# dose and risk calculations

## Introduction 

This chapter discusses the final step in obtaining estimates of doses
and risks to the hypothetical receptors described in the scenarios. As
indicated in [Chapter 9](../Chapter_09_ready%20for%20CDC%20031405.doc),
doses and risks are proportional to "intake of radionuclides by each
ingestion and inhalation exposure pathway, and exposure to radionuclides
from external exposure pathways."(1). The intakes, estimated according
to the approaches outlined in [Chapter
9](../Chapter_09_ready%20for%20CDC%20031405.doc), depend on the
estimated concentrations of radionuclides in various environmental
media: air, water, soil, plants, and animal products. Methods for
estimating concentrations are presented in [Chapter
5](../Chapter_05_Ready%20for%20CDC%20031405.doc) for air, [Chapter
7](../Chapter_07_Ready%20for%20CDC%20031405.doc) for water, and [Chapter
8](../Chapter_08_ready%20for%20CDC%20031405.doc) for the remaining
media. Intakes also depend on the behaviors described in the scenario
specifications ([Chapter
3](../Chapter_03_ready%20for%20CDC%20031405.doc)) that bring the
receptors into contact with these contaminated environmental media.
Because the doses and risks are proportional to intake, linear
coefficients are used to relate intake to dose and risk. These
coefficients have been developed over many decades by the health physics
community through national and international radiation protection
organizations.

## Basic Radiation Concepts

Additional information about radiation assessment and protection
principles, and terminology, can be obtained from Internet sites on
radiation such as those established by EPA
(<http://www.epa.gov/radiation>) and the University of Michigan
(<http://www.umich.edu/~nradinfo>)

### Types of Radiation

Radionuclides released by the SRS into the environment emit two basic
kinds of radiation:

-   Particle radiation - tiny fast-moving particles that have both
    energy and mass (weight)

-   Electromagnetic radiation - pure energy with no weight.

Particle radiation includes alpha and beta particles. An alpha particle
is the positively charged nucleus of a helium atom. Alpha particles lose
energy quickly when they collide with matter; therefore, their ability
to penetrate is slight. A sheet of paper or layer of skin may completely
absorb such particles. However, if radionuclides emitting alpha
particles are inside the body, the alpha particles may cause harm to
body cells. Beta particles are free, mobile electrons. Beta particles
have a greater ability to penetrate matter than alpha particles.
Electromagnetic radiation emitted by radionuclides includes gamma rays
and x-rays. This radiation has more ability to penetrate matter than
most particle radiation. All the types of radiation emitted by
radionuclides may damage living cells by ionizing atoms or molecules
within the cells.

### Radiation Dose 

The term "dose" has several meanings, depending on how it is used. For
this study, several different terms for "dose" are needed to describe
the effects of radiation[^1]. The most fundamental definition of dose is
the *absorbed dose*, which a measure of the amount of energy imparted to
matter (e.g. tissue) by the radiation. Units of the *absorbed dose* are
the rad or gray; the gray, the SI unit of absorbed dose, is equivalent
to one joule of energy absorbed by a kilogram of tissue (J/kg). One gray
equals 100 rad.

Although the amount of energy absorbed per unit mass, as measured by the
absorbed dose, is fundamental to determining the adverse impact of
radiation on the absorbing tissue and ultimately on the health of the
exposed person, the adverse impact also depends upon the type of
radiation absorbed. This is because different types of radiation are
more or less efficient in producing damage in tissue, given the same
amount of energy absorbed per unit mass. These differences are included
in the concept of an *equivalent dose*,[^2] which may be defined as:

H = D·W~R~ (10-1)

Where, H is the equivalent dose (Sievert)

D is the absorbed dose (Gray)

W~R~ is the weighting factor (dimensionless)

The SI unit of equivalent dose is called the *Sievert* (Sv); another
unit commonly used in the United States is the "*rem*," or "Roentgen
equivalent man," which is one one-hundredth of a Sievert. A *millirem*
(mrem) is one one-thousandth of a rem. The weighting factor[^3] accounts
for differences in how energy is imparted to tissue by different types
of radiation. X-rays, gamma rays, and beta particles are generally
assigned weighting factors of one, while alpha particles are generally
assigned weighting factors of twenty.

One difficulty of estimating radiation doses to humans is that human
bodies are variable. To achieve agreement on standards for radiation
protection, and to help comparisons of different radiation dose
assessments, a concept was developed called a *standard* *man*, a
surrogate human having organs of both sexes of reference radii and
masses. Risk assessments are commonly performed using these standard
physiological assumptions.

