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Executive Summary
This most excellent canopy, the air, look you,
this brave overhanging firmament, this
majestical roof fretted with golden fire--why,
it appears no other thing to me than a foul
and pestilent congregation of vapours.
Hamlet, Act II, Scene 2
INTRODUCTION
This report responds to a request by the Environmental
Protection Agency (EPA) that the National Research Council
consider the scientific feasibility of conducting epidemi-
ologic investigations of the health consequences of
current and future air pollution. In particular, the
Research Council was asked to:
· Identify physiologic changes and adverse human
health consequences (acute and chronic) that might be
associated with air pollutants and that require
additional study.
· Identify existing exposure monitoring methods
that can be used in epidemiologic studies and situations
for which such methods need to be developed or improved
to permit epidemiologic studies to be more useful.
· Determine the types of epidemiologic studies and
research strategies that are needed for assessing health
effects of exposure to air pollutants.
.
Identify populations and exposure conditions that
merit additional epidemiologic study to determine health
effects of air pollution.
To address those and related issues, the Research
Council formed the Committee on the Epidemiology of Air
Pollutants in the Board on Toxicology and Environmental
Health Hazards of the Commission on Life Sciences. The
Committee consists of professionals in a variety of
fields, including epidemiology, toxicology, atmospheric
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science, clinical research, biostatistics, risk
assessment, and economics.
The sub ject of the Committee's report is epidemiology
and its methods as applied to air pollution health
effects. The primary goal of epidemiologic studies of
air pollution is to relate health outcomes in human
populations to quantities and types of contaminants in
the air. During recent years, there have been major
changes in the factors that influence such studies, such
as the magnitude of the effects of exposure relative to
background disease rates, the general magnitude of
exposure to air pollution, and the strength of epidemi-
ologic tools available. This report assesses the limits
of available epidemiologic techniques for studying al r
pollution problems and discusses opportunities for
expanding these limits and for using epidemiologic
studies effectively in an overall program of research on
air pollution.
Outdoor concentrations of many air pollutants--such as
sulfur dioxide, particles, ozone, and lead--over most of
the United States have decreased during the last 20
years. Widespread serious, even lethal, episodes of
acute illness due to ambient air pollution were once
common, but are no longer expected. In general, attendant
health problems are likely to be less numerous and less
severe--and therefore more difficult to detect--than in
the past. However, the current picture also includes
locally high concentrations, changing patterns of
pollutant dispersion (due in part to recent control
measures), and recognition of new pollutants, including
those found indoors. Continued efforts to detect and
describe the health effects of air pollution are needed,
because small or infrequent effects spread over large
populations can have important public health consequences,
because air pollution sometimes acts in synergy with
other agents to cause or exacerbate serious disease, and
because the effects of past control measures are not a,1
well understood.
Epidemiology as a discipline has a special rote in the
formulation and evaluation of preventive strategies. It
can detect hazards in populations under actual exposure
conditions, determine the magnitude of their impact on
public health, and provide direct guidance for interven-
tion. One of the major challenges for future studies is
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to assess exposure, particularly to individual pollutants
or classes of pollutants, with enough precision to permit
quantitative estimation of risk. Such assessments must
take into account indoor as well as outdoor exposure.
Assessment of the health effects themselves poses tech-
nical challenges, because each disease known to be caused
by air pollute on has other causes as well. All the
diseases of concern are believed to be multifactorial,
and in most cases our knowledge regarding pathophysiology
is sparse. Numerous factors other than air pollution can
influence the risk of illness, and these must be accounted
for if causal relationships between air pollution and
disease are to be clearly established. Some new and
better research techniques have been developed, and some
are under development. These advances (and the advantages
of experience) make it likely that future epidemiologic
studies can contribute to further reduction of air-
pollution-related illness.
