Environmental Health Perspectives Volume
103, Supplement 6, September 1995
[Citation
in PubMed]
Air Toxics and Asthma: Impacts and End Points
William L. Eschenbacher, Andrij Holian, and Raymond J. Campion
Mickey Leland National Urban Air Toxics Research Center, Houston, Texas
Abstract
The National Urban Air Toxics Research Center (NUATRC) hosted a medical/scientific
workshop focused on possible asthma/air toxics relationships, with the results
of the NUATRC's first research contract with the University of Cincinnati
as the point of discussion. The workshop was held at the Texas Medical Center
on 4 February 1994 and featured presentations by distinguished academic,
government, and industry scientists. This one-day session explored the impact
of various environmental factors, including air toxics, on asthma incidence
and exacerbation; an emphasis was placed on future research directions to
be pursued in the asthma/air toxics area. A key research presentation on
the association of air toxics and asthma, based on the study sponsored by
NUATRC, was given by Dr. George Leikauf of the University of Cincinnati
Medical Center. Additional presentations were made by H. A. Boushey, Jr.,
Cardiovascular Research Institute/University of California at San Francisco,
who spoke on of the Basic Mechanisms of Asthma; K. Sexton, U.S. Environmental
Protection Agency, who spoke on hazardous air pollutants: science/policy
interface; and D. V. Bates, Department of Health Care and Epidemiology at
the University of British Columbia, who spoke on asthma epidemiology. H.
Koren, U.S. Environmental Protection Agency, and M. Yeung, of the Respiratory
Division/University of British Columbia, Vancouver General Hospital, discussed
occupational health impacts on asthma. Doyle Pendleton, Texas Natural Resource
Conservation Commission, reviewed air quality measurements in Texas. The
information presented at the workshop suggested a possible association of
asthma exacerbations with ozone and particulate matter (PM10);
however, direct relationships between worsening asthma and air toxic ambient
levels were not established. Possible respiratory health effects associated
with air toxics will require considerably more investigation, especially
in the area of human exposure assessment. Two major recommendations for
future research resulted from this workshop and an accompanying NUATRC Scientific
Advisory Panel meeting: a need for more complete individual personal exposure
assessments so that accurate determinations of actual personal exposures
to various pollutants can be made; and a need for field experiments
utilizing biomarkers of exposure and effect to more accurately assess the
extent and variability of the biological effects, if any, of individual
air toxics. -- Environ Health Perspect 103(Suppl 6):209-211 (1995)
Key words: asthma, air pollution, respiratory disease, air toxics
This paper was presented at the Workshop on Air Toxics
and Asthma-Impacts and End Points held 4 February 1994 in Houston, Texas.
Manuscript received: January 17, 1995; accepted February 3, 1995.
Address correspondence to Dr. Raymond J. Campion, Mickey
Leland National Urban Air Toxics Research Center, P.O. Box 20286, Houston,
TX 77225-0286. Telephone (713) 792-7459. Fax (713) 792-4407.
Introduction
The Mickey Leland National Urban Air Toxics Research Center (NUATRC)
was established by the Clean Air Act Amendments of 1990 expressly to carry
out research in the environmental health science disciplines on possible
health risks posed by ambient levels of air toxics in urban atmospheres.
The NUATRC, with a board of directors appointed by the President, the Speaker
of the House of Representatives, the Senate Majority Leader, and a nationally
renowned scientific advisory panel, is a public/private research institution
funded by the federal government through the U.S. Environmental Protection
Agency (U.S. EPA) and by private corporations and foundations. It is charged
with carrying out sound, peer-reviewed research to assess the residual risk
to public health from existing levels of the 189 statutorially defined
toxic air pollutants.
Asthma is a serious respiratory disease that is increasing in incidence
and prevalence both in this country and around the world (1,2). It
is affecting nonwhite populations at higher rates than white populations
and seems to be more prominent in urban populations (3,4). The reasons
for these trends are not known, but it has been suggested that environmental
factors, specifically exposure to certain pollutants, are contributors
to these increases (5-8). It was the intent of NUATRC to bring together
experts in the field of air pollution and asthma to address these issues
and provide the scientific community with background information regarding
asthma and air pollution. These experts were also to provide directions
for future research in this area.
The workshop included several presentations to address:
- the approach to regulatory control of pollutants (such as air toxics);
- the techniques for collecting and analyzing pollutant emissions and
exposure data;
- background information regarding the pathophysiology of asthma, especially
the inflammatory aspects of the disease;
- the current knowledge of associations between asthma and the National
Ambient Air Quality Standards (NAAQS);
- the epidemiologic information regarding associations between air toxics
and asthma;
- the relevance of using occupational asthma as a model for more naturally
occurring asthma that might be caused or worsened by environmental exposure;
and
- future approaches to examine the known relationships between air toxics
and the development or worsening of asthma.
The asthma work was particularly relevant to NUATRC's charge since noncancer
environmental disease end points such as asthma have not been receiving
the bulk of environmental health research resources. The increasing asthma
incidences seemed to be focused in urban and minority communities, which
is consistent with growing public interest in environmental equity.