As discussed in previous chapters, especially [Chapters
9](../Chapter_09_ready%20for%20CDC%20031405.doc), exposure to radiation
may result from radionuclides inside or outside the body. Radionuclides
were modeled as entering the body by inhalation and ingestion. Exposures
to external radiation from radionuclides outside the body were modeled
for:

-   Immersion in a plume of air

-   Exposure to contaminated soil

-   Exposure to a contaminated shoreline

-   Exposure to contaminated water while swimming

-   Exposure to contaminated water while boating

The radiation exposure from these external sources tends to be uniform
throughout the body of the exposed person, because the sources are large
compared to the human body. This is generally different from therapeutic
and diagnostic medical exposures, where the radiation is focused on a
particular body organ or region. Once the human is removed from
proximity to the medium (air, water, and soil) contaminated by
radionuclides, the external radiation exposure ceases.

Exposure resulting from radionuclides within the body is substantially
different. First, a radionuclide may lodge in or migrate to a particular
organ of the body, where it may produce most of its damage. Second,
although some types of radiation (alpha and beta) travel short
distances, gamma rays may irradiate body organs some distance from the
location of the radionuclides. Third, although some radionuclides may
lodge in a particular organ (e.g., the lung for inhaled particles), in
time they may migrate to organs that have a biochemical affinity for
them (e.g., Sr tends to migrate to bones). Fourth, even though the
uptake of a radionuclide by inhalation or ingestion may be a short-term
or even one-time event, the radionuclides inside the body may continue
to irradiate body organs. Finally, radionuclides inside the body may
decay or be excreted over time, so their effect on the body lessens over
time. To address this complex biological and physical situation,
mathematical models are used to describe movement and retention of
radioactive material in the body and the doses that are imparted to
various organs. A radionuclide taken into the body will impart a dose to
a person not only for the first year of intake, but in all the following
years until the radionuclide decays or is eliminated. To account for
this long-lasting effect, the time-varying equivalent dose rate from
radioactive material uptake at a given time is integrated (added) over
an appropriate time period. For this study, the time period used is 70
years, representing a typical lifetime.[^4] This integral of equivalent
dose rate for internal radionuclides produces a *committed equivalent
dose*, which is measured in Sieverts.

The models (sometimes called *biokinetic* models) used to describe the
movement of radionuclides in the body and the resulting doses to various
organs are quite complex, as indicated in the following summary:

> "The dosimetric methodology used in FGR-13 is that of the ICRP\... The
> methodology considers two sets of anatomical regions within the body.
> A set of source regions is used to specify the location of
> radionuclide within the body. The set of target regions consists of
> those organs and tissues for which the radiation dose is of interest.
> For a specific radionuclide, the set of source regions consists of
> anatomical regions along the route of intake (respiratory and
> gastrointestinal tract), regions associated with the systemic behavior
> of the radionuclide, and regions along the routes of elimination of
> the radionuclide from the body. A region may consist of multiple
> compartments as necessary to represent the kinetics. Within each
> region the radionuclide is assumed to be uniformly distributed either
> by volume or, in some instances, by surface area. The mean absorbed
> dose to the target region is the fundamental dosimetric quantity.
>
> The energy deposition in the target regions is based on calculations
> of the radiation transport in an anthropomorphic phantom representing
> the newborn, 1 y, 5 y, 10 y, 15-y-old male, and adult male (with
> breasts, ovaries, and uterus added)." (3)

Somewhat simpler models are used to estimate the doses to various organs
in the body from external radiation.

At one time, the usual practice was to calculate doses to individual
bodily organs or tissues. But in 1977, the ICRP recommended in ICRP-26
the concept of a weighted mean whole-body dose (4). It provides a
measure of the dose across multiple organs or tissues, and is determined
by multiplying the dose received by each organ or tissue by a weighting
factor, and then adding all of these weighted doses to arrive at a
single representative dose. ICRP originally called this dose an
*effective dose equivalent* (4). In a more recent recommendation
(ICRP-60, issued in 1991), ICRP called this dose an *effective dose*(2).
The effective dose may be defined as:

H~E~ = Σ~T~ W~T~·H~T~ (10-2)

Where, H~E~ is effective dose (Sv);

> W~T~ is a weighting factor representing the ratio of the stochastic
> risk (cancers and hereditary effects) from irradiation of tissue T to
> that for the whole body when irradiated uniformly;

H~T~ is the equivalent dose in tissue T.

