c/EPA
United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington DC 20460
September 1987
EPA 520/1-87-20
Radon
Reference
Manual
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EPA 520/1-87-20
RADON REFERENCE MANUAL
September 1987
U.S. Environmental Protection Agency
Office of Radiation Programs
Washington, DC 20460
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CONTENTS
Figures
Tables
1. INTRODUCTION 1-1
Purpose 1-1
Organization 1-1
2. WHAT IS RADON? 2-1
Chemical Properties 2-1
Natural Sources of Radon 2-2
Uranium-238 Decay Series 2-5
Radon Decay Products 2-5
Units of Measurement 2-6
3. WHERE DOES RADON COME FROM? 3-1
Geologic Factors 3-1
Identifying Areas with Potential for
High Indoor Radon Levels 3-2
Radon in Rocks 3-2
Radon in Soil 3-5
Radon in Water 3-7
Radon in Earth-Based Building Materials 3-8
4. HOW DOES RADON AFFECT ME?
HOW CERTAIN ARE SCIENTISTS OF THE RISKS? 4-1
Derivation of Risk Estimates 4-2
Relationship Between Radon and Radon
Decay Product Concentration 4-2
Estimation of Cumulative Exposure to
Radon and Radon Decay Products 4-3
Conversion of Cumulative Exposure to
Lifetime Risk 4-4
Projection of Lifetime Risks to
Entire Population 4-10
Relationship Between Smoking and Radon Risks 4-11
Relationship of Radon Risks to Lung Cancer
Mortality Rates 4-16
Uncertainty in Risk Estimates 4-16
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CONTENTS (Continued)
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5. HOW DOES RADON CAUSE LUNG CANCER? 5-1
Mechanism of Lung Cancer Induction 5-1
Risk From Attached and Unattached
Radon Decay Products 5-2
Association of Radon and Lung Cancer 5-3
Other Possible Health Risks from Radon 5-4
6. WHEN DID RADON BECOME A PROBLEM? 6-1
Uranium Miners and High Incidence of Lung Cancer 6-1
Elevated Radon Levels from Contaminated
Building Materials 6-2
Elevated Radon Levels from Natural Sources 6-3
7. DOES EVERY HOME HAVE A PROBLEM? 7-1
Distribution of Radon in U.S. Homes 7-1
Where Radon Has Been Found 7-2
Radon in Multilevel Buildings 7-3
EPA-Sponsored Assessment Programs 7-4
8. HOW DOES RADON GET INTO A HOME? 8-1
Mechanisms Inducing Radon Flow 8-1
Radon Transport from Soil 8-2
Radon Transport Through Water Supplies 8-3
Radon from Earth-Based Building Materials 8-4
9. HOW IS RADON DECTECTED? 9-1
Relationship Between Radon and Decay
Product Concentrations 9-1
Selection of Sampling Methods 9-2
Measurement Condition and Quality Objectives 9-3
Standardized Measurement Conditions 9-3
House Conditions 9-4
Quality Assurance Objectives 9-4
Measurement Instruments 9-6
Alpha-Track Detector 9-6
Charcoal Canister 9-7
Radon Progeny Integration
Sampling Unit (RPISU) 9-8
Continuous Radon Monitor (CRM) 9-9
Continuous Working Level Monitor (CWLM) 9-10
Grab Sampling 9-10
Radon Measurements in Water 9-12
Selecting a Sampling Method 9-12
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CONTENTS (Continued)
Page
10. HOW CAN I GET A RADON DETECTOR? 10-1
Steps to Obtain a Detector 10-1
EPA's Radon Measurement Proficiency
Program (RMP) 10-2
11. HOW SHOULD RADON DETECTORS BE USED? 11-1
Screening Measurements 11-1
Follow-up Measurements 11-3
12. WHAT DO MY TEST RESULTS MEAN? 12-1
Lung Cancer Risk Illustrations 12-1
Radon Risk Evaluation Chart 12-3
13. HOW QUICKLY SHOULD I TAKE ACTION? 13-1
How EPA Arrived at its Guidelines 13-1
Factors EPA Considered 13-2
Interpretation of the Guidelines 13-4
14. ARE THERE OTHER FACTORS I SHOULD CONSIDER? 14-1
Smoking 14-1
Risks to Children 14-2
Time Spent at Home 14-5
Sleeping in the Basement 14-6
Lifetime Exposure Period 14-7
15. HOW CAN I REDUCE MY RISK FROM RADON? 15-1
Stop Smoking 15-2
Avoid Living Areas with Suspected High Levels 15-2
Ventilate Home and Crawl-Spaces 15-2
16. SOURCES OF INFORMATION 16-1
References Cited in Previous Chapters 16-1
References for General Reading 16-15
Glossary
Radiological Unit Definitions
Meaning of Common Unit Prefixes
Conversion Table
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FIGURES
Number .Pa9.e
2-1 Uranium-238 Decay Series 2~3
2-2 Thorium-232 Decay Series 2~U
3-1 Radon Emanation Process ^-6
4-1 Comparison of Absolute Risk and Relative
Risk Projection Models 4~6
4-2 Possible Overlap of Radon and Smoking Related
Lung Cancer Deaths **~15
4-3 Total and Possible Radon Induced Lung Cancer
Mortality By Year 4-17
14-1 Lung Cancer Appearance Rate Following
a Single Exposure to Radon Daughters 14-4
TABLES
4-1 Risk Studies 4-9
4-2 Simplified Derivation of Estimates for Under 600 CWLM
Exposure to Radon Decay Products 4-12
4-3 Relative and Absolute Risk Estimates for Under 600 CWLM 4-19
Exposure to Radon Decay Products
11-1 Follow-up Measurements Made in General Living Areas 11-4
14-1 Lifetime Risk of Excess Lung Cancer Mortality Induced
by Radon Decay Product Exposure (N/1,000) 14-8
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Chapter 1
INTRODUCTION
PURPOSE
The "Radon Reference Manual" (Reference Manual) has been prepared by
EPA to assist public officials in responding to questions about the EPA
pamphlet entitled "A Citizen's Guide to Radon: What It Is and What To Do
About It" ("A Citizen's Guide"). The need for and usefulness of a
reference manual as a source of technical clarification became apparent as
EPA reviewed the numerous comments it received from State and Federal
officials on the March 1986 draft of "A Citizen's Guide." Several
commentators requested more detailed technical information than the general
discussion contained in "A Citizen's Guide." This document provides the
background information developed for and used to prepare the pamphlet.
ORGANIZATION
The Reference Manual organization follows the question and answer format
presented in "A Citizen's Guide." Each section of the Reference Manual
provides a more detailed discussion of the issues underlying each section of
the pamphlet and cites the sources of information used by EPA to formulate
each answer. In addition, the derivations of certain estimates (such as
total lung cancer deaths and radon risk levels) are explained to allow State
officials to compare EPA's methodology with other approaches presented in
the scientific literature.
Chapters 2 and 3 discuss the nature and origin of radon. Chapter 4
presents the risk estimates of radon exposure and the uncertainties
involved in these risk estimates. Chapter 5 discusses how radon causes
lung cancer. Chapter 6 describes the history of the indoor radon problem.
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In Chapter 7, what we know about the geographic distribution of the radon
problem is discussed. Chapter 8 discusses the ways in which radon enters
a home. Chapter 9 describes the various detection devices currently
available and Chapter 10 discusses how to obtain a radon detector.
Chapter 11 lays out the procedures for radon screening and followup
measurements and explains how to interpret the results. In Chapter 12,
the implications of the test results for homeowners are analyzed. Chapter
13 advises on the timing for remedial action. Chapter 14 explains other
factors influencing radon exposure. Chapter 15 discusses mitigation
techniques for immediate, short-term reduction of radon levels. The last
chapter (Chapter 16) lists the technical references cited earlier in the
Manual and provides a selected bibliography, as sources of reference
material for State officials and as recommended reading for homeowners
requesting additional information. Finally, the Reference Manual includes a
glossary, a list of measurement unit definitions and prefix meanings, and a
conversion table between commonly used radiological measurement units and
Standard International (SI) units.
1-2
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Chapter 2
WHAT IS RADON?
"A Citizen's Guide" describes radon as a naturally-occurring radioactive gas
that is not detectable by the human senses. This chapter provides
information on the chemical properties of radon. The primordial natural
elemental sources of radon in our environment — uranium and thorium —
are also discussed, with information on the uranium-238 and thorium-232
decay series. Another section addresses radon's radioactive decay products
and their potential to induce cancer in lung tissue. Finally, a discussion
on the units of measurement used to describe concentrations of radon and
radon decay products is provided as an introduction to the nomenclature
used in later chapters.
CHEMICAL PROPERTIES
Radon is a naturally-occurring, chemically inert, radioactive gas. Because
radon is chemically unreactive with most materials, it is free to travel as a
gas. It can move easily through very small spaces such as those between
particles of soil and rock. Radon is odorless, invisible, and without taste;
thus, it cannot be detected with the human senses. Radon is also
moderately soluble in water and, therefore, can be absorbed by water
flowing through rock or sand containing radon. Its solubility depends on
the water temperature; the colder the water, the greater the radon's
solubility. A measure of gas solubility is given by the solubility
coefficient. The radon solubility coefficient is defined as the ratio of the
radon concentration in water to that in air (Co86). The warmer the water
temperature, the more radon is released and, therefore, the lower the
solubility coefficient. The maximum solubility coefficient of radon is about
0.5 at water temperatures near 0° C, decreasing exponentially as water
temperatures increase. For example, at 20° C, the solubility coefficient is
about 0.25; at 90° C, the coefficient is about 0.1.
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NATURAL SOURCES OF RADON
Thorium and uranium are common, naturally-occurring elements that are
found in low concentrations in rock and soil. Through radioactive decay,
both are constant sources of radon. Radon is produced from the
radioactive decay of the element radium, which is itself a decay product of
either uranium or thorium. - Average soil activity concentrations of
uranium-238 and thorium-232 are each about 0.68 picocuries per gram
(Ne83). Uranium-238 decays in several steps to radium-226, which decays
into radon-222. Radon-222 has a half-life of 3.8 days and, therefore, has
enough time to diffuse through dry, porous soils or to be transported in
water for a considerable distance before it decays. Similarly, thorium-232
decays into radon-220 (a different radon isotope, also called thoron), which
has a half-life of only 55 seconds. Because of its short half-life and limited
ability to migrate into residences, radon-220 is usually a less important
source of radon exposure to humans. The average exposure from indoor
radon-220 decay products has been estimated to be about 25 percent of that
from radon-222 (UNSCEAR82). Only radon-222 is addressed specifically in
"A Citizen's Guide" and is the radon isotope of most concern to the public.
Although radon-220, or thoron, has not been measured separately in most
homes, radon control actions will also reduce exposure to thoron. Radon-222
is in the uranium-238 decay series, illustrated in figure 2-1. The
thorium-232 decay series, which includes radon-220, is illustrated in figure
2-2.
- Radioactive decay is a process in which an unstable atomic nucleus
undergoes spontaneous transformation, by emission of particles or
electromagnetic radiation, to form a new nucleus (decay product),
which may or may not be radioactive. The level of radioactivity is
measured in curies, where 1 curie equals 37 billion disintegrations per
second. The time required for a given specific activity of an isotope
to be reduced by a factor of two is called its half-life. A picocurie
(pCi) is equal to one-trillionth of a curie"Specific activities
concentrations are typically measured in picocuries per gram (in a
solid) or picocuries per liter (in a gas, such as air).
2-2
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Rgure 2-1. Uranium-238 Decoy Series
KEY
Atomic Weight
Symbol
Half-Life
Of = alpha decay
*> beta decay
J = gamma decay
= Minor
Contribution
SOURCE: Putnam. Hayes ft Bartlett. Inc.. September 1987.
2-3
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Figure 2-2. Thorium-232 Decay Series
KEY
Atomic Weight
Symbol
Half-Life
Of = alpha decay
f? = beta decay
J = gamma decay
Minor
Contribution
SOURCE: Putnam, Hayes & Bartlett, Inc., September 1987.
2-4
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URANIUM-238 DECAY SERIES
Radon-222 is preceded in the uranium-238 decay series by radium-226,
which has a half-life of 1,600 years. Radon-222 decays in several steps to
form radioactive isotopes with short half-lives: polonium-218, lead-214,
bismuth-214, and polonium-214 (see figure 2-1). These isotope particles
are commonly referred to as radon decay products. — Radon decay
products are chemically reactive and can attach themselves to walls, floors,
or airborne particles that are inhaled into the lungs. Unattached radon
decay products also can be inhaled and, subsequently, can become
deposited on lung tissue.
RADON DECAY PRODUCTS
The four radon-222 decay products just mentioned all have half-lives of less
than 30 minutes. This short half-life is significant since, once deposited on
lung tissue, the radon decay products can undergo considerable decay
before the action of mucus in the bronchial tubes can clear these
radioactive particles (see Chapter 5). Two of the short-lived decay
products, polonium-218 and polonium-214, emit alpha particles - during the
decay process. Chapter 5 provides an explanation of how alpha particles
can damage lung tissue and lead to lung cancer.
- Radon decay products are also often referred to as radon daughters or
radon progeny.
- An alpha particle is a subatomic particle that has two protons and two
neutrons and has a double positive electrical charge. It is identical to
a helium nucleus.
2-5
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UNITS OF MEASUREMENT
The specific activity of radon or individual radon decay product isotopes
can be measured in picocuries per liter (pCi/l). However, the specific
activity of short-lived radon decay products collectively is also measured in
units called working levels (WL). One working level is defined as the
quantity of short-lived decay products that have the potential to release 130
billion electron volts of alpha particle energy per liter of air. The
correspondence between working levels and picocuries per liter is
discussed in Chapter 10, but it generally depends on the degree of radio-
active equilibrium between radon and radon decay products. Under resi-
dential conditions, radon gas and radon decay products tend to reach a
state such that one working level is approximately equivalent to 200 pCi/l of
radon-222 (assuming 50 percent equilibrium).
2-6
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Chapter 3
WHERE DOES RADON COME FROM?
Radon-222 is found virtually everywhere in at least small amounts because
its predecessor, radium-226 (or, more distantly, uranium-238), is found in
all rock and soil. In outdoor air, radon concentrations are usually less
than one picocurie per liter (pCi/l), with typical concentrations less than
0.5 pCi/l. Higher concentrations of radon outdoors may be observed
during brief periods, such as during a temperature inversion, when a warm
air mass traps a colder one beneath it. Isolated outdoor levels have been
found above 4 picocuries per liter. Indoor air concentrations can vary from
around 0.5 pCi/l to over 2,000 pCi/l, with limited data suggesting that an
average value for homes is likely to be in the range of 1 to 2 pCi/l of
radon (Ne86).
Most indoor radon comes from the rocks and soil around a home, although
other, usually less significant, sources of indoor radon are water and some
construction materials. It is the combination of a number of factors,
however, that determines the indoor levels of radon. These include
geologic factors and building characteristics. The effects of building
design on indoor radon concentration is discussed in Chapter 8.
GEOLOGIC FACTORS
The geologic factors controlling radon occurrence can be grouped into three
broad categories (Nh86): the radium (or uranium) content of nearby rock
and surficial material; the physical characteristics of the surficial material;
and fracturing or faulting of the rock or surficial material. These factors
determine the amount of radon that will be produced in the soil gas and
how easily this radon-contaminated gas will move through the soil. The
amount of radon in the soil gas and the permeability of the surficial material
are probably the most significant natural factors affecting indoor radon
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concentrations, but it is the interaction between the radon in soil gas, soil
permeability, and a home's structural characteristics that determines the
actual indoor radon levels.
Identifying Areas with Potential for High Indoor Radon Levels
Data describing the natural occurrence of radon and radium in the U.S. are
limited to a few small-scale studies, so more indirect methods must be used
to identify areas with potentially elevated radon levels. The presence of
uranium is often used as an indicator to predict areas with potentially
elevated radon levels because uranium is the precursor of radium and
radon. Studies support the contention that there is a relationship between
the uranium content of the ground and radon levels in houses. The higher
the uranium content, the greater the risk of higher indoor radon levels,
regardless of house or foundation type (Ak84). A large volume of uranium
occurrence information has been compiled over the past 40 years, gathered
largely to assist in locating uranium ore. Much of the information was
obtained during the Department of Energy's National Uranium Resource
Evaluation (NURE) program of the 1970s and early 1980s. Although there
are limitations to using uranium information to search for radon, it is quite
useful for screening large areas and determining an area's approximate
radon potential. At a specific location, however, other information, such as
radon concentrations in soil gas and soil permeability (or radon availability
information), must be known to provide an accurate appraisal of the location
in question. EPA is currently developing land evaluation criteria.
Radon in Rocks
An estimated average uranium concentration for the Earth's crust is 2 to
4 parts per million (ppm) - or 0.7 to 1.3 pCi/g (Fi73 and Er73).
One part per million (by weight) uranium-238 is approximately equal to
an activity concentration of 0.33 pCi/g material, or 0.33 pCi/g
radium-226 in equilibrium with uranium. One pCi/g is equal to 37
Becquerels per kilogram. Becquerels (Bq) are the SI units for
radioactivity.
3-2
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However, there can be a wide variability in uranium concentrations, even
within the same rock formation or same rock type. Under the proper
geologic setting, almost any rock type can have an elevated uranium
concentration (e.g., vein deposits with uranium concentrations greater than
1,000 ppm can be found in many types of rock), but the rocks most
commonly enriched in uranium are certain types of granitic rocks, black
(carbonaceous) shales, and phosphatic rocks. It is also true that, in some
cases, rocks normally low in uranium content which are located near
uranium-rich zones may contain uranium and can be responsible for indoor
radon problems.
It is common for uranium concentrations in granites to range between 2 to
10 ppm, with averages around 3 to 4 ppm uranium. Although precise
relationships between uranium content in granitic rocks and radon levels
have not been established, granites with uranium concentrations above 4
ppm may be considered a moderate to high source of radon. Any granite
with more than 10 ppm uranium should be suspected of having a high radon
potential. In particular, granitic rocks have the potential to cause acute
radon problems in some areas of the U.S. because of fracturing, faulting,
and elevated uranium concentrations.
In general, black (carbonaceous) shales are more likely to have uranium
than other shales because of the carbon content and oxidizing conditions
under which the black shale forms. Uraniferous black shales often average
up to 20 ppm uranium, but can contain more than 250 ppm (Sw61). Black
shales, especially phosphatic shales, may produce the greatest number of
indoor radon problems due to their wide distribution and uranium content if
the shales are located close to the surface. Black shales with uranium
contents greater than 4 ppm should be considered at least a moderate radon
source. Uraniferous black shales occur mainly in parts of Wyoming,
Montana, South Dakota, Nebraska, Kansas, Oklahoma, Texas, Tennessee,
Kentucky, Indiana, and New York.
3-3
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Because of uranium's chemical affinity for phosphates, phosphatic rocks
often contain greatly elevated levels of uranium. It is common for
phosphate rocks to average TOO ppm uranium or higher, with more uranium
being associated with greater phosphate content. In addition, localized
phosphate concentrations, such as phosphate nodules in black shales, can
contain much higher uranium concentrations. High grade phosphates occur
in parts of Florida, southern Georgia, and in the Phosphoria Formation in
several Western States. Low-grade phosphate lands occur in North and
South Carolina, coastal Georgia, and T«$>nessee. Some unpublished data
suggest that lower-grade phosphates may not pose as significant a problem
as do other rocks, but it is too soon to know for certain.
Carbonate rocks (limestones and dolomites) usually average only around 2 to
3 ppm uranium. In some instances, however, they can be host rocks for
uranium. This is especially true when fracture or fault zones are present.
It is possible that phosphatic carbonates may be a problem in some areas
due to their weathering characteristics and their potential for above-average
uranium contents, but this has not been confirmed.
