EPA 902/4 78 002
Excerpts from
RADIOLOGICAL QUALITY OF
THE ENVIRONMENT
IN THE UNITED STATES, 1977
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
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The following pages are excerpted from the EPA publication
EPA 520/1-77-009 "RADIOLOGICAL QUALITY OF
THE ENVIRONMENT
IN THE UNITED STATES, 1977"
The document is 295 pages long; to conserve paper, we
have reproduced the most frequently requested information
here. If you wish to read the entire report, you may
request a copy from:
Regional Office of Radiation Programs
USEPA
Room 907J
26 Federal Plaza
New York, New York 10007
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SUMMARY
The purpose of this report is to summarize the individual and
population doses in the United States resulting from each category of
radiation source and to assess these data. When the literature on radi-
ation sources was searched for information, it became readily apparent
that an immense amount of data had been published during the past 15
years. It was therefore considered necessary, first to organize the
sources into the categories described in this report, and secondly, to
summarize, examine and interpret the data with respect to these categories.
In doing so, it was also necessary to assume that the data extracted
from the literature were valid. Because of the many different purposes
for which environmental data were generated, the results are not only
expressed in different units, but they were accumulated over different
time periods and frequently were obtained without quality control. For
this reason, many tables of data carry detailed notes and annotations.
Readers are cautioned that before data in this report are used for their
purposes, they should read the text and the notes to assure proper
interpretation.
The individual and population dose data resulting from the various
categories of radiation sources discussed in this report are summarized
in table 1-1. The information in this table is divided according to
whether the primary mode of exposure is external or internal. Exposure
to direct radiation from radionuclides in the ground, water, buildings,
and air around us, or from radiation-producing machines, such as x-ray
equipment and particle accelerators, is considered to be external exposure.
Exposures of this type usually result in a radiation dose to the whole
body of the person exposed. In contrast, internal exposures occur when
radioactive materials are inhaled, ingested, or absorbed through the
skin. Internal exposures result in radiation doses to specific organs
of the body, such as the lung, gastrointestinal tract, or bones.
It is evident from this table that there are radiation sources for
which data are not available. Consequently, the discussion and comments
that result are based upon the data which were available at the time of
writing. Also, it is worth noting that although population doses from
the different source categories, in general, can be added together to
gain a perspective of overall impact, it does not necessarily follow
that individual doses can be added together because an individual in one
population group generally does not receive the radiation dose common to
another population group. For this reason, the data in table 1-1 only
show totals for population doses in the various source categories.
Dose to United States population
Based upon the limited data in table 1-1, it is apparent that the
source category of highest population dose is the external dose from
cosmic radiation. An overall population dose from ambient ionizing
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radiation is not given because population doses from the worldwide
radiation and terrestrial radiation components is not available. Judging
from the figures given for individual doses from these three categories,
it would appear that the population dose from terrestrial radiation
might be equal to or greater than the 10 million person-rem dose from
cosmic radiation. The second largest source of population dose is from
medical and dental radiology. This dose was estimated to be about 14.8
million person-rem to the U.S. population.
The third largest category of population dose for which data are
available is from the use of radiopharmaceuticals for medical radiation
purposes, which is estimated to contribute an internal dose of approxi-
mately 3 million person-rem per year to the population dose. The fourth
largest category of dose is estimated to be from technologically enhanced
natural radiation which contributes approximately 3 million person-rem
per year to the population dose. Finally, it is of interest to note
that all the population doses from all the other source categories for
which data are available are less than 0.1 percent of the total population
dose.
It is important to mention that the population dose values noted
here are based upon the data available to us at this time. It is possible
that these values, and thus the relative contributions of population
dose from the source categories considered, could change in the future
as more information on this subject becomes available.
Dose to individuals
For individuals, the largest dose is derived from technologically
enhanced natural radiation. It contributes internal doses as high or
higher than 100,000 mrem/y to the tracheobronchial surface tissue of the
lung as a result of the inhalation of radon daughter products from
uranium mill tailings.