Values for tissue weighting factors recommended by ICRP in 1977
\[ICRP-26\] and 1991 \[ICRP-60\] are listed in Table 10-1. As shown, the
weighting factors recommended in ICRP-60 are different from those
recommended in ICRP-26.[^5] Additional information on these weighting
factors may be found in original ICRP documents cited above and in the
documentation for FGR-13 (3), (5), FGR-12 (6), and FGR-11 (7);
information on how these are employed in the GENII-2 code may be found
in Chapter 11 of the GENII SDD.

Table 10‑1 ICRP-26 and ICRP-60 Tissue Weighting Factors

+-------------------------+--------------------+-----------------------+
| Organ or Tissue         | ICRP-26 Weighting  | ICRP-60 Weighting     |
|                         | Factors            | Factors               |
+-------------------------+--------------------+-----------------------+
| Gonads                  | 0.25               | 0.20                  |
+-------------------------+--------------------+-----------------------+
| Breast                  | 0.15               | 0.05                  |
+-------------------------+--------------------+-----------------------+
| Colon                   |                    | 0.12                  |
+-------------------------+--------------------+-----------------------+
| Red bond marrow         | 0.12               | 0.12                  |
+-------------------------+--------------------+-----------------------+
| Lungs                   | 0.12               | 0.12                  |
+-------------------------+--------------------+-----------------------+
| Stomach                 |                    | 0.12                  |
+-------------------------+--------------------+-----------------------+
| Urinary bladder         |                    | 0.05                  |
+-------------------------+--------------------+-----------------------+
| Liver                   |                    | 0.05                  |
+-------------------------+--------------------+-----------------------+
| Esophagus               |                    | 0.05                  |
+-------------------------+--------------------+-----------------------+
| Thyroid                 | 0.03               | 0.05                  |
+-------------------------+--------------------+-----------------------+
| Bone surface            | 0.03               | 0.01                  |
+-------------------------+--------------------+-----------------------+
| Skin                    |                    | 0.01                  |
+-------------------------+--------------------+-----------------------+
| Remainder               | 0.30^\*^           | 0.05^†,‡^             |
+-------------------------+--------------------+-----------------------+
| \*The value 0.30 is     |                    |                       |
| applied to the average  |                    |                       |
| dose among the five     |                    |                       |
| remaining organs or     |                    |                       |
| tissues receiving the   |                    |                       |
| entire dose, excluding  |                    |                       |
| the skin, lens of the   |                    |                       |
| eye, and the            |                    |                       |
| extremities.            |                    |                       |
|                         |                    |                       |
| ^†^The reminder         |                    |                       |
| consists of: adrenals,  |                    |                       |
| brain, small intestine, |                    |                       |
| upper large intestine,  |                    |                       |
| kidney, muscle,         |                    |                       |
| pancreas, spleen,       |                    |                       |
| thymus, and uterus.     |                    |                       |
|                         |                    |                       |
| ^‡^The value 0.05 is    |                    |                       |
| applied to the average  |                    |                       |
| dose to the remainder   |                    |                       |
| tissue group. However,  |                    |                       |
| if a member of the      |                    |                       |
| remainder receives a    |                    |                       |
| dose exceeding the      |                    |                       |
| highest dose in any of  |                    |                       |
| the 12 organs for which |                    |                       |
| weighting factors are   |                    |                       |
| specified, a weighting  |                    |                       |
| factor of 0.025 is      |                    |                       |
| applied to that organ   |                    |                       |
| and weighting factor of |                    |                       |
| 0.025 is applied to the |                    |                       |
| average dose to the     |                    |                       |
| rest of the remainder.  |                    |                       |
+-------------------------+--------------------+-----------------------+

The concept of effective dose is used for doses resulting from both
external and internal exposures. Furthermore, for internal doses, the
concept of effective dose is combined with the concept of committed
dose, yielding the *committed effective dose*, which is sometimes
shortened to *effective dose* and is the time integral of the effective
dose rate. For both internal and external exposures, the effective dose
depends on the age of the exposed individual. This is because the risk
of cancer depends on the latency period over which cancer may develop.
Persons exposed early in life have a higher risk of radiation-induced
disease than persons exposed later in life, because these diseases have
a greater time to develop and because other causes of mortality are less
likely to arise. In addition, for internal exposures, the committed dose
is higher for persons exposed earlier in life than those exposed later
in life, because the residual radionuclides have a longer time to
irradiate body organs. In addition, the models used to derive the organ
doses from internal incorporate age-dependent factors into the models,
e.g., the size of various organs, metabolic rates. For all these
reasons, the coefficients used to relate effective doses to internal or
external exposures are age-dependent. In this study these age-dependent
dose coefficients were used to estimate doses, so the changing ages of
children in the various scenarios would be accounted for.

