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CLEAN AIR RESEARCH
PROGRAM
AIR POLLUTION RESEARCH ADDRESSES RELATIVE
TOXICITY OF DIFFERENT PARTICLE SIZES
Issue:
Outdoor air pollution particles are
currently divided into three
classes based on their size:
• Coarse particulate matter (PM)
consists of particles with a
diameter between 2.5 and 10
micrometers (|im) and deposit
efficiently along the airways.
Particles larger than 10 jam are
generally not inhalable into the
lungs.
• Fine PM consists of particles
with a diameter less than 2.5
Jim and can be inhaled deeply
into the lungs.
• Ultrafme particles, the smallest,
consist of particles with a
diameter smaller than 0.1 jim
and have widespread deposition
within the respiratory tract.
It is not well understood whether
particles with different size
ranges have different abilities to
cause adverse health effects.
The U.S. Environmental
Protection Agency currently
regulates PM on the basis of mass
in both the fine and coarse size
ranges. More than 150
epidemiology studies have
demonstrated an association
between fine PM and acute
mortality and morbidity.
A smaller number of studies have
linked exposure to coarse PM
with increased mortality and
morbidity. However, uncertainty
about the effects of coarse PM
derived from different sources has
led EPA to ask for science to
address the question of
differential toxicity from coarse
PM of urban areas versus PM of
rural areas. There is also concern
that because of the high
concentration of biological
compounds present in coarse PM,
compared with smaller size
fractions, asthmatics may be a
particularly susceptible
subpopulation to coarse particles.
In addition, there is concern that
there may be adverse health
effects associated with exposure
to ultrafine particles, which, if
established, could potentially lead
EPA to propose a a PM standard
for these smaller particles.
Because of these uncertainties,
regulators and scientists both
believe there is more to learn
about the adverse health effects of
different sized PM, especially as
the composition of these particles
varies.
Scientific Objective:
The Clean Air Research Program
in EPA's Office of Research and
Development is conducting a
comprehensive and integrated
research program to compare the
cardiovascular and pulmonary
responses of humans or
appropriate animal models to
different sizes of PM. Both EPA
continued on back
U.S. Environmental Protection Agency
Office of Research and Development
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CLEAN AIR RESEARCH PROGRAM
continued from front
scientists as well as academic
researchers funded by the Agency
are engaged in these studies.
The research program includes
studies which:
• Compare the cardiovascular
and pulmonary response of
healthy human volunteers or
animal models exposed to
coarse, fine, and ultrafme
particles.
• Determine if people with pre-
existing cardiovascular or
pulmonary disease such as
asthma are especially
susceptible to one or all of the
particle sizes.
• Compare the cardiovascular
and pulmonary response to
coarse PM originating from
urban and rural areas.
• Identify the underlying cellular
and molecular mechanisms by
which each size fraction causes
adverse health effects.
• Characterize the relative
toxicities of coarse, fine, and
ultrafme PM from several
different geographical areas
that have different sources of
PM pollution. The chemical
composition of these size
ranges can simultaneously be
associated with the health
outcomes.
• Characterize the relative
toxi city of different particle
sizes from real world sources,
notably near highly trafficked
roadways.
• Conduct epidemiological field
studies to assess size related
health impacts on selected
populations of high risk.
especially near roadways.
Application and Impact:
Research to expand our
knowledge about the health
effects associated with exposure
to different size particles will
provide important information
that will allow EPA to set PM
standards which are optimally
protective of human health.
The research will help EPA
regulators:
• Determine if it is appropriate to
regulate particles based on the
number of particles rather than
size.
• Assess whether ultrafme
particles should be regulated.
Assist with making decisions
on where to position air quality
monitors to obtain the data that
best represents human health
risks.
REFERENCES
Gilmour, MI, et al. Comparative Toxicity of Size
Fractionated Airborne Particulate Matter Obtained
from Different Cities in the USA. Inhalation
Toxicology, 2007; 1:7-16.
Graff, DW, et al. Assessing the Role of Particulate
Matter Size and Composition on Gene Expression
in Pulmonary Cells. Inhalation Toxicology, 2007;
1:23-8.
Samet, JM, et al. A Comparison of Studies on the
Effects of Controlled Exposure to Fine, Coarse and
Ultrafme Ambient Particulate Matter from a Single
Location. Inhalation Toxicology, 2007; 1:29-32.
Frampton M.W., et al. Inhalation of Ultrafine
Particles alters Blood Leukocyte Expression of
Adhesion Molecules in Humans. Environmental
Health Perspectives, 2006; 114(1): 51-58.
Peng R.D., et al. Coarse particulate matter air
pollution and hospital admissions for
cardiovascular and respiratory diseases among
Medicare patients. Journal of the American
Medical Association, 2008; 299(18): 2172-9.
CONTACTS
Robert Devlin, Ph.D., National Health and
Environmental Effects Research Laboratory,
EPA's Office of Research and Development, 919-
966-6255, devlin.robert@epa.gov
M. Ian Gilmour, Ph.D., National Health and
Environmental Effects Research Laboratory, 919-
541-0015, gilmour.ian@epa.gov
JANUARY 2009
U.S. Environmental Protection Agency
Office of Research and Development
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