ISO/TR 21386:2019
(Main)Nanotechnologies — Considerations for the measurement of nano-objects and their aggregates and agglomerates (NOAA) in environmental matrices
Nanotechnologies — Considerations for the measurement of nano-objects and their aggregates and agglomerates (NOAA) in environmental matrices
This document provides some considerations for the collection of environmental samples to be analysed for manufactured NOAA, considerations to distinguish manufactured NOAA from background levels of naturally occurring nanoscale particles of the same composition, and preparation procedures to aid in the quantification of manufactured NM in environmental matrices.
Nanotechnologies — Considérations pour la mesure des nano-objets, et leurs agrégats et agglomérats (NOAA) dans les matrices environnementales
General Information
Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 21386
First edition
2019-03
Nanotechnologies — Considerations
for the measurement of nano-objects
and their aggregates and agglomerates
(NOAA) in environmental matrices
Nanotechnologies — Considérations pour la mesure des nano-
objets, et leurs agrégats et agglomérats (NOAA) dans les matrices
environnementales
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 General considerations . 3
5.1 General . 3
5.2 Considerations for determining background levels of NM . 4
5.3 Distribution of NM in the environment . 4
5.4 Interaction with materials in environmental matrices . 5
5.5 Real-time measurements versus integrated versus spot sampling . 7
5.6 Preparing samples for analysis . 8
5.7 Characterization and quantitation of NOAA . 8
6 Considerations for sampling and analysing NOAA in air . 8
6.1 General considerations . 8
6.2 Transformations and dispersion in the environment . 9
6.3 Sampling considerations . 9
6.4 Preparation for analysis . 9
6.5 Detection and quantitation . 9
7 Considerations for sampling and analysing NOAA in surface water.10
7.1 General .10
7.2 Transformations and dispersion in the environment .10
7.3 Sampling considerations .10
7.4 Preparation for analysis .11
7.5 Detection and quantitation .11
7.5.1 Metal NM .11
7.5.2 Metal oxide NM.12
7.5.3 Carbon-based NM . .12
8 Considerations for sampling and analysing NOAA in sea water.12
8.1 Transformations and interaction with materials in the environment .12
8.2 Sampling considerations .12
8.3 Preparation for analysis .13
8.4 Detection and quantitation .13
9 Considerations for sampling and analysing NOAA in sediment .13
9.1 Transformations and interaction with materials in the environment .13
9.2 Sampling considerations .13
9.3 Preparation for analysis .14
9.4 Detection and quantitation .14
10 Considerations for sampling and analysing NOAA in soil .14
10.1 Transformations and interaction with materials in the environment .14
10.2 Sampling considerations .15
10.3 Preparation for analysis .15
10.4 Detection and quantitation .15
Annex A (informative) Instrumentation/techniques used to quantify and characterize NOAA .16
Bibliography .23
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.
iv © ISO 2019 – All rights reserved
Introduction
There is an interest in determining the concentration of nano-objects and their aggregates and
agglomerates (NOAA) in environmental matrices. Manufactured nanomaterials (NM) enter the
environment via release from the manufacturing process and its waste streams, as well as via the use
of commercial products and their recycle and disposal streams. Such measurement efforts require an
understanding of the occurrence of natural materials that can interfere with the analysis or skew the
results, knowledge of how the environment can interact with NM, and insights that require unique
collection and analytical techniques specific to the composition of the particle. This document provides
a review of published studies that report levels of NOAA in the environment and aspects of collection
and sample preparation. The reader is also directed to the Further Reading section of this document
for information regarding ISO guidance on sampling of air, water, and sediment, as well as a matrix of
measurement techniques.
Not all manufactured NM are discussed here because there might not yet be published studies that
examined them in the environment. On the other hand, collection methods and pre-analytical
procedures might be similar for some or all NOAA in a given environmental matrix. Furthermore,
NOAA isolated from the environment can be characterized using the same instruments and analytical
techniques used for pristine NOAA. Thus, the lack of published studies does not preclude the ability to
collect a specific NM from any environmental matrix and measure the NOAA present.
Although it is recognized that biota (i.e. living organisms) also can interact with NM by sequestering
and/or transforming them, analysis of biota is intentionally excluded so that the scope of this Document
does not become too broad. However, the impact of biota should not be overlooked. Such considerations
could be part of a subsequent Technical Report.