### Risk from Radiation Exposure 

As discussed in the preceding section, the concept of effective dose
incorporates the risk of cancer incidence for various organs in the
body. "The effective dose equivalent is intended to replace the complex
dose distribution pattern from internal and external irradiation by an
equivalent, uniform, whole-body dose." (8). One way to express risks is
the probability of cancer *fatality* (*mortality*) occurring over a
lifetime from exposure to radioactive material. Fatality (mortality) is
the risk of dying of cancer. Another way to express risks is the
probability of cancer *incidence* *(morbidity)* occurring over a
lifetime from exposure to radioactive material. Incidence (morbidity) is
the risk of getting radiation-related cancer whether or not the cancer
is fatal. For the point estimate calculations described in [Chapter
11](../Chapter_11_ready%20for%20CDC%20031405.doc), the effective dose
equivalent, the individual organ doses, the cancer incidence risk, and
the cancer fatality risk were all calculated and recorded on an annual
basis for each receptor in each scenario. For the uncertainty analysis
described in [Chapter 12](../Chapter_12_ready%20for%20CDC_031405.doc),
only the effective dose equivalent over the 39-years studied, not the
risk, was recorded for each receptor in each scenario, because of the
large amount of data involved.

## Calculation of Dose or Risk

Doses and risks are proportional to the intakes calculated according to
the methods outlined in [Chapter
9](../Chapter_09_ready%20for%20CDC%20031405.doc). The constant of
proportionality (dose coefficient, dose conversion factor, or risk
coefficient) depends on the type of exposure; i.e., whether the exposure
is external, inhalation, or ingestion. For external exposure the dose
coefficient depends on the geometry of the contaminated medium relative
to the receptor; for example, the dose coefficient depends on whether
the receptor is immersed in a plume of radioactive contaminants, is
standing on the surface of contaminated ground, or is on a contaminated
body of water. For internal exposure the dose coefficient depends upon
whether the radioactive material was inhaled or ingested. In addition,
for inhaled radionuclides, the dose coefficient depends upon the
inhalation solubility class. The solubility class is important because
in the metabolic models used to determine dose, the solubility of the
nuclide determines how long it stays in the lungs and its ability to
migrate to other organs in the body. The dose coefficient also depends
on the age of the receptor for the reasons described at the end of
Section 10.2.2. Finally, the dose coefficient depends on the identity of
the particular radionuclide causing the exposure. Because different
radionuclides emit different types of radiation (particles and
electromagnetic waves) of different energies as they decay, the doses
produced from internal or external exposure are unique for each
radionuclide.

The constants of proportionality, the dose coefficients or dose
conversion factors, have been compiled for a large number of
radionuclides by assuming a unit concentration in the appropriate
contaminated medium (Bq/m^3^ for immersion or Bq/m^2^ for ground plane)
or a unit uptake (Bq for inhalation and ingestion). These dosimetric
models and the resulting dose coefficients have been developed over many
years and are promulgated by international standards organizations
(e.g., ICRP), national standards organizations (e.g., NCRP), and federal
agencies (e.g., EPA). For this report, the dose and risk coefficients
are almost all based on EPA's April 2002[^6] Update \[FGR-13U\] to
Federal Guidance Report No.13 \[FGR-13\]. These coefficients are almost,
but not quite, identical to those used by the ICRP:

> "The age-specific dose coefficients \[in FGR13\]...were calculated
> using the biokinetic and dosimetric models used in the calculations of
> the risk coefficients. These models are consistent with those used by
> the ICRP in its recent series of publications tabulating dose
> coefficients for the general public, which is similar ICRP-60, but may
> be slightly different." (3)

However, for most radionuclides and organs, these differences are
negligible, especially considering other uncertainties. These minor
differences may be revealed by comparing the documentation for FGR-13
and ICRP-60.

