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Appeodix D: Conceptual Model of Fiber Exposure
Pages 261-266

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From page 261...
... This conceptual model enabled the committee to identify the factors that could be important in determining exposure so that it could seek information in an organized way and attempt to relate the info,.~ation about one fiber type to that for other fibers to facilitate an analysis of comparative exposure potentials. Figure D-1 provides a conceptual overview of the calculations that would be necessary to estimate nonoccupational exposures of humans in the absence of direct measurements.
From page 262...
... - IEnvironmental fluxes 1 (metric tone/year) ~Total fluxes~ ('Detric eons/yr)
From page 263...
... -~.Human intake ratesl (fibers/day) x iBiodis~osition factors~ (~/organ)
From page 264...
... In brief, the factors shown in Figure D-l take into account the following phenomena: Occurrence: Geologic occurrence in the United States. In princ iple, this factor could be measured by the proven and indicated reserves of the mineral, if commerc ial ly important, or by a re let ive abundance f igure for others.
From page 265...
... or as a percentage rate of total inventory (i.e., metric tons discharged per year per metric ton in place, multiplied by 100~. Generally, the release is called a "discharge" when associated with a manufacturing process, but a "release when associated with product use, e.g., when fibers are worn off vinyl asbestos ti les .
From page 266...
... The dose rate and disappearance rate together determine the buildup of tissue burden of fibers. SUGARY Although the above list does not contain all the factors that define exposure at the tissue level, and although the conceptual model captures neither all their relationships nor the difficulty in measuring some of them, the model does give an idea of the complexity of the exposure of an individual to asbestiform fibers.

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