The second category contributing to a high individual dose is
medical radiation which contributes internal doses as high as 5000
mrem/y from radioactive cardiac pacemakers. Artificial teeth were found
to contribute a local tissue dose as high as 1390 mrem/y to the individual
due to their uranium content. Occupational and industrial operations
were found to contribute a dose of 1230 mrem/y to the individual worker,
essentially to maintenance personnel working around boiling water nuclear
power reactors. Finally, the next largest dose is that which might be
received by individuals at the boundary of federal facilities, 258 mrem/y.
As has been mentioned above, the relative contributions from each
of the source categories are subject to revision as may be required by
new data.
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Table 1-1. Summary of dose data from all sources, United States
External
Internal
Source
Individual
dose
(mrem/y)
Population
dose
(person-rem/y)
Individual
dose
(mrem/y)
Population
dose
(person-rem/y)
Ambient ionizing radiation
Cosmic radiation
Ionizing component
Neutron component
Worldwide radioactivity
Tritium
Carbon-14
Krypton-85
Terrestrial radiation
Potassium-40
Tritium
Carbon-14
Rubidium-87
Uranium-238 series
Thorium-232 series
41-45
28-35
0.33-6.8
a.035*
30-95
17
13
25
9.7x10^
9.2X106
4.9X105
Technologically enhanced natural radiation
Ore mining and milling
Inactive uranium mill tailings piles
Phosphate mining & processing (occupational) 10-300*
0.04
1
18-25
16
4x1O'
1
0.6
2-6*
100,000*
b!40-14000
b6,000*
9.2x10^
2.73x10°
C2.5-70000
Fertilizer
Thorium mining and milling
Radon in potable water supplies
Radon in natural gas
Radon in liquefied petroleum gas
Radon in "health" mines
Radon daughter exposure in natural caves
Radon and geothermal energy production
Radioactivity in construction material
Airplane travel
Jet (cosmic), per trip over Atlantic
SST (cosmic), per trip over Atlantic
Coal-fired electric generating station
Oil-fired electric generating station
1.7*
b4,000(dl,250)*
b!5-54 2.73xl06
1-4 30000
2.6(500-crew)*
2.00,000-crew)*
5-70*
0.04*
0.12-2xl06*
15*
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Table 1-1 cont. Summary of dose data from all sources, United States
External Internal
Source
Fallout
Uranium fuel cycle
Mining and milling
Fuel enrichment
Fuel fabrication
Power reactors BWR
PWR
Research reactors
Transportation - Nuclear power industry
Radioisotopes
Reprocessing and spent fuel storage
Radioactive waste disposal
Federal Facilities
ERDA
Department of Defense
Accelerators
Radiopharmaceuticals
Medical radiation
X radiation
Cardiac pacemakers
Occupational and industrial radiation
BWR
PWR
All occupations
Individual
dose
(mrem/y)
P o
*— <\, £
9<0~1
k76 max
M max
-
k<0. 1-258
<0.01
k0.04-4
-
^03
-
U1230
U1080
V0.80
Population Individual Population
dose dose dose
(person-rem/y) (mrem/y) (person-rem/y)
_
2014 -
M.SxlO"^ .2.5
<0.1 "0.3 n0.64
J2xlO-4 J0.66
m!564
m21
- -
n 100-9600
n<170
P23 p!4-257
^480
0.4-65
r<0.1 - S3.3xl06
14.8xl06
<5000
28,400
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Table 1-1 cont. Summary of dose data from all sources, United States
External
Internal
Source
Individual
dose
(mrem/y)
Population
dose
(person-rem/y)
Individual
dose
(mrem/y)
Population
dose
(person-rem/y)
Consumer products
Timepieces
Smoke detectors
Artificial teeth
TV
x<0.5*
Z0.007*
.025-0.043
0.001*
aa!40-1390*
Nonionizing electromagnetic radiation
Broadcast towers and airport radars
All sources
Individual exposure
10
0.1-1
.Maximum individual dose to skin surface
Trachea-bronchial dose
,Lung-rem/y
Stomach dose
^50-year dose commitment divided by 50
Average individual lung dose within 30 km
?Maximum potential exposure per facility
•Maximum potential exposure
Cumulative exposure per facility within
. 80 km radius
^Estimated bone dose within 80 km
Fence line boundary dose
ndithin a radius of 80 km
"Estimated for the year 1973
pFor NFS Reprocessing Plant, West Valley, N.Y.
