Epidemiology and Air Pollution (1985) / Chapter Skim
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3 EXPOSURE ASSESSMENT
3 EXPOSURE ASSESSMENT
Pages 89-126
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From page 89... ...
The chapter then identifies the types of pollutants that the Committee feels require attention, indicating some physical, chemical, and spatiotemporal properties that are relevant to exposure assessment. Sections on special approaches to indoor pollutants and monitoring considerations follow, including opportunities for providing optimal exposure data in future epidemiologic studies.
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From page 90... ...
Exposures can then be remeasured, in conjunction with health effects measurement, to provide a basis for a quantitative estimate of the association between exposure and effect. Exposure assessment has many purposes in air pollution research aside from providing exposure variable measurements for epidemiologic studies.
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From page 91... ...
Research is required to relate a specific ambient exposure to the dose received by a given target tissue in the respiratory tract and to relate that dose, in turn, to a specific health effect. This research will ultimately benefit future epidemiologic studies of air pollution.
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From page 92... ...
EXPOSURE ASSESSMENT 92 FIGURE 1 Framework for exposure assessment.
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From page 93... ...
Most often, data from relatively few central outdoor monitoring stations were used to represent the exposure of all subjects in an entire residential community. Indoor sources that could contribute to total personal exposures to many of the
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From page 94... ...
samplers have been developed for use in a variety of situations, both indoors and outdoors, and they are easily adaptable for providing data on cumulative exposure, time lagged responses, and frequency of periodic exposure peaks. Quantitative chemical analysis now offers precision and sensitivity far greater than those required for most epidemiologic studies.
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From page 95... ...
Outdoor emission sources contribute to outdoor concentrations, which in turn penetrate to a degree into indoor environments; and indoor sources also contribute to indoor concentrations. The relative importance of indoor and outdoor concentrations in determining personal exposure (average or peak)
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From page 96... ...
To assess total personal exposure to air pollutants, one can sample near the breathing zone of the subject with portable instruments or one can find the timeweighted sum of concentrations measured in a series of locations in which the subject spends the day. The latter, indirect approach requires time-activity logs and portable area monitors (rather than smaller monitors that are worn)
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From page 97... ...
Research is also underway to improve the statistical handling of data from indirect personal exposure assessment and to resolve unexplained discrepancies with direct measurements. It might ultimately be more practical and cost-effective to pursue the indirect estimation approach for some epidemiologic studies, inasmuch as accurate, inconspicuous, and affordable personal monitors are not available for all pollutants and quality control of personal monitoring is more difficult than that of area monitoring.
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From page 98... ...
Climate has obvious effects on activity patterns and on housing characteristics that influence air exchange. Not all epidemiologic studies on air pollution require measurement of total personal exposure.
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From page 99... ...
The pollutants vary in several critical ways: from primary emission to secondary product, from outdoor source to indoor source or both, from presenting a direct health threat to indicating other pollutants, and from spreading over vast areas to accumulating in specific microenvironments. Pollutants known to be sufficiently widespread or present in sufficiently high concentrations to warrant study in future epidemiologic investigations include: • Acid aerosols, acid gases, and O3.
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From page 100... ...
Recent data, from both laboratory and epidemiologic studies, have suggested that SO4−2 in ambient air can be a particular cause for concern.16 58 Ambient concentrations of O3 and SO4−2 can be highly correlated and relatively uniform over very large geographic areas in the summer and have the potential for affecting large segments of the population downwind of areas of precursor emission, particularly during major regional photochemical smog episodes.9 29 35 45 63 However, during such episodes, the distribution and speciation of H2SO4, NH4HSO4, and the fully neutralized ammonium sulfate, (NH4) 2SO4 (in decreasing order of presumed toxicity)
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From page 101... ...
Ozone concentrations are proportional to circle diameters. Reprinted with permission from Cleveland et al.8
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From page 102... ...
Exposures to acid aerosols and O3 are modified in accord with the ability of each pollutant to penetrate indoors (e.g., air-conditioned versus non-airconditioned environments during the summer) and to react with surfaces
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From page 103... ...
Personal exposure to NO2 can have both indoor and outdoor components, with the highest exposures occurring indoors in the presence of unvented combustion sources (e.g., gas stoves) .41 A systematic investigation of the health effects of short-term and chronic exposures to NO2 in summer and winter is required.
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From page 104... ...