In general, sandstones are not uraniferous, although continental sandstones
derived from uranium-rich source rocks, such as those found in the
western uranium mining districts, are often uraniferous. The rocks least
likely to contain uranium are basaltic lavas, or their metamorphic
equivalents, and rocks that have similar chemical compositions.
The fracturing and faulting of a rock can alter its radon potential in
several ways. Fracturing and faulting can create extensive migration
pathways for radon, thus increasing the radon flow and enhancing radon
movement into a house. Fractures and faults are sometimes associated with
elevated uranium concentrations because uranium-bearing fluids deposit the
uranium within the fracture or fault zones. Fracture or fault zones with
very high concentrations of uranium and radium seem to be associated with
homes having the most severe indoor radon problems.
3-4
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Soils as well as rock can be affected by fracturing or cracking. Some soils
can shrink and produce cracks with a relatively high permeability.
Sometimes surficial materials can have fractures that can increase
permeabilities up to three or more orders of magnitude (We86). In these
cases of extreme soil permeability, soils with relatively low radium content
may pose potential radon hazards.
Radon in Soil
Soils play two important roles in radon occurrence. Many soils are derived
from the immediately underlying rock, so they tend to have similar mineral
compositions as the parent rock. If the underlying rock is suspected as a
source of radon, the associated soils can also be a potential source of the
radon. Soils contain an average of about 1 to 3 ppm uranium and a similar
amount of radioactivity, but these levels can vary, depending upon the
rock from which the soil was formed and the environmental conditions
during the time of the soil's formation.
Soil radium levels in the U.S. average around 1 pCi/g (De86; My83);
however, even this amount of radium can cause problems in some instances.
Calculations to this effect have shown that what may be considered a normal
level of 1 pCi/g radium in the soil can easily produce between 200 to over
1,000 pCi/l radon in the soil over a range of typical soil conditions (Ta86;
Br83).
Figure 3-1 illustrates how a radon atom produced by radium decay in the
soil or rock can migrate into soil gas and possibly enter a home. Not all of
the radon produced in soil and rock will be available to fill soil pore
spaces. Some of the radon produced will remain trapped within the grains
of the soil or rock itself or will become lodged in adjoining grains and will
not be able to escape into pore spaces. This will be a function of the
grain size and porosity of the parent material. Perhaps the most important
factor in radon production and migration is the presence of water in the
soil. Water in the soil pore enchances the apparent production of radon
3-5
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Figure 3-1. Radon Emanation Process
(Not Drawn to Scale)
• Radium-226
A Radon-222
Of Alpha Particle
R Recoil Range - The distance that a
radon-222 atoms travels when the
radium-226 atom disintegrates
Adapted from WIL83, p. 21,
3-6
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because it reduces radon's recoil range and may prevent radon atoms from
lodging in adjacent soil grains. The radon atom can then diffuse into the
pore's air space where it is available to readily migrate through the soil.
If the pore spaces are totally saturated, as is the case below the water
table or temporarily after a heavy rain, the radon atom will probably not
become part of the soil gas. This is true because water hinders radon's
migration by lowering the diffusion coefficient and by absorbing the radon
atoms (Ta80). In summary, radon transport through soil increases as soil
moisture increases, until the soil moisture content is so great that further
increases in soil moisture begin to reduce radon transport.
Soil permeability also plays a prominent role in determining whether the
radon produced will be able to enter homes. Because soils are one medium
through which radon travels, high soil permeabilities promote higher indoor
radon levels, while low permeabilities retard radon movement and reduce the
probability of radon entering a home. Large amounts of radium in the soil
tend to increase indoor radon levels, although the soil's permeability can
change that tendency. If combined with high permeability, it is possible to
have high indoor radon levels with low radium levels. As mentioned
earlier, fracturing can also increase a soils permeability. It is still
unknown, however, whether it is the average permeability or the zones of
above-average permeability that contribute the most to indoor radon
concentrations. It is theoretically possible that one fracture may be enough
to produce indoor radon problems in areas of normally low permeability.
To summarize, the amount of uranium or radium in an area can only be
used as a rough approximation of an area's radon potential because many
other factors, both natural and manmade, determine if a land's radon
potential will be realized in indoor radon levels. To determine the actual
radon potential at a site, it is necessary to take into account several
variables, including the soil radium content, soil permeability, and
diffusivity.
3-7
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Radon in Water
Another source of indoor radon is groundwater. As with radon in the soil,
the primary risk from radon in water is the risk of lung cancer induced by
inhaling radon that has been released from water into the air. Overall, it
is estimated that drinking water contributes only one percent to seven
percent of the radon found in indoor air (Co85).
Any process that exposes water to air releases radon. Radon is released in
the home during activities such as showering, washing clothes, and flushing
toilets. Most homes are served by public water supplies that are aerated at
treatment facilities before the water reaches the home and, therefore, have
relatively low radon levels. Homes with water from other sources, such as
private wells, may contain extremely elevated radon levels.
The national average population-weighted concentration of radon in drinking
water from public water supplies serving more than 1,000 people is about
210 pCi/l (Co86). The average for all public drinking water supplies from
groundwater sources is about 420 pCi/l (Co86). The highest level of radon
In drinking water, 2,000,000 pGi/l was found in a private well (Co85).
Models have been developed to estimate the relationship between radon in
water and the resulting level of radon in air. Roughly stated, the model
estimates that 10,000 pCi/l of radon in water will lead to 1 pCi/l of radon in
indoor air, assuming normal water usage and household characteristics
(Co86).
The Environmental Protection Agency has published an advanced notice of
proposed rule making for Maximum Contaminant Level Coals (MCLCs) and
National Primary Drinking Water Regulations (NPDWR) including Maximum
Contaminant Levels (MCLs) for radionuclides in water. Including radon. A
final rule has not yet been developed.
3-8
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Radon in Earth-Based Building Materials
Radon is also released from many building materials, but normally at very
low levels. Wood materials tend to emit the least radon, while brick,
cement, and cinder block emit more. Radon is released from all of these
sources at such a low rate that these materials are rarely important
contributors to elevated radon levels. However, there have been a few
cases in which materials containing significant radium concentrations were
used to form building materials. Examples of these situations are houses
built using materials contaminated with uranium or radium mill tailings and
uraniterous phosphogypsum waste. There may also be problems in homes
that use radium-containing heat storage rock (e.g., large pieces of granite)
which circulate volumes of air into the living areas.
For most homes, the greatest contributor of radon will be the underlying
soil, especially if it contains significant amounts of radium. The
contribution of radon from water will not be as significant as the
contribution from soil in most cases. Building materials will contribute' the
least amount of radon to a home, except in those unusual cases where the
materials are derived from naturally- radioactive source or have been
contaminated with radium-containing waste.
3-9
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Chapter 4
HOW DOES RADON AFFECT ME?
HOW CERTAIN ARE SCIENTISTS OF THE RISKS?
As stated in "A Citizen's Guide," an increased risk of developing lung
cancer is the only known health effect associated with exposure to elevated
concentrations of radon. This chapter discusses two related sections of "A
Citizen's Guide," which both address radon health risks. The first of the
pamphlet sections, "How Does Radon Affect Me?," presents EPA's estimate
that 5,000 to 20,000 lung cancer deaths per year are potentially attributable
to radon and then compares this estimate to the 85 percent of 130,000 lung
cancer deaths from all sources that are attributed to smoking. The first
two parts of this chapter discuss the derivation of EPA's population risk
estimates and compare the radon and smoking lung cancer figures. The
second section on risk in "A Citizen's Guide," "How Certain Are Scientists
Of The Risks?," puts the uncertainty underlying radon risk estimates in
perspective and acknowledges the influence of the Science Advisory Board
(SAB) on EPA's estimates. The last part of this chapter expands the
discussion of uncertainty and compares other risk estimates to the SAB
recommendations.
It is important to recognize that the derivation of quantitative risk estimates
is a difficult scientific undertaking that must be based on health risk
studies which are subject to various interpretations. As new information
becomes available (especially regarding the distribution of exposure levels
and the dose/response relationship between radon decay products and lung
caricer), EPA will revise its estimates appropriately. However, the
fundamental purpose of the estimates presented in "A Citizen's Guide" is
not to provide definitive estimates of lung cancer deaths, but rather to
emphasize for homeowners the overall significance of radon risks.
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DERIVATION OF RISK ESTIMATES
The derivation of EPA's risk estimates involves a variety of technical and
medical assumptions. For purposes of explanation, this derivation can be
divided into four steps: (1) determination of radon decay product
concentration from radon concentration; (2) estimation of cumulative radon
decay product exposure; (3) conversion of individual cumulative exposure
to lifetime risk; and (4) projection of individual lifetime risks to the entire
population. Each of the steps is explained in the following discussions.
Relationship Between Radon and Radon Decay Product Concentration
As will be explained further in Chapter 5, it is the radon decay products
rather than the radon itself that are believed to be responsible for most of
the health risk due to indoor radon. Depending on the measurement
device, either radon or radon decay product concentrations can be
measured directly (in picocuries per liter and working levels, respectively).
The relationship between the two units depends on the extent to which
radioactive equilibrium is reached between radon and the decay products.
As decay products are formed from radon, they in turn disintegrate into
other isotopes. If the rate of formation and disintegration of the decay
products is exactly equal, 100 picocuries per liter of radon would exist in
equilibrium with 1 working level of decay products (this state is termed
secular equilibrium). However, other processes (such as attachment of
decay products to the walls or floor) tend to remove some decay products
from the air before they disintegrate, so that secular equilibrium is never
achieved. Based on simultaneous measurements of radon and radon decay
products, it has been found that the equilibrium fraction ranges from 0.3 to
0.7, with an average of around 0.5. Using the average equilibrium fraction
of 0.5, a ratio of 200 picocuries per liter of radon to 1 working level of
decay products is fairly typical for residential environments (Ce85). The
relationship between radon and its decay products is explained in more
detail in Chapter 9. EPA used this ratio to convert radon concentrations to
working levels.
-------
Estimation of Cumulative Exposure to Radon and Radon Decay Products
The biological factor of most interest in determining the cancer risk from
radon decay products is the actual radiation dose delivered to the cells of
the lung. To determine this, it is first necessary to estimate the
cumulative exposure to radon decay products. By convention, cumulative
exposure to radon decay products is measured in working level months
(WLM), which is defined as the exposure a miner receives during 170 hours
(the approximate number of working hours in 1 month) in a 1-working level
environment. However, since exposures to miners and to average
homeowners differ, and since medical estimates of the lung cancer risk
induced by a given radon exposure are based on miner populations,
cumulative residential exposures must be adjusted.
The first adjustment factor is inhalation rate, which determines the volume
of air drawn into the lungs and, hence, the potential for radon decay
products to be inhaled and deposited on the walls of the airways. On
average, the inhalation rate of a miner is somewhat higher than the rate for
the general population as a result of increased physical activity. The
breathing rate of a miner is about 30 liters per minute if half of his activity
is heavy work and half is "light activity" (ICRP79), while the breathing
rate of an average adult is about 15.3 liters per minute (ICRP75). Thus,
one adjustment routinely made when estimating cumulative residential
exposures is to correct the exposure estimate for this difference in average
breathing rate.
A second factor affecting cumulative exposure to the general population is
the duration of exposure over a year. While miners are assumed to be
exposed only for 170 hours each month, residential exposures occur
throughout the portion of the year spent in the residence. EPA's estimates
assume that the resident is exposed to a given radon level 75 percent of
the time (i.e., the resident is in the house 75 percent of the day, on
-------
average). This assumption is based on two studies (Mo76; Oa72), and is
consistent with a more recent British survey (Bn83) (see Chapter 14).
Thus, correcting for both the differences in breathing rate and in the
proportion of time exposed, continuous exposure of an average adult to a
concentration of 1 working level for a year is approximately equal to an
annual cumulative exposure of about 20 WLM for a miner:
365 days x 2k hrs x 0.75 x 15.3 lpm/30 1pm x 1 WLM - 19.71 WLM (effective)
yr day 170 hrs yr
A number of other factors also influence the effective cumulative exposure,
including the size of the lung, the location and type of lung cells irradiated
(which depends on where the decay products are deposited), and the
differences in the sensitivity of lung cells depending on age and sex. Due
to incomplete information, EPA's estimates do not account for potential
variations in lung cell sensitivity, and both sexes and all ages are
considered to be equally sensitive to lung cancer induction. The EPA
estimates also do not address the question of deposition versus number,
type, and sensitivity of cells at risk in the airways. However, the smaller
lung size of children, and, therefore, the differences in age-specific
breathing rates, is accounted for in the EPA estimates.
Conversion of Cumulative Exposure to Lifetime Risk
The objective of this step is to estimate the lifetime risk faced by an
individual who receives a known cumulative exposure. In practice, this is
the most complicated step and the one that encompasses most of the
biological uncertainty. The complexity results both from uncertainties
regarding the mechanism of cancer formation and the limitations of the
epidemiological data used to estimate cancer risk. A large number of
factors are involved, as explained subsequently .
U-H
-------
Estimates of the risk of lung cancer associated with exposure to radon and
radon decay products are obtained primarily from epidemiological studies of
underground miners. For example, in a hypothetical study of 1 million
miners, each exposed to 1 WLM over a lifetime, if 200 miners died of lung
cancer, a lifetime risk estimate of 200 fatal cancers per million persons per
WLM could be derived. However, in the epidemiological studies to date, the
entire population of miners in the study group has not yet died. As a
result, the risks observed over part of a lifetime must be extrapolated in
order to estimate the lifetime risk for a given exposure.
To estimate the risk of exposure beyond the years of observation, various
risk projection models may be used. A relative risk projection model or an
absolute risk projection model are frequently used. Figure 4-1 illustrates
the difference between the two types of risk projection models. The
relative risk model extrapolates an expected percentage increase in lung
cancer risk per unit dose into future years, while an absolute risk model
extrapolates the average observed number of excess cancers per unit dose
into future years of risk. Relative radon risk is stated in terms of the
percentage increases in annual lung cancer risk per WLM of exposure, while
absolute risk is expressed as the number of fatal lung cancers per million
persons per WLM of exposure, per year at risk (or per lifetime).
Because the underlying cumulative risk of lung cancer increases rapidly
with age, the relative risk model predicts a larger cumulative probability of
excess lung cancer towards the end of a person's lifetime. - In contrast,
the absolute risk model predicts a constant incidence of excess lung cancer
across time. Given the incomplete data (i.e., less than lifetime follow-up)
we have now, a relative risk model projects somewhat greater risk than an
absolute risk model.
— Although cumulative risk increases, annual risk (as shown in figure
4-1) peaks during middle age, and then declines due to the greater
competing risk of other causes of death.
4-5
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Rgure 4—1. Comparison of Absolute Risk and Relative Risk Projection Models
ABSOLUTE RISK MODEL
CE
bJ
O
O
_J
z>
~Z-
~Z-
<
a:
LJ
o
§
Excess Cancer
Risk (Constant Value
over the
Baseline Risk)
Risk of Cancer with
Radon Exposure
Baseline Risk of Cancer
Without Radon Exposure
Excess Cancer
Risk (Constant
Proportion of the
Baseline Risk)
AGE
REU\TIVE RISK MODEL
Risk of Cancer with
Radon Exposure
Baseline Risk of Cancer
Without Radon Exposure
AGE
NOTE: The relative and absolute risk levels shown are for
illustration purposes only.
SOURCE: Putnam. Hayes it Bartlett, Inc., September 1987.
4-6
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Scientists have not agreed on which projection mode! is the appropriate
choice for most radiogenic cancers, although evidence is accumulating that
supports the relative risk model for most solid cancers. Reports from the
National Academy of Sciences' Committee on the Biological Effects of Ionizing
Radiation (BEIR80), among others, have favored the use of a relative risk
model for those cancers, other than leukemia or bone cancer, observed to
result from radiation exposure.
Prior to 1983, the EPA Office of Radiation Programs (ORP) used both
absolute and relative risk models to estimate the risk from radon and radon
decay products. Since 1983. ORP has used only relative risk models, and
used a range of 1.2 percent to 2.8 percent increase per WLM as of 1984.
In 1985. the Radiation Advisory Committee of the EPA Science Advisory
Board supported the use of the relative risk model, and the Committee
recommended that a range of one to four percent would better reflect the
uncertainty and range. EPA adopted that recommendation and now uses a
relative risk of one percent to four percent increase in risk per WLM of
exposure.
In addition to the risk projection model assumed, three other factors must
be considered in order to project lifetime risks. The most important of
these factors is the underlying dose/response relationship, that is, how the
risk depends on the level of exposure received. This assumption is
important when extrapolating exposures and risks measured at one level
(e.g., in a mine) to risks from exposures at different (often lower) levels.
In general, threshold levels of exposure below which no risk occurs have
not been identified for physical carcinogens. Theoretically, the smallest
quantity of energy deposition can transform a cell and lead to cancer.
There is evidence at the level of microdosimetry and cell biology
which supports this argument, but there is no definitive proof of it as yet.
EPA's calculations are based on a linear dose/response relationship (with no
threshold), which appears to be consistent with studies to date. Based on
this assumption, a higher cumulative exposure results in a proportionally
higher risk.
4-7
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While a short time ago, one spoke of extrapolating from the high exposures
characteristic of mines to the lower environmental exposure levels, this is
no longer true. Until recently, the exposures reported in most studies of
miners were high: 821 to 1180 cumulative working level months (CWLM) in
U.S. uranium miners (NIOSH85; Th82); 289 to 313 CWLM in Czech uranium
miners (NIOSH85; Th82); 204 to 248 CWLM in Newfoundland fluorspar
miners (Th82); 270 CWLM in Zinkgruven metal miners (Th82); etc. (See
table 4-1.) In contrast, before 1985, estimated exposures in residences
usually ranged from 11 CWLM at 1 pCi/l of radon to 22 CWLM at 4 pCi/l of
radon (18 CWLM to 36 CWLM if a 100 percent occupancy factor was
assumed). Thus, extrapolation downward from the miner data was
required.
However, the recent discoveries in Pennsylvania and New Jersey have
revealed that radon decay product concentrations in some homes can be so
high (e.g., 5 WL to 10 WL) that 2 or 3 years of exposure in the home
would be equivalent to the exposures reported in some of the more highly
exposed study groups of miners. In addition, more recent studies of
miners include cumulative exposures well within the range of the older
assumptions about residential exposure' levels: 31 to 131 CWLM in Ontario
uranium miners (Mu83); 81.4 CWLM in Malmberget metal miners (NIOSH85);
43 CWLM in Norwegian niobium miners (So85); 15 to 25 CWLM in Cornish tin
miners (NIOSH85); 20.2 CWLM in Saskatchewan uranium miners (Ho86); etc.
(See table 4-1.) Furthermore, in the recent large study of Saskatchewan
uranium miners (Ho86), the risk of excess lung cancer death was elevated
for all exposures above 5 CWLM. Therefore, questions of theoretical
thresholds and extrapolating downward are now less important since the
available epidemiological studies now encompass many of the exposure levels
found in the indoor environment. Hence, the linear dose/response
assumption, which is required for extrapolation, is less important.
In addition to the dose/response relationship, a second factor to be con-
sidered is that the incremental risk attributable to radon decay products
depends on the other competing risks to which a person is exposed. In
projecting lifetime risks, competing risks are accounted for by using an
4-8
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Table 4-1
Risk Studies
Study
Population
Absolute
Risk
Relative
Collective
Follow-up in
Mean Person-
(per 10 PY/WLM)(per WLM)
Risk % SMR Exposure Years Reference
(CWLM) (PY)
Zinkgruven
Miners
Chinese
Tin
(12.243 M)
30.40
30.40
2.82 862.00 270
270
1.451 716
436 140
4,866
2,155
(39-48)
Th82
NCRP84/78
NIOSH85
NIOSH85
Crangesberg
Miners
30-40
1,150
NIOSH85
U.S. Metal
Miners
1.99
0.31
292
292
620
25,033 NIOSH85
25,033 Th82
Cornwall
Tin Miners
(1,333 M)
211 15-25
27,631 NIOSH85
Niobium
Miners
(124 M)
50.00
40543 2,970
So85
SOURCE: U.S. Environmental Protection Agency. July 1987.