q!965 data
Based upon data from 5 institutions
^Estimated 1980 dose
Estimated mean active bone marrow dose to adults-
u mrad/y
Average occupational exposure/y
vAverage exposure for all occupations & 3.7
• radiation workers/1000 persons in United States
From digital watches
^From timepieces containing tritium or radium-
activated dials
Estimated
bbDose to the superficial layer of tissue
5 cm from TV set; units of mR/h
- No dose data available
indicates new or revised information
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Table 2-2. Estimated annual cosmic-ray whole-body doses (2.10)
(mrem/person)
Average Annual
Political Unit Dose
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
40
45
60
40
40
120
40
40
35
40
30
85
45
45
50
50
45
35
50
40
40
50
55
40
45
90
75
85
45
Political Unit
Average Annual
Dose
New Jersey 40
New Mexico 105
New York 45
North Carolina 45
North Dakota 60
Ohio 50
Oklahoma 50
Oregon 50
Pennsylvania 45
Rhode Island 40
South Carolina 40
South Dakota 70
Tennessee 45
Texas 45
Utah 115
Vermont 50
Virginia 45
Washington 50
West Virginia 50
Wisconsin 50
Wyoming 130
Canal Zone 30
Guam 35
Puerto Rico 30
Samoa 30
Virgin islands 30
District of Columbia 40
Total United States
45
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Table 2-13. Estimated annual external gamma whole-body
doses from natural terrestrial radioactivity (2.10)
(mrem/person)
Political Unit
Al abama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
*Assumed to be
United States
Average Annual
Dose
70
60*
60*
75
50
105
60
60*
60*
60*
60*
60*
65
55
60
60*
60*
40
75
55
75
60*
70
65
60*
60*
55
40
65
equal to the
average .
Political Unit
Average Annual
Doses
New Jersey 60
New Mexico 70
New York 65
North Carolina 75
North Dakota 60*
Ohio 65
Oklahoma 60
Oregon 60*
Pennsylvania 55
Rhode Island 65
South Carolina 70
South Dakota 115
Tennessee 70
Texas 30
Utah 40
Vermont 45
Virginia 55
Washington 6O*
West Virginia 60*
Wisconsin 55
Wyoming 90
Canal Zone 60*
Guam 60*
Puerto Rico 60*
Samoa 60*
Virgin Islands 60*
District of Columbia 55
Others 60*
Total United States
60
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Chapter 7 - Radiopharmaceuticals
Radiopharmaceuticals are used in the diagnosis and, in some cases,
the treatment of disease. Their use has increased fivefold from 1960 to
1970, and it has been estimated that an increase of sevenfold may be
experienced from 1970 to 1980. If this trend continues, and there are
no technical changes, it is estimated that the whole-body dose to the
United States population in 1980 from the use of radiopharmaceuticals
will be 3.3 million person-rem (7.1).
In June 1976, the Bureau of Radiological Health published a report
on a pilot study of nuclear medicine in United States hospitals. This
study compares current nuclear medicine data obtained from six hospitals
with survey data collected from the same institutions in previous years
(7.2). Although these data cannot be considered to be representative of
nuclear medicine practice in all U.S. hospitals, the study notes that
several trends are apparent.
These trends are:
1. An average increase in nuclear medicine procedures in excess
of 17 percent per year.
2. An increase in the average whole body and gonad radiation
doses per radiopharmaceutical administration when compared
to 1966 national data.
3. A high proportion (21 percent) of nuclear medicine procedures
performed on patients under the age of 30.
The contribution of nuclear medicine to the total medical radiation
exposures to the population may be greater than previously estimated if
the trends indicated in the pilot study are a reflection of the practice
of nuclear medicine throughout the United States.
Although radiopharmaceuticals used in diagnosis and treatment of
disease result in the major doses to man, additional doses to man result
from the manufacture of radiopharmaceuticals and from the discharge of
these materials to the environment from patients and medical facilities.
