This document describes the requirements for the Multimedia Environmental Pollutant Assessment System (MEPAS) chronic exposure module. The module is specifically designed for inclusion in the Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES), which is a platform that allows the linking of various multimedia modules into complete source/transport/exposure assessment systems (Whelan et al., 1997). These requirements can be used by software engineers and testers to ensure this module meets the needs of the clients and users.
2.0 Purpose of MEPAS Chronic Exposure Module
The MEPAS chronic exposure module is designed to take time-varying, contaminant concentrations in environmental media (i.e., groundwater, surface water, air, and soil) and generate average contaminant concentrations in exposure media at the point of exposure or contact with receptors. The total time frame over which the environmental media concentrations occur is divided into discrete exposure intervals (which may or may not overlap) as determined by the user, and an average concentration is determined for each of these intervals. Table 1 shows the exposure pathways addressed by this module as a function of the source or transport media. The exposure module receives input data from source and transport modules, the chemical properties database, as well as data supplied by the user through a module user interface (MUI). The average contaminant concentrations in the exposure media are supplied to receptor intake modules or can serve as the endpoint of the simulation.
3.0 Summary of Requirements for the MEPAS Chronic Exposure Module
This section provides an overall summary of the requirements for the MEPAS chronic exposure module. Detailed input, output, and scientific requirements are described in sections 4.0, 5.0, and 6.0.
The MEPAS chronic exposure module will
Table 1. MEPAS Chronic Exposure Module Exposure Pathways by Transport or Source Medium
|Exposure Pathway||Transport or Source Medium|
|Ingestion of drinking water||Yes||Yes||No||No|
|Dermal contact with water while showering||Yes||Yes||No||No|
|Inadvertent ingestion of water while showering||Yes||Yes||No||No|
|Ingestion of leafy vegetables||Yes||Yes||Yes||Yes|
|Ingestion of other vegetables||Yes||Yes||Yes||Yes|
|Ingestion of meat||Yes||Yes||Yes||Yes|
|Ingestion of milk||Yes||Yes||Yes||Yes|
|Ingestion of fin fish||No||Yes||No||No|
|Ingestion of shellfish||No||Yes||No||No|
|Inadvertent ingestion of water while swimming||No||Yes||No||No|
|Dermal contact with water while swimming||No||Yes||No||No|
|Dermal contact with sediment during shoreline use||No||Yes||No||No|
|Inadvertent ingestion of sediment during shoreline use||No||Yes||No||No|
|Inadvertent ingestion of soil||No||No||Yes||Yes|
|Dermal contact with soil||No||No||Yes||Yes|
|Indoor inhalation of volatile chemicals released from shower water||Yes||Yes||No||No|
|Indoor inhalation of volatile chemicals released from other domestic water uses||Yes||Yes||No||No|
|Inhalation of outdoor air from a passing plume||No||No||Yes||No|
|Inhalation of resuspended soil particles||No||No||Yes||Yes|
|External exposure to radionuclides while swimming||No||Yes||No||No|
|External exposure to radionuclides while boating||No||Yes||No||No|
|External exposure to radionuclides in sediment during shoreline use||No||Yes||No||No|
|External exposure to radionuclides in soil||No||No||Yes||Yes|
|External exposure to radionuclides in outdoor air from a passing plume||No||No||Yes||No|
4.0 Input Requirements for the MEPAS Chronic Exposure Module
Data needed to compute contaminant concentrations in an exposure medium are obtained from three sources. The boundary conditions (i.e., time-varying, contaminant concentrations in the source or transport medium) are obtained from the previous module in the scenario (i.e., a transport or source module). The exposure pathways to consider, the time discretization and exposure duration information, and the physical characteristics of the exposure media (as needed) are obtained from the user through the MUI. The contaminant chemical properties (e.g., water purification factors, bioaccumulation factors, food chain transfer factors, etc.) are obtained from a chemical property database. The boundary conditions are communicated to the module through the Water Concentration File (WCF) for groundwater and surface water transport pathways, the Atmospheric Transport Output (ATO) file for the air pathway, and the Soil Concentration File (SCF) for contaminants at a contaminated soil source. The input data supplied through the MUI is communicated to the model through the Global Input Data (GID) file and the model pre-processor. The GID file is also used to store the contaminant chemical property data.