HEALTH EFFECT S
The Committee finds that evidence from controlled
human exposures, toxicology, and epidemiology is suf-
ficient to warrant concern that current air pollution
still produces substantial adverse health effects in some
segments of the U.S. population. These effects include a
variety of acute and chronic respiratory problems that
have been linked with previous kinds and amounts of
pollution. Acute respiratory effects of concern include
an increase in the frequency of asthmatic attacks,
transient deficits in pulmonary function, and increases
in the frequency of respiratory disease in children and
adults. Future pulmonary research to clarify the basis
for individual variation in response and determine the
relation between acute effects and long-term lung
function will be particularly important in defining new
opportunities for epidemiologic study of air pollution
and acute effects.
Chronic effects that warrant study include chronic
obstructive pulmonary disease (COPD)--a broad term that
encompasses emphysema, bronchitis, and some other
conditions in which there is limitation of airflow in the
lungs--and adverse changes in the rate of growth or
reduction of lung function. Some of these effects in the
U.S. population have been caused by heavy pollution
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exposure over sustained periods in the past; evidence on
possible chronic respiratory effects of current pollution
is sparse, because of methodologic difficulties and a
dearth of recent studies. As gaps in the natural history
of chronic airflow obstruction are filled, some con-
straints in studying the role of air pollution in that
complex syndrome will be relaxed.
The Committee also finds important research questions
about the epidemiology of lung cancer. The contribution
of air pollution to the lung-cancer burden and, in par-
ticular, the interaction of air pollution with cigarette
smoking require further exploration.
Some of the nonrespiratory effects that warrant further
epidemiologic study are the effects of lead on childhood
neurobehavioral development and on blood pressure and the
effects of carbon monoxide on ischemic heart disease.
Possible carcinogenic, mutagenic, or neurotoxic effects
of community exposures to benzene and other volatile
organic substances are also of concern, but full-scale
epidemiologic studies might not yet be feasible except in
selected areas near point sources.
Traditional tools for measuring health effects in
epidemiologic studies of air pollution include routine
collection of morbidity and mortality data, question-
naires, and spirometry. The availability of FEV1 and
other simple, noninvasive measures of pulmonary function
has greatly benefited cross-sectional and longitudinal
epidemiologic studies of respiratory disease. Refinements
and standardization procedures in the use of these older
tools can improve study sensitivity. Some newer tech-
niques in pulmonary function testing, such as airway-
reactivity challenge, expand the range of measurement
capabilities and might provide important opportunities to
study new end points.
Biologic markers in such readily obtained biologic
samples as blood, urine, and sputum can reveal evidence
of exposure or disease in early stages and will find
increasing application in epidemiologic studies of air
pollution effects. These markers will be needed to
provide information on biochemical changes that precede
overt changes in lung function. Such markers could also
identify susceptible persons. The protease-antiprotease
hypothesis in emphysema offers the most promising terrain
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for the development of these new tools. Immunochemical
methods are already capable of detecting extremely small
quantities of connective-tissue breakdown products in
biologic fluids. Current research on the sources of
variation in these measurements and their predictive
value will determine their feasibility for use in
epidemiologic research on air pollution.
EXPOSURE ASSESSMENT
The assessment and measurement of exposure are impor-
tant and difficult aspects of the design and conduct of
epidemiologic studies of air pollution.
meet" refers to a set of multidisciplinary activities that
describes who is exposed to how much of what substances,
for how long, and under what conditions. Whether based
on direct measurements or on modeling, exposure assessment
is a vital part of environmental epidemiology. Air pol-
lutants do not occur independently, but rather as mixtures
of natural, industrial, transportation, and residential
exposures; hence, assessment of exposure to air pollutants
is particularly complex. The Committee considered assess-
ment of exposure relevant to human health and did not
examine exposure relevant to potential environmental
damage.
"Exposure assess-
Most epidemiologic studies of air pollution have
assumed that exposure, however measured, constitutes an
adequate surrogate of the dose of a given pollutant.
Recent advances in toxicology and molecular epidemiology
have emphasized some important distinctions: "exposure"
refers to a concentration of a pollutant measured in the
environment, n internal dose" is the amount of a substance
or its metabolites in body tissues, and "biologically
effective dose" is the amount of a substance that inter-
acts with a particular target tissue or its surrogate.