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A search of available literature unfortunately has not revealed any
information concerning the release of radiopharmaceuticals to the environ-
ment during manufacturing processes, thus, the effect of these materials
cannot be determined.
In order to estimate the total contribution to population doses
from the discharges of radiopharmaceuticals, each medical facility would
require evaluation because of the unique ways each might contribute to
the environmental contamination. Thus, it is concluded that little
inference can be made at this time about the dose and contamination that
results from the discharge from radiopharmaceuticals from patients and
medical facilities.
References
(7.1) NATIONAL ACADEMY OF SCIENCES-NATIONAL RESEARCH COUNCIL. The
effects on populations of exposure to low levels of ionizing
radiation. Report of the Advisory Committee on the Biological
Effects of Ionizing Radiation. NAS/NRC, Washington, D.C.
20006 (November 1972).
(7.2) MCINTYRE, A. B., D. R. HAMILTON and R. C. GRANT. A pilot study
of nuclear medicine reporting through the medicajly oriented
data system. FDA 76-8045, Bureau of Radiological Health,
Rockville, Md. 20857 (June 1976).
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Chapter 8 - Medical Radiation
The responsibility for controlling medical exposure to radiation is
divided between the Federal and the State governments. Within the
Federal Government, the Bureau of Radiological Health in the Department
of Health, Education and Welfare has the responsibility of adminis-
trating the Radiation Control for Health and Safety Act (Public Law 90-
602). The Secretary of Health, Education and Welfare is required by the
act to submit an annual report to the President for transmittal to the
Congress (8.1).
A model State Radiation Control Act containing suggested model
regulations for control of radiation was published by the Council of
State Governments with the cooperation and assistance of interested
Federal Agencies (8.2)- This publication assisted the States in making
regulations compatible with each other and with the Federal Government.
Fifty states, the District of Columbia and the Commonwealth of Puerto
Rico now have laws for the regulation of ionizing radiation (8.S).
The use of radiation by the medical profession is recognized as the
largest manmade component of radiation dose to the United States popu-
lation. This includes medical diagnostic radiology, clinical nuclear
medicine, radiation therapy, cardiac pacemakers, and occupational
exposure of medical and paramedical personnel. However, the main contri-
butor of the total dose from medical exposures is diagnostic x radiation;
the contribution from dental radiation, radiopharmaceuticals, and radi-
ation therapy being far lower. Medical diagnostic radiology accounts
for at least 90 percent of the total manmade radiation dose to which the
U.S. population is exposed. This is at least 35 percent of the total
radiation dose from all sources (including natural radioactivity)
(8.4,8.5).
Genetically significant dose
The Bureau of Radiological Health (BRH), in cooperation with the
National Center for Health Statistics (NCHS), conducted an X-ray Exposure
Study (XES) in 1964 and another in 1970. A dose model was developed for
use in calculating the gonad dose from the XES data and a report was
published in April 1976 illustrating changes in gonad and genetically
significant dose (GSD) from diagnostic x-ray procedures between 1964
and 1970 (8.6). However, the report considers only medical radiographic
examinations and the radiographic portions of fluoroscopy. Dental x-ray
examinations and doses from therapy were not included.
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Ten statistically significant changes in mean gonad dose per exam-
ination from 1964 to 1970 were observed (table 8-1). The largest increase
occurred for barium enema examinations of females (578 mrad to 903 mrad)
and the largest decrease occurred for intravenous or retrograde pyelogram
examinations of males (537 mrad to 207 mrad).
Examination types which involve the abdomen result in high mean
gonad doses while those examination types which involve the head, neck,
thorax and extremities generally result in low mean gonad doses (table
8-1). Therefore, eight examination types produced over 90 percent of
the GSD in 1964 and in 1970 (table 8-2). Theoretically, restriction of
the beam size to the film size would have reduced the 1964 GSD by 33
percent and the 1970 GSD by 21 percent. The change in the estimate of
the GSD from 17 millirads in 1964 to 20 millirads in 1970 was not statis-
tically significant (8.6). This report notes that recent evaluations
indicate that genetic effects should not be considered the primary hazard
of radiation and that increasing emphasis is being placed on the somatic
effects of radiation (8.6).
