&EPA
science in ACTION
www.epa.gov/airscience
CLEAN AIR
PROGRAM
RESEARCH
HAZARDOUS AIR POLLUTANT RESEARCH IMPROVES
RISK ASSESSMENT CAPABILITIES
Issue:
The Clean Air Act identifies 188
chemicals or chemical classes as
hazardous air pollutants, or air
toxics. These chemicals may
cause cancer or other serious
adverse health effects such as
birth defects, reproductive
problems, and impaired
neurological function if exposure
levels are sufficiently high.
In addition to widespread
pollutants such as ozone, the U.S.
Environmental Protection Agency
also regulates air toxics by
requiring industries to use control
technology to limit their release
into the atmosphere. As part of
this effort, EPA assesses the risk
of any residual emissions that
might still be released from these
facilities to determine if they pose
any danger to human health and
the environment.
Science is needed to improve our
understanding of health risks
associated with exposure to
hazardous air pollutants. To this
end, researchers are working to
learn more about how we are
exposed to these pollutants and
what the potential health effects
may be.
Scientific Objective:
The Clean Air Research Program
in EPA's Office of Research and
Development is taking a multi-
pronged and integrated approach
to studying hazardous air
pollutants. Exposure research is
under way to better understand
the impact of industrial and
mobile sources on hazardous air
pollutant emissions, their
distribution in the environment
and actual human exposures,
primarily in urban areas.
At the same time, health effects
research is focused on developing
quantitative models to estimate
the health risks from varied
exposure scenarios.
Key scientific questions being
addressed include:
• What are the relationships
between sources of pollutants,
outside air concentrations and
human exposures of air toxics?
• What are the appropriate
measures of internal dose that
predict acute and chronic
effects of exposure?
• What are the effects of
hazardous air pollutants at low
doses?
• What is the relationship
between acute and chronic
(long-term) toxicity?
• Which chemicals have similar
modes of action so that they
might be regulated together?
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U.S. Environmental Protection Agency
Office of Research and Development
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&EPA
www.epa.gov/airscience
science in ACTION
CLEAN AIR RESEARCH PROGRAM
continued from front
• How is exposure to a hazardous
air pollutant directly linked to
adverse health effects?
Exposure-dose-response models
under development will provide
new insights into how we may be
exposed to hazardous air
pollutants, how they are absorbed
and distributed in our bodies and
what the health effects may be
from a particular exposure. These
quantitative models hold the
promise of providing more
accurate risk estimates over a
variety of exposure conditions.
They will also enable better risk
estimates of compounds for
which relatively little is known if
those compounds can be
compared to other well studied
substances.
Studies have been conducted to
understand how we are exposed
to hazardous air pollutants.
Analyses of the Detroit Exposure
and Aerosol Research Study data
is offering information on the
relationships between air toxics
measured at community
monitoring sites and actual
human exposures. The research
has enabled scientists to predict
outdoor air toxic exposures in
urban areas elsewhere to support
research examining the link
between exposure and health
effects. Another study is
examining emission and
dispersion of air toxics near
roadways.
Application and Impact:
Exposure and health studies of
hazardous air pollutants have
advanced our ability to conduct
risk assessments to protect public
health and provide basic
information to better measure,
model, and estimate exposure of
pollution in communities.
Specifically, the science has been
used by EPA to:
• Establish policies for acute risk
assessments based on target-
tissue concentrations;
• Set emission control standards
for off-road recreational
vehicles
• Evaluate approaches to
modeling exposure.
REFERENCES
EPA's Air Toxics Web site:
http://www.epa.gov/ttn/atw/allabout.html
Benignus V.A., Bushnell P. J. and Boyes W. K.
Acute behavioral effects of exposure to toluene
and carbon monoxide from snowmobile exhaust.
Docket A-2000-01, Document IV-A-143. In
support of Final Regulatory Support Document:
Control of Emissions from Unregulated Nonroad
Engines. Assessment and Standards Division,
Office of Transportation and Air Quality, U.S.
Environmental Protection Agency. EPA420-R-02-
022. September 2002.
http://www.epa.gov/otaq/regs/nonroad/2002/r0202
2.pdf
Boyes, W.K., Evans, M.V., Eklund, C., Janssen P.,
and Simmons, J.E. Duration adjustment of acute
exposure guideline level values for
trichloroethylene using a physiologically based
pharmacokinetic model. Risk Analysis, 25 (3),
677-686, 2005.
Hutzell, W. and Luecken, D. Fate and transport of
emissions for several trace metals over the United
States. Science of the Total Environment, 396(2-
3): 164-179. (2008).
Luecken, D.J. and Cirnorell, A.J. Codependencies
of reactive air toxic and criteria pollutants on
emission reductions. JOURNAL OF THE AIR &
WASTE MANAGEMENT ASSOCIATION. Air
& Waste Management Association, Pittsburgh,
PA, 58(5): 693-701. (2008).
CONTACT
William K. Boyes, Ph.D, National Health and
Environmental Effects Research Laboratory,
EPA's Office of Research and Development, 919-
541-7538, boyes.william@epa.gov.
Alan Vette, Ph.D., National Exposure Research
Laboratory, EPA's Office of Research and
Development, 919-541-1378, vette.alan(g),epa.gov.
JANUARY 2009
U.S. Environmental Protection Agency
Office of Research and Development
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