Future air pollution studies on lead in the United States must also focus on individual point sources, such as smelters.3 Outdoor measurements could well be needed at sites other than a centralized monitoring station; for instance, recent data suggest that people can be substantially exposed to airborne lead in motor vehicles.54 Future studies of environmental lead exposure should differentiate the relative contributions of water, food, workplace, and other sources to total lead exposure, as reflected by such measures as blood or dentin lead. RADON AND ITS PROGENY Radon and its decay products are of much concern, because radon is a primary indoor air pollutant and has common natural environmental sources, such as the earth surrounding residences, building materials used to construct homes, and water that enters homes.36 37 The problem has grown since the 1970s, as homeowners have sealed residential structures to reduce energy consumption.
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From page 105... ...
INDOOR POLLUTANTS: SPECIAL PROBLEMS AND PROSPECTS Documentation of the importance of indoor concentrations of pollutants is profoundly altering air pollution epidemiology. Today in the United States over two-thirds of our time, on the average, is spent indoors.
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From page 106... ...
The results of this survey are illustrated in Figure 4. On the average, indoor concentrations were higher and had a much greater range across homes than outdoor concentrations.
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From page 107... ...
In the last 10 years, the availability of lightweight portable sampling pumps and diffusion badges has allowed investigators to compare total personal exposure to indoor and outdoor pollution simultaneously. These investigations have revealed low correlations between outdoor concentrations and integrated personal exposure for some important pollutants, such as respirable particles and NO2.
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From page 108... ...
Note that the indoor concentrations are higher than the outdoor, and the personal exposures higher still. This indicates that somewhere in their daily activities subjects were receiving a greater exposure to particles than could be explained by the measurements taken either in their homes or outdoors.
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From page 109... ...
Categorical descriptor variables and ambient outdoor concentrations are notoriously poor predictors of personal exposures. Outdoor measures explain less than 1% of the interindividual variance in personal exposure to respirable particles.
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From page 110... ...
Short-term peak concentrations, which can be measured only with continuous monitors, have greater biologic relevance for some pollutants. SITING AND TIMING OF AIR POLLUTION MONITORS In past epidemiologic studies, cost considerations and a simple view of exposure have favored the use of routinely collected data on air quality.
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From page 111... ...
Rather than convert varied exposure to a homogeneous value, epidemiologic studies might need to take advantage of variability itself. Grid approaches to monitor siting appear to have less appeal today than approaches based on expert judgment.
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From page 112... ...
Biologic models concerning the presumed action of air pollutants have not always been explicitly considered in planning epidemiologic studies. For some irritants, such as SO2, the number and duration of peaks might be more relevant than smoothed average concentrations in determining effect.
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From page 113... ...
Lippmann et al.32 used the design of PEPE, which characterized ambient air in regions near Indiana, Pennsylvania, to design a field study of children's response to regional haze at a summer camp. The Harvard Air Pollution Health Study included a number of characterization experiments that ultimately led to the identification and examination of population exposures to both indoor and outdoor pollutants.
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From page 114... ...
A much improved kind of exposure assessment research, which will assist in the design of epidemiologic studies, is the resolution of sources that contribute to measured air concentrations. Most of the work to date has been done on the outdoor sources of particulate matter.
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From page 115... ...
An example from air pollution research is the recent study of urinary mutagenic activity in children residing near a Montana smelter.60 In contrast, with the notable exceptions of blood lead and carboxyhemoglobin measurements, there are no biologic methods for monitoring the extent of exposure of the general population to EPA criteria air pollutants. Such methods might be particularly difficult to develop for short-lived reactive pollutants that exert their effects in the lung.
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From page 116... ...
As the ability to characterize pollutants improves, exposure assessment becomes an increasingly sophisticated tool for epidemiologic studies of air pollution.
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From page 117... ...
Pittsburgh, Pa.: Air Pollution Control Association, 1983.
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From page 118... ...
Chemical element balances and identification of air pollution sources. Environ.
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From page 119... ...
Preprint #83-8.3. Proceedings of the 76th Annual Meeting of the Air Pollution Control Association.
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From page 120... ...
38. National Research Council, Committee on Indoor Pollutants.
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From page 121... ...
Soczek. Evidence for improved ambient air quality and the need for personal exposure research.
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From page 122... ...
Proposed Revisions to the National Ambient Air Quality Standard for Particulate Matter. March 20, 1984.
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From page 123... ...
Personal exposure of volatile organics and other compounds indoors and outdoors: The TEAM Study. Preprint #83-9.12.
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From page 124... ...
Mage. Pilot field study: Carbon monoxide exposure monitoring in the general population.
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From page 125... ...
125 Chapter 4 Concepts and Strategies in Planning Epidemiologic Studies on Air Pollution
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