Dose conversion factors are derived using models that represent the
physics and biology of the interaction of the human body with radiation
or radioactive material. For external exposure the models consider the
geometry and physics of the exposure (immersion in air or water,
exposure to a contaminated ground plane, exposure to shoreline strips of
contamination) coupled with a representation of a standard human body
absorbing the radiation. For internal exposure from inhaled or ingested
radionuclides, the dose conversion factors are based on models
representing the complex interactions of the radionuclide's physical and
chemical attributes with human physiology. Once the dose conversion
factors are developed, they may be applied to any dose assessment,
thereby avoiding the need to repeat the complex modeling for every dose
assessment. Conversion of doses to risks of cancer incidence and
fatality are based on epidemiological data that relate radiation
exposures to the incidence of cancer at various organ sites in exposed
individuals and the subsequent mortality among those individuals.

Given the preceding discussion, the simple formula that relates dose to
intake, stated in [Chapter
9](../Chapter_09_ready%20for%20CDC%20031405.doc),

Dose = Intake \* Dose Conversion Factor (9-1)

may be stated in a more general form:

ED~iae~ = I~ie~·DC~iaec~ (10-3)

Where,

ED~iae~ = Incremental equivalent dose from radionuclide i for age group
a and exposure route e

I~ie~ = Intake of radionuclide i through exposure route e

> DC~iaec~ = Dose conversion factor for radionuclide i for age group a
> exposure route e and inhalation class c inhalation class.

Equation (10-3) recognizes the explicit dependence of the dose
conversion factor, DC~iaec~, on the radionuclide, age of the receptor,
exposure route, and inhalation class; however, equation (10-1) still
retains the linear relationship between dose and intake. Similar
equations can be used to generate risks of cancer incidence and
fatality, by replacing the term ED~iae~, by a cancer incidence term,
RI~iae~, or a cancer fatality term, RF~iae~; in both cases the
conversion factor, DC~iaec~, must be appropriately adjusted. Doses and
risks can be further disaggregated into contributions from specific
organs. Intakes, as discussed in [Chapter
9](../Chapter_09_ready%20for%20CDC%20031405.doc), are based on
radioactive material inhaled or ingested or direct exposure to external
penetrating radiation.

For exposures of persons from inhaling or ingesting radionuclides, the
study used the following coefficients from FGR-13U:

-   Age-dependent dose coefficients for 23 organs and bodily tissues,
    plus effective dose based on ICRP-60 weighting factors (see Table
    10.2).

-   Age-dependent cancer risk coefficients (fatality and incidence) for
    15 cancer sites, plus the sum of cancers across all cancer sites.

Table 10-2 lists the organs and bodily tissues considered in the dose
coefficients, and the cancer sites considered in the risk coefficients.
Table 10-3 lists the age categories considered for the dose and risk
coefficients. (Note that the age categories are different for the dose
and risk coefficients.)

Table 10‑2 Organs, Tissues, and Lung-Compartments, and Cancer Sites,
Addressed in Dose and Risk Conversion Factors in the FGR-13 Update

+-------------+-------------+-------------+-------------+-------------+
| Organs,     |             |             | Cancer      |             |
| Tissues and |             |             | Sites       |             |
| Lung-C      |             |             | Addressed   |             |
| ompartments |             |             | in Risk     |             |
| Addressed   |             |             | Conversion  |             |
| in Dose     |             |             | Factors     |             |
| Conversion  |             |             |             |             |
| Factors     |             |             |             |             |
+-------------+-------------+-------------+-------------+-------------+
| > Adrenals  | > Kidneys   | > Skin      | > Esophagus | Breast      |
+-------------+-------------+-------------+-------------+-------------+
| > Bone      | > Liver     | > Spleen    | > Stomach   | Ovary       |
| > Surface   |             |             |             |             |
+-------------+-------------+-------------+-------------+-------------+
| > Brain     | > Ext       | > Testes    | > Colon     | Bladder     |
|             | ra-thoracic |             |             |             |
|             | > Region    |             |             |             |
+-------------+-------------+-------------+-------------+-------------+
| > Breast    | > Lung      | > Thymus    | > Liver     | Kidneys     |
+-------------+-------------+-------------+-------------+-------------+
| > Stomach   | > Muscle    | > Thyroid   | > Lung      | Thyroid     |
| > Wall      |             |             |             |             |
+-------------+-------------+-------------+-------------+-------------+
| > Small     | > Ovaries   | > Uterus    | > Bone      | Leukemia    |
| > Intestine |             |             |             |             |
| >           |             |             |             |             |
| > Wall      |             |             |             |             |
+-------------+-------------+-------------+-------------+-------------+
| > Upper     | > Pancreas  | > Urinary   | > Skin      | R           |
| > Lower     |             | > Bladder   |             | esidual^\*^ |
| > Intestine |             | > Wall      |             |             |
| > Wall      |             |             |             |             |
+-------------+-------------+-------------+-------------+-------------+
| > Lower     | > Red Bone  | > Effective |             | Total       |
| > Lower     | > Marrow    | > Dose      |             |             |
| > Intestine |             |             |             |             |
| > Wall      |             |             |             |             |
+-------------+-------------+-------------+-------------+-------------+
| ^           |             |             |             |             |
| \*^Residual |             |             |             |             |
| cancer      |             |             |             |             |
| sites.      |             |             |             |             |
+-------------+-------------+-------------+-------------+-------------+