4-9
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actuarial calculation (a life-table analysis) that depends on the age-specific
underlying mortality rate. EPA's current risk projections in the Radon
Risk Evaluation Chart (page 10) in "A Citizen's Guide" use 1980 mortality
rates and the 1980 life table. An important implication of considering
competing risks is that the cumulative lifetime risk is not a linear function
of exposure, even when the dose/response relationship is assumed to be
linear. This non-linearity, which is most apparent at high cumulative
exposures, accounts for the fact that the probability of death cannot exceed
one.
The third factor affecting lifetime risk projections is the assumed induction
period, i.e., the lag or latency between when the exposure occurs and the
onset of disease. Most cancers (including lung cancer) have an average
latency period of between 20 and 30 years, although this period may depend
on age. - The risk estimates in "A Citizen's Guide" assume a minimum
induction period of 10 years in conjunction with a relative risk of 1 to 4
percent per WLM, as well as a linear dose/response relationship.
Projection of Lifetime Risks to Entire Population
To derive the estimates in "A Citizen's Guide" of 5,000 to 20,000 lung
cancer deaths per year from radon requires that the relationship between
individual lifetime risk and exposure be used to project risks to the entire
population. This calculation depends on the size of the population exposed,
the exposure duration and level, and the risk/exposure relationship. The
factors necessary to convert indoor radon levels to individual lifetime risk
have been explained in earlier steps. The third factor, the distribution of
indoor radon levels, is currently uncertain. However, as explained in
Chapter 3, "A Citizen's Guide" assumes an average indoor radon level of
0.004 WL based on a study of New York and New Jersey homes (Ge78).
- For example, the induction period can be modeled by a minimum age
(or latency) before which no cancers appear, together with a minimum
induction period between the time of exposure and the appearance of
cancer.
4-10
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The estimate of 5,000 to 20,000 lung cancer deaths was derived by
calculating the age-average risk per WLM of exposure across the 1980
population. Using a relative risk of 1 percent to 4 percent per WLM, an
average radon decay product concentration of 0.004 WL, and 1980 vita!
statistics results in a calculated range of 4,852 to 19,196 lung cancer
deaths. To reflect the uncertainty underlying these estimates, "A Citizen's
Guide" reports a range of 5,000 to 20,000 lung cancer deaths attributable to
radon exposure. These estimates may be updated in light of new vital
statistics and exposure data.
The entire estimation procedure is summarized in table 4-2. As noted in
this table, several of the steps have been simplified for the sake of
illustration (especially, consideration of age-specific risk and induction
period), resulting in slightly different values than were stated in "A
Citizen's Guide."
RELATIONSHIP BETWEEN SMOKING AND RADON RISKS
Current evidence suggests that smokers are at higher risk from radon
exposures than nonsmokers. Analyses of the U.S. uranium miner cohort
(Wh83; Th85; Ho86), the only group of miners for which extensive
individual smoking data are available, indicate that the joint effects of
smoking and radon are more than additive in causing lung cancer. A
smaller study of residential exposures in Sweden provides further support
for this conclusion (Ed83). A laboratory study of combined cigarette smoke
and radon exposure in rats indicates a synergism between the two factors
in inducing lung cancer, consistent with the hypothesis that radiation acts
as an "initiator" and tobacco smoke as a "promoter" of the carcinogenic
process (Ch81).
In contrast to these results, however, an epidemiological study of Swedish
miners (Ra84) and a study of dogs exposed to radon and cigarette smoke
(Cr78) suggest a less than additive interaction between the two factors.
One speculative explanation of these results is that an increased mucus
4-11
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Table 4-2
Simplified Approximation Of Estimates For
Total U.S. Lung Cancer Deaths Due To Indoor Radon
A. Equation
TOTAL U.S. LUNG
CANCER DEATHS
FROM INDOOR
RADON (1980) = CR * T * FWLM * RRRM * TCR * POP
where:
CR = average (mean) lifetime indoor radon decay
product concentration
0.004 WL-life
T = average interval of lifetime exposure in
hours, following a 10 year minimum induction
period during which no lung cancer will be
observed, assuming 75% occupancy and 73.88
year life span (1980 vital statistics)
.75 * (73.88-10) * 365 *24= 419,691.6
hours/life
FWLM = factor converting average cumulative indoor
exposure in WL hours to working level months
(WLM) for a miner (since risk estimates are
based on miner data), accounting for 170 hours
per month exposure period per WLM (by
definition), and the difference in breathing
rate between the average adult (15.3 liters
per minute) and a miner (30 liters per minute)
1/170 * 15.3/30 = 0.003 WLM per hour.
RRRM = relative lung cancer risk for lifetime
exposure to radon, per WLM, using relative
risk model
1% to 4% per WLM
TCR = underlying annual average of U.S. lifetime
lung cancer risk (1980 vital statistics).
4.584 * 10~4 per person.
POP = 1980 U.S. population
226,545,805
4-12
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Table 4-2 (Continued)
Simplified Approximation Of Estimates For
Total U.S. Lung Cancer Deaths Due To Indoor Radon
B. Calculation:
TOTAL LUNG CANCER DEATHS = 0.004 * 419,691.6 * 0.003
* 0.01 (lower risk estimate)
* 4.584 * 10~4 * 226,545,805
5,230
TOTAL LUNG CANCER DEATHS = 0.004 * 419,691.6 * 0.003
* 0.04 (upper risk estimate)
* 4.584 * 10~4 * 226,545,805
= 20,921
C. Notes:
The above calculations differ from the estimates in "A Citizen's
Guide" of 5,000 to 20,000 lung cancer deaths principally due to
two simplifications used in the equation above:
1. The factor FWLM doesn't include correction for the smaller
lung size and higher breathing rate of children. Both are,
in fact, recognized in the detailed analysis.
2. The product of TCR and POP is replaced in the detailed
analysis by calculations using 1980 mortality rates and 1980
life table statistics. The detailed actuarial analysis more
properly accounts for latency effects, competing risks, and
lower underlying risk of lung cancer at younger ages and,
hence, results in a lower estimate.
Use of the 10 year latent period leaves an average lifespan of
63.88 years [73.88 years-10 years] during which the potential
excess lung cancer risk can be expressed.
SOURCE: Putnam, Hayes & Bartlett, Inc., September 1987.
The numerical assumptions listed in Part A of this
table are based on EPA analysis. Specific sources
are noted in the text.
4-13
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thickness associated with smoking bronchitis shields the target cells in the
lung from the alpha radiation emitted by deposited radon decay products
(Cr78; Sg83).
While subject to revision in light of future scientific findings, EPA believes
the weight of current evidence supports the concept that the risks from
exposure to radon and cigarette smoke are greater than the sum of the
risks from either alone. In fact, they may interact so strongly as to
produce multiplicative risks. When estimating excess lung cancers due to
radon exposure, EPA employs a relative risk model in which the excess is
proportional to radon exposure and to the baseline lung cancer rate in the
population. Implicitly, this model assumes a multiplicative interaction
between radon and all other risk factors for lung cancer, including
smoking.
By far, smoking is the most important risk factor for lung cancer. "A
Citizen's Guide" notes that the American Cancer Society estimates 130,000
people will die of lung cancer from all causes in 1986, and that according to
the U.S. Surgeon General, approximately 85 percent of these (i.e., about
110,000 deaths) could be attributed to smoking. As noted also in "A
Citizen's Guide," 5,000 to 20,000 lung cancers each year may be
attributable to radon. This range for estimated radon induced lung
cancers, moreover, does not fully reflect recent increases in baseline lung
cancer rates or higher estimates of radon levels in homes, and it may be
revised upward in the future. At first, it may seem that the numbers are
inconsistent, since the sum of lung cancers attributable to radon and
smoking approaches or exceeds the total number actually observed.
However, there is no inconsistency. It is implicit in the relative risk model
that smoking and radon exposure are both causal factors for some lung
cancers ~ for about 85 percent of all lung cancers attributable to radon,
indeed, smoking is a joint causal factor. The envisioned overlap in the
estimates of risk from smoking and radon is illustrated in figure U-2.
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80
Illustrative Breakdown of U.S. Lung Cancer Deaths*
(A
I 60
0)
Q
0>
O
c
(0
O
D)
C
40
c
0)
O
20
Current
Smokers
Former
Smokers
Attributable Cause
Smoking
Radon
Radon &
Smoking
Neither
Smoking
nor Radon
Never
Smoked
* Presumes a 20% attributable fraction for radon in each category.
Attributable fraction for smoking in current smokers is 92%, in former
smokers is 83%, and in all categories combined is 85%. Effects of
passive smoking are not considered.
4-15
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RELATIONSHIP OF RADON RISKS TO
LUNG CANCER MORTALITY RATES
Some have pointed out that EPA's estimate of the increase in lung cancer
rate attributable to radon exceeds the actual reported mortality rate of the
disease only a few decades ago. As with the relationship between smoking
and radon, there is no inconsistency. A large part of the increase is
thought to be due to increased exposure to various carcinogens, especially
tobacco smoke, and some of the observed increase in lung cancer mortality
reflects more accurate reporting of the disease. According to the relative
risk model, the rate of radon induced lung cancers (assuming constant
radon exposure rates) increases in proportion to the baseline rate of the
disease, hence it is the proportion of lung cancers attributable to radon
which should remain fairly constant over time — not the absolute rate.
The time trend in observed lung cancer deaths and in the radon
attributable fraction is illustrated in figure 1-3.
UNCERTAINTY IN RISK ESTIMATES
Estimates of the risk of lung cancer associated with exposure to radon
decay products are obtained primarily from epidemiological studies of
underground miners. About 13 groups of miners have been studied (see
table 4-1), and risk coefficients derived for those studies range from 2 to
50 fatal lung cancers per million persons per WLM per year at risk (an
absolute risk estimate), or 0.3 percent to U percent increase per WLM (a
relative risk estimate). Because none of the exposed groups of miners has
been observed long enough to assess the full effects of their exposures, a
risk projection model must be used to estimate the risk for lifetime
exposure.
The risk coefficients, since they are obtained from studies of miners, are
for healthy adult males, about average in smoking habits for employed
4-16
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Rgure 4-3. Total and Possible Radon Induced Lung Cancer Mortality by Year
125000
100000
I
o
LJ
O
1
O
75000
50000
25000
Possible Lung Cancer
Mortality due to Radon
1930
1940
1950
1960
1970
1980
1% Increose/WLM
0.0075 WL for lifetime
Assumptions: Risk Factor
Average Exposure •
Occupancy - 75%
Observation: 8.83% ± 0.55% of total lung cancer
SOURCE: Putnam, Haves it Bartlett, Inc., September 1987. Based on EPA assumptions
and calculations.
4-17
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males. These risk coefficients must be projected for different populations:
populations of different age and sex (women and children), of different
socioeconomic classes, with exposure to different occupational and
environmental pollutants, with different radon decay products, aerosol
exposures, etc. In spite of the uncertainty in these extrapolations, until
epidemiologica! studies for residential exposure are completed, these miner
studies are our best source of risk coefficients.
Risk coefficients and risk estimates sometimes are developed as part of an
epidemiological study; in other cases they may be developed by other
groups using the papers published by the study investigators. Table 4-3
gives both the relative and absolute risk estimates derived from various
investigations that primarily considered miners with less than 600 CWLM of
exposure. EPA chose to exclude studies that reflected lifetime exposures
greater than 600 CWLM from the risk estimate calculations because, until
recently, it was assumed that virtually no members of the public could be
expected to receive over 700 CWLM exposure during their lifetimes.
Studies of miners which EPA did not use to estimate the risks from radon
decay product exposure include the Canadian study of fluorspar miners,
where 25 percent of the person-years of exposure were in excess of 600
WLM, and the full U.S. uranium miner cohort, where 30 percent of the
miners had over 840 CWLM. The reduced level of cancer induction per WLM
of exposure observed above about 700 CWLM causes the risk factor
estimated for the entire U.S. miner cohort to be one-half to one-third lower
than the risk factor estimated for exposures of less than 600 CWLM.
More recent findings regarding indoor radon levels, however, suggest that
many members of the public may be exposed to more than 700 CWLM over
their lifetimes. This means that the risks of cumulative exposures above
700 CWLM need to be addressed and the interaction of competing risks at
the higher exposures must be evaluated. EPA has begun this process and
will continue to re-evaluate the range over which relative risk coefficients
are expected to remain constant.
4-18
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Table 4-3
Relative and Absolute Risk Estimates For Under 600
CWLM Exposure To Radon Decay Products
RELATIVE RISK ESTIMATES
Primary Source Studies
U.S. Uranium Miners (Hg86)
Ontario Uranium Miners (Mu83)
Saskatchewan Uranium Miners (Ho86)
Smoking Malmberget Iron Miners (Ra84)
Non-smoking Malmberget Iron Miners (Ra84)
Non-smoking Navajo Uranium Miners (Sa84)
Secondary Source Estimates
Jacobi et al., 1985 (Jc85)
Steinhausler and Hofmann, 1985 (St85)
NIH Ad Hoc Working Croup, 1985 (NIH85)
Thomas et al., 1985 (Th85)
Archer et al., 1979 (Ar79)
Percentage
Increase in
Fatal Lung
Cancer Per
WLM
0.9 to 1.4
0.9 to 2.3
3.3
2.4
10.7
over 14.0
1.0
1.1
1.2
2.3
2.2 to 3.1
ABSOLUTE RISK ESTIMATES
Secondary Source Estimates
Evans et al., 1981 (Ev81)
NCRP, 1984 (NCRP84/78)
ICRP, 1981 (ICRP81)
Cliff et al., 1979 (CI79)
UNSCEAR, 1977 (UNSCEAR77)
NRC, 1979 (NRC79)
Archer et al., 1979 (Ar79)
Additional
Fatal Lung
Cancers Per
Million Persons
Per WLM
100
100 to 200
150 to 450
200
200 to 450
360
780 to 1170
SOURCE: U.S. Environmental Protection Agency, July 1987.
4-19
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Variations in primary study estimates reflect differences in epidemiological
techniques and duration of the follow-up period; differences in latent period
or lag period used in calculating risk coefficients; and, if dosimetry was
used to estimate the risk coefficient, differences in dosimetric models. The
differences in the estimates for those using published reports as a data
source (i.e., the "secondary source") also reflect the authors' selections
and interpretations of results from the various primary studies. That is,
the authors selected those data sets which they considered best and, either
implicitly or explicitly, weighted the results based on their interpretation.
As mentioned earlier, EPA used a lifetime absolute risk of 360 fatal cancers
per million persons per WLM and a relative risk of 3 percent increase per
WLM until 1983, a relative risk of 1.2 percent increase to 2.8 percent
increase per WLM in 1984; and, in 1985, at the Science Advisory Board's
suggestion, EPA increased the range of relative risk to 1 to 4 percent
increase per WLM. With the exception of the U.S. uranium miners, relative
risk coefficients of radon decay product exposure have ranged from about
one to five percent, with an inverse relationship to cumulative WLM
(EPA78). With the update of the U.S. uranium miners through 1982
(Hg86), all miners have relative risk coefficients of one percent increase
per WLM or more in the range of exposures most relevant to environmental
exposures. Hence, use of a relative risk coefficient of one percent increase
per WLM as a lower bound seems reasonable.
Identifying an upper bound is more difficult. Relative risk estimates have
not been calculated for all studies. However, a crude estimate can be
made, if the Standard Mortality Rates (SMR) and the mean exposure have
been included in the published report, through the following relationship:
Percent Relative Risk = (SMR-100)/mean CWLM. Using data from the
current NIOSH (NIOSH85) and AECB (Th82) reviews, the following
approximate estimates result:
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CRUDE RELATIVE RISK ESTIMATES
FOR EXPOSURE TO RADON DECAY PRODUCTS
Percentage
Increase Per
WLM
Czech Uranium Miners 1.3 to 1.92
Kiruna Iron Miners 1.74
Chinese Tin Miners 1.89 to 2.4
Zinkgruven Zinc Miners 2.3 to 2.8
Norwegian Niobium Miners (based on So85) 4.4 to 7.4
Many of the study groups listed above and in tables 4-1 and 4-3 are small
and not very stable in a statistical sense. However, since one of the large
studies has a relative risk coefficient above three percent increase per WLM
(Ho86) and several smaller studies have relative risk coefficients greater
than three percent, the recommendation of the EPA Science Advisory Board
that the upper bound of risk estimates be placed at a four percent increase
per WLM appears reasonable.
Although the risk coefficients derived from the miner studies are directly
applicable only to healthy adult males, they are the only ones available
now. Support for the theory that they reflect the risk in environmental
exposures is provided by animal studies and by some epidemiological studies
of environmental exposure. The comparability of animal and human risks at
high cumulative exposures is pointed out by the NCRP Report No. 78
(NCRP84/78). Since animals have shown increased risk at low cumulative
exposures, it is expected that humans will also.
In Sweden, epidemiological studies (case control or case reference) have
demonstrated that increased exposure to radon in the residential
environment is associated with elevated lung cancer mortality (Ax79, Ed84).
The risk per unit exposure in these studies appeared to be similar to the
risk per unit exposure in various miner studies. One recent study has
found significantly higher age-adjusted lung cancer rates in counties
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associated with the Reading Prong (Ar87). This suggests risks estimated
using relative risk coefficients for miners will approximate what would be
expected from residential exposures. However, until larger epidemiologica!
studies of residential exposure are completed, the numerical similarity of
risk coefficients in mining and residential environments cannot be
demonstrated conclusively.
In summary, the risk estimates contain the following uncertainties:
• Follow-up is incomplete — more than half of the study group is still
alive in most studies, so the true magnitude of the lifetime risk is still
not known.
• Exposure history is uncertain — there are no personal dosimeters for
radon or radon decay products, and area measurements in mines are a
fairly recent development. Hence, exposures are estimated rather than
directly measured.
• Smoking history — the interaction of smoking with radon decay
product exposure is not yet understood.
• Miners studied are mostly adult males — there are no data on women
and children; therefore, there are no direct risk estimates for those
cases.
• All projection models are best guesses — until the last member of one
of the study groups dies, the true dose-response factor for that group
will not be available.
• The residential exposure levels of the miners were generally unknown.
Even with the uncertainties just listed, most scientists feel that the risk
estimates used today represent the true risks within a factor of about
three.
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Chapter 5
HOW DOES RADON CAUSE LUNG CANCER?
This section of "A Citizen's Guide" notes briefly that inhalation of radon
decay products followed by their radioactive decay within the lungs can
lead to lung cancer. The risk of lung cancer was described in the
previous chapter. This chapter summarizes the general mechanisms by
which radon can lead to cancer and explains the particular uncertainties
associated with the distinction between attached and unattached radon decay
products. Next, the chapter summarizes the epidemiological studies that
associate radon and lung cancer (specific references are cited in Chapter
4). Finally, while lung cancer is the only health effect generally associated
with radon, the last section of this chapter discusses other potential health
effects that might result from radon exposure.
MECHANISM OF LUNG CANCER INDUCTION
The primary concern when discussing the risks from exposure to radon-222
is not exposure to the radon gas itself, but exposure to its decay
products. When radon-222 decays, a number of short half-life decay
products are formed, principally polonium-218, lead-214, bismuth-211, and
polonium-214. Polonium-218, the first decay product, has a half-life of just
over three minutes. This is long enough for most of the electrically
charged polonium atoms to attach themselves to microscopic airborne dust
particles. When inhaled, these small particles have a good chance of
sticking to the moist epithelial lining of the bronchi.
Most dust particles that deposit in the bronchi are eventually cleared
(removed) by mucus, but not quickly enough to keep the bronchial
epithelium from being exposed to alpha particles from the decay of
polonium-218 and polonium-214. Although they cannot travel far, alpha
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particles produced in the lungs can damage sensitive cells. This highly
ionizing radiation passes through and delivers radiation doses to several
types of lung cells. An alpha particle that penetrates the epithelial cells
can deposit enough energy in a cell to kill or to transform it. The
transformed cell, alone or through interaction with some other agent, has
the potential to develop eventually into a lung cancer.