Furthermore, when NM are used for environmental remediation, and there is interest in measuring
residual levels of remediating NM after the environmental medium has been processed. It is anticipated
that the considerations described here would be applicable to those investigations.
The audience for this document is expected to be scientists from the regulatory, academic, or industrial
communities who wish to answer the question of how much manufactured NM is present in a specific
environmental medium. The results could be used for environmental stewardship, for risk assessment,
or to calibrate modelled exposure estimates, although these applications are not discussed here.
NOTE The term NM refers to the identity of the nanomaterial, whereas NOAA is a more inclusive term
encompassing NM and aggregates that are the focus of the analyses described here.
TECHNICAL REPORT ISO/TR 21386:2019(E)
Nanotechnologies — Considerations for the measurement
of nano-objects and their aggregates and agglomerates
(NOAA) in environmental matrices
1 Scope
This document provides some considerations for the collection of environmental samples to be analysed
for manufactured NOAA, considerations to distinguish manufactured NOAA from background levels of
naturally occurring nanoscale particles of the same composition, and preparation procedures to aid in
the quantification of manufactured NM in environmental matrices.
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/TS 80004-1, Nanotechnologies — Vocabulary — Part 1: Core terms
ISO/TS 80004-2, Nanotechnologies — Vocabulary — Part 2: Nano-objects
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 80004-1 and
ISO/TS 80004-2 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
environmental matrices
ambient air, surface water, sediment, soil, estuarine and marine waters and sediments
3.2
ambient air
outdoor air to which people, plants, animals or material may be exposed
Note 1 to entry: Workplace is excluded.
[SOURCE: ISO 4225:1994, 3.6]
3.3
surface water
water in overland flow and storage, such as rivers and lakes, excluding seawater
[SOURCE: ISO 14046:2014, 3.1.3]
3.4
sediment
bottom sediment
naturally-occurring solid material deposited by settling from suspension onto the bottom of bodies of
water, both moving and static
[SOURCE: ISO 6107-2:2006, 13]
3.5
soil
upper layer of the Earth’s crust composed of mineral particles, organic matter, water, air and living
organisms
[SOURCE: ISO 18589-1:2005, 3.2.1]
3.6
estuarine water
water in the lower reaches of a river that is freely connected with the sea, subject to the influence of the
tides and receiving an influx of salt water and fresh water supplies from upland drainage area
[SOURCE: ISO 772:2011, 1.20]
3.7
seawater
marine water
water in a sea or an ocean
[SOURCE: ISO 14046:2014, 3.1.4]
3.8
pore water
water occupying space between sediment particles in freshwater (including soil), brackish and marine
environments
[SOURCE: ISO 11348-1:2007, D.2.4]
3.9
coastal lagoon
shallow body of water, such as a pond or lake, close to the sea and usually with a shallow, restricted
inlet from the sea
[SOURCE: ISO 6107-8:1993, 29]
3.10
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 80004-1:2015, 2.5]
3.11
nanomaterial
NM
material with any external dimension in the nanoscale [as defined in 2.1 of ISO/TS 80004-1] or having
internal structure or surface structure in the nanoscale
Note 1 to entry: This generic term is inclusive of nano-object [as defined in 2.5 of ISO/TS 80004-1] and
nanostructured material [as defined in 2.7 of ISO/TS 80004-1].
Note 2 to entry: See also definitions 2.8 to 2.10 of ISO/TS 80004-1.
2 © ISO 2019 – All rights reserved
[SOURCE: ISO/TS 80004-1:2015, 2.4]
3.12
euphotic zone
upper layer of a body of water where light penetration is sufficient to support effective photosynthesis
[SOURCE: ISO 6107-3:1993, 29]
4 Symbols and abbreviated terms
AAS atomic absorption spectroscopy
CNT carbon nanotube
ICP-MS inductively coupled plasma mass spectroscopy
HDC hydrodynamic chromatography
HPLC high-performance liquid chromatography
HRMS high-resolution mass spectrometry
NOAA nano-objects, their aggregates, and agglomerates
NOM natural organic matter
PM2.5 particulate matter with a diameter of 2,5 µm and smaller
SWCNT single-walled carbon nanotube
TEM transmission electron microscopy
TEM-EDX transmission electron miscroscopy equipped with energy dispersive X-ray detector
UHPLC ultra-high performance liquid chromatography
UV-vis ultraviolet-visible spectrometry
5 General considerations
5.1 General
As the use of NM becomes more widespread, questions about what concentrations exist in the
[1] [2]
environment from their use are likely to be raised. Nowack et al. , Mueller and Nowack , Liu and
[3] [4]
Cohen , and Keller et al. have suggested potential pathways into the environment from manufacturing
waste streams, end-of-use waste streams (e.g. NM in sunscreens that enter the waste stream), and
release from products. In order to determine the concentrations of NM present in the environment,
several issues/questions need to be addressed:
— What are the background levels of naturally occurring materials of the same or similar composition?