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Chapter 11 - Health Effects of Ionizing Radiation Exposure
Potential health effects from exposures to ionizing radiation are
evaluated in this section. In order to make the interpretation of these
estimated health effects more meaningful, the various health effect risk
factors that can be applied will be presented.
No attempt has been made to assign individual exposure values to
the various health effects for the following reasons. First, then, is a
degree of uncertainty for the doses from different radiation sources.
Although reported doses are based on actual data whenever possible, many
of the values represent estimates having a large degree of variability.
A second constraint on estimating potential health effects is the lack
of definitive information on population parameters, especially where
exposures are reported for specific facilities. This is important as
there are differences in sensitivity; for example, children are more
radiosensitive than adults. Therefore, while one might apply such risk
conversion factors to large population groups where some generalizations
as to population parameters are applicable, it is invalid to apply such
generalizations when the population under consideration becomes smaller
and more specific. Besides these two prime reasons, others, such as the
lack of information on the pathway of exposure in many cases, have led
to the decision to handle health effects in this general manner.
EPA has adapted the policy of assuming a linear relationship
between the population exposure to ionizing radiation and its biological
effect. This policy was issued on March 3, 1975, and is included here
in its entirety.
"EPA Policy Statement on
Relationship Between Radiation Dose and Effect
41 FR 2-8409
"The actions taken by the Environmental Protection Agency to protect
public health and the environment require that the impacts of contam-
inants in the environment or released into the environment be prudently
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examined. When these contaminants are radioactive materials and ion-
izing radiation, the most important impacts are those ultimately af-
fecting human health. Therefore, the Agency believes that the public
interest is best served by the Agency providing its best scientific
estimates of such impacts in terms of potential ill health.
"To provide such estimates, it is necessary that judgments be made
which relate the presence of ionizing radiation or radioactive materials
in the environment, i.e., potential exposure, to the intake of radio-
active materials in the body, to the absorption of energy from the
ionizing radiation of different qualities, and finally to the potential
effects on human health. In many situations, the levels of ionizing
radiation or radioactive materials in the environment may be measured
directly, but the determination of resultant radiation doses to humans
and their susceptible tissues is generally derived from pathway and
metabolic models and calculations of energy absorbed. It is also
necessary to formulate the relationships between radiation dose and
effects; relationships derived primarily from human epidemiological
studies but also reflective of extensive research utilizing animals and
other biological systems.
"Although much is known about radiation dose-effect relationships
at high levels of dose, a great deal of uncertainty exists when high
level dose-effect relationships are extrapolated to lower levels of
dose, particularly when given at low dose rates. These uncertainties in
the relationships between dose received and effect produced are recog-
nized to relate, among many factors, to differences in quality and type
of radiation, total dose, dose distribution, dose rate, and radiosen-
sitivity, including repair mechanisms, sex, variations in age, organ,
and state of health. These factors involve complex mechanisms of inter-
action among biological, chemical, and physical systems, the study of
which is part of the continuing endeavor to acquire new scientific
knowledge.
"Because of these many uncertainties, it is necessary to rely upon
the considered judgments of experts on the biological effects of ion-
izing radiation. These findings are well-documented in publications by
the United Nations Scientific Committee on the Effects of Atomic Radi-
ation (UNSCEAR), the National Academy of Sciences (NAS), the Inter-
national Commission on Radiological Protection (ICRP), and the National
Council on Radiation Protection and Measurements (NCRP), and have been
used by the Agency in formulating a policy on relationship between
radiation dose and effect.
"It is the present policy of the Environmental Protection Agency to
assume a linear, nonthreshold relationship between the magnitude of the
radiation dose received at environmental levels of exposure and ill
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health produced as a means to estimate the potential health impact of
actions it takes in developing radiation protection as expressed in
criteria, guides, or standards. This policy is adopted in conformity
with the generally accepted assumption that there is some potential ill
health attributable to any exposure to ionizing radiation and that the
magnitude of this potential ill health is directly proportional to the
magnitude of the dose received.
