7 Issues for the characterization of CNT and CNF aerosols ......................................................................................12

7.1 General ........................................................................................................................................................................................................12

7.2 Characterization of physicochemical properties of CNT and CNF prior to aerosol

generation ................................................................................................................................................................................................ 13

7.2.1 General .....................................................................................................................................................................................13

7.2.2 Size and size distribution ........................................................................................................................................ 13

7.2.3 Shape (rigidity and agglomeration/aggregation) .............................................................................. 14

7.2.4 Surface area ......................................................................................................................................................................... 14

7.2.5 Crystalline structures ................................................................................................................................................ 14

7.2.6 Surface chemistry, functionalization, surface charge, and radical

generation/scavenging potential ...................................................................................................................... 14

7.2.7 Composition, purity, and impurities .............................................................................................................. 14

7.2.8 Biodurability (in vivo and in vitro tests) ................................................................................................... 15

7.3 CNT and CNF aerosol characterization (sampling and measurement) .............................................15

7.3.1 General .....................................................................................................................................................................................15

7.3.2 Size and size distribution of CNT and CNF aerosols ........................................................................ 16

7.3.3 The shape of CNT and CNF aerosols ............................................................................................................... 18

7.3.4 Crystalline structure and defects .................................................................................................................... 18

7.3.5 Surface chemistry........................................................................................................................................................... 18

7.3.6 Composition analysis .................................................................................................................................................. 19

7.3.7 Fibre density ....................................................................................................................................................................... 19

7.3.8 Concentration ..................................................................................................................................................................... 19

7.4 Direct and indirect measurement ...................................................................................................................................... 20

7.4.1 Direct measurement .................................................................................................................................................... 20

7.4.2 Indirect measurement ................................................................................................................................................ 21

Annex A (informative) Physicochemical properties of CNT associated with biological

activity .........................................................................................................................................................................................................................22

Annex B (informative) CNT and CNF aerosol monitoring instruments .......................................................................23

Bibliography .............................................................................................................................................................................................................................26

iii
© ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/TR 23463:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 229, Nanotechnologies.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/TR 23463:2022(E)
Introduction

Inhalation is the primary route of exposure to aerosolised carbon nanotubes (CNTs) and carbon

nanofibres (CNFs). Exposure to CNTs or CNFs can occur in consumer settings as well as in occupational

settings. Occupational exposure to CNTs or CNFs can occur at all phases of the manufacturing, handling,

[1,2]

and formulation of the material into final products . Consumers are potentially exposed to CNTs

or CNFs released as products of degradation, weathering, or mechanical processes (e.g. grinding or

[3,4]

polishing) from consumer products that contain CNT or CNF embedded into a matrix .

Similar to other nanomaterials, the physicochemical properties of CNTs or CNFs are greatly diverse

in terms of diameter, length, shape, arrangement of carbon atoms, surface chemistry, defects, and

impurities. Their different physicochemical characteristics are responsible for different functional

properties such as mechanical, electrical, optical, and thermal properties. Many previous inhalation

toxicity studies of CNT and CNF aerosols reported various hazards from acute inflammation to

carcinogenicity and the toxicological responses to CNT and CNF aerosols vary depending on their

[5]
physicochemical characteristics .

Among the various physicochemical characteristics, morphological factors such as length and rigidity

[6,7]

have been suggested as key parameters related to the toxicity of CNT and CNF aerosols . CNT and CNF

[8]

aerosols can consist of individual primary fibres in the nanoscale and aggregated or agglomerated

[9]

structures, including those with diameters larger than 100 nm . Among various types of CNT and CNF,

the asbestos-like pathogenicity has been observed only in long (>5 μm) and rigid fibres, but not in short

[6]

or tangled CNT . Thus, a better understanding of the characteristics of generated CNT or CNF aerosols

in relation to toxicity end points is key for risk assessment and safer-by-design approaches.

The framework for material characterization for inhalation studies consists of (1) characterization

of as-produced (pristine) or supplied material, (2) characterization of administered material, (3)

[10]

characterization of material following administration, and (4) human exposure characterization .

This document focuses on the first two characterization needs, which include physicochemical

properties (e.g. size, size distribution, aggregation/agglomeration, and shape) and measurement of

concentration (e.g. mass, number, surface area, and volume). These parameters can be measured by

direct (online) or indirect (off-line) methods and each technique needs specific sampling procedures.

However, the limited technologies in the generation and characterization of nanofibres make it difficult

to perform inhalation toxicity studies, although the inhalation exposure to CNT and CNF is highly likely

[9,11] [8]

in the workplace , and research facilities , where they are in use. In this regard, this document

provides the current status of CNT and CNF aerosol characterization used in the inhalation toxicity

tests as well as the physicochemical properties of CNTs and CNFs and their relationship with toxicity

end points.