— How do concentrations of naturally occurring materials change over time/geography?
— Can the manufactured NOAA be distinguished from naturally occurring nano-objects?
— What are the instruments that have been used to quantify and characterize NOAA in the environment?
— What are the proper sample preparation methods? Do they vary with the NM of interest, or do they
vary with the medium?
These questions are considered in the following document.
5.2 Considerations for determining background levels of NM
Many NM of the same chemical composition as manufactured NM can already occur naturally in
the environment, for example substances such as TiO , SiO , and fullerenes, just to name a few. For
2 2
manufactured NM, processes such as top-down manufacturing reduces the size of a large particle to
a smaller one, while bottom-up manufacturing creates larger particles from smaller ones. Naturally-
occurring NOAA can also be produced by top-down processes like erosion of mineral particles via wind
or via weathering (e.g. UV irradiation and rain). Metals (e.g. gold and silver), oxides of iron, silicon,
aluminium, and manganese, and sulphides (e.g. iron sulphide) occur via a bottom-up process from
dissolved metal ions. The bottom-up processes may be abiotic or bio-assisted. In addition, NOAA can be
produced from combustion of biological matter or from chemical precipitation. (Figure 1). Nanoscale
[5]
particles can also be part of cosmic dust or be produced from volcanic activity .
[5]
Figure 1 — Processes that create nano-objects in the environment. Adapted from Sharma et al.
Therefore, some manufactured NM can be indistinguishable from naturally occurring nano-objects,
making it impossible to assess the environmental exposure to these manufactured NM.
5.3 Distribution of NM in the environment
Where, in the environment, naturally occurring nano-objects or manufactured NM exist can depend on
several factors, such as proximity to road surfaces, climate extremes, salinity of water, and the presence of
[3]
objects onto which particles can adsorb. Liu and Cohen predicted concentrations of various metal oxides
in the environment based on global manufacturing, releases from production, and releases from disposal.
Using the “MendNano” modelling program developed by Liu and Cohen (http: //nanoinfo .org/mendnano),
the concentrations of Ag, Al O , CeO , carbon nanotubes (CNTs), Cu-based NM (metal and metal oxides),
2 3 2
Fe-based NM (metal and metal oxides), nanoclays, SiO , TiO , and ZnO were predicted for air, water, soil,
2 2
and sediment in the Los Angeles (LA) region (USA) for a period of one year. The concentrations for any
one matrix ranged more than 3 to fourfold, with TiO at the highest concentration and silver or copper
4 © ISO 2019 – All rights reserved
(as oxide) at the lowest concentration, depending on the matrix. Concentrations in air were predicted
−3 3
to be between 10 and 1 ng/m for all substances, with the concentration of TiO2 predicted to be the
3 −3 3
highest (~1 ng/m ) and copper oxide the lowest (~10 ng/m ). The order of substances from highest
concentration to lowest was TiO > SiO > Fe oxide = ZnO = Al O > nanoclay = CeO > CNT > Ag > Cu
2 2 2 3 2
−2 2
oxide. For water, concentrations ranged from 10 to 10 ng/L, with TiO predicted at the highest
concentration and ZnO at the lowest (Ag was predicted as 0 because it is insoluble in water).
The ranking of substance by concentration in water was roughly the same as that in air, with
TiO > Al O > SiO = Fe oxide > nanoclay > CeO > CNT > Cu oxide > ZnO > Ag. For soil, concentrations ranged
2 2 3 2 2
−3
from 10 to 1 µg/kg soil with the same relative ranking as that for air. Concentrations in sediment were
−1 4
several-fold greater than those for soil, ranging from 10 to 10 µg/kg sediment (Cu oxide was predicted to
have undetectable concentrations in sediment). The ranking of substances by concentration was similar
to that for water, with TiO > Fe oxide > Al O = SiO > nanoclay > CeO > CNT > Cu oxide > ZnO > Ag.
