Environmental Engineering Reference
In-Depth Information
PM
2.5
mass concentrations. In addition to EC, these components include Ni, V, and Pb, and suggestive
evidence exists for other components, such as Al, Zn, and OC. There is also a rapidly growing literature
implicating motor-vehicle-related pollution in human health effects, as indexed by proximity to major
roadways, and by measured concentrations of OC, NO
2
, and UFP. However, there are also metals
in motor vehicle exhaust and resuspended road dust whose role, if any, in causing trafic-related
human health effects at contemporary ambient air concentrations is largely unknown. There is some
evidence that the metals in resuspended road dust may be important. Recent research has suggested
that trafic-generated PM can account for pulmonary effects, with Gent et al. (2009) showing that
the motor vehicle source was associated with a 10%/5 μg
3
increase in wheeze in asthmatic children,
while the road dust source was associated with a 28% increase in shortness of breath. This response is
consistent with the indings reported by Gottipulo et al. (2008) based on the instillation of two kinds
of tire dust into the lungs of male WKY rats in relation to the elemental composition. There were
increases in BALF markers of inlammation and injury, and similar effects were seen for instilled Zn
and Cu. Thus, the acute pulmonary effects of tire dust could be due to the metals.
Furthermore, there is some evidence that adverse health effects are signiicantly associated with
aerosol acidity originating from fossil fuel combustion, which could be due to its irritancy, or to its
role in solubilizing metals within the particles.
14.4.2 a
re
t
Here
s
PeciFic
s
ources
oF
M
etals
t
Hat
c
an
a
ccount
,
at
l
east
in
P
art
,
For
H
ealtH
e
FFects
a
ssociated
witH
PM
2.5
?
It is known that ROFA, which is a mixture that is presumed to be similar in composition to the ly
ash emitted by power plants burning residual oil, and which is notably high in the content of Ni
and V, as compared to other metals, and Utah Valley dust, which is a mixture enriched in steel mill
emissions, were more toxic than other source-related mixtures that have been tested in laboratory
animals
in vivo
, or in cells
in vitro
. For acute pulmonary system responses, it appears, from such
tests, that V and Zn may play prominent roles, and that the effects may depend on interactions
among the metals. For acute cardiovascular effects, Ni appears to play a more important role. By
contrast, other source-related mixtures, such as coal combustion efluents, that are notable for their
content of Se, Fe, and Mn, and resuspended soil that contains more refractory metals, have been
found to be less acutely toxic.
Janssen et al. (2002) modeled source contributions to ambient air PM using emissions data.
Cardiovascular admissions were signiicantly associated with a number of sources (highway vehi-
cles, oil combustion, and metal processing), but there were no signiicant associations of the sources
with COPD or pneumonia admissions.
In summary, toxic metals from power plants, and possibly from resuspended road dust, are
worthy of increased concern.
14.4.3 a
ddressing
r
esearcH
n
eeds
r
elating
to
H
ealtH
e
FFects
oF
c
oMPonents
in
a
Mbient
a
ir
P
articulate
M
atter
There are many reasons why past research has not resolved the roles that PM components may play
in the health-related effects of ambient air PM. These are as follows: (1) concentrations of compo-
nents in ambient air PM generally range from a few μg/m
3
in some refractory metals to less than
10 ng/m
3
for transition metals that are known to generate ROS, raising the issue of biological plausi-
bility; (2) epidemiologic research opportunities have been limited because of the paucity of data on
the concentrations of PM components—even now, when PM
2.5
speciation data have been available
since 2000 for many U.S. cities, they are mostly limited to every third or sixth day; (3) few toxicolo-
gists or clinical researchers have had the resources needed to perform subchronic CAPs inhalation
studies that include speciation data on the PM in the exposure samples; (4) controlled exposures to
pure compounds at concentrations of environmental relevance have been uniformly negative, even
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