Environment International, Vol. 5, pp. 69-72, 1981 Printed in the USA. All rights reserved.
0160-4120/81/020069-04502.00/0 Copyright ©1981 Pergamon Press Ltd.
PERSONAL MONITORING OF AIR POLLUTION EXPOSURES
Samuel C. Morris National Center for Analysis of Energy Systems, Brookhaven National Laboratory, Upton, New York 11973, USA
In industrial hygiene and health physics the goal has been to protect the health of the individual. Therefore monitoring the exposure people actually receive has been the principal concern. In regulating public exposures to air pollution, the focus has been much different. Recently, use of personal monitors and alternative means of estimating actual exposures has expanded rapidly. The role of personal monitors in epidemiology, exposure studies, and in supplementing the existing fixed station monitoring network for establishing trends and for regulatory purposes is discussed. The implications for air quality standards in recent findings of personal and indoor exposures is considered. New developments that are needed, and those that are not needed, are outlined.
air pollution. Even in air pollution epidemiological studies, for which intensive individual medical surveillance was frequently carried out on the participants, air pollution exposures were based on fixed monitoring stations located outdoors, and only in some cases in the neighborhoods where the subjects lived. Only in an unusual study design was an attempt made to base exposure partially on a fixed monitoring station in the residential neighborhood and partially on one in the commercial area where individuals worked (Carnow et al., 1969a, 1969b). There have been a number of advocates for personal exposure monitoring. A task force within the Environmental Protection Agency (EPA) concluded that personal monitors would considerably increase precision of exposure estimates in epidemiological studies and would also be useful for control and enforcement actions (Personal Monitoring Task Force, 1972). O'Keeffe promoted several personal monitoring programs within EPA (Altshuller and O'Keeffe, 1974; Harrison et al., 1976). Because of the relative ease of measurement, several experiments were conducted in which personal exposures were measured by carrying large monitors around (Ott and Mage, 1974; Wright et al., 1975; Cortese and Spangler, 1976). The Harvard School of Public Health, with considerable experience in the development and use of personal exposure monitors in industrial hygiene (Lynch and
In the field of industrial hygiene and health physics, directly monitoring exposure to individuals with small portable or personal devices has long been accepted practice. The goal has been to protect the health of the individual, and so monitoring the exposure that the individual actually receives has been the principal concern. The wide breadth of personal exposure monitoring in industrial hygiene is described by Linch (1974). Establishment of the Occupational Safety and Health Administration (OSHA) and the accompanying increased federal concern with exposure of workers to toxic pollutants served as a spur to technological advance of personal monitoring devices to measure exposure to industrial pollutants, and the commercial development of those devices. In the field of ambient air quality, the focus has been much different. Monitoring has concentrated in networks of fixed stations. Sites were chosen for convenience, enforcement reasons, safeguarding the equipment, in short a variety of purposes generally unrelated to estimating the actual exposure of the population to
Work was supported by the Health and Environmental Risk Analysis Program. U.S. Department of Energy, Washington, DC, under contract No. DE-AC02-76CH00016. 69
70 Burgess, 1974; Theriault et al., 1974; Burgess et al., 1973), initiated a long-term epidemiological study using personal monitoring devices for respirable particles with support from the National Institute of Environmental Health Sciences (Speizer et al., 1977). They adopted a device which had been designed for use in coal mines and had to overcome problems such as obtaining sufficient sample sizes when operating in an ambient environment more than twenty times lower in particulate concentration than the device had been designed for and unexpected problems such as the noise of the pump, which had not been a problem in the coal mine but created a disturbance in the classroom or office (Turner et al., 1979; Dockery and Spengler, 1980). Air pollution has potentially important health effects. In assessing the status of knowledge of these effects it became clear that the weakest link in estimating health effects of air pollution was the accuracy of quantitative exposure estimates in air pollution epidemiological studies. In 1975, the Biomedical and Environmental Assessment Division of Brookhaven National Laboratory organized a workshop to discuss this problem and concluded that the use of personal exposure monitors was essential to the design and performance of definitive studies of the health effects of air pollution (Morgan and Morris, 1976). This led to an Energy Research and Development Administration program to develop personal monitoring devices. Its results contributed substantially to a National Academy of Sciences report two years later on environmental monitoring which recommended that EPA begin the development of personal air quality exposure monitors (Study Group on Environmental Monitoring, 1977). In 1977, the second Brookhaven report on personal exposure monitoring was issued; this examined the potentially large bias in exposure estimates based on fixed station monitoring, and broadened the outlook on potential uses of personal monitoring devices from the narrow epidemiological base in the earlier report (Morgan and Morris, 1977a). The combined findings and other literature to date were summarized in a further report (Morgan and Morris, 1977b). At the same time EPA began to experiment with alternative ways to use data available from fixed network stations to take into account population density (Frank et al., 1977; Horie and Stern, 1976; Horie et al., 1977). Such analysis is a marked improvement over use of fixed station data alone, but can be far from a good estimate of population exposure. People spend most of their time indoors and move about during the day. A more refined approach uses personal activity modeling, weighting air pollution levels in various places by the amount of time individuals spend in such places. More data are required, however. This approach has been used by Moschandreas and Morse (1979) and Dockery and Spengler (1981). A more sophisticated approach
