Nanomaterials Versus Ambient Ultrafine Particles: An Opportunity to Exchange
Mark R. Miller,
Martin J.D. Clift,
Nicholas L. Mills,
Roel P.F. Schins,
Wolfgang G. Kreyling,
Keld Alstrup Jensen,
Thomas A.J. Kuhlbusch,
Per E. Schwarze,
Andrea De Vizcaya-Ruiz,
João Paulo Teixeira,
C. Lang Tran,
Flemming R. Cassee
Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, Scotland, UK
Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, Scotland, UK
Adolphe Merkle Institute, University of Fribourg, Fribourg, Switzerland
Swansea University Medical School, Swansea, Wales, UK
University of Rochester Medical Center, Rochester, New York
Department of Public Health, University of Copenhagen, Copenhagen, Denmark
IUF Leibniz-Institut für Umweltmedizinische Forschung, Düsseldorf, Germany
National Research Centre for the Working Environment, Copenhagen, Denmark
Department of Micro- and Nanotechnology, Technical University of Denmark, Lyngby, Denmark
Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Institute of Epidemiology, Munich, Germany
Air Quality & Sustainable Nanotechnology Unit, Institut für Energie- und Umwelttechnik e. V. (IUTA), Duisburg, Germany
Federal Institute of Occupational Safety and Health, Duisburg, Germany
Norwegian Institute of Public Health, Oslo, Norway
Center for Environment and Health, Katholieke Universiteit Leuven, Leuven, Belgium
Department of Biomedicine and Prevention, University of Rome Tor Vergata, Rome, Italy
Departmento de Toxicología, Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV-IPN), México City, México
Paris Diderot University, Paris, France
National Institute of Health, Porto, Portugal
Instituto de Saúde Pública da Universidade do Porto–Epidemiology (ISPUP-EPI) Unit, Universidade do Porto, Porto, Portugal
Institute of Occupational Medicine, Edinburgh, Scotland, UK
National Institute for Public Health and the Environment, Bilthoven, Netherlands
Institute of Risk Assessment Sciences, Utrecht University, Utrecht, Netherlands
BACKGROUND:A rich body of literature exists that has demonstrated adverse human health eﬀects following exposure to ambient air particulate mat-
ter (PM), and there is strong support for an important role of ultraﬁne (nanosized) particles. At present, relatively few human health or epidemiology
data exist for engineered nanomaterials (NMs) despite clear parallels in their physicochemical properties and biological actions in in vitro models.
OBJECTIVES:NMs are available with a range of physicochemical characteristics, which allows a more systematic toxicological analysis. Therefore, the
study of ultraﬁne particles (UFP, <100 nm in diameter) provides an opportunity to identify plausible health eﬀects for NMs, and the study of NMs pro-
vides an opportunity to facilitate the understanding of the mechanism of toxicity of UFP.
METHODS:A workshop of experts systematically analyzed the available information and identiﬁed 19 key lessons that can facilitate knowledge
exchange between these discipline areas.
DISCUSSION:Key lessons range from the availability of speciﬁc techniques and standard protocols for physicochemical characterization and toxicol-
ogy assessment to understanding and deﬁning dose and the molecular mechanisms of toxicity. This review identiﬁes a number of key areas in which
additional research prioritization would facilitate both research ﬁelds simultaneously.
CONCLUSION:There is now an opportunity to apply knowledge from NM toxicology and use it to better inform PM health risk research and vice
The idea of being able to manipulate materials and particles at the
molecular level sounds like a ﬁlm plot; however, over the last 25 y,
it has become ﬁrmly a part of science fact and a scientiﬁcﬁeld in
its own right: nanotechnology. Although nanotechnology is a rap-
idly growing area of research with real-world applications in virtu-
ally every area of human activity (health care, food and nutrition,
water puriﬁcation, manufacturing, and engineering, to name a few),
the introduction of a wide range of novel materials to the environ-
ment or to humans either by design or inadvertently raises the possi-
bility of harmful and/or unforeseen adverse eﬀects. In response to
this burgeoning ﬁeld, governments and regulatory bodies have
attempted to balance nanotechnology promotion (e.g., the National
Nanotechnology Initiative in the United States and the Interagency
Working Group on Nanotechnology) with risk assessment and regu-
lation (e.g., the EU NanoSafety Cluster and associated projects such
as NANoREG). Nanotoxicology, the study of the toxicity of nano-
scale materials, has advanced in line with nanotechnology in terms
of the amount of literature being published. Indeed, unlike what has
been the case for harmful substances in the past, nanotoxicology is
running more in parallel with developments in nanotechnology.
Address correspondence to V. Stone, School of Life Sciences, Heriot-Watt
University, Edinburgh, UK. Telephone: +44 131 451 3460. Email: v.stone@
V.S. currently receives grant funding from Byk Altana and from The
European Ceramic Fibre Industry Association (ECFIA).
In the past, V.S. has received funding from Unilever and GlaxoSmithKline.
In the past, A.B.S. has received funding for her laboratory from GDF-Suez
K.A.J. has research funding from private companies NanoCover A/S and I/S
N.L.M. has previously consulted for Abbott Diagnostics, Roche, Singulex,
and Beckman Coulter.
A.E. has received funding from Semiconductor Manufacturing Technology
The other authors declare they have no actual or potential competing ﬁnancial
Received 17 December 2015; Revised 12 August 2016; Accepted 30
August 2016; Published 10 October 2017.
Note to readers with disabilities: EHP strives to ensure that all journal
content is accessible to all readers. However, some ﬁgures and Supplemental
Material published in EHP articles may not conform to 508 standards due to the
complexity of the information being presented. If you need assistance accessing
journal content, please contact email@example.com.Ourstaﬀwill work
with you to assess and meet your accessibility needs within 3 working days.
Environmental Health Perspectives 106002-1
A Section 508–conformant HTML version of this article
is available at https://doi.org/10.1289/EHP424.
The original concerns about nanotoxicology were born out of
research into particulate matter (PM) in air pollution (Figure 1;
Beelen et al. 2014;Benbrahim-Talla et al. 2012;Bouwmeester
et al. 2011;Brook et al. 2004;Donaldson et al. 2004;Hoﬀmann
et al. 2007;IARC 2014;Künzli et al. 2005;Lelieveld et al. 2015;
Li et al. 2002,2003;Lim et al. 2012;Lucking et al. 2008;Lynch
et al. 2007;Lynch and Dawson 2008;Oberdörster 2010;
Oberdörster et al. 1990;Pedersen et al. 2013;Peters et al. 2001;
Pope et al. 1995;SCENIHR 2007;Stone et al. 2000a,2000b;
Unfried et al. 2007;WHO 2011,2014). This review examines key
ﬁndings from air pollution and nanotoxicology health eﬀects
research and the comparisons that can be drawn between these dis-
ciplines of particle toxicology. In May 2015, the COST MODENA
(European Cooperation in Science and Technology–Modelling
Nanomaterials Toxicity) project hosted a workshop to exchange
and merge knowledge in PM and nanoparticle toxicology. This
review outlines the systematic comparison of these overlapping
research ﬁelds and identiﬁes lessons for advanced understanding as
well as priority research gaps that must be addressed.
What Can Be Learned from PM Research
That Has Not yet Been Applied Effectively to
The Ultrafine Hypothesis and Nanomaterials
At the end of the previous century, several epidemiological stud-
ies identiﬁed health eﬀects induced by airborne PM at levels that,
at that time, were considered safe (e.g., Brunekreef and Holgate
2002;Dockery et al. 1993). Particles <10 lm in aerodynamic di-
ameter (PM10) can be inhaled by humans and deposit in the respi-
ratory tract (ICRP 1994) (Appendix I), with smaller particles
having higher fractional deposition in the alveoli. Consequently,
ambient PM is frequently regulated as PM10 and PM2:5(<2:5lm
in aerodynamic diameter), the latter of which reﬂects the ﬁne
fraction of PM10. The composition of PM is complex and vari-
able (Appendix I). Although they do not contribute substantially
to the (regulated) mass, ultraﬁne particles (UFPs) have also been
identiﬁed as one of the components that are responsible for the
adverse health eﬀects observed at typical outdoor levels.
Evidence also exists for the involvement of other components in
the toxicity of PM, such as metals (Frampton et al. 1999;Jiménez
et al. 2000;Pope 1991) and biological components (Schins et al.
2004). The relative importance of each component is likely to dif-
fer with composition, reﬂecting diﬀerences in location and time.
In the 1990s, the UFP fraction was hypothesized to be respon-
sible for driving the acute respiratory and cardiovascular eﬀects
of PM (Oberdörster et al. 1995;Seaton et al. 1995). The “UFP
hypothesis”was derived from toxicological evidence from rodent
models that smaller titanium dioxide (TiO2) particles (20 nm)
were more likely than larger TiO2particles (250 nm) to cross the
lung barrier and induce inﬂammation (Ferin et al. 1992;
Oberdörster et al. 1994). Soon after, this hypothesis was sup-
ported by epidemiological evidence (Peters et al. 1997). Owing
to the lack of readily available PM samples, health eﬀect studies
in the following decade used surrogate particles (e.g., carbon
black, diesel engine soot, TiO2, and polystyrene beads) to investi-
gate the mechanisms of toxicity of UFPs, the results of which
were then extrapolated to PM (e.g. Li et al. 1996;Stone et al.
In contrast to ambient PM, which is derived from natural and
combustion processes, nanomaterials (NMs) are prepared deliber-
ately at the nanoscale because they exhibit properties that provide
technological advantages compared with the bulk form of the
same material (The Royal Society and The Royal Academy of
Engineering 2004) (Appendix I). For example, elemental
(graphitic) carbon has semiconductor properties at the nanoscale
(e.g., carbon nanotubes). These advantages expand the number of
possible products and applications, oﬀering great opportunities
and economic gains. Although UFPs and NMs are often derived
from very diﬀerent sources and processes, their physicochemical
characteristics can overlap (Appendix I), suggesting that their
properties, their behaviors, and importantly, their toxicities might
also overlap. In the early 2000s, a number of high-proﬁle national
and international reports highlighted the importance of nanotech-
nology, but they also recognized the potential risks (e.g.,
SCENIHR 2005;The Royal Society and The Royal Academy of
Engineering 2004). These reports led to an increased interest
in UFP toxicology accompanied by a change in terminology
from the mid-2000s.
Ambient PM and UFP Health Effects
Cardiopulmonary: Epidemiologic Evidence
Epidemiology studies clearly demonstrate links between PM10
and PM2:5with both short-term and long-term health eﬀects, par-
ticularly on the respiratory and cardiovascular systems (Dockery
et al. 1993). However, PM includes a range of particle sizes, and
very few studies have included UFP per se as a variable. Using
particle number concentration as a surrogate for UFP, exposure
has been associated with hospital admissions for acute asthma
and increased systolic blood pressure in children (Andersen et al.
2008;Pieters et al. 2015) as well as with rehospitalization in
patients with prior myocardial infarction (von Klot et al. 2005).
For hospitalization with ischemic stroke, a stronger association
was reported with particle number than with PM10 mass concen-
tration (Andersen et al. 2010). Conversely, greater associations
for particle number than mass metrics have been less convincing
for acute myocardial infarction (Lanki et al. 2006).
Particle number concentrations have also been associated
with surrogate markers of cardiovascular health. For example,
elevated levels of ﬁbrinogen, prothrombin factors 1 and 2, and
von Willebrand factor are associated with exposure to UFP
(Hildebrandt et al. 2009). Independent associations have been
observed for UFP and PM2:5with heart rate and heart rate vari-
ability in patients with diabetes mellitus and glucose intolerance
(Peters et al. 2015;Sun et al. 2015). In patients undergoing car-
diac rehabilitation, modulation of the parasympathetic innerva-
tion of the heart, increased blood pressure, and markers of
systemic inﬂammation were all associated with exposure to UFP
(Rich et al. 2012). Epidemiological studies involving biomarkers
related to oxidative stress and inﬂammation revealed that primary
combustion markers from quasi-UFP (PM<0:25) were positively
associated with systemic changes in interleukin 6 (IL-6) and tu-
mor necrosis factor alpha (TNFa), platelet activation, and eryth-
rocyte antioxidant enzyme activity in an elderly population
(Delﬁno et al. 2009). Similarly, elevated plasma ﬁbrinogen and
white blood cells have been associated with UFP exposure (Gong
et al. 2014).
Cardiopulmonary: Preclinical and Clinical Evidence
Several preclinical and clinical studies have addressed the short-
term inhalation and respiratory eﬀects of UFPs. For example,
ﬁeld studies have observed associations for UFPs and carbon
with reductions in lung function among asthmatics (McCreanor
et al. 2007), and healthy adolescents and adolescents with asthma
in New York exhibited an increase in indicators of inﬂammation
(Patel et al. 2013). The majority of preclinical and clinical studies
on UFPs have been conducted with diesel exhaust and diesel
exhaust particles (DEPs), an especially rich source of UFPs
Environmental Health Perspectives 106002-2
Figure 1. Time line showing the increased interest in particulate matter (PM) and nanomaterials (NMs) over the last three decades, highlighting key studies
and research trends in both areas. Number of references per year (noncumulative) based on Pubmed (https://www.ncbi.nlm.nih.gov/pubmed/) search without
further limits applied.
Environmental Health Perspectives 106002-3
(Figure 2). These studies have shown airway inﬂammation in
healthy individuals, including elevated levels of inﬂammatory
cells and mediators (Ghio et al. 2012;Xu et al. 2013;Yamamoto
et al. 2013).
Inhaled UFPs modify numerous aspects of cardiac function,
reducing heart rate variability (Cassee et al. 2011;Pieters et al.
2012), a predictor of cardiovascular risk, and increasing the inci-
dence, duration, and severity of arrhythmia (Delﬁno et al. 2005;
Robertson et al. 2014). Furthermore, UFPs in urban air
(Weichenthal 2012) or diesel engine emissions (Mills et al. 2007)
exacerbate myocardial ischemia (Cascio et al. 2007;Robertson
et al. 2014). Blood vessels ﬁnely regulate blood ﬂow through
changes in the tone of vascular smooth muscle, and UFPs gener-
ally alter the balance in favor of constriction (Møller et al. 2011).
The resulting increased blood pressure (Bartoli et al. 2009) and
the reduced ability of the arteries to relax are usually detrimental.
Vascular dysfunction can be caused by a loss of mediators such
as nitric oxide released by the vascular endothelium (Courtois
et al. 2008;Miller et al. 2009;Møller et al. 2011), by increased
sensitivity to vasoconstrictor factors (Langrish et al. 2009), and
by alterations in baroreceptor/neuroregulatory feedback (Rhoden
et al. 2005;Robertson et al. 2012). Blood components are also
dysregulated, with UFPs tending to increase blood coagulability
(Kilinç et al. 2011;Nemmar et al. 2004), encourage platelet acti-
vation (Cascio et al. 2007;Lucking et al. 2011), and reduce blood
clot clearance (Mills et al. 2005). The cellular and biochemical
mechanisms underlying these eﬀects are wide-ranging, with oxi-
dative stress and inﬂammation being key drivers (Miller et al.
2012)(Figure 3). In combination, these actions promote cardio-
vascular disease. Indeed, long-term exposure to UFPs in animal
models (Araujo et al. 2008;Miller et al. 2013) has been shown to
worsen atherosclerotic vessel disease.