2 2 3 2 2
Although these initial predictions represent the mass concentration of manufactured NM, it is not
known if relative levels of naturally-occurring nano-objects might distribute in the same amounts or
size distributions.
[3]
Furthermore, the levels of NOAA vary with time, season, and weather conditions. Liu and Cohen
predicted the daily and monthly variation in TiO levels in various environmental media in LA County
in California. The levels in air and water fluctuated by a factor of 10 over the course of the month and
even during the course of a day in response to weather conditions. Concentrations in sediment and
[6]
soil were predicted to be stable over a one-year time period. Daher et al. showed that measured total
particulate concentration in LA County varied depending on the season and location of sampling. In
some locations, the total particulate in air was double that in winter compared to the concentration
3 3
in the spring (16,1 ± 2,8 μg/m [mean and standard error] in winter versus 7,9 ± 0,8 μg/m in spring
for Long Beach). These variations suggest that samples should be collected over extended weather
conditions in order to eliminate seasonal fluctuations as a confounder in interpreting data.
5.4 Interaction with materials in environmental matrices
NOAA can be chemically transformed or adsorbed onto naturally occurring materials in the
environment. The degree to which these phenomena happen and the extent of their impact differ based
[7]
on the chemical properties of the NM and the matrix. A report from Denmark by Hartmann et al.
summarized the potential transformation processes in the four major environmental compartments
and the relevance of such transformations for modelling. They describe how photochemical degradation,
oxidation, reduction, dissolution, precipitation, speciation/complexation, sedimentation, adsorption,
and biotransformation can impact or modify several different NM (metal oxides, metals, and carbon-
[7]
based NOAA) in the environment . The extent to which the concentration or sequestration of NOAA
occurs in a matrix is dependent on the physical/chemical nature of the NM and the chemical nature
of the environmental matrix. This report focuses on the impact of these processes on modelling of life
cycle and fate, but they are also applicable to measurement of NOAA and, perhaps more importantly, to
the metric used to describe concentration.
[7]
According to the report by Hartmann et al. , photochemically induced reactions (i.e. oxidation,
reduction, or transformation) occur to the greatest extent in air, to a lesser extent in water, and not at
all in soil or sediment (Table 1). NM with a particular molecular composition might be more subject
to modification than others; thus, metals (e.g. silver and iron) or metal oxides (e.g. TiO and perhaps
CeO ) that have bound to organic matter can be modified by oxidation. In addition, carbon-based NOAA
(e.g. CNTs and carbon black) can be oxidized in air. The results of these changes can alter the surface
properties (if not the chemical identity, such as for silver and iron), thereby leading to changes in
adsorption or agglomeration. Hartmann and coworkers assessed the impact of photochemical reaction
in air on modelling as “high” for these NM (metals such as silver and iron, metal oxides such as TiO and
to some extent CeO , and carbon-based NOAA), but non-existent for other NM that are not prone to such
photo-induced reactions.
Several physical phenomena with NM can occur in the environment, including dissolution, aggregation,
agglomeration, sedimentation, and adsorption. Dissolution occurs primarily in water and sediment,
and to some extent soil depending on the presence of pore water. The impact of dissolution on the
concentration of the NOAA can vary from low to high depending on the NM; thus, dissolution is a key
transformation process of ZnO, Ag, and CuO and plays a significant role in their binding to natural
organic matter (NOM) or larger particles. Therefore, for these metals and metal oxides dissolution in
the presence of water could have a high impact on modelling and measurement. Of course, the ionic
strength, pH, and presence of other materials also play roles in the extent of dissolution. Aggregation
and agglomeration also occur primarily in water, but have an impact on NM in air, soil, and sediment
as well. Thus, aggregation and agglomeration in water tends to have a high impact on the ability to
quantify NM, and a medium impact in air, soil and sediment. Surface charges can change in water with
ionic strength and pH playing a role. The nature of the NM, whether metal, metal oxide, or carbon-based
NM, seems to have little impact on the importance of this physical process, given all types of NM are
[7]
subject to the phenomenon. Sedimentation, according to Hartmann et al. , occurs primarily in water
and to some extent in air. The end result of sedimentation can be to transfer NM from one matrix to
another, such as from air or water to sediment or soil. Thus, the impact on quantitation is high for NMs
in water, and medium for NMs in air. As with aggregation and agglomeration, the nature of the NM has
little impact on the extent of sedimentation, which is most influenced by particle or agglomerate size.
