Human Exposure Assessment for Airborne Pollutants Advances and Opportunities (1991) / Chapter Skim
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2 Framework for Assessing Exposures to Air Contaminants
2 Framework for Assessing Exposures to Air Contaminants
Pages 37-52
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From page 37... ...
Air contaminants found in various industrial, occupational, residential, outdoor, and public access and transportation environments consist of a broad and complex spectrum of chemicals in gaseous and particle-associated forms, as well as particles of biological origin. Ideally, the air contaminants implicated in producing an adverse health or nuisance effect would be identified and an exposure assessment protocol would be designed.
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From page 38... ...
Air concentrations in the industrial environment are controlled by the same factors with the addition of material handling, local process exhaust systems, worker habits, and the use and effectiveness of personal protective equipment. Development of accurate models to predict air-contaminant levels requires information on the above factors.
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From page 39... ...
= the average concentration to which person k is exposed during the time interval At while in microenvironment j; and Atjk = the time spent by person k ire microenvironment j. For acute health effects, t must have a short enough interval to ensure the average reflects the peak concentration that can cause an effect.
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From page 40... ...
The concentration, C,j, is considered to be constant for that location during the interval 6tjk The integrated exposure, ET, then can be calculated for many different situations. For the exposure of the kth person to the ith contaminant, the time-integrated exposure for the kth person is the sum of the individual exposures to the ith contaminant over all of the possible microenvironments: T~ = ~ Cij~tj'.
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From page 41... ...
In this mathematical relationship, volume and time cancel out leaving only the mass term, which is more appropriately considered potential dose, assuming 100% bioavailability and absorption, as defined in Chapter 1. Defining exposure as mass will lead to misinterpretations of exposure by those who conduct exposure assessments, because understanding of concentrations and actual time periods of exposure is critical for analysis and mitigation of adverse exposures.
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From page 42... ...
Personal monitoring can be a useful measure of an individual's exposure to an air contaminant or class of contaminants and has been used extensively by industrial hygienists in occupational settings. When combined with biological markers, personal-exposure data can link air concentrations with internal dose.
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From page 44... ...
Recent advances also have been made in active personal monitors; for example, miniature denuder monitors for assessing personal exposures to acid particles and gases have recently become available (Koutrakis et al., 1989~. Advances in the use of electrochemical sensors for active personal monitoring have recently been reported for NO2 (Penrose et al., in press)
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From page 45... ...
Biological markers of exposure have been used to study some environmental contaminants, such as urinary cotinine for tobacco smoke (Wald et al., 1984~; carbo~hemoglobin levels in blood for exposure to CO (Redford and Drizd, 1982~; and lead levels in blood, teeth, and hair for inhalation and ingestion of lead (Harlan et al, 1985~; and benzoapyrene-DNA adducts (Perera et al., 1988~. Biological markers can be used to measure a specific contaminant, or they may be proxies for a number of contaminants.
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From page 46... ...
Indirect methods supply information on contaminant concentrations in microenvironments and the physical and chemical processes that control those concentrations. Models that predict spatial and temporal concentration distributions of air contaminants in various microenvironments are an important component of an overall human exposure model.
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From page 47... ...
For example, several epidemiological studies of environmental tobacco smoke and cancer determined exposure only by asking the subjects or household members whether they ever were exposed to environmental tobacco smoke. In occupational epidemiology, exposure categories often are determined by a worker's job classification.
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From page 48... ...
To accurately model or estimate total exposures, microenvironments and time spent in them must be identified as a function of air contaminant concentrations. A recent review of adult time-activity pattern studies (Ott, 1988)
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From page 49... ...
Furthermore, it is essential to test and validate models before they are used in exposure and risk assessments to better characterize the uncertainty in the model output. Mitigation Measures The choice of mitigation measures to be applied and the success of those measures in reducing or eliminating exposures to reduce health or nuisance effects are dependent on the sensitivity and accuracy of the model employed.
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From page 50... ...
INTEGRATION OF EXPOSURE-ASSESSMENT TECHl! lIQUES Studies to assess exposures to environmental contaminants, whether to complement environmental epidemiology, disease diagnosis and intervention, risk assessment, or risk management, must consider the three principal methods of exposure assessment: personal monitoring, biological markers, and indirect estimates.
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From page 51... ...
The scientific and regulatory communities, including those responsible for reviewing articles for scientific journals, should use consistently the def~nitions recommended in this document. Toward the development of consistent exposure-assessment practices, the use of personal monitoring as well as microenvironmental monitoring should be considered in long-term studies that examine or determine changes in population exposures to airborne contaminants.
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