Other Target Organs
Although research has predominantly focused upon the inhalation
of UFPs and their impact upon cardiovascular function, a number
of additional, secondary target organs have been investigated (see
Figure 3). Such research has been based upon the hypothesis of
alveolar translocation of UFPs to the bloodstream allowing for
nonspeciﬁc interaction with other essential organs such as the
brain and kidneys. UFP exposure and mucociliary clearance from
Figure 2. Schematic providing an example of the complex composition of
ultraﬁne particles (UFPs) [e.g., urban particulate matter (PM) or particles in
vehicle exhaust], which in urban air often have a carbon core coated with a
diverse range of chemical species including reactive transition metals and or-
ganic hydrocarbons. Detail is not to scale.
Figure 3. Schematic illustrating some of the key mechanisms through which inhaled ultraﬁne particles (UFPs) may inﬂuence secondary organs and systemic
tissues, with emphasis on the means through which inhaled particles may cause cardiovascular events. Note that there are three main pathways linking the pul-
monary and cardiovascular systems (grey arrows, left to right): autonomic regulation, passage of inﬂammatory mediators, and particle translocation. The
arrows between these three pathways highlight the degree of interaction between mechanistic pathways and the challenges involved in broad categorization of
the wide-ranging biological actions of inhaled UFPs. Added to these pathways is the potential for desorbed components to exert eﬀects.
Environmental Health Perspectives 106002-4
the lungs into the gut might also be linked with adverse eﬀects on
lipid metabolism and intestinal villus shortening (Li et al. 2015),
conveying evidence of eﬀects with potential clinical relevance
for gut or liver diseases.
Starting approximately 15 y ago, the eﬀects of PM in the
central nervous system (CNS) gained recognition with reports
that exposure to polluted Mexico City air resulted in oxidative
stress, inﬂammation, neuropathology, and cognitive and behav-
ioral changes in humans and in animals (Calderón-Garcidueñas
et al. 1999,2011). Other studies using a myriad of PM collec-
tion techniques upheld the early ﬁndings related to PM-
induced brain-centric inﬂammatory processes, including those
in regions related to learning and memory (Campbell et al.
2005;Fonken et al. 2011). Such health outcomes could be
explained by ﬁndings that inhaled particles can travel to the
brain via the blood following alveolar deposition, via nose–
brain transport following olfactory mucosa deposition
(Balasubramanian et al. 2013;Elder et al. 2006), or via the
spillover of systemic inﬂammation to the CNS; a combination
of these processes is also possible. Although acute CNS inﬂam-
matory processes cannot be directly measured in living
humans, it is interesting to note that neurodegenerative dis-
eases are on the rise and that there is a well-established—albeit
mechanistically murky—link between inﬂammation and neuro-
degeneration (Akiyama et al. 2000;Amor et al. 2010). Recent
research has focused on one area where animal and human out-
comes have good concordance, namely, behavior and cogni-
tion. For example, Fonken et al. (2011)showedthatmice
exposed to PM2:5(which includes UFPs) had deﬁcits in spatial
learning and memory. Using mice exposed to concentrated
UFPs as neonates, Allen et al. (2014a,2014b) showed that
males had behavioral outcomes that were associated with per-
sistent enlargement of the ventricles and innate immune cell
activation. In population-based studies, several investigators
have now reported associations between traﬃc aerosol expo-
sures and reduced cognitive function in the elderly (Ranft et al.
2009) and in children (Freire et al. 2010;Suglia et al. 2008).
Two U.S.-based case–control studies have also reported
increased odds ratios for autism in association with early-life
exposure to traﬃc-related pollution, speciﬁcally PM2:5
(Becerra et al. 2013;Volk et al. 2013). With the exception that
NM research has demonstrated plausibility for PM transloca-
tion to the brain, very little has been investigated in terms of
the nervous system impacts of NM.
Priority research gap. PM research provides a basis for devel-
oping a strategy to identify potential neurological eﬀects of NMs
in which physicochemical characteristics could be responsible.
Epidemiological studies have also related PM2:5and PM10 air
pollution to reproductive toxicity and to adverse eﬀects on the prog-
eny. A recent systematic review (Stieb et al. 2012)reportedanasso-
ciation between exposure to PM2:5and PM10 and low birth weight,
preterm birth, and small-for-gestational-age birth. Additionally, van
Rossem et al. (2015) found that maternal exposure to PM2:5and
black carbon were associated with increased blood pressure in new-
born children. The eﬀect seems to be mediated by altered placental
vascular structure induced by PM2:5(Veras et al. 2008). Preclinical
studies indicated that adverse health eﬀects of UFP exposures can-
not be excluded, although the potential for hazard has not been well
characterized (Hougaard et al. 2015).
The evidence outlined above demonstrates the impact of am-
bient PM on a range of targets, but in particular the adverse
eﬀects on respiratory, cardiovascular, neurological, and reproduc-
tive systems. For cardiovascular studies, this evidence extends to
UFPs, but direct evidence for the role of UFPs in the induction of
the other disease targets is, in general, still lacking.
Investigation of NM Impacts on Human Health
A few studies are now emerging that demonstrate the eﬀects of
nanomaterials on human health, particularly in an occupational
setting. Lee et al. (2015) investigated workers manufacturing
multiwalled carbon nanotubes and found that although there was
no impact on hematology and blood biochemistry, they did see
an increase in a range of markers of lipid peroxidation in exhaled
breath condensates of the workers, including malondialdehyde,
4-hydroxy-2-hexenal and n-hexanal. Multiwalled carbon nano-
tubes have also been reported to have impacts on a range of end
points in workers exposed for ≥6 mo. These end points include
the targeting of genes associated with cell cycle regulation, pro-
gression, and control, as well as genes involved in apoptosis and
proliferation (Shvedova et al. 2016). The same study also identi-
ﬁed targeting of pathways involved in pulmonary and cardiovas-
cular eﬀects, as well as pathways involved in carcinogenic
outcomes in humans.
Another study followed workers in 14 nanomaterial manufac-
turing or application (or both) factories in Taiwan for 6 mo (Liao
et al. 2014). The nanomaterials that were produced or handled
included silver, iron oxide, gold, titanium dioxide, carbon nano-
tubes, and silicon dioxide. The group working with nanomaterials
exhibited higher levels of antioxidant enzymes and cardiovascu-
lar markers than the workers who handled other materials. In
addition, the study also reported that markers of small airway
damage (Clara cell protein 16) and lung function were signiﬁ-
cantly associated with handling nanomaterials.
Liou et al. (2015) reviewed 15 studies that investigated the
eﬀects of engineered nanomaterials on workers. Of these 15 stud-
ies, 11 were cross-sectional, four were longitudinal, and one was
a descriptive pilot study. All of the 11 cross-sectional studies
showed a positive relationship between various biomarkers and
exposure to engineered nanomaterials. Three of the four longitu-
dinal studies demonstrated a negative relationship, with the
fourth showing a positive relationship after 1 y follow-up. In gen-
eral, the exposure levels identiﬁed were not very high compared
with those used in human inhalation chamber studies; however,
there were some exceptions with higher exposures. The studies
were generally found to be limited by small numbers of partici-
pants, a lack of consistent exposure information, the detection of
generally low exposures, and short intervals between exposure
Taken together, these initial human health studies suggest that
occupational exposure to nanomaterials may have detrimental
impacts on human health. Further work is required over the long
term to ascertain the nature and extent of these eﬀects as well as
their relevance to diﬀerent types of materials.
Lesson 1. A rich body of literature exists that has demon-
strated adverse human health eﬀects following exposure to PM,
with a proportion of that literature providing support for UFP
involvement. In contrast, although initial studies have suggested
an association between exposure to nanomaterials and human
health, relatively few clinical or epidemiology data are available
at the present time.
Figure 4 outlines a range of health eﬀects and biological indi-
cators of disease reported in the literature. This information can
be used to better inform and justify NM study end points.
Mechanisms of UFP-Induced Health Effects
Three hypothetical pathways to explain the cardiovascular eﬀects
of PM predominate: “inﬂammation,”“autonomic regulation,”
and “particle translocation”(Figure 3). The classical hypothesis
Environmental Health Perspectives 106002-5
is that particles inhaled into the lung are taken up by alveolar
macrophages, triggering an inﬂammatory response within the
lung. A suﬃcient particle dose, reactivity, or lack of clearance
leads to ampliﬁcation of the response with a resultant “spill-over”
of inﬂammatory mediators into the blood causing systemic
inﬂammation (Seaton et al. 1995), which is strongly associated
with cardiovascular disease. Alternatively, inhaled particles (or
the inﬂammatory response resulting from inhalation of the par-
ticles) stimulate alveolar sensory receptors (Ghelﬁet al. 2010;
Hazari et al. 2011;Robertson et al. 2014), providing a signal to
the CNS. This response manifests through alterations in auto-
nomic nervous system activity, which directly regulates cardiac
function and, indirectly, other aspects of the cardiovascular sys-
tem (Pope et al. 1999;Rhoden et al. 2005). The identiﬁcation of
the UFP fraction of PM paved the way for a third hypothesis:
The minute size of UFPs allows them to translocate across the
thin alveolar-capillary wall (by an as-yet undetermined mecha-
nism) and enter the circulation themselves to directly aﬀect cardi-
ovascular function (Nemmar et al. 2001;Oberdörster et al. 2002).
There is a wealth of evidence for and against each of these
hypotheses, but in truth, all three are likely to occur; the contribu-
tion of each is dependent on the physicochemical properties of
the UFPs, the cardiovascular end point under investigation, and
the susceptibility of the person/model being explored (Miller
2014). Furthermore, it is highly likely that many of the subtleties
of these pathways have yet to be identiﬁed. The intricacies of
these processes may encompass nonclassical inﬂammatory/oxida-
tive biological mediators such as acute-phase proteins (Saber
et al. 2014) or oxidized phospholipids (Kampfrath et al. 2011),
the release and accumulation of chemical particle surfaces and
constituents within biological compartments (Murphy et al. 2008;
Totlandsdal et al. 2015), particle/plasma–protein interactions
(Deng et al. 2011;Monopoli et al. 2012), and the role of proteins/
inﬂammatory cells in carrying/accumulating particles to suscepti-
ble areas of the body (Schäﬄer et al. 2014). Reports are rapidly
emerging from preclinical models that demonstrate cardiovascu-
lar eﬀects for NMs similar to those shown for UFPs, such as
altered autonomic function (Harder et al. 2005), impaired vasodi-
latation (Leblanc et al. 2010;Møller et al. 2011), blood hypercoa-
gulability (Kim et al. 2012;Radomski et al. 2005), and
aggravated atherosclerosis (Li et al. 2007;Mikkelsen et al. 2011;
Niwa et al. 2007). Identiﬁcation of the biological mechanisms for
these parallel observations will have important consequences for
both ﬁelds of research.
Lesson 2. The information obtained from PM epidemiology
and mechanistic research has provided an evidence base on
which to develop hypotheses to stimulate research into the poten-
tial modes of action for NMs.
Markers of genotoxicity, such as elevated levels of oxidized DNA
nucleobases, bulky DNA adducts, and clastogenic end points in
leukocytes have been documented in biomonitoring studies of
humans. Positive associations between UFP and oxidatively dam-
aged DNA in mononuclear blood cells have been observed
(Bräuner et al. 2007;Vinzents et al. 2005). In contrast, there is a
paucity of studies on UFP-generated oxidative DNA oxidation
products in cultured mammalian cells and experimental animal
models (Møller et al. 2014), as well as a lack of studies on neo-
plastic lesions in the respiratory tract (a priority research gap).
Studies including exposure to traﬃc-related outdoor air pollution
or to DEPs (Stinn et al. 2005;Valberg and Crouch 1999) have
identiﬁed increased lung adenomas in rodent models.
The carcinogenic mechanism is believed to involve genotoxic-
ity by both oxidative reactions and formation of bulky DNA
adducts from polycyclic aromatic hydrocarbons (PAHs), which
may give rise to mutation and structural chromosome damage.
Early genotoxic events such as DNA adducts and small nucleobase
oxidative lesions can be generated by primary (direct) mechanisms
in relevant target cells, whereas oxidative-mediated DNA damage
may also occur as a consequence of secondary inﬂammation-
driven events (Schins and Knaapen 2007). Importantly, the last
mechanism has been discussed as a major contributor to the muta-
genic and carcinogenic properties of DEPs, as well as to those of
poorly soluble nanoparticles such as carbon black and titanium
dioxide in long-term high-dose inhalation studies in rats (Knaapen
et al. 2004). However, the relevance of this mechanism towards
the carcinogenicity of PM and the speciﬁc contribution of the UFP
component herein remains to be elucidated (a priority research
gap). Recent reviews comparing the genotoxicity of DEPs and
NMs have indicated similar mechanistic causes of DNA damage
(Magdolenova et al. 2014), although the dose metric of “mass con-
centration”causes diﬃculties in comparison across studies
(Møller et al. 2015). Interestingly, it has recently been reported
that single- and multiwalled carbon nanotubes could interfere with
the mitotic spindle apparatus (Sargent et al. 2012;Siegrist et al.
Lesson 3. NM research provides an opportunity to better
understand the (mechanistic) role of UFPs in the genotoxicity,
mutagenicity, and carcinogenicity of PM.
Lessons Learned from NM Toxicology That Could Be
Applied to PM
Regulatory standards for ambient PM are promulgated from a
rich body of literature that has demonstrated adverse human
health eﬀects following exposure. Conversely, the toxicological
research on NMs is motivated by a desire to deﬁne material
Figure 4. A range of health eﬀects and biological indicators of disease that
can be used to identify relevant end points for study design.
Environmental Health Perspectives 106002-6
properties that are linked to adverse health eﬀects, thus support-
ing eﬀective risk management. To achieve engineering for safety
goals, it is necessary to understand the toxicity of the NMs them-
selves while recognizing that toxicological assessment is only
one part of an overall risk assessment process. However, it is
impossible to determine safer exposure levels and safer materials
design without ﬁrst understanding dose-speciﬁc toxicological
eﬀects. Studies that address these questions have provided a
wealth of knowledge that might now be useful to better under-
stand the toxicology of PM.
Characterization of Test Materials
In the past, characterization of UFPs has focused on mass and
number concentrations, chemical composition, and size distribu-
tion. Studies initially used existing methods obtained from PM
and materials science research to characterize NMs, but over
time, the methodology has been reﬁned. This reﬁnement has
allowed NM toxicological researchers to generate a list of desired
characterization information (https://www.iso.org/obp/ui/#iso:
std:iso:ts:17200:ed-1:v1:en). A similar list of requested charac-
terization end points was not developed in PM research owing to
the lack of understanding of how diﬀerent physical and chemical
characteristics could interact to inﬂuence PM toxicity. However,
a comparable list for PM health eﬀect studies could be beneﬁcial
for understanding mechanisms as well as for enhancing compara-
bility across ﬁelds. In the future, these techniques will provide an
opportunity for improved monitoring of PM.
Lesson 4. A range of particle characteristics have been shown
to inﬂuence their toxicity. These characteristics should also be
considered in UFP research, where appropriate characteristics
that can be used for the prediction of toxicity have not yet been
identiﬁed. Furthermore, the variance of these characteristics in
space and time should also be determined comparably to the
methods used for NMs.