This document complements the work of other international organizations including the Organization

for Economic Co-operation and Development (OECD) which has published guidelines and guidance

[12,13]

on the performance of inhalation toxicity studies . ISO 10808 describes the characterization of

nanoparticles in inhalation exposure chambers for inhalation toxicity testing. This document is different

from ISO 10808 and focuses on different types of nanomaterials (nanotubes and nanofibres opposed

to nanoparticles) because many characterization methods and important physicochemical parameters

related to the toxicity of CNT and CNF are different from those of nanoparticles. Recommendations and

guidelines to assist investigators in making appropriate choices for the characterization of CNT and

CNF aerosols to be studied are presented in this document.
© ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
TECHNICAL REPORT ISO/TR 23463:2022(E)
Nanotechnologies — Characterization of carbon nanotube
and carbon nanofibre aerosols to be used in inhalation
toxicity tests
1 Scope

This document reviews characterization of CNT and CNF aerosols for inhalation exposure studies. The

document also provides useful information on appropriate characterization of CNT and CNF, which is

required to evaluate and understand the inhalation toxicity of CNT and CNF aerosols. This document

neither provides guidance on aerosol characterization for other carbon nanomaterials, nor provides

guidance for characterization of carbon nanotube and nanofibre aerosols in the workplace or ambient

air.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 80004 (all parts), Nanotechnologies — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given ISO 80004 (all parts), and the

following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
carbon nanotube
nanotube composed of carbon

Note 1 to entry: Carbon nanotubes usually consist of curved graphene layers, including single-wall carbon

nanotubes and multiwall carbon nanotubes.
[SOURCE: ISO/TS 80004-3:2020, 3.3.3]
3.2
multiwall carbon nanotube
MWCNT

multi-walled carbon nanotube (3.1) composed of nested, concentric or near-concentric graphene sheets

with interlayer distances similar to those of graphite

Note 1 to entry: The structure is normally considered to be many single-wall carbon nanotubes nesting each

other, and would be cylindrical for small diameters but tends to have a polygonal cross-section as the diameter

increases.
[SOURCE: ISO/TS 80004-3:2020, 3.3.6]
© ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/TR 23463:2022(E)
3.3
single-wall carbon nanotube
SWCNT
carbon nanotube (3.1) consisting of a single cylindrical graphene layer

Note 1 to entry: The structure can be visualized as a graphene sheet rolled into a cylindrical honeycomb

structure.
[SOURCE: ISO/TS 80004-3:2020, 3.3.4]
3.4
carbon nanofibre
CNF
nanofibre (3.5) composed of carbon
[SOURCE: ISO/TS 80004-3:2020, 3.3.1]
3.5
nanofibre

nano-object (3.28) with two similar external dimensions in the nanoscale and the third dimension

significantly larger
Note 1 to entry: A nanofibre (3.5) can be flexible or rigid.

Note 2 to entry: The two similar external dimensions are considered to differ in size by less than three times and

the significantly larger external dimension is considered to differ from the other two by more than three times.

Note 3 to entry: The largest external dimension is not necessarily in the nanoscale.

[SOURCE: ISO/TS 80004-2:2015, 4.5]
3.6
aerosol
metastable suspension of solid or liquid particles in a gas
[SOURCE: ISO TR 27628:2007, 2.3]
3.7
inhalation chamber system

system prepared to expose experimental animals to an inhaled test substance of predetermined

duration and dose by either nose-only or whole-body method
Note 1 to entry: This system consists of chamber, head-only and nose-only.

Note 2 to entry: The term “nose-only” includes head-only, nose-only, or snout-only.

[18] [12] [13]
Note 3 to entry: [SOURCE: OECD TG 403 , 412 , 413 ]
3.8
nanoparticle generation system

device to make nanoparticle aerosol with controlled size distribution and concentration

[SOURCE: ISO 10808:2010, 3.3]
3.9
aspect ratio
ratio of length to width of a particle
[SOURCE: ISO 10312:2019, 3.8]
© ISO 2022 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/TR 23463:2022(E)
3.10
rigidity

inability to be to bent or forced out of shape or ability of a material to resist deformation

Note 1 to entry: This term applies to CNT or CNF.
Note 2 to entry: Asbestos fibres and MWNT-7 are examples of rigid structures.
3.11
aggregate

particle comprising strongly bonded or fused particles where the resulting external surface area is

significantly smaller than the sum of calculated surface areas of the individual components

Note 1 to entry: The forces holding an aggregate together are strong forces, for example, covalent bonds, or those

resulting from sintering or complex physical entanglement, or otherwise combined former primary particles.