Table 10‑3 Age Categories Addressed in Dose and Risk Conversion Factors
Presented in the FGR-13 Update

+---------------------------------+------------------------------------+
| Dose Conversion Factors         | Risk Conversion Factors            |
+---------------------------------+------------------------------------+
| > Infant                        | > 0-5 Years                        |
+---------------------------------+------------------------------------+
| > 1-Year Old                    | > 5-15 Years                       |
+---------------------------------+------------------------------------+
| > 5-Year Old                    | > 15-25 Years                      |
+---------------------------------+------------------------------------+
| > 10-year Old                   | > 25-70 Years                      |
+---------------------------------+------------------------------------+
| > 15-Year Old                   | > 0-110 Years                      |
+---------------------------------+------------------------------------+
| > Adult                         |                                    |
+---------------------------------+------------------------------------+

For doses and risks from inhalation, the physical and chemical form of
some radionuclides is specified; this is denoted by the subscript "c" in
equation (10-1). The radionuclide "class" is important for some
radionuclides, because the radionuclide's chemical and physical form
affects the rate at which the radionuclide is removed from the lungs and
subsequently migrates elsewhere in the body or is excreted. The study
assumed that most radionuclides were particulates assigned to one of
three absorption types:

-   Type F: Fast dissolution and a high level of absorption to blood.

-   Type M: Intermediate rates of dissolution and levels of absorption
    to blood.

-   Type S: Slow dissolution and a low level of absorption to blood.

It was assumed that some radionuclides existed as a gas or vapor, based
on the Phase II information regarding releases. The assumptions for the
lung absorption types used in this report are listed in Table 10-4 (3),
(9).