Before the development of NM toxicity testing, standard
operating procedures (SOPs) for particle characterization were
rarely in place. Development of SOPs is currently ongoing in the
nanosafety communities as well as via standardization projects
conducted by the European Committee for Standardization
(CEN) and the International Organization for Standardization
(ISO) (European Commission. 2010).
Especially relevant particle parameter protocols for standardi-
zation are those of dispersion, size, agglomeration, and aggrega-
tion in diﬀerent environmental and biological media. Techniques
that can (semi-)automatically obtain multiple size parameters
using transmission electron microscopy will help to satisfy the
challenges of regulatory NM deﬁnitions such as those proposed
by the European Commission (2011). Advances in dynamic light
scattering and coupling to inductively coupled plasma mass spec-
trometry (ICPMS) technologies such as ﬁeld-ﬂow fractionation
multiangle light scattering ICPMS and single-particle ICPMS have
been driven by requirements for particle sizing and behavior in liq-
uid dispersions. Great improvements have also been made in under-
standing the applicability of diﬀerent measurement devices for
airborne particles. These improvements include knowledge of the
care needed in using and interpreting data obtained from charge-
based instruments, particularly instruments using unipolar charging
such as surface area monitors and the Fast Mobility Particle Sizer™
(Asbach et al. 2009;Levin et al. 2016). These instruments can pro-
vide erroneous results when signiﬁcant amounts of agglomerates
and aggregates that are approximately 200 nm or more in size are
present in the aerosol (Todea et al. 2015).
Advances have also been made in chemical analysis of NMs,
where ICPMS is often the preferred method, using either the
single-particle mode or particle extraction protocols (Lee et al.
2014). Nondestructive methods such as Instrumental Nuclear
Activation Analysis (INAA) and X-ray ﬂuorescence (XRF) may
be preferable for bulk chemical characterization to avoid chal-
lenges in developing material-speciﬁc extraction techniques.
New developments also include procedures to identify and
quantify speciﬁc surface coatings/functionalization of NMs using
combinations of diﬀerential thermal gravimetric/diﬀerential ther-
mal analysis–gas chromatography and chemical-speciﬁc methods
such as high-performance liquid chromatography–mass spec-
trometry/optical emission spectroscopy or gas chromatography–
mass spectrometry. Combinations of these methods are particu-
larly important for second- and third-generation NM analysis,
and methods have recently been developed as part of the EU FP7
NANoREG project (European Commission 2013). Further
knowledge transfer of techniques between materials science,
environmental, and nanosafety researchers continues and is
highly likely to be applicable to PM research.
Analysis of surface charge via zeta potential measurements
is straightforward in simple systems (e.g., a pure NM in pH-
controlled water with moderate ionic strength) but becomes chal-
lenging in multicomponent complex systems such as PM in air
pollution. From a toxicological perspective, because zeta poten-
tial varies signiﬁcantly with pH and with the composition of the
test medium, a full assessment should consider all likely media
and biological compartments of interest.
Particle reactivity is currently not well deﬁned, perhaps
understandably given that it is unlikely to be a single parameter.
“Simple”methods include measurement of reactive oxygen spe-
cies, pH and redox potential, and band gap. In recent years, band
gap has been shown to be related to the toxicity of metal oxide
NMs (Zhang et al. 2012). In vitro dissolution can also be an im-
portant indicator of reactivity for some NMs insofar as it is indic-
ative of biodurability/biopersistance, methods which are under
development (CEN/ISO). Recent work has shown that great care
must be taken in the design and harmonization of such experi-
ments to achieve reproducible results (Tantra et al. 2016). These
developments are relevant for both NM and PM research,
although the weight has been strongly tilted towards NM research
in the last decade.
Lesson 5. A range of new and improved techniques for
assessing the physicochemical and nanoscale characteristics of
NMs have been developed. These techniques should be applied
appropriately to inhalation exposure assessment in population
studies to better determine the relationship between particle char-
acteristics and health eﬀects.
It is worth noting that the procedures used for sample prepara-
tion and the mode of exposure used in toxicology studies deter-
mine the requirements for characterization of exposure and fate.
For example, quantiﬁcation and characterization of aerosolized
particles might include aerosol monitors and ﬁlter samples,
whereas particles used as dispersions for exposure would require
analysis via hydrodynamic size distribution, agglomeration state,
sedimentation, and reactivity in the dispersion medium. NMs are
often dispersed in protein-rich media, which can aﬀect both the
biokinetics and the toxicity, whereas ambient UFPs can be dis-
persed to some extent without these additives (Moore et al. 2015).
The improvements in characterization have revealed the
need for correct storage of NM test items over time. For NMs
analyzed by the Organisation for Economic Co-operation and
Development (OECD) working party of manufactured nanomate-
rials (WPMN), this has resulted in storage under argon, in single-
use vials, in the dark. Previously, both nanosafety and PM
researchers have stored dry powders, ﬁlter-bound particles, and
wet suspensions under many diﬀerent conditions. For many am-
bient PM samples, storage under argon at <0C could potentially
Environmental Health Perspectives 106002-7
prevent oxidation/loss of toxicologically relevant (semi)volatile
Since the emergence of nanotoxicology as a discipline, it has
become increasingly recognized that particles can be modiﬁed
upon interactions with cells and tissues, for example, owing to
the inﬂuence of the surrounding media (e.g., proteins). Such bio-
molecule interaction is likely to impact the fate of the particles by
modifying the surface properties and the behavior of the particle
(e.g., agglomeration, solubility, bioavailability, biodurability) as
well as the adsorbed protein properties (Brown et al. 2010a;
Deng et al. 2011). These modiﬁcations could, in turn, alter how
particles are taken up into cells, how they trigger signaling path-
ways, and in what physicochemical format they are translocated
between cells and to distal organs.
Characterization of NMs at various stages throughout the life
cycle of the material is far from simple. For PM, this is further
complicated by the complex mixtures present in ambient air.
Furthermore, it is important to note that consumer exposure to
NMs may be diﬀerent than occupational exposure depending on
the state of the material (e.g., native NMs, NMs embedded in a
product, NM degradation and disposal). In toxicology studies,
many NMs have been studied as dispersions (usually of agglom-
erates) in biological or culture media. Several protocols for NM
dispersion have been developed using diﬀerent dispersion princi-
ples and media (Hartmann et al. 2015); ﬁrst attempts have also
been made to establish harmonized dispersion for regulatory test-
ing (e.g., HA Jensen, H Crutzen, A Dijkzeul, unpublished work,
2014). In contrast, harmonized dispersion protocols have largely
been lacking in PM research.
Lesson 6. Harmonized dispersion protocols can be transferred
to PM research to increase harmonization and comparability
between test methods and results.
There is, however, a major obstacle for PM research, in that
much smaller amounts of PM (obtained via collection) are nor-
mally available than for NM research, where direct synthesis is
often possible. For ambient PM, it is necessary to collect and
extract PM from the collector (e.g., scraping, sonicating, or
chemically extracting from a ﬁlter), which may alter the state of
the PM before its use in toxicology studies. Transformation and
loss of toxicologically important semivolatile compounds during
sampling is also an issue that must be taken into account when
testing collected PM.
Lesson 7. The need to extract PM from ﬁlters can be avoided
by moving the laboratory to the ﬁeld, for example, using in vivo
or air–liquid interface (ALI) systems. In addition, systems such
as particle concentrators (Gupta et al. 2004;Kim et al. 2001)
have been developed; these systems help to ensure suﬃcient
doses over the period of the experiment. However, such toxico-
logical studies in the ﬁeld can be expensive and additionally
Inhalation Exposure and Deposited Dose
The experimental data for total lung deposition of particles are
highly consolidated (ICRP 1994); however, the regional deposi-
tion of NMs is weakly supported by direct experimental data to
validate the models (a priority research gap).
The deposition of NMs depends on three sets of parameters:
particle dynamics, lung geometry, and gas ﬂow dynamics. Owing
to their size, the primary region for the deposition of NMs is the
alveolar region of the human lung (a priority research gap), which
means that the ﬁrst biological matrix encountered is lung surfac-
tant (Gasser et al. 2010). Interaction with NMs may alter the
structure and function of the surfactant proteins (Beck-
Broichsitter et al. 2014;Valle et al. 2015) and subsequently inﬂu-
ence the speciﬁc mammalian cell interactions (Schleh et al.
Lesson 8. NM and parallel UFP inhalation studies can provide
important information on pulmonary deposition and surfactant
interactions and would facilitate the investigation of comparabil-
ity between both types of particles.
For PM and NM toxicology studies, consideration of relevant
particle doses is required. A daily inhalation mass dose for PM
that relates to maximal air-quality standards has been suggested
[WHO Global Air Quality Guidelines (WHO 2016): 10 lg=m3
for PM2:5]. A daily inhaled volume for a moderately active adult
human (75 kg) is typically 20 m3=d. If the mean deposited frac-
tion is 0.3 (Price et al. 2001), the suggested daily mass dose
would be 60 lg=d. However, PM mass is often dominated by
coarse particles, so only a fraction of the 60 lg=d would actually
Therefore, dose might be better expressed as particle num-
ber for such small particles because of their low mass. There is
great variability in ambient UFP numbers, ranging from 500–
10,000 particles=cm3in rural areas to 7500–25,000 particles=
cm3in urban background (Putaud et al. 2010), and with a
European mean concentration of 31,500 particles=cm3at hot
spots (busy streets). To estimate in vivo exposure conditions
based on particle number concentrations, a healthy adult breath-
ing during moderate exercise in ambient air with an assumed
moderate concentration of 30,000 particles=cm3(of which 80–
90% of the particle count is assumed to be UFPs) will inhale
11 particles=cm3. Assuming a mean deposition probability
deposited per day or 1:2×10
10 particles deposited per hour
(Geiser and Kreyling 2010).
To obtain a more relevant assessment of health eﬀects in
vitro, the UFP and NM dose per cell number or area should
reﬂect real inhalation. The initial use of high UFP or NM doses
may be justiﬁed by the need to be able to detect eﬀects of expo-
sure, but such high doses need to be accompanied or followed up
with studies using realistic doses in relation to current informa-
tion concerning occupational and ambient exposures to UFPs or
to speciﬁc NM types.
The respiratory zone of the lung represents by far the largest
compartment for NM deposition. Estimates of lung physiological
data (Stone et al. 1992), together with the above-mentioned
European mean ambient exposure concentration of 31,500
particles=cm3, suggest that on average 8 nanoscale particles de-
posit per day per cell of the alveolar epithelial surface (Geiser
and Kreyling 2010). According to limits imposed by thermody-
namic conditions, the highest possible NM aerosol number con-
centration is approximately 106=cm3, which translates to 700
particles/d/cell or 30 particles/h/cell of the alveolar epithelium.
Because mass is a more frequently used metric, these numbers
must be converted using the eﬀective density of the particles.
This information is useful when verifying relevant in vitro doses.
Models have been published (including experimental veriﬁca-
tion) that can estimate particle deposition onto a monolayer of
cells in vitro (Cohen et al. 2013;Hinderliter et al. 2010;
Teeguarden et al. 2007). These studies identify NMs, and the
eﬀective density of NMs, as important factors in modeling cellu-
lar dose. In essence, only submicrometer and larger NM agglom-
erates will deposit within one hour, whereas NMs <100 nm may
remain suspended for >24 h.
Lesson 9. The models of in vitro NM deposition should be
more widely used for estimation of NM dose in cultured cells to
reﬁne models so that they better reﬂect anticipated airborne
Environmental Health Perspectives 106002-8
exposures. Their application to PM would be more diﬃcult
owing to the size and density diversity of such a mixed particu-
late sample. However, such dosimetry models (DeLoid et al
2015) can in principle deal with size distribution data as well as
with mean size data in cases where such distribution data are
measured. Thus, the lack of a narrow size distribution for PM
should not preclude the more eﬀective use of such modeling
advances to improve dosimetry in both the NM and PM ﬁelds.
Uptake, Clearance, and Fate following Pulmonary Exposure
In rodent models, within 1–2 d of exposure, NM clearance is rela-
tively low compared with clearance of micrometer-sized par-
ticles, and it is associated with more rapid and extensive uptake
into epithelial cells (Kreyling et al. 2002;Semmler-Behnke et al.
2007;Semmler et al. 2004). However, the rodent model is not a
good reﬂection of clearance in humans. For humans, there is evi-
dence that both NMs and micrometer-sized particle clearance
from the conducting airways is less extensive, leading to
long-term particle retention (Möller et al. 2008). Interestingly,
in dogs (Kreyling et al. 1999) and monkeys (Nikula et al.
1997), long-term retention increases substantially in conduct-
ing airways with decreasing particle size. Considering long-
term clearance predominantly from the alveolar region in
these species, macrophage-mediated clearance occurs at a rate
that is one order of magnitude lower than that in rodents
Priority research gap. For the human distal regions of the
lungs, neither macrophage-mediated long-term clearance kinetics
data nor translocation data for NMs into the circulation are cur-
Particle clearance from the lungs can also occur via transport
toward lymph nodes and translocation into the blood circulation,
leading potentially to accumulation in secondary organs and tis-
sues. These pathways will have a limited or lesser relevance for
the clearance of rapidly or moderately soluble particles, respec-
tively (Oberdörster et al. 2005).
Lesson 10. NM inhalation studies provide details of the
potential for UFP biopersistence and transport based upon their
Pioneering studies in the 1990s ﬁrst demonstrated detectable
translocation of nanoscale TiO2particles into the lung intersti-
tium and that translocation is lower for larger particles (e.g.,
21 nm vs. 250 nm diameter) (Ferin et al. 1991;Oberdörster et al.
1994). More recently, a comprehensive list of inhalation studies
and instillation studies using various NMs has provided consen-
sus that, in rodents, relatively small fractions (approximately
1%) of inhaled NMs are translocated across the air–blood bar-
rier, leading to accumulation in secondary organs, including the
liver and spleen (Balasubramanian et al. 2013). Notably, this
rat inhalation study used gold NM of diﬀerent primary particle
sizes but agglomerated to give the same diameter in air of
45 nm. The authors demonstrated size-related translocation
with the smaller 7 nm primary gold particles translocating more
than the 20 nm primary gold particles, suggesting deagglomera-
tion of the 45 nm agglomerates in the lung.
Priority research gap. Based on the observation that in
humans, NM retention in the lung is likely to be longer than in
rodents, it is necessary to consider whether the relatively small
translocation proportions identiﬁed in rodents might be greater in
NM research has facilitated understanding of the biokinetics
and biodistribution of particles such that there is now clear evi-
dence that inhaled NMs can reach and accumulate in secondary
organs (Geiser and Kreyling 2010;Kreyling 2013). Quantitative
biokinetics analysis of NMs applied via the lungs of rodents
demonstrated small fractions of NM (iridium, carbon, gold,
TiO2) in all secondary organs studied, including the brain and
heart, and even in fetuses (Kreyling et al. 2002;Semmler-Behnke
et al. 2007;Semmler-Behnke et al. 2014). An inhalation study
using 20-nm iridium NM was extended to six months after a sin-
gle 1-h inhalation and yielded signiﬁcant retention in the liver,
spleen, kidneys, heart, and brain (Semmler-Behnke et al. 2007;
Semmler et al. 2004). Although the fractions of the total dose that
reach these tissues are very small in rodents, the studies have
highlighted the importance of epithelial barrier health (Heckel
et al. 2004) and that the particle’s protein corona aﬀects biodistri-
bution (Kreyling et al. 2014). As a corollary to biodistribution
studies, in vitro studies with NMs have helped to deﬁne the abil-
ity of particles to breach cellular membranes (Bachler et al.