RISK FROM ATTACHED AND UNATTACHED RADON DECAY PRODUCTS
A scientific question that remains unresolved regards the relative number of
health effects associated with attached versus unattached radon decay
products. When radon decays, most of the decay products become attached
to dust particles or aerosols of submicron size. However, some decay
products may be inhaled before they become attached.
Some models of the ways that radon decay products expose the lungs to
alpha particles suggest that the radiation dose to the lungs from unattached
decay products can be from 9 to 35 times the calculated dose from attached
decay products (Ja81). This is because these models assume that the
unattached decay products preferentially deposit in those portions of the
lung (the main and lower bronchi) known to be the most vulnerable to
induction of lung cancer. In contrast, these models assume that a smaller
proportion of attached decay products deposit in these sensitive areas of
the lungs, therefore producing less lung cancer risk. At the present time,
however, there is little experimental evidence to determine whether these
theoretical models of lung exposure are correct.
If the risk from unattached radon decay products is in fact much greater
than that from attached, there are important implications. Air cleaning
systems which reduce particulate concentrations and, hence, the
concentrations of attached decay products, may not reduce the overall lung
cancer risk unless the total of attached and unattached decay products is
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reduced by a factor of 10 or more. Therefore, air cleaning alone may not
correct a situation of high risk and may, under some circumstances,
actually increase the risk. Monitoring corrective measures which depend on
air cleaning will require radon daughter monitors and may require
concentration measurements of both attached and unattached decay
products. Special instrumentation would be needed for these measurements.
ASSOCIATION OF RADON AND LUNG CANCER
The effect of exposure to "emanations" from radium (actually radon and its
decay products) was first mentioned relative to the lung cancer mortality in
Bohemian uranium miners in the early 1900s (Hu42). The same association
of radon-radon decay product exposure with lung cancer is observed in
current epidemiological studies of underground miners, not only uranium
miners but also fluorspar, iron, zinc, and tin miners exposed to elevated
levels of radon and radon decay products. There have also been some
recent epidemiological studies in Sweden showing increased lung cancer
associated with elevated radon decay product exposure in homes (Ed83;
; Ax79).
Although other occupational carcinogens have been suspected of causing the
increase in lung cancer, available reports conclude that silica, cobalt,
nickel, bismuth, chromium, arsenic, colds, and genetics were not causally
involved in the production of lung cancers in Bohemian miners (Hu12;
Hu66). In more contemporary studies, exposure to diesel exhaust fumes
was excluded as a causal factor (Ho86; Ra84). The only common thread
linking all the miner studies is the exposure to elevated radon and radon
decay product levels.
EPA's risk estimates are based solely on human studies such as those just
discussed. Laboratory studies have also demonstrated, however, that
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exposure to elevated levels of radon decay products is sufficient to induce
increased lung cancer in animals. In neither the French studies of rats
(Ch81) nor the American studies of hamsters and dogs (Cr78) did silica,
uranium, dust, or diesel exhaust fumes contribute appreciably to induction
of lung cancers; only radon decay products appear to produce the lung
cancers observed.
OTHER POSSIBLE HEALTH RISKS FROM RADON
The risk from inhaled radon-222 is small compared to the risk from inhaled
radon-222 decay products; however, the primary risk is still induction of
lung cancer. In addition, if radon-222 is ingested rather than inhaled,
little of the radon or its decay products will be desposited in body tissues,
so the expected health effects are negligible.
Doses from decay products of radon-220, which has one long half-life decay
product, will occur not only in the lung but also in other body tissue.
Significant quantities of radon-220 decay products could be absorbed
and deposited, primarily in bone. Therefore, there might be some risk of
other cancers in addition to lung cancer. However, the lung cancer risk
from radon-220 or radon-222 should still be the most significant, whether
the source of radon is from water (ingestion and inhalation) or soil gas
(inhalation).
5-4
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Chapter 6
WHEN DID RADON BECOME A PROBLEM?
Although radon has always been present in our environment, it was not
until scientists began to analyze the higher incidence of lung cancer among
uranium and zinc miners that radon decay products, and, therefore, radon
gas, were considered a problem. This chapter will discuss the evolution of
radon as a major health concern by highlighting some of the discoveries
concerning elevated radon levels: high lung cancer incidence among
uranium miners in the U.S. and other countries, the existence of radon
decay products in homes built with materials that were contaminated with
uranium mining waste, and the discovery of elevated indoor radon
concentrations from naturally-occurring radon sources.
URANIUM MINERS AND HIGH
INCIDENCE OF LUNG CANCER
As early as 1940, scientists were recommending occupational exposure limits
to safeguard against the possible health risks associated with radon and its
decay products. Radon was first demonstrated to be a problem when
epidemiological studies in the 1950s showed a significantly higher incidence
of lung cancer among underground uranium and zinc miners. This
increased risk of lung cancer was attributed to exposure to high
concentrations of radon present in the mines. - In 1971, the
Environmental Protection Agency established an exposure standard of 4
WLM/year (EPA71). As noted in Chapter 4, a working level month (WLM)
is a unit of cumulative exposure. It is defined as a miner's exposure to
- See Chapter 4 for a discussion of the uncertainties involved with inter-
preting these data, and references to specific epidemiological studies
that have associated radon and lung cancer.
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a radon decay product concentration of one working level for 170 hours.
This time period approximates the number of hours worked in one month by
a miner. By comparison, exposure to one working level in a residential
environment, 75 percent of the time during one year, is equal to about 20
WLM. This conversion includes a correction which considers the higher
breathing rate of underground miners engaged in a more strenuous level of
physical activity than the general population.
ELEVATED RADON LEVELS FROM
CONTAMINATED BUILDING MATERIALS
Beginning in the late 1960s, several significant discoveries were made
linking elevated indoor radon concentrations to radioactive building
materials. In Sweden, residential structures made with alum shale brick
were discovered to have seriously elevated indoor radon levels (Be84). A
few years later, in the United States, homes were discovered in Monticello,
Utah, and Grand Junction, Colorado, that had been constructed with
building materials contaminated with vanadium and uranium mill tailings,
respectively (Ni84; Gr86). In Idaho and Montana, surveys by State
agencies identified more than 100 homes with elevated radon levels
attributable to the high uranium content of concrete made from phosphate
slag, a byproduct of the thermal process for phosphorus reduction (Ka79).
Wallboard constructed with phosphogypsum can also contribute to elevated
radon levels. Elevated indoor radon caused by industrial activity, such as
uranium mill tailings used for building materials, is differentiated from
naturally-occurring indoor radon for a variety of reasons. Regulatory
controls have been imposed on radon exposure in both occupational settings
and residential situations, when the exposure is caused by man's activity.
Radon from natural sources is not regulated. In most cases, radon
exposure from naturally-occurring sources will be a more serious problem
than that from manmade sources.
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ELEVATED RADON LEVELS FROM NATURAL SOURCES
Initially, scientific investigations and cleanup efforts focused on homes
constructed with building materials contaminated with manmade radioactive
waste and on homes built on top of uranium tailings (e.g., in Colorado) or
on reclaimed phosphate rock mining sites (in Florida). However, recent
discoveries have shown that naturally-occurring radon in soil can result in
extremely high indoor radon levels. In December 1984, the Watras home in
northeastern Pennsylvania drew national attention when it was accidentally
discovered to have a radon level of over 2,000 pCi/l. Scientists
investigating the site attributed the high radon concentration in the home to
the uranium-rich soil and rock on which it was built. This area of
Pennsylvania was located on a geologic formation called the Reading Prong.
The Reading Prong is a uranium-bearing formation that extends through
eastern Pennsylvania, northern New Jersey, and southern New York. To
date, the highest levels of indoor radon ever discovered were found in
homes built on this formation. These discoveries have prompted expedited
State and Federal research and assistance to address the problem. Tests in
homes throughout this area confirm that natural deposits of uranium in the
soil and rock beneath a home are a significant source of the elevated indoor
radon levels (Ne85). In early 1986, the greatest concentration of severely
contaminated homes ever found was discovered on a dolomite formation in
Clinton, New Jersey, which is near, but not actually on, the Reading
Prong. In this particular area, 40 of the 105 homes studied had indoor
radon levels exceeding 200 pCi/l, and all 105 homes had levels above 4
pCi/l.
As a result of these discoveries, radon can no longer be considered a
problem isolated to a few areas where industrial activities have caused
increased indoor radon levels. Recent studies predict that elevated radon
levels are likely to be found in homes in States across the U.S. (Ne85).
However, significant numbers of indoor measurements have been made in
only a few areas. EPA has efforts underway that will help to characterize
the distribution of indoor radon levels nationwide, including a national
survey and a program to provide technical assistance to States that wish to
conduct statewide surveys (see Chapter 7).
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Chapter 7
DOES EVERY HOME HAVE A PROBLEM?
This chapter discusses the uncertainty involved in assessing the
distribution of radon in homes across the country. While most houses in
this country are unlikely to have a radon problem, several studies indicate
that the occurrence of elevated radon levels could be very widespread.
Reliable predictive models that identify houses likely to have a problem do
not yet exist. There is, however, current research that helps to answer
some of the questions concerning the potential for radon occurrence.
The first two sections of this chapter summarize existing information on the
distribution of radon in U.S. homes and specific areas of the country where
elevated radon levels have already been detected.
The third section addresses the issue of radon in multilevel buildings.
This topic was originally included in EPA's draft version of "A Citizen's
Guide." However, since current scientific investigation has concentrated on
elevated radon levels in single-family detached dwellings, not much is
known concerning radon distribution within multilevel buildings. Therefore,
EPA omitted this topic in "A Citizen's Guide," but provides some information
in this chapter.
The final section describes some of the EPA-sponsored current and future
programs for radon assessment. These programs will help EPA characterize
the distribution of radon levels nationwide and develop predictive models
that can be used to identify areas with high radon potential.
DISTRIBUTION OF RADON IN U.S. HOMES
Although every home has some radon, the large majority of homes in this
country are not likely to have radon levels exceeding EPA's lowest
recommended action level of M pCi/l (0.02 WL). A study by Andreas C.
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George, et al. (Ce78) estimated the average indoor radon concentration to
be about 0.8 pCi/l (or 0.00*1 WL); this study serves as the basis for the
Radon Risk Evaluation Chart (see Chapter 12). Another study, by A.V.
Nero, aggregated the results of 19 separate studies covering 1500 homes
and estimated that the average radon concentration in a single-family home
is approximately 1.5 pCi/l (or 0.0075 WL) (Ne86). These studies indicate
that 1 to 3 percent of the single-family homes in the nation have radon
concentrations of 8 pCi/I or more. The studies also confirmed that radon
levels tend to follow a lognormal distribution (with a geometric mean of 0.9
pCi/l and a geometric standard deviation of 2.8). However, in developing
these estimates, Nero sought to exclude measurements for which a prior
expectation of elevated levels existed (since these measurements would bias
upward the estimate of an average level). For individual data sets,
geometric means ranged from 0.3 pCi/l to 5.7 pCi/I.
The variation in radon concentration throughout the country is determined
by many different factors, including radon source strength, house
construction, ventilation rates, and air pressure differences between the
indoor air and the soil gas. Radon source strength is one of the most
important contributions to a potential indoor radon problem. Although
current data suggest that areas with significant radon source strength are
limited in geographical scope, there is still much uncertainty concerning the
actual distribution of radon throughout the United States.
WHERE RADON HAS BEEN FOUND
Elevated levels of naturally-occurring indoor radon have been found in
nearly every state across the country. Several areas of the country,
however, have exhibited extremely elevated indoor radon levels. The
highest indoor levels have been measured in the Reading Prong areas of
eastern Pennsylvania, New Jersey, and New York. Another area in New
Jersey, near Clinton, has also exhibited extremely elevated levels. Some
homes in these areas exceeded 10 WL. Surveys in other States have
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indicated that, although we have not identified additional areas with the
extremely high levels found in the Reading Prong, nearly every State will
find some levels above 20 pCi/l.
Another source of elevated indoor radon levels is contaminated building
sites or materials. Several areas in the country have identified these
problems. In Polk and Hillsboro counties in Florida, 15 percent of the
homes built on reclaimed phosphate mining lands had indoor radon
concentrations between 0.03 to 0.10 WL (FRN79). Some homes in Colorado,
Utah, and North Dakota that were built on or near uranium mill tailings, or
with contaminated building materials, also have elevated indoor radon levels.
Another site in Montclair/Clen Ridge, New Jersey was found where homes
were built on land contaminated with radium. Areas like these are not
expected be widespread, and do not affect as many homes as does
naturally-occurring radon.
Another potential contributor to elevated indoor radon levels is radon found
in water (see Chapter 3 for a more detailed discussion of radon in water).
Elevated levels of radon in domestic water supplies have been found in
areas of New England, including Maine and New Hampshire.
Investigations are currently underway in many States to locate areas with
elevated indoor radon problems. As results from these studies are
analyzed, we will be able to refine our predictions of where in the United
States indoor radon may be a problem.
RADON IN MULTILEVEL BUILDINGS
Since most of the current data on radon are from single-family homes, it is
difficult to estimate concentrations in apartment buildings and other
multilevel buildings. The few studies available indicate that concentrations
in multilevel structures are typically a few tenths of a picocurie,
substantially lower than concentrations in single-family homes (Ne85). This
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is possibly because average living or working space is usually well isolated
from the ground. For most apartment dwellings and multilevel buildings,
the major contributions to indoor radon concentrations may be expected to
be outdoor air and building materials. Larger European studies
concentrating on apartment building exposures confirm this expectation
(Ne85).
In areas where the chief indoor radon source is soil gas, upper-floor
dwellers are likely to have a much lower exposure to radon than
ground-floor and basement dwellers. However, in areas where the chief
indoor radon source is the well water, indoor concentrations could be high
in the upper floors, as groundwater may be first aerated at that level. In
general, however, most multilevel buildings and apartments are located in
city areas and are linked to public water supplies rather than to wells.
Public water supplies usually are fed through reservoirs in which the water
is aerated and any dissolved radon is released into the outside air.
ERA-SPONSORED ASSESSMENT PROGRAMS
As part of its overall Radon Action Program, EPA is conducting a number
of activities, including a national survey. The national survey will provide
information on the national distribution of radon concentrations in homes
and should be completed in a few years. Activities also include assistance
to States with the design and conduct of surveys to identify areas with
elevated radon levels. As part of this program, EPA can help States
conduct radon surveys by assisting with survey design and by providing
laboratory support and measurement devices. Many States have requested
EPA assistance and EPA worked with 10 States on radon surveys during the
1986-1987 heating season. EPA will assist as many States as possible
during the next several years. EPA is also conducting research aimed at
developing a predictive model that will help to identify areas with a high
indoor radon potential. Results from this study will not be available for
one to two years.
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In addition to these activities, EPA is conducting a number of other efforts
as part of its overall Radon Action Program. These activities include
mitigation training, demonstration and research projects, cooperative efforts
with other Federal agencies to develop State and private sector capabilities,
and various forms of public information and assistance. Further information
about EPA's radon activities can be obtained by contacting the U.S.
Environmental Protection Agency, Office of Radiation Programs (ANR-464),
401 M Street, S.W., Washington, DC 20460 or your EPA Regional Office.
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Chapter 8
HOW DOES RADON GET INTO A HOME?
The primary source of indoor radon in dwellings is the soil and rock
adjacent to the building; secondary sources include domestic water supplies
from wells and earth-based building materials. Chapter 3 discussed
characteristics of rock, soil, water, and building materials that are
associated with high radon concentrations. This chapter explains how
radon is transported into the home from these sources. Specific areas of
discussion include: (1) flow-inducing mechanisms, (2) factors influencing
radon transport from soil into homes, (3) radon transport through water
supplies, and (4) earth-based building materials as a source of radon.
MECHANISMS INDUCING RADON FLOW
The predominant source of indoor radon is the decay of radium in the soil
adjacent to the building. Generally, the soil is indigenous to the site;
however, in some cases, industrial products such as mill tailings and wastes
from phosphate mining are the dominant source of radon in the soil. Radon
in the soil can enter the home through two gas transport mechanisms:
molecular diffusion (movement from an area of high concentration to low
concentration at constant pressure) and pressure-driven flow (movement
from a high to a low pressure area). Scientific investigations have
indicated that diffusion cannot account for the high levels of indoor radon
discovered in some homes, but, rather, pressure differences between indoor
and outdoor air seem to be the major determinant
Pressure-driven flow, where radon is actually drawn into the structure, is
influenced by several factors. During the heating season, indoor
temperatures are often higher than outdoor temperatures, causing a
tendency for warm indoor air to be displaced by cooler outdoor air. This
tendency is called a stack effect since the warm air tends to rise as in a
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chimney. Inward pressure on the lower walls and floor resulting from this
effect causes radon to be drawn into the home from the surrounding soil.
Wind is another important factor that causes a pressure difference and
drives the flow of radon into a building. Wind causes an exchange between
the air in the structure and the soil. Indoor air flows to the soil on the
leeward side of the building (where outdoor pressures are lower) and flows
from the soil into the house on the windward side (where outdoor pressures
are higher). Barometric pressure and precipitation are two additional
factors that can affect the flow of radon into a structure, although some
scientific uncertainty remains on how these factors affect indoor
concentrations (Ne2/84).
Pressure differences caused by mechanical devices or appliances in the
home are equally important. Exhaust fans in the kitchen or bathroom and
clothes dryers draw air out of the house. Open fireplaces also create a
significant draw on indoor air. On the other hand, some room fans can
draw outdoor air into the house. The net effect of these processes will
determine whether the resulting pressure difference between indoor and
outdoor air will draw radon into the home.
RADON TRANSPORT FROM SOIL
In addition to flow-inducing pressure differences, the transport of radon
into a structure from the soil is affected by other factors such as the rate
of radon production in the soil, the soil permeability and moisture content,
and the building substructure type (see Chapter 3 for a description of the
formation of radon in soil gas). Research suggests that the strength of the
radon source can better explain the differences among radon levels in
various homes than the rate of indoor ventilation (Ne2/84). This indicates
that energy-efficient homes will not necessarily have elevated levels of
radon, although a reduction in air exchange rates may exacerbate already
elevated levels. Soil permeability can strongly affect radon entry, since
the greater the permeability, the easier it is for radon to be transported
through the soil.
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Building substructure also affects the radon entry rate. Of the three
genera] substructure types -- basements, crawl-spaces, and slab-on-grade
— basements tend to be more susceptible to high radon entry rates because
of the large area exposed to the soil and the greater efficiency of the
pressure-driven flow mechanism (Ne2/84). Even if there is a ventilated
crawl-space separating the soil from the house, radon entry into a home
from the underlying soil may still be significant. Once again, pressure
differences between indoor and outdoor air may cause a stack effect. The
stack effect can promote an even greater flux of radon into the crawl-space
if the crawl-space is unvented (Ne2/84). Slab-on-grade foundations are
considered less susceptible to high rates of radon entry. As with all
substructures, however, radon can enter structures with slab-on-grade
foundations through floor and wall cracks, joints, utility openings, floor
drains, and (in the case of basements) sumps. Measurements of elevated
levels in slab-on-grade homes built on reclaimed phosphate mining lands in
Florida affirm the overall importance of soil source strength as a
determinant of indoor radon levels.
RADON TRANSPORT THROUGH WATER SUPPLIES
Radon can also enter the home by being released from water used in daily
activities. As mentioned in Chapter 2, radon can be easily absorbed by
water flowing through soil or rock containing radon gas, especially since
the solubility of radon is greater in the colder water temperatures typical of
groundwater. Studies indicate that while very few public water supplies
contain enough radon to be a significant source of indoor radon, elevated
levels of radon have been observed in water from private wells in some
areas of the country, particularly in the northeast. It is estimated that, in
most cases, radon from drinking water contributes only one to seven
percent of the radon concentration in indoor air.
