€SmPR€CIS
I
ASSESSING HUMAN EXPOSURE TO AIRBORNE POLLUTANTS d va nc es a nd o pportunities Protecting the general public and sensitive subgroups from the harmf u l effects of air pollution has proved a difficult task for all levels of government and the regulated community. Passage of the recent Clean Air Act amendments provides new options and responsihilities, hut improved scientific techniques need to be employed to better understand and to properly reduce the risks from exposure to unhealthful air. Major outdoor air concerns are photochemical smog, acid aerosols, and air toxics. A committee I chaired, which was convened by the National Research Council, recently completed an analysis of new methods and technologies for assessing exposure to air pollutants. It included members with expertise in chemistry, mathematical modeling, engineering, physics, air pollution, exposure assessment, medicine, biology, social science, statistics, and environmental policy. The study was sponsored by the Agency for Toxic Substances and Disease Registry of the US. Public Health Service. We realized that the issues associated with human exposure are complex and require a framework for assessing and analyzing total personal exposure of an individual to contaminants. The framework should allow consideration of all the principal ways in which individuals Prdcis articles are reports of meetings of unusual significance, international or national developments of environmental importance. significant public policy developments, and related items.
By Paul J. Lioy could come into contact with such pollutants. We felt that operating within this framework would help set priorities for reducing risk from actual exposures or provide accurate estimates of exposure to enable management to make decisions about control of potentially harmful pollutants. Exposure to airborne pollutants is only part of a person’s total exposure to a specific pollutant, which includes any inhalation, ingestion, or skin absorption of the pollutant from air, water, food, or soil. Thus, exposure assessments for airborne constituents must take into account the potential contributions from other media, and all routes of exposure must be at least preliminarily assessed for the relative magnitude of their contributions. Such an approach is necessary to define the exposures of concern, to effectively assess risk and make management decisions, to complete environmental epidemiological investigations, and to improve disease diagnosis and intervention. Even if air is the only route of contact considered, we believe an exposure assessment should account for the locations that might lead to contact with high concentrations of the pollutant studied. It was with this understanding of total human exposure that the committee limited its study to air contaminant exposures. The carcinogen benzene is an example of how application of a proper exposure assessment might lead to more effective strategies to reduce the health risk from common
y
airborne chemicals. The Clean Air Act provided the basis for EPA in 1989 to establish regulations for industrial emission of benzene into outdoor air. However, as the Act applies only to outdoor air, no other sources of benzene exposure are included in the subsequent regulation-even though household products, automobile exhaust, and paint may be sources of more than 80% of national benzene exposure. Prioritization of the significance of benzene exposures will help regulators select mitigation measures for outdoor air sources and will truly assist in reducing a population’s exposure to benzene. Indoor sources, including tobacco smoke and evaporation from gasoline stored in attached garages, currently require other approaches (e.g., education and product replacement). The committee identified three major ways of determining human exposure to airborne pollutants. Monitoring the air around an individual with a portable personal air sampler is, of course, the most comprehensive and most accurate. It is also the costliest and most time consuming. The second method is more indirect and involves techniques such as measuring the amount of a contaminant with a stationary monitor a n d extrapolating exposure by means of personal activity records or mathematical models. Exposure to carbon monoxide inside a car, for example, might be roughly calculated from the amount of time spent in the car and the quantity of carbon monoxide in the car under typical operating conditions. The third method involves hioEnvircn. Sci. Technol.. Vcl. 25. No. 8. 1991 1361
logical markers as a measure of the integrated dose within the body and of past contact with pollutants. For example, a marker for airborne lead exposure can be elevated lead levels in the blood. However, this must he weighed against contributions from other media. Other biological markers have been developed or are heing studied that can detect cellular level changes in the body long hefore they produce health effects: however, most require validation. To properly apply these techniques, the committee recommended that researchers use consistent definitions of exposure. The report calls for the scientific and regulatory communities, including journal editors and reviewers of scientific articles, to adhere to standard terms. The committee recommended a set of definitions and defined exposure as contact at a boundary between a human and the environment at a specific environmental contaminant concentration for a specified interval of time. The time interval should, of necessity, be relevant to the biological effect of concern. Many advances in exposure assessment methods and technology have occurred in recent years. New rsonal air sampling equipment,
in particular, has been under-used, especially to provide data to support regulatory decision making. Improved personal air monitors are needed for many potentially harmful contaminants, including certain metals, and various organic chemicals, such as semivolatile compounds and radon and its progeny. Better fixed-site monitors also are needed for many contaminants. Improved instruments-gas chromatographs, mass spectrometers, a n d electrochemical sensorsshould be developed for measuring the concentrations of pollutants in collected air samples. Miniaturization of many instruments is essential if we are concerned with an individual rather than an outdoor site. Analytical techniques with improved specificity and sensitivity for biological markers are needed, especially ways to test for several markers at the same time and to interrelate measurements of the significant routes of exposure. Res e a r c h e r s w h o s t u d y airborne pollutants should adhere to sound statistical methodology in collecting personal activity data. Basic statistical principles often are ignored in questionnaires and surveys used by exposure analysts.
Tlre Journal of Oqanic Chemistry solicits manuscripts that address topics at the interface of organic chemistry and biology.
W
hile such manuscripts should address fundamental problems in organic chemistry (structure, mechanism, synthesis), we encourage submission of manuscripts in which these problems are solved with the use of techniques not traditionally associated with organic chemistry (enzyme kinetics, enzyme isolation and purification, identification of active site residues, etc.). The Journal hopes to foster integrated publications in which the chemical aspects are not separated from the biological aspects. For lnsnuscrlpt format see J. Ofg. Chem. 1990.55 (1). 7A-10A. Send manuscripts to: C. H. Heathcock Editor-in-Chief,The Journal of Organic Chemistry. Department of Chemistry. University of California. Berkeley. CA 94720
-
For subscription infomation American Chemical Society Sales and Distribution 1155 Sixteenth Street. N.W. Washinaton. D.C. 20036 (2&) 872-4363 Toll Free, 1-800-227-5558
1362 Environ. Sci. Technol.. Vol. 25, No. 8, 1991
In order to develop useful models for exposure assessment, researchers also must develop a better understanding of pollutant dynamics. Such fundamental parameters as how, where, when, and at what strength pollutants are dispersed often are lacking. Moreover, many of the methods currently in use for estimating exposure to airborne pollutants have never been verified using independent field measurements. Research should be undertaken to validate these methods. Using advanced measurement techniques in exposure studies does not in itself ensure better data. Quality assurance programs are critical components of exposure studies: researchers should expect to spend at least 15% of the total study budget on making sure that the data are accurate and precise. Awareness is increasing of basic principles that place exposure within a continuum, starting with a pollutant emission and continuing through possible cell-level changes and finally being expressed as impaired health. This awareness will make exposure assessment even more important in the future as it leads to the implementation of practical methods for reducing the risk from airborne contaminants and to efforts to mitigate exposure. A final and major point made in the report is the need to have accurate and realistic assessments to ensure optimal reduction of human exposure. To accomplish this, exposure assessment research should be supported by government programs. Although not stated, such research should also be supported by other sectors, including the regulated community. The committee's report, Human Exposure Assessment for Airborne Pollutants: Advances and Opportunities, is available from the National Academy Press by calling (800)6246242 or (202) 334-3313.
P o u l J. L i o y , Ph.D., is o professor in the Department of Environmental and Community Medicine and director of the Exposure Measurement and Assessment Division ut the liniversity of Medicine and Dentistry of New Jersey in Piscatoway.
