Radiation Dosimetry Factors

Two methods are in general use for evaluation of risk from intake of radionuclides. The first involves use of radiation dosimetry factors to estimate the lifetime radiation dose from the postulated exposure scenario. The total lifetime radiation dose is then multiplied by a health effects conversion factor to obtain the human health risk endpoint (usually cancer incidence or cancer fatality risk). The second method for estimation of radiation risk involves use of slope factors provided by the EPA Health Effect Assessment Summary Tables (HEAST). Slope factors are provided for inhalation and ingestion intake routes, and for external exposure to radionuclides distributed uniformly in contaminated soil. The slope factors and radiation dosimetry factors are contained in the MEPAS database. The radiation dose factors are based on EPA Federal Guidance Reports (FGR) 11 and 12. The dermal absorption dose factors have been calculated by staff of Pacific Northwest Laboratory, using a dosimetric computer program similar to the program used to generate the internal dosimetry numbers of FGR11.

The following table indicates the exposure pathways that may be evaluated using the slope factors and radiation dose factors. 

A summary of the radiation dosimetry and slope factors follows for the parameters included in the MEPAS database.

Inhalation Dose Factor (rem/pCi)

The inhalation dose factor gives the lifetime radiation dose (effective dose equivalent) from inhalation of unit activity (one pCi) of a radionuclide. The dose factors include contributions from radiation decay chain progeny produced within the body after inhalation of the parent radionuclide.

Ingestion Dose Factor (rem/pCi)

The ingestion dose factor gives the lifetime radiation dose (effective dose equivalent) from ingestion of unit activity (one pCi) of a radionuclide. The dose factors include contributions from radiation decay chain progeny produced within the body after ingestion of the parent radionuclide.

Dermal Absorption Dose Factor (rem/pCi)

The dermal absorption dose factor gives the lifetime radiation dose (effective dose equivalent) following dermal absorption of unit activity (one pCi) of a radionuclide. The dose factors include contributions from radiation decay chain progeny produced within the body after absorption of the parent radionuclide. The dermal absorption dose factor is applied to the estimated total absorption of the radionuclide through the skin for dermal contact (water or soil) scenarios.

External Radiation Dose Factor for Submersion in Contaminated Air (rem/hr per pCi/m^3)

The air submersion external dose factor provides the dose rate for exposure to a radionuclide distributed uniformly in air. This exposure pathway is generally not significant compared to the inhalation pathway, except for noble gas radionuclides (i.e. krypton-85) which are not absorbed by the body during inhalation.

External Radiation Dose Factor for Exposure to Contaminated Soil (rem/hr per pCi/m^2)

The ground external dose factor provides the dose rate for exposure to a radionuclide from a radionuclide distributed uniformly in soil. The radionuclide is assumed to be in an infinite contaminated soil layer, although for practical purposes, a contamination depth of 1 meter represents an effective infinite layer (i.e., increasing the depth of contamination below 1 meter will not increase the dose rate).

External Radiation Dose Factor for Exposure to Contaminated Water (rem/hr per pCi/L)

The water immersion external dose factor provides the dose rate for exposure to a radionuclide while immersed in contaminated water. The dose factor is used to estimate the external dose while swimming and boating (partial immersion).

Inhalation Slope Factor (risk/pCi)

The inhalation slope factor provides an estimate of the risk of cancer (incidence) from inhalation of a radionuclide. All slope factors in the MMEDE database were taken from HEAST reports. Values are subject to change as new HEAST reports are issued by EPA.

Ingestion Slope Factor (risk/pCi)

The ingestion slope factor provides an estimate of the risk of cancer (incidence) from ingestion of a radionuclide. All slope factors in the MMEDE database were taken from HEAST reports. Values are subject to change as new HEAST reports are issued by EPA.

External Exposure to Soil Slope Factor (risk/yr per pCi/kg)

The external exposure slope factor provides an estimate of risk per year of exposure from exposure to radionuclides in soil. All external slope factors in the MMEDE database are taken from HEAST reports. Values are subject to change as new HEAST reports are issued by EPA.

Constituent Database Links

Constituent : con
Physical Parameters
Dose Factors
Environmental Decay Half Times
Environmental Transfer Factors
Toxicity Factors