Requirements for the MEPAS Human Health Impact Module

PNNL-SA-32283
Written by: Dennis Strenge

Prepared for the U.S. Department of Energy

Pacific Northwest National Laboratory
Operated by the U.S. Department of Energy
By Battelle

Requirements for the MEPAS Human Health Impact Module

1.0 Introduction

This document describes the requirements for the Multimedia Environmental Pollutant Assessment System (MEPAS) human health impact 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 the MEPAS Human Health Impact Module

The MEPAS human health impact module calculates time-varying, contaminant (chemical and radionuclide) health impacts, as well as dose equivalence for radionuclides, as a function of exposure pathway and receptor. It uses the intake and dose equivalence results from an intake module to estimate health impacts for each exposure pathway. The health impacts for radionuclides are expressed as either the radiation dose equivalence and/or the risk of developing cancer, either as total incidence, fatal incidence, or incidence of severe genetic effects. Health impacts are expressed as the total incidence risk of developing cancer for carcinogenic chemicals, and adverse health effects are experienced as hazard index (HI) for non-carcinogenic chemicals. Table 1 shows the exposure pathways addressed by this module as a function of the transport media. The health impact module receives input data from intake modules, the chemical properties database, as well as data supplied by the user through a module user interface (MUI). The health impact results serve as the endpoint of a simulation.

3.0 Summary of Requirements for the MEPAS Human Health Impact Module

This section provides an overall summary of the requirements for the MEPAS human health impact module. Detailed input, output, and scientific requirements are described in Sections 4.0, 5.0, and 6.0 respectively.

The MEPAS human health impact module will

compute time-varying, contaminant (chemical and radionuclide) health impacts for all exposure pathways listed in Table 1

allow up to 25 constituents to be considered in a scenario

operate under Windows 95 and have a user-friendly MUI with a standard Windows look and feel

meet the module specifications for FRAMES.

Table 1. MEPAS Human Health Impact Module Exposure Pathways for Each Transport Medium.

Exposure Pathway	Transport or Source Medium
	Groundwater	Surface Water	Atmosphere	Soil
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 expousre to radionuclides in soil	No	No	Yes	Yes
External exposure to radionuclides in outdoor air from a passing plume	No	No	Yes	No
Measured concentrations in foods (special foods)	n/a	n/a	n/a	n/a

4.0 Input Requirements for the MEPAS Human Health Impact Module

Data needed to compute receptor health impacts are obtained from three sources.

The boundary conditions (i.e., time-varying, exposure medium concentrations or dose equivalence for the external radiation exposure pathways, and time-varying, intake rates for the remaining pathways) are obtained from the previous module in the scenario.
The health impact control parameters for chemicals and radionuclides, and the health effects conversion factors for radionuclides are obtained from the user through the MUI.
Reference doses, dose conversion factors, and slope factors are obtained from a chemical property database.

The boundary conditions are communicated to the module through the Receptor Intake File (RIF). The input data supplied through the MUI is communicated to the model through the Global Input Data file (GID) and the model pre-processor. The GID file is also used to store the reference doses and conversion factors.

There are some general requirements associated with the MUI, which are

The MUI will operate in Windows 95 and will have a standard Windows look and feel.
The MUI will have on-line help in an HTML format that provides users with an easy-to-understand description of all input parameters required by the MUI.
The MUI will provide users with a choice of units for all input parameters having dimensions associated with them.
The MUI will include a reference feature in which the source of the specified value for each input item can be referenced if the user desires.
The MUI will convert the dimensions of user input data values into the units needed by the model and will always display the exact value and units in which the user originally entered each input data item
The MUI will show the range of values allowed for each input data item, when the cursor is positioned on that item, as a scrolling message at the bottom of the screen. When an out-of-range value is entered in a field, the MUI will indicate this by a red background in the input field and an error message in addition to the allowed range message. Data input values within range are shown with a green field background.