Adsorption onto other particles or NOM, like agglomeration, is dependent on surface properties, which
in turn can be influenced by the ionic character of the matrix (pH, etc.). Adsorption not only impacts the
concentration of NM in soil and sediment, but also in water. The nature of the NM seems to have little
impact on the adsorption, as is the case for agglomeration.
Biodegradation of so-called organic compounds, which are based on carbon chemistry, frequently
plays a role when substances enter the environment and often leads to lowering of the concentration
[7]
of the substance, whereas metals and metal oxides do not biodegrade. Hartmann et al. reported that
biodegradation is not likely to have a great impact on NM, with the exception of carbon-based NM,
such as CNTs. However, biomodification of the surface of NM can occur, which can lead to dissolution,
[5]
complexation, or agglomeration. Similar processes are described by Sharma et al. for naturally
occurring nano-objects. As a result, transformations of the manufactured NM should be considered and
the final concentrations of NM should be adjusted to reflect masking by transformed particles.
[7]
Table 1 — Predicted environmental transformation processes. Adapted from Hartmann et al.
Impact on Matrix
particle con-
Process centration or
Air Water Sediment Soil
likelihood of
occurrence
H sMe, sMeO sMe, sMeO
Photochemical oxi-
Reaction M
dation, etc.
L
Impact: H = high, M = medium, L = Low
s = some of the NM in this class
Me = metal such as silver or iron
MeO = metal oxide such as ZnO, TiO , or CeO
2 2
All = generally applies to all NM.
NOTE A ‘high’ impact is critical to accurately determine or model the fate and behaviour, and thus the concentration, of the
NM. A ‘low’ significance is considered to have a low impact on the fate modelling or measurement of that specific NM and
omitting the process will therefore not result in a large error.
6 © ISO 2019 – All rights reserved
Table 1 (continued)
Impact on Matrix
particle con-
Process centration or
Air Water Sediment Soil
likelihood of
occurrence
H Me, MeO Me, MeO
Dissolution M Me, MeO
L
H All
Aggregation M All All All
L
Physical
H All
Sedimentation M All All All
L
H All All
Adsorption M All
L
H
Biological Biomodification M All All All
L
Impact: H = high, M = medium, L = Low
s = some of the NM in this class
Me = metal such as silver or iron
MeO = metal oxide such as ZnO, TiO , or CeO
2 2
All = generally applies to all NM.
NOTE A ‘high’ impact is critical to accurately determine or model the fate and behaviour, and thus the concentration, of the
NM. A ‘low’ significance is considered to have a low impact on the fate modelling or measurement of that specific NM and
omitting the process will therefore not result in a large error.
A ‘high’ impact is critical to accurately determine or model the fate and behaviour, and thus the
concentration, of the NM. A ‘low’ significance is considered to have a low impact on the fate modelling
or measurement of that specific NM and omitting the process will therefore not result in a large error.
5.5 Real-time measurements versus integrated versus spot sampling
The general aspects of sampling and their applicability to water and sediment are described in
[8]
ISO 5667-1:2006 , which describes the differences between spot samples (grab samples), periodic
samples, continuous samples, series samples, composite samples, and large volume samples. In
addition, benefits of each approach for sampling water are described. For sampling of air, real-time
measurements provide instantaneous information on concentrations of particles but cannot identify
the substance or even particle size distribution. ISO/TR 18196 provides a matrix of measurement
techniques that can be used to quantify or characterize NOAA; the reader can review the document on
the Online Browsing Platform (www .iso .org/obp). To provide information about the identity or size of
the particle of interest, real-time measurements of ambient air can include several instruments that are
employed simultaneously, especially for air samples. Alternatively, a sample could be “grabbed” from the
environment. As a result, the value of ‘real-time’ measurements can be limited without the subsequent
additional measurement of ‘grab samples’. The greatest disadvantage to ‘real-time’ measurements is
that many instruments lack sufficient sensitivity to detect environmentally relevant concentrations of
NOAA, which are often low.
Integrated sampling (i.e. collecting a sample over a long period of time) can be used to detect low
concentrations of the NM of interest but the method requires large volumes of environmental media
(i.e. air or water) to pass through the collection device. Thus, collection periods can extend over long
periods of time (e.g. 24 h for air sampling), and the concentrations determined represent time-weighted
average concentrations of the NOAA in the environment. Peak concentrations cannot be determined.