"In adopting this general policy, the Agency recognizes the in-
herent uncertainties that exist in estimating health impact at the low
levels of exposure and exposure rates expected to be present in the
environment due to human activities, and that at these levels, the
actual health impact will not be distinguishable from natural occur-
rences of ill health, either statistically or in the forms of ill health
present. Also, at these very low levels, meaningful epidemiological
studies to prove or disprove this relationship are difficult, if not
practically impossible, to conduct. However, whenever new information
is forthcoming, this policy will be reviewed and updated as necessary.
"It is to be emphasized that this policy has been established for
the purpose of estimating the potential human health impact of Agency
actions regarding radiation protection, and that such estimates do not
necessarily constitute identifiable health consequences. Further, the
Agency implementation of this policy to estimate potential human health
effects presupposes the premise that, for the same dose, potential
radiation effects in other constituents of the biosphere will be no
greater. It is generally accepted that such constituents are no more
radiosensitive than humans. The Agency believes the policy to be a
prudent one.
"In estimating potential health effects, it is important to rec-
ognize that the exposures to be usually experienced by the public will
be annual doses that are small fractions of natural background radiation
to at most a few times this level. Within the United States, the
natural background radiation dose equivalent varies geographically
between 40 to 240 mrem per year. Over such a relatively small range of
dose, any deviations from dose-effect linearity would not be expected to
significantly affect actions taken by the Agency, unless a dose-effect
threshold exists.
"While the utilization of a linear, nonthreshold relationship is
useful as a generally applicable policy for assessment of radiation
effects, it is also EPA's policy in specific situations to utilize the
best available detailed scientific knowledge in estimating health impact
when such information is available for specific types of radiation,
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conditions of exposure, and recipients of the exposure. In such situ-
ations, estimates may or may not be based on the assumptions of line-
arity and a nonthreshold dose. In any case, the assumptions will be
stated explicitly in any EPA radiation protection actions.
"The linear hypothesis by itself precludes the development of
acceptable levels of risk based solely on health considerations. There-
fore, in establishing radiation protection positions, the Agency will
weigh not only the health impact, but also social, economic, and other
considerations associated with the activities addressed."
Within the context of the overall policy statement reprinted above,
EPA uses primarily the recommendations of the National Academy of
Sciences Committee on Biological Effects of Ionizing Radiation (BEIR)
(11.1) as expressed in their November 1972 report to arrive at dose-to-
health risk conversion factors. Besides the concept of linearity
expressed in the policy statement, it is further assumed that health
effects that have been observed at dose rates much greater than those
represented in this report are indicative of radiation effects at lower
dose rates. Any difference in biological recovery from precarcinogenic
radiation damage due to low dose rates is neglected in the BEIR health
risk estimates. On the other hand, in some cases, the BEIR risk esti-
mates are based on relatively large doses where cell killing may have
reduced the probability of delayed effects being observed and hence,
underestimate the effects at low doses. The dose-risk conversion
factors that EPA has adopted from the BEIR report are neither upper nor
lower estimates of risk, but are computed on the same basis as the risk
characterized as "the most likely estimate" in the BEIR report, that is
they are averages of the two risk models considered in the BEIR report;
relative and absolute risk.
One must caution against interpreting the product of dose and risk
conversion factor as a prediction of actual number of effects to be
sought out in the real world. The dose conversion factors (from concen-
tration to dose) and the risk conversion factors (dose to effects) yield
estimates of the actual dose and effects which have a considerable
range. For example, the BEIR Committee has made a determination, based
on their evaluation of the increase of the ambient cancer mortality per
rem, that ranges from 100 to 450 deaths per million persons per rem
during a 30-year followup period. EPA has chosen average values to be
used for various dose to health effect conversion factors. When new
information becomes available these factors will be revised.
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Chapter 12 - Nonionizing Electromagnetic Radiation
As its name implies, nonionizing electromagnetic radiation does not
produce ionized particles when it is absorbed by the material of interest.
