HUMAN HEALTH IMPACT MODULE

NOTE: The user must be aware that risk and health impact result values of zero in the HIF file, placed there by the MEPAS Human Health Impact Module, could mean several different things depending on the constituents and options chosen. It could mean that
1) the risk or health impact from the constituent is actually zero, meaning that the intake of the constituent was zero;
2) the chemical constituent is not a carcinogen and therefore a risk value of zero was reported;
3) the chemical constituent is only a carcinogen and therefore a hazard quotient of zero was reported;
4) the hazard quotient of the chemical is non-zero but is lower than the user-defined hazard index cutoff number; or
5) there is no IRIS or HEAST toxicity value for the chemical and the user has opted not to use values from other sources. When zeroes are found, the user should check the constituent data in the HLS file and review the input data and choices made in order to interpret the true meaning.

CHEMICAL TAB

CHEMRISK--Calculate lifetime cancer incidence
Range: On or Off

This parameter controls whether or not lifetime cancer incidence will be computed for each chemical constituent. The box should be checked to indicate that cancer incidence results are a desired output result and left unchecked if cancer incidence results are not a desired output.

CHEMLIM--Cancer incidence threshold limit
Units: none
Range: 0.0 to 1.0

This parameter is used to specify a lower cancer incidence reporting limit. Cancer incidence results computed by the model that are below the specified threshold limit will be reported as 0.0 in the HIF file. For this reason, the user should be careful to examine CI results when 0.0 values are reported. The 0.0 could indicate that there is no intake for the exposure route or that the CI computed is lower than the threshold limit.

CHEMHI--Calculate hazard index
Range: On or Off

This parameter controls whether or not a hazard index will be computed for each chemical constituent. The box should be checked to indicate that hazard index results are a desired output result and left unchecked if hazard index results are not a desired output.

RFDLIM--Hazard quotient threshold limit
Units: none
Range: 0.0 to 100.0

This parameter is used to specify a lower hazard quotient reporting limit. Hazard quotient results computed by the model that are below the specified threshold limit will be reported as 0.0 in the HIF file. For this reason, the user should be careful to examine HI results when 0.0 values are reported. The 0.0 could indicate that there is no intake for the exposure route or that the HI computed is lower than the threshold limit.

CE-TOXT--Toxicity data for chemical effects
Units: none
Range: false
Status: Deprecated

This parameter controls the selection of chemical toxicity parameter values from the chemical database. The chemical database contains four toxicity parameters: inhalation slope factor, ingestion slope factor, inhalation reference dose, and ingestion reference dose. There is only one value for each parameter. Some of the values may be zero, although, there is at least one non-zero value for inhalation (slope factor or reference dose) and one for ingestion (slope factor or reference dose). The source (reference) for each value is recorded in the database. Each parameter value reference falls into one of three categories. The first category includes toxicity values obtained from the EPA Integrated Risk Information System (IRIS), which is considered the highest quality source for toxicity parameter values because of the consistent methodology and review process applied in development of the values. The second category includes toxicity values obtained from the Health Effects Assessment Summary Tables (HEAST), which contains toxicity values that are not provided by IRIS, and are considered to be of higher uncertainty. The third category includes toxicity values that are less certain and were developed using very approximate methods.

The parameter CE-TOXC was used to select values based on their source as follows:
true = Use the database values from IRIS or HEAST only.
false = Use the value given in the database regardless of the source (IRIS, HEAST, other).
NOTE: If CE-TOXC = true and the constituent does not have an IRIS or HEAST referenced toxicity value, then no calculation will be performed and a zero value will be reported for the health impact.

RADIONUCLIDE TAB

HE-INC--Calculate lifetime cancer incidence
Range: On or Off

This parameter controls whether or not lifetime cancer incidence will be computed for each radionuclide constituent. The box should be checked to indicate that cancer incidence results are a desired output result and left unchecked if cancer incidence results are not a desired output.

HE-CONINC--Lifetime cancer incidence conversion factor
Units: unit risk per Severt (risk/Sv)
Range: 1.0E-04 to 1.0

This parameter is used to specify the lifetime cancer incidence conversion factor to be used by the code.

HE-FAT--Calculate cancer fatalities
Range: On or Off

This parameter controls whether or not lifetime cancer fatalities will be computed for each radionuclide constituent. The box should be checked to indicate that cancer fatality results are a desired output result and left unchecked if cancer fatality results are not a desired output.

HE-CONFAT--Cancer fatalities conversion factor
Units: unit risk per Severt (risk/Sv)
Range: 1.0E-04 to 1.0

This parameter is used to specify the cancer fatalities conversion factor to be used by the code.

HE-FSH--Calculate lifetime cancer and severe hereditary effects
Range: On or Off

This parameter controls whether or not lifetime cancer and severe hereditary effects will be computed for each radionuclide constituent. The box should be checked to indicate that cancer and severe hereditary effects are a desired output result and left unchecked if they are not a desired output.

HE-CONFSH--Lifetime cancer and severe hereditary effects conversion factor
Units: unit risk per Severt (risk/Sv)
Range: 1.0E-04 to 1.0

This parameter is used to specify the lifetime cancer and severe hereditary effects conversion factor to be used by the code.

HE-CEDE--Calculate radiation dose commitment (CEDE)
Range: On or Off

This parameter controls whether or not radiation dose commitment will be computed for each radionuclide constituent. The box should be checked to indicate that radiation dose commitment results are a desired output result and left unchecked if radiation dose commitment results are not a desired output.

IHEAST--Cancer risk evaluation method

This parameter is used to specify the cancer risk evaluation method to be used by the code. The user must specify one of the two choices
1) ICRP dose and risk factors or
2) HEAST radionuclide slope factors.
The user loses the method choice if either cancer fatalities or lifetime cancer and severe hereditary effects are selected as desired outputs. If either of these choices is selected, the user must use the ICRP dose and risk factors option.

TSOIL--Thickness of contaminated soil/sediment layer
Units: meters (m)
Range: 0.001 to 5.0

This parameter is used to define the thickness of the soil/sediment layer at the exposure location. This parameter is used only for the external exposure from contaminated soil pathway and when the user selects the ICRP cancer risk evaluation method.

DSOIL--Density of contaminated soil/sediment layer
Units: grams per centimeters cubed (g/cm3)
Range: 1.0 to 4.0

This parameter is used to define the density of the soil/sediment layer at the exposure location. This parameter is used only for the external exposure from contaminated soil pathway and when the user selects the ICRP cancer risk evaluation method.

MEPAS Health Impacts Model Internal Default Values
Parameter Description Value Range Units Reference
CRFC Conversion from reference dose to reference concentration 3.5 fixed 70kg per 20m3/day EPA 1991
CURF Conversion from slope factor to unit risk factor for inhalation 0.28571 fixed 20m3/day per 70kg EPA 1991