2015), their interactions with subcellular structures, and there-
fore, the toxicological mechanisms related to particle uptake.
Lesson 11. NM translocation studies provide clear evidence
of the potential for UFPs to translocate from the lung surface into
blood and to distribute throughout the body, accumulating in a
range of secondary organs. The knowledge gained from NM bio-
kinetics and biodistribution studies provides an evidence base to
predict the fate and health eﬀects of UFPs in the body.
In addition to translocation, rodent studies also suggest that
NMs can relocate from the interstitium and epithelium back onto
the epithelial surface via an unknown mechanism (e.g., via mac-
rophages) (Semmler-Behnke et al. 2007). The fraction removed
via the lymphatic or cardiovascular system is relatively small in
contrast. Studies using NMs (sometimes at doses higher than a
few hundred micrograms per lung) such as TiO2, carbon black,
gold, quantum dots, silver nanowires, and carbon nanotubes have
identiﬁed accumulation of NMs in the lung-associated lymph
nodes (Schinwald et al. 2012).
Priority research gap. The development of this research area
using diﬀerent types of NMs and diﬀerent investigative protocols
will be useful in determining the importance of this potential
route of uptake and hence potential translocation within the body.
Pathways of relocation of inhaled NMs in rodent lungs are sche-
matically sketched in Figure 5.
Lesson 12. The diﬀerential clearance and uptake of NMs and
micron-sized particles could also apply to the varied size fractions
of PM, adding to the plausibility of a diﬀerence in their toxicity.
There are a number of mechanisms by which UFPs and NMs
may have an impact on cells, and these mechanistic studies pro-
vide a great opportunity for comparison or alignment of our
understanding of NM and UFP toxicity. Mechanisms including
reactive oxygen species (ROS) and oxidative stress (Miller 2014;
Nel et al. 2006;Stone et al. 2007) feature widely in the literature
for both NMs and UFPs (see below). Endothelial cells and epithe-
lial cells may also generate nitric oxide in response to NMs and
UFPs via stimulation of NOX4 (e.g., in addition to the respiratory
burst generated by inﬂammatory cells exposed to particles, it
appears that particles can also generate ROS directly, including
PM10 (Gilmour et al. 1996), DEPs (Miller et al. 2009), and many
diﬀerent NMs including carbon black (Stone et al. 1998;Wilson
et al. 2002), polystyrene beads (Brown et al. 2001), and a range
of metal/metal oxide particles (Dick et al. 2003;Rushton et al.
2010). Diﬀerent material compositions vary in their potential to
induce ROS production, ranging from copper (Rushton et al.
2010), which has an inherent ability to generate ROS, to amor-
phous nanosilica, which exhibits no intrinsic capacity to generate
oxidants (Napierska et al. 2012). Some NMs do not exhibit intrin-
sic oxidant-generating capacity but will generate ROS upon
Environmental Health Perspectives 106002-9
interaction with cellular targets, causing changes in the intracellu-
lar redox status (Hussain et al. 2009).
However, studies with NMs suggest that the mechanisms of
toxicity may be more diverse than via oxidants, including
direct physical NM–cell interaction, receptor-mediated, or other
unknown mechanisms (the last of which is a priority research
gap) (Thomassen et al. 2011). Increased epidermal growth fac-
tor receptor expression and phosphorylation have also been
observed for DEPs (Pourazar et al. 2008).
Lesson 13. The ability of PM, UFPs, and NMs to generate
ROS and to induce oxidative stress, either intrinsically or via cel-
lular sources, has been well documented and is frequently associ-
ated with mechanisms of toxicity. In addition, both NM and DEP
studies have demonstrated receptor activation, and NM research
has also identiﬁed other potential mechanisms such as direct
physical cell interaction and unknown mechanisms that require
Lesson 14. For NMs and UFPs that generate ROS, the amount
of ROS production is likely to be associated with their physical and
chemical properties. This is important for UFPs because diﬀerent
toxicities could result as compositions vary with time and location.
The induction of oxidative stress by NMs and by PM has been
linked to proinﬂammatory intracellular signaling responses and
cytokine production (Baulig et al. 2009;Brown et al. 2004a,b)as
well as to cytoprotective intracellular molecules such as heat shock
protein 70 (HSP70) (Xin et al. 2015) and nuclear factor (erythroid-
derived 2)-like 2 transcription factor (Nrf2) (Brown et al. 2010b).
Inﬂammatory cells are crucial to clearance; however, excessive
inﬂammation can lead to exacerbation of preexisting diseases
(e.g., asthma, cardiovascular disease) (Donaldson et al. 2000)orto
increases in the incidence of autoimmune, allergic, and other
immune-related diseases (Hussain et al. 2012). Evidence exists
that environmental PM and DEPs can interact with allergens to act
as an adjuvant, leading to allergic sensitization (Alessandrini et al.
2009;Hussain et al. 2011;Li et al. 2008). Although such observa-
tions have also been made for some NMs (e.g., TiO2)(Larsen
et al. 2010), the mechanism of NM–allergen interaction cannot be
related to the particle size alone; instead, other physical and chem-
ical factors such as surface reactivity and chemistry play a role
(Smulders et al. 2015).
Lesson 15. The proinﬂammatory eﬀects of UFPs and NMs
may exacerbate existing disease and increase the incidence of
Figure 5. Exposure to nanomaterials (NMs) via the lungs results in rapid transport into the epithelium and interstitial spaces and long-term retention as
a result of substantial endocytosis by epithelial cells (Type I and Type II) and limited initial phagocytosis by alveolar macrophages. Pathways exist for
the transport of inhaled NMs into the alveolar epithelium and interstitium of rodent lung and further across the endothelial vascular membrane of
blood circulation as well as into the lymphatic drainage system. Some evidence suggests that a predominant route of clearance from the lung tissue is
then via reentrainment back onto the alveolar epithelial surface (via an unknown mechanism) for long-term macrophage-mediated transport toward cili-
ated airways and the larynx. Nanosized NMs may cross the epithelium, whereas larger aggregates/agglomerates are likely to be phagocytosed by alveo-
Environmental Health Perspectives 106002-10
other immune-related diseases. These eﬀects are likely to
be related to multiple physicochemical characteristics of the
The relationship between an NM’s physicochemical charac-
teristics and the observed responses is a key research endeavor
in nanotoxicology. Quantitative structure–activity relationship
(QSAR) models have been developed to identify these key char-
acteristics (Puzin et al.). The roles of some dose metrics such as
particle surface area, solubility (and the ability to release ions),
and aspect ratio have already been conﬁrmed (Brown et al. 2001;
Duﬃn et al. 2002,2007;Johnston et al. 2013;Kermanizadeh
et al. 2016;Oberdörster et al. 1994;Poland et al. 2008;Prach
et al. 2013;Schinwald et al. 2012). QSAR research is an impor-
tant component of nanotoxicology (MODENA MPNS COST
2013). Because PM is a complex mixture, a comprehensive char-
acterization of PM samples is needed, and QSAR methods can be
used to determine which physicochemical characteristics of PM
drive the observed adverse responses. Thus, the QSAR modeling
approach currently being developed for nanotoxicology can also
be relevant to air pollution research.
Lesson 16. There is now an opportunity to review in detail
this rather large mechanistic body of research to look for syner-
gies and diﬀerences between NM and UFP modes of action and
to relate them to physicochemical characteristics. Clarifying the
relationships between these mechanistic end points and the physi-
cochemical characteristics of the NMs or UFPs will be essential
in the further development of QSAR- and modeling-type
In the last decade, NM surface–biomolecule (proteins, lipids,
etc.) corona interactions have been characterized in diﬀerent
media and body ﬂuids to investigate their actions and the fate of
NMs should they enter the circulation. These interactions, when
concerning intracellular proteins, can alter the eﬀects of NMs as
has already been shown for xenobiotic-metabolizing enzymes
(Sanﬁns et al. 2011). In addition, results suggest that the NM
properties can inﬂuence the composition of the corona and that
its composition changes over time and with passage through dif-
ferent tissue and subcellular compartments (Wang et al. 2013).
Lesson 17. Our understanding of the composition of the mo-
lecular corona for NMs can be applied to UFPs because it is
likelytoinﬂuence their uptake, fate, and eﬀects within the
The acute-phase response has been proposed as a mechanism
of particle-induced cardiovascular disease. The acute-phase
response is a general alarm response of the body to various
assaults including bacterial and viral infections, trauma, and so
on. The most widely studied acute-phase protein is C-reactive
protein (CRP), the serum levels of which are associated with risk
of cardiovascular disease in prospective epidemiological studies
(Ridker et al. 2000). Serum Amyloid A (SAA) may also play a
causal role in cardiovascular risk by promoting plaque progres-
sion and atherosclerosis.
Inhalation of TiO2nanoparticles has been shown to cause up-
regulation of the Serum Amyloid A3 (Saa3) gene in the lung
(Halappanavar et al. 2011). Similarly, inhalation and intratracheal
instillation of NMs and carbon nanotubes also increased expres-
sion of Saa3 (Saber et al. 2013,2014). Lung Saa3 mRNA levels
were shown to correlate with deposited surface area of carbon
black and TiO2NMs and with neutrophil inﬂux into bronchioal-
veolar lavage ﬂuid (Saber et al. 2013,2014), consistent with
SAA being a neutrophil chemoattractant (Badolato et al. 1994).
Moreover, Saa3 mRNA levels in lung tissue were shown to cor-
relate with SAA3 levels in plasma following pulmonary exposure
to carbon nanotubes (Poulsen et al. 2015). DEPs have also been
shown to induce a pulmonary acute-phase response such as up-
regulation of C-reactive protein and serum amyloid A (Saber
et al. 2014).
Priority research gap. Both PM and NM research studies
need to consider a wider array of biological mediators, for exam-
ple, acute-phase proteins or new carriers of the oxidative signal.
NM research also oﬀers methodological reﬁnements for biologi-
cal assessment of ambient PM, including means to account for
particle-related interference (e.g., light absorbance, ﬂuorescence
quenching, protein binding), which may occur in some cellular
(Pulskamp et al. 2007;Wörle-Knirsch et al. 2006) and mutage-
nicity assays (Clift et al. 2013).
Lesson 18. Evidence for the ability of NMs to interfere in var-
ious assays means that study designs for NM and UFP research
require consideration of control procedures to limit the potential
to confound result interpretation.
Over the past decade, there has been a progressive approach
toward standardized protocols to provide a better understanding
of the biological impact of NMs [the International Alliance for
NanoEHS Harmonization, the EU FP7 (Risk Assessment of
Engineereed Nanoparticles) ENPRA and NanoTest projects].
These projects have helped in understanding the pitfalls and
advantages of the diﬀerent biochemical test systems used within
nanotoxicology (e.g., Guadagnini et al. 2015).
Lesson 19. Standardized protocols for assessing biological
responses to NMs, once wholly available, could be applied to
both UFPs and PM.
Conclusions and Recommendations
A comparison of the UFP and NM literature has identiﬁed at least
19 immediate unifying lessons, as well as a number of areas
where further research is needed to better understand both ﬁelds
of research. In fact, in this review, we identiﬁed that UFP and
NM toxicology are not two distinct ﬁelds; rather, they overlap
extensively with the potential to extrapolate from one to the other
in many respects. Firstly, ambient PM research provided evi-
dence of potential health impacts for UFPs, and NM toxicology
has largely provided essential evidence of the mechanistic plausi-
bility of these health eﬀects. PM research provides indications of,
at least in part, the potential disease eﬀects to consider, and early
initial human health studies involving workers suggest this may
also be true for other materials; however, more work is required
to conﬁrm this hypothesis. It seems safe to conclude that UFPs
and NMs share the same general biological mechanisms of
adverse eﬀects, such as oxidative stress and inﬂammation.
However, NM toxicology has also provided a signiﬁcantly better
understanding of the role of physicochemical characteristics of
particles regarding their toxicity, including factors in addition to
size and surface area, such as solubility, charge, composition,
coating, and agglomeration/aggregation. This information is im-
portant because it means that not all NMs are created equal in
terms of their toxic potential, and likewise, not all ambient PM or
UFPs have the same potential to induce health eﬀects. Although
more work could be performed to compare the mechanism of tox-
icity of UFPs with that of NMs, a more eﬀective use of resources
might be to translate the techniques for physicochemical charac-
terization into the PM ﬁeld to better enable identiﬁcation of PM
sources that are responsible for health eﬀects, allowing their
more eﬀective management. Integration of both ﬁelds of research
will provide greater potential for justiﬁcation, interpretation, and
application of the wealth of important knowledge that has been
gathered over the last few decades.
Environmental Health Perspectives 106002-11
Editor's Note: In the Advance Publication of this article,
João Paulo Teixeira was missing from the author list. The author
and his aﬃliation have been added in this version of the article.
The authors thank B. Ross and D. Balharry for practical support
for the workshop. This work was supported by and performed
with the context of the European Union Modelling Nanomaterial
Toxicity–European Cooperation in Science and Technology (EU
MODENA COST) action (TD1204), which funded the workshop
in May 2015 (http://www.modena-cost.eu).
Akiyama H, Arai T, Kondo H, Tanno E, Haga C, Ikeda K. 2000. Cell mediators of
inflammation in the Alzheimer disease brain. Alzheimer Dis Assoc Disord
14(Supplement):S47–S53, PMID: 10850730,https://doi.org/10.1097/00002093-
Alessandrini F, Beck-Speier I, Krappmann D, Weichenmeier I, Takenaka S, Karg E,
et al. 2009. Role of oxidative stress in ultrafine particle-induced exacerbation
of allergic lung inflammation. Am J Respir Crit Care Med 179(11):984–991,
Allen JL, Liu X, Pelkowski S, Palmer B, Conrad K, Oberdörster G. 2014a. Early post-
natal exposure to ultrafine particulate matter air pollution: Persistent ventricu-
lomegaly, neurochemical disruption, and glial activation preferentially in male
mice. Environ Health Perspect 122(9):939–945, PMID: 24901756,https://doi.org/
Allen JL, Liu X, Weston D, Prince L, Oberdörster G, Finkelstein JN, et al. 2014b.
Developmental exposure to concentrated ambient ultrafine particulate matter
air pollution in mice results in persistent and sex-dependent behavioral
neurotoxicity and glial activation. Toxicol Sci 140(1):160–178, PMID: 24690596,
Amor S, Puentes F, Baker D, Van Der Valk P. 2010. Inflammation in neurodegenera-
tive diseases. Immunology 129(2):154–169, PMID: 20561356,https://doi.org/10.
Andersen ZJ, Olsen TS, Andersen KK, Loft S, Ketzel M, Raaschou-Nielsen O. 2010.
Association between short-term exposure to ultrafine particles and hospital
admissions for stroke in Copenhagen, Denmark. Eur Heart J 31(16):2034–2040,
Andersen ZJ, Wahlin P, Raaschou-Nielsen O, Ketzel M, Scheike T, Loft S. 2008.
Size distribution and total number concentration of ultrafine and accumulation
mode particles and hospital admissions in children and the elderly in
Copenhagen, Denmark. Occup Environ Med 65(7):458–466, PMID: 17989204,
Araujo JA, Barajas B, Kleinman M, Wang X, Bennett BJ, Gong KW et al. 2008.