Information on internal dose and biologically effective
dose is not generally available, but should be developed.
In the interim, epidemiologic studies of air pollution
will continue to rely on outdoor and indoor ambient
exposure data, including data based on personal
monitoring.
Today, air pollution monitoring is a highly developed
field of applied science, with sophisticated analytic
devices for measuring many contaminants, both indoor and
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outdoor. However, advances in measurement technology do
not in themselves provide a valid rationale for a given
study. Many studies that are possible might be
unimportant or of unlikely productivity.
With present knowledge, air pollutants can be divided
into three categories of sources: outdoor, such as
sulfates, ozone, and lead; outdoor and indoor, such as
fine particles, nitrogen oxides, and carbon monoxide; and
indoor, such as volatile organic compounds, radon and its
progeny, formaldehyde, and woodsmoke. In reviewing the
physical, chemical, and biologic characteristics of
pollutants, the Committee noted that some emissions are
"fresh" (from local sources) and some "aged" (from
distant sources). The Committee identified and assessed
some pollutants of concern, including "older" pollutants
(some of which are regulated), such as acid aerosols,
ozone, nitrogen dioxide, carbon monoxide, lead, and radon
and its progeny. Emerging classes of pollutants that
might require epidemiologic and exposure studies include
volatile organic compounds and products of incomplete
combustion.
Documentation of the importance of indoor concentra-
tions of pollutants is profoundly altering air pollution
epidemiology. More than two-thirds of the time of the
average U.S. citizen is spent indoors. Therefore, the
presence of even moderate amounts of pollutants indoors
can influence the classification of a person with regard
to pollutant exposure. A goal of exposure assessment in
epidemiologic studies of air pollution is to minimize the
misclassification of study subjects by exposure magnitude
or type. To this end, further development of integrated
exposure assessment will be vital for air pollution
epidemiology. The Committee recognizes that total
personal exposure to an air pollutant is a conceptually
important measure for epidemiology, in that it provides
the most valid overall predictor of the risk of any
air-pollution-related health effect. Several factors
that can modify personal exposure might also be relevant
in planning exposure assessment for epidemiologic
studies, including activity, respiratory tract physiology,
and weather patterns. Many of the established air pol-
lution monitoring networks were not originally designed
to represent personal exposure or to test explicit
biologic models that considered such factors.
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Future epidemiologic studies of air pollution will
often require selective use of more accurate quantitative
measures of exposure (such as personal monitors) than
have been used in the past, if they are to link exposure
to disease. In particular, the usefulness of central
monitoring station data to represent individual exposure
will be limited. Where the effects studied are common
and the risks of developing an effect are low but impor-
tant, minimizing the misclassification of exposure will
be necessary to increase the chance of finding differences
between groups exposed to different extents. Research is
needed to characterize pollutants and to validate the use
of surrogate measures. Exposure assessment data can be
used during study planning to improve several aspects of
study design, including selection of study populations,
specification of the relevant physical, chemical, or
biologic characteristics of pollutants, and determination
of needed sample size.
CONCEPTS AND STRATEGIES IN PLANNING
EPIDEMIOLOGIC STUDIES ON AIR POLLUTION
Success in protecting the public from very high
exposures to air pollution has fostered a situation in
which both research questions and research strategies to
address them must be more focused and more precise than
in the past, when both exposures and effects were more
apparent. Specification of the details of a research
question--including type of exposure, temporal features,
health effect of concern, population at risk, and known
risk factors aside from air pollution--is a vital part of
study planning.
Several different types of research questions regarding
air pollution can be addressed epidemiologically. Some
pose greater inherent difficulty than others and neces-
sitate more restricted answers. In general, questions
involving dose-response relations at low doses or
thresholds for chronic effects are the most severely
constrained. Advances in these matters will depend
largely on the development of more sensitive tools for
measuring both exposure and effect. Questions that deal
with attributable risk (the proportion of a given effect
in a population that is due to air pollution) are
uniquely appropriate for epidemiology and should play a
larger part in future research.