Specific input requirements for the MUI are as follows:

For radionuclide exposures, allow the user to select from the following cancer risk evaluation methods: A) ICRP dose and risk factors or B) EPA HEAST radionuclide slope factors.
When the ICRP dose and risk factors are to be used, the MUI will allow the user to supply the following parameters: thickness of soil layer and dry bulk density of soil layer (for the soil that receives contamination from air deposition).
For chemical exposures, allow the user to select from the following as endpoints in the analysis: 1) lifetime cancer incidence or 2) hazard index. When the user selects evaluation of hazard index results, the user will be allowed to specify a threshold value below which results are reported as zero. (Note: regardless of what the user selects, the analysis will still be limited to evaluations possible based on the values provided in the input file (*.RIF). For example, the input file may only contain intake rates for hazard index evaluations, in which case the human health impact module will not be able to generate cancer risk results).
Allow the user to limit the analysis to toxicity values of specific quality, as defined by the source of the values available in the MEPAS database. The analysis can be only for chemicals having toxicity values from the EPA IRIS and HEAST databases, or the analysis can include all toxicity values provided.

The data obtained from the RIF by the MEPAS human health impact module, and required for the module to perform its computations include average dose equivalence for the external radiation exposure to outdoor air pathway, average exposure medium concentrations for the other external radiation pathways, or average intake rates for the remaining pathways, for a specified time interval, contaminant (including progeny), and exposure location as contained in the RIF. Multiple exposure locations are allowed only for the atmospheric transport analysis.

As needed, the following data are obtained from the chemical properties database:

reference doses for noncarcinogenic chemicals
slope factors for carcinogenic chemicals
slope factors and dose conversion factors for radionuclides.

5.0 Output Requirements for the MEPAS Human Health Impact Module

The MEPAS human health impact module is required to produce a Health Impacts File (HIF) that contains time-varying, average contaminant risk or hazard index for each exposure pathway in accordance with the FRAMES data file specifications. The module also is required to produce a list file (*.HLS file) in ASCII format that documents the data actually read in by the model. The following data is output to the HIF:

time varying, average cancer incidence risk for each carcinogenic chemical contaminant, for each exposure pathway, time interval, and exposure location - multiple exposure locations are allowed only for the atmospheric transport analysis.
time varying, average hazard index for each noncarcinogenic chemical contaminant, for each exposure pathway, time interval, and exposure location - multiple exposure locations are allowed only for the atmospheric transport analysis.
time varying, average cancer incidence risk, and/or fatal cancer risk, and/or risk of cancer plus severe hereditary effects, and/or radiation dose equivalence for each radionuclide contaminant, for each exposure pathway, time interval, and exposure location - multiple exposure locations are allowed only for the atmospheric transport analysis.

6.0 Scientific Requirements for the MEPAS Human Health Impact Module

The scope of the human health impact analysis is determined by the modules that are connected to the exposure module (e.g. atmospheric transport and groundwater), and by the selections the user makes in the human health impact module MUI. The mathematical formulations for this module are provided in Strenge and Chamberlain (1995).

Scientific requirements for the impact module are as follows:

Use cancer incidence risk as the health impact measure for carcinogenic chemicals, determined by multiplying the pollutant intake by a predetermined relationship between intake and cancer incidence risk (i.e., a slope factor). A value of zero will be reported for chemicals that do not have a slope factor value for an exposure pathway.
Use the hazard quotient as the health impact measure for noncarcinogenic chemicals, determined by dividing the pollutant intake by a predetermined reference dose (an estimate of a daily intake rate that an average individual can tolerate without the risk of adverse health consequences during a lifetime). A value of zero will be reported for chemicals that do not have a reference dose for an exposure pathway.
Calculate dose equivalence for radionuclides by multiplying the pollutant intake by a factor relating intake to dose equivalence (i.e., a dose conversion factor) for ingestion, inhalation, and dermal contact exposure pathways.
Calculate dose equivalence for radionuclides by multiplying the pollutant concentration in the exposure medium by a factor relating the exposure medium concentration to dose equivalence (i.e., a dose conversion factor) for the external radiation exposure pathways (except for outdoor air).
Determine the cancer incidence risk for the ingestion, inhalation, and external exposure to soil pathways for radionuclides by multiplying the pollutant intake by a predetermined relationship between intake and cancer incidence risk (i.e., a slope factor) or by multiplying dose equivalence by the appropriate conversion factor relating dose equivalence to risk (i.e., a health effects conversion factor), as indicated by the user.
Determine risk (cancer incidence risk and/or fatal cancer risk and/or risk of cancer plus severe hereditary effects) for all other exposure pathways and risk output combinations not covered under requirements above for radionuclides by multiplying dose equivalence by the appropriate conversion factor relating dose equivalence to risk (i.e., a health effects conversion factor).

7.0 References

Strenge, D. L. and P. J. Chamberlain II. 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.