Ambient particulate pollutants in the ultrafine range promote early atheroscle-
rosis and systemic oxidative stress. Circ Res 102(5):589–596, PMID: 18202315,
Asbach C, Fissan H, Stahlmecke B, Kuhlbusch TAJ, Pui DYH. 2009. Conceptual limita-
tions and extensions of lung-deposited Nanoparticle Surface Area Monitor
(NSAM). J Nanopart Res 11(1):101–109, https://doi.org/10.1007/s11051-008-
Bachler G, Losert S, Umehara Y, von Goetz N, Rodriguez-Lorenzo L, Petri-Fink A,
et al. 2015. Translocation of gold nanoparticles across the lung epithelial tissue
barrier: Combining in vitro and in silico methods to substitute in vivo experi-
ments. Part Fibre Toxicol 12(1), PMID: 26116549,https://doi.org/10.1186/s12989-
Badolato R, Wang JM, Murphy WJ, Lloyd AR, Michiel DF, Bausserman LL, et al.
1994. Serum amyloid a is a chemoattractant: Induction of migration, adhesion,
and tissue infiltration of monocytes and polymorphonuclear leukocytes. J Exp
Med 180(1):203–209, PMID: 7516407.
Balasubramanian SK, Poh KW, Ong CN, Kreyling WG, Ong WY, Yu LE. 2013. The
effect of primary particle size on biodistribution of inhaled gold nano-agglom-
erates. Biomaterials 34(22):5439–5452, PMID: 23639527,https://doi.org/10.1016/j.
Bartoli CR, Wellenius GA, Diaz EA, Lawrence J, Coull BA, Akiyama I, et al. 2009.
Mechanisms of inhaled fine particulate air pollution-induced arterial blood
pressure changes. Environ Health Perspect 117(3):361–366, PMID: 19337509,
Baulig A, Singh S, Marchand A, Schins R, Barouki R, Garlatti M, et al. 2009. Role of
components in the pro-inflammatory response induced in airway
epithelial cells. Toxicology 261(3):126–135, PMID: 19460412,https://doi.org/10.
Becerra TA, Wilhelm M, Olsen J, Cockburn M, Ritz B. 2013. Ambient air pollution
and autism in Los Angeles county, California. Environ Health Perspect
121(3):380–386, PMID: 23249813,https://doi.org/10.1289/ehp.1205827.
Beck-Broichsitter M, Ruppert C, Schmehl T, Günther A, Seeger W. 2014.
Biophysical inhibition of pulmonary surfactant function by polymeric nanopar-
ticles: Role of surfactant protein B and C. Acta Biomater 10(11):4678–4684,
Beelen R, Raaschou-Nielsen O, Stafoggia M, Andersen ZJ, Weinmayr G, Hoffmann
B, et al. 2014. Effects of long-term exposure to air pollution on natural-cause
mortality: Ananalysis of 22 European cohorts within the multicenter ESCAPE
project. Lancet 383(9919):785–795, PMID: 24332274,https://doi.org/10.1016/
Benbrahim-Talla L, Baan RA, Grosse Y, Lauby-Secretan B, El Ghissassi F, Bouvard V,
et al. 2012. Carcinogenicity of diesel-engine and gasoline-engine exhausts and
some nitroarenes. Lancet Oncol 13(7):663–664, PMID: 22946126,https://doi.org/10.
Bouwmeester H, Lynch I, Marvin HJ, Dawson KA, Berges M, Braguer D, et al.
2011. Minimal analytical characterization of engineered nanomaterials needed
for hazard assessment in biological matrices. Nanotoxicology 5(1):1–11, PMID:
Bräuner EV, Forchhammer L, Möller P, Simonsen J, Glasius M, Wåhlin P, et al.
2007. Exposure to ultrafine particles from ambient air and oxidative stress-
induced DNA damage. Environ Health Perspect 115(8):1177–1182, PMID:
Brook RD, Franklin B, Cascio W, Hong Y, Howard G, Lipsett M, et al. 2004. Air pollu-
tion and cardiovascular disease: a statement for healthcare professionals from
the Expert Panel on Population and Prevention Science of the American Heart
Association. Circulation 109(21):2655–2671, PMID: 15173049,https://doi.org/10.
Brown DM, Dickson C, Duncan P, Al-Attili F, Stone V. 2010a. Interaction between
nanoparticles and cytokine proteins: Impact on protein and particle functional-
ity. Nanotechnology 21(21):215104, PMID: 20431193,https://doi.org/10.1088/0957-
Appendix I. Physicochemical characteristics of ambient ultrafine particles
(UFPs) and engineered nanomaterials (NMs).
Ambient ultrafine particles
•Ambient air particulate matter (PM) composition is complex, including
coarse (2:5–10 lm), ﬁne (<2:5lm), and UF (<100 nm) particles.
•Urban UFPs derive mainly from combustion processes (e.g., traﬃc) and
subsequent particle nucleation, coagulation, and vapor condensation.
•Urban UFPs often contain transition metals or organic
chemicals, that is to say, complex composition (See Figure 2).
•A mixture of insoluble and soluble particles and droplets may lead to
the release of several constituents from one
particle in the lung.
•Size distribution, particle morphology, chemical
composition, and concentration vary over time and place.
•Although relatively large in terms of number, UFPs
contribute relatively little to the mass of PM compared with coarse
•Controlled exposures are impeded by temporal variability, which com-
plicates mechanistic studies.
•UFPs are always surrounded by gaseous pollutants.
•A number of deﬁnitions exist that usually stipulate at least one dimen-
sion is in the nanoscale (1–100 nm). Many NMs have three dimensions
in the nanoscale, making them nanoparticles.
•NMs are often referred to as engineered or manufactured because they
are designed and generated for a speciﬁc purpose.
•NMs are made in a wide variety of chemistries, consisting of single ele-
ments (e.g., carbon, metals), compounds (e.g., metal oxides, salts), or
complex composites (e.g., core-plus-shell structure).
•NMs can vary signiﬁcantly in particle morphology and chemical com-
position but are well deﬁned at production and close to production
•Spatial and temporal variance in airborne concentration may vary
•Controlled exposures are possible, enabling detailed
•NMs can be handled in a standardized manner, facilitating studies of
Environmental Health Perspectives 106002-12
Brown DM, Donaldson K, Borm PJ, Schins RP, Denhart M, Gilmour P, et al. 2004a.
Calcium and reactive oxygen species-mediated activation of transcription fac-
tors and TNF-alpha cytokine gene expression in macrophages exposed to
ultrafine particles. Am J Physiol Lung Cell Mol Physiol 286(2):L344–L353, PMID:
Brown D, Donaldson K, Stone V. 2004b. Effects of PM
in human peripheral blood
monocytes and J774 macrophages. Respir Res 5:29, PMID: 15613243,https://doi.org/
Brown DM, Donaldson K, Stone V. 2010b. Nuclear translocation of Nrf2 and
expression of antioxidant defence genes in THP-1 cells exposed to carbon
nanotubes. J Biomed Nanotechnol 6(3):224–233, PMID: 21179939,https://doi.org/
Brown DM, Wilson MR, MacNee W, Stone V, Donaldson K. 2001. Size-dependent
proinflammatory effects of ultrafine polystyrene particles: A role for surface area
and oxidative stress in the enhanced activity of ultrafines. Toxicol Appl
Pharmacol 175(3):191–199, PMID: 11559017,https://doi.org/10.1006/taap.2001.9240.
Brunekreef B, Holgate ST. 2002. Air pollution and health. Lancet 360(9341):1233–
1242, PMID: 12401268,https://doi.org/10.1016/S0140-6736(02)11274-8.
Calderón-Garcidueñas L, Engle R, Antonieta Mora-Tiscareño AM, Styner M,
Gómez-Garza G, Zhu H, et al. 2011. Exposure to severe urban air pollution influ-
ences cognitive outcomes, brain volume and systemic inflammation in clinically
healthy children. Brain Cogn 77(3):345–355, PMID: 22032805,https://doi.org/10.
Calderón-Garcidueñas L, Wen-Wang L, Zhang YJ, Rodriguez-Alcaraz A, Osnaya N,
Villarreal-Calderón A, et al. 1999. 8-hydroxy-2'-deoxyguanosine, a major muta-
genic oxidative DNA lesion, and DNA strand breaks in nasal respiratory epi-
thelium of children exposed to urban pollution. Environ Health Perspect
107(6):469–474, PMID: 10339447,https://doi.org/10.1289/ehp.99107469.
Campbell A, Oldham M, Becaria A, Bondy SC, Meacher D, Sioutas C, et al. 2005.
Particulate matter in polluted air may increase biomarkers of inflammation in
mouse brain. Neurotoxicology 26(1):133–140, PMID: 15527881,https://doi.org/
Cascio WE, Cozzi E, Hazarika S, Devlin RB, Henriksen RA, Lust RM, et al. 2007.
Cardiac and vascular changes in mice after exposure to ultrafine particulate
matter. Inhal Toxicol 19(suppl1):67–73, PMID: 17886053,https://doi.org/10.1080/
Cassee FR, Mills NL, Newby DE. 2011. Cardiovascular Effects of Inhaled Ultrafine
and Nano-Sized Particles. Oxford, UK:Wiley.
Clift MJD, Raemy DO, Endes C, Ali Z, Lehmann AD, Brandenberger C, et al. 2013.
Can the Ames test provide an insight into nano-object mutagenicity? Investigating
the interaction between nano-objects and bacteria. Nanotoxicology 7(8):1373–
1385, PMID: 23078217,https://doi.org/10.3109/17435390.2012.741725.
Cohen J, Deloid G, Pyrgiotakis G, Demokritou P. 2013. Interactions of engineered
nanomaterials in physiological media and implications for in vitro dosimetry.
Nanotoxicology 7(4):417–431, PMID: 22393878,https://doi.org/10.3109/17435390.
Courtois A, Andujar P, Ladeiro Y, Baudrimont I, Delannoy E, Leblais V, et al. 2008.
Impairment of NO-dependent relaxation in intralobar pulmonary arteries:
Comparison of urban particulate matter and manufactured nanoparticles.
Environ >Health Perspect 116(10):1294–1299, PMID: 18941568,https://doi.org/
Delfino RJ, Sioutas C, Malik S. 2005. Potential role of ultrafine particles in associ-
ations between airborne particle mass and cardiovascular health. Environ
Health Perspect 113(8):934–946, PMID: 16079061,https://doi.org/10.1289/
Delfino RJ, Staimer N, Tjoa T, Gillen DL, Polidori A, Arhami M, et al. 2009. Air pollution
exposures and circulating biomarkers of effect in a susceptible population:
Clues to potential causal component mixtures and mechanisms. Environ
Health Perspect 117(8):1232–1238, PMID: 19672402,https://doi.org/10.1289/ehp.
DeLoid GM, Cohen JM, Pyrgiotakis G, Pirela SV, Pal A, Liu J, et al. 2015. Advanced
computational modeling for in vitro nanomaterial dosimetry. Part Fibre Toxicol
12:32, PMID: 26497802,https://doi.org/10.1186/s12989-015-0109-1.
Deng ZJ, Liang M, Monteiro M, Toth I, Minchin RF. 2011. Nanoparticle-induced unfolding
of fibrinogen promotes Mac-1 receptor activation and inflammation. Nat
Nanotechnol 6(1):39–44, PMID: 21170037,https://doi.org/10.1038/nnano.2010.250.
Dick CA, Brown DM, Donaldson K, Stone V. 2003. The role of free radicals in the
toxic and inflammatory effects of four different ultrafine particle types. Inhal
Toxicol 15(1):39–52, PMID: 12476359,https://doi.org/10.1080/08958370304454.
Dockery DW, Pope CA III, Xu X, Spengler JD, Ware JH, Fay ME, et al. 1993.
An association between air pollution and mortality in six U.S. cities. N
Engl J Med 329(24):1753–1759, PMID: 8179653,https://doi.org/10.1056/
Donaldson K, Stone V, Gilmour PS, Brown DM, MacNee W. 2000. Ultrafine par-
ticles: Mechanisms of lung injury. Phil Trans R Soc Lond A 358(1775):2741–
Donaldson K, Stone V, Tran CL, Kreyling W, Borm PJ. 2004. Nanotoxicology. Occup
Environ Med 61(9):727–728, PMID: 15317911,https://doi.org/10.1136/oem.2004.
Duffin R, Tran L, Brown D, Stone V, Donaldson K. 2007. Proinflammogenic effects
of low-toxicity and metal nanoparticles in vivo and in vitro: Highlighting the
role of particle surface area and surface reactivity. Inhal Toxicol 19(10):849–
856, PMID: 17687716,https://doi.org/10.1080/08958370701479323.
Duffin R, Tran CL, Clouter A, Brown DM, MacNee W, Stone V, et al. 2002. The im-
portance of surface area and specific reactivity in the acute pulmonary inflamma-
tory response to particles. Ann Occup Hyg 46(suppl1):242–245, https://doi.org/10.
Elder A, Gelein R, Silva V, Feikert T, Opanashuk L, Carter J, et al. 2006.
Translocation of inhaled ultrafine manganese oxide particles to the central
nervous system. Environ Health Perspect 114(8):1172–1178, PMID: 16882521,
European Commission. 2010. EC Mandate M/461. MANDATE ADDRESSED TO CEN,
CENELEC AND ETSI FOR STANDARDIZATION ACTIVITIES REGARDING
NANOTECHNOLOGIES AND NANOMATERIALS. http://ec.europa.eu/growth/
tools-databases/mandates/index.cfm?fuseaction=search.detail&id=443#0 [accessed 12
European Commission. 2011. Definition of a nanomaterial. http://ec.europa.eu/
environment/chemicals/nanotech/faq/definition_en.htm [accessed 12 November
European Commission. 2013. Protocol for quantitative analysis of inorganic and
organic MNM surface coatings Deliverable 2.4. http://www.nanoreg.eu/images/
2015_12_03_NANoREG_Factsheet_D2.4.pdf [accessed 12 November 2016].
Ferin J, Oberdörster G, Penney DP. 1992. Pulmonary retention of ultrafine and
fine particles in rats. Am J Respir Cell Mol Biol 6(5):535–542, PMID: 1581076,
Ferin J, Oberdörster G, Soderholm SC, Gelein R. 1991. Pulmonary tissue access of
ultrafine particles. J Aerosol Med 4(1):57–68, https://doi.org/10.1089/jam.1991.4.57.
Fonken LK, Xu X, Weil ZM, Chen G, Sun Q, Rajagopalan S, et al. 2011. Air pollution
impairs cognition, provokes depressive-like behaviors and alters hippocampal
cytokine expression and morphology. Mol Psychiatry 16(10):987–995, PMID:
Frampton MW, Ghio AJ, Samet JM, Carson JL, Carter JD, Devlin RB. 1999. Effects
of aqueous extracts of PM
filters from the Utah Valley on human airway epi-
thelial cells. Am J Physiol 277(5 Pt 1):L960–L967, PMID: 10564181.
Freire C, Ramos R, Puertas R, Lopez-Espinosa MJ, Julvez J, Aguilera I, et al. 2010.
Association of traffic-related air pollution with cognitive development in children.
J Epidemiol Community Health 64(3):223–228, PMID: 19679705,https://doi.org/10.