Waterborne radon is released into the home when the water is exposed to
air and/or when its heated. Thus, radon is released from water through
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the use of items such as showers, washing machines, dishwashers, and
toilets. Domestic activities that involve heating water result in a higher
transfer of the radon to air. These activities contribute to the
concentration of radon in indoor air and, hence, inhalation exposure.
Radon that remains in the water can be ingested, although research
indicates that ingestion is generally not the most significant source of
exposure and, therefore, is not the primary concern. It is the release of
radon from water to air and the subsequent inhalation that normally
dominate exposure (NCRP84/77).
RADON FROM EARTH-BASED BUILDING MATERIALS
Radon can also emanate from earth-based building materials containing
elevated concentrations of radium, although, in the U.S., this source of
radon is substantially less significant than radon coming from the soil
(Ne83). An example of a case in which building materials were considered
a major source of elevated indoor radon levels occured in Sweden, where
houses were built using alum shale, a material high in radium (Sw80). In
the U.S., some homes were built using phosphate slag as an ingredient in
concrete (Ka79). Other examples of building materials known to have
slightly elevated radium concentrations include fly ash used in concrete,
phosphogypsum (a waste product from processing phosphate ore) used in
wall board, and red mud (a byproduct of bauxite ore processing sometimes
used for bricks) (Ne83). In each situation above, the source of radon was
building materials contaminated by wastes from industrial activities. With
the exception of these examples and similar incidences, the predominant
source of radon entry is naturally-occurring radon in the soil.
As mentioned in "A Citizen's Guide," natural materials used in construction
(e.g., shale or granite) may sometimes contain naturally elevated radium
levels and could emanate radon. Such materials might be used, for example,
in the construction of fireplaces or in solar heating systems in which heat
is stored in large beds of stone.
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Chapter 9
HOW IS RADON DETECTED?
Since radon cannot be detected by the human senses, special equipment is
needed to measure the concentration of radon and its decay products.
Since both radon and radon decay products may be measured, this chapter
first explains the concepts required to convert from one unit to another.
Homeowners should be made aware of the types of devices available for
radon detection and the different purposes for each sampling method. While
"A Citizen's Guide" briefly describes the charcoal canister and alpha track
detector, this chapter explains the three general methods for radon
sampling and describes in detail seven measuring systems that are currently
in use. For further information concerning each of the detection devices
mentioned, consult EPA's "Interim Indoor Radon and Radon Decay Product
Measurement Protocols" (EPA86a). An explanation of screening and
follow-up measurement protocols is provided in Chapter 11.
RELATIONSHIP BETWEEN RADON AND
DECAY PRODUCT CONCENTRATIONS
As mentioned in Chapter 5, most of the health risk from indoor radon is
associated with radon decay products. Therefore, measuring the
concentrations of the alpha-emitting radon decay products (also referred to
as the Potential Alpha Energy Concentration or PAEC) would be an
appropriate choice. For various reasons, however, measurements are
frequently made of radon concentrations rather than of radon decay
products. Radon concentrations, which are measured in units of picocuries
per liter (pCi/l), can be converted into working levels (WL), the unit of
measurement for radon decay products, by assuming an average relationship
between radon and its decay products.
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In a closed space, a given activity concentration of radon (which represents
a rate of radioactive decay per unit volume) tends to reach a state of
equilibrium with its decay products, where the rates of formation (via decay
of the predecessor element) and decay of each decay product are equal. In
perfect equilibrium, 100 pCi/l of radon are in balance with exactly 1 WL of
radon decay products. However, a number of factors tend to cause the
radon decay product concentration to be lower than it would be in
equilibrium (e.g., plate-out on walls and floors). The degree of
disequilibrium is measured by the equilibrium fraction. The equilibrium
fraction is the ratio of decay product concentration to the radon
concentration multiplied by 100:
Equilibrium Fraction = [WL] x 100
[pCi/l]
Data collected from typical houses in which radon and its decay products
were measured concurrently indicated that this equilibrium fraction ranges
from 0.3 to 0.7, with an average of around 0.5 (Ce85). With an
equilibrium fraction of 0.5, 200 pCi/l of radon is equivalent to 1 WL. Using
this relationship, measurements of either radon or its decay products can
be compared (i.e., divide picocuries per liter by 200 to estimate working
levels).
SELECTION OF SAMPLING METHODS
EPA has issued two reports recommending measurement techniques and
strategies. The first report, titled "Interim Radon and Radon Decay
Product Measurement Protocols" (EPA86a), provides guidance for making
measurements in residences using the seven techniques evaluated by EPA
and found to be satisfactory; procedures for other instruments may be
added as they are evaluated by EPA. The second report, titled "Interim
Protocols for Screening and Follow-up Radon and Radon Decay Product
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Measurements" (EPA87a), outlines the recommended strategy for making
reliable, cost-effective measurements in homes. Below is a brief description
and explanation of the recommendations in the two reports.
MEASUREMENT CONDITIONS AND QUALITY OBJECTIVES
EPA protocols provide procedures for measuring radon concentrations with
continuous radon monitors, charcoal canisters, alpha-track detectors, and
grab radon techniques. The protocols also recommend procedures for
measuring radon decay product concentrations with continuous working level
monitors, radon progeny integrating sampling units, and grab radon decay
product methods. The discussion of each method includes recommended
quality control procedures, such as frequency of calibration, desirable
operational checks, and background and replicate measurements.
There are, however, some general guidelines concerning standardized
measurement conditions and quality assurance objectives which apply to all
measurement devices.
Standardized Measurement Conditions
EPA's protocols specify that measurements be made when the radon and
radon decay product concentrations are likely to be the most stable, e.g.,
in a closed building with a minimum level of ventilation (EPA86a). Such
measurements will generally be higher than the average concentrations to
which the occupants are exposed.
Making measurements under standardized conditions is important for two
reasons. First, measurements should be reproducible, i.e., the
measurement results can be related to either potential or actual exposures
in the house and have the smallest possible variability with the technique.
The most reproducible measurements are those taken when the house
conditions are standardized, with the house closed, and after sufficient time
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has elapsed for the concentrations to stabilize. Reproducible results are
especially important when deciding whether remedial action is necessary or
when evaluating the effectiveness of remedial action.
Second, it is important to quantitatively estimate the variability associated
with the results of a measurement. This variability can only be estimated
from data taken under similar conditions and, since average living
conditions are difficult to define and reproduce, specifying standard
conditions allows for valid application of the estimates of error.
House Conditions
Measurements should be made under "closed-house" conditions. To a
reasonable extent, windows and external doors should be closed, allowing
for normal entry and exit. In addition, external-internal air exchange
systems (other than a furnace) such as high-volume attic and window fans
should not be operated. For measurement periods of three days or less,
these conditions should exist for 12 hours prior to beginning the
measurement (EPA86a).
Severe weather will also affect the measurement results. Again, measure-
ments of less than three days should not be conducted if severe storms
with high winds are predicted. Wind-induced differences in air pressure
between the house interior and exterior will increase the variability of
radon concentrations. Rapid changes in barometric pressure increase the
chance of a large shift in the interior and exterior air pressures, affecting
the rate of radon influx.
Quality Assurance Objectives
Another important part of measurement is quality assurance. The objective
of quality assurance is to ensure that data are scientifically sound and of
known precision and accuracy. The following are several aspects of quality
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assurance that should be included in any measurement program: controlled
calibrations, replicate measurements, background measurements, and routine
sensitivity checks.
Controlled calibrations are samples collected or measurements made in a
known radon environment such as a calibration chamber. Detectors
requiring laboratory readout, such as charcoal canisters, alpha-track
detectors, and RPISU samplers, would be exposed in the calibration
chamber and then analyzed. Instruments providing immediate results, such
as continuous working level monitors and continuous radon monitors, should
be operated in a chamber to establish calibration.
There are two types of calibration measurements that should be made for
alpha-track detectors and charcoal canisters. The first measurements
determine and verify the conversion factors used to derive the
concentration results. These measurements, commonly called spiked
samples, are done at the beginning of the measurement program and
periodically thereafter. The second calibration measurements monitor the
accuracy of the system. These are called blind calibration measurements
and consist of detectors that have been exposed in a radon calibration
chamber. They are not labelled as such when sent to a processing
laboratory.
Background measurements, or blanks, should also be conducted frequently.
Such measurements should be made using unexposed passive detectors or
should be instrument measurements conducted in very low (outdoor) radon
concentration environments and separated from the operating program.
Generally, these should be equivalent in frequency to the spiked samples
and should also not be identified as blanks when submitted for analysis to
external laboratories. In addition to these background measurements, the
organization performing the measurements should calculate the lower limit of
detection (LLD) for the measurement system. This LLD is based on the
system's background and can restrict the ability of some measurement
systems to measure low concentrations.
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Duplicate measurements provide an estimate of the precision of the
measurement results. Duplicate measurements should be included in at least
10 percent of the samples. If enough measurements are made, the number
of duplicates may be reduced, as long as enough are used to analyze the
precision of the method.
A quality assurance program should include a written plan for satisfying
the preceding objectives. A system for monitoring the results of the four
types of quality assurance measurements should also be maintained
continuously and made available for inspection.
The EPA has established a Radon/Radon Progeny Measurement Proficiency
Evaluation and Quality Assurance (RMP) Program. This program enables
participants to demonstrate their proficiency in measuring radon and radon
decay product concentrations and to have their quality assurance programs
evaluated. Contact the Radon Quality Assurance Coordinator at (919)
511-7131 for further information about this program.
MEASUREMENT INSTRUMENTS
Alpha-Track Detector
The alpha-track detector (ATD) consists of a small piece of plastic enclosed
in a container with a filter-covered opening. Alpha particles emitted by
radon decay products in the air strike the plastic and produce
submicroscopic damage tracks. At the end of the measurement period, the
detectors are returned to a laboratory, where the plastic is placed in a
caustic solution that accentuates the damage tracks so they can be counted
using a microscope or an automated counting system. Data generated at a
calibration facility is used to correlate the number of tracks per unit area
to the radon concentration in air.
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Many factors contribute to the variability of the ATD results, including
differences in the detector response within and between batches of plastic,
non-uniform plateout of decay products inside the detector holder,
differences in the number of tracks used as background, variations in
etching conditions, and differences in readout. The variability in ATD
results decreases as the number of net tracks counted increases, so
counting more tracks over a larger area of the detector will reduce the
uncertainty of the result. Deploying duplicate ATDs will also reduce the
error. However, if cost considerations make it necessary to deploy single
ATDs, the data obtained should be evaluated and used taking into
consideration the relative errors associated with counting the area and
number of net tracks specified to the processing laboratory.
The advantages of the alpha-track detector include its relatively low cost
(about $20 to $50 per detector including the analysis) if installed by the
homeowner. Because of its small size, the alpha-track detector is not
intrusive. The primary disadvantage of this detector is the relatively long
measurement period it requires. For currently available models, three
months is the minimum recommended exposure period. Also, this detection
device is not always precise for measurements of low radon concentrations.
Charcoal Canister
Like the alpha-track detector, charcoal canisters are passive devices
requiring no power to function. The activated charcoal allows continuous
adsorption and desorption of radon, and the adsorbed radon undergoes
radioactive decay during the measurement period. Therefore, the technique
does not uniformly integrate radon concentrations during the exposure
period.
The charcoal canister measurement technique is described in detail by
Cohen and George (Co83 and Ce8^). The charcoal canister now used by
several groups is a circular container, 6 to 10 centimeters in diameter and
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approximately 2.5 centimeters deep, filled with 25 to 100 grams of activated
charcoal. One side of the container is fitted with a screen that keeps the
charcoal in but allows air to diffuse into the charcoal. When the canister is
prepared by the supplier, it is sealed with a cover until it is ready to be
deployed.
To initiate the measurement, the cover is removed to allow air to diffuse
into the charcoal bed. Radon in the air will be adsorbed onto the charcoal
and will subsequently decay, depositing decay products in the charcoal. At
the end of a measurement period, the canister is resealed and is returned
to a laboratory for analysis.
At the laboratory, the canisters are analyzed for radon decay products by
placing the charcoal, still in its canister, directly on a gamma detector.
Gamma rays of energies between 0.25 and 0.61 MeV are counted. It is
usually necessary to correct for the reduced sensitivity of the charcoal due
to absorbed water. This may be done by weighing each canister when it is
prepared and then reweighing it when it is returned to the laboratory for
analysis. Any weight increase is attributed to water absorbed by the
charcoal. The weight of water gained is correlated to a correction factor
that should be empirically derived (Ge84), and used to correct the
analytical results.
Radon Progeny Integrating Sampling Unit (RPISU)
This continuous sampling unit consists of an air sampling pump that draws
a continuous flow of air through a detector assembly containing a filter and
at least two thermoluminescent dosimeters (TLDs). One TLD measures the
radiation emitted from radon decay products collected on the filter, and the
other TLD is used for background gamma correction. The pump and
assembly are usually operated for three to seven days. At the end of that
time, the unit is removed and the detector assembly is returned to the
analytical laboratory. The analysis consists of measuring the light given
off by the TLD during heating.
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This device provides a short-term measurement of radon decay product
concentration, rather than radon gas levels. There is extensive experience
in the use of RPISUs, and measurement errors are well established. The
drawbacks of using a RPISU are its cost and the difficulty of handling the
device. These devices may be both heavy and difficult to move, and
trained personnel are required for installation and removal. In addition,
most RPISUs cost about $500 to $3,000 for the device, and $5,000 to $10,000
for the analysis equipment. While the analysis is relatively accurate, the
RPISU is sensitive to airborne particles and, therefore, may not work
properly if there are high concentrations of particulates in the air.
Continuous Radon Monitor (CRM)
A CRM samples the ambient air by pumping air into a scintillation cell after
passing it through a particulate filter that removes dust and radon
decay products. As the radon in the air decays, the ionized radon decay
products plate out on the interior surface of the scintillation cell. The
radon decay products decay by alpha emissions, and the alpha particles
strike the coating on the inside of the cell, causing scintillations to occur.
The scintillations are detected by the photomultiplier tube in the detector,
which generates electrical signals. The signals are processed and the
results are either stored in the memory of the CRM or printed on paper
tape by the printer. The CRM must be calibrated in a known radon
environment to obtain the conversion factor used to convert count rate to
radon concentration.
The CRM may be a flowthrough-cell type or a periodic-fill type. In the
flowthrough-cell type, air flows continuously into and through the
scintillation cell. The periodic-fill type fills the cell once during each
preselected time interval, counts the scintillations, then begins the cycle
again.
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Continuous Working Level Monitor (CWLM)
A CWLM samples the ambient air by filtering airborne particles as the air is
drawn through a filter cartridge at a low flow rate of about 0.1 to 1 liter
per minute. An alpha detector such as a diffused-junction or
surface-barrier detector counts the alpha particles produced by the radon
decay products as they decay on the filter. The detector is normally set to
detect alpha particles with energies between 2 and 8 MeV. The alpha
particles emitted from the radon decay products polonium-218 and
polonium-214 are the significant contributors to the events that are
measured by the detector. The event count is directly proportional to the
number of alpha particles emitted by the radon decay products on the
filter. The unit typically contains a microprocessor that stores the number
of counts and elapsed time. The unit can be set to record the total counts
registered over specified time periods. The unit must be calibrated in a
calibration facility to convert count rate to working level (WL) values.
This may be done initially by the manufacturer and should be done
periodically therafter by the operator.
The cost of a CWLM device ranges from $2,500 to $10,000, and a three-day
measurement can cost from a few hundred dollars to nearly one thousand
dollars.
Crab Sampling
The term "grab sampling" refers to very short-term (about five minutes)
sampling. This method consists of evaluating a small volume of air from the
home for either radon or radon decay product concentration.
In the radon grab sampling method, a sample of air is drawn into and
sealed in a flask or cell that has a zinc sulfide phosphor coating on its
interior surfaces. One surface of the cell is fitted with a clear window that
is put in contact with a photomultiplier tube to count light pulses
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(scintillations) caused by alpha disintegrations from the sample interacting
with the zinc sulfide coating. The number of pulses is proportional to the
radon concentration in the cell.
The cell is counted about four hours after filling to allow the short-lived
radon decay products to reach equilibrium with the radon. Correction
factors are applied to the results to compensate for decay during the time
between collection and counting and to account for decay during counting.
Crab sampling measurements of radon decay product concentrations in air
are performed by collecting the decay products from a known volume of
collection. Several methods for performing such measurements have been
developed and have been described by George (CeSOb). Comparable results
may be obtained using all of these methods. This summary, however, will
describe two procedures that have been most widely used with good results:
the Kusnetz procedure and the modified Tsivoglou procedure.
The Kusnetz procedure (Ku56; ANSI73) may be used to obtain results in
working levels (WL) when the concentration of individual decay products is
not important. Decay products in up to 100 liters of air are collected on a
filter in a 5-minute sampling period. The total alpha activity on the filter
is counted any time between 40 and 90 minutes after sampling is completed.
Counting can be done using a scintillation-type counter to obtain gross
alpha counts for the selected period. Counts from the filter are converted
to disintegrations using the appropriate counter efficiency. The
disintegrations from the decay products may be converted into working
levels using the appropriate "Kusnetz factor" for the counting time utilized.
The Tsivoglou procedure, as modified by Thomas (Ts53; Th72), may be
used to determine WL and the concentration of the individual radon decay
products. Sampling is the same as in the Kusnetz procedure; however, the
filter Is counted three separate times following collection. The filter is
counted between 2 and 5 minutes, 6 and 20 minutes, and 21 and 30 minutes
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after sampling is completed. Count results are used in a series of
equations to calculate concentrations of the three radon decay products and
VVL.
The cost of a measurement can be several hundred to several thousand
dollars since a trained technician must be sent on site to take the grab
sample. The advantages of grab sampling are that the test period is
relatively short, results are ready immediately, and conditions during the
measurement are known to the sampler. One disadvantage, however, is the
relatively high cost. In addition, grab sampling does not provide a
long-term average and house conditions must be controlled for 12 hours
prior to measurement.
RADON MEASUREMENTS IN WATER
Radon in drinking water can be detected either by the liquid scintillation
method or by using alpha-track detectors (BI85). The liquid scintillation
method uses a liquid which emits light when struck by a nuclear particle.
The water sample containing radon is mixed with this liquid and the light
flashes are then counted on a liquid scintillation counting system (Co86).
Alpha-track detectors, similar to those used to measure radon in air, can
be placed in the bottom of a weighted cup which is inverted and placed at
the bottom of a toilet tank. As the water rises in the tank the cup traps
air and the radon gas can emerge from the water and cause a track to be
formed on the detector (Co86).
SELECTING A SAMPLING METHOD
The choice of an appropriate measurement method depends on whether the
measurement is intended as a quick screening measurement, or as a
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follow-up to determine average exposure. In practice, the choice of a
measurement system is often dictated by availability. If alternative systems
are available, the cost or duration of the measurement may become the
deciding factor. Each system has its own advantages and disadvantages,
and the user must exercise some judgment in selecting the system best
suited to the individual situation. More information on this subject is found
in Chapter 11 and in EPA's "Interim Protocols for Screening and Followup
Radon and Radon Decay Product Measurements" (EPA87a).
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Chapter 10
HOW CAN I GET A RADON DETECTOR?
"A Citizen's Guide" advises homeowners to contact their State radiation
protection offices or EPA regional offices to obtain information on vendors
or testing services provided by State or local governments or private firms.
In the event that information about obtaining detectors is not available, this
chapter provides information on methods for obtaining measurement devices.
In addition, the EPA-sponsored Radon Measurement Proficiency (RMP)
program is also discussed.
STEPS TO OBTAIN A DETECTOR
The choice of an appropriate measuring device depends upon several
considerations. The purpose of the measurement (quick screening or
follow-up), how much difficulty is involved, and how much a homeowner is
willing to spend are all factors a homeowner should consider prior to
investigating types of detectors and companies selling testing devices.