Table 10‑4 Assumptions for Lung Absorption Classes by Element

+--------------+--------+---------------------------------------------+
| Element      | Abso   | Comments^†^                                 |
|              | rption |                                             |
|              | Cla    |                                             |
|              | ss^\*^ |                                             |
+--------------+--------+---------------------------------------------+
| Americium    | M      | Default absorption type recommended in      |
| (Am)         |        | ICRP-72.                                    |
+--------------+--------+---------------------------------------------+
| Argon (Ar)   | NA     | No absorption occurs for noble gases.       |
+--------------+--------+---------------------------------------------+
| Carbon (C)   | G      | Type G was assumed because it was           |
|              |        | recommended in FGR-13 for CO~2~.            |
+--------------+--------+---------------------------------------------+
| Cesium (Cs)  | F      | Default absorption type recommended in      |
|              |        | ICRP-72.                                    |
+--------------+--------+---------------------------------------------+
| Hydrogen     | HT: G  | Type G was assumed for tritium released as  |
| (^3^H -      |        | a gas (HT) in accordance with FGR-13. Type  |
| tritium)     | HTO: V | G is also appropriate for tritium released  |
|              |        | as an organic. Type V is assumed for        |
|              | O      | tritium released as water vapor (HTO) in    |
|              | BT^‡^: | accordance with FGR-13.                     |
|              | V      |                                             |
+--------------+--------+---------------------------------------------+
| Iodine (I)   | G      | Iodine was released in several forms. Type  |
|              |        | G was assumed because it resulted in dose   |
|              |        | and risk conversion factors between those   |
|              |        | for a particulate and elemental I.          |
+--------------+--------+---------------------------------------------+
| Plutonium    | M      | Default absorption type recommended in      |
| (Pu)         |        | ICRP-72.                                    |
+--------------+--------+---------------------------------------------+
| Sulfur (S)   | V      | FGR-13 recommends Type V for sulfur         |
|              |        | dioxide. (Note that if S is released as a   |
|              |        | particulate, ICRP-72 recommends Type M.)    |
+--------------+--------+---------------------------------------------+
| Strontium    | M      | Default absorption type recommended in      |
| (Sr)         |        | ICRP-72.                                    |
+--------------+--------+---------------------------------------------+
| Thorium (Th) | S      | Default absorption type recommended in      |
|              |        | ICRP-72.                                    |
+--------------+--------+---------------------------------------------+
| Uranium (U)  | M      | Default absorption type recommended in      |
|              |        | ICRP-72                                     |
+--------------+--------+---------------------------------------------+
| \*F: fast;   |        |                                             |
| M: medium;   |        |                                             |
| S: slow; G:  |        |                                             |
| gas; V:      |        |                                             |
| vapor; NA:   |        |                                             |
| not          |        |                                             |
| applicable.  |        |                                             |
|              |        |                                             |
| **^†^**Lung  |        |                                             |
| absorption   |        |                                             |
| classes are  |        |                                             |
| not listed   |        |                                             |
| for          |        |                                             |
| radioactive  |        |                                             |
| isotopes of  |        |                                             |
| elements     |        |                                             |
| released     |        |                                             |
| only into    |        |                                             |
| surface      |        |                                             |
| waters.      |        |                                             |
| Although     |        |                                             |
| GENII        |        |                                             |
| requires     |        |                                             |
| that lung    |        |                                             |
| absorption   |        |                                             |
| class        |        |                                             |
| assumptions  |        |                                             |
| be input for |        |                                             |
| these        |        |                                             |
| isotopes,    |        |                                             |
| the assumed  |        |                                             |
| values are   |        |                                             |
| not used in  |        |                                             |
| the dose and |        |                                             |
| risk         |        |                                             |
| calculations |        |                                             |
| because      |        |                                             |
| inhalation   |        |                                             |
| exposure is  |        |                                             |
| not assessed |        |                                             |
| for the      |        |                                             |
| surface      |        |                                             |
| water        |        |                                             |
| pathways     |        |                                             |
| considered   |        |                                             |
| in this      |        |                                             |
| report.      |        |                                             |
|              |        |                                             |
| ^‡^OBT:      |        |                                             |
| organic      |        |                                             |
| bound        |        |                                             |
| tritium.     |        |                                             |
+--------------+--------+---------------------------------------------+

For external exposures resulting from (1) immersion in a "cloud" of
radionuclides in air, and (2) proximity to a contaminated ground
surface, the study used the following coefficients from FGR-13U:

-   Adult dose coefficients for 23 organs and bodily tissues, plus
    effective dose based on ICRP-60 weighting factors (see Table 10-1).

-   Age-specific cancer risk coefficients (fatality and incidence) for
    15 cancer sites, plus the sum of cancers across all cancer sites.

As noted, FGR-13U provides only adult dose conversion factors for these
types of external exposures. The authors of FGR-13 believe that use of
adult external dose coefficients for all age groups should normally
result in small errors (usually \<30%). The FGR-13 authors believe that
these errors are likely to be negligible compared to the errors
associated with the simplified exposure scenarios assumed to calculate
the dose conversion factors (e.g., the phantoms were in constant
position in relation to the radiation source, and shielding was not
considered) \[FGR-13\]. The risk coefficients for these types of
external exposures use the same age ranges as those listed in Table
10-3.

For external exposures while swimming in water or while boating, dose
and risk coefficients from FGR-12 were used because coefficients for
immersion in contaminated water are not included in FGR-13U. These
(adult) dose coefficients are provided for fewer organs than those in
the FGR-13 update, and the weighting factors used to calculate effective
dose equivalent are from ICRP-26 (because they are based on FGR-12)
rather than ICRP-60 (see Table 10-1). Risk was estimated by multiplying
the calculated doses for water immersion and boating by the following
health effects conversion factors:

-   Fatality: 0.05 Sv^-1^

-   Incidence: 0.06 Sv^-1^

Finally, the dose and risk coefficients were grouped into four age
groups: 0 to 5 years, 5 to 15 years, 15 to 25 years, and 25 to 70 years.
This assumption allowed for better correlation between the doses and
risks calculated as a function of age group. Dose and risk conversion
factors for these calculations were determined by interpolating between
appropriate dose and risk conversion factors obtained from the update to
FGR-13 and from FGR-12. The three combined age groups are summarized in
Table 10-5. Also listed is the exposure duration used for each age
group.