Gasser M, Rothen-Rutishauser B, Krug HF, Gehr P, Nelle M, Yan B, et al. 2010. The
adsorption of biomolecules to multi-walled carbon nanotubes is influenced by
both pulmonary surfactant lipids and surface chemistry. J Nanobiotechnol
8(1):31, PMID: 21159192,https://doi.org/10.1186/1477-3155-8-31.
Geiser M, Kreyling WG. 2010. Deposition and biokinetics of inhaled nanoparticles.
Part Fibre Toxicol 7:2, PMID: 20205860,https://doi.org/10.1186/1743-8977-7-2.
Ghelfi E, Wellenius GA, Lawrence J, Millet E, Gonzalez-Flecha B. 2010. Cardiac oxi-
dative stress and dysfunction by fine concentrated ambient particles (CAPs)
are mediated by angiotensin-II. Inhal Toxicol 22(11):963–972, PMID: 20718632,
Ghio AJ, Smith CB, Madden MC. 2012. Diesel exhaust particles and airway inflam-
mation. Curr Opin Pulm Med 18(2):144–150, PMID: 22234273,https://doi.org/10.
Gilmour PS, Brown DM, Lindsay TG, Beswick PH, MacNee W, Donaldson K. 1996.
Adverse health effects of PM10 particles: Involvement of iron in generation of
hydroxyl radical. Occup Environ Med 53(12):817–822, PMID: 8994401.
Gong J, Zhu T, Kipen H, Wang G, Hu M, Guo Q, et al. 2014. Comparisons of ultrafine
and fine particles in their associations with biomarkers reflecting physiological
pathways. Environ Sci Technol 48(9):5264–5273, PMID: 24666379,https://doi.org/
Guadagnini R, Kenzaoui BH, Walker L, Pojana G, Magdolenova Z, Bilanicova D, et al.
2015. Toxicity screenings of nanomaterials: Challenges due to interference with
assay processes and components of classic in vitro tests. Nanotoxicology
9(suppl1):13–24, PMID: 23889211,https://doi.org/10.3109/17435390.2013.829590.
Gupta T, Demokritou P, Koutrakis P. 2004. Development and performance evaluation of a
high-volume ultrafine particle concentrator for inhalation toxicological studies. Inhal
Toxicol 16(13):851–862, PMID: 15513817,https://doi.org/10.1080/08958370490506664.
Halappanavar S, Jackson P, Williams A, Jensen KA, Hougaard KS, Vogel U, et al.
2011. Pulmonary response to surface-coated nanotitanium dioxide particles
includes induction of acute phase response genes, inflammatory cascades,
and changes in microRNAs: A toxicogenomic study. Environ Mol Mutagen
52(6):425–439, PMID: 21259345,https://doi.org/10.1002/em.20639.
Harder V, Gilmour PS, Lentner B, Karg E, Takenaka S, Ziesenis A, et al. 2005.
Cardiovascular responses in unrestrained WKY rats to inhaled ultrafine carbon
Environmental Health Perspectives 106002-13
particles. Inhal Toxicol 17(1):29–42, PMID: 15764481,https://doi.org/10.1080/
Hartmann NB, Jensen KA, Baun A, Rasmussen K, Rauscher H, Tantra R, et al.
2015. Techniques and protocols for dispersing nanoparticle powders in aque-
ous media-is there a rationale for harmonization?. J Toxicol Environ Health B
Crit Rev 18(6):299–326, PMID: 26397955,https://doi.org/10.1080/10937404.2015.
Hazari MS, Haykal-Coates N, Winsett DW, Krantz QT, King C, Costa DL, et al. 2011.
TRPA1 and sympathetic activation contribute to increased risk of triggered
cardiac arrhythmias in hypertensive rats exposed to diesel exhaust. Environ
Health Perspect 119(7):951–957, PMID: 21377951,https://doi.org/10.1289/ehp.
Heckel K, Kiefmann R, Dorger M, Stoeckelhuber M, Goetz AE. 2004. Colloidal gold
particles as a new in vivo marker of early acute lung injury. Am J Physiol Lung
Cell Mol Physiol 287(4):L867–L878, PMID: 15194564,https://doi.org/10.1152/
Hoffmann B, Moebus S, Möhlenkamp S, Stang A, Lehmann N, Dragano N, et al.
2007. Residential exposure to traffic is associated with coronary atherosclero-
sis. Circulation. 116(5):489–496, PMID: 17638927,https://doi.org/10.1161/
Hildebrandt K, Rückerl R, Koenig W, Schneider A, Pitz M, Heinrich J, et al. 2009.
Short-term effects of air pollution: A panel study of blood markers in patients
with chronic pulmonary disease. Part Fibre Toxicol 6(1):25, PMID: 19781092,
Hinderliter PM, Minard KR, Orr G, Chrisler WB, Thrall BD, Pounds JG, et al. 2010.
ISDD: A computational model of particle sedimentation, diffusion and target
cell dosimetry for in vitro toxicity studies. Part Fibre Toxicol 7(1):36, PMID:
Hougaard KS, Campagnolo L, Chavatte-Palmer P, Tarrade A, Rousseau-Ralliard D,
Valentino S, et al. 2015. A perspective on the developmental toxicity of inhaled
nanoparticles. Reprod Toxicol 56:118–140, PMID: 26050605,https://doi.org/10.
Hussain S, Boland S, Baeza-Squiban A, Hamel R, Thomassen LCJ, Martens JA,
et al. 2009. Oxidative stress and proinflammatory effects of carbon black and tita-
nium dioxide nanoparticles: Role of particle surface area and internalized
amount. Toxicology 260(1–3):142–149, PMID: 19464580,https://doi.org/10.1016/j.
Hussain S, Vanoirbeek JAJ, Hoet PHM. 2012. Interactions of nanomaterials with
the immune system. Wiley Interdiscip Rev Nanomed Nanobiotechnol 4(2):169–
183, PMID: 22144008,https://doi.org/10.1002/wnan.166.
Hussain S, Vanoirbeek JAJ, Luyts K, De Vooght V, Verbeken E, Thomassen LCJ,
et al. 2011. Lung exposure to nanoparticles modulates an asthmatic response
in a mouse model. Eur Respir J 37(2):299–309, PMID: 20530043,https://doi.org/
IARC (International Agency for Research on Cancer). 2014. Monographs on the
Evaluation of Carciongenic Risks to Humans Volume 105: Diesel and Gasoline
Engine Exhausts and Some Nitroarenes Lyon, France:IARC. https://monographs.
iarc.fr/ENG/Monographs/vol105/mono105.pdf [accessed 19 September 2017].
ICRP (International Commission on Radiological Protection). 1994. Human
respiratory tract model for radiological protection. A report of a Task Group
of the International Commission on Radiological Protection. Ann ICRP 24(1–
3):1–482, PMID: 7726471.
Jiménez LA, Thompson J, Brown DA, Rahman I, Antonicelli F, Duffin R, et al. 2000.
Activation of NF-jBbyPM
occurs via an iron-mediated mechanism in the
absence of IjB degradation. Toxicol Appl Pharmacol 166(2):101–110, PMID:
Johnston H, Pojana G, Zuin S, Jacobsen NR, Møller P, Loft S, et al. 2013.
Engineered nanomaterial risk. Lessons learnt from completed nanotoxicology
studies: Potential solutions to current and future challenges. Crit Rev Toxicol
43(1):1–20, PMID: 23126553,https://doi.org/10.3109/10408444.2012.738187.
Kampfrath T, Maiseyeu A, Ying Z, Shah Z, Deiuliis JA, Xu X, et al. 2011. Chronic fine par-
ticulate matter exposure induces systemic vascular dysfunction via NADPH oxidase
and TLR4 pathways. Circ Res 108(6):716–726, PMID: 21273555,https://doi.org/10.
Kermanizadeh A, Gosens I, MacCalman L, Johnston H, Danielsen PH, Jacobsen
NR, et al. 2016. A multilaboratory toxicological assessment of a panel of 10
engineered nanomaterials to human health—ENPRA project—the highlights,
limitations, and current and future challenges. J Toxicol Environ Health B Crit
Rev 19(1):1–28, PMID: 27030582,https://doi.org/10.1080/10937404.2015.1126210.
Kilinç E, Van Oerle R, Borissoff JI, Oschatz C, Gerlofs-Nijland ME, Janssen NA,
et al. 2011. Factor XII activation is essential to sustain the procoagulant effects
of particulate matter. J Thromb Haemost 9(7):1359–1367, PMID: 21481175,
Kim S, Jaques PA, Chang M, Froines JR, Sioutas C. 2001. Versatile aerosol concen-
tration enrichment system (VACES) for simultaneous in vivo and in vitro evalu-
ation of toxic effects of ultrafine, fine and coarse ambient particles Part I:
Development and laboratory characterization. J Aerosol Sci 32(11):1281–1297,
Kim H, Oh SJ, Kwak HC, Kim JK, Lim CH, Yang JS, et al. 2012. The impact of intra-
tracheally instilled carbon black on the cardiovascular system of rats:
Elevation of blood homocysteine and hyperactivity of platelets. J Toxicol
Environ Health A 75(24):1471–1483, PMID: 23116452,https://doi.org/10.1080/
Knaapen AM, Borm PJA, Albrecht C, Schins RPF. 2004. Inhaled particles and lung
cancer. Part A: Mechanisms. Int J Cancer 109(6):799–809, PMID: 15027112,
Kreyling WG. 2013. Dosimetry of nanomaterials after different routes of exposure.
Toxicol Lett 221(suppl):S6–S6, https://doi.org/10.1016/j.toxlet.2013.06.022.
Kreyling WG, Blanchard JD, Godleski JJ, Haeussermann S, Heyder J, Hutzler P,
et al. 1999. Anatomic localization of 24- and 96-h particle retention in canine
airways. J Appl Physiol 87(1):269–284, PMID: 10409585.
Kreyling WG, Hirn S, Möller W, Schleh C, Wenk A, Celik G, et al. 2014. Air-bloodbar-
rier translocation of tracheallyinstilled gold nanoparticles inversely depends on par-
ticle size. ACS Nano 8(1):222–233, PMID: 24364563,https://doi.org/10.1021/nn403256v.
Kreyling WG, Semmler M, Erbe F, Mayer P, Takenaka S, Schulz H, et al. 2002.
Translocation of ultrafine insoluble iridium particles from lung epithelium to
extrapulmonary organs is size dependent but very low. J Toxicol Environ Health
A 65(20):1513–1530, PMID: 12396866,https://doi.org/10.1080/00984100290071649.
Künzli N, Jerrett M, Mack WJ, Beckerman B, LaBree L, Gilliland F, et al. 2005.
Ambient air pollution and atherosclerosis in Los Angeles. Environ Health
Perspect 113(2):201–206, PMID: 15687058,https://doi.org/10.1289/ehp.7523.
Langrish JP, Lundbäck M, Mills NL, Johnston NR, Webb DJ, Sandström T, et al.
2009. Contribution of endothelin 1 to the vascular effects of diesel exhaust inha-
lation in humans. Hypertension 54(4):910–915, PMID: 19687345,https://doi.org/10.
Lanki T, de Hartog JJ, Heinrich J, Hoek G, Janssen NAH, Peters A, et al. 2006. Can
we identify sources of fine particles responsible for exercise-induced ischemia
on days with elevated air pollution? The ULTRA study. Environ Health Perspect
114(5):655–660, PMID: 16675416,https://doi.org/10.1289/ehp.8578.
Larsen ST, Roursgaard M, Jensen KA, Nielsen GD. 2010. Nano titanium dioxide
particles promote allergic sensitization and lung inflammation in mice. Basic
Clin Pharmacol Toxicol 106(2):114–117, PMID: 19874288,https://doi.org/10.1111/
Leblanc AJ, Moseley AM, Chen BT, Frazer D, Castranova V, Nurkiewicz TR. 2010.
Nanoparticle inhalation impairs coronary microvascular reactivity via a local
reactive oxygen species-dependent mechanism. Cardiovasc Toxicol 10(1):27–
36, PMID: 20033351,https://doi.org/10.1007/s12012-009-9060-4.
Lee S, Bi XY, Reed RB, Ranville JF, Herckes P, Westerhoff P. 2014. Nanoparticle size
detection limits by single particle ICP-MS for 40 elements. Environ Sci Techn ol
48(17):10291–10300, PMID: 25122540,https://doi.org/10.1021/es502422v.
Lee JS, Choi YC, Shin JH, Lee JH, Lee Y, Park SY. 2015. Health surveillance study
of workers who manufacture multi-walled carbon nanotubes. Nanotoxicology
9(6):802–811, PMID: 25395166,https://doi.org/10.3109/17435390.2014.978404.
Lelieveld J, Evans JS, Fnais M, Giannadaki D, Pozzer A. 2015. The contribution of
outdoor air pollution sources to premature mortality on a global scale. Nature
525(7569):367, PMID: 26381985,https://doi.org/10.1038/nature15371.
Levin M, Witschger O, Bau S, Jankowska E, Koponen IK, Koivisto AJ. 2016. Can we
trust real time measurements of lung deposited surface area concentrations
in dust from powder nanomaterials?. Aerosol Air Qual Res 16(5):1105–1117,
Li N, Hao M, Phalen RF, Hinds WC, Nel AE. 2003. Particulate air pollutants and
asthma: a paradigm for the role of oxidative stress in PM-induced adverse
health effects. Clin Immunol 109(3):250–265, PMID: 14697739,https://doi.org/10.
Li N, Kim S, Wang M, Froines J, Sioutas C, Nel A. 2002. Use of a stratified oxidative
stress model to study the biological effects of ambient concentrated and diesel
exhaust particulate matter. Inhal Toxicol 14(5):459–486, PMID: 12028803,
Li N, Xia T, Nel AE. 2008. The role of oxidative stress in ambient particulate matter-
induced lung diseases and its implications in the toxicity of engineered nano-
particles. Free Radic Biol Med 44(9):1689–1699, PMID: 18313407,https://doi.org/
Li R, Navab K, Hough G, Daher N, Zhang M, Mittelstein D, et al. 2015. Effect of ex-
posure to atmospheric ultrafine particles on production of free fatty acids and
lipid metabolites in the mouse small intestine. Environ Health Perspect
123(1):34–40, PMID: 25170928,https://doi.org/10.1289/ehp.1307036.
Li XY, Gilmour PS, Donaldson K, MacNee W. 1996. Free radical activity and pro-
inflammatory effects of particulate air pollution (PM10) in vivo and in vitro.
Thorax 51(12):1216–1222, PMID: 8994518.
Li Z, Hulderman T, Salmen R, Chapman R, Leonard SS, Young SH. 2007. Cardiovascular
effects of pulmonary exposure to single-wall carbon nanotubes. Environ Health
Perspect 115(3):377–382, PMID: 17431486,https://doi.org/10.1289/ehp.9688.
Environmental Health Perspectives 106002-14
Liao H-Y, Chung Y-T, Lai C-H, Wang S-L, Chiang H-C, Li L-A, et al. 2014. Six-month
follow-up study of health markers of nanomaterials among workers handling
engineered nanomaterials. Nanotoxicology 8(suppl1):100–110, PMID: 24295335,
Lim SS, Vos T, Flaxman AD, Danaei G, Shibuya K, Adair-Rohani H, et al. 2012. A
comparative risk assessment of burden of disease and injury attributable
to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a sys-
tematic analysis for the Global Burden of Disease Study 2010. Lancet
380(9859):2224–2260, 1416 PMID: 23245609,https://doi.org/10.1016/S0140-
Liou S-H, Tsai CSJ, Pelclova D, Schubauer-Berigan MK, Schulte PA. 2015.