Samuel C. Morris would take into account variations in breathing rate for different activities. One personal monitor corrects for individual respiration rate automatically (Sibbett and Moyer, 1979). Increased efforts at energy conservation in buildings resulting in increases in indoor air pollution levels renewed interest in the importance of indoor exposures not captured by the outdoor fixed monitoring network (Hollowell et aL, 1978; Moschandreas et al., 1978; U.S. Comptroller General, 1980). There began to be reports on air quality in homes (Spengler et al., 1979), in cars (Colwil and Hickman 1980; Peterson and Sabersky, 1975; Cortese and Spengler, 1976), and in public places (Hinds and First, 1975; Elliott and Rowe, 1975; Repace and Lowrey, 1980). EPA began doing more work with available personal exposure monitoring devices. The conclusion emerged that patterns of air pollution exposure in the population may be much different from that observed at fixed monitoring stations. In 1979, EPA held a symposium on the development and use of personal exposure monitors (Mage and Wallace, 1979). EPA is currently sponsoring the development and evaluation of a number of personal exposure monitoring devices (Wallace, 1981). In addition, EPA has begun or has in the planning stage a number of field studies using personal exposure monitors. Role of Personal Exposure Monitors While it is still early for definitive epidemiological results from the Harvard studies, that effort has already begun to pay benefits through the exposure data that it has made available. The only reliable way to evaluate estimates of personal exposure based on activity models, indoor levels, etc., is comparison with personal monitoring data. The data becoming available begin to allow better evaluation of the role of personal monitors. Dockery and Spengler found that, for mean respirable particulate and mean sulfate exposure, personal activity modeling and, to a lesser extent, indoor concentrations alone were good approximations to exposures measured with personal monitors. Thus, for population estimates, indoor fixed monitoring with personal activity models may be sufficient. There still remains considerable individual scatter, however, so that for epidemiological studies in which individual exposure estimates are important, personal monitoring remains necessary. There also appears to be considerable variation in elemental content of respirable particles (Colome and Spengler, 1979). The need for personal monitoring in studies concerned with exposure by particle composition thus remains unresolved. For carbon monoxide, nitrogen dioxide, and ozone, concentration variations in time and space can be large, and short term peak exposures are likely to be important. Fixed outdoor monitors are incapable of pro-
Personal monitoring of air pollution exposures
viding accurate estimates of population exposure under these circumstances. The shorter the exposure averaging time of interest and the greater the areal variability of concentrations, the less useful the fixed monitor. At this time there is insufficient data available to determine the extent personal activity models and more extensive fixed sampling might serve, but it seems likely personal monitors are the only adequate solution. To summarize the role of personal exposure monitors, their role in epidemiology is well established. Their role in exposure studies is being actively explored. Their role in supplementing the existing fixed station monitoring network for establishing trends and for regulatory purposes is relatively unexplored, and in general awaits more data from exposure studies. In principle, there is no reason that sample populations with personal monitors could not replace the current network in providing estimates of air quality for most purposes. Costs would be higher. The major obstacle is the compartmentalization of responsibilities in government. Different agencies are responsible for air quality outdoors, in the workplace, in public buildings, and in residences. It is unreasonable to regulate parts of the overall air pollution exposure without consideration of the total exposure. There is sufficient information now available to indicate that "unregulated" exposures in homes, automobiles, and public gatherings can exceed ambient air quality standards.
Implications for Ambient Air Quality Standards Air quality standards, for the most part, are based on epidemiological studies which did not measure total exposure of the population. Lack of complete exposure data introduces considerable uncertainty in the epidemology and thus in the standard. The basis for standards also includes toxicology and clinical studies unaffected by this problem. Ambient standards are thus an inappropriate basis on which to judge the seriousness of high indoor air pollution exposures since to some extent they are based on evidence that public health is protected if outdoor levels are kept below the standard without regard to indoor levels. Ambient standards which are heavily based on results of controlled clinical exposures or occupational epidemiology may be more suitable for judging high indoor air pollutant concentrations. Care must be taken, however, since clinical and occupational studies generally exclude highly susceptible populations. Routine exposures of the population in unregulated situations to concentrations exceeding ambient standards either mean that the standards themselves are needlessly high or that the public is at risk from such unregulated exposures. A new era of air pollution epidemiology based on total exposure is needed to solve this dilemma. Personal monitoring clearly has a key role in this.
Needs Needs and direction for personal monitoring development and research have been extensively described (Morgan and Morris, 1977b; Wallace, 1979; Hamilton, 1979). There is a pressing need for more field studies of personal exposure levels of various population groups. The limited data available has produced a revolutionary change in thinking about air pollution exposure. The potential implications demand a much broader data base. Use of available personal monitors can contribute greatly. The second need is for further development and improvement of monitoring devices. Particular needs in this area are for measurement of short time average exposures for which personal monitors are the only way of measuring actual exposure. This, in general, will require active samplers, but systems using passive sampiers may be devised which can collect one-hour average samples. Coupled with sampling over short averaging periods is the need to allow easy recording of location and activity. As important as determining needs is an understanding of what is n o t needed. Although when measuring concentrations over short averaging times there must be a way of maintaining the information (either chemically or electronically), there is no need for immediate display of the information. In fact if the person carrying the monitor has access to real-time display, high exposures may be avoided and the results biased. This situation, in which an individual is monitored as part of a representative sample of a larger population, is much different than one (such as industrial exposure) in which the monitor is to protect the individual. Similarly, population exposure data is typically analyzed weeks or even months after the exposure and so real-time telemetering of the data to a central depository is unnecessary.
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