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The importance of specifying research questions cannot
be overemphasized. Furthermore, to provide credible
estimates of low risks, epidemiologic studies will require
attention at all stages to all potential sources of error;
the Committee discussed a few concepts relevant to
managing potential sources of error, with particular
attention to air pollution studies. Another factor that
has become an integral part of epidemiologic research
planning concerns estimating the cost-effectiveness of
various ways to answer specific questions.
Epidemiologic methods that could be applied to air
pollution questions include descriptive epidemiology or
univariate studies; ecologic studies; cohort studies;
case-control methods, including the nested case-control
method; cross-sectional studies; and intervention studies
Case-control studies are generally quicker and less
expensive than longitudinal studies, but have been used
only infrequently for air pollution effects, partly
because it is difficult to reconstruct past exposures
with adequate precision. Prospective longitudinal
studies based on individual measurements of exposure and
effect are likely to provide the strongest basis for
epidemiologic inference on air pollution, but they might
take years of observation, are generally expensive, and
often require a tradeoff between sample size and duration
of followup. Cross-sectional studies, in which exposure
and effect data are collected concurrently during a
single period, can also be useful for studying air
pollution effects under some circumstances.
Epidemiologists can develop productive studies on air
pollution by taking advantage of several different types
of special (and sometimes transient) situations. Analo-
gous exposures in the workplace, migrant populations,
pristine environments, and highly polluted areas overseas
might provide opportunities to circumvent various
methodologic constraints.
Development of productive epidemiologic strategies in
a difficult field like air pollution research will
require time, organization, and patience. Necessary
characteristics of the milieu for such research include
opportunities for interaction among epidemiologists,
clinicians, and toxicologists; provisions for training
and career development of new scientists; opportunities
for assembling multidisciplinary research groups; stable
8
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administrative and financial support; adequate overall
funding; and an appropriate range of contact with
government personnel.
APPLICATION OF EPIDEMIOLOGY
TO SELECTED RESEARCH QUESTIONS
The Committee uses epidemiologic approaches to selected
questions in air pollution research to illustrate the
points made in its report. Using a framework that con-
siders critical components of study strategy and design,
the Committee addresses questions involving four health
effects of concern: acute respiratory infection, chronic
obstructive pulmonary disease (COPD), asthma, and lung
cancer. The same framework is applied to the study of
five types of pollutants likely to be of continuing con-
cern in the United States: woodsmoke, nitrogen oxides,
persistent ozone and acid aerosols, episodic ozone ana
acid aerosol haze, and radon.
The illustrated approaches use a range of study
methods and several ways of measuring exposure and effect
variables and identifying opportunities for study. For
example, effects of air pollution on upper respiratory
infections
themselves
in children under the age of 2 seem to lend
to relatively straightforward prospective
study; the end point is common, and the exposure history
reasonably reliable, although the researcher needs to be
especially concerned with indoor pollutants. Case-control
studies of specific outcomes, such as acute bronchiolitis
in infants. would not require prohibitively large numbers
of subjects. Study of some acute effects or episodic
exposures--such as asthmatic attacks, exacerbations or
chronic lung disease, and exposure to ozone and acid
aerosol haze--might be approached with small panels of
subjects and individual regression models for each
subject based on the probability of an adverse event on a
given day.