Assessing the first wave of epidemiological studies of nanomaterial workers. J
Nanopart Res 17:413, PMID: 26635494,https://doi.org/10.1007/s11051-015-3219-7.
Lucking AJ, Lundback M, Mills NL, Faratian D, Barath SL, Pourazar J, et al. 2008.
Diesel exhaust inhalation increases thrombus formation in man. Eur Heart J 29
(24):3043–3051, PMID: 18952612,https://doi.org/10.1093/eurheartj/ehn464.
Lucking AJ, Lundbäck M, Barath SL, Mills NL, Sidhu MK, Langrish JP, et al. 2011.
Particle traps prevent adverse vascular and prothrombotic effects of diesel
engine exhaust inhalation in men. Circulation 123(16):1721–1728, PMID: 21482966,
Lynch I, Cedervall T, Lundqvist M, Cabaleiro-Lago C, Linse S, Dawson KA. 2007.
The nanoparticle-protein complex as a biological entity; a complex fluids and sur-
face science challenge for the 21st century. Adv Colloid Interface Sci 134–135:167–
174, PMID: 17574200,https://doi.org/10.1016/j.cis.2007.04.021.
Lynch I, Dawson KA. 2008. Protein-nanoparticle interactions. Nano Today 3(1–
Magdolenova Z, Collins A, Kumar A, Dhawan A, Stone V, Dusinska M. 2014.
Mechanisms of genotoxicity. A review of in vitro and in vivo studies with engi-
neered nanoparticles. Nanotoxicology 8(3):233–278, PMID: 23379603,https://doi.org/
McCreanor J, Cullinan P, Nieuwenhuijsen MJ, Stewart-Evans J, Malliarou E, Jarup
L, et al. 2007. Respiratory effects of exposure to diesel traffic in persons with
asthma. N Engl J Med 357(23):2348–2358, PMID: 18057337,https://doi.org/10.
Mikkelsen L, Sheykhzade M, Jensen KA, Saber AT, Jacobsen NR, Vogel U, et al.
2011. Modest effect on plaque progression and vasodilatory function in
atherosclerosis-prone mice exposed to nanosized TiO
. Part Fibre Toxicol
8(1):32, PMID: 22074227,https://doi.org/10.1186/1743-8977-8-32.
Miller MR. 2014. The role of oxidative stress in the cardiovascular actions of
particulate air pollution. Biochem Soc Trans 42(4):1006–1011, PMID: 25109994,
Miller MR, Borthwick SJ, Shaw CA, McLean SG, McClure D, Mills NL, et al. 2009.
Direct impairment of vascular function by diesel exhaust particulate through
reduced bioavailability of endothelium-derived nitric oxide induced by super-
oxide free radicals. Environ Health Perspect 117(4):611–616, PMID: 19440501,
Miller MR, McLean SG, Duffin R, Lawal AO, Araujo JA, Shaw CA, et al. 2013. Diesel
exhaust particulate increases the size and complexity of lesions in athero-
sclerotic mice. Part Fibre Toxicol 10(1):61, PMID: 24330719,https://doi.org/10.
Miller MR, Shaw CA, Langrish JP. 2012. From particles to patients: Oxidative stress
and the cardiovascular effects of air pollution. Future Cardiol 8(4):577–602,
Mills NL, Tornqvist H, Gonzalez MC, Vink E, Robinson SD, Soderberg S, et al. 2007.
Ischemic and thrombotic effects of dilute diesel-exhaust inhalation in men
with coronary heart disease. N Engl J Med 357(11):1075–1082, PMID: 17855668,
Mills NL, Tornqvist H, Robinson SD, Gonzalez M, Darnley K, MacNee W, et al. 2005.
Diesel exhaust inhalation causes vascular dysfunction and impaired endoge-
nous fibrinolysis. Circulation 112(25):3930–3936, PMID: 16365212,https://doi.org/
MODENA MPNS (Materials, Physical and Nanosciences) COST. 2013. MODENA:
Modelling nanomaterial toxicity. www.modena-cost.eu [accessed 12 November
Møller P, Danielsen PH, Karottki DG, Jantzen K, Roursgaard M, Klingberg H, et al.
2014. Oxidative stress and inflammation generated DNA damage by exposure
to air pollution particles. Mutat Res Rev Mutat Res 762:133–166, PMID:
Møller P, Hemmingsen JG, Jensen DM, Danielsen PH, Karottki DG, Jantzen K,
et al. 2015. Applications of the comet assay in particle toxicology: Air pollution
and engineered nanomaterials exposure. Mutagenesis 30(1):67–83, PMID:
Møller P, Mikkelsen L, Vesterdal LK, Folkmann JK, Forchhammer L, Roursgaard M,
et al. 2011. Hazard identification of particulate matter on vasomotor dysfunc-
tion and progression of atherosclerosis. Crit Rev Toxicol 41(4):339–368, PMID:
Möller W, Felten K, Sommerer K, Scheuch G, Meyer G, Meyer P, et al. 2008.
Deposition, retention, and translocation of ultrafine particles from the central
airways and lung periphery. Am J Respir Crit Care Med 177(4):426–432, PMID:
Monopoli MP, Aberg C, Salvati A, Dawson KA. 2012. Biomolecular coronas provide
the biological identity of nanosized materials. Nat Nanotechnol 7(12):779–786,
Moore TL, Rodriguez-Lorenzo L, Hirsch V, Balog S, Urban D, Jud C, et al. 2015.
Nanoparticle colloidal stability in cell culture media and impact on cellular interac-
tions. Chem Soc Rev 44(17):6287–6305, PMID: 26056687,https://doi.org/10.1039/
Murphy G Jr, Rouse RL, Polk WW, Henk WG, Barker SA, Boudreaux MJ, et al.
2008. Combustion-derived hydrocarbons localize to lipid droplets in respiratory
cells. Am J Respir Cell Mol Biol 38(5):532–540, PMID: 18079490,https://doi.org/
Napierska D, Rabolli V, Thomassen LC, Dinsdale D, Princen C, Gonzalez L, et al.
2012. Oxidative stress induced by pure and iron-doped amorphous silica nano-
particles in subtoxic conditions. Chem Res Toxicol 25(4):828–837, PMID:
Nel A, Xia T, Mädler L, Li N. 2006. Toxic potential of materials at the nanolevel. Science
311(5761):622–627, PMID: 16456071,https://doi.org/10.1126/science.1114397.
Nemmar A, Hoylaerts MF, Hoet PH, Nemery B. 2004. Possible mechanisms of the
cardiovascular effects of inhaled particles: Systemic translocation and pro-
thrombotic effects. Toxicol Lett 149(1-3):243–253, PMID: 15093270,https://doi.org/
Nemmar A, Vanbilloen H, Hoylaerts MF, Hoet PH, Verbruggen A, Nemery B. 2001.
Passage of intratracheally instilled ultrafine particles from the lung into the
systemic circulation in hamster. Am J Respir Crit Care Med 164(9):1665–1668,
Nikula KJ, Avila KJ, Griffith WC, Mauderly JL. 1997. Sites of particle retention and
lung tissue responses to chronically inhaled diesel exhaust and coal dust in rats
and cynomolgus monkeys. Environ Health Perspect 105(suppl 5):1231–1234,
Niwa Y, Hiura Y, Murayama T, Yokode M, Iwai N. 2007. Nano-sized carbon black
exposure exacerbates atherosclerosis in LDL-receptor knockout mice. Circ J
71(7):1157–1161, PMID: 17587728,https://doi.org/10.1253/circj.71.1157.
Oberdörster G. 2010. Safety assessment for nanotechnology and nanomedicine:
concepts of nanotoxicology. J Intern Med 267(1):89–105, PMID: 20059646,
Oberdörster G, Ferin J, Finkelstein G, Wade P, Corson N. 1990. Increased pulmo-
nary oxicity of ultrafine particles? II Lung lavage studies. J Aerosol Sci
Oberdörster G, Ferin J, Lehnert BE. 1994. Correlation between particle size, in vivo
particle persistence, and lung injury. Environ Health Perspect 102(suppl 5):173–
179, PMID: 7882925,https://doi.org/10.2307/3432080.
Oberdörster G, Gelein RM, Ferin J, Weiss B. 1995. Association of particulate air
pollution and acute mortality: Involvement of ultrafine particles?. Inhal Toxicol
7(1):111–124, PMID: 11541043,https://doi.org/10.3109/08958379509014275.
Oberdörster G, Sharp Z, Atudorei V, Elder A, Gelein R, Lunts A, et al. 2002.
Extrapulmonary translocation of ultrafine carbon particles following whole-
body inhalation exposure of rats. J Toxicol Environ Health A 65(20):1531–1543,
Oberdörster G, Oberdörster E, Oberdörster J. 2005. Nanotoxicology: An emerging
discipline evolving from studies of ultrafine particles. Environ Health Perspect
113(7):823–839, PMID: 16002369.
Patel MM, Chillrud SN, Deepti KC, Ross JM, Kinney PL. 2013. Traffic-related air
pollutants and exhaled markers of airway inflammation and oxidative stress
in New York City adolescents. Environ Res 121:71–78, PMID: 23177171,
Pedersen M, Giorgis-Allemand L, Bernard C, Aguilera I, Andersen A-MN, Ballester
F, et al. 2013. Ambient air pollution and low birthweight: a European cohort study
(ESCAPE). Lancet Respir Med 1(9):695–704, PMID: 24429273,https://doi.org/10.
Peters A, Dockery DW, Muller JE, Mittleman MA. 2001. Increased particulate air
pollution and the triggering of myocardial infarction. Circulation 103(23):2810–
2815, PMID: 11401937,https://doi.org/10.1161/01.CIR.103.23.2810.
Peters A, Hampel R, Cyrys J, Breitner S, Geruschkat U, Kraus U. 2015. Elevated par-
ticle number concentrations induce immediate changes in heart rate variability: A
panel study in individuals with impaired glucose metabolism or diabetes. Part Fibre
Toxicol 12:7, PMID: 25888845,https://doi.org/10.1186/s12989-015-0083-7.
Peters A, Wichmann HE, Tuch T, Heinrich J, Heyder J. 1997. Respiratory effects
are associated with the number of ultrafine particles. Am J Respir Crit Care
Med 155(4):1376–1383, PMID: 9105082,https://doi.org/10.1164/ajrccm.155.4.
Pieters N, Koppen G, van Poppel M, de Prins S, Cox B, Dons E, et al. 2015. Blood
pressure and same-day exposure to air pollution at school: Associations with
Environmental Health Perspectives 106002-15
nano-sized to coarse PM in children. Environ Health Perspect 123(7):737–742,
Pieters N, Plusquin M, Cox B, Kicinski M, Vangronsveld J, Nawrot TS. 2012. An epi-
demiological appraisal of the association between heart rate variability and par-
ticulate air pollution: A meta-analysis. Heart 98(15):1127–1135, PMID: 22628541,
Poland CA, Duffin R, Kinloch I, Maynard A, Wallace WA, Seaton A, et al. 2008.
Carbon nanotubes introduced into the abdominal cavity of mice show
asbestos-like pathogenicity in a pilot study. Nat Nanotechnol 3(7):423–428,
Pope CA III. 1991. Respiratory hospital admissions associated with PM10 pollution
in Utah, Salt Lake, and Cache Valleys. Arch Environ Health 46(2):90–97, PMID:
Pope CA III, Thun MJ, Namboodiri MM, Dockery DW, Evans JS, Speizer FE, et al.
1995. Particulate air pollution as a predictor of mortality in a prospective study
of U.S. adults. Am J Respir Crit Care Med, 151(3 Part1):669–674, PMID: 7881654,
Pope CA III, Verrier RL, Lovett EG, Larson AC, Raizenne ME, Kanner RE, et al. 1999.
Heart rate variability associated with particulate air pollution. Am Heart J 138(5
pt 1):890–899, PMID: 10539820,https://doi.org/10.1016/S0002-8703(99)70014-1.
Poulsen SS, Saber AT, Mortensen A, Szarek J, Wu D, Williams A, et al. 2015.
Changes in cholesterol homeostasis and acute phase response link pulmonary
exposure to multi-walled carbon nanotubes to risk of cardiovascular disease.
Toxicol Appl Pharm 283(3):210–222, PMID: 25620056,https://doi.org/10.1016/j.
Pourazar J, Blomberg A, Kelly FJ, Davies DE, Wilson SJ, Holgate ST, et al. 2008.
Diesel exhaust increases EGFR and phosphorylated C-terminal Tyr 1173 in the
bronchial epithelium. Part Fibre Toxicol 5:8, PMID: 18460189,https://doi.org/10.
Prach M, Stone V, Proudfoot L. 2013. Zinc oxide nanoparticles and monocytes:
Impact of size, charge and solubility on activation status. Toxicol Appl Pharm
266(1):19–26, PMID: 23142470,https://doi.org/10.1016/j.taap.2012.10.020.
Price OT, Asgharian B, Miller FJ, Cassee FR, de Winter-Sorkina R. 2001. Multiple
path particle dosimetry model (MPPD v1.0): A model for human and rat airway
particle dosimetry. RIVM. http://rivm.openrepository.com/rivm/handle/10029/
257628 [accessed 12 November 2016].
Pulskamp K, Wörle-Knirsch JM, Hennrich F, Kern K, Krug HF. 2007. Human lung epi-
thelial cells show biphasic oxidative burst after single-walled carbon nanotube
contact. Carbon 45(11):2241–2249, https://doi.org/10.1016/j.carbon.2007.06.054.
Putaud JP, Van Dingenen R, Alastuey A, Bauer H, Birmili W, Cyrys J, et al. 2010. A
European aerosol phenomenology - 3: Physical and chemical characteris-
tics of particulate matter from 60 rural, urban, and kerbside sites across
Europe. Atmos Environ 44(10):1308–1320, https://doi.org/10.1016/j.atmosenv.
Radomski A, Jurasz P, Alonso-Escolano D, Drews M, Morandi M, Malinski T, et al.
2005. Nanoparticle-induced platelet aggregation and vascular thrombosis. Br J
Pharmacol 146(6):882–893, PMID: 16158070,https://doi.org/10.1038/sj.bjp.0706386.
Ranft U, Schikowski T, Sugiri D, Krutmann J, Krämer U. 2009. Long-term exposure
to traffic-related particulate matter impairs cognitive function in the elderly.
Environ Res 109(8):1004–1011, PMID: 19733348,https://doi.org/10.1016/j.envres.
Rhoden CR, Wellenius GA, Ghelfi E, Lawrence J, González-Flecha B. 2005. PM-
induced cardiac oxidative stress and dysfunction are mediated by autonomic
stimulation. Biochim Biophys Acta 1725(3):305–313, PMID: 16005153,
Rich DQ, Zareba W, Beckett W, Hopke PK, Oakes D, Frampton MW, et al. 2012. Are
ambient ultrafine, accumulation mode, and fine particles associated with
adverse cardiac responses in patients undergoing cardiac rehabilitation?.
Environ Health Perspect 120(8):1162–1169, PMID: 22542955,https://doi.org/10.
markers of inflammation in the prediction of cardiovascular disease in
women. N Engl J Med 342(12):836–843, PMID: 10733371,https://doi.org/10.
Robertson S, Gray GA, Duffin R, McLean SG, Shaw CA, Hadoke PWF, et al. 2012.
