Exposure Pathway and Human Health Impact Assessment Models

PNL-10523
UC-630

MULTIMEDIA ENVIRONMENTAL POLLUTANT
ASSESSMENT SYSTEM (MEPAS)^®:

EXPOSURE PATHWAY AND HUMAN HEALTH IMPACT
ASSESSMENT MODELS

D. L. Strenge
P. J. Chamberlain

May 1995

Prepared for
the U.S. Department of Energy
under Contract DE-AC06-76RLO 1830

Pacific Northwest Laboratory
Richland, Washington 99352

Copyright 1989 Battelle Memorial Institute

PREFACE

    The Multimedia Environmental Pollutant Assessment System (MEPAS) is a physics-based environmental analysis code that integrates source-term, transport, and exposure models for endpoints such as concentration, dose, or risk. Developed by Pacific Northwest Laboratory^(a), MEPAS is designed for site-specific assessments using readily available information. Endpoints are computed for chemical and radioactive pollutants. For human health impacts, risks are computed for carcinogens and hazard quotients for noncarcinogens. This system has wide applicability to a range of environmental problems using air, groundwater, surface-water, overland, and exposure models. With this system, a user can simulate release from the source, transport through air, groundwater, surface water, or overland, and transfer through food chains and exposure pathways to the exposed individual or population. Whenever available and appropriate, U.S. Environmental Protection Agency guidance and models were used to facilitate compatibility and acceptance.

    Although based on relatively standard transport and exposure computation approaches, the unique feature of MEPAS is that these approaches are integrated into a single system. The use of a single system provides a consistent basis for evaluating health impacts for a large number of problems and sites. Implemented on a desktop computer, a user-friendly shell allows the user to define the problem, input the required data, and execute the appropriate models. This document describes mathematical formulations used in the MEPAS exposure assessment and human health impact component.

(a)     Pacific Northwest Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.

SUMMARY

The Multimedia Environmental Pollutant Assessment System (MEPAS) provides physics-based models for human health risk assessment for radioactive and hazardous pollutants. MEPAS analyzes pollutant behavior in various media (air, soil, groundwater and surface water) and estimates transport through and between media and exposure and impacts to the environment, to the maximum individual, and to populations. MEPAS includes 25 exposure pathway models, a database with information on more than 650 contaminants, and a sensitivity module that allows for uncertainty analysis.

Four major transport pathways are considered in MEPAS: groundwater, overland, surface water, and atmospheric. Descriptions of the mathematical basis of each of these components will be published in companion reports. Guidelines for determining input parameter values are provided in Buck et al. (1995).

This report describes the exposure pathway and health impact assessment component of MEPAS, which provides an estimate of health impacts to selected individuals and populations from exposure to pollutants. The exposure pathway analysis starts with pollutant concentration in a transport medium and estimates the average daily dose to exposed individuals from contact with the transport medium or a secondary medium contaminated by the transport medium.

The average daily dose is then used to estimate a measure of health impact appropriate to the type of pollutant considered.

Discussions of the exposure pathway models include the assumptions and equations used to convert the transport medium concentrations to exposure medium concentrations. The discussion for a given exposure pathway defines the transport pathways leading to the exposure, the special processes considered in determining the pollutant concentration in the exposure medium, and the exposure model used to estimate the average daily dose. Models for the exposure pathway and health impact assessments require definition of several parameters. A summary of the notation used for these parameters is provided. The default values used in MEPAS for these parameters are presented and discussed.