Research to understand air pollution and the origin of
COPD will require great care and ingenuity. The occur-
rence of new cases of COPD is relatively infrequent, so
prospective studies of the role of air pollution in the
etiology of this syndrome would be infeasible, owing to
cost and time considerations. One could instead study
the onset of COPD retrospectively or study the develop-
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ment of early physiologic or biochemical markers that
presage the onset of the complete disease. The latter
strategy is limited at present by gaps in our understand-
ing of the natural history of COPD. All retrospective
methods for studying this subject, however, will suffer
from the lack of reliable, precise data on individual
lifetime exposure to ambient pollutants. Rate of decline
in such lung-function measurements as the FEV1 currently
are the most sensitive relevant markers for COPD; in this
approach, desirable samples for cohorts are smaller than
might be expected, and small samples could be used to
study persistent exposures to such pollutants as ozone
and acid aerosol. Large multicenter case-control studies
and the use of short-term indicators of mutagenic and
carcinogenic effects are feasible, although not neces-
sarily easy, for the study of the relation of air
pollution and lung cancer. An unusually large cohort
like that under study by the American Cancer Society
might also present opportunities for prospective study.
For studying the effects of woodsmoke, ecologic
studies might be especially helpful initially, whereas
indoor monitoring is crucial for studying the effects of
nitrogen dioxide. In some studies of air pollution
effects, it might be useful to eliminate direct smoking
as a confounder by restricting study subjects to non-
smokers; however, only by including smokers can inter-
actions between air pollution and smoking be detected.
CONCLUSIONS AND RECOMMENDATIONS
Results of well-conducted epidemiologic studies can
provide unique and valuable information about the health
effects of air pollution. In view of the primary
responsibility of the Environmental Protection Agency
(EPA) for determining and acting on air quality in the
United States, the Committee makes the following major
recommendation:
The Environmental Protection Agency should
develop a long-term plan for research on air
pollution; and population-based studies, in
the form of a program in epidemiology, should
be an integral part of that plan.
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CHARACTERISTICS OF A PROGRAM IN AIR POLLUTION
EPIDEMIOLOGY
To be productive and cost-effective, the epidemio-
logic program should have the following four major
characteristics:
· Maintenance of a capability to interpret and
synthesize current knowledge about air pollution and,
accordingly, to plan relevant short-term epidemiologic
research and make appropriate changes in long-term
research.
.
Inclusion of mechanisms for the creation of
multidisciplinary teams to plan and conduct
population-based epidemiologic research on the
adverse health effects of air pollution.
· Means of ensuring stable, lonq-term epidemio-
logic research in a context that supports the career
development of the researchers and thus limits
disruptive changes in personnel.
.
Exploration of collaboration with agencies
that collect or could collect relevant data, after
.
careful consideration of overall long-term data needs.
A productive epidemiologic research program must
have a dual character with respect to sensitivity to
outside forces. Part of the program must be dedicated
to responding to rapidly changing conditions that
offer important opportunities for study, to the
varying concerns of regulators, and to new information
from technologic development and parallel disciplines.
In particular, toxicology, clinical research, and
epidemiology should be viewed as parts of the same
framework; advances in any one can drive new efforts
in the others. Another part of the program, engaged
in long-term research strategies or longitudinal
studies, must remain relatively isolated and free
from abrupt change, although the incorporation of new
elements will sometimes be desirable.
It is important that the EPA program staff at all
levels include highly trained and experienced
epidemiologists, regardless of whether research is
conducted intramurally or extramurally. Continuous
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access to both advice and review from scientists
outside the institution will also be needed.
Given the constraining and difficult nature of
today's questions about air pollution, stable research
teams with expertise in several critical fields will
be most productive. Epidemiologists in the teams
should collaborate with atmospheric scientists,
statisticians, and health effects scientists in all
phases of research, from study design through inter-
pretation. The present structure of many universities
and government research agencies often makes it
difficult to arrange such collaboration. Financial
and administrative mechanisms that encourage develop-
ment of these teams must be implemented; and the EPA
program staff itself must have a multidisciplinary
composition.
The program should assess the value of large data
systems developed for reasons other than air pollution
studies (such as the National Health and Nutrition
Examination Survey, the National Health Interview
Survey, and the National Ambulatory Medical Care
Survey) as resources in air pollution research. Some
of them might be modified and linked to air pollution
exposure data to develop a feasible and cost-effective
research approach that affords very large samples.
Modification in the routinely collected air sampling
data alone might be appropriate, to facilitate use of
these data in some types of epidemiologic studies.