Diesel exhaust particulate induces pulmonary and systemic inflammation in
rats without impairing endothelial function ex vivo or in vivo. Part Fibre Toxicol
9:9, PMID: 22480168,https://doi.org/10.1186/1743-8977-9-9.
Robertson S, Thomson AL, Carter R, Stott HR, Shaw CA, Hadoke PWF, et al. 2014.
Pulmonary diesel particulate increases susceptibility to myocardial ischemia/
reperfusion injury via activation of sensory TRPV1 and b1 adrenoreceptors. Part
Fibre Toxicol 11:12, PMID: 24568236,https://doi.org/10.1186/1743-8977-11-12.
Rushton EK, Jiang J, Leonard SS, Eberly S, Castranova V, Biswas P, et al. 2010.
Concept of assessing nanoparticle hazards considering nanoparticle dosemet-
ric and chemical/biological response metrics. J Toxicol Environ Health A
73(5):445–461, PMID: 2015558,https://doi.org/10.1080/15287390903489422.
Saber AT, Jacobsen NR, Jackson P, Poulsen SS, Kyjovska ZO, Halappanavar S,
et al. 2014. Particle-induced pulmonary acute phase response may be the
causal link between particle inhalation and cardiovascular disease. Wiley
Interdiscip Rev Nanomed Nanobiotechnol 6(6):517–531, PMID: 24920450,
Saber AT, Lamson JS, Jacobsen NR, Ravn-Haren G, Hougaard KS, Nyendi AN,
et al. 2013. Particle-induced pulmonary acute phase response correlates with
neutrophil influx linking inhaled particles and cardiovascular risk. PloS One
8(7):e69020., PMID: 23894396,https://doi.org/10.1371/journal.pone.0069020.
Sanfins E, Dairou J, Hussain S, Busi F, Chaffotte AF, Rodrigues-Lima F, et al. 2011.
Carbon black nanoparticles impair acetylation of aromatic amine carcinogens
through inactivation of arylamine N-acetyltransferase enzymes. ACS Nano
5(6):4504–4511, PMID: 21526848,https://doi.org/10.1021/nn103534d.
Sargent LM, Hubbs AF, Young SH, Kashon ML, Dinu CZ, Salisbury JL, et al. 2012.
Single-walled carbon nanotube-induced mitotic disruption. Mutat Res 745(1-
2):28–37, PMID: 22178868,https://doi.org/10.1016/j.mrgentox.2011.11.017.
SCENIHR (Scientific Committee on Emerging and Newly Identified Health). 2005.
Opinion on the appropriateness of existing methodologies to assess the
potential risks associated with engineered and adventitious products of
nanotechnologies. Brussels, Belgium:European Commission. http://ec.europa.
eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_003.pdf [accessed 12
SCENIHR working group. 2007. The appropriateness of the risk assessment
methodology in accordance with the technical guidance documents for new and
existing substances for assessing the risks of nanomaterials. Brussels, Belgium:
European Commission. http://ec.europa.eu/health/archive/ph_risk/committees/
Schäffler M, Sousa F, Wenk A, Sitia L, Hirn S, Schleh C, et al. 2014. Blood protein
coating of gold nanoparticles as potential tool for organ targeting. Biomaterials
35(10):3455–3466, PMID: 24461938,https://doi.org/10.1016/j.biomaterials.2013.12.100.
Schins RP, Knaapen AM. 2007. Genotoxicity of poorly soluble particles. Inhal Toxicol
19(Suppl 1):189–198, PMID: 17886067,https://doi.org/10.1080/08958370701496202.
Schins RP, Lightbody JH, Borm PJ, Shi T, Donaldson K, Stone V. 2004.
Inflammatory effects of coarse and fine particulate matter in relation to chemi-
cal and biological constituents. Toxicol Appl Pharmacol 195(1):1–11, PMID:
Schinwald A, Murphy FA, Prina-Mello A, Poland CA, Byrne F, Movia D, et al. 2012.
The threshold length for fiber-induced acute pleural inflammation: Shedding
light on the early events in asbestos-induced mesothelioma. Toxicol Sci
128(2):461–470, PMID: 22584686,https://doi.org/10.1093/toxsci/kfs171.
Schleh C, Kreyling WG, Lehr CM. 2013. Pulmonary surfactant is indispensable in
order to simulate the in vivo situation. Part Fibre Toxicol 10:6, PMID: 23531298,
Seaton A, MacNee W, Donaldson K, Godden D. 1995. Particulate air pollution and
acute health effects. Lancet 345(8943):176–178, PMID: 7741860.
Semmler M, Seitz J, Erbe F, Mayer P, Heyder J, Oberdörster G, et al. 2004. Long-
term clearance kinetics of inhaled ultrafine insoluble iridium particles from the
rat lung, including transient translocation into secondary organs. Inhal Toxicol
16(6-7):453–459, PMID: 15204761,https://doi.org/10.1080/08958370490439650.
Semmler-Behnke M, Lipka J, Wenk A, Hirn S, Schäffler M, Tian F, et al. 2014. Size
dependent translocation and fetal accumulation of gold nanoparticles from
maternal blood in the rat. Part Fibre Toxicol 11:33, PMID: 25928666,
Semmler-Behnke M, Takenaka S, Fertsch S, Wenk A, Seitz J, Mayer P, et al. 2007.
Efficient elimination of inhaled nanoparticles from the alveolar region: Evidence for
interstitial uptake and subsequent reentrainment onto airways epithelium. Environ
Health Perspect 115(5):728–733, PMID: 17520060,https://doi.org/10.1289/ehp.9685.
Shvedova AA, Yanamala N, Kisin ER, Khailullin TO, Birch ME, Fatkhutdinova LM, Li
X. 2016. Integrated analysis of dysregulated ncrna and mrna expression pro-
files in humans exposed to carbon nanotubes. PloS One 11(3):e0150628, PMID:
Siegrist KJ, Reynolds SH, Kashon ML, Lowry DT, Dong C, Hubbs AF, et al. 2014.
Genotoxicity of multi-walled carbon nanotubes at occupationally relevant doses.
Part Fibre Toxicol 11:6, PMID: 24479647,https://doi.org/10.1186/1743-8977-11-6.
Smulders S, Golanski L, Smolders E, Vanoirbeek J, Hoet PHM. 2015. Nano-TiO
ulates the dermal sensitization potency of dinitrochlorobenzene after topical
exposure. Br J Dermatol 172(2):392–399, https://doi.org/10.1111/bjd.13295.
Stieb DM, Chen L, Eshoul M, Judek S. 2012. Ambient air pollution, birth weight and
preterm birth: A systematic review and meta-analysis. Environ Res 117:100–
111, PMID: 22726801,https://doi.org/10.1016/j.envres.2012.05.007.
Stinn W, Teredesai A, Anskeit E, Rustemeier K, Schepers G, Schnell P, et al. 2005.
Chronic nose-only inhalation study in rats, comparing room-aged sidestream
cigarette smoke and diesel engine exhaust. Inhal Toxicol 17(11):549–576,
Stone V, Brown DM, Watt N, Wilson M, Donaldson K, Ritchie H, et al. 2000a.
Ultrafine particle-mediated activation of macrophages: intracellular calcium
Environmental Health Perspectives 106002-16
signaling and oxidative stress. Inhal Toxicol 12:345–351, PMID: 26368634,
Stone V, Johnston H, Clift MJD. 2007. Air pollution, ultrafine and nanoparticle toxi-
cology: Cellular and molecular interactions. IEEE Trans Nanobioscience
6(4):331–340, PMID: 18217626,https://doi.org/10.1109/TNB.2007.909005.
Stone KC, Mercer RR, Freeman BA, Chang LY, Crapo JD. 1992. Distribution of lung
cell numbers and volumes between alveolar and nonalveolar tissue. Am Rev
Respir Dis 146(2):454–456, PMID: 1489139,https://doi.org/10.1164/ajrccm/146.2.454.
Stone V, Shaw J, Brown DM, MacNee W, Faux SP, Donaldson K. 1998. The role of
oxidative stress in the prolonged inhibitory effect of ultrafine carbon black on
epithelial cell function. Toxicol In Vitro 12(6):649–659, PMID: 20654455.
Stone V, Tuinman M, Vamvakopoulos JE, Shaw J, Brown D, Petterson S, et al.
2000b. Increased calcium influx in a monocytic cell line on exposure to ultra-
fine carbon black. Eur Respir J 15(2):297–303, PMID: 10706495.
Suglia SF, Gryparis A, Wright RO, Schwartz J, Wright RJ. 2008. Association of
black carbon with cognition among children in a prospective birth cohort
study. American Journal of Epidemiology 167(3):280–286, PMID: 18006900,
Sun Y, Song X, Han Y, Ji Y, Gao S, Shang Y, et al. 2015. Size-fractioned ultrafine
particles and black carbon associated with autonomic dysfunction in subjects
with diabetes or impaired glucose tolerance in Shanghai, China. Part Fibre
Toxicol 12:8, PMID: 25884677,https://doi.org/10.1186/s12989-015-0084-6.
Tantra R, Bouwmeester H, Bolea E, Rey-Castro C, David CA, Dogne JM, et al. 2016.
Suitability of analytical methods to measure solubility for the purpose of nano-
regulation. Nanotoxicology 10(2):173–184, PMID: 26001188,https://doi.org/10.
Teeguarden JG, Hinderliter PM, Orr G, Thrall BD, Pounds JG. 2007. Particokinetics
in vitro: Dosimetry considerations for in vitro nanoparticle toxicity assess-
ments. Toxicol Sci 95(2):300–312, PMID: 17098817,https://doi.org/10.1093/
The Royal Society and The Royal Academy of Engineering. 2004. Nanoscience
and nanotechnologies: opportunities and uncertainties. London, UK: The
Royal Society. https://royalsociety.org//media/Royal_Society_Content/policy/
publications/2004/9693.pdf [accessed 12 November 2016].
Thomassen LCJ, Rabolli V, Masschaele K, Alberto G, Tomatis M, Ghiazza M, et al.
2011. Model system to study the influence of aggregation on the hemolytic
potential of silica nanoparticles. Chem Res Toxicol 24(11):1869–1875, PMID:
Todea AM, Beckmann S, Kaminski H, Asbach C. 2015. Accuracy of electrical aero-
sol sensors measuring lung deposited surface area concentrations. J Aerosol
Sci 89:96–109, https://doi.org/10.1016/j.jaerosci.2015.07.003.
Totlandsdal AI, Låg M, Lilleaas E, Cassee F, Schwarze P. 2015. Differential proinflam-
matory responses induced by diesel exhaust particles with contrasting PAH and
metal content. Environ Toxicol 30(2):188–196, PMID: 23900936,https://doi.org/10.
Unfried K, Albrecht C, Klotz LO, von Mikecz A, Grether-Beck S, Schins RPF. 2007.
Cellular responses to nanoparticles: target structures and mechanisms.
Nanotoxicology 1(1):52–71, https://doi.org/10.1080/00222930701314932.
Valberg PA, Crouch EAC. 1999. Meta-analysis of rat lung tumors from lifetime inha-
lation of diesel exhaust. Environ Health Perspect 107(9):693–699, PMID:
Valle RP, Wu T, Zuo YY. 2015. Biophysical influence of airborne carbon nanomateri-
als on natural pulmonary surfactant. ACS Nano 9(5):5413–5421, PMID:
van Rossem L, Rifas-Shiman SL, Melly SJ, Kloog I, Luttmann-Gibson H, Zanobetti
A, et al. 2015. Prenatal air pollution exposure and newborn blood pressure.
Environ Health Perspect 123(4):353–359, PMID: 25625652,https://doi.org/10.
Veras MM, Damaceno-Rodrigues NR, Caldini EG, Maciel Ribeiro AAC, Mayhew
TM, Saldiva PHN, et al. 2008. Particulate urban air pollution affects the func-
tional morphology of mouse placenta. Biology of Reproduction 79(3):578–584,
Vinzents PS, Møller P, Sørensen M, Knudsen LE, Hertel O, Jensen FP, et al. 2005.
Personal exposure to ultrafine particles and oxidative DNA damage. Environ
Health Perspect 113(11):1485–1490, PMID: 16263500.
Volk HE, Lurmann F, Penfold B, Hertz-Picciotto I, McConnell R. 2013. Traffic-related
air pollution, particulate matter, and autism. JAMA Psychiatry 70(1):71–77,
von Klot S, Peters A, Aalto P, Bellander T, Berglind N, D'Ippoliti D, et al. 2005. Ambient
air pollution is associated with increased risk of hospital cardiac readmissions of
myocardial infarction survivors in five European cities. Circulation 112(20):3073–3079,
Wang F, Yu L, Monopoli MP, Sandin P, Mahon E, Salvati A, et al. 2013. The biomolecular
corona is retained during nanoparticle uptake and protects the cells from the damage
induced by cationic nanoparticles until degraded in the lysosomes. Nanomedicine
9(8):1159–1168, PMID: 23660460,https://doi.org/10.1016/j.nano.2013.04.010.
Weichenthal S. 2012. Selected physiological effects of ultrafine particles in acute cardio-
vascular morbidity. Environ Res 115:26–36, PMID: 22465230,https://doi.org/10.1016/j.
Wilson MR, Lightbody JH, Donaldson K, Sales J, Stone V. 2002. Interactions
between ultrafine particles and transition metals in vivo and in vitro. Toxicol
Appl Pharmacol 184(3):172–179, PMID: 12460745.
WHO (World Health Organization). 2011. World Health Statistics 2011. Geneva,
Switzerland:World Health Organization.
WHO. 2014. World Health Statistics 2014. Geneva, Switzerland:World Health Organization.
WHO. 2016. Global Air Quality Guidelines: Ambient (outdoor) air quality and health.
http://www.who.int/mediacentre/factsheets/fs313/en [accessed 12 November
Wörle-Knirsch JM, Pulskamp K, Krug HF. 2006. Oops they did it again! Carbon
nanotubes hoax scientists in viability assays. Nano Lett 6(6):1261–1268, PMID:
Xin L, Wang J, Wu Y, Guo S, Tong J. 2015. Increased oxidative stress and
activated heat shock proteins in human cell lines by silver nanoparticles.
Hum Exp Toxicol 34(3):315–323, PMID: 24980441,https://doi.org/10.1177/
Xu Y, Barregard L, Nielsen J, Gudmundsson A, Wierzbicka A, Axmon A, et al. 2013.
Effects of diesel exposure on lung function and inflammation biomarkers
from airway and peripheral blood of healthy volunteers in a chamber
study. Part Fibre Toxicol 10:60, PMID: 24321138,https://doi.org/10.1186/
Yamamoto M, Singh A, Sava F, Pui M, Tebbutt SJ, Carlsten C. 2013. MicroRNA expres-
sion in response to controlled exposure to diesel exhaust: Attenuation by the anti-
oxidant N-acetylcysteine in a randomized crossover study. Environ Health
Perspect 121(6):670–675, PMID: 23584289,https://doi.org/10.1289/ehp.1205963.
Zhang H, Ji Z, Xia T, Meng H, Low-Kam C, Liu R, et al. 2012. Use of metal oxide
nanoparticle band gap to develop a predictive paradigm for oxidative stress
and acute pulmonary inflammation. ACS Nano 6(5):4349–4368, PMID: 22502734,
Environmental Health Perspectives 106002-17