Once these decisions are made, the homeowner is advised to contact the
State radiation protection office or regional EPA office by letter or phone
for information on types of devices; these offices are listed in local
telephone books and in "A Citizen's Guide." State representatives can
provide a list of vendors that provide measurement services within the
State. EPA suggests that a homeowner contact several of the listed
companies and request information concerning qualifications, warranties, and
costs. With this information, a homeowner can make an informed decision
concerning testing devices.
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ERA'S RADON MEASUREMENT PROFICIENCY PROGRAM (RMP)
EPA is sponsoring a voluntary program, known as the Radon/Radon
Progeny Measurement Proficiency and Quality Assurance (RMP) program,
which is designed to evaluate the qualifications and expertise of firms and
laboratories with respect to radon measurement and analysis. The RMP
program is not designed for laboratory accreditation and EPA does not
certify, recommend, or endorse participating laboratories.
In the RMP program, testing periods are referred to as test rounds. Each
round consists of two tests: a performance test and a follow-up test.
Successful completion of either test is considered successful completion of
the test round. Both tests follow the same procedures as described below.
All testing is conducted at the radon chamber at EPA's Eastern
Environmental Radiation Facility (EERF) in Montgomery, Alabama. Each
participating company may enroll with any or all of the seven measurement
methods described in EPA's "Interim Indoor Radon and Radon Decay
Products Measurement Protocols" (EPA86a). Once a company is enrolled,
EPA specifies the number of each type of detector to be submitted, and the
detectors are exposed to known radon and/or radon decay product
concentrations. The radon or radon decay product concentrations are not
revealed to the companies. After exposure, the detectors are returned to
the companies, which then have two working weeks to analyze their
detectors and report the results to EPA for evaluation.
EPA evaluates the results by comparing the companies' results to the known
levels of exposure. If a company's results are within the established
screening-measurement criteria, and the company meets all other program
requirements, they pass the performance test. If a company fails any of
the program requirements, the method is automatically retested in the
follow-up test. Companies that fail again in the follow-up test are not
listed in the proficiency report for that test round, but may participate in
the next test round.
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EPA conducts the test rounds semi-annually, and issues reports of the
results. State-specific proficiency reports list the companies that serve
each State. The report is issued to States for public distribution. A more
detailed report, the Cumulative Proficiency Report, lists the performance
record for each participating company as well as other information. This
report is issued to participants as well as to State officials.
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Chapter 11
HOW SHOULD RADON DETECTORS BE USED?
It is widely recognized that radon concentrations in homes can vary greatly
over time (FI84; Ge83; He85; Ny83; St79; Wi86). Furthermore,
concentrations at different locations in the same house can often differ by a
factor of two or more (Ce84; He85; Ke84). Because of these temporal and
spatial variations, EPA cannot use the result of a single measurement to
provide an accurate estimate of health risks or to make a well-informed
decision on the need for remedial action. What EPA has recommended,
therefore, is a system for making the least number of measurements possible
to obtain accurate and reliable results.
EPA recommends a two-step strategy, beginning with a screening
measurement made under closed-house conditions in an area where radon
concentration is greatest (usually the basement or ground level).
Depending on the results of the screening measurement, a second series of
follow-up measurements may be recommended to assess more completely the
average concentrations in the living areas of the house. EPA recommends
that any decision concerning permanent corrective action to reduce indoor
radon concentrations be made only after the completion of follow-up
measurements.
SCREENING MEASUREMENTS
EPA advises that the first measurement in a house be a screening
measurement. A preliminary screening can determine quickly and
inexpensively whether or not occupants may be exposed to high radon
concentrations and if additional measurements are needed. Another use of
screening measurements is in multiple-house surveys designed to identify.
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as efficiently as possible, houses that contain high concentrations.
Screening measurements should be inexpensive and simple, so that
unnecessary time or money is not spent in houses that do not pose a health
threat. EPA's guidance emphasizes, however, that the screening
measurement alone does not provide a homeowner sufficient information to
decide on the need for remedial action.
A screening measurement should provide information about the maximum
concentrations to which the occupants may be exposed, and should also be
reproducible during occupied conditions. Therefore, EPA recommends that
screening measurements be made in (1) the lowest area of the house that
the residents currently use or could adapt for use as a living area, and (2)
under closed-house conditions. In many houses, the lowest livable area will
be a basement that could be converted to a den, playroom, or bedroom
without major structural changes. The highest concentrations of radon or
radon decay products will usually be found in areas of the house closest to
the underlying soil. Radon concentrations should be highest and most
stable when doors and windows are not opened for more than a brief
period.
There is a growing body of data (EPA85; Ce83; Ge81) indicating that
basement concentrations tend to be a factor of two to three times higher
than concentrations in rooms above the basement. Therefore, if the result
of a screening measurement is very low, there is a high probability that the
long-term average concentrations in the rooms currently used as living
areas are even lower, and the homeowner can eliminate the need for further
measurements. There has been some criticism that EPA's protocols will
result in a significant number of erroneous identifications of high levels.
This may be true; however, EPA believes that a false positive measurement
result is less serious because it will result in further measurements, which
would reveal that the concentrations in the house are low. Adherence to
the EPA protocols for screening measurements will decrease the number of
false negatives and as well as the number of houses that contain
concentrations high enough to warrant remedial action (EPA86a) but that
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are not identified as such because of a low screening measurement result.
The outcome of a false negative is that no further measurements are made,
and potentially high concentrations may never be identified. In the interest
of reducing radon exposures, therefore, EPA believes that a significant rate
of false positives is preferable to a high rate of false negatives.
Another EPA recommendation is that all short-term measurements (i.e.,
measurements of less than three months in duration) be made during
periods of the year when windows are normally kept closed. For most
climates in this country, this will be during the winter months. The intent
of this recommendation is to ensure that short-term measurements are made
during the time of highest and most stable concentrations. The occupants
should be instructed to keep windows and doors closed during the
measurement period. Doors should be opened only for a few minutes to get
in and out of the house. External-internal air exchange systems such as
high-volume attic and window fans should not be operated, except for
furnaces, which may be essential to the occupant's comfort.
FOLLOW-UP MEASUREMENTS
The EPA guidance for follow-up measurements is intended to provide
homeowners with an estimate of annual concentrations in living areas, while
minimizing excessive exposures. This guidance closely parallels the tiered
set of recommendations to homeowners described in "A Citizen's Guide"
regarding the need for and urgency of remedial action. The need to make
follow-up measurements depends upon the results of the screening
measurement. A summary of recommended follow-up measurements appears
in table 11-1.
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Table 11-1
Follow-up Measurements
Made in General Living Areas
Instrument
Alpha-Track
Detector
Charcoal
Canister
Radon Progeny
Integrating
Sampling Unit
Continuous
Working Level
Monitor
Screening Result
Greater than 20 pCi/l
3-month measure-
ments (may be less
than 3 months if
laboratory uses
adequate lower limit
of detection), made
under closed-house
(winter) conditions*
Measurements of
2 to 7 days made
under closed-house
conditions
100-hour measure-
ments, made under
closed-house
conditions
24-hour measure-
ments, made under
closed-house
conditions
Screening Result
Less than 20 pCi/l
12-month measurements
made under normal living
conditions
4 measurements made
under normal living
conditions every 3 months
4 100-hour
measurements made
under normal living
conditions every 3 months
4 21-hour
measurements made
under normal living
conditions every 3 months
Continuous
Radon Monitor
21-hour measure-
ments, made under
closed-house conditions
4 24-hour measurements
made under normal living
conditions every 3 months
If the result of the screening measurement is greater than about 200
pCi/l, a short-term follow-up measurement in a few days or weeks
would be more appropriate.
SOURCE: EPA87a.
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If the screening measurement result is less than about 4 pCi/l - or 0.02
WL, follow-up measurements are probably not required. If the screening
measurement was made in a lowest livable area of the house, under closed-
house conditions, then there is relatively little chance that the
concentrations in the general living areas on non-basement floors of the
house are greater than about 4 pCi/l or 0.02 WL as an annual average.
If the result of the screening measurement is less than about 20 pCi/l or
0.1 WL, but greater than about 4 pCi/l or 0.02 WL, EPA recommends that
the follow-up measurement consist of an integrated measurement or series of
measurements over a 12-month period made in several living areas of the
house. Although there is the possibility that the average long-term
concentrations in the living areas of the house will be in the range where
remedial action should be considered, the levels are not high enough to
warrant immediate action. Follow-up measurements spanning a year are
recommended for estimating exposures because the result will incorporate
the variations in concentration due to seasonal and lifestyle differences.
This measurement provides the household with the best measure of the
long-term concentrations to which they are actually exposed.
If the screening measurement result was greater than about 20 pCi/l
or 0.1 WL, EPA recommends that a short-term follow-up measurement over
at least 21 hours be made in several living areas of the house under
closed-house conditions. EPA recommends a short-term follow-up
measurement because an additional year of exposure to these concentrations
could cause a significant increase in health risk. A short-term follow-up
measurement quickly provides the occupants with a reproducible result that
is a conservative estimate of the annual average concentration. The higher
the result of the screening measurement, the shorter should be the duration
of the follow-up measurement.
Q /
- EPA has published guidance levels in the traditional radon and radon
decay product units that are still widely used in the United States.
See the Conversion Table at the end of this Reference Manual to
convert to SI units.
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Follow-up measurements should be made in areas of the house currently
used as living areas. Whenever possible, EPA recommends that separate
follow-up measurements be made on at least two different floors of the
house. EPA also advises that one of the measurements be made in a
bedroom, because most people spend more time in their bedrooms than in
any other room in the house (Ch74; Mo76; Sz72). Follow-up measurements
should not be made in kitchens or in bathrooms, because exhaust fans or
high concentrations of airborne particles caused by cooking can affect the
results of short-term radon and radon decay product measurements. The
results of the measurements in the different living areas should be
averaged; the average result can be compared to guidance levels (published
in terms of annual average concentrations in EPA86b) in order to estimate
health risks and to decide on the need for remedial action. It should be
noted that the EPA recommendations discussed here were not designed to
apply to measurements made for real estate transactions, where the
measurement time period is a serious constraint.
The EPA guidance for making radon and radon decay product measurements
in homes is interim, and EPA plans to update the documents based on new
information as it becomes available'. As screening and annual averagd
measurements are gathered and analyzed, EPA may refine the protocols. In
the meantime, however, the intent of the recommendations in the protocol
documents is to help both individual homeowners as well as States and other
organizations perform measurements that produce consistent and useful
results.
11-6
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Chapter 12
WHAT DO MY TEST RESULTS MEAN?
The results of the follow-up measurements described in the previous
chapter provide an indication of the average radon concentration to which a
homeowner is exposed. As explained in "A Citizen's Guide," the risk
caused by this exposure depends on the duration of exposure; "A Citizen's
Guide" presents estimates of total population risk that are based on a
75 percent occupancy rate and a lifetime of approximately 70 years (see
Chapter 4 for a detailed explanation of the total population risk estimates).
In this section of "A Citizen's Guide," the individual risks resulting from
exposure to various radon concentrations are presented in two ways.
First, individual risks are illustrated in charts which depict the expected
number of additional lung cancer deaths resulting from radon exposure at H
pCi/l, 20 pCi/l, and 200 pCi/l assuming 70 years of exposure; and at 200
pCi/l assuming 10 years of exposure from birth to 10 years of age.
Second, the risk from exposure to radon is compared to other health risks
(risks from chest x-rays and from smoking) in the Radon Risk Evaluation
Chart. The follow-up measurement results and the Radon Risk Evaluation
Chart together allow the homeowner to estimate the individual risk he or
she may face.
This chapter explains the derivation of the risk estimates presented in the
lung cancer risk illustrations on page 9 of "A Citizen's Guide," and the
Radon Risk Evaluation Chart on page 10. The first section of the chapter
considers the risk illustrations and the second discusses the Radon Risk
Evaluation Chart.
LUNG CANCER RISK ILLUSTRATIONS
The risk illustrations on page 9 of "A Citizen's Guide" provide a visual
representation of individual risks attributable to various levels of radon
-------
exposure. For the most part, the derivation of the risk estimates follows
the first three steps of risk estimation described in detail in Chapter 4 of
this Manual. Important assumptions underlying the risk estimates include:
(1) a linear dose/response model; (2) a relative-risk projection model, witti
a risk ranging from 1 to 4 percent per WLM of exposure; (3) a life-table
analysis to account for competing risks, based on 1980 vital statistics; (*»)
an age-dependent correction of exposure to account for anatomical and
physiological differences between the underground miners (the population
from whom the risk estimates are derived) and the general population; and
(5) a 10-year minimum induction period to account for the latency period of
cancer. The range in the relative risk estimates accounts for the range of
fatal cancers cited in the text under each risk illustration; however, due to
competing risks, the high and low fatal cancer estimates do not vary by a
factor of four. Finally, a 75 percent occupancy rate is assumed to estimate
annual exposure (this assumption implies about 20 WLM per year for
exposure to a 1 WL environment. This figure includes a correction for the
breathing rate difference between miners and average adults.
As noted, "A Citizen's Guide" illustrates the risks for three radon
concentration levels after 70 years of exposure, and at 200 pCi/l after 10
years of exposure. In calculating the latter estimate, it was assumed that
the exposure is received in the period between birth and age 10. As a
result of anatomical differences between children and adults (principally the
smaller lung size of children) and the influence of competing risks, this
assumption results in a somewhat higher estimate of fatal cancers than
would have been calculated for 10 years of exposure received later in life.
Finally, in presenting the risk illustrations, "A Citizen's Guide" notes that
on average, about 4 people out of 100 die of lung cancer from all causes
combined. This figure is derived from a cohort analysis using 1980 vital
statistics and 1980 standard mortality rates (NCHS83; NCHS85).
12-2
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RADON RISK EVALUATION CHART
The Radon Risk Evaluation Chart was developed to try to place the risk
associated with radon and radon decay product exposure into some
perspective. Fatal lung cancer risks associated with chest x-rays and
smoking cigarettes were selected as relatively commensurable risks, but also
risks that most people could understand. The risks associated with various
radon concentrations employ the same assumptions used for the risk
illustrations on page 9 of "A Citizen's Guide" over an average 70-year
lifetime. The sources of x-ray and smoking risk estimates are described in
the following discussions.
The risk of lung cancer from a chest x-ray was taken as 92 x 10~ per low
g /
LET rad (derived from relative risk estimates in BEIR80). - The lung
dose in a chest x-ray was taken as 9 to 20 millirad per exposure (Sc73),
using mean active bone marrow dose as a surrogate for lung dose. The
risk of a chest x-ray is then 0.9 x 10 to 1.8 x 10 per exposure.
The smoking risk was estimated by calculating the cumulative risk of dying
of lung cancer for a life table cohort. The calculations made using 1980
vital statistics showed 4.74 percent of the cohort would die of lung cancer.
This risk was then reapportioned for the general population on the basis of
data from several sources (NIH85; OSH80; OSH82). In this apportionment,
the risk in nonsmokers was taken as 20 to 25 percent of the risk of the
general population, the risk for 1-pack-a-day smokers as 8 to 10 times that
for nonsmokers, and the risk of 2-pack-a-day smokers as 18 to 20 times
that for nonsmokers.
- A rad is a unit of absorbed radiation dose that represents the energy
imparted by ionizing radiation to a unit mass of absorbed tissue. One
rad is equal to 0.01 joules per kilogram. A millirad is one thousandth
of a rad. LET represents Linear Energy Transfer and is an
expression of "the amount of energy lost per unit distance. Greater
energy loss per unit distance increases the dose and results in more
cell damage. Thus, low LET rads have a lesser biological effect than
high LET rads.
12-3
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The estimates of risk relative to nonsmokers may be overestimates since
they are weighted heavily by the data on males. The risk in female
smokers relative to nonsmokers is lower than in males and is not well
documented. There is some indication that it is increasing as female
smoking habits become more like those of males and so, in this document,
female and male risks are made about the same in magnitude. If the female
risks for smokers versus nonsmokers remains the same as they are now, the
risks for smoking in this document are biased slightly high.
Finally, the Radon Risk Evaluation Chart compares various radon
concentrations with average indoor and outdoor levels. The average indoor
level (0.8 pCi/l) is derived from a study of New Jersey and New York
homes (Ce78). The average continental outdoor radon level ranges from
0.08 pCi/l to 0.25 pCi/l, with a figure of about 0.2 pCi/l used in the Radon
Risk Evaluation Chart (UNSCEAR82; Ce83; Ne2/8U).
12-4
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Chapter 13
HOW QUICKLY SHOULD I TAKE ACTION?
To provide homeowners with specific guidance in the event that elevated
indoor radon levels were present in their homes, "A Citizen's Guide"
presents recommended timeframes for action based on various annual
average radon concentrations. These recommendations are organized in a
four-tier scheme, with higher radon levels warranting faster action. This
chapter describes how EPA arrived at these guidelines, summarizes the
factors that were considered, and provides additional discussion of the
intent of the guidelines themselves.
HOW EPA ARRIVED AT ITS GUIDELINES
EPA was faced with a difficult and sensitive task in developing the action
guidelines found in "A Citizen's Guide." The Agency had to balance the
need to compel people to take action with the need to avoid frightening
them. To do this, the Agency considered various alternatives along a
decisionmaking spectrum.
On one end of the spectrum, EPA considered simply presenting the risks
from radon and stating that, in general, one's risk increases with
exposure. This alternative was thought to be the least intrusive on an
individual's decisionmaking, while relying the most on that individual's
ability to understand and evaluate those risks. On the other end of the
spectrum, EPA considered providing very little risk information and simply
stating that at a certain radon concentration, homeowners should take action
to reduce their exposure within a given timeframe. This alternative was
thought to provide the homeowner with the most specific guidance but
offered the least flexibility in evaluating personal risk.
-------
Based on the results of several discussion groups consisting of EPA
personnel and homeowners who were somewhat knowledgeable about radon,
it became very apparent that homeowners desire definite guidance on how
quickly to take action if they discover a radon problem. While no level of
radon can be considered risk free, an absence of specific guidance could
alarm homeowners unnecessarily and could cause them to attempt to reduce
radon levels below the point at which reduction is currently feasible.
Consequently, the Agency chose to provide homeowners with some fairly
specific recommendations as to how quickly action should be taken to reduce
exposure at various radon concentrations. In addition, however, EPA chose
to include detailed risk information to allow homeowners some flexibility in
applying the EPA guidelines to their personal situations. In other words, a
homeowner could choose to delay, or even forgo, remedial action based on
his or her acceptance of the associated risk. By providing information on
the risks at various concentrations of radon, a homeowner can more easily
make this kind of decision.
FACTORS EPA CONSIDERED
In developing the action guidelines, the Agency considered it important to
not only indicate a level at which action should be taken almost immediately,
but also to indicate a level that could be used as a target for corrective
action. To meet this objective, EPA arrived at the four-tier scheme of
action guidelines contained in "A Citizen's Guide." These guidelines are
meant to provide homeowners with some indication of whether and how
quickly they may need to take remedial action based on their indoor radon
concentration.
To choose the values and timeframes of the four tiers, EPA considered a
number of factors. One of the factors EPA considered — perhaps the most
important factor — was the potential risk from exposure to indoor radon.
Radon exists at low levels at all times in the environment. As noted in
13-2
-------
earlier chapters, the health risks from radon are significant even at
relatively low levels, often in excess of the risks associated with regulated
environmental contaminants. Therefore, EPA considered the effect of
recommending that homeowners reduce the radon levels in their homes as
low as possible. Our experience, however, indicated that it is difficult, if
not impossible, to reduce indoor radon to levels that approach average
outdoor radon concentrations (0.08 pCi/l to 0.25 pCi/l). The next step
involved taking a practical look at what reductions were possible given the
state of current knowledge about radon reduction. The choice of 0.02 WL
(4 pCi/l) as a lower bound reflects this consideration.