THE FOCUS FOR RESEARCH
-
For the immediate future, the epidemiologic
research program should focus on the following
exposures and effects of concern:
.
- Persistent air pollution problems, including
the-health effects of acid sulfate particles, ozone,
nitrogen dioxide, carbon monoxide, lead, and radon.
It should be flexible enough to address emerging
problems, such as the health effects of products of
incomplete combustion and volatile organic chemicals.
· Lung disorders in which air pollution might
play a role, including chronic obstructive pulmonary
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disease, asthma, decreased rate of lung growth or
increased rate of lung decline with anion, and
increased susceptibility to acute respiratory
infections.
.
The Quantitative contribution of air nol-
lutants to lung cancer in human populations. For
this purpose, it could take advantage of the existing
funding arrangement between EPA and the National
Cancer Institute for the support of epidemiologic
studies of this problem.
Many important questions about the n traditional"
pollutants remain unanswered. For example, the acute
and chronic respiratory effects of acid aerosol and
ozone exposures, which might result only from outdoor
sources, are not well understood. A large population,
perhaps in excess of 100 million, is exposed to
ambient ozone at high concentrations during the
spring and summer. Shifts in coal combustion to the
south central states will result in an increase in
the area and population exposed to acid aerosols. No
systematic epidemiologic study has been designed to
assess either the acute or chronic effects of this
type of shift in exposure. Exposures to acid aerosols
are likely to increase more in rural areas than in
urban areas, so consideration should be given to
locating baseline and followap studies in rural areas.
As new automotive fuels, new industries, new fuel
sources, new commercial products for the home, and
new building ventilation patterns are introduced,
they might yield new pollutants and pollution patterns
that require epidemiologic evaluation. These changes
will result in increased exposures to volatile and
particulate organic compounds, radon, carbon monoxide,
and other potentially hazardous materials.
Indoor air pollution can be a major factor--in
some instances the principal factor--in determining
total personal exposure (averaged and acute) to air
pollutants. Epidemiologic studies must therefore
consider indoor or outdoor concentrations, or both,
depending on the health response and pollutant being
examined. For example, average and peak exposures to
nitrogen dioxide are determined primarily by the
presence of unvented indoor combustion sources. Peak
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exposures higher than those in most urban outdoor
environments occur often in residences that use
unvented gas or kerosene as a cooking or heating
fuel. Therefore, to assess the health effects of
nitrogen dioxide, EPA should study respiratory
infection, pulmonary function changes, and, as soon
as possible, biochemical indicators in association
with indoor exposures and simultaneous outdoor
exposures.
There have been important advances in air monitor
-
ing instruments and inferential data analysis tech-
niques. Air pollution is a complex mixture of gases,
vapors, and particles; epidemiologic studies will
often benefit from detailed characterization of its
components. For instance, the chemical composition
and acidity of size-fractionated particles should be
characterized where appropriate. In some cases, new
techniques for biologic characterization are also
appropriate. Detailed characterization can help to
determine the air pollution components most closely
associated with health outcomes, potential con-
founders, and the relative contributions of various
sources.
The most readily observed health effects of air
pollution are in the respiratory system. The pro-
portion of the overall disease burden from common
respiratory diseases that are attributable to air
pollution has not yet been established. This part of
the disease burden includes both the development of
disease de nova and the exacerbation of pre-existing
disease.
Air pollution might have nonrespiratory effects
that, although not emphasized in this report, also
deserve study. These include neurobehavioral
deficits and essential hypertension related to lead
exposure, ischemic heart disease related to carbon
monoxide, and carcinogenesis and mutagenesis related
to various volatile hydrocarbons.
Respiratory cancers, which are the most common
cause of cancer death in men and will soon be in
women, are attributable largely to cigarette smoking.
However, attempts to assign proportions of this
disease burden to separate causal agents, such as air
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pollution, are frustrated by the multifactorial and
interactive etiology of these cancers. It is par-
ticularly important to understand the role of air
pollutants in lung cancer, inasmuch as interactive
effects might multiply the number of cases that could
be prevented by reducing exposures.