Note 2 to entry: Aggregates are also termed secondary particles and the original source particles are termed

primary particles.
[SOURCE: ISO 26824:2013, 1.3]
3.12
agglomerate

collection of weakly or medium strongly bound particles where the resulting external surface area is

similar to the sum of the surface areas of the individual components

Note 1 to entry: The forces holding an agglomerate together are weak forces, for example van der Waals forces or

simple physical entanglement.

Note 2 to entry: Agglomerates are also termed secondary particles and the original source particles are termed

primary particles.
[SOURCE: ISO/TS 80004-2:2015, 3.4]
3.13
biodurability

ability of a material to resist dissolution (3.14) and mechanical disintegration from chemical and

physical clearance mechanisms
[SOURCE: ISO/TR 19057:2017, 3.3]
3.14
dissolution
process of obtaining a solution containing the analyte of interest

Note 1 to entry: Dissolution is the act of dissolving and the resulting species may be molecular or ionic.

[SOURCE: ISO/TR 19057:2017, 3.6]
3.15
aerodynamic diameter

diameter of a sphere of 1 g cm density with the same terminal settling velocity in calm air as the

particle, under the prevailing conditions of temperature, pressure and relative humidity

Note 1 to entry: The particle aerodynamic diameter depends on the size, density and shape of the particle.

Note 2 to entry: Aerodynamic diameter is related to the inertial properties of aerosol particles.

[SOURCE: ISO 4225:2020, 3.1.5.13]
© ISO 2022 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/TR 23463:2022(E)
3.16
differential mobility analysing system
DMAS

system to measure the size distribution of submicrometer aerosol particles consisting of a DEMC (3.19),

a particle charge conditioner, flow meters, a particle detector, interconnecting plumbing, a computer,

and suitable software
[SOURCE: ISO 15900: 2020, 3.12]
3.17
geometric mean diameter
GMD

measure of the central tendency of particle size distribution using the logarithm of particle diameters

Note 1 to entry: The GMD is normally computed from particle counts and when noted may be based on surface

area or particle volume with appropriate weighting, as:
ΔNdln()
∑ ii
i=m
ln(GMD)=
where
d is the midpoint diameter for the size channel, i
N is the total concentration
∆N is the concentration within the size channel, i
m is the first channel
n is the last channel
[SOURCE: ISO 10808:2010, 3.5]
3.18
geometric standard deviation
GSD

measure of the width or spread of particle sizes, computed for the DMAS (3.16) by

Ndln −ln()GMD
∑ ii
i=m
ln(GSD)=
N−1
[SOURCE: ISO 10808:2010, 3.6]
3.19
differential electrical mobility classifier
DEMC

classifier that is able to select aerosol particle sizes from a distribution that enters it and pass only

selected sizes to the exit

Note 1 to entry: A DEMC is sometimes called a Differential Electrical Mobility Spectrometer (DEMS). A DEMC

classified aerosol particle sizes by balancing the electrical force on each particle in an electrical field with its

aerodynamic drag force. Classified particles have different sizes due to their number of electrical charges and

a narrow range of electrical mobility determined by the operating conditions and physical dimensions of the

DEMC.
[SOURCE: ISO 10801: 2010, 3.2]
© ISO 2022 – All rights reserved
---------------------- Page: 9 ----------------------
ISO/TR 23463:2022(E)
3.20
count median diameter
CMD

diameter equal to GMD (3.17) for particle counts assuming a logarithmic normal distribution

Note 1 to entry: The general form of the relationship as described in ISO 9276-5:2005 is

()rp− s
CMDx==x e
50,,rp50
where
e is the base of natural logarithms, e = 2,718 28;
p is the dimensionality (type of quantity) of a distribution
p = 0 is the number,
p = 1 is the length,
p = 2 is the area, and
p = 3 is the volume or mass;
r is the dimensionality (type of quantity) of a distribution, where
r = 0 is the number,
r = 1 is the length,
r = 2 is the area, and
r = 3 is the volume or mass;
s is the standard deviation of the density distribution

x is the median particle size of a cumulative distribution of dimensionality, r.