Before making the final decision to recommend 4 pCi/l as a target for
corrective action, EPA examined alternative action guidelines, such as the 8
pCi/l recommendation made by NCRP. Data available at the time indicated
that even at an 8 pCi/l action level, as many as one million homes might be
affected (Ne9/8i»). Based on that information, EPA chose the lowest
technologically feasible target level, i.e., 4 pCi/l, in order to encourage as
much reduction of risk to the population as possible.
Another concern was the availability of contractors to fix homes. In
selecting its recommended timeframes for action, the Agency felt it
important to choose realistic timeframes that would not result in an
excessive demand on the then developing mitigation industry. Again, the
use of a tiered system emphasizes the need for faster action at higher
radon concentrations. EPA believes that the timeframes for action in "A
Citizen's Guide" are realistic and attach an appropriate sense of urgency
for various radon concentrations based on the associated risks, but do not
create unwarranted mitigation activity.
Finally, EPA's choice of action levels recognizes the desirability of
consistency with previous EPA actions and with existing State programs.
In earlier guidance to the State of Florida, EPA recommended 0.02 WL as a
target for radon mitigation for houses built on phosphate lands (EPA78).
13-3
-------
EPA has also established 0.02 WL as a remedial action standard for
Superfund cleanups and for remediation under the Uranium Mill Tailings
Radiation Control Act of houses built on or near uranium mill tailings.
Based in part on these EPA actions, a number of States have already
established indoor radon programs using 0.02 WL as a mitigation target. In
combination with the other factors EPA considered, the issue of consistency
reaffirmed our choice of 0.02 WL (4 pCi/l) as a goal for radon reduction.
INTERPRETATION OF THE GUIDELINES
There are several important things to remember when interpreting EPA's
guidelines. First, the guidelines are based on annual average radon levels
in lived-in areas of the house. EPA strongly recommends that homeowners
make follow-up measurements (to determine average levels) before making
final decisions about mitigation.
The intent of these guidelines is to communicate the point that there is a
greater risk, and thus a greater urgency for remedial action, as radon
concentrations increase. The guidelines do not represent standards for
indoor radon. EPA does not intend (nor does it currently have authority)
to regulate indoor radon levels. Rather, the decision to pursue mitigation
depends on the homeowners' level of risk acceptance and individual living
habits. The purpose of "A Citizen's Guide" is to provide homeowners with
the risk information they need to make informed decisions.
Finally, the use of 0.02 WL as a target for corrective action simply
represents a lower technological bound of radon reduction achievable with
current methods. Similarly, there is nothing definitive about the use of
1 WL as a trigger for immediate action. Homeowners should compare their
follow-up measurements to the entire range of action guidelines and should
evaluate their personal risk using the information provided in "A Citizen's
Guide." Having made this evaluation, they may choose to act more or less
quickly than "A Citizen's Guide" recommends, depending on their
perceptions of their individual risk.
13-U
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Chapter l/i
ARE THERE OTHER FACTORS I SHOULD CONSIDER?
The earlier questions in "A Citizen's Guide" discuss the risks from radon in
general. The question "Are There Other Factors I Should Consider?"
applies to several conditions that could significantly influence risks for an
individual homeowner or household. In evaluating their risks, homeowners
should take these factors into account. However, as noted in the general
discussion of radon risk presented in Chapter 4, the precise risk
implications of many factors are still uncertain. The objective of this
chapter is to discuss the uncertainties underlying the five factors cited in
"A Citizen's Guide": (1) smoking; (2) risks to children; (3) time spent at
home; (4) sleeping in the basement; and (5) lifetime exposure period.
SMOKING
In general, stopping smoking will reduce one's overall risk of lung cancer.
However, the interaction between radon decay product exposure and
smoking is not well understood. There are data from human and animal
studies that could support widely varying models, including models that:
(1) suggest that the combined risks from radon decay products and smoking
are less than the risks attributed to each carcinogen separately (Cr78;
Lu79; Ax78; Da79); (2) suggest that there is no interaction between the
two types of exposure (Ch81; Ra84); or (3) suggest that the combined
risks from the two carcinogens are greater than the sum of the risks that
would be calculated separately (called a synergistic model) (Wh83; Lu79).
For example. Sterling (Sg83) has proposed that increased mucus in the
lung, such as that associated with smoking, leads to reduced lung cancer in
smoking miners compared to non-smoking miners exposed to radon decay
products, workers exposed to arsenic, and workers exposed to chloromethyl
ethers. This is in line with findings by Cross, et al. (Cr78) that fewer
-------
lung cancers occurred in smoking dogs than in non-smoking dogs exposed
to radon decay products. Other scientists, such as Dr. E.A. Martell,
argue that smoking promotes the cancer-causing effects of radon decay
products (C6EN5/86). Such a result could be attributed to the naturally
elevated levels of polonium-210 (an alpha emitter) present in tobacco, or to
the tendency for tobacco tars present in the lungs of smokers to promote
the deposition of radon decay products in the lung. In any case, it seems
clear that the interaction between smoking and radon decay products is not
simple and more study is needed. However, since smoking increases the
overall risk of lung cancer and since it may also greatly increase the
risk attributable to radon exposure, EPA advises homeowners to stop
smoking.
Since EPA uses a relative risk model (a synergistic model with simple
multiplicative interaction) to project radon risks, the potential interaction
between radon exposure and smoking is important (see Chapter 4 for a
discussion of relative risk). In the current relative-risk projection model,
the age-specific baseline lung cancer mortality rates are multiplied by the
appropriate risk conversion factor to calculate the number of cancers due to
radon daughter exposure up to a specific age. Therefore, anything that
increases the baseline lung cancer mortality rates (such as smoking) will
increase the calculated risk due to radon exposure as long as an
age-constant, time-constant relative risk coefficient is used in the model.
RISKS TO CHILDREN
The risks of exposure to radon decay products for infants and children
compared to adults are uncertain. In general, differences may exist for
two reasons: (1) the exposure risk resulting from a given radon decay
product concentration in the home may differ at different ages due to
physiological and anatomical differences (e.g., lung size and breathing
rate), and (2) the sensitivity to induction of lung cancer per unit of
exposure may also differ by age.
14-2
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NCRP Report No. 78 shows a higher dose calculated per unit exposure in
infants and children than in adults (NCRP84/78). A similar conclusion was
reached by Hofmann and Steinhausler (St77). They estimated that
exposures received during childhood are about 50 percent greater than
adult exposures. It appears that the smaller bronchial area of children as
compared with that of adults more than offsets their lower per-minute
breathing volume; therefore, for a given concentration of radon-222 decay
products, the dose to their bronchi is greater (see Chapter 4).
However, there is still a great deal of uncertainty concerning the effect of
radon exposure on children. Indeed, tables 10.1 and 10.3 of NCRP Report
No. 78 indicate that children may be at a lower risk than persons older
than 20 years of age. This result is arrived at, however, through the use
of certain assumptions that are significantly different than those used by
the EPA.
The NCRP risk estimates, like the EPA individual risk estimates, are based
on a life-table analysis of a lifetime risk projection model. However, the
NCRP uses an absolute-risk projection model with a relatively low risk
coefficient: 10 cases per million person WLM per year at risk, which is the
smallest of those listed by the National Academy of Sciences' Committee on
the Biological Effects of Ionizing Radiation (BEIR80). Another critical
assumption in the NCRP estimates is that the risk of lung cancer following
irradiation decreases exponentially with a 20-year half-life, and, therefore,
exposures occurring early in life present very little risk. This exponential
decline is illustrated for an absolute risk projection model in figure 14-1
(assuming a 5-year minimum induction period and no tumors before age 40),
and is explained further in Ha81.
In contrast, EPA, as noted in Chapter 4, uses a relative-risk projection
model. EPA's risk projection model uses a time-constant relative risk
coefficient (one to four percent increase in base-line risk per unit
exposure) to calculate the risk of excess lung cancer deaths. EPA
questions the assumed decrease in risk used by NCRP. If lung cancer risk
14-3
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LU
UJ
O
a
CL
Figure 14-1. Lung Cancer Appearance Rate Following a Single
Exposure to Radon Daughters
ABSOLUTE RISK MODEL A - NO DECAY
(A-D
Exposure
Exposure
3
o
cc
CD
99
a:
ABSOLUTE RISK MODEL B - 20 YEAR HALF-LIFE
Exposure
(B-1)
Exposure
20
40
AGE
60
80
(A-1J Model A-exposure at age <40. (A- 2) Model A-exposure at age >40.
(B-1) Model B-exposure at age <40. (B-2) Model B-exposure at age >40.
Latency.
Adopted from Ho81, p. 309.
14-4
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decreased over time with a 20-year half-life, the excess lung cancer
observed in Japanese A-bomb survivors would have decreased during the
period of observation (1950-1980); to the contrary, their absolute lung
cancer risk has increased markedly (Ka82).
The question of the sensitivity of children to induction of lung cancer is
virtually unanswered for radon exposure, and not well answered for x-ray
or gamma-ray exposure. However, the evidence developing in Japan
indicates that the relative risk is higher the younger the age of exposure
and for the same age at death; similarly, the absolute risk is higher the
younger the age of exposure for all cancers except leukemia (Ka82). Since
this information is available and appears to have stronger support in each
succeeding report on the Japanese A-bomb survivors, it seems prudent to
mention the possibility that children are more susceptible than adults to
radiation induced cancers. The major uncertainty in the data right now
appears to be whether those exposed as children will continue to develop
two or three times more cancer than those exposed as adults for the
remainder of their life spans, or if the increased susceptibility will diminish
at some age.
TIME SPENT AT HOME
The risk estimates given in "A Citizen's Guide" assumed that 75 percent of
a person's time is spent at home. At lower levels of exposure (below 0.01
WL), spending more or less time at home would, respectively, linearly
increase or decrease lung cancer risk, provided that indoor exposure at
home is the dominant source of radon exposure (as is normally true).
In a variety of EPA rulemakings, the Agency has also assumed that, on
average, residents spend 75 percent of their time in their homes. This
assumption is taken from two studies (Mo76 and Oa72) which estimate
radiation exposure and population dose in the United States. Similar
findings have been reported for England; that is, people spend about 75
percent of their time in their dwellings (Bn83).
14-5
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The risk estimates also assume that the remaining 25 percent of a person's
time is spent in a virtually radon-free environment. However, if this is not
the case, homeowners should adjust their individual risk to reflect this.
SLEEPING IN THE BASEMENT
In most cases, indoor radon originates in the soil and rock below and
around the house and, thus, enters a home through the basement floor or
walls (if a basement is present) or through the lowest floor slab. Although
radon is then carried to other parts of the house, radioactive decay and
ventilation of the upper floors tend to cause the highest radon levels to
occur in the basement. As a result, individuals spending a large portion of
their time in the basement (such as when they sleep in a basement
bedroom) will face a slightly higher risk from radon. In some cases,
homeowners can verify whether higher levels indeed are present in the
basement by taking radon measurements in multiple locations in the house
(as recommended for follow-up measurements; see Chapter 11).
In some cases, lower floor and basement levels may not be higher than
elsewhere in the house. For example, if a major source of radon is water,
showers or dishwashers could be the principal entry routes of radon.
Similarly, if building materials or fireplace stones are the major source of
radon, the principal radon entry point could be on the first floor. Interior
hollow block foundation supports, if present, could provide a route for
radon to enter on the first floor. Finally, a central air circulation system
would tend to distribute radon throughout the home if basement intakes are
used. However, in all of these cases, the impact on radon distribution in
the home is still relatively uncertain, and it is generally thought that water
or building materials are usually not the primary sources of indoor radon in
most homes. Until more is learned, it appears to be prudent to assume that
radon levels are highest in the basement when evaluating risk to the
homeowner.
1U-6
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LIFETIME EXPOSURE PERIOD
There are a number of factors that can affect estimates of lifetime risk to
the individual homeowner. The risk estimates in "A Citizen's Guide" assume
that the homeowner is exposed to a constant concentration of radon decay
products for about 74 years (the average life expectancy). However, an
individual's risk is affected by both cumulative exposure and by exposure
rate. Variations in the radon decay product concentration, duration of
exposure, and age at which exposures started can all affect the estimate of
lifetime risk for an individual. Table 14-1 displays risk estimates for
several different choices of these parameters, including the set of
assumptions (i.e., lifetime exposure beginning at birth) used to create the
chart on page 10 of "A Citizen's Guide."
In addition, an individual may occupy a number of different residences
throughout a lifetime, each with a potentially different radon decay product
concentration. It is, therefore, important to remember that the risk
estimates presented in "A Citizen's Guide" should be used only as indicators
of what might be true under specified conditions. It should also be noted
that even short exposures to high radon decay product concentrations can
be associated with significantly increased risks (e.g., as shown in the
chart on page 9 in "A Citizen's Guide," the lifetime risk from 10 years of
exposure to 1 WL is 14 to 24 chances out of 100 of dying of lung cancer;
or, as shown in table 14-1, it can be seen that 1 year of exposure at 1 WL
at almost any age under 60 years appears to have a greater risk than a
lifetime of exposure at 0.01 WL).
14-7
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Table 14-1
Lifetime Risk Of Excess Lung Cancer Mortality
Induced By Radon Decay Product Exposure (N/1000)
Cumulative
Age At First Exposure
Exposure Year
Birth 1
5
10
20
Lifetime
i—
x>
I
00 5 Years 1
5
10
20
Lifetime
15 Years 1
5
10
20
Lifetime
Radon Decay Product Exposure
0.01
0.1-0.5
0.7-3
2-6
3-12
7-26
0.2-0.7
1-3
2-7
3-12
6-24
0.1-0.5
0.6-3
1-5
2-9
4-17
0.02
0.2-1
1-56
3-12
6-23
13-52
0.3-1
2-7
3-13
6-22
12-46
0.3-1
1-5
2-9
4-17
9-34
0.04
0.5-2
3-11
6-24
12-46
26-98
1-3
4-14
7-26
11-44
24-90
0.5-2
3-10
5-19
9-33
17-67
0.05
0.6-2
4-14
8-30
15-57
32-121
1-4
4-17
8-32
15-57
29-112
0.7-3
3-13
6-23
11-42
22-82
Level (WL)
0.10
1-5
7-27
15-59
29-110
63-211
2-7
9-34
16-63
29-110
58-204
1-5
7-26
12-46
21-81
42-155
0.50
6-24
34-127
74-254
134-412
265-627
9-34
42-155
78-268
135-416
246-605
7-27
32-120
57-204
100-328
188-513
1.00
12-47
66-232
140-425
245-611
436-772
17-66
82-279
148-445
247-618
411-762
13-52
63-221
110-355
186-521
328-692
Table continued
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Table 14-1 (Continued)
Lifetime Risk Of Excess Lung Cancer Mortality
Induced By Radon Decay Product Exposure (N/1000)
Cumulative
Age At First Exposure
Exposure Year
25 Years 1
5
10
20
Lifetime
40 Years 1
5
(— i
r io
V.O
20
Lifetime
60 Years 1
5
10
20
Lifetime
0.01
0 .1-0.4
0.5-2
1-4
2-7
3-13
0.1-0.4
0.4-2
0.9-3
2-6
2-7
0.1-0.2
0.2-0.8
0.3-1
0.4-2
0.4-2
0.02
0.2-0.8
1-4
2-8
4-15
6-25
0.2-0.7
1-4
2-7
3-12
4-15
0.1-0.4
0.4-2
0.6-3
0.8-3
0.8-3
Radon Decay
0.04
0.4-2
2-8
4-15
7-29
13-50
0.4-2
2-7
3-14
6-23
7-29
0.2-0.8
0.8-3
1-5
2-6
2-7
Product Exposure Level (WL)
0.05
0.5-2
2-10
5-19
9-36
16-61
0.5-2
2-9
4-17
7-29
9-34
0.2-1
1-4
2-6
2-8
2-8
0.10
1-4
5-19
10-38
18-71
31-117
0.9-4
5-18
9-34
15-56
18-69
0.5-2
2-8
3-13
4-16
4-16
0.50
5-19
24-91
47-167
88-296
144-425
5-18
22-85
42-153
70-241
8-282
2-10
10-40
16-61
20-74
20-75
1.00
10-38
47-171
90-303
166-481
258-613
9-36
44-160
81-275
133-402
160-449
5-19
20-77
32-116
39-138
39-139
Assumptions: 1 percent - 4 percent per WLM Relative Risk Coefficient, 1980 Life Table, 1980 Vital Statistics, 75 percent Occupancy Factor;
General Population.
SOURCE: U.S. Environmental Protection Agency, July 1987.
-------
Chapter 15
HOW CAN 1 REDUCE MY RISK FROM RADON?
Scientists commonly agree that the risk of lung cancer is dependent on both
the level of indoor radon in the home and the length of time one is
exposed. For homes with high radon entry rates, "A Citizen's Guide"
recommends several short-term steps that, if taken immediately, can reduce
the risk from radon. EPA stresses that although these techniques can be
implemented quickly, they are unlikely to provide a long-term solution.
For further information on permanent mitigation measures as well as these
short-term mitigation techniques, consult EPA's "Radon Reduction Methods:
A Homeowners Guide." In addition, EPA has a guidance document available
that provides technical information on both short-term and longer-term
mitigation techniques, "Radon Reduction Approaches For Detached Houses:
Technical Guidance" (EPA/625/5-86-019).
Ideally, the short-term mitigation methods discussed here should be
implemented during periods of decisionmaking or when waiting for test
results. In addition, these short-term actions should be taken as soon as
possible if homeowners find levels of radon above 1 WL or 200 pCi/l after
the screening measurement. Homeowners finding levels below 1 WL (200
pCi/l) and above 0.02 (4 pCi/l) WL may wish to use these short-term
techniques whenever practical. Clearly, the urgency to implement
mitigation techniques will depend on the level of radon detected, with
higher levels requiring immediate attention. This chapter discusses the
four short-term techniques recommended in "A Citizen's Guide": (1) stop
smoking, (2) avoid living areas with high exposure, (3) ventilate the home,
and (4) ventilate crawl- spaces.
-------
STOP SMOKING
Although the interrelationship between smoking and radon exposure remains
unclear, stopping smoking immediately reduces one's overall risk of lung
cancer. As discussed in Chapter 14, medical studies are currently unable
to determine whether smoking increases or decreases lung cancer risks from
radon. However, the relationship between smoking and lung cancer is well
established, and some researchers believe there is a strong synergistic
effect between radon and tobacco smoke. On this basis, EPA believes it
appropriate to recommend that homeowners stop smoking.
AVOID LIVING AREAS WITH SUSPECTED HIGH LEVELS
Research performed on houses with elevated radon concentrations found that
the distribution of radon throughout a house is not uniform. In general,
those living areas closest to the source of radon entry had higher radon
levels than those farther away. In most houses, the primary source of
radon entry is from the soil and rock underneath the house. Other sources
include potable drinking water and building materials. Since drinking water
and building materials have been determined to be usually an almost
negligible source, the underlying soil is the main contributor (Ne83).
Therefore, EPA recommends that homeowners spend as little time as possible
in the basement or in parts of the home directly above the soil or other
areas of the home that have been found to have elevated levels of radon.
VENTILATE HOME AND CRAWL-SPACES
Indoor radon concentrations are determined by the balance between the rate
of entry from radon sources and the rate of removal, by ventilation or
radioactive decay. Proper ventilation techniques within the home have been
15-2
-------
found to reduce radon concentrations by about 30 to 90 percent, depending
on the time of year (ASHRAE81). This reduction is due to both the
removal of radon-laden air and the dilution of the total indoor volume with
cleaner incoming air.
Natural ventilation occurs in a home because of temperature and pressure
differences between indoor and outdoor air. Changing seasonal
temperatures and winds are major natural forces causing this occurrence.
Because natural ventilation takes place through all passageways connecting
indoor and outdoor air, indoor air can be exchanged with outdoor air even
when doors and windows are closed.
