Human Exposure Assessment for Airborne Pollutants Advances and Opportunities (1991) / Chapter Skim
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1 Principles of Exposure Assessment
1 Principles of Exposure Assessment
Pages 17-36
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From page 17... ...
However, accurate data on exposure, i.e., contaminant concentrations at the boundary between a human and the environment and the duration of contact, are also crucial to valid risk assessment, but advances in exposure assessment have not been fully integrated into standard risk-assessment practice. Exposure assessment has seen important conceptual and practical advances.
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From page 18... ...
, whose mandate is to prevent or mitigate adverse human health effects and diminution in quality of life resulting from exposure to hazardous substances in the environment. In response to its charge and to national needs for improved understanding about exposures to environmental hazards, the committee has reviewed the new developments and developing technologies in exposure assessment, identified knowledge and technological gaps, and recommended research and development to fill those gaps.
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From page 19... ...
Total human exposure accounts for all exposures a person has to a specific contaminant, regardless of environmental medium (air, water, food, and soil) or route of entry (inhalation, ingestion, and dermal absorption)
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From page 20... ...
Dose is not considered in detail in this report, except in discussions of biological markers. The National Research Council's Committee on Biologic Markers has portioned dose into two components: internal dose and biologically effective dose (NRC, 1989~.
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After risk assessment shows that a contaminant poses an adverse health risk, regulatory agencies develop risk management plans. Such a plan involves formulating cost-effective mitigation efforts to reduce the risk associated with exposure to a contaminant and to monitor progress toward risk reduction.
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From page 22... ...
. More effective methods were not used for many reasons, including technological limitations in environmental monitoring methods, lack of adequate concentration-predictor models, unavailability of adequate human biological markers of exposure, limitations in available resources, inadequate understanding of media and routes of entry, and narrow public-health mandates of individual regulatory agencies.
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From page 23... ...
It commonly was assumed that the one or two routinely monitored contaminants or indicators (e.g., total suspended particles or sulfur dioxide) at fixed sites either were related to the health outcomes under study or were proxies for contaminants that posed a potential health threat.
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As a result, measurement of personal exposures to NO2 with particular emphasis on indoor air is now used in the evaluation of health effects associated with NO: and in developing and specifying effective mitigation measures.
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From page 26... ...
. Conceptual Framework for Human Exposure Assessment Efforts to assess and reduce total human exposure to environmental contaminants and relate exposure to acute and chronic health effects or nuisance effects4 must be guided by a theoretical framework or methodology.
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Specification of a person's or a population's exposure to an environmental contaminant or categories of contaminants should take into account a time scale related to the biological response studied unless the exposure assessment is intended to provide data on the range of biological responses. Specification of biological response requires information on contaminant toxicity and quantitative assessment of the exposures associated with the effects.
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From page 29... ...
These definitions of internal dose and biologically effective dose are consistent with those given in recent NRC reports: Biologic Markers in Pulmonary Toxicology and Biologic Markers i': Reproductive Toxicology. Physico-pharmacokinetic models are used to describe or calculate a relationship between exposure and target-tissue concentrations of environmental contaminants.
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From page 30... ...
. For example, exposure investigations conducted for various volatile organic compounds have shown that emissions in outdoor-air environments might not accurately reflect the major sources of exposure, because significant exposures occur in indoor environments, especially for certain contaminants, such as benzene and tetrachloroethylene (Wallace, 1987~.
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From page 31... ...
Community Studies Community studies involve segments of the general population and quantification of single-medium or total exposure to individual contaminants or complex matures. If the significant microenvironments or personal activities are identified, the significant biological effects can be determined or estimated through risk assessment (Johnson and Paul, 1981, 1983; Wallace, 1986; Lioy et al., 1988; Wallace et al., 1988~.
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From page 32... ...
Their use is based upon the assumptions that the exposure estimates of a plume impact represent actual exposures, and the results can be used to predict biological impacts using health criteria developed by other studies (Schroy, 1981; Fenstermacher and Ottinetti, 1987; Lipton and Lynch, 1987~. EPA conducts engineering studies under the Clean Air Act, the Federal Insecticide, Fungicide and Rodenticide Act, and the Toxic Substances Control Act (TSCA)
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From page 33... ...
Industries also use engineering studies to help identify causative agents when occupational or environmental health effects are identified, as well as to check for compliance with EPA and OSHA regulations and to define mitigation methods for actual or potential exposures. Animal Studies Animals exposed to contaminants in actual environments can be used as exposure sentinels.
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From page 34... ...
More subtle long-term measurements of exposures are required when the outcome is a subtle change in the human biological or behavioral system. Development of disease and death due to low-level, long-term exposure is very diff~cuIt to relate to specific contaminants using morbidity and mortality studies because of multiple intervening exposures.
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From page 35... ...
The plan developed to gather data for an exposure assessment should take into account the time scale related to the biological response being studied. Exposure assessment is an equal partner with toxicology in defining human health risk and identifying exposure-response relationships and should be funded by government programs according to priorities commensurate with the importance of exposures to environmental contaminants.
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