Human Exposure Assessment for Airborne Pollutants Advances and Opportunities (1991) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-16
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Such an approach would need to rely heavily upon the application of scientific knowledge in risk assessments. The success of such an approach would therefore depend upon assessments of human exposures to toxic substances, because the exposure component of a risk assessment often entails greater uncertainty than the hazard component, and because reducing human exposure is directly relevant to reducing health risk for a given toxic substance.
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The following report describes a conceptual framework and methods for assessing and analyzing the totality of exposures of an individual to air contaminants in the course of all activities over specified increments of time. Accurate and realistic assessment of human exposures from all environmental media can help to ensure that appropriate priorities are set to achieve optimal reduction of human exposures to significant contaminants.
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As part of the information-gathering process, the committee sponsored a 2-day symposium in October 1988, to obtain current "formation on the uses of exposure analyses, measurement instrumentation, analytical and survey techniques, biological markers, and study design THE COMMIT SHE'S APPROACH TO ITS CHARGE In response to its charge, the committee focused on human exposure to airborne contaminants that can be inhaled or absorbed through the skin and potentially can cause adverse health effects or discomfort for an individual. The committee did not consider in detail exposure to airborne contaminants that come in contact with humans only after the contaminants have transferred to another environmental medium (e.g., deposition of airborne contaminants into food or ingestion of contaminated soil or water)
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An array of techniques can be employed, ranging from basic techniques for estimating the number of people exposed, to sophisticated methodology employing contaminant monitoring, modeling, and biological markers. Art organizing construct was developed by the committee to facilitate its evaluation of exposure-assessment techniques.
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FRAMEWORK FOR ASSESSING EXPOSURES TO AIR CONTAMINANTS Exposure assessments for airborne constituents must be considered within a framework that recognizes the potential contributions from other environmental media. Furthermore, to achieve effective risk assessment, risk management, environmental epidemiology, and diagnosis and intervention in environmental medicine, all media and routes of exposure should be assessed for the relative magnitude of their contributions before an intensive assessment of one medium is conducted.
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. Studies to assess exposures to environmental contaminants, whether they are intended to improve environmental epidemiology' disease diagnosis and intervention, risk assessment, or risk management, need to consider the three principal methods of exposure assessment: personal monitoring, biological marker measurements, and indirect methods (e.g., microenvironmental concentration measurements coupled through models to time-activity data obtained from questionnaires)
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These compounds often are of concern from a health perspective, and stable, known quantities can be difficult to prepare. Sampling Techniques and Strategy Most advances in exposure-assessment science have occurred in the development of samplers and measurement techniques for fixed-site and personal air monitor studies; the latter have focused on activities and sources that contribute to individual and population exposures.
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Sorbent improvements are needed to allow long-term sampling for a wide variety of analyses. Personal air monitoring is the most direct approach for assessing human exposure to airborne pollutants.
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Continued improvements in LC combined with mass spectrometry are beginning to fill this gap. USE OF BIOLOGICAL MARKERS IN ASSESSING HUMAN EXPOSURE TO AIRBORNE CONTAMINANTS Biological markers in an exposed individual can provide information about an original contaminant, a metabolite of a contaminant, or the product of an interaction between a contaminant agent and some target molecule or cell.
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Analytical techniques with improved chemical specificity and sensitivity for biologically significant markers are needed for exposure assessments; especially needed me flexible assays that ~ analyze several markers simultane,Qusly or be readily adapted to analyze numerous markers sequentially. For such techniques, validation studies are needed to link biological markers conclusively to causative agents.
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. MODELS USED IN ASSESSING HUMAN EXPOSURE TO AIRBORNE CONTAMINANTS Mathematical models use systems of equations to quantify and explain the relationships between air-pollutant exposure and important variables, such as emission rates from contaminant sources, as well as for estimating exposures in situations where direct measurements are unavailable.
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Exposure Models Models for predicting exposures to populations have been developed but have not been adequately validated. Limited validation studies of the EPA's "Simulation of Human Air Pollution Exposure Model," for example, show that the average exposure values are well predicted but also show substantial discrepancies in the tails of the distribution.
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It is clear, however, that the field of air contaminant exposure assessment has advanced significantly as a result of indoor-a~r pollution studies. Further progress will be achieved as exposure study designs more completely address and rank potential contributions from all environmental media to all relevant microenv~ronments.
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