Forced or mechanical ventilation relies on the use of fans that force an
increase in air exchange rates by drawing in outdoor air or exhausting
indoor air while replacing it with cleaner air from the outside.
In return, natural air exchange rates rely heavily on pressure differences
arising from temperature differentials and wind effects. These factors
cause small pressures across walls separating indoor and outdoor air. As a
result, the stack effect discussed in Chapter 8 is created, in which
pressure at the bottom of the wall causes air flow toward the heated
interior and pressure at the top of the wall causes air flow toward cooler
temperatures. The stack effect causes the exchange of indoor air with
outdoor air, which is drawn from the understructure during the heating
season (Ne85).
For natural and forced ventilation to be effective mitigation techniques,
homeowners must open all windows in the home to ensure uniform ventilation
throughout the house. For example, opening windows only on the north
side of a house may have the effect of causing pressure differences to
occur between indoor and outdoor air. Winds blowing by these windows will
depressurize the house, causing pressure driven air to flow into the house.
The appropriate action is to open windows on all sides of the house to allow
pressure differences to equalize. The same technique should be applied to
15-3
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crawl-spaces. Vents should be opened on all sides of the crawl-space to
allow uniform air flow.
As mentioned in "A Citizen's Guide," the ventilation methods just discussed
should be implemented only when weather permits. This means that this
type of ventilation is relatively inexpensive for only about four months of
the year. Proper ventilation during summer and winter months requires
different methods, usually at a greater cost. Again, for further
information on permanent ventilation methods and the recommended
short-term mitigation techniques, consult EPA's "Radon Reduction Methods:
A Homeowners Guide" or the more detailed document, "Radon Reduction
Approaches For Detached Houses: Technical Guidance" (EPA/625/5-86-019).
15-4
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Chapter 16
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-------
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16-3
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EPA86a
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Erikson, Ralph L. "Crustal Abundance of Elements and
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Ev81
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Fi73
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16-5
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FI84 Fleischer R.L. and L.C. Turner "Indoor Radon Measurements
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FRN79 "Indoor Radiation Exposure Due to Radium-226 in Florida
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Ce84 George, A.C., 1984, "Passive, Integrated Measurements of
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Gr86 Green, L.L., P.A. Gerry, K. Novak, et al. Indoor Air
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GLOSSARY
Absolute Risk
Projection Model
A model which estimates the risk of exposure
beyond the years of observation of a studied
population by projecting the average
observed number of excess cancers per unit
dose into the future years at risk.
Absorbed Dose
The amount of energy per unit mass trans-
ferred to human or animal tissue from
radiation. Measured in rads or grays
standard international (SI unit). One gray
equals one joule per kilogram. One rad
equals 0.01 gray.
Activity
The rate of atomic disintegration, measured
in curies.
Activity Concentration
(specific activity)
Activity per unit volume. Commonly
measured in picocuries per liter (in air) or
picocuries per gram (in a solid).
Aeration
Exposing to the action of air. For example,
a liquid can be aerated by agitation or by
means of a fine spray.
Aerosols
Atomized particles of a substance suspended
in air.
-1-
-------
Air Changes per Hour
(ach)
Air Exchange Rate
A measure of the movement of a volume of
air in a given period of time (i.e., of the
Air Exchange Rate). One air change per
hour is equivalent to replacing all of the air
in a house in a one-hour period. Air
changes also may be expressed in cubic feet
per minute.
The rate at which air inside a house is
exchanged or replaced with air from outside
the house as a result of ventilation, seepage
through cracks, open windows or doors, etc.
Measured in air changes per hour (ach).
Alpha Activity
The rate of atomic disintegration or
radioactive decay that is accompanied by
release of an alpha particle. Measured in
curies.
Alpha Particle
Alpha Energy
A positively charged subatomic particle
emitted from a nucleus during some types of
radioactive decay, indistinguishable from a
helium atom nucleus and consisting of two
protons and two neutrons.
The energy released when an alpha particle
emitted during radioactive decay is halted by
collision with a substance (e.g., lung
tissue). The amount of energy depends on
the velocity of the alpha particle, which in
turn depends on the source of radioactive
decay (e.g., decay of U-238 versus Ra-226).
-2-
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Alum Shale Brick
Alveola
Attached Radon
Decay Product
Brick building material made with a type of
shale rock that has been found to contain
naturally elevated levels of uranium.
- Tiny air sacs in the lung.
A radon decay product that is attached to a
particle of dust or other material in the air.
Basaltic Lavas
A dense, dark igneous rock formed by
cooling volcanic material that can contain
uranium minerals at low levels. Uranium
minerals are finely disseminated through the
rock and concentrations are typically of low
grade.
Basement Foundation
Underlying structure of a building or
dwelling. Usually constructed of cinder
block or cement. May have a dirt floor.
One of three types of substructures
commonly used in U.S. home construction
(see Crawl-Space and Slab-On-Crade
Foundation).
Bequerel (Bq)
The SI unit of radioactivity equal to one
disintegration per second. One picocurie
equals 0.037 Bequerel.
Beta Particle
A negatively charged subatomic particle
(electron) emitted from a nucleus during
some types of radioactive decay.
-3-
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Beta Energy
The energy released when a beta particle is
halted by collision with a substance. The
amount of energy depends on the source of
radioactive decay (see Alpha Energy).
Black Shales
A laminar type of sedimentary rock found in
parts of the central United States
characteristically rich in organic matter,
such as marine black shale and carbonaceous
shale. Although the uranium content is
normally less than 0.005 percent U30g, the
uranium level tends to be higher than in
other sedimentary rock.
Breathing Rate
- The rate of oxygen/air intake by the lungs.
Bronchial Epithelium
- The cellular lining of the bronchi.
Bronchi
Carbonaceous
The two main branches leading from the
trachea to- the lungs.
Relating to, containing, or composed of the
element carbon.
Carbonate Rock
Rock composed principally of carbonates,
especially if at least 50 percent by weight.
Carbonate is an ester or salt of carbonic
acid. Calcium carbonate and calcium
magnesium carbonate are principal
constituents of limestone and dolomite rock.
Carcinogen
Cancer-causing agent. Any agent that in-
cites development of a carcinoma or any
other form of malignancy.
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Cohort
A large homogeneous group of people tested
in epidemiological or socioeconomic studies.
EPA's lung cancer estimates are based on
calculations for a cohort of 100,000 people.
Concentration Gradient
The change in concentration (mass per unit
volume) per unit distance.
Crawl-Space
An area beneath some types of houses which
are constructed so that the floor is raised
slightly above the ground, leaving a space
between the floor and ground to allow access
to utilities and other services. (See
Slab-On-Crade Foundation and Basement
Foundation.)
Cumulative Working
Level Month (CWLM)
A unit of cumulative radon exposure. The
sum of lifetime exposure to radon working
levels expressed in total working level
months.
Curie (Ci)
A unit of radioactivity, defined as that
quantity of any radioactive nuclide which
spontaneously undergoes 3.7 x 10
disintegrations per second. One gram of
radium-226 has an activity of one curie.
Decay Series
The consecutive members of a family of
radioactive isotopes formed by sequential
radioactive decay. A complete series
commences with a long-lived parent such as
U-238 and ends with a stable element such
as Pb-206. See figures 2-1 and 2-2.
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Depressurization
A condition that occurs when the air
pressure inside a house is lower than the air
pressure outside. Normally, houses are
under slightly positive pressure.
Depressurization can occur when household
appliances that consume or exhaust house
air, such as fireplaces or furnaces, are not
supplied with enough makeup air. Radon-
containing soil gas may be drawn into a
house more rapidly under the depressurized
condition.
Diffusive Flux (J)
Diffusion is the condition of spontaneous
movement and scattering of particles of
liquids, gases, and solids. Diffusive Flux is
the weight of a material diffusing across unit
area per unit of time in response to a
pressure or concentration gradient.
Measured in grams per square centimeter per
second. Used to characterize the rate of
radon movement into a home.
Diffusivity (D)
The constant by which Diffusive Flux and
Concentration Gradient are related at
constant pressure under Pick's First Law of
Diffusion:
J = - D * A£
Dolomite
A brittle calcium magnesium carbonate rock
occurring abundantly in white to pale pink
rhombohedral crystals.
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Earth-Based Building
Materials
Materials such as cinder block and brick
which are formed using naturally-occurring
minerals and rocks.
Effective Dose Equivalent
Electron Volt (eV)
Epidemiology
Epithelial Lining
Dose equivalent weighted by a factor which
measures the relative sensitivity of the
tissue to a radiation-induced cancer.
A unit of energy commonly used to measure
energy releases during radioactive decay.
The division of medical science concerned
with defining and explaining the inter-
relationships of the host, agent, and
environment in causing disease.
Cellular tissue covering surfaces, forming
glands, and lining most cavities of the body.
Equilibrium Factor
Equivalent Dose
An adjustment used in converting from
picocuries per liter (pCi/l) to working level
concentration (WL) which takes into account
the possible absence of radioactive
equilibrium between radon and its decay
products.
The absorbed dose weighted to account for
its relative biological effectiveness by use of
quality and modifying factors. Measured in
rem or sievert (SI unit).
-7-
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Exposure
The amount of radiation present in an
environment, not necessarily indicative of
absorbed energy, but representative of
potential health damage to the individual
present. Measured in roentgen.
Follow-up Measurement
A measurement taken after an initial
screening measurement to determine annual
average exposure to home occupants.
Forced or Mechanical
Ventilation
Ventilation induced by means of a fan or
other mechanical device.
Gamma Ray or
Photon Radiation
Emission of a high-energy photon, especially
as emitted by a nucleus in a transition
between two energy levels.
Grain Size
Half-Life
The size of a microscopic particle of regular
crystalline structure. Grain size affects a
number of important macroscopic physical
properties, such as yield point and porosity.
The time it takes for one-half of any
quantity of identical radioactive atoms to
undergo decay.
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Indoor Radon
Concentration
Concentration of radon or radon decay
products in a house. Concentration is
dependent on the geologic formation under
the house and the structural conditions of
the house, as well as other factors.
Inversion Condition
Ionizing Radiation
A meteorologic condition in which
temperature increases with altitude,
generally caused by a warm air mass
overlying a colder one.
Subatomic particles or photons that have
sufficient energy to produce ionization
directly in their passage through a
substance.
Isotope
One of two or more types of atoms having
the same atomic number but different mass
number (e.g., radon-220 and radon-222).
LET (Linear Energy
Transfer)
The energy lost by a charged particle
passing through a substance per unit length
of path.
Leukemia
A form of cancer In the blood. Any of
several diseases of the hemopoietic system
characterized by uncontrolled leukocyte
proliferation.
-9-
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Lifetime Risk
Exposure-induced risks reported as a
function of the distribution of age in a
population.
Long-Term Mitigation
Mitigation by a homeowner to permanently
reduce elevated radon levels in a house.
Maximum Contaminant
Level Goals (MCLCs)
Maximum Contaminant Level Coal - a
non-enforceable health goal under the Safe
Drinking Water Act, set at levels which
would result in no known or anticipated
adverse health effects and allow an adequate
margin of safety.
Maximum Contaminant
Levels (MCLs)
Maximum Contaminant Level - an enforceable
standard under the Safe Drinking Water Act,
set as close to the MCLC as feasible taking
into consideration cost, availability of
treatment technologies, and other practical
considerations.
Micron
A unit of length equal to one millionth of a
meter or one thousandth of a millimeter.
Modifying Factor
Molecular Diffusion
A numerical factor used to modify calculation
of the Equivalent Dose to account for
variation of the LET and radiation effects
with tissue type and exposure.
The transfer of mass between adjacent layers
of fluid in laminar flow.
-10-
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Naturally-Occurring
Permeability
Occurring naturally in the soil. Not caused
by industrial or other human activity.
The capacity of a porous rock, solid, or
sediment to transmit a fluid without damage
to the structure of the medium.
Picocuries Per Liter
(pCi/l)
A unit of measurement of activity
concentration. A curie is the amount of any
radionuclide that undergoes exactly 3.7 x
10 radioactive disintegrations per second.
One picocurie per liter is equal to 10
curies per liter.
Porosity
Property of a solid which contains many
minute channels or open spaces that are
capable of absorbing liquids.
Pressure Driven Air Flow
Air flow in a home that is caused by
differences in pressure between the indoor
and outdoor air.
Quality Factor
The factor by which absorbed dose is to be
multiplied to obtain a quantity that
expresses, on a common scale, for all
ionizing radiations, the irradiation incurred
by exposed persons.
Radiation Dose
The total amount of ionizing radiation
absorbed by material or tissues, in the sense
of absorbed dose (expressed in rads),
exposure (expressed in roentgens), or dose
equivalent (expressed in rems).
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Radioactive Decay
Radioactive Equilibrium
Radioactive Particles
Radionuclide, Nuclide
Radium (Ra)
Radon (Rn)
Radon Bearing
- The spontaneous transformation of a nuclide
into one or more different nuclides
accompanied by either the emission of energy
and/or particles from the nucleus, nuclear
capture or ejection of orbital elements, or
fission.
- A state in which the rate of formation of
atoms by decay of a parent radioactive
isotope is equal to its rate of disintegration
by radioactive decay, so that the activity of
the parent and the decay product assume a
constant proportion (equal to one to one, if
the parent has only one mode of radioactive
decay). Because radon decay products tend
to attach readily to surfaces (plate out),
equilibrium between radon and its .decay
products is seldom reached.
- Products of radioactive decay.
- Any naturally-occurring or artificially
produced radioactive element or isotope.
- A naturally-occurring radioactive element
found in rock and soil. Atomic number 88.
- A colorless, naturally-occurring, radioactive,
inert gaseous element formed by radioactive
decay of radium atoms. Chemical symbol is
Rn, atomic number 86.
- Containing or emitting radon.
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Radon Progeny, Daughters,
Decay Products
Radon Source Strength
Terms used interchangeably to refer to the
intermediate products in the radon decay
chain. Each decay product is the ultra-fine
radioactive particle that decays into other
radioactive decay products until, finally, a
stable nonradioactive lead atom is formed and
no further radioactivity is produced. The
Rn-222 decay chain has 12 decay products,
including the stable lead isotype, Pb-206.
The intensity, power, or concentration of
radon action from its point of origin. Refers
to the general intensity of radon evolution
from a specific soil or rock type beneath a
house.
Recoil
The disattachment of radon decay products
from solid surfaces as a result of alpha
decay, causing the atom to re-enter the air.
Relative Biological
Effect (RBE)
An evaluation of the impact of a given type
of radiation on tissue based on the LET of
the radiation type. RBE equals the product
of the Quality Factor and the Modifying
Factor.
Relative Risk
The ratio of the rate of disease in exposed
to unexposed populations.
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Relative Risk Projection
Model
A model which estimates the risk of exposure
beyond the years of observation of a studied
population by projecting the currently
observed percentage increase in cancer risk
per unit dose into future years.
REM (Roentgen Equivalent
Man)
A unit of equivalent dose equal to the
amount that produces the same damage to
humans as one roentgen of high voltage
x-rays. Equal to 0.01 sievert. Related to
Absorbed Dose by the RBE: Equivalent
Dose (Rem) = RBE * Absorbed Dose (Rad).
Screening Measurement
A measurement taken under closed-house
conditions in the lowest livable area of a
house. This initial measurement is
recommended to determine whether a
follow-up measurement is necessary.
Short-Term Mitigation
Temporary measures to reduce elevated
radon levels in a house. Usually performed
during the time between screening and
follow-up measurement results.
Slab-on-Crade Foundation
A substructure type in which the foundation
is at approximately the same level
("on-grade") as the surrounding ground
surface. Generally, a poured concrete slab.
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Soil Gas
Those gaseous elements and compounds that
occur in the small spaces between particles
of the earth or soil. Rock can contain gas
also. Such gases can move through or leave
the soil or rock depending on changes in
pressure. Radon is a gas which forms in
the soil wherever radioactive decay of radium
occurs.
Solubility Coefficient
A measure of gas solubility in a liquid.
Radon solubility coefficient is defined as the
ratio of radon concentration in water to that
in air (Co86).
Stack Effect
In houses and other buildings, the tendency
toward displacement (due to the difference in
temperature) of internal heated air by
unheated outside air which is caused by the
difference in density of outside and inside
air. Sfmilar to the air and gas in a duct,
flue, or chimney rising when heated due to
its lower density compared with that of
surrounding air or gas.
Subatomic Particles
The electrons, protons,
comprising atoms.
and neutrons
Submicron
Below one micron in size or diameter. Less
than one-millionth of a meter.
Substructure/
Understructure
The underlying structure of a building or
house. May be a basement, slab-on-grade
foundation, crawl-space, etc.
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Surficial Material
Synergistic Model
Thorium-232
Thoron
Trachea
Unattached Radon Decay
Product
- Surface or near surface soil deposits.
- A form of cancer causality whereby two or
more carcinogens act synergistically to cause
cancer with a greater probability than if
each were acting alone.
- A radioactive isotope of the element Thorium
in the actinium series, symbol Th, atomic
number 90, atomic weight 232.
- Conventional name for the isotope of radon
with an atomic weight of 220 (radon-220).
Sometimes symbolized Tn.
- The windpipe. The duct by which air
passes from the larynx (in the throat) to the
bronchi and the lungs.
A radon decay product that is not electro-
statically attached to dust or particles in the
air. Capable of attaching to lung tissue if
inhaled.
Uraniferous
Uranium-238
- Of or containing uranium.
- A highly toxic, radioactive metallic isotope of
the element uranium in the actinide series,
symbol U, atomic number 92, atomic weight
238. Undergoes radioactive decay,
eventually to radium-226.
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Uranium Ore
A mineral deposit that can be mined to
recover uranium.
Ventilation
The act of admitting fresh air into a space
in order to replace stale or contaminated air,
achieved by blowing air into the space.
Ventilation an be achieved both naturally and
mechanically.
Working Level (WL)
A unit of measure of the concentration of
radon decay products defined as the
quantity of short-lived decay products that
will result in 1.3 x 10 MeV of potential
alpha energy per liter of air.
Working Level Month
(WLM)
A unit of radon exposure equivalent to an
exposure to one working level of radon
decay products for one working month (170
hours).
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RADIOLOGICAL UNIT DEFINITIONS
Measured Quantity Unit
Energy
1 Joule
Unit Definition
6.24 X 1012 MeV (million electron
volts)
Source Activity
Source Activity
Source Activity
Exposure
Bequerel (Bq) =
Curie (Ci)
Picocurie (pCi) =
Roentgen (R)
1 disintegration per second
2.22 dis/min = 0.037 Bq
3.7 x 10 disintegrations
per second
-12
10 curies
2.22 disintegrations per minute
0.037 Bq
-4
2.58 x 10 coulombs per
kilogram (in air)
Absorbed Dose
Rad
= 0.01 joules per kilogram =
62. H x 106 MeV/g
Absorbed Dose
Cray
= 1 joule per kilogram = 100 rads
Equivalent Dose
Rem
= RBE x (dose in rads)
Equivalent Dose
Sievert
= RBE x (dose in grays)
Relative Biological
Effectiveness RBE
= quality factor x modifying factor
Indicates Standard International (SI) unit.
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MEANING OF COMMON UNIT PREFIXES
Prefix
Abbreviation
Unit Multiple
Gig a
Mega
Kilo
Cent!
Mill!
Micro
Nano
Pico
C
M
k
c
m
X4
n
P
109
106
103
1
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CONVERSION TABLE
FROM COMMON RADIOLOGICAL UNIT TO
STANDARD INTERNATIONAL (SI) UNIT
Multiply Common Unit By To Get SI Unit
Curies 3.7 x 10 Bequerels
Picocuries 0.037 Bequerels
Picocuries per liter 37 Bequerels per cubic meter
Rad 0.01 Grays
Rem 0.01 Sieverts
MeV 1.60290 x 10~13 Joules
_M
Roentgen 2.58 x 10 Coulombs per kilogram
(in air)
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