However, the value of integrated sampling is that the sample can be prepared in a way that enhances
the sensitivity for quantitation; for example, concentrating the NM of interest and separating materials
and substances that can interfere with analysis.
5.6 Preparing samples for analysis
In general, samples collected from any environmental matrix need to be prepared for analysis to
separate extraneous material and to concentrate the NOAA to improve quantitation. The following
table provides typical preparation methods and subsequent instrumentation for metallic NM. Many of
these techniques are applicable to other NM. Furthermore, NOAA such as those associated with soil
particles or NOM might need to be extracted from matrix components, and the concentration methods
may impact the aggregation state or surface properties of the NM. These procedures are described in
the sections pertaining to those matrices.
Table 2 — Common methods for separation and segregation of metallic NOAA. Modified from
[9]
daSilva et al.
Method Procedure Size Range
Ultracentrifugation Acceleration up to 10 xg 100 Da to 10 GDa
Filtration Size fractionation Down to 1 kDa
Nano-filtration Size-exclusion membrane 0,5 nm to 1 nm
Size-exclusion chromatography Packed porous beads as stationary phase 0,5 nm to 40 nm
Hydrodynamic chromatography Physical separation in a narrow conduit 2,0 nm to 200 nm
Physical separation in an open tube based on
Field-flow fractionation 1 nm to 1 000 nm
applied field
Electrophoretic mobility Charge-size distribution along a gradient 3 nm to 1 000 nm
Micro-filtration Size-exclusion membrane 100 nm to 1 000 nm
xg = times gravity
Da = Daltons
GDa = giga Daltons
kDa = kilo Daltons
5.7 Characterization and quantitation of NOAA
Selecting the most appropriate measurement method is not within the scope of this Report. However,
[10]
ISO/TR 18196:2016 provides a list of analytical techniques that have been used to quantify and
characterize NM, advantages and disadvantages, measurand, limitations, and relevant standards of
each technique. A condensed list is provided in Annex A.
6 Considerations for sampling and analysing NOAA in air
6.1 General considerations
[11]
Ostraat et al. reviewed sampling strategies and analytical methods for measuring airborne NM.
Among the issues that were identified as relevant to the strategies were suitable dose metrics because
instruments that can measure surface area (SA) will be quite different from those that measure particle
number or mass. In addition, Solomon et al. of the US Environmental Protection Agency reviewed
different samplers to collect and quantify airborne contaminants contained in particulate matter of
[12]
diameter 2,5 micrometres or smaller (PM2.5) . Although the information is specific to collection of
PM2.5 particulates and quantifying their concentrations, there are lessons that can be learned regarding
selection of filters depending on the substance of interest. For example, Polytetrafluoroethylene (PTFE)
8 © ISO 2019 – All rights reserved
filters are not acceptable if the composition of the carbon-based NM is to be determined because carbon
content cannot be distinguished from the Polytetrafluoroethylene (PTFE).
6.2 Transformations and dispersion in the environment
[13]
Large particles can adsorb smaller particles and act as reservoirs. Catinon et al. showed that large
particles (25 μm to 1 000 μm diameter) of sand, clay, pollen, and organomineral particles contained
measurable levels of As, Ba, Cd, Co, Cu, Fe, Ni, Pb and Zn. These background levels of elements can impact
the analyses of NOAA of interest.
6.3 Sampling considerations
Strategies used for air quality determinations can have utility for measurement of NM. Solomon et
[12]
al. describe multi-city sampling of ambient air for PM2.5 determinations. Their strategy adjusted for
nitrate and sulfate levels known to exist in the air of each city. Samples were collected over 20 d during
a specific season, and for 24 h per sample period. It is important to include “field blanks” to account for
interaction of the filter medium with subsequent analyses.
Sampling over long time periods provides more data to generate robust statistical inferences about
background NM parameters. Furthermore, seasonal variations need to be taken into account; for
[6] [14]
examples, Daher et al. and McGinnis et al. describe the seasonal and spatial variations of airborne
ultrafine particles in a large metropolitan area. These variations are likely to exist in other areas and
for other environmental media. McGinnis et al. also describe how collection points can be spatially
separated in such a way to identify if a source is regional or local. Furthermore, McGinnis et al. indicate
that the Chemical Speciation Network can provide data on annual trends of PM2.5 levels for specific
urban locations.