Presentations
K. Sexton of the U.S. EPA discussed the roles that scientists and policy
makers have in the decision-making process for setting priorities and developing
regulations regarding exposure to and health effects from pollutants such
as air toxics. He explained that there are many circumstances when decisions
have to be made regarding limits of exposure to particular substances, with
little scientific information to support those decisions. He emphasized
the need for continued data collection regarding air toxics, with information
needed on emissions, ambient exposures and both cancer and noncancer health
end points such as asthma. He also suggested that research should be narrowly
focused and directed toward the type of data needed for statutory requirements.
D. Pendleton of the Texas Natural Resource Conservation Commission described
current technology for monitoring ambient pollutant concentrations including
air toxics and presented information on recent trends concerning these concentrations
in different regions of Texas. He also described interactions between the
Texas Natural Resource Conservation Commission and the U.S. EPA as they
affect future directions in data collection for source emissions and human
exposures to air pollutants such as the
air toxics.
H. Boushey of the University of California, San Francisco, discussed
what is currently known about the underlying pathophysiology of asthma.
He described the hypotheses that environmental exposures (allergens, viruses,
pollutants, etc.) may all play roles in the development and worsening of
this disease. He provided recent evidence for the role of the immune system
and cell-derived mediators in the development of the airway inflammation
that is now considered the hallmark of asthma. He emphasized that in order
to study the causative factors that can contribute to the development of
asthma, we should recognize that we are dealing with multifactorial exposures
and that these cofactors (e.g., environmental tobacco smoke) should be included
in our assessment.
H. Koren of the Health Effects Research Laboratory of the U.S. EPA described
current information on the association between NAAQS, pollutants, and asthma.
The body of scientific data suggests that ozone and sulfur dioxide
can cause or worsen asthma. However, epidemiologic data to support these
conclusions are limited and most of the positive data come from controlled
chamber exposure studies. He suggested that controlled human clinical studies
should be performed with air toxics to evaluate the physiologic, biochemical,
and cellular responses to these agents.
D. Bates of the University of British Columbia in Vancouver described
the epidemiologic evidence that currently exists suggesting associations
between environmental exposure to pollutants and asthma. As did H. Boushey,
he emphasized that we are dealing with multifactorial exposures to a variety
of substances, and the interplay between these substances may be as important
as the impact of the individual substances themselves. He encouraged the
implementation of further epidemiologic studies using objective measures
of lung function and biomarkers of exposure and effect to address associations
of pollutants and asthma. He especially emphasized the need for personal
exposure data to help in these studies.
M. Yeung, also from the University of British Columbia in Vancouver,
presented what is currently known about occupational asthma and also described
a model based upon occupational asthma that could be used to explain the
development of asthma outside the workplace. This approach could be promising
in that several interactive factors can be examined to determine the relative
contribution of each factor to the development of the disease. These factors
include both intrinsic or host elements (allergic nature, smoking history,
etc.) and extrinsic factors (pollutant exposures, viral illnesses, antigen
exposures, etc.). Cohorts of individuals can be extensively characterized
and then followed in different environmental settings to determine development
or worsening of airways disease.
G. Leikauf of the University of Cincinnati provided a rationale for a
list of 30 air toxics that potentially could contribute to the development
or worsening of asthma. His approach involved an initial determination of
the presence of the air toxic in the environment and then the development
of an hypothesis that classes of chemicals could be either asthmogenic or
irritants based upon their chemical properties and known ability to sensitize.
Using this list of air toxics, he suggested that development of exposure
and epidemiological studies to better understand the relationship between
these substances and asthma and the interaction between these substances
and other environmental factors in causing and worsening asthma were immediate
needs.
In response to G. Leikauf's presentation, B. Goldstein of the University
of Medicine and Dentistry of New Jersey pointed out that of the various
potential sources of exposure to air pollutants air toxics in the outdoor
environment may have the least impact upon the development of lung disease.
He suggested that indoor pollutants, followed by the NAAQS pollutants, may
play a greater role in the development of lung disease such as asthma. He
also emphasized (as did many of the previous speakers) the importance of
examining mixtures of compounds and the interplay between these compounds,
including environmental tobacco smoke, aeroallergens, and chemicals.
In summary, the workshop provided valuable and current information regarding
the pathophysiology of asthma and the possible role of criteria pollutants
and air toxics in causing or worsening asthma. With regard to air toxics,
it appears that little is known about their potential contribution to the
development or worsening of the disease. It was the recommendation of the
workshop that the following research directions be pursued:
- Exposure assessment studies should be conducted to more accurately
characterize the actual individual exposures to air toxics, including the
development of more precise ambient air and personal monitoring methodology.
In addition, the relative contribution of indoor and outdoor sources should
be determined.
- Experimental field utilization of biomarkers of exposure and effect
should be initiated for use in exposure assessment and epidemiologic studies.
These studies would be directed to the relationship between personal exposure
to various pollutants and the health effects encountered by the individual.
It appears that some relevant biomarkers have been developed but await
large-scale field testing for determination of their utility.
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