The limits of an epidemiologic research program
depend on the questions under consideration. Only by
considering each research question carefully can one
understand the limits of investigative methods and
discuss them productively. In general, studies of
chronic health effects are more difficult than studies
of acute effects. The major problems include uncer-
tainties in measurements of long-term exposure, the
relative rarity of chronic diseases (which strains
statistical power), and limitations in our under-
standing of the biology underlying the gradual
evolution of chronic damage. Epidemiologic studies
can show whether exposure to a complex pattern of
polluted air increases the risk of adverse health
effects in human populations, but studies are often
limited in their ability to delineate the quanti-
tative relationships between concentrations or
sources of specific air pollutants and health. Such
delineation requires interpretation of epidemiologic
data in conjunction with toxicologic and clinical
research.
Susceptibility to the effects of air pollution
varies widely; studies that focus on sensitive
subgroups, necessary in themselves, are an important
part of strategies to detect and measure the effects
of air pollution in the general population. The
sensitive-subgroup approach to increasing the
effectiveness of air pollution epidemiology must be
furthered by broad-based efforts (toxicology,
clinical research, and epidemiology) to clarify the
precise nature and degree of sensitivity of such
groups as the young, the elderly, those with increased
airway reactivity, and those with particular pre-
existing diseases. Opportunities for carrying out
epidemiologic studies on populations exposed to
unusual magnitudes or patterns of air pollution must
be specifically sought. By circumventing various
methodologic constraints, these studies might provide
information that would not otherwise be easily
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obtained. The opportunities include the use of
occupational cohorts exposed to high concentrations,
groups living in pristine environments or in highly
polluted environments, and groups subjected to marked
temporal changes in pollution. Collaboration with
researchers in other countries might be necessary.
NEW RESEARCH TOOLS AND OPPORTUNITIES
Some constraints in air pollution epidemiology
could be removed by complementary research to develop
and explore the application of new tools for measuring
exposure and effect. Such research and development
is especially needed in two categories:
.
New methods for assessing personal exposure
and response to air Pollution to be selectively
incorporated into epidemiologic studies, with
attention to the cost-effectiveness of these methods.
,
.
Epidemiologic studies designed to determine
the characteristics and the Predictive value of
potentially useful physiologic biochemical, and
morphologic markers of subclinical effects.
Personal exposure monitoring and modeling are
sometimes needed in epidemiologic research to define
study populations, optimal sample sizes, relationships
of surrogate measures to exposures, and the extent of
exposure misclassification associated with the use of
central monitoring data. Depending on the design of
a given study, only a sample of the study population
might require such detailed monitoring; various
strategies need to be explored and their performance
documented.
Markers of physiologic, biochemical, and cellular
morphologic changes will be increasingly important in
air pollution studies. FEV1, a physiologic test of
lung function, has been used successfully to measure
differences related to air pollution between popula-
tions. Serial measurement of FEV1 has also proved
to be sensitive and effective in following the growth
and decline of lung function in large populations.
In adults, a more rapid than normal decline in FEV
predicts premature death from pulmonary failure.
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Although FEV1 is a simple and highly reproducible
test, its interpretation in terms of organ or cellular
pathology is complex and subject to some judgment.
Some biochemical indicators of air pollutant
exposure or early effects--such as blood lead and
carboxyhemoglobin concentrations, urinary mutagens,
and indexes of genotoxic damage--have already been
successfully applied in population studies. other
biochemical indicators, designed to detect early
pathologic processes in the lung, have recently shown
promise and require further development and valida-
tion. Insights into the pathogenesis of emphysema
have been particularly fruitful in opening pos-
sibilities for biochemical markers related to the
breakdown of connective tissue in the lung. Develop-
ment of biochemical markers for epidemiologic studies
requires particular attention to constraints imposed
by the need to study large groups of relatively
healthy people.
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Representative terms from entire chapter:
air pollutants