Chemical and/or morphology (i.e. filter sampling coupled with electron microscopy) characterization
can be combined with other techniques to provide temporal information about airborne NM
characteristics. This strategy assumes the physico-chemical characteristics of the NOAA are sufficiently
different from background NM to allow their differentiation.
[12]
What type of filters should and/or can be used depends on the particle of interest . As mentioned
above, Polytetrafluoroethylene (PTFE) filters cannot be used if the particles are carbon-based because
Polytetrafluoroethylene (PTFE) interferes with the analysis. If the collected air is from urban settings,
it is likely to contain high levels of nitrates or sulfates. To minimize artefacts for the collection of
aerosol nitrate, Solomon et al. recommend that samples be collected using a denuder (coated with MgO
or Na CO ) followed by a single filter. According to Solomon et al., measuring nitrate on a quartz-fibre
2 3
filter prepared for carbon analysis can result in a significant positive artefact for aerosol nitrate. Also,
the Polytetrafluoroethylene (PTFE) filter used for mass and X-ray fluorescence (XRF) analyses should
not be used for ion analysis, particularly nitrate and ammonium ions, as these species are lost during
XRF analysis.
6.4 Preparation for analysis
No preparation is anticipated for real-time measurements. However, for grab sampling onto filter
media, equilibration of the filter is a long-standing practice where gravimetric measurements are used.
The extent to which the filter is equilibrated depends on the filter medium (see Annex). In addition,
if particles captured onto the filter are analysed for composition, the extraction solvent depends on
[12]
the filter medium. Again, Solomon et al. provide a table with examples of extraction methods for
different filter media.
6.5 Detection and quantitation
Key attributes for instruments suitable for field studies include the following: low cost; limited size
resolution with 2 to 5 distinct size bins < 100 nm; simple to operate, including minimal training to
collect and interpret data as well as minimal maintenance and calibration; and robust and reliable
operation in a wide variety of conditions, including high and low airborne particle concentrations
[15]
and broad particle chemistry sensitivity . In addition, sizes > 100 nm are captured by most of these
instruments so agglomerates can also be measured. The disadvantage of these instruments is that they
cannot characterize the particle or determine the chemical nature of the substance. Thus, real-time
measurements should be supplemented with grab sample analyses.
[10]
ISO/TR 18196:2016 provides a list of analytical techniques that have been used to quantify and
characterize NM, advantages and disadvantages, measurand, limitations, and relevant standards of
each technique. Categories and examples of real-time instruments that detect and measure airborne
particles are listed in Annex A.
7 Considerations for sampling and analysing NOAA in surface water
7.1 General
As previously mentioned, detection of NOAA in surface water or aqueous waste streams is complicated
by the presence of NOM, which is mainly in the form of humic substances, electrolytes, bacteria,
[16][17]
natural colloids, suspended materials and other constituents that can interfere with detection of
NOAA, adsorb NOAA, or obfuscate background levels of naturally occurring substances. Separation of
NOAA from these other constituents, concentration of NOAA to improve detection, and preparation of
samples for analysis are critical steps in the process prior to detection. The procedures described in
ISO/TR 16196 and ISO 5667-1, ISO 5667-4, and ISO 5667-6 provide guidance on techniques that can
be used to improve detection. ISO/TR 16196 describes sample preparation methods of nanomaterials
prior to treatment of biological systems; however, there may be insights into preparation methods prior
to analysis. ISO 5667-1, ISO 5667-4, and ISO 5667-6 describe procedures and equipment for sampling
of natural water (ISO 5667-1), lakes (ISO 5667-4), and rivers (ISO 5667-6). These standards may be
previewed on the ISO Online Browsing Platform (www .iso .org/obp).
7.2 Transformations and dispersion in the environment
All substances in surface water can interact with NOM and NM are no exception. Adsorption of ions
[18] [19]
and substances onto NOM is not uncommon , but Wang et al. demonstrated that higher NOM
concentrations, in addition to pH, ionic strength, and dissolved oxygen, enhance dissolution of Cu from
[20]
nano-Cu. Similarly, Zhang et al. discuss how Ag undergoes several transformations to AgCl, Ag S, or
Ag O in water depending on the concentration of organic matter, dissolved oxygen, pH, and intensity of
sunlight.
In addition to interacting with NOM, it is also possible that NM
...
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