50, r
[SOURCE: ISO 10808:2010, 3.7]
3.21
mass median aerodynamic diameter
MMAD

calculated aerodynamic diameter which divides the particles of an aerosol in half based on mass of the

particles

Note 1 to entry: Fifty percent of the particles by mass will be larger than the median diameter and 50 per cent of

the particles will be smaller than the median.
[SOURCE: EPA IRIS Glossary; ISO 15779:2011, 3.30]
3.22
mobility diameter

diameter of a spherical particle that has the same mobility as the particle under consideration

Note 1 to entry: Mobility diameter is generally used to describe particles smaller than approximately 500 nm,

and is independent of the density of the particle
[SOURCE: ISO/TR 27628:2007, 2.10]
© ISO 2022 – All rights reserved
---------------------- Page: 10 ----------------------
ISO/TR 23463:2022(E)
3.23
particle density

ratio obtained by dividing the mass of a sample of aggregate particles by the volume, including both

permeable and impermeable pores within the particles (but not including the voids between the

particles)

Note 1 to entry: It is expressed as mass per unit volume, i.e. kilograms per cubic meter (kg/m )

[SOURCE: ISO 20290-1, 3.2]
3.24
specific surface area
surface area per unit mass of a particle or material
[SOURCE: ISO/TR 27628:2007, 2.19]
3.25
respirable fraction
mass fraction of inhaled particles which penetrate to the unciliated airways
[SOURCE: ISO 7708:1995, 2.11]
3.26
inhalable fraction

fraction of total airborne particles of given particle size inhaled through the nose and mouth

Note 1 to entry: Adapted from ISO 7708:1995, 2.3.

Note 2 to entry: The fractions specified in 3.3 to 3.8, as defined at specific particle size (characterized by

thermodynamic and aerodynamic diameters), are independent of the basis of measurement, e.g. mass, area or

particle count.

Note 3 to entry: A significant portion of the inhaled particles may be exhaled, but since these are smaller particles

their effect on the mass deposited may be minimal.
[SOURCE: ISO 13138:2012, 3.3]
3.27
nanomaterial

material with any external dimension in the nanoscale or having internal structure or surface structure

in the nanoscale

Note 1 to entry: This generic term is inclusive of nano-object and nanostructured material.

Note 2 to entry: See also engineered nanomaterial, manufactured nanomaterial and incidental nanomaterial.

[SOURCE: ISO/TS 80004-1:2015, 2.4]
3.28
nano-object

discrete piece of material with one, two or three external dimensions in the nanoscale

Note 1 to entry: The second and third external dimensions are orthogonal to the first dimension and to each

other.
[SOURCE: ISO/TS 80004-2:2015, 2.2]
© ISO 2022 – All rights reserved
---------------------- Page: 11 ----------------------
ISO/TR 23463:2022(E)
3.29
nanoparticle

nano-object (3.28) with all external dimensions in the nanoscale where the lengths of the longest and

the shortest axes of the nano-object do not differ significantly

Note 1 to entry: If the dimensions differ significantly (typically by more than 3 times), terms such as nanofibre

(3.5) or nanoplate (3.30) may be preferred to the term nanoparticle.
Note 2 to entry: Ultrafine particles may be nanoparticles.
[SOURCE: ISO/TS 80004-2:2015, 4.4]
3.30
nanoplate

nano-object (3.28) with one external dimension in the nanoscale and the two other external dimensions

significantly larger

Note 1 to entry: The larger external dimensions are not necessarily in the nanoscale.

[SOURCE: ISO/TS 80004-2:2015, 4.6]
3.31
nanotube
hollow nanofibre (3.5)
[SOURCE: ISO/TS 80004-2:2015, 4.8]
3.32
particle
minute piece of matter with defined physical boundaries
Note 1 to entry: A physical boundary can also be described as an interface.
Note 2 to entry: A particle can move as a unit.
Note 3 to entry: This general definition applies to particle nano-objects.
[SOURCE: ISO 26824:2013, 1.1]
3.33
primary particle

original source particle (3.32) of agglomerates (3.12) or aggregates (3.11) or mixtures of the two

Note 1 to entry: Constituent particles of agglomerates or aggregates at a certain actual state may be primary

particles, but often the constituents are aggregates.

Note 2 to entry: Agglomerates and aggregates are also termed secondary particles.

[SOURCE: ISO 26824:2013, 1.4]
3.34
hazard
source with a potential to cause injury and ill health

Note 1 to entry: Hazards can include sources with the potential to cause harm or hazardous situations, or

circumstances with the potential for exposure leading to injury and ill health.
[SOURCE: ISO 45001:2018, 3.19]
© ISO 2022 – All rights reserved
---------------------- Page: 12 ----------------------
ISO/TR 23463:2022(E)
4 Abbreviated terms
APM aerosol particle mass analyser
APS aerodynamic particle sizer
CMD count median diameter
CML count median length
DCFH-DA 2'-7'dichlorofluorescein diacetate
DMAS differe
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.