Table 10‑5 Exposure Groupings and Corresponding Combined Dose and Risk
Factor Age Groups

  -------------------- ---------------------------- ----------------------
  Age / Gender         Exposure Group\              Dose and Risk Factor
                       \[Duration (years)\]         Age Group

  \<1 male             Infant (male only) \[1\]     0 -- 5

  1 -- 4 male          Preschool (male only) \[4\]  0 -- 5

  5 -- 11 male         Schoolage (male only) \[7\]  5 -- 15

  12 -- 17 male        Teenage (male only) \[6\]    15 - 25

  18 -- 70 male        Adult male \[varies\]        25 -- 70
                       **^\*^**                     

  18 -- 70 female      Adult female \[varies\]      25 -- 70
                       **^\*^**                     

  ^\*^The exposure                                  
  duration of the                                   
  adult age groups                                  
  depends on the year                               
  that the individual                               
  reaches age 18.                                   
  Exposure duration                                 
  lasts from the year                               
  of the 18^th^                                     
  birthday until the                                
  end of 1992, when                                 
  one child would be                                
  38 and the other 29.                              
  -------------------- ---------------------------- ----------------------

## References

1.  GENII SDD. Napier, B.A., et al. GENII Version II Software Design
    Document. PNNL for U.S. Environmental Protection Agency. November
    2002.

2.  ICRP-60. International Commission on Radiation Protection.
    Recommendations of the International Commission on Radiation
    Protection. ICRP Publication 60. Pergamon Press, Oxford. 1991.

3.  FGR-13. Eckerman, K. F., et al. Cancer Risk Coefficients for
    Environmental Exposure to Radionuclides. Federal Guidance Report
    No. 13. EPA 402-R-99-001. Oak Ridge National Laboratory and U.S. EPA
    Office of Radiation and Indoor Air. September 1999.

4.  ICRP-26. International Commission on Radiation Protection.
    Recommendations of the International Commission on Radiation
    Protection. ICRP Publication 26. Pergamon Press, Oxford. 1977.

5.  FGR-13U. U.S. Environmental Protection Agency. Federal Guidance
    Report 13 Cancer Risk Coefficients for Environmental Exposure to
    Radionuclides: CD Supplement. EPA 402-C-99-001, Rev. 1. Oak Ridge
    National Laboratory and U.S. EPA. April 2002.

6.  FGR-12. Eckerman, K.F. and J.C. Ryman. External Exposure to
    Radionuclides in Air, Water, and Soil. Federal Guidance Report
    No. 12. EPA 402-R-93-081. Oak Ridge National Laboratory and EPA
    Office of Radiation Programs. September 1993.

7.  FGR-11. Eckerman, K. F., et al. Limiting Values of Radionuclide
    Intake and Air Concentration and Dose Conversion Factors for
    Inhalation, Submersion, and Ingestion. Federal Guidance Report
    No. 11. EPA-520/1-88-020. Oak Ridge National Laboratory and EPA
    Office of Radiation Programs. September 1988.

8.  Shapiro, Jacob. Radiation Protection. Harvard University Press,
    Cambridge, MA. 1990.

9.  ICRP-72. International Commission on Radiation Protection.
    Age-Dependent Doses to Members of the Public from Intake of
    Radionuclides, Part 5. Compilation of Ingestion and Inhalation Dose
    Coefficients. ICRP Publication 72. Pergamon Press, Oxford. 1996.

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[^1]: The terms discussed here are appropriate for the low doses and
    stochastic health effects usually associated with exposures to
    environmental radioactivity.

[^2]: Except where noted, ICRP-60 terminology is used in this chapter.

[^3]: In ICRP-60 and other ICRP recommendations preceding ICRP-60, a
    weighting factor was called a quality factor (2).

[^4]: ICRP-26 recommended a 50-year time period for members of the
    public as well as radiation workers. ICRP-60 recommends a 70-year
    time period for members of the public and a 50-year time period for
    radiation workers.

[^5]: These weighting factors were calculated under somewhat different
    assumptions. ICRP-26 weighting factors are based on the risk of
    fatal cancers and hereditary defects in the first two generations.
    ICRP-60 weighting factors are based on risks for both fatal and
    non-fatal cancers, the risk of hereditary defects over all future
    generations, and the relative loss of live expectancy given a fatal
    cancer or a severe generic disorder.

[^6]: A supplement was first issued in 2000, but this supplement
    contained errors in the viewer and was replaced by the April 2002
    version. The interactive viewer is entitled "Federal Guidance Report
    13 CD Supplement, Cancer Risk Coefficients for Environmental
    Exposure to Radionuclides" EPA, rev 1 April 2002 and is avaialnble
    from the Office of Air and Radiation.