There are some general requirements associated with the MUI, which are
The MUI also must allow the user to input the following exposure control data, which will apply globally to all four source and transport media:
The duration of each time interval is equal to the exposure duration, which is defined by the user for each of the four source and transport media. Also, the MUI allows the user to select the exposure pathways to be included in the analysis. Only those pathways that make sense for the current scenario are available as options to the user. For example, if the groundwater medium is the only medium being considered, then dermal contact while swimming is not an available exposure pathway and should either be grayed out or not shown at all. The allowed exposure pathways for each medium are given in Table 1.
The MUI must allow the user to define additional parameters that are needed in the analysis. These parameters are identified in the following requirements:
The exposure module also provides an option to customize the exposure data specific to each exposure pathway. Specific requirements related to this feature are as follows:
The MEPAS chronic exposure module will obtain data from the WCF file whenever a ground water or surface water exposure pathway is selected. This data will include time-varying, instantaneous, aqueous concentrations for each contaminant (including progeny).
The MEPAS chronic exposure module will obtain data from the SCF file whenever a soil exposure pathway is selected. This data will include the initial, instantaneous, total soil concentration on a bulk volume basis (i.e., total mass of contaminant per bulk volume of soil) for each contaminant (including progeny).
The MEPAS chronic exposure module will obtain data from the ATO file whenever an atmospheric exposure pathway is selected. The following data will be obtained:
As needed, the following data are obtained from the chemical properties database
5.0 Output Requirements for the MEPAS Chronic Exposure Module
The MEPAS exposure module is required to produce an Exposure Pathway File (EPF) that contains time-varying, average contaminant concentrations in the exposure medium at the defined exposure point in accordance with the FRAMES data file specifications. The module also is required to produce a listing file (*.ELS file) in ASCII format that documents the data actually read in by the model and provides a summary of intermediate calculation results (e.g., computed leach rate constants for agricultural soil, etc.). The following data is output to the EPF:
6.0 Scientific Requirements for the MEPAS Chronic Exposure Module
The scope of the exposure analysis is determined by the transport or source modules connected to the exposure module (e.g. atmospheric transport, aquifer, etc.), and by the selections the user makes in the MUI. The mathematical formulations for this module are provided in Strenge and Chamberlain (1995).
The contaminant concentration in the source or transport medium is the starting point for the exposure analysis. Except for the atmospheric transport medium, this concentration is an instantaneous value. For the atmospheric transport medium, the concentrations are averaged over a one-year period and the deposition rates are annual average values. The transport medium may or may not be the medium of exposure. For example, the groundwater transport pathway generates estimates of contaminant concentration in the groundwater at the well. In this case, the well water is also the medium of exposure, although some modifications to the concentration are possible during transfer through the treatment plant and distribution system to the individuals exposed during domestic water uses. When the well water is used for irrigation of agricultural crops, the exposure medium is not the well water, but the foods produced. For agricultural pathways, models are used to estimate the transfer of pollutants from the irrigation water to the food consumed by humans.
The processes affecting the transfer of contaminants from the transport or source medium to the exposure medium are defined in the following list of scientific requirements for the exposure module:
Strenge, D. L. and P. J. Chamberlain. 1995. Multimedia Environmental Pollutant Assessment System (MEPAS): Exposure Pathway and Human Health Impact Assessment Models. PNL-10523. Pacific Northwest Laboratory, Richland, Washington.
Whelan G., K. J. Castleton, J. W. Buck, G. M. Gelston, B. L. Hoopes, M. A. Pelton, D. L. Strenge, and R. N Kickert. 1997. Concepts of a Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES). PNNL-11748, Pacific Northwest National Laboratory, Richland, Washington.