The Application of Microexposure Event Modeling to the Evaluation of Water-Related Exposures. J. A. Rothrock, P. S. Price, R. E. Keenan, E. S. Ebert, C. F. Chaisson, and W. R. Muir, McLaren/Hart, Inc., 1685 Congress Street, Portland, ME 04102; TAS-Environ, 4350 North Fairfax Drive, Suite 300, Arlington, VA 22203; and Hampshire Research Institute, 1600 Cameron Street, Suite 100, Alexandria, VA 22314
Microexposure Event Assessment (MEA) is a form of probabilistic analysis that applies Monte Carlo to more complex exposure models. Exposures to individuals in the population of interest are estimated as a series of separate exposure events. This allows the risk assessor to incorporate interindividual (e.g., physiological and behavioral parameters) and temporal variation into the exposure assessment process. MEA is applied using a prototype of LifeLine(tm) software to examine a hypothetical population of individuals exposed to a contaminant in a surface water body used as a public water supply. The individuals are exposed through the tap water in their homes (from drinking and showering) or through the consumption of fish and shellfish from affected water bodies. The model considers the mobility of individuals and the likelihood of a home having contaminated tap water. Age-specific probability density functions for body weight, inhalation rate, and whole body surface area are used to physiologically characterize the individuals. Distributions are also used to determine fish/shellfish consumption rates, house-specific tap water concentrations, and age-specific tap water intake rate. Individuals’ exposures are modeled throughout their lifetime, and the model calculates the maximum 1-, 14-, and 30-day dose for each year; the annual average total dose; the lifetime average daily dose; and highest daily and annual average doses for tap water ingestion, total tap water exposure, and total exposure (including fish/shellfish consumption). Several different exposure scenarios are examined, including variations in the air-water partition coefficient of the contaminant, the bioconcentration factor, and the fraction of the population receiving contaminated tap water.
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