Absorbed energy is converted to electronic excitation and to molecular
vibration and rotation. The ionization potentials of the principal
components of living tissue (water, and atomic oxygen, hydrogen, nitrogen,
and carbon) are between 11 and 15 electron volts (eV). Michaelson
(12.1) considers 12 eV to be the lower limit for ionization in biological
systems, while noting that some weak hydrogen bonds in macromolecules
may have lower ionization potentials. As a point of reference, an
ultraviolet wavelength of 180 nanometers corresponds to an energy of
about 7 eV. Thus, for practical purposes, the nonionizing part of the
electromagnetic spectrum includes the ultraviolet, visible, infrared,
radiofrequency and lower frequency regions. The electromagnetic fields
from electric power distribution at 50 and 60 Hz are included, although
these fields are not radiative in nature.
Discussion
There is a large difference in the exposure standards of the United
States and the U.S.S.R., those of the latter being much more restrictive.
The level for unlimited occupational exposure in the Soviet Union is 10
yW/cm2, and the proposed environmental level is 1 yW/cm2. Controversy
continues over the validity of the Soviet standard. The Soviet standard
was adopted in Poland in 1961, pending an independent evaluation. In
1972, the Polish standard was revised and the occupational level was set
at 200 uW/cm2, and the environmental limit was set at 10 pW/cm2 (22.33).
Research is now underway in this country and elsewhere to determine
and assess any possible biological effect of long-term exposure to low
levels of nonionizing radiation and to examine the validity of the
present occupational exposure standard of 10 mW/cm2. Also of concern
are the effects of high peak power, low average power, pulsed radiation
and the questions of the need for and how to develop standards for the
frequency range below 10 MHz where there is currently no exposure
standard. Four types of overlapping exposure can be distinguished: (1)
exposure in the general environment to intentional signals from the
broadcast services, radars, leakage radiation, and other sources, (2)
occupational exposures, (3) exposure to leakage radiation from consumer
devices such as microwave ovens, and (4) intentional medical exposures.
Occupational exposure is subject to control by OSHA. Intentional
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medical exposure is given at the discretion of a physician, but a
performance standard is now being developed by the Food and Drug Admin-
istration for leakage and scatter from microwave diathermy units. There
is no direct control of environmental exposure from microwave diathermy
apparatus. Indirect controls of environmental exposures are the limi-
tation put on effective radiated power by the FCC, their requirement for
posting areas about domestic satellite stations where levels exceed 10
mW/cm2, and the operational procedures employed in using both government
and nongovernment sources. Also, any telecommunications system planned
for purchase by the government, as a condition for spectrum approval, is
reviewed by IRAC-OTP to assess among other factors whether levels in
excess of 10 mW/cm2 will occur and whether operational measures have
been provided to insure that people are not exposed above this level.
Two types of environmental exposure can be distinguished. One is
the relatively high radiation level from high power sources such as some
radars and satellite communications stations where the power density in
the useful beam can exceed that thought to be safe for human occupancy
even outside the boundary of the facility (12.15). The problems assoc-
iated with such sources are recognized and instrumentation and techniques
for analyzing exposure from them are available. The other type of
environmental exposure arises from the superposition of the fields from
many sources at different frequencies. This exposure may be high or low
depending on the location and types of sources contributing to the
exposure and includes the specific source problem as a special case.
Nonionizing environmental radiation data are needed to interpret the
results of current biological effects research and establish the pre-
dominant frequencies in the environment so that future research for the
validation of standards can be appropriately directed.
Summary
General environmental surveys have been completed in seven cities
in the Eastern United States. The data and population exposure impli-
cations for the first four of these are presented here and analysis is
continuing on the other three. The measurement program will now continue
in several cities in the Western United States.
The results to date suggest that probably 99 percent of the urban
population is exposed at levels which would be permitted even under the
restrictive proposed.Soviet standard of 1 uW/cm2. The general environ-
mental data cannot be used to estimate the levels to which the remaining
1 percent of the population is exposed. Further information will require
a detailed analysis of specific sources and a detailed knowledge of the
locations of the persons exposed to such sources.
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